U.S. patent application number 12/994907 was filed with the patent office on 2011-04-07 for two-stage high-temperature preheated steam gasifier.
This patent application is currently assigned to Boson Energy SA. Invention is credited to Wlodzimierz Blasiak, Weihong Yang.
Application Number | 20110078951 12/994907 |
Document ID | / |
Family ID | 41377827 |
Filed Date | 2011-04-07 |
United States Patent
Application |
20110078951 |
Kind Code |
A1 |
Blasiak; Wlodzimierz ; et
al. |
April 7, 2011 |
TWO-STAGE HIGH-TEMPERATURE PREHEATED STEAM GASIFIER
Abstract
A gasifier combines two reactors using externally generated
preheated high temperature steam injection into the first reactor,
where the heating demand for gasification is supplied by the
sensible energy from the steam. The gasifier can produce a medium
and higher LCV syngas. The first reactor is a fixed bed
gasification section where the coarse feedstock is gasified, and
the second reactor is an entrained-bed gasification section where
the liquid and fine feedstock is gasified. Solid coarse feedstock
is devolatilized in the first fixed bed reactor of the gasifier
with high-temperature steam, and subsequently, in the second
reactor subjected to a higher temperature sufficient to crack and
destroy tars and oils. Activated carbon may be formed as
co-product. The gasifier may be used with various solid and liquid
feedstocks. The gasifier is capable of gasifying such different
feedstocks simultaneously.
Inventors: |
Blasiak; Wlodzimierz;
(Saltsjo-Duvnas, SE) ; Yang; Weihong; (Taby,
SE) |
Assignee: |
Boson Energy SA
Luxembourg
LU
|
Family ID: |
41377827 |
Appl. No.: |
12/994907 |
Filed: |
May 29, 2009 |
PCT Filed: |
May 29, 2009 |
PCT NO: |
PCT/SE2009/050630 |
371 Date: |
November 29, 2010 |
Current U.S.
Class: |
48/63 ; 201/16;
202/99; 48/197R; 48/62R |
Current CPC
Class: |
Y02P 20/145 20151101;
C10J 3/16 20130101; C10J 3/14 20130101; C10J 2200/152 20130101;
C10J 2300/0903 20130101; Y02E 50/14 20130101; C10J 2300/092
20130101; Y02E 50/10 20130101; C10J 3/485 20130101; C10B 49/06
20130101; C10J 2300/094 20130101; C10J 2200/09 20130101; C10J
2300/0916 20130101; C10J 2300/0946 20130101; Y02P 20/129 20151101;
C10J 2300/1637 20130101; C10J 2300/0973 20130101; C10J 3/721
20130101; C10J 3/36 20130101; C10J 2300/0956 20130101; C10B 53/02
20130101 |
Class at
Publication: |
48/63 ; 48/197.R;
48/62.R; 202/99; 201/16 |
International
Class: |
C10J 3/20 20060101
C10J003/20; C10J 3/02 20060101 C10J003/02; C10B 49/02 20060101
C10B049/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 2008 |
SE |
0801266-8 |
Claims
1-9. (canceled)
10. A two-staged gasifier (21) for producing synthesis gas and,
optionally, activated carbon, from a coarse carbonaceous feedstock,
which gasifier comprises: a first reactor (3) provided with an
inlet (2) for a coarse carbonaceous feedstock (1), a first inlet
(7) for steam; and a second reactor (4) provided with a second
inlet (9) for steam, optionally together with air or oxygen; and an
outlet (12) for synthesis gas; wherein the first and second
reactors are separated by a narrowed portion (20) having a reduced
cross-section for restricting passage from the first reactor to the
second reactor of solid carbonaceous unreacted substance, wherein
the first reactor is capable of being operated at a temperature of
at least 600.degree. C., and the second reactor is capable of being
operated at a higher temperature, characterized in that the second
reactor (4) is the lower reactor, and the first reactor (3) is the
upper reactor and is a fixed bed reactor, a grate (8) is provided
at the bottom end of the first reactor, inlet (7) is located
adjacent to the bottom of the first rector, so as to enable
preheated steam having a temperature of at least 700.degree. C. to
be fed into the first reactor from below grate (8) via inlet (7),
said second reactor is provided with an inlet (19) for a fine solid
carbonaceous feedstock and/or a liquid carbonaceous feedstock,
inlet (9) is located adjacent to the bottom of the second rector so
as to enable preheated steam having a temperature of at least
700.degree. C., optionally together with preheated air or oxygen of
same temperature, to be fed to the second reactor from below via
inlet (9), and in that a second narrowed portion (18) having a
reduced cross-section is provided at the bottom end of the second
reactor (4).
11. The two-stage gasifier of claim 10, wherein one or more, and
preferably all of the inlets (7, 9, 19) enter into the gasifier
tangentially in corresponding portions (20, 18, 16) of the gasifier
having inner, circular cross-sections.
12. The two-stage gasifier of claim 10, wherein the inlet (19)
comprises at least two inlets (19a, 19b) separated at a maximum
distance from each other along the circumference of the circular
cross-section.
