There is a certain amount of carbon monoxide (CO >: 20%), so it is called blast furnace gas. Blast furnace gas contains a lot of combustible components and mixed with a lot of dust, and the temperature is usually 150 ~ 400℃. The waste gas discharged from the top of the furnace generally passes through a gravity dust collector first. Then washing treatment and deep dust removal are carried out. Washing treatment is to realize gas washing and cooling by convection contact between gas and water in washing tower or venturi tube. The water after washing and cooling is blast furnace gas washing wastewater. The water temperature of the wastewater is above 60℃, and the main impurities are solid suspended solids, dust sludge (air sludge), oxides, coke powder, etc. In addition, it also contains some inorganic salts and toxic substances such as phenols, cyanide and heavy metals. .
1 Status of governance
At present, the precipitation treatment of large and medium-sized blast furnace gas washing wastewater can be divided into natural precipitation and coagulation precipitation.
1. 1 natural precipitation method
Natural sedimentation is the main treatment method of blast furnace gas washing wastewater in Capital Iron and Steel Company, Panzhihua Iron and Steel Company, Xiangtan Iron and Steel Company and Shanghai No.1 Iron and Steel Plant. In the past, the washing wastewater of blast furnace gas in Laigang was treated by two concentration tanks with D= 12m, which could not meet the industrial water consumption and discharge standards. Later, the horizontal sedimentation tank was used for natural sedimentation, and the sedimentation efficiency was about 90%. The content of suspended solids in the effluent is less than 100mg/L/L, the water temperature is about 40℃ after cooling, and the water circulation rate reaches 90%. Except some indicators (such as lead and phenol) sometimes exceed the standard, the treated wastewater can basically meet the discharge standard. Most foreign blast furnace gas washing wastewater is treated by natural precipitation method [2], which is characterized in that the wastewater is discharged into sedimentation tank or concentration tank by gravity, cooled by cooling tower after treatment, and the effluent suspended solids SS is recycled.