GB1593768A - Method for the far-reaching desulphurization of gas yielded during the rapid carbonization and/or partial gasification of coal dust - Google Patents

Description

(54) METHOD FOR THE FAR-REACHING DESULPHURIZATION OF GAS YIELDED DURING THE RAPID CARBONIZATION AND/OR PARTIAL GASIFICATION OF COAT DUST (71) We, L. & C. STEINMULLER GmbH, a German Company, of 527 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 method for the far-reaching desulphurization of gas yielded during the rapid carbonization and/or partial gasification of coal dust.

In order to protect the environment a number of official regulations have been issued which include the limitation of the emission of sulphur dioxide (SO2). Coal power stations, which serve to supply current, are particularly affected by these.

Methods are knows some still being developed, some used in the first operational plants wherein, after combustion of the coal, the flue gases formed are desulphurized. The plants for this method require very heavy investment costs, which leads to an increase in the expense of current production of the order of magnitude of more than 20%.

Furthermore, with these methods, further environmental problems may arise if the gypsum which generally accumulates, cannot be taken up by the relevant industry for further processing.

According to other proposals, the coal is completely gasified before combustion, the resulting gas is desulphurised and then burnt in the steam generator. With the combination of steam-turbine and gas-turbine processes, which is aimed at today in every large power station, the fuel for the gas turbine is then obtained at the same time. The disadvantage, however, is that the plant cannot be decoupled, that is to say, on failure of the gas producing plant, for example, the whole power station is out of operation because the steam generators are only adapted for firing by gas but not by coal dust.

Further proposals are based on extracting the sulphur from the coal before the combustion of the coal dust by rapid carbonization and rapid partial gasification, to such an extent that the sulphur dioxide formed by the burning of the sulphur in the coke dust remains below the emission limit. If the carbonization alone is not sufficient, an additional partial gasification of the coke dust is provided, until an appropriate amount of sulphur has been converted into the gas form. The carbonization gas and/or partial gasification gas produced is cleaned and then burnt in the firing of the gas turbine and of the steam generator. It is also possible, by further partial gasification, to deliver additional gas from the power station to the outside to other consumers or to convert this gas appropriately beforehand.

With the last-mentioned method, it is necessary or at least very advisable for the desulphurization operation, which takes place in a few seconds and at high temperatures, to keep the hydrogen content in the carbonization and/or partial gasification gas and if used of the heating or carrier gas as high as possible in order to accelerate the desulphurization of the coal dust or coke dust. If heating gas is introduced into the reaction chambers to cover the heat requirements for the carbonization and/or partial gasification, generally as a carrier for the conveying of the dust through the reaction chamber at the same time, then after mixing with the carbonization and/or partial gasification gas, a hydrogen content generally becomes established which suffices for the desulphurization of the dust. After separation from the coke dust produced, the gas is cooled and freed of sulphur and if necessa ray from the other components, in the following gas cleaning plant. Some of this purified gas may then be returned to the reaction chamber for the carbonization and partial gasification process, either as a heat ing or carrier gas or to enrich the proportion of hydrogen needed there. The disadvantage of this method is that the gas coming from the reaction chamber first has to be cooled because of the method used in the gas purification. Depending on the tar content in this gas, the heat can, in some circumstances, only be used up in a temperature of about 300"C to 400"C; the heat still contained above that is wasted. The part of the purified gas which is returned to the reaction chamber for the carbonization and/or partial gasification must again be heated to as high a temperature as possible. in order to keep partial combustion processes as low as possible, either during the carbonization and/or the partial gasification. On the other hand, it is not necessary for the gas conveyed to the reaction chamber to be freed of tar etc.; it is sufficient for the hydrogen sulphide to be largely extracted from the gas.

According to another proposal, which is the subject of our British Patent Application 51170/77 (Serial No 1 590 995), the coke dust yielded during the carbonization and/or partial gasification is subjected to further desulphurization by aftertreatment by means of gases containing hydrogen but free of hydrogen sulphide.

Methods are also known wherein limestone (or dolomite) is introduced together with the coal into the fluidized bed of a carbonization or gasification reaction chamber, to absorb the hydrogen sulphide formed in this chamber.

Proposals are also known, wherein these substances are introduced into the reaction chamber separately from the coal dust. They have in common the disadvantage, however, that limestone and dolomite have to be removed with the coke formed or the ash still containing carbon. If such coke or carbon and ash are to be burned in the steam generator of a power station, the limestone or dolomite or a substantial proportion thereof are also introduced into this steam generator.

