U.S. patent application number 12/848451 was filed with the patent office on 2011-02-17 for waste processing system.
Invention is credited to Scott Edmondson, David Sweeting, Bruce Toase.
Application Number | 20110036280 12/848451 |
Document ID | / |
Family ID | 43587819 |
Filed Date | 2011-02-17 |
United States Patent
Application |
20110036280 |
Kind Code |
A1 |
Toase; Bruce ; et
al. |
February 17, 2011 |
WASTE PROCESSING SYSTEM
Abstract
A small scale integrated waste processing system for the thermal
destructions of waste. The system comprises a compactor (12) for
densifying waste and expressing air, a pyrolyzer (13) to receive
waste delivered from the compactor, a gasifier (14) with an ash
vessel (23) that receives dried waste, and an oxidizer (15)
receiving gas from the gasifier to be combusted. Heat energy from
the oxidizer can be routed back to the pyrolyzer.
Inventors: |
Toase; Bruce; (Portishead,
GB) ; Sweeting; David; (Redland, GB) ;
Edmondson; Scott; (Great Sommerford, GB) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ, LLP
P O BOX 2207
WILMINGTON
DE
19899
US
|
Family ID: |
43587819 |
Appl. No.: |
12/848451 |
Filed: |
August 2, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61233239 |
Aug 12, 2009 |
|
|
|
Current U.S.
Class: |
110/235 ;
110/346 |
Current CPC
Class: |
F23G 5/46 20130101; F23G
2206/10 20130101; Y02E 20/12 20130101; F23G 2201/303 20130101; F23G
5/033 20130101; F23G 2900/50209 20130101; F23G 2206/203 20130101;
F23G 2201/304 20130101; F23G 2201/40 20130101; F23G 5/027 20130101;
F23G 2201/603 20130101; F23G 2201/80 20130101; F23G 5/50 20130101;
F23G 2206/202 20130101 |
Class at
Publication: |
110/235 ;
110/346 |
International
Class: |
F23G 5/00 20060101
F23G005/00 |
Claims
1. A waste processing system comprising a compactor for densifying
waste and expressing air, a pyrolyzer to receive waste delivered
from said compactor, a gasifier receiving waste from said
pyrolyzer, and an oxidizer receiving gas from the gasifier to be
combusted.
2. The waste processing system of claim 1 wherein the pyrolyzer
includes a screw and a feed tube, wherein said screw is arranged
therethrough said feed tube.
3. The waste processing system of claim 1 wherein energy from an
output gas of the oxidiser is used to provide heat to the
pyrolyzer.
4. The waste processing system of claim 1 further comprising a heat
reclaimer to process excess heat from the oxidizer.
5. The waste processing system of claim 4 wherein the heat
reclaimer is an indirect heat exchanger.
6. The waste processing system of claim 4 wherein energy from the
heat reclaimer is used for absorption chilling and/or air
conditioning and/or refrigeration and/or space heating and/or
process heating and/or distillation and/or desalination.
7. The waste processing system of claim 4 wherein energy from the
heat reclaimer is used for electrical energy generation.
8. The waste processing system of claim 1 including an ash vessel
to receive ash from the pyrolyzer or gasifier.
9. The waste processing system of claim 2 wherein the feed tube of
the pyrolyzer is anchored to the gasifier to allow said feed tube
to expand towards its free end.
10. The waste processing system of claim 9 further including a main
pyrolyzer tube and an expansion gaiter, wherein the feed tube is
inserted into said main pyrolyzer tube with a clearance and sealed
by said expansion gaiter.
11. The waste processing system of claim 1 wherein the pyrolyzer
operates at over 500.degree. C.
12. The waste processing system of claim 1 wherein the oxidizer
operates at over 850.degree. C.
13. The waste processing system of claim 1 wherein the equipment
parts of said system are housed within two ISO containers for
mobility.
14. A method of processing waste comprising densifying waste and
expressing air therefrom in a compactor, delivering the waste from
a compactor to a pyrolyzer, heating the waste for thermal
decomposition of organic material by action of heat alone in the
pyrolyzer, receiving waste from the pyrolyzer in a gasifier,
gasifying waste in the gasifier, receiving the gas from the
gasifier in an oxidiser, and oxidising the gas to be combusted.
