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Title:
METHOD AND INSTALLATION FOR CONVERTING WASTE INTO FUEL
Document Type and Number:
WIPO Patent Application WO/2010/033017
Kind Code:
A1
Abstract:
The invention relates to a method for converting waste into fuel, comprising the steps of supplying waste, separating the collected waste into a combustible and a non- combustible fraction, discharging the non- combustible fraction, and converting the combustible fraction at increased temperature and pressure to relatively hard and brittle fuel agglomerates. The invention further relates to an installation for converting waste into fuel, comprising a device for supplying waste, a device placed in series with the supply device for separating the collected waste into a combustible and a non- combustible fraction, a device placed in series with the separating device for discharging the non-combustible fraction, and a device placed in series with the separating device for converting the combustible fraction at increased temperature and pressure to relatively hard and brittle fuel agglomerates.

Inventors:
JANSEN ABRAHAM (NL)
Application Number:
PCT/NL2009/000183
Publication Date:
March 25, 2010
Filing Date:
September 17, 2009
Export Citation:
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Assignee:
UNITED ENERGY HOLDING B V (NL)
JANSEN ABRAHAM (NL)
International Classes:
C10L5/46
Foreign References:
DE3227896A11984-01-26
EP1434003A22004-06-30
EP1502667A12005-02-02
Other References:
DATABASE WPI Week 200065, Derwent World Patents Index; AN 2000-667852, XP002561865
DATABASE WPI Week 200438, Derwent World Patents Index; AN 2004-404780, XP002561919
Attorney, Agent or Firm:
BARTELDS, Erik (Sweelinckplein 1, GK The Hague, NL)
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Claims:
Claims

1. Method for converting waste into fuel, comprising the steps of : supplying waste, separating the collected waste into a combustible and a non-combustible fraction, discharging the non-combustible fraction, and converting the combustible fraction at increased temperature and pressure to relatively hard and brittle fuel agglomerates . 2. Method as claimed in claim 1, characterized in that the combustible fraction is converted to fuel agglomerates at a temperature of more than 2000C, preferably a temperature in the order of 240 to 29O0C, more preferably a temperature of about 2700C. 3. Method as claimed in claim 1 or 2, characterized in that prior to conversion the combustible fraction is dried to a moisture content in the order of 2 to 10%, preferably 3 to 5%.

4. Method as claimed in claim 3, characterized in that during conversion the combustible fraction is further dried under the influence of the increased temperature and pressure.

5. Method as claimed in any of the foregoing claims, characterized in that the combustible fraction is converted to fuel agglomerates in a low-oxygen environment.

6. Method as claimed in any of the foregoing claims, characterized in that after forming the fuel agglomerates are cooled in a low-oxygen environment.

7. Method as claimed in any of the foregoing claims, characterized in that the combustible fraction is converted to fuel agglomerates by being subjected to a kneading and compressing process.

8. Method as claimed in any of the foregoing claims, characterized in that the combustible fraction is kept free of additives, in particular petrochemical additives.

9. Method as claimed in any of the foregoing claims, characterized in that prior to conversion salt is removed from the combustible fraction.

10. Installation for converting waste into fuel, comprising: a device for supplying waste, a device placed in series with the supply device for separating the collected waste into a combustible and a non-combustible fraction, a device placed in series with the separating device for discharging the non-combustible fraction, and a device placed in series with the separating device for converting the combustible fraction at increased temperature and pressure to relatively hard and brittle fuel agglomerates.

11. Installation as claimed in claim 10, characterized in that the converting device is adapted to heat the combustible fraction to a temperature of more than 2000C, preferably a temperature in the order of 240 to 29O0C, more preferably a temperature of about 2700C.

12. Installation as claimed in claim 10 or 11, characterized by a drying device placed upstream of the converting device and adapted to dry the combustible fraction to a moisture content in the order of 2 to 10%, preferably 3 to 5%.

13. Installation as claimed in any of the claims 10-12, characterized in that the converting device is adapted to further dry the combustible fraction.

14. Installation as claimed in any of the claims 10-13, characterized in that the converting device is placed in a low-oxygen space.

15. Installation as claimed in claim 14, characterized in that the converting device is adapted to cool the formed fuel agglomerates.

16. Installation as claimed in any of the claims 10-15, characterized in that the converting device is adapted to subject the combustible fraction to a kneading and compressing process.

