U.S. patent application number 13/081390 was filed with the patent office on 2012-04-19 for apparatus for biomass torrefaction, manufacturing a storable fuel from biomass and producing offsets for the combustion products of fossil fuels.
Invention is credited to JOHN A. PAOLUCCIO.
Application Number | 20120093701 13/081390 |
Document ID | / |
Family ID | 38710672 |
Filed Date | 2012-04-19 |
United States Patent
Application |
20120093701 |
Kind Code |
A1 |
PAOLUCCIO; JOHN A. |
April 19, 2012 |
APPARATUS FOR BIOMASS TORREFACTION, MANUFACTURING A STORABLE FUEL
FROM BIOMASS AND PRODUCING OFFSETS FOR THE COMBUSTION PRODUCTS OF
FOSSIL FUELS
Abstract
Apparatus for biomass torrefaction which includes a serpentine
elongated housing, the housing having three generally U-shaped
axial portions having first and second axial extremities and an
intermediate section, the first and second axial extremities are
disposed in normal use at a higher elevation than the first and
second axial extremities, the intermediate section being configured
for holding a liquid. Other forms of the invention include the
method for biomass torrefaction which includes providing a quantity
of biomass, providing a liquid heat transfer fluid, providing at
least a first housing for holding the heat transfer liquid,
elevating the temperature of the liquid heat transfer liquid, heat
treating the biomass by passing it through the heat transfer liquid
in the first housing at a temperature and duration sufficient to
accomplish torrefaction of the wood. In some forms of the method,
the process further includes the step of pelletizing the biomass
prior to performing the treating step.
Inventors: |
PAOLUCCIO; JOHN A.;
(Modesto, CA) |
Family ID: |
38710672 |
Appl. No.: |
13/081390 |
Filed: |
April 6, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11618868 |
Dec 31, 2006 |
7942942 |
|
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13081390 |
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60747803 |
May 21, 2006 |
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Current U.S.
Class: |
422/600 ;
422/129 |
Current CPC
Class: |
C10L 9/083 20130101;
Y02E 50/10 20130101; C10L 5/363 20130101; C10B 53/02 20130101; Y02E
50/30 20130101; Y02E 50/14 20130101; C10L 5/44 20130101; F23K 1/00
20130101; Y02E 50/15 20130101; F23K 2201/20 20130101 |
Class at
Publication: |
422/600 ;
422/129 |
International
Class: |
B01J 8/00 20060101
B01J008/00 |
Claims
1. Apparatus for biomass torrefaction which comprises a serpentine
elongated housing, said housing having at least a first generally
U-shaped axial portion having first and second axial extremities
and an intermediate section, the first and second axial extremities
are disposed in normal use at a higher elevation than the first and
second axial extremities, said intermediate section being
configured for holding a liquid whereby axial movement of wood of
associated wood from said first axial extremity to said second
axial extremity immerses the wood in a liquid in said intermediate
section.
2. The apparatus as described in claim 1 wherein said serpentine
elongated housing further includes a second generally U-shaped
axial portion having first and second axial extremities and an
intermediate section, the first and second axial extremities
thereof being disposed in normal use at a higher elevation than the
first and second axial extremities thereof, said intermediate
section being configured for holding a liquid, said second
generally U-shaped axial portion being coupled to said first
generally U-shaped axial portion by a first elevated axial section
of said housing whereby said first and second generally U-shaped
axial portions are disposed in fluid communication.
3. The apparatus as described in claim 2 wherein said serpentine
elongated housing further includes a third generally U-shaped axial
portion having first and second axial extremities and an
intermediate section, the first and second axial extremities
thereof being disposed in normal use at a higher elevation than the
first and second axial extremities thereof, said intermediate
section being configured for holding a liquid, said third generally
U-shaped axial portion being coupled to said second generally
U-shaped axial portion by a second elevated axial section of said
housing whereby said first, second and third generally U-shaped
axial portions are disposed in fluid communication.
4. The apparatus as described in claim 1 wherein said first axial
portion is a pre-heat portion.
5. The apparatus as described in claim 2 wherein said second axial
portion is a heat treatment section.
6. The apparatus as described in claim 3 wherein said third axial
section is a cooling section.
7. The apparatus as described in claim 2 further including a vent
in said first elevated axial sections whereby moisture and volatile
organic compounds can escape.
8. The apparatus as described in claim 3 further including
respective first and second vents in said first and second elevated
axial sections whereby moisture and volatile organic compounds can
escape.
9. The apparatus as described in claim 1 further including a wire
mesh enclosure for containing biomass in a pellet form, said
enclosure being dimensioned and configured for passage through said
serpentine elongated housing.
10. The apparatus as described in claim 3 including a plurality of
wire mesh enclosures for containing biomass in a pellet form, each
of said enclosures being dimensioned and configured or axial
movement in said serpentine elongated housing.
11. The apparatus as described in claim 3 further including a
conveyor for serially moving wire mesh enclosures through the axial
extent of the serpentine elongated housing.
12. The apparatus as described in claim 11 wherein said conveyor
includes elongated members joining respective wire mesh enclosures
whereby a succession of alternating elongation members and wire
mesh enclosures are joined together.
13. The apparatus as described in claim 12 wherein each of said
elongated members is a chain.
14. The apparatus as described in claim 3 further including a heat
recovery system for recovering heat added to an associated biomass
being heat-treated in said apparatus.
15. The apparatus as described in claim 3 further including
apparatus for the raising the temperature of an associated heat
transfer fluid within said second portion to a temperature in the
range of substantially 380 to 550.degree. F.
Description
RELATED APPLICATIONS
[0001] This application is division of application Ser. No.
11/618,868 filed on Dec. 31, 2006 and which matured into United
States patent issued on and which was a continuation in part of
provisional U.S. provisional application 60/747,803, filed May 21,
2006 entitled Method and Apparatus for Biomass Torrefaction and
Manufacturing a Storable Fuel from Biomass.
BACKGROUND OF THE INVENTION
[0002] The invention relates to methods and apparatus for producing
a combustible fuel, torrefaction of biomass, producing carbon
dioxide offsets as well as an article of manufacture. Carbon-offset
programs are the latest rage. Various entities have promised to
mitigate greenhouse gas emissions from diverse activities. Europe
established a cap-and-trade system last year that limits carbon
dioxide emissions from about 50 percent of industry to reach its
emissions goals as dictated by the Kyoto Protocol. Officials
modeled the system on the sulfur dioxide trading market established
in the U.S. in 1995, which has successfully cut levels of acid
rain. As the trading market evolves, some environmentalists think
that voluntary offset programs could join existing cap-and-trade
market schemes to cut emissions even more substantially.
[0003] The need for an immediate solution to replace our depleting
and air polluting fossil fuel energy sources is of the utmost
importance. The increase in the use of non-renewable coal and oil
requires an immediate replacement fuel to prevent severe economic,
health and social problems. One solution is renewable solar energy
that replaces the use of coal in electric power generating plants.
This approach has not been widely utilized.
[0004] Fossil Fuel use for electric power plants, heat energy and
transportation is continuing to increase at an alarming rate. Coal
fired power plants use most of the coal and produce most of the
fossil fuel air pollution. For each ton of carbon burned, 3.67 tons
of carbon dioxide is generated. The global use of carbon emissions
are over 7 billion tons per year and is expected to reach 14
billion tons per year by 2050.
[0005] The concentration of carbon dioxide in our atmosphere has
increased over 35% since the late 18.sup.th century. The level is
now at 379 parts per million by volume and climbing. Estimated
increases in the last year are alarming.
[0006] Many scientists believe that it will take a joint effort in
many areas with many new, yet to be invented, technologies to
simply hold the concentration of carbon dioxide to present levels.
One recent example of some ideas was recently presented by industry
and governments on Global Warming. These include these 7 steps (New
York Times 11-30-06)
1. New inventions that can capture 90% of the carbon dioxide from
800 new billion-watt coal-burning power plants. 2. Build 880 new
nuclear power plants in lieu of new coal power plants. 3. Increase
auto efficiency for 2 billion cars from 30 to 60 miles per gallon.
4. Increase the use of wind power 80 fold and use that energy to
make hydrogen fuel for cars. 5. Raise the efficiency of 1,600 full
size power plants, that utilize energy locked in coal, from 40 to
60%. 6. Conservation--Cut 25% of electricity use in homes, offices
and stores. 7. Increase solar generated electricity by 700
fold.
[0007] These are worthwhile goals, however, the cost to implement
these technologies would be staggering and some of these
technologies create new problems. The ultimate solution requires
innovative technologies. Many scientists say the only real long
term prospect for significantly substituting for fossil fuels is a
breakthrough in harvesting solar power.
[0008] Fossil fuels with their very high carbon content, are the
predominate fuels today. They have been relatively easy to extract
from the earth and to use with minimum processing and have a high
heat content. It has only been in recent years has the negative
impact of using this "Non-Renewable Fossil Fuel" on such a large
scale that the negative impact to our environment has been fully
recognized. In addition, fossil fuels are being depleted at an
alarming rate and alternative energy resources must be found to
fuel the world. Throughout the world all nations are facing the
challenge of developing clean solar "Renewable Energy Fuels" to
replace coal and other fossil fuels. Nuclear and other promising
energy sources are at best many decades away from being practical
on a large scale basis.
[0009] Carbonized wood and charcoal have long been known as high
quality fuels that produce high energy and little smoke, however,
they are costly to produce. Wood has returned as one of the fuels
of choice out of necessity, but its moisture content along with the
smoke and volatile organic compounds given off during burning have
limited its use. With the necessary increase in the use of wood
even with its air pollution burning problems, it is being used more
and more today. Collecting and transporting wood having a low
density such as 10 to 15 pounds per cubic foot has been solved with
newer and better technologies that include chipping, shredding,
milling and pelletizing where the wood is converted into practical
pellet forms with a density of 40 plus pounds per cubic foot. This
has opened new opportunities to further improve the burning
properties of wood as a more practical replacement for fossil
fuel.
[0010] Over the last 25 years an improved fuel source using wood
that has been heated in the absence of oxygen has received
considerable attention. This treated wood is called torrefied wood
(TW). Numerous attempts have been made to produce this high energy,
low pollution fuel with very limited success. Even with all the
various methods considered, none has been practical. Even though
coal fired electric power plants have found that using some
torrefied wood mixed with coal greatly reduces the air pollution
generated, the high cost of producing consistent quality torrefied
wood simply does not exist with all prior art methods of
production.
[0011] Wood has been used as a fuel for thousands of years. Wet
wood may contain over 50% water. When burned, incomplete combustion
occurs and it uses most of its energy to turn the water into steam
and produces considerable smoke and thousands of forms of noxious
gasses. Dry wood, as used in many fireplaces, may contain
approximately 22 percent moisture. For any specific wood being
burned, the dryer the wood being burned, the more complete the
combustion. Dry wood burns cleaner than wet wood, but incomplete
combustion still occurs, resulting in the formation of carbon
monoxide and many volatile organic compounds and other undesirable
air polluting gases. The pollution levels produced are unacceptable
for most air pollution agencies. Some agencies are banning wood
burning but accepting the use of wood pellets in special heaters
because wood pellets typically contain less moisture (approximately
10%). However, a substantial amount of volatile organic compounds
still exists in very dry wood. When wood pellets formed from dry
wood are burned they can generate nitrogen oxides and other
greenhouse gases and smog.
