EP2986914B1

EP2986914B1 - Improvements in waste processing

Info

Publication number: EP2986914B1
Application number: EP14717839.6A
Authority: EP
Inventors: Rifat Al Chalabi; Ophneil Henry Perry
Original assignee: Chinook End Stage Recycling Ltd
Current assignee: Chinook End Stage Recycling Ltd
Priority date: 2013-04-17
Filing date: 2014-04-14
Publication date: 2017-12-13
Anticipated expiration: 2034-04-14
Also published as: WO2014170647A1; EP2986914A1; GB2513143B; GB2513143A; GB201306943D0

Description

The present invention relates to waste processing and particularly to a system and method for generating energy from waste material and/or reclaiming material from waste. In particular the invention relates to an apparatus and a method for processing municipal waste by thermally removing coatings and/or impurities from materials which are capable of being recovered from the waste, for example removing coatings and impurities from metals that are capable of being recycled, and then post-processing any carbonaceous residue.
Pyrolysis and gasification are processes that convert organic materials, such as biomass, or materials containing organic content into carbon monoxide and hydrogen by heating the raw material to high temperatures in an environment containing little or no oxygen. The resulting gas mixture is called synthesis gas or syngas. Synthetic gas is made predominately of carbon monoxide (CO), and hydrogen.
Pyrolysis is an efficient method for extracting energy from many different types of organic materials and provides clean waste disposal. In a pyrolysis reaction the material is heated in an atmosphere comprising substantially no oxygen. Depending on the material being processed, a by-product of the pyrolysis process can be carbonaceous residue which may include carbon, cokes and char. Such residues are collectively referred to herein as "char". Energy recovered from combustion of syngas from pyrolysis is more efficient than direct combustion of the solid original waste, particularly since more of the organic materials contained in the processed material are converted into energy (higher thermal efficiency). Gasification is similar to pyrolysis except insofar as a small amount of oxygen is present.
Syngas may be burned directly in internal combustion engines or used to produce alcohols such as methanol, ethanol and propanol, and also hydrogen. For electrical generation from steam turbines, a waste-heat boiler is used to recover the heat generated from combusting the syngas. It is known to use thermal treatment chambers to destroy the gases, tars, and other environmentally unsound components that are emitted from the material as it is processed and become entrained in the gas produced. To destroy these components they must be heated to a temperature in excess of approximately 850°C for a minimum residency time. Excess hot gasses from this thermal treatment chamber can have heat recovered therefrom for use in powering, for example, a waste heat boiler which drives a steam turbine and thereby generates electricity.
At present there are two known types of pyrolysis/thermal de-coating, these being continuous process and batch process.
Continuous processing is good for large volumes of substantially consistent supply material that enables steady state process conditions. Typically, the material passes constantly through some form of oven at a steady speed so that by the time it exits from oven it is fully pyrolysed/de-coated. This process is very good for large volumes of a substantially homogeneous mixture of waste, as it relies on steady state conditions to ensure the complete process is achieved, i.e. the oven temperatures and feed rates are set at a desired level and remain constant.
Batch processing is beneficial where either low volumes are being processed or where there is a large variation in the type of material to be processed from batch to batch, e.g. calorific content, water content etc. For example, a batch containing predominantly paper and wood would require different processing conditions than, for example, a batch containing predominantly shredded rubber (e.g. car tyres).
One problem with the batch process is that, while it enables great flexibility in the processing cycle by allowing process variation between batches, the batch process does not produce a steady rate of syngas, in particular at the beginning and at the end of each batch where there is a ramp up and a ramp down of syngas production.