17. Installation as claimed in claim 16, characterized in that the converting device comprises an extruder.

18. Installation as claimed in claim 17, characterized in that the extruder comprises a shaft with kneading elements which is reciprocally movable in axial direction.

19. Installation as claimed in any of the claims 10-18, characterized by a salt-removing device placed upstream of the converting device . 20. Fuel agglomerate, evidently formed by applying the method as claimed in any of the claims 1-9, and/or in an installation as claimed in any of the claims 10-19.

Description:
Method and installation for converting waste into fuel

The invention relates to a method for converting waste into fuel and to an installation for performing this method. The invention relates more particularly to the manufacture of agglomerates of organic material and/or agglomerates of organic material and plastic for use respectively as fuel from biomass and as regular fuel. These fuel agglomerates are suitable for use in modern coal-fired high-efficiency power stations for generating electricity. In addition, the fuels can be used in grate-fired installations and in fluidized bed plants.

Waste has heretofore usually been burned in waste incineration plants (WIPs) or tipped in rubbish dumps. WIPs have the drawback of having a relatively low combustion efficiency, in the order of 20 to 25%. The dumping of waste has the drawback that it requires a great deal of space. The invention now has for its object to make inefficient combustion in WIPs and dumping of waste wholly or partially unnecessary.

This is achieved according to the invention with a method comprising the steps of supplying waste, separating the collected waste into a combustible and a non-combustible fraction, discharging the non-combustible fraction and converting the combustible fraction at increased temperature and pressure to relatively hard and brittle fuel agglomerates .

Preferably applied variants of this method are described in sub-claims 2 to 9.

The invention also relates to an installation with which the above described method can be performed. Such an installation comprises according to the invention a device for supplying waste, a device placed in series with the supply device for separating the collected waste into a combustible and a non-combustible fraction, a device placed in series with the separating device for discharging the non-combustible fraction, and a device placed in series with the separating device for converting the combustible fraction at increased temperature and pressure to relatively hard and brittle fuel agglomerates.

Preferred embodiments of this installation form the subject-matter of sub-claims 11 to 19.

Finally, the invention further relates to a fuel agglomerate formed by applying the above described method and/or in an installation as described above.

The invention is now described on the basis of an example, wherein reference is made to the accompanying drawing, in which: Fig. 1 shows a flow diagram of the method according to the invention,

Fig. 2 is a schematic representation of an installation according to the invention on industrial scale,

Fig. 3 shows a detail view of the part III of the installation of fig. 2,

Fig. 4 shows a detail view of the part IV of the installation of fig. 2, and

Fig. 5A and 5B show recordings made with an electron microscope of the structure of respectively a fuel agglomerate and the waste forming the basis thereof.

The method according to the invention consists of two phases which are completed successively, wherein the efficiency of the second phase depends on the quality of the first phase.

The first phase of the method is the refining of three types of waste, i.e.

I) domestic waste, ii) office waste comparable to domestic waste, and iii) material from domestic waste obtained elsewhere, to components which, after processing, are suitable to function as starting material for the second phase of the method. The material from domestic waste obtained elsewhere usually consists here of a mixture of paper (-like) waste and plastic, together referred to as high calorific waste.

The second phase of the method consists of converting the materials refined specially for this purpose in the first phase into compressed, stable and brittle agglomerates. These agglomerates, which have a so-called Hardgrove index in the order of 51 to 53, more particularly 52, are particularly intended for use as fuel in energy generation plants, such as modern coal-fired high efficiency electricity power stations. These power stations have combustion efficiencies in the order of 40 to 45%, so twice as high as WIPs, and have lower emissions of CO2/ NOx and other harmful gases. WIPs are moreover wholly unsuitable for burning high calorific waste, since the combustion temperature would then rise too high and damage could be caused to the WIP.

The first phase I of the method consists of a series of steps as shown schematically in fig. 1. During the first part Ia of first phase I the waste collected and stored in step 1 is reduced in step 2 to a particle size of for instance 5 to 10 cm. Use can be made here of a hammer mill or - depending on the type of waste (for instance a preprocessed mixture of paper and plastic) - a shredder. In step 3 the non-combustible fraction NC (metal, glass, stone, soil and so on) is separated from the waste flow as well as is possible in the light of economic and environmental considerations. This separation takes place for instance using filters based on gravitational force or by applying screens. The non-combustible fraction NC is then further separated in several more steps, first into metals and other materials, and subsequently into ferrous and non-ferrous metals. Diverse equipment can be used here, such as overhead magnets, eddy current devices and the like.

