U.S. patent application number 14/258125 was filed with the patent office on 2014-08-14 for waste management system.
The applicant listed for this patent is Coldunell Limited. Invention is credited to John Gerard Sweeney.
Application Number | 20140223908 14/258125 |
Document ID | / |
Family ID | 51296456 |
Filed Date | 2014-08-14 |
United States Patent
Application |
20140223908 |
Kind Code |
A1 |
Sweeney; John Gerard |
August 14, 2014 |
Waste Management System
Abstract
A system and method of integrated waste management having a
source of a combustible waste material, a separator for separating
the combustible waste material from a recyclable material, an
airless drier for drying the combustible waste material to generate
a pyrolysis feedstock, and a pyrolyser for pyrolysing the pyrolysis
feedstock to form char and pyrogas. The system and method for power
generation may also use an oxidiser for the high-temperature
oxidation of syngas generated from the pyrolysis feedstock to
generate heat for power production.
Inventors: |
Sweeney; John Gerard; (Iver,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Coldunell Limited |
Esher |
|
GB |
|
|
Family ID: |
51296456 |
Appl. No.: |
14/258125 |
Filed: |
April 22, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13261112 |
Feb 14, 2012 |
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14258125 |
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Current U.S.
Class: |
60/645 ; 110/222;
110/224; 48/89; 48/99; 60/670 |
Current CPC
Class: |
F23G 5/006 20130101;
C10J 2300/0946 20130101; F23G 2201/80 20130101; F23G 2201/10
20130101; F23G 2201/40 20130101; F23G 2201/60 20130101; C10J
2300/0906 20130101; C10J 2300/0909 20130101; C10J 2300/1606
20130101; Y02E 20/12 20130101; F01K 23/067 20130101; F23G 5/02
20130101; C10J 2300/1675 20130101; Y02E 20/18 20130101; F23G 5/46
20130101; C10J 3/62 20130101; F23G 2201/303 20130101; F23G 2206/203
20130101 |
Class at
Publication: |
60/645 ; 110/222;
110/224; 60/670; 48/99; 48/89 |
International
Class: |
F01K 13/00 20060101
F01K013/00; C10J 3/80 20060101 C10J003/80; F01K 7/16 20060101
F01K007/16; F23G 5/033 20060101 F23G005/033; F23G 5/04 20060101
F23G005/04 |
Claims
1. An integrated waste management system, comprising: a source of a
combustible waste material; a separator for separating the
combustible waste material from a recyclable material; an airless
drier for drying the combustible waste material to generate a
pyrolysis feedstock; a pyrolyser for pyrolysing the pyrolysis
feedstock to form char and pyrolysis gas; a gasifier for converting
the char into syngas; and an outlet in said airless drier for
supplying heated steam output from the airless drier generated
during pyrolysis feedstock generation to the gasifier.
2. The integrated waste management system according to claim 1,
wherein the separator comprises one or more of a trommel, a
magnetic separator, a ballistic separator, an eddy current
separator, automated optical separation means and a shredder.
3. The integrated waste management system according to claim 2,
wherein the airless drier is adapted is for drying the combustible
waste material with super-heated steam as the drying medium.
4. The integrated waste management system according to claim 3,
wherein the airless drier is sealed to prevent the ingress of
atmospheric air.
5. The integrated waste management system according to claim 4,
wherein the airless drier comprises an insulating outer
surface.
6. A power generation system comprising the waste management system
according to claim 5, further comprising an oxidizer for the
high-temperature oxidation of syngas and/or pyrolysis gas generated
from the pyrolysis feedstock to generate heat for electrical power
production.
7. The power generation system according to claim 6, wherein the
power is electrical power.
8. The power generation system according to claim 7, wherein the
oxidizer comprises an outlet for supplying surplus heat to: (i) the
airless drier; and/or (ii) the pyrolyser.
9. The power generations system according to claim 8, wherein the
airless drier comprises an outlet for supplying steam evolved in
the drying step of the airless drier to the gasifier.
10. The power generation system according to claim 9, wherein the
system comprises a steam cycle apparatus.
11. The power generation system according to claim 10, wherein the
steam cycle apparatus comprises a steam turbine unit for electrical
power production.
12. The power generation system according to claim 11, further
comprising a heat recovery unit for supplying excess heat energy to
the airless drier.
13. The power generation system according to claim 11, further
comprising a heat recovery unit for supplying excess heat energy to
the airless drier from a steam cycle apparatus.
