GB2324304A

GB2324304A - Method of making refuse-derived fuel and fuel made by the method

Info

Publication number: GB2324304A
Application number: GB9707498A
Authority: GB
Inventors: Muneo Azegami; Raad Chalabi
Original assignee: CPIS Ltd
Current assignee: CPIS Ltd
Priority date: 1997-04-14
Filing date: 1997-04-14
Publication date: 1998-10-21
Also published as: JPH10287890A; GB9707498D0

Abstract

A method of making a hybrid fuel comprises the steps of pulverizing refuse, mixing the pulverized refuse with an additive which includes calcium oxide and a calcium and/or sodium based bentonite. The additive reacts with the pulverized refuse to produce an intermediate mixture which is then mixed with coal to produce a hybrid fuel. The ratio of intermediate mixture to coal depends upon the burning requirements of the hybrid fuel.

Description

TITLE: "Method of making a hybrid fuel and fuel made by the method" THE PRESENT INVENTION relates to a method of producing a hybrid fuel and more particularly relates to a method of producing a hybrid fuel from coal and a refuse-derived fuel. Such a hybrid fuel is particularly, though not exclusively, suitable as a fuel in electricity generation.

Coal is currently a favoured fuel in electricity generation because of its distinct cost advantage over alternatives, most notably oil, which is presently very expensive. The coal fuel is pulverized at the site of a power station and is then continuously fed into the burner of the power station to generate energy to drive the turbines. The ignition temperature of coal is high and its burning rate is low. There has long been the requirement to increase the burning rate of coal. Pulverization of the coal prior to feeding the coal into the burner enhances the solid coal's diffusion in air and thus increases the oxidation rate and hence the burning rate of the coal. Any mechanism that increases the efficiency of the pulverization process and/or increases the diffusion of coal in air, also improves the efficiency of coal as a fuel.

Pulverized coal fuel has several limitations which are summarized below.

Typically energy demand in an electricity distribution network supplied by a power station varies substantially throughout a 24 hour period, typically with more electricity being required during the day than during the night. Such fluctuations in electricity demand dictate a corresponding variation in the feed rate of fuel into the burners of the power station. It is difficult to arrange for a furnace burning only pulverized coal to operate satisfactorily with wide variations in coal feed rate so that changes in the feed rate of pulverized coal to match electricity demand requirements is problematic in coalbased electricity generation plants. If the feed rate of coal is reduced by 30% or more, then burning stops.

Furthermore, re-starting a coal-fired burner once burning has stopped is very difficult and hence expensive.

Prior proposals to solve this problem have involved modification of the burners and/or decreasing the particulate size of the coal powder to a micron level.

Both of these prior proposed solutions have considerable limitations. Consequently, in practice, coal burners are usually complimented by oil burners which has the undesirable effect of increasing the overall cost of electricity generation.

It is an object of the present invention to provide a method of producing a fuel which overcomes the aforementioned problems associated with coal as a fuel.

In EP-A-0566419 there is disclosed a method of making a fuel from municipal refuse, comprising comminuting the refuse, mixing the refuse with an additive containing calcium oxide and forming the product into pellets, wherein said additive includes, in addition to calcium oxide, a calcium based and/or sodium based bentonite, and after mixing the refuse with the additive, the additive is allowed to react with the refuse, and thereafter the resultant material is formed into pellets and said pellets are subsequently dried in an atmosphere containing carbon dioxide.

The atmosphere in which the pellets are dried may, for example, contain in excess of 25% CO2 by volume.

A method having the characteristics recited above is herein referred to as being "of the kind specified" and the resulting fuel is herein referred to as a "refuse derived fuel of the kind specified".

In accordance with one aspect of the invention, there is provided a powdered solid fuel comprising a mixture of pulverized coal and pulverized refuse derived fuel.

Preferably the refuse derived fuel is a refuse derived fuel of the kind specified.

According to another aspect of the invention, there is provided a method of making a powdered solid fuel comprising forming a refuse derived fuel of the kind specified, blending the refuse derived fuel with coal, and pulverizing the refuse derived fuel and the coal together to form a homogeneous powdered product.

A fuel in accordance with the first noted aspect of the invention may be made, alternatively, by any of various variant methods.

Thus, for example, the addition of calcium or sodium based bentonite may not be necessary in some circumstances. Furthermore, instead of forming the refuse derived fuel into pellets which are subsequently pulverized with coal, the coal may be added to the refuse or to the refuse/calcium oxide mixture at some stage prior to pelletizing, or may be added with the calcium oxide, and the powdered fuel may be produced simply by pulverizing the resulting mixture of coal and refuse derived fuel. It may even be practicable to dispense with the pelletizing stage.

