GB2156849A - Fuel blocks - Google Patents

Abstract

A fuel block is described, which is composed of coal dust and a binder formed from an aqueous slurry of cellulosic materials such as paper, card or rag pulp, with a substantial component of fat or a wax or oil. The mixture is introduced into a hopper and pressed into blocks by two rams the external cylinders of which have perforated portions to allow the escape of water during pressing.

Description

SPECIFICATION Fuel blocks The present invention relates generally to fuel blocks, and particularly to fuel blocks which can be made by utilising recycled waste materials. The present invention also comprehends a method and apparatus for manufacturing fuel blocks.

There are many different types of fuel blocks currently commercially available. Many of these are based almost exclusively on compressed coal dust or small coal particles, for the production of which extremely high pressures are required. Moreover, because of the bulk nature of the raw matlerial, namely coal dust, the manufacturing plant for such fuel blocks is usually cited very close to a coalfield from where the dust originates. However, during the coal distribution process much of the larger lump coal is broken down into smaller particles and dust but because it has been transported far from the original site, and because of the high costs, there is no economic way it can be recycled to the fuel block pressing plant. Moreover, many materials which are combustible, and which could be used for fuel are not in practice used because of the inconvenience of their waste product form.For example, waste engine oil, animal fats, paraffin wax, and other waxes, although having large contents of hydrocarbons and being highly suitable for use as a fuel, cannot be used because no suitable fuel-burning apparatus capable of operating on such materials is available. Likewise, cellulosic waste materials such as newsprint, cardboard, rag pulp and the like cannot conveniently be used as a fuel for heating purposes, particularly domestic heating purposes, because the density of the materials is so low in comparison with the calorific value thereof that any fire fed with such fuel would have to be refuelled inconveniently often.

The coal dust arising during coal distribution, particularly shipping, on the other hand, although being a dense highly calorific fuel material, cannot conveniently be used because of its particulate form which makes it difficult to introduce an adequate supply of oxygen to support combustion.

The present invention seeks to provide a fuel block incorporating a combination of at least some of the waste materials referred to hereinabove, which will be wholly combustible, clean and easy to use, and which will be suitable for burning in a wide range of currently available appliances. In particular fuel blocks made in accordance with the principles of the present invention can be used in many existing closed solid fuel appliances.

According to one aspect of the present invention, therefore, there is provided a fuel block comprising coal dust bound together with a binder material comprising an aqueous slurry of cellulosic material such as paper and/or rag pulp, mi ed with fat, oil or wax.

Preferably, the coal dust constitutes between 70% and 80% by weight of the fuel block; and the most effective proportions have been found to be 74% by weight of coal dust and 26% by weight of binder in the mixture from which the block is pressed. Of course a proportion of the original water content of the slurry is pressed out during production, and of the remainder, an additional proportion will dry out during storage. The fuel block is usable straight from the press, however.

In the binder the constitutents are mixed in the ratio of between 20% and 30% by weight of dry paper and between 35% and 80% by weight of animal fat, wax or oil, the remainder being constituted by the water in the slurry. In the preferred composition these ratios are 25% of any paper, 42% of animal fat, and 33% of water. Whatever the original mixing ratios, once the fuel block has been pressed the final fat content should be not less than 12% of the total weight of the fuel block.

Conveniently, but not essentially, a coating of water impermeable and preferably combustible material is applied to the fuel block after pressing and possibly further drying such as air drying has taken place.

Because the fuel block is pressed to a relatively low moisture content there need be no delay in production whilst waiting for drying. Further, the whole of the solid content of the fuel block made in accordance with the principles of the present invention is combustible, whereas some previous attempts to bind coal dust to make a useful fuel block without the aid of a very high pressure industrial press have involved the use of binders which are not themselves combustible and which consequently detrimentally affected the combustion properties of the finished block and also increased the ash content to an unacceptable level.

According to a further aspect of the present invention a machine for making fuel blocks from a slurry containing cellulosic and/or hydrocarbon material, comprises a hopper having lateral transfer means in the lower part thereof, and a press having a press chamber which opens into the hopper to allow slurry to be conveyed directly into it by the said lateral transfer means.

