GB1589999A - Process and plant for the treatment of flue gases for example flue gases from power stations which are fuelled by fossil fuels especially by coal - Google Patents

Description

(54) PROCESS AND PLANT FOR THE TREATMENT OF FLUE GASES. FOR EXAMPLE FLUE GASES FROM POWER STATIONS WHICH ARE FUELLED BY FOSSIL FUELS, ESPECIALLY BY COAL (71) We, STEAG AG, a German Company, of Bismarckstrasse 54, 4300 Essen, 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 per.

formed, to be particularly described in and by the following statement: The invention relates to a process for the treatment of flue gases, for example flue gases from power stations which are fired with fossil fuels, especially by coal, in which before the gases are released into the atmosphere, all or part thereof are subjected to dust removal, for example by electrostatic filters or cyclone separators, and to gas cleansing. The invention also relates to a plant for carrying out this process.

The object of such processes and plants is the removal of specific materials or chemical compounds from the flue gases before they are emitted into the atmosphere. On the one hand, it is a matter of separating sulphur compounds, namely SO2 and SO3, from the flue gases so that these compounds cannot for their part pollute or damage the environment. On the other hand, dust particles must in increasingly high percentages be removed from the gases.

The treatments mentioned above are well known. In particular, a process is known in which the flue gases are passed first to electrostatic filters from which in many of these plants the gases emerge with a dust content of 100 to 150 mg/m3 (in the normal state). A drawback is the exceptionally high cost of such electrostatic filters.

Only a fraction of these costs are attributable to the electrostatic filters of other known plants which, on the basis of their low degree of removal, produce a dust output of about 600 mg/m (in the normal state). On the other hand, these quantities are too high as an emission to atmosphere and can consequently no longer suffice in view of the higher requirements in respect of emission protection. Moreover, electrostatic filters operate particularly effectively with average to high SO3 content, so that for this reason a high sulphur content in the gases is desirable.

It is known that outlet gases with a low acid dew point can be dedusted by cloth filters. This also holds good for power stations, which use a coal with a low sulphur content. The use of cloth filters is only economical, however, if it is possible to choose the filter material according to the gas temperatures. The filters which are applicable for this purpose are, however, sensitive to certain gaseous components in the gases. For instance, certain artificial fibres or fabrics are only stable if the gases have no S03 admixtures. Glass fibres are not resistant to fluoride but otherwise can be used up to 2000C.

Gas cleansing of known plants operates mostly by wet processes. Dry processes are, however, also known. In some of these processes the gas temperatures are below the actual gas cleansing at 4000C; for instance, this is the case with processes in which there is an adsorption of the sulphur on metal oxide.

Other processes desulphurise the gases at 1000 to 300 C. In fluidised bed desulphurisations with limestone; temperatures reach about 900"C. Such processes have the advantage that no loss of temperature in the flue gases is connected with the gas cleansing. Drawbacks are incurred, especially with the methods of gas flow met with in practice, because of the relatively high dust content of the washed gases. Depending on the form of the adsorption, on the loss in pressure, on the size of the waste and on other factors, certain degrees of dedusting cannot be exceeded. It must, however, be borne in mind in this connection that with high dust content in the gases downstream of the simple electrostatic filters of such a plant, the dust content in the purified gases rises and, consequently, the dust content of the purified gas may exceed the limiting values of the highly efficient electrostatic filters described above, and even also the permissible emission values.

At the basis of the invention is the problem of further noticeably reducing damage to the environment from the power stations described above by considerably reducing, in an economical manner, the dust content of gases emitted into the atmosphere.

According to the invention, this can be achieved by a process in which the untreated flue gases are subject to a first coarse dust removal step and then cleansed by the dry separation of 502/503 and/or fluorine compounds, and the so purified gases, or a partial stream thereof, are subjected to a further and relatively fine dust removal step through a cloth filter to remove remaining dust before the gases are released into the atmosphere.

