EP0202264A1

EP0202264A1 - Gasification methods and apparatus

Info

Publication number: EP0202264A1
Application number: EP85905521A
Authority: EP
Inventors: James David Willis
Original assignee: James Willis Associates Ltd
Current assignee: JAMES WILLIS ASSOCIATES LIMITED
Priority date: 1984-11-09
Filing date: 1985-11-04
Publication date: 1986-11-26
Also published as: ZA858577B; ZM8385A1; WO1986002940A1; GB8428329D0

Abstract

Un appareil de gazéification destiné à convertir la biomasse en un produit gazeux utilisable par exemple comme promoteur de combustible possède une chambre de combustion qui est au moins partiellement constituée ou garnie de graphite de préférence sous forme de briques à surface lisse, de blocs ou d'autres éléments de forme. Un appareil de gazéification pour le même usage peut posséder une chambre de réaction dans laquelle la charge de biomasse subit les étapes précoces du processus de gazéification, cette chambre de réaction étant incorporée dans une partie de l'appareil de gazéification que l'on peut faire vibrer de manière continue ou par intermittence.A gasification apparatus for converting biomass into a gaseous product usable, for example, as a fuel promoter has a combustion chamber which is at least partially made of or lined with graphite preferably in the form of smooth-surfaced bricks, blocks or stones. other form elements. A gasification apparatus for the same use may have a reaction chamber in which the biomass feed undergoes the early stages of the gasification process, this reaction chamber being incorporated into a portion of the gasification apparatus that can be made. vibrate continuously or intermittently.

Description

GASIFICATION METHODS AND APPARATUS

DESCRIPTION

This invention relates to the gasification of organic material comprising biomass and provides improved methods and improved apparatus for this purpose. The material subjected to gasification by the methods and in the apparatus of this invention can be any essentially organic material comprising biomass. The invention thus includes the gasification of waste vegetable and animal matter of all kinds, many of which represent serious disposal problems at present. Such materials include wood, paper, sawdust, wood-shavings, leaves, grasses, root vegetables, straw, coal, peat and many other waste materials derived from horticultural, agricultural and industrial operations.

Gasifiers have long been known and used for the generation of useful gas products, for instance as substitutes for petrol and other liquid fuels for the operation of internal combustion engines and for use as starting products in chemical reactions. Gasifiers generally consist of a combustion chamber, into which the biomass or other material is fed, either batch-wise or continuously and generally under gravity. The actual process of combustion usually occurs at the base of a descending mass of feedstock. Operation can be arranged to occur either by an up-draft mode or by a down-draft mode and the feedstock is thus partly dried by the combus¬ tion air or other gas passing through it_*

In accordance with one aspect of the present invention, the combustion chamber of a gasifier is at least partly formed or lined by means of graphite, which is in such a physical state and shape as not substantially to participate chemically in the gasifi¬ cation reaction, whereby the graphite acts as a catalyst or promoter. Preferably, the graphite is in the form of slabs, blocks, ricks or other shaped components and their surfaces or, at least, those surfaces of the graphite components which contact the biomass undergoing gasifica¬ tion are made smooth, e.g. they are polished or otherwise given an essentially even surface. Also, the graphite components are preferably made of compressed high-density material. It is found that, in operation of many kinds of gasifier, soot and other forms of non-combusted carbon may form a deposit upon parts of the surfaces of the region where the combustion, reduction and other reactions take place. Preferably, the graphite blocks or other components are located in these areas of the surfaces of the gasifier. When used under the same general conditions as when gasification is carried out, without the graphite, so that carbon deposition occurs, the deposition takes place on the graphite. This stores heat generated in the gasification process and radiates this heat so as to consume the deposited carbon. This is generally formed in a less dense soot-like form and can undergo combustion, in the absence or presence of oxygen, to produce carbon com- pounds such as hydrocarbons and the oxides. Thus, the graphite lining promotes the production and gasification of less dense forms of carbon.

