GB2466260A

GB2466260A - Waste reduction and conversion process with syngas production and combustion

Info

Publication number: GB2466260A
Application number: GB0822984A
Authority: GB
Inventors: Stephen Mattinson
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-12-17
Filing date: 2008-12-17
Publication date: 2010-06-23
Also published as: GB0822984D0

Abstract

A waste reduction and conversion to heat and syngas process is undertaken during waste flow along an elongate reaction vessel 38, through a substantially inert gas zone 1, a reducing zone of syngas 3-5, separated from an oxygenating gas, such as air, by the inert zone, a barrier layer 7 separating the inert zone 1 and reducing zone 3-5. The inert gas is exhaust from combustion of syngas in an internal combustion engine 17. The waste moves under gravity through a syngas polishing zone 2, a pyrolysis zone 3,4 and a gasification zone 5, and syngas from the gasification zone 5 is fed to the syngas polishing zone 2 without going through the pyrolysis zone 3,4 via a scrubber 19. New material added to the vessel is heated using heat taken from the hotter end of the vessel. The waste can be organic, such as wood chips or husks.

Description

System for fue11in an engine from waste HELD OF THE 1NVENTTON The present invention is related to the field of waste treatment, to energy from waste, to converters for generating syngas from waste, and to means for running engines from syngas.

The word waste, as used in this document, refers to wood, wood chips, bark, vines, tree branches, acorns, husks, skip waste, waste containing organic material, waste containing hydrocarbons, or any mixture of these materials that may be suitable for use in the current invention, whether these are normally considered a waste product or not. The word syngas, as used in this document, refers to a range of fuel gases which are derived from waste and are sometimes known as synthesis gases.

Other aspects of the present invention particularly relate to the cleaning or polishing of syngas to remove impurities. Still other aspects of the present invention relate to the pre-treatment of the waste. The particular pre-treatments which the invention relates to, include the drying of the waste and the pre-heating of the waste. Further aspects of the present invention relate to methods of cooling the solid char produced by burning waste, and to methods of reducing the amount of syngas which escapes while the solid char is removed from the reaction column.

Another aspect of the present invention relates to method of loading waste into the reaction column, and to methods of reducing the amount of gases which escape while waste is being loaded into the reaction column. Another aspect of the present invention relates to the running of engines such as gas engines from syngas. Particular features of the running of such gas engines includes the cleaning of the exhaust gases, the cooling of the exhaust gases, and the suppression of noise from exhaust gases.

BACKGROUND OF THE INVENTION

It is well known that the volume of waste, especially that of waste containing organic matter or hydrocarbons can be reduced by heating. It is also known that during initial heating, pyrolysis may release a hydrocarbon rich gas, while leaving behind some of the carbon as a char. Known pyrolysis apparatus enclose the waste so as to restrict the entry of air and collect the gas. It is also known that by passing air and water vapour over the hot char, it is possible to convert the carbon in the char to carbon monoxide and the water to hydrogen. This is referred to here as a gasification process in order to distinguish it from the pyrolysis process described earlier.

Furthermore, it is known that pyrolysis and gasification can usefully be carried out in sequence with waste being first heated until it gives off pyrolysis gases, and the resulting char then further heated to gasification temperatures. It is also known that the gases resulting from pyrolysis can usefully be augmented by being passed over the char in the gasification process.

It is known that such systems may be operated continuously with high quality gas being produced, with the tar from pyrolysis being largely destroyed during gasification.

A disadvantage of known systems is however that the gases emerging straight from such a gasification process tend to contain unwanted impurities. A first reason why such gas tends to contain impurities is that in order to provide high calorific value gas, the process should be carried out in a reducing atmosphere. Such an atmosphere makes it hard to ensure that all the carbon is burnt, leaving the possibility that the break up of char yields particles which are then entrained in the gas stream. A second reason for the impurities is the presence of particles of incombustible material in the char. As the carbon around these incombustible particles is burnt off, the particles can be released into the moving gas. A third reason for the impurities is the presence in the gasification region of elements such as Sulphur, Chlorine, and Nitrogen, which have a tendency to produce acid gases. Of these reasons, both particles of carbon and particles of incombustible material tend to cause problems. They can foul, accumulate in and eventually obstruct piping, they can block valves, and cause wear in blowers. Acid gases are a problem, since they can attack the metal of pipe work and other fittings. if the syngas from such known systems is fed to an engine, then particulate matter arising as described above can increase the amount of maintenance required by the engine, or even reduce the engine life. Acid gases are also a problem in that they can cause corrosion, so increasing maintenance and reducing the useful life of the engine. As a consequence of these impurities, some known systems provide one or more filters, and pass the syngas through these before it is used. However, the impurities removed end up in the filters where they reduce efficiency and cause the filters to require maintenance. Known filters include fabric filters, electrostatic filters, and wet gas scrubbers.

