U.S. patent application number 12/899809 was filed with the patent office on 2011-12-01 for method for controlling syngas production in a system with multiple feed materials using a molten metal bath.
This patent application is currently assigned to Ze-Gen, Inc.. Invention is credited to William H. Davis, Kevin Donahue, Irving B. Morrow, JR., Igor Polovtsev.
Application Number | 20110289845 12/899809 |
Document ID | / |
Family ID | 45020921 |
Filed Date | 2011-12-01 |
United States Patent
Application |
20110289845 |
Kind Code |
A1 |
Davis; William H. ; et
al. |
December 1, 2011 |
METHOD FOR CONTROLLING SYNGAS PRODUCTION IN A SYSTEM WITH MULTIPLE
FEED MATERIALS USING A MOLTEN METAL BATH
Abstract
Processes and apparatus for treating organic and inorganic
materials in a metal bath contained in a high temperature reactor
to produce synthesis gas are provided. Two or more feed materials
that possess differing syngas generation potentials are mixed in a
mixer and fed as a composite feed stream into a gasifier to produce
syngas. The feed materials are prepared and analyzed for heat value
prior to injection and the composition of materials in and exiting
the reactor are monitored. By controlling the feed rate of the
mixture into the gasifier as well as the feed rates of one or more
of the individual feed materials into the mixer, the syngas is
produced at a target production rate, with target energy content
(BTU). Based upon the results of the analysis and monitoring,
oxygen, steam, and/or other feed materials are also injected into
the reactor, to control processing and synthesis gas quality.
Potential feed materials include, but are not limited to,
construction and demolition (C&D) debris, municipal solid waste
(MSW), other sewage-related solids, waste tires, and other
substances that contain varying levels of organic compounds capable
of producing a syngas.
Inventors: |
Davis; William H.;
(Winchester, MA) ; Morrow, JR.; Irving B.;
(Harvard, MA) ; Donahue; Kevin; (Harvard, MA)
; Polovtsev; Igor; (Forest Hill, MD) |
Assignee: |
Ze-Gen, Inc.
Boston
MA
|
Family ID: |
45020921 |
Appl. No.: |
12/899809 |
Filed: |
October 7, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11400973 |
Apr 10, 2006 |
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12899809 |
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12105325 |
Apr 18, 2008 |
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11400973 |
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60670332 |
Apr 12, 2005 |
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60912440 |
Apr 18, 2007 |
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Current U.S.
Class: |
48/197R |
Current CPC
Class: |
C10J 2300/1653 20130101;
Y02E 20/18 20130101; C10J 2300/0946 20130101; C01B 3/348 20130101;
C01B 2203/0261 20130101; C01B 2203/1047 20130101; C01B 2203/1235
20130101; C01B 2203/0455 20130101; C01B 2203/0244 20130101; C10J
3/723 20130101; C10J 2300/0903 20130101; C10J 3/57 20130101; C10J
2200/156 20130101; C01B 2203/0495 20130101; C01B 2203/0415
20130101; C01B 2203/84 20130101; C10J 2200/154 20130101; C01B
2203/0485 20130101; C10J 2300/0906 20130101; Y02E 20/16
20130101 |
Class at
Publication: |
48/197.R |
International
Class: |
C10J 3/46 20060101
C10J003/46 |
Claims
1-16. (canceled)
17. A method of producing syngas using a gasifier, comprising:
establishing a target production rate and a target energy content
for syngas output from the gasifier; providing at least first and
second feed materials as a mixture to the gasifier; monitoring
syngas being produced by the gasifier; and based on data obtained
by the monitoring step, adjusting a feed rate of the mixture to
attempt to maintain the target production rate, and adjusting a
feed rate of at least one of the first and second feed materials to
attempt to maintain the target energy content.
18. The method as described in claim 17 where the first and second
materials each have different energy content.
19. The method as described in claim 17 further including:
analyzing data generated by the monitoring step to identify levels
of carbon monoxide, hydrogen and total hydrocarbons in the syngas;
and determining BTU content of the syngas.
20. The method as described in claim 17 where the first feed
material is construction & demolition (C&D) waste.
21. The method as described in claim 20 wherein the second feed
material is one of: municipal solid waste (MSW), rubber, refuse
derived fuels, wastewater sludge, scrap tires, and combinations
thereof.
22. The method as described in claim 17 wherein the monitoring is
initiated after the gasifier is at a steady state.
23. A method of syngas production using a syngas production
chamber, comprising: establishing a target production rate at a
target energy content; providing a set of one or more first feed
materials, where each of the set of one or more first feed
materials has a BTU content value above the target energy content;
providing a set of one of more second feed materials, where each of
the set of one or more second feed materials has a BTU content
value below the target energy content; and prior to gasification in
the syngas production chamber, mixing first feed material and
second feed material to create a mixture; controlling a feed rate
of the mixture into the syngas production chamber such that an
output mass flow rate of the syngas from the syngas production
chamber is maintained at or near the target production rate;
controlling a feed rate of at least one of the first feed or second
materials such that the syngas output from the syngas production
chamber is maintained at or near the target energy content.
24. The method as described in claim 23 wherein at least two of the
first feed materials are mixed prior to mixing the first feed
material and second feed material.
25. The method as described in claim 23 wherein at least two of the
second feed materials are mixed prior to mixing the first feed
material and second feed material.
26. The method as described in claim 23 wherein at least two of the
first feed materials are mixed and two of the second feed materials
are mixed prior to mixing the first feed material and second feed
material.
27. A computer-implemented method of controlling syngas production
where first and second feed materials are mixed and supplied to a
gasifier, comprising: establishing a target production rate and a
target energy content for syngas output from a gasifier;
controlling a feed rate of a mixture of the first and second feed
materials into the gasifier such that an output mass flow rate of
the syngas from the gasifier is maintained at or near the target
production rate; and controlling a feed rate of at least one of the
first feed or second materials such that the syngas output from the
gasifier is maintained at or near the target energy content.
Description
RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 12/105,325, filed Apr. 18, 2008, entitled
"Method for Controlling Syngas Production in a System with Multiple
Feed Materials," by Davis, et al., which claims the benefit of U.S.
Provisional Patent Application Ser. No. 60/912,440, filed Apr. 18,
2007, entitled "Method for Controlling Syngas Production in a
System with Multiple Feed Materials," by Davis, et al. This
application is also a continuation-in-part of U.S. patent
application Ser. No. 11/400,973, filed Apr. 10, 2006, entitled
"Process and Apparatus using a Molten Metal Bath," by Davis, et
al., which claims the benefit of U.S. Provisional Patent
Application Ser. No. 60/670,332, filed Apr. 12, 2005, entitled
"Process and Apparatus using a Molten Metal Bath," by Davis, et al.
Each of these is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present invention relates generally to syngas production
methods.
[0004] 2. Background of the Related Art
[0005] Organic and inorganic materials can be converted into
vitrified material and a synthesis gas mixture of CO and H.sub.2
(commonly referred to as "syngas") by various means. It would be
desirable to convert such materials into higher value, beneficially
usable products (e.g., conversion of large amounts of municipal
solid waste into relatively small volumes of unleachable vitreous
material and metals, and large volumes of syngas containing
significant BTU value).
[0006] In the past, attempts have been made to convert wastes and
other organic materials into syngas. Such processes include the
steam conversion of organic material, which requires a substantial
energy input. Other processes involved the use of metal baths or
the use of plasma technologies. One of the greatest challenges in
gasifying such feed materials is the feeds' unpredictable nature
(e.g., the feed materials' chemical and physical characteristics
could change dramatically in a short period of time).
[0007] It is known in the prior art to provide gasification systems
that convert municipal solid waste (MSW) and construction and
demolition waste (C&D) into clean energy. As described in U.S.
