DK165736B - PROCEDURE FOR THE REMOVAL OF HARMFUL MATERIALS FROM COGAS - Google Patents

Abstract

1. A process for the dry removal of polluants from the exhaust gases of combustion processes in the processing of stones and earths, characterised in that the exhaust gases are brought into contact with a sorbent in the form of solids particles at 50 to 100 degrees C in a solids circulation system formed by a fluidised bed reactor (1), a solids separator (2) and a recycling line (3), and that the laden sorbent is completely or almost completely supplied to a cement production process.

Description

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The present invention relates to a process for the dry removal of noxious substances from the flue gases from combustion processes in the silicate industry, especially in cement production. In order to satisfy the debt environmental regulations, plants in the silicate industry are increasingly equipped with devices for separating harmful gases.

In the known wet cleaning process, after a dust removal, the flue gases are usually treated with a circulating wash liquid and cooled so much that a reheat to approx. 20 ° C above the dew point becomes necessary to avoid corrosion damage. The resulting amount of reaction products is also generally too large for it to be returned in its entirety to the manufacturing process. Wet cleaning procedures are therefore usually associated with large construction and operating costs, often counteracting a consistent realization of the flue gas cleaning.

In the manufacture of cement, attempts have also already been made to stir the flue gases dry at 300 to S30 ° C. Hereby, however, it has been found that at temperatures above 500 ° C, the flue gases frequently contain less than 100 mg / Nin of the principally harmful substance SC 2, while most of the sulfur introduced into the temperature range by the fuel in the cement-making process adsorbed by the raw flour and bound in the clinker.

Such favorable conditions do not exist in other firing processes in the silicate industry. There, besides the fuel sulfur, other harmful substances such as chlorides and fluorides must be removed from the flue gas without the actual product exhibiting a significant adsorption capacity for the harmful substances.

In the cement-making process, however, sulfur is also introduced into the combustion process through the raw flour. This sulfur is partly derived from organic or sulphidic sulfur compounds which are already decomposed by

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2 low temperatures and leads to the release of SO2 during the pre-steaming of the raw flour, whereby SO3 content of up to 6000 mg / Nm can occur. Since, at the usual flue gas temperatures in the cement process, practically no adsorption of SO2 by the feedstock is effected, a flue gas desulphurisation device must also be provided, although the sulfur introduced sulfur is subject to the process only for a minor part. flue gas.

10 Dry cleaning at temperatures of 200 to 400 ° C

however, independent of the adsorbent used and independent of the ratio of adsorbent to harmful substances, is not very effective. In general, only less than 60% of the harmful substances can be removed from the flue gas if one does not want to switch to expensive and, because of the usually large amount of dust, only conditional reliable cleaning processes with catalysts.

Thus, the object is to propose a method for removing harmful substances from the flue gases from firing processes in silicate industries, which are generally applicable and more economical than the known methods.

The process according to the invention is characterized in that the flue gases in a solid circulation system formed by a vortex reactor, a solid separator and a return line formed at 50 to 100 ° C are contacted with an adsorbent in the form of solid particles and when the resulting product is supplied completely or almost completely. a cement-making process.

With the process of the invention, not only can it be arbitrarily increased arbitrarily in other low-temperature drying processes frequently for short contact time, but also a product which requires no special processing or deposition, which, with the economics of the usual methods, is often very congested.

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3 The flue gases preferably have a temperature of from 50 to 100 ° C prior to flow into the solid-state circulation system. If this is not possible, the flue gases can also be cooled to 50 to 100 ° C in the vortex reactor by injection of water. Since in silica burning systems, there is usually a final dust separator, it can be used as a solid separator in the solid circulation system.

The main advantage of the process according to the invention consists in the use of adsorbents used in the manufacture of cement materials such as raw flour, limestone with more than 90% CaCOg, burnt lime, lime hydrate or partially calcined raw flour, which can then be added again to a cement-making process. .

Finally, it is also preferred that the temperature of the fluidized bed reactor is controlled to an optimum value and the adsorbent addition is adjusted depending on the content of harmful substances in the purified gas.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail with reference to the desulfurization of flue gases from a cement-making process, with reference to the drawing, in which fig. 1 shows a simplified reproduced process flow image.

