DK154008B - PROCEDURE FOR CLEANING HOT ROEGGAS FOR SULFUR DIOXIDE OR OTHER UNWANTED ACID GAS COMPONENTS FROM HOT ROEGGAS AND APPARATUS FOR EXERCISING THE PROCEDURE - Google Patents

Description

in

DK 154008 B

The present invention relates to a process for the purification of hot flue gas from sulfur dioxide or other undesirable acidic gas components, in which an absorbent in the form of an aqueous solution or aqueous suspension is contacted with the flue gas while drying the reaction products formed by the absorbent and sulfur dioxide. whereupon the reaction products are separated into a textile barrier filter, and an apparatus for carrying out the method.

Several methods are known for removing sulfur dioxide from flue gas from coal-fired power plants. The most common methods are based on wet cleaning with lime or limestone as absorbent. The gas washer 15 is then usually designed as a tower with nozzles in which large quantities of absorbent liquid are recycled. This is made of finely divided limestone or limestone which, with absorbed sulfur dioxide, forms reaction products in the form of calcium sulphite and sulphate. These compounds are relatively heavily soluble and therefore the washing liquid remains rich in solid particles, although most of the lime is utilized for reaction with absorbed SO2 · Therefore, the risk of clogging the apparatus with these compounds is always present, although in recent years considerable 25 progress in eliminating, inter alia, this problem with wet scrubbing with lime. Power consumption is also relatively high, since large volumes of liquid are to be transported. The liquid, ie. the slurry additionally contains abrasive solid particles which cause substantial maintenance costs to e.g. pumps, pipelines and nozzles. In the gas washer, the gas is cooled approximately to saturation temperature - or approx. 50-55 ° C - which means that the gas often needs to be reheated to avoid annoying flue gas near the chimney.

An alternative approach to this completely wet system significantly simplifies and offers significant benefits

DK 154008 B

2 in relation thereto. In this alternative, the heat of the flue gas is utilized to completely evaporate the water in the absorption liquid while drying the reaction products to a dry powder which is then separated together with the incoming substance, e.g. fly ash, following the combined drying and absorption process. The absorbent is injected during comminution into a nozzle or rotary atomizer in the first stage which consists of a separate reaction chamber which is completely separate from the substance separator constituting the second stage. As fabric separators, both textile filters and electro filters of conventional types are used.

The process of the invention is characterized in that the absorbent is introduced into a filter chamber in finely divided form 15 and mixed with the flue gas stream supplied to the filter chamber, and the mixture is imparted for a residence time in the filter chamber of between 1 and 15 seconds during approximately complete surface evaporation of the reaction products. the flue gas stream is passed through the filter material in the filter placed in the filter chamber during deposition of the reaction products formed on the filter material.

The process according to the invention results in a high efficiency, is reliable and requires only low investment costs compared to the known methods.

In an advantageous embodiment of the process according to the invention, a particularly good separation is obtained when capillary bound water is evaporated from the reaction products after their deposition on the filter material during further reaction between residual sulfur dioxide in the flue gas, the absorbent and the released water.

The apparatus of the invention comprises a reaction chamber with inlet for the gas and an atomizer for supplying a 3

DK 154008 B

absorbent in the form of an absorbent in the form of an aqueous solution or aqueous suspension for the flue gas in the reaction chamber and a filter chamber with aggregates for separating the reaction products formed from the gas. The apparatus according to the invention is characterized in that the reaction chamber is integrated in the filter chamber, in which the separating assembly consists of a fabric filter barrier, and that the volume of the reaction chamber between the gas inlet and the filter material is dimensioned so that the flue gas flow has an average residence time of between 1 and 15 seconds in the chamber. .

The invention is based on the surprising realization that the drying step and the separation step can be carried out in an integrated chamber, unlike known methods, whereby separate apparatus units are always utilized in the process. The reason for this is first and foremost that the risk of clogging of the filter material has been judged to be very high when an aqueous absorbent is to be added directly into the filter chamber, which could then be assumed to give a strong increased gas resistance over the separator. According to the invention nozzles or other means for atomizing the absorbent within the filter chamber itself are arranged in such a way that incoming hot gas flushes them and is directed so that the mixture of liquid droplets and cooled gas does not directly reach the filter medium without first flowing freely in the filter chamber. chamber for a period of 1-15 seconds. Most of the water in the injected absorbent evaporates, and a certain residual moisture content is found in the fabric even after it has been filtered out on the filter medium.

Furthermore, it has surprisingly been found that a large residual content of water can be accepted in the separated substance without any inconvenience in the form of an increased pressure drop across the filter. In addition, in these experiments with an apparatus of the type specified,

DK 154008 B

4 is so large that the filter media has been completely wet, without the expected disadvantages being observed. Contrary to what might be expected, the permeability does not appear to be adversely affected by the moisture present.

