U.S. patent application number 14/752459 was filed with the patent office on 2016-01-07 for systems and methods for recovering carbon dioxide from industrially relevant waste streams, especially ethanol fermentation processes, for application in food and beverage production.
This patent application is currently assigned to PIONEER ENERGY INC. The applicant listed for this patent is Pioneer Energy Inc. Invention is credited to Kevin D Hotton, Matthew J Lewis, Andrew C Young.
Application Number | 20160003532 14/752459 |
Document ID | / |
Family ID | 55016754 |
Filed Date | 2016-01-07 |
United States Patent
Application |
20160003532 |
Kind Code |
A1 |
Young; Andrew C ; et
al. |
January 7, 2016 |
SYSTEMS AND METHODS FOR RECOVERING CARBON DIOXIDE FROM INDUSTRIALLY
RELEVANT WASTE STREAMS, ESPECIALLY ETHANOL FERMENTATION PROCESSES,
FOR APPLICATION IN FOOD AND BEVERAGE PRODUCTION
Abstract
A system for recovering CO2 via liquefaction and purification
from a vented CO2 gas stream comprising a compressor; a dehydrator;
a scrubber; a refrigerator having one or more stages; and a
separation subsystem adapted to ensure non-condensable gas content
in the final product meets industry standards. The liquid CO2
product is of sufficient purity to be used in applications
requiring beverage-grade CO2. The system can be utilized as a
single-brewery installation to reduce venting from ethanol
fermenters to an absolute minimum, produce a high purity liquid CO2
product for use in-process or external sales, and offset the
purchasing of expensive, industrial CO2 of inferior purity.
Inventors: |
Young; Andrew C; (Wheat
Ridge, CO) ; Lewis; Matthew J; (Lakewood, CO)
; Hotton; Kevin D; (Arvada, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pioneer Energy Inc |
Lakewood |
CO |
US |
|
|
Assignee: |
PIONEER ENERGY INC
Lakewood
CO
|
Family ID: |
55016754 |
Appl. No.: |
14/752459 |
Filed: |
June 26, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62020883 |
Jul 3, 2014 |
|
|
|
Current U.S.
Class: |
62/617 |
Current CPC
Class: |
Y02P 20/129 20151101;
C01B 32/50 20170801 |
International
Class: |
F25J 3/02 20060101
F25J003/02; F25J 3/08 20060101 F25J003/08 |
Claims
1. An apparatus for recovering via purification and liquefaction of
carbon dioxide gas from a vented CO2 waste gas stream, comprising:
a chassis adapted for installation inside a space-limited
production facility; one or more compressors for compressing the
raw CO2 gas stream; one or more dehydrators for removing water from
the compressed CO2 gas stream; one or more scrubbers containing
solid-state adsorbent for deodorizing and purifying the inlet CO2
gas stream; a refrigerator having one or more stages for lowering a
temperature of the dehydrated, deodorized, compressed CO2 stream;
and a separation subsystem system adapted to separate the liquefied
CO2 product from any remaining contamination by non-condensable
gases, especially oxygen.
2. The apparatus of claim 1, wherein the final oxygen content is
less than 30 parts per million.
3. The apparatus of claim 1, wherein the final water content is
less than 20 parts per million.
4. The apparatus of claim 1, wherein the liquid CO2 product has no
foreign color, taste, or odor.
5. The apparatus of claim 1, wherein the liquid CO2 product meets a
beverage-grade standard.
6. The apparatus of claim 1, wherein the one or more compressors
compress the raw natural gas stream to a pressure range of 75 psia
to 300 psia.
7. The apparatus of claim 1, wherein the chassis is mounted on a
cart having one or more wheels.
8. The apparatus of claim 1, wherein the refrigerator further
comprises: a high-stage refrigeration loop having at least one heat
exchanger for lowering the temperature of the dehydrated,
deodorized, compressed CO2 gas stream; and a low-stage
refrigeration loop having at least one heat exchanger for further
lowering the temperature of the dehydrated, deodorized, compressed
CO2 gas stream.
9. The apparatus of claim 1, wherein the refrigerator further
comprises: an autocascade loop having mixed refrigerants for
lowering the temperature of the dehydrated, deodorized, compressed
CO2 gas stream.
10. The apparatus of claim 9, wherein the mixed refrigerants are
hydrocarbons.
11. The apparatus of claim 9, wherein the mixed refrigerants are
nonflammable refrigerants.
12. The apparatus of claim 1, wherein the refrigerator cools the
compressed CO2 gas stream to a temperature range of -15.degree. C.
to -55.degree. C. sufficient to liquefy the entire CO2 stream in a
single heat exchanger.
13. The apparatus of claim 1, wherein one or more of the
dehydrators employ a desiccant bed.
14. The apparatus of claim 13, wherein two desiccant beds are
employed in alternation, and wherein heat required to dry the two
desiccant beds is derived from waste heat from a power generator
that drives the compressors and the refrigerator.
15. The apparatus of claim 1, wherein the separation subsystem
comprises a phase separator.
16. The apparatus of claim 1, wherein the separation subsystem
comprises a liquid storage dewar.
17. The apparatus of claim 1, wherein the separation subsystem
comprises one or more cyclones to separate liquids from gasses.
18. A method for recovering a liquid CO2 product from a vented CO2
gas stream, comprising: a compression step for compressing the raw
CO2 gas stream utilizing a compressor to a pressure range of 75 to
300 psia; a dehydration step for removing water from the compressed
CO2 gas stream utilizing one or more condensers and one or more
desiccant beds; a deodorizing step for removing trace organic
compounds, flavors, and odors from the dehydrated, compressed CO2
gas stream utilizing an appropriate solid-state adsorbent; a
refrigeration step for reducing a temperature of the dehydrated,
compressed, deodorized CO2 gas stream utilizing a refrigerator
having one or more stages to a temperature range of -15.degree. C.
to -55.degree. C.; and a separation step for driving the
non-condensable gas contamination, especially oxygen, in the final
liquid CO2 product below relevant purity standards.
19. The method of claim 18, further comprising: a transportation
step for bringing a mobile CO2 recovery system inside a cramped
production craft brewery that is venting fermenter gas; and a
deployment step for connecting said CO2 recovery system to a vented
CO2 gas source.
20. The method of claim 18, wherein the final oxygen content is
less than 30 ppm.
21. The method of claim 18, further comprising: vaporizing the
liquid CO2 product to purge tanks, vessels, and lines.
22. The method of claim 18, further comprising: vaporizing the
liquid CO2 product to carbonate beverages intended for sale.
23. The method of claim 18, further comprising: Re-selling the
liquid CO2 product to local consumers of high quality CO2.
24. The method of claim 18, wherein the refrigeration step utilizes
an autocascade refrigerator having mixed nonflammable hydrocarbon
refrigerants.
25. The method of claim 18, wherein the refrigeration step cools
the natural gas stream to a temperature range of -37.degree. C. to
-43.degree. C.
26. The method of claim 18, wherein two desiccant beds are employed
in alternation, and wherein convection required to dry the two
desiccant beds is derived from CO2 gas vented from storage.
27. A system for recovering a vented CO2 gas stream into a liquid
CO2 product of sufficient purity for the downstream application,
comprising: one or more compressors for compressing the vented CO2
gas stream; a dehydrator subsystem for removing water from the
compressed CO2 gas stream; a deodorizing subsystem for removing
trace organic compounds, flavors, and odors from the dehydrated,
compressed CO2 gas stream; a refrigeration subsystem for lowering
the temperature of the dehydrated, compressed, deodorized CO2 gas
stream to a low temperature, comprising an auto-cascade
refrigeration loop having mixed nonflammable hydrocarbon
refrigerants; and a separation subsystem adapted to remove
non-condensable contaminants from the liquid CO2 product to meet
specific purity standards.
28. The system of claim 27, wherein the dehydration subsystem
employs two desiccant beds alternation, wherein convection required
to dry the two desiccant beds is derived from CO2 gas vented from
the liquid storage dewar.
29. The system of claim 27, wherein the oxygen content in the
liquid CO2 product is less than 30 ppm.
30. The system of claim 27, further comprising a chassis for
holding system components for brewery installation, said chassis
mountable to a cart, an indoor floor, or an outdoor surface.
31. The system of claim 27, wherein the refrigeration subsystem
comprises: a high-stage refrigeration loop having at least one heat
exchanger for lowering a temperature of the dehydrated, compressed
CO2 gas stream; and a low-stage refrigeration loop having at least
one heat exchanger for further lowering the temperature of the
dehydrated, CO2 natural gas stream.
32. The system of claim 27, wherein the refrigeration subsystem
cools the vented CO2 gas stream to a temperature range of
-15.degree. C. to -55.degree. C. sufficient to liquefy the entire
process stream in a single heat exchanger.
33. A method for recovering vented CO2 gas, comprising: compressing
the raw CO2 gas stream to a pressure range of 75 to 300 psia;
reducing a temperature of the CO2 gas stream to a temperature range
of -15.degree. C. to -55.degree. C.; and separating non-condensable
gas components from the liquid CO2 product in a phase separator or
liquid storage vessel.
36. The method of claim 35, further comprising: removing water from
the raw natural gas stream to achieve a final aqueous content below
20 ppm.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 62/020,883 filed Jul. 3 2014 entitled "Systems And
Methods For Recovering Carbon Dioxide From Industrially Relevant
Waste Streams, Especially Ethanol Fermentation Processes, For
Application In Food And Beverage Production" which is incorporated
herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to enabling the recovery of
carbon dioxide (CO2) from industrially relevant waste streams
containing a sufficiently high concentration of CO2. The invention
is most readily applicable to the burgeoning beverage alcohol
industry (microdistilleries, craft vintners, and craft breweries)
in the United States, most especially the craft beer brewing
industry. In a craft brewery, carbon dioxide can be recovered from
fermentation tanks, bright beer tanks, and other process vessels,
tanks and lines. The recovered CO2 can then be used in forced
carbonation, kegging, canning, bottling, purging, and other
applications associated with production of packaged beer. More
specifically, this invention relates to a modular system for
separating carbon dioxide from non-condensable gases such as
nitrogen and oxygen, while dehydrating, deodorizing, and purifying
the carbon dioxide to a quality sufficient for beverage
applications, and also liquefying the carbon dioxide and
transferring it into a storage vessel so that it can be re-used
(which would reduce the amount of carbon dioxide that is vented by
breweries, as well as the reduce the amount of carbon dioxide that
breweries have to purchase for plant operations).
BACKGROUND OF THE INVENTION
[0003] The statements in this section merely provide background
information related to the present disclosure and may not
constitute prior art.
[0004] Large-scale recovery systems are commercially available for
large producers of vented carbon dioxide waste streams. Processing
capabilities of these systems exceed 50 kg/hr of CO2. These large
and complex recovery systems require a permanent installation with
extended utility lines (process water, waste water, cooling glycol,
process heat, and electricity) to facilitate operation. The
economics of such an installation are proportional to its size and
complexity. The processing rate, space and infrastructure
requirements, and cost make these commercially available CO2
recovery systems irrelevant for processes that generate waste CO2
streams of lesser magnitudes.
[0005] Because economic and space constraints are virtually
limitless for conventional large-scale CO2 recovery systems and the
large-scale conventional predominantly lager-producing breweries
that house them, the process utilized to recover CO2 is not fully
optimized for the application. Large breweries produce beer at a
steadier rate when compared to smaller craft breweries who actively
pursue seasonal and recipe variations in their production schedule.
Given the reliability of upstream CO2 production and the
consistency of utilities (heat, water, cooling glycol, and
electricity) in a large brewery, conventional CO2 recovery systems
are designed to run at steady-state at a single design point, with
large-volume, ceiling-mounted balloons to account for small
variations in CO2 production rates. This final detail is most
certainly too costly, large, and unwieldy for potential clients
producing moderate CO2 waste streams.
[0006] In most CO2 recovery applications, the recovered stream is
liquefied for convenient, high-density storage. High pressure and
low temperature are used by liquefaction processes that convert a
chemical species from a vapor at standard temperature and pressure
to a liquid at the process conditions. The designer engineer has a
choice to provide either a higher pressure or a lower temperature
to economically optimize the liquefaction process. In these
conventional CO2 recovery systems where space and cost are
inconsequential, the higher pressure option is chosen since there
is enough floor space for a three-to-four stage compressor. A
common process pressure in this application would be 250-300 psig.
At 250 psig, pure carbon dioxide liquefies at -23.degree. C. This
enables the purchase and use of a conventional, off-the-shelf
industrial refrigeration system which achieves a minimum evaporator
temperature of -30.degree. C. Common refrigerants in such a
readily-available unit include propane, R-22, or R-404a.
