WO2006077405A1

WO2006077405A1 - Fuel processor

Info

Publication number: WO2006077405A1
Application number: PCT/GB2006/000178
Authority: WO
Inventors: Matthias Grundmann
Original assignee: Bioflame Fuels Limited
Priority date: 2005-01-19
Filing date: 2006-01-19
Publication date: 2006-07-27
Also published as: GB2422332A; GB2422332B; GB0501084D0

Abstract

A fuel processor is provided for processing a carbon- based fuel, the processor comprising a fuel processing chamber which is arranged, in use, substantially upright. In use, fuel to be processed moves downwards through the chamber, and heated processing gas moves upwards through the chamber. The fuel may be discharged from the processor through a processed fuel outlet, with the rate of discharge controlled by a discharge unit. By varying the rate of discharge of the discharge unit, the residence time of the fuel in the processor can be finely controlled. Furthermore, the fuel moves downwards through the processor under the influence of gravity, ensuring that the first product in is the first product out.

Description

Fuel Processor

The present invention relates to a fuel processor and more particularly to a processor suitable for processing carbon-based fuels in a pyrolysis process . Preferably, the fuel processor can also be used as a drying apparatus or even to produce charcoal .

The prior art has several examples of fuel processor in which a carbon-based fuel is treated by heating it and maintaining it at a temperature beyond its self-ignition point in a controlled environment to enhance its qualities as a fuel- by producing an end- product that is dry, energy-rich, friable, hydrophobic , sterile and which will combust in a smokeless manner . The end product can be burned in a power station, for example .

Carbon-based fuels that can be treated by such a fuel processor include most organic materials , such as agricultural and commercial waste including wood, plastics and used tyres .

One such prior-art example is given in GB 2 378 498 A, in which organic material for processing is supported on a conveyor which travels progressively through a drying enclosure, a processing enclosure and finally a cooling enclosure .

With all fuel processors of this type it is necessary to expose the raw fuel to a controlled atmosphere comprising several process gases at a known temperature . The pyrolysis process seeks to remove moisture and substances that would otherwise produce smoke and/or noxious fumes when the processed fuel is ultimately combusted. In the processor, at temperatures above the self-ignition temperature of the raw fuel , it is vitally important to control (i . e . inhibit) the amount of oxygen present since if too much oxygen comes into contact with the raw fuel it will burn . Accordingly, prior art apparatuses employ elaborate arrangements to seal the processing chamber .

Another important factor that must be controlled is the residence time of the raw fuel in the processor since this , together with the temperature inside the processor and the composition of the process gases, determines the quality of the processed fuel .

Additionally, such processors must be efficient and of simple, reliable and robust construction .

Embodiments of the present invention aim to provide a fuel processor that addresses , at least partly, the aforementioned problems .

The invention is defined in the attached independent claims to which reference should now be made . Further, preferred features may be found in the sub-claims appended thereto .

According to a first aspect of the invention, there is provided a fuel processing apparatus for processing a carbon-based fuel , the apparatus comprising a substantially upright fuel processing chamber, arranged such that in use fuel moves downwards through the chamber during processing of the fuel , and wherein in use the fuel is processed by heated processing gas which is arranged in use to move upwards through the chamber .

Preferably the apparatus has a processing gas intake and a processing gas outlet , which may in a preferred embodiment be connected so that at least a portion of the processing gas may be re-circulated through the processing chamber.

Preferably the processing gas intake is in fluid connection with a base region of the processing chamber (e . g. by means of a tube) so that in use the processing gas is conveyed to a base region of the processing chamber, from where it then moves upwards through the fuel in the chamber .

In a preferred arrangement the apparatus comprises a fuel intake and a fuel outlet . The fuel intake is preferably located at an upper region of the apparatus and the fuel outlet is preferably located at a lower region of the apparatus so that , in use , fuel to be processed enters the processing chamber towards the top thereof and processed fuel is removed from the chamber from towards the bottom thereof . The fuel is preferably arranged to fall (move downwards) from the fuel intake to the fuel outlet by the influence of gravity.