15. The method of claim 14 including processing excess heat from
the pyrolyzer in a heat reclaimer.
16. The method of claim 15 including using the energy from the heat
reclaimer for a process selected from the group consisting of
absorption chilling, air conditioning, refrigeration, space
heating, process heating, distillation and desalination.
17. The method of claim 15 including using the energy from the heat
reclaimer for electrical energy generation.
18. The method of claim 14 including operating the pyrolyzer at a
temperature of over 500.degree. C.
19. The method of claim 14 including operating the oxidiser at a
temperature of over 850.degree. C.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on provisional application Ser.
No. 61/233,239, filed Aug. 12, 2009, all of the details of which
are incorporated herein by reference thereto.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a waste processing
system.
[0003] Modern methods for the thermal destruction of waste, to meet
environmental standards, are usually conducted on a large scale to
be economical and safe. Therefore, in smaller local applications,
waste management solutions are more limited. Incineration is a
common method of waste destruction/reduction in larger
applications, however, such a process has become socially
unacceptable due to a large footprint (both carbon footprint and
physical space required), high profile, potential for air and water
pollution, and reliance on vehicles with associated emissions and
CO.sub.2.
[0004] An example of a situation where smaller scale thermal
destruction is desirable is on board an ocean going ship, at a
hospital, or in a mobile situation such as for military
applications where a base may be relocated with some regularity.
Furthermore, such an operation can be utilized in any business that
wishes to treat its waste at source.
SUMMARY OF THE INVENTION
[0005] Accordingly, the present invention seeks to provide a waste
processing system for use where there is a local need for effective
waste disposal and a potential to use energy generated by the
process. More particularly, it is an object of the present
invention to provide a relatively small scale integrated waste
management system for thermal destruction of waste.
[0006] The waste processing system according to the invention
comprises a compactor for densifying waste and expressing air, a
pyrolyzer to receive waste delivered from said compactor, a
gasifier receiving waste from said pyrolyzer, and an oxidiser
receiving gas from the gasifier to be combusted.
[0007] It is intended that the invention is a continuous feed waste
processing system.
[0008] Preferably the pyrolyzer processes waste therethrough by use
of a screw arranged through a main tube.
[0009] Preferably ash is removed from the gasifier stage via an ash
vessel wherein ash can accumulate.
[0010] In another aspect of the present invention there is provided
a method of processing waste comprising densifying waste and
expressing air therefrom in a compactor, delivering the waste from
a compactor to a pyrolyzer, heating the waste for thermal
decomposition of organic material by action of heat alone in the
pyrolyzer, receiving waste from the pyrolyzer in a gasifier,
gasifying waste in the gasifier, receiving the gas from the
gasifier in an oxidiser, and oxidising the gas to be combusted.
[0011] Preferably energy from the output gas of the oxidizer is
used to provide heat to the pyrolyzer. It is also preferred that
excess heat remaining in the gas once it has completed the
pyrolysis process is reclaimed. Heat reclamation can be by use of
an indirect heat exchanger such as a waste heat boiler. There is
also potential to use reclaimed heat for electrical generation,
absorption chilling for refrigeration and/or air conditioning,
space heating, process heating with hot water or steam and/or
distillation or desalination.
[0012] Observable benefits of technology according to the invention
include: [0013] The plant can run on residual (leftover) waste and
so does not compromise recycling [0014] CO.sub.2 emmission
reduction over conventional incineration [0015] Elimination of
requirement for transport vehicles by treatment of waste at source
[0016] Low visual impact and low noise [0017] Significant saving on
energy and waste disposal cost [0018] Small footprint, easily
integrated into existing premises and existing services.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 shows an overview of a waste processing system
according to the invention,
[0020] FIG. 2 shows an overview from the opposite side of the waste
processing system from FIG. 1,
[0021] FIG. 3 shows a cross section view of a gasifier and
pyrolysis chamber according to the invention,
[0022] FIGS. 4a, 4b and 4c show further section views taken from
FIG. 3,
[0023] FIGS. 5 to 8 show a series of perspective views of a further
embodiment of the waste processing system of the invention, and
[0024] FIG. 9 shows an end view of the further embodiment from
FIGS. 5 to 8.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0025] FIGS. 1 and 2 illustrate an external view of the components
of a waste processing system according to the invention. The
apparatus 10 includes a shredder 11, a compactor 12, a pyrolyser
13, a gasifier/ash vessel 14, an oxidiser 15, a heat reclaimer 31
and an outlet flue 16. Each stage of the system is discussed in
detail below.
