GB2217730A

GB2217730A - Improvements in processes for producing agglomerated solid fuel briquettes

Info

Publication number: GB2217730A
Application number: GB8909631A
Authority: GB
Inventors: Anthony Macdonald Hildon
Original assignee: LINSLADE CHEMICALS Ltd
Current assignee: LINSLADE CHEMICALS Ltd
Priority date: 1988-04-27
Filing date: 1989-04-27
Publication date: 1989-11-01
Also published as: GB8909631D0; GB8809964D0

Abstract

In a process for the manufacture of fuel briquettes green briquettes are pre-formed using as a binder a sugar solution such as molasses with no acid addition as catalyst or not more than 3% acid addition. The curing process for the green briquettes is carried out in a vibrating fluid bed oven in which at least over the initial part of the curing process a shallow layer of briquettes preferably not more than 3 inches thick and more preferably not more than 1 inch thick is used. Fast hot gas flows are used with gas temperatures in the range of 180 DEG C to 700 DEG C and flow rates in the range 140 to 2000 cu.ft. per minute per square foot of fluid bed deck. The oxygen content of the gas is between 1 and 19% by volume and preferably between 1 and 8%.

Description

Improvements in Processes for producing Agglomerated Solid Fuel Briquettes The present invention relates to an improved process for the curing of combustible solid fuel material in the form of shaped briquettes or ovoids comprising compressed agglomerated fuel particles held together by a suitable binding agent, and in particular to smokeless solid fuel briquettes having a low volatile fuel content. The invention is thus mainly concerned with solid fuel briquettes manufactured from low volatile coal particles, preferably anthracite duff.

In U.K. Patent Application GB 2189806A there is described a process for producing solid fuel briquettes comprising agglomerated combustible particulate material and a binding medium wherein the process includes the steps of compressing a mix of the particulate material and the binding medium to form low strength "green" briquettes, and of subjecting the green briquettes to hardening and partial or complete curing treatment with fluid at elevated temperature in a vibrating fluidised bed dryer.

Molasses has been used as a binder for briquettes but this binder has required an acid to catalyse the process that brings about the curing of the briquette. Normally phosphoric acid or sulphuric acid in amounts of 10% or more is used as catalyst or activator. Whilst the molasses phosphoric acid binder system yields good hard briquettes the overall process has a number of disadvantages. The acids can damage equipment and are expensive. Also when the briquettes are stored they can develop unsightly efflorescence. This latter disadvantage is sometimes corrected by adding further costly coating treatments.

If attempts are made with present processes to cure briquettes using molasses alone or with smaller amounts of acid binder say up to 3% a number of problems occur. The briquettes cure relatively slowly at normally allowable temperatures (up to about 280"C) and become very soft during curing so that breakage can be very high. Also the briquettes tend to ignite more readily in the absence of phosphoric acid and this can lead to serious fires in industrial equipment.

The object of the present invention is to obviate the aforesaid disadvantages.

According to the invention in a process for the manufacture of smokeless (or non smokeless) fuel briquettes the binder used in preforming green briquettes is a sugar solution and the curing of the green briquettes takes place in a vibrating fluid bed oven in which at least over the initial part of the curing process a shallow layer of briquettes is used, and fast hot gas flows through the bed are used.

The briquette layer is not more than three briquettes deep (about 3") and is preferably two briquettes deep (about 2") and most preferably a single layer of briquettes. Under these conditions the briquettes cure surprisingly rapidly with significant curing in 1 to 2 minutes and substantially complete curing in 3 to 7 minutes using the fast hot gas flows described in U.K. Patent Application GB 2196643A and the faster flows described hereafter. There is also a significant reduction in the amount of breakages.

Using shallow beds, particularly beds of one briquette depth at least for the initial part of the process the temperatures of the hot gas can be raised with the briquettes rarely catching fire, and even when briquettes do occasionally catch fire the fire does not propagate as it does in deeper beds.

The sugar solution may comprise molasses or sucrose, advantageously without added acid. Whilst the preferred sugar solution was molasses we found that sucrose could be used. The sugars were preferably used in the form of concentrated aqueous solutions.

Hot gas temperatures in the range 1800C to 7000C can be used. Thus high temperatures say 3000C to 6000cm preferably 300 to 5000C, can be advantageously used at the beginning of the process where the heating up and drying stages occur and lower temperatures say 180"C to 3200C can be used towards the end of the process. It was found that these high gas temperatures could be used without fires occuring, even when using oxygen containing gases e.g. 1 to 19% oxygen by volume normally 8 to 11% oxygen.

