U.S. patent application number 13/664548 was filed with the patent office on 2013-02-28 for waste treatment apparatus and method.
This patent application is currently assigned to Pyropure Limited. The applicant listed for this patent is Pyropure Limited. Invention is credited to Howard Morgan Clarke, Michael Benjamin Elder.
Application Number | 20130047901 13/664548 |
Document ID | / |
Family ID | 36241416 |
Filed Date | 2013-02-28 |
United States Patent
Application |
20130047901 |
Kind Code |
A1 |
Clarke; Howard Morgan ; et
al. |
February 28, 2013 |
WASTE TREATMENT APPARATUS AND METHOD
Abstract
In apparatus and method for waste treatment by pyrolysis,
treated waste is flushed through a grid (18) to trap recyclable
material in the pyrolysis chamber (24). Pyrolysis is carried out at
a temperature of from 400-700.degree. C. and off-gases are
dissolved in a solution in scrubber (13) for disposal in a water
course. Water is introduced into the chamber as superheated steam
via pipes (5) so as both to flush away treated material and clean
the chamber. Recyclable waste is separated from non-recyclable by
treating non-recyclable waste by pyrolysis, and flushing treated
non-recyclable waste away through liquid exhaust (8). Apparatus is
made as a modular, free-standing unit and comprises plugs for
connection to an electricity supply, to a water supply, and to a
sewerage system (16) and has a chamber with a volume in the range
0.01-0.5m.sup.3.
Inventors: |
Clarke; Howard Morgan;
(Liss, GB) ; Elder; Michael Benjamin; (Liss,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pyropure Limited; |
Southampton |
|
GB |
|
|
Assignee: |
Pyropure Limited
Southampton
GB
|
Family ID: |
36241416 |
Appl. No.: |
13/664548 |
Filed: |
October 31, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12282334 |
Oct 7, 2008 |
8307770 |
|
|
PCT/GB2007/000853 |
Mar 12, 2007 |
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13664548 |
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Current U.S.
Class: |
110/229 ;
110/171; 110/259; 110/346 |
Current CPC
Class: |
F23G 2203/70 20130101;
F23J 15/022 20130101; F23J 15/04 20130101; F23G 5/40 20130101; F23G
5/027 20130101; F23G 2200/00 20130101; F23G 2201/30 20130101; F23G
5/44 20130101 |
Class at
Publication: |
110/229 ;
110/346; 110/259; 110/171 |
International
Class: |
F23G 5/027 20060101
F23G005/027; F23J 1/02 20060101 F23J001/02; F23G 5/44 20060101
F23G005/44 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 10, 2006 |
GB |
0604907.6 |
Claims
1.-81. (canceled)
82. A cyclic process for waste treatment comprising: introducing
waste into a chamber; heating the waste to effect pyrolysis of the
waste at a temperature of from about 300.degree. C. to about
700.degree. C.; introducing oxygen into the chamber to effect
gasification of the waste at a temperature of at least about
400.degree. C.; and flushing the combusted waste from the chamber
with water and/or steam.
83. The process of claim 82, wherein the temperature to effect
gasification is from about 400.degree. C. to about 800.degree.
C.
84. The process of claim 82, wherein the temperature to effect
pyrolysis is from about 400.degree. C. to about 600.degree. C.
85. The process of claim 82, wherein the water enters the chamber
and is converted to steam therein.
86. The process of claim 82, comprising flushing the combusted
waste from the chamber into the sewage system.
87. A pyrolysis apparatus comprising: a sealable chamber including
a waste treatment zone in the chamber; a first port for introducing
waste into the chamber; an exit port for flushing treated waste
from the chamber; a heating element; an oxygen supply for supplying
oxygen to the waste treatment zone to allow gasification of waste
in the waste treatment zone; and a water supply for flushing
treated waste from the waste treatment zone with water and/or
steam; wherein the apparatus is adapted to pyrolyse the waste at a
temperature of from about 300.degree. C. to about 700.degree. C.,
followed by gasification of the waste at at least about 400.degree.
C.
88. The apparatus of claim 87, wherein the temperature to effect
gasification is from about 400.degree. C. to about 800.degree.
C.
89. The apparatus of claim 87, wherein the apparatus is adapted to
operate in cycles, such that at the end of a waste treatment cycle
the chamber is ready to begin a further waste treatment cycle and
each cycle comprises: introducing waste into the chamber; heating
the waste to an elevated temperature to effect pyrolysis of the
waste; introducing oxygen into the chamber to effect gasification
of the waste; and flushing the combusted waste from the chamber
with water and/or steam.
90. The apparatus of claim 87, wherein the chamber comprises an
output for connection to a sewer so that the treated waste can be
flushed into the sewage system.
91. The apparatus of claim 87, further comprising: a gas treatment
solution; and a conduit arranged to contact gases exiting the
chamber with the solution.
92. A process for waste treatment comprising: introducing waste
into a chamber; heating the waste to an elevated temperature to
effect pyrolysis of the waste; introducing oxygen into the chamber
to effect gasification of the waste; and flushing the combusted
waste from the chamber with water and/or steam, wherein the water
enters the chamber and is converted to steam therein.
93. The process of claim 92, wherein the process is cyclic such
that at the end of a waste treatment cycle the chamber is ready to
begin a further waste treatment cycle.
94. The process of claim 92, wherein the temperature to effect
pyrolysis is from about 300.degree. C. to about 700.degree. C.
95. The process of claim 92, wherein the temperature to effect
gasification is from at least about 400.degree. C.
96. The process of claim 92, wherein the temperature to effect
gasification is from about 400.degree. C. to about 800.degree.
C.
97. A pyrolysis apparatus comprising: a sealable chamber including
a waste treatment zone in the chamber; a first port for introducing
waste into the chamber; an exit port for flushing treated waste
from the chamber; a heating element; an oxygen supply for supplying
oxygen to the waste treatment zone to allow gasification of waste
in the waste treatment zone; and a water supply for flushing
treated waste from the waste treatment zone with water and/or
steam.
98. The apparatus of claim 97, wherein the temperature to effect
pyrolysis is from about 300.degree. C. to about 700.degree. C.
99. The apparatus of claim 97, wherein the temperature to effect
gasification is from at least about 400.degree. C.
100. The apparatus of claim 97, wherein the temperature to effect
gasification is from about 400.degree. C. to about 800.degree.
C.
101. The apparatus of claim 97, wherein the apparatus is adapted to
operate in cycles, such that at the end of a waste treatment cycle
the chamber is ready to begin a further waste treatment cycle and
each cycle comprises: introducing waste into the chamber; heating
the waste to an elevated temperature to effect pyrolysis of the
waste; introducing oxygen into the chamber to effect gasification
of the waste; and flushing the combusted waste from the chamber
with water and/or steam
102. The apparatus of claim 97, wherein the chamber comprises an
output for connection to a sewer so that the treated waste can be
flushed into the sewage system.