There are a couple of problems associated with this. Firstly, syngas is normally treated in a treatment chamber after production to heat and/or combust it, and the hot exhaust gases are then often used for power generation, e.g. to power a boiler. As there is cyclic fluctuation in the syngas production rate from the batch process, the thermal treatment chamber must be sized to accommodate maximum syngas production and is therefore underutilised for much of the cycle. This is compounded by the batch to batch fluctuation in the material which may result in different peaks of maximum syngas production. Specific types of material produce short, high peaks and other materials producing long, flat peaks. Accordingly, for a system designed for variable materials, the thermal oxidiser must be sized to be able to destroy all the syngas produced at the maximum peak, resulting in it being run substantially under capacity for much of its operational life.
This leads to a further problem with the batch process method in that, to destroy syngas, the thermal oxidiser must be maintained at a minimum temperature, typically in excess of 850°C. During periods where there is insufficient syngas produced by the processing of the material to maintain this temperature, it is necessary to burn virgin fuel, typically natural gas, in a burner of the thermal treatment chamber so as to maintain this temperature and ensure that any impurities in the syngas entering the oxidiser are destroyed. This use of virgin fuel reduces the overall efficiency and cost effectiveness of the process and, in some stages to the cycle, can consume a large amount of energy. As well as reducing the efficiency of the system, the use of fossil fuels offsets the environmental benefits of recovering energy from waste.
A further specific problem occurs in both batch processing systems and in continuous processing systems when processing low calorific value waste, in particular waste that has a relatively high content of low calorific value organic matter therein, for example a relatively high wood content. As will be appreciated wood has a low calorific value compared to other organic material such as plastics, rubbers etc. When heated in the absence of oxygen these materials break down to form char. As this residue has a very high carbon content it does not break down further within the usual processing time for the waste. The result is that at the end of the process, not only is there a residual char from the process but the energy output of the process is greatly reduced since a relatively high portion of the energy of the waste remains in the char. US 2009/020052 discloses an apparatus having the features specified in the preamble of claim 1 and a method having the features specified in the preamble of claim 10. It is the purpose of the present invention to produce a batch process system that addresses at least some of the problems associated with the state of the art.
According to a first aspect there is provided an apparatus arranged to process waste having an organic content, the apparatus comprising: a first processing chamber arranged to receive and heat said waste in a reduced or substantially zero-oxygen atmosphere to produce syngas and carbonaceous material; a second processing chamber arranged to receive and heat carbonaceous material in a reduced oxygen atmosphere to gasify it to produce carbon monoxide; and a thermal treatment chamber having a syngas inlet configured to receive syngas from the first chamber and the carbon monoxide from the second chamber, said thermal treatment chamber configured to heat the gas therein to break down any volatile organic compounds or long chain hydrocarbons therein. According to the invention, the apparatus comprises means for controlling the oxygen content within the second processing chamber comprising a control system configured to monitor a property of the gas produced in the first processing chamber and to control a flow of oxygen containing gas into the second processing chamber in response to said property. A reduced or substantially zero-oxygen atmosphere may comprise an atmosphere with an oxygen level lower than atmospheric air or standard conditions. The atmosphere may be oxygen-depleted. The reduced or substantially zero-oxygen atmosphere may comprise less than 20% oxygen. Alternatively, the reduced or substantially zero-oxygen atmosphere may comprise less than 15%, 12%, 10%, 8%, 6%, 5%, 4%, 3%, 2%, or 1% oxygen by volume. In one embodiment the oxygen level is at trace levels, or 0%. The reduced or substantially zero-oxygen atmosphere may comprise an oxygen level sufficiently low to prevent the organic waste being fully oxidised, for example, to prevent the formation of carbon dioxide.
In the second processing chamber, since there is a low level of oxygen, a gasification process occurs. In a gasification process the oxygen reacts with the carbon to produce carbon monoxide and accordingly carbonaceous materials can be consumed in a gasification process in the second processing chamber. This enables more of the energy to be recovered from the waste as the energy stored within the carbonaceous residue created in the first processing chamber can be recovered.