13. A process of gasifying a coarse carbonaceous feedstock using a
two-stage gasifier, such as the gasifier (21) specified in claim
10, having two reactors (3,4), a first (3) and a second (4),
respectively, separated by a narrowed portion (20), in order to
produce synthesis gas, optionally together with activated carbon,
comprising the steps of: (a) feeding a coarse carbonaceous
feedstock to the first stage reactor (3) of the gasifier; (b)
subjecting the coarse carbonaceous feedstock to steam in the first
stage reactor at an operational temperature of at least 600.degree.
C. of the reactor, to effect gasification of the carbonaceous
feedstock, characterized in the second reactor (4) is the lower
reactor, ant the first reactor (3) is the upper reactor and is a
fixed bed reactor, that no oxygen is fed to the first stage reactor
(3), but only preheated steam having a temperature of at least
700.degree. C., and in a further step (c), wherein any solid and/or
liquid carbonaceous materials obtained from step (b) are subjected
to preheated steam, optionally together with air or oxygen, in the
second stage reactor operating at a temperature of at least
700.degree. C. to obtain any combination of the following products:
activated carbon; CO; CO.sub.2, and heat of combustion.
14. The process of claim 13, comprising a further step (d) of
simultaneous feeding of a fine solid carbonaceous, or liquid
carbonaceous feedstock, into the second stage reactor of the
gasifier.
15. The process of claim 13, wherein in step (c) the steam entering
the second stage reactor is preheated to a temperature of
700-1600.degree. C., and preferably 800-1200.degree. C.
16. The process of claims 13, wherein oxygen is used instead of
air.
17. The process of claim 13, wherein no air or oxygen is supplied
to the gasifier.
18. The process of claim 14, wherein in step (c) the steam entering
the second stage reactor is preheated to a temperature of
700-1600.degree. C., and preferably 800-1200.degree. C.
19. The process of claims 14, wherein oxygen is used instead of
air.
20. The process of claim 14, wherein no air or oxygen is supplied
to the gasifier.
21. The two-stage gasifier of claim 11, wherein the inlet (19)
comprises at least two inlets (19a, 19b) separated at a maximum
distance from each other along the circumference of the circular
cross-section.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to a two-stage
high-temperature steam gasifier for producing synthesis gas and,
optionally, activated carbon, from a coarse carbonaceous feedstock,
and more particularly to a gasifier capable of simultaneously
gasifying a coarse solid carbonaceous feedstock and a fine solid
carbonaceous feedstock or a liquid carbonaceous feedstock. The
present invention also relates to a process of gasifying a coarse
carbonaceous feedstock using a two-stage gasifier having two
reactors in order to produce synthesis gas, optionally together
with activated carbon, wherein no oxygen is fed to the first stage
reactor, but only preheated steam having a temperature of at least
700.degree. C.
BACKGROUND OF THE INVENTION
[0002] Gasification is a high-temperature thermal decomposition
process of converting a solid feedstock, such as solid coal,
petroleum coke, biomass, and/or solid waste, a liquid feedstock,
such as black liquid oil, or a gaseous feedstock, into a fuel gas,
consisting primarily of hydrogen (H.sub.2) and carbon monoxide
(CO), with lesser amounts of carbon dioxide (CO.sub.2), water
(H.sub.2O), methane (CH.sub.4), higher hydrocarbons, and nitrogen
(N.sub.2) using reactants such as air, steam, and oxygen, either
alone or in any combination thereof.
[0003] The thermal gasification processes are highly endothermic
chemical reactions. The general methods for supplying heat for the
gasification use either of the following: a) an external source,
e.g. sensible heat from hot char recirculation, and/or sensible
heat from a heated gasification agent, b) reaction heat from
oxidization of a part of the feedstock (incoming carbonaceous
materials), and c) exothermal reaction heat from a non-carbonaceous
material such as calcined lime and CO.sub.2.
[0004] The application of the technology of partial combustion of
incoming carbonaceous materials has been widely adopted. By means
of the technology, the non-combustible gas, CO.sub.2, is produced,
and, as it is not removed, it leads to a diluted syngas, and the
LCV (low caloric value, a measure for the burning value of the dry
gas mass) of the produced syngas becomes limited. Moreover, the
presence of CO.sub.2 resulting from partial combustion (oxidation)
leads to a small partial pressure of other gas species, which is
not favorable for other valuable gasification reactions, such as
for example, the water-gas shift reaction. Thus, the hydrogen
content in the syngas will be negatively affected.
[0005] The idea of supplementing most of the energy required for
the gasification process using sensible heat has recently been
considered, and positive results have been shown. For example, US
2004/0060236 A1 teaches an economic small scale gasification system
for gasifying solid fuel into pyrolysis gas, wherein heated mixed
gas of steam and air is introduced into a reformer along with the
pyrolysis gas producing reformed high temperature crude gas. The
mixed gas of air and steam is preferably heated to at least
300.degree. C., and more preferably at least 400.degree. C. Any
type of heat exchanger or heater may be employed as the air/steam
heating device for heating the mixed gas of air and steam.
[0006] U.S. Pat. No. 6,837,910 teaches an apparatus and method for
gasifying liquid or solid fuel, wherein a heated mixed gas of steam
and air is introduced into at least one of the thermal
decomposition area of the solid or liquid fuel and the reforming
area of the thermal decomposed gas. The mixed gas of air and steam
is heated to a temperature of at least 700.degree. C., and more
preferably higher than 800.degree. C.