Description
[0001] The present invention relates to waste treatment apparatus
and method, in particular apparatus and method for treatment of
waste from a range of sources, including commercial premises and
domestic and multi-occupancy residences.
[0002] Pyrolysis for the disposal of domestic (sanitary) waste is
known from WO 00/20801. Small pyrolysis units are installed on
ships for processing minor quantities of sanitary waste. These
units use a multi-step process, requiring a vacuum pump to evacuate
air before beginning pyrolysis and to actively evacuate residue
from the unit following waste treatment. In addition to only
processing small amounts of homologous sanitary waste the units are
situated in close proximity to the user, often within a toilet
cubicle.
[0003] Large scale industrial pyrolysis of waste is known from
inter alia, US 2004/0168621, EP 0724008, EP 692677, EP 0505278, and
EP 0610120. Industrial size pyrolysis plants require waste to be
transported to them. They operate continuously at high temperatures
and due to instantaneous exposure to these high temperatures and
the types of waste that are processed, these plants tend to produce
large quantities of noxious gases, including dioxins. These off
gases are typically passed to a combustion chamber. Exhaust gases
from this chamber are then optionally subjected to additional
processing before release to the atmosphere, or may be diverted to
supply heat within the unit.
[0004] Smaller scale pyrolysis is also known from inter alia; JP
2005140346, JP 2002081623, JP 2001062437, JP 60105815, EP 1371713,
U.S. Pat. No. 3,779,182, WO 02/40618, GB 2289324, and GB
2310485.
[0005] Pyrolysis is also known in relation to domestic ovens, for
example in the self cleaning mechanism of US 2005/0145241.
[0006] Municipal waste disposal is a growing problem, with the
majority of this waste being buried in landfill sites. A need to
reduce the volume of waste for disposal is leading to an increased
drive to recycle. In regard to domestic waste this requires a level
of compliance from residents and has varying levels of success.
[0007] Suitable locations for new landfill sites are relatively
uncommon due to strict hydro-geological requirements, avoidance of
water table contamination and other environmental considerations.
In short, there is an increasing scarcity of suitable waste burial
sites and an urgent need for alternative methods of waste
disposal.
[0008] Incineration is one of the more widely used alternatives to
landfill, however, this requires the production of large scale
industrial plants, a time consuming and expensive process.
Additionally, public opinion is often against the building of these
plants, particularly on the basis of objections to gas release into
the local area. The fumes produced by waste combustion are
unavoidable and necessitate the incorporation of complex gas
processing mechanisms to remove pollutants.
[0009] Waste pyrolysis is an alternative to landfill and
incineration, but requires continuously operating industrial
pyrolysis plants. Waste has to be collected and transported to
these plants before being processed. Due to the heterogeneity of
waste being processed and the high pyrolytic temperatures toxic
emissions are commonly produced. It is not desirable to release
these to the atmosphere and thus, as for incineration plants,
complex gas processing systems have to be incorporated into
plants.
[0010] It is an object of the invention to provide a process and
apparatus to treat waste on site on a domestic and large domestic
scale. It is an object of specific embodiments of the invention to
do so for multi-occupancy residences and also individual domestic
residences and commercial enterprises such as supermarkets and
restaurants. A further object is to reduce and/or remove the need
for the transport of waste and prevent waste ending up as landfill,
allowing local authorities to meet the requirements of recycling
directives. A still further object of the invention is to enable
greater efficiency in collecting recyclable materials, improving
public compliance by facilitating the recycling process.
[0011] Accordingly, the invention provides a process for waste
treatment and apparatus for carrying out waste treatment by a
combination of pyrolysis and combustion steps, the process and
apparatus incorporating one or more, in any and all combinations,
or all of the aspects of the invention described herein.
[0012] A first aspect of the invention comprises a process for
waste treatment by pyrolysis and combustion, wherein treated waste
is flushed through a grid to trap recyclable material. Apparatus of
this aspect comprises a pyrolysis chamber having a grid between a
waste treatment zone and an exit from the chamber.
[0013] A second aspect of the invention comprises pyrolysis of
waste at a temperature of from 400-700.degree. C.
[0014] A third aspect of the invention comprises dissolving
off-gases generated by pyrolysis and combustion in a solution and
disposing of the solution, for example in a sewer. Apparatus of
this aspect comprises a tank containing a gas treatment solution,
an exhaust port for exit of gases from the pyrolysis chamber and a
conduit arranged in combination with the tank such that the gases
exiting the chamber are dissolved in the solution, which can then
be disposed of.
[0015] A fourth aspect of the invention comprises introducing water
into the chamber as superheated steam so as both to flush away
treated material and clean the chamber. Apparatus for this aspect
comprises pipework in walls of the chamber via which in use water
enters the chamber, the water being heated by the hot chamber walls
and entering the chamber as superheated steam.
[0016] A fifth aspect of the invention provides for separation of
recyclable waste from non-recyclable waste in mixed waste
comprising treating non-recyclable waste in the mixed waste by
pyrolysis and combustion, and flushing treated non-recyclable waste
away whilst retaining recyclable waste.
[0017] A sixth aspect of the invention is a modular pyrolysis and
combustion apparatus, which is free-standing and comprises plugs
for connection to an electricity supply, to a water supply, and to
a sewerage system.
[0018] A seventh aspect of the invention is a pyrolysis and
combustion apparatus having a chamber with a volume in the range
from 0.01-0.5 m.sup.3.
[0019] In more detail, a first aspect of the invention provides a
process for waste treatment comprising introducing waste into a
chamber, heating the waste to an elevated temperature to effect
pyrolysis of the waste, introducing oxygen into the chamber to
effect combustion of the waste, and flushing the combusted waste
from the chamber with water, wherein the combusted waste is flushed
through a grid to trap recyclable material. Treated waste is mostly
fine ash and is easily washed through the grid and away into e.g. a
sewer or other water course. Waste is thus treated on site.
[0020] The grid can be located outside the chamber, for example
between an exit from the chamber and an entrance into the water
course. But, it is preferably located in the chamber, conveniently
forming a or part of a shelf, and the method can comprise placing
waste introduced into the chamber on the grid.
[0021] The method enables separation of recyclable waste, and can
therefore comprise transferring recyclable material from the grid
to a receptacle outside the chamber. Collected recyclable material
can be taken away for recycling--again, avoiding unnecessary
land-fill use. The term "recyclable waste" herein refers to
commonly recyclable materials that are not reduced to ash following
a waste treatment cycle of the invention; typically these materials
are metal and glass.
