GB1601405A - Process for the high-speed carbonization of coal ground to dust - Google Patents

Description

N (54) PROCESS FOR THE HIGH-SPEED CARBONIZATION OF COAL GROUND TO DUST (71) We, L & C STEINMULLER GmbH, a German Company, of 5270 Gummersbach, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a process for the high-speed carbonization of coal ground to dust In high-speed carbonization, in contrast to normal coking of lump coal, only seconds or fractions of seconds are available for the course of the reactions. Whereas, during the normal coking, slow reactions taking place during the conversion of the coal predominate, during high-speed carbonization, the reactions taking place quickly determine the whole course of the coal conversion.Thus the products emerging from the reaction chamber during high-speed carbonization differ very considerably, in amount, nature and composition, from those during normal chamber coking.

Apart from the carbonization temperature, the time factor and the nature of the heat transfer play an important part.

Processes are known wherein the coal to be carbonized in grain sizes up to a millimetre is mixed with coke of the same grain size, heated by partial combustion, in mechanical apparatuses and the volatile components of the coal which are driven out are drawn off from these apparatuses. The disadvantage of this process consists in that, when caking coals are used, these form lumps with the coke and have to be comminuted again in the mixing device, with considerable mechanical expense. Furthermore, the volatile components which are driven out have to flow through a more or less large layer of coke to the offtake point, as a result of which, fission and decomposition of the volatile components occur, which is not always desirable.

For example, it is possible that the sulphur extracted from the coal with the hydrogen and conveyed away in the form of hydrogen sulphide may again be separated on the way through this pile of coke and again accumulate on the coke. This point is of particular importance for the conditions for keeping the air pure when using the coke as fuel.

Processes are also known, wherein the coal to be carbonized is simply introduced into a very hot pile of coke, the coal being carbonized on the way to the discharge point of the coke. Here, too, the same disadvantages arise as in the above-mentioned proposal, and with caking coals there is not possibility of comminuting the lumps again.

Processes are further known wherein the coal dust is carbonized during pneumatic conveying by the supply of hot heating gases.

The gas produced in the plant itself and then purified generally serves as heating gas.

Limits are, however, imposed on the heating of this purified gas in appropriate heat exchangers, which are far from sufficient to ensure the appropriate supply of heat for the carbonization. For this reason, these heating gases are highly heated by partial combustion and then introduced into the reaction chamber. This partial combustion reduces the calorific value of this heating gas, however, particularly when air, not oxygen, is used for the partial combustion. The aount of coal to be carbonized must then be so great that the gas emerging therefrom is able to raise the calorific value of the mixture between heating gas and raw coal gas so that a gas which corresponds to the original value of the heating gas again emerges from the carbonization plant.This density of charge, that is to say kilograms of coal dust per cubic metre of heating gas, is limited, however, by the necessary temperatures for the carbonization on the one hand and the tolerable heating-gas temperatures on the other hand.

The change in the energy situation in recent years has led to the fact that coal has made a considerable gain over oil and natural gas as an energy carrier. Apart from use for the production of current in power stations, the simultaneous production of gas and current in power stations is acquiring ever more importance, and possibly also the appropriate by-products of coal such as benzene, tar etc. The gas obtained from the coal is to be used not only as fuel gas but also--possibly after appropriate conversion-as synthetic gas in the chemical industry, as reduction gas in the metallurgical industry or as gas similar to natural gas in the public gas supply. For this reason, it is necessary to develop processes which meet these new requirements of the energy supply.

The object of the present invention is to indicate a process which renders it possible to obtain from the coal, gas condensable and solid components, which meet the particular requirements of the following user points.

According to the present invention there is provided a method for the high-speed carbonization of coal ground to dust to obtain products of different composition, in which the high-speed carbonization takes place during pneumatic conveying in one or more stages, and gas from the carbonization is purified, highly preheated and supplied to the or each stage as an injection means for the coal dust to be carbonized and as an injection means for hot coke dust serving as a heat carrier from the high-speed carbonization of the coal dust and/or from a subsequent high-speed gasification of the carbonized coal dust, characterised in that up to 10 kg of coal dust and coke dust per standard cubic metre of carbonization gas are introduced with the gas into the reaction chamber for the high-speed carbonization, the coke dust being obtained from the process and heated to a relatively high temperature by partial combustion with air on the way to the injection point and being separated from the resulting flue gases before entry into the high-speed carbonization.

By a "standard cubic metre" as used herein is meant one cubic metre at standard temperature and pressure, i.e. at 0 C and 760 mm pressure.

Any kind of coal, caking or non-caking coal, can be used according to the invention.

With caking coals, it may be advisable for the high-speed carbonization to be preceded by a high-speed oxidation stage, wherein oxygen is transmitted to the coal by means of an oxidation agent, the coal being freed of its caking capacity in the outer layers of the coal grain. This high-speed oxidation is effected during the pneumatic conveying, the oxidation agent being the conveying means at the same time and may be flue gas or air, oxygen-enriched air, or mixtures of water vapour and oxygen. The high speed oxidation is effected at temperatures between 350"C and 450"C and lasts less than 4 seconds.

