Production of producer gas

Abstract

 A gas producer for producing producer gas from a fuel such as coal effectively combines the unknown updraught and downdraught processes. The producer has an upper section (8) where an upperfire bed (16) is located and a lower section (9) where a lower bed (14) is located. A gas outlet (4) is positioned between the upper and lower beds. To ensure satisfactory feed conditions through the upper section, the walls of this section diverge downwardly. The angle at which they diverge should be less than the angle of repose of the fuel used.

Description

[0001] THIS invention relates to a gas producer for the production of producer gas.

[0002] It has been proposed to arrange a gas producer so that it has the advantages of both the known updraught and downdraught processes. To achieve this, gas is taken off from the middle of the furnace and air is introduced at the top and at the bottom to create fire beds both above and below the gas offtake.

[0003] Although this proposal has been put forward, it has not to our knowledge ever been developed to the stage of commercial operation, and it is the object of the present invention to construct a gas producer working on this principle which will be practical to operate.

[0004] According to the present invention, there is provided a gas producer comprising a chamber for containing a body of fuel from which gas will be produced, the chamber having a tapering upper section which is narrower at the top than at the bottom and in which an upper fire bed will; in use, be located and a lower section in which a lower fire bed will, in use, be located, means for introducing air simultaneously to both the upper and lower sections, and a gas outlet between the upper and lower sections.

[0005] It will be apparent that the conditions in the upper section are equivalent to the known downdraught process, and that the conditions in the lower section are equivalent to the known updraught process. The gas produced is clean. That.which is produced in the upper section of the chamber is clean because the volatile constituents of the fuel are broken down in the way known for a downdraught process. The gas from the lower section of the chamber is also clean, because this is produced from the coke residue from the downdraught process in the upper section, and all the volatile constituents have been driven off in the downdraught portion of the process before the coke reaches the updraught portion.

[0006] The use of a taper in the upper section helps to prevent hang-ups of fuel. The initial application of heat to the fuel causes it to swell, but since the chamber widens as the fuel moves down the chamber, an increased volume is available for the fuel as it passes down.

[0007] In order to ensure that all the fuel particles are subjected to the same conditions as they pass through the producer, it is desirable to shape the upper end of the chamber so that there are no void areas. This can be done by arranging the fuel inlet with a cross-sectional area equal to the cross-sectional area of the upper end of the upper section, and choosing the angle of taper of the upper section so that it is lest than the angle of repose of the fuel. The fuel will then completely fill the upper section, and a fuel particle at the edge of the section will be subjected to substantially the same conditions a₅ a particle in the center of the section.

[0008] The chamber is preferably surrounded by a water-cooled jacket. The gas outlet preferably includes an annular space surrounding the upper section and open at its bottom to the interior of the chamber with the gas leaving the producer through an outlet pipe close to the top of the annular space. The space thus acts as a manifold and ensures that gas is drawn evenly from all the way around the chamber. Additionally the upward flow of the gas from the fuel in the bed to the outlet pipe has some effect in allowing dust to settle out of the gas. Furthermore, the annular space can be waterjacketed so that some cooling of the gas is achieved before it leaves the producer.

[0009] The producer is preferably arranged to operate under.suction. The gas produced is sucked out of the producer itself, and this causes air to be sucked in. Air inlets are provided at the top and at the bottom of the chamber, so that air flows in to both of the fire beds.

[0010] The invention will now be further described, by way of example, with reference to the accompanying drawing which is a schematic cross-section through a gas producer according to the invention.

[0011] The gas producer shown in the drawing has a fuel inlet 1 and an ash outlet 2. Between the inlet 1, and the outlet 2, the producer has a chamber surrounded by a water jacket 3. The producer also has a gas outlet 4, air inlets 5 and 6 and a poking hole 7. The interior of the producer is divided into an upper section generally indicated at 8 and a lower section generally indicated at 9. The upper section 8 has a conical inner wall 10.

[0012] An eccentric plate type grate 12 is provided at the bottom of the producer above the ash outlet 2.

[0013] Around the upper section 8, there is an annular space 13 through which gas passes on its way to the gas outlet 4.

[0014] The operation of the producer will be described after start-up and once it is running at a steady state.

[0015] Both the upper section 8 and the lower section 9 will be.full of fuel in various stages of being consumed. Fresh fuel is charged into the inlet 1 and ash is discharged from the outlet 2. Fire beds indicated by phantom lines at 16 and 14 are present in both upper and lower sections. Air is drawn in through the air inlet 5 and passes through the fuel in the inlet 1 to the fire bed 16. In the case where the fuel is coal, the coal burns in the oxygen from the air. In this fire bed 16, the coal is burnt to coke and the tars and volatiles in the coal are burnt to C0₂. Generally, insufficient oxygen is able to reach the lower edge of the fire.bed 16 to completely combust the coal, and this therefore remains as coke.