In accordance with another feature of the invention, a gasifier includes a reaction chamber, in which feedstock undergoes such processes as drying and pyrolysis prior to reduction and combustion and this reaction chamber is incorporated in a part of the gasifier which is arranged to undergo vibration continuously or intermittently. Preferably, the rate of vibration is in the range from 20 to 40 Hz and thus is well below the usual rate of about 50 Hz. Most preferably, vibration is effected at about 30 Hz.

The invention also resides in a method of gasification of material comprising biomass, which comprises subjecting the material to heat in a reaction chamber under up-draft or down-draft conditions and in the absence of oxygen or in the controlled presence of oxygen, wherein the material in the reaction chamber is subjected intermittently or continuously to vibration at a rate in the range from 20 to 40 Hz and preferably from 25 to 35 Hz, more preferably from 28 to 32 Hz and most preferably at about 30 Hz.

In order that the various aspects and features of the invention may be fully understood and appreciated, the construction of a preferred form of the gasifier according to this invention is described below, in con¬ junction with the accompanying drawings, by way of illustration only. In the drawings:

Fig. 1 shows a diagrammatic side elevational view of the gasifier according to the invention;

Fig. 2 shows a diagrammatic vertical sectional view of the gasifier, taken on the line II-II of Fig. 1;

Fig. 3 shows a diagrammatic perspective view of the lower part of the gasifier of Figs. 1 and 2, in order to illustrate in more detail the construction of the combustion chamber incorporated in the gasifier of the invention.

The gasifier of the invention consists of a number of interrelated components, including a lower combustion chamber 1 and an upper reaction chamber 2. When operated for instance in the up-draught mode, feedstock is delivered to the top of the reaction chamber 2 and moves down toward and into the combustion chamber 1; combustion and reduction of the feedstock material and the initial products of the sequence of reactions occur in the chamber I and pyrolysis and drying of the incoming feedstock occur in the chamber 2. As described in more detail below, the combustion chamber 1 is located within an apparatus component or unit of generally cubic external shape, which incorporates a heat exchange unit 3 and a lower grate 4 for supporting the materials undergoing combustion. The reaction chamber 2 consists of a preferably upright cylindrical structure which, at its lower end, is fitted into a corresponding circularly- shaped aperture in the upper part of the combustion chamber 1, a gas-tight seal being provided between the combustion chamber 1 and the reaction chamber 2. However, the reaction chamber 2 has freedom to undergo movement, for instance by way of vibration, relative to the com- bustion chamber 1, in the manner and for the purposes described later in more detail.

The upper part of the reaction chamber 2 is surrounded by a condensate collection reservoir 5 and, at its uppermost end, the reaction chamber 2 is surmounted by a gas off-take hood 6, which incorporates a central feed device 7 for directing feedstock into the apparatus by way of the top of the reaction chamber 2. The feed¬ stock delivery arrangements preferably include a rotary or other feedstock distributor 8, incorporated in the feed device 7.

The part of the apparatus consisting of the reaction chamber 2, the surrounding condensate reservoir 5 and the gas offtake hood 6, with the associated components, is preferably supported from the part of the apparatus comprising the combustion chamber 1 by means of an opposed pair of vertical supports or suspension arms 9, which are secured to either side of the combustion chamber 1 and extend upwardly from it, so as to terminate in upper bearing members 10. These receive supporting stub shafts or axles 11 attached to opposite parts on the outside of the condensate reservoir 5. In this way, the reaction chamber 2 and the attached parts are capable of a controlled degree of free movement relative to the combustion chamber 1 and its associated parts, particularly in a direction at right-angles to the axis passing through the stub shafts or axles 11. An electro-mechanical or other vibrator unit 12 is incorporated in the apparatus and is preferably mounted upon the outside of the combustion chamber 1, as best shown in Fig. 1, and includes a vibrator member 13 attached, as described in detail below, to the lower part of the reaction chamber 2. Thus, the reaction chamber 2 and the parts attached to it and the feedstock contained in it can be subjected to vibration as required. This enables problems which can arise in operation, for instance through channelling or bridging of the feedstock, to be overcome, leading to more efficient gasification, as described below in more detail.

