GB2282387A

GB2282387A - Briquette and preparation of same

Info

Publication number: GB2282387A
Application number: GB9318480A
Authority: GB
Inventors: Ian Seward
Original assignee: Hepworth Minerals and Chemicals Ltd
Current assignee: Hepworth Minerals and Chemicals Ltd
Priority date: 1993-09-07
Filing date: 1993-09-07
Publication date: 1995-04-05
Also published as: GB9318480D0

Abstract

Briquettes are formed from a mixture comprising particles of, for example, coal, an alkaline, aqueous phenolic resin, an ester curing agent and a thickening agent for imparting green strength. The thickening agent may be an inorganic binder, eg. a silicate, acrylic polymer, vinyl polymer or phenolic polymer. A biocide, such as o-phenyl phenol, may be incorporated in the mixture.

Description

Title: Briquette and preparation of same Description of Invention The present invention relates to the preparation of briquettes, for example a coal briquette. By a coal briquette, we mean a coherent body comprising a large number of particles of coal bound together.

Various binders have been used to bind together the particles of coal in a briquette. The particles must be formed into the required briquette before the binder cures. In the interval between forming of a briquette and curing of the binder, the uncured briquette is susceptible to damage. In some cases, the sole binder imparts sufficient strength to the newly formed briquette (green strength) and subsequently imparts greater strength when the binder has cured. In other cases, although the cured binder imparts sufficient strength to the briquette, the main binder does not impart sufficient green strength to the newly formed briquette and it is necessary to incorporate a further ingredient which will provide adequate green strength until the main binder is cured.

Binders for use in coal briquettes are selected to avoid the release of harmful substances during combustion of the briquettes. Low cost is also an important consideration in the selection of a suitable binder. Starch has been used as a thickening agent to impart the necessary green strength. The presence of water is necessary, in order for the starch to bind the particles. The presence of moist starch in coal briquettes facilitates the growth of fungi and other organisms on or in the briquettes. It has therefore been proposed that biocides should be incorporates in coal briquettes comprising carbohydrate binders.

The presence of biocides in coal briquettes is undesirable. Substances evolved during the combustion of coal briquettes are usually discharged directly to the atmosphere.

Carbohydrate binders other than starch, for example guar gum and xanthan gum have been proposed for use in coal briquettes.

The invention is also useful in the preparation of other bodies comprising a large number of particles bound together (for convenience, called herein briquettes).

According to a first aspect of the present invention, there is provided a method of preparing briquettes wherein there is prepared an aqueous mixture comprising particles, an alkaline phenolic resin, a curing agent for the resin and a thickening agent capable of increasing the viscosity of water, wherein the mixture is formed into briquettes and is then permitted to cure. The thickening agent may be selected from the group comprising inorganic binders, acrylic polymers, vinyl polymers and phenolic polymers.

We have found that the growth of organisms on or in the briquettes is less likely to occur in the case of briquettes prepared by a method in which the thickening agent is selected from this group than is the case with briquettes prepared using a carbohydrate thickening agent.

According to a second aspect of the invention, there is provided a method of preparing briquettes wherein there is mixed with particles, an aqueous resin composition which contains a phenolic biocide, the mixture is formed into briquettes and the resin is caused or permitted to cure.

Preferably, a curing agent for the resin is mixed with the particles and aqueous resin composition before the mixture is formed into briquettes.

The mixture may further comprise a thickening agent for imparting green strength to the newly-formed briquettes.

According to a third aspect of the invention, there is provided a briquette comprising particles, a phenolic binder and a phenolic biocide.

The particles may be of coal, other mineral or metallic particles, for example ferro manganese or ferro silicon particles used in the production of cast iron.

The invention also provides a briquette comprising particles of coal and at least two of: an inorganic binder, a first phenolic polymer, a second phenolic polymer, an acrylic polymer and a vinyl polymer.

