Process for preparing pellets for firing industrial furnaces

Abstract

To provide a method for producing pellets which are capable of providing free flowing powder suitable for burning an industrial furnace from municipal waste.SOLUTION: A method includes the steps of: (i) providing waste material including one or more thermoplastic materials of more than 40% and one or more cellulosic materials of more than 30%, on the basis of the total dry weight of waste, the waste having a particle size distribution with more than 80% larger than 5 mm and more than 95% smaller than 60 mm; (ii) passing the waste material through a pelletizer with holes between 4 and 16 mm and a length ratio of more than 2, and passing the resultant pellets through a second pelletizer with holes between 4 and 10 mm and a length ratio of more than 2 to provide pellets with a diameter between 4 and 10 mm and a length of between 3 and 50 mm; and (iii) grinding the pellets in a hammer mill to form powdery fuel. The powdery fuel has a particle size with 25 and 70 wt.% between 2 and 3.15 mm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a process for preparing pellets from waste material, to the pellets obtainable by said process, and to a process for firing industrial furnaces. [Background technology]

[0002] Processes for firing industrial furnaces are, for example, those used to generate electricity. Furnaces for generating electricity are among the most demanding and efficient furnaces currently in use. Other industrial furnaces that require high process stability are blast furnaces in steel production and cement and lime kilns.

[0003] Furnaces are typically fed with powdered (pulverized) coal, oil, or gas. The fuel is typically supplied through a number of burners, lances (or tuyere). When the furnace is used to generate electricity, the heat of combustion is used to produce steam, which is used to drive a turbine.

[0004] The amount of pulverized coal that can be injected depends on the quality of the coal and coke, the furnace geometry, and operating practices. Furthermore, pulverized coal has low bulk density and poor storage properties. Therefore, the coal is pulverized immediately before use. The main disadvantage of pulverized coal is the fact that it comes from non-renewable sources and therefore causes significant CO2 emissions.

[0005] To mitigate the burden of CO2 emissions, alternative fuels have been proposed and are being used to some extent. Such alternative fuels need to allow for their use in a seamless process. They must be transportable before and after milling. Furthermore, alternative fuels must allow for injection into the flame and exhibit good combustion characteristics (time to complete burn, time to virtually complete burn with hot spots).

[0006] Alternative fuels proposed for use in high-end industrial furnaces include plastic pellets, mixed plastic / biomass pellets, wood pellets, and sewage sludge pellets.

[0007] One advantage of using pure plastic waste is that it generally has low thermal conductivity and high energy content. A disadvantage of using pure plastic waste is that such mixtures, derived from, for example, household, urban, or municipal waste, are relatively valuable products that can be used to create (recycled) plastic products. A further disadvantage is that, despite their high calorific value, waste plastic pellets are difficult to process to obtain a suitable particle size distribution. Milling causes the plastic to heat up and behave like rubber, to the point where cryogenic milling is necessary. However, cryogenic milling is too expensive.

[0008] The delivery of alternative fuel to the furnace can vary depending on the nature of the waste material and the type of furnace being fed. There are several ways to directly use alternative fuel in furnace technology. Such techniques include direct use by injecting powdered alternative fuel through a lance or at the level of the lance, co-grinding pellets with coal as described in WO 2015 / 155193, or mixing the coal with powdered alternative fuel before injecting the mixture into the furnace.

[0009] Alternative fuels used directly in furnaces have processing problems such as dust formation, powder transportation, etc. Preferably, such fuels are made from selected waste fractions of household, urban, or municipal waste. However, such waste fractions represent very heterogeneous materials from which pellets are made. However, industrial furnaces require relatively homogeneous materials to ensure smooth operation.

[0010] Therefore, these alternative fuels are only used to partially replace fossil fuels in high-end furnaces. Generally, the amount of alternative fuel in practice is less than 30%, and in any case less than 50% for powdered coal. Powdered coal is a relatively homogeneous material, and the significant base load of coal dampens the variations in refuse-derived pellet material.

[0011] US2010 / 116181 describes pelletizing plastic / cellulose materials with a relatively low amount of plastic (less than 40% by weight), which, according to WO2008 / 107042, can be milled into particles, mostly less than 2 mm, that can be used as a secondary fuel in combination with powdered charcoal. Secondary fuels with low amounts of plastic have relatively low combustion values, which is a disadvantage if such fuels are to completely replace coal.

