GB2489959A

GB2489959A - Continuous process pyrolyser

Info

Publication number: GB2489959A
Application number: GB1106217.1A
Authority: GB
Inventors: Mark Moulden; Robert Eden
Original assignee: Process Ltd
Current assignee: Process Ltd
Priority date: 2011-04-13
Filing date: 2011-04-13
Publication date: 2012-10-17
Anticipated expiration: 2031-04-13
Also published as: GB2489959B; GB201106217D0

Abstract

A continuous process pyrolyser 10 comprises an elongate processing chamber 12 having a hot gas inlet at one end for material to be pyrolysed. A first outlet 42 for char and a second outlet 32 for syngas at the opposite end are provided, and a feeding means 40 extends from the inlet at least substantially to the outlet for feeding the material through the pyrolyser. A gas flow path 16 extends around the exterior of the processing chamber such that hot gas passing through the gas flow path heats the exterior surface of the processing chamber. The downstream end of the gas flow path is in fluid communication with the processing chamber inlet so that, after passing through the gas flow path the hot gas passes through the processing chamber in direct contact with the material passing therethrough.

Description

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PYROLYSER

The present invention relates to pyrolysers that pyrolyse material to produce syngas. In particular this invention relates to continuous process pyrolysers.

Pyrolysis is a well known process in which material, predominantly material containing organic matter, is heated in a substantially oxygen free environment to produce syngas, which comprises carbon monoxide and hydrogen, and char. --Typically the material being pyrolysed will be fed through the pyrolyser by either a screw feed or other rotary means. The pyrolyser is usually heated externally by passing hot gas over its exterior. While this is effective heat transfer into the material being processed is by contact with the sides of the pyrolyser and accordingly to impart sufficient heat into the material to achieve an acceptable processing time a large temperature differential is needed between the hot gas being used to heat to the material and the material itself as the heat transfer through the pyrolyser wall is not particularly efficient. Often gas temperatures in excess of 1000 degrees are used which in turn means that special high temperature materials are needed and often a refractory coating on container will be required around the exterior of the hot gas passage way.

Furthermore, due to the necessity for a large surface area/volume ration to get the required heat into the material usually small diameter pyrolysers are used which limits the throughput.

it is the purpose of the present invention to provide an improved pyrolyser.

According to a first aspect of the invention there is provided a continuous process pyrolyser comprising: a elongate processing chamber having: an inlet at one end for material to be pyrolysed; a first outlet for char, and a second outlet for syngas, at the opposite end; and a feeding means extending from the inlet at least substantially to the outlet for feeding the material through the pyrolyser; a gas flow path extending around the exterior of the processing chamber such that hot gas passing therethrough heats the exterior surface of the processing chamber; wherein the downstream end of the gas flow path is in fluid communication with the processing chamber inlet so that, after passing through the gas flow path the hot gas passes through the processing chamber in direct contact with the material passing therethrough. The feed means may comprise a feed screw.

In one embodiment the pyrolyser further comprises a variable pyrolyser bypass valve in the hot gas flow path prior to the gas entering the processing chamber and a controller configured to control the variable pyrolyser bypass valve to vary the amount of gas passing through the pyrolyser.

In an alternative embodiment the pyrolyser further comprises a hot gas extractor in the hot gas flow path prior to the gas entering the processing chamber and a controller configured to control the hot gas extractor to vary the amount of gas passing through the pyrolyser.

The hot gas flow path preferably forms a helical flow path around the exterior of the processing chamber.

A hopper may be located above the inlet end of the pyrolyser and the hot gas flow path can open into the hopper.

Preferably the hopper is closable at the upper end thereof to, in use, prevent the hot exhaust gas escaping therefrom.

A feed screw may be provided within the hopper extending in the direction of the pyrolyser inlet to feed material from the hopper towards the pyrolyser inlet.

Preferably the hot gas flowing around the outside of the pyrolyser flows in the opposite direction of the material passing therethrough and the hot gas flowing through the processor flows in the same direction as the material passing therethrough.