[0012] Carbonized wood is a three thousand year old technology that
has been looked at to help replace coal. However, the process is
inefficient because, in part, it consumes too much energy. A very
promising improvement in technology was developed in the 1980's by
the French when they commercially converted wood into torrefied
wood. Torrefied wood has the moisture and most volatile organic
compounds (VOC's) driven out resulting in a high percentage of
carbon content. In addition, the chemistry and structure of the
wood itself is converted into a new form by continued exposure to
heat. The French process used heat treatment by an inert gas to
drive out the unwanted moisture and volatile organic compounds and
stopped the process before it became carbonized. The torrefied wood
burned clean but production costs were high along with a complex
system with high potential for fires that prevented this from
practical commercial use.
[0013] Several inventions since have tried to perfect and improve
the torrefaction process by using high pressure steam, high
temperature inert gas, superheated steam and other gas, pressure
and vacuum methods. Some of these technologies claimed to improve
efficiencies but all have failed to overcome the practical
conversion of wood into torrefied wood in a simple, easy, quick,
practical, safe, uniform and economic way. What these prior
technologies accomplished was demonstration projects that showed
how using torrefied wood in co-firing with coal could result in
cleaner burning with less air pollution generated. Again, all prior
art methods have been too complex, too expensive, and have not been
practical for commercial use.
[0014] A number of prior art methods exist for producing torrefied
wood. These methods all use inert gas, high pressure steam, or
superheated steam in the heat treatment process. These prior art
methods primarily use convection heat transfer between the wood
surface and the heat source such as a steam or inert gas medium.
Using any type of inert gas or steam involves large containment
systems with large amounts of surface area, high equipment costs,
high energy costs, slow treatment rates, and low overall operating
efficiencies with resultant high production costs. Maintaining an
oxygen free inert gas environment to these systems adds to the
complexity and costs.
[0015] With all these prior art methods the systems and equipment
has to be complex and large to contain the inert gas or stream heat
transfer medium. The high operating pressures required with steam,
sometimes over 600 psi, require heavyweight materials for
construction of the equipment utilized and typically utilize batch
processes rather than continuous processes. These convection batch
systems are inefficient and costly to perform, thus, the final
product produced by such convection systems is expensive.
[0016] The torrefied wood produced in all prior art methods does
not contain the heat transfer fluid (HTF) of this invention. Thus,
the heat content is less at about 8,000 to 9,000 Btu per pound.
[0017] Even though torrefied wood works extremely well, as a fuel
in co-firing with coal to reduce pollution, very little has been
produced due to the overall processing inefficiencies and high
costs of all prior art systems.
Torrefied Wood Properties
[0018] Torrefaction produces a high quality fuel from wood with a
faster combustion rate, less smoking and hydrophobic
characteristics. Torrefied wood is very resistant to moisture and
decay and is friable. It can be ground and used with coal in
co-firing to obtain less air pollution.
[0019] Torrefaction of wood, prior art technologies, include
convection heating with direct contact with inert gas as the
heating medium or indirect contact with steam. Retorts, pressure
chambers, kilns and rotary drums are used to contain the wood and
inert gas. Temperatures in the range of 240.degree. C. to
280.degree. C. (464 F to 536 F) are typical. Pressures range from
atmospheric to that of high pressure steam at 600 psi or more.
Exposure times vary widely and may be 1 to 3 hours. Under high
pressure steam with the higher temperatures, the torrefaction time
can be reduced to less than an hour. Small wood pieces can be
torrefied faster than large pieces.
[0020] Temperature considerations inherent in the process include:
Wood exposed to less than 200.degree. C. (392.degree. F.) result in
water evaporation where the wood is dehydrated. Little or no
combustible products are formed. Therefore, using a heat transfer
fluid at a temperature of approximately 350.degree. F. is
reasonable for pre-heating the wood, in a manner that prevent
combustion from occurring, before the wood enters the heat
treatment section 14.
[0021] When wood is heated to 160.degree. C. (320.degree. F.) it
loses water and very little else. It also retains its physical
mechanical properties and remains hygroscopic. When wood is exposed
to 180.degree. C. to 280.degree. C. (or 355.degree. F. to
536.degree. F.) it gives off moisture, carbon dioxide, and large
amounts of acetic acid and VOC's. Complex endothermic reactions
occur during this 355.degree. F. to 536.degree. F. heating period
along with changes to the physical and chemical properties
including the wood becoming more friable and hydrophobic.
Toffefaction is achieved during this high temperature heating
process where the moisture content is reduced to 3% or less, the
mass is reduced by approximately 30%, retention of 90% of the
original energy and removal of most smoke producing agents. These
temperatures, moisture removal percentage and exposure times vary
with the type and density of biomass material being torrefied.
[0022] When wood is heated to above 280.degree. C. (or 536.degree.
F.) the reactions become exothermic and the wood starts to be
gasified instead of being torrefied. When gasification occurs the
wood is transformed into combustible gasses including methane,
carbon monoxide, hydrogen and tars. Wood is gasified for certain
purposes but this is not desired for torrefaction as described
herein.
[0023] Prior art temperatures of 250.degree. C. to 270.degree. C.
(482.degree. F.-518.degree. F.) are the standard with "convection"
heating. The higher the temperature the faster the wood is
torrefied. Smaller particles, such as pellets, can be torrefied
faster than large particles such as briquettes.
Switchgrass--General Information on One Potential Energy Crop
[0024] Almost any biomass can be used as a fuel source, however,
switchgrass has many advantages that make it an ideal material to
consider with this invention.
[0025] Many years ago, switchgrass dominated the vast prairies of
the United States. The industrial revolution, fossil fuel use and
agricultural use of the land ended the dominant role of switchgrass
as a carbon dioxide and energy storage sink. Switchgrass stands
about 10 feet tall and grows in most areas. It needs little water
and can produce over 10 tons of dry biomass fuel per acre.
[0026] Switchgrass can produce 185 GJ (175.5 MBtu or 175,000,000
Btu) of energy per 10 tons of biomass. Each acre of even marginal
crop producing value can produce an average of 10 tons of
switchgrass. Switchgrass has an energy output to input ratio of
approximately 20:1. This makes it one of the highest net energy
yields of any other practical biomass per acre.
[0027] Currently, state of the art switchgrass pellets have a very
high net energy yield per acre as compared to other biomass forms.
It has the highest energy output to input ratios, the greatest
economic advantage over fossil fuels and the greatest potential to
offset carbon dioxide from fossil fuels. When switchgrass pellets
are substantially improved with this unique high temperature
immersion torrefaction process and method of this invention,
hereinafter referred to as "torrefied wood pellets" (TWP), they
becomes a practical replacement or supplement for fossil fuel such
as coal for use in electric power plants. Co-firing 15% torrefied
wood pellets (TWP) to 85% coal has been successfully tested in a
number of electric power plants that resulted in significant
pollution reduction.
[0028] Switchgrass can be repetitively harvested over 10 years
before re-planting is necessary. One third of the carbon dioxide
collected by the plant is sequestered back into the soil by its
root system that remains after harvesting.
[0029] When switchgrass is used as a pelleting material in existing
mills a doubling of production occurs over hardwood and softwood
sawdust.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The invention will be better understood by reference to the
accompanying drawings in which:
[0031] FIG. 1 is a diagrammatic view of the path wood would travel
from biomass to a pellet mill and then to the process in accordance
with the present invention where the wood is converted to torrefied
wood pellets (TWP). The fully processed torrefied wood pellets
(TWP) are diagrammatically illustrated as being distributed to
electric power plants; to the heater for this process; and to
storage facilities to be used as energy and pollution
"offsets".
[0032] FIG. 2 is a schematic elevation view of one form of the
immersion heat treatment system for producing torrefied wood.
[0033] FIG. 3A is a plan view of the serpentine body 18 system.
[0034] FIG. 3B is an elevation view of the serpentine body 18
system with multiple sections separated by elevated axial sections
13,15.
[0035] FIG. 3C is a partial elevation view illustrating the loading
of a capsule 40 into the inlet of the pipeline and the pre-heating
12 section and the elevated axial section 13.
[0036] FIG. 3D is a partial elevation view of the heat treatment
section 14 and the elevated axial sections 13, 15.
[0037] FIG. 3E is a partial elevation view of the cooling 16
section and the capsule 40 with torrefied wood pellets (TWP)
exiting the system.
[0038] FIG. 4 is a partial schematic view of the heat treatment 14
section and the system heater 30 of heat transfer fluid 34 being
circulated in the system.
[0039] FIG. 5A is an enlarged elevation view of the elevated axial
sections 13,15 with gasses and vapors being vented out exhaust
piping 51.
[0040] FIG. 5B is a partial section view of the heat treatment
section of the serpentine body where a capsule 40 of wood pellets
(WP) 44 is being heated with heat transfer fluid 34 and converted
to torrefied wood pellets (TWP) 47.
[0041] FIG. 6A is an end view of the inlet 11 of the serpentine
body showing the capsule 40, conveyor 61, and guides. Hinged covers
11a with exhaust system 51 may be used at the inlet 11 opening
between loadings to help capture and remove the large amounts of
water vapor generated in the pre-heat section.
[0042] FIG. 6B is the inlet 11 of the pre-heat 12 section and the
heat transfer fluid 33 liquid level in the serpentine body 18.
Water vapor 50 is shown exiting the inlet 11 exhaust system 51 at
the hinged covers 11a.
[0043] FIG. 6C is a schematic view of the wire basket capsule 40
with hinged opening.
[0044] FIG. 7A is a schematic view of wood 44 with moisture, gasses
and volatile organic compounds 53 within.
[0045] FIG. 7B is a schematic view of wood 44 being treated by the
high temperature heat transfer fluid 34 in the heat treatment
section 14. Moisture, gasses and volatile organic compounds (VOC's)
53 are shown being driven out of the wood as a gas 52.
[0046] FIG. 7C is a schematic view of the completed torrefied wood
47. Virtually no moisture, and gasses or volatile organic compounds
(VOC's) 53 are present. Residual heat transfer fluid (HTF) 69 is
shown within the torrefied wood pellets (TWP) 47.
[0047] FIG. 8 is a plan schematic view of the serpentine or
curvilinear pipeline 18 system in a circular shape embodiment as
opposed to the more linear arrangement illustrated in FIGS.
1-3E.
[0048] FIG. 9 is a schematic view of multiple circular serpentine
body systems 18, as shown in FIG. 8, headered together to produce a
much greater quantity of torrefied wood pellets (TWP) 47. An
incoming train 64 delivering wood pellets (WP) 44 and a leaving
train 65 with finished torrefied wood pellets (TWP) 47 is
shown.
[0049] FIG. 10 is a schematic view of multiple straight serpentine
bodies 18 joined together by a header to provide increased
capacity. The versatile serpentine body system can be of various
shapes and sizes. An incoming train 64 delivering wood pellets (WP)
44 and a leaving train 65 with finished torrefied wood pellets
(TWP) 47 is shown.
[0050] FIG. 11 is a diagrammatic chart of the phases of wood when
exposed to "Time and Temperature" along with its relative Energy
value. The torrefaction phase occurs as soon as most of the
moisture, gases, acids and other organic materials are driven out
of the wood during the heat treatment phase. The closer the biomass
is converted from wood to charcoal, the more energy is used to
drive out the remaining moisture, gases and organics. The most
practical energy efficient fuel point is torrefied wood with its
high percentage of carbon content and lack of moisture, gasses and
volatile organic compounds (VOC's).
[0051] FIG. 12 is a chart of the carbon dioxide concentration in
our atmosphere over the last thousand years with a future
projection. The curves show the expected carbon dioxide CO.sub.2
concentration results based on the following:
[0052] Curve A: This is the expected increase in CO.sub.2 at the
present rate of use of fossil fuels. During the last 200 to 300
years CO.sub.2 has increased about 35% due to fossil fuel use. The
rate is increasing rapidly as developing nations use more fossil
fuels.
[0053] Curve B: This curve shows how the concentration could
decrease if 50% of coal presently used was replaced with the
torrefied wood product in accordance with the present invention in
co-firing electric power generation plants.
