Sodium-calcium dual-alkali flue gas desulfurization method and system

Abstract

The invention provides a sodium-calcium dual-alkali flue gas desulfurization method and system. The method comprises the steps of flue gas desulfurization and sodium-based desulfurizer regeneration; in the flue gas desulfurization step, a sodium hydroxide solution is adopted as a desulfurization starting agent, the prepared sodium hydroxide solution is directly put into a desulfurization tower to wash flue gas to remove sulfur dioxide in the flue gas; in the sodium-based desulfurizer regeneration step, liquid obtained through a desulfurization reaction is reduced into a sodium-based desulfurizer through calcium hydroxide contained in a regeneration reaction tank, in the sodium-based desulfurizer regeneration process, the regeneration reaction tank is mechanically stirred, semi-aqueous calcium sulfite is filtered out from the regenerated sodium-based desulfurizer through a filter membrane filter and then oxidized into gypsum through air, and after the pH value of a clear solution obtained through filtering of the filter membrane filter is regulated by supplementing alkali, the clear solution is returned into the desulfurization tower to be used repeatedly as an absorption solution. According to the method and system, the gypsum quality can be improved, the alkali amount consumed in the regeneration process can be decreased, a spray system can be prevented from being blocked due to scaling, and the better sulfur dioxide absorption effect is achieved.

Description

technical field [0001] The invention relates to the technical field of flue gas treatment, in particular to a method and system for flue gas desulfurization with sodium calcium double alkali. Background technique [0002] The traditional limestone-lime flue gas desulfurization process uses calcium-based desulfurizers to absorb sulfur dioxide, and calcium-based desulfurizers react with sulfur dioxide to form calcium sulfite and calcium sulfate. Fouling in the desulfurization tower and pipes, causing blockage. Scaling and clogging seriously affect the normal operation of the desulfurization system, and even seriously affect the normal operation of the boiler system. In order to avoid the unfavorable factors brought by calcium-based desulfurizers, most calcium-based desulfurization processes need to be equipped with corresponding forced oxidation systems (aeration systems), which increases initial investment and operating costs. The use of cheap calcium-based desulfurizers is...

AI Technical Summary

Problems solved by technology

[0022] 1) In the process of flue gas desulfurization, while sodium hydroxide reacts with sulfur dioxide, it also reacts with carbon dioxide to form sodium carbonate, and a large amount of sodium carbonate is discharged into the regeneration tank, consuming more calcium hydroxide

[0023] 2) During the regeneration process of sodium-based desulfurizer, sodium sulfite and calcium hydroxide react quickly, but sodium sulfate and calcium hydroxide react more difficultly, which makes the content of sodium sulfate in the desulfurization circulating water continuously increase, and the desulfurization efficiency continues to decline, resulting in smoke Gas emissions exceed the standard, which also leads to a significant increase in caustic soda consumption

[0024] 3) In the regeneration process of sodium-based desulfurizer, in order to oxidize calcium sulfite hemihydrate to produce gypsum, the method of aeration and oxidation is adopted while stirring. This method is easy to oxidize sodium sulfite to sodium sulfate, because sodium sulfate is difficult to react with calcium hydroxide , it is necessary to continuously replenish sodium hydroxide or sodium carbonate, which increases the consumption of alkali

In addition, sodium sulfate will also reduce the quality of gypsum

[0025] 4) Due to the poor sedimentation effect of calcium sulfite, it enters the spray system, and it is easy to cause scaling under the condition of high pH value

[0026] 5) Due to the aeration and oxidation of calcium sulfite hemihydrate in the regeneration process, the oxidation effect is poor, and the calcium sulfite hemihydrate cannot be completely oxidized, resulting in high water content and a large amount of calcium sulfite in gypsum, which affects the quality of gypsum

[0027] The above reasons lead to a large consumption of sodium and alkali in the dual-alkali desulfurization system, and the long-term operation cost is extremely high

At the same time, the fouling of the desulfurization system is serious, and it can only be used during environmental monitoring and acceptance

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