GB2437146A

GB2437146A - Fuel gel

Info

Publication number: GB2437146A
Application number: GB0621260A
Authority: GB
Inventors: Alan Charles Norman Tucker
Original assignee: PRODIGY RES AND DEV Ltd
Current assignee: PRODIGY RES AND DEV Ltd
Priority date: 2006-10-26
Filing date: 2006-10-26
Publication date: 2007-10-17
Anticipated expiration: 2026-10-26
Also published as: GB2437146B; GB0621260D0

Abstract

A fuel gel comprises a gelled hydrocarbon and granulated plastics material. The gelled hydrocarbon comprises 0.2% - 1.0% by volume of an activator, 0.2% - 1.0% by volume of a gelling agent and a hydrocarbon fuel. The invention also comprises a method of combusting plastics material comprising the steps of granulating a plastics material, and preparing a gelled hydrocarbon fuel by mixing 0.2% - 1.0% by volume of an activator and 0.2% - 1.0% by volume of a gelling agent with a hydrocarbon fuel. The gelled hydrocarbon fuel is mixed with the granulated plastics material, and the resulting gel and plastics material suspension is combusted. The combustion process may be used for generating electricity or for destroying used cars or refrigerators.

Description

-1-2437146

FUEL GEL

The present invention relates to a fuel gel, and to a method for combusting plastics material for the purpose of generating energy from such waste.

The United Kingdom produces 400,000 Tons of plastic waste every year, and very little of this is recycled. Under European Union legislation, 25% of this material must be recycled, but the remaining 300,000 Tons require dumping in landfill sites. The only realistic alternative to landfill is high temperature combustion, as waste plastic may not be chemically treated. The high temperature combustion must be conducted at temperatures in excess of 1800 C to ensure complete dissociation of noxious chemicals produced which Combustion of the plastic waste produces vast amounts of heat, which can be harnessed for the production of electricity or other industrial processes. The heat produced from combusting 400,000 Tons of plastic waste could produce in excess of 1400MW of power continuously per year. If this combustion process is extended to the 30 million Tons of all UK waste produced each year it would generate 6000MW of heat and 2000MW of power, or in other words one tenth of the UK energy requirements.

Further, there has been a marked increase in the dumping and landfill of household electrical items such as microwaves and refrigerators. The dumping of refrigerators is particularly problematic because of the CFC's contained therein that must not be released into the environment. Safe destructive combustion of this waste is therefore important.

Attempts to make a fuel using waste plastic have already been made, for example in GB 2,388,606 where a hydrocarbon fuel was gelled using aluminium oxalate and mixed with shredded plastics material. Aluminium oxalate is no longer freely available on humanitarian grounds (it is an essential component of Napalm), and is not effective in gelling commercially available hydrocarbon fuels because they contain antigelling agents.

Therefore, the present invention is directed to a fuel that can be made from waste plastics material and commercially available hydrocarbon fuels, and is capable of producing sufficient heat to totally destroy waste materials and dissociate noxious waste gas products.

According to the present invention there is provided a fuel gel comprising: -a gelled hydrocarbon comprising 0.2% -1.0% by volume of an activator and 0.2% -1.0% by volume of a gelling agent and the remainder a hydrocarbon fuel; and -granulated plastics material mixed with the gelled hydrocarbon.

According to a second aspect of the present invention there is provided a method of combusting plastics material comprising the following steps: -granulating plastics material; -preparing a gelled hydrocarbon fuel by mixing 0.2% -1.0% by volume of an activator and 0.2% -1.0% by volume of a gelling agent with a hydrocarbon fuel; and -mixing the gelled hydrocarbon with the granulated plastics material; and -combusting the gelled hydrocarbon and plastics material suspension.

As used herein the term "hydrocarbon fuel" refers to an untreated fuel, such as commercially available paraffin, "gelled hydrocarbon" refers to the hydrocarbon fuel when treated to become a gel, and a "fuel gel" refers to a suspension, of granulated plastics material in the gelled hydrocarbon.