The more impurities that have to be removed, the greater the cost of supplying, maintaining or replacing such filters. In addition to the production of syngas, the combustion of syngas in known systems also involves impurities, filters, and maintenance costs. A further disadvantage of known systems is that the syngas emerging from the reaction vessel is hot. This makes the gas difficult to pipe, pump, and store. II also increases the volume of the syngas, thereby reducing its volume calorific value, and making it difficult to run an internal combustion engine from it. Known systems therefore generally provide some means of cooling the syngas, however, it is difficult for known system to benefit from this heat, resulting in it being wasted by being sent to atmosphere. The ash remaining from known systems is also hot, which again makes it difficult to handle. Known systems sometimes cool the ash using water, which not only consumes the water, but wastes the heat. In addition, engines also need cooling, and it is difficult for known systems to benefit from this heat. A further disadvantage of known systems using internal combustion engines is that the engine exhaust transmits noise which can be a nuisance if released.

SUMMARY OF THE INVENTION

It is an object of the invention to overcome some of the disadvantages of prior art systems for fuelling an engine from waste. These disadvantages include some of the disadvantages resulting from known systems for the generation of syngas from waste, some of the disadvantages of known systems for combusting the syngas, and some of the disadvantages of known systems for running engines from syngas. An object of the invention is to add filtering for syngas, and for the exhaust gases from an engine, in which the added filters do not suffer from blockage due to the build up of matter, and where the added filters do not require the provision or periodic replacement of a specially provided filter material. Another object of the invention is to provide some heat to the waste in a waste to energy converter, thus making it easier to ignite and maintain the combustion of the waste. Another object of the invention is to provide a zone of substantially inert gas which can be interposed between the zone containing inflammable pyrolysis gas, and the air, thus preventing mixing, unwanted combustion, or even dangerous explosion. This substantially inert zone makes it easier to move waste from the open air into the converter. Another object of the invention is to control the gas flows and therefore the pressure so that the top of the column may controlled so as to be at near atmospheric pressure, thereby simplifying the entry of new waste into the top of the converter column.

Another object of the invention is to balance the gas flows and therefore the pressure differences along a converter column so that the bottom of the column may controlled so as to be at near atmospheric pressure, thereby simplifying the removal of ash from the bottom of the converter column.

A preferred embodiment of the invention comprises a vessel in the form of a vertical reaction column. Waste is preferably loaded into the top of this column, moves down under gravity, is processed, and the resulting ash removed from the bottom. The column is preferably circular in cross section. The gas flows in the column are preferably managed by a series of blowers, and there are preferably a number of inlets and outlets for gas arranged in order from the top to the bottom of the column. These inlets and outlets therefore divide the column up into a number of zones, and waste moves progressively through each of the zones from the topmost zone to the bottom most zone. The upper zones are preferably below combustion temperature, and parts of the column enclosing the upper zones may preferably be constructed of low cost material. The lower zones are preferably hot, and parts of the column enclosing the lower zones may preferably made of refractory material, and thermally insulated. Other than this, the upper and lower zones preferably form a single cylinder offering little or no resistance to the downward movement of the waste. As the waste moves slowly down the column by gravity, its temperature is preferably gradually increased, until it yields pyrolysis gases which burn to further heat the waste, and turn it to a carbon-rich char. The waste then preferably continues down the column, where further combustion produces even higher temperatures and chemical reactions cause the char to release carbon as carbon monoxide and water vapour to release hydrogen. The reaction column may preferably contain a series of zones, one above the other.

In a first preferred embodiment, starting from the top, the functions of the zones are as described in the following... The topmost zone is preferably the exhaust gas polishing zone, and contains cool, newly loaded waste. This waste may preferably have been recently shredded, have a large surface area, and have significant exposed moisture content in its bruised organic matter. The exhaust gas from an engine is preferably passed through this zone in order to remove impurities or polish the exhaust gas. As the exhaust gas filters through the waste, carbon and other particles entrained in the exhaust gases are trapped and incorporated in the waste bed. Tar and oil in the exhaust gases can also be deposited on the large surface area exposed in the shredded waste. At the same time, acid gases tend to dissolve out of the exhaust gas and into moisture contained in the waste. All these processes allow the polished exhaust gases to be released to the atmosphere with less pollution nuisance than would be the case if the waste had not been run through the exhaust gas polishing zone. n addition, the noise carried with the exhaust may be suppressed, especially when the exhaust gas encounters the heavier material in the waste. Making the exhaust gas polishing zone the topmost zone provides the cleanest, coolest, counter-flow gas polishing. Using the top zone for exhaust gas polishing also allows the exhaust gases to exit at the top of the column, which has several advantages. One advantage is that the exhaust gas polishing zone separates the inflammable gases below from the air above, so that they cannot mix, bum, or explode. A further advantage is that the top of the vessel does not need to be sealed, and the waste may be fed continuously from the shredder if required. It will be appreciated that although some of these advantages will be lost, where there is no engine, the exhaust gas polishing zone is then not needed, and can be omitted. The top of the reaction column then needs to be sealed, but the remainder of the invention, and in particular the remaining zones may be implemented substantially unchanged.