14. The power generation system according to claim 13, further
comprising a flue gas remediation unit for trapping pollutants.
15. An integrated method of waste management comprising: (a)
providing a source of a combustible waste material; (b) separating
the combustible waste material from a recyclable material present
in the source; (c) drying the combustible waste material in an
airless drier to generate a dried pyrolysis feedstock; (d)
pyrolysing the dried pyrolysis feedstock to form char and pyrolysis
gas; (e) converting the char into syngas in a gasifier; and (f)
supplying heated steam output from the airless drier generated
during pyrolysis feedstock generation to the gasifier.
16. The integrated method of waste management according to claim
15, wherein the source of combustible waste material is domestic
waste comprising food scraps, paper, cardboard, plastics, rubber,
garden waste, clothing fabric and/or wood.
17. The integrated method of waste management according to claim
16, wherein separation of the combustible waste material comprises
the use of one or more of a trommel, a magnetic separator, a
ballistic separator, an eddy current separator, optical separation
means and a shredder.
18. The integrated method of waste management according to claim
17, wherein the combustible waste material is dried in the airless
drier with the use of super-heated steam.
19. The integrated method of waste management according to claim
18, wherein the combustible waste material is dried to yield a
pyrolysis feedstock with a moisture content of 0 to 20% by
weight.
20. The integrated method of waste management according to claim
19, wherein the combustible waste material is dried to yield a
pyrolysis feedstock with a moisture content of 2 to 18% by
weight.
21. The integrated method of waste management according to claim
20, wherein the combustible waste material is dried to yield a
pyrolysis feedstock with a moisture content of 5 to 15% by
weight.
22. The integrated method of waste management according to claim
15, further comprising power generation.
23. The integrated method of waste management according to claim
22, wherein the power is electrical power.
24. The integrated method of waste management according to claim
23, further comprising the steps of: (g) oxidizing the syngas and
pyrolysis gas at high-temperature in an oxidizer to generate heat
for power generation.
25. The integrated method of waste management according to claim
24, wherein electrical power generation comprises the use of a
steam cycle.
Description
[0001] The present invention relates to a waste management system
and to a power generation system including the waste management
system. The waste management system of the present invention
generally relates to waste materials which include combustible
matter.
[0002] The clean, effective and environmentally-friendly disposal
of domestic and industrial waste materials, including combustible
waste materials, provides on-going challenges for industry,
national governments and local authorities.
[0003] Waste disposal methods such as burying waste in landfills at
municipal tips have many drawbacks. These include the need for
large tracts of land which may otherwise be better utilised, the
prospect of wind-blown litter, the attraction to rats and other
vermin which may provide a health risk to the community, unpleasant
odours and the generation of greenhouse gases such as methane which
may result from the biodegradation of waste.
[0004] Other disposal methods include incineration which involves
the combustion of the waste material. Although often convenient for
the disposal of hazardous materials, incineration is an unpopular
method of waste disposal where there is the prospect of toxic gases
and other pollution being released into the atmosphere. Traditional
incinerators are also known to have large carbon footprints and
high profiles.
[0005] As an alternative to the waste disposal methods outlined
above, the use of combustible waste materials as fuels for
generating energy is known. In a world of diminishing fossil fuel
reserves, the uncertainty of regular supplies of gas and oil often
due to geopolitical factors, and the environmental risks posed by
nuclear energy, generating energy from waste materials is
considered an attractive field of endeavour. This is because it
addresses both the problems of waste management and the provision
of alternative fuel sources. However, many of the known methods are
resource, cost and energy inefficient. Accordingly, alternative
means of waste management and the conversion of waste materials
into sources of energy have been sought which are resource, cost
and energy efficient. The present invention aims to achieve some of
these means.
[0006] According to the present invention there is provided an
integrated waste management system, comprising:
[0007] a source of a combustible waste material;
[0008] a separator for separating the combustible waste material
from a recyclable material;
[0009] an airless drier for drying the combustible waste material
to generate a pyrolysis feedstock; and
[0010] a pyrolyser for pyrolysing the pyrolysis feedstock to form
char and pyrogas.
[0011] Further according to the invention, there is provided an
integrated method of waste management comprising:
[0012] (a) providing a source of a combustible waste material;
[0013] (b) optionally separating the combustible waste material
from a recyclable material present in the source;
[0014] (c) drying the combustible waste material in an airless
drier to generate a dried pyrolysis feedstock; and
[0015] (d) pyrolysing the dried pyrolysis feedstock to form char
and pyrogas.
