U.S. patent application number 15/602795 was filed with the patent office on 2018-11-29 for method for recycling streams in a separations process.
The applicant listed for this patent is Andrew Baxter, Larry Baxter, David Frankman, Eric Mansfield. Invention is credited to Andrew Baxter, Larry Baxter, David Frankman, Eric Mansfield.
Application Number | 20180340731 15/602795 |
Document ID | / |
Family ID | 64401074 |
Filed Date | 2018-11-29 |
United States Patent
Application |
20180340731 |
Kind Code |
A1 |
Baxter; Larry ; et
al. |
November 29, 2018 |
Method for Recycling Streams in a Separations Process
Abstract
A method and apparatus for recycling streams in a separations
process comprising: determining a measured reading of a parameter
of the separations processor is in a suboptimal range; separating,
via a separation unit having a volume of contact fluid, the inert
gas from the pollutant gas in the inlet flue gas stream to form a
clean gas stream and a purified pollutant gas stream; removing at
least 1% of the volume of contact fluid to form a removed volume of
contact liquid; performing some unit operations on the removed
volume of contact fluid; injecting the clean gas stream into the
inlet flue gas stream to form a flue gas stream of lower pollutant
concentration; and, repeating at progressively lower pollutant
concentration, as the inlet stream until the processor determines
that a measured reading of the parameter has been returned to a
substantially optimal range.
Inventors: |
Baxter; Larry; (Orem,
UT) ; Mansfield; Eric; (Spanish Fork, UT) ;
Baxter; Andrew; (Spanish Fork, UT) ; Frankman;
David; (Provo, UT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Baxter; Larry
Mansfield; Eric
Baxter; Andrew
Frankman; David |
Orem
Spanish Fork
Spanish Fork
Provo |
UT
UT
UT
UT |
US
US
US
US |
|
|
Family ID: |
64401074 |
Appl. No.: |
15/602795 |
Filed: |
May 23, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 53/002 20130101;
B01D 2258/0283 20130101; Y02C 20/40 20200801; B01D 2252/2056
20130101; B01D 2257/504 20130101; B01D 2252/205 20130101; B01D
53/1475 20130101; B01D 2257/302 20130101; B01D 2257/404 20130101;
B01D 2252/20431 20130101; B01D 53/1493 20130101 |
International
Class: |
F25J 3/08 20060101
F25J003/08 |
Claims
1. A method for recycling streams in a separations process,
comprising: providing a processor communicatively coupled to a
non-transitory storage medium, the non-transitory storage medium
comprising data storage, the data storage comprising instructions;
determining, via the processor, that a measured reading of a
parameter of the separations processor is in a suboptimal range;
providing an inlet flue gas stream comprising an inert gas and a
pollutant gas; separating, via a separation unit comprising a
volume of contact fluid selected from the group consisting of
aliphatic hydrocarbons with substituted halogens, aliphatic
hydrocarbons without substituted halogens, aromatic hydrocarbons
with substituted halogens, aromatic hydrocarbons without
substituted halogens, cyclic hydrocarbons with substituted
halogens, cyclic hydrocarbons without substituted halogens, and
combinations thereof, the inert gas from the pollutant gas in the
inlet flue gas stream to form a clean gas stream and a purified
pollutant gas stream; removing at least 1% of the volume of contact
fluid to form a removed volume of contact liquid; performing at
least one unit operation on the removed volume of contact fluid,
the at least one unit operation selected from a group consisting of
increasing the temperature of the removed volume of the content
fluid by at least 2 degrees Celsius, decreasing the temperature of
the removed volume of the content fluid by at least 2 degrees
Celsius, vaporizing at least 5% of the removed volume of the
content fluid, removing at least 1 of an amount of impurities
disposed in the removed volume of the content fluid, distilling at
least 50% of the removed volume of the content liquid, and
combinations thereof; injecting the clean gas stream into the inlet
flue gas stream to form a flue gas stream of lower pollutant
concentration; performing at least one other operation on the
purified pollutant gas stream; and repeating the preceding steps of
the method using the flue gas stream, at progressively lower
pollutant concentration, as the inlet stream until the processor
determines that a measured reading of the parameter has been
returned to a substantially optimal range or the processor receives
a communication informing the processor that the measured reading
of the parameter has been returned to a substantially optimal
range, or separation process has improved or the processor receives
a notification that the separation unit can return to a full
load.
2. The method as in claim 1, wherein the separation unit uses a
cryogenic carbon capture process and condenses the pollutant gas;
the contact fluid consists of isopentane.
3. The method as in claim 2, wherein the separation unit can return
to a full pollutant load when its temperature drops below a set
operational temperature.