[0007] Other known systems using high-temperature air/steam/oxygen
as high as 1000.degree. C. for a biomass/waste gasification process
have also been applied (Lucas C., Szewczyk D., Blasiak W., Mochida
S., High Temperature Air and Steam Gasification of Densified
Biofuels, Biomass and Bioenergy, Vol. 27, No. 6, December 2004,
pages 563-575). A char free hydrogen rich gas, where the process is
performed with only steam at a temperature of 1000.degree. C. and
at a conventional pressure of about 1 atm has been proposed by
Ponzio Anna, Yang Weihong, Lucas, C, Blasiak W., in Development of
a Thermal Homogenous Gasifier System using High Temperature Agent,
CLEAN AIR--International Journal on Energy for a Clean
Environment., Vol. 7, No. 4., 2007.
[0008] In US 2003/0233788 A1, a method for gasifying carbonaceous
materials into fuel gases is disclosed. It involves the formation
of an ultra-superheated steam (USS) composition substantially
containing water vapor, carbon dioxide and highly reactive free
radicals thereof, at a temperature of about 1316.degree. C. to
about 2760.degree. C. The USS composition comprising a high
temperature flame is contacted with a carbonaceous material for
rapid gasification/reforming thereof. The USS is formed by burning
s substantially ash-free fuel with "artificial air" comprising an
enhanced oxygen gas and water vapour, wherein the "artificial air"
is at least about 60 mole percent. The oxygen:fuel ratio will have
to be controlled so that soot is not is not formed. The use of
enhanced oxygen gas in the method will obviously increase the
operation cost of the method.
[0009] According to US 2003/0233788 A1, steam-only gasification has
been investigated and used commercially since about 1950-1960.
However, because of the limited heat in the steam, the problems
associated with steam-only gasification include low achievable
reaction temperatures, i.e. typically less than about 815.degree.
C., where long residence times and high energy consumption
prevail.
[0010] All the above prior art only use one-stage reactor, either a
fixed bed, or a fluidized bed gasifier.
[0011] It is known that the thermal conversion of
biomass/waste/coal can be understood as comprising two mainly
highly endothermic stages: devolatilization of volatiles, and char
conversion, respectively. As indicated by previous studies, 90% of
the volatile content in the total weight of biomass will be
released instantaneously if it would be heated above 600.degree. C.
The second stage is char conversion. In order to get char-free ash,
i.e. 100% char conversion, a much higher temperature is needed for
the thermal conversion of char. Generally, this temperature should
be higher than 1000.degree. C., depending on the ash melting
point.
[0012] Fixed-bed gasifier types are widely used in small-scale
energy production (<10 MW.sub.th) due to its very simple
construction and operation. It has been found that if the design of
a gasification fixed-bed reactor follows the above two stages, it
would be more efficient from many point of views.
[0013] There are extensive works on this way of operation for the
fixed bed gasifier. Secondary air injection to the gasifier is
often used. For example, Pan et al. (Y. G. Pan, X. Roca, E. Velo
and L. Puigjaner, in Removal of tar by secondary air injection in
fluidized bed gasification of residual biomass and coal, Fuel 78
(1999) (14), pp. 1703-1709) reported 88.7 wt. % of tar reduction by
injecting secondary air just above the biomass feeding point in the
fluidized bed at a temperature of 840-880.degree. C.
[0014] Nary et al. (Biomass gasification with air in an atmospheric
bubbling fluidized bed. Effect of six operational variables on the
quality of produced raw gas, Industrial and Engineering Chemistry
Research 35 (1996) (7), pp. 2110-2120) performed secondary air
injection in the freeboard of a fluidized bed gasifier and observed
a temperature rise of about 70.degree. C. which resulted in a tar
reduction from 28 to 16 g/Nm.sup.3.
[0015] The Asian Institute of Technology (AIT), Thailand, modified
a biomass gasifier which resulted in a fuel gas with a tar
production of about 50 mg/Nm.sup.3, which is about 40 times less
than a single-stage reactor under similar operating conditions (T.
A. Milne and R. J. Evans, Biomass Gasification "Tars": Their
Nature, Formation and Conversion. NREL, Golden, Colo., USA, Report
No. NREL/TP-570-25357 (1998). This concept involves a downdraft
gasifier with two levels of air intakes. The produced tar in the
biomass pyrolysis process will pass through a high-temperature
residue char bed at the bottom and will be decomposed at the
elevated temperature.
[0016] Bhattacharya et al. in A study on wood gasification for
low-tar gas production, Energy 24 (1999), pp. 285-296, reported a
similar gasifier with char produced inside the gasifier itself to
act as a filter to further reduce tar production considerably at 19
mg/Nm.sup.3 higher CO and H.sub.2 concentration in fuel gas.
[0017] Cao et al. in A novel biomass air gasification process for
producing tar-free higher heating value fuel gas, Fuel Processing
Technology 87 (2006) 343-353, reported a work of two-region
fluidized bed reactor. In this work, an assisting fuel gas and
second air stream were injected into the upper region of the
reactor in order to reduce the tar compositions. Experimental
results showed a heating value of about 5 MJ/Nm.sup.3.