Patent Application Publication No. 2006/0228294, which is
representative, these systems may comprise a refractory, induction
furnace that receives the feed material into a molten metal bath,
wherein a mix of organic and non-organic material is treated
resulting in metal recovery and efficient production of synthesis
gas (syngas). The syngas can be used to fuel a combined-cycle
generator to provide municipalities with clean, renewable
electricity.
[0008] Though many of those attempts appear to have been
technically possible and/or may have been successful in pilot scale
demonstrations, these technologies did not allow for appropriate
scaling or commercialization of the process because of the
difficulty is processing the material in an economical manner,
reliability of operation, controlling temperature and other key
process variables, such as oxygen and steam input, etc. It would be
highly desirable to have a commercially viable method for the
conversion of large volumes (e.g., tons per hour) of organic and
inorganic materials into synthesis gas of sufficient BTU value for
commercial use and vitreous material which is useable (or at least
environmentally benign)
[0009] One of the technical objectives that must be reached to
ensure commercial success of the gasification technology is to
achieve a high efficiency of synthesis gas generation from the
processed waste streams.
BRIEF SUMMARY OF THE INVENTION
[0010] The present invention provides methods and apparatus for the
conversion of feed materials containing organic and inorganic
components in a refractory lined vessel having one or more inlets
and outlets, and partially filled with molten metal and vitreous
material, to provide for production of syngas. The syngas is formed
by the partial oxidation of the organic components of the feed
materials and recovery of the vitreous material and metals from the
inorganic components of feed materials. The method includes (1)
providing one or more feed materials, from which air has been
extracted and analyzing the feed materials for heat value; (2)
injecting the feed materials directly into the molten metal; (3)
monitoring the composition of the molten metal, the vitreous
material, the synthesis gas and the reactor temperature; (4)
injecting oxygen, steam and/or co-feeding one or more additional
feed materials of higher heat value than the analyzed feed
materials, with the amounts injected being based upon the analysis
and monitoring results; and (5) continuously removing synthesis gas
and periodically removing metal and/or vitreous material from the
reactor. An overall process diagram is presented on FIG. 1 and is
more fully discussed hereinafter.
[0011] Two or more feed materials that possess differing syngas
generation potentials are mixed in a mixer and fed as a composite
feed stream into a gasifier to produce syngas. By controlling the
feed rate of the mixture into the gasifier as well as the feed
rates of one or more of the individual feed materials into the
mixer, the syngas is produced at a target production rate, with
target energy content (BTU). Potential feed materials include, but
are not limited to, construction and demolition (C&D) debris,
municipal solid waste (MSW), other sewage-related solids, waste
tires, and other substances that contain varying levels of organic
compounds capable of producing a syngas.
[0012] In a representative embodiment, two or more feed materials,
each preferably having a different BTU value, are mixed to create a
blend, which is then fed to a gasifier. The mixture of materials
having various BTU content produces a blend having a final BTU
content value. Desired operating conditions are a target production
rate, which typically represents a mass flow rate exiting the
gasifier (or, more generally, the gasification stage), at a target
energy content. According to the process, a feed rate of the
mixture into the gasifier is sped up or slowed down to produce a
constant or substantially constant mass flow of syngas (i.e. the
target production rate), while the feed rate(s) of one or more of
the individual feed materials are adjusted as necessary to maintain
the target energy content. The feed rates are adjusted using one or
more control signals. The control signals are generated by a
controller, which derives the values of these signals by analyzing
data received from components that monitor the syngas. In
particular, together with temperature measurements, syngas mass
flow measurements are taken in exhaust ducting from the gasifier,
e.g., by means of a pitot tube or other velocity or flow measuring
devices. This real-time data is then analyzed, for example, for
carbon monoxide, hydrogen and/or total hydrocarbons levels, to
determine the BTU content of the syngas output from the gasifier.
Using the data, a controller adjusts the material feed rate(s)
accordingly to attempt to maintain the syngas target production
rate at the target energy content.
[0013] The invention also provides an apparatus for the processing
of organic and inorganic feed material comprising (1) a refractory
lined vessel having one of more inlets and one or more outlets, and
suitable for the containment of molten metal; (2) feed material
preparation units (such as dryer and shredders); (3) analyzers for
continuously analyzing the feed material prior to injection into
the vessel; (4) injectors for injecting air-extracted feed material
into the vessel; (5) monitors for the composition of the metal, the
vitreous material and the synthesis gas; (6) injectors for
injecting steam into the vessel at a predetermined level above
which the molten metal would be contained; (7) oxygen and co-feeds
injectors for injecting these materials into the vessel at a
predetermined level below which the molten metal would be
contained; (8) controllers for regulating the amount of steam,
oxygen, and co-feed injection, responsive to the results of said
analyzers and monitors; and (9) outlets in the vessel for
continuously removing syngas.
[0014] The foregoing has outlined some of the more pertinent
features of the invention. These features should be construed to be
merely illustrative. Many other beneficial results can be attained
by applying the disclosed invention in a different manner or by
modifying the invention as will be described.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] For a more complete understanding of the present invention
and the advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawings,
in which:
[0016] FIG. 1 is a flow chart of a process of the present invention
for processing a waste stream, including preferred optional
features of the invention;
[0017] FIG. 2 is a schematic illustration of a feeding arrangement
in one embodiment of the present invention;
[0018] FIG. 3 is a schematic illustration of a feeding arrangement
in another embodiment of the present invention;
[0019] FIG. 4 is a schematic illustration of a product feed
arrangement into the reactor for use in the present invention and a
preferred reactor configuration;
[0020] FIG. 5 is an illustration of the chemical zones in the
reactor;
[0021] FIG. 6 illustrates a process flow to provide syngas at a
target production rate having a target energy content according to
the subject matter herein;
[0022] FIG. 7 is data processing system for use in a control system
that implements the process flow shown in FIG. 6;
[0023] FIG. 8 is a representative mixing system in which the method
described herein is implemented;
[0024] FIG. 9 is an embodiment where a single feedstock is added to
a primary feedstock (e.g., C&D waste) to produce and maintain
syngas at a target production rate and BTU value; and
[0025] FIG. 10 is another embodiment where multiple feedstocks are
added to a primary feedstock to produce and maintain the syngas at
the target production rate and BTU value.
DETAILED DESCRIPTION OF THE INVENTION
[0026] Gasification of waste is a well-developed technology.
According to the disclosure herein, an optimization is provided
whereby two or more feed materials, preferably of varying energy
(e.g., BTU) content values, are blended (mixed) and supplied to the
gasifier. The syngas output from the gasifier preferably has
associated therewith a "target" (or desired) production rate at a
target energy content. This is desirable where, for example, the
syngas is being used to operate a gas turbine or the like. Thus,
for example, production rate typically is a fixed number of tons
per hour (or some other temporal metric), and target energy content
is some desired BTU content value at that target production rate.
Using two or more feed materials, preferably of different BTU
values, a mixture or blend is created in advance of the
gasification stage.
[0027] The present invention provides for the conversion of one or
more feed materials containing organic and inorganic components in
a refractory lined vessel (as described below) which, in operation,
is partially filled with molten metal and vitreous material. The
feed materials are analyzed and selected to provide for optimal
production of syngas formed by the partial oxidation of the organic
components of the feed materials and recovery of vitreous material
and metals from the inorganic components of feed materials.
[0028] In particular, preferably the materials having various BTU
content values are blended together for a final BTU content value.
The target production rate and target energy content of the syngas
are the desired operating conditions. According to the described
process, the feed rate of the mixture into the gasifier is sped up
or slowed down to produce a constant or substantially constant mass
flow of syngas; in addition, and as necessary, the feed rate(s) of
one or more of the individual feed materials (into the mixing unit)
are adjusted to maintain (or attempt to maintain) the target energy
content. Preferably, together with temperature measurements, syngas
mass flow measurements are taken in exhaust ducting from the
gasifier, e.g., by means of a pitot tube or other velocity or flow
measuring devices, to calculate real-time data values. This data is
then analyzed, for example, for carbon monoxide, hydrogen and total
hydrocarbons levels, to determine the BTU content of the syngas.
