Method for zero discharge treatment of desulfurization wastewater suitable for multiple working conditions

A method for zero discharge treatment of desulfurization wastewater suitable for multiple working conditions, comprising following steps:

• recovering heat from high-temperature flue gas generated by a boiler (1) through an economizer (2) and an air preheater (3), feeding the high-temperature flue gas into a dust collector (4) for dust removing, then flowing the high-temperature flue gas into a desulfurization absorption tower (6) to remove acidic pollutants, and discharging the high-temperature flue gas through a chimney (7);
• separating a gypsum slurry generated by the desulfurization absorption tower (6) in a gypsum cyclone (9), wherein a separated overflow slurry is fed into a filtrate water tank (13) by the gypsum cyclone (9), and a separated underflow slurry enters a gypsum dehydrator (10) for dehydration by the gypsum cyclone (9);
• and filtering, by a filter cloth of the dehydrator, a water from the separated underflow slurry in the gypsum dehydrator (10), and feeding the filtered water into a gas-liquid separation tank (11) for gas-liquid separation, wherein a separated drainage water is fed into a wastewater collection tank (15) by the gypsum dehydrator (10);
• under a condition that a concentration of HCl in the high-temperature flue gas is less than a preset HCl concentration value, when an amount of a drainage water currently output by the gas-liquid separation tank (11) is greater than an amount of the desulfurization wastewater required to be discharged, dividing a drainage water collected by the wastewater collection tank (15) into two paths, wherein one path of the drainage water passes through the filtrate water tank (13) and enters the desulfurization absorption tower (6), and the other path of the drainage water is fed into a wastewater drying tower (27) through a spray water tank (25);
• at the same time, pumping, by a flue gas port, the high-temperature flue gas to the wastewater drying tower (27) for steam drying treatment, evaporating a water in the drainage water into the high-temperature flue gas, and directing the high-temperature flue gas output from the wastewater drying tower (27) to the dust collector (4) for dust removal;
• under conditions that the concentration of HCl in the high-temperature flue gas is greater than or equal to the preset HCl concentration value, and a concentration ratio of SO2 to HCl in the high-temperature flue gas is greater than or equal to a preset ratio, when the amount of the drainage water currently output by the gas-liquid separation tank (11) is greater than or equal to the amount of the desulfurization wastewater required to be discharged, feeding part of the drainage water in the wastewater collection tank (15) into a wastewater concentration tower (18), feeding a remaining wastewater in the wastewater collection tank (15) into the filtrate water tank (13) and then into the desulfurization absorption tower (6);
• at the same time, directing a path of the high-temperature flue gas output from the dust collector (4) to the wastewater concentration tower (18) for countercurrent contact with a desulfurization wastewater in the wastewater concentration tower (18) to reduce the desulfurization wastewater in the wastewater concentration tower (18) and increase solid content thereof;
• treating the high-temperature flue gas in the wastewater concentration tower (18) through a mist eliminator (19) before entering the desulfurization absorption tower (6), and feeding a slurry at a bottom of the wastewater concentration tower (18) into a thick slurry tank (22), feeding a slurry in the thick slurry tank (22) into the spray water tank (25) after being clarified by a clarifier (24) and then feeding a slurry in the spray water tank (25) to the wastewater drying tower (27) for evaporation and drying treatment;
• and
• under conditions that the concentration of HCl in the high-temperature flue gas is greater than or equal to the preset HCl concentration value, and the concentration ratio of SO2 to HCl in the high-temperature flue gas is less than the preset ratio, when the amount of the drainage water currently output from the gas-liquid separation tank (11) is less than the amount of the desulfurization wastewater required to be discharged, transporting all the drainage water in the wastewater collection tank (15) to the wastewater concentration tower (18), and then feeding part of the separated overflow slurry from the filtrate water tank (13) into the thick slurry tank (20);
• evaporating, reducing, and concentrating two parts of the slurry in the wastewater concentration tower (18), and then directing the two parts of the slurry to the clarifier (24);
• sending a supernatant from the clarifier (24) to the spray water tank (25), and then to the wastewater drying tower (27) for evaporation and drying.