GB2227024A

GB2227024A - Coal briquetting process

Info

Publication number: GB2227024A
Application number: GB8900633A
Authority: GB
Inventors: Rodney Taylor; Simon Kelly; Stuart Hale
Original assignee: Coal Industry Patents Ltd
Current assignee: Coal Industry Patents Ltd
Priority date: 1989-01-12
Filing date: 1989-01-12
Publication date: 1990-07-18
Anticipated expiration: 2009-01-12
Also published as: GB8900633D0; GB2227024B

Abstract

Fine coal is briquetted using a binder and an ammonium compound in the mix. The briquettes can show a significant increase in curing rate and improved water resistance.

Description

BRIQUETTING PROCESS The present invention concerns a briquetting process. More especially it concerns such a process which gives improved cure rate and green strength in "cold" briquetting, that is briquetting at temperatures of up to 1000C.

Our UK Published Patent Application No. 2,187,754 discusses a variety of cold briquetting processes and discloses a useful process utilising a combination of molasses and inorganic hardening agent as binder. Our co-pending application No. 8721757 discloses a variation of the process of G.B 2,187,754 in its use of concentrated sugar solutions. The disclosures of both these applications are incorporated herein by reference.

A great many cold briquetting processes in which a water containing binder is used, require a curing stage often including mild heat treatment at temperatures up to 8000C in order to produce briquettes of adequate final strength to withstand mechanical handling.

It has now been discovered that the incorporation of minor quantities of an ammonium compound into a mixture of coal and a molasses based binder especially under the normal operating temperatures of industrial processing, can increase the rate of cure in a subsequent hardening or curing step both in terms of strength development and in terms of water resistance. Some ammonium compounds may also give rise to improved green crushing strength.

The present invention provides a process for the cold briquetting of fine coal comprising mixing fine coal with a molasses based binder to produce a briquetting mix, briquetting the mix and hardening it at an elevated temperature, characterised by the presence in the briquetting mixing of an ammonium compound in an amount, such that during the subsequent hardening stage the hot crushing strength and the water resistance of the briquette is improved.

Of particular interest are those results obtained with ammonium sulphate. This additive has been found to increase markedly the cure rate whilst having no adverse effect on green strength - it can be anticipated that these features coupled with the low cost of ammonium sulphate makes it a very promising additive for the molasses process. In the case of ammonium chloride, whilst showing the greatest improvement in the cure rate, it is less preferred because of its adverse effect upon green strength and because it is available only in a finely divided form which gives rise to handling problems. The ammonium salt may be pre-mixed with dry coal, either alone, or in combination with other hardening agents, prior to adding molasses based binders.But preferably the ammonium salt is added to the coal at the same time as or after the coal is mixed with binder and optionally other hardening agents. Specific ammonium salts and coal/binder mixes should be routinely tested to ensure that they are satisfactory and yield briquettes of the desired appearance and properties. Preferably, the ammonium salt is used in an amount of 1Z by weight of the mix.

Preferred coals are high rank non-caking coals, especially those having low smoke-emissions such as anthracite. Desirably the coal is of a particle size mainly below 3mm, and anthracite duff is especially suitable. The invention is also applicable to coals for power stations or steam raising and to coal blends containing caking coal components and/or treated coals e.g. by mild oxidation or pyrolysis. The coal may be crushed or be the direct product of coal cutting.

The briquetting step of the present invention includes all methods of forming agglomerates from fine coal, and these agglomerates may be of any size or shape according to market requirements. There may be mentioned forming agglomerates by extrusion, ring-roll or roll-pressing, die-pressing, rotary table pressing and pelletising, e.g. on a disc pelletiser.

The hardening (curing) stage in the briquetting process, to give the required strength and water resistance of the product, is preferably carried out at temperatures of the order of 2000C to 3000C for up to an hour. Hot curing may be conveniently carried out by passing the briquettes on a conveyor through an oven, in an atmosphere which may contain nitrogen, carbon dioxide, water vapour and/or oxygen. It is to be noted that the hot curing step does not correspond to a carbonisation step, and thus not only are there energy savings, but the solid yield on a dry basis is very high.

Additionally, there is a reduced risk of pollution.

The present invention will now be described by way of example only.

Example Three salts have been tested by the following procedure. A mix was prepared by adding 11 parts by weight of binder (consisting of 10 parts of molasses and 1 part phosphoric acid) to 88 parts anthracite duff and 1 part of iron ore. After mixing, this was passed through a roll press and the briquettes produced tested for green strength and curing characteristics at 2500C. The properties of the briquettes from this control mix were then compared with briquettes produced from a mix containing 11 parts w/w binder, 87 parts anthracite duff 1 part iron ore and lZ w/w of ammonium additives. The results (see attached table) show that all three salts significantly increased the rate of strength development, and that this development was matched with an acceptable water resistance.It was found that the salt addition could be made either before or after the addition of the binder - in both cases an improvement in curing characteristics was observed.