The first processing chamber and/or the second processing chamber may be batch processing chambers. As batch processing results in an uneven production of gas, as described in relation to the Figures, the use of the two processing chambers can assist in evening out the production of gas from the apparatus.
The means to control the oxygen content of the second batch processing chamber may be such that the oxygen content in the second batch processing chamber is higher than the oxygen content in the first batch processing chamber.
Means may be provided for providing a flow of hot gas to the first processing chamber and a flow of hot gas to the second processing chamber for heating the material therein, the system further comprising valve means for introducing oxygen containing gas into the flow of hot gas to the second chamber.
The apparatus may further comprise valve means to selectively divert at least a portion of the gas exiting the first processing chamber to pass through the second processing chamber prior to entering the thermal treatment chamber.
A conduit can be provided between the thermal treatment chamber and the first processing chamber for re-circulating hot gas from the thermal treatment chamber to the first processing chamber. A diverter valve can be provided in said conduit, said diverter valve for selectively diverting the re-circulating hot gas between the first processing chamber and the second processing chamber. The apparatus may also comprise a flow rate controller to control the flow rate of re-circulated gas.
The apparatus may comprise an outlet from the thermal treatment chamber leading to at least one of a waste-heat boiler and a syngas engine.
The apparatus may be provided with a carbon monoxide sensor downstream of the first processing chamber that monitors and produces an electrical output signal indicative of the carbon monoxide content of the gas produced from the first processing chamber.
The apparatus may further comprising a diverter valve in said conduit, said diverter valve for selectively diverting the re-circulating hot gas between the first processing chamber and the second processing chamber.
In one embodiment the first processing chamber is a rotating or tilting oven having a first size and the second processing chamber has a second size smaller than the first size.
The apparatus may further comprise at least one heat source configured for providing a flow of hot gas to the first and second processing chambers. The heat source may be configured to provide a flow of hot gas with substantially zero oxygen content to the first processing chamber so as to pyrolyse the material therein.
The apparatus may comprise a means of adding H₂O to the second processing chamber to gasify the carbonaceous material therein to produce syngas comprising carbon monoxide and hydrogen.
According to a second aspect there is provided a method of processing organic-based material or waste, comprising: heating, in a first processing chamber, material having an organic content in a reduced or substantially oxygen free environment to produce syngas and carbonaceous material; heating in a second processing chamber carbonaceous material produced in the first processing chamber in a reduced oxygen environment to produce carbon monoxide; receiving syngas from the first processing chamber and carbon monoxide from the second processing chamber in a thermal treatment chamber and heating said syngas and carbon monoxide therein to break down any volatile organic compounds or long chain hydrocarbons entrained therein. According to the invention, the method further comprises monitoring a property of the gas produced in the first processing chamber; and controlling a flow of oxygen containing gas into the second processing chamber in response to said property so as to control the oxygen content within the second processing chamber.
The first processing chamber and/or the second processing chamber may be operated in a batch processing mode.
Controlling the oxygen content of the second batch processing chamber may be such that the oxygen content in the second batch processing chamber is higher than the oxygen content in the first batch processing chamber.
In one embodiment the method may further comprise: providing a flow of hot gas to the first processing chamber for heating the material therein; providing a flow of hot gas to the second processing chamber for heating the material therein, wherein the method further comprises introducing oxygen containing gas into the flow of hot gas to the second chamber.
The method may comprise one or more of the following:

selectively diverting at least a portion of the gas exiting the first processing chamber to pass through the second processing chamber prior to entering the thermal treatment chamber;
providing a return conduit from the thermal treatment chamber to the first processing chamber and re-circulating hot gas from the thermal treatment chamber to the first processing chamber via said conduit;
identifying when said syngas production rate from the first processing chamber falls below a second predetermined value and diverting said re-circulated gas from said first processing chamber to said second processing chamber to isolate said first batch processing pyrolysis chamber from said re-circulated gas flow;
directing hot gases from the thermal treatment chamber to at least one of a waste-heat boiler and a syngas engine;
providing a carbon monoxide sensor downstream of the first processing chamber for monitoring the carbon monoxide content of the gas and producing an electrical output signal indicative of the carbon monoxide content of the gas produced from the first processing chamber;
monitoring a property of the gas produced in the first processing chamber and controlling the flow of oxygen containing gas into the second processing chamber in response to said property;
selectively diverting the re-circulating hot gas between the first processing chamber and the second processing chamber;
controlling the flow rate of re-circulated gas; and
providing at least one heat source configured for providing a flow of hot gas to the first and second processing chambers.

The heat source may be configured to provide a flow of hot gas with substantially zero oxygen content to the first processing chamber so as to pyrolyse the material therein.
The method may comprise: monitoring a property of the syngas indicative of the syngas production from the first processing chamber; identifying from said monitored property when the syngas production rate from the first processing chamber falls below a first predetermined value; and increasing the oxygen content in the second processing chamber.
The method may include controlling the amount of hot gas and the amount of oxygen diverted through said second processing chamber so as to maintain a substantially constant flow rate of syngas into said thermal treatment chamber.
In one embodiment the method may comprise identifying when said syngas production rate from the first processing chamber falls below a second predetermined value and diverting said re-circulated gas from said thermal treatment chamber to said second processing chamber to isolate said first batch processing pyrolysis chamber from said re-circulated gas flow.
The method may comprise: during the processing cycle, maintaining the second processing chamber at a temperature sufficient for gasification; and controlling the flow of oxygen into the second processing chamber such that carbon dioxide can be produced upon demand.
The method may comprise providing a means of adding H₂O to the second processing chamber to gasify the carbonaceous material therein to produce syngas comprising carbon monoxide and hydrogen.
Using the method and apparatus of the invention, the gas produced in the first processing chamber can be selectively diverted through a second processing chamber and have its oxygen content increased so as to cause the syngas produced by the first processing chamber to be supplemented by the carbon monoxide produced by the second processing chamber so as to enrich the gas flow from the first process.
The invention will now be described by way of example with reference to the drawings in which:

Figure 1 is a typical syngas production curve for a batch pyrolysis cycle;
Figure 2 is a carbon monoxide production curve for char;
Figures 3 to 5 are schematic diagrams for apparatus in accordance with the invention; and
Figure 6 is a flowchart for a method of the invention.