[0007] Again, due to plentiful utilities and a fixed, static
installation, these larger systems use a continuous aqueous
scrubbing system to remove trace dissolved organics as part of the
CO2 purification process. This consumption of process water imposes
a high operations cost, and can be replaced by alternate methods as
will be addressed. Also the presence of noncondensable gases is a
problem in conventional CO2 recovery systems. Because the
higher-pressure process is employed, dissolved gases have a much
higher tendency to remain dissolved in the recovered CO2 product
stream. The solution is to again use a costly plant utility, this
time in the form of process heat and cooling glycol. A small
distillation column with a reboiler and overhead condenser is
employed to actively drive out noncondensable gases from the
high-pressure product stream. The need for this is greatly reduced
by opting for a lower-pressure process.
[0008] In the United States, the past ten years have seen a massive
growth in the so-called craft beer industry. The Brewers
Association is the prominent trade group associated with these
breweries and defines a craft brewery as an operation that produces
less than 6 million barrels of beer per year (1 US beer barrel=31
US gallons; Source: Brewers Association, Boulder, Colo.,
http://www.brewersassociation.org/statistics/craft-brewer-defined/,
retrieved Jun. 22, 2014). This industry has nearly tripled in total
production volume over the past ten years, from about 6 million
barrels of beer produced in 2004 to over 15 million barrels brewed
in 2013.
[0009] Beer (an aqueous solution of 3-10% ethanol by volume) is
produced by the anaerobic fermentation of glucose by the yeast
Saccharomyces cerevisiae. In this process every molecule of glucose
yields two molecules of ethanol as the desired product, along with
two molecules of carbon dioxide as a byproduct. This byproduct is
not entirely unwanted however, since consumers of beer prefer to
have the beverage carbonated. This carbonation step alone is not
sufficient to utilize all the CO2 produced during a batch
fermentation, but other applications around a typical brewery would
be able to make use of such a recovered waste stream. Typical
applications of a recovered carbon dioxide stream in a production
brewery include carbonation of the final beverage product whether
in bottles, cans, or kegs, purging all process lines and vessels to
exclude air, dispensing beverages in the on-site tasting room or
brewpub, and filling and reselling tanks of beverage-grade CO2 for
other products such as soft drinks and carbonated water.
[0010] Currently carbon dioxide is being vented in large quantities
at numerous locations by craft beer breweries. This activity
entails significant loss of income that could be earned by
recovering the vented carbon dioxide. Still more financial losses
are entailed by purchasing carbon dioxide from industrial gas
supply houses to support plant operations such as force
carbonation, bottling (or canning or kegging) and purging tanks or
process lines. Furthermore, the venting of carbon dioxide has
raised environmental issues that could cause state and/or federal
regulators to take action to fine, shutdown, or highly regulate
their operations.
[0011] The fermentation of sugars by yeast to generate ethanol
results in the formation of carbon dioxide as a byproduct. For each
molecule of ethanol generated, a molecule of carbon dioxide is also
generated. Thus the production of 1 barrel (31 gallons U.S.) of
beer at 5% alcohol by volume (ABV) will generate 9.8 lb of carbon
dioxide. Therefore, a brewery producing 10000 bands per year at 5%
ABV will produce on average 270 lb CO2 per day, which must be
released from the vessel(s) during the fermentation to avoid
stalling the fermentation or mechanically overpressuring the
fermentation tank.
[0012] The United States craft beer industry is expanding rapidly,
with a near linear growth curve since 2007, accounting for the
production of 15.6 million barrels of beer in 2013. (Source:
www.brewersassociation.com Growth-infographic-main.png, 2014), This
beer production level indicates carbon dioxide production in the
range of 1.5-2.0 million lbs per year (depending on average ABV),
and nearly all of it is vented to atmosphere, because up until the
present invention no technology has been accessible to craft
brewers to recover carbon dioxide from their beer production due to
the size and economic constraints outlined earlier.
[0013] This venting produces significant quantities of harmful
CO.sub.2 emissions while producing no useful product. If this
vented CO2 could be utilized to replace purchased CO2 for force
carbonation, bottling, purging, and other plant uses, significant
environmental and economic benefits would accrue. For example, the
market value of purchasing industrial CO2 ranges from $0.10 to
$0.50 per pound, depending on transportation and logistics factors.
Recovery of this stream represents $200 to $1000 per ton of
recovered CO2. This is a very significant savings for small to
mid-sized breweries. However, this problem is not relegated to the
contiguous United States. Craft and regional breweries are on the
rise across other continents and on various island nations, often
with significantly less infrastructure to facilitate the affordable
transport of industrial CO2. Accordingly many small international
breweries pay $0.50 to $2.00 per pound of CO2, making recovery of
this precious commodity an economic imperative.
[0014] Furthermore, CO2 in craft breweries of average size is
typically vented from the fermenter tank headspace, through a down
coming blow-off arm directly into the plant where the cellar
operators work. Carbon dioxide, being heavier than air, tends to
accumulate on the floor space, presenting a significant workplace
hazard. If sufficient air exchange is not available to keep CO2
concentrations below 5000 ppm, adverse health effects such as
dizziness, confusion, and drowsiness are likely to occur. At still
higher concentrations, asphyxiation is a possibility.
[0015] Most beers are force carbonated in the range of 2.2-2.6
volumes of CO2. A `volume` of CO2 indicates the amount of CO2
contained in a given volume of beer, when it is expanded down to
standard atmospheric conditions, compared to the volume of the beer
itself. For example, 2.4 `volumes` of CO2 in a barrel of beer
represents 2.4 barrels of CO2 per barrel of beer at atmospheric
pressure and temperature, which is 1.2 lb of CO2. Therefore, a
brewery producing 10000 barrels per year, force carbonating to an
average of 2.4 volumes, will require 32 lb CO2 per day for force
carbonation. In addition to force carbonation, there are other uses
for CO2 in the brewery, namely bottling (or canning or kegging) and
purging of tanks and process lines.
[0016] Typically, breweries utilize carbon dioxide purchased from
industrial gas supply houses, which is acquired from
ammonia/urea/fertilizer production and/or large scale fuel ethanol
production. This industrial commoditized CO2 source is extensively
processed to meet stringent beverage-grade purity standards.
However, any variability in the purification steps to remove trace
chemicals, hydrocarbons, nitrogen compounds, carbon monoxide,
dissolved oxygen, or lubricating oils can result in a finished beer
with unpleasant taste, odor, or even health consequences. CO2
produced from brewery fermentation, on the other hand, would be
free of these contaminants, as it originates from a sterile
fermenter with controlled conditions, and is produced from the same
beer that is being carbonated, in an anaerobic fermentation
environment. Economically this is a compelling case since the
processing cost of purifying the recovered CO2 for reuse within
beverage-grade specs (including <30 ppm dissolved oxygen) is
greatly reduced by starting with a much cleaner feedstock when
compared to conventional industrial CO2 feedstocks.
[0017] It is highly financially and environmentally disadvantageous
to vent valuable carbon dioxide that could be utilized in the
brewery for force carbonation and purging of tanks and process
lines or packaged and resold to nearby consumers of beverage-grade
CO2. It is even more financially and environmentally
disadvantageous to utilize large quantities of carbon dioxide
purchased from industrial gas supply houses, while perfectly useful
CO2 of superior purity is already being produced in the
facility.
[0018] Therefore, there exists an important need for a solution to
address the problem of recovering carbon dioxide in the brewery to
the maximum extent and to minimize or eliminate the purchasing of
carbon dioxide generated outside the facility, while still being
cost-effective and meeting beverage grade purity standards.
[0019] Accordingly, as recognized by the present inventors, what
are needed are a novel method, apparatus, and system for recovering
CO2 from brewery processes into a storage vessel that can be easily
by the brewery for force carbonation, bottling (or canning or
kegging), purging of tanks and process lines, and for other
purposes. As recognized by the present inventors, what is also
needed is a CO2 recovery apparatus that can recover the CO2 at a
cost that is less than the cost of CO2 delivered from outside the
facility, that can interface with a typical craft brewery facility,
that can maintain beverage grade CO2 purity standards, and that can
be of sufficient capacity to recover most if not all of the CO2
that is produced at the facility.
[0020] Due the required CO2 flow rates, space requirements, cost,
complexity, and infrastructure requirements, commercially available
conventional CO2 recovery systems are inapplicable to a new market
segment that represents well over 1 million pounds of annual CO2
emissions.
Therefore, it would be an advancement in the state of the art to
provide an apparatus, system, and method for cost-effectively
recovering carbon dioxide from a craft-scale brewery that currently
vents the CO2 produced at its facility. It would also be an
advancement in the state of the art to provide a system that is
accessible to craft breweries due to its cost-effectiveness,
compatibility, and capacity to recover CO2 from said brewery.
[0021] It is against this background that various embodiments of
the present invention were developed.
BRIEF SUMMARY OF THE INVENTION
[0022] The present invention is designed to enable the recovery of
carbon dioxide (CO2) from industrial waste streams containing a
majority of CO2. Processes that produce such streams include
pharmaceutical synthesis via batch fermentation, fuel ethanol
plants utilizing starchy feedstocks, anesthetic asphyxiation in
slaughterhouses, ammonia production via steam reforming of natural
gas, coal and biomass gasifiers, various thermochemical and
Fischer-Tropsch-type gas-to-liquids conversions, soft drink
bottling plants, plastics production facilities using the solvent
properties of CO2 for materials property enhancements, coffee and
tea decaffeination towers, so-called green dry cleaners, medical
sterilization, and production of beverage alcohol products. Due to
recent entrepreneurial market trends in the United States, many of
these previously large-scale operations are being performed by
various smaller businesses. Production plants of sufficient size
and sophistication recognize the economic implications of
recovering and utilizing a carbon dioxide waste stream. However,
smaller operations often lack the capital required for installation
of recovery equipment. Therefore, a technological gap exists
between the laboratory and industrial scales for recovery,
purification and storage of CO2 where it is currently being vented
and wasted. The inventors have filled this gap by developing a
novel process which is optimized for this economically relevant
scale.
[0023] Whereas the problem of carbon dioxide recovery in breweries
was previously recognized, systems have been previously developed
for this purpose. Although the manufactures claim that systems can
be built to accommodate small production volumes, the systems tend
to be tailored to the needs of large production breweries outside
of the craft beer arena. These systems are typically very
expensive, have large footprints, require extensive facility
modification, and are generally not accessible to craft breweries
(production less than 6 million barrels of beer per annum).
[0024] Craft breweries face a number of challenges when evaluating
CO2 recovery, most of which are related to the rapid growth of
their market share of the beer brewing industry. In general, craft
breweries are being forced to expand beer production rapidly to
keep up with increasing demand. This means that brewhouses,
fermentation tanks, bottling lines, packaging, and storage must all
be expanded within existing production buildings. As a result,
craft breweries are limited by the availability of working capital
and physical space especially concerning equipment not directly
related to beer production and packaging. Moreover, permanent
modification of the facility and/or operations to accommodate a CO2
recovery system is generally not acceptable if it slows or
interrupts the production of beer.
[0025] The system design presented in the present application
solves the problems with existing systems provided by other
manufacturers. The present system is intentionally designed to be
cost-effective, compact, and compatible with typical craft brewery
facilities. Most importantly, the system is intentionally designed
to interface with the typical craft brewery operation in a
minimally invasive way, which has no adverse effect on the rate of
production of beer, while adding a only a minimal workload to
brewery cellar operators.
[0026] The inventors realized that what is needed is a system that
can draw CO2 from both fermentation tanks and bright beer tanks at
operating conditions typically experienced in a craft brewery.
Further, that the system can be interfaced into the brewery through
flexible installations, and that the system can be compact enough
to be easily relocated within a facility. Further, that the
approach to the CO2 recovery can be designed to use less expensive
processing equipment, to reduce up-front capital cost. Further,
that the system can have variable capacity to match the rate of CO2
production to maximize the uptime of the system and the economic
benefit. Further, that the system can recover CO2 at an energy cost
much less than the cost of purchasing CO2 from a gas supply house.
Further, that the system can treat the recovered CO2 to beverage
grade quality standards. Finally, that the system can make
available for storage and usage the recovered CO2 at a temperature
and pressure that is useful in a brewery.
[0027] Accordingly, the inventors have invented an approach to draw
the effluent gas (which is mainly carbon dioxide) from the
fermentation and bright beer tanks, from pressures as low as 0
psig, and to separate the CO2 from any non-condensable gases
present, and to dehydrate and deodorize the CO2, and to
cryogenically (thus purifying via phase separation) liquefy the CO2
and to make the CO2 available for immediate use or transfer into
bulk storage.
[0028] The inventors have invented a process in which the effluent
gas (which is mainly CO2) is compressed to a pressure between 75
psia to 300 psia (and more preferably to between 130 psia to 160
psia), The CO2 is then cooled to a temperature of between
-15.degree. C. to -55.degree. C. (and more preferably to between
-37.degree. C. to -43.degree. C.) which causes liquefaction of the
CO2.