[0054] Curve C: This curve shows how CO.sub.2 concentrations would
level off if 100% of the current coal use were offset by the
torrefied wood product in accordance with the present invention on
a pound per pound carbon basis.
[0055] Curve D: This curve shows how the CO.sub.2 concentration
would start to become lower and approach levels in the past if
torrefied wood products in accordance with the present invention
were used as offsets and used to replace coal in electric power
generating plants. Torrefied wood pellets could also be used for
home heating and stoves and many other uses that should be
encouraged to bring our CO.sub.2 level back to near normal levels
before fossil fuel use.
[0056] Curve E: This shows the normal baseline CO.sub.2
concentration since the year 1,000 AD as a reference line or goal
to achieve in the future.
ADVANTAGES OF THE INVENTION
[0057] Various embodiments of the invention have some or all of the
following advantages. A paramount advantage is the creation of a
new and improved type of renewable energy fuel called torrefied
wood pellets (TWP) made from treating wood pellets to replace or
supplement non-renewable fossil fuel such as coal in order to
reduce air pollution. The present invention turns wood into a
pelletized form that is a near pollution free fuel with high carbon
content that can withstand decay and decomposition from moisture,
insects and microbes and can be easily transported and stored for
hundreds of years.
[0058] The present invention finally allows for the safe,
economical, practical production of turning wood into torrefied
wood or enhanced torrefied wood for use as a fuel and for energy or
pollution "Offsets". For greatest efficiency, the biomass should be
collected, air dried and pelletized before it is delivered to the
processing facility as described in this invention. The ideal forms
of wood biomass is wood pellets, but wood briquettes and wood logs
may also be used, however longer processing times would be
required. All three of these biomass forms are readily available
today. Lumber, logs and other forms of wood can also be used but
the uniformity of pellets with higher density are preferred for
continuous flow heat treatment operations.
[0059] The Immersion heat treatment as described in this invention
can use biomass that has been collected and pelletized, and then
convert it into torrefied wood pellets and the torrefied wood
products in accordance with the present invention.
[0060] The following list some of the many benefits and
advantages:
1. Waste wood and other normally unused biomass could be put to a
practical use instead of being placed in landfills or incinerated
or left to decay where it returns carbon dioxide, methane and other
gasses to our air. 2. Farmers could put to use large areas of near
worthless land and restore it to grow energy biomass crops for
energy production. 3. Switch grass may be one of the most energy
efficient biomass crops to grow for energy use. It may produce 2 to
3 times the energy of corn. 4. New industries could be formed to
harvest, collect, chip, shred, mill, pelletize, and transport the
biomass for production into the torrefied wood products in
accordance with the present invention. 5. Millions of jobs could be
generated throughout the world to man the growing, harvesting,
collecting, transporting, milling, pelletizing, processing,
distributing, managing and storage of torrefied wood products in
accordance with the present invention for energy use and offsets.
6. The air we breathe would benefit from every pound of torrefied
wood produced. When the goal of total carbon "off-set" is achieved,
in replacing fossil fuel, the concentration of carbon dioxide may
stop increasing and actually start to decrease to a normal
"natural" level of concentration. Then the level could be lowered
to a more natural concentration level as in the past, 1800s. 7. The
health of all life including people, animals, fish and plants would
improve with a shift toward normalization of the carbon dioxide
concentration level. Many other harmful fossil fuel gases and
pollutants would also be eliminated from the environment along with
"zero" added carbon dioxide due to "Renewable Energy" torrefied
wood use as a side benefit. 8. Acid rain will be diminished, as
coal use is diminished, as it causes crops and forests to die and
causes lakes to turn baron of life. 9. Poor developing nations can
utilize the teachings of this invention to move forward with
modernizations and offset the greenhouse gases they produce. For
example: This inventor made a recent trip to China to assist in the
development of an egg processing plant. They used high sulfur
containing coal to produce steam heat and electricity. The air was
polluted for miles around and the air was thick with black smoke.
Health problems of catastrophic proportion are occurring in many
developing nations due to burning poor quality fossil fuels. The
teachings of this invention would assist them in being better
stewards of the land and move toward cleaner fuels and "Off-Sets"
to replace fossil fuel use. 10. Recent air quality sampling tests
conducted in multiple stations in California revealed that up to
25% of the air pollution can be traced to China and other overseas
countries. The teachings of this invention can help these countries
generate clean heat and energy and help curb global air pollution.
11. The health of all nations would improve in many ways. Science
and the medical profession know very little about the long range
effect of air pollution on living tissue. The term air pollution in
this case refers to all the smoke, gases, dust, pollen, etc. that
is frequently referred to as smog. They do know that certain
debilitating medical problems result from long term exposure but
the combination of pollutants is so complex that the long range
impact to health is not very well known. What is known is that it
is safer to avoid unnecessary exposure to these unnatural fossil
fuel contaminants. 12. This invention can result in a tremendous
increase in plant growth for specific production of biomass for the
production of torrefied wood products in accordance with the
present invention. Some nations may contract with the USA and other
nations to grow certain crops, harvest it, and process it into
torrefied wood products in accordance with the present invention
for fuel or offsets. Some nations that grow plants for producing
illegal drugs may instead grow plants for producing biomass for
fuel in the form of torrefied wood products in accordance with the
present invention. Society would benefit. 13. This invention would
require more cropland, forests and plant growth. This would bring
with it a resurgence of wildlife and natural habitats where
endangered species could prosper. Many underdeveloped nations have
decimated their woodlands by clear cutting, burning for conversion
to farming and used most for fuel. The teachings of this invention
can help restore these nations' forests and woodlands. 14. As more
plants are grown, the carbon dioxide level will decrease. Plants
act as air and water filters and extract harmful chemicals during
growth. This invention alters our environment more toward a natural
previous state. 15. Existing factories and industries that still
use fossil fuels can apply for energy or pollution "offsets" when
they plan on expanding their facility. The torrefied wood products
in accordance with the present invention become a very practical
means of allowing these facilities to expand and reduce the net
amount of carbon dioxide entering our air. For example, a factory
that needs to offset a certain value (X) of carbon equivalent
offsets could purchase (X) amount of torrefied wood products in
accordance with the present invention for long range storage. The
added energy they would use in their expansion would equal the
energy in the (X) amount of offsets purchased. In essence, for
every pound of "Carbon" stored as an offset in the torrefied wood
products in accordance with the present invention would equal one
pound or "carbon" used in the fossil fuel burned, resulting in
"Zero" net added pollution. 16. This invention provides the world
with the only immediate practical solution to a clean energy fuel
to replace fossil fuel coal on a large scale. If, for example
torrefied wood pellets (TWP) were to replace only 1% of the coal
used each year in existing electric power plants, the torrefied
wood products in accordance with the present invention used would
cover an area the size of a football field and be 4 miles high!
Currently, over 7 billion tons of fossil fuel is burned each year.
It is very difficult to comprehend the volume of carbon dioxide
produced by its combustion. 17. This invention, in a preferred
form, may be achieved with a relatively simple four (4) foot
diameter serpentine or curvilinear tubular body. The body may, for
example, have some physical similarity to the Alaskan pipeline. 18.
This invention uses a feedstock or petroleum derived heat transfer
Paraffinic fluid that can be heated to 600.degree. F. and maintain
a very low vapor pressure. This allows for atmospheric operation of
the entire pipeline system. This invention need only heat the fluid
to less than 480.degree. F. For example the heat treatment portion
of the invention may operate at several inches of water pressure at
450 F and the pre-heat and cooling sections at 300 F may operate at
a small fraction of one inch vapor pressure that is very close to
ambient pressure so both the wood pellets entering and torrefied
wood pellets leaving the system can safely be open to ambient air.
19. This high temperature heat transfer fluid allows for simple
direct immersion "conduction" heat treatment of the wood in order
to quickly convert it to torrefied wood. The treatment time may be
reduced to minutes instead of hours as with some prior art
methods.
[0061] 20. Direct immersion heating in a liquid results in
considerably faster heat transfer to occur as compared to inert gas
or steam as in prior art systems. An example of convection and
conduction can be better understood when comparing the sensation of
heat one feels in the following: One can stand to be in a dry sauna
at 180.degree. F. for long periods of time that may be 2 hours
(convection heating). One can stand to be in a steam room at 125 F
for one half hour (convection heating). But, one can only stand to
be in a hot tub at 110.degree. F. for 5 or 10 minutes. The direct
immersion in the hot tub is an example of conduction heating.
21. The need for special and expensive oxygen free gases to be
supplied to the containment system is virtually eliminated due to
the unique serpentine body design with elevated axial sections on
each side of the heat treatment section. 22. The first costs,
operating costs and total production costs of the entire equipment
of this invention is a mere fraction of those of prior art.
Therefore, torrefied wood pellets (TWP) can be produced at such low
cost as to make its use extremely practical as a replacement or
supplement to coal. The primary barrier to the practical use of
torrefied wood pellets (TWP) in co-firing with coal has been the
high cost and quality of torrefied wood pellets (TWP) production
and this invention solves these problems. 23. Residual heat
transfer fluid (HTF) that remains on or in the torrefied wood (TW)
fibers is in itself a clean burning fuel and actually adds to the
calorific value or the finished torrefied wood pellets (TWP)
product. The heating level may increase 5 to 10% or more depending
on the heat transfer fluid (HTF) used, the exposure time and type
of biomass material used. Due to heat transfer fluid (HTF) costs,
most is drained off of the torrefied wood pellets (TWP) and is
reused in the system over and over. Algae and many plants such as
soy, peanut, palm, and corn can produce oils, waxes or bio-fuels.
Some, in combination may, if processed to a form that has a low
vapor pressure at high temperatures, be used as a heat transfer
fluid (HTF). Many synthetic, feedstock and petroleum sources of
heat transfer fluid (HTF) can also be used. 24. As the teachings of
this invention become known, other manufactures of high temperature
heat transfer fluids will also develop other fluids that can be
used. This competition should result in even lower operating costs
and an improved final product. 25. As the teachings of this
invention become known new agricultural, and genetic practices
should lead to the development of energy crops that like
switchgrass will yield more energy per acre and have improved
properties for processing into torrefied wood. 26. The USA and the
rest of the world will reduce its dependence on fossil fuels. 27.
High quality fossil fuels are diminishing at a rapid rate. This
invention can greatly extend existing supplies for future
generations. 28. Coal is used more than any other fossil fuel. In
addition, most coal is not of high quality. Desired coal has a high
carbon content, low sulfur and low heavy metal content. This higher
quality coal is becoming more difficult to find. More use of lower
quality coal is being used and this requires more complex and
costly air pollution controls. This invention can greatly reduce
the use of the low quality coal.
SUMMARY OF THE INVENTION
[0062] It has now been found that these objects and advantages may
be achieved in apparatus for biomass torrefaction which includes a
serpentine elongated housing, the housing having at least a first
generally U-shaped axial portion having first and second axial
extremities and an intermediate section, the first and second axial
extremities are disposed in normal use at a higher elevation than
the first and second axial extremities, the intermediate section
being configured for holding a liquid
[0063] In some forms of the apparatus the serpentine elongated
housing further includes a second generally U-shaped axial portion
having first and second axial extremities and an intermediate
section, the first and second axial extremities thereof is disposed
in normal use at a higher elevation than the first and second axial
extremities thereof. The intermediate section may be configured for
holding a liquid, the second generally U-shaped axial portion may
be coupled to the first generally U-shaped axial portion by a first
elevated axial section of the housing whereby the first and second
U-shaped axial portions are disposed in fluid communication. The
serpentine elongated housing may further include a third generally
U-shaped axial portion having first and second axial extremities
and an intermediate section, the first and second axial extremities
thereof may be disposed in normal use at a higher elevation than
the first and second axial extremities thereof, the intermediate
section may be configured for holding a liquid, the third generally
U-shaped axial portion may be coupled to the second generally
U-shaped axial portion by a second elevated axial section of the
housing whereby the first, second and third U-shaped axial portions
are disposed in fluid communication.