As a higher moisture content of the fabric is acceptable, a significantly higher excretion rate of SC> 2 can be expected in the system of the invention. Experiments have shown that with flue gases from combustion with low sulfur content coal can increase the excretion rate from approx. 75% to approx. 97% by completing the process with a higher moisture content of the substance in the filter. The invention also results in a substantial reduction in investment costs over the conventional technique, since it is only necessary to build a chamber, with the considerable savings this entails for steel structures, stairs and corridors, and not least insulation.

The invention is explained in more detail below with reference to the drawing, which schematically shows an apparatus according to the invention. In the drawing, a filter chamber 1 is shown to which the hot flue gas is passed through a gas inlet 2.

At its transition to the chamber is provided a nebulizer 3 to which the absorbent in the form of an aqueous solution or aqueous suspension is passed through a liquid conduit 4. In the filter chamber 1 is placed a textile barrier filter 6 in the form of a number of filter hoses 7. The space between the gas inlet 2 and the barrier filter 6 form a reaction chamber V in which the reaction between the absorbent and the sulfur dioxide in the flue gas takes place during drying of the reaction products. The reaction chamber V is dimensioned so as to the amount of flue gas Q that the average residence time of the flue gas in the reaction chamber V is between 1 and 15 seconds. The ratio of the volume of the reaction chamber V in m 2 to the amount of flue gas Q in m Thus, the second is between 1 and 15 seconds. By placing the nebulizer 3 at the transition of the gas inlet 2 to the reaction 5

DK 154008 B

chamber V is obtained an effective mixture of the feed absorbent in the flue gas Q. The substantially dry substance consisting of the reaction products formed is deposited 5 on the filter hoses 7 as the purified gas passes through the filter material and leaves the filter chamber 1 via an outlet for purified gas 8 which is provided with means 9 for cleaning the hoses. Underneath the filter hoses 7 are placed bottom pockets 10 for collecting the separated material, which 10 is later taken out through lock assemblies 11.

The invention is further illustrated in the following embodiment.

A gas quantity of approx. 15500 m 2 / h with a temperature of 148 ° C is fed to a test device consisting of a modified 15 hose filter from which hoses have been removed so that an empty space is formed in the center of the filter chamber. The height of the filter is approx. 6.5 m and it has a square cross section of 2.3 x 2.3 m. The filter contains a total of 75 filter tubes corresponding to a filter surface of 150 m ^. The gas is introduced through the top of the filter chamber into a vertically disposed channel which opens approx. 0.2 m below the top of the filter chamber. At the same height is arranged a nozzle of conventional two-media type. The sulfur dioxide content of the incoming gas is measured at approx. 500 ppm. By applying approx. 6.5 l / min. of a ca. The 4% suspension of calcium hydroxide reduces the sulfur dioxide content of the outgoing gas to approx. 75 ppm at a temperature in the exhaust gas of 75 ° C. The pressure drop across the filter varies between 102 and 118 mm water column, depending on the cleaning of the filter hoses, which is done by compressed air. 1

The invention is described above in connection with the removal of sulfur dioxide from a gas stream. However, the invention is not limited thereto, but is within the scope of the claims applicable to the removal of other undesirable acidic gas components.

Claims (3)

A process for purifying hot flue gas from sulfur dioxide or other undesirable acidic gas components, in which an absorbent in the form of an aqueous solution or aqueous suspension is contacted with the flue gas during drying of the reaction products formed by the absorbent and sulfur dioxide, the reaction products are separated into a textile barrier filter, characterized in that the absorbent is introduced into a filter chamber (1) in finely divided form and mixed with the flue gas stream (Q) supplied to the filter chamber, and that the mixture is given a residence time in the filter chamber (V) of between 1 and 15. seconds during approximately complete surface evaporation of the reaction products, after which the flue gas flow is passed through the filter material in the filter (6) disposed in the filter chamber while depositing the reaction products formed on the filter material (7). Process according to claim 1, characterized in that 20 capillary bonded water is evaporated from the reaction products after their deposition on the filter material (7) during further reaction between residual sulfur dioxide in the flue gas, the absorbent and the released water. An apparatus for purifying hot flue gas for sulfur dioxide or other undesirable acidic gas components comprising a reaction chamber (V) with inlet for the gas and an atomizer (3) for supplying an absorbent in the form of aqueous solution or aqueous suspension to the flue gas. the reaction chamber (V) and a filter chamber (1) with 30 aggregates (6) for separating the reaction products formed from the gas, characterized in that the reaction chamber (V) is integrated into the filter chamber (1), in which the separating assembly consists of blocking filters (6) of and the volume of the reaction chamber (V) 35 between the gas inlet (2) and the filter material (7) is dimensioned such that the flue gas flow has an average residence time of between 1 and 15 seconds in the chamber part (V).