[0026] As a pre-feed treatment, the waste is processed through the
shredder 11 to homogenize it and act as a separator for
contaminants, mainly consisting of materials that may be injurious
to mechanical handling.
[0027] The greater the homogeneity of the waste feed, the smoother
the operation of the thermal plant, leading to increased processing
capacity of the plant and increased life of the components.
Preferably, before entering the shredder 11, large items and other
damaging materials are removed. Separation may be performed by hand
or automated depending on the application and available manual
resources.
[0028] Size reduction of the waste has an added advantage of
increasing surface area and therefore the effectiveness of the
pyrolysis process.
[0029] Once shredded the waste is compacted through a reducing cone
using a screw compactor 12. This method of feeding has several
benefits: it densifies the waste, making it easier to transport; it
expresses air from the waste; it also provides a seal between
atmosphere and the thermal process (the seal being formed by the
waste itself). This seal ensures that air is not drawn into the
process. If it were, combustion would be promoted rather than
pyrolysis as intended to occur at the next step of the system. The
compactor 12 provides a continuous feed (as opposed to a batch
feed) which is beneficial to the process and eliminates the need
for a rotary valve or lock hopper system.
[0030] The first stage of the thermal process is pyrolysis, defined
as the thermal decomposition of organic material by the action of
heat alone. No other reagents are utilized, just heat.
[0031] For delivery from the compactor 12 to the pyrolyzer 13 waste
is fed along a joining duct 19 toward a further screw 18 located
within pyrolyzer tube 17. The tube 17 is externally heated using
gases from later in the process. In this manner the waste is heated
from ambient temperature, whilst adding no other reagents. The heat
first dries the waste then decomposes organic molecules to form a
gas and vapor mixture mostly made up of water, carbon monoxide and
carbon dioxide, hydrogen, methane and ethane. The balance of the
material is left as a carbon char and ash.
[0032] Inert materials (e.g. metals and glass) are merely heated
and pass through the tube unaffected.
[0033] As a general overview, the pyrolyzer 13 indirectly heats
combustible waste material to a high temperature, e.g. to over
500.degree. C., in the absence of air or oxygen. This is achieved
by passing the combustible waste material through the heated tube
17, a pyrolysis tube, by means of an auger (e.g. screw 18). The
pyrolysis tube 17 is contained within a pyrolysis chamber through
which hot exhaust gases from the outlet of the oxidiser 15 are
passed. These hot gases pass over the outside of the pyrolysis tube
and transfer heat from the exhaust gases to the tube by convection
and radiation. The hot tube 17 then transfers heat into the
combustible waste material by conduction and radiation from the
inner surface of the tube wall. The heat energy heats up the
combustible waste material to approximately 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 17.
[0034] The main benefit of the pyrolyzer 13 is that it produces an
excellent feedstock for the gasifier 14, being dry, hot,
pre-pyrolyzed and homogenous. This makes the operation of the
subsequent gasifier 14 simpler and more efficient.
[0035] Preferably the pyrolysis chamber 13 comprises an insulating
outer surface to retain heat and to improve the overall energy
efficiency of the systems and methods according to the
invention.
[0036] At the oxidizer end of pyrolyzer tube 17 the resultant char
and ash is discharged into a refractory-lined vessel (the gasifier
14). The apparatus 10 can be operated either in pyrolysis mode, or
in gasification mode.
[0037] When in pyrolysis mode, the resultant char and ash is stored
in the gasifier 14 before being discharged into ash containers via
another screw system 20 visible in FIG. 1.
