SK278406B6 - Removing method of harmful substances from waste gases - Google Patents

Abstract

The procedure described in this patent is based on that principle, that the waste gas is directed up to the fluid layer created based on the sorbent and this layer indicates the temperature of 50 up to 100 Celsius degrees which is controlled with use of water injection, the mixture is exhausted of the mentioned fluid layer, this mixture contains of waste gas and solid substances and it is directed to the separator solid substances and the solid substances containing the exhausted sorbent are led of the solid substance separator back to the fluid layer and the reflux system of solid substances is created, as a result of that. The waste gas is cooled properly, to have a temperature 50 up to 100 Celsius degrees, before it is getting in the input closed to the fluid layer.

Description

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 waste gases, usually after dust removal, are treated with the liquid circulating in the circuit and cooled to the extent that they need to be reheated to a temperature above about 20 ° C to prevent melting. corrosion damage. The dropping amount of reaction products is generally also too large to be returned to the production process. Wet scrubbing processes are therefore most often associated with high equipment and operating costs, which often hinder a continuous waste gas cleaning reaction.

In the manufacture of cement, attempts have already been made to purify the waste gases at a temperature of 300 to 850 ° C dry. However, it became apparent that, at temperatures above 500 ° C, the waste gases often contained 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 fuel is absorbed by the crude cement powder and bound in clinker.

However, such favorable proportions do not occur in other combustion processes in the industrial processing of stone and soil. There, the 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 has no worth mentioning ability to absorb the pollutants.

In the cement production process, however, sulfur is also carried into the combustion process by the raw powder. This sulfur originates in part from organic or sulphide sulfur compounds which decompose already at low temperatures and lead to SO ₂ evolution during preheating, with sulfur dioxide contents of up to 6000 mg / Nm ³ . As a result, the the process of the cement, the conventional exhaust gas temperature there virtually no uptake of sulfur dioxide _SO2 raw material, must be the cement plant provided with a device for desulfurization of waste gases, while the sulfur is clogged with the fuel, according to the of the process is contained in the waste gases only 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 off-gas, unless, however, to switch to expensive and, in view of the most commonly occurring, high dust levels, only under certain conditions an operationally safe catalyst cleaning process.

Thus, the task is to propose a method for removing pollutants from the waste gases of the combustion processes of industrial stone and soil processing, which would be generally applicable and more economical than the known methods.

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 solid particles at 50-500 ° C in a fluidized bed reactor, the solid particles are separated from the gas stream and returned to the fluidized bed reactor. For example, raw cement powder, limestone containing more than 90% calcium carbonate CaCO ₃ , quicklime, hydrated lime or partially calcined feedstock powder are used as sorbent 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 the sorbent are regulated in dependence on the pollutant content of the pure gas. A further advantage of the process is that the sorbents removed from the circuit can be recycled to the cement production process without further action. Preferably, the solids particles are separated from the gas stream in a conventionally operating solids separator, in particular a multi-pole electrostatic filter, from which the fine-grained solids enriched in heavy metals are discharged and used as an additive to the finished cement clinker.

With the method according to the invention, not only can the contact time, which is often too short for other dry cleaning processes at the lower temperature range, be arbitrarily prolonged, but also a product which does not require any particular further processing or depositing is obtained. the prior art35 bov.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details are explained by way of an example of the desulfurization of the waste gases from the cement production process and by means of the process diagram shown in simplified form in FIG. First

DETAILED DESCRIPTION OF THE INVENTION

The solids circulation system, consisting of a fluidized bed reactor 1, a solids separator 2 and a 50 return line 3, is supplied with water for atomization, via a line 5 with sorption means and via a line 7 with 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 conveying 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 60 of the amount of circulating solids is discharged via line 7 from the solids circulation system and a suitable it is brought to the cement production site.

The individual components contained in the residual substance, for example heavy metals, can be discharged through line 10 after selective separation 65 from the other substances. The waste gases leave at a temperature of 100 to 450 ° C, depending on whether and which heat recovery devices are arranged ( waste heat boiler, hot water preparation, mill). If the gases are not passed through the mill, their dust content is 100 g / Nm ³ . In the latter case, the dust load can be up to 1000 g / Nm ³ and it may make sense to remove the preliminary dust by means of an electrofilter or mechanical separator in order to limit the solids circulation in the circulation system to solids to an amount optimal for desulfurization. Optionally, 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 less than 50 mg / Nm ³ .

The SO ₂ content of 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 in accordance with the regulations in Germany range of about 400 mg / Nm ^3, Switzerland about 500 mg / ^Nm3.

A further advantage of the process 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 particles and can be almost completely separated from other residual substances in a conventional working solids separator 2, for example in a multi-pole electrofilter, and independently of the reaction products fed back to 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 - unless this is not detrimental to the product of the combustion process at the appropriate point - be returned to the production process of the product, since these are themselves bound stably and are not soluble in water. In cement production, it is possible to mix them in grinding clinker or cement. Depending on the circumstances, treatment for recovering the pollutants in metallic or otherwise usable 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 tonnes 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 was} 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, quantifiable amounts of mercury and cadmium.

By spraying water immediately above the inlet region, which extends in the manner of a Venturi nozzle, a 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 solid particles was added to the fluidized bed reactor, and the sorbent removed back was added per hour 2000 to 2300 t and fresh sorbent per hour about 300 kg calcium hydrate and about 2000 kg cement raw powder .

The purified waste gas contained less than 50 mg of dust per Nm ³ , less than 400 mg of sulfur dioxide

SO ₂ , less than 5 mg of HCl and less than 1 mg of HF.

Claims (2)

Process for dry removal of pollutants from waste gases from combustion processes of industrial processing of stone and soil, in which the waste gas is contacted with a fine-grained sorbent produced or used in the production of cement, in particular raw powder, limestone with more than 90% CaCO ₃ , quicklime, calcium hydrate or partially calcined feedstock powder, wherein the adsorbed sorbent is returned completely or almost completely to the cement production, using a fluidized bed reactor and a solids separator connected to the fluidized bed reactor. characterized in that the waste gas (6) is passed through a fluidized bed of sorbent having a temperature of 50 to 100 ° C, which is controlled by the injection of water, and a mixture consisting of waste gas and solids is withdrawn from the fluidized bed. and leads to a solids separator and solids content When the sorbent is exhausted, it is returned from the solids separator back to the fluidized bed to form a solids circulation system. Process according to claim 1, characterized in that the waste gas is cooled to 50 to 100 ° C before entering the fluidized bed.