Summary of a.
Limestone-gypsum wet flue gas desulfurization technology is currently the most widely used a desulfurization technology, the basic process is as follows:
Boiler flue gas after the electric dust, through the booster fan, GGH (optional) after cooling into the absorption tower. In the absorption tower flue gas flows up and is downward flow of slurry by countercurrent washing cycles. Circulating slurry is set up through the shotcrete layer of nozzle to the absorption tower, so that the removal of SO2, SO3, HCL and HF, and at the same time under the processing of "forced oxidation process" reaction by-products are imported air oxidation of gypsum (CaSO4 • 2 h2o), and consume as absorbent of limestone. Circulating slurry through the slurry circulating pump up to the spray layer, through the nozzle atomization, can be used to good contact with gas and liquid. Each pump is usually connected with their respective spray layer, the system usually adopt unit.
In the absorption tower, gypsum, limestone and so2 reacts this part of the gypsum slurry by gypsum slurry pump discharge, entering the gypsum dewatering system. Dehydration system mainly includes the gypsum hydrocyclone (as a level 1 dewatering equipment), the slurry distributor and vacuum belt dryer.
After purification treatment of flue gas flow through the two levels of demister mist, here will clean the slurry droplets carried by flue gas in the removal. At the same time, according to the specific program of demister with process water from time to time to wash. Demister irrigation has two purposes, one is to prevent the demister blocked, 2 it is to wash water as make-up water at the same time, the steady absorption tower level.
In the absorption tower export, flue gas is cooled to 46-55 ℃ or so commonly, and saturated by water vapor. Through the GGH heat of flue gas to 80 ℃ above, in order to improve the lifting height and diffusion ability of flue gas.
Finally, clean through stack into the chimney flue gas into the atmosphere.
Main advantage of gypsum method is: the applicable range, high desulfurization efficiency of coal, high utilization rate of absorbent, equipment operation rate, high reliability, high desulfurization agent, the limestone source is rich and cheap.
From the boiler or furnace flue gas after dust under the action of induced draft fan into the absorption tower, absorption tower for counter-current spray air tower structure, integrating absorption and oxidation function, upside is absorbing area, lower for the oxidation zone, after cleaning cycle of the gas and absorption tower in slurry reverse contact. System commonly 3-5 slurry circulating pump, each corresponding to a layer of circulation pump atomization spray layer. When only one unit operation or the load is small, can shut down the 1-2 spray layer, the system still keep high liquid gas ratio, which can achieve the required desulfurization effect. Absorption area upper secondary demister, demister, the free water in the outlet flue gas does not exceed 75 mg/Nm3. After absorbing SO2 slurry into the circulation oxidation zone, in cyclic oxidation zone, calcium sulfite oxidation by blowing air into gypsum crystals. At the same time, absorbed by the sorbent preparation system to supply fresh limestone slurry oxidation system, used to supplement the burn limestone, keep absorbing slurry pH value. Product size reaches a certain density to the by-product desulphurization system, forms through dehydration gypsum.
Process flow diagram
3. Technical characteristics
Wet desulphurization gypsum desulphurization is one of the most commonly used.
But the shortcoming of limestone/gypsum method is obvious: the high cost of initial investment, operating cost is high, covers an area of big, complex system management operation, wear corrosion phenomenon is relatively serious, by-product gypsum difficult to handle (as sales problems can only be stacked), wastewater more difficult.
The technology and abandon the difference between the absorber slurry in the blowing air and force CaSO3 oxidation to CaSO4 (gypsum), a by-product of desulfurization gypsum. While blowing air produced more homogeneous slurry, easy to achieve 90% desulfurization efficiency, and easy to control fouling and plugging. Due to limestone is cheap and easy to transport and to save, so since 8 0 s limestone has become the main method of gypsum desulfurization agent. Today's choosing a coal-fired power plant flue gas desulfurization equipment at home and abroad, the limestone/gypsum forced oxidation system become wet flue gas desulfurization technology of choice.
Using limestone/lime as desulfurization absorbent, lime writing broken ground into powder mixed with water to form a absorption of serous, when using lime as absorbent, lime powder after digestion treatment made absorber slurry water. Within the absorption tower, absorption of touch the mixed slurry and flue gas, sulphur dioxide in flue gas with the calcium carbonate in the slurry and the oxidation of blowing air for chemical reaction to be removal, the final reaction products of gypsum.