Particularly if the plastics material is retrieved from landfill, or collected unsorted from general household waste, the plastics material must be sorted from other types of refuse. There are six groups of plastic suitable for use in the production of the fuel gel. These are polyethylene terephthalate (PET), high density polyethylene (HDPE), polyvinyl chloride (PVC), low density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS). Of these, only PET is truly suitable for recycling as reusable plastic. To separate these plastics from other waste materials the skilled man will appreciate that a number of methods may be used. For example by shaking the plastics out from other, generally heavier, refuse. Further, there is no requirement to sort out the harder plastics from the softer plastics for use in the present invention, as all groups of plastic as outlined above can be suspended in the gel together.

Prior to the production of the fuel gel, it is important that the waste plastics material is ground to a suitable size before it is mixed with the gelled hydrocarbon and combusted. If the particles of plastic are too large, then they will be too heavy in remain in suspension. Therefore the plastics material is initially baled, shredded and then granulated. It has been found that the optimum diameter for the granules is substantially 5mm or smaller, though any granule size of up to 10mm in diameter will be sufficient if the gelled hydrocarbon is suitably viscous.

The baling, shredding and granulating process is well known in the industry, as this process is currently employed when recycling plastics material. Other uses for the granules include the production of plastic bottles, cloth for car roof linings or even nappy liners. The skilled man will appreciate that any known method of baling, shredding and granulating the plastic collected can be used for this stage in the process. A prior cleaning step is preferable, as this will remove any substance from the waste plastic that may leave combustion residues.

The granulated plastics material is then added to a gelled hydrocarbon.

The gelled hydrocarbon is produced from a hydrocarbon fuel. Whilst any suitable hydrocarbon fuel may be used in the production of the gel it is preferred that the fuel will be paraffin or diesel fuel, particularly for use in Energy from Waste plants. Though it is more expensive to produce, for environmental reasons it is also preferable to use biofuel (ethanol). Of course, depending on the application of the fuel gel any suitable fuel gel may be used, including heavy fuel oil.

Commercially available hydrocarbon fuels all contain an anti-gelling agent to stop them gelling in vehicle fuel tanks in very cold weather.

Therefore the first stage of the gelling process is to add 0.2 -I.0% by volume of activator to the fuel. A gel may then be made of the mixture by the addition of 0.2 -1.0% by volume of a gelling agent. It is known to gel a hydrocarbon fuel such as diesel or paraffin using an activator and a gelling agent, one example being found in US patent 5,417,287 in the name of Smith et al, which produces a hydrocarbon gel for use in rock formation fracturing. In this instance the gel is pumped at high hydraulic pressure to cause cracks in a rock formation.

It has been found that the most suitable activators are ferric salts, aluminium salts, aluminates and aluminium metal. Ferric salts that have been found to work as the activator include ferric citrate, ferric ammonium sulphate, ferric chloride, ferric sulphate, ferric ammonium citrate and ferric gluconate.

It has been found that the most suitable gelling agent is an organic phosphate of the formula HPO4RR', where R is an alkyl or alkaryl group having from 6 to 18 carbon atoms and R' is hydrogen or an aryl, alkaryl or alkyl group having from I to 18 carbon atoms.

The percentages of activator and gelling agent used when making the gel affect the viscosity of the gel. The viscosity of the gel is important for different applications of gel, and the ability to support particles. It is found that 0.2 -0.4% by volume each of activator and gelling agent produces a very thin gel, which is capable only of supporting the smallest of plastics granules.

0.5% by volume each of activator and gelling agent gelling agent was found to be the optimum proportion to produce a gel that supports average sizes of granule. 0.6% by volume each of an activator and gelling agent produces a much thicker gel and 0.75% -1.0% by volume each of activator and gelling agent produces a very thick gel that may be used to support very heavy weight granules.

The granulated plastic is then mixed with the gelled fuel. Any known commercial mixer or stirrer of a suitable size can be used for this process.

Once produced, the plastic granules will remain in fixed suspension indefinitely. The fuel gel displays many useful properties. The fuel gel is dynamically stable, and does not separate, and will withstand centrifuging for an hour at 1200rpm. The fuel gel further exhibits pseudo non-Newtonian properties on pouring from a vessel -when poured slowly the gel hangs from the vessel but returns very quickly into the vessel when it is made upright.