The zone beneath the exhaust gas polishing zone is preferably the syngas gas polishing zone. In this zone, the waste is used to polish the syngas before it is either used, or fed to an engine. In either case it can be important that certain impurities are removed from the syngas. This includes any impurities which may remain in the syngas even after polishing, as well as impurities generated by the engine. These impurities include particulates, which cause wear, tar which can condense and stop mechanical components from moving or create blockages, and acid gases which can corrode pipe work and metal parts. In the case of an engine, such impurities can cause problems by reducing the life of the engine or even stop it working completely. Therefore, the syngas is preferably passed through the un-burnt waste so that the syngas is filtered or polished. The syngas polishing zone not only provides an almost zero-maintenance filter, but also makes the tars and carbon particles available for conversion into syngas. This stage is also useful in that the syngas yields some heat to the waste, thus making the syngas contract and easier to inject into the engine. It is however important that the exhaust gases are cooled before being allowed into the exhaust gas polishing zone, and that the syngas is cooled before being allowed into the syngas polishing zone. This cooling must take the temperature of the exhaust and syngas down below 100 degrees centigrade, so that steam falls out of the gases and does not condense on the waste. This cooling preferably takes the temperature of the exhaust gases down below 50 degrees centigrade to limit the amount of moisture available to condense on the waste. After exiting from the syngas polishing zone, the waste then preferably passes into the pyrolysis zone where it is progressively heated, causing the release of pyrolysis gases which are then burnt. To allow for waste that might be wet, difficult to heat, or which may be packed too densely to allow heat transfer by radiation or unforced convection, updraft pyrolysis is used. The heat generated during the burning of the hotter, material at the bottom of the zone is therefore carried up and heats the cooler, new material descending from above. The temperature in the pyrolysis zone is preferably about 250 degrees centigrade. The waste then preferably passes into the gasification zone. In order to destroy the bulk of the tar from the pyrolysis stage, the pyrolysis gases are also fed through the gasification zone. The high temperatures attained, break down or "crack" the tars into lighter, more volatile components. At the same time, the carbon in the waste reacts with water vapour to produce carbon monoxide and hydrogen. The temperature in the gasification zone is preferably about 800 degrees centigrade. In order to maximise the amount of moisture that the system can tolerate, and therefore the amount of high calorific value hydrogen it can generate, heat is preferably conserved by passing all hot gases through heat exchangers, and by lagging the pyrolysis column and the hotter pipes. Cooled syngas may preferably be fed back into the bottom of the reaction column to cool the ash and make it easier to extract. The power fed to the blower used to pump the cooled syngas back into the reaction vessel may preferably be controlled so that the pressure near the bottom of the reaction column is about zero, so that ash removal does not involve either the loss of valuable syngas gas, or the ingress of air into the bottom of the gasification zone. Note that by controlling the pressure near the bottom of the gasification zone, rather than the pressure at the bottom of the gasification zone, a barrier layer of ash is created across which there is very little pressure difference, and through which little gas flows.

In a second preferred embodiment, starting from the top, the functions of the zones are as described in the following... The topmost zone is a heating zone, where the waste is heated by air which has in turn been heated by passing though heat exchangers. The heat for those heat exchangers is derived from the hot syngas, and from the coolant responsible for cooling the engine. The heating zone takes the temperature of the waste up to 100 degrees centigrade.

Since only air is pumped into this zone, little moisture is introduced, and the net effect is to reduce the moisture content of the waste, rather than increase it. The heating zone is open to atmosphere, thus allowing the easy entry of waste. This entry of waste may be continuous if desired. Beneath the heating zone is the drying zone. The hot exhaust gases from the engine are fed into the drying zone. No cooling is applied to these exhaust gases, and the exhaust pipes may preferably be lagged, so that the temperature of the exhaust gases is over 100 degrees centigrade when they enter the drying zone. As the exhaust gases pass through the waste in the drying zone, their temperature drops to about 100 degrees as water in the waste is vaporised and joins the exhaust gases before leaving the reaction column. After leaving the drying zone, the waste then preferably passes into the pyrolysis zone where it is progressively heated, causing the release of pyrolysis gases which are then burnt. To allow for waste that might still be wet, difficult to heat, or which may be packed too densely to allow heat transfer by radiation or unforced convection, provision is made to continuously inject and ignite a fuel gas. The amount of fuel gas is adjusted so that it is just sufficient to maintain the required temperature within the pyrolysis zone. The temperature in the pyrolysis zone is preferably about 250 degrees centigrade. The waste then preferably passes into the gasification zone. In order to destroy the bulk of the tar from the pyrolysis stage, the pyrolysis gases are induced to flow downwards through the gasification zone. The high temperatures in the gasification zone break down or "crack" the tars into lighter, more volatile components. At the same time, the carbon in the waste reacts with water vapour to produce carbon monoxide and hydrogen. The temperature in the gasification zone is preferably about 800 degrees centigrade. In order to maximise the amount of moisture that the system can tolerate, and therefore the amount of high calorific value hydrogen it can generate, heat is preferably conserved by passing all hot gases through heat exchangers, and by lagging the reaction column and all hot pipes. Cooled syngas is may preferably be fed back into the bottom of the reaction column to cool the ash and make it easier to extract. The power fed to the blower used to pump the cooled syngas back into the reaction vessel may preferably be controlled so that the pressure near the bottom of the reaction column is about zero, so that ash removal does not involve either the loss of valuable syngas, or the ingress of air. Note that by controlling the pressure near the bottom of the reaction column, rather than the pressure at the bottom of the reaction column, a barrier layer of ash is created across which there is very little pressure difference, and through which little gas flows.