[0012] EP1083212A describes the preparation of pellets of plastic and cellulosic materials which can be used as a secondary fuel in combination with powdered charcoal.

[0013] Therefore, there is a need in the field for a process that can produce alternative fuels that are suitable for feeding industrial furnaces, especially those that generate electricity, even to completely replace coal.

[0014] Additionally, there is a need for processes that can produce alternative fuels with improved handling characteristics, such as reliable transport of the powder. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] International Publication No. 2015 / 155193 [Patent Document 2] US Patent Application Publication No. 2010 / 116181 [Patent Document 3] International Publication No. 2008 / 107042 [Patent Document 4] European Patent Application Publication No. 1083212 Summary of the Invention

[0016] The object of the present invention is to provide a process for making pellets containing plastic and biomass (cellulose fibers) that can be used to completely and reliably replace fossil fuels in high-end industrial furnaces used in modern facilities to generate electricity.

[0017] A further object is to provide a process for reliably operating high-end industrial furnaces on alternative fuels with improved handling characteristics.

[0018] In a first aspect, the present invention relates to a method for producing pellets from municipal and / or other waste materials that can provide a free-flowing powder suitable for firing in an industrial furnace, the process comprising the steps of: (i) providing a waste material that includes greater than 40% of one or more thermoplastic materials, based on the total dry weight of the waste, and greater than 30% of one or more cellulosic materials, based on the total dry weight of the waste, wherein the waste has a particle size distribution of greater than 80% greater than 5 mm and greater than 95% less than 60 mm; and (ii) passing the waste material through a pelletizer having holes of 4 to 16 mm, preferably 6 to 16 mm, and a length ratio of greater than 2, and passing the pellets through a second pelletizer having holes of 4 to 10 mm and a length ratio of greater than 2 to provide pellets having a diameter of 4 to 10 mm and a length of 3 to 50 mm.

[0019] The pellets obtained by the process of the first aspect can be milled in a hammer mill to obtain a powder that exhibits good flow properties, preferably 25-70% by weight of the powder having a particle size of 2-3.15 mm.

[0020] These pellets unexpectedly make it possible to completely replace powdered coal in high-end industrial furnaces, such as those used in power plants.The present invention therefore also relates to pellets with specific properties obtained by double pelletizing.

[0021] In one embodiment of the present invention, pellets are obtainable by the process of the present invention, but preferably by a process comprising two pelletizing steps.

[0022] The pellets preferably have one or more of the following properties: -Diameter of 4 to 10 mm Curl hardness of -8 to 40 kgf -Contains substantially homogeneous molten plastics obtained or obtainable by pelletizing waste materials twice - and / or a bulk density of 470 g / L or greater

[0023] More preferably, the pellets of the present invention have the following combination of properties: - 4~10mm diameter - contains more than 40% by weight of plastic material and more than 30% by weight of cellulosic material compared to dry waste A bulk density of 470 g / L or more, preferably about 500 g / L or more, more preferably 550 g / L or more - comprises substantially homogeneously molten plastics, as can be analyzed by milling pellets in a hammer mill as defined below to obtain a ground material having a density of 220 g / L or greater.

[0024] Pellets can be effectively crushed, for example, in a hammer mill (such as a California Pellet Mill, 11.5x28) with a 6.4 mm screen and a tip speed of 108 m / s. The particles resulting from twice-pelletized material have much better flow characteristics than particles resulting from once-pelletized material. Under such conditions, once-pelletized material requires too high an energy input to be effectively crushed.

[0025] The twice-pelletized pellets, when milled in a hammer mill, contain relatively low, and preferably substantially no, plastic film or fragments of fibrous material, which is advantageous because this is important for achieving good flow characteristics. Without being bound by theory, it is believed that this improved milling behavior is caused by the molten plastic further impregnating the fibrous material.

