Entrained-flow bed coal gasification black water advanced treatment process

Abstract

The invention provides a gasification black water treatment process which comprises the following steps: (1) introducing gasification black water into an electromagnetic reaction tank which is made ofa metal material or alloy; mounting permanent magnets above and below the reaction tank, and forming a magnetic field perpendicular to the water flow direction in the reaction tank; (2) enabling thegasification black water to enter a coagulation tank and a flocculation tank from the electromagnetic reaction tank, adding a silicon removing agent and a coagulant into the coagulation tank, and adding a flocculating agent into the flocculation tank; precipitating through an inclined plate precipitation tank; and (3) filtering by a filter to remove residual suspended solids. After the gasification black water is treated by the process disclosed by the invention, the hardness is less than 20mg / L, the soluble silicon is less than 20mg / L, the suspended solid content is less than 3mg / L, and the chloride ions are less than 20mg / L, so that the gasification black water can be completely recycled in a gasification system, the scaling rate of the gasification system is reduced by 90%, and the amount of discharged wastewater is reduced by 80%.

Description

technical field [0001] The invention belongs to the field of coal chemical industry, in particular to an entrained bed coal gasification black water treatment process. Background technique [0002] The coal gasification unit is the source of the entire coal chemical industry. The most widely used coal gasification technology is entrained bed gasification (including coal water slurry and pulverized coal gasification). This type of gasification process uses water washing to remove coal ash in the synthesis gas. Therefore, a large amount of wastewater (containing suspended coal ash, soluble calcium magnesium silicon, ammonia nitrogen, etc.) is produced, which is generally called gasification black water in the industry. At present, the gasification black water treatment process generally adopts the flocculation precipitation method in the industry. The coagulant polyacrylamide is mixed into the black water, and the cinder is settled through the clarification tank. The overflow ...

AI Technical Summary

Problems solved by technology

Because the current gasification black water treatment process is too simple, it can only remove most of the suspended solids in the black water. The content of suspended solids in the treated gray water is about 40-100mg / L, and the concentration of calcium and magnesium ions is about 400-600mg / L. Dissolved silicon is 100-120mg / L, so it causes very serious scaling problems in the gasification system; in order to slow down scaling, a typical coal gasification unit that processes 3,000 tons of raw coal per day needs to discharge 120t / h of waste water per hour, and at the same time The gray water discharged to the biochemical treatment system also causes slagging, scaling, and fouling of the reverse osmosis membrane in the biochemical system

Scaling and blockage caused by incomplete black water treatment is a problem in the gasification industry. The industry has been trying to solve it. The most common process is adding alkali to remove calcium and magnesium. However, because this method needs to increase the pH of gray water to above 10.5 to obtain better calcium Magnesium removal rate, while the pH of the buffer system composed of high-concentration ammonia and carbon dioxide in gray water is stable at 8-8.5, a large amount of chemicals must be added, resulting in high cost; Sulfate ions, the former will cause corrosion of gasification system pipes and equipment, while the latter will intensify calcium sulfate scaling in gasifiers and black water pipelines, reducing the effect of emission reduction

Therefore, after some coal gasification enterprises tried the process of adding alkali to remove calcium and magnesium, they did not use it for a long time

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