They lead to contamination in the steam generator which endangers the operational reliability of this part of the installation.

It has also been proposed already to make the grain size of the limestone or dolomite introduced into one or two fluidized beds disposed one above the other so large in comparison with that of the coal dust that the resulting coke dust is separated from the dolomite or limestone by sieving. Since abrasion occurs in all processes in which solids move, generally in a manner which cannot be controlled or cannot be controlled well, even with these proposals so much additive comes together with the coke dust into the combustion chamber of a steam generator, that here, too, the contamination phenomena can have undesirable consequences.

It is therefore the object of the present invention to indicate a method which renders it possible to desulphurize the gas yielded during the rapid carbonization and/or partial gasification of coal dust, at high temperatures, to such an extent that it can be returned, without cooling, to the carbonization and/or partial gasification chamber, and also possibly, for example to an aftertreatment chamber for the further desulphurization of coke dust.

According to the present invention, there is provided a method for the far-reaching desulphurization of gas yielded during the rapid carbonization and/or partial gasification of coal dust, characterised in that, after separation of the coke dust and hot gas formed during the rapid carbonization and/ or partial gasification, a portion of the hot gas is passed in periodic flow through reaction chambers which are filled with dolomite, limestone or other substances which absorb sulphur from sulphurous gases to effect a farreaching desulphurization of said portion of the hot gas, said portion of the hot gas being used as heating or carrier gas for the rapid carbonization and/or rapid partial gasification and/or for contact with the coke dust to effect a far-reaching desulphurization thereof, while the rest of the gas from the rapid carbonization and/or partial gasification is supplied, after cooling, to gas purification means.

According to the present invention, only the portion of the gas which is needed as heating or carrier gas in the carbonization and/or partial gasification and/or for the aftertreatment of the previously desulphurized coke dust or as gas for the enrichment of gases with hydrogen is treated with dolomite, limestone or other sulphur absorbing substances at the temperature at which it emerges from the carbonization and/or partial gasification. The rest goes, directly after cooling, to the gas purifying plant, where all by-products etc. are removed from the gas.

The additives necessary for the treatment of the gas are used with such a grain size that the treatment can be effected in a stationary or moving pile, in a fluidized bed or during pneumatic conveying through the gas to be treated itself. A separator for separating gas from dolomite, limestone or other sulphur absorbing substances follows, particularly with the last two methods.

Since dolomite, limestone and other sulphur absorbing substances can be regener ated. it is proposed, in a further development of the invention, that treatment chambers filled with additives should be made at least in duplicate so that, after the additives have become saturated in one treatment chamber, the flowing gas can be switched over to a second, so that the regeneration of the saturated additive can be effected in the first treatment chamber.

The gas to be treated should be desulphurized to an H2S content of about 0.1% by volume. It is not necessary to remove other substances contained in the gas.

The proposed invention can also be used in other fields, for example where coke dust produced during the rapid carbonization and/or partial gasification is to be aftertreated for further desulphurization. With this method, coke dust from the rapid carbonization and/or partial gasification is further treated with gases containing hydrogen over a period of up to a maximum of 2 hours for further desulphurization at temperatures which generally lie between 800"C and 950"C. The gas treated with dolomite, limestone or other sulphur absorbing substances immediately after the separation of gas and coke dust may also be used as a treatment gas here, so that it can be used in the treatment chamber for the further desulphurization practically at the temperature at which it emerges from the carbonization and/or partial gasification process.

The advantages of the invention are: saving heat losses by recycling at least some of the gas produced during the rapid carbonization and/or partial gasification, separated from the coke dust produced and largely freed of H2S in the carbonization and/or partial gasification chamber at substantially the same temperature as when it emerged, saving of costs for cooling and heating apparatuses, possible use of the gas cleansed of hydrogen sulphide, not only in the method for rapid carbonization and partial gasification but also, for example, in the method for the aftertreatment of coke dust produced during the rapid carbonization and/or partial gasification for far-reaching desulphurization or for other high temperature applications.