Thus, after mixing the refuse with the calcium oxide and coal, and after allowing the refuse to react with the calcium oxide, the mixture may simply be dried, preferably in a CO2 enriched atmosphere, for example containing in excess of 25% CO2 by volume, and the dried mixture pulverized.

The coal is preferably added in the form of granules having a size of 1 mm or less, but it may be added, alternatively or additionally, in the form of larger pieces or lumps, (leaving the final pulverization stage to reduce such granules or lumps to powder). As a further possibility, of course, the refuse derived fuel may be pulverized then mixed with pulverized coal and the powders blended to form a homogeneous mixture. However, it is generally more efficient to mix the coal with the refuse derived fuel before pulverization.

In any of the above embodiments, the resulting powdered fuel preferably comprises between 60% and 90% by weight of coal, i.e. between 40% and 10% by weight of refuse derived fuel.

Advantageously, the resulting powdered fuel preferably comprises between 65% and 85% by weight of coal, i.e. between 35% and 15% by weight of refuse derived fuel.

Conveniently, the resulting powdered fuel preferably comprises between 70% and 80% by weight of coal, i.e. between 30% and 20% by weight of refuse derived fuel.

A preferred embodiment of the invention is described below with reference to the accompanying schematic flow chart.

The Applicants' prior European Patent Application No. 93302950.6 (EP-A-0566419) discloses a method for producing a refuse-derived fuel of the kind specified (hereinafter referred to as RDF).

Substantially as described in European Patent Application No. 93302950.6, refuse is introduced into a receiving pit, indicated at 10 in the flow chart. A quantity of additive, described in more detail below, is added to the refuse in the pit 10 to ensure an initial stabilisation of the refuse and therefore to control the smell, etc. The refuse is then removed from the pit by mechanical means, such as a crab, conveyor belt, or moving platforms, into a trommel 20 with an inner rotating screen, or into a series of such trommels, allowing any metal articles or fragments, such as batteries, etc. of small size, to be removed at an early stage of the process. The apparatus includes appropriate additional devices (not shown) for removing metal and glass at this stage.

The waste stream is then introduced into a primary crusher 30 to reduce it to a predetermined particle size, and a further metal/glass separation process is applied to the crushed waste, as indicated schematically at 40. The resultant crushed waste, further stripped of metal and glass, is now introduced to a secondary granulator/shredder 50, for a further size reduction. In this second phase, additional quantities of the additive are introduced into the waste in the secondary crusher 50 to ensure that the intended chemical reaction between the additive and the organic waste proceeds.

The output of this phase of the process, i.e. the treated, shredded waste after it leaves the secondary granulator/shredder 50 is then fed into a waste reactor 60, described below, in which, under controlled conditions, further quantities of the additive are added in order to maximise the reaction between the waste and the additive.

In this waste reactor 60, the reaction between the waste and the additive is brought to a high degree of completion. It must be understood that domestic waste, as received, is a heterogeneous composite containing proteins, fat, sugar, cellulosics and plastics. This organic mixture, when attacked by the additive under the operational conditions of the waste reactor and within the designed parameters of that reactor, will be almost completely hydrated. It is believed that the additive attacks the majority of the carbon nitrogen bonds in the waste and strips away the nitrogen from the molecular structure of the organic waste stream, and by doing so eliminates the sites for bacterial attack which are normally present in the waste. Moreover, this method of addition of the additive under strong mechanical agitation and at various points in the RDF making process as described earlier, and particularly the addition of the additive at the granulator/shredder phase 50 allows the heterogeneous waste to become more homogeneous. This homogeneity is a consequence of the chemical reaction between the additive and the waste. This chemical reaction is enhanced by the mechanical action of the crushers and granulators and dramatically enhanced by the operational conditions and system design of the waste reactor 60.

The conditions in the waste reactor are intended to enhance the reaction between the waste and the additive.

That reaction is sensitive to several key parameters, namely (a) the moisture content of the waste, (b) the temperature at which the reaction takes place, (c) the homogeneity of the waste/additive mix, (d) the pH of the waste stream. All these variables are fully controlled in the waste reactor.

In a preferred embodiment, the output from the waste reactor 60 may then be processed mechanically in an apparatus 70 to produce pellets of defined geometrical shape. This is achieved by using pelletizing presses or other mechanical means that will transform the shredded treated waste to separate pellets. Of course, as noted above, this pelletizing process is a preferred, rather than an essential step.