According to a second aspect of the invention there is provided a pyrolysis system comprising a pyrolyser according to claim 1 and a char burner having an inlet for receiving char from the char outlet of the pyrolyser and a hot gas outlet, and a conduit from the hot gas outlet of the char burner to the hot gas inJet of the pyrolyser.

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The char burner is also provides with an oxygen inlet though which oxygen can be introduced to the char burner to cause it to combust. The oxygen is supplied in a stoichiometric or sub-stoichiometric ration for the combustion so that the hot gas leaving the char burner contains substantially no oxygen.

Preferably the char burner has an auxiliary fuel burner and an auxiliary fuel inlet for receiving auxiliary fuel, for example natural gas or landfill gas.

The char burner may also have a syngas inlet for burning syngas. The burner may burn syngas during a start up procedure prior to the system reaching steady state conditions during which time the syngas quality may be insufficient for direct utilisation, for example in a syngas engine.

Preferably a further conduit is provided for recirculating the hot gas from the variable pyrolyser bypass valve or the hot gas extractor into the char burner.

Excess heat from the char burner not required for the pyrolysis process may be used for energy generation, for example to produce steam to drive a turbine, or may be used to precondition the material prior to pyrolysis, for example the heat may be used to dry the material.

According to a third aspect of the invention there is provided a method of pyrolysing organic waste the method comprising: passing material to be processed through the pyrolyser in a first direction to produce syngas and char; passing hot gas, containing substantially no oxygen, over the exterior of the processor in a second direction so as to heat material therein by heat exchange through the pyrolyser wall; and subsequently passing said hot gas through the pyrolyser in the first direction to directly heat the material therein.

The method may further comprise providing a hopper containing the material to be fed into the pyrolyser and passing the hot gas through the material in the hopper prior to passing it through the processing chamber so as to pre-heat the material in the hopper.

Preferably the method comprises providing a pyrolyser bypass outlet in the flow path upstream of the hopper and controlling the volume of gas passing through the bypass outlet to vary the amount of hot as passing through the processing chamber.

The method may further comprise providing a feed screw in the hopper to feed the material therein towards the pyrolyser inlet.

Preferably the hot gas has a temperature in the range 500°C to 700°C. The temperature differential between the hot gas passing around the pyrolyser and the material exiting therefrom may be in the range of 40°C to 120°C., more preferably the temperature differential between the hot gas passing around the pyrolyser and the material exiting therefrom is in the range of 60°C to 100°C.

The invention will now be described by way of example in relation to the accompanying drawings in which: Figure 1 is a schematic diagram of a pyrolyser of the present invention; and Figure 2 is a schematic diagram of a pyrolysis system of the invention.

Referring to the drawing a pyrolyser 10 is shown. The pyrolyser has a processing chamber 12 through which material being processed passes. The material may be any material containing organic matter for example, but not limited to, municipal solid waste, wood chippings, agricultural by-products etc. which will preferably have been dries to remove at least some of their water content.

The pyrolyser has an outer skin 14 that substantially surrounds the processing chamber 12 to create a space therebetween defining a hot gas flow path 16.

The hot gas flow path has one inlet 18 and two outlets 20, 22. In use a flow of hot exhaust gas is supplied to the inlet 18 so that it flows through the flow path 16.

Rifling or flow directors 24 are provided in the space between the processing chamber 12 and the outer skin 14 to direct the hot gas flowing therethrough in a helical or spiral flow path around the exterior of the processing chamber.

As the hot gasses pass around the exterior of the processing chamber 12 they heat the processing chamber walls and thereby impart heat into the material flowing therethrough causing its temperature to become raised and for it to pyrolyse.

One of the outlets 20 from the hot gas flow path opens into a hopper 26 that contains a supply of the material to be processed 28. The hopper is closed to prevent the ingress of oxygen into the material being pyrolysed to prevent it from combusting. As it is consumed in the pyrolysis process the material in the hopper can be replenished through an airlock or a star valve 44 that allows the slid material to be passed into the hopper without allowing the hot gas exiting outlet 20 to escape therefrom.

