IE63118B1

IE63118B1 - Method of reducing the combustion temperature in the combustion chamber of a furnace or heating boiler which is heated by means of fuel briquettes

Info

Publication number: IE63118B1
Application number: IE358189A
Authority: IE
Inventors: Gert-Wilhelm Lask
Original assignee: Applied Ind Materials
Priority date: 1988-12-23
Filing date: 1989-11-07
Publication date: 1995-03-22
Also published as: EP0374402B1; DK658689D0; EP0374402A2; ATE85641T1; CA2005833A1; EP0374402A3; DE58903530D1; JPH03121194A; DK658689A; DE3843449A1; TR25967A; ES2039056T3; PT92629B; JPH0668110B2; PT92629A; IE893581L; GR3007517T3; DE3843449C2

Abstract

Fuel briquets with a finely disperse carbon carrier of petroleum coke or of a mixture of mainly petroleum coke and coal (preferably non-caking coal) with a binder mixed with a finely disperse combustion inhibitor in the form of calcium carbonate and/or dolomite, which has been added in a quantity of more than 2% by weight to the starting mixture of the fuel briquet, volatile constituents having been expelled from the fuel briquet. A manufacturing process is also indicated.

Description

This invention relates to the reduction of the combustion * temperature in the combustion chamber of a furnace or heating boiler which is heated by means of fuel briquettes. The term • fuel briquettes' denotes those which are used for the production of heat in domestic systems, and which are used for firing heating boilers, in power stations and the like.

Fuel briquettes, which comprise petroleum coke or which mainly comprise petroleum coke as the granular carbon carrier, result in very high temperatures being reached on combustion, which damage the combustion appliances. The briquettes do not possess sufficient strength, and easily disintegrate on handling and on combustion. Fuel briquettes of this type generate temperatures which are too high on combustion, and destroy the apparatus used for combustion, from simple furnaces to heating boilers. Petroleum coke frequently contains an appreciable amount of sulphur, e.g. in amounts from 0.8 to 6 % or more. The same applies to the binder also, particularly when pitch is used for this purpose. In this respect fuel briquettes which comprise or mainly comprise petroleum coke as the granular carbon carrier generate too much sulphur dioxide, and also produce nitrogen oxides, for other reasons. This also applies to briquettes of the composition described initially (US Patent 20 36 642), which are manufactured in order to achieve an increased strength by means of a special binder mixture, which also contains calcium hydroxide as a binder in an amount of about 2 weight %. The mixture of starting materials employed here is moulded at about 250°C, heat-treated, and shaped to form the finished fuel briquette after cooling.

* It is known that sulphur bonding agents may be added in an amount of 10 to 30 weight % in order to desulphurise briquettes based on carbon-containing material, e.g. coal and/or petroleum coke (US 45 15 601) . It is also known that raw briquettes can be subjected to heat-treatment, which serves to improve the weatherresistance of the raw briquette (US 41 11 755).

In practice, experimental fuel briquettes with granular ash-rich M hard coal as the carbon carrier have become known, to which granular calcium carbonate has been added as a desulphurisation agent, taking stoichiometric requirements into account. The combustion temperatures produced from fuel briquettes such as these lead to no problems, and are determined by the ash content of the hard coal. The sought-after desulphurisation effect is unsatisfactory, and the corresponding fuel briquettes have scarcely made any impact in practice.

The underlying object of the invention is to reduce the combustion temperature in the combustion chamber of a furnace or heating boiler which is fired with fuel briquettes.

This object is achieved by means of a method of reducing the combustion temperature in the combustion chamber of a furnace or heating boiler, characterised in that fuel briquettes are used, with a granular carbon carrier which has a grain size of less than 3 mm, mainly comprising petroleum coke and in addition comprising coal (preferably non-caking coal) with a binder and with an admixed granular combustion inhibitor in the form of calcium carbonate and/or dolomite which has a grain size less than 1 mm and is added in an amount greater than 2 weight % of the starting mixture, wherein volatile constituents are expelled from the fuel briquette by heat-treatment from 100eC to 500®C.