In a variant the waste reactor 60 is disposed upstream of the granulator/shredder 50, rather than downstream of it.

The reaction between the additive and the waste in the granulator/shredder 50 will achieve up to 70% of the reaction, and in the waste reactor 60 the reaction will reach up to 90% completion. This implies that the waste becomes more homogeneous and easier to process. Therefore, as a consequence, the pelletization process in apparatus 70 is less energy and time-consuming than in existing RDF making processes. This has a favourable effect on the economics of the RDF making process.

The pellets are then introduced into a drier 80 using hot air which is rich in carbon dioxide. This carbon dioxide results from conventional combustion of fuel, such as LPG, which is used to heat the air for the drying operation. The pellets are dried in this air/carbon dioxide mixture at a temperature ranging from 1050C to 1850C and for period of from 15 minutes to 30 minutes, to drive out residual moisture from the pellets, thus reducing their moisture content to between 1% and 5% by weight. The nature of the additive employed and the drying mechanism, particularly the presence of carbon dioxide, implies that under these conditions, each treated pellet will have a hard outer layer encapsulating a quantity of reacted waste and additive.

The utilization of the additive allows the dried pellets, even if they have a moisture content as high as 5%, to be biologically inert.

The above-described process, which is a continuous process, allows the conversion of the heterogeneous waste stream into a homogeneous reacted intermediate mixture with a calcium carbonate outer shell and nearly fully carbonized inner core. The reaction is achieved in all the phases of the process in the following manner.

(a) At the granulation/shredding phase 50, the reaction proceeds up to 70% completion.

(b) At the waste reactor phase 60, the reaction is complete up to 90%.

(c) At the pelletizing phase 70, the reaction proceeds up to 95% completion.

(d) At the drying phase 80 the reaction reaches 100% completion.

As described below, these pellets, in accordance with the present invention, are subsequently mixed with coal and the mixture pulverized to produce a homogeneous powdered fuel constituting a hybrid fuel mixture. As noted, in a variant, the pelletizing process is omitted, with the shredded product from the waste reactor 60 (or from the granulator/shredder 50 where this succeeds the waste reactor) being submitted to a drying process, preferably in an atmosphere containing CO2, after which the dried product is mixed with coal and subsequently the mixture is pulverized to produce the hybrid fuel.

Alternatively, or additionally, coal may be added at the waste reactor and/or before the drying stage, the dried mixture being subsequently pulverized to produce the hybrid fuel. As noted above, it is preferable to carry out the drying in an atmosphere containing CO2. It is also practicable, instead of pelletizing the mixture, to densify the mixture in a densifying press, for example to produce cakes or slabs, which will be broken up and pulverized during the pulverizing stage.

As described above, important elements in the part of the preferred embodiment described which is concerned with the production of the refuse derived fuel are the composition of the additive utilised in the process and its method of addition, i.e. the multifeed approach, where the additive is added at the storage pit 10, the granulator /shredder 50 and the waste reactor. The nature and mode of operation of the waste reactor is also significant.

The additive that is utilised in the process is preferably a composite mixture of calcium oxide (lime), a calcium based and/or sodium based bentonite, and a starch binder such as a blend of D-glucose and C-mannose. These components when blended correctly into ratios by weight ranging from 0 to 30% for the starch binder, 45 to 80% for the calcium oxide, and 45% to 20% for the bentonite, will act in a synergistic manner to impart the desired properties on the process and the end product, as described earlier. Thus, the starch binder may be omitted if desired. Other binders may, of course, be used, for example hydrocarbon binders.

The calcium oxide under the wet/moisture conditions of the waste attacks the carbon-nitrogen bonds, and the hydroxyl groupings, in the molecular structure of the waste, the reaction in question being an acid/base reaction. The rate of that reaction is very much dependent on the pH of the waste stream; the higher the pH, the higher is the rate of the reaction. Also the reaction rate depends on the temperature at which the reaction takes place. Thus, there is a dramatic increase in the reaction rate as the temperature in the waste increases from 600C to 900C. The importance of the presence of the bentonite is that it entraps the organic fatty acids present in the waste composite, thus causing a localised increase in pH and hence accelerating the calcium oxide attack on the waste stream.

Where the refuse derived fuel is not to be pelletized, the starch binder, or other binder, may be omitted, (even where the fuel is pelletized).