Passing the hot gas through the hopper preheats the material therein so that when it enters the processing chamber 12 via inlet 30 the material temperature will already be raised towards the temperature at which pyrolysis occurs, thereby reducing the amount of heat needed in the processing chamber 12 to raise the material to pyrolysis temperature. This enables a greater proportion of the indirect heating through the processing chamber walls to be used in pyrolysing the material 28 as opposed to heating the material to pyrolysis temperature.

The hot gas enters the hopper and, as it has no other means of escape, passes through the material to be processed and enters the processing chamber 12 via a processing chamber inlet 30, passes therethrough, and exits via a processing chamber gas outlet 32. As the gas passes through the processing chamber it directly heats the material therein. As the material becomes heated it pyrolyses and produces syngas and char. The syngas combines with the hot gas and exits the processing chamber via the gas outlet 32 for onward use, for example to power a syngas engine or for combustion to power a steam generator.

The second outlet 22 in the gas flow path has a variable flow means 34 attached thereto to control the amount of hot gas exiting via that outlet 22. The variable flow means 34 may be a variable speed extraction fan or may be a flow control valve. The flow passing through the outlet 22 can be varied to control the flow passing through the processing chamber.

During a processing cycle the pyrolyser, which is operating in continuous process, will have substantially steady state conditions and as such it is unlikely to be necessary to significantly vary the flow passing through the variable flow means 34 during processing. However if different materials are used in the pyrolyser they will each need a different amount of heat input to pyrolyse theme and accordingly the flow means 34 would need adjusting between processing different materials so as to vary the proportion of the flow passing through the material in the processing chamber 12 so as to vary the heat input thereto. As more heat is imparted to the material from the same amount of gas by direct contact with the hot exhaust gas than indirectly through the processing chamber walls the volume of gas passing through the processing camber 12 will vary the total heat input into the material.

Alternatively there may be some circumstances where it is beneficial to vary the amount of gas passing through the processing chamber during a continuous process.

for example if the hot gas is provided by another industrial process the temperature and flow rate of that gas may be dependant on that other process and may be variable.

By varying the proportion of the hot gas that passes through the processing chamber 12 during processing the pyrolyser can ensure the correct heat input irrespective of variation of the incoming gas temperature/flow. The variable flow means may be controlled by a controller 36 in response to parameters of the outgoing syngas which is measured by sensors 38. Measured parameters may include one or more of temperature, H2 content, CO content or calorific value of the syngas.

A feed screw 40 extends along the length of the processing chamber and ensures a constant movement of the material being processed from the hopper 26 through the processing chamber inlet 30, through the chamber 12 and out of the char outlet 42. As the material progresses through the pyrolyser it becomes heated and pyrolyses to produce syngas and char.

As the pyrolysis process is dependant on the heating of the material 28 in a substantially oxygen free environment it will be appreciated that the hot gas inputted into the pyrolyser via the hot gas inlet 18 contains no, or substantially no, oxygen.

The hopper 26 is provided with a second screw feed 46 that continues to move material within the hopper towards the processing chamber inlet. This prevents

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bridging of the material within the hopper which, in the absence of the screw feed 46 could occur. This phenomenon occurs when the material at the bottom of the hopper is drawn into the processing chamber 12 but, due to the nature of the material within the hopper it forms a self supporting mass with a void beneath it. The use of the additional screw feed 46 prevents this phenomenon. Although shown as a screw fed it will be appreciated that any mechanism to agitate the material it the hopper may be used to prevent bridging.

As will be understood from the forgoing the present invention utilises two methods of heat transfer into the material to be pyrolysed, indirect heat transfer through the walls of the chamber and direct heat transfer as the gas passes through the material being pyrolysed. Simple control of the amount of the hot gas that passes through the processing chamber, and therefore comes into direct contact with the material being processed, enables an accurate control of the heat input into the material to be achieved.