The processing gas is preferably arranged to travel in the opposite direction to that of the fuel , so that by means of this counter current updraft system, the incoming hot processing gas passes first through the fuel lower down the processor, i . e . first through the fuel with the longest residence time . Then, as the gas passes up through the processor, it passes through the fresher fuel higher up the processor (with a shorter residence time) . Thus , as the fuel becomes drier lower down the processor, so it meets the hotter drier gas , ensuring that the final fuel product has the required dryness . Also, with the processor being arranged substantially vertical in use , the flow of the fuel through the processor is controlled by gravity . This ensures that the product passes out of the processor in the same order that it entered the processor, i . e . that the first product in is the first product out and the last product in is the last product out . In other words , because the fuel passes out of the processor in the same order that it entered the processor, it can be ensured that each part of the fuel is resident in the processor for the desired period of residence time . In a preferred arrangement the processing chamber is elongate and has a longitudinal axis arranged in use substantially upright and preferably, but not necessarily, vertical . In a particularly preferred embodiment the fuel processor is a hollow cylinder . Preferably, the hot processing gas flows downwards through a central tube concentric with and along the longitudinal axis of the chamber, then upwards through the fuel in the chamber around the central tube . More preferably, the hot gas is then re-circulated through down return pipes disposed along, or through a thin sleeve around, the outside of the chamber . By circulating the hot gas in this manner, additional (secondary) heating of the fuel is achieved as the gas passes down the central tube or down the return pipes .

A charging unit is preferably provided to control the flow of fuel product fed into (entering) the processor . Furthermore, a discharging unit is preferably provided to control the flow of fuel product out of (discharged from) the processor . The discharging unit enables a flow rate to be set and maintained, providing absolute and variable control of the fuel residence time within the processing chamber .

Preferably, the hot gas is superheated steam, which may be generated from the product being processed. Superheated steam provides an effective gas for removing moisture from the fuel product . It also provides a substantially oxygen-free atmosphere, and as such is cheaper than using an inert gas .

The temperature of the processing gas in the processing chamber is preferably in the region of 250 ⁰C, so that a dry, energy rich product can be obtained by means of the pyrolysis process . The temperature can of course be varied depending on the desired qualities of the product to be obtained. For example, the temperature may be lower (e . g . below 200 ⁰C) if it is desired only to dry the product , but not for it to undergo pyrolysis . On the other hand, a higher temperature can be used (e . g . 600 ⁰C) if it is desired to produce charcoal from a carbon-based product . Also, it is possible to dry products that are not carbon based in addition to products that are carbon based in the former example .

Preferably, a heat source and a heat exchanger are provided between the processing gas outlet and the processing gas intake, so that the gas exiting the gas outlet may be re-heated using the heat exchanger before being re-circulated to the gas intake . The heat exchanger may be either an indirect heat exchanger or a direct heat exchanger . As a heat source, a combustion unit may be provided or waste heat from a heat- generating source such as a power plant may be used. The invention also includes a method of processing a carbon-based fuel , the method comprising passing processing gas upwards through a downwardly moving mass of fuel in a processing chamber in which fuel to be processed enters the chamber at an upper region thereof and processed fuel is withdrawn from a lower region thereof .

The method preferably includes re-circulating processing gas through the mass of fuel .

The invention also includes a fuel processing plant incorporating an apparatus according to any statement herein .

The invention also includes fuel processed in accordance with any apparatus or method described herein . A preferred embodiment of the present invention will now be described by way of example only with reference to the accompanying diagrammatic drawing in which: Figure 1 shows , in somewhat schematic cross- section, a fuel processor in accordance with an embodiment of the present invention.

With reference to Figure 1 , there is shown generally at 10 a fuel processor in accordance with an embodiment of the present invention. The processor 10 comprises a generally cylindrical main housing 12 having a gas intake 14 , a gas outlet 16 , a raw fuel intake 18 and a processed fuel outlet 20. Within the main housing 12 are located a series of concentric vessels including a processing chamber 22 in which, in use , the raw fuel from the raw fuel intake 18 is exposed to processing gas from the gas intake 14. In use, the processing gas is at a regulated temperature, which is at or above the temperature at . which the raw fuel self-ignites when the processor is being used to perform pyrolysis .

The processing gas travels in the direction shown by arrows A from the gas intake 14 down a central pipe 24 , then out through the bottom of the pipe and up through the processing chamber 22 , containing the fuel to be treated, then down through an outer (annular) sleeve 26 before exiting through the gas outlet 16 to a heat exchanger not shown . The heat exchanger can be supplied with heat using a combustion unit or using waste heat generated by a power plant . Thus , the processing gas can then be re-heated using the heat exchanger and re-circulated to the gas intake 14. Clearly, using waste heat ensures that the energy efficiency of the fuel processor is maximised. The fuel enters the processing chamber 22 as raw fuel from the raw fuel intake 18 and moves under gravity towards the bottom of the chamber 22 where it is discharged by a discharger 35 and removed by an auger (not shown) through the processed fuel outlet 20. The discharger 35 may be a rotary discharger such as a rotating cone (as shown) or it may be a paddle discharger . The discharger should be able to withstand a large head of pressure, as a large volume of fuel is positioned above it .

