NZ203969A - Making fuel pellets from organic fibre:bruising prior to pelletising - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £03969 2039^9 NO DRAWINGS Complete Specifics CIMs: ■&><&.?>} ..gi&.AX/kk Publication Dais: . P.O. Jcarm.I, .

NEW ZEALAND PATENTS ACT, 1953 ^/vso^ No.: Date: COMPLETE SPECIFICATION A PROCESS FOR MAKING FUEL PELLETS FROM ORGANIC FIBROUS MATERIAL pyWe, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V. Carel van Bylandtlaan 30, 2596 HR The Hague, the Netherlands, a Netherlands Company hereby declare the invention for which k/ we pray that a patent may be granted toxEWc/us, and the method by which it is to be performed, to be particularly described in and by the following statement: - - 1 - (followed by page la) - 203969 -A PROCESS ron MJVKTHG FUEL PKT.T.TTTG FROM • ORGANIC riDROUS MRTEREfij-- This invention relates to a process for making fuel pellets from organic fibrous material and to fuel pellets thus obtained.

Such processes are already known. New Zealand Patent Specification No.182994 for instance describes a process wherein the moisture content of canminuted fibrous material, such as sawdust, is adjusted to 16-28%w and the material is pelletized at a temperature of 163-177°C.

According to the process of the present invention a much lower pelletizirig temperature can be applied.

Moreover it has been found that by bruising the fibrous material in a crusher, preferably a roll crusher, the cuticles of the material, if this is of the very wet type such as leaves, are damaged which results in a reduction of the drying time of 80-85% compared with only cutting the material, such as leaves into pieces.

Furthermore, this bruising results in considerable fibrillation, which has a favourable influence on the coherence forces of the pellets due to entanglement of the fibres.

Thus the present invention relates to a process for producing fuel pellets frctn organic fibrous material, which con-prises bruising the material to a maximum particle size of 5 x the diameter of the holes of the die in a pel-letizer, whereafter the material is dried to 20-10%w of water on total material, optionally at least a part of the material is chopped, and then the total material is pelletized in the die-pelletizer at a pellet temperature of 70-135°C, preferably 70-120°C, more preferably 70-100°C. The pellets may be further dried in the field . 2 03 9 6 9 If the organic fibrous material is of the very wet type, such as pine-apple plant waste containing more than 70 %w of water, the material is mechanically dewatered to 70-40 %w, preferably 60-40 %w, of water on total material at the same time 5 bruising the material to said maximum particle size. This mechanical dewatering is not necessary if the material has a moisture content up to 70 %w, e.g. 30-60 %w, such as certain types of wood waste, e.g. mixtures of sawdust, bark fibres and bark chips.

Preferably the bruising is carried out in such a way that 10 the particle size of the material shows seme variation. The smaller particles then fill the voids between the larger .particles, resulting in a lower pelletizing energy and a still better entanglement of the fibres.

If desirable, water or steam may be used during the 15 pelletizing to facilitate the pellet-formation, e.g. 3-5 %w of water or steam.

Suitable diameters of the holes of the die pelletizer are in the range of from 5-30 mm.

The pellets preferably have a diameter of 10-20 mm, and 20 more preferably 13-18 mm, and an average length of e.g. -60 mm. Preferably the pelletizing is carried out in such a way that sane variation in the length is obtained, resulting in a higher bulk density and therefor lower transport costs.

According to the invention the material may be mixed with 25 other fine materials, e.g. coal or charcoal powder before pelletizing and then pelletized. Also the material may be mixed with certain chemicals to prevent soot formation when burning the pellets, or with hydrophobic compounds to decrease moisture absorption of the pellets.

Furthermore the pellets may be treated with hot oil to carbonize the outer skin thus decreasing the moisture sensivity, making storage in wet surroudings possible.

The present pellets may be used directly as industrial 203969 fuel, especially in boilers for electric power generation, as well as for domestic purposes. They can also be used for thermal gasification or the manufacture of liquid and solid fuels, e.g. charcoal by carbonizing e.g. by heating in a closed burning 5 chamber.

The invention will in present Example 1 be elucidated for pineapple plant waste and in Example 2 for maize waste.