Water is then expelled under controlled conditions in step 4 to a moisture content of 4 to 5%. Use can be made here of a belt drier, which has the advantage compared to a drum drier that, as a result of the low drying temperatures, no volatile organic compounds are formed and fire cannot occur. The water escapes in the form of water vapour WV. Separated in the same step are salt crystals S, which result from dissolved salts during the drying. This takes place through the plates of the belt drier which act as a screen. Hot gases released during the second phase of the method to be discussed hereinbelow are used for the drying.

As final component of the first part Ia of first phase I the organic fraction ORG (paper, wood cellulose etc.) is coarsely separated in step 5 from plastic component P.

During the second part Ib of first phase I, when a biomass fuel must be produced, the organic fraction ORG is purified in step 6 to a 100% biomass fraction BM. That is, the organic fraction ORG is fully purified, or at least up to a content of 97% of non-organic material is removed. During this purification the final remnants of non-combustible material NC are also separated, as are the final remnants of plastic P. This plastic P can be discharged, but can also be used in the production of regular fuel, i.e. fuel which does not consist wholly of biomass . The biomass BM resulting from purification step 6 is further homogenized and finally fed to the second phase of the method.

When regular fuel must be produced, an already very homogenous mixture is formed under controlled conditions from organic material and plastics in the second part Ib of first phase I (step 7) . The plastics P separated during purification of the biomass BM are also fed to this mixture. The content of plastics P in the homogenized mixture may otherwise not amount to more than about 30%, since brittle fuel granules cannot otherwise be formed. The homogenous mixture of organic material ORG and plastic P is finally fed to second phase II of the method.

Finally, it is also possible for the plastic fraction P resulting after the separation in step 5 to be used as raw material for the preparation of oil products (step 8) . Plastics separated in purification step β can here also be added.

The second phase II of the method, in which the compressing takes place, makes use of a device which is referred to by applicant as a "Tempress" and which is based on the principle of extrusion. This device has been specially developed to convert a combustible fraction originating from waste into solid, brittle fuel granules. The device comprises, in addition to the extruder, peripheral equipment required for environmental reasons (emissions legislation) .

The second phase II of the method comprises in the first instance the steps of extruding the homogenized starting material (pure biomass BM or a mixture of organic material ORG and plastics P) and cooling the extruded material, which can then take the form of agglomerates. The extruded material can then once again be compressed and cooled.

During treatment of the material in the "Tempress" extruder it is both compressed and kneaded by a combined movement of the shaft or shafts in the extruder. The pressure and temperature of the material increase substantially here because the material has a higher moisture content than is usual in extrusion processes. During drying in first phase I of the method the moisture content of the material is reduced to about 4 to 5%, while a usual starting point during extrusion is a moisture content of 0.5 to 1%. The moisture in the material results in a great increase in pressure during heating. The temperature which the material reaches during this treatment is more than 200 0 C, and preferably lies in the order of 240 to 290 0 C. A temperature of about 27O 0 C has more particularly been found to be very suitable. Decarbonization, also known as torrefaction, takes place at said combination of high pressures and temperatures. A brittle material is hereby obtained which is moreover very homogenous, as can be seen from comparing fig. 5A, which shows the finally formed fuel, to fig. 5B which shows the starting material. The formed fuel is very stable even without the addition of additives. Such additives, for instance petroleum cokes, which have been used in the past, are not permitted in many countries in fuel recovered from waste. The "Tempress" extruder is therefore suitable for operation at higher temperatures and pressures than conventional extruders, and is in addition dimensioned for processing larger quantities of starting material than is usual in extruders. During a first phase of the extrusion process the material is also degassed. Water vapour or steam is released here which may contain volatile constituents such as C x H y and chlorine . The released gases are collected and, if necessary, washed with water in a flue gas purification system. Water-soluble substances are transferred to a wastewater treatment plant and the washed gases, which may still contain volatile organic compounds, are fed back to the burners of the drying installation (step 4 of first phase I) .