[0018] U.S. Pat. No. 6,960,234 discloses a multi-faceted gasifier
and related methods. It is a gasifier combing a fixed bed
gasification section and an entrained flow gasification section.
Activated carbon may be formed in the upper fixed bed section and
in the entrained flow section.
[0019] U.S. Pat. No. 6,647,903 discloses a method and apparatus for
generating and utilizing combustible gas using a gasifier
comprising first and second reaction sections, wherein oxidizing
gas is introduced into both sections. The invention operates in a
manner that enhances tar destruction while forming output fuel gas
products H.sub.2 and CO. In addition some methane may also be
formed. In a certain mode of operation, activated carbon may be
generated.
[0020] JP 6256775 discloses two-stage complete gasification of
organic matter for methane synthesis, wherein in a first stage
gasification process organic matter is gasified in the presence of
steam and oxygen, and, in a second stage gasification process
gaseous un-reacted matter and tar gas are gasified at a higher
temperature than in the first stage gasification process. A
gasifier comprising two stages is also disclosed. In order to
disturb solid carbonaceous material from passing from the first
stage gasification process to the second stage gasification
process, the passage between the two stages may be narrowed, or a
filter may be set between the two stages. The gasifier includes two
inlets for oxygen and steam, one in the first stage, and the other
in the second stage.
[0021] The aim of secondary air/oxygen and/fuel injection in above
works is increasing the temperature in freeboard in order to
decompose tar, and improve the steam-reform reaction. However, the
injection of secondary air will not only increases the diluents
contents, notably nitrogen, but will also reduce the combustible
contents generated from gasification. This results in a decrease of
LCV of the fuel gas produced. Furthermore, injection of secondary
air makes it hard to control the composition of the produce
gas.
[0022] U.S. Pat. No. 6,960,234, mentioned above, also states that
fixed-bed gasification requires coarse fuels (typically 1/4'' to
2'' in diameter, and that limiting technical features of fixed-bed
gasification include: tar and oil carry over with the syn gas;
difficulty in using coal/fuel fines because they clog the void
space between the coarse fuels in the fixed bed; and difficulty in
using liquid hydrocarbon feedstocks.
[0023] In order to be able to produce medium and high low calorific
value (LCV) combustible gases, and gasify both solid and
liquid/fine feedstock simultaneously, and also produce other
added--value materials, such as activated carbon, a novel fixed bed
gasifier is proposed herein. Such gasifier is specified in claim 1.
Also, a method of gasifying a coarse carbonaceous feedstock, using
a two-staged gasifier having two reactors, in order to produce
synthesis gas, optionally together with activated carbon, wherein
no oxygen is fed to the first stage reactor, but only preheated
steam having a temperature of at least 700.degree. C. is also
claimed and disclosed. Such method is provided for in claim 4.
SUMMARY OF THE INVENTION
[0024] Thus, for a two-stage gasifier of the prior art, such as
disclosed by JP 6256775 and specified by the preamble of claim 1
comprising: a first reactor provided with an inlet for a coarse
carbonaceous feedstock, and a first inlet for steam; and a second
reactor provided with a second inlet for steam, optionally together
with air or oxygen; and an outlet for synthesis gas; wherein the
first and second reactors are separated by a narrowed portion
having a reduced cross-section for restricting passage from the
first reactor to the second reactor of unreacted solid carbonaceous
substance, wherein the first reactor is capable of being operated
at a temperature of at least 600.degree. C., and wherein the second
reactor is capable of being operated at a higher temperature, the
above object has been achieved by means of the technical features
of the characterizing portion of said claim, according to which the
second reactor is the lower reactor, the first reactor is the upper
reactor, a grate is provided at the bottom end of the first
reactor, said first inlet for steam is located adjacent to the
bottom of the first rector, so as to enable preheated steam having
a temperature of at least 700.degree. C. to be fed into the first
reactor from below the grate via said inlet, said first reactor is
provided with an outlet for synthesis gas, the second reactor is
provided with an inlet for a fine solid carbonaceous feedstock
and/or a liquid carbonaceous feedstock, said second inlet for steam
is located adjacent to the bottom of the second rector, so as to
enable preheated steam having a temperature of at least 700.degree.
C., optionally together with preheated air or oxygen of same
temperature, to be fed to the second reactor from below via said
inlet, and a second narrowed portion having a reduced cross-section
is provided at the bottom end of the second reactor.
[0025] Accordingly, in one aspect the present invention relates to
a two-stage gasifier as set out above.
[0026] In the gasifier of the invention simultaneous gasification
of solid coarse material, on the one hand, and solid fine and/or
liquid material, on the other, is enabled. Carbonaceous coarse
material is fed to the first reactor and carbonaceous (waste)
liquid and/or carbonaceous fine solid material is fed to the second
reactor.
[0027] In a further preferred embodiment of the two-stage gasifier
one or more, and preferably all of the inlets for steam, air,
oxygen and carbonaceous (waste) liquid and/or carbonaceous fine
solid material enter into the gasifier tangentially in
corresponding portions of the gasifier, which portions have an
inner, circular cross-sections.