In one example of a method of preparing briquettes which embodies the invention, particles of coal are conveyed to a continuous mixer, for example a mixer having a mixing screw. There is also fed to the mixer an aqueous phenolic resin composition. This composition is in an essentially liquid condition.

It may comprise a resin which is liquid at ambient temperatures or a resin which is soluble in or dispersible in water or an alkaline, aqueous liquid. The coal and the resin composition enter the mixer at respective rates such that the weight of resin composition in the mixer is within the range 3% to 5% of the weight of coal present in the mixer.

The mixture formed in the mixer is conveyed to means for moulding briquettes, for example a roll press. The mixture is formed into briquettes and these are conveyed to a storage position, where the resin is permitted to cure at ambient temperature.

The aqueous resin composition contains 45% to 50% by weight solids, being a potassium phenolate or a sodium phenolate. Suitable alkaline phenolic resin compositions are disclosed in EP 85512, GB 2 154 593, GB 2 059 972, EP 86615 and GB 2 158 448. Alkaline phenolic resin compositions used as and proposed for use as foundry binders are suitable.

There is also introduced into the mixer a curing agent for the phenolic resin. Esters are suitable curing agents. The curing agent may be delivered directly into the mixer or mixed with the resin composition before the resin composition enters the mixer. The rate at which the curing agent flows towards the mixer may be such that the weight of curing agent in the mixer is from 10% to 30% of the weight of resin composition present in the mixer.

The curing agent is preferably an ester which is a liquid at ambient temperature. Alternatively, the curing agent may be a solution of an ester. A combination of esters may be used. Esters used as curing agents for phenolic foundry binders are suitable.

There is preferably incorporated in the resin composition a phenolic biocide. A suitable biocide is o-phenyl phenol. The weight of biocide may be up to 0.5% of the weight of the resin composition. Additional or alternative biocides may be incorporated in the resin composition but biocides containing halogen elements are preferably avoided.

There is also introduced into the mixer a thickening agent which will impart green strength to the composition when it is first formed into briquettes.

The thickening agent may be an aqueous solution of a silicate. Additionally or alternatively, the thickening agent may include an aqueous dispersion of clay, a polyacrylic acid binder, a vinyl polymer, a powdered phenolic resin which is soluble in or dispersible in water or a modified phenolic resin, for example a terpene-modified phenolic resin. Suitable terpene-modified phenolic resins are used in elastomeric compositions. The weight of thickening agent used may be from 0.2% to 3% of the weight of coal.

The process may be modified by mixing the ingredients in a batch mixer, rather than in a continuous mixer.

Other binders used in the foundry industry may be used in conjunction with or in substitution for the alkaline phenolic resin as the main binder, curing agents being used as appropriate.

Biocides other than phenolic compositions may be incorporated in the resin composition. Alternatively, the biocide may be mixed with the coal or another ingredient before being mixed with the resin composition.

Claims

1. A method of preparing briquettes wherein there is prepared an aqueous mixture comprising particles, an alkaline phenolic resin, a curing agent for the resin and a thickening agent capable of increasing the viscosity of water and wherein the mixture is formed into briquettes and is then permitted to cure.

2. A method according to Claim 1 wherein the thickening agent is selected from the group comprising inorganic binders, acrylic polymers, vinyl polymers and phenolic polymers.

3. A method according to Claim 1 or Claim 2 wherein the curing agent is an ester.

4. A method according to any preceding claim wherein a biocide is incorporated in the mixture, prior to forming of the mixture into briquettes.

5. A method according to Claim 4 wherein the biocide is a phenol.

6. A method of preparing briquettes wherein there is mixed with particles an aqueous resin composition which contains a phenolic biocide, the mixture is formed into briquettes and the resin is caused or allowed to cure.

7. A method according to Claim 6 wherein a curing agent for the resin is mixed with the particles and aqueous resin composition.

8. A briquette comprising particles, a phenolic binder and a phenolic biocide.