U.S. patent application number 11/691312 was filed with the patent office on 2007-09-27 for method for producing a homogeneous biomass fuel for gasification applications.
Invention is credited to John Paul Gaus, Philip D. Leveson.
Application Number | 20070220805 11/691312 |
Document ID | / |
Family ID | 38531852 |
Filed Date | 2007-09-27 |
United States Patent
Application |
20070220805 |
Kind Code |
A1 |
Leveson; Philip D. ; et
al. |
September 27, 2007 |
Method for producing a homogeneous biomass fuel for gasification
applications
Abstract
A method for producing a gasifier feedstock with uniform
gasification characteristics from a number of biomass sources which
each exhibit differences in their drying, pyrolysis, devolatization
or gasification characteristics. The method allows biomass from a
wide range and sources and with a wide range of gasification
characteristics to be utilized within a gasifier without
modification of the gasifier unit. The method produces a fuel
pellet with controllable size, density and moisture content. The
method smoothes any changes in calorific value which may exist
between different feedstocks. It has been found that the
gasification characteristics of a pellet formed in this way is
strongly dependant upon the shape, moisture content and density of
the pellet formed and less sensitive to the origin of the biomass
feedstock.
Inventors: |
Leveson; Philip D.; (Hannawa
Falls, NY) ; Gaus; John Paul; (Watertown,
NY) |
Correspondence
Address: |
POWELL GOLDSTEIN LLP
ONE ATLANTIC CENTER
FOURTEENTH FLOOR 1201 WEST PEACHTREE STREET NW
ATLANTA
GA
30309-3488
US
|
Family ID: |
38531852 |
Appl. No.: |
11/691312 |
Filed: |
March 26, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60785933 |
Mar 24, 2006 |
|
|
|
Current U.S.
Class: |
44/605 |
Current CPC
Class: |
Y02E 50/30 20130101;
C10J 2300/0916 20130101; C10L 5/363 20130101; C10L 5/44 20130101;
C10J 3/00 20130101; C10L 5/46 20130101; C10L 5/42 20130101; C10J
2300/0903 20130101; Y02E 50/10 20130101; C10L 5/48 20130101 |
Class at
Publication: |
044/605 |
International
Class: |
C10L 5/00 20060101
C10L005/00 |
Claims
1) A method for producing a homogeneous gasifier fuel from a
plurality of different biomasses, wherein each biomass exhibits
differing drying, pyrolysis, devolatization or gasification
characteristics, comprising: a) drying each type of biomass to a
moisture content in the range of from about 0% to about 50%; b)
reducing the characteristic length of the biomass particles to the
range of from about 0.01 inches to about 0.1 inches; c) combining
and mixing the different types of biomass together; d)
densification of the biomass to produce a solid with a
characteristic length in the range of from about 1 cm to about 5
cm; e) densifying the biomass such that the particles contains a
voidage fraction less than about 25%; and, f) feeding the pellet
into a suitable gasification designed for the size, shape, void
fraction and moisture content of a fuel described in a) through e)
above.
2) The method of claim 1, wherein a binding agent is added prior to
densification to aid in particle coagulation.
3) The method of claim 1, wherein a cubic structure is formed with
a characteristic length in the range of about 0.5 cm to about 8
cm.
4) The method of claim 1, wherein a cubic structure is formed with
a characteristic length in the range of about 1 cm to about 3
cm.
5) The method of claim 1, wherein a cylinder-like structure is
formed having a characteristic diameter of from about 0.1 cm to
about 3 cm and having a characteristic length of from about 0.5 cm
to about 3 cm.
6) The method of claim 1, wherein a cylinder-like structure is
formed with a characteristic diameter of from about 0.2 cm to about
1 cm and having characteristic length of from about 0.6 cm to about
1.2 cm.
7) The method of claim 1, wherein the biomass is steam treated to
improve the compaction qualities of the cellulostic matter.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims benefit of co-pending U.S.
Provisional Patent Application No. 60/785,933, filed Mar. 24, 2006,
entitled METHOD TO PRODUCE A HOMOGENEOUS BIOMASS FUEL FOR
GASIFICATION APPLICATIONS, and commonly assigned to the assignee of
the present application, the disclosure of which is incorporated by
reference in its entirety herein.