[0016] The integrated system and method of waste management of the
present invention provide a cost and energy efficient means of
processing industrial and domestic waste materials, whereby
combustible materials suitable for downstream conversion into
energy are obtained and waste materials not considered suitable for
energy conversion, but which are recyclable, can be separated and
processed separately in a recycling plant. Accordingly, minimal
compromise of eco-friendly recycling efforts can be achieved with
the present invention thus contributing to the overall ecological
benefits of waste material processing.
[0017] Pyrolytic processes are generally more efficient the lower
the moisture content of the material being pyrolysed. In the
present invention, the use of an airless drier provides significant
overall energy savings in terms of running the system, as
approximately 30% less energy is required to operate an airless
drier per unit weight of material being dried compared to a
conventional air drier. Furthermore, reduced waste material drying
times typically of 40 to 50 minutes less are required with the
airless drier compared with other forms of drying, thereby adding
to the overall efficiency of the system in terms of processing
times.
[0018] Further according to the invention, there is provided a
power generation system comprising the waste management system
according to the invention and further comprising an oxidiser for
the high-temperature oxidation of syngas and pyrogas generated from
the pyrolysis feedstock to generate heat for power production.
[0019] Even further according to the invention, there is provided a
method of power generation according to the invention comprising
the integrated method of waste management according to the
invention, and preferably further comprising the steps of:
[0020] (d) gasifying the char to generate syngas; and
[0021] (e) oxidising the syngas and/or pyrogas at high-temperature
in an oxidiser to generate heat for power generation.
[0022] By having an integrated power generation system comprising
an integrated waste management system according to the invention,
all of the steps from the deposit at a waste processing plant of a
source of a combustible waste material through to power generation
(eg, electrical power generation from a conventional steam turbine
unit) can be carried out at one site. This provides significant
cost and resource savings because it reduces transportation costs
(eg, between a waste separation plant, a waste drying plant and
pyrolysis, gasification and oxidation/power generation plants) and
it also enables improved overall energy efficiency through the
provision of heat energy feedback loops between the various
components of the systems.
[0023] Furthermore, combustion processes known in the art for power
generation generally undergo pyrolysis, gasification and oxidation
of syngas (or other combustion gases) as a single step process. In
contrast, the system and method of power generation according to
the present invention is adapted to separate the pyrolysis of a
dried waste material pyrolysis feedstock, the gasification of the
pyrolysis products and oxidation of the combustible gases from the
gasification step. This allows a high degree of control over each
step than in a single step process such as that which takes place
in a conventional mass burn incinerator used for power
generation.
[0024] Furthermore, in the present invention, preferably all of the
combustible waste material is heated in the pyrolyser or gasifier
to a uniform temperature (typically 250 to 600.degree. C.) not
exceeding 900.degree. C. In conventional incineration on a hearth,
there are often hot spots and cold spots resulting in some
combustible waste material not being heated sufficiently and
remaining unburnt in the resulting ash residue. Conversely, some of
the combustible waste material may be overheated and may release
toxic gaseous combustion by-products. In contrast, in the present
invention it can be ensured that substantially all of the
combustible waste material is thermally decomposed in the pyrolyser
or gasifier. Also, that essentially none of the combustible waste
material is overheated so that gaseous and/or volatile toxic
pollutants are kept to a minimum.
[0025] Additionally, in accordance with the invention, combustion
(oxidation) in the oxidiser is with a medium calorific value gas
(ie, syngas and/or pyrogas) in a highly controlled oxidising
environment with uniform oxidation temperatures. In this manner,
hot spots and cold spots are again kept to a minimum or eliminated
compared to the combustion zone in a conventional mass burn
incinerator thereby resulting in substantially complete combustion
of the gases with lower concentrations of carbon monoxide and
volatile organic compounds in the exhaust gases emanating from the
oxidiser. Furthermore, a uniform oxidation temperature results in
the generation of lower levels of temperature-generated nitrogen
oxides (thermal NO.sub.x), while the pyrolysis and gasification
processes due to their reducing nature subdue the generation of
fuel-generated nitrogen oxides (fuel NO.sub.x). Accordingly, the
nitrogen oxide levels in the exhaust gases of the oxidiser used in
the present invention are typically lower than that of a
conventional mass burn incinerator.