[0038] Trials of prototypes of the invention indicated that the
pyrolyzed waste material at this stage of the process is reduced by
mass to 30% of its original weight and wherein 25% of that 30% was
metal and glass. Therefore, the waste product was <5% of its
volume compared to the raw waste. The residue from over sixty large
refuse sacks fitting into six buckets. Of course, these reduction
ratios are dependent on the nature of the waste.
[0039] The gasifier 14 receives char and pyrogas from the pyrolysis
tube 17 where char falls out of the end of the pyrolyzer 13 and
forms a char bed in the bottom of the gasifier 14. In the preferred
form the gasifier 14 is of an updraft gasifier type. Steam and air
is injected at the bottom of the char bed and percolates upwards
through the char undergoing various chemical reactions and reducing
the steam and char to carbon monoxide and hydrogen commonly known
as syngas. This reaction 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 the pyrogas in the freeboard
above the gasifier char bed and is passed to the oxidiser 15 by
pipe 21. Ash containing a small amount of unreacted carbon is
discharged from the bottom of the gasifier into an airtight ash
container to prevent uncontrolled ingress of air into the bottom of
the gasifier 14.
[0040] The advantage of an updraft gasifier as utilized in the
present system is that it is a simple design and less sensitive to
particle size, homogeneity and moisture content than other types of
gasifiers (e.g. compared to a downdraft or fluidised bed gasifier).
The simple design makes the gasifier easier to operate, more
reliable and cheaper to build which are all clear advantages for a
compact system according to the invention. However, other types of
gasifiers may be employed such as downdraft gasifiers and cross
flow gasifiers depending upon the selected energy recovery
option.
[0041] Preferably the gasification chamber 14 comprises an
insulating outer surface to retain heat and to improve the overall
energy efficiency of the invention.
[0042] It is not mandatory to actively gasify in the gasifier 14
for all waste processing systems according to the invention, but it
will be necessary to actively gasify for applications where
maximising energy recovery (heat or power) is required. Although
large waste processing plants utilise steam gasification, it will
be possible to opt for exhaust gas gasification since exhaust gas
is more readily available than steam in smaller systems.
[0043] When in exhaust gas gasification mode the exhaust gases can
be re-circulated to the bottom of the gasifier using a gasification
fan (26) and recirculation pipework (27) (seen in FIGS. 7 and 8
which describe a further embodiment below). If high temperature
exhaust gases (typically 1000.degree. C.) are extracted upstream of
a heat recovery indirect heat exchanger, the recirculation pipework
is used to cool the exhaust gases to a lower temperature (typically
300.degree. C.) that is acceptable for the gasification fan. This
is achieved by having a long length of un-insulated pipe.
[0044] Alternatively, if the exhaust gases are extracted downstream
of the indirect heat exchanger (at typically 200-300.degree. C.),
then the recirculation pipework can be shorter and insulated.
[0045] The gases generated in the pyrolyzer 13 and gasifier 14 are
fed forward into the oxidizer 15, a refractory-lined combustion
vessel maintained at approximately 1100.degree. C. The gases are
combusted by mixture with a controlled amount of air in this
environment. This is a highly exothermic reaction, which is what
maintains the temperature. Some products from this reaction go
forward to the pyrolyzer 13, to be used to heat the waste in the
pyrolysis stage. Such an aspect of the invention improves energy
efficiency and economy.
[0046] As mentioned, the oxidizer 15 receives mixed pyrogas and
syngas via pipe 21. The oxidizer 15 mixes syngas with air where it
is oxidised to release chemical energy in the form of heat.
Oxidizer outlet temperature is controlled by adjusting the amount
of excess combustion air that is introduced into the oxidizer. Good
combustion is achieved by ensuring that the syngas and combustion
air is mixed well in a turbulent environment with a long residence
time at a high temperature. Typically the oxidizer temperature is
maintained at 1100.degree. C., but it can be operated as low as
850.degree. C. Preferably the residence time of the gases within
the oxidizer 15 is greater than two seconds. Sufficient mixing and
turbulence is achieved by injecting the combustion air into the
oxidizer 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 the syngas injection port.
[0047] Preferably the oxidizer 15 comprises an insulating outer
surface to retain heat and to improve the overall energy efficiency
according to the invention.