[0028] In a further preferred embodiment of the two-stage gasifier
the inlet for carbonaceous (waste) liquid and/or carbonaceous fine
solid material comprises at least two inlets separated at a maximum
distance from each other along the circumference of the circular
cross-section.
[0029] In another aspect the present invention relates to a process
of gasifying a coarse carbonaceous feedstock, using a two-stage
gasifier having two reactors, a first and a second, respectively,
in order to produce synthesis gas, optionally together with
activated carbon. Such process is provided for in claim 4, and
includes the following steps: (a) feeding a coarse carbonaceous
feedstock to the first stage reactor of the gasifier; (b)
subjecting the coarse carbonaceous feedstock to steam in the first
stage reactor at an operational temperature of at least 600.degree.
C. of the reactor, to effect gasification of the carbonaceous
feedstock, in which process no oxygen is fed to the first stage
reactor, but only preheated steam having a temperature of at least
700.degree. C., and which process further includes a step (c),
wherein any solid and/or liquid carbonaceous materials obtained
from step (b) are subjected to preheated steam, optionally together
with air or oxygen, in the second stage reactor operating at a
temperature of at least 700.degree. C. to obtain any combination of
the following products: activated carbon; CO; CO.sub.2, and heat of
combustion.
[0030] In a preferred embodiment, the process comprises a further
step (d) wherein a fine solid carbonaceous, and/or liquid
carbonaceous feedstock, is/are being fed simultaneously into the
second stage reactor of the gasifier. Accordingly, in this
embodiment both a coarse feedstock and a fine solid and/or liquid
carbonaceous feedstock may be fed simultaneously into the
gasifier.
[0031] In another a preferred embodiment of the process externally
generated preheated steam having a temperature of at least
700.degree. C. is also fed into the second stage reactor. With this
embodiment internal combustion, also referred to as partial
combustion or oxidation, in the gasifier can be kept to a minimum,
since the required energy is provided externally. Consequently,
supply of air or oxygen is not required for heat generation by
internal combustion in this embodiment. Also, when air or oxygen is
not being fed to the second reactor the yield of activated carbon
can be maximised.
[0032] In a further preferred embodiment of the process, air is fed
to the second reactor (i.e. in addition to the high temperature
steam). With this embodiment especially high quality synthesis gas
can be obtained, since carbon is converted also to CO, and not only
to activated carbon. Also, depending on the ratio of steam/air,
internal combustion can still be avoided (i.e. production of
CO.sub.2). At the same time the ratio of CO:activated carbon also
can be controlled by controlling the ratio of steam/air.
[0033] In a further preferred embodiment of the process pure oxygen
is used (instead of air). In this embodiment the process can be
used for industrial purposes. Also, the need for separation of
by-products is minimized, and undesired dilution of the gaseous
product is kept to a minimum.
[0034] Further embodiments and advantages will become apparent from
the detailed description and claims.
[0035] The terms "internal combustion", "partial combustion" and
"partial oxidation" have been used interchangeably to denote
combustion occurring inside the gasifier.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 shows a system flow diagram generally illustrating
the inventive gasification process for biomass and solid waste.
[0037] FIG. 2 illustrates a cross-sectional view of an embodiment
of the gasifier 21.
[0038] FIG. 3 is a plan view of the inventive gasifier showing the
tangential liquid feedstock injection via inlets 19a and 19b.
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
THEREOF
[0039] The inventive gasifier combines two reactors using
externally generated preheated high temperature steam injection
into the first reactor, where the heating demand for gasification
is supplied by the sensible energy from the steam. The gasifier can
produce a medium and higher LCV syngas. The first reactor is a
fixed bed gasification section where the coarse feedstock is
gasified, and the second reactor is an entrained-bed gasification
section where the liquid and fine feedstock is gasified. Solid
coarse feedstock is devolatilized in the first fixed bed reactor of
the gasifier by means of high-temperature steam, and subsequently,
in the second reactor subjected to a higher temperature sufficient
to crack and destroy tars and oils.
[0040] Activated carbon may be formed as co-product. The gasifier
may be used with various solid and liquid feedstocks. The gasifier
is capable of gasifying such different feedstocks
simultaneously.
[0041] The idea behind the present invention is that the gasifier
21 is separated into two stages: a first upper stage 3 for
devolatilization of volatiles, which first stage only uses
externally generated high-temperature preheated pure steam
(preferably 700.degree. C.-1000.degree. C.), and a second lower
stage 4 for char thermal conversion, using a high-temperature
(preferably 700-1600.degree. C., more preferably 800-1200.degree.
C.) preheated mixture of air and steam, oxygen and steam, or steam
only as shown in FIG. 1. The reactor 3 includes a fixed bed
comprising grate 8.
[0042] In the first reactor 3, the energy used for the
devolatilization process is supplied both by the sensible energy of
steam fed into the first reactor via inlet 7, and by the hot stream
coming from the second reactor through the narrowed portion 20. The
temperature in the first reactor is controlled at the level of at
least 600.degree. C. by the quantity and the temperature of the
steam fed into said reactor.