4. The method as in claim 1, wherein a measured pollutant load
value for the process is decreased to a lesser measured pollutant
load value by decreasing the load for the process, to correct for
the measured reading of the parameter of the separations processor
that is in a suboptimal range, the method further comprising the
step of increasing the load for the process to substantially normal
levels after the processor has received a communication that the
measured reading of the parameter of the separations processor that
previously was in a suboptimal range has been restored to a
measured reading of the parameter substantially falling within an
optimal range.
5. The method as in claim 1, wherein the purified pollutant stream
is also recycled and reinjected into the inlet flue gas stream.
6. The method as in claim 1, additionally comprising: injecting a
contact fluid as a vapor into the inlet flue gas stream; separating
the contact fluid from the purified pollutant gas stream to form a
contact fluid stream; performing other desired unit operations on
the contact fluid stream; and reinjecting the contact fluid stream
into the inlet flue gas stream.
7. The method as in claim 6, wherein the contact fluid is injected
as a liquid into the separation unit.
8. The method as in claim 6, wherein the contact fluid is selected
from the group consisting of aliphatic fluids, aromatic fluids,
cyclic hydrocarbons with substituted halogens, and cyclic
hydrocarbons without substituted halogens.
9. The method as in claim 1, wherein the inert gas is selected from
the group consisting of nitrogen, oxygen, water, air, and
combinations thereof.
10. The method as in claim 1, wherein the pollutant gas is selected
from the group consisting of carbon dioxide, sulfur oxides,
nitrogen oxides, fly ash, mercury, arsenic, other pollutants
present in flue gas, and combinations thereof.
11. An apparatus for recycling streams in a separations process;
comprising: an inlet flue gas stream, comprising a quantity of
inert gas and a quantity of pollutant gas; a contact fluid injected
as a vapor into the inlet flue gas stream; a separation unit
configured to separate the inert gas from the pollutant and the
contact fluid in the inlet stream to form a clean gas stream, a
mixed stream; a second separation unit configured to separate the
contact fluid from the pollutant gas in the mixed stream to form a
purified pollutant stream and a contact fluid stream; an injection
point where the contact fluid stream may be reinjected into the
flue gas stream; and an injection point where the clean gas stream
may be reinjected into the inlet flue gas stream to form a flue gas
stream of lower pollutant concentration.
12. The apparatus as in claim 11, wherein the contact fluid is
injected as a liquid into the separation unit.
13. The apparatus as in claim 11, wherein the contact fluid is
selected from the group consisting of aliphatic fluids, aromatic
fluids, cyclic hydrocarbons with substituted halogens, and cyclic
hydrocarbons without substituted halogens.
14. The apparatus as in claim 11, wherein the inert gas is selected
from the group consisting of nitrogen, oxygen, water, air, and
combinations thereof.
15. The apparatus as in claim 11, wherein the pollutant gas is
selected from the group consisting of carbon dioxide, sulfur
oxides, nitrogen oxides, fly ash, mercury, arsenic, other
pollutants present in flue gas, and combinations thereof.
16. The apparatus as in claim 11, wherein the clean gas stream is
recycled until the separation unit drops below a set operational
temperature.
17. The apparatus as in claim 11, wherein the purified pollutant
stream is also recycled and reinjected into the flue gas
stream.
18. An apparatus for recycling streams in a separations process,
comprising: an inlet flue gas stream, comprising a quantity of
inert gas and a quantity of pollutant gas; a contact fluid injected
as a vapor into the inlet flue gas stream or as a liquid into the
separation unit; a separation unit configured to separate the inert
gas from the pollutant and the contact fluid in the inlet stream to
form a clean gas stream and a mixed stream; a second separation
unit configured to separate the contact fluid from the pollutant
gas in the mixed stream to form a purified pollutant stream and a
contact fluid stream; a number of additional unit operations
through which the purified pollutant stream or the contact fluid
stream may pass; an injection point where the contact fluid stream
may be reinjected into the flue gas stream; and an injection point
where the clean gas stream may be reinjected into the inlet flue
gas stream to form a flue gas stream of lower pollutant
concentration.
19. The apparatus as in claim 18, wherein the flue gas stream
comprises carbon dioxide and nitrogen, and the contact fluid is
isopentane.