[0026] Preferably, the separator used in accordance with the
invention comprises one or more of a trommel, a magnetic separator,
a ballistic separator, an eddy current separator, optical
separation means and a shredder. This enables the adaptability of
the invention to separating different types of waste dependent upon
the waste composition. For example, waste from a source containing
only household biowaste and paper-based waste may typically only
require a separator comprising a trommel and a shredder. On the
other hand, the same household biowaste which also contained
recyclable plastics materials (eg, bottles, food wrappers, etc) may
also include an automated optical separation component to separate
these recyclable materials from the waste. Prior to separation of
the combustible waste material into its various components, an
automated bag opener may be used to open bags of waste material
transported to a waste management plant from an external location
such as a municipal refuse tip.
[0027] Preferably, the airless drier dries the combustible waste
material with super-heated steam (typically at 135 to 145.degree.
C.) as the drying medium. In the airless drier, preferably drying
is conducted in the absence of oxygen to prevent the combustion of
the combustible waste material. Accordingly, preferably the airless
drier substantially prevents the ingress of atmospheric air during
a drying operation. To keep heat loss to a minimum, preferably the
airless drier comprises an insulating outer surface to retain heat
and to improve the overall energy efficiency of the system. Airless
drying systems known in the art are described in GB 2 281 383 A and
GB 2 378 498 A.
[0028] In the systems and methods of the invention, the combustible
waste material typically has an initial moisture (eg, H.sub.2O)
content in the range of 30 to 40% by weight. After drying of the
combustible waste material in the airless drier, preferably the
pyrolysis feedstock has a moisture content of 0 to 20% by weight,
more preferably 2 to 18% by weight, and even more preferably 5 to
15% by weight.
[0029] Preferably, the waste management system further comprises a
pyrolyser for the pyrolysis feedstock to pyrolyse the dried
combustible waste material and form char and pyrogas. Preferably,
the pyrolysis of the feedstock takes place at a temperature in the
range of 250 to 600.degree. C. Char is the solid residue product of
the incomplete combustion of organic materials. Pyrogas is
typically defined as a combination of gases including methane,
water vapour, carbon monoxide and hydrogen in addition to
non-combusted volatile organic compounds present in the waste
materials, including tars and other high molecular weight
components.
[0030] Preferably, the waste management system further comprises a
gasifier for converting the char and/or pyrogas into syngas by a
gasification process. Syngas (otherwise known as "synthesis gas")
is defined as a pure or near pure mixture of carbon monoxide and
hydrogen generated from the high-temperature reaction of carbon
present in char or other organic compounds with water steam and air
or oxygen. Preferably, gasification takes place at a temperature in
the range of 850 to 900.degree. C.
[0031] In one aspect of the invention, the airless drier comprises
the pyrolyser. That is, the airless drier can be adapted with
higher temperature (eg, 250 to 600.degree. C.) settings than for
its drying mode (eg, 110 to 150.degree. C.) to act as a pyrolysis
apparatus. This has the benefit of having one less component
present in the system according to the invention, thus providing
waste management plant space and cost savings.
[0032] Preferably, the integrated waste management system includes
an airless drier which generates heated steam output derived from
the moisture extracted from the combustible waste material during
the drying process, wherein a portion of the heated steam output
which is otherwise released into the atmosphere may be supplied to
the gasifier to assist with the energy and reaction requirements of
the gasifier by providing heat and water steam. This feature can
contribute to the overall energy efficiency of the system according
to the invention.
[0033] Preferably, the power generated according to the power
generation system and method of the invention is electrical power.
Preferably, electrical power production comprises the use of a
steam cycle apparatus. The steam cycle apparatus may be a
conventional steam turbine unit well-known to the person skilled in
the art. A portion of the heated steam output of the airless drier
can be used to pre-heat the steam cycle of a steam turbine unit.
Furthermore, the steam cycle apparatus may be adapted to direct
heat energy to assist the energy requirements of the airless drier.
This may be achieved by a direct transfer of heat energy or via a
heat retention unit. Again, each of these features may assist in
contributing to the overall energy efficiency of the systems
according to the invention.