Referring more particularly to Figs. 2 and 3, the combustion chamber 1 is desirably constructed of a highly-refractory material, such as steel plate, welded together to provide the desired construction in the customary way. The generally cubic construction of the combustion chamber 1 enables it to be made in a relatively inexpensive manner. The combustion chamber 1 consists of an opposed pair of generally rectangular steel plates 14, joined at their upright edges by a second opposed pair of generally rectangular steel plates 15. Each of the plates 15 forms the external wall of a heat exchange reservoir, itself forming a part of the heat exchange unit 3; the internal wall of each heat exchange reservoir is a further steel plate, preferably angled at two places, so that the heat exchange reservoir formed between one of the plates 15 and the associated one of the plates 16 has a greater width at the top than at the bottom, as shown in section in Fig. 2 and in perspective view, partly broken away, in Fig. 3. The plates 14 also form the end walls of the heat exchange reservoirs of the heat exchange unit 3. A lower steel plate 17 closes the underside of each reservoir, being welded to the lower edges of the plates 14, 15 and 16, and the upper part of each reservoir is closed by part of a generally square plate 18, which forms a cover or lid for the combustion chamber 1 and includes a central circular aperture 19 in which the lower end of the reaction chamber 2 is accommodated, as described in more detail below. The aperture 19 is located in the part of the plate 18 which surmounts the combustion chamber 1, this part typically comprising the entire length, between the plates 14, and the middle half of the width, between the angled plates 16, of the cover plate 18. At diagonally-opposed points in the cover plate 18, at least one each of flanged inlet and outlet pipes 20, 21 are provided, the inlet pipe 20 serving for the input of heat exchange fluid into the top of one reservoir of the heat exchange unit 3 and the outlet pipe 21 providing for the withdrawal of the heat exchange fluid after it has traversed down the reservoir on one side across the base and up through the heat exchange reservoir on the other side of the combustion chamber 1.

The lower part of the combustion chamber 1 is formed by an array of generally parallel steel tubes 22, constituting the grate bars of the grate 4, which extend between opposed pairs of apertures 23 (best seen in Fig. 3) formed in the lower parts of the opposing steel plates 16 and enabling the heat-exchange fluid introduced via the inlet pipe 20 into one heat exchange reservoir to flow through the grate 4 immediately beneath the main combustion region and into the other heat exchange reservoir of the unit 3. The tubes 22 forming the bars of the grate 4 are mutually parallel and are preferably located at a carefully controlled mutual spacing so as to control the size of the particles of ash which can pass through the grate 4 in operation of the gasifier.

The inside surfaces of the combustion chamber 1, above the grate 4 formed by the tubes 22 and at least up to the level of the lower angles in the plates 16, are lined by means of high-density graphite 24. This is preferably provided in the form of a number of generally rectangular graphite slabs 24 having well-polished surfaces, particularly the internal surfaces 24a which come into contact with the feedstock as it undergoes combustion in the chamber 1. In Fig. 3, the chain-dotted line 25 indicates the edge of the area of the graphite slab 24 lining the inside of the right-hand heat exchange reservoir which is overlapped by the end of the graphite slab 24 (not shown) forming the lining of the near right- hand side of the combustion chamber 1, i.e. against the inside of the lower part of the plate 14.