20. The apparatus as in claim 19, wherein the flue gas stream is
simulated, additionally comprising: bottled nitrogen to be injected
into a closed loop system; bottled carbon dioxide to be injected
into the closed loop system; a solenoid valve through which the
injected bottled nitrogen is regulated; a pressure transducer
communicatively coupled to the solenoid valve, configured to
control the solenoid valve to maintain a constant set pressure; the
pressure transducer placed on the suction side of a blower; a
flowmeter placed after the blower; the flowmeter communicatively
coupled to the blower to maintain a constant flow rate; a
separation unit configured to separate the carbon dioxide from the
nitrogen in the closed loop system; an inlet stream of nitrogen and
carbon dioxide flowing into the separation unit, a first outlet
stream of cleaned nitrogen, and a second outlet stream of purified
carbon dioxide emerging from the separation unit; a first analyzer
configured to monitor the concentration of carbon dioxide in the
inlet stream entering the separation unit; a second analyzer
through which the cleaned nitrogen stream passes, the second
analyzer configured to measure the concentration of carbon dioxide
in the cleaned nitrogen stream; a combination point where the
purified carbon dioxide stream and the carbon dioxide supply are
injected into the cleaned nitrogen stream; the solenoid valve
placed after the combination point; a first mass flow controller
communicatively coupled to the first and second analyzers, the
first mass flow controller configured to regulate the injection
rate of the bottled carbon dioxide; a second mass flow controller
configured to monitor the flow rate of the purified carbon dioxide
stream and enable feed-forward control over the first mass flow
controller; and a third mass flow controller communicatively
coupled to the second mass flow controller, configured to release
excess carbon dioxide.
Description
TECHNICAL FIELD
[0001] The disclosure relates to separations equipment for
sequestering pollutants.
BACKGROUND
[0002] Greenhouse gas emissions are among the highest forms of
pollution, and are closely monitored. Carbon dioxide (CO2) is the
highest source of these greenhouse gas emissions, accounting for
80.9% of all greenhouse gas emissions in the U.S. in 2014,
according to the EPA. Efforts are being made to reduce the amount
of CO2 emissions. One method is that of carbon capture or
sequestration. This is used mainly in industrial processes and
power plants, to remove the CO2 before the flue gases are released
to the atmosphere.
[0003] Flue gas is a product of combustion of wood, coal, natural
gas, or other fossil fuels, and is released through a smokestack.
Thus, it has a high CO2 concentration. There are many methods in
development and in use to decrease the CO2 content of flue gas. It
is important to verify that these methods are effective.
[0004] In monitoring and regulating CO2 emissions, simulations are
often used. For example, the National Institute of Metrology
created a Smoke Stack Simulator (SMSS) to study accurate
measurement methods for flue gas flow rates. The SMSS was created
to model many systems, with the capability to simulate flow fields
by generating different swirls. Similarly, the flue gas itself can
be simulated. Flue gas is typically composed mainly of carbon
dioxide, water vapor, nitrogen, and oxygen. There may also be a
small percentage of fly ash or other pollutants. The majority of
the flue gas is usually made up of nitrogen--typically, two-thirds
or more.
BRIEF SUMMARY
[0005] Contacts and carrier fluids may be used, such as:
[0006] 1,1,3-trimethylcyclopentane, 1,4-pentadiene, 1,5-hexadiene,
1-butene, 1-methyl-1-ethylcyclopentane, 1-pentene,
2,3,3,3-tetrafluoropropene, 2,3-dimethyl-1-butene,
2-chloro-1,1,1,2-tetrafluoroethane, 2-methylpentane,
3-methyl-1,4-pentadiene, 3-methyl-1-butene, 3-methyl-1-pentene,
3-methylpentane, 4-methyl-1-hexene, 4-methyl-1-pentene,
4-methylcyclopentene, 4-methyl-trans-2-pentene,
bromochlorodifluoromethane, bromodifluoromethane,
bromotrifluoroethylene, chlorotrifluoroethylene, cis 2-hexene,
cis-1,3-pentadiene, cis-2-hexene, cis-2-pentene,
dichlorodifluoromethane, difluoromethyl trifluoromethyl ether,
dimethyl ether, ethyl fluoride, ethyl mercaptan,
hexafluoropropylene, isobutane, isobutene, isobutyl mercaptan,
isopentane, isoprene, methyl isopropyl ether, methylcyclohexane,
methylcyclopentane, methylcyclopropane, n,n-diethylmethylamine,
octafluoropropane, pentafluoroethyl trifluorovinyl ether, propane,
sec-butyl mercaptan, trans-2-pentene, trifluoromethyl
trifluorovinyl ether, vinyl chloride, bromotrifluoromethane,
chlorodifluoromethane, dimethyl silane, ketene, methyl silane,
perchloryl fluoride, propylene, or vinyl fluoride.