[0022] The grid is hence preferably moveable, and the method
preferably comprises moving the grid between a first position in
which the grid traps the recyclable material and a second position
in which the recyclable material can be transferred into a
receptacle. The grid can thus easily, and optionally automatically,
be emptied, whether once a pyrolysis cycle or after several cycles
of waste treatment. For operator convenience, the grid may be
operated via a control system, such as one associated with
automatic monitoring and operation of the apparatus.
[0023] In a further embodiment, the method comprises agitating the
grid during pyrolysis of the waste. This can assist transfer of
heat into the middle of the waste and thus assist more complete
pyrolysis of all waste in the chamber.
[0024] Pyrolysis and combustion apparatus of this aspect comprises
a sealable chamber, a waste treatment zone in the chamber, a port
for introducing waste into the chamber, a port for the exit of
treated waste, a heating element, and a grid between the waste
treatment zone and the exit port. In use, non-treated material,
which generally contains a high proportion of recyclable material,
such as glass and metal, is caught and not flushed away but can
instead be recycled.
[0025] Suitably, the grid forms a shelf across the chamber to
support the waste being treated. The grid can also be or be part of
a basket in the chamber. The grid can thus be used to locate and/or
hold waste in the treatment zone during pyrolysis. In an apparatus
described in more detail below, the grid forms a shelf towards the
bottom of the chamber and a little raised from the floor of the
chamber. Waste lies on and is supported by the shelf. After
treatment by pyrolysis and combustion water flushes the resultant
ash through the grid onto the floor and then out of the chamber,
large particles typically of undegraded material, being trapped.
The floor is generally angled down towards a valved exit port where
water exits the chamber.
[0026] The grid is preferably moveable between a first position in
which it traps undegraded material during flushing of the chamber
and a second position in which the undegraded material can be
transferred to a receptacle outside the chamber. This facilitates
emptying of the recyclables from the chamber.
[0027] A control apparatus for moving the grid between the first
and second positions and a mechanism for agitation of the grid can
be associated with the grid.
[0028] A purpose of the grid is to trap particulate material and
not allow this into the water course, whilst allowing the ash
residue to be easily flushed away. To this end, the grid may
comprise a plurality of apertures sized 15 mm or less in diameter,
10 mm or less in diameter, 7 mm or less in diameter or 5 mm or less
in diameter. In a particular embodiment, the grid comprises a
plurality of apertures sized about 3 mm in diameter. Generally the
apertures can be of any shape, though round or square apertures are
more typical. The grid apertures should not be so fine that they
are clogged in use by the ash residue of the waste treatment cycle,
and so are preferably at least 1 mm, more preferably at least 2 mm
in diameter.
[0029] The apparatus can also comprise a combination of two or more
grids. For example, there may be a first grid having a plurality of
apertures of a first size, and a second grid between the first grid
and the exit port and having a plurality of apertures of a second
size, wherein the first size is bigger than the second size. This
second, smaller aperture grid, with apertures typically 2 mm or
more, or 3 mm or more smaller than those of the first, and located
closer to the exit of the chamber separates trapped material into
two divisions by size and can prevent or reduce the clogging when
there is just one. Suitable aperture combinations are first
grid--15 mm or less, second grid--10 mm or less, preferably 7 mm or
less, or first grid--12 mm or less, second grid--10 mm or less,
preferably 7 mm or less, or first grid--12 mm or less, second
grid--7 mm or less, preferably 5 mm or less.
[0030] The grid may also be or form part of a basket within the
chamber and preferably removable from the chamber. In use, waste is
conveniently placed in the basket outside the chamber and the
basket, now holding the waste, placed into the chamber to be
treated.
[0031] A process for waste treatment in accordance with a second
aspect of the invention comprises introducing waste into a chamber,
heating the waste to an elevated temperature to effect pyrolysis of
the waste, introducing oxygen into the chamber to effect combustion
of the waste, and flushing the combusted waste from the chamber
with water, wherein the elevated temperature to effect pyrolysis is
from 400-700.degree. C. Operating at these temperatures with rapid
cooling of the chamber and its contents once treatment is finished
and using a relatively short treatment cycle time tends to avoid
formation of some of the more noxious contaminants associated with
standard pyrolysis units or form them to a lesser degree, whilst
ensuring that substantially all waste, other than recyclable
components, can be treated. Hence an advantage of the invention is
that scrubbing of off gases can be carried out with reduced on-site
emissions, and a particularly preferred embodiment of the invention
can be operated with substantially zero emissions on site--off
gases being vented away from the apparatus, e.g. via vents in the
sewer system.
[0032] The pyrolysis temperature is preferably from 500-700.degree.
C., more preferably from 500-600.degree. C. In a specific
embodiment of the process, described in more detail below, the
system operates at about 550.degree. C.
[0033] It is further preferred that combustion is carried out at
elevated temperatures, typically 400.degree. C. or higher,
preferably at least 450.degree. C. more preferably at least
500.degree. C. In typical operation of an apparatus of the
invention, the chamber is heated to the pyrolysis temperature and
then combustion is carried out as the next step without specific
separate heating or cooling of the chamber. Heat generated by
combustion generally maintains an elevated temperature within the
waste and depending upon its calorific content may slightly
increase the temperature so chamber heaters are generally turned
off during combustion. Heat can be removed from the chamber by
passing off gases through a radiator or a heat exchanger and
recovered heat can be used for other purposes. Chamber temperature
can also be controlled by controlling flow of air into the
chamber.
[0034] Generally chamber temperature during combustion does not
rise above 800.degree. C. and preferably not above 750.degree. C.
or 700.degree. C.
[0035] In a particular embodiment of the invention comprising a
large chamber volume an air circulation device, preferably
comprising a fan, is included to disperse the warm air evenly
throughout the chamber as the chamber is being heated in
preparation for pyrolysis. Air can be heated or reheated by heaters
in the circulation path. This ensures that the heat is directed
into the waste load more effectively--thus speeding up its
degradation during pyrolysis. Air circulation may continue during
pyrolysis and/or combustion phases. In smaller chambers the reduced
waste load tends to allow heat to penetrate sufficiently rapidly
without the need for air circulation.
