PYROLYSIS AND GASIFICATION PROCESS AND APPARATUS

Abstract: A method of adjusting the temperature of a gasifying agent comprising steam used in the gasification step of a two-stage pyrolysis and gasification process for converting solid carbonaceous materials into heat energy, comprises dividing a supply of a gasifying agent which consists of or comprises steam into two streams hereinafter referred to as a first stream and a second stream; passing only said first stream through a conduit which is heated by the secondary combustion of the off gases from pyrolysis and gasification; and recombining said first and second streams before the combined stream is passed into the zone in which gasification takes place; the proportion of said first and second streams being adjusted so as to achieve a desired combined stream temperature prior to entry into the gasification zone.

Description: PYROLYSIS AND GASIFICATION PROCESS AND APPARATUS This invention relates to a pyrolysis and gasification process and apparatus. In recent years there has been considerable interest in methods of disposal of solid waste carbonaceous materials and significant advantages over conventional incineration techniques have been found in a pyrolysis and gasification process whereby waste is converted in an efficient* manner into useable energy as described in WO 97/15640 and WO 97/15641. In the process described in WO 97/15640 and WO 97/15641 solid carbonaceous material, in particular waste material is subjected to a two stage process in which the waste material is firstly pyrolysed at a relatively low temperature in the substantial absence of air or oxygen to yield a gaseous product and a solid product, the solid product being thereafter in a separate step and at a different part of the apparatus being subjected to a high temperature gasification step by reaction with a gasifying agent, which may comprise air, steam and/or recycled flue gas, so as to yield a second gaseous product which is combined with the pyrolysis gas and conducted to a secondary combustion chamber when it is combusted to yield heat energy, a part of which is used to effect the aforementioned pyrolysis step. A particularly useful gasifying agent or constituent of the gasifying agent, to use in the gasifying step of such processes is steam because it yields when reacted with carbonaceous materials hydrogen and carbon monoxide which has high calorific value and which therefore can produce a large amount of heat energy. However, there is a problem in using steam in such a waste disposal process in that the reduction of steam is a highly endothermic process and can only occur at high temperature (in excess of 850°C) . This means that when steam is used as the gasifying agent it must be introduced into the gasifying chamber at a temperature substantially higher than 850°C. Moreover, it is important to be able to control the temperature of the gasifying agent in order to control the gasification process, bearing in mind, for example, that the nature of the pyrolysed solid used in the gasification process will vary depending on the nature of the carbonaceous material which is being pyrolysed. A way has now been discovered of achieving both the necessary high temperature when steam is used in or as the gasifying agent and also controlling the temperature of the gasifying agent, so as to be able to control the gasification process. According to the present invention there is provided a method of adjusting the temperature of a gasifying agent comprising steam used in the gasification step of a two-stage pyrolysis and gasification process for converting solid carbonaceous materials into heat energy, which method comprises dividing a supply of a gasifying agent which consists of or comprises steam into two streams hereinafter referred to as a first stream and a second stream; passing only said first stream through a conduit which is heated by the secondary combustion of the off gases from., pyrolysis and gasification; and recombining said first and second streams before the combined stream is passed into the zone in which gasification takes place; the proportion of said first and second streams being adjusted so as to achieve a desired combined stream temperature' prior to entry into the gasification zone. The invention also provides a pyrolysis and gasification process for converting solid carbonaceous waste materials into heat energy when comprising a method of adjusting the temperature of the stream of gasifying agent as defined above. Furthermore the invention provides an apparatus for performing the pyrolysis and gasification process as defined above which comprises: one or more gasification chambers; one or more pyrolysis tubes, said one or more pyrolysis tubes being disposed within a pyrolysis chamber heated by the combustion of off gases from the gasification chamber (s) and pyrolysis tube(s); valve means for splitting a stream of gasifying agent consisting of or comprising stream into two streams, a first stream and a second stream; a first conduit provided in said pyrolysis chamber for conducting said first stream of gasifying agent through said pyrolysis chamber said first conduit permitting heat exchange to said first stream of gasifying agent; a second conduit for conducting said second stream of gasifying agent along a route by-passing said pyrolysis chamber; and means for recombining said first and second conduits prior to connection with said one or more gasification chambers. The invention will now be illustrated by way of example with reference to the accompanying drawing which shows in diagrammatic section the relevant parts of a pyrolysis and gasification apparatus to which the invention relates. For a diagrammatic representation of a typical Overall arrangement reference can be made to Figures 5 and 6 which appear in both WO 97/15640 and WO 97/15641 the full contents of which are incorporated herein by reference. In the drawing a pyrolysis tube 1 is screw-fed from its right hand end in an air-tight manner with solid carbonaceous fuel, which can be solid waste material, the pyrolysis tube passing through pyrolysis chamber 2 which heats the tube to effect pyrolysis of the solid carbonaceous material. The pyrolysed solid is ejected at the left hand end of the pyrolysis tube into a gasification chamber 3 in which the bed 4 of the pyrolysed solid is treated at high temperature with gasifying agent admitted through pipe 5. Tap 6 permits exhausted process material to be removed from the bottom of the gasification chamber. Off-gases from the gasification process and also the pyrolysis tube exit the gasification chamber at 7 and are subjected to secondary combustion with air. or oxygen (not shown) the resulting hot gaseous mixture being passed through the pyrolysis chamber 2 so as to heat the pyrolysis tube. (In practice the chamber 2 will usually contain several pyrolysis tubes, but only one is shown in this diagram, for simplicity) . The novel arrangement of the present invention is shown in the part of the apparatus which is used to feed the* gasifying chamber with gasifying agent. A supply of gasifying agent which comprises steam is piped in at 8 and two conduits are provided. The first conduit 9 passes through the pyrolysis chamber and is arranged as a heat exchanger, which can be in the form of a sinuous pipe as shown, somewhat reminiscent of the tubing of a trombone. The second conduit 10 by-passes the pyrolysis chamber. The proportions of the streams of gasifying agent passing through conduits 9 and 10 can be adjusted using valves or dampers 11 and 12. Conduits 9 and 10 are recombined at junction 13 prior to the inlet pipe 5. The flow of gasifying agent and the valves or dampers 11 and 12 are controlled in conventional manner by means of conventional temperature measurement and electronic controls so that the proportions of gasifying agent passing through the conduits 9 and 10 result in the temperature of the gasifying agent in pipe 5 being at optimum for the gasification process and the overall process. It will be understood that variations in the above-described specific method, process and apparatus can be made by the skilled person without departing from the present invention as claimed in the following claims .