[0007] The present disclosure describes systems and methods for
recycling separated gases to simulate flue gas. Gases that may be
used include an inert gas selected from the list comprising
nitrogen, oxygen, air, water, and combinations thereof. A pollutant
gas may also be used, selected from the list comprising carbon
dioxide, sulfur oxides, nitrogen oxides, fly ash, mercury, arsenic,
other pollutants present in flue gas, and combinations thereof. The
present disclosure will discuss using only carbon dioxide and
nitrogen as an example, however other gases may be used as
mentioned above. If other gases are used, there may be obvious
variations to the process described in this disclosure. The given
example is meant to demonstrate one application of the systems and
methods, and is not meant to limit the scope of the invention. Flue
gas may be simulated by mixing the desired gases--in this case,
carbon dioxide and nitrogen--from a supply source. The
concentration of carbon dioxide in this simulated flue gas stream
may range from 3% to 30% carbon dioxide. The simulated flue gas
stream may be monitored by a pressure transducer. The pressure
transducer may allow control over a valve through which the supply
nitrogen may be regulated, keeping the simulated flue gas stream at
a set pressure. In some preferred embodiments, the set pressure may
be constant and positive, and may range from 0.1 psig to 2 psig. In
some other embodiments, such as using a compressed simulated flue
gas, the set pressure may range from 50 psig to 100 psig. The valve
may be a solenoid valve, an actuated ball valve, or a mass flow
controller. The supply carbon dioxide may be injected and regulated
through a mass flow controller (MFC 1).
[0008] The simulated flue gas stream may also be monitored by a
flowmeter. The flowmeter may communicate with a blower for the
simulated flue gas stream, allowing the blower to operate in such a
way to maintain a constant set flow rate for the simulated flue gas
stream. The set flow rate may be set by the operator and may be at
least 5 SCFM. In some embodiments, the set flow rate may be between
5 SCFM and 100 SCFM.
[0009] There may be a first analyzer placed before the separation
unit. This analyzer may monitor the conditions of the simulated
flue gas stream, including the concentration of carbon dioxide in
the simulated flue gas stream just before entering the separation
unit.
[0010] The simulated flue gas stream may then enter the separation
unit. The separation unit may employ any carbon dioxide (or other
pollutant gas) separation process, and may be able to process the
entire flow rate of the simulated flue gas stream. For example, in
some preferred embodiments, the separation unit may be a Cryogenic
Carbon Capture process capable of processing 5 to 100 SCFM of
simulated flue gas, using carbon dioxide as the pollutant gas. The
separation unit may remove the carbon dioxide from the simulated
flue gas stream, forming two outlet streams: a clean gas stream and
a purified carbon dioxide stream. The purified carbon dioxide may
consist only of carbon dioxide from the simulated flue gas stream.
The clean gas stream may consist of all other non-carbon dioxide
gases from the simulated flue gas stream, as well as any carbon
dioxide that was not removed by the separation unit. In some
preferred embodiments, such as one using the Cryogenic Carbon
Capture process, the carbon dioxide concentration in the clean gas
stream may range from 0.10% to 3%.
[0011] Both streams exiting the separation unit may be recycled,
but they may pass through other steps before recombining. The clean
gas stream may pass through a second analyzer, placed after the
separation unit. This analyzer may monitor the concentration of
carbon dioxide in the clean gas stream. When compared to the carbon
dioxide concentration data from the first analyzer, which is placed
in the simulated flue gas stream, the performance of the separation
unit may be monitored.
[0012] The purified carbon dioxide stream may pass through a mass
flow controller (MFC 2). MFC 2 may monitor the flow rate of the
purified carbon dioxide stream. This flow rate data may enable
feed-forward control on another mass flow controller (MFC 3 (110))
through which excess carbon dioxide may be released. This excess
carbon dioxide may be vented, compressed and stored, or returned to
the supply from which it came. Similarly, in some embodiments, the
excess nitrogen may be vented or stored via a fourth mass flow
controller (MFC 4).
[0013] In some preferred embodiments, the purified carbon dioxide
stream may exit the separation unit at a high pressure. This
pressure may be in the range of 70 psig to 150 psig. The pressure
of the purified carbon dioxide stream may need to be decreased
before continuing in the process, especially if the clean gas
stream is at a lower pressure. A pressure regulator may be
implemented for this purpose. The purified carbon dioxide stream,
after passing through the pressure regulator, may be lowered to a
pressure in the range of 30 psig to 50 psig. In some embodiments,
the purified carbon dioxide stream may be a liquid, and may need to
be vaporized using a heater or a warm process stream before
continuing in the process. In these embodiments wherein the
purified carbon dioxide stream is a liquid, the excess carbon
dioxide flowing through MFC 3 may remain a liquid and be pumped
into a bottle.
[0014] The purified carbon dioxide stream and the clean gas stream
may then combine. The point at which the purified carbon dioxide is
injected may be important. It may be located at a point
sufficiently downstream of the second analyzer that the recycled
and carbon dioxide is not picked up by the second analyzer, and
sufficiently upstream of the first analyzer that the gas is well
mixed in the simulated flue gas stream before passing through the
first analyzer. The carbon dioxide supply may also be injected at
this same combination point through MFC 1. The first analyzer may
also provide data that allows the controller to regulate each of
the mass flow controllers. MFC 1 and MFC 3 may be controlled such
that the concentration of carbon dioxide in the simulated flue gas
stream is kept at a set value, as measured by the first
analyzer.
