The process flow of wet flue gas desulfurization and denitrification technology in various countries in the world

The process flow, form and mechanism of wet flue gas desulfurization in various countries in the world are similar, mainly using slurry such as limestone (CaCO3), lime (CaO) or sodium carbonate (Na2CO3) as detergent to wash the flue gas in the reaction tower, Thereby removing SO2 in the flue gas. This process has a history of 50 years. After continuous improvement and perfection, the technology is relatively mature, and has high desulfurization efficiency (90%-98%), large unit capacity, strong adaptability to coal types, low operating costs and The by-products are easy to recycle and so on.

The limestone (lime)-gypsum wet flue gas desulfurization process has been widely used in the field of wet desulfurization because the absorbent is cheap and easy to obtain. The process is characterized by high desulfurization efficiency (>95%), high utilization rate of absorbent (>90%), and can adapt to high concentration SO2 flue gas conditions. The disadvantages are high infrastructure investment costs, large water consumption, and corrosive desulfurization wastewater. The main thing is that the raw material limestone needs to be purchased, and the by-product calcium sulfite is not easy to handle.

Coking plants can generally adopt ammonia desulfurization technology. Ammonia desulfurization can not only remove SO2 in the flue gas, but the ammonium sulfate and ammonium bisulfate fertilizer products produced can also be processed and utilized in the ammonium sulfate recovery workshop of the coking plant to generate ammonium sulfate products. At the same time, the system uses a certain concentration of ammonia water as a desulfurizer, and can use the remaining ammonia water in the recovery workshop to reduce the load on the ammonia distillation system in the recovery workshop, killing three birds with one stone. Ammonia desulfurization uses a liquid absorbent to wash the flue gas to remove SO2. The equipment used is relatively simple, easy to operate, and has high desulfurization efficiency.

Ammonia desulfurization is not an integrated technology, and denitrification cannot be carried out at the same time, and a denitrification system needs to be built separately; the quality of the by-product ammonium sulfate fertilizer is affected by the quality of ammonia water, and its purity is difficult to meet the standard requirements. Therefore, ammonia desulfurization has certain requirements on the quality of ammonia water, and ammonia water filtered by a ceramic membrane filter can be used; after desulfurization, the flue gas temperature is low, and the emission is easy to form flue gas tailing, so a flue gas heating device needs to be added; ammonium sulfate salt solution Crystallization in the tower is easy to adhere to the tower wall or spray pipe, causing pipe blockage and severe corrosion. The requirements for equipment material selection are high, and the corrosion is serious. Anti-corrosion and cleaning devices need to be considered.

Due to the particularity of the coke oven production process, the hot flue gas discharged from the chimney contains sulfur dioxide, nitrogen oxides, and dust, and the content of nitrogen oxides is high. NOx in the flue gas is mainly produced under the high-temperature combustion conditions of the gas. The coke oven gas contains more than 50% hydrogen, the combustion speed is fast, and the flame temperature is as high as 1700-1900 degrees. The nitrogen and oxygen in the gas will be violently separated at about 1300 degrees. Oxidation reaction to generate NOx.