[0016] Below the fire bed 16, there is a reduction zone where the reactions



take place. The resulting producer gas then flows through a layer of unreactive coke to the annular space 13 and then to the outlet 4. The unreactive coke continues to pass down the chamber as ash is withdrawn from the bottom and passes into a reduction zone above the lower fire bed 14. In this reduction zone, the carbon of the coke combines with carbon dioxide produced in the lower fire bed 14 to produce carbon monoxide which again passes to the annular space 13 and the outlet 4. In the lower fire bed 14., the coke remaining in the chamber is burnt to ash and carbon dioxide. The ash is extracted through the grate 12 and the outlet 2.

[0017] The process which has just been described works particularly well with bituminous coal as the feed stock. However a very wide variety of other fuels can also be used.

[0018] The gas leaving the chamber through the outlet 4 does not require much cleaning. In practice it is passed through cyclones acting as dedusters and then through a heat exchanger to cool the gas. The gas can then be fed to the area where it will be consumed.

[0019] Air is preferably sucked into the chamber of the producer by means of suction applied to the outlet 4. The suction can be by means of a fan arranged downstream of-the cyclones and heat exchanger. Using this method, it is not necessary for the chamber to have a tight fitting lid. Although some air may still be'drawn in through the fuel present in the hopper, this will not affect the performance. Furthermore, it is easier to use the poke holes 7 since hot gasses will not be blown out when these are opened to poke the .charge inside the producer.

[0020] The inner wall 10 of the upper section 8 is inclined to the vertical at an angle a. For most coals, this angle can be about 30°, but other fuels may require different angles, normally in the range 5 to 45°. The factors to be taken into account in determining this angle are the swelling index of the fuel and the angle of repose taken up naturally by an inclined side of a heap of the fuel. If this condition is met, fuel will be in contact with the inner wall 10 throughout the length of the wall. There will thus be no void areas where gas can collect.

[0021] In the lower section 9, the walls have parallel sides.

[0022] Since there is a water jacket on both sides of the space 13, there will be an appreciable cooling of the gas produced in this space before the gas leaves the producer through the outlet 4.

[0023] The eccentric grate 12 is of a known type. An external operating bar will be provided so that the grate can be rotated periodically to force ash through to the outlet 2.

[0024] The air inlet to the lower fire bed 14 is through the inlet 6 and through the apertures in the grate 12.

[0025] It is necessary to control the amount of moisture entering the producer with the inlet air. The amount of moisture entering is relevant to the proportion of hydrogen in the gas produced.

[0026] Moisture can conveniently be added to the air flowing to the inlets- 5 and 6 by means of a steam take-off pipe from the heat exchanger downstream of the producer. The amount of steam being admitted to the inlet air flow can conveniently by-gauged by placing a temperature sensor in the inlet air line.

Claims

1. A gas producer comprising a chamber for containing a body of fuel from which gas will be produced, the chamber having a tapering upper section which is narrower at the top than at the bottom and in which an upper fire bed will, in use, be located and a lower section in which a lower fire bed will, in use, be located, means for introducing air simultaneously to both the upper and lower sections, and a gas outlet between the upper and lower sections.

2. A producer as claimed in Claim 1, wherein the chamber is surrounded by a water-cooled jacket.

3. A producer as claimed in Claim 1 or Claim 2, wherein the gas outlet includes an annular space surrounding the upper section and open at its bottom to the interior of the chamber, and an outlet pipe at the top of the annular space.

4. A producer as claimed in Claim 3, wherein the annular space is provided with a water jacket.

5. A producer as claimed in any preceding claim, including a fuel feed pipe of uniform cross-sectional area equal to the cross-sectional area of the narrower, top end of the upper section, and connected to the top of the upper section.

6. A producer as claimed in Claim 5, wherein the means for introducing air includes an air inlet opening into the fuel feed pipe.

7. A producer as claimed in any preceding claim, including a suction fan downstream of the gas outlet for drawing air in through an air inlet to the upper section and through a grate at the bottom of the chamber to the lower section.

8. A producer as claimed in any preceding claim, wherein the tapering upper section is conical.

9. A producer as claimed in Claim 8, wherein the walls of the tapering upper section make an angle of between about 5 and 45° with the vertical.

10. A producer as claimed in Claim 9, wherein the walls of the tapering upper section make an angle of approximately 30⁰ with the vertical.

11. A method of operating a gas producer as claimed in any one of Claims 1 to 8, including the step of choosing the angle which the walls of the tapering upper section make with the vertical so that this angle is less than the angle with the vertical made naturally by the inclined surface of a heap of the fuel to be used.

Drawing