SK915086A3 - Removal method of harmful substances from waste gases - 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

Method of removing pollutants from waste gases

Technical field

The invention relates to a method for dry removal of pollutants such as sulfur dioxide, hydrochloric acid, chlorine, hydrogen fluoride and heavy metals from the waste gases of the stone and soil processing industry.

BACKGROUND OF THE INVENTION

Using known wet scrubbing processes, the gases, usually after dust removal, are treated with the liquid circulating in the circuit and cooled to the extent that they are again necessary to a temperature in excess of about 20 ° C to prevent damage due to corrosion. The dropping amount of reaction products is generally as much too large as it would be possible to return the entire amount to the production process. Therefore, wet scrubbing processes are most often associated with high equipment and operating costs, which often hinder a continuous waste gas treatment reaction.

In the manufacture of cement, attempts have already been made to purify the waste gases at a temperature of 300 to 850 ° C in the dry state. However, it has become clear that, at temperatures above 500 ° C, the waste gases often contain less than 100 mg / Nm ³ of SO ₂ , which is at the forefront of the pollutants, since most of the sulfur introduced into the production process together with the fuel is absorbed. raw cement powder and bound in clinker.

However, such favorable ratios do not occur in other combustion processes in the industrial processing of stone and soil. There, pollutants other than chlorides and fluorides must be removed from the waste gases, rather than the sulfur contained in the fuel, and the product itself does not have any worth mentioning ability to absorb.

In the cement production process, however, sulfur is also carried into the combustion process by the raw powder. The sulfur is derived in part from organic sulphide or sulfur compounds to be at low temperatures disintegrate during the preheating and result in the release of sulfur dioxide S0 _2, wherein the content of sulfur dioxide may be up to 6000 mg / ^Nm3. As a result, the the process of the cement, the usual temperatures of the waste gases there virtually no uptake of sulfur dioxide _SO2 raw material, it must be the cement plant provided with zariadaním desulfurization waste gases, while the sulfur is clogged with the fuel, depending on the The process is only contained in the waste gases in a minimal amount.

Dry cleaning at 200 to 400 ° C is independent of the sorbent used and independent of the sorbent to pollutant ratio, but is also not very effective. Usually, only less than 60% of the pollutants can be removed from the waste gas, but unless they want to switch to expensive and high dust levels, the only way to do this is to use an operationally safe method of cleaning under certain conditions.

Thus, it is an object of the present invention to provide a process for the removal of pollutants from the waste gases of the combustion processes of industrial stone and soil processing, which is generally applicable and more economical than the known methods.

catalysts.

SUMMARY OF THE INVENTION

Surprisingly, it has been found that this objective can be achieved if the waste gases are brought into contact with a sorbent consisting of a stream of solid particles at 50 to 100 ° C in a fluidized bed reactor, the solid particles are degassed and returned to the fluidized bed reactor, As a sorbent, a raw cement powder, limestone containing more than 90% calcium carbonate CaCO 2, quicklime, hydrated lime or partially calcined raw powder is used and a new sorbent is continuously added to the circuit and the spent sorbent is discharged from the circuit.

Preferably, the waste gases are cooled to 50-100 ° C prior to entering the fluidized bed reactor. Alternatively, the waste gases may also be cooled to 50-100 ° C in a fluidized bed reactor by water injection. In addition, it is remembered that the temperature in the fluidized bed reactor and the addition of sorbent are controlled depending on the pollutant content of the pure gas. A further advantage of the process is that the sorbents discharged from the circuit can be recycled to the cement production process without further delay. Preferably, the solid particles are separated from the gas stream in a conventionally operating solids separator, in particular a multipole electrofilter, whereby the finely divided solids enriched with heavy metals are discharged and used as an additive of ready-made cement clinker.

With the method according to the invention, not only can the contact times, which are often too short for other dry cleaning processes at the lower temperature range, be prolonged arbitrarily, but also a product that does not require any particular further processing or depositing is obtained. .

Overview of the drawings

Further details are explained by way of an example of the desulfurization of cement waste gases and by way of a method diagram in FIG. First

The manufacturing process illustrated in the Examples

The solids circulating system, consisting of the fluidized bed reactor 1, the solids separator 2 and the return line 3, is supplied with water for atomisation, through the line 5 with sorption means and through the line 7 with the waste gas to be desulfurized. The maximum desulphurized waste gas exits the fluidized bed reactor 1, is freed from dust in the solids separator 2 and enters the stack through the blower device 8 and the line 9. A conveyor device is arranged below the solids separator 2, by means of which the separated dust is conveyed to the return line 3 and finally fed back to the fluidized bed reactor 1. Part of the quantity of circulating solids is discharged through the line 7 to the solids at a suitable location. is fed to cement production.