Using the data, a controller adjusts the feed rates
accordingly.
[0029] As used herein, the phrase "target production rate" should
not be construed as being limited to a single value, as a "rate"
may include a range of acceptable values (typically, the mass flow
rate). Also, the word "maintain" in the phrase "maintain production
rate" does not require that the associated production rate or
energy content be exactly equal to a given value. Also, the word
"mixed" or "mixing" may be considered synonymous with "blend" or
"blending."
[0030] FIG. 6 illustrates this basic process flow. A gasifier 100
receives a feed mixture from a mixer 102 using a feeder. The mixer
102 is supplied with at least a first feed material 101 and a
second feed material 103. First feed material is fed to the mixer
102 at a fixed or adjustable rate using a feeder; second feed
material is fed to the mixer 102 at a fixed or adjustable rate
using a feeder. The output of gasifier 100 is syngas having a
target production rate with target energy content. Monitor 104 in
exhaust ducting (or other structure) measures syngas mass flow rate
and analyzer 106 analyzes the CO, H.sub.2 and other hydrocarbons to
determine the energy (e.g., BTU) content of the syngas. The
resulting data (perhaps with other data, such as temperature
readings) is supplied to controller 108, which may be implemented
in any convenient manner such as a computer, programmable logic
controller (PLC), a combination thereof, or the like. The
controller 108 takes the data and compares it to target production
rate and target energy content. Controller 108 then generates a
first control signal to adjust the feed rate of the material into
the gasifier as necessary to reach and then maintain (or attempt to
maintain) constant the target production rate. Controller 108 also
generates second and/or third control signals and as necessary to
adjust the feed rate(s) of one or both of the feed materials into
the mixer 102; this operation maintains (or attempts to maintain)
constant the target energy content. This control operation may be
initiated at any convenient time, e.g., after a steady state of the
process is achieved.
[0031] The above-described operation ensures a consistent BTU value
of syngas production.
[0032] Among the suitable feed materials are waste materials such
as municipal solid waste (MSW), refuse derived fuels (RDF),
including RDF based upon MSW, construction and demolition wastes
(C&D), wastewater sludge, scrap tires, plastic wastes, medical
waste, waste oils, as well as other non-waste materials such as
coal or petroleum coke. Most preferred are MSW, C&D and other
materials, which due to their carbon, hydrogen and oxygen content,
can be efficiently converted to syngas by the practice of this
invention. The advantages of the present invention are most
relevant to the processing of solid feed materials, although
non-solid material (e.g., semi-solid mixtures and liquid feeds) may
also be suitably processed.
[0033] The present invention is particularly well suited to the
processing of MSW, C&D and RDF. Prior approaches could not
effectively deal with the challenges posed by the highly variable
compositional makeup of MSW, particularly the inconsistency of its
BTU content. For example the BTU of MSW and C&D can typically
range from about 7500 BTU/cu ft (for streams containing high
percentages of wood, paper and plastics) to as low as about 3000
BTU/cu ft for streams containing low percentages of the foregoing
high BTU components and/or high percentages of low BTU material
such as rock, glass, water and metal).
[0034] The present invention effectively deals with this BTU
variability. The processes and apparatus herein (i) analyze the
feed materials for heat value (e.g., preferably continuously using
neutron beam-induced gamma radiation spectroscopy or by taking
frequent samples and analyzing their heat value by calorimeter or
other conventional methods) of incoming stream before introducing
it into the reactor, (ii) monitor (preferably continuously or by
periodic sampling) the composition of the molten metal for carbon
content and metals; (iii) monitor (preferably continuously) the
composition of the gaseous stream in the headspace of the reactor
or in the off-gas stream (e.g., for H.sub.2, H.sub.2O, H.sub.2S,
CO.sub.2 and carbon monoxide content by use of one or more gas
analyzers and the temperature of such stream) and (iv) based upon
the analysis and monitoring results, oxygen and/or co-feeds (other
feedstocks such as shredded tires, petroleum coke etc. of known
and/or higher BTU value) are injected (preferably dynamically
blending), in order to achieve and maintain the desired BTU value
in the off-gas stream.
[0035] Many of these feed materials (e.g., MSW) have highly
variable composition and physical form. In accordance with this
invention, prior to injection into the reactor, the feed materials
are prepared and analyzed for their heat values.
[0036] Feed material preparation includes the extracting of air
from the feed material. The presence of air, which is 79% nitrogen,
would result in a dilution of the syngas concentration and reduce
its BTU value. In the practice of this invention, BTU value of the
gas generated will preferably be in the range of 280-450
BTU/ft.sup.3. The feeder should ensure that essentially all of air
contained in the waste is extracted. The most common concern in the
material feeds is the presence of air, with the concern being based
upon the nitrogen and other inert components which are present, not
the oxygen component. It is preferred than the air or other inert
gas content of the feed be less than about 1% of the weight of the
feed, most preferably below about 0.5%. Although higher percentages
will undesirably result in dilution of the syngas, somewhat higher
percentages may be acceptable depending on the intended use of the
syngas.
[0037] Depending on the nature of the feed material, the process of
this invention will also typically include sizing, separating and
drying steps to prepare the feed prior to injection. For example,
for MSW, the feed material would typically go through:
[0038] 1. a sizing process (e.g., reduced in size to less than 1''
to 2'' to simplify any later extraction of inorganic materials and
facilitate injection),
[0039] 2. a separation process (e.g., to separate out ferrous and
non ferrous metals, concrete and glass.
[0040] 3. a drying process to reduce the moisture content of the
feeds. For example, the moisture content in many feeds can vary
from 20% to 60% moisture. In order to achieve optimal gasifier
performance, a stable moisture level below 10-20% is most
preferred. Further, in order to minimize the risk of steam
explosion moisture levels below 10% is generally required.
[0041] For some feed materials one or more of these steps may not
be needed and/or will have been previously provided. For example,
the feed material (e.g., RDF prepared by a third party) may be
received already sized and/or dried. To the extent some or all of
this preparation steps are needed, they can be carried using
standard waste industry equipment available from multiple vendors
(e.g., Alan-Ross Machinery Corporation, Northbrook, N.Y. and others
provide suitable sizing equipment).
[0042] The material is fed into a refractory-lined vessel such as
an induction furnace, arc furnace or any other type of high
temperature molten bath reactor. The reactor design should
preferably be selected to assure that (i) it is sufficiently sized
for the selected feed volumes and (ii) the amount of molten metal
to be contained therein can be controlled at any given time so that
the carbon content in the molten bath does not exceed about 4% by
weight (based upon the weight of the molten metal). For example,
for a 250 tpd MSW processing plant, a 40 ton steel capacity
induction furnace preferably should be used, and have additional
volume above the molten bath (head space) to accommodate gases
rapidly exiting the bath, foaming of the vitreous material and the
accumulation thereof during operation.
[0043] The preferred reactor configuration requires the reactor be
equipped with the induction channels installed at the bottom of the
vessel. Such a configuration is known as a channel furnace (e.g.,
available from Ajax Tocco Magnetothemic, Inc., Warren, Ohio).
Electric power may be supplied in such a manner that electrical
current is flowing through the channels. The molten metal may be
heated by induction currents induced by alternating current flowing
through the coils or loops. This allows unrestricted access to the
reactor through the walls for tapping. In addition it allows
multiple choices for refractory lining of the top cylinder
including carbon graphite brick. As an alternative, a stand-alone
induction furnace may be used to generate a molten bath, which is
then charged into the reactor. The channel reactor (as shown in
FIG. 4) is a refractory-lined vessel (1) with the molten metal
material in it.
[0044] The metal is most typically iron, but other metals such as
nickel, chromium, tin, etc. may also be advantageously used (e.g.,
to effect the conversion of chlorinated material in the feed to
desired chlorine-containing form, such as HCl, or if a lower
melting metal is necessary or desirable). A preferred variant is to
use a separate standard induction furnace to melt steel and then
charge it molten into the reactor.