[0026] In a further aspect of the present invention, a process for firing an industrial furnace according to the present invention comprises the steps of: (i) providing pellets prepared by or obtainable by: (a) providing a waste material comprising more than 40% of one or more thermoplastic materials, based on the total dry weight of the waste, and more than 30% of one or more cellulosic materials, based on the total dry weight of the waste, wherein the waste has a particle size distribution in which more than 80% is greater than 5 mm and more than 95% is less than 60 mm; (b) passing the waste material through a pelletizer having holes of 4 to 16 mm, preferably 6 to 16 mm, and a length ratio of more than 2; and (c) passing the pellets through a second pelletizer having holes of 4 to 10 mm and a length ratio of more than 2; (ii) milling the pellets in a mill so that 25 to 70% by weight have a particle size of 2 to 3.15 mm; and (iii) feeding powdered fuel into a furnace flame, wherein the fuel is used in an amount that provides more than 70% of the energy requirements of the furnace.

[0027] The pulverized fuel according to the invention is preferably used in an amount of about 90% or more of the energy requirements of the furnace, and even more preferably substantially all (a1) of the energy requirements are provided by the pulverized fuel according to the invention.

[0028] A further aspect of the invention relates to the use of pellets comprising more than 40% by weight of one or more thermoplastic materials and more than 30% by weight of one or more cellulosic materials, based on the total dry weight of the pellets, which pellets are produced or producible by passing waste material comprising said plastics and cellulosic materials through a pelletizer having holes of 4 to 16 mm, preferably 6 to 16 mm, and a length ratio of more than 2, and passing the pellets through a second pelletizer having holes of 4 to 10 mm and a length ration of more than 2, as fuel for industrial furnaces after being crushed, preferably to a particle size of 2 to 3.15 mm, of which 25 to 70% by weight is 2 to 3.15 mm.

[0029] The pellets obtained after the two pelletizing processes have more advantageous properties than regular pellets, and it was unexpected that such an additional processing step would lead to pellets that could be used in one of the most demanding processes even to completely replace coal.

[0030] The twice-pelletized pellets can be converted into a powder with very good flow and runnability by grinding in standard equipment, for example a hammer mill, thereby achieving improved bulk, transport, and better dosing characteristics compared to the once-pelletized material.

[0031] The pellets have a very high cold crushing strength, resulting in negligible fines generation in the stockhouse and good resistance to collapse during transport.

[0032] The pellets obtainable by the process of the invention therefore have many new properties that can be advantageously used to fire industrial furnaces.

[0033] Further benefits and advantages of the present invention will become apparent from the detailed description, with appropriate reference to the accompanying drawings. DETAILED DESCRIPTION OF THE INVENTION

[0034] In a first aspect, the present invention relates to a method for producing pellets from municipal and / or other waste materials that can provide a free-flowing powder suitable for firing in an industrial furnace, the process comprising the steps of: (i) providing a waste material that includes greater than 40% of one or more thermoplastic materials, based on the total dry weight of the waste, and greater than 30% of one or more cellulosic materials, based on the total dry weight of the waste, wherein the waste has a particle size distribution of greater than 80% greater than 5 mm and greater than 95% less than 60 mm; and (ii) passing the waste material through a pelletizer having holes of 4 to 16 mm, preferably 6 to 16 mm, and a length ration of greater than 2, and passing the pellets through a second pelletizer having holes of 4 to 10 mm and a length ration of greater than 2 to provide pellets having a diameter of 4 to 10 mm and a length of 3 to 50 mm.

[0035] The pelletizer dies are preferably cylindrical, although flat dies are known and can be used as well, and a first flat die and a second cylindrical die, or a first cylindrical die and a second flat die, can be used.

[0036] The term "thermoplastic material" means a thermoplastic polymer. The waste material used to prepare the pellets of the present invention comprises at least 40% thermoplastic material, preferably at least 45% or at least 50% by weight of thermoplastic material, for example about 55% or about 60% by weight of thermoplastic material.

[0037] Generally, the amount of plastic material in the pellets is about 80% or less, preferably 70% or less. Thus, suitable ranges include 40-80% by weight plastic, or most preferably 50-70% by weight plastic.

[0038] Examples of thermoplastic polymers for use herein are described in US 2010 / 0116181. Typically, the thermoplastic material or component may be a packing material or any type of plastic waste.

[0039] Preferably, at least 20% by weight of the thermoplastic material is a polyethylene homopolymer or copolymer, more preferably at least 40% by weight, even more preferably at least 50% by weight, and most preferably at least 60% by weight.