Referring more particularly to Figs. 1 and 2, the reaction chamber 2 consists of a generally cylindrical steel casing 26, which is open at the bottom and has a number of vapour vents 27 towards its upper end. The vapour vents 27 are preferably provided with external louvres 28 which ensure that any liquid condensing on the upper part of the reaction chamber 2 above any of the vents 27 runs down into the condensate collection reservoir 5 and cannot get back through the vents 27 into the reaction chamber 2 itself. The reservoir 5 consists of a generally cylindrical steel housing 29 surrounding approximately the upper two-thirds of the reaction chamber 2 and completed at its upper and lower ends by means of circular plates 30,31, so that the only access into the interior of the condensate reservoir 5 is through the vapour vents 27. At one or more locations at the lowest part of the reservoir 5, an outlet or drain connection 32 is provided, which enables the condensate which collects in the reservoir 5 to be withdrawn and used as required, in accordance with one or other of the various ways described further below. Above the upper plate 30, the assembly com¬ prising the reaction chamber 2 and the condensate collection reservoir 5 is completed by means of the gas takeoff hood 6, which includes a lateral gas offtake connection 33 communicating with the space inside the hood. The reaction chamber 2 is surmounted, inside the hood 6, with a conical upper part 34, which includes one or more gas vents 35, whereby gases formed in the combustion chamber 1 and/or in the reaction chamber 2 can pass from the reaction chamber 2 via the vents 35 into the hood 6 and from there to further processing by being withdrawn through the gas offtake 33. The conical upper part 34 of the reaction chamber is in turn surmounted by an upright tubular feedstock inlet 36, forming part of the feed device 7 and containing an air lock screw feeder 37. This feeder 37 consists essentially of an upright rotatable shaft 38 connected, in a manner not shown, to a source of rotary power, such as an electric motor. The shaft 38 carries a helical feed screw 39 having the aforementioned feedstock distributor 8 secured to its lower end. Rotation of the feed device 7, by means of the motor, serves to rotate the shaft 38 and the feedscrew 39 attached to it also rotates the feedstock distributor 8 within the upper part 34 of the reaction chamber 2. The action of the distributor 8 ensures that incoming feedstock is appropriately distributed over substantially the whole of the circular cross- section of the reaction chamber 2. It will be appre- elated from Fig. 2 that this distribution takes place at the top of the reaction chamber 2 and typically above the water vapour vents 27 and their protecting louvres 28.

Figs. 2 and 3 also show how the supports 9 carrying at their top the axles 11 forming the main bearing arrangement for the reaction chamber 2 and the associated parts are attached to the opposed plates 15 forming two of the external sides of the reaction chamber 2. In order to allow the reaction chamber 2, the condensate collection reservoir 5, the gas hood 6 and the other associated parts mounted for vibratory movement on the supports 9, to have the appropriate freedom to vibrate relative to the com¬ bustion chamber 1, the lower end of the tubular reaction chamber 2 is arranged to provide a sufficient clearance 40 between itself and the aperture 19 in the square plate 18 forming the cover of the combustion chamber 18. The necessary gas-tight seal between these parts is provided by a temperature-resistant bellows 41, which is typically a conical structure similar to a loudspeaker cone and is sealed at its lower outer periphery 42a to the top surface of the plate 18 and at its inner upper periphery 42b to the periphery of the reaction chamber 2. The vibrator unit 12, as shown in Fig. 1, is mounted by means of a framework 43 upon the plate 14 forming one side of the generally cubic combustion chamber 1. On this frame 43, the vibrator unit 12 itself is mounted and the vibrator member 13 formed by the arm attached to the unit 12 and oscillated by it when the unit 12 is energized is attached at its other end 44 to a pivot joint 45 attached to the outside of the reaction chamber 2 immediately above the upper seal 42b.