[0064] In some embodiments the first axial portion is a pre-heat
portion, the second axial portion is a heat treatment section and
the third axial section is a cooling section. The apparatus may
also include vents in both the first and second elevated axial
sections whereby moisture and volatile organic compounds can
escape
[0065] In various forms of the invention, the apparatus includes
one or more wire mesh enclosures for containing biomass in a pellet
form. This enclosure may be dimensioned and configured for passage
through the serpentine elongated housing. The apparatus may also
include a conveyor for serially moving wire mesh enclosures through
the axial extent of the serpentine elongated housing and the
conveyor may include elongated members joining respective wire mesh
enclosures whereby a succession of alternating elongation members
and wire mesh enclosures are joined together. The elongated members
may each be a chain. Some forms of the apparatus include a heat
recovery system for recovering heat added to an associated biomass
may be heat-treated in the apparatus. Some forms of the apparatus
include structure for raising the temperature of an associated heat
transfer fluid within the second portion to a temperature in the
range of 380 to 550.degree. F.
[0066] Other forms of the invention include the method for biomass
torrefaction which includes providing a quantity of biomass,
providing a liquid heat transfer fluid, providing at least a first
housing for holding the heat transfer liquid, elevating the
temperature of the liquid heat transfer liquid, heat treating the
biomass by passing it through the heat transfer liquid in the first
housing at a temperature and duration sufficient to accomplish
torrefaction of the wood. In some forms of the method, the process
further includes the step of pelletizing the biomass prior to
performing the treating step. The step of providing a liquid heat
transfer fluid may include providing a heat transfer fluid that is
combustible whereby residual heat transfer fluid entrained within
and on the surface of the wood increases the energy output
available when the treated wood is burned. The step of providing a
first housing may includes providing a serpentine elongated first
housing that has at least a first generally U-shaped axial portion
having first and second axial extremities and an intermediate
section, the first and second axial extremities are disposed in
normal use at a higher elevation than the first and second axial
extremities, and the intermediate section is configured for holding
a liquid.
[0067] Similarly, the method may include a step of providing a
first housing that further includes providing a housing that
includes a second generally U-shaped axial portion having first and
second axial extremities and an intermediate section and the first
and second axial extremities thereof are disposed in normal use at
a higher elevation than the first and second axial extremities
thereof and the intermediate section is configured for holding a
liquid and the second generally U-shaped axial portion is coupled
to the first generally U-shaped axial portion by a first elevated
axial section of the housing whereby the first and second U-shaped
axial portions are disposed in fluid communication.
[0068] The method may include a step of providing a first housing
that further includes providing a housing that includes a third
generally U-shaped axial portion having first and second axial
extremities and an intermediate section and the first and second
axial extremities thereof are disposed in normal use at a higher
elevation than the first and second axial extremities thereof and
the intermediate section may be configured for holding a liquid as
well as the second generally U-shaped axial portion may be coupled
to the first generally U-shaped axial portion by a second elevated
axial section of the housing whereby the first, second and third
U-shaped axial portions are disposed in fluid communication. In
addition the process may include a step of providing a heat
transfer liquid that includes providing a heat transfer liquid that
is a paraffinic hydrocarbon and/or combustible heat transfer fluid
that possess properties of a low vapor pressure at high operating
temperatures.
[0069] The method may further include the step of providing vents
in the first and second elevated axial sections whereby moisture
and volatile organic compounds can escape in the step of providing
a biomass includes providing the biomass in a pellet form and the
step of depositing heat transfer fluid in the lower elevation of
each U-shaped axial portion whereby biomass moving axially through
the housing will sequentially move into an out of a pool of heat
transfer fluid. The method may also include the step of providing
one or more wire mesh enclosures for containing biomass in a pellet
form and also include the step of providing a conveyor for serially
moving wire mesh enclosures through the axial extent of the
housing. All embodiments of the present invention will utilize heat
treating the biomass by immersion of the biomass into a heat
transfer fluid whereby heat transfer by conduction occurs. The
temperature of the heat transfer liquid will ordinarily be in the
range of 400 to 480.degree. F. in at least a part of the biomass
heat treating process and process may include the step of
subjecting the wood fibers to these temperatures in an oxygen free
atmosphere for a period of time where an endothermic reaction
occurs to convert the wood into torrefied wood. In other cases the
temperature range of the liquid may be in the range of 350 to
480.degree. F. in an oxygen free atmosphere for a period of time
where an endothermic reaction occurs to convert the wood into
torrefied wood.
[0070] The step of providing a liquid heat transfer fluid includes
providing a liquid heat transfer fluid having vapor pressure that
is less than 3 psia at 450.degree. F. although in many cases the
liquid heat transfer fluid may have a vapor pressure that is less
than 0.073 psi at 450.degree. F.
[0071] The invention also includes an article of manufacture that
includes a combustible article of manufacture which includes
torrefied biomass having a combustible oil entrained therein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0072] The present invention utilizes the "renewable" biomass
derived from solar energy. The teachings of this invention turn
this "renewable" biomass into a new compact, clean burning fuel
with a high carbon content that can supplement of replace coal in
electric power generating plants. This fuel is referred to herein
as torrefied wood products in accordance with the present
invention, or enhanced torrefied wood pellets (ETWP) or torrefied
wood pellets (TWP). The term TWP, as used herein will be understood
to refer not only cube shaped module of biomass that has been
torrefied in accordance with the present invention as well as other
shapes including modules, comminuted material, pellets, cubes,
having ether individual pieces that are either uniform or
non-uniform. In some embodiments various procedures for
densification of the torrefied biomass will be employed.
[0073] This invention includes a method and apparatus to produce a
renewable solar energy fuel. Not only can this new fuel be used in
co-firing with coal in electric power plants it can also be used as
an Energy and Pollution "Off-Set", sometimes referred to as a
"Carbon Off-Set" for long term storage. For every ton of carbon in
enhanced torrefied wood pellets (ETWP) used, one ton of coal need
not be burned, and saves 3.67 tons of net carbon dioxide from
entering our air.
[0074] The apparatus and method of the present invention will
ordinarily utilize energy crops (produced solely for the purpose of
providing energy), however, the apparatus and methods of the
present invention may also use biomass that would otherwise be left
to decay and/or decompose. Ants, termites and microbes generate
methane gas from biomass and that is considered one of the main
Green House gases.
[0075] The apparatus and method of the present invention have many
advantages over other carbon reduction methods as mentioned above
and with many of the other promising future technologies. For
example, the teachings of this invention can immediately result in
a reduction in the use of coal just by using enhanced torrefied
wood pellets (ETWP) in co-firing with coal in existing electric
power plants. Eventually enhanced torrefied wood pellets (ETWP) can
replace coal use for electric power generating plants. Enhanced
torrefied wood pellets (ETWP) are friable and compatible with
existing coal handling and firing equipment in co-firing. This
makes this renewable fuel very attractive for all existing coal
burning facilities.
[0076] Farmers are actively engaged in developing "Energy" crops to
produce bio-fuels such as ethanol and bio-diesel. One particular
encouraging biomass energy crop is called switchgrass. The central
plains of the United States had tens of thousands of acres of
switchgrass when the buffalo roamed the United States prairies.
Current technologies have already made this an important fuel
source with many of the technical problems already solved. Existing
technologies exist to harvest, dry and mill the wood biomass
material including switchgrass into a densified pellet form for use
as a fuel. A great many pellet mills produce millions of tons of
wood pellets per year for home heating and stoves. Pellet mills can
drastically reduce operating costs and increase efficiently with
greater production volumes. Many mills are waiting for an outlet
that can utilize this wood based fuel. The major problem with these
wood pellets produced is that they tend to absorb moisture and
break down quickly. They have to be used quickly and do not store
well. They also contain moisture and volatile organic compounds
that produce too much smoke and contaminants when burned for most
energy applications.
[0077] The need for a solution to developing a new processing
method that is simple, safe, efficient and practical for major
commercial use, has been a driving force leading to the development
of this substantial improvement over the prior art. The apparatus
and method of the present invention overcomes all the previous
problems that prevented torrefied wood from becoming a practical
coal replacement fuel.
[0078] Finally, a new clean burning, high carbon content, dense
friable fuel for immediate use in co-firing with coal and for use
as energy and pollution offset can be produced at a fraction of the
cost of all prior art methods. This invention can result in the
eventual total replacement of coal and save billions of tons of
carbon from fossil fuels from entering our air. This in turn can
make a significant impact on our quest to reduce the increase in
the concentration of carbon dioxide entering the atmosphere.
[0079] The increase of coal use in China alone is staggering. They
are commissioning about one large coal fired plant per week to keep
up with their growing energy needs. The pollution generated in
China from these coal fired plants is creating tremendous health
problems for all in the path of the contaminants emitted. Millions
of people are at risk from breathing the unhealthy air not only in
China but here in the United States. Recent air sampling tests in
California showed about 25% of the contaminants drifting along the
coast originated in China. It is very important for developing
nations to take advantage of this clean renewable fuel technology
and turn away from coal use for the health and well being of
all.
[0080] In a preferred embodiment of the invention, pelletized wood
is subjected to heat treatment by sequentially moving the wood
through respective liquids disposed in axial sections of a tubular
body. This immersion heat treatment process utilizing conduction
includes submerging and conveying the wood through a high
temperature heat transfer fluid within an elongated, serpentine,
tubular vessel. The pipeline is shaped to create multiple end
abutting U-shaped axial sections in fluid communication. Respective
U-shaped axial sections are a pre-heat section, heat treatment
section and a cooling section. These respective axial sections are
dimensioned and configured to hold a heat transfer fluid. Each of
these axial sections is isolated from any axial adjacent axial
sections by an elevated axial section that is at a higher elevation
than heat transfer fluid disposed in each of the adjacent U-shaped
axial sections. The elevated axial sections isolate and create an
oxygen free zone on both the inlet and outlet ends of the heat
treatment section where heat treatment occurs at high temperature,
in the area of 400.degree. F. to 500.degree. F., in order to
prevent combustion of the wood. The entire processing system of
wood and heat transfer fluid in the pipeline operates at near
atmospheric pressure. The temperature of the wood entering and the
torrefied wood pellets (TWP) leaving the system is below the
combustion temperature of the wood product being treated. The
temperature in the heat treatment section and elevated axial
sections 13, 15 may be well above combustion temperatures if
exposed to oxygen in air.
[0081] Utilizing the serpentine body, the steps of the method are:
First the three U-shaped serpentine body sections are filled with
heat transfer fluid to desired levels well below the peaks of the
U-shaped pipeline sections. As the hot heat transfer fluid enters
the U-shaped pipeline an equal volume of air, (that contains
oxygen) is displaced and exits the ends of the pipeline and the
exhaust vent at the tops of the elevated axial sections or vapor
chambers 13, 15. As soon as any wood pellets enter the system water
vapor in the form of steam is driven out of the wood pellets and
displaces the air with oxygen into the vapor chambers and out the
exhaust vent port. The steam is inert and does not support
combustion. The heat treatment section operates at a high
temperature. If the wood pellets or torrefied wood pellets were to
be exposed to air with oxygen at the approximately 450 F
temperature combustion could occur. The construction of the
U-shaped pipeline sections prevents that from occurring.
[0082] The vapor chambers constantly receive steam vapor and
volatile organic compounds (VOC's) gasses during wood processing.