[0034] The steam turbine unit will typically comprise a boiler
designed to rapidly quench the exhaust gases which are generated in
the oxidiser. Typically, this quenching of exhaust gas temperature
is from 450.degree. C. to 200.degree. C. Quenching over this
temperature range preferably takes place in less than about 0.5
seconds. Rapid quenching of the exhaust gases is to minimise the
potential for the de novo synthesis of toxic compounds such as
dioxins and furans in the boiler, which may be released into the
atmosphere creating a pollution hazard. Such de novo synthesis is
also minimised because of the effectiveness of the sequential steps
(eg, controlled temperature) of pyrolysis, gasification and
oxidation steps of the power generation system of the invention,
which assists in destroying the precursors of de novo synthesis at
each step.
[0035] Preferably, the power generation system of the invention
further comprises a flue gas remediation unit for trapping
pollutants released in either the pyrolysis, gasification or
oxidation steps. This is because environmental pollution
legislation is likely to require flue gas remediation of acid gases
(eg, HCl, SO.sub.x species, HF, etc), the removal of particulates
and the reduction of NO.sub.x species from exhaust gases emanating
from the oxidiser and/or steam turbine unit employed in the present
invention. This can be achieved by means of conventional wet or dry
scrubbers. In particular, a sodium bicarbonate reagent in addition
to a bag filter may be used for the remediation of HCl, SO.sub.2
and particulate matter from exhaust gases. The use of a selective
catalytic reduction unit can be used for the remediation of
NO.sub.x. A temperature of about 180 to 220.degree. C., and
preferably about 200.degree. C., is typically the optimal
temperature for both of the remediation processes.
[0036] If flue gases are exhausted from the steam turbine unit at
greater than 200.degree. C., energy is wasted. Accordingly, a heat
recovery unit may be incorporated in the systems according to the
invention typically downstream of a steam turbine unit. In
practice, the heat recovery unit cools down the exhaust gases to
about 140.degree. C., thereby providing the option of directing
heat energy to the airless drier for the heating of the superheated
steam heating medium. This improves the overall efficiency of a
plant operating the system according to the invention. Typically,
140.degree. C. is selected as a suitable exhaust flue gas exit
temperature. This helps to prevent unsightly pluming at a stack
outlet, acid gas condensation and as well provides heat to the
airless drier with a high temperature differential.
[0037] Alternatively, power may be generated according to the
invention using apparatus utilising the organic rankine cycle, the
stirling cycle, the brayton cycle, the direct combustion of syngas
in a gas engine or a gas turbine, or in a fuel cell. Also, the
provision of heat in the form of steam or hot water may be
generated for process use or for refrigeration using absorption
chillers.
[0038] In an aspect of the invention, the oxidiser preferably
comprises an outlet and means for supplying surplus heat to the
airless drier and/or the pyrolyser. This can contribute to the
overall energy and operational efficiency of the system and enables
the system to operate when local domestic power demand may be
reduced (eg, at night time), but the on-going production of the
pyrolysis feedstock, pyrogas, char and syngas is desired.
[0039] The source of the combustible waste material may be any
domestic or industrial waste containing combustible materials. Such
materials may be food scraps, paper, cardboard, plastics, rubber,
clothing fabrics, garden waste and building materials such as wood.
The combustible waste material is preferably an organic
material.
[0040] The preparation of the combustible waste material for drying
in the airless drier comprises the use of a separator. The
separator may include one or more components adapted for separating
waste materials with different physical properties. In particular,
the separator may include a trommel (a rotatable cylinder
comprising holes for separating materials by a pre-determined size)
in series or alone for sorting the waste material by size, a
ballistic separator for sorting the waste material by weight,
magnets for extracting and eliminating ferrous metallic waste, an
eddy current separator for extracting and eliminating non-ferrous
metallic waste and an automated optical separator for extracting
recyclable materials, such as plastics and glass. Valuable metallic
wastes and recyclable plastics materials may be shipped elsewhere
for recycling. Furthermore, waste material considered too large or
too heavy for the airless drying process may be transferred to a
shredder for size and weight reduction as appropriate prior to
drying.
[0041] As an example of a separation step for the combustible waste
material used in the system and methods according to the invention,
a shipment of waste from a domestic refuse tip may be deposited in
a trommel having holes of a pre-determined size (eg, 80 mm in
diameter) in its wall. Rotation of the trammel about its
longitudinal axis results in separation of the combustible waste
material into a fine waste component (eg, <80 mm) and a bulky
waste component (eg, >80 mm) dependent on the diameter of the
trommel wall holes. The fine waste component is subjected to a
magnetic separator for the extraction of non-combustible ferrous
metals. It is then transferred to a vessel ready for feeding to the
airless drier. The bulky waste component is processed so that
metals, plastics, glass and other recyclable and/or non-combustible
components are removed. The processed bulky component is then
subjected to an automated optical separator to remove the remaining
recyclable components and is then fed to a shredder for conversion
to a material of similar particle size to the fine waste component.