The poured gel demonstrates decreased viscosity with increasing strain rate and even behaves as a super-fluid. As such, the fuel gel can be pumped without undue power using existing commercially available pumps because of these properties.

Once produced, the fuel will be combusted. Because the fuel gel is impossible to atomise in a normal pressure jet burner to obtain the 1800 C temperature to destroy the waste it is preferred that a torroidal burner is used.

Current low temperature incinerators do not produce sufficient heat (about 800 C) to incinerate the fuel, and may not dissociate any noxious gases, for example chlorine cyanogens or dioxin, produced by the burning of the plastic.

The torroidal burner will destroy the noxious gases mentioned above and form normal combustion products during combustion such as water vapour, carbon dioxide and nitrogen oxide. Further combustion residues will be nonexistent.

The carbon-based paraffin and plastic will be gasified, the gelling agent will be oxidised/vaporised, and any residues will be the result of ineffective cleaning of the plastic during the granulating process. Although these residues will be minimal, provision will be made in the torroidal burners for ashing out during maintenance periods.

The fuel gel will be particularly suitable for torroidal burners as they do not require the fuel to be atomised into fuel droplets or fuel mist to burn.

Combustion is fully achieved by controlling the volume and velocity of the cyclonic air supplied above the burning gel.

The intense heat produced by torroidal combustion can be used for a range of different applications. One preferred application of the heat is in the production of electricity. As plastics material is a hydrocarbon based material, it has a calorific value in excess of coal and only slightly less than that of oil.

When suspended in gelled paraffin the granulated plastic waste will burn with the characteristics of oil fuel. 400,000 Tons of plastic waste suspended in paraffin gel will provide 1400MW of energy annually, which is equivalent to one power station. The method by which the heat may be harnessed to produce electricity is outside the scope of the invention, but the skilled man will appreciate how this may be achieved.

Further applications of the fuel gel include using the fuel gel in brick kilns, cement kilns, or lime kilns, as no residues of combustion are left behind.

Further, the heat produced when incinerating the fuel gel in a torroidal burner is sufficient to safely destroy household goods such as televisions, computers and even refrigerators and cars.

By way of example only the method of the present invention and applications thereof will be described in detail, with reference the drawings wherein: Figure 1 shows a flow diagram of the method of the invention; Figure 2a shows a cross section of a conventional coal fired power station furnace; Figure 2b shows a power station furnace converted to use the fuel gel; Figure 2c shows a cross section along line A-A on Figure 2b; Figure 3 shows a schematic representation of a power station layout; Figure 4a shows a gas or oil incinerator as currently used to incinerate waste.

Figure 4b shows an incinerator using the fuel gel and a torroidal burner; Figure 5a shows a cross section of a brick kiln; Figure 5b shows a cross section of a brick kiln using the fuel gel; Figure 6a shows a cross section of a cement kiln adapted to use the fuel gel; Figure 6b shows a cross section of a vertical kiln using the fuel gel; Figure 7 shows a rotating kiln for use in combusting refrigerator and other household electronic goods; Figure 8 shows a rotating kiln and fixed chamber for use in combusting refrigerator and other household electronic goods; and Figure 9 shows a modified kiln for combusting crushed car blocks.

Turning first to Figure 1, there is shown a method of producing the fuel gel. Box 10 contains the steps necessary to produce the granulated plastics material for the production of the fuel gel, and box 11 has the steps to produce the gelled hydrocarbon. Turning to box 10, waste plastics material is collected at step 12 from landfill or from common household waste. Once collected, this waste plastic material is sorted from other types of waste manually or by shaking and then cleaned. It is then baled, shredded and granulated at step 13. This may be done in a known shredder capable of producing granulated plastics material. In one example, a mix of waste plastics material comprising material from the groups of polyethylene terephthalate (PET), high density polyethylene (HDPE), polyvinyl chloride (PVC), low density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS) are retrieved from landfill and are sorted from other waste, cleaned and then dried. Once dried the plastics material is baled for transport, shredded and granulated to a particle size of approximately 5mm in diameter.

