AU773890B2 - Preparation of briquettes having a low binder content - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: YARRABOLDY BRIQUETTE PTY LTD (ACN 053 019 220)

COMPANY

Actual Inventor: Russell Wilson ANDERSON Address for Service: Invention Title: CULLEN CO., Patent Trade Mark Attorneys, 239 George Street, Brisbane, QId. 4000, Australia.

PREPARATION OF BRIQUETTES HAVING A LOW BINDER CONTENT Details of Associated Provisional Application: No. PQ3597 filed on 21 October 1999 The following statement is a full description of this invention, including the best method of performing it known to us: PREPARATION OF BRIQUETTES HAVING A LOW BINDER CONTENT FIELD OF THE INVENTION This invention relates to the preparation of briquettes which can utilise a process for the agglomeration of industry fines, and particularly coal, into briquettes for conversion from a waste product to a commercially useful product.

The invention will be described with reference to briquettes made from coal but it should be appreciated that the invention may extend to other types of industry fines.

BACKGROUND ART Briquetting of coal is a process whereby coal particles such as coal dust and the like can be agglomerated into large sizes making them D more suitable for furnaces and other heating apparatus.

One common manufacturing process for briquetting fine coals is where the mixture is fed into the briquetting under high temperatures (usually over 2000C). Various binders such as pitch or bitumen can be used which melt at the operating temperature. Sometimes, the coal itself can contribute to the binding process at these high temperatures.

A disadvantage with briquetting coal at high temperatures is the energy input required. For this reason, it is also known to have a "cold i' briquetting" process which is a process usually carried out either with no heating, or with heating up to 1000C. The cold briquetting process requires the use of different types of binders which are able to hold the coal particles together to provide an acceptable briquette. The binders must also hold the briquette together during the combustion process to prevent premature, partial, or complete disintegration of the briquette and therefore the loss of uncombusted coal through the furnace grate.

It appears to be known to use molasses and lime as binders in a coal briquetting process. The molasses is usually diluted with water and is mixed with the coal particles. Lime is then added and the resultant mass is compressed into briquettes. A disadvantage with these binders is that the binder content is rather high which reduces the energy value of the coal briquette. Merely reducing the binder content results in a briquette which is brittle and has other undesirable properties. Additionally, the molasses has an included water content and addition of too much molasses also increases the water content in the formed briquette which reduces the energy value, and penalties are often imposed for moisture levels above an agreed amount.

OBJECT OF THE INVENTION After much research and experimentation, a method has now been developed to manufacture coal briquettes which contain a low binder content but which can still be briquetted to form useful briquettes.

A process has also been developed whereby the amount of water in the briquette can be reduced without requiring external heating to displace the water.

A process has also been developed to reduce or minimise sulphur emissions from burning of the briquettes.

It is an object of the invention to provide a method and a product which may overcome the abovementioned disadvantages or provide the public with a useful or commercial choice.

In one form, the invention resides in a method of manufacturing a coal briquette containing a low binder content, the method comprising the steps of: contacting coal particles with 0.25% 4% molasses at a •temperature of above 600C, adding calcium oxide to the mixture at a sufficient rate to heat the product to drive off water, and forming the mixture into briquettes.

In a broader form, other types of lime may be added to step For instance, hydrated lime or calcium hydroxide may be used.

In another form, there is provided a coal briquette which can be manufactured by the above method and which contains between 0.25% 4% by weight of molasses as a binder, and between 0.25% 10% by weight of lime.

While not wishing to be bound by theory, it appears that the quantity of molasses as a binder can be significantly reduced (typically to approximately 1% by weight) by raising the temperature of the molasses to above 60'C and typically to about 80"C. This seems to increase the viscosity of the molasses allowing it to coat the coal particles more thoroughly to give better binding at lower binder weights.

Addition of calcium oxide (quick lime) to the coal particles containing the molasses results in an exothermic reaction which raises the temperature of the mixture to draw out moisture from the product.

The particular molasses and lime binders also appear to react with sulphur in the coal particles to fix the sulphur in the ash and therefore reducing or preventing sulphur emissions.

If the binder is thoroughly homogenised with a fine particle sized coal, the sulphur fixing or sulphur retention in the ash is surprising and logo unexpected.

By the use of molasses in the ratio described, and calcium oxide, briquettes can be formed using coal particles which are extremely fine and where conventional thinking requires that more binder and not less binder is required.

It is found that the process allows coal briquettes to be made from industrial fines such as washery fines where a majority of the fines size are -0.063mm.

While the invention is particularly suited for coal fines, coarser coal particles may also be used such as particles of up to 1mm. Particles other than coal particles could be used such as other forms of industrial fines.

The molasses may be the waste molasses from a sugar mill.

This waste molasses (also called C-molasses) is unable to be further crystallised due in part to contaminants in the molasses which prevent crystallisation of the remaining sugar.

The amount of molasses is lower than conventional briquettes and is typically down to approximately 1% by weight of the briquette which is a remarkably lower amount than previously thought possible.

The molasses is heated to above 600C and preferably to 800C, although other temperatures are envisaged which increase the viscosity of the molasses sufficiently to allow it to spread out much further and to coat the coal particles very readily. Of course, temperatures over 800C will increase energy input costs and it is considered that a temperature of about 800C is suitable for the purpose.

The calcium oxide can be quick lime and the quick lime is added at a sufficient rate to draw as much moisture as possible from the product.