Because there is the danger at the high temperatures of spontaneous combustion of the material, which is after all intended as fuel, the extrusion process is performed in a low-oxygen environment. The material will also still have such a high temperature for some time during the subsequent cooling that there is a danger of fire, so that this cooling can also take place in a low-oxygen environment. The "Tempress" extruder and the subsequent cooling line can for instance be placed in a closed space filled substantially with an inert, non-combustible gas. The air which is used during cooling, and which will have become hot therein, can otherwise be fed to the driers .

The formed fuel agglomerates have a combustion value comparable to that of pit coal for use in power stations. This value varies for pit coal from about 20 to 28 MJ/kg, and for the fuel agglomerates formed using the method described here between about 20 and 22 MJ/kg. The agglomerates can therefore be burned with pit coal , optionally after first being ground in a ball mill . The agglomerates can also be mixed with wooden granules, which are sometimes used as biofuel in coal-fired power stations.

Because the fuel agglomerates contain a relatively large amount of calcium, originating from paper and cardboard in the waste, the sulphur therefrom is bonded during combustion with pit coal. The fuel agglomerates thus contribute toward a cleaner combustion.

Fig. 2 shows a schematic representation of an installation 100 with which the above described method can be performed. The upper part of this diagram is shown on larger scale in fig. 3, while one of the three processing lines in the lower part of the diagram is shown on larger scale in fig. 4.

Installation 100 comprises an intake station 101 (fig. 3) with an apparatus 102 for opening supplied bales of waste material. Following on therefrom is an apron conveyor 103 and a hammer mill 104. Via a belt the reduced waste material reaches an overhead magnet 105 where ferrous metal is separated. This is discharged via a belt to a container 140. The remaining material reaches a drum screen 106 via a number of belts. Here it is divided into three fractions for processing and a residual fraction. This residual fraction is discharged to an apparatus 116 which once again makes bales thereof.

A first fraction moves from drum sieve 106 to a star screen 107. Material screened out here passes via a belt to a container 104. The second fraction is guided to an apron conveyor 112 and from there to a hammer mill 113, while the third fraction simply drops onto a belt.

After passing through respectively star screen 107 and hammer mill 113 all three fractions are guided past the same appliances. First the material again passes a magnet 108, 110, 114 where the ferrous metal is separated, this eventually being collected in a container 140. The material is then carried along a ferrous/non-ferrous separator 109, 111, 115. The non-combustible materials screened here are again moved to a container 140, while the combustible fraction is carried via a belt 120 to a dynamic intermediate storage 121 (fig. 4) .

Dust released during all these separating operations is otherwise extracted by suction devices 17, 18, 19. In these extractors a further separation can also take place by means of cyclones. The extracted dust can, to the extent that it is combustible material, be fed to the part of the installation where the fuel agglomerates are formed.

From the dynamic intermediate storage 121 the material enters a compacting device 122, and from there a feed device 123 which feeds the material in dosed manner to a belt drier 124. The separation of salt crystals also takes place in this belt drier 124. From belt drier 124 the material is guided to a fine screen 125. A part of the material which passes through this screen 125 is carried to a dynamic intermediate storage 126, while the screened material is carried to a dynamic buffer 130. The material leaving intermediate storage 126 is guided to a structuring press 127 and from there to "Tempress" 128. After undergoing the extrusion operation in the "Tempress" the material, which meanwhile has the form of fuel agglomerates, is guided to a dynamic cooling unit 129. This cooling unit 129 is situated, like the "Tempress", in a separate space 138 where a low-oxygen atmosphere prevails. From this cooling unit 129 the fuel agglomerates reach dynamic buffer 130 where the material screened by fine screen 125 is also located.

From dynamic buffer 130 the fuel agglomerates and the screened material are guided to a press 131 where fuel pellets are pressed therefrom. After leaving the pellet press 131 the material is cooled again in a vertical cooling unit 132 and then guided to a grit/powder separator 133. Fine material that is separated here is returned to dynamic buffer 130, while the fuel pellets are guided further to a storage 134. From this storage 134 a silo 135 at a time is filled, from which the fuel is delivered.

Arranged at different locations are extraction devices

136, 137 with which dust can be extracted and, after separation, optionally fed back to the installation. Although the invention has been elucidated above on the basis of an example, it will be apparent that it is not limited thereto and can be varied in many ways within the scope of the following claims.