So as to raise the pressure differences across the cooling zone to equal that across the larger pyrolysis zone, the cross sectional area at the bottom of cooling zone 6 may preferably be reduced so increasing the velocity of the cool syngas, and therefore the pressure drop across the cooling zone.

According to the present invention, a vessel which confines heated waste and collects the resulting syngas is supplied with a substantially continuous flow of substantially inert gas. Said substantially inert gas is the result of the combustion of a fuel gas. Said fuel gas is derived from said syngas. Said combustion occurs in an engine. Said engine is an internal combustion engine. Said substantially inert gas forms a substantially inert zone inside said vessel. Said syngas forms a reducing zone inside said vessel. Said reducing zone is separated from oxygenating gas by said substantially inert zone. Said oxygenating gas is substantially air. Said substantially inert zone and said reducing zone are separated by a barrier layer. The flow of gas across said barrier layer is reduced by ensuring that the pressure on one side of said barrier layer is substantially the same as that on the other side of said barrier layer. The pressure on one side of said barrier layer is maintained by a blower so as to make it substantially the same as that on the other side of said barrier layer. The output of said blower is controlled by a controller. Said controller adjusts the power fed to said blower according to a signal from a differential pressure gauge measuring the pressure across said barrier layer. Said differential pressure gauge, said controller, and said blower provide a negative feedback loop, which acts to substantially eliminate the pressure difference across said barrier layer.

According to the present invention, there is further provided a vessel which produces syngas from hot carbon, in which a portion of said syngas is cooled and fed back into said vessel. Said vessel turns said hot carbon into ash. The location at which the cooled syngas re-enters said vessel is close to the point at which said ash is removed from said vessel. The location at which the cooled syngas re-enters said vessel is located between the location at which said syngas leaves said vessel, and the location at which said ash is removed from the vessel. After re-entering said vessel, the cooled syngas passes through the ash and leaves the vessel with said syngas. Said syngas is cooled by passing it through a heat exchanger. Said syngas is urged fhrniicili id hif pxrhincypr liv i h1nwr Siid h1nwr i rrntrn11d n tht fh nr'iir nepr th gases though the barrier region is from the exhaust polishing zone into the syngas polishing zone. The pressure difference across the barrier region is controlled by adjusting the output of blowers.

Further aspects and features of the invention are set forth in the non-limiting exemplary embodiments of the invention which will now be described with reference to the accompanying Figures of drawings.

LIST OF FIGURES

FIGURE 1 shows a side elevation of a system in which the invention is applied to the polishing of the syngas.

FIGURE 2 shows a side elevation of a system in which the invention is applied to drying and heating the waste.

DETMLED DESCRTPTTON OF THE EXEMPLARY EMBODIMENT

Two exemplary embodiments of the present invention will now be described with the help of the figures. In the following description the same reference numbers have been used to indicate the same parts in different figures. Different reference numbers have been used to indicate parts in different embodiments of the invention.

In FIGURE 1, the cylindrical body of converter 38 encloses in order from top to bottom, exhaust gas polishing zone 1, syngas polishing zone 2, first pyrolysis zone 3, second pyrolysis zone 4, and gasification zone 5. Beneath zone 5, the conical bottom of converter 38 encloses cooling zone 6. In operation, first pyrolysis zone 3, second pyrolysis zone 4, and gasification zone 5 are all at raised temperatures, and converter 38 is insulated in those areas by a layer of insulating material 34.

In operation, waste 11 containing carboniferous material, is continuously loaded into the top of converter 38. The waste then passes slowly downwards under the influence of gravity through exhaust gas polishing zone 1, syngas polishing zone 2, first pyrolysis zone 3, second pyrolysis zone 4, gasification zone 5, and cooling zone 6 in turn. As it passes down the converter, the waste is heated and ignited as necessary by the combustion of fuel gas injected through valve 35. It is then processed, and is eventually ejected from the bottom of the converter by conveyor 9 as ash 10.

Exhaust gas polishing zone 1 is separated from syngas polishing zone 2 by barrier region 7.