[0029] One of several ways to achieve such a low temperature range
is to utilize a unique refrigeration unit also invented by the
present inventors. The unique autocascade refrigeration unit
utilizes an autocascade refrigeration stage, in a compact, portable
chassis for delivery to brewery. However, the present invention is
not limited to utilizing the specific refrigeration unit shown and
described.
[0030] Accordingly, one embodiment of the present invention is a
system for recovering CO2 from fermentation and/or bright beer
tanks, comprising a chassis or skid adapted to hold the system for
installation in the brewery; a condensate trap for removing free
water from the CO2 stream; a dehydrator for removing water from the
CO2 stream; a carbon bed for deodorizing the CO2 stream; a
compressor for compressing the CO2 stream to a pressure between 75
psia to 300 psia (and more preferably to between 130 psia to 160
psia); a refrigerator for lowering the temperature of the CO2
stream to an ideal temperature range, preferably approximately
-15.degree. C. to -55.degree. C., (and more preferably -37.degree.
C. to -43.degree. C.), which causes liquefaction of the CO2; and a
storage vessel adapted to contain the liquefied CO2, and to vent
non-condensable gases from its headspace. Because the CO2 is
liquefied and stored and/or used, the CO2 is not vented to the
atmosphere. Because the CO2 is liquefied and stored cryogenically,
the CO2 is free from bacteria or other microbiological
contaminants. Because the system relieves non-condensable gases,
the liquefied and stored CO2 is of beverage grade quality
standards, particularly with respect to oxygen content as well as
common industrial contaminants that are not present inside sanitary
beer fermentation vessels. As such, the stored and liquefied CO2
can be used in the brewery for force carbonation, bottling, and
purging of tanks and process lines without further treatment, thus
replacing CO2 purchased and delivered CO2 from outside the
facility.
[0031] Yet another embodiment of the present invention is the
system described above, further comprising a foam trap to remove
free water and foam from the inlet stream, in place of the
aforementioned condensate trap. Yet another embodiment of the
present invention is the system described above, where the foam
trap detects the presence of foam by way of an optical sensor and
sprays water automatically to collapse it. Yet another embodiment
of the present invention is the system described above, further
comprising an automatic water drain to manage the free water level
in the foam trap.
[0032] Yet another embodiment of the present invention is the
system described above, wherein the dehydrator employs a desiccant
bed, to dehydrate the CO2 stream. Yet another embodiment of the
present invention is the system described above, wherein two
desiccant beds are employed in alternation, wherein heat required
to dry the two beds is provided by a process heater, which heats
air that is provided by a blower to drive the hot air through the
beds and dry them. Yet another embodiment of the present invention
is the system described above, where the gas from the headspace of
the CO2 storage vessel is heated and used for the regeneration of
the beds.
[0033] Yet another embodiment of the present invention is the
system described above, further comprising a boost blower upstream
of the compressor to raise the suction pressure from a vacuum to at
least 0 psig at the main compressor. Yet another embodiment of the
present invention is the system described above, further comprising
one or more variable frequency drives (VFDs) to control the speed
of the main compressor and/or the boost blower, to track the rate
of CO2 production in the facility.
[0034] Yet another embodiment of the present invention is the
system described above, wherein the compressor compresses the CO2
stream to a pressure of no more than approximately 300 psia.
[0035] Yet another embodiment of the present invention is the
system described above, where there is one single stage of
refrigeration, having at least one heat exchanger for lowering the
temperature of the CO2.
[0036] Yet another embodiment of the present invention is the
system described above, wherein the refrigerator comprises a dual
refrigeration loop, containing both a high-stage refrigeration loop
having at least one heat exchanger for cooling the low-stage
refrigeration loop, and possibly a second heat exchanger for
lowering the temperature of the dehydrated CO2 stream; and a
low-stage refrigeration loop having at least one heat exchanger for
further lowering the temperature of the CO2 stream.
[0037] Yet another embodiment of the present invention is the
system described above, wherein either the single stage
refrigeration loop, (if applicable) or the low-stage of a dual
refrigeration loop (if applicable) is an autocascade loop having
mixed refrigerants. Yet another embodiment of the present invention
is the system described above, wherein the mixed refrigerants are
non-flammable. Yet another embodiment of the present invention is
the system described above, wherein the mixed refrigerants are
hydrocarbons.
[0038] Yet another embodiment of the present invention is the
system described above, wherein the storage vessel is an insulated
and/or refrigerated vessel, wherein the liquefied CO2 is filled
into the vessel through a dip tube contained in the vessel, with a
vent valve so that the non-condensable gases in the headspace are
allowed to vent from the vessel to maintain its pressure. Yet
another embodiment of the present invention is the system described
above, where there is a phase separator that removes the
non-condensable gases from the liquefied CO2 stream before the
liquefied CO2 stream is stored or used. Yet another embodiment of
the present invention is the system described above, where the
phase separator is fitted with a liquid transfer pump to transfer
the liquefied CO2 into a closed storage tank.
[0039] Yet another embodiment of the present invention is the
system described above, wherein some or all of the various
operations within the system are managed by automatic
electro-mechanical control elements. Yet another embodiment of the
present invention is the system described above, further comprising
one or more microcontroller(s) programmed to automatically control
some or all of the various operations. Yet another embodiment of
the present invention is the system described above, wherein the
control system is comprised of both electro-mechanical control
elements and one or more microcontroller(s) programmed to maintain
control over some or all of the various operations of the system.
Yet another embodiment of the present invention is the system
described above, further comprising a sensor network to provide
feedback to the microcontroller(s).
[0040] Another embodiment of the present invention is a method for
recovering CO2 in a brewery, comprising the following steps: (1)
bringing a CO2 recovery system to a brewery venting CO2 and
connecting the system to fermentation and bright beer tanks; (2)
removing free water from the inlet using a condensate trap or
removing both free water and foam using a foam trap, if necessary;
(3) removing water vapor from the CO2 stream utilizing a
dehydrator; (4) compressing the CO2 stream utilizing a compressor;
(5) lowering the temperature of the CO2 stream utilizing a
refrigerator, which causes liquefaction of the CO2; and (6)
transferring the liquefied CO2 into a storage utilizing a vessel
adapted to contain it.
[0041] Yet another embodiment of the present invention is the
method described above, wherein the dehydration step employs
desiccant beds. Yet another embodiment of the present invention is
the system described above, wherein two desiccant beds are employed
in alternation, wherein heat required to dry the two beds is
derived from a process heater.
[0042] Yet another embodiment of the present invention is the
method described above, wherein the refrigeration step utilizes an
auto cascade refrigerator having mixed non-flammable refrigerants.
Yet another embodiment of the present invention includes two stages
of refrigeration. Yet another embodiment of the present invention
is the method described above, wherein the refrigeration step cools
the CO2 stream to a temperature range of -15.degree. C. to
-55.degree. C.
[0043] Yet another embodiment of the present invention is the
method described above, wherein some or all of the various steps of
the method are controlled by an automatic control system. comprised
of a combination of electro-mechanical and microcontroller-based
control elements, and further having a sensor network to provide
feedback to the control system.
[0044] Other features, utilities and advantages of the various
embodiments of the invention will be apparent from the following
more particular description of embodiments of the present
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] The invention will be understood by the following detailed
description in conjunction with the accompanying drawings, wherein
like reference numerals designate like structural elements, and in
which:
[0046] FIG. 1 shows an engineering drawing of a CO2 recovery system
relevant for craft breweries. System components and subsystems are
labeled.
[0047] FIG. 2 shows a schematic for a typical installation in a
craft brewery with a centralized CO2 manifold/foam trap already in
place. The CO2 recovery system is plumbed in parallel to the main
CO2 collection line headed to the foam trap. This ensures seamless
operational transition to recovering CO2 under the purview of
standard brewery practice.
[0048] FIG. 3 shows a simplified process flow diagram for
capturing, boosting, drying, scrubbing, compressing, liquefying,
and storing CO2 as required to recover this waste stream.
[0049] FIG. 4 shows a perspective view of one embodiment of a CO2
recovery system according to one embodiment of the present
invention. This particular embodiment is designed to recover a
nominal flow rate of 1 ton CO2 per day.
[0050] FIG. 5 shows a detailed piping and instrumentation diagram
of a typical CO2 recovery system.
DETAILED DESCRIPTION OF THE INVENTION
[0051] The following description is merely exemplary in nature and
is in no way intended to limit the scope of the present disclosure,
application, or uses.
DEFINITIONS
[0052] The following terms of art shall have the below ascribed
meanings throughout this specification, unless otherwise
stated.
[0053] Throughout this disclosure a CO2 recovery "system," "unit,"
or "apparatus," or any reference to a single commercially viable
module, will refer to an apparatus module that can process a given
number of pounds (kilograms) of carbon dioxide per day. Volumetric
flow rates of trace compounds including air, humidity, ethanol
vapor, trace organics including higher alcohols, aldehydes, ethers,
and esters are considered negligible. Multiple modules can be
combined for higher gas flow rates and to address the cyclic
behavior of manifolded fermenter effluent flow rates. Product flow
estimates and sinusoidal characteristics are based on direct flow
measurement of CO2 effluent from a batch fermentation of a typical
ale product at a major craft brewery, and are provided for
explanation purposes only, and are not intended to be limiting the
scope of the present invention in any way. Different flow rates and
characteristics associated with production variations between craft
breweries as well as other CO2-venting industries will require
different modular configurations to address the specific case and
will by definition affect the quantities of products. It is
important to note the quality of recovered CO2 will not vary
appreciably due to the active purification steps taken in the
recovery process.
[0054] The abbreviation CO2 always refers to the molecule carbon
dioxide. The word "day" shall imply "a day of operations," which
shall be a 24-hour day, but could also be an 8-hour day, a 12-hour
day, or some other amount of operational time. Furthermore,
time-based production numbers will assume the recovery system has
sufficient inlet conditions and supporting utilities to run at 100%
duty. Real variations in production will cause the flow control of
the CO2 recovery system to adjust below the maximum operating rate,
and will reduce the total processed quantity of CO2.
[0055] The terms fermenter effluent, blowoff, vent gas, headspace,
carbonation, and fermentation gas all refer to CO2 that is produced
in tandem with ethanol during anaerobic fermentation of glucose via
glycolysis by the yeast Saccharomyces cerevisiae. This is an ideal
waste stream that can be recovered by the outlined invention.
[0056] Desiccation describes the physical removal of water by a
solid adsorption medium to reduce the humidity dew point
temperature of the inlet CO2 gas to a value below the coldest
possible process temperature. This ensures consistent operation by
avoiding the potential for water ice accumulation and plugging
inside the process.
[0057] Deodorization or scrubbing refers to heterogeneous
adsorption by activated carbon of trace organic components present
in fermentation CO2, especially esters, aldehydes, and terpenes.
This ensures the purity of the recovered product so that it can be
reused transparently regardless of the flavoring of the desired
product.
[0058] Beverage-grade CO2 is an industry-specific classification
that defines a baseline purity of CO2 gas for production of
carbonated beverages. The primary distinction is 30 ppmv or less of
oxygen contamination, but other purity specifications are implied,
including the absence of other flavor, odor, condensable, and
noncondensable species.
[0059] Industrial CO2 is nomenclature for commercially available
conventional CO2. This commodity stream is recovered from
large-scale industrial sources other than beverage-grade ethanol
fermentations. Because the CO2 feedstocks for industrial CO2 are so
varied and geographically disparate, the potential for
contamination in the procurement and transportation chain is much
higher than in-house recovered CO2. This is a distinct competitive
and economic advantage of the proposed invention.
[0060] An autocascade refrigeration system is a single-condenser
system containing a mixture of refrigerants which approximates the
behavior of a conventional cascade refrigeration system yet in a
smaller form-factor. This is one of the proposed solutions to
achieving the cooling required in the liquefaction of recovered
CO2.
Overview of the CO2 Recovery Process
[0061] It makes no financial or environmental sense to vent clean,
valuable carbon dioxide (CO2) that could be used in-house to offset
significant expenditures or sold to other manufacturers requiring
beverage-grade CO2 at great profit. It makes no financial or
environmental sense to pay elevated prices for a commodity
feedstock of middling purity that is typically transported
thousands of miles by truck, boat, or aircraft, requiring huge
amounts of money on vehicle fuel for transportation and at the same
time this feedstock is being vented in the very same facility
requires it for manufacturing its products. The problem is that CO2
being vented in the facility is not suitable for reuse directly,
due to low pressure, high humidity, high volume required for
storage, and trace contaminants, including oxygen which will ruin
the company's finished products. What is therefore needed is a
mobile, modular system with a minimal footprint and minimal
operational impact that can be installed in any typical craft
brewery rapidly and with minimal hardware changes or associated
installation costs. It is to meet this need that the inventors have
developed a novel CO2 recovery process which is significantly
different from conventional CO2 recovery technology to service the
booming worldwide craft brewery industry.