It is however also possible to introduce caking coals into the high-speed carbonization without this preliminary stage of oxidation, if specific flow conditions are adhered to at the point of introduction. For the rapid transfer of heat from the injection gas and coke dust to the coal dust, a rapid mixing of these substances is necessary, which is achieved by an appropriate introduction with swirl, that is to say vorticity of the streams. This swirling flow brings the grains of dust very quickly to the boundary walls of the reaction chamber, however, and it is therefore necessary, when using caking coal dust which has not been preoxidized, to ensure a specific distance from the injection point to the reaction wall.During this distance, the coal-dust grain must be heated very rapidly beyond the plastic range of the coal, if possible to temperatures of the order of magnitude above 700 C. The distance should be not less than one metre. In order to be able to bring this about, heating speeds of the order of magnitude of 2x 104 C/minute, if possible more than 5 x 104 "C/minute are necessary. For comparison, it may be mentioned here that in normal chamber coking, the heating speed amounts to about three degrees per minute. Adhering to these preliminary requirements when caking coals are used may possibly not be adequate in operational plants, particularly when different kinds of coal with different caking capacities are used. It may be advisable to use the preoxidation stage in every case when caking coals are used.

Apart from the nature of the coal and the grain size of the coal dust, temperature and time are the most important factors during the high-speed carbonization.

In general, the coal dust is ground to grain sizes < 0.2 mm, preferably c0.1 mm and is dried at the same time. If a high-speed oxidation stage is used first, the dust is supplied to the high-speed carbonization at temperature of about 400"C. If this is not the case, the coal dust can pass to the high-speed carbonization at the temperature at which it leaves the grinding installation, but it can be heated directly or indirectly to 400"C by transfer of the heat of the carbonization products to the coal dust. If a coal with 30% volatile constituents is introduced into the high-speed carbonization plant, for example, and carbonized at 900"C for example, then 2/3 rds of these volatile components are driven out already after about 0.5 seconds.

These volatile components then contain a high calorie gas, > 6000 kcal per cubic metre, more than half of which consists of methane and heavy hydrocarbons, the rest of hydrogen and a smaller proportion of carbon monoxide and carbon dioxide. The amount of condensable components, tar, benzene, etc. may be greater than with slow coking, because here insufficient time is available for higher decomposition processes. The hardcoke dust still contains about 1/3rd of the volatile components after 0.5 seconds. If this hard-coke dust is then further carbonized separately at the same temperature, then a gas emerges from it, about 3/4 of which consists of hydrogen and which has calorific values of the order of magnitude of about 3000 kcal per cubic metre. No more condensable components emerge.

The shorter the carbonization time-at least up to a limiting value-the more highcalorie is the gas obtained and the condensable components are the more unadulterated, that is to day present in the original state. As the carbonization temperature increases, the yield of condensable components decreases, because these are then decomposed to a greater extent. In general carbonization temperature between 800"C and 1200 C should be used and carbonization times wich amount to less than 6 seconds.

The said example shows that with the variation in the carbonization temperature and carbonization time, different compositions of the volatile components driven out are reached, so that the high-speed carbonization can easily be adapted to the requirements imposed by the conversion or utilization points for the gaseous, condensable and solid residues of the high-speed carbonization. The coke dust is generally burnt in following steam generators to produce steam and so current, but can also be used, for example, in coking plants as fillers for the coking of coals which in themselves are not very suitable, as reduction agents in chemistry and metallurgy, and as active coke. The coke dust from the high-speed carbonization can naturally be supplied immediately afterwards to a high-speed gasification and there be wholly or partially gasified for the production of useful gases.

In order to be able to produce the required products in one or individual stages of the high-speed carbonization, it is necessary that these products should not be adulterated, as would be the case, for example, by supplying heating gases which had been highly preheated by partial combustion, or by carbonization in a pile of coke dust and coal dust where unwanted decomposition processes take place. For this reason, it is proposed that gas which has been produced in this stage and has been reheated after gas purification should be used in the same stage as injection gas for the coal dust to be carbonized and the hot coke dust serving as a heat carrier. This heating temperature, for which heat is transferred from hot products produced in the high-speed carbonization plant to the gas to be heated, should be abot 700"C with the materials available today.The injection gas is distributed over the coal dust and coke dust to be injected so that the charge density of about 10 kg of dust per standard cubic metre of gas is not exceeded. With a coke dust temperature of 1350 C for example and a coal temperature of 400"C for example and an injection-gas temperature of 700"C for example, about 0.8 kg of coke dust per kilogram of coal is necessary in order to achieve a carbonization temperature of 800 C, a cubic metre of injection gas being available. For a carbonization temperature of 1000 C, about 1.9 kg of coke dust per kilogram of coal dust would be necessary, here again one cubic metre of gas being available for the injection.At the injection point, therefore, the charge would amount to about 10 kg of solids per standard cubic metre of gas, through the gas resulting during the carbonization, with complete carbonization, at the end of a charge at 800 C for example, about 3 kg per cubic metre of gas would be present and at 1000 C about 4.5 kg per cubic metre of gas.