For washery coal fines, an amount of about 1% by weight of calcium oxide is suitable. The calcium oxide provides an exothermic reaction and removes free moisture either by evaporation or by formation of hydrates or complexes S.where the moisture does not adversely affect the energy value of the formed briquette.

While Australian coals are usually low in sulphur, some coal fine ponds may require more of the calcium oxide to fix the sulphur which means that the variations in the lime could be quite substantial.

Another aspect of the invention is directed to a method to speed up the scheming/curing process of the briquettes. In this method, formed briquettes are stockpiled, and as the briquettes are added to the stockpile, the briquettes are subjected to a blast or flow of gas which causes be smaller particles to be distributed to the extremities of the stockpile while the larger particles are distributed in a central region of the stockpile. This can ensure that the central stockpile region is left unobstructed vertically thereby allowing the scheming/curing process to proceed with maximum speed.

The blast or flow of gas is typically in the form of an airstream.

The airstream is such to blow smaller particles to the extremities of the stockpile. It is considered that a person skilled in the art would be able to determine the volume and velocity of the gas stream to achieve this result.

BRIEF DESCRIPTION OF THE DRAWING An embodiment of the invention will be described with reference to the accompanying drawing which illustrates stockpiling of briquettes.

BEST MODE In an example, coal washery fines having over 60% of the mass with a particle size of -0.063 and with over 95% of the mass being less than -0.50 or 0.25 is initially air dried. The air dried material is mixed in with 1% by weight of molasses and is heated to approximately 800C to allow the molasses to coat the fine particles. Thereafter, calcium oxide 4% by weight) is added and the mixture is thoroughly mixed. An exothermic reaction is observed with the rate of calcium oxide addition being measured to ensure that the product does not heat up so quickly to fragment the briquettes. The final product is passed to a known type of briquetting machine to form briquettes, pellets, extrusions, and the like.

Referring to figure 1 there is illustrated a stockpiling method. In the method, large quantities of briquettes are stockpiled by means of a radial conveyor/stacker or similar apparatus 10. The apparatus 10 is known in the art. The briquettes 11 are placed on the stacker and conveyed to the stockpile 12. At the discharge end 13 of the stacker, the briquettes fall away from the stacker and on to stockpile 12. Below discharge end 13 is a blower 14. The blower 14 causes a blast of air to flow immediately below discharge end 13. Consequently, any smaller particles passing over the stacker are blown to the extremities of the stockpile 15, while the larger particles or briquettes drop to a central area 16. This ensures that the central area or the centre stockpile region 16 is left unobstructed vertically, thereby allowing the -00. scheming/curing process to proceed with maximum speed.

It should be appreciated that various other changes or modifications may be made to the embodiments describes without departing from the spirit and scope of the invention. For instance, the invention need not be limited to coal fines and other industry fines may also be used. The coal may be any bituminous or non-bituminous coals, crushed coal, or coal fines recovered from a coal cleaning process (such as a washing process).

Claims (14)

1. A method of manufacturing a coal briquette containing a low binder content, the method comprising the steps of: contacting coal particles with 0.25% 4% molasses at a temperature of above 600C, adding lime to the mixture at a sufficient rate to heat the product to drive off water, and forming the mixture into briquettes.

2. The method of claim 1, wherein the lime is calcium oxide and/or hydrated lime.

3. The method of any one of the preceding claims, wherein the coal particles comprise industrial fines such as washery fines where a majority of the fines size are -0.063mm.

4. The method of any one of the preceding claims, wherein the binder is thoroughly homogenised with the coal particles.

The method of any one of the preceding claims, wherein the coal particles are up to 1mm in size.

6. The method of any one of the preceding claims, wherein the molasses is the waste molasses from a sugar mill.

7. The method of any one of the preceding claims, wherein the amount of i "'"molasses is approximately 1% by weight of the briquette.

8. The method of any one of the preceding claims, wherein the molasses is heated to above 600C to about 800C. •ooo

9. The method of any one of the preceding claims, wherein the lime is about 1% by weight of calcium oxide.

The method of any one of the preceding claims, wherein coal washery fines having over 60% of the mass with a particle size of -0.063mm and with over 95% of the mass with a particle size of -0.50mm is initially air dried, the air dried oooo material is mixed in with 1% by weight of molasses and is heated to approximately 8000 to allow the molasses to coat the fine particles, thereafter, calcium oxide 4% by weight) is added and the mixture is thoroughly mixed, an exothermic reaction is observed with the rate of calcium oxide addition being measured to ensure that the product does not heat up so quickly to fragment the briquettes, the final product is passed to a known type of briquetting machine to 8 form briquettes, pellets, extrusions, and the like.

11. The method of any one of the preceding claims, wherein formed briquettes are stockpiled, and as the briquettes are added to the stockpile, the briquettes are subjected to a blast or flow of gas which causes be smaller particles to be distributed to the extremities of the stockpile while the larger particles are distributed in a central region of the stockpile.

12. The method of claim 11, wherein the gas is air.

13. A briquette made by the method of any one of the preceding claims.

14. The method of any one of the preceding claims where the coal particles are substituted by other forms of industrial fines which are combustible. Dated this 16 th day of April 2004 YARRABOLDY BRIQUETTE COMPANY PTY LTD (ACN 053 019 220) By their Patent Attorneys CULLEN CO. S o.o.. o•.