Study On Water Quality Control Technology Of Refinery Wastewater Evaporation Process

There was large number of low temperature waste-heat in the refinery. The refinery wastewater was treated by the low temperature multi-effect evaporation technology, which can achieve the refinery’s energy saving effectively. In order to guarantee the normal operation of the system, the water quality was COD< 10mg/L, Si<20mg/L, turbidity≤ 3NTU. In this paper, the drainage of secondary settling tank of refinery in Dalian was treated by adsorption-coagulation technology. It was mainly inspected water quality characteristics of drainage and the removal efficiency organic、silicon and suspended solids by coagulants and adsorbents treatment. And it was researched adsorption-coagulation integration of the preliminary design. The following conclusion were put forward by the experiment.(1)The wastewater characteristics of secondary settling tank of refinery:pH=6.0 to 7.0 was weakly acidic; COD was 72.5mg / L; the silicon content was 221.3mg / L, turbidity was 31.3NTU. The content of each index was low. UVS, IR and GC / MS analysis showed that the water contains mainly ware aromatic substances, hydrocarbons, amides substances.By laser particle size analysis,90% of water samples particle diameter ware mainly distributed in the range of 1～10μm.(2)The removal efficiency of pollutants was treated by coagulant in water.Three kinds of coagulants:Fe (Ⅱ/Ⅲ) Al composite coagulant, MgCl2, PAC ware selected. The amount of coagulant added. pH, temperature and stirring intensity on the pollutants removal efficiency of wastewater ware investigated. The analytic hierarchy process (ahp) was used to evaluate coagulation in refining wastewater treatment. The results showed that:the total score of Fe (Ⅱ/Ⅲ) Al composite coagulant was highest (0.59). Treatment conditions:coagulant dosage was 300mg/L, pH= 6.0～7.0. The amount of HPAM (2%) was 5mg/L. The result of experiment was ECOD= 24.9%, Esi= 93.7%, turbidity= 2NTU.(3) The removal efficiency of pollutants was treated by adsorbtent in water.The removal efficiency of organic by activated carbon was better than clay adsorbent. Three kinds of adsorbents (woodiness powder activated carbon, molecular sieve ZSM-5B, coal powder activated carbon) ware selected. The amount of adsorbent added, pH, temperature and adsorption time on the pollutants removal efficiency of wastewater ware investigated. The analytic hierarchy process (ahp) was used to evaluate adsorption in refining wastewater treatment. The results showed that:the total score of woodiness powder activated carbon was highest (0.51). The correlation coefficient R2 of Fruendlich equation of wood powder active carbon was more than 0.9,1/n= 0.29865. So woodiness powder activated carbon was better than other adsorbent for organic matter adsorbing. Treatment conditions:adsorbent dosage was 0.5g/L, pH= 6.0-7.0. The amount of HPAM (2%) was 5mg/L. The result of experiment was ECOD= 68.7%.(4) Coagulation - adsorption - settling integration testThe results of three different units showed that: the adding site of adsorbent before coagulant was good for COD removal efficiency. Adsorption time was 20min. Then coagulant and HP AM coagulation time was 11 min. After mechanical clarify the reactor, the water quality was COD=9.38mg/L, turbidity=1.6NTU, Si = 14.83mg/L.(5)The dynamics of flocculation and sedimentation theory as the guidance, the mechanical accelerated clarification tank and the inclined plate settler were be redesigned. The wastewater was treated by wood powder active carbon, then added coagulant for coagulation. The size of floc was increased when the slurry through cylinder with baffle plate. The lower part of the sludge bed layer would absorb a part of pollutants. Adsorption - coagulation sedimentation could be conducted in the same device. It could reduce the area.