Box 11 shows the steps necessary in producing the gelled hydrocarbon fuel. In this example the hydrocarbon fuel is paraffin. First, the activator ferric citrate is added to the hydrocarbon fuel 14. A gelling agent, a phosphate ester of the formula HPO4RR', is added to the mixture at step 15 to produce a gelled hydrocarbon fuel. At step 16 the granulated plastics material is mixed with the gelled hydrocarbon fuel in a commercial mixer to produce the fuel gel.

The fuel gel is then introduced in to a torroidal burner 17 that combusts the fuel at a temperature in excess of 1800 C, which dissociates all of the noxious fumes produced when incinerating plastics material at lower temperatures. The combustion products namely water vapour, carbon dioxide and nitrogen oxide are released at step 18. A major product of combustion is heat 19, which can be harnessed in a range of different applications, discussed in detail below.

A first use of the heat produced by combustion of the fuel gel is in the generation of electricity. The furnaces of coal or oil power stations can be converted for use with the fuel gel. Figure 2a shows a conventional coal fired power station furnace 20 where combustion takes place. Air is provided to the furnace by air box 21. During combustion, the hot gas 22 generated is used to heat steam which is fed to the turbines.

Figures 2b and 2c show the furnace after conversion to use the fuel gel, with a gelled fuel supply 23 present thereunder, which continually supplies the fuel gel to the furnace. The torroidal hot gas path is shown by lines 24. New air box 25 replaces air box 21 as it is required for use with the torroidal burner.

Figure 3 shows a conversion of a power station site layout to support the use of the fuel gel. There is shown a schematic layout of the site generally indicated 30, having a storage area or dump 31 for the sorted plastic material, which is transported to a granulator 32 along a conveyor system 33.

Hydrocarbon fuel is fed from a tank 34 to a mixer 35 with a supply of gelling agent and activator in tank 36. The granulated plastics material is fed into the mixer 35, and when the fuel gel is prepared it is pumped into the boiler house to heat water and drive turbines in the turbine hall 37. Electricity is generated by the turbines and enters the national grid via the transformer 38.

The fuel gel may also be used to destroy by combustion other household or industrial waste, as the heat generated by the burning of the fuel gel in a torroidal burner is sufficient to dissociate the harmful chemicals produced during incineration of all of the waste. Figure 4a shows a prior gas or oil powered incinerator 40 having a waste burner 41 and an outlet 42 where waste ash is removed. Waste material to be incinerated enters the incinerator through inlet 43. Figure 4b shows a torroidal burner 44 in use to combust the waste material, which has been adapted to use the fuel gel. The fuel gel is pumped into the incinerator 44 up through pipe 45. The waste material to be incinerated enters via inlet 46. So that the waste material is more efficiently incinerated it has gone through an initial granulation or shredding stage, which increases its surface area.

A yet further use of the fuel is in a brick kiln. A prior art brick kiln 50, as shown in Figure 5a, uses gravity fed heavy fuel oil 51 to bring the kiln to clay firing temperature. The heavy fuel oil 51 is as thick as tar, has to be pre-heated, contains a high percentage sulphur and is rich with heavy metals, for example vanadium. As well as the implications regarding pollution, the fuel 51 also leaves large post incineration carbon deposits 53, that are time consuming and difficult to clean. The fuel 51 is difficult to pump and atomise, hence the gravity feed from the roof 52 of the kiln 50. The converted brick kiln 54 in Figure 5b uses the fuel gel 55. The fuel gel 55 has the advantage over heavy fuel oil 51 in that the combustion thereof does not produce the large carbon deposits, and therefore the kiln cleaning down time is reduced.

Further operating costs will also be lower because no fuel line trace heating would be required.