Due to the combined heat transfer a much more efficient heat extraction from the hot gas can be achieved and accordingly the temperature of the hot gas being used can be reduces from the currently used 1000°C to a range of 500°C to 700°C, preferably around 600°C. This reduction in the temperature of the gas being used enables the pyrolyser to be produced using less exotic materials as the temperatures are well within the operating conditions of many stainless steels.

Furthermore as the hot gas passes not only around the exterior of the processing chamber but also through the processing chamber the temperature differential across the pyrolyser wall is greatly reduced to a LiT of 40°C to 120°C, preferably of 60°C to 100°C. As the LiT is much smaller the relative expansion and contraction of the different parts of the pyrolyser is not so pronounced which is beneficial and facilitates pyrolyser design.

Another significant advantage of the pyrolyser of the present invention is that the additional heating of the entrained gas assists in imparting heat into the material passing through the pyrolyser. With previous designs the diameter of the processing chamber 12 was limited in relation to its length as a specific surface area/volume ratio was needed to transfer the required heat to the material via the processing chamber F., wall. The design of the present invention allows extra direct heating and accordingly the surface area to volume ratio of the processing chamber 12 can be reduced and the diameter of the processing chamber 12 can be increased which allows for a greater throughput of material, or alternatively allows for a reduced pyrolyser footprint for a like for like throughput.

Referring to Figure 2 a pyrolysis system 200 is shown. The system comprises a pyrolyser 10 as shown in Figure 1 and a char burner 202. Char is conveyed from the char outlet of the pyrolyser 10 to the char burner by a conveyor 204 but it willS be appreciated that any suitable conveying means may be used. The char burner is provided with an airlock (not shown) at either end to prevent ambient air from freely entering the burner with the char.

The char burner 202 has a hot gas outlet 206 attached to a hot gas conduit 208 that connects the outlet 206 of the char burner 202 to the hot gas inlet of the pyrolyser 10.

In this manner the hot gas produced by burning the char is used to, at least in part, heat the pyrolysis process.

The char burner 202 has an oxygen inlet 210 through which oxygen, or oxygen containing gas, can be introduced into the char burner 202. As some of the hot gas exiting the burner comes into direct contact with the material being pyrolysed it is important that the gas produced in the char burner contains little or no oxygen. The oxygen inlet has a valve 212 to control the influx of oxygen into the char burner to ensure that only a stoichiometric amount required for combustion, or a sub-stoichiometric amount is introduced into the char burner.

An auxiliary fuel burner 214 is also located in the char burner 202. The auxiliary fuel burner is used to initiate and/or sustain the combustion of the char and can also be used to supplement the heat output of the char burner if the pyrolyser requires more heat than is produced by burning of char alone. This may be particularly required during start up of the pyrolysis process.

The auxiliary fuel burner may burn any suitable fuel, fore example it may be configured to burn natural gas or landfill gas. Alternatively, or additionally the burner may be configured to burn syngas produced from the pyrolyser. The burner may burn syngas during a start up procedure prior to the system reaching steady state conditions during which time the syngas quality may be insufficient for direct utilisatiori, for example in a syngas engine.

S It will be appreciated that although only one burner is shown in the drawings for ease of reference the char burner 202 may include different burners for burning different gas, for example it may contain a separate natural gas burner and syngas burner.

A conduit 216 joins the second outlet 22 of the pyrolyser 10 to the char burner so that the hot gas exiting the pyrolyser which is not passed through the processing chamber may be re-circulated through the char burner. As this incoming gas will already be heated this reduces the required duty of the char burner to heat the pyrolyser and accordingly heat produced by the char burner may also be used directly, for example to drive a steam generator.

