China is a country with coal as its main energy source, and the average content of coal in China reached 1.78%, more than 80% of the coal direct combustion in a variety of ways, the number of annual emissions of sulfur dioxide into the atmosphere each year is quite large. "Eight five" during the annual emissions of sulfur dioxide in the exhaust gas of the average is 1668 * 104Tons, from coal accounted for about 87%, if you do not use the control measures, is expected to 2010 SO2The emissions will reach 33000000 tons. Sulfur dioxide is the main cause of acid rain, acid rain to Lake acidification, aquatic organism reduction; soil acidification, hinder the growth of forage crops and forests; the various buildings subjected to corrosion damage. Therefore, to explore the method of removing sulfur dioxide in coal combustion process is of great significance to Protect environment. Method for removing sulfur dioxide in coal combustion process are: dry desulfurization, wet desulfurization, oxidation desulfurization, desulfurization, regeneration of semi dry desulfurization.

1, dry desulfurization

Dry desulfurization is mainly used for solid alkaline absorbent, such as limestone (CaCO3Lime (Ca) and (OH)2Absorption of sulfur dioxide (SO) etc.2), the formation of desulfurization product of calcium sulfate (CaSO4). As the main mechanism of dry desulfurization:

1.1 solid alkaline absorbent in the furnace of the following decomposition reaction

CaCO3To CaCO+CO2Or Ca (OH)2To CaO+H2O

1.2 sulfur dioxide diffused into calcium oxide (CaO) surface, and the chemical reaction

CaO+SO2+O2To CaSO4

Dry desulfurization is the basic method of desulfurization in combustion process, is widely used.

2, wet desulfurization

The alkaline substances in aqueous solution or suspension for wet desulfurization desulfurization medium is the use of sulfur dioxide in water has good solubility and the characteristics of neutralization oxidation further cause. Wet desulfurization mainly lime desulfurization and ammonia desulfurization.

2.1: Lime desulfurization desulfurization method of lime milk with limestone and hydrated lime as desulfurizer, the sulfur dioxide in the liquid phase through a series of sulfurous acid, then reacted with lime and limestone, gypsum formation (CaSO42H2O).

2.1.1 sulfur dioxide diffusion into the liquid phase and the chemical reaction in liquid phase:

SO2+H2O, H2SO3

H2SO3To 2H+SO32-

H2SO3+O2To H2SO4

2.1.2 limestone and lime dissolution:

CaCO3+H+To Ca2++CO2+H3O

Ca (OH)2+H+, Ca2++H2O

The formation of 2.1.3 sulfate:

Ca2+SO42-+2H2O, CaSO42H2O

2.2 ammonia desulfurization: ammonia desulphurization with ammonia is used as a desulfurization agent, first in the absorption of sulfur dioxide absorption tower, ammonium sulfite and ammonium bisulfite generated, then the decomposition reaction generated in sulfuric acid tower.

The reaction of 2.2.1 absorption tower:

SO2+NHa+H2O, (NH42SO)3

(NH42SO)3+SO2+H2O, NH4HSO3

2.2.2 decomposition in reaction tower:

(NH42SOa+H)2SO4To SO2+H2O+ (NH42SO)4

NH4HSO2+H2SO4To SO2+H2O+ (NH42SO)4

Wet desulfurization is currently the world's most widely used, a method of desulfurization technology is the most mature, the desulfurization rate is higher.

3, oxidation desulfurization by oxidation of the sulfur dioxide in the flue gas into three sulfur dioxide, three sulfur dioxide reacts with water to form sulfuric acid. Sulfuric acid can be recycled directly, can also use alkaline substances and salt. Electron beam oxidation desulfurization are mainly sulfur dioxide and sulfur dioxide by catalytic oxidation.

The catalytic oxidation of 3.1 sulfur dioxide catalytic oxidation of sulfur dioxide to sulfur dioxide and oxygen mixed gas is heated to a certain temperature (400 - 500 DEG C), the catalyst (for example, five of two vanadium and activated carbon), sulfur dioxide is oxidized by oxygen, generating three sulfur dioxide. The catalytic oxidation mechanism of sulfur dioxide:

3.1.1 of sulfur dioxide and oxygen to the catalyst surface diffusion

3.1.2 catalyst for sulfur dioxide and oxygen adsorption

3.1.3 sulfur dioxide and oxygen on the surface of the catalyst reaction