[0036] The duration of the pyrolysis phase varies according to
waste volume, with a limit dictated by chamber volume. Apparatus of
the invention are generally designed for use in domestic and
multi-occupancy residences and small commercial premises. Waste
generally enters the chamber at ambient temperature, the chamber is
then sealed and the heaters are activated to heat the chamber to
the operating temperature. In apparatus made and tested to date,
this heating phase typically takes 2-20 minutes, preferably 5-10
minutes, being dependent on the operating temperature required, the
chamber volume, and volume of waste in the chamber. In use, it is
found that off-gases can evolve in fractions as the temperature
increases and this is believed to result in reduced production of
certain toxic components, notably dioxins and fluorins compared to
industrial pyrolysis. Processes carried out in such apparatus
generally comprise holding the waste at the elevated temperature
for 10-90 minutes, preferably for 20-60 minutes. In a specific
embodiment of the process, described in more detail below, the
pyrolysis phase has a roughly 30 minute duration.
[0037] In some embodiments of the invention intelligent timing
systems are used to control the length of the cycle. These systems
can monitor the temperature of the off-gases being produced and
adjust the cycle duration accordingly. Use of these systems
improves the power efficiency of the process. In one example, a
control system monitors the temperature of the off-gases or of the
load, such as via a thermocouple located proximal to the waste in
the chamber, and triggers commencement of combustion once a
predetermined temperature (say, about 450.degree. C.-500.degree.
C.) is reached. In another example, a control system monitors the
temperature of the off gases from the chamber and when the
temperature has dropped to a pre-determined level (say 300.degree.
C.-400.degree. C.) initiates the end of the combustion and the
beginning of cooling and cleaning of the chamber by introduction of
water (as superheated steam). Another option is to monitor the rate
of cooling of the chamber, and once this reaches or approaches the
natural cooling rate of the chamber, then initiate the end of
combustion.
[0038] In an example of the invention operating in situ, the
apparatus is set up with a pre-programmed pyrolysis phase, based on
the chamber volume and anticipated nature of the waste to be
processed. The phase may be set up such that the elevated
temperature is held for the duration of the pyrolysis phase and
such that 50% or more of the waste is degraded, preferably 70% or
more, more preferably 80% or more. In practice it is problematic
and energy inefficient to ensure 100% treatment, especially when
recyclable material is present such as metals and glass, which
would not be degraded and which can be extracted for recycling.
From expected waste volume and content the system may be set up for
a given property so that from 60%-95% of waste by weight is
pyrolysed.
[0039] In a third aspect of the invention a process for waste
treatment comprises introducing waste into a chamber, heating the
waste to an elevated temperature to effect pyrolysis of the waste,
introducing oxygen into the chamber to effect combustion of the
waste, flushing the combusted waste from the chamber with water,
dissolving gases generated by the pyrolysis and/or combustion in
solution, and disposing of the solution. Hence, rather than emit
these gases or subject them to treatment by combustion the gases
are dissolved.
[0040] A disadvantage of known pyrolysis plants and incinerators is
the generation of dioxins and fluorins by initial phases of waste
treatment, dealt with by combustion of off-gases, generating
intense heat. Planning objections on environmental grounds are
raised due to the risk that inadequate combustion will release
toxic chemicals into the atmosphere. In the present invention it is
found that levels of dioxins, florins and other contaminants,
carried away in the water flushed through the chamber are
acceptably low and so low as not to pose environmental problems, or
at least fewer than when such components are combusted. Disposal in
a water course is easy and not unsightly and does not release
contaminants into the immediate vicinity of the pyrolysis plant.
The solution can be discharged into the sewerage system.
[0041] In use of a specific embodiment of the invention far fewer
noxious gases are produced than would usually be expected following
pyrolysis and/or combustion. Factors implicated in this unexpected
result are believed to be related to the indirect heating of the
waste from an ambient temperature (below 100.degree. C.) combined
with the relatively low maximum temperature and rapid cooling
phase.
[0042] Waste gases produced by pyrolysis and/or combustion are
suitably passed through an aqueous agitation system, to assist
dissolution of gases. Gases can be bubbled through the solution,
optionally containing softened water and optionally containing
additives to promote dissolution of the gases.
[0043] Not all gases may be dissolved in the solution and it is
preferred that gases are subsequently filtered within a gas
cleaning chamber. The method also may comprise discharging
undissolved gases into the sewage system. Hence, in an embodiment,
filtered exhaust gases that have not been dissolved in solution or
retained within the filter are discharged into the sewer. These
gases then pass up the soil pipe to vent through venting stacks.
The filtered exhaust produced is substantially colourless and
odourless, principally consisting of carbon dioxide and carbon
monoxide for example.
[0044] In preferred embodiments, all of the by-products of the
process are disposed of into the sewer.
[0045] A further but associated process of the invention, for waste
treatment in a cycle, comprises providing fresh solution for
dissolving gases generated by pyrolysis and/or combustion, carrying
out a waste treatment process according to the invention, including
dissolving off-gases in the solution and disposing of the now used
solution, and repeating the cycle. The process may include
monitoring generation of waste gases within the chamber and
triggering flushing combusted material from the chamber after the
generation of waste gases has fallen below a predetermined
temperature. Evolution of gases diminishes as the process
approaches completion, so monitoring gases is an efficient means of
tracking when there is little waste left to be treated.
[0046] A pyrolysis apparatus of this aspect comprises a sealable
chamber, a waste treatment zone in the chamber, a port for
introducing waste into the chamber, a port for the exit of treated
waste, and a heating element, the apparatus further comprising a
tank to contain a gas treatment solution, an exhaust port for exit
of gases from the chamber and a conduit arranged in combination
with the tank and the exhaust port such that the gases exiting the
chamber are contacted with and can be dissolved in the
solution.
[0047] In an embodiment of the invention set out below, the conduit
bubbles the gases through the solution. Another arrangement is for
the gases to pass through an atmosphere saturated with vapour from
the solution or for gases to be combined with droplets of the
solution, for example by passing the gases through a spray of the
solution. Solution containing dissolved gases is returned to or
retained within the tank, which can be emptied as part of a cycle
or separately.
[0048] A gas cleaning chamber comprising a filter for filtration of
gases not dissolved in the solution is optionally downstream of the
conduit. The gas filter used in an example comprises carbon
granules, and the filter is suitably removable, for example to
enable washing and reuse. Preferably the filter is a ceramic
filter. Typically the filter is changed annually. Used filters can
be disposed of via a specialist landfill site.
[0049] A fourth aspect of the invention provides a process for
waste treatment comprising introducing waste into a chamber,
heating the waste to an elevated temperature to effect pyrolysis of
the waste, introducing oxygen into the chamber to effect combustion
of the waste, and flushing the combusted waste from the chamber
with water, wherein the water is introduced into the chamber as
superheated steam.
[0050] In use, the steam cools and cleans the chamber and flushes
away the ash residue of treated material. This is convenient and
efficient. The chamber is left looking clean and hence more
acceptable for users. There is reduced risk of residue in the
chamber which is unsightly or has unpleasant odour.