The shredded bulky waste component is then transferred to the
vessel containing the fine waste component ready for drying in the
airless drier.
[0042] The airless dryer used in the present invention may employ
dry superheated steam as the heating medium for drying the
combustible waste material. The use of super-heated steam in the
airless drier has many benefits over a conventional air drier as
follows.
[0043] Because the specific heat capacity of steam is more than
twice that of air, more than twice the amount of heat can be
transferred to the product being dried for the same mass flow of
steam compared to heated air. As a result, with the same
temperature differential between the moist combustible organic
waste material and the drying medium, the fan power required to
achieve a given heat transfer may be more than halved.
[0044] Further benefits of using super-heated steam are that due to
its lower viscosity than air (about 50% lower), it is able to
percolate through the combustible organic waste material being
dried, thereby speeding up the drying process.
[0045] The airless dryer is typically a closed system which
operates on full recirculation principles and not a combination of
re-circulated water vapour/steam combined with ambient fresh air
introduced during drying from outside the dryer. Furthermore,
indirect fired heat exchangers may be used to prevent the ingress
into the airless drier of ambient fresh air which may lead to
undesirable combustion of the material being dried. Further, to
prevent the ingress of ambient air (or significant quantities
thereof) and steam leakage, the airless drier should be constructed
with a high level of air tightness. The absence of
oxygen-containing air in the drier during the drying process helps
prevents the combustion or explosion of flammable products present
in the combustible organic waste material during drying. The
airless drier may be insulated to help prevent heat loss.
[0046] The pyrolyser indirectly heats the combustible waste
material to a high temperature (typically at about 600.degree. C.,
but generally in the range of 250 to 600.degree. C.) in the absence
of air or oxygen. This may be achieved by passing the dried
combustible waste material (pyrolysis feedstock) through a heated
pyrolysis tube by means of an auger. The pyrolysis tube is
contained within a pyrolysis chamber through which hot exhaust
gases from the outlet of the oxidiser or another source may be
passed. The hot exhaust gases pass over an outer surface of the
pyrolysis tube and transfer heat to the tube by convection and
radiation. The hot pyrolysis tube then transfers heat into the
combustible waste material by conduction and radiation from an
inner surface of the inner tube wall of the tube. The heat energy
heats the combustible waste material typically to about 600.degree.
C. and thermally degrades the material to pyrogas and char. The
absence of air or oxygen prevents the combustible waste material
from combusting within the pyrolysis tube. The benefits of
employing the pyrolyser in the present invention include the
production of an excellent pyrolysis feedstock for the gasifier
which is dry, hot, pre-pyrolysed and homogenous. This makes the
subsequent operation of the gasifier simpler and more
efficient.
[0047] Preferably, the pyrolysis chamber comprises an insulating
outer surface to retain heat and to improve the overall energy
efficiency of the systems and methods according to the
invention.
[0048] In another aspect of the invention, the pyrolyser may have a
modular design with a single pyrolysis tube or a plurality of
pyrolysis tubes contained within a pyrolysis chamber and/or one
pyrolysis chamber or a plurality of pyrolysis chambers. These
arrangements can help to optimise the surface area in the pyrolyser
to assist in the heat transfer from the heated gases from the
outlet of the oxidiser or other source to the combustible waste
material being pyrolysed, thereby improving the energy efficiency
of the system.
[0049] The gasifier receives the char and pyrogas from the
pyrolysis tube or tubes. The char typically exits the pyrolyser
from an outlet in a pyrolysis tube and is transferred into the
gasifier forming a char bed at a bottom inner surface of the
gasifier. The gasifier is preferably an updraft gasifier type,
wherein steam and air are injected at a lower surface of the char
bed adjacent a bottom inner surface of the gasifier and percolates
upwards through the char undergoing various chemical reactions and
reducing the steam and char to syngas comprising mostly carbon
monoxide and hydrogen. This reaction typically occurs at about
850.degree. C. and is self-regulating by means of the endothermic
and exothermic nature of competing reactions and their different
reaction rates at different temperatures. The syngas combines with
pyrogas from the pyrolyser in the headspace above the gasifier char
bed and all gases are passed to the oxidiser by a pipe system.