The auger (not shown) incorporates a cooling apparatus , such as a water j acket , to reduce the temperature of the processed fuel to below the temperature at which it self-ignites . The auger then deposits the processed fuel in a processed fuel holding vessel (not shown) . An auger may also be provided to convey the raw fuel to the raw fuel intake 18.

A drain 28 removes condensate, which may typically include the compounds that it was necessary to remove from the raw fuel in order to prevent the fuel giving off smoke and/or noxious fumes when burned later in a power plant . Accordingly the condensate must be filtered carefully to render it safe for disposal . Some compounds filtered from the condensate may in fact be useful commercially .

Valves 30 , 32 , which in this case are rotary valves , provide an airlock at each of the raw fuel intake 18 and the processed fuel outlet 20 , thus sealing the processing chamber 22 and preventing the ingress of air from the outside atmosphere . This is important to prevent oxygen from entering the processing chamber . In addition, a further rotary valve may be provided at the discharge end of the processed fuel outlet 20. The process gas contains super-heated steam, which assists in drying the raw fuel , and air, which includes oxygen . The air is present in the processor when a start-up operation of the processor is commenced, as described in more detail below. The superheated steam is produced from moisture released from the fuel as it is heated.

If excess oxygen enters the system, it may cause the fuel to combust at localised sections in the processing chamber . This combustion, if not countered, could then spread through the fuel leading to a dangerous , uncontrollable (runaway) fire situation . However, the fuel processor embodying the invention has an important , in-built safety mechanism for preventing such a fire situation from occurring .

Namely, as the air contacts the fuel , at least two chemical reactions take place . Firstly, combustion occurs . The oxygen in the air stream combines with the carbon in the fuel to produce carbon dioxide in an exothermic reaction :

C + O₂ → CO₂ (+HEAT) . . . . (1)

Secondly, some of the carbon dioxide becomes reduced to carbon monoxide by contact with the burning charcoal in an endothermic reaction :

CO₂ + C (+HEAT) → 2CO . . . . (2 )

Hence, the exothermic reaction is automatically controlled by the endothermic reaction . In other words , although excess air entering the processing chamber will cause Reaction (1) to occur at temperatures above the self-ignition point of the fuel , the carbon dioxide so produced will cause the endothermic Reaction (2 ) , thus preventing the runaway combustion of the fuel . By this inherent mechanism of the fuel processor, an otherwise dangerous situation can be prevented from occurring .

The process gas from the gas outlet 16 , which is mainly superheated steam, with some carbon dioxide , is re-circulated through the processor via the heat exchanger and the gas intake 14 together with a regulated quantity of fresh air .

Thus , the temperature in the processing chamber 22 can be carefully regulated. In addition, if desired, a carbon monoxide sensor may be provided inside the fuel processor, for example in the processing chamber 22. The sensor can be used to detect the presence of carbon monoxide in the processor, and to alert an operator if the amount of carbon monoxide exceeds a predetermined level . Thus , the operator can be made aware promptly if there is any unwanted ingress of oxygen into the fuel processor .

Next , start-up operation of the fuel processor will be described, in the case that the fuel processor is used to perform pyrolysis . To commence use of the fuel processor, raw fuel is fed into the processing chamber 22 through the raw fuel intake 18. At this stage , the processed fuel outlet 20 is closed, by means of the discharger 35 and rotary valve 32. As the raw fuel is fed into the processing chamber 22 , it falls to the bottom of the chamber and flows around the annular cross-section of the chamber, thus forming an even distribution of fuel in the processing chamber. More raw fuel is fed into the processing chamber 22 until the chamber is filled to a desired height .

After the processing chamber has been filled with raw fuel , the air inside the fuel processor is heated by means of the heat exchanger and heat source provided between the processing gas outlet 16 and the processing gas intake 14. The hot gas (air) then circulates around the fuel processor along the path indicated by the arrows A in figure 1 , as already described above . As the hot gas circulates through the processing chamber 22 , the temperature in the chamber increases to around 100 ⁰C . Moisture is released from the raw fuel as steam. As more steam is produced from the fuel , and as the air/steam mixture is heated through the heat exchanger and re-circulated, the temperature increases above its initial value (limited to around 100 ⁰C) and superheated steam forms .

When the required operating temperature is reached, which is around 250 °C for the pyrolysis process , continuous processing of the raw fuel to obtain processed fuel can commence . After the start-up operation, the fuel in at least a bottom section of the processing chamber 22 must be discarded as it will not have been sufficiently processed.