[0015] The combined clean gas, purified carbon dioxide, and supply
carbon dioxide form the recycle stream. The supply nitrogen may
later injected into this recycle stream through the valve. This
valve may be regulated using data from the pressure transducer to
maintain the set pressure mentioned above. After the point of
nitrogen injection, the simulated flue gas may be reformed and
again flows into the separation unit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] A more particular description of the invention briefly
described above is made below by reference to specific example.
Several examples are depicted in drawings included with this
application. An example is presented to illustrate, but not
restrict, the invention.
[0017] FIG. 1 is a schematic diagram of an experimental system
which simulates and separates flue gas in a regulated and monitored
environment.
[0018] FIG. 2A is an illustration of the system of FIG. 1.
[0019] FIG. 2A is an illustration of the piping and instrumentation
shortly before and after the separation unit.
[0020] FIG. 3 is a schematic diagram of a system which simulates,
separates, and recycles flue gas, including a device to lower the
pressure of the purified carbon dioxide stream.
[0021] FIG. 4 is a schematic diagram of a system which simulates
flue gas, separates it into a carbon dioxide component and a clean
gas component, and recycles the components.
[0022] FIG. 5 is a schematic diagram of the system in FIG. 1, in
the embodiment that the purified carbon dioxide stream is a liquid,
only displaying the section of the system after the separation
unit.
[0023] FIG. 6 is a method diagram of the system in FIG. 1.
DETAILED DESCRIPTION
[0024] The systems and methods disclosed herein relate to
simulating flue gas and separating gases in the flue gas stream,
then recycling the gases to again simulate the flue gas. These
methods may be used to test the effectiveness of a separation unit.
For example, carbon dioxide and nitrogen may be combined at a
desired concentration to simulate a flue gas. This simulated flue
gas may be regulated and analyzed, and then sent through a
separation unit. The separated streams which may be formed--one of
clean gas comprised mostly of nitrogen and one of purified carbon
dioxide--may also be analyzed to monitor the effectiveness of the
separation unit and the measurement devices. The step of
determining, via the processor, that a measured reading of a
parameter of the separations processor is suboptimal may refer to
determining via input from a sensor that a parameter, such as
temperature of a section of the system performing the process,
pressure level at a section of the system performing the process,
flow rate at a conduit of the system, pollutant concentration, or
some other parameter is at a suboptimal level. Such parameter may
be any parameter for which data is stored by the master controller,
which may be a computer system. In some embodiments a suboptimal
level is determined when the measured reading of the parameter
falls out of an acceptable range known by one skilled in the art
and the overall output of the separation process is affected
negatively. Referring to cleaning of flue gas, optimal conditions
may be defined as a ratio of a certain amount of pollutant in the
flue gas to a certain amount that is precipitated and removed from
the flue gas. Suboptimal conditions may be when the ratio drops to
less than 10% of the ratio under optimal conditions; however,
depending on the settings of the apparatus, the optimal conditions
may be adjusted. For example, in some setting it may be desired to
remove 99% of the pollutant by precipitation; in other settings, it
may be desired to remove greater than 80% of the pollutant by
precipitation. Returning to a substantially optimal range may refer
to returning within 5% or greater of the ratio of the optimal
conditions; for example, if the optimal ratio is 90%, and the ratio
drops to 79%, then that may be considered as a suboptimal
condition; then if the ratio returns to between 85% and 100%
inclusive, then that may be considered as returning to an optimal
condition, which may also mean returning or exceeding an optimal
condition threshold.
[0025] Processor (700), which may be connected wirelessly or
wirelessly to controllers, sensors, and other components of the
system, may be any computing processor from a server or master
controller adapted for monitoring of equipment.