[0043] In the first reactor 3, high-temperature steam is mixed with
coarse feedstock (biomass) 1 entering via inlet 2. When the biomass
is heated by the high-temperature steam, the devolatilization
process occurs as:
##STR00001##
[0044] Simultaneously, due to the presence of steam, steam reacts
with the volatiles:
C.sub.mH.sub.n+H.sub.2OCO+H.sub.2 (2)
CO+H.sub.2O.fwdarw.CO.sub.2+H.sub.2 (.sup.3)
[0045] A little oxygen released from the pyrolysis (which occurs in
the first reactor, and also in the second reactor when a liquid
and/or solid fine feedstock is being injected) and from the second
reactor 4 reacts according to the following:
C.sub.mH.sub.n+(m/2+n/4)O.sub.2.fwdarw.mCO+n/2H.sub.2O (4)
CO+1/2O.sub.2.fwdarw.CO.sub.2 (5)
H.sub.2+1/2O.sub.2.fwdarw.H.sub.2O (6)
CO+H.sub.2O.fwdarw.CO.sub.2+H.sub.2 (7)
[0046] Since the reactor temperature in the first stage reactor 3
is controlled at the level of at least 600.degree. C., and the
residence time is controlled, and the gases in the first reactor
are located in an environment which is very much in lack of oxygen,
any solid and/or liquid char produced in the first reactor will not
be reacted with any oxidizers in said reactor. Consequently, any
solid and/or liquid char will instead fall into the second reactor
4 by the action of the gravity.
[0047] In the second reactor 4, the energy used for char the
conversion process is preferably supplied by the sensible energy of
mixture of steam and air, and from partial oxidization of char. In
order to achieve char-free conversion, the temperature in the
second reactor should be higher than that of the ash melting point,
in order for the ash to form slag. Normally, for wood biomass the
ash melting point can be 1300.degree. C. The reactor 4 includes an
entrained bed comprising grate 5.
[0048] The main reactions when there is no other feedstock (liquid
and fine particle) injection are:
TABLE-US-00001 Gasification: C + O.sub.2 => CO.sub.2 - 393.5
kJ/mol (8) C + H.sub.2O => CO + H.sub.2 + 131.3 kJ/mol (9) C +
2H.sub.2O => CO.sub.2 + H.sub.2 + 90.2 kJ/mol (10) Partial
Oxidation: C + 0.5O.sub.2 => CO - 110.5 kJ/mol (11) Boudouard
reaction: C + CO.sub.2 => 2CO - 172.4 kJ/mol (12) Water Gas
Shift: CO + H.sub.2O => CO.sub.2 + H.sub.2 - 41.1 kJ/mol (13)
Methanation: CO + 3H.sub.2 => CH.sub.4 + H.sub.2O - 206.1 kJ/mol
(14) Hydrogenation: C + 2H.sub.2 => CH.sub.4 - 75 kJ/mol
(15)
[0049] When a second feedstock (liquid and fine particles) is
injected into the second reactor, all the reactions from (1) to
(15) will occur.
[0050] Many reactions occur simultaneously and it is difficult to
control the process precisely as indicated here. Nevertheless, by
careful selection of the process parameters (temperature, residence
time and oxygen/steam ratios) in this invention, it is possible to
maximize certain desired products, such as activated carbon and
syngas.
[0051] Further on, the activated carbon can be treated as a
co-production from thermal conversion of carbon-based materials
through this invention. Generally, in the prior art the preparation
of activated carbon involves two steps: carbonization of the raw
material in absence of oxygen at high temperature (500-1000.degree.
C.) in order to eliminate maximum amounts of oxygen and hydrogen
elements, and activation of the carbonized product at a higher
temperature in the presence of oxidizing gas such as water, carbon
dioxide or both. The activation shall be carried out under well
controlled conditions in order to achieve a desired conversion.
[0052] In this invention, the feedstock is first gasified by
high-temperature pure steam (at the level of at least 600.degree.
C.) in the first reactor 3, then the carbon is preferably activated
in the second reactor 4 by high-temperature steam.
[0053] In this invention, as generally illustrated by FIG. 1, high
temperature steam, and optionally air or oxygen (over 700.degree.
C.), will be obtained mainly by use of a honeycomb regenerative
heat exchanger as explained in, for example, EP 0 607 921, or in
co-pending PCT/SE2009/050019, the relevant contents of which
disclosures are incorporated herein by reference.
[0054] FIG. 2 illustrates a cross-sectional view of the gasifier
21. Carbonaceous feedstock 1 enters at the top of the gasifier,
through a feed inlet 2, and proceeds downward moving through the
first reactor 3, then pass the grate 8, then enters second reactor
4, then pass the grate 5 until it becomes a molten ash at the
bottom 6. The feedstock can include biomass, coal, municipal solid
waste, or any combination thereof. The particle size of the coarse
carbonaceous feedstock 1 is typically from 0.5 cm to 1.8 cm, and
preferably from 0.5 to 1.2 cm.