In the preferred embodiment of the invention the press chamber includes a section which is permeable to allow the escape of liquid from the slurry during pressing. Such escaped liquid may be recycled and re-used for forming slurry to be used subsequently, particularly if it contains a proportion of volatile and/or hydrocarbon materials.

The finished block may be wrapped in a preformed container or alternatively a "skin" of water-impermeable material may be formed on the outside of the finished pressed block by suitable techniques such as spraying. This technique may conveniently be used with a cellulose film, a plastics film or one using a bitumen emulsion having an adequately short air-drying time to enable the encased blocks to be handled without transferring contaminat ing material by contact.

Embodiments of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a flow diagram illustrating a first example of the process according to the in vention for producing the fuel blocks Figure 2 is a flow diagram of an alternative process employing the principles of the present invention; Figure 3 is a perspective view of a machine for making the fuel blocks of the invention, with certain parts removed for clarity; Figure 4 is a partial sectional view and partial plan view from above as seen from the planes ll-ll and Ill-Ill of Fig. 3; and Figure 5 is a sectional view of an alternative embodiment taken from the same horizontal level as the level ll-ll in the embodiment. of Fig. 1.

Referring first to Fig. 1, the first exemplary process for producing fuel blocks according to the present invention comprises, as shown in the drawing, mixing dry paper and water to form a slurry in which the paper is broken down first by saturation with the water and then by mechanical agitation. Subsequently the slurry is mixed with fat in the same or different mixing vessel to produce a binder. In the binder the dry paper content is 25% whilst the fat content accounts for 42% of the total weight of the binder mix, the remainder of the weight being accounted for by the water content. The animal fat content of the binder may alternatively be replaced by wax such as paraffin wax or a wax and oil mixture and both waste oil and waste wax can be used for this purpose.The binder may be prepared at a site remote from the press and transported to the site where coal dust is available since the latter constitutes the major proportion of the finished fuel block and therefore would represent the higher transport cost. The binder and coal dust are introduced into mixing apparatus which then transfers the mixed binder and coal dust to the press set to operate at about 2500 Ibs/sq.in. The press has apertures to allow the escape of water from the mixture, which escape is promoted by the presence of the animal fat or wax and oil mixture, and it has been found that although the water is necessary for the formation of the initial slurry, and the paper content is necessary to bind the coal dust together, the presence of the fat helps to remove a major proportion of the water simply by press ing due to the displacement of water by the fat in contact with the solid materials in the mixture.

In the alternative process illustrated in Fig.

2, dry paper and water are mixed to form a slurry which is then introduced to the coal dust to form a prepared mixture without the animal fat. This can then be transported to the pressing site where animal fat or, as before, an oil and wax misture, is added to the mixture under agitation and the finished mixture then pressed in the same way to produce dry blocks. The term "dry" will be understood to compose less than 10% water, and in tests it has been found that the water content may be as low as 8.5% with the coal dust accounting for 74%,, the paper 6.5% and the fat 11 % of the finished product. Further, moisture may evaporate from the blocks during storage so that the relative proportions of the other constituents effectively increases because the total weight of the block reduces.

Referring now to Figs. 3, 4 and 5 of the machine for making compressed fuel blocks has a supporting framework 11 on which all moving parts are supported. The framework 11 includes a support plate 1 2 carried between two uprights 13, 14 and horizontal support members 1 5 only one of which can be seen in Fig. 1.A similar pair of horizontal members 16, 1 7 parallel to the members 1 5 support the upper edges of a hopper 1 8 the lower region of which is supported on the support plate 1 2. Also carried on the support plate 1 2 are two hydraulically actuated presses generally indicated with the reference numerals 1 9 and 20 and each comprising a cylindrical press chamber 21, 22 having a water-permeable wall (in this case achieved by providing a plurality of small holes in the wall) a piston chamber 23, 24.These components of the presses are secured together and to the mounting plate 1 2 by means of respective transverse flanges, namely flanges 27, 28 securing the piston chambers 23, 24 to the plate 12 and to the press chambers 21, 22 and flanges 29, 30 securing the piston chambers 23, 24 to the press rams 25, 26.