[0026] FIG. 1 is a schematic drawing of a system (101) for testing
the effectiveness of a flue gas carbon dioxide separation unit
(100). In this example, the separation unit employs cryogenic
carbon capture as its separation process. However, other pollutant
separation methods may be used. System 101 includes a simulated gas
stream (200) composed of nitrogen and carbon dioxide, although
other gases may be used. The system also includes supply carbon
dioxide (122) and supply nitrogen (120). The supply carbon dioxide
(122) and supply nitrogen (120) may be bottled. The supply nitrogen
(120) is injected into the system through a valve (114), which may
be a solenoid valve, an actuated ball valve, or a mass flow
controller. FIG. 1 shows a solenoid valve (114), although a
different valve may be used. The supply carbon dioxide (122) is
injected into the system through a first mass flow controller (MFC
1) (106). The simulated flue gas stream (200) passes through a
blower (112) which regulates the flow rate of the simulated flue
gas stream (200). This is done using data from a flowmeter (116)
placed after the blower (112), which monitors the flow rate of the
simulated flue gas stream (200). The blower (112) may operate to
keep the simulated flue gas stream (200) at a constant flow rate
set by the operator. This flow rate may be at least 5 SCFM. The
simulated flue gas stream (200) may also pass through a first
analyzer (102), which may monitor the concentration of carbon
dioxide in the simulated flue gas stream (200) before entering a
separation unit (100). In the separation unit (100), the carbon
dioxide is removed from the simulated flue gas stream (200) and
leaves the separation unit (100) as a purified carbon dioxide
stream (202). All remaining gas leaves the separation unit (100) as
a clean gas stream (204), consisting of nitrogen and any carbon
dioxide that was not removed.
[0027] The clean gas stream (204) passes through a second analyzer
(104), which may also monitor the carbon dioxide concentration.
When comparing the carbon dioxide concentration in the clean gas
stream (204), as measured by the second analyzer (104), to the
carbon dioxide concentration in the simulated flue gas stream
(200), as measured by the first analyzer (102), the effectiveness
of the separation unit (100) may be monitored. The difference in
amount of carbon dioxide between the two streams is equal to the
amount of carbon dioxide removed from the flue gas stream. After
passing through the second analyzer (104), the clean gas stream
(204) is then recycled with the purified carbon dioxide stream
(202).
[0028] In some preferred embodiments, before recombining with the
clean gas stream (204), the purified carbon dioxide stream (202)
may pass through a second mass flow controller (MFC 2) (108). In
some embodiments, MFC 2 (108) may be replaced by a flowmeter. MFC 2
(108) monitors the flow rate of the purified carbon dioxide stream
(202). A PID controller may use data from MFC 2 (108) to enable
feed-forward control over MFC 1 (106), meaning data from MFC 2
(108) is fed forward to the PID to control the output of MFC 1
(106), rather than using data from the first analyzer (102). If the
flow rate through MFC 2 (108) increases, the flow rate through MFC
1 (106) decreases accordingly to maintain a set constant
concentration as monitored by the first analyzer (102). If a
process upset occurs and more carbon dioxide is released into the
system than is necessary to maintain the set concentration, the
flow rate through MFC 2 (108) will be high enough that the PID will
output a negative value for the flow rate through MFC 1 (106). In
this case, there is excess carbon dioxide in the system that may
need to be released through a third mass flow controller (MFC 3
(110)). If the output for MFC 1 (106) is negative, the PID
controller will use the absolute value of the negative output as
the output for MFC 3 (110). There may be no supply carbon dioxide
(122) flowing through MFC 1 (106), and excess carbon dioxide being
released from the purified carbon dioxide stream (202) through MFC
3 (110). The following table gives an example of the feed-forward
control mechanism.
TABLE-US-00001 TABLE 1 CO2 required to CO.sub.2 through maintain
setpoint MFC 2 concentration PID Controller MFC 1 MFC 3 (kg/hr)
(kg/hr) output (kg/hr) (kg/hr) 0 5 100% 5 0 3 5 40% 2 0 5 5 0% 0 0
7 5 -40% 0 2
[0029] In some other embodiments, the PID controller may use data
from the first analyzer (102) to control the output through MFC 1
(106) and MFC 3 (110), keeping the concentration of carbon dioxide
constant at the set point as monitored by the first analyzer (102).
This may render MFC 2 (108) unnecessary. However, MFC 2 may still
be used to enable the mass balance described below.
[0030] When excess carbon dioxide may be released through MFC 3
(110), the released gas may be vented to the atmosphere, compressed
and stored, or returned to the carbon dioxide supply.
[0031] When the purified carbon dioxide stream (202) and the clean
gas stream (204) combine, the supply carbon dioxide (122) may also
be injected via MFC 1 (106). Data from the first analyzer (102) and
the second analyzer (104) may be used by the operator or
controller, along with data from MFC 1 (106), MFC 2 (108) and MFC 3
(110), to close a mass balance on carbon dioxide around this
combination point (107). In some preferred embodiments, an
indicator on an HMI may perform the calculations. The mass balance
calculation may be used to ensure that all measuring instruments
used in the process are calibrated and operating correctly. The
calculation is to verify that the mass of the carbon dioxide
entering the combination point (107) is equal to the mass of the
carbon dioxide leaving the combination point (107). An example
calculation uses the following equation:
FT x 2 1 x 1 1 x 2 + M F C 1 + M F C 2 M F C 3 = 0 ##EQU00001##
Where FT is equal to the flow rate as measured by the flowmeter
(116), x1 is equal to the mass fraction of carbon dioxide in the
simulated flue gas stream (200) as measured by the first analyzer
(102), x2 is the mass fraction of carbon dioxide in the clean gas
stream (204) as measured by the second analyzer (104), MFC1 is the
flow rate of the supply carbon dioxide stream (400) through MFC 1
(106), MFC2 is the flow rate of the purified carbon dioxide stream
(202) through MFC 2 (108), and MFC3 is the flow rate of the excess
carbon dioxide through MFC 3 (110). If the mass balance is
incorrect, the HMI may signal an error, and the operator may choose
to recalibrate the instruments.