[0048] To enable the process to start, a start-up burner 30 is
located within the oxidiser 15. This is used to warm up the
apparatus to operating temperature prior to waste feed. A
conventional burner using any conventional fuel (gas or oil) can be
used.
[0049] Since there is an excess of heat remaining in the gas once
it has completed the pyrolysis process this may be reclaimed using
a heat reclaimer 31 in the form of an indirect heat exchanger such
as a waste heat boiler. The specifications of heat reclamation
depend on the environment of the waste processing system.
[0050] Whatever gas cooling is used, with heat reclamation or not,
an exit temperature of 200.degree. C. for the gases from flue 16 is
recommended, in order to avoid acid gas condensation and also so
that the gas is at a good temperature for acid remediation, which
local legislation may require.
[0051] There is potential for electrical generation from the
reclaimed heat, alternatively it may be desirable to utilize the
heat itself in uses relevant to a particular situation, like
absorption chilling. Uses for excess heat include space heating or
process heating with hot water or steam, air conditioning,
distillation and/or desalination.
[0052] The use of sodium bicarbonate and a bag filter is
recommended for the remediation of HCl, SO.sub.2 and particulate
matter. However, this remains a choice of the end user, dependent
on the legislative framework in which the plant will be expected to
operate and the nature of the waste being processed.
[0053] Most preferably the system of the invention is maintained
under negative pressure by the use of ID (induced draft) fans at
the back of the plant (not illustrated in FIGS. 1 to 8, but FIGS. 7
and 8 do show a volume 28 where an ID fan could be located within
the ISO container). This ensures process safety, because any leak
or failure in the process will not lead to gases leaving the
process, but air entering it instead. Care should be taken to back
up the fan function so that in no circumstance can the plant be
left operating (and producing gas) without some negative pressure
being maintained.
[0054] The fans discharge gas via a flue (not illustrated) to
atmosphere. Said flue 16 need only be about one meter taller than
the roof of the structure housing the plant, provided there are no
other higher occupied buildings in the immediate vicinity,
dependent upon the legislative framework in which the plant will be
expected to operate.
[0055] FIGS. 5 to 9 illustrate a preferred form of the invention,
specifically wherein the components of the waste processing system
are housed within two (ISO standard) shipping containers such that
the system is readily portable.
[0056] In other respects the function and operation of the
components is analogous to the plant described above so the same
reference numerals have been used (assuming a given component is
visible). It should be noted with reference to FIGS. 7 and 8 that a
heat reclaimer is not shown but a volume 28 is provided within the
ISO container where such a heat reclaimer could be located.
[0057] Referring to FIGS. 5 to 9, a shredder 11 takes waste
material, preferably delivered through an openable door 25 in the
side of the container which can become a platform for an operator
to stand upon.
[0058] Shredded material is compacted by a screw compactor 12 then
fed to the pyrolyzer stage 13. Char and gas is delivered to the
gasifier 14 where ash can be removed via a screw 20 to an ash bin
23 located (when assembled) outside the ISO container. For transit
ash bin 23 may be housed within one of the containers, depending on
available space.
[0059] Syngas from the updraft gasifier 14 is fed through pipe 21
to the oxidizer stage 15 where heated gas (mixed with air/oxygen)
can be utilized to provide energy for heating the pyrolyzer
stage.
[0060] Operation of the waste processing system is controlled and
monitored via a control panel 24, preferably with a view screen
visible through a sidewall of the ISO container. Operating
parameters can be predetermined and alerts raised if conditions
exceed certain limits. Adjacent the control panel in FIG. 9 is an
induced draft fan 29 as previously described, to maintain a
negative pressure and minimize leakage.
[0061] An integrated system with separate pyrolysis, gasification
and oxidation has a number of advantages over conventional
incineration. Most combustion processes undergo pyrolysis,
gasification and oxidation at the same place at the same time. By
contrast, separate pyrolysis, gasification and oxidation in a
compact system according to the invention allows much better
control of each of the individual processes. For example, it can be
ensured that all waste material is heated to a uniform temperature
and that none of it is heated above 900.degree. C. In conventional
incineration on a hearth there are hot spots and cold spots. Some
pieces of waste are not heated sufficiently and come out in the ash
unburnt. Conversely some pieces of waste are overheated and release
all their noxious constituents in the gaseous phase.