The additive as stated earlier is preferably added to the waste at various points of the process namely the pit 10, the shredder/granulator 50 and the waste reactor 60. In the case of the pit the level of addition is between 0% - 2.0% of the weight of the waste; in the case of the crusher the addition level is between 1% and 5% of the weight of the waste, and in the case of the waste reactor, the addition level is between 0% and 5% of the weight of the waste. Taking all additions into consideration therefore the total addition of the additive to the waste is between 2% and 7% of the weight of the waste. The additive referred to may be added to the refuse during, or in advance of, transportation of the refuse to the treatment plant instead of, or in addition to, being added to the storage pit (10) at the treatment plant. Such addition of the additive serves to control the biological degradation of the refuse during this stage, thus dramatically reducing the offensive odour resulting from the normal decomposition or decay of the refuse.

Examples of formulations of the additive successfully used to manufacture refuse derived fuel using the aforementioned process are set out below.

% bv weight (1) Calcium oxide (Lime) = 50 Calcium Bentonite = 45 Starch = 5 (2) Calcium oxide = 50 Calcium Bentonite = 50 Starch = 0 As indicated above, the additive is preferably added at various points of the process, for example in the pit, at the granulation/shredding phase and at the waste reactor. The dosage is adjusted at each of these feed points to ensure the maximum reaction possible between the waste and the additive at each of the phases in which it is added. The total addition levels are a function of the selected additive composition and could vary from 2% up to 7% or more by weight of the waste being processed.

The conditions under which the reaction between the additive and the waste is maximised requires the use of the waste reactor which is a key design feature of the process.

Since waste is a variable raw material, whose composition and rate of degradation is a function of time, temperature and environmental conditions and since the desired reaction between waste and the additive is sensitive to many parameters, the waste reactor is needed to ensure the conversion of the organic waste into a biologically inert product. The use of the waste reactor enables the following parameters to be controlled in the process.

(a) The concentration of additive in the waste and its homogeneous interaction within the waste.

(b) The moisture content of the waste.

(c) The temperature at which the waste is made to react with the additive.

(d) The pH conditions under which the reaction takes place.

(e) The residence time in the waste reactor.

The waste reactor 50 comprises two compartments.

The first compartment which receives the treated waste from the secondary granulator/shredder has the following features.

(a) It allows mechanical agitation of the waste.

(b) It allows the addition of additional quantities of additive.

(c) It allows the addition and/or removal of steam.

(d) It allows the waste to be heated.

(e) It allows all the above to be done in an interactive manner.

The residence time of the waste in the first compartment of the waste reactor under those carefully controlled conditions is critical to the successful reaction between the additive and the waste. That compartment of the waste reactor is therefore designed to place the treated waste stream under the ideal conditions for the reaction between the additive and the waste to reach its optimum level in that phase. The waste then feeds from this first compartment of the waste reactor to the second compartment and within that second compartment and for a short residence time, the reaction between the additive and the waste reaches 90% completion.

The first compartment of the waste reactor is generally a cubical, rectangular, or cylindrical container with rotary blades therein to allow the uniform blending of the additive into the waste. This compartment has inlets to allow the addition of steam and additive to the waste and an outlet or outlets to allow the homogenised waste to feed into the second compartment of the waste reactor.

This second compartment is a horizontal cylindrical tube with a single or twin screw feeder. The waste spends a further residence time in this second compartment whilst being subjected to the shearing action of the screw or screws before being fed, as the output from said second compartment, into a densifying press or pelletizer 70, if indeed the aforementioned pelletizing process is to be used.

As an example, the temperature conditions in the first compartment of the waste reactor to maximise the rate of reaction between the additive and the waste should be between 60 and 800C, the moisture content being between 30 and 55% by weight, and the pH being between 10 and 12. The waste should have a residence time in this first compartment of between 20 and 60 minutes and a residence time in the second compartment of the waste reactor of between 5 and 20 minutes.

As an example, with a particular waste stream, a 90% reaction has been achieved between the waste and the additive under the following conditions:- temperature = 700C; moisture content = 40%; pH = 11; residence time in the first chamber of the waste reactor = 30 minutes; and residence time in the second chamber of the waste reactor = 10 minutes.

The above described method steps are all involved in the production of a refuse-derived fuel (RDF) to which, as has been previously mentioned, coal is added in order to produce a hybrid fuel.

