The method of cleaning flue gases from sulfur oxides and nitrogen

 

(57) Abstract:

Usage: cleaning of exhaust gases in heat power engineering and other industries with emissions of sulfur and nitrogen oxides. The inventive spray dryer serves exhaust gases and aqueous suspension of hydroxide or calcium carbonate with a water content of at least 88 wt.%. After using suspension contains not less than 29 wt.% water. Then the exhaust gases are served at the stage of absorption in a circulating aqueous solution of urea with a concentration of 5 to 100 g/l at 80 - 95oC. the Spent absorption solution contains 300 - 350 g/l of ammonium sulfate. His process used a suspension from the stage spray drying. The resulting suspension of gypsum is dried by spraying the exhaust gases supplied to the purification from sulfur dioxide. The resulting product contains at least 86 wt.% calcium sulphate, no more than 7 to 10 wt.% hydroxide or calcium carbonate, humidity no more than 5%. table 1.

The invention relates to a method for cleaning exhaust gases from sulfur and nitrogen oxides in power and can be used in other industries with similar emissions.

A known method of cleaning exhaust and the temperature of the flue gases. When this suspension is dried by the heat of the gases.

Closest to the invention to the technical essence is known a two-stage method of cleaning flue gases from nitrogen oxides and sulfur [2] At the first stage spend processing gases suspension of Ca(OH)2or CaCO3in the spray dryer. Waste slurry output and processed prior to the formation of gypsum. At the second stage of cleaning, the gas is treated with an aqueous solution of an alkaline reagent. The described method of cleaning gases is not without waste.

The task of the invention is the creation of non-waste technology of purification of exhaust gases from sulfur dioxide and oxides of nitrogen in the increasing use of reagents simplify processing technology absorption solution and the spent slurry of Ca(OH)2, increasing the yield of the final product.

The problem is solved by the interaction of the exhaust gases with a slurry of a hydroxide or carbonate of calcium a moisture content of not less than 88% After interaction with the suspension of unreacted oxides of sulfur and nitrogen interact with 5 to 100 g/l aqueous solution of urea at a temperature of 80 - 95oC. the Spent absorption solution exceed the CaCO3the degree of purification from nitrogen oxides pulp carbonate will be slightly higher, because the pulp carbonate is present, the urea reacts with NOx in the spray drying. However, the final degree of purification will not change (example).

Example. For cleaning do 60 thousand m3the flue gases of thermal power stations with a temperature of 130 - 240oC.

The concentration of SO20.8 to 3.0 g/m3< / BR>
The concentration of NOx0.3 to 0.8 g/m3< / BR>
The concentration of CO210 16 about.

The spray dryer serves a suspension of Ca(OH)2or calcium carbonate and exhaust gases. The flow of suspension is 4.3 t/h, the water content is not less than 88% for three cycles of the interaction of sulfur dioxide with hydroxide or calcium carbonate, resulting in the content of the latter is reduced by 50% as a result of the process is formed pulp consisting of Ca(OH)2, CaSO42H2O and CaCO3with the content of 29% and Then the exhaust gases fed into the absorber for the removal of nitrogen oxides and residues of sulfur dioxide. For irrigation absorber using an aqueous solution of urea with a concentration of 5 to 100 g/l Density irrigation 0.8 to 1.2 l/m3. The velocity of the gas in the cross section of the apparatus of 3.2 4 m/s Protonnyi solution circulates in the apparatus prior to the accumulation in it of ammonium sulfate at a concentration of 300 to 350 g/l, then send it to interact with the used pulp cleaning of gases from sulfur dioxide. This unreacted with SO2Ca(OH)2or CaCO3decomposes with the formation of gypsum and ammonia (25 m3/h). Suspension of gypsum contains 25% Ca(OH)2. It is dried in the spray dryer flue gases supplied to the purification from sulfur dioxide. In the drying process contained in the slurry of Ca(OH)2partially interacts with the sulfur dioxide. The result is a product that contains not less than 86% CaSO4and no more than 7 to 10% Ca(OH)2(or CaCO3) with a humidity of not more than 5% of the Released ammonia is fed into the exhaust before the dryer, which interacts with sulfur dioxide.

Thus, according to the developed technology, waste absorption solutions will be converted into marketable gypsum and from the scheme remove only the cleansed gases (table).

The process in these terms allows to increase the degree of use of Ca(OH)2up to 93% as it passes three levels of interaction:

a) with sulfur dioxide in the exhaust gases during their cleaning;

b) with ammonium sulfate used in the absorption solution;

in) with sulfur dioxide in the environment is ery clean up to 99% Solved the problem with waste absorption solution, additionally, the yield of the final product increases to 86%

Data cleaning of flue gases from the SO2a suspension of Ca(OH)2recycle and NOxand SO2the urea solution with recycling and returning the ammonia purification step is shown in the table.

The method of cleaning flue gases from sulfur and nitrogen oxides, comprising processing the cleaned gases to the first stage of cleaning with an aqueous suspension of the hydroxide or carbonate of calcium in the mode of spray drying with output and processing of the products removed prior to the formation of gypsum and rinse the cleaned gas absorption with an aqueous solution of the reagent in the second stage of purification, characterized in that the suspension on the first cleaning step is served with a water content of at least 88 wt. and remove with a water content of not less than 29 wt. as a reagent in the second stage of filtration using urea with a concentration in solution of 5 to 100 g/l at 80 95oAnd recycling of products after the first cleaning steps leading by mixing with the spent absorption solution after the second stage of purification.

 

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