AU594535B2 - Process of burning high-salt coal - Google Patents

Description

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COMMONWEALTH OF AUSTRALIA 5 .4 5 PATENTS ACT 1952-69 COMPLETE SPECIFICATION

(ORIGINAL)

Cliass Application Number: Lodged: I t. Class Complete Specification Lodged: "fee Accepted: Published: 9 S 9 'priority 9 9 .5 S S 9.

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S 96 Name of Applicant: Address of Applicant: *Atual Inventor: Address for Service: METALLGESELLSCHAFT AKTIENGESELLSCHAFT Reuterweg 14, D-6000 Frankfurt/Main, Federal Republic of Germany GURUDAS SAMANT and CARL HAFKE EDWD. WATERS SONS, 50 QUEEN STREET, MELBOURNE, AUSTRALIA, 3000.

Complete Specification for the invention entitled: PROCESS OF BURNING HIGH-SALT COAL The following statement is a full description of this invention, including the best method of performing it known to

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DESCRIPTION

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9 This invention relates to a process of burning high-salt coal which has a chlorine content of at least 50/ by weight and has in the ash of the coal a total content of at least 100% by weight of alkali chloride and alkali sulfate, wherein the coal has particle sizes below 12 mm and the ash has a melting point not in excess of 800 0

C.

The combustion of such high-salt coal, 10 which contains ash having a very low melting point, will result in a melting of the ash. This gives rise to difficulties in process technology, particularly during a combustion in a fluidized bed, a circulating fluidized bed, or a multiple-hearth furnace.

14 German Patent 1,546,650 discloses a process of burning high-salt coal in a pulverized-coal furnace.

The finely ground coal is first degasified by a partial combustion in the presence of added kaolin for combining with alkali. Said cperations are performed at temperatures 20 of about 10000C. Slag is withdrawn in a liquid state. In that known process the volatilization of alkalis is reduced so that leas alkalis will be deposited on surfaces disposed outside the combustion chamber. The alkalis combine with the added kaolin to form aluminum alkali silicates. But a release of substantial quantities of chlorine and sulfur is not prevented. This gives rise to great corrosion problems in the succeeding parts of the plant.

German Patent Publication 25 01 503 describes a process of decreasing the sulfur content of

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0 to the exhaust gases from fluidized bed furnaces. The granular coal is covered with dolomite or limestone and during the combustion the sulfur contained in the coal is reaczed to form CaSO 3 and CaSO 4 and is thus combined. Th'at publication discloses also an addition of lime to s-uspended coal fuel in order to reduce the melting temperature of the ash.

It is an object of he invention to effect an economical combustion of high-salt coal without a risk of disturbances caused by the low melting point of the ash. In the process described first hereinbefore this is accomplished in accordance with the invention in that the coal particles are at least partly covered with at least one oxide, hydroxide, carbonate or sulfate of calcium or magnesium and the covered coal is burnt at temperatures having a maximum in excess of the melting point of the ash of the untreated. coal.

It has been found that the substances stated will effect a sufficient increase of the melting poiht of the ashes of said coals so that said ashes will not melt if sufficiently low combustion temperatures are maintained.

An increase of the amount of impregnating material applied to the coal particles will increase the temperature at which the ash is melted. AS a rule of thumb it can be said that at least two moles of the impregnating substances should be used per mole of sodium chloride in the coal. Dolomite may also be used as an impregnating substance.

The high-salt coal can be covered or

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impregnated, in a mixer, a tumbling barrel or a pelletizing barrel. In such equipment, the coal particles may be contacted with an, aqueous suspension of the impregnating material or may be moistened on the surface and may then be contacted with the dry impregnating material.

The impregnating granular coal may be formed into shaped bodies, such as briquettes or pellets, and said shaped bodies can then be supplied to the burning equipment.

Preferred combustion temperatures are in the 10 range from 650 to 850 0C. In said temperature range the NaC1 vapor pressure is not in excess of 1.3 millibars so that there is no risk of a deposition of salt in the equipment which succeeds the burning equipment. Besides, the impregnation of the coal particles will substantially prevent an evolution of NaC1 vapors during the combustion.

The combustion is effected in equipment which is known per se, in a fluidized bed, a circulating fluidized bed or a multiple-hearth furnace. A combustion in a circulating fluidized bed has been described in Published German 20 Applications 25 39 546 and 26 24 302 and in the corresponding U.S. Patents 4,165,717 and 4,111,158.

For a combustion of the impregnated coal in a circulating fluidized bed, an addition of granular inert material having particle sizes below 3 mm is recommended.

A particularly desirable inert material consists of furnace ash. Such inert material will improve the trickling of the ash. The inert material is preferably added in a quantity of 2 to 20 by weight of the ash content of the untreated high-salt coal.