The solids circulation system of a fluidized bed reactor 1, a solid separator 2 and a return line 3 is supplied via a conduit 4 atomizing water, via a conduit 5 adsorbent and via a conduit 6 the flue gas to be desulfurized. The largely desulfurized flue gas leaves the vortex reactor 1 30 at the top, is freed from the solid dust separator 2 for dust and comes to the chimney via a blower 8 and a conduit 9.

Underneath the solid separator 2 is arranged a transport device by which the separated dust is transported to the return line 3 and finally again discharged into the fluidised-bed reactor 1. A subset of the circulating solid particles is discharged via a conduit 7 from the solid.

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the fabric circulation system and is applied to the cement manufacturing process at a suitable location.

Some components contained in the solid, e.g. heavy metals, after selective separation can be carried out separately from the other substances via a conduit 10.

The flue gases occur, depending on whether and which heat recovery devices (waste heat boiler, hot water preparation, mill) are provided, with a temperature of from 100 to 450 ° C. Their dust content is 10 to 100 g / Nm 2 when not passed over a mill. In the latter case, the dust load may be up to 1000 g / Nm, and a prior dust removal by means of an electro-filter or mechanical separator may be appropriate in order to limit the solids circulation in the solids circulation system to the optimum amount of desulphurisation. Optionally, in such cases, the separate addition of adsorbents may be disregarded. The dust content of the flue gas is reduced in the solid separator to less than 50 mg / Nm 2.

The content of SO 2 in the flue gas varies according to the raw material composition up to 6000 mg / Nm. It can be lowered to a value less than 50 mg / Nm 2 in the purified gas by the process of the invention. The permissible levels of SO ~ are currently 3 400 in Germany at 400 mg / Nm and in Switzerland at 500 3 mg / Nm.

A further advantage of the method is that, in order to improve the economy of the burning processes, such fuels containing heavy metals including harmful Class I substances such as cadmium, thallium, mercury and similar metals can also be used.

These harmful substances are predominantly bonded in the fluidized-bed reactor to the particularly fine-grained solid particles and can, in a classy working solid separator, e.g. a multi-field electrofilter, is separated almost completely from the other residues and is excreted un-

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depending on the reaction products returned to a cement manufacturing process.

The solid particles thus extinguished have, on the one hand, a high concentration of noxious substances, but on the other hand constitute only a small amount of the total reaction products. They may, to the detriment of the product of the burning process in question, be returned to a suitable location in the product-making process where they themselves are bonded rigidly and water-insoluble. In the cement manufacture, it appears to mix them in the clinker or cement grinding. Optionally, a treatment for the recovery of the harmful substances in metallic or other useful form is also considered. By the method of the invention, 90% of the said harmful substances can be separated from the flue gas and disposed of in an environmentally friendly manner.

The process of the invention was experimentally used in a cement manufacturing plant. The sulphite content of the feedstock was 0.3 to 0.4% relative to the weight of the feedstock, whereby the SO . Using the process, the SO 2 content could be lowered to values clearly below 400 mg / Nm. As the adsorbent, crude flour to which there was mixed lime flour in an amount such that approx. 50% of the stoichiometric required calcium was thereby met.

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Claims (7)

Method for dry removal of noxious substances from the flue gases from burning processes in the silicate industry, characterized in that the flue gases in a solids circulation system (50) formed in a fluidized bed reactor (1), a solid separator (2) and a return line (3) ° C is contacted with an adsorbent in the form of solid particles and the product obtained is fed to a cement-making process. Process according to claim 1, characterized in that the flue gases are cooled to 50 to 100 ° C before entering the solid-state circulation system. Process according to claim 1, characterized in that the flue gases in the vortex reactor (1) are cooled to 50 to 100 ° C by injection of water. Process according to any one of claims 1 to 3, characterized in that as the solid separator (2), the final dust separator present in a combustion plant is used. Process according to any one of claims 1 to 4, characterized in that as the adsorbent is used for the preparation of cement used materials such as raw flour, limestone with more than 90% CaCO 2, burnt lime, 25 hydrate or partially calcined crude flour. Process according to any one of claims 1 to 5, characterized in that the temperature of the fluidized-bed reactor is controlled by injection of water and the adsorbent addition depending on the content of harmful substances in the purified gas. Process according to any one of claims 1 to 6, characterized in that the solids are separated from a classifying working solid separator, preferably a multi-field electrofilter, and that the fine grained with heavy metals, in particular of class I, enriched the solid clinker at a cement manufacture or a separate treatment process.