[0040] The term "cellulosic material" as used herein refers to fibers such as paper, carton, wood, cardboard, cotton, rayon, and / or viscose. The waste material used in the present invention contains at least 30% by weight of cellulosic material, preferably 35% by weight or more. Generally, the amount of cellulosic material is about 60% by weight or less, preferably about 50% by weight or less, based on the total dry weight of the pellet. Suitable ranges include 30-60% by weight of cellulosic material, preferably 30-50% by weight of cellulosic material. Cellulosic material can also be referred to as biomass.

[0041] As used herein, the term "pellets" or "pellets" is used to refer to pellets of the present invention comprising one or more thermoplastic materials and one or more cellulosic materials. The pellets are not limited by the degree of heterogeneity. The pellets of the present invention may be commercially available Subcoal® pellets, which can be pelletized twice.

[0042] Suitable processes for making pellets are described in the art, for example, as described in US6635093. However, it should be noted that in order to obtain pellets that are sufficiently homogeneous with respect to the (molten) plastic and cellulose material, the pellets should be pelletized twice. Nevertheless, by knowing the required final properties of the pellets of the present invention, it may be possible to obtain such properties by using special dies or other processes.

[0043] The pellets generally have a uniform size range (diameter) of 4 to 10 mm, preferably 6 to 10 mm, and the length of the pellets generally is 3 to 50 mm, preferably 4 to 40 mm, and even more preferably 5 to 30 mm.

[0044] The pellets can be produced by selecting waste plastics and biomass from sources such as garbage or paper recycling plants. Different selected waste streams can be combined to achieve the desired mix of plastics and cellulosic materials. The feedstock is preferably shredded to a size of 5 cm or less, preferably 4 cm or less, in its largest dimension. In a further embodiment, the feedstock is shredded to a size of about 3.5 cm or less, preferably about 2.5 cm.

[0045] Preferably, the waste has a particle size distribution such that more than 80% is greater than 5 mm and more than 95% is less than 60 mm. Preferably, more than 90% is less than 40 mm. In a more preferred embodiment, the waste has a particle size such that about 20% by weight or more has a size greater than 30 mm.

[0046] The material can be dried to a moisture content of about 2-15% by weight, preferably 5-15% by weight, more preferably less than 10% by weight, and the material is pressed through a die with suitable holes. Drying is preferably performed after shredding.

[0047] The die holes can have a diameter of about 4 to 20 mm and an aspect ratio of 2 to 20, preferably at least 4. Preferred dimensions are 4 to 16 mm, more preferably 6 to 16 mm, in diameter for the first pelletizer, and 6 to 10 mm in diameter for the second pelletizer. The aspect ratio or length ratio (these phrases are used interchangeably) is at least 2, meaning that the die thickness (defining the length of the path the material takes through the die) is at least twice the diameter of the holes. The aspect ratio (length divided by diameter, or length ratio) is preferably about 4 to 15, more preferably about 6 to 12.

[0048] The holes in the first and second pelletizers may be the same or different, with the holes in the first pelletizer being the same diameter or larger. In another embodiment, the holes in the first pelletizer are smaller than the holes in the second pelletizer.

[0049] The two pelletization steps allow for effective melting of the plastic impregnating the fibrous or film-like material, helping to improve grindability. During the first pelletization step, the material is generally heated to below or about 100°C, preferably 70-90°C, which allows for shearing and grinding of the raw material. During the second pelletization step, the temperature of the pellets is preferably increased to above about 100°C, preferably above about 105°C, and may be increased up to about 120°C. The temperature during the second pelletization step is generally about 5°C or higher, preferably about 10°C or higher, e.g., up to 20°C or 30°C higher than in the first pelletization step. This relatively higher temperature in the second pelletization step allows for further melting of the plastic. The improved melted and impregnated pellets exhibit significantly higher bulk densities and are relatively easily distinguishable from prior art pellets.

[0050] The heating value or calorific value or calorific value of any fuel is the energy released per unit mass or volume of fuel when it is completely burned. The amount is determined by returning all combustion products to their original pre-combustion temperatures, especially condensing any vapors produced. That is, it is the amount of heat released during the complete combustion of that specified amount.

