Method and system for recovering magnesium salt from desulfurization wastewater

Abstract

The invention discloses a method for recovering magnesium salt from desulfurization wastewater. The method comprises the following steps: step A, removing heavy metals from desulfurization wastewater;step B, further removing calcium from a clarified water body produced in the step A; step C, concentrating the clarified water body produced in the step B; and step D, carrying out freeze crystallization on the water body produced in the step C, so as to obtain a magnesium sulfate product. The provided method for recovering the magnesium salt from the desulfurization wastewater is advanced in process technology and simple in pretreatment, the overall process route is greatly shortened compared with a process route in the prior art, and the magnesium resources in the wastewater can be effectively recycled. The invention further provides a system for the method.

Description

technical field [0001] The invention relates to the technical field of recovery of environmental protection resources, in particular to a method and system for recovering magnesium salts from desulfurization wastewater. Background technique [0002] Desulfurization wastewater mainly refers to the discharge water from the absorption tower during the wet desulfurization process of boiler flue gas. Wet desulfurization includes calcium desulfurization based on limestone and quicklime and magnesium desulfurization based on magnesium oxide. Compared with calcium desulfurization, Magnesium desulfurization has many advantages: the desulfurization activity of magnesium-based desulfurizer is high, the dosage is only 40% of that of limestone, the energy consumption of the circulating slurry pump is low, and the size of the tower body is reduced. It not only has high desulfurization efficiency, but also reduces equipment investment and operation. Cost, and can avoid fouling, clogging an...

AI Technical Summary

Problems solved by technology

The disadvantages of this method are: the electrocoagulation electrode is easily passivated, the energy consumption is high, and the electrode consumption is fast, which leads to an increase in operating costs; the desalination rate and recovery rate of ED concentration are low; ED cleaning and maintenance are frequent and complicated; power plant desulfurization wastewater is passed through After nanofiltration, the monovalent salt content is still high, and ED consumes a lot of energy

The disadvantage of this type of technology is that there is no nanofiltration membrane for salt separation, and RO is directly used to concentrate, resulting in high pressure in the RO system, and the crystallized salt obtained by evaporating the concentrated solution is not pure.

The defects of patent 4 are as follows: if the flocculant and polymer are added during the pretreatment process, if the dosage is not well controlled, the subsequent ultrafiltration and nanofiltration systems will be polluted; since some chemicals are added before evaporation, it is easy to It leads to fouling of the evaporator heat exchanger, which affects the heat transfer efficiency of the evaporator; the evaporated mud cake needs to be reprocessed, which cannot realize resource utilization; pretreatment requires additional acid and alkali, which consumes chemicals

[0008] The above technologies all adopt membrane technology features such as ultrafiltration, nanofiltration or reverse osmosis. Due to the high hardness of desulfurization wastewater and the complex composition of incoming water, slight fluctuations in the purification process of the pretreatment process will cause risks such as membrane clogging or damage.

In addition, the above-mentioned technologies are insufficient for the extraction of valuable substances in desulfurization wastewater, and the economic benefits are not high

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