As shown in the accompanying flow chart, the RDF, exiting the waste reactor 60 or, in the preferred embodiment, exiting the dryer 80 (if the pelletizing and drying process is used) enters a mixing unit 90. Coal, most preferably in the form of granules, is then added to the RDF in the mixing unit 90 in a ratio of between 10% and 40% RDF to 90% to 60% coal by weight. In a more preferred embodiment, this ratio is between 15% and 35% RDF to 85% to 65% coal by weight. In a most preferred embodiment, the ratio is between 20% to 30% RDF to 80% to 70% coal by weight.

The resulting hybrid mixture is then pulverized at 100 as shown in the flow chart, to produce a homogeneous powder mix, preferably having a particle size of less than 1 mm in diameter. This resultant homogeneous powder blend is the hybrid fuel, being the end product of the process of the present invention. Of course, it should be appreciated that the mixing unit 90 and/or the pulverizer 100 may not be located at the same site as the rest of the equipment.

In particular, the pelletized refuse derived fuel may be made at a first location, stored at a second location and transported, for example by road or rail, to a power station where the mixing of the refuse derived fuel with coal, and the pulverizing of the mixture, may be carried out just prior to feeding the resulting powdered fuel to the power station furnace burners.

It has been found that the addition of the RDF to coal as hereinbefore described, has a synergistic effect resulting in a hybrid fuel which demonstrates superior performance to that of either coal on its own or the RDF on its own. This improved performance over 100% coal is evident when the hybrid fuel is burned in a standard coal burning power plant.

It has also been found that the resulting hybrid fuel comprising between 10% and 40% RDF to 90% to 60% coal by weight is easier to pulverize than either coal on its own or the RDF on its own. In other words, the mixture comprising refuse derived fuel and coal can be pulverized more efficiently than either coal on its own or RDF on its own, and the particle size required can be produced in a shorter processing time.

The conversion of domestic waste to RDF transforms the domestic waste into a biologically inert, storable and transportable solid with a uniform calorific value. The result of this is that it is more economically viable to blend the RDF with coal as a hybrid fuel than to simply blend raw domestic waste with coal as a hybrid fuel which in the past has been unacceptable due to the varying calorific value of domestic waste, its non-biologically inertness, its non-storability, its low fluidity and its difficulty in being pulverized to uniformly small powder particles.

Furthermore, it has been found that a hybrid fuel produced by the process of the present invention has a superior air mixing capability (diffusion in air) in comparison to 100% powdered coal. Also, the hybrid fuel has superior initial burning stability and burning rate when compared to 100% powdered coal, thus increasing the burning efficiency of the hybrid fuel with respect to 100% powdered coal.

It has been found that the bulk density of the hybrid fuel allows the operator of an electricity generating power station to vary the rate at which the hybrid fuel is fed into the burner in a manner that has not previously been possible with 100% powdered coal.

Further still, it has been found that, despite the fact that the calorific value of the RDF is lower than that of coal, since RDF has a higher burning rate than coal, the resulting hybrid fuel produces similar power (calories per unit time) as coal on its own. Therefore, the hybrid fuel can be fed into an unmodified boiler usually used for burning only pulverized coal. However, a standard coal burner requires an oil burner to assist combustion of the coal and to keep the coal burning. However, using the hybrid fuel of this invention, the oil burner is not required since the hybrid fuel has a lower ignition temperature than coal and has a higher burning rate.

It is to be appreciated that whilst the invention has been described with reference to specific embodiments, various modifications could be effected without departing from the scope of the invention. For example, instead of mixing the RDF with coal in a ratio of between 10% and 40% intermediate mixture to 90% to 60% coal by weight, various other ratios can be used depending upon the specific burning requirements of the fuel.

Claims

1. A powdered solid fuel comprising a mixture of pulverized coal and pulverized refuse derived fuel.

2. A powdered solid fuel according to claim 1, wherein the refuse derived fuel is made by comminuting municipal refuse, mixing the comminuted refuse with an additive which includes calcium oxide and a calcium based and/or sodium based bentonite, causing or allowing said additive to react with the comminuted refuse and wherein the refuse derived fuel is subsequently pulverized, before or after mixing with the coal.

3. A powdered solid fuel according to claim 1 or claim 2, wherein the refuse derived fuel is in the form of pellets which have been dried in an atmosphere containing carbon dioxide.

4. A method of making a powdered solid fuel comprising the steps of comminuting municipal refuse, mixing the comminuted refuse with an additive which includes calcium oxide and a calcium based and/or sodium based bentonite, causing or allowing said additive to react with the comminuted refuse, blending the resultant refuse derived fuel with coal and pulverizing the refuse derived fuel and coal together to form a homogeneous powdered product.