[0051] Calorimetry measures higher heating value (HHV) and uses the following procedure: A sample is completely combusted using pure oxygen, producing carbon dioxide and water. Water is initially produced as steam. However, once the entire sample is combusted (i.e., the test is complete), the water vapor condenses. This condensation process releases additional heat. Technically, this additional heat is the latent heat from the conversion of water from a vapor to a liquid phase. The combination of the heat released during the combustion of the sample and the subsequent heat released during the conversion of water vapor to a liquid provides the maximum heat possible. This is known as the higher calorific value (HCV) or higher heating value (HHV).

[0052] If the process keeps the produced water in a vapor state, no latent heat is recovered. This is known as the lower calorific value (LCV) or lower heating value (LHV). LHV is the heat of combustion only and does not include the heat released during condensation of the water vapor. LHV is an important measurement for most combustion systems that convert heat to power or energy.

[0053] HHV and LHV are effective for complete combustion of fuel into CO2 and H2O.

[0054] The calorific value (LCV) of pellets is generally about 19-28 GJ / tonne, which is lower than full plastic materials, which generally have a calorific value of 31-35 GJ / tonne (dry weight).

[0055] Preferably, halogen elements such as chlorine are present in the pellets in an amount of less than 1 wt. %, more preferably less than 0.3 wt. %. High inputs of this element may lead to corrosion of the dry and / or wet gas scrubbing systems, as well as chlorine emissions via the effluent of the top gas scrubber.

[0056] The oxygen content of the pellets is preferably in the range of 20 to 30% by weight of the dry weight pellets.

[0057] The hydrogen content of the pellets is preferably in the range of 6 to 8% by weight of the dry weight pellets.

[0058] Preferably, the pellets contain 1 to 10% by weight of moisture, more preferably about 5% by weight or less. The moisture content may be less than 2% or less than 1%.

[0059] Preferably, the pellet strength is about 8 kgf or more, more preferably about 10 kgf or more. Generally, the strength is about 40 kgf or less, and often about 25 kgf or less. However, it is possible to have even harder pellets, for example, having a strength of up to 70 kgf or less, e.g., 60 kgf or less. It may be preferable to have a strength of about 30 kgf or less.

[0060] Hardness can be measured with a Kahl pellet hardness tester, available from Amandus Kahl GmbH & Co. KG, Hamburg. The advantage of sufficient strength is that the pellets have a relatively high density, allowing for efficient transport, and this strength prevents the formation of large amounts of fines during transport. The Kahl pellet hardness tester is one of the industry's standard testing methods.

[0061] The pellets obtained or obtainable by the process of the present invention can be milled in a hammer mill so that the powder exhibits good flow properties and preferably 25-70% by weight of the powder has a particle size of 2-3.15 mm.

[0062] These pellets even unexpectedly make it possible to completely replace powdered charcoal in high-end industrial furnaces.The pellets preferably have one or more of the specific properties obtained by double pelletizing.

[0063] Preferred properties include one or more of the following: -Diameter of 4 to 10 mm Curl hardness of -8 to 40 kgf - Substantially homogeneous molten plastic obtained by pelletizing waste materials twice -Bulk density of 470g / L or more

[0064] The pellets can be ground in a hammer mill (e.g., a 11.5x28 with a 6.4 mm screen and a tip speed of 108 m / s, such as a California Pellet Mill). The resulting particles preferably have a bulk density (tapped) of 220 g / L or greater.

[0065] When hammer milled, the pellets contain virtually no plastic film or fibrous strands, which would be detrimental to flow properties.

[0066] The pellets are crushed into relatively small particles less than 3.15 mm. Generally, the weight percentage of particles larger than 3.15 mm is about 15% by weight or less, preferably about 10% by weight or less, and even more preferably about 7.5% by weight or less. More preferably, more than 95% by weight, more preferably more than 98% by weight, of the crushed material is smaller than 3.15 mm. However, the particles are not dusty. Preferably, more than 25% by weight, more preferably more than 30% by weight, is larger than 2 mm. Additionally, preferably, about 75% by weight or more is larger than 1 mm.

[0067] In one embodiment, preferably the ground material comprises about 30% by weight of material having a size between 2 and 3.15 mm, and even more preferably about 40% by weight or more of material.