With a temperature of the coke dust at 1250 C, for example, the ratio of coke dust to coal dust would increase to about 1.1, at 1000 C to about 3.2, and the charge densities at the end of the carbonization chamber accordingly.

The coke dust which is used as a heat carrier originates either from the high-speed carbonization or from a high-speed gasification which may follow. In order to adapt the temperature of the extracted coke dust to the entry temperatures into the high-speed carbonization, this coke dust is heated to the appropriate temperature by partial combustion of the coke dust by addition of an oxidation agent, which is the conveying means at the same time, for example air, on the conveying path, generally pneumatic, from the extraction point to the supply point.

The heated coke dust is separated from the conveying means and then fed to the injection gas. The amount of coke dust to be fed in as a heat carrier is the less the higher the preheating temperature of the coal dust is.

The limit of this preheating temperature is the lower temperature limit of the plastic range of the coal. If the coal dust has been pre-oxidized, then it has in any case reached temperatures of about 400"C before it is supplied to the carbonization section. If a pre-oxidation has not been carried out, it is advisable to heat the coal dust to this temperature by heat exchange with the hot products emerging from the high-speed carbonization, for example by direct heat transfer from the gaseous and vaporous components emerging from the high-speed carbonization to the coal dust. In the latter case, these gases and vapours or portions thereof are mixed directly with the coal dust and separated from one another again after the heat exchange.

During the high-speed carbonization of coal dust, it is of particular importance that a considerable proportion of the sulphur originally present in the coal should be extracted from the coal by the hydrogen of the coal and the hydrogen of the carrier gas and be supplied to the gas purification in the form of hydrogen sulphide. This desulphurizing process likewise depends on temperature and time, for on the one hand there is a specific temperature, for each coal, at which the desulphurization takes place in an optimum mannered0 to 75geand on the other hand, particularly with very high carbonization temperatures, when certain time limits are exceeded, a back decomposition of the hydrogen sulphide occurs and hence accumulation of the sulphur on the coke dust.

The production of specific gas qualities, specific amounts of by-products with a simultaneous predetermined decarbonization therefore generally leads to a certain compromise in the carbonization conditions, unless a certain result of the high-speed carbonization is predominant.

The advantage of the present invention consists in that, as a result of the ability to regulate carbonization temperature and time in the high-speed carbonization, with the heat carriers used here, the products from the coal can be obtained in such a wide range of variation in their composition that they are suitable for the most varied following utilization and/or conversion steps.

WHAT WE CLAIM IS: 1. A method for the high-speed carbonization of coal ground to dust to obtain products of different composition, in which the high-speed carbonization takes place during pneumatic conveying in one or more stages, and gas from the carbonization is purified, highly preheated and supplied to the or each stage as an injection means for the coat dust to be carbonized and as an injection means for hot coke dust serving as a heat carrier from the high-speed carbonization of the coal dust and/or from a subsequent high-speed gasification of the carbonized coal dust, characterised in that up to 10 kg of coal dust and coke dust per standard cubic metre of carbonization gas are introduced with the gas into the reaction chamber for the high-speed carbonization, the coke dust being obtained from the process and heated to a relatively high temperature by partial combustion with air on the way to the injection point and being separated from the resulting flue gases before entry into the high-speed carbonization.

2. A method for the high-speed carbonization of coal ground to dust, as claimed in claim 1 and substantially as hereinbefore described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (2)

**WARNING** start of CLMS field may overlap end of DESC **. process likewise depends on temperature and time, for on the one hand there is a specific temperature, for each coal, at which the desulphurization takes place in an optimum mannered0 to 75geand on the other hand, particularly with very high carbonization temperatures, when certain time limits are exceeded, a back decomposition of the hydrogen sulphide occurs and hence accumulation of the sulphur on the coke dust. The production of specific gas qualities, specific amounts of by-products with a simultaneous predetermined decarbonization therefore generally leads to a certain compromise in the carbonization conditions, unless a certain result of the high-speed carbonization is predominant. The advantage of the present invention consists in that, as a result of the ability to regulate carbonization temperature and time in the high-speed carbonization, with the heat carriers used here, the products from the coal can be obtained in such a wide range of variation in their composition that they are suitable for the most varied following utilization and/or conversion steps. WHAT WE CLAIM IS:

1. A method for the high-speed carbonization of coal ground to dust to obtain products of different composition, in which the high-speed carbonization takes place during pneumatic conveying in one or more stages, and gas from the carbonization is purified, highly preheated and supplied to the or each stage as an injection means for the coat dust to be carbonized and as an injection means for hot coke dust serving as a heat carrier from the high-speed carbonization of the coal dust and/or from a subsequent high-speed gasification of the carbonized coal dust, characterised in that up to 10 kg of coal dust and coke dust per standard cubic metre of carbonization gas are introduced with the gas into the reaction chamber for the high-speed carbonization, the coke dust being obtained from the process and heated to a relatively high temperature by partial combustion with air on the way to the injection point and being separated from the resulting flue gases before entry into the high-speed carbonization.

2. A method for the high-speed carbonization of coal ground to dust, as claimed in claim 1 and substantially as hereinbefore described.