The steam and VOC gasses are constantly exiting the exhaust ports
on top of the vapor chambers. The exhaust ports are in fluid
communication with the serpentine body and vapor relief ductwork
leading to condensers and or heater fuel inlet or stack flares
where waste combustible gases are burned. Pressure relief valves
(not shown) may also be in the relief ductwork exhaust line to help
maintain a stable, very low pressure of several inches of water
column above the vapor pressure of the heat transfer fluid in the
heat treatment section for better control.
[0083] The exhaust steam and VOC gasses may be directed through the
exhaust vent pipe to a condenser. This may be air or water cooled
using standard existing technology. The steam may be condensed into
water and some of the VOC gasses may be captured and condensed into
a liquid for other use. The VOC gasses may also be routed to the
burner section of the heater and used as a fuel. It has also been
common to route the exhaust gasses to a Gas Flare Stack where the
gasses are burned.
[0084] When wood is heated, at high temperature in the absence of
oxygen, for a certain period of time, it gradually turns into
torrefied wood. Torrefied wood lacks the moisture and volatile
organic compounds (VOC's) and is chemically and structurally
different than the wood entering the system. It burns considerably
cleaner than wood as almost all the moisture, gasses and
undesirable volatile organic compounds have been removed. Torrefied
wood has a high percentage of carbon and may be used directly as a
fuel or be co-fired with coal in electric power generating
plants.
[0085] The term "wood" as used herein is intended to comprehend
trees, grasses, agricultural waste, sawdust, lumber waste and most
other forms of plant material. More particularly, in the preferred
form of this invention the biomass described may be an energy crop
such as switchgrass. Pellet mills have been increasingly used to
convert biomass into a convenient compacted form for transport and
use. The average bulk density of collected biomass is 10 to 15
pounds per cubic foot. By using a pellet mill the compacted wood
density is increased to 40 pounds per bulk packed cubic foot or
more. The density of the pellet may be over 60 pounds per cubic
foot. Wood pellets (WP) are the final product of pellet mills and
are used for wood stoves, heating, and boilers. The problem with
using wood pellets is they still contain significant quantities of
moisture, gasses and volatile organic compounds (VOCs) that are
released during combustion. In addition, wood pellets (WP) are
hydroscopic and very susceptible to degrading due to moisture
absorption and cannot be stored for long periods.
This invention includes: 1. A new processing method--an immersion
torrefaction process. This process makes use of a heat transfer
fluid to heat treat wood by direct "Conduction". 2. A unique
equipment configuration--Serpentine body system with elevated axial
sections. This allows for continuous product flow through multiple
sections at different temperatures, separated by elevated axial
sections 13, 15 at near atmospheric pressure. 3. A practical
renewable fuel from biomass--torrefied wood (TW) in the form of
pellets (TWP). The terms torrefied wood pellets (TWP); enhanced
torrefied wood pellets ETWP or torrefied wood products in
accordance with the present invention are used herein for all forms
of torrefied wood including but not limited to pellets, briquettes,
logs, or lumber. The term TWP will be understood to be any
compressed torrefied wood, including plant matter, in cube or other
form factor. 4. The torrefied wood pellets (TWP) produced in this
process may also be enhanced by absorbing part of the heat transfer
fluid within the torrefied wood pellets (TWP) The heat transfer
fluid (HTF) has a high heat energy content and may increase the
torrefied wood pellets (TWP) heat output to over 10,000 Btu/lb.
This form may also be referred to as Enhanced TWP or ETWP in this
application. 5. Partial torrefaction can also be provided where it
is desired to produce a less heat treated form of torrefied wood,
at least with certain biomass materials. In such cases the process
primarily removes the moisture and volatile organic compounds
(VOC's) by using lower heat transfer fluid (HTF) temperatures and
or shorter heat treatment time periods. 6. A new practical energy
and pollution "offset" product in the form of torrefied wood
products in accordance with the present invention to offset carbon
use by fossil fuels. 7. A practical method to reduce the added
concentration of carbon dioxide in the atmosphere caused by fossil
fuels by creating and using torrefied wood. This torrefied wood can
co-fire with coal as a fuel for power plants. In addition,
torrefied wood (TW) resists decomposition for hundreds of years and
can be used as an Energy "offset" when factories want to expand
operations. This "offset" feature also allows more time for
development of other clean burning renewable energy fuels and other
promising technologies. 8. This invention utilizes a "Bootstrap"
energy transfer concept that results in an extremely practical and
efficient process. Most of the energy gained in the torrefied wood
pellets (TWP) cooling section is transferred and used in the wood
pre-heat section. In addition heat recovery or pre-heating can be
utilized from my previous patent U.S. Pat. No. 4,539,916 Apparatus
for cleaning Flue Gases and other Gases.
[0086] In a preferred form of this invention wood pellets (WP) 44
are loaded into wire strainer baskets called capsules 40. The wood
containing capsules 40 are loaded by conveyor 61 system into the
inlet 11 of the pre-heat 12 section of the system. The horizontal
section of the pre-heat section 12 section is full of heat transfer
fluid (HTF) 33 at an average temperature of 240.degree. F. to
280.degree. F. The wood 44 is heated from its initial temperature,
say 80.degree. F. to 280.degree. F. The pre-heat section 12 drives
out most of the moisture and some gases from the wood as the
temperature increases above 212 F. (This is a 200.degree. F.
sensible heat gain of the wood). The moisture content at
approximately 10%, gasses and volatile organic compounds (VOC's) 53
are mostly driven out of the wood in this pre-heat section 12
section. The moisture or water within the wood turns into steam
when heated to 212.degree. F. at atmospheric pressure as is this
case. Approximately 132 Btu sensible heat and 1,000 Btu of latent
heat energy are used to turn one pound of water from 80.degree. F.
into steam at 212 F. Therefore, pre-drying the entering wood 44 is
important to maintain high efficiency from an energy standpoint but
more importantly is the removal of as much moisture from the wood
as possible in the pre-heat section so less is mixed with the VOC's
in the heat treatment section. This allows for cleaner burning of
the VOC's when they are burned.
[0087] The capsule 40 with wood pellets (WP) 44 then passes through
an elevated axial section 13 that is above the level of the heat
transfer fluid (HTF) 33, which separates the pre-heat section 12
from the heat treatment 14 section. The elevated axial section 13
is oxygen free and is a chamber where the moisture vapor and gasses
migrate and these drive out the air with oxygen. These vapors exit
the elevated axial section 13 by exhaust piping 51 and may be
routed to a condenser, after burner and or boiler. The exhaust
piping contains a low pressure relief valve that allows for a
fairly constant slight positive pressure of several inches water
column above the vapor pressure of the heat transfer fluid in the
heat treatment section.
[0088] Considerable water vapor is continuously being generated in
the torrefaction process. The water vapor comes from the entering
wet wood as it comes in contact with the heat transfer fluid, in
the pre-heat section. Most of the water vapor exits inlet 11. The
inlet 11 is at atmospheric pressure because this large inlet is
mostly open to the ambient air. The steam and surrounding air is
drawn away by an exhaust system. The exhaust at the vapor chambers
has a slight pressure build-up of a couple of inches of water,
above the vapor pressure of the heat transfer fluid in the heat
treatment section, due to the heated gases and heat transfer fluid
vapor pressure.
[0089] This water vapor would simply exit the inlet 11 and form a
fog around the area. An exhaust system with a fan and duct or a
hood may be used in some embodiments to capture and remove the
water vapor and some of the surrounding air. Hinged covers with
exhaust ducts embodiments provide much better exhaust control. All
the generated water vapor and surrounding moist air may be simply
exhausted out of an elevated stack. Ordinarily, there will be
substantially continuous venting through a duct. (If the water was
merely dumped to the ambient the entire area would be engulfed in a
fog and the system operators would not be able to see.)
[0090] The relief valves at the vapor chamber exhaust vents (not
shown) may be as simple as a hinged horizontal flapper either
having a weight (including any attached weight) corresponding to
the, slightly above, the desired vapor pressure of the heat
transfer fluid in the heat treatment section.
[0091] The moisture content in the exhaust from this elevated axial
section 13 is relatively high and the volatile organic compounds
(VOCs) concentration is low. The elevated axial section or vapor
chamber 13 is dimensioned and configured to allow each capsule 40
to rise above the level of the heat transfer fluid 33.
[0092] The wood pellets (WP) 44 are then conveyed by a conveyor
system 61 into the heat treatment 14 section where the wood pellets
(WP) 44 are heated to 440-480.degree. F. The wood 46 in the wood
pellets (WP) 44 continue to take in heat energy, in an endothermic
reaction and undergo chemical and structural changes and expel most
of the volatile organic compounds (VOC's) 53. The wood 46 is
gradually converted into torrefied wood pellets (TWP) 47. The heat
transfer fluid 34 may average 440.degree. F.-480.degree. F. in this
section. The liquid level of the heat transfer fluid 34 may be
several feet higher than the top of the horizontal pipeline 18 to
insure that the capsule 42 is submerged during the horizontal
travel in this heat treatment 14 section.
[0093] The capsule 42 then travels the pipeline 18 incline to
another elevated axial section 15 that separates the heat treatment
14 section from the cooling 16 section. The capsule 43 with
torrefied wood pellets (TWP) 47 may be above 440-480.degree. F.
and, if exposed to air with oxygen, may be combustible and burst
into flames. The elevated axial section 15 is "oxygen free" and is
a chamber where the moisture vapor and gasses migrate. These vapors
50 exit the elevated axial section 15 via the exhaust piping 51.
These exhaust gasses, identified by the reference numeral 52, may
be routed to a condenser, afterburner (not shown) and or heater 30.
The moisture content in the exhaust from this elevated axial
section is very low and the volatile organic compounds (VOC's)
concentration is high.
[0094] The capsule 43 with torrefied wood pellets (TWP) then enters
and travels through the cooling 16 section where the torrefied wood
pellets (TWP) 47 are cooled from 480.degree. F. to 280.degree. F.
(A 200.degree. F. drop in temperature). The torrefied wood pellets
(TWP) temperature only needs to drop below 350.degree. F. to avoid
combustion problems when exposed to air. The heat transfer fluid
(HTF) 35 in this section is circulated and transferred from the
pre-heat 12 section in a "Boot Strap" manner where heat energy is
transferred between the heat transfer fluid (HTF) 33 and wood
pellets (WP) 44 in the pre-heat section 12 section and between the
heat transfer fluid (HTF) 35 and torrefied wood pellets (TWP) 47 in
the cooling 16 section. These heat energy values essentially cancel
out each other, thereby, help making this a very energy efficient
system, except for latent heat and transmission losses. The capsule
43 with torrefied wood pellets (TWP) 47 then travels up the incline
pipeline 18 to a point above the heat transfer fluid (HTF) 35
liquid level and excess heat transfer fluid (HTF) 35 is drained
from the torrefied wood pellets (TWP) and capsule 43. The torrefied
wood pellets (TWP) 47 then exits the system where they are air
cooled and allowed to continue draining off any excess heat
transfer fluid (HTF) 35.
[0095] During this process heat transfer fluid (HTF) 69 is absorbed
into the torrefied wood pellets (TWP) 47 and the amount absorbed
depends on the type of biomass, time in process, density of pellet
and temperature and type of heat transfer fluid (HTF) 20. The HTF
used in the preferred embodiment of this invention has a heat
content of 19,550 Btu/pound. More specifically, the heat transfer
fluid (HTF) is a Paraffinic hydrocarbon made from feedstock or oil.
It would be advantageous to use a low cost heat transfer fluid
(HTF) made from biomass feedstock with a high energy content and a
low vapor pressure at the operating temperature of 400 to
500.degree. F. Oil is commonly used as a fuel with boilers and any
absorbed heat transfer fluid (HTF) simple enhances the heat energy
content of the torrefied wood pellets (TWP).
