Characteristics and Treatment Process of Desulphurization Wastewater from Power Plant

Characteristics and Treatment Process of Desulphurization Wastewater in Power Plant
Power plant desulfurization wastewater treatment process must take into account the following pollutant removal efficiency and extent:
(1) pH;
(2) Float solids;
(3) gypsum supersaturation;
(4) heavy metal and COD content.
For the power plant desulfurization wastewater, generally acidic (pH 4 ~ 6), suspended solids in the 9000 ~ 12700mg / L, generally containing mercury, lead, nickel, zinc and other heavy metals and arsenic, fluorine and other non-metallic pollutants. As the desulfurization wastewater is weak acid, so many heavy metal ions have good solubility. Therefore, the treatment of desulfurization wastewater is mainly chemical and mechanical separation of heavy metals and other precipitable substances, such as fluoride, sulfite and sulfate.
1. In general, desulfurization wastewater treatment includes the following four steps:
(1) Wastewater neutralization
The reaction tank consists of three compartments, each filled with self-flow into the next compartment, in the desulfurization wastewater into the first compartment at the same time by adding a certain amount of lime slurry, through constant stirring, the pH value from 5.5 or so Rose to more than 9.0.
(2) heavy metal precipitation
The addition of Ca (OH) 2 not only increased the pH value of the wastewater, but also precipitated hydroxide such as Fe3 +, Zn2 +, Cu2 +, Ni2 +, Cr3 + and other heavy metal ions. In general, the trivalent heavy metal ions are more likely to precipitate than the divalent ions. When the pH reaches 9.0 to 9.5, most heavy metal ions form insoluble hydroxides.
At the same time, the Ca2 + in the lime slurry can react with the F part of the waste water to produce the insoluble CaF2, and it is complexed with As3 + to form Ca (AsO3) 2 and other insoluble matter. At this time, Pb2 + and Hg2 + are still left in the waste water, so organic sulfide (TMT-15) is added to the second compartment to react with Pb2 + and Hg2 + to form insoluble sulfide.
(3) flocculation reaction
After the first two chemical precipitation reaction, the waste water also contains many small and scattered particles and colloidal substances, so in the third compartment by adding a certain proportion of flocculant FeClSO4, so that they condensed into large particles and deposited in the wastewater The cationic polymer electrolyte is added as a coagulant at the exit of the reaction cell to reduce the surface tension of the particles, to enhance the growth of the particles, to further promote the precipitation of hydroxides and sulfides, and to make the small flocs become more Large, more easily deposited floc, while the desulfurization of suspended solids in the wastewater also sink down.
(4) Concentration / clarification
The flocculated wastewater is overflowed from the reaction tank into the clarifying / concentrating tank containing the stirrer. The flocs are deposited at the bottom step and concentrated by neutral sludge. Most of the sludge is discharged through the sludge pump to the mortar pool, and a small portion of the sludge is returned to the wastewater reaction tank as a contact sludge to provide the nuclei required for precipitation.
The upper part of the water through the clarification / enrichment pool around the overflow port to the water tank, the water tank set up to monitor the water pH and suspended solids on-line monitoring instruments, if the pH and suspended solids to meet the drainage design standards through the water pump Effluent, otherwise it will be sent to the wastewater reaction tank to continue processing until qualified.
Although the domestic power plant desulfurization of different water quality, but overall seems to have the following characteristics:
1) was weakly acidic;
2) high content of heavy metals;
3) high salinity, high chloride ion, accelerated corrosion rate;
4) contains a large number of fouling ions, the preparation of water containing SO42-, CO3-, Ca2 +, Mg2 +, Ba2 + and other easy to scale ions;
5) suspended solids content is high, small particles.