[0051] To carry out the flushing, water can be introduced into the
chamber via piping in walls of the chamber, the water being heated
to form superheated steam as it passes through the piping. In this
way the water is heated to the desired temperature by the chamber
heat. Also, the chamber is cooled in readiness for a next cycle of
use.
[0052] The combustion phase includes a step of allowing access of
oxygen to material in the chamber, typically supplied as air. The
process preferably comprises introducing oxygen into the chamber
via piping in walls of the chamber and subsequently introducing
water into the chamber via the same piping. This efficiently uses
common piping, simplifying system design. Piping can be in the
walls, outside the walls or in the chamber. The pipe work for the
introduction of oxygen (in air) and, later water, to the chamber
generally has a diameter in the range of 3-15 mm, more preferably
from 5-8 mm.
[0053] A large volume of steam is generated from a small volume of
water, so the process is efficient compared to use of water only
for the flushing. The chamber may thus be flushed with a volume of
water which is 50% or less of the volume of the chamber, preferably
35% or less of the volume of the chamber.
[0054] In an example set out below, the process comprises
introducing the superheated steam into the chamber through a nozzle
which directs the steam at the combusted waste. This can help break
down the structure of the residue and aid flushing of the
chamber.
[0055] The process can also or separately comprise introducing the
steam into the chamber via a nozzle which directs the steam at the
walls of the chamber. This can help clean chamber walls and aid
flushing.
[0056] In a preferred arrangement, the process comprises
introducing the steam into the chamber via a plurality of nozzles
directed, inter alia, at the combusted material (i.e. towards the
position in the chamber where the material is expected to be) and
at the walls of the chamber. The steam is preferably introduced
into the chamber via a moveable jet.
[0057] Apparatus of this aspect comprises a sealable chamber, a
waste treatment zone in the chamber, a port for introducing waste
into the chamber, a port for the exit of treated waste, a heating
element, a water tank, and a conduit between the water tank and the
chamber passing via pipework in walls of the chamber so that in use
water entering the chamber is heated by the chamber wails and
enters the chamber as superheated steam.
[0058] One or more nozzles, preferably fixed, may be provided for
direction of the steam entering the chamber.
[0059] An oxygen supply (generally as air) is preferably linked by
piping to the chamber and arranged such that in use oxygen is
supplied to the chamber via the piping, and, subsequently, water is
supplied to the chamber via the same piping. Flow rates vary with
factors including chamber size and we have operated embodiments
with air flow rates of from 25-200 litres/min.
[0060] A fifth aspect of the invention provides a process for
separation of recyclable waste from non-recyclable waste in mixed
waste comprising introducing the mixed waste into a chamber,
heating the mixed waste to an elevated temperature to effect
pyrolysis of the non-recyclable waste, introducing oxygen into the
chamber to effect combustion of the non-recyclable waste, flushing
the combusted waste from the chamber with water whilst retaining
the recyclable waste in the chamber, and transferring the retained
recyclable waste to a separate container.
[0061] A sixth aspect of the invention provides a modular pyrolysis
and combustion apparatus comprising a sealable chamber, a waste
treatment zone in the chamber, a port for introducing waste into
the chamber, a port for the exit of treated waste, and a heating
element, wherein the apparatus is free-standing and comprises plugs
for connection to an electricity supply, to a water supply, and to
a sewerage system.
[0062] An apparatus for domestic or small business use may comprise
a plug for connection to a mains electricity supply. Bigger
apparatus may connect to a 3-phase supply.
[0063] A water softening unit is generally part of the apparatus,
as are retractable wheels for ease of installation and removal.
[0064] A seventh aspect of the invention provides a pyrolysis
apparatus comprising a sealable chamber, a waste treatment zone in
the chamber, a port for introducing waste into the chamber, a port
for the exit of treated waste, and a heating element, wherein the
chamber volume is in the range from 0.01-0.50 m.sup.3.
[0065] The chamber volume is preferably in the range from 0.02-0.30
m.sup.3, more preferably from 0.03-0.20 m.sup.3 or from 0.04-0.10
m.sup.3. Chambers with volumes of about 0.06 m.sup.3 and about 0.14
m.sup.3 have been successfully tested to date.
[0066] In embodiments of the invention, two or more aspects of the
invention are combined in a particular process or apparatus. Very
preferred methods comprise methods of all aspects of the invention
and very preferred apparatus comprise apparatus of all aspects of
the invention.
[0067] An apparatus of the invention for use in multi-occupancy
dwellings comprises a sealable destruction chamber, the walls of
which are formed of heat resistant materials, for example, of
stainless steel and may include: a heating element, generally of an
ohmic type; a reflective layer (to reflect heat towards the core of
the chamber); an insulation layer; and a water jacket (to cool the
outside surface). The chamber itself normally contains a safety
system, such as pressure release valves, to operate in the event of
the internal pressure breaching a predetermined threshold. The
chamber is typically rounded, and may be circular or oval in
shape.
[0068] The lid of the chamber is preferably heavily insulated and
usually forms an airtight boundary with the chamber. Typically this
is achieved through the use of seals which can be formed of a
rubber material and the lid may contain a cooling system for the
protection of these seals.
[0069] The chamber of one embodiment has an approximately 500 mm
diameter with a depth of approximately 650 mm giving a capacity of
approximately 130 litres (0.13 m.sup.3); this will accommodate 2 or
3 white rubbish sacks. As chamber size and/or percent fill
increases, effective transfer of heat to the core of the chamber
becomes compromised; optionally the contents are agitated to ensure
effective dissipation of heat.
[0070] This apparatus is suitable for multi-occupancy residences
and generally requires a 3 phase electricity supply. In a smaller
domestic setting a smaller chamber uses less power and so 3 KW
heating elements are sufficient.
[0071] An output from the chamber is normally connected to the
sewer, typically via a valved pipe, preferably of a 75-100 mm
diameter. The valve is placed at some distance from the destruction
chamber to prevent exposure to high temperatures e.g. greater than
100.degree. C. A separate pipe connects the destruction chamber via
a radiator or heat exchanger to a combination of one or more gas
scrubbing and gas cleaning chambers. These preferably utilise
softened tap water in a closed cycle and typically vent gases to
the atmosphere via a sewer connection, downstream of the
aforementioned valve. The gas scrubbing chamber typically uses
about 4 litres of water and is usually refilled with clean water
before each pyrolysis cycle. The primary function of the radiator
is to cool off-gases prior to scrubbing and filtration. The
radiator facilitates heat loss from the passing gases such that
they are cooled from approximately 600.degree. C. to 200.degree.
C., and are preferably cooled to below 100.degree. C. The radiator
can be used to recycle heat for other purposes, such as to heat
water for domestic washing or heating.