FIELD OF THE INVENTION
[0002] The present invention relates to the production of a
homogenous gasifier fuel feedstock with uniform gasification
characteristics from a number of biomass sources which each source
exhibits differences in their drying, pyrolysis, devolatization or
gasification characteristics.
BACKGROUND OF THE INVENTION
[0003] Gasification processes convert carbon-containing solids or
liquids into combustible gases that ideally contain all the energy
originally present in the feed. In reality this is not easily
achieved, although with good thermal management it is possible to
operate with energy efficiencies in excess of 90%. Extensive
research has been conducted into the area of biomass gasification.
The technique yields a combustible gas from a biomass solid.
Gaseous fuels have many advantages over solid fuels as they can be
utilized with controllable heat realization rates and devices can
be started up or shut down very rapidly. Biomass is a very broad
definition and includes all solids derived from plant matter as
well as organic municipal waste. Suitable biomasses include, but
are not limited to, sawdust, wood, straw, alfalfa seed straw,
barley straw, bean straw, corn cobs, corn stalks, cotton gin trash,
rice hulls, paper, municipal solid waste, barks and animal wastes
and combinations of the foregoing. It is interesting that almost
all biomass has the same approximate ratio of carbon to hydrogen to
oxygen, which is summarized as CH.sub.1.4O.sub.0.6. The
stoichiometric gasification equation is shown below:
CH.sub.1.4O.sub.0.6+0.2O.sub.2.fwdarw.CO+0.7H.sub.2 (1)
[0004] An energy balance across Equation 1 reveals that the
products contain more energy than the reactants, hence some of the
biomass is burnt to offset this imbalance. Although the chemical
composition of all biomass is similar their gasification behaviors
are not. Biomasses from different sources can have vastly different
drying and devolatization characteristics leading to vastly
different charcoal-like structures. These different gasification
behaviors, coupled with different physical structures, have caused
difficulties for gasifier designers in that design modifications
are required for almost every type of biomass utilized. This can be
illustrated by considering the classic Imbert design. The Imbert
design is a vertical gasifier consisting of a straight biomass
holding section followed by a tapered section which terminates at
the throat. Nozzles are situated just above or at the tapered
section to allow for the introduction of oxidants. The angle and
final throat diameter dictates the final throughput capability of
the unit. Due to vastly different biomass behaviors the design
allows that the tapered throat be interchangeable with throats of
different tapers and final diameters. When the unit is being
commissioned various throats are tested until favorable gasifier
performance is attained.
[0005] The use of biomass as a feedstock for gasification systems
is becoming increasingly economically as well as environmentally
attractive. The syngas produced by gasification should ideally be
used locally, utilizing the fuel to produce power, using the fuel
to offset natural gas in heating applications or to convert the
syngas into a liquid fuel are all viable options. The conversion of
the syngas to a liquid fuel can be readily accomplished by the
catalytic reduction of carbon monoxide by hydrogen to produce
methanol, ethanol or synthetic middle distillates. In this case the
fuel can be readily transported to be the market place.
[0006] A typical biomass has an energy density of approximately 18
kJ/g on a dry basis. On a wet basis this value can be substantially
less and can even be less than zero, indicating that the fuel is
not capable of burning in a sustainable manner while liberating
energy. On a dry basis biomass has a calorific value about half
that of coal. The low energy density, its low packing density and
difficulty in handling make the economics of transporting biomass
large distances unfeasible. Thus, the utilization of biomass for
small to medium scale distributed energy producing processes has
some synergy. The biomass for such a process would be sourced
locally and probably within a twenty mile or so radius. Power may
be generated and used to reverse feed already saturated power
delivery lines. In such a system local communities would utilize
locally grown biomass and potentially make use of some volume of
waste currently being land filled to generate their own power or
convert the material into fuels. In effect, a community could
become power and fuel self-sufficient while producing essentially
no or nominal greenhouse gas emissions.
[0007] The technique of gasifier fuel densification also promotes
the transportation characteristics and handling of biomass. During
densification the inter- and intra-particle void spaces are vastly
reduced in volume. The resulting solid is much smaller and
therefore requires less volume for transportation. The technique
allows for particles of approximately the same characteristic
dimension to be created.