Within the hopper is located a screw auger 31 on a shaft 32 which projects through the rear part 34 of the hopper 1 8 and is driven by a belt (not shown) from an electric motor 35 which can be seen in Fig. 1.

An aqueous slurry of material as described above including coal dust, and the binder is introduced into the hopper 1 8 from a mixing vessel not illustrated. The slurry in the lower part of the hopper 1 8 is transferred laterally by the screw auger 31 towards the forward end 35 of the hopper 18.

The two piston chambers 23, 24 are located so that they intersect the wall 35 at the front of the hopper 1 8 as can be seen in Fig.

2. A section of each of the piston chambers 23, 24 where these extend within the hopper 1 8 is cut away, namely from a region closely adjacent the floor of the hopper to a point partway up the hopper and above the highest level of the screw auger 31 so that upon rotation of the screw auger 31 in a direction by the arrow A in Fig. 2, the slurry is conveyed laterally towards the front wall 35 and enters the piston chambers 23, 24. These two openings are not visible in Figs. 1 or Fig. 2 of the drawings.The axial length of the pistons within the piston chambers 23, 24 is such that these openings are closed, or rather blocked by the pistons themselves as they are lowered upon actuation of the rams 25, 26 and remain completely blocked even when the lowermost face of the piston reaches its lowest point so that no material from the hopper can enter through the openings into the piston chamber above the pistons. Axial passages are formed in the pistons, however, to allow the escape of liquid from the upper face of the block being pressed. The upper part of the piston chambers 23, 24 have suitable liquid escape passages leading to a subsidiary collection gallery 80 which is upwardly open and has a discharge duct 81 leading straight down through the plate 1 2 to open into a main drainage chamber 44.

The two actuator rams 25, 26 are operated alternately, and the actuator chambers beneath the operating pistons in the respective rams 25, 26 are interconnected by a coupling hose 37 whilst the upper ends of the two rams 25, 26 are connected to a pressure source 38 by two hydraulic lines 39, 40 respectively. In this embodiment the pressure source 38 is in the form of an hydraulic compressor which can be driven electrically or from any other suitable power source.

As well as being secured to the plate 1 2 the two press chambers 21,22 are mounted on respective support plates 41, 42 which are in turn carried by the side walls 43 of the main drainage chamber generally indicated 44 the side walls 43 of which are suspended from the plate 1 2. The drainage chamber 44 thus constitutes an integral and reinforcing part of the press as well as acting to collect liquid escaping from the press chambers 21, 22 through the perforations in the side walls of these chambers. A duct, not shown, leads the escaping liquid to a suitable discharge or back to the slurry mixing chamber (not shown) in which slurry is being mixed for introduction into the hopper 1 8.

Beneath the plates 41, 42 are located respective closure plates 45, 46 which are attached to respective linkages 47, 48 connected to respective actuators 49, 50 which are fed from the compressor 38 in accordance with control signals received from micro switches (not shown) located in the path of the plates 45, 46. Attached to the plate 45 is an arm 51 connected to a pusher 52, and a similar arm 53 linked to the linkage 48 attached to the actuator 50 is connected to a pusher 54 beneath the plate 46.

The two plates 45, 46 are guided by the linkages 47, 48 so as to be held firmly against displacement axially of the press chambers 21, 22 and, moreover, the actuators 49, 50 are controlled to operate alternately, that is the actuator 49 is advanced at the same time as the actuator 50 is retracted, and the actuator 50 is advanced at the same time as the actuator 49 is retracted. In this way the closure plates 45, 46 are alternately positioned under the press chambers 21, 22 so that whilst one of the rams 25, 26 is extending to compress material in one of the press chambers 21, 22 the other ram is retracting and allowing material from the hopper 1 8 to enter the piston chambers 23, 24.

