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Desulfurization Equipment

Desulfurization Equipment

Exhaust system

Flue gas desulfurization, FGD for short, is the technique of removing sulfur oxides from flue gas or exhaust gas of other industries. It is divided into dry method and wet method. The dry method adopts lime powder, active carbon, active manganese oxides, etc. as absorbents. The wet method adopts ammonia or sodium hydroxide as absorbents. The technique of the coal firing of FGD is the one that most popular and high efficiency. In a quite long time, FGD will be the main method to control SO2 discharge for the coal-fired power plant.

Wet FGD technique

The wet FGD techniques around the world are much the same in terms of technical process, form, and mechanism. The slurry of CaCO3, CaO or Na2O3 is mainly used as washing agent to wash flue gas in the reaction tower to remove SO2. Depending on the continuous improvement in fifty years, FGD technique is mature with high desulfurization rate (90%-98%), large unit capacity, strong adaptability for coal kind, low operation fee, and easy recycling of by-products.

The main reaction mechanism of CaO and CaCO3 methods:

CaO method:SO2+CaO+1/2H2O→CaSO3•1/2H2O

CaCO3 method: SO2+CaCO3+1/2H2O→CaSO3•1/2H2O+CO2

The commercial development is its main advantages. It has rich absorbent resource and low cost; its waste residuals can be discarded, or recycled as gesso. Currently, CaO/ CaCO3 method is the most popular FGD technique. Its desulfurization rate can reach over 90% for high sulfur fuel, and over 95% for low sulfur coal.

Its main disadvantages are begriming, jamming, corrosion and wearing of equipment. To solve these problems, the equipment manufacturers have developed Generation Ⅱ and Ⅲ techniques of CaO/ CaCO3 FGD.
The re-heating problem of flue gas during the wet process affects the investment of the whole FGD technique. Because the flue gas after the wet desulfurization has the lower temperature (45℃),which is lower than the dew point, while if the flue gas is directly emitted into the chimney without re-heating, which can easily form the acid fog that corrodes the chimney, which is bad for the diffusion of flue gas. So the wet FGD device always has a flue gas re-heating system. Currently, the mature technique is recycling (rotary) flue gas heat exchanger (GGH). GGH is expensive with a high investment share for the whole FGD technique.
For oxy-fuel combustion technique using natural gas as fuel, the desulfurization is not necessary for exhaust gas.
The desulfurization tower technique is recommended for the customers who use petroleum coke, coke oven coal gas, and heavy oil to cut the cost.

 

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