[0072] The gas scrubbing and gas cleaning chambers control two
phases of gas output. Preferably gas scrubbing is the first phase,
comprising a water agitation system which causes gas contaminants
to dissolve into solution. Preferably gas cleaning is the second
phase, utilising a carbon filter containing carbon granules.
Generally this filter is removable; it may be washed and reused at
intervals. More preferably a ceramic filter, with or without
coating, is used. This can be changed annually.
[0073] The process works at elevated temperatures to enable
pyrolysis, these typically range from 400-700.degree. C., more
typically from 500-600.degree. C., and in a specific embodiment the
invention operates at about 550.degree. C. This temperature is
found to enable structural breakdown of the contents. Lower
temperatures may result in incomplete breakdown of certain waste
products such as bone, while higher temperatures may produce more
noxious gases and lead to problems with emissions or the materials
used for the structure of the machine.
[0074] An option, especially when the load has a relatively high
moisture content, is to add an extra initial step of maintaining
the load at a temperature at about 100.degree. C. to drive off the
excess water. Thus, the heaters can be maintained at, say, about
150.degree. C.-200.degree. C. and the temperature of the chamber
monitored. Once the temperature begins to rise above 100.degree.
C., indicating that the moisture content is reduced to a
considerably lower level, the heaters can then be increased e.g. to
500.degree. C.
[0075] Water is introduced into the chamber following the
combustion phase, and is preferably softened tap water; this
prevents the build up of lime scale deposits. The resulting hot
water may be discharged to the sewer, diverted into a domestic
heating system or used to preheat the next load. Further optionally
water may be diverted from the outer water jacket to the
destruction chamber following pyrolysis.
[0076] In a typical operation of the apparatus, waste enters the
destruction chamber and the lid is sealed, the chamber is then
heated, to about 550.degree. C. The off-gases produced during
pyrolysis are monitored; as waste is destroyed the levels of these
gases reduce, once they drop below a predetermined threshold the
heaters are switched off. Air is then passed through the heating
coil and admitted into the chamber, this is at approximately
500.degree. C.+ on entry. Entry of the air initiates combustion of
the residual waste within the destruction chamber. No external heat
is applied at this stage but the heat from the pyrolysis stage is
retained. The incoming airflow is maintained at approximately 100
litres/min, as higher flow rates may cause the chamber temperature
to rise unacceptably. Gas output is monitored during combustion,
and while waste is present the chamber output exceeds the air
input. When the gas output drops below a set threshold the airflow
is shut off and 6-7 litres of water are introduced through the pipe
system. More water may be required for larger loads. The water
enters the chamber at approximately 500.degree. C.+ as superheated
steam and Inconel.TM. pipe work is used within the machine in order
to withstand the thermal shock of this process. Entry of the
superheated steam results in a rush of gas, so the sewer connection
is opened immediately prior to introduction of the steam. The steam
cleans the inside of the chamber and washes the ash products into
the sewer. Non-combusted material is retained by the metal grid,
this can be removed for recycling or left in the machine for
another cycle(s). Some pyrolyzable material may require two or
three cycles before it is completely destroyed. Approximately 1
minute after the introduction of the steam the internal temperature
of the destruction chamber has reduced to below 100.degree. C. and
the lid can be safely opened and the apparatus used again.
[0077] Unpyrolysed waste may be retained in the destruction chamber
following completion of the pyrolysis cycle due to the location of
one or more grids in front of the chamber output. In use, glass
and/or metal in the waste is not destroyed by the pyrolysis and
after the chamber is flushed with steam/water the glass and/or
metal is captured in the grid. The grid apertures are designed to
allow ash from treated waste to pass through and so are generally
at least 1 mm in diameter; in more detail, the apertures are
generally approximately square or approximately circular with
dimensions of about 10 mm.times.10 mm if square or having a
diameter of 10 mm if round, or less, preferably being about 7
mm.times.7 mm or about 7 mm in diameter, or less, more preferably
about 5 mm.times.5 mm or about 5 mm in diameter or less. In a
specific embodiment, grid apertures of dimension about 3 mm.times.3
mm have been used. Said grids may be removed from the machine on
completion of a pyrolysis cycle to transfer unprocessed material to
a separate receptacle, and this removal may be carried out manually
or as part of an automated process.
[0078] The apparatus can suitably be adaptable to fit existing
facilities in buildings and it may prove desirable to limit (the
size of) objects that can enter the system. Accordingly the
apparatus may include a feeding device to restrict the dimensions
of material that can be introduced to the system. Optionally, the
invention may include an apparatus to agitate the contents of the
destruction chamber during pyrolysis in order to aid effective heat
distribution. Further optionally, the invention may include a
mechanism to prevent or mitigate the direct impact of waste into
the destruction chamber.
[0079] Waste production/disposal is known to be intermittent; it is
desirable for the invention to be able to effectively manage `busy`
and `quiet` times. Accordingly the invention may include an
apparatus to control waste input, preferably this is in the form of
a buffer storage system, and optionally this may comprise a storage
hopper and/or conveyor belt.
[0080] An apparatus of the invention is used for destruction of
waste in a multi-occupancy dwelling. This invention removes the
need for the transport of waste from the site of production to
sites of destruction/disposal. It further reduces the demand on
landfill sites and allows local authorities to comply with
impending European directives on waste disposal.
[0081] The invention can provide a method of low gaseous emission
pyrolysis. Due to the gradual (rather than instantaneous) exposure
of the load to heat, the waste content and the comparatively low
temperatures required for pyrolysis of this waste, fewer noxious
chemicals are produced in comparison to industrial scale pyrolysis.
Those dioxins and fluorins which are produced during pyrolysis are
relatively water soluble and thus, following gas processing, are at
acceptable levels for disposal via the sewer.
[0082] The pyrolysis system can be adapted according to the
individual customer; the type and amount of waste dictate the
required size of the unit and the temperatures needed. In an
example described below the apparatus and process are controlled by
a programmable logic controller. Preferably, subsequent embodiments
of the invention will utilise a microprocessor for this action, as
this will reduce production costs.
[0083] The invention is now illustrated in the following specific
embodiment with reference to the accompanying drawings in
which:--
[0084] FIG. 1 shows a schematic cross-sectional view of a pyrolysis
apparatus; and
[0085] FIG. 2 shows schematic isometric view of the apparatus.
[0086] Referring to the drawings, a pyrolysis apparatus has the
following features:--
PARTS LIST AND KEY
[0087] 1. Storage Chute [0088] 2. Loading Door Mechanism [0089] 3.
Loading Door [0090] 4. Lid [0091] 5. Air/water tubes [0092] 6.