[0055] In the first rector 3, the feedstock is heated by a
combination of the sensible heat carried by the high-temperature
steam (over 700.degree. C.), and the sensible heat carried by the
flue gas produced by char oxidization and gasification in the
second reactor 4. High-temperature steam carried by pipe 7 for the
feedstock gasification in the first reactor enters a narrowed
portion or throat 20 through a port (ports) 11. The amount of
high-temperature steam added at port 7, is set to keep the
temperature at point 3 (first reactor) between 600-900.degree. C.,
and preferably above 700.degree. C. At the point around 8 (grate),
when air or oxygen is being fed into the second reactor a hot
combustion flame may occur as the surplus oxygen burns with the
pyrolysis gases released from feedstock 1, and form any liquid
and/or fine solid feedstock being fed into the second reactor.
[0056] The temperature in the reactor 3 is controlled by the
temperature and flowrate of injection of steam from point 7, and
the temperature and quantity of surplus oxygen from reactor 4. The
residence time of the feedstock 1 inside reactor 3 is mainly
controlled by the gap of the grate 8.
[0057] In order to accomplish a good mixing between the
gasification agents (steam) with the feedstock 1, a throat 20 is
provided. The diameter of the throat is generally smaller than that
of the hearth of reactor 3. The inclination of the conical portion
14 should preferably be around 45-60.degree.. The diameter of the
steam injection port 11 should preferably be 2-3 times smaller than
that of the throat 20.
[0058] After the coarse carbonaceous feedstock has been
devolatilized by high-temperature steam in the first reactor 3, the
remaining fixed carbon has become activated carbon char and ash
solids, which continue to move downward through the grate 8, then
enter a throat 20, then enter into the second reactor 4, where they
are oxidized and gasified by a mixture of high-temperature air (or
oxygen) and steam. When no air or oxygen is being fed with the
steam into reactor 4, no oxidation will occur in reactor 4, but
only gasification. The temperature of the second reactor 4 is
further increased to a temperature slightly above the ash softening
point of the fuel at the grate 5. The pipe 9 carries the preheated
high-temperature steam or mixture of high-temperature air (or
oxygen) and steam to the port 10, which then enters into the second
throat 18.
[0059] For wooden pellets produced from wood grown in Sweden, the
ash softening point typically ranges from 1350-1400.degree. C. If
slag formation of the ash is to be avoided, the maximum peak
temperature in the reactor 4 during operation is maintained at a
temperature at least 50.degree. C. below the ash softening point,
with 100.degree. C. below as the normal and thus preferred maximum
condition.
[0060] The temperature in reactor 4 is controlled by the preheating
temperature, flowrate and the ratio of steam to carbon, and, when
air or oxygen also is being used with the steam, the ratio of steam
to oxygen of the mixture.
[0061] The diameter of the second narrowed portion or throat 18 is
generally smaller than that of the diameter of reactor 4, and
preferably also smaller than that of the first narrowed portion or
throat 20. The inclination of the conical portion 17 should
preferably be around 45-60.degree.. The diameter of the steam
injection port 10 should preferably be 3-5 times smaller than that
of the throat 18.
[0062] The ash is dropped into bottom 6 through throat 18, and may
be taken out batch-wise from the reactor.
[0063] The syngas flows out through the exit pipe 12. Since the
temperature in the first reactor 3 is high enough, and also steam
is present, most of the tar is destroyed and converted to syngas.
The main chemical constituents of syngas are hydrogen, carbon
monoxide, and methane, and carbon dioxide.
[0064] The inventive design of the gasifier has the ability to
advantageously control the ratio of hydrogen to carbon monoxide in
the syngas, since the gasifier enables control within wide ranges
of steam to oxygen ratio within the gasifier.
[0065] In one embodiment of operation of the reactor, by
controlling the temperature in the second reactor 4 at 700.degree.
C., i.e. the same temperature as first reactor 3, and by only
feeding steam to the second reactor, all tars and oils are consumed
by the high-temperature steam. This converts most of the
fixed-carbon to activated carbon within the gasifier. Therefore,
the gasifier and process described herein can also effectively
generate activated carbon. This mode of operation is very effective
for generating activated carbon, and will also improve the quality
of the activated carbon obtained. If gasification is to be
maximized, on the other hand, the second reactor should be operated
at a higher temperature than the first reactor.
[0066] The invention can consequently also be used to produce
activated carbon. There are two methods in which activated carbon
is created within the gasifier. In the first one, only the first
reactor is used, i.e. only high-temperature steam is injected
through pipe 7. The high-temperature mixture of steam and air from
pipe 9 is closed. Another and more preferred method is to have both
reactors running, but from pipe 9, only high-temperature steam is
injected. In this case, the activated carbon is collected into dry
directly. The second method has surprisingly been found to be apt
to give higher quality of the activated carbon char. This is
believed to be due to that the high-temperature steam injected from
pipe 9 makes the pores of the activated carbon opening in the
second reactor 4. Activated carbon having wider pores than in the
prior art may thus be obtained by means of the method of the
invention. The size (diameter of pores) can be controlled by the
temperature of steam in the reactor 4. Generally, a higher
temperature of steam increases the pore number of the activated
carbon.
[0067] Thus, the present invention is capable of achieving a
bi-generation (gas and activated carbon) from one and the same
feedstock 1. The desired ratio of the products can be decided upon
according to the type of feedstock available, price of the
products, and so on.
[0068] Further on, this invention can be used to treat both coarse
particles (diameter larger than 0.5 cm) of carbonaceous materials
and fine particles and or liquid feedstock.