Under the condition of the high gas flows disclosed in GB 2196634 A single briquette layers and high gas temperatures as aforesaid the curing process occurs surprisingly rapidly. The high curing rate can be increased further by increasing the gas flow rate even further, and beyond any previously disclosed rates. In the case of the present invention gas flows of 140 to 2000 cu.ft. per minute per square ft. of fluidised bed deck can be used. Preferred intermediate ranges are 250 to 1500 and 400 to 1200.

These very high flow rates can be used throughout the whole process but it is preferred to use them only at the earlier parts of the process say the first 75%, preferably the first 60% most preferably the first 40%.

These higher flow rates and differential flow rates can be achieved in a number of ways e.g. using more holes in the base of the oven, in the earlier parts of the oven, using higher pressure etc. Thus the bed of briquettes is subjected to these differing gas flows as it moves automatically along the oven under the vibrating action.

It was also discovered that if lime (0.5 to 10%) was added to the mix the breakages could be reduced even further.

It is advantageous to recycle the gases so that they pass through the hot gas generator for the oven. This has two advantages - firstly, considerable amounts of fuel are saved - secondly, the combination of the very high temperatures employed, and the presence of oxygen in the recycle gas oxidises many of the objectionable and sometimes odorous components in these gases. As previously stated, the oxygen level can be 1 to 19% by volume but in order to achieve this oxidation the oxygen level is preferably 1 to 12% and most preferably 1 to 8%. This oxidation of the fumes and impurities can in fact provide a large proportion of the heat required and in some cases all the heat can be obtained in this way. This feature of oxidation is a;?plicable not only to briquetting using sugar solution as a binder but -also to processes using other binders including molasses with normal amounts of phosphoric or sulphuric acid binder. Also by recycling the gases the quantities of gases that need to be discharged to the atmosphere or to a suitable incinerator or gas treatment plant are greatly reduced.

The vibrating bed equipment used can be as described in UK Patent Applications GB 2196643A and GB 2189806 A. Thus the briquettes are fed on to one end of a vibrating deck of a fluid bed oven and the briquettes automatically travel along the bed and are discharged from the other end.

The vibrating fluidised bed and any necessary ancillary equipment is preferably made of heat resistant material such as stainless steel. The equipment is also preferably fitted with explosion proof relief panels.

Claims

1. A process for the manufacture of fuel briquettes wherein the binder used in pre-forming green briquettes is a sugar solution and the curing of the green briquettes takes place in a vibrating fluid bed oven in which at least over the initial part of the curing process a shallow layer of briquettes is used and fast hot gas flows through the bed are used.

2. A process according to claim 1, wherein the binder is molasses with 0-3% acid addition as catalyst.

3. A process according to claim 1 or 2, wherein the depth of said layer is between about 1 inch and 3 inches.

4. A process according to any preceding claim, wherein the gas temperature is in the range 180QC to 7000C.

5. A process according to claim 4, wherein the gas temperature at least over said initial part of the curing process is in the range 300"C to 6000C.

6. A process according to claim 5, wherein the gas temperature is in the range 3000C to 5000C.

7. A process according to claim 5 or 6 wherein the gas temperature is within the stated temperature range during the initial part of the curing process where the heating up and drying stages occur and the lower temperature range of 180"C to 3200C is used in the later stages of the process.

8. A process according to any preceding claim, wherein the gas has an oxygen content of 1 to 19% by volume.

9. A process according to claim 8, wherein the oxygen content is 1 to 12% by volume.

10. A process according to claim 9, wherein the oxygen content is 1 to 8% by volume.

11. A process according to any preceding claim, wherein the gas flow rate through the bed is 140 to 2000 cu.ft. per minute per square foot of fluid bed deck.

12. A process according to claim 11 wherein the gas flow is 250 to 1500 cu.ft. per minute.

13. A process according to claim 12 wherein the gas flow is 400 to 1200 cu.ft. per minute.

14. A process according to any of claims 4 to 6 wherein said rate of gas flow takes place during the first 40% to 75% of the curing process.

15.. A process according to any preceding claim wherein lime in an amount between 0.5 and 10% by weight is added to the mix forming the green briquettes.

16. A process for the manufacture of fuel briquettes wherein the curing of the green briquettes takes place in a vibrating fluid bed oven through which hot gas flows and wherein the oxygen content of the gas is in the range of 1 to 19% by volume.

17. A process according to claim 16, wherein the oxygen content of the gas in the range 1 to 12% by volume.

18. A process according to claim 17 wherein the oxygen content of the gas is in the range 1 to 8% by volume.

19. A process for the manufacture of fuel briquettes substantially as hereinbefore described.