[0062] In the CO2 recovery process, raw fermentation CO2 is first
dehydrated and then compressed. The dry, compressed gas is then
passed through an activated carbon bed which deodorizes the process
gas by removing trace organic components. The dry, compressed,
deodorized gas is then refrigerated down to optimally cold
temperatures, causing the carbon dioxide to liquefy, while trace
noncondensable gases remain in a dissolved gaseous phase. An
optional two-phase separator with pressure control is then employed
to separate non-condensable gases (mainly nitrogen and oxygen) from
the liquid CO2 phase. Alternately, this action can be performed in
an integrated storage vessel which further reduces the cost and
complexity of the process. Because the liquid CO2 product is always
at a colder temperature than ambient conditions inside a production
facility, partial vaporization of the CO2 occurs, and some venting
is permitted by the pressure control device. As this process
continues, non-condensable gases are preferentially stripped from
the liquid CO2 product stream and vented safely to atmosphere,
further enhancing the purity of the recovered product. If this step
is performed in a separate phase separator, the liquid CO2 product
is then sent to an insulated liquid storage dewar by differential
pressure balancing. Otherwise, the product is already been sent to
the liquid storage dewar, also by differential pressure balancing.
Eliminating a cryogenic product pump further simplifies the process
and reduces cost when compared to conventional CO2 recovery
technologies. Once the liquid CO2 product is stored in the onsite
dewar, it is vaporized through a provided ambient vaporizer for
direct use in the brewing process.
[0063] Therefore, this CO2 recovery process solves a large market
gap that has existed for over two decades by providing an in-house
CO2 recovery system appropriate for the small size of the vast
majority of breweries worldwide. This allows these small,
cash-strapped companies to see a much-needed savings on a major
brewing commodity as well as address a major environmental concern
and source of a workplace hazard.
[0064] The innovative design of the CO2 recovery system according
to the principles of the present invention leverages a valuable
in-house waste stream using a novel autocascade refrigeration
subsystem. This design allows for very compact and cost-effective
purification and recovery of fermentation CO2 inside a small-scale
production brewery. The recovered liquid CO2 is stored on-site in a
liquid storage dewar and can be vaporized and used directly in the
brewing process, or used to fill vessels for sale at a profit to
outside organizations. The unique design of the CO2 recovery
process produces a system that can be sized to fit through doorways
of standard dimensions. Craft breweries typically inhabit old
repurposed buildings and are experiencing rapid production growth,
which makes space in around the brewery a limited resource. The CO2
recovery system, which can process 300 pounds/day of fermentation
gas, onto a cart with casters and a handle that measures 28 inches
wide by 40 inches deep by 64 inches tall. Larger units can be
manufactured that process up to approximately 600-900 pounds/day
and still fit within a standard 36-inch-wide, 80-inch-tall door.
CO2 effluent leaving beer fermenters in the active anaerobic phase
measures >99% CO2 composition by volume on a gas chromatograph.
The vented fermenter gas also contains other compounds such as
water vapor, hydrogen sulfide, carbon monoxide, oxygen, and
nitrogen, as well as trace organic compounds including alcohols,
aldehydes, ethers, esters, ketones, and terpenes.
[0065] Beverage-grade CO2 is an exacting standard defined by the
International Society of Beverage Technologists (ISBT;
http://www.bevtech.org/) that requires a minimum 99.9% purity by
volume, as well as a maximum 30 ppm by volume of oxygen
contamination. The full specification is listed in Table 1. A brief
skimming of the table shows contaminants that are not present in a
beer fermenter to begin with, including ammonia, nitric oxide,
nonvolatile residue, phosphine, and aromatic hydrocarbons. These
compounds are however present in processes which are conventional
sources of industrial CO2. Economically, industrially available CO2
requires a lot more effort and technology to produce a product
consistent with the beverage CO2 specification. Therefore,
tailoring a CO2 recovery system to accommodate craft breweries,
there is an inherent superiority from both a purity and a
transportation standpoint.
[0066] The process described in this patent application has been
demonstrated to achieve a maximum oxygen contamination of 1.1 ppm
by volume, with a corresponding inlet air contamination of 3%. Due
to partial pressure concerns the minimum CO2 purity required for
successful liquefaction in the present invention is 80%. If methane
linear relationship is assumed between inlet air contamination and
product purity, even an inlet air contamination of 20% will result
in 7.3 ppm oxygen contamination, well below the industry standard
of 30 ppm. The samples discussed were procured via CO2 recovery
from active fermenters at a major craft brewery at two dates eight
months apart, using two separately constructed systems implementing
the proposed CO2 recovery system, and measured by an independent
third-party lab with ion exchange chromatography. Other contaminant
results include hydrogen which was undetectable at the instrument
threshold of 0.1 ppm, a maximum of carbon monoxide at 0.1 ppm (cf.
10 ppm in the standard), and a maximum of 2 ppm nitrogen, which is
considered a neutral contaminant. Indeed, in an effort to
constantly innovate, craft breweries have begun serving beers
carbonated with varying proportions of a CO2/nitrogen (N2) gas
mixture. Full purity results are displayed it Table 2. The
processes described in this patent application are distinguishable
from conventional CO2 recovery technologies which operate at system
pressures of 250-300 psig or higher. As noted in the introduction,
ethane preferred embodiment of the present invention recovers CO2
at a significantly reduced pressure of 150 psig. This design
modification provides a myriad of benefits, including process
simplicity, opportunity for miniaturization, improved capital
economics, lower ambient noise concerns, enhanced process safety,
downstream equipment cost savings, and easier removal of
noncondensable contaminants. Because no CO2 recovery solutions
exists# for craft breweries, their purchased industrial CO2 is
stored in higher pressure containers consistent with the
conventional process. A lower pressure product consistent with the
preferred embodiment of the present invention can't be transported
into a higher pressure vessel without an active control element,
which is absent from the design. This requires a separate lower
pressure storage solution to receive the recovered product, and
physically prevents any contamination of the two different CO2
sources. This is an important distinction which prevents clients
from force-feeding their superior recovered CO2 into the higher
pressure backup storage tank, which would violate leasing terms
that are standard with gas supply companies. By incorporating a
separate, lower pressure storage solution and vaporizer as part of
the CO2 recovery system itself, purity, contractual, and process
parameters are all maintained within specifications. This also
makes a separate phase separator for removing noncondensable gases
extraneous, which further lowers the capital cost of the system and
simplifies the process. It is also much easier to drive out
dissolved gases from a lower pressure liquid, and can even occur
passively, instead of a higher pressure system which requires an
active driving force to remove noncondensable gases to meet purity
specifications. Therefore the lower pressure design point provides
far-reaching economic benefits when compared with conventional
technology, in addition to opening up a large, previously untapped
market segment.
[0067] The present invention has already been designed, fabricated,
tested, and installed in multiple typical production craft
breweries. All the above benefits have been observed and supported,
including the design processing rate of 12.5 pounds of CO2 per
hour. The superior purity numbers reported in Table 2 were taken
from installations of this CO2 recovery process in active
production breweries. Furthermore, extensive taste testing of
carbonated beverages (both water and flagship beer products) was
performed by long-time employees in the industry with well-trained
palates at three major craft breweries. All results indicated even
or superior flavor and odor characteristics when sampling beverages
prepared with CO2 recovered by a produced embodiment of the present
invention when compared to samples prepared with conventionally
purchased industrial CO2. This satisfies the odor and taste
stipulations of beverage-grade CO2 as outlined in Table 1.
Potential Economics of Small-Scale CO2 Recovery
[0068] One of many illustrative scenarios is presented here to
demonstrate the potential profitability of a CO2 recovery process
representative of the present invention. In this scenario, the
example brewery uses exactly as much CO2 as it is able to capture
with the CO2 recovery system, thus replacing its entire expenditure
on purchased CO2. Other scenarios would be if the brewery is able
to capture more CO2 than it consumes, leaving excess inventory for
sale, or if the brewery uses more CO2 than it can capture, in which
case the make-up inventory would be provided by the existing gas
supplier, but at a much reduced usage rate which is still a large
economic improvement. This economic analysis is illustrative of the
invention only and is not meant to limit the scope of the present
invention.
[0069] In one embodiment, a CO2 recovery system processes 300
pounds of fermentation CO2 per day. Assuming a premium industrial
peak electricity cost of $0.20/kWh and a negotiated industrial CO2
cost of $0.15 per pound (which can range to upwards of $0.50 or
even $1.00 per pound, depending on geographic location), the CO2
recovery system will use an average of 600 Wh per kilogram of
recovered CO2. The output produced by such a CO2 recovery unit will
fall within beverage-grade CO2 purity specifications.
[0070] At the indicated prices, the purchased CO2 displaced by
in-house recovery would be valued at $1,350 in a 30-day month. At
an electricity consumption of 600 Wh/kg, this system would cost
$491 to operate, yielding a savings of $859, or 64% of the previous
cost associated with purchasing industrial CO2. This is a rather
conservative economic scenario. For instance, many areas located
next to regional power plants will have lower electricity rates.
Craft brewers also experience negative economies of scale with
their gas suppliers. Since they are relatively small clients, their
independent negotiating power is less and they commonly pay
$0.20-0.30 per pound of delivered industrial CO2. International and
offshore craft breweries have such outrageous delivered CO2 prices
that a purchase of a CO2 recovery system consistent with the
present invention will realize full payback periods of six months
or even less, all while utilizing a product of superior purity.
Preferred System Schematics of the CO2 Recovery System
[0071] The present invention in its various embodiments provides
highly efficient and economic solutions to close the loop in
production facilities which simultaneously vent one CO2 stream
while purchasing another. In one embodiment, the CO2 recovery
system is a mobile, modular system that can be rapidly installed in
parallel within an existing craft brewery to recover CO2 for reuse
in the beer production process.
[0072] FIG. 3 shows a schematic diagram of one embodiment of a
process of CO2 recovery according to the principles of present
invention. CO2 vented from the headspace of a bank of fermenters
enters the recovery system from the vessel labeled "Fermenters."
Depending on the specific configuration of the CO2 vent manifold in
the brewery, the process gas is optionally boosted in pressure by
the equipment labeled "Blower." This gas is first dehydrated in the
unit operation labeled "Dry Bed," which is actually a pair of
desiccant beds which removes humidity from the inlet CO2 via
adsorption. One bed is being actively regenerated while the other
is online and is drying the CO2 stream. The dehydration step is
followed by the "Scrubber" which deodorizes the fermenter CO2 gas
via adsorption with activated carbon. The dry, deodorized gas is
then compressed at the "Compression" step which raises the pressure
from the inlet fermenter pressure to the elevated process pressure.
The dry, compressed gas is then refrigerated at "Refrigeration,"
causing the CO2 gas to liquefy, while the noncondensable gases
become dissolved in solution but do not undergo a phase change. The
liquefied CO2 product is then transferred into storage ("Liquid
CO.sub.2 Storage"). In this embodiment, the storage vessel doubles
as the liquid-gas phase separator, which passively evolves the
noncondensable gases from the liquid CO2 product. This is the
simplest and most economical configuration which allows for
separation of the noncondensable species by venting from the
headspace of liquid storage to maintain pressure control. When the
brewery has demand for CO2 gas in the process, the liquid CO2
product is sent through an ambient vaporizer, ensuring the
headspace of the storage never gets used in the downstream brewery
process.
[0073] FIG. 1 shows a constructed version of a preferred embodiment
of the present invention. The relevant unit operations as
referenced in FIG. 3 are clearly labeled. Two main additions to
note in FIG. 1 are the "Control Panel" which contains the
microcontroller-based and electromechanical-based control system
which enables autonomous operation of the CO2 recovery unit and the
"Foam Trap" which protects the adsorption beds on the system from
krausen, foam, trub, malt solids, hop solids, wort proteins, and
yeast which can become entrained in the fermenter blowoff. The foam
trap acts as a catch-all liquid separator which will trap and drain
all potential inlet liquids from humidity condensation to krausen.
An optical sensor will observe and foam or liquid phase and then
proceed to lower the liquid level in the vessel with a washdown
cycle that sprays water from the top and pumps inventory out the
bottom. The other unit operations of note that are shown in FIG. 1
are the "Dry Beds," "Activated Carbon," "Main Compressor," and
"Refrigeration."