SUMMARY OF THE INVENTION
[0008] The invention comprises, in one embodiment thereof, a method
for producing a gasifier fuel with uniform gasification
characteristics from a number of biomass sources which each exhibit
differences in their drying, pyrolysis, devolatization and char
oxidation characteristics. The combination of these differences
leads to large variations in their gasification behavior. Moreover,
the invention relates to a method of producing a homogeneous fuel
by grinding and mixing each biomass constituent, drying and then
forming a solid pellet through the application of pressure and/or a
binding agent.
[0009] The preparation method allows biomass from a wide range and
sources and with a wide range of gasification characteristics to be
utilized within a gasifier without modification of the gasifier
unit, while maintaining the gasifier throughput rate and thermal
profile. The method produces a fuel pellet with controllable size,
density and moisture content. The method smoothes any changes in
calorific value which may exist between different feedstocks. It
has been found that the gasification characteristics of a pellet
formed in this way is strongly dependant upon the shape, moisture
content and density of the pellet formed and less sensitive to the
origin of the biomass feedstock. The method allows for large
variations in the ratios of biomass components. The method also
allows fuels which may otherwise be problematic, for example due to
ash content, to be blended with biomasses which do not exhibit the
same issue to produce a fuel which can then be readily used.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0010] Biomass comes in many forms, including woody biomass such as
forest products and the wastes derived from wood including saw dust
and paper and cardboard products. Non-woody forms of biomass
include animal wastes, decomposable municipal waste, food
production waste and energy crops. In both cases the biomass is an
organic matter of recent origin. The physical form and typical
associated moisture contents of the biomasses described above are
vastly different, however, on dry ash free basis the chemical
composition and calorific value of the fuels above are similar.
Traditionally, using a wide range of range of fuels in gasification
device has proved difficult, even though chemically speaking the
biomasses are similar; this is attributed to differences in the
gasification behavior of different biomass materials.
Thermogravimetric studies have found rates of biomass gasification
vary over an order of magnitude depending upon the source and type
of biomass. One possible explanation is that associated minerals in
the biomass may act to catalytically aid or retard the thermal
depolymerization which occurs during devolatization and
pyrolysis.
[0011] In gasification system the ability to operate with a number
of different fuels offers tremendous advantages such as the ability
to purchase cheap and readily available feedstocks. This ability
minimizes the biomass stock piles as seasonally available fuels
can. This ability is particularly attractive for biomass fuelled
systems where the economics do not allow for the biomass to be
transported long distances.
[0012] In the present invention a biomass preparation method is
described which allows a wide range of fuels to be combined to
produce a homogeneous fuels. The method results in a compacted
solid which is designed to impose a slight heat and mass transfer
limitation, such that the pellet reacts at the rate of heat and
mass transfer and not at the rate dictated by the biomass
composition. Thus, even as the ratios of the constituent components
are changed the gasification properties remain similar.
[0013] The biomass may be processed using a number of commercially
available pieces of equipment. In some cases it may be preferable
to initially air dry the biomass by leaving the biomass exposed to
air and sun. This method can dramatically reduce the inherent
moisture contents of a number of biomasses. Alternatively, the
coarse biomass can be crudely dried by force venting feed silos,
possibly with the application of heat. Once the feed is dried to
the desired level the biomasses are pulverized using a shredding,
hammering chipping or other device or technique known to those
skilled in the art. It is possible to combine the different types
of biomass at any point through out the process, although extremely
satisfactory results may be achieved through the blending after the
pulverizing stage. The biomass is reduced in size such that the
characteristic particle length is substantially smaller than that
of the final fuel pellet. After size reduction the biomass may be
further dried. Rotary driers may be utilized with satisfactory
results. Densification can be performed a number of ways with
extrusion pelletizers or briquetting machines being cost effect
techniques. The final fuel pellet may be transferred to a storage
silo prior to gasification.
[0014] The economics of the process may be improved through the use
of waste heat produced during the gasification process or by the
utilization of the gas produced from the gasification process. An
example would be to utilize waste heat to dry and/or preheat the
biomass to the predetermined levels.
[0015] Although only a few exemplary embodiments of this invention
have been described in detail above, those skilled in the art will
readily appreciate that many modifications are possible in the
exemplary embodiments without materially departing from the novel
teachings and advantages of this invention. Accordingly, all such
modifications are intended to be included within the scope of this
invention as defined in the following claims. It should further be
noted that any patents, applications and publications referred to
herein are incorporated by reference in their entirety.
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