Residual ash containing a small amount of unreacted carbon is
discharged from an outlet in the bottom inner surface of the
gasifier into an airtight ash container to prevent uncontrolled
ingress of air into the bottom of the gasifier. The residual ash is
disposed of.
[0050] The advantage of using an updraft gasifier is that it
enables a simple gasifier design and is less sensitive to particle
size, homogeneity and moisture content than other types of
gasifiers such as downdraft gasifiers or fluidised bed gasifier.
The simple design of the updraft gasifier makes the gasifier easier
to operate, more reliable and cheaper to build which are all
advantages over other types of gasifier. However, a downdraft
gasifier or a fluidised bed gasifier could if necessary also be
used in accordance with the invention.
[0051] An updraft gasifier may further include a cyclone inducer
for the headspace gases. This facilitates a very low particulate
loading in the syngas or pyrogas which is transferred to the
oxidiser for oxidising. The transfer of low levels of particulate
material from the char present in the gasifier to the oxidiser
further assists in minimising undesirable oxidation by-products
from the exhaust gases of the oxidiser.
[0052] In one aspect of the invention, the gasifier may receive
steam for driving the gasification process from the outlet of the
airless drier in order to improve the overall energy efficiency of
the systems and methods according to the invention.
[0053] Preferably the gasification chamber comprises an insulating
outer surface to retain heat and to improve the overall energy
efficiency of the systems and methods according to the
invention.
[0054] In another aspect of the invention, the arrangement of the
pyrolyser and gasifier may be modular such that one pyrolysis tube
or a plurality of pyrolysis tubes may feed a gasifier and/or one
gasifier chamber or a plurality of gasifier chambers may provide
syngas to the oxidiser.
[0055] Syngas and pyrogas from the gasifier are supplied to the
oxidiser by pipe. The oxidiser mixes the syngas and pyrogas with
air where it is oxidised at high temperature to release chemical
energy in the form of heat. The oxidiser outlet temperature is
controlled by adjusting the amount of excess combustion air that is
introduced into the oxidiser. Good combustion is achieved by
ensuring that the syngas (or syngas/pyrogas mixture) and combustion
air are mixed well in a turbulent (eg, cyclonic) environment with a
long residence time at a high temperature. Typically, during the
oxidation process, the oxidiser temperature is maintained at about
1250.degree. C., but it can be operated at temperatures as low as
850.degree.C. Typically, the residence time of the syngas (or
syngas/pyrogas mixture) within the oxidiser is greater than 2
seconds. Typically, good mixing and turbulence are achieved by
injecting the combustion air into the oxidiser at high velocity
(greater than 20 m/s) and directing the jet of combustion air (or
plurality of combustion air jets) into the centre of a syngas (or
syngas/pyrogas mixture) injection port. The air and syngas (or
syngas/pyrogas mixture) is injected tangentially to induce cyclonic
rotation of the exhaust gases within the oxidiser. This further
mixes the combusted exhaust gases and may also assist in trapping
particulate materials present in the exhaust gases leading to a
cleaner overall process.
[0056] Preferably, the oxidiser comprises an insulating outer
surface to retain heat and to improve the overall energy efficiency
of the systems and methods according to the invention.
[0057] Preferably, the system according to the invention (eg, in
the form of a waste management or power generation plant) is
maintained under negative pressure. This may be achieved with the
use of one or more induced draft (ID) fans. The use of the ID fans
helps to ensure process safety where a leak or other failure in the
system does not result in gases exiting the system, but atmospheric
air enters instead. Care is generally taken to back-up an ID fan
function so that a plant employing the system of the invention is
not left operating (and producing gas) without some negative
pressure being maintained.
[0058] Specific embodiments of the present invention are further
described with reference to the drawings, in which:
[0059] FIG. 1 is a schematic diagram of an embodiment of a power
generation system according to the invention comprising a waste
management system according to the invention.
[0060] FIG. 2a is a schematic diagram of an embodiment of a waste
management system according to the invention showing the
preparation of an airless drier (wet) feedstock.
[0061] FIG. 2b is a schematic diagram of a power generation system
according to the invention comprising a waste management system
according to the invention following on from the embodiment of FIG.
2a with treatment of the airless drier (wet) feedstock through to
power generation.