[0074] As mentioned, the system that is enclosed inside the
container labeled "Refrigeration" is preferably a single-compressor
autocascade refrigeration system. An autocascade is a closed-loop
refrigeration cycle that relies on a single refrigeration
compressor as its prime mover. The working fluid in an autocascade
refrigeration cycle is a mixture of refrigerants, which can be
either flammable or nonflammable, as required by the process
requirements or safety standards associated with particular
installations. The preferred embodiment of the invention uses a
mixture of nonflammable refrigerants in the autocascade
refrigeration cycle. The condenser used in the autocascade
refrigeration cycle is air-cooled, which removes the need for a
chilled glycol utility stream which would burden already overloaded
glycol systems in craft breweries and advances the design intent of
a mobile, modular system with minimal input/output connections and
process utility requirements. Because an autocascade refrigeration
system contains a mixture of refrigerants, a two-phase vapor-liquid
system develops inside the refrigeration system. The liquid phase
is then flashed across a pressure reducing device which further
cools it, whereupon it exchanges heat with the vapor stream to
partially condense the refrigerant in preparation for the final
refrigeration evaporator heat exchanger. The autocascade
configuration is preferred since this process has elected for a
lower pressure operating point when compared to convention CO2
recovery technology. The autocascade refrigeration system is
capable of achieving the low process temperature, ranging anywhere
from -80 to -30.degree. C., or colder or warmer as required.
Furthermore, because an autocascade refrigeration system operates
on a single compressor, it is a compact, space-saving subsystem
which is required for the most economically relevant
applications.
[0075] In an alternative embodiment a conventional cascade
refrigeration system can be employed wherein two parallel
refrigeration loops contain refrigerants of differing vapor
pressures. These two refrigeration loops establish different
operating temperatures, wherein the higher temperature loop
exchanges heat with the lower temperature loop, which ultimately
cools the process gas. These configurations can be air-cooled or
glycol-cooled or process water-cooled, as required by the
application.
[0076] FIG. 2 shows an example installation in a typical production
craft brewery with an existing CO2 vent gas manifold. As can be
seen the previous installation has the blowoff arms dropping down
vertically from the vessels labeled "Fermenter" where they are then
manifolded into a common line and leave the left side of the
drawing to an existing, centralized foam trap. The installed CO2
recovery system is installed in parallel to the existing CO2 vent
manifold with tees that are installed into the existing blowoff
arms. Each individual fermenter is then run through a hand valve
which allows brewery cellar operators to valve on fermenters that
are actively producing CO2 and valve off fermenters that are idle
or empty and presumably full of air, which would negatively affect
the capture efficiency and product purity of the recovery process.
FIG. 2 emphasizes the simplicity of installation and operation
which is a core design principle and distinguishes this technology
from commercially available solutions. CO2 gas enters the recovery
system and liquid CO2 product leaves to storage. Water is made
available to the optional foam trap which is used intermittently
for washdown during inlet krausen events. The foam is
simultaneously pumped to a floor drain or tote during the washdown
cycle. Aside from electricity required to power the system, no
other utilities are required or consumed by the recovery
solution.
[0077] FIG. 4 shows a constructed version of an alternate
embodiment of the present invention. This system is constructed to
handle a higher capacity than the preferred embodiment, with the
capability to liquefy 2000 pounds of CO2 per day. This system can
also be operated at a slightly elevated pressure than the preferred
embodiment, which allows for a warmer temperature in the
refrigeration subsystem. This process temperature is achieved in
the unit depicted by FIG. 4 with a standard cascade refrigeration
system employing two separate refrigeration compressors. This
configuration also has a liquid phase separator with pressure
control which enhances removal of noncondensable gases at this
elevated pressure before the CO2 is transferred into storage. These
design parameters are typically favored for higher-throughput
systems which are installed in larger breweries. Larger craft
breweries usually have more floor space and process utilities which
are required to support a CO2 recovery system of this design.
Process Parameter Selection
[0078] The CO2 recovery process takes an un-used, vented, fermenter
CO2 gas stream, and produces a high purity, locally available
liquid CO2 product suitable for reuse in the very same brewing
facility. This process is unlike conventional CO2 recovery
technology which requires a static installation occupying a large
footprint and consuming valuable brewery utility streams, resulting
in a much larger system and more costly operations. In conventional
CO2 recovery technology, purification steps are complex and many,
with liquid water scrubbers, actively heated stripping columns and
overhead condensers. This creates a complex, expensive, and
cumbersome system that is not mobile or modular and would not be
useful in any craft brewery. Furthermore, the cost and complexity
require an economy of scale of processing capacity which is an
order of magnitude larger than what a craft brewery is capable of
producing. In contrast, the present invention is able to achieve a
high purity product and an efficient recovery rate without using a
complex system comprising multiple unit operations with elaborate
upstream and downstream infrastructure including high-volume,
low-pressure, ceiling-mounted feed gas storage balloons, as well as
a completely engineered and custom fabricated sanitary hard
plumbing manifold leading from the fermenters. The inventors were
able to achieve this previously unknown result by carefully
selecting the process operations and process parameters as
described in detail in this application.
[0079] In summary, the inventors have found that it is possible to
achieve this type of efficient CO2 recovery and purification via
liquefaction by running the refrigeration subsystem to achieve a
process temperature preferably in the range of approximately
-15.degree. C. to approximately -55.degree. C. (and even more
preferably -37.degree. C. to -43.degree. C.), at a pressure
preferably in the range of approximately 75 psia to approximately
300 psia (and even more preferably under about 130 to 160 psia).
The inventors also realized that this can be achieved utilizing a
novel refrigeration unit. The inventors have discovered that the
process parameters described here allow this type of purification
and recovery to occur at the craft brewery scale, something that
has not been achieved before in CO2 recovery systems. By utilizing
these process parameters, the inventors were able to optimize the
design of the entire system that utilizes this process, allowing
the inventors to simplify the system to the point where it can be
made portable and modular. The inventors have found that when one
compresses and cools to the temperature and pressure ranges
described here, it is possible to achieve this significant
purification and recovery result in a portable apparatus.
[0080] In one embodiment, the process works by reducing the
temperature of the raw, fermenter CO2 stream to an ideal
temperature range. Unlike a conventional refrigeration cycle of
existing CO2 recovery systems, the temperature is colder in order
to facilitate a lower operating pressure as well as ease of removal
of non-condensable gases. However, it is not so cold (below
-56.6.degree. C.) in which the carbon dioxide freezes into a solid
block which would plug the process plumbing and heat exchangers
which would have to be disassembled to remove the blockage. The CO2
recovery process temperature and pressure parameters were finely
calibrated by the inventors in order to achieve this efficient
recovery process, making it feasible to make the process work on a
portable scale suitable for craft brewers, a previously unserved
and very large brewery market segment. Because of the ideal cold
temperature range, a moderate process pressure is needed which can
be achieved with a two-stage compressor. Existing CO2 recovery
systems do not operate at this cold of a process temperature, and
so are forced to achieve the liquefaction at a higher pressure.
This requires a three- or four-stage compressor which entails more
capital expenditure and a larger installed footprint. Furthermore,
non-condensable gases are more soluble in the liquid CO2 product at
elevated pressures and so require a distillation column with a
heated reboiler and a chilled overhead condenser to remove oxygen
contamination below the 30 ppm standard for beverage-grade CO2.
This distillation column again adds significant cost, complexity,
and space to the installed recovery CO2 system.
[0081] In addition, because of the ideal temperature range, the
load the compressor is reduced and the need for a distillation
column is eliminated, reducing system complexity and operating
costs. In addition, because of the ideal temperature range, instead
of a complete distillation column to protect against oxygen
contamination in the final product, no active separation system is
needed aside from the phase separation that happens passively in
the bulk liquid CO2 storage vessel. A stripping column is the
bottom half of a distillation column and includes a reboiler, while
the top half above the inlet is referred to as a fractionating
column and includes an overhead condenser. In an alternate
embodiment of the present invention with a moderately higher
operating pressure, a simple phase separator is sufficient to drive
off some noncondensable gases before the product is sent into
storage. (A distillation column is twice as complex as a stripping
column.)
[0082] One unique feature of the present invention is an ideal
temperature and pressure range of the process stream required to
perform the liquefaction of the fermenter CO2 gas. This allows the
liquid CO2 product to get separation from noncondensable gas
contamination, especially oxygen. The inventors recognized that
refrigeration is less expensive than compression in terms of
capital equipment, but more expensive in terms of operating (power)
costs; however, they realized that this is greatly beneficial since
this is the only configuration that supports minimization of the
process to suit installation and operation in a craft brewery. The
inventors also recognized that by reducing the temperature of the
raw gas stream to a lower temperature range than previously
achieved in a mobile scale, a lower compression ratio (and hence
operating pressure) is possible while still achieving desirable
results. Such a lower operating pressure results in an overall
lower capital cost for the entire system because lower-pressure
components and subsystems can be utilized.
[0083] The ideal temperature and pressure ranges for the CO2
recovery process were selected as follows by the inventors. A most
preferred temperature range for the process is -37.degree. C. to
-43.degree. C., but temperature ranges from -15.degree. C. to
-55.degree. C. are feasible, and more preferably between
-30.degree. C. and -45.degree. C., and possibly between -20.degree.
C. to -50.degree. C. There would be little benefit to going below
-55.degree. C. and a significant cost to go below that temperature,
as dry ice starts to form at -56.6.degree. C., and it is desirable
to avoid forming any amount of solid CO2. Accordingly, based on the
above temperature ranges, a most preferred pressure range is
130-160 psia, and preferably 120-175 psia. However, pressure ranges
of 75-300 psia are possible in various embodiments of the CO2
recovery process. Higher pressures are also possible in some
embodiments since CO2 liquefies at 930 psia at 25.degree. C.
Existing CO2 recovery systems utilize higher pressures because they
have not been able to achieve such low process temperatures on any
scale.
[0084] In addition, many single-brewery CO2 recovery systems rely
on higher compression and moderate refrigeration temperatures to
cool the process gas. Unexpectedly, the inventors found active
refrigeration to offer many advantages, as described here. On a
high level, the CO2 recovery process utilizes compression,
refrigeration, and purification. If one were to assume that each of
the three sub-processes have been optimized and has equal cost and
complexity, what this implies is that by optimizing one of the
three sub-processes, it is possible to save on the capital and
operating costs of the other sub-processes. The inventors had the
insight that by improving the middle of the three
processes--namely, refrigeration--it was possible to significantly
save on the cost and complexity of the two processes before and
after it--namely, compression and separation. After the vented,
dehydrated, deodorized CO2 fermenter gas is compressed and
refrigerated to the ideal pressure/temperature ranges described
above, there is a simple liquid/vapor separation either in the
storage vessel in the preferred embodiment or in a separate phase
separator in an alternate embodiment. The gaseous impurities that
leave the liquid/vapor separator are vented safely to atmosphere.
Meanwhile, the liquid CO2 product is ready for use from the liquid
storage vessel after passing through an ambient vaporizer. That is,
after compression and refrigeration, the stream components that
remain are primed for removal of noncondensable contaminants
without any further processing equipment.
[0085] In summary, the existing single-brewery CO2 recovery systems
are able to recover and purify fermentation CO2, resulting in a
liquid CO2 product in storage with significant cost, complexity,
and footprint requirements. By carefully selecting the process
parameters and utilizing a novel system design and a unique
refrigeration system able to reach very cold temperatures on a
mobile, modular system suitable for installation in a craft
brewery, the inventors have been able to achieve something on the
portable scale that is unprecedented in CO2 recovery
technology.
[0086] In summary, the CO2 recovery process offers the following
primary value propositions, which separate it from conventional CO2
recovery systems: [0087] 1. Mobility, which is essential for
installation in a craft brewery. [0088] 2. The CO2 recovery system
has minimal process inputs or outputs and a minimized reliance on
process utilities from the installation facility. The minimal
requirements for operation are electrical service to power the unit
and fermentation CO2 gas to provide a feedstock to the system.
[0089] 3. The system is compact due to choice of ideal operating
temperatures and pressures, which minimizes the installed
footprint, which allows installation inside cramped, busy craft
breweries. [0090] 4. Using a novel configuration and application,
the inventors are able to eliminate active purification unit
operations, which greatly reduces capital cost and utilities
consumption, while maintaining production of a very high purity
liquid CO2 product.
Experimental Results
[0091] The inventors have built and tested several embodiments of
the present invention. This section presents various experimental
results from such tests.
[0092] The criteria required for a CO2 sample to meet beverage
grade certification according to the International Society of
Beverage Technologists (ISBT) are listed inTable 1 (Source:
Fountain Carbon Dioxide Quality Guideline, International Society of
Beverage Technologists, September 2006).