[0096] The air cooled torrefied wood pellets (TWP) 47 are then
conveyed 61 to a central packaging system where the capsules 40
unload the torrefied wood pellets (TWP) 47 contained within the
capsules 40. The torrefied wood pellets (TWP) 47 are then packaged
for distribution and or distributed in bulk. Examples of bulk
distribution include: [0097] 1. torrefied wood pellets (TWP) 47 are
delivered in bulk form in train cars 65 to electric power plants 67
to be co-fired with coal. [0098] 2. torrefied wood pellets (TWP) 47
are delivered to the heater 30 system of this invention to provide
virtually all the heat energy necessary to process the wood pellets
(WP) 44 into torrefied wood pellets (TWP) 47. [0099] 3. torrefied
wood pellets (TWP) 47 or torrefied wood logs or torrefied wood
products in accordance with the present invention 47 are packaged
and delivered to major storage facilities where they are stored for
long periods as Energy and Pollution "offset" 68.
[0100] Preferred embodiments of the present invention include at
least some of the following specific features. The invention
relates to methods and apparatus for biomass torrefaction,
manufacturing a storable fuel from biomass and producing offsets
for the combustion products of fossil fuels and a combustible
article of manufacture. The serpentine body 18 with raised elevated
axial sections 13, 15 is preferred in the production of torrefied
wood pellets (TWP) or torrefied wood products in accordance with
the present invention 47 for fuel or long range storage including a
carbon Offset 68 for use of fossil fuel.
[0101] Direct contact "Conduction" heating between liquid heat
transfer fluid (HTF) 20 and wood 44 provides fast and efficient
heat treatment of wood into torrefied wood 47. The continuous
serpentine body 18 includes multiple U-shaped axial sections in
fluid communication with elevated axial sections 13,15 disposed in
between adjacent U-shaped sections. This cooperates with a
continuous conveyor 61 system to transport capsules 40 sequentially
from the pre-heat section 12, to the heat treatment 14 and then to
the cooling section 16).
[0102] The preferred apparatus and method utilizes a capsule 40
system for containment of wood pellets, briquettes, logs,
composition wood, lumber or other wood forms as it is conveyed
through the system. A Conveying 61 system that may utilize cable,
continuous chain, track, wheel or rollers moves the Capsules 40
through the Serpentine body 18. Some embodiments include a Heat
Recovery Transfer between pre-heat section 12 and cooling 16
section. This saves energy and helps make system very
efficient.
[0103] The apparatus and method includes a control for time in the
heat treatment 14 section and precise temperature control due to
use of a liquid heat transfer fluid 20 instead of steam or inert
gas as typically used in the prior art. The present apparatus and
method permit the use of an extremely simple system, equipment,
controls and operation that is also extremely efficient, 90% to 95%
plus effectiveness of energy production. The system in accordance
with the present invention is practical for a wide size range
including small, medium, large, and super large torrefaction wood
pellet 47 systems. The system is also ideal for multiple
independent systems with a common header. This allows for standby
and for processing different wood 44 products at the same time. The
system utilizes a unique raised serpentine body 18 with elevated
axial sections 13,15 above the heat transfer fluid (HTF) 20 level,
to eliminate the need for an expensive "oxygen free" gas supply
system. The system utilizes a continuous process that may be
operated 24/7 as opposed to much less efficient batch systems. More
particularly, this continuous operation may be attained with only a
modest manpower requirement. The present invention cuts
manufacturing time for producing torrefied wood by up to 80% over
prior art methods.
[0104] The wood 44 utilized in the system may be trees, prunings,
grasses including switchgrass, waste wood, composition wood,
lumber, agricultural waste and wood biomass of almost any type.
(Thus, the term "wood" as used herein includes all biomass
including but not limited to both traditional woody materials as
well as herbaceous plant matter.) It is preferred that the overall
carbon element content of the wood be 50% or more in most
applications. The wood cells contain cellulose, sugars, water,
gasses, volatile organic compounds (VOC's) and other digestible
materials found in biomass. The untreated wood cells are
hydrophilic (absorb water) and could be consumed by insects or
microbes if left to natural decomposition. Since collected biomass
may only weigh 10# to 15# per cubic foot bulk weight, it is now
becoming an industry wide standard to compact or densify it to make
transport and handling more practical. Collected biomass 62 is
commonly collected and delivered to a pellet mill 63 where it is
densified 3 or 4 times and pressed into mainly pellets or other
solid forms. The final wood pellets (WP) 44 density may be 40
pounds per bulk cubic foot. When pressed into logs the density is
even higher. However, larger pellets take longer to process than
smaller pellets.
[0105] The wood pellets (WP) 44 may be formed from most forms of
biomass (It will be understood that term "wood" is used herein to
include all biomass.). The pellets 44 may be manufactured from a
biomass 62 such as switchgrass or other wood sources that has been
processed through a pellet mill 63 and densified and pressed into
pellets. The weight may be 40 pounds per bulk cubic foot. The
moisture content may be 5 to 10%. The volatile organic compounds
(VOC's) and other gasses may be 10% or more. The carbon content
varies with biomass type and environmental conditions. The fuel
energy content may be 8,000 Btu/pound but undesirable smoke and
volatile organic compounds (VOC's) form during combustion making
wood burning an environmental concern that greatly limits its use
as a fuel. Being hydrophilic in nature it is very subject to
humidity and breaks down quickly as it absorbs water. This speeds
up decomposition and requires it to be used quickly after it leaves
the pellet mill.
[0106] The system for turning wood pellets (WP) 44 into torrefied
wood pellets (TWP) 47 in the present system includes subjecting the
pellets to immersion in high temperature heat transfer fluid 34 at
440 to 480.degree. F. for approximately 15 minutes. The high
temperature energy drives out the unwanted water, gasses, and many
volatile organic compounds (VOCs). The high energy intake,
endothermic reaction, causes a molecular transformation of the
cellulose, sugars and cell content into a hydrophobic friable high
carbon based product without the unwanted water, gasses and
volatile organic compounds (VOCs). The wood cells have now becoming
"torrefied" and the new fuel formed from wood pellets that are
called torrefied wood pellets 47 (TWP) herein.
1. Torrefied wood pellets 47 (TWP). This also refers to torrefied
briquettes and torrefied logs. This is a partially carbonized form
of wood that has very desirable fuel properties. The wood cells are
now hydrophobic and repel absorption of water and have no
digestible properties, therefore, no danger of decay or natural
decomposition by insects or microbes. Like carbonized wood, the
life expectancy may be hundreds of years or more. When wood is
torrefied it is essentially no longer wood as we know it. It is
more like a friable hard plastic like material. The density is
increased to about 50 pounds per bulk cubic foot. The pellet
material may now have a density of 60 to 70 pounds per cubic foot.
Torrefied wood pellets (TWP) 47 is used in this invention
description for clarity. However, torrefied wood (TW) or torrefied
wood pellets (TWP) may be in other forms and shapes including
briquettes, logs or torrefied wood products in accordance with the
present invention for use as "offsets. 2. Heat transfer fluid 20
(HTF). A preferred embodiment utilizes a heat transfer fluid having
a low vapor pressure. Ideally the vapor pressure is less than 3 psi
and ideally less than 0.04 psi. This low pressure enables the
construction of apparatus that is less expensive and less
substantial because it does not have to function at high pressure.
(In other words, the apparatus required does not have to be
constructed to sustain high pressures such as that commonly
associated with, for example, pressure cookers used for cooking
foods. This fluid, characterized by the manufacturer as having a
feedstock that is paraffinic hydrocarbon, can be heated to
600.degree. F. and still maintain a very low vapor pressure.
[0107] This allows for near atmospheric operation of the entire
serpentine body 18 system. This invention may only require a fluid
temperature of 450.degree. F. and the vapor pressure would be
extremely low at only 0.04 psia. The density of the fluid at
450.degree. F. is approximately 6 pounds per gallon. The heat of
combustion is 19,550 Btu/lb. The fluid is nontoxic and can be mixed
with other oils. An example of one heat transfer fluid (HTF) 20
than is suitable is "Paratherm HE" that is manufactured by
Paratherm Corporation in West Conshohocken, Pa. This fluid is
characterized by the manufacturer as having a feedstock that is
paraffinic hydrocarbon (single cut). More detail appears in the
manufacturer's publication entitled Paratherm-HE/HEEngBul. Many
other plant feedstock, synthetic, or oil based heat transfer fluids
(HTF) can be used. A variety of other heat transfer fluids, with
similar properties, may also be used. From an environmental
standpoint it is preferable that the heat transfer fluid be derived
from plants making the HTF 100% renewable energy. (Note: If fossil
fuel petroleum (non-renewable energy) is used in making the HTF the
TWP would be less than 100% renewable energy by the percentage of
carbon in the HTF contained on and in the TWP. An additional
consideration is the energy that may be extracted from the final
product because of residual heat transfer fluid on and in the final
product. In those forms of the present invention where the final
product will be utilized as fuel, it is essential that the
substance be combustible and have a low vapor pressure at high
temperatures. In addition, the selection of the fluid may consider
the energy in the fluid because the chosen fluid be absorbed within
and stay on the surface of the torrefied wood produced by the
present invention and thus affect the characteristics of the final
product.
[0108] Each Capsule 40 in the preferred embodiment of the present
system is preferably a cylindrical wire mesh basket (or perforated
metal) that contains the wood pellets 44 and travels through the
serpentine body 18. At least one end is hinged so it may be opened
for pellets to be loaded and unloaded. The perforations are smaller
than the pellet diameters. In a preferred form of this invention
the capsule would be 3' diameter by 6' long. This would hold 40
cubic feet of wood pellets. The wood pellets (WP) 44 weight at
50#/CF would be 2,000 pounds or 1 ton. The capsule may have guide
strips to prevent friction wear or contact with the interior of the
serpentine body 18. The capsule may be of any size and shape and
may contain internal screened areas for increased heat transfer
fluid (HTF) flow and escaping gases.
[0109] The capsules 40 are moved through the system by a Conveyor
61. A continuous flow cable or chain conveyor transports the
capsules 40 through the serpentine body 18. Standard existing
conveyor 61 technology would be used. The cable or chain will glide
over a metal wear strip (not shown) in case any cable drag
occurred. In no case will the cable come in contact with the
serpentine body 18 interior. The conveyor 61 cable support system
will prevent any wear contact with the interior surface of the
serpentine body 18. A mating clamp system may engage and disengage
cable during transport.
[0110] The serpentine body 18 is characterized by U-shaped axial
sections. The axial sections are referred to herein as pre-heat
section 12, heat treatment section 14 and cooling section 16
sections. Disposed intermediate adjacent U-shaped are elevated
axial sections 13, 15 of the serpentine body 18 of this invention.
In a preferred form of the invention the serpentine body 18 is a
continuous 48'' diameter steel pipe with ASME welded joints and
covered with exterior insulation and a metal jacket insulation
protection covering (not shown). The material specifications of the
pipeline may be very similar to the piping used for the Alaskan
Pipeline. This pipeline can be of various sizes and shapes and two
shapes are preferred as shown on FIGS. 7 and 9. However, almost any
size and shape can be used. This size could handle over 1 ton of
torrefied wood pellets (TWP)/minute or 60 tons/hr or 1,440
tons/day. Multiple systems may be preferred instead of larger
systems due to the readily available 48'' diameter steel piping and
low cost. The round pipe diameter shape minimizes heat loss and is
ideal for the heat transfer fluid (HTF) and capsules 40.
