DE3507635A1 - Process for producing coal gas - Google Patents

Abstract

The invention relates to a process for coal gasification, wherein calcium-containing compounds are added in such quantities that calcium aluminates are formed. The latter are converted into alkali metal aluminates, in particular in an alkali solution from which aluminium hydroxide precipitates which is further processed to give alumina. The remainder of the slag or ash is suitable as a raw material for producing cement clinker.

Description

Process for producing coal gas

The invention relates to a method for producing coal gas under Heating of coal in a controlled atmosphere to over 1,200 OC and removal of the Slag or ash.

It is well known that coal contains mineral components and mineral ones Admixtures that are left over from coal gasification in the form of slag or ash form. These residues have so far been viewed as an inferior product that at best as ballast, for example for road or track construction, use finds. Often slag and ash have to be deposited and put in landfills thus poses a disposal problem.

The invention is based on the object of the aforementioned method to be improved in such a way that the slag or ash is used in a better way can be.

The method according to the invention is thereby able to achieve this object characterized in that the coal contains calcium-containing compounds, preferably limestone or quicklime, can be added in such an amount that there is a proportion A1203 / CaO / SiO2 adjusts, in which ß-dicalcium silicate and calcium aluminates are formed; that the crushed slag or ash in a lye stage with an alkali solution treated to decompose the calcium aluminates with the formation of dissolved alkali aluminates will; and that in a manner known per se from that enriched with alkali aluminates Alkali solution aluminum hydroxide precipitated and filtered out and further processed into alumina will.

The invention is based on the knowledge that the mineral Substances in the feed coal essentially consist of various calcium and aluminum silicates consist, the content of aluminum oxide, based on the total proportion of mineral Substances that can reach more than 30% by weight.

According to the invention, the possibility is created, if necessary, this clay already capable of electrolysis in an economical manner as a by-product. This is of considerable economic importance, especially with regard to that bauxite is not available in minable quantities in many countries.

The remaining mineral substances undissolved during the leaching process are of a quality that can be used as a raw material for the production of cement clinker suitable.

The method according to the invention thus solves all disposal problems of solid gasification residues and contributes to the proceeds of coal gasification to increase considerably.

In addition, the addition of calcium-containing compounds promotes catalytic effect the gasification process of coal.

It is from the triangular state diagram of the A1203 / CaO / SiO2 system known that in certain proportions ß-dicalcium silicate and calcium aluminates arise, but these processes were previously used for the recovery of boiler ash.

The inventive method is not dependent on the type of Coal gasification. It can be entrained-flow dust gasification, fluidized bed gasification or pressurized gasification in a countercurrent fixed bed. Also it doesn't matter whether the gasification residues as liquid slag or dry Ash accrues. For dry ash discharge, all you have to do is ensure that the calcium-containing aggregates are sufficiently mixed with the coal.

For this purpose, the coal to be gasified is preferably either supplied in the form of compacted agglomerates, in the form of a slurry with water or as a fine-grained mixture.

Furthermore, as mentioned, the slag or ash must be treated before it is treated be crushed in the lye stage. For this purpose, it is particularly advantageous that the calcium-containing compounds are added to the coal in such an amount and the ash or slag after the coal gasification is cooled so slowly that In a temperature range from 350 to 550 OC, the B-dicalcium silicate turns into g-dicalcium silicate converts. In this crystal modification, which in the A1203 / CaO / SiO2 system has a Assuming a proportion of more than 50% by weight CaO, an increase in volume occurs approx. 10% by volume. The consequence of this is a kind of explosive effect, which is called bursting and a trickling of the slag or the ash lumps in particles of the order of magnitude with a grain diameter of less than 0.1 mm.

This powder provides very good conditions for further treatment with.

Preferably, the alkali solution passes through with its enrichment Aluminum content the lye level several times.

Various alkali solutions are used to carry out the leaching Question. A sodium carbonate solution is preferably used as the alkali solution.

A particularly advantageous procedure is that for Precipitation of the aluminum hydroxide carbon dioxide, which is leached from the coal gas has been blown into the alkali solution enriched with alkali aluminates will. The carbon dioxide usually has to be washed out of the coal gas anyway, to increase its calorific value or to generate synthesis gas.

The invention is described below with the aid of a preferred exemplary embodiment explained in more detail in connection with the accompanying drawing.