[0093] The initial hurdle to validate the present invention was to
demonstrate purity results that are as good or better than
industrially available CO2. Toward this end a pilot unit was
constructed and installed in a major craft brewery for operational
testing. Operations were satisfactory and a significant amount if
liquid CO2 was recovered. A sample was collected and sent off for
testing. Results are listed as Sample 1 in Table 2. A simplified
analysis was performed since many contaminants can be eliminated
simply by knowing they are not present in the fermenters to begin
with. Noncondensable gases, especially oxygen, were the primary
liability for contamination, and a result of 1.1 ppm is clearly a
superior sample when compared to the 30 ppm allowed by the industry
standard. Furthermore, a gas analysis typical of commercially
available industrially sourced CO2 is shown in Table 3. The oxygen
content listed in that assay is 1.570 ppm, which is nearly 50%
inferior to the performance of the present invention. In addition.
gas assay points are typically located at the beginning of the
transportation chain, upon which the liquid product is transferred
between multiple trucks and tanks of varying quality. There is a
very real potential for contamination along the way. The sample
recovered by the proposed CO2 recovery technology was sampled from
the storage container at the brewery, guaranteeing on-site quality
control. By miniaturizing CO2 recovery technology that connects the
source to the application, a very real potential for human error is
removed. Taste testing of water and major flagship beer products at
this and two other major craft breweries of recovered CO2 with this
pilot unit proved even or better than the industrial CO2 control
samples.
[0094] The superior purity result permitted design, fabrication,
construction, and installation of a production version of the
present invention. This unit was installed at a larger scale major
craft brewery again for operational testing and purity analysis.
Once operations were deemed acceptable, hundreds of liters of
recovered liquid CO2 were collected and stored for reuse in purging
fermenters and bright tanks in the brewery cellar. A liquid sample
was again drawn and sent off for analysis. Again, the species of
interest given the surrounding cleanliness and sterility of
upstream and downstream vessels was oxygen. Results came back very
consistently at 1 ppm oxygen as shown under Sample 2 in Table 2.
Again, the in-house recovered CO2 was significantly superior in
quality to purchased industrial CO2.
TABLE-US-00001 TABLE 1 ISBT Guidelines for Beverage Grade Carbon
Dioxide Volumetric Metric concentration threshold Purity 99.9% min
Moisture 20 ppm max Oxygen 30 ppm max Carbon monoxide 10 ppm max
Ammonia 2.5 ppm max Nitric oxide/nitrogen dioxide 2.5 ppm max each
Nonvolatile residue 10 ppm (weight) max Nonvolatile organic residue
5 ppm (weight) max Phosphine 0.3 ppm max Total volatile
hydrocarbons 50 ppm max Acetaldehyde 0.2 ppm max Aromatic
hydrocarbon 20 ppb max Total sulfur content 0.1 ppm max Sulfur
dioxide 1 ppm max Odor of solid CO2 No foreign odor Appearance in
water No color or turbidity Odor and taste in water No foreign
taste or odor
TABLE-US-00002 TABLE 2 Ion-exchange chromatography results for
noncondensable contamination of recovered CO2 from craft brewery
fermenters. Sample 1 Sample 2 Date Mar. 22, 2013 Nov. 18, 2013
Hydrogen <0.1 ppm <1 ppm Oxygen 1.1 ppm 1 ppm Nitrogen
<0.1 ppm 2 ppm Carbon monoxide 0.1 ppm <10 ppb
TABLE-US-00003 TABLE 3 Example purity assay of commercially
available industrially-sourced liquid carbon dioxide. Volumetric
Concentration Moisture 0.260 ppm Oxygen 1.570 ppm Argon + Oxygen
0.160 ppm Nitrogen 4.480 ppm Carbon monoxide 0.120 ppm Total
hydrocarbon 0.810 ppm Total sulfur 0.003 ppm Ammonia 0.000 ppm
Acetaldehyde 0.000 ppm Nitrogen oxides 0.000 ppm Aromatic
hydrocarbons 0.000 ppm
Detailed Schematic of the CO2 Recovery Process
[0095] A detailed process and instrumentation diagram (P&ID)
for the recovery of vented CO2 is now described according to one
embodiment of the CO2 recovery system as shown in FIG. 5. The
P&ID depicts the flow vented, wet fermentation CO2 through the
various components of the recovery process. In brewery
applications, the vented CO2 is obtained downstream of any air
locks, trub buckets, or foam traps (not shown).
[0096] The CO2 recovery system is designed to receive vented carbon
dioxide gas from the fermenters in a production craft brewery. The
recovery system processes the vented fermenter gas into a liquid
product stream that meets the stringent purity requirements
required to be classified as beverage grade carbon dioxide.
[0097] The CO2 recovery process begins at an optional foam trap
(501). This foam trap provides a second layer of protection of the
process from liquid ingress. This is in addition to any upstream
air locks or foam traps already installed in the brewery. Liquid
entering the system would damage all downstream components,
including the desiccant material, the deodorizing adsorbent, the
compressor itself, and the refrigeration heat exchangers. Final
product purity would also be compromised since only 20 ppm of water
is permissible in the final product. The foam trap provides a
collection volume for any humidity condensation or krausen foam
that may travel from the fermenters' blowoff arms to the inlet of
the recovery system. An optical sensor detects a high level of
accumulation in the foam trap and begins a washdown cycle, which
simultaneously mists liquid water into the foam trap and pumps it
from the bottom of the vessel.
[0098] The humidified fermenter CO2 enters a regenerative
adsorption desiccant system for dehydration that removes any water
that exists in the process gas. The resulting CO2 gas has an
aqueous dew point below -73.degree. C. (lower than the coldest
temperature in this embodiment) which reduces the potential for ice
formation in the refrigeration or storage portions of the system.
The maximum dew point can be adjusted based on the system's
operating temperature at its coldest point (after the autocascade).
One can see from FIG. 5 that there are two desiccant beds (503) in
parallel, allowing one to be regenerated by dry, hot air or CO2
from other parts of the process while the other bed is valved into
the main process line and is actively drying the inlet fermenter
gas. The regeneration of the offline dry bed is accomplished with
alternating process flow by actuating the four-way valves (502) and
adding heat, which in this embodiment is accomplished with electric
band heaters (504).
[0099] The conditions required for liquefaction of the CO2 stream
begin at the two-stage compressor (506). The suction pressure is
continually monitored by a pressure transmitter on the inlet gas
downstream of the optional foam trap. The reading of the pressure
transmitter informs the variable frequency drive (VFD; 505) of an
appropriate speed at which to operate the compressor, which
determines the instantaneous processing rate of the entire process.
The frequency output of the VFD drives the electric motor that is
mechanically coupled to both stages of compression. The compressor
is oil-free to maintain purity specifications and is air-cooled to
reduce installation size, avoid reliance on plant utilities, and to
simplify operation. In this embodiment, two stages of compression
are used to bring the fermenter effluent to a sufficiently high
pressure to enable liquefaction of the CO2. If the desiccant beds
were not placed upstream of the compressor the rise in pressure of
the humidified process CO2 would cause partial condensation of
moisture content. This would lead to complications including
microbial growth, corrosion of mechanical components, and potential
damage to the compressor pistons due to the incompressible nature
of liquid water. In short, compression occurs in two stages, where
the compressor is air-cooled and on speed control, which tracks the
variable CO2 flow rate leaving the fermenters. This flow control
minimizes variations in the slightly positive fermenter pressure,
which is a critical parameter for maintaining on-spec production of
quality beer products. Once the gas is sufficiently dehumidified
and at high pressure, it is sent through a deodorizing scrubber
filled with activated carbon (507). The preferred type of activated
carbon is ideal for removing trace organic compounds from a gaseous
CO2 stream. The most preferred specification for the activated
carbon is a particle size distribution with over 90% of the
particles falling with the range of 2.00 mm (10 mesh) to 4.75 mm (4
mesh) and with an iodine number, mg/g, equal to 1050 minutes. The
carbon bed will last for approximately 30 days of full-time
operation with typical loading from common ale recipes produced by
craft breweries. The activated carbon is then dumped and refilled.
The loaded carbon is sent back to the manufacturer for regeneration
within stringent conditions to preserve the pore size and internal
microstructure of the activated carbon particles. The carbon can
then be sent back to the client at a reduced rate to further
improve the process economics.
[0100] Once the fermenter CO2 gas is dehumidified, compressed, and
deodorized, it is now ready to begin the chilling process to
liquefy the CO2 at the elevated operating pressure. In the
preferred configuration and in FIG. 5 the optimally cold
temperature is achieved by an autocascade refrigeration subsystem,
described previously in greater detail. While FIG. 5 shows a
simplified diagram of the refrigeration system omitting some of the
details, the three major components are represented: compressor
(508), air-cooled condenser, and process evaporator (509). In a
preferred embodiment the air-cooled condenser is controlled by a
feedback loop that measures the liquid CO2 product temperature and
changes the fan speed accordingly. This is a technique to minimize
energy consumption required to operate the recovery unit. Because
dry ice can form at process temperatures in a low-pressure
scenario, operation of the refrigeration system is locked out by a
pressure transmitter that measures the discharge pressure of the
compressor. Once the system pressure is sufficiently high to
protect against dry ice formation, the refrigeration compressor is
commanded on to commence liquefaction of the CO2 product.
[0101] The final process vessel (510) in FIG. 5 can represent
either a standalone phase separator located prior to bulk storage
or it can represent the final liquid CO2 storage dewar. In either
configuration, the vessel is operated under level control, which
prevents flooding of the liquid CO2 product into areas of the
process or into the production facility. The headspace of the
vessel is composed primarily of CO2 gas, but the majority of any
noncondensable gases introduced to the process will reside here as
well. The vessel is pressure relieved at a pressure near the
operating pressure, which is near 160 psig for the preferred
embodiment. This pressure is significantly lower than conventional
CO2 recovery process, so the noncondensable gases easily leave
through the natural venting process associating with internal
pressure regulation. This removes an otherwise very complicated
distillation column from the process which is required by the
conventional process to remove noncondensable gases in solution to
meet beverage grade purity standards.
[0102] Once the vented headspace gas leaves the top of the phase
separator or storage vessel, it does not directly vent to
atmosphere. Staying consistent with the design intent of a compact,
self-sufficient design with minimal reliance on utilities and
electricity consumption, the vent gas is leveraged to regenerate
the offline desiccant bed. The vent gas travels through the
pressure control regulator which greatly reduces its pressure. This
low pressure, predominantly CO2 gas stream travels through one of
two four-way valves (502) and into the offline desiccant bed,
whereupon the gas becomes heated by the vessel heater (504), marked
"Q" to represent heat input. The heater on the desiccant bed which
is actively dehumidifying the inlet process gas remains off until
the bed is saturated. Logic for transitioning the beds is based on
a combination of inputs from temperature transmitters, flow
transmitters, timers, and humidity transmitters. The combination of
elevated temperature and the convective medium provided by the
flowing gas desorbs water molecules from the desiccant material and
transports the water vapor through second four way valve (502),
whereupon it vents safely into the atmosphere. In an alternate
embodiment, a regenerative blower can be added to augment the
regenerating gas flow rate. In another embodiment the heaters can
be applied directly to the regenerating gas prior to the vessels
instead of heating the vessel walls directly.
[0103] The absence of a cryogenic liquid transfer pump should be
noted as yet another example of an intentional simplification and
cost reduction of the present invention.
Refrigeration Subsystem Embodiments
[0104] In order to achieve the ideal temperature range to achieve
liquefaction and purification of CO2 at a moderate pressure as
described in this application, a highly novel and original
refrigeration system was designed, built, and tested. The
refrigeration system allows for efficient, small-scale recovery of
fermenter CO2 into a liquid product stream that meets the stringent
purity specifications outlined in Table 1. In particular, it
enables the efficient removal of noncondensable gases, especially
oxygen (02), from the liquid CO2 stream, where its presence would
unfavorably impact the taste and flavor characteristics of the
packaged beer products.
[0105] Since temperatures lower than -40.degree. C. are preferred
in this invention, in some embodiments cascade and/or autocascade
refrigeration systems may be used. In a preferred embodiment of the
present invention, an autocascade refrigeration system is utilized,
as shown and described in relation to FIG. 5. Some of the features
and advantages of such an autocascade refrigeration system is now
discussed, along with alternative embodiments. In a typical
refrigeration system, the maximum difference between the warm and
cold temperature of a refrigeration cycle is limited by properties
of the refrigerant and/or losses associated with the transport of
the refrigerant. For larger temperature differences, one has to
arrange several refrigeration cycles "above" each other, each cycle
spanning a certain temperature difference. A typical cascade
refrigeration system is made up of separate but connected
refrigeration stages, each of which have a primary refrigerant
wherein the refrigerants work in concert to reach the desired
temperature. The principal is to condense refrigerants that are
capable of achieving ultra-low temperatures that would otherwise
not be able to condense at room temperature. The reason that two
refrigeration stages are used is that a single stage cannot
economically achieve the high compression ratios necessary to
obtain the proper evaporating and condensing temperatures.