[0032] The combination point (107) of the purified carbon dioxide
stream (202) and supply carbon dioxide stream (400) with the clean
gas stream (204) may be located carefully. The combination point
(107) may be sufficiently upstream of the first analyzer (102) that
the gases are well mixed before passing through the first analyzer
(102), and sufficiently downstream of the second analyzer (104)
that the purified carbon dioxide and the injected supply carbon
dioxide (122) are not picked up by the second analyzer (104).
[0033] The stream leaving the combination point (107) is a mixture
of the purified carbon dioxide stream (202), the clean gas stream
(204), and the supply carbon dioxide stream (400); and may be
referred to as the recycled gas stream (404). In some preferred
embodiments, the supply nitrogen (120) may then be injected into
the recycled gas stream (404) through the solenoid valve (114). The
stream that may leave this injection point is the simulated flue
gas stream (200), which may then continue through the process
toward the separation unit (100). The pressure transducer (118) may
be placed after this injection point, and on the suction side of
the blower (112). The PID controller may use data from the pressure
transducer (118) to control the output of the solenoid valve (114),
and keep the simulated flue gas stream (200) at a constant set
pressure. In some preferred embodiments, this pressure may be in
the range of 0.1 psig to 2 psig. In some other embodiments, such as
using a compressed simulated flue gas stream, this pressure may
range from 50 psig to 100 psig. The pressure-regulated simulated
flue gas stream (200) may then pass through the blower (112) and
recycle through the process.
[0034] FIG. 2A is an illustration of the system 101 depicted in
FIG. 1. It shows one possible arrangement of the embodiment of the
flue gas recycling system in FIG. 1. FIG. 2B further illustrates a
section of FIG. 2A, showing more detail of the system just before
the first analyzer (102) and just after the separation unit (100).
In FIG. 2b, the simulated flue gas stream (200) has already passed
through the pressure transducer (118) and thus has a constant
pressure. It then passes through the first analyzer (102), the
blower (112), and the flowmeter (116) before entering the
separation unit (100). The figure also shows the clean gas stream
(204) and the purified carbon dioxide stream (202) leaving the
separation unit (100).
[0035] FIG. 3 is a schematic diagram of a system (301) that is
similar to system 101. In system 301, all the components and
processes of system 101 may be present. Additionally, system 301
contains a fourth mass flow controller, a pressure regulator.
[0036] System 301 may be identical to system 101 from the injection
point of the supply nitrogen (120) until the separation unit (100).
In system 301, the clean gas stream (204) may emerge from the
separation unit (100) and pass through the second analyzer (104),
just as in system 101. The clean gas stream (204) may also branch
off and pass through a fourth mass flow controller (MFC 4) (300).
The PID controller may receive data from the pressure transducer
(118) and use this data to control MFC 4 (300). MFC 4 (300) may be
closed except for when an error occurs and the pressure is too
high. In this case, excess clean gas may be released through MFC 4
(300). This released excess clean gas may be vented to the
atmosphere or compressed and stored. Clean gas that is not released
through MFC 4 (300) may continue to the combination point (107)
where the clean gas stream (204), the purified carbon dioxide
stream (202), and the injected supply carbon dioxide stream (400)
combine.
[0037] In system 301, the purified carbon dioxide stream (202) may
emerge from the separation unit (100) at a high pressure. This
pressure may be around 150 psig. The pressure of the purified
carbon dioxide stream (202) may then need to be reduced before
recycling through the process. The purified carbon dioxide stream
(202) may pass through a pressure regulator (302), which may lower
the pressure to approximately 30-50 psig. The purified carbon
dioxide stream (202) may then pass through MFC 2 (108), which may
further reduce the pressure to the range of the set pressure
maintained by the pressure transducer (118) and the solenoid valve
(114). After passing through MFC 2 (108), the purified carbon
dioxide stream (202) may then proceed to the combination point
(107). If there is excess carbon dioxide, as determined by the same
methods as system 101, it also may need to be released through MFC
3 (110). There may be a compressor (not shown in FIG. 3) placed
after MFC 3 (110) to compress the released excess carbon dioxide,
so that it may be stored.
