Method for wet desulfurization flue gas dewhitening and desulfurization wastewater emission reduction

Abstract

A method for wet desulfurization flue gas dewhitening and desulfurization wastewater emission reduction, comprising the following steps: exchanging heat between the desulfurization wastewater discharged from the wet flue gas desulfurization absorption tower and the original flue gas, while reducing the temperature of the original flue gas, Realize the temperature rise of desulfurization wastewater; the heated desulfurization wastewater is directly contacted with the cooling air to cool down by air cooling, and part of the water in the desulfurization wastewater is vaporized and then enters the cooling air; the desulfurization wastewater after air cooling continues to exchange heat with the original flue gas Raise the temperature, then continue to directly contact with the cooling air to cool down, and repeat this cycle. This method simultaneously solves the problems of flue gas "de-whitening" and desulfurization wastewater discharge reduction, as well as the crystallization and recovery of soluble desulfurization products, and creates a better "de-whitening" effect at lower investment and operating costs. The discharge creates conditions, and at the same time realizes the oxidation, concentration, cooling crystallization and product recovery of soluble desulfurization products.

Description

technical field [0001] The invention relates to wet flue gas desulfurization, in particular to a method for flue gas whitening, desulfurization waste water reduction and recovery of soluble desulfurization products. Background technique [0002] Wet flue gas desulfurization has been adopted by more than 85% of flue gas desulfurization systems in the world due to its technical and economic advantages such as high desulfurization efficiency, low-cost and easy-to-obtain desulfurizers, and resource utilization of desulfurization products. However, limited by the technical defects of the "white plume" produced by wet desulfurization and the discharge of desulfurization wastewater, the trend of domestic flue gas desulfurization has evolved from wet desulfurization to (semi) dry desulfurization. However, (semi) dry desulfurization has inherent technical defects such as low mass transfer efficiency, large flue gas resistance, and difficult disposal of desulfurization products, resul...

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Problems solved by technology

[0005] The above-mentioned "dewhitening" method of condensing, cooling and dehydrating the net flue gas after desulfurization has the following disadvantages: 1) The condenser on the side of the net flue gas is in the SO 2 At the acid dew point temperature, the pH of the condensate generated is only 2-3, and the heat exchange surface of the condenser is easy to adhere to slurry and dust, which affects the heat exchange and mass transfer efficiency, and has high anti-corrosion requirements for equipment (usually more expensive fluoroplastics are used) ; 2) The cooling liquid in the clean flue gas and the condensing heat exchanger uses a gas-liquid partition wall to exchange heat, and the heat transfer temperature difference can only reach about 15°C. In addition, the poor thermal conductivity of the fluoroplastic material makes the condensing heat exchanger The coefficient is small, resulting in a large heat exchange area of ​​the condensing heat exchanger, large smoke wind resistance, and low heat exchange efficiency, which can only reduce the net flue gas temperature by about 5°C, resulting in MGGH still needing to raise the net flue gas temperature by 30°C to meet the requirements. "De-whitening" requirements under unfavorable weather conditions; 3) The condensate on the outer wall of the condenser is entrained by the flue gas for the second time, and is vaporized again in the heat release section of MGGH, which seriously affects the "whitening" effect

4) Due to the large size of the condenser and the large resistance to the flue gas, it involves a large-scale transformation of the booster fan in the existing flue gas system and the flue behind the tower. The transformation investment is high, and it is limited by site conditions

However, for dust removal equipment, in order to avoid SO 3 For dew point corrosion, the temperature of the flue gas entering the dust collector must be controlled above 120°C. For this reason, the evaporation capacity of the original flue gas to water is extremely limited, and it is still necessary to discharge part of the desulfurization wastewater or consume energy to evaporate and concentrate it.

At the same time, in the case of a large amount of desulfurization wastewater, the above-mentioned raw flue gas evaporation desulfurization wastewater method is used to achieve zero discharge of desulfurization wastewater. On the one hand, the moisture content of the raw flue gas entering the desulfurization system increases. The reduction directly leads to the reduction of the heat transfer temperature difference of the subsequent MGGH and reduces its heat transfer efficiency, which is extremely unfavorable for the "whitening" of the flue gas

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