[0069] FIG. 3 shows a cross-sectional view of the gasifier 21,
which shows the tangential liquid/fine particles feedstock
injection. Two injection lances 19 (19a and 19b) are shown
connecting to the reactor 4. Liquid feedstock, such as the liquid
residues collected after a micro-oven pyrolysis process of the
Automotive Shredder Residue (ASR), and fine or pulverized feedstock
can be injected into the reactor 4. The injected feedstock enters
into the reactor 4 tangentially and mixes with the high-temperature
air/steam coming from the grate 5. The tangential injection can
increase the residence time of the liquid and/or fine feedstock.
The entrained flow gases pass through the upper fixed bed grate 8,
then enter reactor 3 before leaving the gasifier at the exit pipe
12. The injection port 19 should be located to the lower part of
the hearth of the reactor 4 in order to increase the residence
time. Generally, for a small-scale gasifier, the location of this
injection port(s) is 10 cm above the inclination wall 17.
[0070] The residue time can be controlled by the injection
velocity, and the angle of the injection lance to the gasifier.
[0071] In a preferred embodiment, the walls of the gasifier consist
of two layers: an outer steel cover, preferably 5.0 mm thick, and
an inner layer of fibrous ceramic insulation, preferably a high
temperature resistant, high quality ceramic. The ceramic used at
walls 13 and 14 can preferably operate with, i.e. withstand, a
maximum temperature of 1400.degree. C. A suitable material may be
composed of: Al.sub.2O.sub.3 45%, SiO.sub.2 36%, Fe.sub.2O.sub.3,
0.9% and CaO 16%. The ceramic used for the walls at 15, 16 and 17
is preferably apt to operate at a higher temperature of
1400-1500.degree. C. The maximum allowed working temperature of
this wall material is 1600.degree. C. A suitable material may have
the following composition: Al.sub.2O.sub.3 61%, SiO.sub.2 26%,
Fe.sub.2O.sub.3, 0.5%, CaO 2.6%, ZrO2 2.95%, and BaO 3.3%. The
ceramic materials are supported by a steel shell.
[0072] In a preferred embodiment refractive ceramic tubes are used
as the grates 8 and 5. The composition of these ceramic tubes can
for example be 97% ZrO.sub.2, and 3% of MgO.
[0073] A high temperature mixture of steam, optionally together
with air or oxygen, being fed through pipe 9 enters the throat 18
which below the grate 5. This high temperature mixture of air and
steam can keep the ash in a molten state in the throat 18, which
ash finally drops to the bottom 6, and can be taken out in
batches.
Example 1
[0074] 97 kg/h of wood pellets 1 with a diameter around 8 mm is
feed into the first reactor from the inlet 2 by weight at room
temperature (15.degree. C.). The properties of the wood pellets are
shown in Table 1.
TABLE-US-00002 TABLE 1 Proximate and ultimate analysis of the
feedstocks used Proximate analysis Wood Pellets (WP) Total Moisture
(SS187170) 8% Ash content (SS-187171) 0.5-0.6% (dry) LHV
(SS-ISO562) 17.76 MJ/kg (as received) Volatile matter (SS-ISO) 84%
(dry) Density 630-650 kg/m.sup.3 Ultimate analysis (dry
compositions) Wood Pellets Sulphur (SS-187177) S 0.01-0.02% Carbon
(Leco-600) C 50% Hydrogen (Leco-600) H 6.0-6.2% Nitrogen (Leco-600)
N <0.1% Oxygen (Calculated) O 43-44% Ash fusion temperatures
(oxidizing conditions) Wood Pellets Initial deformation, IT
1350-1400.degree. C. Softening, ST 1450-1500.degree. C.
Hemispherical, HT 1500.degree. C. Fluid temperature, FT
1500-1550.degree. C.
Example 2
[0075] A 60 kg/h of Refuse Derived Fuel (RDF), a pellet formed fuel
made from paper fiber mixed with other substances such as fabric
fiber, wood chips and plastics, was used as feedstock, with a
diameter of about 8 mm, and was feed into the first reactor 3 from
the top 1 by weight, i.e. by the action of gravity, at room
temperature (15.degree. C.). The properties of the RDF pellets are
shown in Table 2.
TABLE-US-00003 TABLE 2 Proximate and ultimate analysis of the RDF
feedstock used Proximate analysis Refused Derived Fuel (RDF) Total
Moisture (SS187170) 2.9% Ash content (SS-187171) 6.0% (dry) LHV
(SS-ISO562) 26.704 MJ/kg (as received) Volatile matter (SS-ISO)
84.4% (dry) Density 472 kg/m.sup.3 Ultimate analysis (dry
compositions) RDF Sulphur (SS-187177) S 19 0.09% Carbon (Leco-600)
C 63.3% Hydrogen (Leco-600) H 8.9% Nitrogen (Leco-600) N 0.3%
Oxygen (Calculated) O 20.95% Ash fusion temperatures (oxidizing
conditions) RDF Initial deformation, IT 1210.degree. C. Softening,
ST 1220.degree. C. Hemispherical, HT 1230.degree. C. Fluid
temperature, FT 1240.degree. C.
* * * * *