Gas flows are controlled so that the pressure difference across barrier region 7 is kept low, thereby reducing the interchange of exhaust and syngas. This is done by measuring the differential pressure between the bottom of exhaust gas polishing zone 1 and the top of syngas polishing zone 2 using differential pressure gauge 37. The combined output of blowers 22 and 27 is controlled by controller 15 in such a way as to reduce any pressure difference across barrier region 7. To give two examples of the operation of this control, if differential pressure gauge 37 shows that the pressure at the top of syngas polishing zone 2 is greater than that at the bottom of exhaust gas polishing zone 1, then controller 15 increases the combined output of air blowers 22 and 27, thereby tending to increase the pressure at the top of syngas polishing zone 2, as well as in the zones below syngas polishing zone 2. Alternatively, if differential pressure gauge 37 shows that the pressure at the top of syngas polishing zone 2 is less than that at the bottom of exhaust gas polishing zone 1, then controller 15 reduces the combined output of air blowers 22 and 27, thereby tending to reduce the pressure in syngas polishing zone 2 as well as in the zones below syngas polishing zone 2.

Syngas polishing zone 2 is separated from first pyrolysis zone 3 by barrier region 8. Gas flows are controlled so that the pressure difference across barrier region 8 is kept low, thereby reducing the interchange of syngas and pyrolysis gas. This is done by measuring the differential pressure between the bottom of syngas polishing zone 2 and the top of first pyrolysis zone 3 using differential pressure gauge 36. Controller 15 controls the output of syngas blower 16 in such a way as to reduce any pressure difference across barrier region 8. To give two examples of the operation of this control, if differential pressure gauge 36 shows that the pressure at the top of first pyrolysis zone 3 is greater than that at the bottom of syngas polishing zone 2, then controller 15 increases the output of blower 16, thereby tending to increase the pressure in syngas polishing zone 2. Alternatively, if differential pressure gauge 36 shows that the pressure at the top of first pyrolysis zone 3 is less than that at the bottom of syngas polishing zone 2, then controller 15 reduces the output of blower 16, thereby tending to reduce the pressure in syngas polishing zone 2.

Air 24 enters blower 22, and is forced through heat exchanger 21. The heated air is then fed via inlet 23 into pyrolysis zones 3 and 4 of converter 38. Air 26 enters blower 27, and is forced through heat exchanger 25. The heated air is then fed via inlet 23 and into pyrolysis zones 3 and 4 of converter 38.

Once it is through inlet 23, the heated air divides into two.

One part of the heated air rises upwards through first pyrolysis zone 3. In order to start the conversion process, fuel gas is injected into first pyrolysis zone 3 through valve 35 and ignited.

During start up, or if it is decided not to run the engine on syngas, the syngas is vented by opening valve 40, and any gas vented through valve 40, ignited and allowed to flare off At the same time, value 41 is shut to prevent syngas reaching the engine, and valve 42 opened to allow a suitably constituted supply of natural gas to enter the engine and run it in order to generate the exhaust needed to pressurise exhaust gas polishing zone 1 and prevent syngas from syngas polishing zone 2 from rising and escaping to atmosphere. In first pyrolysis zone 3, pyrolysis gases emitted from the heated waste burn providing additional heat to continue the process. The temperature within the pyrolysis zone is sampled by thermometer 20. If the temperature in the pyrolysis zone as measured by thermometer 20 falls below a predetermined threshold, then the flow of fuel gas is resumed or maintained to maintain combustion. After passing through first pyrolysis zone 3, the pyrolysis gases are routed through pipe 28 to the top of gasification zone 5. Pipe 28 is thermally insulated by an extension to layer of insulation 34.

Some of the heated air coming through inlet 23 flows downwards through second pyrolysis zone 4. Second pyrolysis zone 4 receives solid waste that is already burning, and the additional air causes additional combustion, a further rise in temperature, and further pyrolysis.

After passing though pyrolysis zone 4, the gases continue downwards into gasification zone 5.

The temperature in gasification zone 5 is higher than the temperature in pyrolysis zone 4, resulting in the cracking of tars to lighter, more gaseous syngas. Other reactions which take place in the reducing atmosphere of gasification zone 5 include the reactions between carbon and water vapour to form carbon monoxide and hydrogen.

The gases resulting from the reactions in gasification zone 5 are referred to here as syngas.

Syngas is taken out of converter 38 via outlet 29, through hot gas filter 39, and then through heat exchanger 25. Heat exchanger 25 reduces the temperature of the syngas, and also causes water vapour to condense so that water 12 can be removed.

Syngas cooled by heat exchanger 25 is urged by blower 31 into inlet 32 of cooling zone 6. The rising cooled syngas acts to cool the descending ash, so making it easier for screw 9 to discharge it. The pressure at the bottom of cooling zone 6 is measured by pressure gauge 33.

The power fed to blower 31 is adjusted by controller 15 so that the pressure measured by pressure gauge 33 is about atmospheric pressure. A barrier layer 12 separates the bottom of cooling zone 6 and screw 9. Since both sides of barrier layer 12 are near atmospheric pressure, the amount of syngas that escapes when screw 9 removes ash 10 is small.

The heights of zones 1, 2, 3, 4, and 5, are arranged, bearing in mind the gas flows through each zone, the size of the waste particles, and the lift resulting from the elevated temperature of each zone, so that the top of exhaust gas polishing zone 1, and the bottom of cooling zone 6 can simultaneously be maintained near atmospheric pressure.