EXAMPLE 1 Pineapple plant waste, e.g. from plantations, had a bulk density of 200-300 kg/m3 and a water content of about 78 %w on total material. The heating value was about 2-3 MJ/kg and the 15 size below about 500 mm. This material, viz. leaves, stems and stumps, but predominantly leaves (65 %w) was mechanically de-watered by squeezing on one or more three-roll-crushers to about 56 %w of water on total material, while by the bruising action of the rolls the cuticles of the material, in particular of the 20 leaves, were damaged to facilitate the release of water. This bruised material had an average length of about 35 mm, the majority being shorter than 60 mm.

The resulting cake was loosened in a rotary chopper to allow for- effective drying.

The material was thermally dried to -about 18 %w water on total material, with hot air in a rotary cascading drier in cocurrent flow with the combustion gases. Other driers, such as a grate stoker, could also be used.

The dried material was classified and the fragments larger 30 than 65 mm were adequately chopped in a rotary chopper to a size below 65 mm. The classified and the chopped material was pelletized in a three-roll die extrusion pelletizer at a pressure of 7 kN/cm2, the holes of the die having a diameter of 13 itm and a length of 65 mm. During this pelletizing, which was carried 35 out continuously, the friction and compaction in the die caused r set // tfa ^ <r ^ V- v i- 2 03 96 9 _ 4 - the temperature of the die and pellets to rise until a stationary condition settled after about 15 minutes at about 80°C for the die and about 75°C for the pellets.

The pellets had a diameter of 13 mm an a length of 20-60 mm.

The pellets were then cooled with a forced air flow to room temperature,- while being classified by a vibrating screen, and transferred to a warehouse for despatch.

The pellets had sufficient strength to be handled by mechanical conveyors. Their heating value was about 18 MJ/kg, their water content about 14%w on total material, their density 1.1 g/cm3 and the bulk density was 675 kg/m3.

The output of the pellet mill was almost 50 kg pellets per kilowatt hour electrical energy consumed by the pellet mill.

The fines ex-screening may be recycled. The air ex-pellet cooler may be used as secondary air in the furnace of the drier.

As fuel for firing this furnace mechanically dewatered material, thermally dried material, or the pellets may e.g. be used. The amount required will amount to about 20%w, of the pineapple waste intake.

EXAMPLE 2 Maize waste (stalls and leaves) with a water content of 62 %w on total material was squeezed and crushed to a water content of 48 %w on total material. This product was dried in a 25 stove to 17 %w water on total material.

The length of the thus obtained straw feed stock before densification was about 30-50 mm and the bulk density 135 kg/m3. Pellets were produced with various diameters, i.e. 8, 10 and 15 mm. The length over width ratio of the holes of the pelletizer 30 was chosen between seven and eight in those cases. This resulted in an average pressure of 11 kN/cm2 and a material density of about 1.2 g/cm3. The temperature of the die became in stationary

Claims (1)

1. 2 03 96 9 - 5 - operation 85°C and that of the pellets 75°C. The water content of the cooled product was 13%w. The output of the pellet mill was about 30 kg/kWh. The calorific value of the pellets was 19.8 MJ/kg. "2 O '* \ ';20396$;- 6 -;WHAT WE CLAIM IS:;1. A process for producing fuel pellets from organic fibrous material, which comprises bruising the material to a maximum particle size of 5 x the diameter of the holes of the die in a pelletizer, whereafter the material is dried to;20-10%w of water on total material, optionally at least a part of the material is chopped, and then the total material is pelletized in the die pelletizer at a pellet temperature of 70-135°C.;2. A process according to claim 1, wherein the organic fibrous material is mechanically dewatered to 70-40 %w, preferably 60-40 %w of water on total material at the same time bruising the material to said maximum particle size.;3. A process according to claim 1 or 2, wherein the pelletizing is carried out at a pellet temperature of 70-120 °C.;4. A process as claimed in any one of claims 1-3, wherein the organic fibrous material is pineapple plant waste or maize waste.;5. A process as claimed in any one of claims 1-4, wherein water or steam is used during pelletizing.;6., A process according to any one of claims 1-5, wherein the pellets have a diameter of 10-20 rrm and a length of 20-60 mm.;7. A process according to any one of claims 1-6, wherein the bruising is carried out in a roll crusher.;8. A process according to claim 1, substantially as hereinbefore described with special reference to the Examples.;9. Fuel pellets produced by the process of any one of claims 1-8.;10. Fuel pellets according to claim 9, which are at least partially carbonized.;DATED THIS;A. J. PARK & SON PER O/;AGENTS FOR THE APPLICANTS*