[0068] (Tapped) bulk density is measured as follows: a quantity of pellets is poured into a 100 mL cylinder (2.5 cm diameter) and the amount of pellets present in grams is measured. Tapping is performed by placing the beaker on a vibrating surface (0.5 mm vertical vibration, 240 times per minute) for 5 minutes and measuring the amount of pellets. Tapped density is the amount in grams divided by the measured amount.

[0069] Pellets obtained or obtainable by pelletizing twice have a higher bulk density. Pellets obtained by pelletizing once generally have a bulk density of less than 460 g / L. Pellets according to the present invention generally have a bulk density of 470 g / L or more, preferably 480 g / L or more. Generally, the density is 700 g / L or less. The bulk density of the pellets is more preferably about 500 g / L or more, and even more preferably about 550 g / L or more.

[0070] The grinding was tested with a hammer mill (California Pellet Mill, 11.5x28) with a 6.4 mm screen and a tip speed of 108 m / s, used according to the manufacturer's instructions.

[0071] The bulk density (tap) of the ground pellets (particulate matter) is generally 220 g / L or greater, preferably 230 g / L or greater, in contrast to standard pelletized materials of the prior art, which generally have bulk densities after milling that are often less than 200 g / L.

[0072] Preferably, the average particle size of the ground particles is less than 2.5 mm, preferably greater than 1 mm.

[0073] Grinding in an industrial environment is generally carried out in a suitable mill such as a hammer mill, a jet mill, etc. Preferably, a hammer mill is used.

[0074] Grinding pellets that have been pelletized alone in such equipment to a particle size of less than 3 mm appears to result in a material with particles and a significant amount of small plastic fluff material (plastic film components and fiber material). This fluff material severely affects flow and handling properties, thereby hindering both the transport and feeding of the particles into the furnace. Also, combustion is unstable. When grinding is performed on pellets according to the present invention, virtually no fluff material is observed.

[0075] A process for firing an industrial furnace according to the present invention comprises the steps of: (i) providing pellets as described above; (ii) milling the pellets in a mill so that preferably 25-70% by weight have a particle size of 2-3.15 mm; and (iii) feeding powdered fuel into the furnace flame, wherein the fuel is used in an amount that provides more than 70% of the energy requirements of the furnace.

[0076] Preferably, fuel is used in an amount that provides more than 80%, more preferably more than 90% of the energy requirements of the furnace.

[0077] In an even more preferred embodiment, the pellets are provided as a complete replacement for fossil fuels in power generation.

[0078] In a further aspect, the present invention relates to the use of the above pellets as fuel for industrial furnaces after crushing, preferably so that 25-70% by weight of the particles have a size of 2-3.15 mm.

[0079] The particles have adiabatic flame temperatures ranging from about 1200°C to about 2500°C and a thermal energy density of 1280 to 2000 Nm 3 The air is blown into the orbit of the industrial furnace at a rate in the range of 1000 / kg*1000. The temperature generally depends on the type of furnace.

[0080] The present invention will now be described in more detail, specifically with reference to examples, but is not intended to limit the present invention. [Example]

[0081] Examples 1-2 and Comparative Experiment A A series of tests was conducted using RDF containing about 45% plastic, about 40% biomass, about 5% other materials, and about 10% moisture.

[0082] The primary and secondary (if applicable) pelletizations were carried out through a die with a 6 mm hole and a length of 70 mm (aspect ratio 11.7). The die speed was approximately 200 rpm.

[0083] The pellets obtained after the first pelleting step had a bulk density of 460 g / L, while the twice pelleted pellets had a bulk density of 508 g / L. The following tests were carried out.

[0084] Comparison of crushed single pellets of Φ6mm: - Use a hammer mill screen with a Φ6.4 mm hole screen at a speed of 96 Hz. It was not useful to also test at lower tip speeds, as problems arose at this speed (as can be concluded from the high energy consumption).

[0085] Comparison of crushed double pelletized Φ6mm pellets: - Use a hammer mill screen with a Φ6.4 mm hole screen at a speed of 48 Hz. - Use a hammer mill screen with a Φ6.4 mm hole screen at a speed of 96 Hz.