The cooled syngas from heat exchanger 25 is then purified by gas scrubber 19. Gas scrubber 19 removes impurities and elements that cannot be destroyed or turned into a harmless gases by combustion. These impurities and elements include sulphur. Gas scrubber 19 has cold water running through it and also performs further cooling of the gas stream. This further cooling takes the temperature of the gas down to around 50 degrees centigrade.

After passing through gas scrubber 19, the syngas is induced to flow into syngas polishing zone 2 via inlet 14. Syngas polishing zone 2 is full of cool waste, including waste which has been shredded and acts to clean or polish the gas. The polished gas exits from syngas polishing zone 2 via outlet 18. With valve 41 in the open condition, and valve 40 closed and valve 42 closed, the polished gas is fed to and runs engine 17.

Engine 17 is a gas engine, complete with its own cooling system, air intake, lubrication system, and starter mechanism. Engine 17 powers an electric generator which supplies blower 16, blower 22, blower 27, blower 31, ash transport screw 9, controller 15, and other equipment.

Surplus electrical power is given or sold to the grid.

The exhaust from engine 17 is fed to heat exchanger 21. The pressure needed to make the gas flow out of the engine cylinders and into heat exchanger 21 is provided by the exhaust stroke of engine 17 itself. Heat exchanger 21 reduces the temperature of the exhaust gases, and also causes water vapour to condense so that water 12 can be removed. The cooled exhaust gases are then fed into exhaust gas polishing zone 1 through inlet 13. After passing upwards through exhaust gas polishing zone 1, the cleaned exhaust gases are allowed to escape to atmosphere.

In FIGURE 2, the cylindrical body of converter 38 encloses in order from top to bottom, heating zone 51, drying zone 52, first pyrolysis zone 3, second pyrolysis zone 4, and gasification zone 5. The conical bottom of converter 38 encloses cooling zone 6. In operation, first pyrolysis zone 3, second pyrolysis zone 4, and gasification zone 5 are all at raised temperatures, and converter 38 is insulated in those areas by a layer of insulating material 34.

In operation, waste 11 containing carboniferous material, is continuously loaded into the top of converter 38. The waste then passes slowly downwards under the influence of gravity through heating zone 51, drying zone 52, first pyrolysis zone 3, second pyrolysis zone 4, gasification zone 5, and cooling zone 6 in turn. As it passes down the converter, the waste is heated and ignited as necessary by the combustion of fuel gas injected through valve 35. The waste is then processed and is eventually ejected from the bottom of the converter by conveyor 9 as ash 10.

Air 26 enters blower 27, and is urged through heat exchanger 25. The heated air is then fed via inlet 23 and into pyrolysis zone 3 of converter 38 Drying zone 52 is separated from first pyrolysis zone 3 by barrier region 8. Gas flows are controlled so that the pressure difference across barrier region 8 is kept low, thereby reducing the interchange of the exhaust gases in drying zone 52 and the pyrolysis gas in first pyrolysis zone 3. This is done by measuring the differential pressure between the bottom of drying zone 52 and the top of first pyrolysis zone 3 using differential pressure gauge 36. Controller 15 controls the output of blower 27 in such a way as to reduce any pressure difference across barrier region 8. To give two examples of the operation of this control, if differential pressure gauge 36 shows that the pressure at the top of first pyrolysis zone 3 is greater than that at the bottom of drying zone 52, then controller 15 reduces the output of blower 27, thereby tending to reduce the pressure in first pyrolysis zone 3. Alternatively, if differential pressure gauge 36 shows that the pressure at the top of first pyrolysis zone 3 is less than that at the bottom of drying zone 52, then controller 15 increases the output of blower 27, thereby tending to increase the pressure in first pyrolysis zone 3.

In order to start the conversion process, fuel gas is injected into first pyrolysis zone 3 through valve 35 and ignited. During start up, or if it is decided not to run the engine on syngas, the syngas is vented by running blower 58 and opening valve 40. Any gas vented through valve 40 is ignited and allowed to flare off At the same time, value 41 is shut to prevent syngas reaching the engine, and valve 42 opened to allow a suitably constituted supply of natural gas to enter the engine and run it in order to generate the exhaust needed to pressurise drying zone 52 and prevent pyrolysis gas from first pyrolysis zone 3 from rising and escaping to atmosphere through outlet 54. In first pyrolysis zone 3, pyrolysis gases emitted from the heated waste burn providing additional heat to continue the process. Burning is enabled by air which enters the top of first pyrolysis zone 3 through inlet 23. The temperature within the pyrolysis zone is sampled by thermometer 20. If the temperature in the pyrolysis zone as measured by thermometer 20 falls below a predetermined threshold, then the flow of fuel gas is resumed or maintained, so as to maintain combustion. After passing through first pyrolysis zone 3, the pyrolysis gases continue downward, through second pyrolysis zone 4, and into the top of gasification zone 5. Insulation 34 contains the heat, and allows the temperature to increase as the gases move downwards and combustion occurs.

