What Is Desulfurization?

Desulfurization refers to the removal of sulfur in fuel before combustion and the desulfurization process before the emission of flue gas. Is one of the important technical measures to prevent air pollution. ^[1]

Through domestic and foreign desulfurization technology and domestic

Physical method: Usually, gravity separation or magnetic separation method is used to remove iron sulfide (pyrite) from coal. The sulfur in this form accounts for about 2/3 of the sulfur in coal. Chemical method: After pulverizing coal, it is mixed with an aqueous solution of ferric sulfate, heated in a reactor to 100-130 ° C, and ferric sulfate reacts with pyrite to transform into ferrous sulfate and monomer sulfur. The former is oxidized and recycled, and the latter Recycled as a by-product. Gasification method: Coal is incompletely oxidized by a gasifier at a high temperature of 1000 to 1300 ° C, and becomes coal gas. Most of the sulfur in coal is gasified into hydrogen sulfide when it is gasified, and then it is removed by liquid absorption or solid adsorption. Liquefaction method: Coal liquefaction includes synthesis method, direct cracking hydrogenation method and hot melt hydrogenation method. In the liquefaction process, sulfur and hydrogen react to form hydrogen sulfide and escape, so a high calorific value, low sulfur, and low ash fuel is obtained. Flue gas desulfurization is divided into dry method and wet method. The former uses solid powder or particles as the adsorbent, such as lime powder blowing method, activated carbon method and activated manganese oxide method. The latter uses a liquid as an absorbent, such as an ammonia absorption method, a limestone or lime milk absorption method, a magnesium oxide absorption method, a sodium (potassium) absorption method, and an oxidation absorption method. Fuel desulfurization can recover sulfur, reduce sulfur oxide pollution, and increase the heating value of fuel.

SO2 absorption equation by droplets

SO2 (gas) + H2O H2SO3 (liquid)

The absorbed SO2 reacts with the absorbent of the solution to form calcium sulfite;

Ca (OH) 2 (liquid) + H2SO3 (liquid) CaSO3 (liquid) + 2H2O

Ca (OH) 2 (solid) + H2SO3 (liquid) CaSO3 (liquid) + 2H2O

(3) After the CaSO3 in the droplet reaches saturation, it begins to crystallize out;

CaSO3 (liquid) CaSO3 (solid)

CaSO3 in part of the solution reacts with oxygen dissolved in the droplets,

Oxidation to calcium sulfate;

CaSO3 (liquid) + 1 / 2O2 (liquid) CaSO4 (liquid)

CaSO4 (liquid) has low solubility and crystallizes out

CaSO4 (liquid) CaSO4 (solid)

Reaction of SO2 with remaining Ca (OH) 2 and recycled ash

Ca (OH) 2 (solid) Ca (OH) 2 (liquid)

SO2 (gas) + H2O H2SO3 (liquid)

Ca (OH) 2 (liquid) + H2SO3 (liquid) CaSO3 (liquid) + 2H2O

CaSO3 (liquid) CaSO3 (solid)

CaSO3 (liquid) + 1 / 2O2 (liquid) CaSO4 (liquid)

CaSO4 (liquid) CaSO4 (solid)

Double alkali equation

2NaOH + SO2 Na2SO3 + H2O

Na2SO3 + SO2 + H2O 2NaHSO3

Ca (OH) 2 + Na2SO3 2 NaOH + CaSO3

4NaHSO3 + 2Ca (OH) 2 2Na2SO3 + 2CaSO3 · H2O + H2O

2Na2SO3 + O2 + 2Ca (OH) 2 + 4H2O 4NaOH + 2CaSO4 · 2H2O

Technology outlook for desulfurization industry

Desulfurization technology has always been an important subject of concern in environmental protection work. The mainstream desulfurization process will still be widely used at home and abroad. Constrained by technical conditions and economic costs, the limestone-gypsum wet and spray drying process is the preferred process for various desulfurization requirements. However, because the electron beam method and seawater desulfurization are in the experimental research stage or the application area is limited, the market share is limited, but it will develop in some areas. Flue gas desulfurization technology-CFB-FGD of flue gas circulating fluidized bed desulfurization process will become one of the important technical means for incineration of flue gas desulfurization in the future. This technology has been successfully commercialized abroad, and the market prospects are promising ^[3] .