Heating Plates [0093] 7. Access Drawer [0094] 8. Chamber Exhaust
(liquid) [0095] 9. Gas Exhaust Control Valve [0096] 10. Gas Cooling
Radiator [0097] 11. Liquid Bleed Valve [0098] 12. Liquid Exhaust
Control Valve [0099] 13. Wet Scrubber [0100] 14. Filtration System
[0101] 15. Filtration Return-Protection Valve [0102] 16. Exit to
Foul Water [0103] 17. Cage [0104] 18. Mesh [0105] 19. Treatment
zone [0106] 20. Hinges [0107] 21. Exit Port for Liquid [0108] 22.
Exit Port for Gas [0109] 23. Access Door to Cage [0110] 24. Chamber
[0111] 25. Sealing Plate [0112] Loading Sensor (not shown) [0113]
Seals (not shown) [0114] Lid Cooler (not shown) [0115] Insulation
for chamber (not shown) [0116] Water Jacket on Chamber (not shown)
[0117] Air Compressor (not shown) [0118] Air tank (not shown)
[0119] Water Pump (not shown) [0120] Water Header Tank (not shown)
[0121] Gas Flare (not shown)
Main Components:
Heating Chamber
[0122] The chamber (24) is manufactured from stainless steel
(Austenitic Chromium-Nickel Steel) grade 316. Other materials, e.g.
titanium, can be used. The weld material used in fabrication
retains the corrosion resistant properties of the main body of the
chamber. The chamber is resilient to the frequent heating/cooling
cycles, and the material requires a heat treatment and finishing
process within its manufacture.
[0123] The chamber has dimensions of 450.times.450.times.700 mm,
with a wall thickness of 1.5 mm (the walls can also be up to 4 mm
thick). On the top face of the chamber is a flat sealing plate (25)
which is ground to a flat surface (+/-0.1 mm max) across the top
surface. The chamber also features two outlets, an exit port (21)
leading to an exhaust (8) at the base for liquid waste (approx 60
mm dia) and an exit port or outlet (22) at the top of one of the
sides for the gas and vapour (approx 38 mm dia).
Lid
[0124] The lid (4) is manufactured from a similar material as the
heating chamber, although it is manufactured from a flat plate. The
surface is finished so the lid and chamber form a critical sealing
surface. The lid is also reinforced on its rear to avoid any
warping or distortion due to repetitive heating and cooling cycles.
The lid is designed to be as robust as possible. The lid houses the
hinge mechanism (20) on its rear and gives a mating surface for
sealing on its underside. The lid also contains the seals
(discussed below). The lid features an integrated water cooling
surface (not shown) which runs around the rim of the lid, directly
above the seals. This prolongs the product life cycle.
Seals
[0125] PTFE coated silicone rubber seals (not shown) are used to
seal any non-permanent mating faces, such as the chamber lid and
access drawer. All other mating surfaces feature a soft metal
gasket arrangement.
Access Drawer
[0126] The drawer (7) is used to remove any incompatible materials
that have not been decomposed by the process. The drawer features a
water cooling circuit (not shown) similar to the lid that is used
to cool the mating surfaces of the seat. The working surface of the
drawer is a fine mesh (18) of a 3 mm aperture (up to a 5 mm
aperture can also be used) which allows movement of solids, liquids
and gases in the system. The drawer also features a sensor that
informs the operator that the drawer has reached a certain
predetermined capacity, and requires emptying.
Heating Elements
[0127] Flat plate heaters (6) are used on all four vertical sides
of the chamber. The heaters are assembled to give maximum contact
with the outside of the chamber.
Air/Water Tubes
[0128] The tubes (5) are used to pass water and air around the
outer surfaces of the chamber. This is performed to preheat the
waste prior to direct injection of the superheated air and steam at
the latter phases of the process. The tubes are manufactured from
Stainless Steel material (Inconel.TM. material can also be used),
of 5 mm diameter.
Heat Insulation
[0129] On the outside of the heaters are many efficient insulating
layers (not shown) which work to both reflect heat back into the
chamber and reduce heat emissions to the outer surfaces of the
assembly. This insulation ensures that all heating energy is used
in a useful way to directly heat the waste product.
[0130] On the underside of the lid is a layer of ceramic plate (not
shown) (5 mm thick) which is bonded onto the stainless steel lid.
This reduces external heat loss and increases the product lifespan
of seals etc.
Cooling Radiator
[0131] The radiator's primary function is to cool the gas which has
been emitted from the product, prior to any filtration. The cooling
prolongs the life and retains maximum efficiency of the filtration
equipment.
[0132] The radiator (10) consists of a 38 mm tube (or same diameter
as the chamber gas exhaust), which is bent in 2 axes. Fine
horizontal fins are welded to the outside of the tube to increase
heat loss of the passing gases. This reduces the exhaust gases from
temperatures in the region of 600.degree. C. down to 200.degree. C.
or below.
Wet Scrubber
[0133] The wet scrubber (13) is placed after the gas radiator in
the system and removes particulate matter from the passing gases
and dissolves gases in the scrubbing liquid for disposal
subsequently. Inside the scrubbing device is a series of stacked
jets producing a very fine mist of water. The mist attracts
particulates to the outer surfaces of the mist droplets, and these
are `pulled out` of the gas flow and into the liquid waste stream.
Within the scrubber is a series of openings which guide the flow of
the waste gases directly past the mist jets.
Purification Systems
[0134] A ceramic filter (14) is preferably used. This cleans the
exhaust gases prior to release to the foul water system. The filter
screws onto a fixed manifold having a rubber seal which mates onto
the manifold. Gases pass into the centre of the filter via a tube
with an external thread which secures the filter to the manifold.
The gases pass through the porous membrane of the filter and
through to the return tube in the manifold. In normal use, the
filter is replaced approximately every year. In alternative
embodiments an activated carbon filter is used, this is replaced
approximately every 90 days.
Waste Gas Flare
[0135] After the purification systems there is optionally a small
gas flare outlet to burn off any flammable gas by-products from the
waste. The flare is sited and specified so that it does not
compromise safe and secure operation of the unit. However, in
preferred embodiments a waste gas flare is not required due to the
combination of low processing temperatures and gas cleaning
systems.
Other Key Components:
Loading Chute
[0136] The chute (1) is fabricated from a corrosion resistant
material. It has a storage capacity less than the chamber,
eliminating the possibility of overloading.
[0137] There is a sensor (not shown) within the chamber which
records the level that the waste has been loaded to, and when this
level has been reached a separate solenoid/mechanism arrangement
(not shown) locks off access to the system via the external chute.
The chute also features an access door (not shown) which allows an
operator to manually load the system on demand.