In the following examples, two different high-salt coals from the German Democratic Republic have been used. Said coals had particle sizes up to 12 mm and the following properties:

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Analysis, based on dr-y coal Ash (at 500 0 Oo by weight Total carbon, 1% by weight Total sulfur, by weight Hydrogen, by weight Chlorine Nitrogen Upper heating value, kJ/kg Lower heating value, kJ/kg Melting point of ash, C 11.8 51.4 2.4 F.0 1.7 0.4 21,180 19,860 705 14.7? 52.*5 2.2 5.7 3.8 0.4 22,230 20,980 700 Coal A Coal B a sample of 3 The melting point of ash is measured using mm. x 3 mm in a heating microscope.

The ash produced at 500 0 had the following a 4 composition:

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*9 4 S S Fr om Coal A by weight From Coal B by weight Na 2 0 CaC S i0 2 Mg0 A1 2 0 3 Fe 2 0 3 KO2 Ti2 so Cl 3 Residual carbon 19.2 14.6 1.5 2.4 0.7 2.9 0.3 0.05 38.2 14.*4 6.8 24.*6 10.5 0.6 1.9 0.8 0.4 0.05 27.7 25,9 8.2 -ii' I' ~ipl7ng-*F~~.

t -6- The experiments had the following results: Example 1 200-g portions of coals A and B having particle sizes from 0.1 to 6 mm are burnt without additives in a muffle furnace at 800 0 C with a supply of air. After the combustion the ash has been entirely melted.

s. Example 2 200-g portions of coals A and B having 10 particle sizes below 6 mm are covered with Ca(OH) 2 in a small tumbling barrel. In the impregnated coals the mole ratio of CaO:2NaC1:Na 2 SO4 is about 5.7:1:1. After the combustion in the muffle furnace at 850 C the ash

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is loose and loose ash agglomerates are found only at a few points.

a* Example 3 200-g portions of coals A and B are covered 'a with Ca(OH)2 as in Example 2. In the impregnated coal the mole ratio of CaO:2NaC1:Na 2 SO4 is about 2.8:1:1. The impregnated coal is mixed with 60 g ash from a coalfired furnace. The main components of said ash consist of 54% by weight SiO 2 23.6% by weight A1 2 0 7% by weight Fe203 and 4% by weight Ca0. The combustion is effected 0 at 875 C. After the combustion the ash is loose and does 26 not contain agglomerates.

Example 4 2 00-g granular coal Aare moistened with -7water and covered with CaCO 3 on a small tumbling barrel. In the impregnated coal the mole ratio of CaO:2NaC1:Na 2 SO4 is about 3.7:1:1. The co-'ered coal is mixed with 40 g ash from a coal-fired furnace. The main constituents of that ash were 51.9% by weight Si0 2 20% by weight A1 2 0 3 21.9% by weight CaO, and 4.4% by weight Fe 2 0 3 After a combustion at 900°C the ash is loose and does not contain agglomerates.

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S" 10 200 g of coal B (particle size up to 6 mm) are moistened with water and covered with CaSO 4 ,2H20 The mole ratio of CaSO 4 :2NaCl:Na 2

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4 is about 3.5:1:1.

After a combustion at 850 in a muffle furnace the ash is loose and contains no agglomerates.

*4 15 Example 6 0 e 1000 g of finely ground coal A (particle size: about 40% by weight below 45 um) is moistened and mixed with finely ground dolomite. The mole ratio of (MgO+CaO):2NaCl:na 2

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4 in the mixture is 4:1:1. The 20 mixture is first pelletized with an addition of water.

The diameter of the pellets is about 10 to 12 mm. When the pellets have been dried at about 10000 in a drying cabinet, the pellets are burnt at 100000 in a muffle furnace. The ash is loose and contains no agglomerates.

Claims (4)

1. A process of burning high-salt coal which has a chlorine content of at least 5 by weight and has in the ash of the coal a total content of at least 10 by weight of alkali chloride and alkali sulfate, wherein the coal has particle sizes below 12 mm and the ash has a melting point not in excess of 800 0 C, characterized in that the coal particles are at least partly covered with at least one oxide, hydroxide, carbonate or sulfate of calcium or magnesium and the covered coal is burnt in a fluidized bed, in a circulating fluidized bed or in a multiple-hearth furnace at temperatures having a maximum in excess of the melting point of the ash of the untreated coal.

2. A process according to claim 1, characterized in that the covered coal is burnt in the presence of inert granular solids.

3. A process according to claim 1, characterized in that shaped bodies are formed from the covered coal before being burnt. o 0

4. A process according to claim 1, characterized in that the covered coal is burnt at temperatures from 600 to 8500C. DATED this 13th day of December, 1989 METALLGESELLSCHAFT AG WATERMARK PATENT TRADEMARK ATTORNEYS, "The Atrium", 290 Burwood Road Hawthorn, Victoria, 3122 AUSTRALIA SKP/AGB:JJC (2/8) 0 'I i ;i