IE69466B1 - A process for manufacturing fuel briquettes - Google Patents

Description

A process for manufacturing fuel briquettes* The invention relates to a process for manufacturing fuel « briquettes.

There are many known processes for briquetting 5 carbonaceous material such as fine coals or cokes, using various techniques and various binders.

For example, GB 2203165A, EP 252332A, DE 3335240/1/2-A, DE 3314764A and EP 0135785B all describe processes for manufacturing fuel briquettes using binders based on polyvinyl alcohol (PVA). Various other binders such as starch and molasses may also be added.

GB 2196643A, WO 84/04534A, GB2201423A, GB 2189806A, DE 3136163A and DE 3227395A all describe processes for producing solid fuel briquettes using lignosulphonate.

These processes are following reasons: generally unsatisfactory for the (a) emissions from process can be difficult to clean up, (b) the relatively high cost of the binders, 20 (c) the process control is difficult technically, (d) the strength and weather resistance of the finished briquette are not always acceptable.

UK 2213830A, DE 3940103A, EP 368041A and DE 3641999A all describe briquetting processes using organic hinders particularly starch.

Again, there is a problem with these conventional processes in that weathering of the briquette is often not -2satis factory and the briquettes must be stored in dry conditions.

It is also known to use bitumen (GB 215549IA and GB 2185755), pitch (GB 1,020,098), or guar gum (WO 88/00232), as binders. Again, such processes are not entirely satisfactory.

There is therefore a need for an improved process for manufacturing fuel briquettes.

This invention is directed towards providing such an improved process.

According to the invention there is provided a process for manufacturing fuel briquettes comprising the steps of: crushing coal or coke based material to a size less than 5 mm; drying the fine coal material to a moisture content of less than 1.5% by weight moisture; mixing the dried fine coal material with up to 10% by weight of a binder composition comprising starch and a cross linking agent including ammonium sulfamate; pressing the coal\binder mixture into shaped briquettes; and heating the briquettes in an oven to achieve a briquette core temperature of at least 180”C.

In a preferred embodiment cf the invention, the binder composition is prepared by reacting in situ gelatinised starch with sulfamate at elevated temperature in one process step to form starch-sulfamate.

In another embodiment of the invention, the starch cross linking agent includes ammonium peroxodisulphate.

In a particularly preferred embodiment of the invention, the starch cross linking agent comprises ammonium sulfamate and ammonium peroxodisulphate.

Typically the weight ratio of ammonium sulfamate to ammonium peroxodisulphate is from 5:1 to 1:1.

The starch may, for example, be a maize starch, a wheat starch or a potato starch.

Typically, the fine coal material is drie*d in a fluidised bed.

Typically, the shaped briquettes are dried in an oven at an oven temperature of from 200°C to 240°C.

In a particularly preferred embodiment of the invention, the sulfamate binder is added to the fine coal material prior to delivery of the mixture to a pug mill.

In one embodiment of the invention ammonium peroxodisulphate binder is added to a pug mill.

The invention also provides briquettes whenever prepared by the process of the invention.

Detailed Description of_the Invention The invention will be more clearly understood from the following description thereof given by way of example only with reference to the accompanying drawings in which:Fig. 1 is a schematic view of crushing and drying steps of a process of one embodiment of the invention, « Fig. 2 is a schematic view of binder addition and a briquetting steps of the process of the invention, and Fig. 3 is a schematic view of a curing process step of the invention, and Fig. 4 is a schematic view of binder addition and briquetting steps of another process of the invention.

Referring to the drawings and initially to Fig. 1 thereof, in the briquetting process of the invention coals of different types are delivered into feed hoppers 2 and onto a conveyor 4 for delivery to a holding hopper 3 from which a blend of coals are delivered along a conveyor 5 into a crusher or mill 6 where the coal material is crushed to a size range which typically is less than 3 mm. Crushed coal material is then led along a conveyor 7 into a fluidised bed 8 where the fine coal material is dried to approximately 1.5% moisture by weight. The dried coal material is collected on a collecting conveyor 9. This conveyor also collects fine coal from a cyclone 13 and from a bag filter 12.

Referring to Fig. 2, dried crushed fine coal material is delivered along a feed conveyor 15 into a main hopper 16 from which it is delivered onto a weigh belt 17. Dry powder additives or the like may be delivered onto the weigh belt 17 from an additive hopper 18. The fine coal material is then delivered along a chute 19 into a ribbon mixer 20 into which a sulfamate binder composition is injected from a sulfamate binder feed line 21. The fine coal/binder mixture is then delivered through a pug mill 25 and from there through a briquetting press 26 where the mixture is formed into ovoid-shaped briquettes. The ovoids are delivered along a conveyor 27 into an oven 30.

Referring to Fig. 3, in the oven 30, the ovoids are dried using gases at approximately 200°C and they remain in the oven for a residence time which depends on the size of the ovoids. For ovoids of 40 g weight the residence time is approximately 45 minutes until the ovoids reach a temperature of approximately 200°C and contain little or no moisture. The hot ovoids are then delivered from the oven 30 onto a conveyor 31 to a cooler 32 and they are cooled (using cold air) to a temperature of less then 40sC.