Figures 6a and 6b show a cement or lime kiln conversion. Dry cement powder is produced by feeding crushed Portland Stone at entrance 61 into inclined rotary kiln 60. In order to produce powdered cement the kiln must generate temperatures in excess of 1000 C to convert free sulphur to calcium sulphate. Prior art cement kilns are fired by coal or heavy fuel oil because these fuels contain sulphur and iron impurities -the sulphur aiding the production of calcium sulphate, and the iron as a catalyst allowing the cement to be made at lower temperatures. With this in mind, for this particular application the fuel gel will be made using a hydrocarbon fuel such as high sulphur diesel oil, which would contain suitable quantities of sulphur to make the cement. The fuel gel is gravity fed into the cement kiln via pipe 62 and is incinerated along the rotating body of the kiln 63, which is in excess of 60 meters long for a sufficient residence time within the kiln. The kiln 60 may also be used to incinerate domestic waste, which may be shredded and fed into the kiln via feed 61. At cement kiln temperatures all waste including shredded metal is oxidised to ash and gas.

Rotary kilns and vertical kilns 64 (as shown in Figure 6b) are also used for the production of lime. In a vertical kiln 64, powdered limestone is fed directly into the top of the kiln 65, and the fuel burner 66 is positioned beneath the kiln.

Referring now to Figures 7 to 9, there is shown yet further applications for the fuel gel. Figure 7 shows the gel being used in a rotating kiln generally indicated 70, adapted from a cement kiln for incinerating refrigerators and other electronic goods 71. Disposal of refrigerators is a problem because of the CFC refrigerant liquid held therein. The refrigerators must be incinerated whole because an initial step of shredding is not cost effective. It would need to be done under negative pressure to prevent the CFC's from escaping, and the shredding equipment required is prohibitively expensive. The refrigerators and other electronic goods 71 enter the body of the rotary kiln 72 via conveyor system 73. The body 72 is in excess of 60 meters long and the goods 71 pass through the kiln, which is fired by the fuel gel, with a transit time of three hours, which is sufficient to oxidise the refrigerator steel case, aluminium coolant coils, compressor and insulation. The furnace is maintained at negative pressure by forced draft fan 74 and induced draft fan 75 to prevent the release of CFC's before they dissociate. The hot exhaust from the induced draft fan is passed through a heat exchanger (not shown) to extract the heat. A standby afterburner 76 is employed to destroy any unburnt toxic gasses.

An alternative long residence time kiln 80 is shown in Figure 8.

Electronic goods 81 are loaded on conveyor system 82 into a section of rotating kiln 83 approximately 40 meters in length for a transit time of three hours. The goods 81 then drop into a second chamber 84, where they are further incinerated by gravity fed fuel feeds 85 which introduce the fuel gel.

Ash from the incinerated goods can be removed via door 86 after incineration.

Negative pressure is provided by induced draft fan 87 and forced draft fan 88, and standby afterburner 89 is present to destroy any unbumt gases.

Figure 9 shows a crushed car block incinerator schematic.

Automobiles contain a vast quantity of different materials such as plastics, glass, rubber from their tyres as well as printed circuit boards, oils, paint and air conditioning fluid. It is not economic to dismantle a car into its constituent parts, as the cost of doing so is in excess of the cost of the parts retrieved. In normal practice, the car is drained of oil, petrol, air conditioning fluids, and glycol coolant before scrap disposal and then crushed.

A crushed car block may be combusted using the fuel gel, with a residence time of several hours depending on the size of the block to be destroyed. A small car block will weigh approximately 500 Kg, and a large car block can weigh up to 3000 Kg. In Figure 9, there is shown a fixed circular inclined refractory kiln generally indicated 90, which is 60 meters in length.

Crushed car blocks in aluminium skid mounted open top boxes 91 that are pre-filled with fuel gel approach the incinerator along conveyor 92, and are pushed through entry door 93 by hydraulic ram 94. The fuel gel inside the boxes 91 is ignited by an oil burner ignitor 95 as the boxes 91 make their way through the kiln with a residence time of 10 hours. The kiln is heated by gravity fuel feeds 96 which feed the fuel gel into the kiln. Air flow is maintained by torroidal air supplies 102 and induced draft fan 97 and forced draft fan 98. Heat is removed by heat exchanger 99, and exhaust leaves the kiln via pipe 100. Any remaining noxious gasses released may be destroyed by an afterburner (not shown). After incineration, the ash leaves the kiln through outlet 101.