By using the dry gas cleansing processes known per se after the filters effecting the first dust removal, which filters are in principle arbitarily designable, one profits from the special properties of the dry gas cleansing to provide desulphurised and dry gases which can be further dedusted in the subsequent further dust removal by cloth filters. For the truly high temperatures of the gases thus treated can be withstood by durable filter materials because the harmful gas components have been previously removed and the relatively high dust content at the outflow from the gas cleansing, viz in the cloth filters, can be reduced to the desired value. The economy of the process according to the invention also results from the possibility of using a simple first dust filter stage and on the possibility of selecting the fine filter materials.

According to the invention, therefore, compared with the well-known plants, at the input end of the plant, that is to say in the first worse dust filtering stage, one is working not with higher but rather with lower degrees of separation, and the following gas cleansing installation may also produce higher dust contents. Nevertheless, the final dust content of the gases is substantially reduced as compared with known plants without this leading to higher costs. This is due on the one hand to the cheapened first filtering stage and to the favourable utilisation conditions for the subsequent cloth filters brought about in the desulphurisation installation. These filters deliver purified gas dust contents with an order of magnitude of less than 10 mg/m3 (in the normal state).

Plant in accordance with the invention is schematically illustrated in the accompanying block diagram and will now be described, by way of example, with reference thereto.

The flue gases emerge from the power station, i.e. from the boiler furnaces thereof with a dust content of 10 to 15 mg/m3 (in the normal state), that is with a very high dust content. They then pass into arbitrarily designed filters, for example cyclone separators and/or electrostatic filters, where the gases are subjected to a first coarse dust removal step.

This part of the plant can be designed to be of suitably low capital cost. The gases emerge from this first filtering stage with a substantially lower dust content, for example 600 600 mg/m3 (in the normal state). They then pass into a dry gas cleansing installation in which certain components of the gases, especially sulphur and/or fluorine compounds, are removed by a method known per se. At the same time the dust content is reduced in the gas cleansing plant to a value of 100 to 200 mg/m3 (in the normal state).

In the plant according to the invention illustrated in the block diagram, a cloth filter device is inserted after the gas cleansing installation. This cloth filter, in which the cleansed gases are subjected to a further and relatively fine dust removal step, releases the gases with a content not greater than 10 mg/m3 (in the normal state); generally, however, the dust content is substantially lower.

For this reason it is also possible at any given time to subject only partial streams to the processing steps described and to lead other partial streams through the indicated by-pass channels, thus leaving them untreated, and to feed them back into the partial streams treated in the respective installations or equipments.

WHAT WE CLAIM IS: 1. A process for the treatment of flue gases, for example flue gases which are fired by fossil fuels, especially by coal, in which the untreated flue gases are subjected to a first coarse dust removal step, for example by electrostatic filter or cyclone separator, followed by gas cleansing wherein the gases are cleansed by the dry separation of SO2 /SO3 and/or fluorine compounds, and the so purified gases, or a partial stream thereof, are subjected to a further and relatively fine dust removal step through a cloth filter to remove remaining dust before the gases are released into the atmosphere.

2. A process according to Claim 1, wherein the flue gases initially have a dust content of approximately 10 to 15 g/m3 and, immediately after the first dust removal have a dust content of approximately 600 mg/m3 prior to the dry gas cleansing after which thegases have a dust content of 100 to 200 mg/m , and the gases after the further dust removal have a dust content not greater than 10 mg/m3.

3. Plant for carrying out the process according to Claim 1 or 2, comprising a first worse dust filter stage adapted to receive untreated flue gases, followed by a gas cleansing installation which effects said dry gas cleansing, and a relatively fine dust filter device which provides said cloth filter disposed downstream of said installation.

5. A process for the treatment of flue gases, substantially as herein described.

6. Plant for the treatment of flue gases, substantially as herein particularly described with reference to the accompanying drawing.

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

Claims (1)

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

   above by considerably reducing, in an economical manner, the dust content of gases emitted into the atmosphere.

   According to the invention, this can be achieved by a process in which the untreated flue gases are subject to a first coarse dust removal step and then cleansed by the dry separation of 502/503 and/or fluorine compounds, and the so purified gases, or a partial stream thereof, are subjected to a further and relatively fine dust removal step through a cloth filter to remove remaining dust before the gases are released into the atmosphere.