The components contained in the residual substance, for example heavy metals, can be discharged via line 10 after selective separation from the other substances. The waste gases leave at a temperature of 100 to 450 ° C, depending on whether and which heat recovery equipment is arranged (boiler). for waste heat, hot water preparation, mill). If the gases are not passed through the mill, their dust content is 100 g / Nm ³ .

In the latter, up to 1000 g / Nm ^3, and normally dust by case, the dust load may make sense to remove the electrofilter or mechanical separator in order to limit the circulation of solids in the circulation system to solids to an amount that is optimal for desulphurisation.

It is also possible, in such cases, to dispense wholly or in part with the special addition of sorbents. The dust content of the waste gases is reduced in the solids separator 2 to an amount of less than 50 mg / Nm ³ .

The sulfur dioxide content of the SO ₂ in the waste gas is up to 6000 mg / Nm ³ , depending on the composition of the raw material. This can be reduced in the pure gas by the process according to the invention up to a value of less than 50 mg / Nm ³ . The permissible amount of sulfur dioxide according to the statutory regulations in Germany range of about 400 mg / Nm ^3, Switzerland about 500 mg / ^Nm3.

A further advantage of the method is that fuels which contain heavy metals, including class I pollutants such as cadmium, thallium, mercury or the like, can also be used in the combustion process to improve economy. In the fluidized bed reactor 1, these pollutants are predominantly bound to particularly fine-grained particles and can be almost completely separated from other residual substances in a classically operating solids separator 2, for example in a multipole electrofilter, and independently of the reaction products brought back into the cement production process. .

The solid particles carried in this way show, on the one hand, a high concentration of pollutants, but, on the other hand, only a small amount of all the reaction products falling off. These may - if not harmful to the particular product of the combustion process - be recycled at a suitable point in the product production process, since they are themselves bound stably and are not soluble in water. In the manufacture of cement, it is possible to mix them in grinding clinker or cement. Alternatively, the treatment for recovering the pollutants in metallic or otherwise useful form is also contemplated. With the method according to the invention it is possible to separate 90% of the pollutants from the waste gases and to ensure that they do not burden the environment.

The process according to the invention was used in a cement production plant with two rotary kilns which are loaded with 800 or 1500 tons of cement clinker. In total, 100,000 to 260,000 Nm ^{3 of} waste gas having a temperature of 85 to 160 ° C and a dust content of 700 to 1000 mg / Nm ^{3 were} dropped per hour. In addition, the waste gas per Nm ³ contained 2000 to 3600 mg of SO ₂ , 200 to 250 mg of HCl and 80 to 100 mg of HF, as well as small quantitatively non-quantifiable amounts of mercury and cadmium.

By spraying water immediately above the inlet region, which extends in the manner of a venturi nozzle, of the fluidized bed reactor, the waste gases were cooled to 60-70 ° C. At about the same point of the inlet region, a sorbent consisting of particulate solids was added to the fluidized bed reactor, while the sorbent was returned to the fresh sorbent per hour about 300 kg of calcium hydrate and about 2000 kg of cement raw powder per hour. .

The purified waste gas contained Nm ^{3 of} less than 50 mg of dust, less than 400 mg of SO ₂ , less than 5 mg of HCl and less than 1 mg of HF.

Claims (2)

The method of dry removal of pollutants from combustion processes and fine-grained soils is used in the production of limestone with more hydrate calcium raw powder, 1. The fuel gases from the stone processing are contacted with or contacted with powder, lime, in which the waste gas is absorbed by the sorbent produced by the cement, in particular raw material such as 90% CaCO3, burnt or partially calcined. a cementitious reactor comprising a fluidized bed reactor and a solids separator connected to the fluidized bed reactor, characterized in that the waste gas (S) is passed upstream through a fluidized bed of sorbent having a temperature of 50 ° C. up to 100 ° C, which is controlled by water injection, a mixture consisting of off-gas and solids is withdrawn from the fluidized bed, leading to a solids separator, and solids containing spent sorbent are removed from the solids separator back into the fluidized bed, forming a circulating solids system. The process according to claim 1, characterized in that the waste gas is cooled to a temperature of 50 to 100 ° C before entering the fluidized bed.