[0106] The cascade refrigeration system comprises two separate
circuits, each using refrigerants appropriate for its temperature
range. The two circuits are thermally connected by the cascade
condenser, which is the condenser of the low-temperature circuit
and the evaporator of the high-temperature circuit. Refrigerants
that may be selected for the high-temperature circuit include R-22,
ammonia, R-507, R-404a, and so forth. For the low-temperature
circuit, a high-pressure refrigerant with a high vapor density
(even at low temperatures) should be selected (such as
ethylene).
[0107] The condenser of the first stage A, called the "first" or
"high" stage, is fan cooled by the ambient air. In some
embodiments, a liquid coolant may be used. The evaporator of stage
A is used to cool the condenser of stage B, called the "second" or
"low" stage. The unit that makes up the evaporator of stage A and
the condenser of stage B is referred to as the "inter-stage" or
"cascade condenser." Cascade systems use two different
refrigerants, one in each stage. The two-stage cascade system uses
these two refrigeration systems connected in series to be able to
achieve temperatures as low as -85.degree. C.
[0108] In an autocascade refrigeration system, in contrast, a
single compressor system that can achieve temperatures as low as
-100.degree. C. is utilized. An autocascade refrigeration system is
a complete, self-contained refrigeration system in which multiple
stages of cascade cooling effect occur simultaneously by means of
vapor-liquid separation and adiabatic expansion of various
refrigerants. Physical and thermodynamic features, along with a
series of counterflow heat exchangers and an appropriate mixture of
refrigerants, make it possible for the system to reach low
temperature. The autocascade is a cooling/freezing system using one
compressor and two or more different refrigerants and heat
exchangers to reach a lower temperature, wherein the first
refrigerant cools the next and so on. The components of an
autocascade refrigeration system include a vapor compressor, an
external air- or water-cooled condenser, a mixture of refrigerants
with descending boiling points, and a series of insulated heat
exchangers.
[0109] The autocascade refrigeration system uses mixed refrigerants
along with internal heat transfer and phase separation to achieve
optimally cold temperatures through a single compressor. The most
basic autocascade cycle uses only a single phase-separator and one
additional heat-exchanger (compared to a standard refrigeration
cycle) to mimic the behavior of a conventional two-stage cascade
refrigeration system.
[0110] The refrigerant in the autocascade cycle is compressed as a
gas and then sent through a condenser where heat is removed to
liquefy the refrigerant. Because an autocascade uses mixed
refrigerants of differing vapor pressures, the condensation of the
gas is only partial. The refrigerant with the higher vapor pressure
remains predominately gaseous whereas the refrigerant with a lower
vapor pressure is liquefied. This two phase flow is then sent to a
vessel where the gas and liquid phases are separated. The liquid
stream is dropped in pressure to provide a cooling effect which is
used--in a heat-exchanger--to further chill and condense the gas
stream. The gas stream (now liquefied) is then dropped in pressure
to provide the final useful cooling duty desired. In this way, an
autocascade cycle essentially replaces two stages of conventional
cascade refrigeration.
[0111] The above description is of the simplest autocascade cycles
possible. Significantly more complex cycles are possible for use
with the present invention. In some embodiments of the present
invention, additional "staged" phase-separation steps with their
corresponding internal heat transfer cooling afterwards can be used
to reach even colder temperatures.
[0112] As a result of its multiple refrigerants and unique design,
the autocascade design of the present invention can attain colder
temperatures in a single stage than possible in a conventional
cascade refrigeration cycle, so much so that a single stage
autocascade refrigerator can replace a two-stage (or more) cascade
refrigerator. While such an autocascade unit would not be as energy
efficient as a two-stage conventional cascade system, it would be
simpler and cheaper to build and operate. Because the CO2 recovery
system primarily needs to be very compact and affordable to obtain,
the trade of reduced capital and operating costs at the expense of
increased energy costs offered by the autocascade is potentially
highly attractive and may be considered a preferred embodiment.
[0113] The temperatures reached by the autocascade may be altered
by altering a composition of the mix of refrigerants. Depending a
variety of conditions that vary between installations, including
higher air contamination, elevated operating pressures, and
excessive electricity rates, the CO2 recovery system may thus be
tuned to reach appropriate temperatures for effective operation
with the gas composition at hand.
[0114] In a preferred embodiment, the CO2 recovery system is an
innovative air-cooled autocascade system, as discussed previously
in relation to FIG. 5. This allows for a more thermodynamically
efficient design while keeping the system compact and portable.
While the thermodynamic efficiency is not necessarily optimal,
because the CO2 recovery system is installed in an environment
where space and purchase price are at a premium, it is sensible to
trade some thermodynamic efficiency for a more mechanically compact
design.
[0115] In the autocascade system, one refrigeration compressor is
employed, with the process gas temperature typically ranging from
-15.degree. C. to -55.degree. C., depending upon the particulars of
the design. In the preferred configuration, the refrigeration
system is of an autocascade design. The refrigeration cycle
utilizes air-cooled heatexchangers to eliminate the need for liquid
coolant which may not be available at all operating sites. However,
if water or chilled ethylene glycol is available, the refrigeration
cycle can be modified to utilize this resource for enhanced
refrigeration performance.
[0116] In one alternative embodiment not shown in the figures, the
refrigeration system is a conventional cascade refrigeration which
employs two separate refrigeration compressors. Both stages are
air-cooled, and exchange heat between the two stages with a compact
countercurrent heat exchanger. The first stage is similar to the
warmer stage of a standard cascade refrigeration cycle (but with
two evaporators, one for the process gas and one for the other
stage of refrigeration) and the second, colder stage, is also a
standard cascade design.
[0117] Yet another embodiment is very similar to the system
described in the preceding paragraph. In this embodiment the warmer
stage of the cascade refrigeration system does not exchange heat
with the process gas in a pre-cooling step. The warmer stage only
exchanges heat with the lower temperature cascade refrigeration
loop and loses heat through an air-cooled condenser. The colder
stage is the only refrigeration loop which exchanges heat with the
process gas, achieving a process temperature suitable for
liquefaction of CO2 in a single compact heat exchanger.
[0118] For improved thermodynamic efficiency, both refrigeration
loops may be used, in series, to chill and liquefy CO2 from the
inlet gas stream. This requires two evaporators on the warmer
refrigeration loop (the cascade evaporator/condenser heat-exchanger
and a second heat-exchanger whose duty chills the CO2 gas stream as
well as provides some superheat to the vapor returning to the
refrigeration compressor suction inlet). Various alternative
designs can range from a simple, single stage refrigeration cycle
to three or more stages of cooling. Further any stage of a single
or multi-stage configuration could be of a cascade design, or
alternatively, an autocascade refrigeration stage, or alternatively
of the hybrid design according to the present invention.
Dehydration Subsystem
[0119] Dehydration is necessary to remove entrained water moisture
and any trace humidity content from the raw fermenter CO2 gas
stream before refrigeration to avoid water ice formation, which
would damage or destroy equipment. Due to the very cold
temperatures reached by the refrigeration system, as low as
-70.degree. C. in some embodiments, it is essential to remove any
trace humidity content in the raw CO2 gas stream. Therefore, a very
efficient dehydration system is needed to take the inlet CO2 gas
(which is saturated with moisture at the fermenter temperature) to
a humidity equivalent to having a dew point below the coldest
process temperature which can be as low as -60.degree. C. in some
embodiments. The present desiccant system, described below, is able
to remove any trace humidity content that is required by the very
cold temperature refrigeration. The dehydration system should be
tuned to produce processed gas that has a dew point that is lower
than the coldest temperature produced by the refrigeration
system.
[0120] In a preferred embodiment, some water condensation happens
in the gas transmission lines leading from the bank of fermenters
to the CO2 recovery system. Final dehydration occurs in desiccant
dryer beds. Examples of desiccants used in the desiccant beds
include silica, alumina, silica alumina, calcium oxide, molecular
sieves (such as zeolites), activated charcoal/carbon, and other
like materials.
[0121] According to the beverage-grade CO2 purity standard as
defined by the ISBT and as outlined in Table 1, the moisture level
permitted in the final liquid CO2 product is capped at 20 parts per
million (ppm). In addition to this specification there is a process
restraint which requires the dew point of the process gas to be
reduced to a value below the coldest process temperature. The only
method of water removal which satisfies these criteria is
heterogeneous adsorption of water by a solid desiccant medium. The
approach also provides a low pressure drop solution which improves
overall process economics.
[0122] Dehydration is typically carried out in the prior art using
a four (4) step process that is less effective operation, requires
larger beds, and longer hold time. The beds of the present
invention in its preferred embodiment are smaller and more
efficient because the inventors have developed a novel 21/2 step
dehydration process. The prior art four-step process includes: (1)
actively dehydration, (2) depressurizing, (3) regenerating, and (4)
re-pressurizing. If four steps are used, then four beds are needed.
But the inventors have developed a novel dehydration process using
only two beds by optimizing the cycle into only 21/2 steps. The
21/2 steps of the dehydration process include: (1) actively
dehydrating, (2) regenerating, and a 1/2-step re-pressurizing
cycle, which is quick, but enough to operate with only two beds. It
is important to mention that the 1/2-step re-pressurization only
works due to the moderate pressure of the system, which is only
feasible with the very cold refrigeration temperature. Four-way
valves simplify switching between the two beds in the 21/2 step
process. During the valve switch momentary pressure communication
occurs between the two beds to equalize the pressures at an
intermediary value. Once the switch is complete the process quickly
reestablishes itself at steady-state pressure values.
[0123] Adsorbent molecular sieves can achieve moisture contents as
low as 0.1 ppm, thereby mitigating the risk of damaging process
components located in the cryogenic section such as pipes, heat
exchangers, and expansion devices by freezing water inside them.
The molecular sieve material is typically distributed inside round
vessels in a packed bed configuration. Like other desiccants,
molecular sieves have limited adsorption capacity and must be
replaced or regenerated at given service intervals. For continuous
dehydration service, a multi-bed system must be utilized where one
bed is in service while the other is being replaced or regenerated,
and the beds can be seamlessly switched in and out of service.
[0124] In general, alternating two-bed systems are used where bed
"A" is in service and the process stream is dehydrated. At the same
time, a dry, hot regeneration gas is flowed through bed "B" in a
counter-current direction to remove moisture from the surface of
the adsorbent material. Once the regeneration is complete, a set of
valves are actuated such that the process gas is directed into bed
"B" and the regeneration gas is flowed through bed "A"
countercurrent to the process flow. This cycle can be repeated
indefinitely until the adsorbent exceeds its useful life, usually
years.
[0125] Typically, the adsorbent beds are sized so that cycle times
are on the order of hours. The packed bed diameter is tuned to
provide an acceptable superficial velocity, and the height is
adjusted to achieve the required holding capacity. The diameter is
limited by pressure containment, and the bed height is limited by
overall pressure drop and/or crush strength of the adsorbent
material. Optimal sizing can be iteratively obtained by balancing
the time required for regeneration with the time available to
adsorb water before the holding capacity is reached.
[0126] Most regenerative dehydration units employ a
temperature-swing process, where the regeneration gas is externally
heated. The regeneration gas must carry enough energy to bring the
adsorbent material to an elevated temperature, as well as to
provide the heat of desorption of the water mass. Additional heat
is required to overcome the thermal losses through the piping,
vessel wall, and effluent gas. After the removal of the water at
the regeneration temperature, the external heater is taken off line
and the regeneration gas cools the bed back to the process
temperature.
[0127] A standard valving arrangement requires four on-off valves
per bed, to allow the process stream and regeneration gas to flow
through one bed at a time in a counter-current fashion. During the
switchover, all eight valves are actuated simultaneously to swap
beds. If a pressure difference exists between the process stream
and the regeneration gas, a pressure equalization valve between the
two beds is required. Pressure equalization must be done gradually
to avoid adsorbent attrition, adding to cycle time. If the process
gas is not compatible with the regeneration gas, vent valves and
inert purge valves may be required to expel the unwanted gas and
condition the beds prior to pressure equalization and/or
switchover.
[0128] In a preferred embodiment of the present invention, two 5 A
molecular sieve adsorbent beds are used. The process stream is a
predominantly CO2 gas stream containing up to 2% water by volume,
at a maximum volumetric flow rate of 2 standard cubic feet per
minute (CFM). The design inlet conditions are 78.degree. F. and a
pressure ranging from 0-2 psig; however the unit can operate
satisfactorily at off-design conditions. The vessel is sized to
provide a maximum superficial velocity of 35 ft/min at flow rates
up to 2 CFM. The packed height is 18 inches, resulting in a cycle
time of 6 hours at the maximum flow rate. Longer cycles are
possible at lower flow rates.