Referring to Figure 1, a graph of syngas production rate against time is shown for a full cycle of a batch processing chamber. An example of an apparatus for performing this operation is disclosed in WO 2006/100512 and although described in this operation as being a pyrolysis reaction it will be appreciated by the skilled person that there could be some oxygen content within the processing chamber resulting in some gasification.
The chamber is loaded and the process started at T₁. As the chamber becomes heated the pyrolysis process starts and the syngas production increases until, at T₂, the material is pyrolysing at a substantially steady rate. In reality the production rate during this period will fluctuate about an average value. At time T₃, the majority of the material in the chamber has pyrolysed and the syngas production starts to reduce until T₄, when all of the organic material has pyrolysed. The processing chamber can then be emptied of the non-pyrolysable materials (e.g. metals), refilled, and processing of the next batch started. As described above, for certain types of materials, in particular those having a high wood content, a pyrolysis reaction also forms a carbonaceous material, referred to herein as char, from these materials. The result of this is that a substantial amount of the energy from the material is still retained in the residue form the pyrolysis process.
The curve shown in Figure 1 is typical of municipal waste. It will be appreciated that the curve shown is a generic curve for this type of waste and that the actual shape of the curve will change depending on the exact content of the waste.
Referring to Figure 2, a graph of carbon monoxide production rate against time is shown for a batch processing chamber when gasifying the char formed in the first process. Once the char is at the required temperature the rate of oxidation is dependent upon the surface area of the char and the oxygen available for the oxidation process. Accordingly, the shape of the curve can be modified as required by altering the oxygen available for oxidation to occur. It will therefore be appreciated that the reaction can be stopped whilst maintaining the char at oxidation temperatures by heating the char with gas that contains no oxygen and the carbon monoxide production can be produced on demand by adding oxygen containing gas to the oxygen free gas prior to it contacting the heated char.
In both of these cycles the syngas/carbon monoxide being produced can either be combusted in the presence of oxygen in a thermal treatment chamber to produce heat for conversion to energy (e.g. via a boiler and steam turbine), or can be treated in the thermal treatment chamber in the absence of oxygen to break down any long chain hydrocarbons or VOC's therein and the gas can then be used to power a syngas engine to produce electricity.
The thermal treatment chamber must raise the temperature of the syngas to a predetermined temperature, typically in excess of 850° C for a minimum amount of time to destroy the any VOC's or long chain hydrocarbons. The presence of sufficient oxygen within the treatment chamber will dictate if the syngas is combusted or if it is just heated.
Referring to Figure 3 a waste treatment apparatus of the invention is shown. A first waste processing chamber 10 is heated with a flow of hot gasses from heat source 12, the flow of hot gasses being controlled by a valve 14 which is operated by a controller 16. The processing chamber is preferably a tilting oven type as described in patent application WO 2006/100512 .
The first processing chamber 10 is used for heating 200 the material being processed, e.g. the municipal solid waste. Preferably no oxygen is present in the hot gases produced by the first heat source 12 such that the material in the first processing chamber 10 pyrolyses to release syngas. The syngas production rate for this first processing chamber 10 is substantially as shown in Figure 1, i.e. it has a ramp up phase, a production phase and a ramp down phase. Syngas produced in the first processing chamber 10 passes through a conduit 18 into the thermal treatment chamber 20, via valve 22. The syngas is heated or combusted in the treatment chamber 20 and the hot gases exit the treatment chamber 20 via conduit 24. If the gasses are heated but not combusted in the treatment chamber 20 then the gas exiting the treatment chamber 20 will be syngas. If, however, the gasses are combusted in the treatment chamber the gases exiting the treatment chamber 20 will be hot exhaust gases. In either case heat can be recovered from the gas for conversion into usable energy, for example in a heat exchanger of a boiler. In the case of the syngas not being combusted in the treatment chamber, after heat is recovered therefrom the gas can be used, for example in a syngas engine, to produce electricity.