[0045] Steam injection ports, which are located in the reactor
above the molten bath layer, are provided. Suitable means to inject
a predetermined amount of steam into the reactor include simple
steam lances such as stainless steel nozzles manufactured by
Spraying Systems Inc. Steam injection is effectively used to
control the temperature of the process due to the endothermic
reaction of water and carbon. In this process, injected steam
reacts with the [C] which is present during operation above the
bath, as shown in the following reaction:
C+H.sub.2O.dbd.H.sub.2+CO dH.about.130 kJ/mole
This reaction will not only consume excess energy and reduce oxygen
consumption but also will yield additional volumes of hydrogen in
the exhaust. This is an endothermic reaction, which can rapidly and
efficiently reduce the temperature in the reactor without
jeopardizing synthesis gas output.
[0046] It is important that the steam be injected above the molten
bath or in the vitreous layer, rather that into the metal itself,
because most of elemental carbon will float to the top of the melt,
and this area above the bath will also be the area which will need
to be cooled fastest in case of higher than average heat value
product fed into the reactor.
[0047] Oxygen should be injected directly into the metal bath or in
the vitreous layer, rather than in the metal itself. Suitable means
to inject predetermined amounts of oxygen into the reactor include
lances to inject oxygen from the top reactor and tuyere tubes to
inject oxygen from the bottom of the reactor. Preferably, oxygen is
supplied using one or more supersonic oxygen lances, which generate
a gas stream capable of penetrating deep into the metal bath (i.e.,
the exit of the lances are above the molten metal layer, but
sufficiently adjacent thereto so that that the supersonic stream
penetrates the molten metal layer). Alternatively, tuyere tubes to
inject oxygen into the molten metal from the bottom of the reactor
may also be used. Submerged lances and tueyers are possible but
they significantly increase the possibility of catastrophic metal
spill. Therefore, a preferred method of oxygen supply is by means
of supersonic oxygen lances installed above the melt level, which
generate a gas stream capable of penetrating deep into the metal
bath.
[0048] Oxygen, after being injected into the molten metal, reacts
with iron, forming iron oxide. When being fed into the reactor, the
material feed submerges into the metal layer of the molten bath,
where it is exposed to elevated temperatures in excess of
2900.degree. F. These temperatures immediately initiate thermal
decomposition of the material.
[0049] The size of the reactor, the positioning of oxygen and steam
injection nozzles, and the form of the exhaust gas passageway, will
be selected dependent upon the product throughput and on the type
of feed. It is advantageous to have oxygen and steam lances
installed in the upper section of the reactor above the molten
pool. Supersonic oxygen lances located above the molten pool and
pointed downwards deliver oxygen into the bath itself not above it.
One of the manufacturers of such lances is Process Technology
International Inc, Tucker, Ga.
[0050] During processing, the organic portion of the material is
converted into hydrogen and carbon and the inorganic constituents
are melted and/or dissolved in the molten bath. The metal oxides
are reduced to metals, which accumulate on the bottom of the molten
bath, while all other inorganic compounds form the vitreous layer
at the top of the molten bath. Carbon formed in this process floats
to the surface of the molten bath. While doing so, it reacts with
iron oxide reducing it to iron. In addition to this mechanism,
direct carbon oxidation by oxygen with the formation of carbon
monoxide also takes place. This continuous movement of waste and
iron oxide up and iron down in the molten bath provide a necessary
stirring action and facilitates the whole process.
[0051] The reactor should preferably be equipped with a tapping
mechanism, which may be of the same type which is used to tap blast
furnaces and electric arc furnaces. The reactor is equipped with
tapping mechanisms for excess metal and for the vitreous layer. The
vitreous layer and accumulated metal are periodically tapped to
maintain a constant level of the molten bath in the reactor.
Suitable tapping mechanisms include: tapping drills, which are
supplied by a number of manufacturers (e.g., Woodings Industrial
Corporation, Mars, Pa.) and a mud gun to plug the drilled hole.
Size and type of the drill and gun will be determined by refractory
thickness and its composition.
[0052] Though it is preferable to have a continuous tapping of
metal and vitreous material in a full-scale process, similar
results can be achieved with periodic tapping of the reactor, which
can be easier to implement. While in operation, vitreous material
and metal will accumulate in the reactor. The level of the molten
bath should be carefully controlled, and if it rises above a
pre-set point the tapping mechanism for the metal and/or vitreous
material layer will be activated. The simplest and most reliable
way to do so is to stop the feed, vent syngas from reactor, then
tap sidewall of reactor at the level where the start-up amount of
iron would be with standard tapping drill. Vitreous material and
metal is then poured out of the reactor until the level of the bath
reaches the drilled tapping hole. This hole is then filled with mud
through use of a mud gun. This is a short procedure and the reactor
is ready for operation again. Metals of suitable composition can be
sold (e.g., to foundries) after collection, and the vitreous
material may also be beneficially used (e.g., as aggregate).
[0053] Feed material analysis is performed, so as to ascertain the
nature of the feed prior to the injection thereof into the reactor,
and additional feeds (as discussed below) can be simultaneously
injected to address this variability. The process also includes
monitoring the composition of the molten metal, the vitreous
material, the synthesis gas, and the reactor temperature. The feed
can be analyzed either prior to, during, or subsequent to its
preparation, with analysis of the feed after its preparation
generally being most preferred, because the prior sizing, drying,
and air extraction simplifies the analysis.
[0054] Composition, temperature and volume of syngas are
continuously analyzed. Concentrations of O.sub.2, CO, CO.sub.2,
H.sub.2, H.sub.2S, H.sub.2O and particulate in the syngas are
continuously monitored in real time (e.g., using available
monitoring equipment such as available from Rosemout Analytical
Inc.).
[0055] Further, the compositions of the molten metal and the
vitreous material are intermittently analyzed. The metal samples of
tapped metal are analyzed for metal composition and melting
temperature in any commonly available metallurgical laboratory. If
melting temperature of alloy approaches the operating temperature,
some pig iron may be added to the feed to lower the temperature.
Samples of vitreous material are sent to a laboratory such as Hazen
Research Inc., Golden, Co. for oxide composition and carbon
content.
[0056] The data from this analysis, together with the analysis of
the feed material, are used to control the process as discussed
below.
[0057] Steam, oxygen, and/or co-feeds of additional feed materials
of higher heat value than the analyzed feed materials are injected
into the molten metal bath, with the amounts injected being based
upon the analysis and monitoring results as described above. The
introduction of steam above the metal bath and oxygen directly into
the metal bath are used to maintain the optimal concentration of
oxygen in the reactor at all times, and to maintain a reduced
oxidation environment. The amount of oxygen and steam injection
will be controlled based upon reactor temperature input waste
composition data provided by waste analyzer and by exhaust gas
composition. Additional feed materials of higher heat value than
the analyzed feed materials (e.g., scrap tires or rubber waste, if
the principle feed material is MSW) can also be injected to help
assure the quality of the syngas (e.g., if a portion of the MSW
feed is of lower than desired heat content).
[0058] If the temperature of the bath falls, induction power is
increased. In the case of temperature increase, steam may be
injected on the top of the bath to cool the process down with
endothermic reaction discussed above. Normally water vapor
concentration in the exhaust will be low if it increases, carbon
concentration of the feed is dropped, and oxygen feed rate will be
reduced. Other parameters may also be used to effectively adjust
the gas cleanup train's performance.
[0059] The analysis is designed to continuously and accurately
estimate the heat value of the feed on a real-time basis prior to
injection into the reactor and this can be done by analyzing the
compositional makeup of the feed materials. One such analytical
approach particularly useful herein is based upon neutron
radiation, which is capable of inducing secondary gamma radiation
in a wide range of material, and the gamma radiation is specific to
elements. Almost all known elements including carbon, silicon,
aluminum, calcium, oxygen and hydrogen will emit secondary gamma
radiation. For example, when a feed material is irradiated by a
neutron beam impulse produced by a neutron beam generator, the
material will emit gamma radiation for a short period of time and
an associated device measures these gamma ray emissions.