Claims

CLAIMS

1. A fuel gel comprising: -a gelled hydrocarbon comprising 0.2% -1.0% by volume of an activator and 0.2% -1.0% by volume of a gelling agent and the remainder a hydrocarbon fuel; -granulated plastics material mixed with the gelled hydrocarbon fuel.

2. A fuel gel as claimed in claim I wherein the activator is taken from the group comprising ferric salts, aluminium salts, aluminates and aluminium metal.

3. A fuel gel as claimed in claim I or claim 2 wherein the gelling agent is an organic phosphate of the formula HPO4RR' where R is an alkyl or alkaryl group having from 6 to 18 carbon atoms and R' is hydrogen or an aryl, alkaryl or alkyl group having from I to 18 carbon atoms.

4. A fuel gel as claimed in any of the preceding claims, comprising 0.4 - 0.6% by volume each of the activator and the gelling agent.

5. A fuel gel as claimed in any of the preceding claims, comprising 0.5% by volume each of the activator and the gelling agent.

6. A fuel gel as claimed in any of the preceding claims, wherein the hydrocarbon fuel is paraffin or diesel.

7. A fuel gel as claimed in any of the preceding claims, wherein the granulated plastics material comprises one or more of polyethylene terephthalate (PET), high density polyethylene (HDPE), polyvinyl chloride (PVC), low density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS).

8. A fuel gel as claimed in any of the preceding claims wherein the granules of the granulated plastics material are less than 10mm in diameter.

9. A fuel gel as claimed in claim 8, wherein the granules are less than 5mm in diameter.

10. A method of combusting plastics material comprising the following steps: -granulating plastics material; -preparing a gelled hydrocarbon fuel by mixing 0.2% -1.0% by volume of an activator and 0.2% -1.0% by volume of a gelling agent with a hydrocarbon fuel; -mixing the gelled hydrocarbon fuel with the granulated plastics material; and -combusting the gel and plastics material suspension.

11. A method as claimed in claim 10, wherein the activator is taken from the group comprising ferric salts, aluminium salts, aluminates and aluminium metal.

12. A method as claimed in claim 10 or claim 11, wherein the gelling agent is an organic phosphate of the formula HPO4RR' where R is an alkyl or alkaryl group having from 6 to 18 carbon atoms and R' is hydrogen or an aryl, alkaryl or alkyl group having from I to 18 carbon atoms.

13. A method as claimed in any of claims 10 to 12, comprising 0.4 -0.6% by volume each of the activator and the gelling agent.

14. A method as claimed in any of claims 10 to 13, comprising 0.5% by volume each of the activator and the gelling agent. -17-

15. A method as claimed in any of claims 10 to 14, wherein the hydrocarbon fuel is selected from paraffin, diesel, biofuel (ethanol) or heavy fuel oil.

16. A method as claimed in any of claims 10 to 15, wherein prior to granulation the plastics material is collected and sorted form other waste material.

17. A method as claimed in any of claims 10 to 16, wherein the gel and plastic suspension are combusted in a torroidal incinerator.

18. A method as claimed in any of claims 10 to 17, wherein the plastics material is at least one from the following group: polyethylene terephthalate (PET), high density polyethylene (HDPE), polyvinyl chloride (PVC), low density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS).

19. A method as claimed in any of claims 10 to 18 wherein the plastics material is granulated to less than 10mm in diameter.

20. A method as claimed in claim 19, wherein the plastics material is granulated to less than 5mm in diameter.

21. A method as claimed in any of claims 10 to 20, wherein the heat generated from combusting the fuel gel is used to generate electricity.

22. A method as claimed in any of claims 10 to 20, wherein the heat generated from combusting the fuel gel is used in a kiln.

23. A method as claimed in any of claims 10 to 20, wherein the heat generated from combusting the fuel gel is used to totally destroy cars, refrigerators or other household electrical goods.