Beneath the grate 4 and the combustion chamber 1 per se, the gasifier is extended downwardly to provide a location for a burner 46 which initiates the combus¬ tion. A downwardly-directed conical base member 47 is provided, which incorporates a transverse rotary air-lock ash removal valve 48, leading to an ash discharge outlet. 49c The ash removal valve 48 consists of a rotary rod having opposed angled inner faces 50, located in a part-tubular housing attached to the lower part of the base member 47 and terminating on the outside of the valve 48 an operating means (Fig. 1) , such as a rotary handle or squared shaft section. Beneath the tube grate 4 within the downward extension of the reaction chamber 2, an air distribution duct 53 is provided, comprising four interconnected sections of tubing having a plurality of inwardly-directed air discharge holes 54, whereby combustion initiated in the burner 46 leads to the generation of a large mass of burning gas, which is distributed through the holes 54 and passes into the region immediately below the tube grate 4. Between the duct 53 and the tube grate 4, a baffle plate 55 having an upturned inner edge region 56 is preferably provided so as to direct the combustion air into the combustion chamber 1. The air distribution duct 53 is fed from outside the combustion chamber 1 by means of the burner 46, which comprises a gas nozzle 57 fed from a gas input line 58, the nozzle 57 being surrounded by an inlet manifold 59 which completely surrounds the gas burner 46. At a suitable location between the outlet from the gas nozzle 57 and the inlet 60 to the air distribution duct 53, an ignition spark electrode 61 is provided, with appropriate external circuitry (not shown) , to cause ignition of the gas/air mixture dis- charging from the manifold 59 into the air distribution duct 53 at the inlet 60. In the upper part of the inlet manifold 59, an upright air inlet tube 62 is provided, which contains a pivotable or other air induction control mechanism, such as a throttle valve 63. This enables control of the amount of air drawn into the manifold 59. The tube 62 is surmounted by an air induc¬ tion inlet 64. The inlet manifold 59.also receives through its upper wall a connection tube 65 including a solenoid-operated or other remotely-controllable valve 66 which is connected by means of a flexible coupler 67 to the drain connection 32 from the lowest part of the condensate collection reservoir 5. The valve 66 can be operated either so that the collection reservoir 5 is connected via the drain connection 32 and the connection tube 65 to the manifold 59 or the valve 66 can be operated so that the reservoir 5 drains to a branch line 68, so that condensate can be discharged from the apparatus, e.g. for use elsewhere or for disposal. in operation, in the up-draft mode, feedstock is supplied to the inlet 36 and is conveyed in a controlled fashion into the interior of the reaction chamber 2 by means of the screw-feeder 37 and the feedstock distributor 8. The gas offtake 33 is typically connected to a controllable source of low pressure or suction and ig¬ nition gas is supplied via the input line 58 to the gas burner 46 and the spark electrode 61 is operated in order to provide ignition. Burning of the gas at the outlet from the nozzle 57 creates a venturi effect which, under the operative control of the throttle valve 63, provides controlled mixing of the gas supplied via the burner 46 and the induction air supplied via the inlet 64. Thus there is the possibility for complete control of the hot gaseous combustion mixture supplied via the duct 53 and the holes 54 to the area within the baffle plate 55 immediately below the tubular grate 4. Heat exchange fluid such as water is supplied to the inlet pipe 20 and this passes via the respective heat exchange reservoir and the apertures 23 to the tubes 22 of the grate 4 and then to the other heat exchange reservoir, the liquid heat exchange medium then being discharged via the outlet pipe 21. The biomass is fed under gravity down¬ wardly in the reaction chamber 2 and is dried and subjected to controlled combustion by virtue of the hot gases being generated within the combustion chamber 1 and rising into the reaction chamber 2. The polished surfaces 24 of the graphite slabs 24 surrounding the lower part of the combustion chamber 1 ensure that the course of the reaction between the products of gasification within the combus- tion chamber 1 is controlled and the reaction is promoted, without the process of combustion having any^•substantial effect upon the graphite forming the slabs 23. It has been found that if an apparatus of the kind described above in relation to the drawings is operated without the graphite slabs or equivalent components 24 soot will begin to deposit upon the respective surfaces, under the cooling effect of the fluid passing through the heat exchange unit 3. By providing carbon, not in the form of thermally- deposited soot, but as one or more massive and dense slabs preferably with a smooth or even a highly-polished surface, it is found that the condensation of soot takes place on to the graphite and after operation of the apparatus for a time, steady-state conditions are achieved and the carbon constituted by the soot forms a continuously and readily deposited and readily effloresced and removed layer, which provides a major element of control of the carbon balance of the whole sequence of reactions taking place in the gasifier. Any condensable vapours generated in the combustion chamber 1 and rising into the reaction chamber 2 are formed into liquid in the upper part of the chamber 2 and, on running down the inside surfaces, pass from the inside of the reaction chamber 2 to its outside through the vents 27 under the louvres 28. Such vapour condenses into a liquid which collects at the bottom of the reservoir 5 before passing into the drain connection 32 and from there via the flexible coupler 67 and the communicating tube 65, under the control of the valve 66, back to the inlet manifold 59. The apparatus thus allows for partial or complete recycling to the combustion chamber 1 of liquid products obtained by the condensation of vapours after the products of the gasification process taking place in the apparatus have passed to the upper part of the reaction chamber 2.