[0062] Referring to FIG. 1, there is an electrical power generation
system 1 having a combustible waste material source 2, a waste
separator 3 for the combustible waste material and an airless drier
4 for drying the combustible waste material (not shown) to yield a
pyrolysis feedstock (not shown).
[0063] System 1 has a pyrolyser 5 for producing char and pyrogas
(not shown) from the pyrolysis feedstock, a gasifier 6 for
producing syngas (not shown) from the char, and an oxidiser 7 for
the high temperature (eg, .about.1250.degree. C.) oxidation of the
syngas and pyrogas in the presence of air to produce heat as
depicted by arrow 8. The heat is used to generate electrical power
from a conventional steam turbine unit 9.
[0064] In use, combustible waste material from source 2 is supplied
along belt 10 to separation means 3 for separation into a
combustible waste component and other waste materials of value
including recyclable materials not for combustion, such as metal,
glass, plastics, etc (not shown). The combustible waste component
is then fed along belt 11 to airless drier 4 where it is dried at
110 to 150.degree. C. using super-heated steam, until substantially
all of the moisture (ie, primarily water) is removed from the
combustible waste to yield the pyrolysis feedstock.
[0065] The pyrolysis feedstock is transferred to pyrolyser 5 along
enclosed belt 12 for pyrolysis in an oxygen-free atmosphere at
about 600.degree. C. Pyrolysis results in a mixture of char and
pyrogas (not shown). The char and pyrogas are transferred to
gasifier 6 along pipe 13. The char is gasified in gasifier 6 at
about 850.degree. C. resulting in hydrogen and carbon monoxide
gaseous products (not shown) otherwise referred to as syngas. In an
alternative embodiment, the airless drier 4 can also act as the
pyrolysis apparatus when its operating temperature is increased to
600.degree. C.
[0066] The syngas and pyrogas may alternatively be stored for later
use or else are transferred to oxidiser 7 along pipe 14 where
combustion of the syngas and pyrogas takes place at about
1250.degree. C. generating heat depicted by arrow 8 for driving
steam turbine unit 9. Steam turbine unit 9 generates electrical
power which is fed into electrical grid 15, which may be a
localised grid (eg, in a factory or processing plant) or else part
of a domestic power supply grid.
[0067] Dependent upon the current energy requirements, at various
stages of system 1 excess heat energy 16,26 released by airless
drier 4 or excess heat energy 17 released by oxidiser 7 can be
selectively directed to assist the energy requirements of other
components of system 1. Specifically, heat energy 16 in the form of
steam evaporate can be directed to gasifier 6. Heat energy 26 in
the form of steam evaporate can be directed to steam turbine unit 9
to preheat condensate return within the steam turbine unit. Heat
energy 17 from oxidiser 7 can be directed to pyrolyser 5.
Furthermore, excess heat energy 18 in the form of steam evaporate
from turbine unit 9 can be directed to airless drier 4. Excess heat
as depicted by arrow 23 can be be transferred to heat recovery unit
24 for transfer to airless drier 4 as depicted by arrow 25. These
options for heat energy feedback enables a series of efficient heat
energy feedback mechanisms contributing to the overall energy
efficiency and adaptability of system 1.
[0068] To further enable the energy efficiency of system 1, the
various components may be partially or fully covered with
heat-resistant insulating layer 19,20,21,22 for improving heat
retention in system 1.
[0069] Referring to FIG. 2a there is a schematic overview of an
aspect of an further embodiment of the waste management system
according to the invention, wherein a wet feedstock is generated
for the airless drier (refer FIG. 2b). FIG. 2a shows the sequence
of providing a combustible waste material and separation of the
material into recyclable (combustible) components resulting in the
drier (wet) feed stock as well as non-combustible components (eg,
metals) or combustible waste components not desirable for
combustion (eg, plastics).
[0070] Referring to FIG. 2b there is a schematic overview of the
continuation of the waste management process according to an
embodiment of the present invention wherein the drier (wet) feed
stock prepared according to the embodiment shown in FIG. 2a is
dried in an airless drier to yield a dried feedstock. The dried
feedstock is pyrolysed to form char and pyrogas, the char and
pyrogas is gasified to form pyrogas and syngas as well as an ash
residue waste, and then the pyrogas/syngas mixture is mixed in a
cyclone device prior to oxidisation with air to yield a high
temperature exhaust for heating a boiler to drive a conventional
turbine for power generation.
* * * * *