Problems and optimization reconstruction of water reuse near zero discharge project in a urea production enterprise
In view of the problems existing in the reclaimed water reuse near zero discharge project of a urea production enterprise in Ningxia province such as:low removal rates of silicon and CODCr,serious fouling and short service life of RO membrane,low quality of condensed water from secondary steam evaporation and crystallization,salt imbalance in entire process design and high operating costs,a reconstruction was carried out.Many measures were adopted during the reconstruction,which includes:replacing sodium aluminate-liquid alkali-pure alkali softening with double alkali softening,replacing sodium metaaluminate with magnesium agent for silicon removal,adopting biological aerated filter to transform ammonia nitrogen into nitrate,using powdered activated carbon to re-move CODCr by coagulation adsorption,adding decarbonization device to reduce alkalinity of evaporative crystalliza-tion influent,rebuilding water-salt balance,raplacing DTRO with HLRO.Through the reconstruction,the removal rates of silicon in sewage and concentrated water in desalinated water station were increased from 26％,75％to above 95％,the removal rate of CODCr was increased from 0 to 60％,the cleaning frequency was reduced by 75％,the service life of RO was decreased from 0.5-2.0 a to 1.5-3.0 a,the mass concentration of TDS of secondary steam condensate decreased from 1 000-1 200 mg/L to about 600 mg/L,the mass concentration of NH3-N de-creased from 45-55 mg/L to about 25 mg/L,the electricity consumption was reduced from 5.71 kW·h/t[water]to 5.18 kW·h/t[water],and the operation cost was decreased from 20 yuan/t[water]to 12 yuan/t[water].
chemical softeningsilicon removal ratezero dischargecoagulation adsorptionmembrane con-centration
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