[0060] The spectrum generated thereby is resolved in frequency and
time elapsed from the neutron beam pulse and can accurately predict
elemental composition (H, C, O, Si, Al, Ca and other element-based
concentrations) of the analyzed stream. These measurements are done
in a pulse mode, with more than one pulse per second. It typically
takes about 15 seconds for software to analyze the signal and
generate commands to the control module. Accordingly, the material
feed stream analyzer should be installed at a point allowing
sufficient time for the system to respond prior waste being fed
into reactor. One such suitable neutron beam generator/gamma
radiation detector/analyzer system is available from HIEnergy
Technologies, Irvine, Calif. or STS-Rateck, St Petersburg, Russia.
Through the measurement of the composition of the feed material, a
real time estimated heat value of the analyzed stream is
established prior the material being fed into reactor. Based upon a
predetermined computer algorithm, a controller will then adjust
process parameters to better treat the incoming stream. The
algorithm generates a theoretical heat value based on the elemental
composition of the analyzed feed stream. It also generates required
adjustments to the process parameters: feed rate, induction furnace
heat, lime or soda ash addition, oxygen and steam flow.
[0061] In addition, the same measurements would preferably be used
for estimating inorganic additions to the slag, such as aluminum,
calcium, silicon and others. Using this analysis and a computer
algorithm, a controlled amount of flux can be added to the feed
stream to achieve desired viscosity of the slag layer. Correct
viscosity of the slag layer is important because it allows for fast
and reliable removal from the reactor. In order to achieve optimal
vitreous material removal, its viscosity is preferably about 250
poise at a temperature of 200.degree. F. below the reactor's
operation temperature.
[0062] The step of injecting the prepared feed materials into the
metal bath is also important. The materials are directly injected
into the metal layer. The feed materials can be fed from the top of
the reactor into the center of a molten metal bath and are
preferably fed directly into the metal layer itself (i.e., the
feeding tube is immersed in the molten metal or molten vitreous
material). In each instance, it is important that the injection not
result in the entrainment or addition of air or inert gases (e.g.,
use of conventional feeding lances utilizing air or nitrogen for
material transport would unacceptably add air into the vessel). The
type of feed mechanisms suitable for use in this invention includes
auger extruder feeders (e.g., Model No. GPT2-2-400-00, manufactured
by Komar Industries, Columbus, Ohio) and ram feeders (e.g., as
manufactured by Robson Handling Technology, Recycling Equipment
Corporation and others). The feed material (or at least a
substantial portion thereof) reaches the bath in a solid form
because it is pushed through the feeding tube fast enough not to be
gasified in it. It is important that such feed mechanisms assure
that waste is delivered underneath and not above the metal or
vitreous layers and in a fast enough manner so that the waste does
not undergo an unacceptably high rate of decomposition in the
feeding tube.
[0063] To achieve these objectives preferably involves one of the
following three variants of the feeding step:
[0064] 1. Product from the hopper (1) (FIG. 2) is gravity fed into
the charge box (2). The gate (3) is in a closed position. The ram
(4) moves forward and compresses the product with high pressure so
that essentially all of the air from it escapes through the hopper
(1). The amount of pressure delivered to the ram, and the sizes of
the charge box, are determined by the type of product to be
converted and by the required throughput of the overall system.
[0065] 2. Product from the hopper (1) (FIG. 3) is gravity fed into
the charge box (2). The gate (3) is in a closed position. Gate (3)
opens and the ram (4) moves forward, pushing the product into the
box (5). Gate (3) is closed. Gate (6) is closed as well. All the
air is evacuated by suction (8) from box (5). Gate (6) opens and
ram (7) moves product into the reactor (9).
[0066] 3. Product is forwarded to the hopper. From hopper product
is forwarded into extruder feeder, which moves it into the
reactor.
[0067] The preferred method of feeding material is into the molten
metal itself. When product is fed on the top of the molten bath,
special precautions need to be taken to eliminate the possible
discharge of the volatile organic compounds, carbon dioxide, and
water to the output of the reactor. To avoid this, additional
reaction space for the gas phase would preferably be added. This
part of the reactor also needs to be furnished with oxygen and
steam injection ports to maintain control over the atmosphere in
the reactor and allow appropriate corrections if the product stream
is changed.
[0068] Product is fed directly into the vitreous layer of the
molten bath (see FIG. 4). In one of the variants, the feeder itself
(1) is inserted into the metal through the vitreous material. The
compressed chunk coming out of the feeder is pushed down through
the passageway (2) into the reactor underneath the vitreous
material (3). This feeding arrangement has a significant advantage
over top charging, because it eliminates or minimizes the
possibility of the presence of volatile organic compounds in the
synthesis gas and reduces particulate load on any associated gas
treatment system thereby reducing requirements for the reactor
size. The end of the feeder can be furnished with grating designed
to cut though the compressed log of the material, and by doing so
increases product surface area. Though water cooled tubes can be
used in this arrangement, it is preferable to use a graphitized
alumina unit (such as one manufactured by Vesuvius, Falconer, N.Y.)
which is a combination of refractory (graphitized alumina or
graphite) bottom submerged section of the tube, and water cooled
colorized copper upper section.
[0069] If the product stream includes chlorine- or
fluorine-containing compounds, lime can be added into the vitreous
material to neutralize them. After being fed into the furnace, the
feed product is exposed to the molten bath, whether it sinks into
the vitreous material (if fed from the top) or is already submerged
into it. The temperature of the molten bath may be as high as
approximately 3000.degree. F., or higher. All inorganic compounds
are melted. Special fluxes, such as but not limited to, soda ash
and borax, may be added to the melt in order to lower melting
temperatures for some of the oxides contained in the product. Lime
may be added to the feed to correct pH of the vitreous
material.
[0070] This process will continuously remove synthesis gas and
periodically remove metal and/or vitreous material. These materials
are removed through one or more outlets from the refractory-lined
vessel and the removal can be accomplished by a conventional means
well known in the metal manufacturing and/or waste processing arts.
Synthesis gas generated in this process exits the reactor through a
top opening. The reactor volume and dimensions above the bath are
designed to maximize the synthesis gas production efficiency and to
reduce particulate load in the gas stream. Additional boilers,
scrubbers and compressors can be installed downstream depending on
the specific requirements of the plant.
[0071] During operation, the temperature and level of the molten
bath are preferably continuously monitored. When exposed to the
extremely high temperatures of the molten bed, organic compounds
contained in the feed start to decompose into carbon and hydrogen.
Hydrogen will immediately leave the bath. Part of the carbon will
dissolve in the molten metal, and the remainder will move toward
the top of the bath. Concurrently with the waste, oxygen is feed
into the reactor. The oxygen dissolves in iron with the formation
of FeO.
[0072] Gas leaving the gas treatment system has heat value ranging
from 290 BTU/cft to 450 BTU/cft and will be of suitable quality to
be used in combined-cycle (CC) power plant. When such a unit is
installed inline with combined-cycle power plant, one would be able
to generate 1600 kW of electricity from each ton of material fed
into the reactor, which is a significant improvement in comparison
with the other waste gasifiers combined with CC power plant.
