Nowadays, in the current environmentally friendly desulfurization process of power plants, most of the desulfurizers used are limestone powder. The quality, fineness, particle distribution and reactivity of limestone powder are the key factors affecting the desulfurization effect. For the specific desulfurization process in actual operation, the following three types of desulfurization in power plants are generally used:

 Dry desulfurization process

The dry desulfurization process refers to spraying the desulfurizing agent into the flue gas in a dry form. The desulfurizing agent can be sprayed with the lime powder or other absorbent, and can be simultaneously injected into the catalytic absorbent, which can be sprayed into the flue or the furnace, and can be sprayed again. To adjust the temperature, it is also possible not to spray water, and the desulfurized ash is discharged in a dry state.

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Semi-dry desulfurization process

It means that the desulfurizing agent is added in a wet state, and the moisture in the slurry is evaporated by the sensible heat of the flue gas. During the drying process, the desulfurizing agent reacts with the sulfur dioxide in the flue gas to form a dry powdery product. In order to improve the desulfurization efficiency, lime powder digestion is usually used as a desulfurizing agent. If a bag filter is used in combination, the desulfurization efficiency of 10% – 15% can be improved. Semi-dry flue gas desulfurization technology mainly includes rotary spray drying method, gas suspension absorption method and humidification ash circulating desulfurization technology.

Limestone–gypsum wet desulfurization process

The limestone powder is added with water to make a slurry as an absorbent pumped into the absorption tower and fully contacted with the flue gas. The sulfur dioxide in the flue gas is oxidized with calcium carbonate in the slurry and air blasted from the lower part of the tower to form calcium sulfate. After reaching a certain degree of saturation, the crystal forms dihydrate gypsum. The gypsum slurry discharged from the absorption tower is concentrated and dehydrated to have a water content of less than 10%, and then sent to a gypsum silo by a conveyor, and the flue gas after desulfurization is removed by a mist eliminator, and then heated by a heat exchanger. After warming up, it is discharged into the atmosphere by the chimney.

In the limestone-gypsum wet desulfurization process, the absorbent slurry in the absorption tower is repeatedly circulated and contacted with the flue gas through the circulation pump, the utilization rate of the absorbent is high, and the desulfurization efficiency is good, so the limestone-gypsum wet desulfurization process is also a common choice for the current power plant desulfurization.

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21th Nov 2018