   By using the dry gas cleansing processes known per se after the filters effecting the first dust removal, which filters are in principle arbitarily designable, one profits from the special properties of the dry gas cleansing to provide desulphurised and dry gases which can be further dedusted in the subsequent further dust removal by cloth filters. For the truly high temperatures of the gases thus treated can be withstood by durable filter materials because the harmful gas components have been previously removed and the relatively high dust content at the outflow from the gas cleansing, viz in the cloth filters, can be reduced to the desired value. The economy of the process according to the invention also results from the possibility of using a simple first dust filter stage and on the possibility of selecting the fine filter materials.

   According to the invention, therefore, compared with the well-known plants, at the input end of the plant, that is to say in the first worse dust filtering stage, one is working not with higher but rather with lower degrees of separation, and the following gas cleansing installation may also produce higher dust contents. Nevertheless, the final dust content of the gases is substantially reduced as compared with known plants without this leading to higher costs. This is due on the one hand to the cheapened first filtering stage and to the favourable utilisation conditions for the subsequent cloth filters brought about in the desulphurisation installation. These filters deliver purified gas dust contents with an order of magnitude of less than 10 mg/m3 (in the normal state).

   Plant in accordance with the invention is schematically illustrated in the accompanying block diagram and will now be described, by way of example, with reference thereto.

   The flue gases emerge from the power station, i.e. from the boiler furnaces thereof with a dust content of 10 to 15 mg/m3 (in the normal state), that is with a very high dust content. They then pass into arbitrarily designed filters, for example cyclone separators and/or electrostatic filters, where the gases are subjected to a first coarse dust removal step.

   This part of the plant can be designed to be of suitably low capital cost. The gases emerge from this first filtering stage with a substantially lower dust content, for example 600 600 mg/m3 (in the normal state). They then pass into a dry gas cleansing installation in which certain components of the gases, especially sulphur and/or fluorine compounds, are removed by a method known per se. At the same time the dust content is reduced in the gas cleansing plant to a value of 100 to 200 mg/m3 (in the normal state).

   In the plant according to the invention illustrated in the block diagram, a cloth filter device is inserted after the gas cleansing installation. This cloth filter, in which the cleansed gases are subjected to a further and relatively fine dust removal step, releases the gases with a content not greater than 10 mg/m3 (in the normal state); generally, however, the dust content is substantially lower.

   For this reason it is also possible at any given time to subject only partial streams to the processing steps described and to lead other partial streams through the indicated by-pass channels, thus leaving them untreated, and to feed them back into the partial streams treated in the respective installations or equipments.

   WHAT WE CLAIM IS:

   1. A process for the treatment of flue gases, for example flue gases which are fired by fossil fuels, especially by coal, in which the untreated flue gases are subjected to a first coarse dust removal step, for example by electrostatic filter or cyclone separator, followed by gas cleansing wherein the gases are cleansed by the dry separation of SO2 /SO3 and/or fluorine compounds, and the so purified gases, or a partial stream thereof, are subjected to a further and relatively fine dust removal step through a cloth filter to remove remaining dust before the gases are released into the atmosphere.

   2. A process according to Claim 1, wherein the flue gases initially have a dust content of approximately 10 to 15 g/m3 and, immediately after the first dust removal have a dust content of approximately 600 mg/m3 prior to the dry gas cleansing after which thegases have a dust content of 100 to 200 mg/m , and the gases after the further dust removal have a dust content not greater than 10 mg/m3.

   3. Plant for carrying out the process according to Claim 1 or 2, comprising a first worse dust filter stage adapted to receive untreated flue gases, followed by a gas cleansing installation which effects said dry gas cleansing, and a relatively fine dust filter device which provides said cloth filter disposed downstream of said installation.

   5. A process for the treatment of flue gases, substantially as herein described.

   6. Plant for the treatment of flue gases, substantially as herein particularly described with reference to the accompanying drawing.