[0073] The gaseous stream may be further treated as necessary or
desirable. A preferred method of treating particulate and
impurities in the syngas is to treat it with plasma discharge in a
manner which treats these particulate and impurities, but does not
significantly oxidize or "burn" the CO portion of the syngas. The
types of plasma discharge most suitable include microwave and
inductive coupling plasma, which are capable of generating an
appropriate type of non-equilibrium plasma electrode-less
discharge. In such case, non-equilibrium plasma generators are
installed at the inlet of the specially-designed reactor. All, or
only the contaminated portion of the syngas, may be fed into the
reactor through this inlet. Some oxygen can also be added to the
process in order to convert carbon (C) to carbon monoxide (CO). The
plasma discharge acts as a catalyst for a number of processes and
produces particulate-free syngas at the outlet of reactor. If
configured properly, plasma discharge can also convert H.sub.2S
contained in the syngas into hydrogen and elemental sulfur, which
is separated from the gas stream. Plasma processing does not
destroy pollutants in the gas stream by itself, but rather it
creates favorable conditions for pollutant removal processes and
therefore must be used in conjunction with conventional pollution
control technologies.
[0074] Though most of chloride, fluoride and up to 40% of sulfur
will be captured in the vitreous material, additional syngas
cleaning may be necessary or desirable. In this case, to
substantially clean the gas of chlorine, fluoride and sulfur, a dry
scrubber, injecting sodium hydroxide or lime, can be installed in
the exhaust. After that, ceramic filters or cyclone separators may
treat gases, in order to eliminate any residual particulates.
Another method is to use a sodium hydroxide solution in the wet
scrubber installed before the compressor.
[0075] Though the molten bath and vitreous material layers both act
as effective particulate filters, some of the carbon dust,
especially when the reactor is fed from the top, can escape the
molten bath and become airborne. Special oxygen injection ports may
be located above the bath and direct oxygen flow in the upper
portion of the reactor in order to supply sufficient amounts of
oxidizer to convert carbon dust into carbon monoxide. To prevent
particulates from exiting the reactor, the gas-exiting velocity
should be lower than the dust-settling velocity. This can be
achieved by adding expansion chambers in the exhaust section of the
reactor. Another way of minimizing or eliminating particulate
material is to install a cyclone on the exit from the reactor.
[0076] The molten bath reactor can be envisioned as separated into
zones (FIG. 5). In the first zone, in the proximity of oxygen
lances with excess of oxygen, the following main reactions
occur:
Fe+1/2O.sub.2.dbd.FeO dH.about.-260 kJ/mole(T=1600 K)
with FeO being the dominant form of iron oxide in the reactor's
preferred operating temperature range. Other reactions include:
2Fe+3/2O.sub.2.dbd.Fe.sub.2O.sub.3 dH.about.-800 kJ/mole
[C]+O.sub.2.dbd.CO.sub.2
All products of those reactions travel towards the top of the
molten metal bath.
[0077] In the second zone, which has a lack of oxygen, carbon and
any non-dissociated material feed are moving towards the top and
are dissolved in the melt when they meet iron oxide. Reactions
leading to the formation of carbon monoxide occur as follows:
FeO+[C].dbd.Fe+CO dH.about.150 kJ/mole(T=1600 K)
Fe.sub.2O.sub.3+[C].dbd.2Fe+3CO dH.about.454 kJ/mole
CO+FeO.dbd.Fe+CO.sub.2 dH.about.-20 kJ/mole
Carbon participating in this reaction exists in the reactor in
three forms: free carbon, carbon dissolved in the melt, and carbon
contained in still-not-disintegrated waste. Some of the carbon
dioxide formed in zone one is reduced to CO:
CO.sub.2+[C]=2CO dH.about.160 kJ/mole
This gas continues to react with carbon, forming carbon monoxide.
This is an exothermic reaction, which provides a heat source for
the process. Special precautions need to be taken not to allow
overheating of the system. The temperature of the reactor should be
carefully controlled, and if it exceeds 3000.degree. F., steam
injection should be activated.
[0078] Heat contained in the gases can be recuperated in a heat
exchanger. After the dry scrubber, the synthesis gas will be
saturated with water, which may be removed after the gas is
compressed (4) and cooled below its dew point.
[0079] A concrete example of the process is shown in FIG. 8. This
embodiment is merely representative and not limiting. The system
includes a number of components including feed bins 301 and 302,
sensors 303, a computer control system 304, feed mixers 305, feed
controllers 306, composite mixers 307 and 309, feed controllers
308, final mixer 310, syngas production chamber 311 and syngas
analyzer 312. Each feed bin 301 and 302 provides a feedstock
material to its associated feed mixer 305. The feed controller 306
associated with a feed mixer controls the volume of feedstock
provide to the composite mixer 307 or 309. The feed controller 308
associated with each composite mixer 307 or 309 controls the volume
of combined feed (created in composite mixer 307 or 309) supplied
to the final mixer 310. Final mixer 310 provides the combined
materials to the syngas production chamber 311, and the output of
the chamber is monitored by the syngas analyzer 312. The computer
system 304 provides the overall system control.
[0080] In particular, to operate this system, sensors 303 and
syngas analyzer 312 are used to monitor variation in the feed
materials and the syngas production rate. The resultant data are
transmitted to a computer program in computer system 304 containing
pre-programmed equations that are used to adjust material input
rates to achieve the desired syngas production range. In this
process, preferably historic data plus real-time test results on
the feed material are used to determine the syngas generation
potential of each material. Preferably, each feed material is
sorted and placed into separate tanks (e.g., feed bins 301) based
on whether it can generate syngas above or below the target syngas
production rate. The feed bins 301 hold materials that generate
syngas above the target rate, and the feed bins 302 hold materials
that generate syngas below the target rate. The number of bins, of
course, is merely illustrative. In this embodiment, the resultant
two types of feed materials are further mixed, and based on sensor
data, fed to the syngas production chamber 311 to produce the
target range of syngas production rate.
[0081] Referring to FIG. 8, in this embodiment, the syngas
generation process is optimized by using the computer system 304 to
control feed material rates, preferably as determined by real-time
syngas composition data and mixing equations. The term "real-time"
may also include near or "substantially" real-time data, so there
is no explicit requirement that control operations be carried out
instantaneously. Additionally, the computer system may also
consider historical feed material analysis data, such as elemental
content and organic content, with the real-time feed material
analysis from the sensors 303 to further optimize the blending of
the feed materials and thus the syngas production rate. Further,
the analysis on the feed materials by the sensors 303 may also
identify potential materials that could upset the syngas generation
process, such as materials that contain an excessive level of
inorganic compounds. In such case, the particular feed controller
306 might be de-actuated for a given time to ensure that such
materials are not provided to the production chamber.
[0082] The process begins after each feed material has been sorted
by its syngas generation potential into individual feed bins 301
and 302. Each feed material is then fed to a feed mixer 305. The
feed mixers 305 could be rotary dryers, traditional mixing tanks,
rotating drums or any other device capable of mixing each feed
material to produce a consistent composition. Materials in feed bin
301, which have a syngas generation potential above the target
syngas production rate, preferably are fed by computer system 304
to an "above" composite mixer 307, while materials in feed bin 302,
which have a syngas generation potential below the target syngas
production rate, preferably are fed by the computer system 304 to a
"below" composite mixer 309. Preferably, materials from the
composite mixer 307 and composite mixer 309 are then fed at
specific rates as determined by the computer system 304 into a
final mixer 310 prior to being fed to the syngas production chamber
311. A representative production chamber 311 is of the type
described in U.S. Patent Application Publication No. 2006/0228294,
or as described in U.S. Pat. No. 5,571,486. The particular
production chamber 311 is not a limitation of the present
invention.
[0083] The size of the mixing tanks, the material feed rates, and
the residence/mixing time of each material are ultimately
determined by the target range of syngas production rate. For
example, a narrow target range will require larger tanks and longer
mixing times.
[0084] A feed controller 306, controlled by the computer system
304, sets the feed rate of each feed mixer 305 by adjusting the
operating parameters of the physical dispensing device. A
dispensing device could be a screw drive, a conveyor system, or any
other mechanical means of moving feed material from the feed mixers
305 to the composite mixers 307 and 309. Also, it is assumed that
simple level sensors are used to ensure that the dispensing devices
that move materials from the feed bins 301 and 302 to the feed
mixers 305 operate in a manner that, in a preferred embodiment,
ensure each feed mixer 305 remains full at all (or substantially
all) times.