Claims: CLAIMS 1. A method of adjusting the temperature of a gasifying agent comprising steam used in the gasification step of a two-stage pyrolysis and gasification process for converting solid carbonaceous materials into heat energy, which method comprises dividing a supply of a gasifying agent which consists of or comprises steam into two streams hereinafter referred to as a first stream and a second stream; passing only said first stream through a co-nduit which is heated by the secondary combustion of the off gases from pyrolysis and gasification; and recombining said first and second streams before the combined stream is passed into the zone in which gasification takes place; the proportion of said first and second streams being adjusted so as to achieve a desired combined stream temperature prior to entry into the gasification zone. 2. A pyrolysis and gasification process for converting solid carbonaceous materials into heat energy when comprising a method of adjusting the temperature of the stream of gasifying agent as claimed in claim 1. 3. An apparatus for performing the pyrolysis and gasification process as claimed in claim 2 which comprises: one or more gasification chambers; one or more pyrolysis tubes, said one or more pyrolysis tubes being disposed within a pyrolysis chamber heated by the combustion of off gases from the gasification chamber (s) and pyrolysis tube ( s ) ; valve means for splitting a stream of gasifying agent consisting of or comprising stream into two streams, a first stream and a second stream; a first conduit provided in said pyrolysis chamber for conducting said first stream of gasifying agent through said pyrolysis chamber said first conduit permitting heat exchange to said first stream of gasifying agent; a second conduit for conducting said second stream of gasifying agent along a route by-passing said pyrolysis chamber; and means recombining said first and second conduits prior to connection with said one or more gasification chambers. . An apparatus as claimed in claim 3 wherein said first conduit comprises a sinuous metal pipe. 5. An apparatus as claimed in claim 3 or claim 4 comprising temperature measurement means and electronic control means for operating said valve means to adjust the proportions of gasifying agent or stream in said first and second streams.

Inventors: SHARPE JOHN ERNEST ELSOM, SHARPE, JOHN, ERNEST, ELSOM
Applicants: COMPACT POWER LTD, SHARPE JOHN ERNEST ELSOM, COMPACT POWER LIMITED, SHARPE, JOHN, ERNEST, ELSOM
Application year: 2001
Main classification: C10J3
IPC codes: C10J3