The vibrator 12 can be energised continuously or intermittently and it serves to provide a number of useful results. Depending upon the nature of the feedstock, which can be wet or dry and can include any material of an organic nature, for example sawdust, wood-shavings or chippings, plant material and so on, there is always the possibility despite the systematic supply of the feedstock through the feed device 7 and the distributor 8 of the formation of bridges or channels within the mass of partly- consumed feedstock in the reaction chamber 2. Vibration of the entire apparatus, which is possible because of the freedom of movement given by virtue of the mounting on the axles 11 at the upper ends of the supports 9 and the resultant ability of the reaction chamber 2 to vibrate rapidly within the upper part of the combustion chamber 1, under the further protection of the flexible coupler 67 and the seal 41, causes the feedstock to fall in the reaction chamber 2 and so there :is a continuous and progressive removal of bridges and the refilling of channels throughout the mass of feedstock undergoing gasification. In addition, a component of the vibratory movement is transmitted to the combustion chamber 1 itself. either directly through the frame 43 or as a result of the entire apparatus going into resonance. This ensures that the parts of the structure surrounding the combustion chamber 1 also undergo vibration and this movement ensures that ash formed above the tube grate 4 is continuously shaken loose and falls through the gaps between the tubes 22, which are preferably arranged, irrespective of the nature, state of comminution or type of material under¬ going gasification, to have a free gap, with the tubes 22 parallel, within the range from 3-13 mm and preferably from 6-10 mm and most preferably about 8 mm. The ash is continuously prevented from building up on or above the grate 4 and instead falls into the base 47, where intermittent operation of the valve 48 allows the ash to be discharged via the outlet 49. The gaseous products of the combustion reaction initiated in the chamber 1 can be taken off via the gas outlet 33 for further use. It is also possible to use the gasifier of the invention, such as the particular construction described above in relation to the drawings, in the down-draft mode. One way in which this can be done is simply to reverse the positions of the inlet manifold 59 and the gas take-off 33, while supplying the feedstock in the same way as described above. When this mode of operation is used, induction air is supplied via the gas connection 33, any condensation which takes place in the upper part of the reaction chamber 2 results in the collection of liquid condensate in the reservoir 5 as already described and this would typically be discharged from the apparatus, by appropriate operation of the solenoid valve 66, so that the drain connection 32 leads to the branch line 68. One aspect of the invention consists of the construction of a gasifier having a combustion chamber, at least part of the inside surface of which, immediately adjacent the region where combustion takes place, is formed or lined with monolithic or other smooth- surfaced slabs or components of graphite, preferably compressed or high-density graphite.

In accordance with another feature of the invention, a gasifier of whatever principle of construction includes an upright reaction chamber capable of receiving feed¬ stock under gravity at its upper end and this is mounted for continuous or intermittent vibration for the purposes of encouraging progressive downward movement of the mass of feedstock in the reaction chamber and the breaking up of bridges and prevention of excessive channelling within the mass of feedstock.

The invention also provides a method of operation of a gasifier having a principle of construction such that continuous or intermittent vibration of part of the gasifier, typically a reaction chamber, can be carried out. It is common practice to effect the vibration of gasifiers at 50 Hertz, i.e. 50 cycles per second. In accordance with a particular feature of the present invention, it has been discovered that, for operation of a gasifier for the treatment of general biomass and organic feedstock, the standard rate of vibration of 50 Hertz is too fast. This conventional rate of vibration has been found to cause unnecessary compaction of the mass of material undergoing gasification. A feature of the present invention is the discovery that the rate of vibration of the vibratable parts of the gasifier should lie in the range from 20 to 40 Hertz, most preferably in the range from 25 to 35 Hertz and even more preferably in the range from 28 to 32 Hertz; most preferably, vibration is effected substantially at the rate of 30 Hertz. The vibrator unit, such as the unit 12 described above in relation to the drawings, is preferably a conventional electro-magnetic DC solenoid component, supplied at the appropriate number of cycles per second to produce the desired rate of vibration. It has been found that, where the relevant parts of the gasifier are formed from steel sheet assembled by being welded together, no cracks appear in the welds or the other connections between the various components if the preferred range of rates of vibration mentioned in relation to the invention is selected. In contrast, use of a standard rate of vibration of 50 cycles per second is known to subject the whole structure to un- desirable resonance, so that cracks can be formed in connections such as welds and it is even known for the structure to begin to break up under such more rapid vibration. It has also been discovered that the rate of vibration should preferably not be lower than the rate of 20 Hertz mentioned above, in carrying out the invention, as this is not efficient and such a slow rate of vibration would have no materially beneficial effect upon the rate of descent and the avoidance of bridging, channelling and other disadvantageous features within the mass of feedstock.