The position of the pistons in the piston chambers 23, 24 is sensed by means of micro-switches 55, 56 and 57, 58. The lowermost two of these namely switches 56, 58 detect when the piston has reached its required lowermost position. A delay is introduced after this condition has been detected before the associated actuator 49, 50 is energised to withdraw the associated closure plate 45, 46. Suitable micro-switches (not shown) detect the movement of the closure plates and control the application of hydraulic pressure to the recently extended ram causing this to extend further now ejecting the pressed block from the chamber. This movement transfers fluid through line 37 to the opposite ram and when the opposite ram reaches its uppermost position, detected by one of the micro-switches 55, 57, a new press cycle is initiated with the displacement of the rams 25, 26 being reversed.

A suitable mixture for use with the press described herein above comprises the following constituents: 41bs by weight of dry paper, 1 5 litres of water, 21bs of sawdust (again dry weight) 81bs of coal dust and 11 b animal waste fat.

This produces a slurry which is suitable for introduction into the hooper 1 8.

Turning now to Fig. 3. an alternative embodiment has been illustrated, capable of improving the press performance. In the alternative embodiment, identical reference numerals have been used to identify the same or similar components. This embodiment is largely similar to that of the embodiment of Figs. 1 and 2 with the exception that the screw auger 31 is supported only from one end. from which end it is driven and the piston chambers 23, 24 have relatively large openings in the side walls thereof, identified by the reference numerals 60, 61 respectively for allowing the mixture to be fed into the piston chambers 23, 24.

At the forward end of the hopper 1 8 is located a piston chamber closure mechanism generally indicated 62 and comprising a chamber closure member 63 having a complex form which will be described in greater detail below, and which is supported on two parallel arms 64, 65 pivoted about a vertical axis 66 parallel to the two piston chambers 23, 24 and equidistantly located between them. The shape of the closure member 63 is defined by three cylindrical surfaces and two flat parallel end surfaces. The first cylindrical surface, generally indicated 67 is a convex surface and this meets two concave cylindrical surfaces 68,69, which themselves intersect along a line parallel to the generatrix of the cylindrical surface 67 whereby to form a cupsoid shape.

The two concave cylindrical surfaces 68,69 have the same radius of curvature as the outer walls of the piston chambers 23, 24 and are positioned, with respect to the axis 66 such that each acts to cover and thereby close one of the openings 60, 61 in the piston chambers 23, 24 when the arms 64, 65 are moved to one or the other of their angular end positions. For this purpose a fluid pressure actuator 70 having an actuator arm 71 connected to the radially outer end of one of the arms 64, 65, in this case the upper arm 64 acts to displace the arms 64, 65, and consequently the closure member 63 between two angular end positions in one of which the piston chamber 23 is closed by the concave cylindrical surface 69 and in the other of which the piston chamber 24 is closed by the concave cylindrical surface 68.Actuator of the ram 70 is synchronised with the actuation of the rams 25, 26 and the closure member 63 also acts to pack the mixture in the hopper more firmly into the press chamber and allows a longer fuel block to be made since it effectively raises the level of the mixture in the piston chambers 23, 24 which can be pressed. In the embodiment of Figs. 1 and 2 as the pistons are lowered any material in communication with the hopper and above the horizontal level of the hopper floor, even though within the piston chamber 23 or 24 as appropriate, is liable to be expelled from the piston chamber as the piston is lowered whereas in the embodiment of Fig. 3 the effective pre-compressed length of the fuel block within the piston chamber 23 or 24 extends to the upper edge of the opening 60 or 61.

The pressing sequence is modified slightly over that of the embodiment of Figs. 1 and 2, therefore, in that the actuator 25, say, is fully raised whilst the actuator 26 is fully lowered.

This means that the piston chamber 23 will be open whilst the piston chamber 26 is closed. The ram 70 is then activated to retract, drawing the piston chamber closure member 63 to the positon illustrated in Fig. 3 where the piston chamber 23 becomes closed preventing the escape of any material which has entered due to the action of the auger 31.