[0085] A sensor 303 monitors each feed stream. These sensors may
include, but are not limited to, devices that measure secondary
radiation such as a CMOS or CCD image sensors plus a source of
primary radiation including white or infrared light. Feed material
sensor data is then sent to the computer system 304. This data may
be used to detect variation in the composition of the feed stream.
Preferably, this information is used by the computer system 4 as an
adjustment factor in determining the feed rates to the composite
mixers 307 and 309, and final mixer 310.
[0086] Immediately after exiting the syngas production chamber 311,
and after any required cooling, a syngas analyzer 312 determines
the syngas production rate. Production data include, but is not
limited to, the determination of volumetric flow rate, hydrogen gas
concentration, and carbon monoxide concentration. Potential methods
for rapid syngas analysis include, but are not limited to, Raman
Spectroscopy and GC Mass Spectroscopy (GCMS). Data from the syngas
analyzer 312 is sent to the computer system 304.
[0087] After receiving continuous real-time data from the feed
controllers 306 and 308, the material sensors 303, and the syngas
analyzer 312, the computer system 304 then relates the target
production rate and target energy content data with the real-time
feed rate and composition data. The computer system 304 then
executes a computer program based, for example, on the equations
presented below, to maintain the syngas at the target production
rate and target energy content. As noted above, typically the
target production rate is controlled by adjusting the feed rate of
the material into the gasifier, whereas the target energy content
typically is controlled by having the computer system 304 inform
each feed controller 306 and 308 to dispense the appropriate amount
of the feed materials into the composite mixers 307, 309, and
310.
[0088] The number and organization of the feed bins and feed mixers
shown in FIG. 8 is also merely representative of the general
concept shown in FIG. 6, and the present invention should be deemed
to cover all such embodiments, however configured.
[0089] FIG. 9 illustrates a more simplified embodiment where only a
single feedstock Product 2 is added (blended or mixed) to a primary
feedstock, Product 1, in this case construction and demolition
waste (C&D). In the drawing the Product 1 feeder is illustrated
by reference number 400 and the Product 2 feeder is illustrated as
reference number 402. The materials are combined in blender/mixer
404 and provided to gasifier 406. The output syngas 410 is analyzed
to provide a gas analysis 412, which is then provided to the
computer system 414 to provide the one or more feedback control
signals 416 and/or 418 to the respective feeders.
[0090] In this example, the C&D waste is being processed in a
facility that may include several stages (not shown): C&D
handling and sorting, C&D pre-processing, C&D debris
post-processing, gasification, and, optionally,
post-gasification/energy generation. These stages may be carried
out in a single building, facility or enclosure, or in co-located
processing facilities. Thus, for example, the handling and sorting,
and pre-processing stages are performed in a first enclosure, while
the post-processing and gasification stages are carried out in a
second, nearby building, facility or enclosure. Preferably, the
C&D processing takes place in a continuous or
partially-continuous manner as bulk debris is received at the
processing facility. A representative end-to-end system of this
type is described in U.S. patent application Ser. No. 12/021,987,
filed Jan. 29, 2008, the disclosure of which is incorporated herein
by reference.
[0091] As noted above, an object of having multiple feeds is to
equalize the BTU content of the feed materials to the gasifier to
produce a constant or substantially constant BTU gas output. In
this example, construction and demolition wastes (C&D), which
have been appropriately sorted and dried, are provided as the main
feed component to the gasifier. Because it is a waste material, the
incoming BTU content ranges from approximately 5,000-7,000 BTU/lb;
thus, for a constant system feed rate, the energy content of the
output gas would vary percentage-wise equally. Preferably, the
product syngas has a content of approximately 325 BTU/lb. To
produce a constant BTU output, it is thus necessary to add a higher
BTU content material. In this example, this higher BTU content
material (Product 2) is waste rubber (e.g., chrome rubber), which
has a consistent content of more than 10,000 BTU/lb. The rubber is
blended or mixed with the C&D waste in blender/mixer 404. The
blend ratio may be set volumetrically, although this may not be an
optimal approach. Thus, preferably, the system uses one or more of
GCMS, infrared and other analytical equipment to measure for
hydrogen, carbon monoxide, methane and other hydrocarbons, as well
as for mass flow.
[0092] The results of the analysis 412 are fed to a combination
computer/PLC system 414, which utilizes the analytical data in
conjunction with mass flow and energy content of the various
species to determine a real-time (or near real-time) syngas energy
value. This energy value when compared to the desired value enables
the computer system 414 to produce a signal 418 to speed up or slow
down the high BTU feed stock or, in the case of a higher desired
mass flow, to enable the computer system 414 to produce a signal
416 to slow down the primary feed stock (and perhaps the rubber
feeder as well) while maintaining BTU content. These output signals
are produced in real-time (or substantially near real-time) to
minimize energy fluctuations in the syngas. Preferably, materials
are fed to the system with gravimetric feeders 400 and 402.
[0093] Of course, the particular type of waste material that is
added to the primary feed will vary depending on the primary feed
characteristics and BTU content, the availability of other feed
stocks, as well as the energy content of those additional
materials. Thus, for example, in appropriate circumstances
municipal solid waste (MSW) may be used as an additive, as its
energy content (approximately 4,000-5,000 BTU/lb) varies more than
most other waste streams. Most areas of the world produce MSW, so
it may be a convenient additive. Of course, higher BTU content
material availability will vary considerably depending on
location.
[0094] FIG. 10 shows another embodiment. The system utilized here
is an expansion of that shown in FIG. 9. Here, one or materials of
lower BTU content are fed with one or more high energy content
materials, such as waste plastics, paper, rubber, or sludge to
produce a constant output gas. In this example there are four
materials (500, 502, 504 and 506) although this is not a
limitation. The mentioning of specific high energy wastes is not to
be inclusive, but only an example of such feed stocks. Preferably,
the system described here also incorporates component availability
and switches automatically from one high energy product to another
as needed.
[0095] Representative mixing calculations are now described. In
particular, it can be shown via an energy balance on the syngas
production chamber 311 that the energy potential (E) of the feed
material entering the production chamber 311 must be equal to the
energy generated (R) by the combustion reaction within the chamber.
If X is the mass feed rate to the chamber 311 and H is the energy
potential per mass unit of the feed material, it can be shown the
incoming potential energy rate (E) is equal to the product of X and
H, which is equal to the energy R generated by the production
chamber:
E(energy/time)=X(mass/time).times.H(energy/mass)=R(energy/time)
(1)
Because a constant mass feed rate to the chamber 311 and a steady
state process is assumed, and because it is also assumed the energy
potential of the feed materials to the composite mixers (307, 309)
is constant, the cumulative mass feed rate of the mass streams
exiting the composite mixing tanks (307, 309) must be equal to mass
feed rate entering the chamber. Thus, if HL is the "below-target"
energy potential of the feed stream from the composite mixer 307
and HH is the "above-target" energy potential of the composite
mixer 309 and X.sub.b and X.sub.a are the respective mass rates
exiting the composite mixers 307 and 309, it can be shown that:
(HL(energy/mass).times.X.sub.a(mass/time))+(HH(energy/mass).times.X.sub.-
b(mass/time))=R(energy/time) (2)
[0096] A target energy generation level can be represented via the
following variables:
[0097] R.sub.t=target energy generation rate,
[0098] R.sub.1=lower limit energy generation rate, and
[0099] R.sub.u=upper limit energy generation rate.
[0100] Now, because the actual energy (R.sub.a) generated by the
production chamber 311 can be accurately deduced from composition
measurements made by the syngas analyzer 312, the variation in the
energy generation rate (R.sub.v) from the target level can be
established:
R.sub.v=R.sub.a-R.sub.t (3)
[0101] Consider if R.sub.v is positive. This indicates the feed
rate X.sub.a to composite mixer A (which has the lower energy
potential HL) must be increased and the feed rate X.sub.b to
composite mixer B (which has the higher energy potential HH) must
be decreased by an equivalent mass rate to decrease the overall
variation R.sub.v.