The gasifier of this invention can form part of a so-called total energy system, wherein the gas mixture produced by operation of the apparatus is used to operate a gas-driven power unit, if desired after intermediate storage and after undergoing further chemical reaction. The power unit can be an internal combustion engine, for example, and it can be coupled to and can operate an electrical generator, a suction pump and/or a gas com¬ pressor and the one or more of such components can be used to effect further treatments upon the gaseous products derived from the gasifier.

Claims

CLAIMSs

1. A gasifier for the gasification of organic material comprising biomass, having a combustion chamber, in which the gasification reaction is carried out, which is at least partly formed or lined by means of graphite.

2. A gasifier according to claim 1, wherein the graphite is in a physical state and shape which does not substantially participate chemically in the gasification reaction, whereby the graphite acts as a catalyst or promoter.

3. A gasifier according to claim 1 or 2, wherein the graphite is in the form of one or more shaped components.

4. A gasifier according to claim 3, wherein at least those surfaces of the graphite components which contact the biomass undergoing gasification are smooth.

5. A gasifier according to any preceding claim, wherein the graphite comprises compressed high- density material.

6. A gasifier according to any preceding claim, wherein the graphite is located in at least those parts of the combustion chamber where non-combusted carbon deposits may form in carrying out the gasifica- tion reaction.

7. A gasifier for the gasification of organic material comprising biomass, having a reaction chamber in which, in operation, feedstock undergoes drying and/or pyrolysis prior to reduction and combustion, wherein the reaction chamber is incorporated in a part of the gasifier which is arranged to undergo vibration continuously or intermittently.

8. A gasifier according to claim 7, wherein the reaction chamber can vibrate at a rate in the range from 20 to 40 Hz.

- 18-

9. A gasifier for the gasification of organic material comprising biomass, having a combustion chamber, in which the gasification reaction is carried out, which is at least partly formed or lined by means of graphite and a reaction chamber in which, in operation, feedstock undergoes drying and/or pyrolysis prior to reduction and combustion, wherein the reaction chamber is incorporated in a part of the gasifier which is arranged to undergo vibration continuously or intermittently.

10. A gasifier according to any of claims 1 to

6 or 9, wherein the combustion chamber is enclosed by a heat exchange unit comprising a lower grate, a pair of heat exchange reservoirs disposed upon opposite sides of the combustion chamber and having their lower parts in communication, an inlet for heat exchange fluid in the upper part of one of the reservoirs and an outlet for heat exchange fluid in the upper part of the other reservoir.

11. A gasifier according to claim 10, wherein the grate comprises a plurality of tubes interconnecting the heat exchange reservoirs.

12. A gasifier according to any of claims 7 to 11 , wherein the reaction chamber comprises an upright cylindrical structure fitted at its lower end into an aperture in the combustion chamber, a gas-tight seal being provided between the exteriors of the chambers and the reaction chamber, the combustion chamber and the seal being arranged to allow vibration of the part incorpora¬ ting the reaction chamber.

13. A gasifier according to claim 12, wherein a vibrator having a vibrator member attached to the reaction chamber is mounted upon a fixed part of the apparatus.

14. A gasifier according to claim 13, wherein the reaction chamber is mounted upon opposed upright arms so as to be free to vibrate and the arms and the vibrator unit are mounted upon the exterior of the combustion chamber.

15. A gasifier according to any preceding claim, wherein a condensate collection reservoir surrounds the upper part of the reaction chamber and a feedstock inlet device incorporated in a gas off-take hood is located at the top of the reaction chamber.

16. A gasifier for the gasification of organic material comprising biomass, substantially as described with reference to the accompanying drawings.