[0129] In the preferred configuration, the regeneration gas is the
vapor stream leaving the liquid CO2 storage dewar, which has trace
amounts of noncondensable gasas at a temperature and pressure near
ambient. The regeneration gas is actively heated with an electric
band heater mounted directly onto the desiccant bed undergoing
regeneration of its adsorbent inventory. The heater delivers
thermal energy to the regenerating desiccant bend obtaining a
satisfactorily regenerated isothermal temperature profile around
450.degree. F. After 4.5 hour, the power to the electric heater is
removed, and the bed is cooled from 450.degree. C. to 40.degree. C.
by the unheated regeneration gas in 1 hour. There is 0.5 hour of
standby time to execute the switchover between beds.
[0130] The process gas flows downward through the bed and the
regeneration gas flows upward, lifting the adsorbed water from the
bed. The system utilizes a simplified valve arrangement based on
two 4-way cross-port valves (as seen in FIG. 5). The process gas
flows through one circuit of the valve while the regeneration gas
flows through the other circuit in a counter-current direction.
With this configuration, the function of eight simple on-off valves
can be replicated by two 4-way valves placed at the entrance and
exit of each bed. At the time of switchover, both valves turn
simultaneously. Because both the process gas and the regeneration
gas are predominantly CO2, no vent and purge step is necessary.
[0131] In summary, a preferred embodiment of the final dehydration
subsystem is an alternating two-bed system, able to dry up to 2 CFM
of moisture-saturated CO2 gas in 6 hour cycles. The system has
several unique features that save on capital expense and conserve
energy. Use of four-way valves instead of on-off valves simplifies
piping and controls while saving space and expense. The location of
the desiccant beds upstream of the compressor and using vented gas
from storage as the regeneration gas eliminates a blower, while
making the switchover process faster and more seamless. Finally,
the system is designed to remain as compact and simple as possible,
allowing enhanced opportunity for installation in a variety of
cramped craft breweries.
[0132] Alternative embodiments of the CO2 dehydration system could
employ systems involving more than two beds, and/or use other
methods of moisture capture, including alternative desiccants, or
water capture using coolers or freezers.
Controls Subsystem
[0133] An automatic control subsystem is a required element of any
physical separation process, being necessary to manage the various
components of the system, maintain a satisfactory performance in
the case of changing conditions, and reduce the burden on the
system operator to a reasonable level. The CO2 recovery unit
utilizes a novel control system that is totally autonomous,
requiring minimal operator oversight and intervention. The defining
feature of the control system is the ability to automatically track
changes in CO2 production in real-time, therefore avoiding large
inlet buffer tanks, and maximizing the amount of CO2 captured.
[0134] Capacity control is achieved by varying the rotational speed
of the compression subsystem in real-time. In the present
embodiment, a pressure transmitter feeds back an electrical signal
proportional to the pressure at the compressor inlet to a variable
frequency drive (VFD). The VFD compares this signal to a
user-adjustable pressure setpoint, and adjusts the speed
accordingly to maintain the setpoint pressure. When CO2 production
is insufficient to maintain the setpoint pressure at the lowest
possible speed, an automatic interlock stops the compression
equipment until the pressure rises to a satisfactory level, at
which point the compression will resume under automatic capacity
control.
[0135] The dehydration system is also managed by the automatic
control subsystem. In the present embodiment, a humidity
transmitter feeds back an electrical signal proportional to the
relative humidity at the compressor inlet to a setpoint relay. If
the humidity exceeds the setpoint, the relay will operate and
suspend the compression and refrigeration equipment. During the
interruption, regeneration of the other dehydration bed continues,
and is indicated by the operation of a temperature switch. When the
temperature switch operates, the regeneration is complete, and
after a cool-down period the controller will operate the
directional valves that switch dehydration beds, and automatically
restart the compression and refrigeration equipment. In an
alternative embodiment, the aforementioned elements could be
controlled by timing relays instead of humidity and temperature
transmitters.
[0136] An innovative feature of the control system is management of
the refrigeration subsystem in the case of changing load and
ambient temperature conditions. Since the refrigeration system is
ultimately air-cooled, it is necessary to adjust the amount of
air-flow across the air-cooled refrigerant condenser in order to
maintain satisfactory condensing temperature and pressure, and
adequate refrigeration capacity. In the present embodiment, a
temperature transmitter feeds back an electrical signal
proportional to the refrigerant condensing temperature to a
setpoint relay, which can select between discrete fan speeds to
maintain the refrigerant condensing temperature near the setpoint.
In an alternative embodiment, the temperature transmitter could
feed back to a VFD (or other type of motor speed control device) to
maintain the refrigerant condensing temperature. In the present
embodiment, when the CO2 production drops below the minimum
required to fully load the refrigerator, a temperature switch set
to a user adjustable setpoint in the liquid CO2 product line will
suspend the refrigeration equipment in order to save energy until
the product temperature rises to an adequate level, at which point
the refrigeration equipment will restart under automatic
control.
[0137] Another innovative control feature of the CO2 recovery
process was introduced to prevent the formation of solid CO2 (dry
ice) in the system, which is undesirable. Observing the CO2 phase
equilibrium diagram, it can be seen that CO2 cannot exist as a
liquid if its partial pressure is below 75.1 psia. Therefore, if
the pressure at the refrigerant evaporator is below this threshold,
a temperature switch will operate and lock-out the refrigeration
equipment until the pressure rises above the threshold. Further
noting the CO2 phase diagram, above the triple point pressure of
75.1 psia, liquid CO2 will begin to nucleate solid phase on
surfaces having temperatures below -56.6.degree. C. Therefore, if
the temperature of the refrigerant at its coldest point drops below
this threshold, a temperature switch will operate and suspend the
refrigeration equipment for a period of time sufficient to allow
the refrigerant to warm above the threshold and also melt any dry
ice formed.
[0138] The control subsystem as described above was carefully
designed to maximize process up-time and minimize operator
monitoring and intervention. Thus, the control system was designed
and constructed to be fully autonomous, having only one button
press necessary to bring the process from full stop to full
automatic operation (run mode), and only one further button press
to safely shut down the system (stop mode). A network of
electromechanical safety switches and process interlocks allow the
system to operate safely and satisfactorily without continuous
operator monitoring. However, process status, alarms, and
maintenance reminders are displayed to the operator through an
array of lights and other indicators mounted on the control
panel.
Various Use Cases of the Present Invention
[0139] Several alternative use cases of the present invention are
now presented. These use cases are illustrative of the possible
applications of the present invention and are not meant to be
exhaustive or limiting.
[0140] The present invention relates to enabling the recovery of
carbon dioxide (CO2) from industrially relevant waste streams
containing a sufficiently high concentration of CO2. The invention
is most readily applicable to the burgeoning beverage alcohol
industry (microdistilleries, craft vintners, and craft breweries)
in the United States, most especially the craft beer brewing
industry. In a craft brewery, carbon dioxide can be recovered from
fermentation tanks, bright beer tanks, and other process vessels,
tanks and lines. The recovered CO2 can then be used in forced
carbonation, kegging, canning, bottling, purging, and other
applications associated with production of packaged beer. More
specifically, this invention relates to a modular system for
separating carbon dioxide from non-condensable gases such as
nitrogen and oxygen, while dehydrating, deodorizing, and purifying
the carbon dioxide to a quality sufficient for beverage
applications, and also liquefying the carbon dioxide and
transferring it into a storage vessel so that it can be re-used
(which would reduce the amount of carbon dioxide that is vented by
breweries, as well as the reduce the amount of carbon dioxide that
breweries have to purchase for plant operations).
[0141] Microdistilleries are another growing business model
domestically and abroad which generates large volumes of vented CO2
produced during ethanol fermentation of glucose by yeast. Many
small-scale distilleries use traditional techniques involving open
fermenters which make capture of the CO2 gas difficult. However,
many are investigating floating-head open fermenters which would
allow CO2 recovery, and many others are starting with brewery-type
closed sanitary fermentation vessels, which has been demonstrated
as a feasible CO2 source. Many other microdistilleries source their
wash from craft brewers who could potentially be utilizing CO2
recovery consistent with the present invention. A distillery could
use CO2 around the production facility to purge tanks, vessels, and
lines, drive pneumatic controls elements, and even produce some
recently popular carbonated high-proof alcoholic beverages. Sales
of superior quality CO2 to outside organization always remains as a
viable revenue model.
[0142] Microvintner operations have become recently popular in the
United States and other countries as regions look to capitalize on
their local fruit crops. Wine fermentation is conducted in a
variety of vessels similar to microdistilleries, with some designs
more appropriate for CO2 recovery than others. But there still
remains a largely unserved market for wine producers who vent CO2
from fermentation and purchase industrial CO2 to produce and sell
sparkling wine-type alcoholic beverages. The present invention
would be very appropriate for such an operation even with
intermittent CO2 production from seasonal fermentations.
[0143] The present invention is designed to enable the recovery of
carbon dioxide (CO2) from industrial waste streams containing a
majority of CO2. Processes that produce such streams include
pharmaceutical synthesis via batch fermentation, fuel ethanol
plants utilizing starchy feedstocks, anesthetic asphyxiation in
slaughterhouses, ammonia production via steam reforming of natural
gas, coal and biomass gasifiers, various thermochemical and
Fischer-Tropsch-type gas-to-liquids conversions, soft drink
bottling plants, plastics production facilities using the solvent
properties of CO2 for materials property enhancements, coffee and
tea decaffeination towers, so-called green dry cleaners, medical
sterilization, and production of beverage alcohol products. Some of
these processes require food- and beverage-grade CO2 to produce
their products, but others don't. Many industrial processes have a
very real economic need for CO2 recovery at a small scale but do
not operate within stringent food, beverage, or sanitary
constraints. For these applications in alternate industries the
purification steps can be removed, further simplifying,
miniaturizing, and reducing cost of the CO2 recovery system.
Potential Macro-Environmental and Macroeconomic Impact
[0144] Previously, the impact of the technology on a single brewery
was discussed to show that it would be highly profitable. This is
the key to the propagation of the technology to a large number of
craft breweries. In this section, the macro-environmental and
macroeconomic effect of the technology is discussed once it has
been put into broad use, showing that it could have a major impact
in both increasing efficiency of operation, offsetting an expensive
commodity cost, and reducing carbon emissions.
[0145] In the United States alone, almost 13 million barrels (bbl)
of beer (1 US beer barrel=31 US gallons) by craft brewers in 2012,
over 90% (12 million bbl/year) of which is produced by breweries
producing 3000 bbl annually or greater. Due to certain limits on
miniaturization of the process, the minimum brewery size that can
be serviced is 3000 bbl/yr. Assuming a metric that a 60,000 bbl/yr
brewery produces an average of 1 ton CO2/day, that is sufficient
market, in the United States alone, for 1300 CO2 recovery systems
units. If there was 50% market penetration then almost 100 tons of
wasted high-quality CO.sub.2 would be avoided. Meanwhile, an
economic gain of $7 million to $36 million per year is expected
industry wide by offsetting the cost to purchase and deliver
industrially-sourced CO2 of inferior quality.
Long-Felt, Unsolved Need for Craft Brewery-Scale CO2 Recovery
Technology--Trade Association Data
[0146] According to annual production numbers for craft breweries
published by the Brewers Association, breweries which are currently
producing 3000 bbl beer per year or greater combine to produce an
average of nearly 200 tons of vented CO2 per day (396,000
pounds/day) in 2012. (Source: Brewers_Association.sub.--2012.xls,
Brewers Association, Boulder, Colo., April 2013) This astounding
figure demonstrates the long-felt and unsolved need for CO2
recovery technology at the craft brewery scale to address this
issue. A survey of commercially available CO2 recovery systems
tailored to brewers shows that no existing technology exists in a
compact fashion, at this scale, and with the ability to preserve
stringent purity requirements, all key innovations of the present
patent application. This discussion is merely illustrative and
exemplary, and is not intended to limit the scope of the present
invention or its application or uses.
[0147] The inventors have completed the construction of a craft
brewery-scale, production-quality CO2 recovery unit according to
one of many embodiments of the present application, and have
completed field testing in two major craft breweries near Denver,
Colo., United States.
[0148] While the methods disclosed herein have been described and
shown with reference to particular operations performed in a
particular order, it will be understood that these operations may
be combined, sub-divided, or re-ordered to form equivalent methods
without departing from the teachings of the present invention.
Accordingly, unless specifically indicated herein, the order and
grouping of the operations is not a limitation of the present
invention.
[0149] While the present invention has been particularly shown and
described with reference to embodiments thereof, it will be
understood by those skilled in the art that various other changes
in the form and details may be made without departing from the
spirit and scope of the present invention.
* * * * *
References