Comprehensive utilization of desulfurization gypsum


Release time:

2020-04-03

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Desulfurization gypsum is the product of wet desulfurization of coal-fired flue gas, mainly from thermal power people off the plant. With the application and promotion of the comprehensive utilization technology of desulfurization gypsum, the view of sulfur gypsum has changed, and the waste discharged from the previous factory has become a resource material, which has aroused greater interest.

Comprehensive utilization of desulfurization gypsum in the field of building materials

Desulfurization gypsum is the product of wet desulfurization of coal-fired flue gas, mainly from thermal power people off the plant. With the application and promotion of the comprehensive utilization technology of desulfurization gypsum, the view of sulfur gypsum has changed, and the waste discharged from the previous factory has become a resource material, which has aroused greater interest. At present, the added value of the comprehensive utilization of desulfurization gypsum is generally not high, and the climate environment in the south also limits the application and promotion of the comprehensive utilization technology of desulfurization gypsum. Therefore, it is necessary to review and summarize the progress of the comprehensive utilization of desulfurization gypsum in the field of building materials, which is helpful to the research, development and application of the comprehensive utilization technology of desulfurization gypsum in the field of building materials in the future.

1. Formation of desulfurization gypsum

At present, the most commonly used wet desulfurization method is limestone-gypsum desulfurization process, which mainly uses cheap and easily available limestone as desulfurization absorbent, limestone is crushed and ground into powder and mixed with water to make absorption slurry. The process system mainly includes slurry preparation system, flue gas system, SO2 absorption system, slurry emptying and recovery system, gypsum dehydration system, process water system, compressed air system, electrical and control system. The absorption tower is the core device of the absorption system, and most of them are countercurrent spray towers. The flue gas containing sulfur dioxide enters the absorption tower from the lower part of the spray area and is fully contacted with the evenly sprayed limestone absorption slurry, and is discharged through the chimney after removing mist droplets, heating and warming. The slurry after sulfur absorption is oxidized and dehydrated into desulfurization gypsum. The oxidation process affects the formation of calcium sulfate crystals in the desulfurization gypsum, and the dehydration process affects the particle size distribution of the desulfurization gypsum (coarse and heavy particles flow into the secondary dehydration, and lighter and fine particles including fly ash overflow). Oxidation and dehydration process to see the desulfurization gypsum quality and desulfurizer, SO2 absorption, process control is very big, from these links to improve the quality of desulfurization gypsum.

Some characteristics of desulfurization gypsum itself bring difficulties to its comprehensive utilization: ① high water content, strong viscosity, easy to adhere to the loading, transportation and lifting equipment, causing material blockage, affecting normal production; ② fly ash and carbon particles change the appearance of desulfurization gypsum color, affecting its use in decorative materials; ③ particle size distribution is narrow, it is easy to cause bleeding, stratification and other phenomena of cementitious materials or products made of desulfurization gypsum; large bulk density has an important impact on its storage, production and product performance ④ the bulk density reaches 1kg/cm3; ⑤ the existence and composition fluctuation of impurities such as calcium sulfite increase the difficulty of its high value-added utilization.

2. Physical and chemical properties of desulfurization gypsum

Desulfurization gypsum is wet powder containing 10% ~ 15% attached water. Normal desulfurization gypsum is almost white and is yellowish white or grayish brown with the change of impurity content. The particle diameter of desulfurization gypsum is generally not more than 90μm, and more than 85% of the particle size is concentrated between 30 ~ 60μm, the distribution range is narrow, and the particle gradation is not as reasonable as that of natural gypsum powder after grinding. After grinding, the coarse particles of natural gypsum powder are mostly impurities, and the fine particles are mostly gypsum, while the coarse particles of desulfurization gypsum are mostly gypsum, and the fine particles are mostly impurities.

The chemical composition of desulfurization gypsum is similar to that of natural gypsum. The main minerals are calcium sulfate dihydrate, and the calcium sulfate dihydrate content of desulfurization gypsum is generally higher than 90%. FGD gypsum contains minerals in addition to calcium sulfate dihydrate (different crystal structure), may also calcium sulfite, fly ash, carbon particles, containing sodium, containing unreacted CaCO3 particles, potassium, magnesium and other sulfate or chloride composition of soluble salts, etc., and natural gypsum contains impurities mainly clay minerals.

3. Comprehensive utilization of desulfurization gypsum

Foreign research on desulfurization gypsum began in the late 1970 s and early 1980 s, and has now formed a relatively complete research, development and application system. Understanding and learning foreign desulfurization gypsum comprehensive utilization technology and experience can be used as a reference for the research and development and application promotion of desulfurization gypsum comprehensive utilization technology in China. Desulfurization gypsum in Japan is mainly used for the production of cement and gypsum board. Because gypsum contains two crystalline water, it has a good inhibitory effect on high temperature barrier and combustion when a fire occurs, and gypsum board has great development as a fire partition board for residential interior walls. The EU desulfurization gypsum use direction of gypsum board, self-leveling gypsum, pouring gypsum, retarder and gypsum block, which is mainly used for the production of gypsum board. The use of desulfurization gypsum in the United States has gypsum board, cement and concrete, filling materials and roadbed materials, mining, waste stabilization and solidification, agriculture, etc., mainly the production of gypsum board. The development of FGD gypsum application in foreign countries is mainly due to good environmental awareness, supporting policy guidance and high value-added development.

Domestic desulfurization gypsum utilization research late, desulfurization gypsum utilization is mainly used as a cement coagulant, the preparation of construction gypsum powder, fertilizer, the transformation of soda saline and other aspects; with the increase in the amount of desulfurization gypsum, its application scope needs to be expanded, the use of added value needs to be improved. At present, most people carry out a lot of research and development on desulfurization gypsum discharged from thermal power plants, but in fact, the quality of desulfurization gypsum is affected by factors such as coal-fired varieties, desulfurizers, desulfurization processes and equipment and their control parameters. At present, there is little systematic research on this aspect in China, which requires the change of ideas, the promotion of policies and the participation of the whole society.

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