The closure member 63 also acts to scoop in a further proportion of the material within the hopper 1 8 and to press this laterally into the piston chamber 23. The ram 25 is then actuated and by transfer of fluid through the line 37 the ram 26 is raised. When a predetermined line pressure has been exerted by the ram 25, this being detected by a suitable pressure sensor (not shown) in the fluid pressure line, this pressure in maintained for a period of about 8 seconds to allow the escape of water from the compressed material within the piston chamber 23.At the end of this timed period the ram 25 is raised very slightly by a distance of, say a quarter or half inch to release the pressure on the closure gate at the bottom of the press chamber so that, upon actuation of the ram 49 this can be opened without excess effort which would be required if it were opened whilst the pressure on the ram 25 were maintained. Subsequent to opening of the gate pressure is again supplied to the ram 25 causing this fully to lower thereby ejecting the pressed block onto the conveyor table such as that illustrated in Fig.

1. The retraction of the actuator 49 with opening of the gate at the bottom of the piston chamber 23 is accommpanied by extension of the ram 50 and advance of the pusher 54 displacing the previously formed block away from the position immediately underneath the press chamber 24 and closure of the gate 46 so that the press chamber 24 is now ready for a subsequent pressing operation. While this is happening the screw auger 31 is activated to advance material within the hopper 1 8 laterally through the opening 61 and into the press chamber 24. The ram 70 is then caused to advance scooping a further proportion of material within the hopper 18 into the press chamber 24 whereupon the cycle just described in relation to the piston chamber 23 is repeated for the press chamber 24 identically.

Claims (16)

1. A fuel bock comprising coal dust bound together with a binder material comprising an aqueous slurry of paper, card or rag pulp, mixed with fat, oil or wax.

2. A fuel block as claimed in Claim 1, in which the coal dust constitutes between 70 percent and 80 percent by weight of the fuel block.

3. A fuel block as claimed in Claim 1 or Claim 2, in which the binder constitutes between 30 per cent and 20 per cent by weight of the fuel block.

4. A fuel block as claimed in any of Claims 1 to 3, in which the binder is composed of between 20 per cent and 30 per cent by weight of dry paper and between 35 per cent and 5 per cent by weight of fat, the remainder being constituted by the water component of the binder prior to admixture with the coal dust.

5. A fuel block as claimed in any preced ing Claim, in which the coal dust constitutes approximately 74 per cent by weight of the fuel block and the binder constitutes approximately 26 per cent by weight thereof.

6. A fuel block as claimed in any preceding Claim, in which the fat content is greater than 1 2 per cent by weight of the block.

7. A fuel block as claimed in any preceding Claim, in which there is a water impermeable coating applied to the surface thereof.

8. A fuel block as claimed in Claim 7, in which the coating comprises a combustible material having at least a partial proportion of bitumen as a constituent thereof.

9. A process for the manufacture of fuel blocks, in which paper, card, rag or other cellulosic material is formed into an aqueous slurry by the addition of water and agitated, and animal fat or paraffin wax is added to the slurry thus formed to constitute a binder for admixture with coal dust under pressure sufficient to expel at least a substantial proportion of the water.

10. A process as claimed in Claim 9, in which coal dust is added in predetermined proportions to the said aqueous slurry prior to the introduction of the animal fat, wax or oil component.

11. A process as claimed in Claim 9, or Claim 10, further comprising the step of applying a water impermeable coating to the fuel block after pressing.

1 2. A process as claimed in Claim 11, in which further dehydration after pressing is performed prior to coating the block.

1 3. A process for manufacturing a fuel block substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.

14. A fuel block substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.

1 5. A binder for use in making a fuel block comprising an aqueous mixture of a cellulosic slurry constituted by paper, card or rag pulp, and an animal fat constituent, the latter constituting at least 35% by weight of the mixture.

16. A binder as claimed in Claim 15, in which the animal fat content constitutes 42% and dry paper constitutes 25% by weight of the binder.