Syngas cooled by heat exchanger 25 is urged by blower 31 into inlet 32 of cooling zone 6. The rising cooled syngas acts to cool the descending ash, so making it easier for screw 9 to discharge it.

The pressure at the bottom of cooling zone 6 is measured by pressure gauge 33. The power fed to blower 31 is adjusted by controller 15 so that the pressure measured by pressure gauge 33 is about zero. The low pressure at the bottom of cooling zone 15 reduces the amount of syngas that escapes when screw 9 removes ash 10.

The heights of zones 51, 52, 3, 4, and 5, are arranged, bearing in mind the gas flows through each zone, the size of the waste particles, and the lift resulting from the elevated temperature of each zone, so that the top of heating zone 51, and the bottom of cooling zone 6 can simultaneously be maintained near atmospheric pressure.

The cooled syngas from heat exchanger 25 is then passed through heat exchanger 46 where further heat is removed. After passing through heat exchanger 46, the syngas is purified by gas scrubber 19. Gas scrubber 19 removes impurities and elements that are harmful to engine 17.

Gas scrubber 19 has cold water running through it and also performs further cooling of the gas stream. With valve 41 in its normal open condition, and valve 40 closed and valve 42 closed, the scrubbed gas is fed to and runs engine 17.

Engine 17 is a gas engine, complete with air intake, lubrication system, and starter mechanism.

Engine 17 powers an electric generator which supplies blower 27, blower 31, blower 45, blower 56, blower 58, ash transport screw 9, controller 15, and other equipment. Surplus electrical power is given or sold to the grid.

Pressurised coolant containing anti-corrosion, and anti-freezing agents circulates through engine 17 and heat exchanger 57. The flow of coolant is promoted by a pump, and enhanced by placing the engine on the ground, below heat exchanger 57. The flow of coolant removes heat from engine 17, and thereby helps to keep engine 17 at an efficient working temperature.

As the waste in converter 38 is consumed, new waste 11 is continuously loaded into the top of heating zone 51 of converter 38. This new waste is in general cold and contains moisture. Once in heating zone 51, the new waste starts to be heated. Initial heating comes in part from air 55, propelled by blower 56, and blown through heat exchanger 57 into inlet 47 of heating zone 51.

Additional heating of the waste results from additional air 44 propelled by blower 45 through heat exchanger 46 and into inlet 49 of heating zone 51. Of this additional air 44, about half travels upwards through the top half of heating zone 51, while the other half travels downward through the bottom half of heating zone 51. The upwardly travelling part of additional air 44 heats the descending waste in counter-flow fashion, before being released to atmosphere at 48.

The downward moving half of additional air 44 heats the gradually descending waste in parallel or concurrent fashion, before being released to atmosphere at outlet 50.

Although the most important effect of additional air 44 and air 55, is to heat the waste, the passage of additional air 44 and air 55 also causes the waste to loose moisture.

The temperature of the waste as it moves from the bottom of heating zone 51 into the top of drying zone 52 is about 100 degrees centigrade.

The hot exhaust gas from engine 17 passes through inlet 53 into drying zone 52. The pressure needed to make the gas flow out of the engine cylinders and into inlet 53 is provided by the exhaust stroke of the engine itself. Half of the exhaust gas passes upwards through the top half of drying zone 52, and are released to atmosphere through outlet 50. These exhaust gases dry the waste in counter-flow fashion. The other half of the exhaust gases, flow downwards though drying zone 52 and dry the gradually descending waste in parallel or concurrent fashion, before being released to atmosphere at outlet 54. Since the exhaust gases are produced by engine 17 at over 100 degrees centigrade, as they pass through the waste, they tend to turn moisture into water vapour, which then passes with the exhaust gases out to atmosphere. The exhaust gases also tend to heat the waste, and may heat it to over 100 degrees centigrade.

It will be understood that the present invention has been described above by way of examples only and that the above descriptions should not be taken to impose any limitation on the scope of the claims.

Claims

Claims A process to confine and heat waste in a reaction vessel and collect resulting syngas, a supply of a substantially continuous flow of substantially inert gas, such as the result of the combustion in an internal combustion engine of a fuel gas itself derived from said syngas, a substantially inert zone of inert gas inside the vessel, a reducing zone of syngas inside the vessel, separated from an oxygenating gas of substantially air by said inert zone, a barrier layer separating the inert zone and reducing zone.
2. A process of Claim 1, in which the flow of gas across said barrier layer is reduced by ensuring that the pressure on one side of said barrier layer is substantially the same as that on the other side of said barrier layer.
3. A process of either preceding claim, in which the pressure on one side of said barrier layer is maintained by a blower so as to make it substantially the same as that on the other side of said barrier layer.
4. A process of any preceding claim, in which the output of said blower is controlled by a controller, which adjusts the power fed to said blower according to a signal from a differential pressure gauge measuring the pressure across said barrier layer; the differential pressure gauge, controller, and blower being interconnected in a negative feedback loop, to substantially eliminate the pressure difference across said barrier layer.