For larger ovoids a longer residence time is required. For example, for 110 g ovoids the residence time is typically 90 minutes.

The sulfamate binder mixture is prepared by reacting in situ gelatinised starch with sulfamate at elevated temperature in a tank 40 from which the starch sulfamate mixture is led to a steam jet cooker 42 which is supplied with steam from a boiler 43. A flowmeter 44 is used to monitor the flow of starch sulfamate. The starch may be maize starch or possibly wheat starch.

We have found that during the curing process, at raised temperatures, the sulfamate reacts with the starch and sinters the starch. This has the effect of making the final briquettes substantially waterproof.

Referring to Fig. 4 in the modified process illustrated the starch cross linking agent used comprises a mixture of ammonium sulfamate and ammonium peroxodisulphate (also known as ammonium persulphate) . The ammonium sulfamate is added as described above with reference to Fig. 2. The ammonium peroxodisulphate is dissolved in water in a tank 50 and delivered through a flowmeter 51 along a < persulphate delivery line 52 directly to the pug mill 25.

It is not necessary to cook the persulphate solution. » Typically the weight ratio of sulfamate to persulphate is from 5:1 to 1:1. We have found that the use of persulphate as a co-binder accelerates the chemical reaction and reduces the residence time required for drying in the oven.

Heretofore, to produce briquettes using starch, it was necessary to use a resin in combination with the starch.

Such processes, however, were expensive both in raw materials and operation. The present invention in complete contrast, however, provides a process which is relatively inexpensive and effective.

Example 1 100 kg of coal (anthracite for smokeless briquettes) is dried to less than 1.5% free moisture and crushed to less than 5 mm, preferably to less than 3 mm size.

The crushed coal mixture is then mixed with 3 kg of pregelled maize or wheat starch to which 0.3 to 0.5 kg of ammonium sulfamate has already been added. kg of water is then added and the mixture is mixed in a high energy mixer until the mixture becomes tacky. 4.

The mixture is then briquetted in a roll press and the briquettes thus formed are heated in an oven.

A typically 40 gram briquette prepared as above is heated for 45 minutes and the resultant dry briquette has a crushing strength of approximately 100 to 150 kg and is substantially weatherproof.

Example 2 Using the method of Example 1 0.3 to 0.5 kg of ammonium sulfamate are added to 100 kg of dried crushed coal and mixed dry. kg of a maize or wheat starch is cooked until gelled. (20 minutes at over 70°C in an ordinary cooker - 3 minutes in a steam jet cooker).

The binder composition is then added to the coal mixture and blended in a high energy mixer. Briquettes are shaped in a roll press and heated for typically 45 minutes in an oven at 200 to 240°C for a typical 40 g briquette. This yields briquettes of similar strength to those of Example 1 which are also substantially weatherproof.

Example 3 Using the method of Example 1 as modified by the description above with reference to Fig. 4 a solution containing 0.1 to 0.3 kg of ammonium peroxodisulphate is added to the pug mill to accelerate the reaction and reduce the residence time in the oven. The quantities of the coal, sulfamate etc are typically the same as in Example 1.

The invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail.

Claims (9)

1. A process for manufacturing fuel briquettes comprising the steps of: crushing coal or coke based material to a size less than 5 mm; drying the fine coal material to a moisture content of less than 1.5% by weight moisture; mixing the dried fine coal material with up to 10% by weight of a binder composition comprising starch and a cross linking agent including ammonium sulfamate; pressing the coal\binder mixture into shaped . briquettes; and heating the briquettes in an oven to achieve a briquette, core temperature of at least 180°C. A process as claimed in claim 1 wherein the binder composition is prepared by reacting in situ gelatinised starch with sulfamate at elevated temperature to form starch-sulfamate. A process as claimed in claim 1 or 2 wherein the starch cross linking agent includes ammonium * peroxodisulphate. t fc. A process as claimed in any of claims 1 to 3 wherein the starch cross linking agent comprises ammonium sulfamate and ammonium peroxodisulphate.

2. 5. A process as claimed in claim 4 wherein the weight ratio of ammonium sulfamate to ammonium peroxodisulphate is from 5:1 to 1:1.

3. 6. A process as claimed in any preceding claim 5 wherein the starch is selected from one or more of a maize starch, a wheat starch and a potato starch.

4. 7. A process as claimed in any of claims 1 to 6 wherein the fine coal material is dried in a 10 fluidised bed.

5. 8. A process as claimed in any preceding claim wherein the shaped briquettes are dried in an oven at an oven temperature of from 200°C to 240°C.

6. 9. A process as claimed, in any preceding claim 15 wherein the sulfamate binder is added to the fine coal material prior to delivery of the mixture to a pug mill.

7. 10. A process as claimed in any of claims 3 to 9 wherein ammonium peroxodisulphate binder is added 20 to a pug mill.

8. 11. A process substantially as hereinbefore described with reference to the drawings and examples.

9. 12. Briquettes whenever prepared by a process as claimed in any preceding claim.