A second processing chamber 26 is also provided. The second processing chamber 26 is loaded with char produced from the pyrolysation of the material being processed in the first processing chamber. Hot gas produced from a further heat source is passed through the second processing chamber (which may also be of the type described in WO 2006/100512 ). The gas entering the second processing chamber 26 via valve 28 can have its oxygen level controlled. A source of oxygen containing gas 30, for example air, can be added 204 to the gas flow via valve 32. The oxygen reacts with the hot char to gasify it to produce carbon monoxide which passes through CO conduit 34 to the thermal treatment chamber 20 via a valve 36. It will be appreciated that the CO production rate of the second processing chamber will be dependent upon its temperature and on the oxygen content of the gas. Although the oxygen source 30 is shown as being discrete from the heat source it will be appreciated that the oxygen level of the hot gases supplied can be controlled within the heat source 28.
As will be understood, although the second processing chamber is discussed as producing carbon monoxide it may also produce hydrogen (the other main component of syngas) and carbon dioxide if any moisture is present.
The second processing chamber 26 is preferably maintained at a temperature sufficient for oxidation to take place. This may be done by passing substantially dry, hot gas containing no oxygen therethrough. As the material has already been fully pyrolysed it is inert in the absence of oxygen. The production of carbon monoxide in the second processing camber can then be controlled by adding oxygen to the hot, dry gas. In addition, hydrogen may be produced by adding steam to the gas passing through the second processing chamber.
In one mode of operation, the two processing chambers can be run in parallel for the same processing time and when the carbon monoxide sensor 38, and optionally hydrogen sensors, detect that the material in the first processing chamber is fully processed, the first and second chambers can be isolated from the hot gas, emptied, and refilled. The oxygen content of the gas being supplied to the second processing chamber 26 can be controlled to ensure that all the char in the second processing chamber is gasified by the time the first processing chamber has finished its cycle.
In an alternative mode of operation when the syngas production rate from the first processing chamber reaches T₃ and starts to drop off 206, as detected by the carbon monoxide sensor 38, the oxygen content of the gases passing through the second processing chamber 26 can be increased 204 (or alternatively gas containing oxygen can start to be passed through the second processing chamber). Accordingly the production rate of carbon monoxide, and optionally hydrogen, from the second processing chamber 26 increases and substantially balances the reduction in production rate from first processing chamber 10. This results in a more continuous production of syngas which can be particularly beneficial when the gas is being used to power a syngas engine.
This apparatus 100 can therefore uses the syngas produced in the second processing chamber 26 to compensate for the shortfall in the production rate of syngas from the first processing chamber 10 at the start and end of the cycle.
Once syngas production in the first processing chamber 10 is complete by virtue of the material therein being fully pyrolysed the first processing chamber 10 can be opened 210 and replenished with a fresh batch of organic-based material for processing and restarted. As the syngas production ramps up from the fresh batch of organic-based material in the first processing chamber the amount of oxygen being supplied to the second processing chamber 26 is reduced 214 so that the total syngas flow to the thermal treatment chamber is substantially constant.
As the speed of the gasification reaction in the second processing chamber 26 can be controlled by the addition of a varying level of oxygen and optionally steam, it can be controlled so that gasification is complete when the first processing chamber is in peak production. A further carbon monoxide sensor 46 is provided downstream of the second processing chamber 26 which detects when the gasification in the second processing chamber is complete. The second processing chamber 26 can then be opened, emptied and replenished.
The carbon monoxide sensor 38 located in the conduit 18 downstream of the first processing chamber 10 measures and produces an electrical signal indicative of the carbon monoxide content of the gas produced from the first batch processing pyrolysis chamber. As syngas is primarily a mixture of carbon monoxide and hydrogen the carbon monoxide content of the gas exiting the first processing chamber 10 is a good indicator of the level of syngas being produced therein and can be used to determine if the syngas production meets a required level 202 or if there is a shortfall in syngas.
A control system 16 receives the output from the carbon monoxide sensor 38 and controls the valves 14, 22, 28, 32 and 36 in response thereto. In particular the controller controls the amount of oxygen that passes into the second processing chamber 26.
Referring to Figure 4 an alternative arrangement is shown. In this arrangement, instead of having its own independent heat source as shown in Figure 3, the second processing chamber 26 receives its hot gas from the thermal treatment chamber 20. The thermal treatment chamber 20 will have a burner therein for burning fuel to heat the gas therein. Accordingly some of the hot gas form the thermal treatment chamber 20 can be re-circulated through the second processing chamber 26. As this gas will not contain any oxygen the char in the second processing chamber 26 will be heated to an elevated temperature by this recirculating gas.