[0038] FIG. 4 is a schematic diagram of a simulated flue gas
recycling system (401). In system 401, a carbon dioxide supply
stream (400) and a nitrogen supply stream (402) are used to create
a simulated flue gas stream (200). The simulated flue gas stream
(200) may then flow toward a separation unit (100), where it is
separated into a clean gas stream (204) and a purified carbon
dioxide stream (202). The clean gas stream (204) and the carbon
dioxide stream may later combine and are recycled back toward the
separation unit (100). The supply carbon dioxide (122) and the
supply nitrogen (120) may be injected into the recycle stream as
needed.
[0039] FIG. 5 is a schematic diagram of a system (501) similar to
system 101, wherein the purified carbon dioxide stream (202) is a
liquid. It may be the same as system 101 after the combination
point (107) of the recycle streams and before the separation unit
(100). In system 501 the clean gas stream (204) may emerge from the
separation unit (100) and immediately return to the combination
point (107), or first pass through the second analyzer (104) as in
system 101. The liquid purified carbon dioxide stream (500),
however, may pass through a different process than in system 101.
The liquid purified carbon dioxide stream (500) may first pass
through MFC 2 (108) to measure its flow rate. This data may be used
as in system 101 to control the output of MFC 3 (110), which may
release excess carbon dioxide when needed. The excess carbon
dioxide stream may still be a liquid (502), and may simply be
bottled and stored. The liquid purified carbon dioxide stream (500)
that is not released through MFC 3 (110) may the pass through a
heater (506), which may vaporize the liquid purified carbon dioxide
stream (500). The vaporized purified carbon dioxide stream (510)
may then continue to the combination point (107), where the carbon
dioxide supply may be injected through MFC 1 (106). There may be a
mass flow controller (MFC 5) (508) placed just before the
combination point to further aid in monitoring the stream and in
verifying the mass balance. The stream leaving this combination
point (107) may consist of combined clean gas, vaporized purified
carbon dioxide, and supply carbon dioxide (122), and may be the
same as the recycled gas stream (404) in system 101.
[0040] FIG. 6 depicts a diagram of a method for separating and
recycling simulated flue gas. Step 602 is forming the simulated
flue gas by combining a quantity of at least two supply gases. For
example, the simulated flue gas may be formed by combining nitrogen
and carbon dioxide. In this case, the nitrogen would be referred to
as the inert gas and the carbon dioxide would be referred to as the
pollutant gas.
[0041] Step 604 is measuring and controlling initial concentrations
and flow rates. This may be done using equipment and methods
depicted in FIG. 1 and FIG. 3. The carbon dioxide, or other
pollutant gas, concentration in the simulated flue gas stream (200)
may be monitored and controlled to stay at a set constant
concentration. The pressure and flow rate of the simulated flue gas
stream (200) may also be monitored and controlled to stay at a
constant set value using valves, pumps, flowmeters, and pressure
transducers. This may be an especially important step for
applications of the method that are for experimental purposes.
[0042] Step 606 is passing the simulated flue gas through a
separation unit (100) to separate the pollutant gas from the inert
gas. The simulated flue gas stream (200) is the only inlet into the
separation unit (100). The two outlet streams from the separation
unit (100) are a clean gas stream (204), consisting of the inert
gas and any pollutant gas that was not removed by the separation
process; and a purified pollutant stream, which contains all the
pollutant gas that was removed from the simulated flue gas stream
(200) during the separation process. For example, if the simulated
flue gas stream (200) consisted of only nitrogen and carbon
dioxide, then the purified pollutant stream would consist only of
carbon dioxide, and the clean gas stream (204) would consist of
mostly nitrogen with a small amount of carbon dioxide.
[0043] Step 608 is measuring the concentration of pollutant gas in
the clean gas stream (204). This may aid in controlling the
concentration of the simulated flue gas stream (200), or in
monitoring the effectiveness of the separation unit (100). Step 610
involves measuring the flow rate of the purified pollutant gas
stream. This may also aid in controlling the concentration of the
simulated flue gas stream (200), and may also be used in a mass
balance to check the performance of the measurement instruments, as
described in system 101.
[0044] Step 612 is combining and recycling the separated streams.
Once the clean gas stream (204) and the purified pollutant stream
have both been measured, they may again combine to form a recycled
gas stream (404). Step 614 is injecting clean gas and pollutant gas
into the recycled gas stream (404) as needed to maintain the
desired concentrations and flow rates as measured in step 604. Once
the clean gas and pollutant gas have been injected into the
recycled gas stream (404), the simulated gas stream is again formed
and may then continue through the process, starting at step
604.
* * * * *