Thus , the discharger 35 is used to discharge a volume of fuel from the processing chamber 22. This fuel is then conveyed away from the fuel processing chamber by means of the water-cooled auger (not shown) and discarded . In fact , it may be possible to subsequently process this fuel as raw fuel . At this stage , continuous processing of fuel can commence . Raw fuel is fed into the fuel processor through the fuel intake 18 so that it is again filled to the required height . Then, the discharger 35 can be adjusted such that the fuel flows out of the fuel processor at a set rate, depending upon the required residence time of the fuel in the processor . Thus , the residence time can be finely controlled by means of the discharger 35. Furthermore, because the fuel flows downwards through the fuel processing chamber 22 under the influence of gravity, it is ensured that it is discharged in a first in/first out fashion, and is therefore always resident in the fuel processing chamber 22 for the required time period set according to the discharge rate of the discharger 35. A level sensor may be provided in the upper region of the fuel processing chamber, to detect when the height (thus also volume) of the fuel falls below a set value . When this occurs , more raw fuel can be allowed to enter the processing chamber through the raw fuel intake . In this way, the amount of fuel in the processing chamber is "topped up" in accordance with the rate at which fuel is discharged from the bottom of the processing chamber by the discharger 35.

Alternatively, it may be possible to use a charging unit to set the flow rate of fuel entering the processing chamber, and to discharge fuel in accordance with the rate at which fuel enters the processor, for example by linking the level sensor to the discharger . In other words , the charging unit could be used to control the residence time of the fuel .

It can be seen from the attached figure 1 , that the processing gas from the processing gas inlet 14 enters the fuel processing chamber 22 at a base region distanced from (above) the bottom of the apparatus . In other words , the lower end of the inner tube 24 is separated by a predetermined distance from the discharger 35. As already described, when the processing gas exits the tube 24 it rises through the fuel in the fuel chamber 22 , as shown by the arrows A in figure 1.

This means that the bottom region of the fuel processing chamber 22 forms a cooling zone 36 , as it is not heated to the same extent as the rest of the chamber by the fuel processing gas . This cooling zone 36 therefore cools the fuel product before it is discharged by the discharger 35. This helps to prevent the processed fuel product exiting the fuel processor from subsequently combusting on contact with air, by reducing its temperature to below its self-ignition point .

In a further modification of the fuel processor, a louvred outlet may be provided towards the top of the processing chamber 22 , through which the processing gas passes before entering the outer sleeve 26. The louvred outlet causes the processing gas to spin in the upper region of the processing chamber 22 , which separates carryover in the gas stream and serves to distribute fuel , being fed in through the fuel intake 18 , evenly around the annular plane of the chamber . In a still further modification, one or more flow agitators , such as paddles , may be provided in the processing chamber . Such flow agitators can be used to ensure an even distribution of fuel and to ensure that the processing gas passes through all regions of the fuel , as opposed to following only a preferred path through the fuel . This may be necessary either if the fuel is a very dense , compact fuel or if the fuel has a large diameter .

The fuel processor may be several metres in length (height) and one or more metres in diameter, although it can of course be larger or smaller than this depending on the processing volume requirements . A typical residence time for fuel to undergo the pyrolysis process may be in the region of 1 to 3 hours , although this of course depends on factors such as the type of fuel used, the dimensions of the processor, temperature and the processing gas flow rate .

Furthermore , by varying the temperature to which the processing gas is heated, the fuel processor may be used to perform other functions instead of pyrolysis . For example, by lowering the temperature , the processor can be used as a drying apparatus for drying fuel to a desired moisture content . Alternatively, by increasing the temperature, the processor can be used to produce charcoal from carbon-based products . Thus , the processor is advantageously versatile in function.

As already described, because the withdrawal of the processed fuel is under the control of the discharger 35 , and because the raw fuel in the chamber 22 moves under the influence of gravity, the residence time of the fuel in the processing chamber can be controlled precisely.

Claims

Claims :

1. A fuel processing apparatus for processing a carbon-based fuel , the apparatus comprising : a fuel processing chamber for processing the carbon-based fuel , the fuel processing chamber being arranged substantially upright in use such that , in use , fuel moves downwards through the chamber and is processed by heated processing gas which is arranged in use to move upwards through the chamber .

2. A fuel processing apparatus according to claim 1 , wherein the apparatus is a hollow cylinder .

3. A fuel processing apparatus according to any preceding claim, wherein the fuel processing chamber is elongate and has a longitudinal axis arranged substantially upright in use .

4. A fuel processing apparatus according to any preceding claim, further comprising a fuel intake and a fuel outlet .

5. A fuel processing apparatus according to claim 4 , wherein the fuel intake is located at an upper region of the apparatus .

6. A fuel processing apparatus according to claim 4 or 5 , wherein the fuel outlet is located at a lower region of the apparatus .