When the controller 16 deems necessary, which may be when the first processing chamber 10 is producing syngas or alternatively when the syngas production form the first processing chamber 10 is reduced towards the start and end of its cycle, the controller 16 can increase the oxygen content, and optionally the moisture content, of the gas passing through the second processing chamber 26 to cause the material therein to gasify. The source of oxygen 30 may include a source of oxygen and water, or steam, the supply of both of which can be controlled independently of one another to maintain a desired carbon monoxide and optionally hydrogen output 212. A high temperature fan 40 may be provided to circulate some of the hot gases from the thermal treatment chamber 20 to the second processing chamber 26. Apart from the different heat source for the second processing chamber the apparatus operates in the same manner as described above, and the gas not circulated through the second processing chamber 26 exits the thermal treatment chamber via conduit 24.
Referring to Figure 5, a further arrangement of the invention is shown. The apparatus is substantially the same as described in relation to Figure 4 except that the independent heat source 12 that provides hot gas to the first processing chamber 10 is replaced with a recirculation conduit 42 connecting the thermal treatment chamber 20 to the first processing chamber 10. A high temperature fan 44 is provided in the conduit 42 to drive the hot gas through the conduit. In this manner the first processing chamber can rely upon the heat produced in the thermal treatment chamber 20 to heat the material in the first processing chamber 10. The controller 16 operates the system as described above. It will be appreciated that the parallel sections of re-circulation conduit joining the thermal processing chamber 20 to the first processing chamber 10 and the second processing chamber 26 may be combined such that the conduit feeding hot gas into the second processing chamber 26 branches off from the conduit 42.
By controlling the valves 14, 22, 28, 36 gas can be directed to the first processing chamber 10, the second processing chamber 26, or both processing chambers. The valves also allow the first processing chamber 10 and the second processing chamber 26 to be isolated 208 from the hot gas flow so that they can be emptied and refilled whilst the process is maintained on the syngas produced from the other processing chamber.
As the invention operates a two-step process to pyrolyse the material to release energy and produce char, and then gasifies the char to release the remainder of the energy, the process allows more of the energy in the raw material (municipal waste) to be recovered and thereby increases the overall efficiency of the system.
As the variance in system syngas production is reduced, the thermal oxidiser can be specified to a size to fully combust the substantially constant level of syngas being produced as opposed to being sized to cope with the maximum syngas as is currently the case.
During initial start-up of the system it will be necessary to burn some virgin fuel to heat the thermal treatment chamber, however, once started, the thermal treatment chamber can run the burner that heats the gas therein on syngas. As the system substantially produces a constant syngas flow there is no period during its operation when there is a large shortfall in the syngas required to maintain the thermal treatment chamber at its operational temperature. Accordingly, the system reliance on virgin fuel is reduced and the overall system efficiency and environmental credentials are increased by virtue of reduced fossil fuel consumption.
A further advantage of substantially steady state production is that it significantly reduces the ripple in the power output enabling a much more steady power generation to be achieved.
Yet further, as the downtime between batches in the first processing chamber 10 can be effectively filled by using production in that period to gasify the char in the second processing chamber, production from a single system is increased.
The above apparatus may also provide other benefits to the system. For example, as it is possible to enable a substantially constant amount of syngas to be produced and consumed in the thermal treatment chamber, the apparatus will provide a more steady state output of excess gas for the waste-heat boiler. This will have a knock-on effect and help to minimise any fluctuation in electrical output of a generator powered by the waste-heat boiler. Furthermore, for maximum efficiency and reliability, electrical generation equipment generally operates best under the steady state conditions that the invention helps to provide.
Although even when used in the first mode of operation described above the downtime between batch changes is not overcome, the overall efficiency when processing material containing a large amount of material having a relatively low energy content, e.g. wood, is improved by the two-stage processing.
Overall control of the components of the system, e.g. the first processing chamber, the thermal treatment chamber etc will be apparent to the person skilled in the art.