[0086] The screens, power consumption and speeds are shown in the table below along with the bulk densities. [Table 1]

[0087] The products of Examples 1 and 2 were analyzed for particle size distribution according to the methods of DIN 18123:2011-04 and DIN-EN 15149-1&-2:2011-01. The sieve fractions for 0.5 mm, 1 mm, 2 mm, 3.15 mm, and >3.15 mm gave the following results: [Table 2]

[0088] From these results, it appears that grinding double-pelletized pellets in a hammer mill equipped with a screen with Φ6.4 mm holes reduced the energy consumption per amount of pellets (kg) compared to grinding single-pelletized pellets (compare Experiment A with 2). Furthermore, particles are produced instead of fluff, and the bulk density increases from approximately 200 to 230 (a 15% increase). Higher capacities are possible when grinding double-pelletized pellets due to lower energy consumption.

[0089] Example 3 Pellets were prepared from selected solid refuse, with an energy content of 23 GJ / tonne and reduced in size to less than 50 mm, by pelletizing twice through a die with holes of 6 mm diameter and an aspect ratio of approximately 11.

[0090] The pellets exhibited a density of 625 g / L and were substantially darker and more homogeneous in texture than the pellets obtained after the first pelleting step.

[0091] Milling was carried out in a California hammer mill with a tip speed of 108 m / s and a 6.4 mm screen. The results are shown in the following table. Additionally, the ground material was shaken by hand and sieved over a 3 mm screen sieve. This allowed the fluff to remain on the screen. The amount of fluff was very low. [Table 3]

Claims

1. 1. A method for producing pulverized fuel suitable for firing industrial furnaces from municipal and / or other wastes, the method comprising: (i) providing a waste material comprising greater than 40% of one or more thermoplastic materials, based on the total dry weight of the waste, and greater than 30% of one or more cellulosic materials, based on the total dry weight of the waste, wherein the waste has a particle size distribution of greater than 80% greater than 5 mm and greater than 95% less than 60 mm; (ii) passing the waste material through a pelletizer having holes of 4 to 16 mm and a length ratio of greater than 2 and passing the pellets through a second pelletizer having holes of 4 to 10 mm and a length ratio of greater than 2 to provide pellets having a diameter of 4 to 10 mm and a length of 3 to 50 mm; (iii) milling the pellets in a hammer mill to form a powdered fuel; A method wherein 25 to 70% by weight of said pulverized fuel has a particle size between 2 and 3.15 mm.

2. The method of claim 1, wherein the pellets have a curl hardness of 8 to 40 kgf.

3. 3. The method of claim 1 or 2, wherein the pellets have a bulk density of 470 g / L or greater.

4. A method according to any one of claims 1 to 3, wherein the pulverulent fuel has a bulk density of 220 g / L or more.

5. 5. The method according to any one of claims 1 to 4, wherein the calorific value (LCV) of the pellets is between 19 and 28 GJ / tonne.

6. 6. The method of any one of claims 1 to 5, wherein the hydrogen content of the pellets is in the range of 7 to 8% by weight of the dry weight pellets.

7. A method according to any one of claims 1 to 6, wherein the oxygen content of the pellets is in the range of 20 to 30% by weight of the dry weight pellets.

8. The pellets are one or more thermoplastic materials in an amount of 40 to 70% by weight, based on the total dry weight of the pellets; - 30 to more than 50 wt. % of one or more cellulosic materials, based on the total dry weight of the pellets.

9. The method according to any one of claims 1 to 8, wherein the pellets have a diameter of 6 to 10 mm and a length of 4 to 40 mm.

10. Use of the pulverulent fuel according to any one of claims 1 to 9 as a fuel for industrial furnaces.

11. 1. A method of firing an industrial furnace, comprising: Providing a powdered fuel according to any one of claims 1 to 9; delivering the powdered fuel into a flame of the industrial furnace; The method wherein said pulverized fuel is used in an amount that provides greater than 70% of the energy requirements of said industrial furnace.

12. 12. The method of claim 11, wherein the pulverized fuel is used in an amount that provides greater than 90% of the energy requirements of the industrial furnace.

13. 13. The method of claim 11 or 12, wherein the industrial furnace is used in a method for generating electricity.

Images