The figure shows schematically a flow diagram of the process according to the invention. Coal and limestone or quick lime are in one of the analytical compositions the coal corresponding quantity ratio of a coal gasification 1 supplied. there the coal is gasified with the help of oxygen and water vapor as gasification agents, and the mineral components of the supplied coal are turned into ashes or slag of the composition expedient for the present case.

The raw gas produced during coal gasification, depending on the one used Gasification process larger or smaller amounts of water vapor, hydrocarbons, Phenols and other accompanying substances may contain is in a gas cooling system 2 cooled down to the extent that the aqueous and organic condensates are largely fail, whereby in general the greater part of the dissipated heat is generated is used by steam in a waste heat boiler.

The raw gas freed from the majority of the condensable substances passes through then a catalytic conversion 3, in which the intended use of the coal gas appropriate concentration of carbon monoxide and hydrogen adjusted will. In a subsequent gas cleaning 4, the so-called converting gas is from Sulfur compounds freed. The exhaust gas enriched in hydrogen sulfide from Gas cleaning can be done depending on the content of other ingredients and the economic Can be processed into elemental sulfur or sulfuric acid.

After the sulfur compounds have been removed, the cleaned converting gas is released finally in a C02 wash 5, where larger or smaller depending on the intended use Washed out proportions of the carbon dioxide contained in the gas will. The process stages of gas cleaning and CO2 scrubbing can also be combined into a single system "Selective gas scrubbing" can be summarized. The one washed out of the coal gas Carbon dioxide is preferably used to precipitate that to be recovered by this process Aluminum hydroxide is used.

The ash or slag discharged from the gas generator is in a special cooling system 6 cooled in such a way that in the temperature range between 350 OC and 550 OC the transformation of what is present in the ashes or slag or intermediately formed B-dicalcium silicate (ß-C2S) takes place in Ef-dicalcium silicate. The resulting increase in volume of the dicalcium silicate trickles down the slag or ash in very fine-grained parts, which can be easily and with technical Treat with aqueous alkaline solutions within reasonable reaction times. The trickling material is then advantageously in a countercurrent in several Stages working alkaline leaching 7 with a circulating soda solution brought into contact. The largest part of that contained in the pourable material goes here Calcium aluminate converts into water-soluble sodium aluminate. After separation of the leach residues with the aid of thickeners and filters 8, silica which has gone into solution is simultaneously dissolved in a caustic cleaning 9 by adding calcium oxide, milk of lime or MgO slurry converted into calcium or magnesium silicates.

These substances, which are now in solid form, are used in a subsequent Solid / liquid separation (filtration) 10 separated.

From the clear and enriched in sodium aluminate, purified Lye is in an aluminum hydroxide precipitation 11 by blowing in carbon dioxide the dissolved aluminum precipitated from the CO2 scrubbing 5 as Al (OH) 3. From the resulting The A1 (OH) 3 becomes cloudy in a subsequent solid / liquid separation (filtration) 12 filtered off and washed alkali-free. The aluminum hydroxide A1 (OH) 3 can then be used in processed into alumina (A1203) in a calcining plant.

The filtrate (in the figure referred to as Al-poor lye) is added in a regeneration 13 with soda, around the precipitation processes and the subsequent solid / liquid separations to compensate for any loss of sodium compounds. The regenerated alkaline Soda lye goes back into the alkaline countercurrent leaching 7.

The solid residues of the leaching separated off in the filtration 8 of the bar can together with the precipitated Ca or Mg silicates of the filtration 10 can be used as raw material for the production of cement clinker.

Example In a coal gasifier, with the help of oxygen and Water vapor as a gasification agent at a temperature in the gasification zone of more than 1,200 OC per hour about 12,000 kg of feed coal with the following properties gasified: moisture approx. 10.0% by weight ash (in terms of weight) approx. 15.8% by weight sulfur content (i.waf) approx. 1.0% by weight The ash has the following analytical composition: 41.6 % By weight SiO2 36.5% by weight Al2O3 7.0% by weight Fe203 8.8% by weight CaO 1.8% by weight MgO 0.6 % By weight K2O + Na2O 2.8% by weight TiO2 0.4% by weight SO3 0.5% by weight others Of the Before it is fed into the gasifier, feed coal is converted into about 3,200 kg of limestone every hour mixed in with the following analytical composition: 96.0% by weight of CaCO3 0.8% by weight MgCO3 1.0% by weight SiO2 2.0% by weight Al203 0.2% by weight Other From the coal gasifier approx. 3,500 kg of ash with the following composition of the ignition residue are produced per hour this ash discharged: 20.7% by weight SiO2 19.1% by weight Al203 52.2% by weight CaO 1.1 Wt% MgO 3.3 wt% Fe2O3 0.2 wt% K2O + Na2O 1.3 wt% TiO2 1.9 wt% SO3 0.2 % W / w Others After cooling to a temperature of less than 550 OC, drizzled more than 80% by weight of the ash to dust with a grain diameter of less than 0.1 mm. Coarse grain with a grain diameter> 1 mm is sieved off and the fine grain is then fed to a two-stage leaching process.