5. A method of making a powdered solid fuel comprising the steps of comminuting municipal refuse, mixing the comminuted refuse with an additive which includes calcium oxide and a calcium based and/or sodium based bentonite, causing or allowing said additive to react with the comminuted refuse, shaping the mixture, in which coal is blended at the step of the reaction and/or before shaping with prior mixing with the refuse, and pulverizing the refuse derived fuel to form a powdered product.

6. A method according to claim 4 or claim 5, wherein the refuse derived fuel is blended with the coal in a ratio of between 10% and 40% refuse derived fuel to 90% to 60% coal by weight.

7. A method according to claim 4, 5 or 6, wherein the refuse derived fuel is blended with the coal in a ratio of between 15% and 35% refuse derived fuel to 85% to 65% coal by weight.

8. A method according to any one of claims 4 to 7, wherein the refuse derived fuel is blended with the coal in a ratio of between 20% and 30% refuse derived fuel to 80% to 70% coal by weight.

9. A method according to any one of claims 4 to 8, wherein prior to mixing the refuse derived fuel with coal, the refuse derived fuel is formed into pellets and said pellets are subsequently dried in an atmosphere containing carbon dioxide, and said coal is added in the form of granules.

10. A method according to any one of claims 4 to 9, wherein the refuse derived fuel and the coal are pulverized into a substantially homogeneous product having a particle size of less that lmm diameter.

11. A method according to any one of claims 4 to 10, wherein said additive includes starch as a binder.

12. A method according to any one of claims 4 to 11, wherein after mixing the comminuted refuse with said additive, the mixture is maintained for a predetermined time within a reactor, in which the moisture content, temperature and pH are controlled.

13. A method according to claim 12, wherein the moisture is between 30% and 55% by weight, the temperature is between 60 and 80 C, the pH is between 10 and 12, and the mixture is maintained in the reactor for between 20 and 60 minutes.

14. A method according to claim 12, wherein said reactor comprises a first reactor compartment in which the mixture is subjected to the action of rotary blades and a second compartment which comprises a cylindrical tube with a single or twin screw feeder, the mixture being passed from said first compartment to said second compartment after a residence time in said first compartment, the moisture content within the first reactor compartment being between 30% and 55% by weight, the temperature in said first compartment being between 60 and 80 C, the pH in said first compartment being between 10 and 12, the residence time in said first compartment being 20 to 60 minutes and the residence time in said second compartment being 5 to 20 minutes.

15. A method according to any one of claims 12, 13 or 14, wherein some of said additive is mixed with the refuse during comminution of the refuse, for example by shredding and/or crushing, further said additive being subsequently mixed with the comminuted refuse in the reactor.

16. A method according to any of claims 12 to 15, wherein steam is supplied to said reactor.

17. A method according to any of claims 12 to 16, wherein the reaction between the additive and the refuse reaches 70% completion in the comminuting phase, for example in the shredding and/or crushing phase, and reaches 90% completion in the waste reactor.

18. A method according to any one of claims 12 to 17, dependent upon any one of claims 7 to 9, wherein the reaction between the additive and refuse reaches 70% completion in the comminuting phase, for example in the shredding and/or crushing phase, reaches 90% completion in the waste reactor, reaches 95% completion in the pelletizing phase and reaches 100% completion in the drying phase.

19. A method according to any of claims 12 to 18 wherein untreated refuse is first dumped into a pit, where an initial quantity of said additive is added, the refuse and additive are then removed from the pit and metal articles or fragments, or glass are removed, after which the refuse is introduced into a primary crusher to reduce it to a predetermined particle size, the resultant crushed waste is further stripped of metal and glass and is thereafter introduced into a secondary crusher, where it is further reduced in particle size and where further said additive is mixed with the refuse before the refuse is passed to said reactor compartment.

20. A method according to claim 19 wherein up to 2% of said additive, by weight of the refuse, is added in said pit, from 1% to 5% of said additive, by weight of the waste, is added in the secondary crusher, and up to 5% by weight of the waste is added in said reactor, the total addition of said additive to the waste during the process being from 2% to 7% by weight of the refuse.

21. A method according to any of claims 12 to 19 wherein the waste is heated in the reactor.

22. A fuel substantially as hereinbefore described.

23. A method substantially as hereinbefore described with reference to the accompanying drawing.

24. Any novel feature or combination of features disclosed herein.