Cage
[0138] The system is housed within a cage (17). The framework has
castors (not shown) to allow the unit to be removed easily due to a
breakdown etc. The cage also has fixed outlets (not shown) for all
services needed--foul water, fresh water and 3 phase (single phase
may be used if feasible) electricity. Services are simply plugged
in and are easily disconnected.
[0139] There is a lockable front access door (23) which allows an
operator to perform basic maintenance tasks. The cage also protects
equipment from vandalism.
Chamber Water Jacket
[0140] On the outside of the chamber and lid insulation there is a
water jacket (not shown). This ensures that the insulation and
chamber do not overheat and it gives the system the ability to cool
rapidly on demand.
Control Electronics
[0141] A programmable logic controller (PLC) (not shown) controls
the operation of the system, and monitor sensors (not shown) that
are positioned throughout most mechanisms and active components
within the system. All electronics are housed within a weatherproof
enclosure (not shown), and positioned at a low point in the
cage.
Air Compressor
[0142] An air compressor (not shown) is used to run the pneumatic
cylinders (not shown) that open and close the lid and chute door
and to provide air to be injected for combustion. The compressor is
also used in transporting air through the tubes on the outside of
the chamber for the air injection phase in the cycle. The
compressor feeds a reservoir tank (not shown) which allows the
system to have a certain capacity of stored air. This means that
the compressor is not constantly running, which improves the life
cycle of the unit. The compressor is also housed in a sealed
enclosure (not shown) to ensure low noise emissions.
Water Pump
[0143] A pump is used to move water from a header tank and around
the system, feeding components such as the cooling circuit, water
jacket and the water injection feed into the heating chamber
(24).
Valves
[0144] A network of high spec valves (9, 11, 12, 15) is used to
control and throttle the flow of liquid and gas between the
chamber, exhaust, radiator, wet scrubber and purification systems
and to enable periodic change of water in the scrubber. These are
controlled remotely by the programmable logic controller.
Process Cycle
1. Loading of Waste
[0145] The chamber lid is opened and the waste enters the chamber
(which is at ambient temperature) via the storage chute. The lid is
then closed and the chamber is sealed.
2. Heating
[0146] The panel heaters are activated and the interior temperature
is raised to between 500-550.degree. C. The liquid exhaust valve is
closed and the emitted gases during the heating phase are passed
through the cooling and purification system.
[0147] The temperature ramping period takes approximately 5-10
minutes, after which time the temperature is maintained via a
thermostat. Due to the efficiency of the chamber insulation the
power applied to the heaters is throttled to maintain the interior
chamber temperature.
[0148] The gases produced by the waste are monitored and the
moisture in the waste is emitted as a vapour and passed to the
exhaust. The mass of a full load of typical waste reduces by
approximately 70%.
[0149] The temperature is held for approximately 30 minutes.
3. Air Injection (Also Known as the Combustion Phase)
[0150] After the heating phase has completed the external panel
heaters are turned off and air is passed through the tubes around
the outside of the chamber (which preheats the air to a superheated
temperatures) and injected into the top of the chamber. The
injectors are such that the air is sprayed as a widely dispersed
stream, as opposed to a concentrated jet. The air is initially
pulsed to reduce stress in the system, and after a certain period
the air is injected constantly.
[0151] The flow rate of the air is kept to around 50 l/min (rates
of from 25 to 1001/min, and also outside these ranges may be used,
depending on system size and configuration). This low rate is
maintained to ensure that internal pressure levels within the
chamber are not increased too rapidly, as this will compromise the
effectiveness of the seals.
[0152] With the introduction of air, the waste begins to glow. The
volume of the waste decreases further, typically reaching around 5%
of its original volume. The waste is converted to a very fine
ash.
[0153] Smoke and particulate levels in the system increase during
the air injection phase. All gaseous exhausts are passed through
the wet scrubber and through the purification system. The
combustion phase lasts approximately 15 minutes.
6. Steam Injection
[0154] When the combustion phase has completed the air injection is
turned off, the gas exhaust valve is closed, the liquid exhaust
valve is opened and water flows through the same tubes as the air,
around the outside of the chamber and is injected as superheated
steam. The steam is initially injected in a series of pulses, then
as a constant stream. The pulses are 1 second on, 3 seconds off for
30 pulses, then continuously on for 3 minutes. The water is
injected at approximately 2 l/min.
[0155] The steam both flushes the ash out through to the exhaust,
and cleans the internal faces of the chamber. The steam has a
cooling effect on the chamber, and after approximately 1 minute the
internal temperature of the chamber drops to below 100.degree. C.
After the steam injection has completed the lid opens and the
system is ready for its next cycle. Any incompatible waste that has
not been decomposed by the cycle is held in the drawer, and can be
removed and recycled.
EXAMPLE 1
[0156] Apparatus of the invention was tested for its ability to
treat domestic waste whilst ensuring that gas and water emissions
did not exceed the limits imposed by environmental legislation.
[0157] A mixed bag of waste was prepared, based on analysis of
typical breakdown of domestic waste, containing 100 g garden waste,
100 g paper and cardboard, 200 g PVC, 300 g meat by-products and
table salt and 100 g polyester, making a total weight of 800 g
mixed waste.
[0158] This mixed waste was treated in apparatus of the invention
using parameters determined to provide waste destruction in a
relatively short period of time, these parameters being a pyrolysis
temperature of 550.degree. C. for 75 minutes followed by combustion
with an air flow of from 40-50 litres/min for 15 minutes followed
by steam injection to wash the ash residue into the water
collection tank (the tank being used in the emissions test instead
of a sewer connection).
[0159] This treatment was found to destroy all of the mixed waste,
ie. convert it all to ash which was flushed from the chamber with
the steam/water.
[0160] Testing of the off-gases gave the following results:--
TABLE-US-00001 TABLE 1 Off-gas data NO (NOx) SOx HCL mg/m.sup.3
mg/m.sup.3 mg/m.sup.3 Ex. 1 6 185 <47 Limit stipulated by 400
200 60 environmental legislation
[0161] Separately, the wet scrubber water, to be discharged to the
sewer in normal operation, was tested for levels of heavy metals
and dioxins with the following results:--
TABLE-US-00002 TABLE 2 Off-water Data Thal- Mer- Arse- Cad- Chro-
Nick- Di- lium cury nic mium mium Lead el oxins Ex. 1 0.002 0.04
38.5 1.4 25.7 125 127 0.01 Limit stipulated 0.05 0.03 150 50 500
200 500 0.3 by environmen- tal legislation
[0162] Hence, the off-gases and the off-water were inside the
emissions limits stipulated in the environmental legislation.
[0163] The invention hence provides treatment of waste by pyrolysis
and apparatus for doing so.
* * * * *