The leaching takes place in countercurrent at temperatures of approx. 45 OC in Agitator reactors. The one with a flow rate of approx. 30 m3 / h of the second leaching stage Regenerated lye fed in countercurrent contains: approx. 60 g / l Na2CO3 approx. 1.2 g / l Al203 pH = 13.5-14 The from the first leaching stage then to Lye cleaning promoted lye enriched in aluminate contains approx. 18 g / l Al203 pH = 13.5 From a total of 686 kg of Al203 in the ashes from the coal gasifier were discharged, thus about 504 kg A1203 are in solution as sodium aluminate gone, which corresponds to a yield on A1203 of approx. 73.5%. In one out Thickening and filtering existing subsequent separation stage is from the solid leaching residue severed.

Here, about 2,900 kg / h of solid substance fall (calculated as an ignition residue) with the following main components: 24.1% by weight SiO2 5.1% by weight A1203 61.0% by weight CaO 3.9% by weight Fe203 1.5% by weight TiO2 In order to keep the alkaline leaching in solution To remove gone silica, is also in the agitated reactors existing so-called leaching cleaning milk of lime is added and the silica precipitated as calcium silicate and then with the help of a thickener and of Filter separated from the aluminate liquor. The filter residue will be with the solid Residues from the separation stage of alkaline leaching are combined and can be used as Serving raw material for the production of cement clinker. The clear filtrate from the caustic cleaning is mixed with a small amount of solid aluminum hydroxide for inoculation and then conveyed into the precipitation reactor for the precipitation of the aluminum hydroxide. Here, by blowing in carbon dioxide, the carbon dioxide from the CO2 scrubbing of the coal gas treatment is generated originates, from the aluminate liquor aluminum hydroxide is precipitated.

The precipitated aluminum hydroxide is thickened with the help of a thickener and the filter connected behind it is separated and washed alkali-free. All in all after washing, approx. 490 kg of A1 (OH) 3 are obtained, from which by subsequent calcination about 320 kg / h of alumina (Al203) can be obtained.

The filtrate from the aluminum hydroxide precipitation is about 15 kg / h Na2CO3, calculated 100%, regenerated and fed back to the second leaching stage.

Overall, the following mass balance of the processing results of the ashes from coal gasification: Amounts used: Products obtained from the ashes: 12,000 kg feed coal 320 kg A1203 3,200 kg limestone 2,900 kg raw material for cement-15 kg of Na2CO3, clinker (calculated as 100 Zig- ignition residue) calculates 15 kg CaO 100 % calculated - blank page -

Claims (5)

Method for producing coal gas Patent claims 1, method for producing coal gas by heating coal in a controlled atmosphere to over 1,200 OC and discharge of the slag or ash, characterized in that the coal contains calcium compounds, preferably limestone or burnt Lime can be added in such an amount that there is a quantitative ratio of A1203 / CaO / SiO2 sets, in which B-dicalcium silicate and calcium aluminates are formed; that the crushed Slag or ash in a lye stage with an alkali solution to decompose the Calcium aluminates are treated to form dissolved alkali aluminates; and that in a manner known per se from the alkali solution enriched with alkali aluminates Aluminum hydroxide is precipitated and filtered out and further processed into alumina. 2. The method according to claim 1, characterized in that the calcium-containing Compounds of coal in such an amount are added and the ashes or Slag after coal gasification is cooled so slowly that it is in a temperature range from 350 to 550 OC converts the p-dicalcium silicate into y-dicalcium silicate. 3. The method according to claim 1 or 2, characterized in that the Alkali solution with enrichment of its aluminum content passes through the lye stage several times. 4. The method according to any one of claims 1 to 3, characterized in that that a sodium carbonate solution is used as the alkali solution. 5. The method according to any one of claims 1 to 4, characterized in that that for the precipitation of the aluminum hydroxide carbon dioxide, which was washed out of the coal gas is blown into the alkali solution enriched with alkali aluminates.