Claims

CLAIMS: I A continuous process pyrolyser comprising: a elongate processing chamber having: a hot gas inlet at one end for material to be pyrolysed; an first outlet for char and a second outlet for syngas at the opposite end; and a feeding means extending from the inlet at least substantially to the outlet for feeding the material through the pyrolyser; a gas flow path extending around the exterior of the processing chamber such that hot gas passing therethrough heats the exterior surface of the processing chamber; wherein the downstream end of the gas flow path is in fluid communication with the processing chamber inlet so that, after passing through the gas flow path the hot gas passes through the processing chamber in direct contact with the material passing therethrough.
2 A continuous process pyrolyser according to claim 1 comprising a variable pyrolyser bypass valve in the hot gas flow path prior to the gas entering the processing chamber and a controller configured to control the variable pyrolyser bypass valve to vary the amount of gas passing through the pyrolyser.
3 A continuous process pyrolyser according to claim 1 comprising a hot gas extractor in the hot gas flow path prior to the gas entering the processing chamber and a controller configured to control the hot gas extractor to vary the amount of gas passing through the pyrolyser.
4 A continuous process pyrolyser according to any previous claim wherein the hot gas flow path forms a helical flow path around the exterior of the processing chamber.
5 A continuous process pyrolyser according to any previous claim further comprising a hopper located above the inlet end of the pyrolyser and wherein the hot gas flow path opens into the hopper.
6 A continuous process pyrolyser according to claim 6 wherein the hopper is closable at the upper end thereof to, in use, prevent the hot exhaust gas escaping therefrom.
7 A continuous process pyrolyser according to claim 5 or claim 6 further comprising a feed screw within the hopper extending in the direction of the pyrolyser inlet to feed material from the hopper towards the pyrolyser inlet.
B A continuous process pyrolyser according to any one of-the previous claims wherein the hot gas flowing around the outside of the pyrolyser flows in the opposite direction of the material passing therethrough and the hot gas flowing through the processor flows in the same direction as the material passing therethrough.
9 A continuous process pyrolyser according to any one of the previous claims wherein the feed means comprises a feed screw.
A pyrolysis system comprising: a pyrolyser according to anyone of claims I to 9; a char burner having an inlet for receiving char from the char outlet of the pyrolyser and a hot gas outlet, and a conduit between the hot gas outlet of the char burner and the hot gas inlet of the pyrolyser.
11 The pyrolysis system according to claim 10 wherein the char burner is further provided with an oxygen inlet though which oxygen can be introduced to the char burner.
12 The pyrolysis system according to claim 11 further comprising an oxygen control valve and a controller configures to control the amount of oxygen entering the char burner.
13 The pyrolysis system according to any one of claims 10 to 12 wherein the char burner further comprises an auxiliary fuel burner and an auxiliary fuel inlet for receiving auxiliary fuel.S
14 The pyrolysis system according to any one of claims 10 to 13 wherein the char burner further comprises a syngas inlet for burning syngas.
The pyrolysis system according to any one of claims 10 to 14 further comprising a further conduit between the variable pyrolyser bypass valve or the hot gas extractor and the char burner for recirculating the hot gas therebetween.
16 A method of pyrolysing organic waste the method comprising: passing material to be processed through the pyrolyser in a first direbtion to produce syngas and char; passing hot gas, containing substantially no oxygen, over the exterior of the processor in a second direction so as to heat material therein by heat exchange through the pyrolyser wall; and* subsequently passing said hot gas through the pyrolyser in the first direction to directly heat the material therein.
17 The method according to claim 16 further comprising: providing a hopper containing the material to be fed into the pyrolyser; passing the hot gas through the material in the hopper prior to passing it through the processing chamber so as to pre-heat the material in the hopper.
18 The method according to claim 16 or claim 17 further comprising providing a pyrolyser bypass outlet in the flow path upstream of the hopper and controlling the volume of gas passing through the bypass outlet to vary the amount of hot as passing through the processing chamber.
19 The method according to any one of claims 16 to 18 further comprising providing a feed screw in the hopper to feed the material therein towards the pyrolyser inlet.
The method according to any one of claims 16 to 19 wherein the hot gas has a temperature in the range 500°C to 700°C. a.
21 The method according to any one of claims 16 to 20 wherein the temperature differential between the hot gas passing around the pyrolyser and the material exiting therefrom is in the range of 40°C to 120°C.s
22. The method according to claim 21 wherein the temperature differential between the hot gas passing around the pyrolyser and the material exiting therefrom is in the range of 60°C to 100°C.