[0111] A preferred form of the serpentine body 18 has the axial
extremities thereof in abutting relationship with the serpentine
body 18 forming a circle, in plan view as shown in FIG. 8. This
design allows for a continuous conveyor 61 system to move capsules
40 in a very efficient manner. However, this design uses more land
space than the other preferred shape and would be more costly to
construct. Other preferred forms of the body 18 utilize a
serpentine body 18 wherein the axial extremities of the serpentine
body aligned in coaxial relation with a rectilinear axis and
substantially all of the serpentine body is either above or below
that rectilinear axis. Stated another way, in such an embodiment
the serpentine body 18 is a straight line in plan view as shown in
FIGS. 9 and 10. This design is more efficient, land space wise, but
requires a more extensive conveyor 61 system. This shape may be the
least costly to construct. Various combinations of these layouts
may be utilized to accommodate the space available.
[0112] The pre-heat section 12 (P--H Section) is shown in FIG. 2
with the inlet thereof above the heat transfer fluid (HTF) 20
level. The serpentine body 18 then slopes downward to a horizontal
position. The horizontal portion of the pipeline is full of heat
transfer fluid (HTF) 20 to a point several feet above the top of
the horizontal portion to insure total immersion of the wood
pellets 44 in heat transfer fluid (HTF) 20. The serpentine body 18
then slopes upward to form an elevated axial section 13 above the
level of the heat transfer fluid (HTF) 20. This acts to separate
the pre-heat section 12 from the heat treatment section 14. Water
vapor, gasses and volatile organic compounds (VOC's) driven out of
the wood pellets (WP) 44 migrate along the inside top portion of
the pipeline and exit at the open inlet 11 area and the elevated
axial section 13. Water vapor will mainly be expelled at the inlet
11 and pre-heat 12 section as the water in the wood quickly turns
to steam when heated to 212 F. The heat transfer fluid (HTF) 20 in
the pre-heat section 12 section usually varies between 320 and
250.degree. F. or less.
[0113] The heat treatment section 14 (HT Section) is shown, in FIG.
2, in-between the pre-heat section 12 and cooling section 16. The
heat treatment 14 section is where the wood pellets (WP) 44 are
converted to torrefied wood 47 (TWP). The direct exposure of the
wood to the high temperature heat transfer fluid 34 quickly heats
the wood by conduction. The time and temperature vary with size and
type of biomass pellet being converted. For example if switchgrass
were the biomass milled into wood pellets (WP) 44, the exposure
time, for example, will ordinarily be 15 minutes at 480.degree. F.
heat transfer fluid (HTF) temperature more or less. Most of the
water and gases have been driven out before the wood reached this
section. Very complex chemical changes take place during this heat
treatment process. The order of gasses being driven out is
moisture, carbon dioxide gas, carbon monoxide, and other volatile
organic compounds. It is at this point where endothermic reactions
and torrefaction occurs and remains until a practical limit is
reached as shown in FIG. 11. This limit is determined by tests for
each form of biomass. After this practical point is reached more
gasification would occur as the torrefied wood is further changed
to a form of carbonized wood and that would not be practical. The
object of this invention is to treat the wood to within the
torrefaction stage.
[0114] The wood biomass exposed to the heat transfer fluid (HTF) 34
undergoes a partial low level form of pyrolysis (gasification)
where gasses are driven out of the wood. The wood undergoes
chemical and structural changes. The result is wood that has a
higher percentage of carbon, higher heat content and much less
volatile organic compounds than un-treated wood. Once the wood
approaches the heat transfer fluid (HTF) 34 temperature additional
heat energy is still required in an endothermic reaction to
complete the transformation process from wood to torrefied wood.
During this time in the process very complex and mostly unknown
chemical conversion changes occur in the wood material as it become
torrefied.
[0115] The torrefied wood pellets (TWP) 47 have a heating value
that approaches 9,000 to 10,000 Btu per pound as compared to 10,000
to 15,000 Btu per pound for bituminous coal which is the primary
fuel for electric power plants. However, even with only 2/3 the
energy content of coal the torrefied wood pellets (TWP) 47 produce
"Zero" net air pollution because it is considered a "Renewable
Energy Fuel", whereas "Non-Renewable" coal produces "100%" air
pollution mainly in the form of carbon dioxide and other greenhouse
gases. The very good news from limited tests where torrefied wood
pellets (TWP) 47 has been used in co-firing with coal, as a
combined fuel for power plants, has resulted in much cleaner
burning and less harmful air pollution. This combination fuel has
had very limited use due to the very high cost, non-uniformity, and
scarcity of torrefied wood pellets (TWP) 47. It is the intent of
this invention to change this so that torrefied wood pellets (TWP)
47 are inexpensive, uniform, and plentiful and used in a much
higher percentage with coal to drive down the added carbon dioxide
entering our air from fossil fuel.
[0116] The cooling Section 16 will ordinarily receive the hot
torrefied wood pellets (TWP) 47 at about 450.degree. F. or less and
gradually cool the torrefied wood pellets (TWP) 47 to 250.degree.
F. or less. As the cooled torrefied wood pellets (TWP) 47 travel up
the inclined/vertical serpentine body 18 the heat transfer fluid
(HTF) 20 drains off the torrefied wood pellets (TWP) 47 surfaces
and fall back into the horizontal part of the cooling section 16 of
the serpentine body 18. The circulating heat transfer fluid (HTF)
20 between the pre-heat section 12 and cooling 16 section exchange
heat and conserves considerable energy. This circulation is
achieved with the pumps 24, 25. In essence an exact change of
energy occurs except for latent heat losses. Ideally, the pre-heat
section 12 increases the wood pellets (WP) 44 from 80 to
280.degree. F. or a 200.degree. F. rise. Then the cooling 16
section cools the torrefied wood pellets (TWP) 47 from 450 to
250.degree. F. or a 200.degree. F. drop in temperature. The
200.degree. F. rise and drop in temperature cancel out the sensible
heat input and heat output for very efficient operation. The latent
heat used to drive our moisture and gasses is dependent on the
moisture content of the entering wood pellets (WP).
[0117] The process in accordance with the present invention that
converts wood into torrefied wood pellets (TWP) uses heat energy to
preheat the wood to drive out moisture. Then the wood is heated to
the desired torrefaction temperature. Heat energy drives out
additional moisture and volatile organic compounds. In addition,
heat energy is consumed by the wood in an endothermic reaction that
occurs within the wood cells that alters the molecular structure
and chemistry of the wood cells. This endothermic phase transition
uses heat energy without raising the temperature of the torrefied
wood. In addition, the heat loss from the equipment and exposed
piping system surfaces and other losses need to be added to
determine the overall efficiency of the process. As compared to all
other prior art methods of torrefaction, using steam, air, inert
gas, vacuum and superheated steam, this immersion heat transfer
fluid invention 10 method uses considerably less energy. Immersion
conduction heating puts about a thousand times as many molecules in
direct contact with the wood 44 being torrefied than other methods.
A fraction of the containment volume is used with heat transfer
fluid (HTF) 20 in lieu of other steam or inert gas heat transfer
methods. Finally, this invention provides a method of making
torrefied wood pellets (TWP) 47 in a manner that is practical,
utilizing materials that are plentiful and at very low cost so the
method and apparatus may be used extensively everywhere.
[0118] The air cool and drain section 17 is shown in FIGS. 3A-3E.
After the torrefied wood pellets (TWP) 47 leave the cooling 16
section, the surface temperature may still be 250.degree. F. The
torrefied wood pellets (TWP).47 may be air cooled by natural air
movement or by cooling fans. The drained off heat transfer fluid
(HTF) 20 is captured in a trough and reclaimed for recycled
use.
[0119] Filters 26, 27, 28 are shown in FIG. 2: Each of the sections
12, 14, and 16 has a filter system in the return heat transfer
fluid (HTF) 20 line. Bits of wood, debris and other contaminants
are captured and removed from the heat transfer fluid (HTF) 20
before it reaches the circulating pumps 23, 24, 25. The heat
transfer fluid (HTF) circulating pump 24 transfers fluid between
the pre-heat section 12 and the cooling section 16. A main pump 23
circulates the high temperature heat transfer fluid (HTF) 34 from
the return outlet at the heat treatment section 14 to the heater 30
where it is heated to 480.degree. F. or any other desired
temperature.
[0120] Each piping section, including the pre-heat section 12, heat
transfer section 14 and cooling section 16 has provisions for
maintaining the desired level of heat transfer fluid (HTF) 20. A
liquid level sensor 21 activates a fill valve from a heat transfer
fluid (HTF) 20 storage tank 31 for make-up, if the level is too
low. This also maintains a constant level of heat transfer fluid
(HTF) 20 in each section of the entire serpentine body 18 system.
Many existing technologies exist to maintain liquid level. The
fluid level in the pre-heat and cooling sections will be lower than
the level in the heat treatment section due to the vapor pressure
of the heat transfer fluid in the heat treatment section and the
pressure setting of the relief valves in the vapor chamber vent
systems.
[0121] Each piping section, including pre-heat section 12, heat
transfer section 14 and cooling section 16 has provisions for
maintaining the desired maximum level of heat transfer fluid (HTF)
20. When the liquid overflow sensor 22 is activated it drains off
excess heat transfer fluid (HTF) 20 and directs it to a storage
tank 31 for future use. Many existing technologies exist to
maintain liquid overflow conditions. The system also includes a
heater 30. The heater 30 may be fueled with renewable energy
torrefied wood pellets (TWP) fuel to avoid using any fossil
fuel.
[0122] Coal is the primary fuel used for electric power generation
plants and is the main source of man made air pollution in the
world. Oil use is the second main source. Natural gas is relatively
clean as compared to oil and coal but it also creates carbon
dioxide which is a greenhouse gas. Coal has many impurities and
heavy metals and many other gases are formed during burning. This
application mainly refers to carbon dioxide; however, those skilled
in the art will recognize that many other greenhouse gases and
other contaminants are produced with coal use.
[0123] The present disclosure utilizes several terms of the art.
The term "Co-firing" as used herein refers to utility companies
mixing a small percentage of wood biomass with coal in the coal
firing equipment of a large coal-burning, utility boiler. The term
"Greenhouse gasses" refers to emissions produced by the combustion
of non renewable fossil fuels such as coal. The advantage of
co-firing includes displacing the fossil fuel coal and lowering
utility carbon dioxide emissions from fossil fuels. Carbon dioxide
emissions from wood and agricultural waste is generally considered
"carbon" neutral, that is, it gives up what was taken in during the
growth cycle.
[0124] As countries try to reduce CO.sub.2 emissions, utilities
will receive benefits by reducing emission of greenhouse gases
resulting from reducing the combustion of fossil fuels and
substituting emissions from wood fuel. These CO.sub.2 "offsets" are
the basis for the benefits granted by a government. Known waste
wood and wood pellets fuels contain too high a percentage of
moisture and volatile organic compounds for use as an
environmentally friendly fuel. This invention converts the wood
pellets into dry, torrefied wood pellets that have most of the
volatile organic compounds removed. The torrefied wood pellets burn
cleanly, approach coal in carbon content and mix easily with coal
in existing firing equipment.
[0125] Unlike previous wood and wood pellets that were only used in
3 to 8% mix with coal, TWP can be used at 15% or higher. It is
expected that TWP can replace coal completely with few
modifications to equipment. A goal of this invention is to use
torrefied wood pellets and other biomass energy such as bio-diesel
in the transporting and processing of the wood and or grasses into
torrefied wood pellets in order to reduce the use of any fossil
fuels. Bio-diesel may be used as the fuel in the transport vehicles
to avoid the use of fossil derived diesel fuel. In addition,
bio-diesel electric power generators are increasing in use with
hydrocarbon and sulfur emissions essentially eliminated and CO
emissions reduced by 50%.