7. A fuel processing apparatus according to any preceding claim, further comprising a charging unit for controlling the flow of fuel into the fuel processing chamber .

8. A fuel processing apparatus according to any proceeding claim, further comprising a discharging unit for controlling the flow of fuel out of the fuel processing chamber.

9. A fuel processing apparatus according to claim 8 , wherein the discharging unit is a rotary discharger .

10. A fuel processing apparatus according to claim 9 , wherein the rotary discharger is a rotating cone discharger .

11. A fuel processing apparatus according to any of claims 4 to 10 , further comprising valves , provided at each of the fuel intake and the fuel outlet , for preventing the ingress of air into the fuel processing chamber.

12. A fuel processing apparatus according to claim 11, wherein the valves are rotary valves .

13. A fuel processing apparatus according to any preceding claim, further comprising a processing gas intake and a processing gas outlet .

14. A fuel processing apparatus according to claim 13 , wherein • the processing gas intake and the processing gas outlet are connected .

15. A fuel processing apparatus according to claim 13 or 14 , wherein the processing gas intake is in fluid connection with a base region of the fuel processing chamber .

16. A fuel processing apparatus according to any of claims 13 to 15 , further comprising a central tube concentric with and along the longitudinal axis of the fuel processing chamber, j oined to the processing gas intake at its upper end and being open at its lower end, such that in use , the processing gas flows downwards through the central tube and upwards through the fuel in the fuel processing chamber around the central tube .

17. A fuel processing apparatus according to claim 16, further comprising a thin sleeve around, or one or more down return pipes disposed along, the outside of the fuel processing chamber, such that in use, the processing gas flows downwards through the sleeve or one or more down return pipes after flowing upwards through the fuel processing chamber .

18. A fuel processing apparatus according to any of claims 13 to 17 , further comprising a heat source and a heat exchanger provided between the processing gas intake and the processing gas outlet .

19. A fuel processing apparatus according to claim 18 , wherein the heat exchanger is a direct heat exchanger .

20. A fuel processing apparatus according to claim 18 , wherein the heat exchanger is an indirect heat exchanger.

21. A fuel processing apparatus according to any of claims 18 to 20 , wherein the heat source is a combustion unit .

22. A fuel processing apparatus according to any of claims 18 to 20 , wherein the heat source is waste heat from a power plant .

23. A fuel processing apparatus according to any preceding claim, further comprising one or more flow agitators provided in the fuel processing chamber .

24. A fuel processing apparatus according to any preceding claim, wherein the fuel processing chamber has a louvred outlet at an upper region .

25. A fuel processing apparatus according to any preceding claim, further comprising a carbon monoxide sensor.

26. A fuel processing apparatus according to any preceding claim, wherein a bottom region of the fuel processing chamber forms a cooling zone .

27. A method of processing a carbon-based fuel , the method comprising : passing processing gas upwards through a downwardly moving mass of fuel in a processing chamber in which the fuel to be processed enters at an upper region thereof and the processed fuel is discharged from a lower region thereof .

28. A method according to claim 27 , wherein the fuel moves downwards through the processing chamber under the influence of gravity.

29. A method according to claim 27 or 28 , wherein the processed fuel is discharged at a predetermined rate .

30. A method according to any of claims 27 to 29 , wherein the fuel is resident in the fuel processing chamber for a predetermined period of time .

31. A method according to any of claims 27 to 30 , further comprising re-circulating the processing gas through the mass of fuel .

32. A method according to any of claims 22 to 31 , wherein the processing gas mainly comprises superheated steam.

33. A method according to claim 32 , wherein the superheated steam is produced from moisture in the fuel being processed.

34. A method according to any of claims 27 to 33 , wherein the fuel being processed undergoes pyrolysis .

35. A method according to claim 34 , wherein the temperature of the processing gas is around 250 ⁰C .

36. A method according to claim 34 or 35 , wherein combustion of carbon in the fuel due to the presence of excess oxygen is corrected by an endothermic reaction using the product of the combustion as a reactant .

37. A method according to any of claims 27 to 33 , wherein the fuel is processed to form charcoal .

38. A method according to claim 37 , wherein the temperature of the processing gas is around 600 ⁰C .

39. A method according to any of claims 27 to 33 , wherein the fuel is dried.

40. A method according to claim 39 , wherein the temperature of the processing gas is around 200 ⁰C .

41. A fuel processing apparatus according to any of claims 1 to 26 and substantially as described herein with reference to the accompanying drawing .

42. A method of processing a carbon-based fuel according to any of claims 27 to 40 and substantially as- described herein with reference to the accompanying drawing .