[0062] In the process described it is possible to ensure that all
material is heated and thermally decomposed, but none of the waste
material is overheated and the amount of pollutants that are
volatized is less. In addition to this, the process combusts a
medium calorific value gas in a highly controlled oxidizing
environment. Again, there are no hot spots or cold spots compared
to the combustion zone in a conventional mass burn incinerator.
This results in complete combustion of the gases with lower
concentrations of carbon monoxide and volatile organic compounds. A
uniform oxidation temperature results in the generation of less
temperature generated nitrogen oxides (thermal Nox) while the
pyrolysis and gasification process subdue the generation of fuel
generated nitrogen oxides (fuel Nox) due to their reducing nature.
This means that the nitrogen oxide levels in the exhaust gas are
typically lower than that of a mass burn incinerator.
[0063] Furthermore, the low off-gas velocity of an updraft gasifier
results in a very low particulate loading in the syngas to the
oxidizer.
[0064] The result of all these features is that the un-cleaned
exhaust gas at the oxidizer outlet is cleaner than that of an
equivalent mass burn incinerator prior to flue gas remediation.
[0065] In one form the system of the invention preferably includes
a heat reclamation heat exchanger (e.g. a boiler). Such a boiler is
designed to quench the exhaust gases from 450.degree. C. to
200.degree. C. as quickly as possible (typically 0.25 seconds).
This is in order to minimise the potential for de-Novo synthesis of
dioxins and furans. De-Novo synthesis is also minimised because of
the effectiveness of the pyrolysis, gasification and oxidation
system to destroy the pre-curlers of de-Novo sythesis.
[0066] As previously mentioned, the system is maintained at a
slight negative pressure (typically <-5 mbarg) by an ID fan to
prevent fugitive gaseous emissions. Although air leakage into the
system is beneficial for environmental and health and safety
issues, it is detrimental to the performance of the process and
must be minimised. This requires careful specification and design
of all flanges, connections, expansion joints and valves and
instrumentation using common engineering practice.
[0067] Thermal expansion of components, as the system is heated up
from ambient temperature to operating temperature, needs to be
accommodated in the design. Of particular difficulty is the thermal
expansion of the pyrolysis tube 17 which may expand by up to three
inches. This is a concern because it is important that air is not
leaked into the pyrolysis tube causing pyrolysis to cease and
combustion to occur. The solution to this problem is to anchor the
pyrolysis tube 17 to the gasifier 14 with a static flange and allow
the tube 17 to expand towards the feed end. This means that the
greatest thermal expansion occurs at the cold end of the pyrolyzer
13. A simple fabric expansion gaiter 22 can be used to seal between
the pyrolysis tube 17 and the pyrolysis chamber 13 at the cold end.
Also, because the feed system is static, the thermal expansion of
the pyrolysis tube 17 towards the feed system needs to be
accommodated. This is achieved by inserting the feed tube into the
pyrolysis tube with a generous clearance to prevent jamming. A gas
tight seal is achieved by using the fabric expansion gaiter.
[0068] The waste processing system of the present invention is
defined as an "advanced thermal conversion process" (by the UK
Department for Environment, Food and Rural Affairs--DEFRA).
[0069] The invention accepts a variable and broad range of wastes
with a continuous rather than batch feed with no pre-treatment
required and can dispose of waste at source. Furthermore, it
generates very low levels of emissions, especially when considering
its size.
[0070] Flue gas remediation can be easily added to ensure that the
gaseous emissions meet any legislative requirements.
[0071] Most preferably the system has a small footprint, is light
weight, highly automated with low skill required, can be skid
mounted, quickly and easily started up and shut down, and easy to
integrate with minimal servicing required.
[0072] In its preferred form the waste processing system of the
invention is containerized as illustrated to provide mobility, i.e.
equipment components are constructed so as to fit into two
twenty-foot ISO containers. The benefit of this is rapid deployment
and relocation in the field without the need for special haulage or
cranes.
* * * * *