[0102] Ultimately, to produce an energy generation rate within a
target range, preferably calculations that employ differential
equations are iterated by the computer system. 304. Also, prior to
executing these calculations an initial design should be
established, based upon a target energy production range for
specific mass feed rate that specifies the volume of each mixing
tank. For example, for a given mass feed rate, larger mixing tanks
produce longer residence times for a given feed material, which
decreases variations in material concentration over time (which
subsequently decreases the rate of variation of energy generation
by the production chamber 311).
[0103] The following is a sample calculation. Using applied
differential equations and assuming perfect mixing due to the
relatively minute change in the overall composition within each
mixer caused by the addition of new feed material, it can be shown
that the time rate of change for a given feed material, A is given
by the following equation:
dA/dt=rate of amount gained-rate of amount lost (4)
[0104] Because the volume of any mixing container is known, i.e.,
constant, a differential equation can be created for each mixing
vessel that can render a solution for the mass of A present in a
mixing vessel at any given time. For example, if A is entering a
mixing vessel at 10 pounds per minute and there is 5 pounds of A in
the tank initially:
dA/dt=10-A/5 (5)
Solving this equation, it can be shown that:
A=50-25(e-t/5) (6)
Thus for the given feed rate, a set time can be entered to
determine the mass of A present in the system. This mass value can
then be multiplied by the syngas generation density, i.e., the
amount of syngas generated by unit of mass of A, to calculate the
syngas production rate for A.
[0105] The computer system 304 can execute similar calculations for
each feed material to determine its contribution to the overall
syngas production rate and then adjust each feed rate via the
controller modules 306 to optimize the target syngas production
rate based upon the sensor data. For example, if the syngas
analyzer 312 reports a syngas production rate that is below the
target range, the feed rate of the "above-target" materials can be
increased and the feed rate of the "below-target" materials can be
decreased to keep the syngas production rate within the target
range.
[0106] Further, although an embodiment of the invention has been
described in the context of an "above-target" and "below-target"
materials, there may be multiple such levels (such as below,
intermediate, above, or the like) or even just one level.
[0107] FIG. 7 illustrates a representative computer system 304. A
data processing system 200 suitable for storing and/or executing
program code will include at least one processor 202 coupled
directly or indirectly to memory elements through a system bus 205.
The memory elements can include local memory 204 employed during
actual execution of the program code, bulk storage 206, and cache
memories 208 that provide temporary storage of at least some
program code to reduce the number of times code must be retrieved
from bulk storage during execution. Input/output or I/O devices
(including but not limited to keyboards 210, displays 212, pointing
devices 214, etc.) can be coupled to the system either directly or
through intervening I/O controllers 216. Network adapters 218 may
also be coupled to the system to enable the data processing system
to become coupled to other data processing systems or devices
through intervening private or public networks 220.
[0108] The computer may be connected to another computer or system
over a network, such as wide area network (WAN), local area network
(LAN), protected network (e.g., VPN), a dedicated network, or some
combination thereof. More generally, the various system components
illustrated in FIG. 8 may be controlled with any collection of one
or more autonomous computers (together with their associated
software, systems, protocols and techniques) linked by a network or
networks. The control system calculations comprise a set of
preferably software-based functions (e.g., applications, processes,
execution threads, or the like) or firmware-based functions that
provide the described mixing method.
Example
[0109] Dried pelletized refuse derived fuel (RDF) with a capacity
of 250 tons per day (TPD) is processed in a 40-ton channel
induction reactor (Ajax Model VS-40), modified to have a sealed lid
and increased dimensions to provide additional head space. RDF at a
rate of 10.4 tons an hour (TPH) is fed into the reactor through a
feeding mechanism, consisting of a screw type educator feeder. This
feeder accomplishes two tasks: air extraction from the RDF, and
product movement with the required speed to the feeding tube. The
feeding tube is a graphitized alumina pipe with internal diameter
(ID) of 4''. It is installed in the center of the reactor lid.
[0110] The RDF feed material as received has moisture content of
about 35% and contains material of varying size. The feed material
is prepared as follows: it is dried using a Eagle II (available
from Sweet Manufacturing Company, Springfield, Ohio) to a moisture
level of 7%, sized using a shredder (Model # VVZ-310 available from
Vecoplan, LLC, High Point, N.C.) to an average size of about 1
inch, and air is extracted from the dried and sized feed material
using an extruder/feeder (Model # GPT2-400-0, manufactured by Komar
Industries, Columbus, Ohio), resulting in the feed material having
less than about 1% air by weight.
[0111] The composition of the prepared material is then analyzed
for C, H, O, Al, Si, Ca, Fe, Ni and other components and the heat
content thereof is predicted using a neutron beam analyzer (Model #
NBW-1 available from STS-Ratek, St. Petersburg, Russia).
[0112] The reactor lid is also equipped with oxygen and steam
lances and a gas outlet. The reactor is sealed from the atmosphere
and is initially charged with 40 tons of molten iron. Oxygen is
continuously fed into the reactor at a rate of 66,000 cubic feet an
hour (cft/hr). Organic materials are decomposed in the reactor with
formation of 325,000 cft/hr of H, 256,160 cft/hr of carbon monoxide
and 1700 lb/hr of vitreous organic material. Gaseous products exit
the reactor through the exhaust passage. The vitreous organic
material is accumulated in the form of slag layer on top of the
bath.
[0113] The temperature and level of the bath, the gas composition,
and the temperature and volume of the syngas leaving the reactor
are each measured. The composition of the syngas is continuously
analyzed for CO, H.sub.2, H.sub.2O, O.sub.2, H.sub.25 using a gas
analyzer (Model # MLT 4 available from Emerson, St Louis, Mo.). The
composition of the metal and the vitreous layers are intermittently
analyzed in a commercial metallurgical laboratory.
[0114] The results of these measurements are used to control
amounts of oxygen, steam, and/or co-feeds into the reactor. When
the temperature of the molten bath rises above desired level, steam
injection into reactor is activated and the endothermic steam shift
reaction results in temperature reduction of the process and
additional hydrogen production. When the compositional analysis of
the feed material indicates that it is below a predetermined heat
value, additional oxygen and/or scrap tires (which is a higher BTU
value co-feed than RDF) are injected into the reactor to maintain
the BTU value of the syngas in a range between 350 and 450 BTU/cu
ft.
[0115] After a predetermined amount of vitreous organic material
accumulates in the reactor, the level of the molten bath rises to
the desired level. Feed to the system is interrupted and oxygen
feed is gradually phased out. The reactor is purged of combustible
gases and a tap hole is drilled in the sidewall of the reactor at
the level of the original metal bath. All products accumulated in
the reactor above this hole are poured out into a specially
designed cart. The vitreous organic material and metal are later
separated with metal being available for sale to (e.g., steel
mills) and the vitreous organic material being available for use as
construction aggregate. After the tapping operation is completed
(which typically takes about 40-60 minutes), the tap hole is sealed
with a mud gun and processing of the waste into combustible gas
resumes.
[0116] While the above describes a particular order of operations
performed by certain embodiments of the invention, it should be
understood that such order is exemplary, as alternative embodiments
may perform the operations in a different order, combine certain
operations, overlap certain operations, or the like. References in
the specification to a given embodiment indicate that the
embodiment described may include a particular feature, structure,
or characteristic, but every embodiment may not necessarily include
the particular feature, structure, or characteristic. Further,
while given components of the system have been described
separately, one of ordinary skill will appreciate that some of the
functions may be combined or shared in given systems, machines,
devices, processes, instructions, program sequences, code portions,
and the like.
[0117] Having described our invention, what we now claim is set
forth below.
* * * * *