Claims

An apparatus arranged to process waste having an organic content, the apparatus comprising:
a first processing chamber 10 arranged to receive and heat said waste in a reduced or substantially zero oxygen atmosphere to produce syngas and carbonaceous material;

a second processing chamber 26 arranged to receive and heat the carbonaceous material in a reduced oxygen atmosphere to gasify it to produce carbon monoxide;

a thermal treatment chamber 20 having a syngas inlet configured to receive syngas from the first chamber 10 and the carbon monoxide from the second chamber 26, said thermal treatment chamber 20 configured to heat the gas therein to break down any volatile organic compounds or long chain hydrocarbons therein; and

characterised in that the apparatus comprises means for controlling the oxygen content within the second processing chamber 26 comprising a control system 16 configured to monitor a property of the gas produced in the first processing chamber 10 and to control a flow of oxygen containing gas into the second processing chamber 26 in response to said property.
An apparatus according to claim 1 wherein the first processing chamber 10 and/or the second processing chamber 26 are batch processing chambers.
An apparatus according to claim 2 further wherein:
the means to control the oxygen content of the second batch processing chamber 26 are such that the oxygen content in the second batch processing chamber 26 is higher than the oxygen content in the first batch processing chamber 10.
An apparatus according to any preceding claim further comprising means for providing a flow of hot gas to the first processing chamber 10 and a flow of hot gas to the second processing chamber 26 for heating the material therein, the system further comprising valve means 32 for introducing oxygen containing gas into the flow of hot gas to the second processing chamber 26.
An apparatus according to any preceding claim further comprising valve means to selectively divert at least a portion of the gas exiting the first processing chamber 10 to pass through the second processing chamber 26 prior to entering the thermal treatment chamber 20.
An apparatus according to any preceding claim further comprising a conduit 42 between the thermal treatment chamber 20 and the first processing chamber 10 for re-circulating hot gas from the thermal treatment chamber 20 to the first processing chamber 10.
An apparatus according to any preceding claim further comprising an outlet 24 from the thermal treatment chamber 26 leading to at least one of a waste-heat boiler and a syngas engine.
An apparatus according to any preceding claim further comprising a carbon monoxide sensor 38 downstream of the first processing chamber 10 that monitors and produces an electrical output signal indicative of the carbon monoxide content of the gas produced from the first processing chamber 10.
An apparatus according to any previous claim further comprising a means of adding H₂O to the second processing chamber 26 to gasify the carbonaceous material therein to produce syngas comprising carbon monoxide and hydrogen.
A method of processing organic-based material or waste, comprising:
heating, in a first processing chamber 10, material having an organic content in a reduced or substantially oxygen free environment to produce syngas and carbonaceous material;

heating in a second processing chamber 26 carbonaceous material, produced in the first processing chamber 10, in a reduced oxygen environment to produce carbon monoxide;

receiving syngas from the first processing chamber 10 and carbon monoxide from the second processing chamber 26 in a thermal treatment chamber 20, and heating them therein to break down any volatile organic compounds or long chain hydrocarbons; characterised in that the method further comprises monitoring a property of the gas produced in the first processing chamber 10; and

controlling a flow of oxygen containing gas into the second processing chamber 26 in response to said property so as to control the oxygen content within the second processing chamber 26.
A method according to claim 10 wherein:
controlling the oxygen content of the second batch processing chamber 26 is such that the oxygen content in the second batch processing chamber 26 is higher than the oxygen content in the first batch processing chamber 10.
A method according to any one of claims 10 to 11 further comprising:
providing a flow of hot gas to the first processing chamber 10 for heating the material therein;

providing a flow of hot gas to the second processing chamber 26 for heating the material therein; and wherein

the method further comprises introducing oxygen containing gas into the flow of hot gas to the second processing chamber 26.
A method according to any one of claims 10 to 12 further comprising selectively diverting at least a portion of the gas exiting the first processing chamber 10 to pass through the second processing chamber 26 prior to entering the thermal treatment chamber 20.
A method according to any one of claims 10 to 13 further comprising
providing a return conduit 42 from the thermal treatment chamber 20 to the first processing chamber 10 and re-circulating hot gas from the thermal treatment chamber 20 to the first processing chamber 10 via said conduit.
A method according to any one of claims 10 to 14 further comprising:
monitoring a property of the syngas indicative of the syngas production from the first processing chamber 10;

identifying from said monitored property when the syngas production rate from the first processing chamber 10 falls below a first predetermined value;

increasing the oxygen content in the second processing chamber 26.