[0126] If, for example is took 20 pounds of carbon in biomass fuels
to harvest, transport and process 100 pounds of carbon in torrefied
wood pellets then it could be considered 80% efficient. However,
the net contribution of CO.sub.2 emissions would be "zero". That
is, 120 pounds of carbon was removed during the plant growth cycle
and 120 pounds of carbon would be placed back into the environment
when the torrefied wood pellets were used as fuel. One could also
say it takes 120 pounds of renewable carbon in biomass to offset
100 pounds of carbon in non-renewable coal. The net result is still
100 pounds of non renewable carbon is prevented from entering our
environment.
[0127] Wood contains water, cellulose, hemicellulose, lignin and a
small proportion of soluble extractives, (lipids and terpenes) and
other carbon related compounds. During the overall processing
operations virtually all of the water and most of the volatile
gases are removed. Most of the moisture is driven out of the wood
in the pre-heat section and may be vented or condensed with
conventional technology. The volatile organic compounds that are
driven out of the wood during the process may be condensed and
separated into usable by-products. The volatile organic compounds
may also be used as fuel for the heater or burned in stack flares.
The volatile organic compounds burn much cleaner without moisture
present.
[0128] When wood, containing moisture, is burned the formation of a
great number of undesirable gases are formed due to the moisture
content. This includes smoke with carbon monoxide, methane,
nitrogen oxides (NOx) and other smog polluting gases. The cooling
smoke and gases form soot, creosote and other toxic substances.
This invention removes virtually all moisture within the wood and
this allows for much cleaner burning. The torrefied wood pellets
formed during this process are moisture free and have reduced
Volatile organic compounds and have a very high concentration of
carbon.
[0129] The biomass that would have been left to decompose into
methane and other gases as it gives up the collected suns energy
can be processed into useful torrefied wood pellets. The torrefied
wood pellets then provides for practical energy use with clean
burning emissions and practical offsets for fossil fuel use. This
is a win-win-win condition. Numerous other social, economic,
environment health and global benefits results from this invention.
In essence this invention can help solve the greatest environmental
pollution problem since man started using coal and fossil fuels to
generate electricity.
[0130] Coal mining, extraction, processing and delivery has a side
effect that is also environmentally disadvantageous. This process
also takes energy and resources and generates pollution before it
reaches the electric power generating plant. High quality coal with
low sulfur content is becoming scarcer and the future for coal
points to lower quality.
[0131] With conduction heating, as in this system, lower
temperatures or 450.degree. F. or less will result in higher
quality, more uniform torrefaction and still process torrefied wood
pellets (TWP) faster than prior art methods.
[0132] Advantageously, the pellet mill will be close to a TWP
processing plant so that it will be practical to use the flue gases
from the heater to preheat the wood prior to it being milled into
wood pellets. This could be done in accordance to the teachings of
John A. Paoluccio's prior U.S. Pat. No. 4,539,916. Other existing
heat transfer technologies such as a stack heat recovery coil may
also be used to heat air indirectly for pre-drying the wood.
[0133] The description herein refers to a liquid heat transfer
fluid. It will be understood that a liquid heat transfer fluid has
superior heat transfer characteristics because of conduction.
[0134] Reference numerals used in this application:
TABLE-US-00001 10 Invention. Immersion Heat Transfer Fluid
Torrefaction Process. 11 Loading Inlet. Vapor and gases escape as
wood pellets (WP) within a capsule are immersed in heat transfer
fluid (HTF). 12 Pre-heat Section. wood pellets (WP) are heated by
heat transfer fluid (HTF) from 80 to 280.degree. F. 13 Elevated
Section or vapor chamber. This separates pre-heat Section from the
heat treatment section. 14 heat treatment section. wood pellets
(WP) are immersed in heat transfer fluid (HTF) and torrefied. 15
Elevated axial section or vapor chamber. This separates the heat
treatment section from cooling Section. 16 Cooling Section.
torrefied wood pellets (TWP) are cooled by heat transfer fluid
(HTF) from 480.degree. F. to 280.degree. F. 17 Unloading Outlet and
Drain Section. heat transfer fluid (HTF) drains off torrefied wood
pellets (TWP) in capsule. 18 Serpentine body with Insulation. Note:
In the preferred form of the invention this would be a 48''
diameter steel pipeline with exterior insulation that would be very
similar to the Alaska Pipeline specifications. 19 Access port and
hatch to inspect and service system. Prefer 30'' diameter access.
20 Heat Transfer Fluid: This fluid allows for "Conduction" heating
between the immersed wood and fluid. (Also referred to by reference
numerals 33, 34, 35 when disposed in specific sections of the
apparatus.) 21 Liquid level sensor. This sends a signal to a float
fill valve to maintain desired heat transfer fluid (HTF) level. An
indicator alarm may alert the plant operator if heat transfer fluid
(HTF) is low. 22 Overflow port. If for any reason the heat transfer
fluid (HTF) level rises to this level the overflow fluid will be
directed to a storage reservoir. An indicating alarm may alert the
plant operator. 23 Circulating Pump. This pump circulates heat
transfer fluid (HTF) through heat treatment section and Heater. 24
Circulating Pump. This pump circulates heat transfer fluid (HTF)
from pre-heat Section to cooling Section. 25 Circulating Pump. This
pump circulates heat transfer fluid (HTF) from pre-heat Section to
cooling Section. 26 Filter. This removes particles and contaminants
from heat transfer fluid (HTF) in the heat treatment section. 27
Filter. This removes particles and contaminants from heat transfer
fluid (HTF) in pre-heat Section. 28 Filter. This removes particles
and contaminants from heat transfer fluid (HTF) in cooling Section.
29 Heat Exchanger. These may be used to add heat or remove heat
during certain periods. 30 Heater. In Preferred form of the
invention this uses torrefied wood pellets (TWP) as fuel to heat
heat transfer fluid (HTF). 31 Storage Tanks for heat transfer fluid
(HTF) with storage capacity to hold all heat transfer fluid (HTF)
during emergency. Source of make-up heat transfer fluid (HTF) to
sections as required by liquid level sensors and also may receive
overflow heat transfer fluid (HTF). 32 Inlet valve that allows heat
transfer fluid heat transfer fluid (HTF) make-up to enter system if
sensor detects a low level. 33 Heat transfer fluid HTF in pre-heat
section. This may be at 240 to 300.degree. F. 34 Heat transfer
fluid HTF in heat treatment section. This may be at 400 to
500.degree. F. 35 Heat transfer fluid HTF in cooling section. This
may be at 240 to 300.degree. F. 36 Heat transfer fluid HTF in
Storage tanks. These may vary from ambient storage temperature to
overflow temperature. 37 Fossil fuel supply to heater or boiler. 38
Co-firing fuel or torrefied wood pellets (TWP) fuel at boiler or
heater. 39 Flue gas exhaust. This may include a heat exchanger or
may be directed to an Apparatus for Cleaning Flue Gasses and other
Gasses per my previous Pat. No. 4,539,916 to preheat biomass prior.
40 Capsule: This is a wire mesh basket and holds the wood pellets
(WP) entering the pre-heat Section. 41 Capsule: Wood Pellets (WP)
immersed in heat transfer fluid (HTF) in pre-heat Section 12 at
240-280.degree. F. 42 Capsule: Wood Pellets (WP) immersed in heat
transfer fluid (HTF) in heat treatment section. Wood is being
torrefied @ 440-480.degree. F. 43 Capsule: Wood Pellets (WP)
immersed in heat transfer fluid (HTF) in cooling Section. torrefied
wood pellets (TWP) are cooled to 280.degree. F. 44 Wood Pellets
(WP). This is biomass that has been processed through a pellet mill
and densified and pressed into pellets. 45 Wood material in Wood
Pellets (WP). This may be any carbon based biomass that contains
cellulose, sugars, water, gasses, volatile organic compounds
(VOC's) typically found in wood. 46 Wood process in turning wood
pellets (WP) into torrefied wood pellets (TWP). Wood is immersed in
a heat transfer fluid and undergoes a heat treatment process that
changes the structure and composition of wood into a torrefied
form. 47 torrefied wood pellets (TWP). This is a form of wood that
has been heat treated into torrefied wood. However, torrefied Wood
(TW) or torrefied wood pellets (TWP) may be in other forms and
shapes including briquettes or fireplace logs or torrefied wood
products in accordance with the present invention for use as
offsets. 48 Biomass. This includes all forms of biomass such as
trees, grasses, waste wood and sawdust and agricultural waste. The
preferred form of biomass source for this invention is switchgrass.
49 Switchgrass, or biomass, collected, dried, shredded and turned
into compact pellets at a pellet mill. 50 Expelled gasses: Includes
water vapor, gasses and volatile organic compounds (VOC's). 51
Exhaust piping of expelled gasses to condenser, boiler and or
exhaust. 52 Gasses being expelled from wood pellets (WP) due to
immersion in heat transfer fluid (HTF). 53 Liquid, solid and gas
forms of water, gasses or volatile organic compounds (VOC's) in
wood pellets (WP). 54 Heat transfer fluid (HTF) piping from Heater
to heat treatment section. 55 Heat transfer fluid (HTF) piping from
heat treatment section to filter, pump and Heater. 56 Heat transfer
fluid (HTF) piping from cooling section to filter and transfer
pump. 57 Heat transfer fluid (HTF) piping from pre-heating section
transfer pump to cooling section. 58 Heat transfer fluid (HTF)
piping from pre-heating section to filter and transfer pump. 59
Heat transfer fluid (HTF) piping from pre-heating section transfer
pump to cooling section. 60 Heat energy entering wood pellets (WP).
61 Conveyor system. 62 Trees, switchgrass, agricultural waste,
waste wood and other biomass. 63 Pellet Mills where biomass is
densified into wood pellets. 64 Train cars delivering wood or wood
pellets (WP) to processing facility 65 Train cars delivering
torrefied wood pellets (TWP) for fuel use or storage as Offsets. 66
Electric power generation plant 67 Carbon dioxide generated from
power plants, industry and transportation 68 offset for long range
storage 69 Heat transfer fluid (HTF) absorbed within torrefied wood
pellets (TWP)
[0135] While the present invention has been described in terms of a
process that first forms the biomass into pellets followed by heat
treatment, those skilled in the art will recognize that the biomass
may be formed into pellets after the treatment described herein
without departing from the spirit of the present invention.
However, it will be understood that the process of forming the
biomass into pellets increases the density of the biomass and
thereby simplifies the handling of the biomass. In addition, as
noted above smaller pellets may be processed more rapidly than
larger pellets.
[0136] Although the description above contains many specifics,
these should not be construed as limiting the scope of the
invention, but as merely providing illustrations of some of the
presently preferred embodiments of this invention. Thus, the scope
of this invention should be determined by the appended claims and
their legal equivalents. Therefore, it will be appreciated that the
scope of the present invention fully encompasses other embodiments
which may become obvious to those skilled in the art, and that the
scope of the present invention is accordingly to be limited by the
appended claims, in which reference to an element in the singular
is not intended to mean "one and only one" unless explicitly so
stated, but rather "one or more." All structural, chemical, and
functional equivalents to the elements of the above-described
preferred embodiment that are known to those of ordinary skill in
the art are expressly incorporated herein by reference and are
intended to be encompassed by the present claims. Moreover, it is
not necessary for a device or method to address each and every
problem sought to be solved by the present invention, for it to be
encompassed by the present claims. Furthermore, no element,
component, or method step in the present disclosure is intended to
be dedicated to the public regardless of whether the element,
component, or method step is explicitly recited in the claims. No
claim element herein is to be construed under the provisions of 35
U.S.C. 112, sixth paragraph, unless the element is expressly
recited using the phrase "means for."
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