Supplementary laboratory scale tests indicate that the ammonium salts could produce a similar level of improvement with solely the molasses/phosphoric acid binder, ie omitting the iron ore additive.

TABLE Influence of Ammonium salts on the Green Strength and Cure Rate of Molasses/Phosphoric Acid Bound Briquettes ADDITIVE CONTROL AMMONIUM AMMONIUM AMMONIUM SULPHATE ~~~~~~~~ SULPHATE PHOSPHATE CHLORIDE 101b Green Shatter + 1 1/4 35 54 46 31 + 7/8 42 60 53 38 Green Crushing Strength (KR) 3.7 3.8 4.1 1.4 Hot Crushing Strength (Kg) (Curing Time - mins) 5 2.5 4.3 3.4 3.8 10 7.8 19.0 13.7 32.0 15 21.1 63.6 68.0 93.6 20 71.9 123.1 96.4 113.4 25 92.2 134.0 96.6 125.0 30 105.7 117.67 99.7 118.19 24 hour Water Resistance (Kg) (Curing Time - mins) 5 D 4.8 1.2 2.5 10 3.2 30.0 8.6 38.0 15 27.0 122.0 65.3 118.0 20 93.5 139.4 110.2 115.4 25 109.0 133.60 116.9 130.6 30 101.4 128.44 112.8 119.4

Claims

CLAIMS 1. A process for the cold briquetting of fine coal comprising mixing fine coal with a binder to produce a briquetting mix, briquetting the mix and hardening it at an elevated temperature, characterised by the presence in the briquetting mix of an ammonium compound in an amount, such that during the hardening stage, the rate of cure and the subsequent water resistance of the briquette is improved.
2. A process according to claim 1 wherein the binder comprises molasses, sugar solution and an inorganic hardening agent.
3. A process according to claim 1 or 2 wherein the binder comprises molasses in an amount of from 5-15Z by weight of the mix together with an acid and, optionally, a hardening agent selected from iron oxide (or iron ore), calcium carbonate (or limestone), calcium phosphate (or phosphate rock) and aluminium oxide (or bauxite).
4. A process according to any of claims 1 to 3 wherein the binder is a mixture of molasses and phosphoric acid.
5. A process according to any preceding claim, wherein the ammonium compound is ammonium sulphate.
6. A process according to any preceding claim wherein the ammonium compound is ammonium phosphate.
7. A process according to any preceding claim wherein the ammonium compound is mixed with dry coal before addition of the binder.
8. A process according to any of claims 1 to 6 wherein the ammonium compound is mixed with the coal simultaneously with or after addition of the binder.
9. A process according to any preceding claim, wherein the ammonium compound is present in an amount of up to 3X by weight of the mix.
10. A process according to any preceding claim wherein the coal is a high rank non-caking coal.
11. A process for the cold briquetting of fine coal substantially as hereinbefore described with reference to the Example.

11. A process according to claim 10, wherein the coal is anthracite duff.

12. A process for the cold briquetting of fine coal substantially as hereinbefore described with reference to the Example.

Amendments to the claims have been filed as follows CLAIMS 1. A process for the cold briquetting of fine coal comprising mixing fine coal with a binder to produce a briquetting mix, briquetting the mix and hardening it at an elevated temperature, characterised in that the binder comprises molasses or sugar solution and an inorganic hardening agent, and by the presence in the briquetting mix of an ammonium compound in an amount, such that during the hardening stage, the rate of cure and the subsequent water resistance of the briquette is improved, 2.A process according to claim 1 wherein the binder comprises molasses in an amount of from 5-15t by weight of the mix together with an acid and, optionally, a hardening agent selected from iron oxide (or iron ore), calcium carbonate (or limestone), calcium phosphate (or phosphate rock) and aluminium oxide (or bauxite).

3. A process according to any of claims 1 or 2 wherein the binder is a mixture of molasses and phosphoric acid.

4. A process according to any preceding claim, wherein the ammonium compound is ammonium sulphate.

5. A process according to any preceding claim wherein the ammonium compound is ammonium phosphate.

6. A process according to any preceding claim wherein the ammonium compound is mixed with dry coal before addition of the binder.

7. A process according to any of claims 1 to 5 wherein the ammonium compound is mixed with the coal simultaneously with or after addition of the binder.

8. A process according to any preceding claim, wherein the ammonium compound is present in an amount of up to 3% by weight of the mix.

9. A process according to any preceding claim wherein the coal is a high rank non-caking coal.

10. A process according to claim 9, wherein the coal is anthracite duff.