Q
5. A process of any preceding claim, configured to produce syngas from hot carbon, (\J in which a portion of said syngas is cooled and fed back into said vessel, to turn hot carbon into ash.
6. A process of Claim 5, in which the location at which the cooled syngas re-N... enters said vessel is close to the point at which said ash is removed from said vessel.
7. A process of Claim 5, in which the location at which the cooled syngas re-enters said vessel is located between the location at which said syngas leaves said vessel, and the location at which said ash is removed from the vessel.
8. A process of Claim 5, in which after re-entering said vessel, the cooled syngas passes through the ash and leaves the vessel with said syngas.
9. A process of Claim 5, in which syngas is cooled by passing it through a heat exchanger urged by a blower.
10. A process of Claim 9, in which the blower is controlled so that the pressure near the point at which the cooled syngas re-enters said vessel and the pressure at the point at which said ash is removed from said vessel are about the same.
11. A process for producing engine fuel from waste combustion, in which waste moves downwards under gravity through an elongate reaction vessel, from a syngas polishing zone, to a pyrolysis zone and then to a gasification zone, and in which syngas from the gasification zone is fed to the syngas polishing zone without going through the pyrolysis zone.
12. A process of Claim 11, in which the syngas is cooled by a heat exchanger before being fed into the syngas polishing zone.
13. A process of Claims 11 or 12, in which water is extracted by a heat exchanger from the syngas before it is fed into the syngas polishing zone.
14. A process of Claims 11 to 13, in which syngas is fed though a gas scrubber, to remove sulphur from the syngas.
15. A process of Claims 11 to 14, in which syngas is urged out of the gasification zone and into the syngas polishing zone by a blower.
16. A process of Claims 11 to 15, in which the syngas polishing zone is separated from the pyrolysis zone by a barrier region in which the movement of gases is low.
17. A process of Claim 16, in which the barrier region is maintained by keeping the pressure difference across it low.
18. A process of any of Claims 11 to 16, in which he pressure on the syngas polishing zone side of the barrier region is prevented from becoming lower than the pressure on the pyrolysis zone side of the barrier region, so any net flow of gases though the barrier region is from the syngas polishing zone into the pyrolysis zone.
19. A process of Claim 18, in which the pressure difference across the barrier region is controlled by adjusting the output of blowers.

O)
20. A process of any of Claims 11 to 19, in which the pyrolysis zone is fed with a supply of oxygenating gas, such as air.
21. A process of any of Claims 11 to 20, in which gases move through the (\J pyrolysis zone in the opposite direction to the movement of the waste.

T
22. A process of any of Claims 11 to 21, in which gas is fed from the pyrolysis zone to the gasification zone through a pyrolysis gas pipe, N... including a means, such as a blower, of driving increased gas flow.

T
23. A process of any of Claims 11 to 22, in which the pyrolysis zone is fed with a supply of fuel gas whose flow is initiated or increased when the temperature of the gases in the pyrolysis zone drops and reduced or ceased when the temperature in the pyrolysis zone rises.
24. A process of any of Claims 11 to 23, using fuel gas partially or substantially composed of syngas.
25. A process of any of Claims 11 to 24, including a gasification zone fed with a supply of oxygenating gas, such as air.
26. A process of Claim 25, in which gases move through the gasification zone in the same direction as the movement of the waste, after the waste has passed through the gasification zone, it passes into a cooling zone before transfer out of the converter.
27. A process of Claims 25 or 26, in which the stream of syngas from the gasification zone is cooled by being fed through a heat exchanger divided into two, a minor part and a major part the minor part flows into the cooling zone, the major part flows through the syngas polishing zone and into an engine.
28. A process of Claims 11 to 27, in which, before the waste moves into the pyrolysis zone, the waste is passed through the exhaust gas polishing zone.
29. A process of Claims 11 to 28, in which the exhaust gases from the engine are cooled and water extracted, such as by a heat exchange, then fed through the exhaust gas polishing zone which can be open to the air and waste moves from the exhaust gas polishing zone to the syngas polishing zone.
30. A process of Claims 11 to 29, in which the exhaust gas polishing zone is separated from the syngas polishing zone by a barrier region in which the movement of gases is low, the barrier region being maintained by keeping the pressure difference across it low by controlled adjustment of blower output, the pressure on the exhaust gas polishing zone side of the barrier region being prevented from becoming lower than the pressure on the syngas polishing zone side of the barrier region, so any net flow of gases though the barrier region is from the exhaust polishing zone into the syngas polishing zone.
31. A reaction vessel for production of syngas from waste material using the process of any preceding claim, comprising an upright column fed with waste material a continuous flow supply of inert gas to form a substantially inert zone within the vessel, means for effecting a downward waste movement and progressive waste heading through successive layers or stages including syngas polishing, pyrolysis and gasification, using heat generated during burning of the hotter material at the end of the vessel to heat cooler, new material added. a) (\J