WHAT WE CLAIM IS: 1. A method for the far-reaching desulphurization of gas yielded during the rapid carbonization and/or partial gasification of coal dust, characterised in that, after separation of the coke dust and hot gas formed during the rapid carbonization and/or partial gasification, a portion of the hot gas is passed in periodic flow through reaction chambers which are filled with dolomite, limestone or other substances which absorb sulphur from sulphurous gases to effect a fear-reaching desulphurization of said portion of the hot gas, said portion of the hot gas being used as heating or carrier gas for the rapid carbonization and/or rapid partial gasification and/or for contact with the coke dust to effect a far-reaching desulphurization thereof, while the rest of the gas from the rapid carbonization and/or partial gasification is supplied, after cooling, to gas purification means.

2. A method as claimed in claim 1 characterised in that two reaction chambers filled with dolomite, limestone or other sulphur absorbing substances are connected in parallel, the gas to be desulphurized flowing through the one chamber during which the sulphur compounds are transferred to the dolomite, limestone or other sulphur absorbing substances, while the sulphur compounds previously absorbed are driven off in the other chamber.

3. A method as claimed in claim 1 or 2, characterised in that the grain size of the dolomite, limestone or other sulphur absorbing substances is selected so that the treatment is carried out in the reaction chamber for the desulphurization of the gas in a stationary or moving pile, in a fluidized bed or during the pneumatic transport through the gas to be treated, and after treatment of the gas, a separation of treated gas and any dolomite, limestone or other sulphur absorbing substances which may have been entrained by the gas is effected in a separator.

4. A method for the far-reaching desulphurization of gas yielded during the rapid carbonization and/or partial gasification of coal dust, as claimed in claim 1 and substantially as hereinbefore described.

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

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. treatment chamber. The gas to be treated should be desulphurized to an H2S content of about 0.1% by volume. It is not necessary to remove other substances contained in the gas. The proposed invention can also be used in other fields, for example where coke dust produced during the rapid carbonization and/or partial gasification is to be aftertreated for further desulphurization. With this method, coke dust from the rapid carbonization and/or partial gasification is further treated with gases containing hydrogen over a period of up to a maximum of 2 hours for further desulphurization at temperatures which generally lie between 800"C and 950"C. The gas treated with dolomite, limestone or other sulphur absorbing substances immediately after the separation of gas and coke dust may also be used as a treatment gas here, so that it can be used in the treatment chamber for the further desulphurization practically at the temperature at which it emerges from the carbonization and/or partial gasification process. The advantages of the invention are: saving heat losses by recycling at least some of the gas produced during the rapid carbonization and/or partial gasification, separated from the coke dust produced and largely freed of H2S in the carbonization and/or partial gasification chamber at substantially the same temperature as when it emerged, saving of costs for cooling and heating apparatuses, possible use of the gas cleansed of hydrogen sulphide, not only in the method for rapid carbonization and partial gasification but also, for example, in the method for the aftertreatment of coke dust produced during the rapid carbonization and/or partial gasification for far-reaching desulphurization or for other high temperature applications. WHAT WE CLAIM IS:

1. A method for the far-reaching desulphurization of gas yielded during the rapid carbonization and/or partial gasification of coal dust, characterised in that, after separation of the coke dust and hot gas formed during the rapid carbonization and/or partial gasification, a portion of the hot gas is passed in periodic flow through reaction chambers which are filled with dolomite, limestone or other substances which absorb sulphur from sulphurous gases to effect a fear-reaching desulphurization of said portion of the hot gas, said portion of the hot gas being used as heating or carrier gas for the rapid carbonization and/or rapid partial gasification and/or for contact with the coke dust to effect a far-reaching desulphurization thereof, while the rest of the gas from the rapid carbonization and/or partial gasification is supplied, after cooling, to gas purification means.

2. A method as claimed in claim 1 characterised in that two reaction chambers filled with dolomite, limestone or other sulphur absorbing substances are connected in parallel, the gas to be desulphurized flowing through the one chamber during which the sulphur compounds are transferred to the dolomite, limestone or other sulphur absorbing substances, while the sulphur compounds previously absorbed are driven off in the other chamber.

3. A method as claimed in claim 1 or 2, characterised in that the grain size of the dolomite, limestone or other sulphur absorbing substances is selected so that the treatment is carried out in the reaction chamber for the desulphurization of the gas in a stationary or moving pile, in a fluidized bed or during the pneumatic transport through the gas to be treated, and after treatment of the gas, a separation of treated gas and any dolomite, limestone or other sulphur absorbing substances which may have been entrained by the gas is effected in a separator.

4. A method for the far-reaching desulphurization of gas yielded during the rapid carbonization and/or partial gasification of coal dust, as claimed in claim 1 and substantially as hereinbefore described.