The term ’volatile constituents' means water vapour, and also hydrocarbons. Tests have shown that volatile constituents are released even at very low temperatures. The volatile constituents stem from the starting mixture, e.g. from the binder. Where no volatile constituents are present, the heat- * treatment is still carried out, however. A satisfactory heattreatment is obtained even at temperatures a little above 100eC.

The heat-treatment temperature should not exceed 500°C. The calcium carbonate and/or dolomite in the briquettes fulfil a new purpose, namely that of a combustion inhibitor. The amount of calcium carbonate and/or dolomite additive is sufficient for this purpose, and the additive is admixed with the starting mixture in a sufficiently finely-divided form for this purpose. The fuel briquettes undergo a hardening process on heat-treatment. They do not disintegrate on handling. Moreover they retain their shape to a sufficient extent during combustion, even when burning away. During the combustion of the fuel briquettes, a layer of calcium-containing ash of adequate thickness is continuously formed around the individual briquettes. This ash layer surrounds the unburnt core like a closed shell, as it were, and forms a diffusion barrier for the oxygen which is necessary for the combustion of the carbon carrier. This diffusion barrier only permits the passage of so much oxygen, so that deleter iousiy high temperatures are not produced. The amount of admixed combustion inhibitor is thus preferably adjusted to an amount corresponding to 3 weight % of the starting mixture. The ash layer becomes thicker as the diameter of the unburnt core becomes smaller, and it forms a more stable shell as the material burns away, so that deleterious high temperatures are not produced during the entire combustion of the fuel briquettes. On the other hand, the temperatures produced are sufficient for desulphurisation; calcium sulphite or calcium sulphate and magnesium sulphite or magnesium sulphate are formed, respectively, which go into the ash. The method can therefore also be employed when using petroleum coke with a high sulphur content. The degree of desulphurisation achieved is 80% or more.

Fuel briquettes in which the binder is a bituminous briquetting binder, e.g. pitch have proved to be effective; the binder is admixed with the starting mixture in an amount of 5 to 10 weight %, preferably in an amount of about 8 weight %. Fuel briquettes have also proved to be effective in which the binder is sulphite lye. The latter is admixed with the starting mixture in an amount of 5 to 10 weight %, preferably in an amount of about 6 weight % of the starting mixture. Other binders may be used within the scope of the invention. The combustion inhibitor is preferably exclusively calcium carbonate. The grain size of the carbon carrier in the fuel briquettes according to the invention should not be too large, but as a rule should be less than 3 mm.

A small proportion of coarse grains is not detrimental. The grain size of the combustion inhibitor must be adjusted so that the effects described are obtained. In this respect, a grain size of less than 1 mm is preferably employed.

The fuel briquettes used within the scope of the invention may be manufactured in various ways, using the devices which are customary in briquetting technology. In particular, briquetting presses may be employed. To manufacture fuel briquettes of the cited composition, the granular carbon carrier, the binder and the granular combustion inhibitor are mixed, preforms are formed from the mixture, and the latter are then hardened by heat1 5 treatment at a temperature below the reaction temperature of the combustion inhibitor and are freed from volatile constituents to a sufficient extent, inasmuch as the latter are present. Hydrocarbons are released even at 300°C. Water vapour is also released at temperatures from 100°C if the preforms contain water. The heat-treatment may be carried out in a rotary kiln which has a bed consisting of granular petroleum coke which forms an immersion bed for the preforms (see DE P 37 27 464.3-24) . The above-mentioned hardening process takes place under particularly mild conditions in the immersion bed.

Claims

CLAIMS :

1. A method of reducing the combustion temperature in the combustion chamber of a furnace or heating boiler, characterised in that fuel briquettes are used, with a granular carbon carrier which 5 has a grain size of less than 3 mm, mainly comprising petroleum coke and in addition comprising coal (preferably non-caking coal) with a binder and with an admixed granular combustion inhibitor in the form of calcium carbonate and/or dolomite which has a grain size less than 1 mm and is added in an amount greater than 10 2 weight % of the starting mixture, wherein volatile constituents are expelled from the fuel briquette by heat-treatment from 100°C to 500°C.

2. A method according to claim 1, substantially as hereinbefore described.