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Flue Gas Desulphurizatio

1、Flue Gas Desulphurization Overview

By researching on abroad and domestic desulphurization processes, the desulphurization methods can be generally divided into 3 categories as: pre-combustion desulphurization, in-combustion desulphurization and after-combustion desulphurization, wherein the after-combustion desulphurization is also known as FGD (Flue gas desulphurization). The FGD technology can be divided into the following five categories according to the desulphurization agent type: CaCO3-based (limestone) type, MgO-based type, Na2SO3-based type, NH3-based type and organic alkali-based type. The CaCO3-based (limestone) type is commonly applied in the present world and the proportion is more than 90%. As per the absorbent and desulphurization byproducts state (wet or dry) in the desulphurization process, the desulphurization technology can also be divided into wet method, dry method and semi-dry (wet) method.

2、Limestone – gypsum method of flue gas desulphurization

This process is the world's most widely used technology, which is applied in the coal-fired power plants of more than 90% in Japan, Germany and the United States.

Its working principle is: the limestone powder is made into slurry by adding water, which is pumped into the absorbing tower for fully mixing with flue gas. The sulfur dioxide in flue gas and the calcium carbonate in the slurry will react with the help of air pumped from under, during which period the calcium sulfate will be produced. When the calcium sulfate reaches certain saturation, it becomes dihydrate gypsum. The gypsum slurry discharged from the absorbing tower will be concentrated and dehydrated, and then its water content will be less than 10%. Conveyor will send the dry gypsum to storage for stacking. After desulphurization, the flue gas will be discharged into the atmosphere by chimney by passing through the mist eliminator and heat exchanger. The absorbent slurry in the absorbing tower will be circulated by pump, so it can contact with the flue gas repeatedly, accordingly its utilization rate is high and the calcium-sulfur ratio is low. Generally, the desulphurization efficiency is greater than 95%.




Process Flow Diagram

3、CFA Desulphurization of Gas Circulating Fluidized

3.1Desulfurization process principle

Flue gas enters from the bottom of the reactor (absorbing tower). A Venturi device is set at the bottom of absorbing tower, and the flue gas will speed up after passing through the Venturi tube, which will ensure that the flue gas will take dust particles to the up-going section of reactor, where it forms a suspension fluidized bed. A pair of two-way fluid nozzles is installed in the Venturi tube, and the fresh lime and water is sprayed through the nozzles into the absorbing tower. Absorbent and the sulfur dioxide contained in flue gas react to produce CaSO3 of CaSO4. After desulphurization process, the flue gas carrying large amounts of solid particles will be discharged from the top of absorbing tower, and then enters the recycling dust collector. The solid particles separated by dust collector will return to the absorbing tower again… the solid particles will be cycled up to one hundred times, so the absorbent utilization rate is higher.

Process schematics

3.2 System configuration

1)Flue system ;

2)Reaction tower, including nozzle;

3)Cyclone dust collector;

4)Desulphurization agent recycling bins;

5)ESP or bag filter;

6)Lime storage system;

7)Lime slurry preparation system;

8)By-product processing system;

9)Activated carbon systems (according to process needs, optional)