The Study Of Coal Gas Scrubbing Wastewater Treatment

Coal gas scrubbing wastewater mainly comes from large enterprises of gas, steel, glass, metal smelter and fertilizer industries. It has the characteristics of high temperature and SS (suspended substance). The initial indexes of the coal gas scrubbing wastewater are:COD 569mg/L, pH 3.9～4.9, SS 284mg/L, turbidity 121NTU, volatile phenol 13.34mg/L, S2-16.8mg/L, rigidity 212 mg/L, Fe2+ 25～28 mg/L and ammonia 460 mg/L. It is thus clear that the discharge of coal gas scrubbing wastewater is not only a waste of resources but also a very serious pollution to the environment. Developing the research of treating coal gas scrubbing wastewater has great significance to reduce the enterprises'water consumption indicators, enhance the safety and efficiency of gas production and improve the effectiveness of developing and utilizing water resources.The target of this research is choice an oxidation and flocculation way which is efficient and economical. With that way, we can treat the coal gas scrubbing wastewater well, prove the effluent water quality, and increase the use ratio of water resource. According to the characteristics coal gas scrubbing wastewater from a chemical plant in BaiYin city, GanSu province. The treatment technologe was chosen which consists flocculation, Chemical oxidation and antiincrustation corrosion. With that process, NaClO is the oxidant. Alum is the flocculant. The antiincrustation corrosion inhibitor choosing experiment was completed by cooperation of Blue Star Cleaning Co., Ltd and us. The best experiment condition was found out through the experiment, and the mechanisms of oxidation, desulfuration and flocculation were analysed in depth.Studies show that, the desulfuration and turbidity removal effect of NaClO was better than other oxidants, the highest desulfurization rate can reached 96.19%, the turbidity removal rate can reached 99.67%; using alum as flocculant, the pH of raw water wasn't need to adjust. It can be used in pH by 6～7, the dosage of alum powder is 0.288t/d. The subside time is about 5 min, the removing rate of COD is about 20%, the removing rate of turbidity is more than 60%, and it wasn't increase the sulfate in water. The cost is 374.4RMB/d. It is cheaper and better than other flocculants. At the same time, the monitor control index of NaClO dosage was discussed through experiments. By researching the relationship between ORP (Oxidation Reduction Potential) and the dosage of NaClO, an result can be obtained that under the condition which temperature is 55℃, pH is 6.35 and NaClO dosage is 2.4%. The removing rate of CODCr in coal gas scrubbing wastewater can reach 80%. At the same time, the ORP is 198mV. Therefore, using ORP as monitor control index of oxidant dosage is feasible.