Regarding the treatment of coking wastewater and "zero discharge"”

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Regarding the treatment issues of coking wastewater and “zero discharge” 1. The generation of coking wastewater - (1) external and internal moisture of coal entering the furnace, (2) combined moisture, (3) process washing water. Assuming that the internal and external moisture of the coal entering the furnace is 12%, the amount of wastewater (called residual ammonia) in a coking plant with a scale of 900,000 tons of coke (full) per year is approximately 16~20m3/h. 2． The sources of coking wastewater - (1) remaining ammonia water, (2) crude benzene separation water, (3) final cooling drainage, (4) tar separation water, (5) phenol salt decomposition water, (6) refined phenol separation water, (7) Gumalon drainage, etc. 3． Composition characteristics of coking wastewater - (1) High phenol content: The phenol content of the remaining ammonia water is generally 2000~2500mg/L. (2) High ammonia content (including volatile ammonia and fixed ammonium), generally containing 8~15g/L of volatile ammonia and 3~35g/L of fixed ammonium. (3) The COD value is high, usually several thousand mg/L. (4) Contains a lot of suspended tar, usually several hundred mg/L. 4． The treatment process of contemporary coking wastewater - residual ammonia → solvent removal of phenol → ammonia evaporation → biological removal of phenol → external drainage. 5. Contemporary dephenolization processes for remaining ammonia water include (1) Steam dephenolization method - use circulating hot steam to blow off the phenolic compounds in the remaining ammonia water, and then spray it with NaOH solution to absorb the phenol in the water vapor to generate sodium phenolate (salt). The dephenolization efficiency of this method is low, about 80%. Therefore, it is no longer used in China. (2) Solvent extraction dephenolization method - the solvent has: Solvent oil, crude benzene, light benzene, N-503-kerosene, etc. The process is residual ammonia → oil removal → solvent extraction → oil-water re-separation → phenol-containing solvent and dephenolated ammonia (send steamed ammonia process). Phenolic solvent → desulfurization → back extraction (alkali washing) → phenate and solvent (return to circulation). This method has a high dephenolization efficiency of more than 90%. 6. The contemporary ammonia evaporation process for residual ammonia water is divided into (1) according to the heating method.: Steam stripping and distillation, thermal oil, tube furnace. (2) Divide according to different recycled products: Recycling and producing yellow blood salts with HCN and non-yellow blood salts. (3) According to the method of recovering fixed ammonium: Lime water method and NaOH solution method. The obtained ammonia vapor is generally sent to produce ammonium sulfate or concentrated ammonia water, or is used for ammonia decomposition, ammonia incineration, or as an alkali source for wet desulfurization. 7. Contemporary biological dephenolization treatment methods, taking Shanghai Baosteel Chemical Company as an example: (1) In the first phase, Nippon Steel technology is introduced, and the treatment process is: steaming ammonia wastewater → pre-aeration to remove HCN → surface aeration → precipitation and separation → → activated carbon treatment → discharge to the Yangtze River. (2) The American Chester method introduced in the third phase, the process flow is: Remove phenolized ammonia water through solvent → Ammonia evaporation device → Adjusting tank → Pre-aeration for 18.8h → Aeration for 76h → Sedimentation tank → Denitrification filtration → Denitrification and precipitation → Re-aeration → Cyanide treatment → Fluoride treatment → Mixing → Flocculation → Final precipitation → Final pH adjustment → Emission. (3) A/O and A/OO processes used in the first and second phases of transformation: •A/O process: Wastewater → oil removal tank → air flotation tank → homogenizing and regulating tank → anaerobic tank → anoxic tank → aerobic tank (aeration 18~30h) → second sedimentation tank → coagulation and sedimentation tank → external drainage. •A/OO process: Water inlet → anoxic (A) section → aerobic section 1 (nitrification section) (aeration 8~12h) → first sedimentation tank → aerobic section 2 (nitrification section) (aeration 10~18h) → second sedimentation tank → water outlet. 8. Issues worthy of research and discussion on contemporary biological dephenolization methods: (1) Secondary air pollution problem of aeration method. (2) Secondary pollution problem caused by adding multiple chemicals. 9. Possible ways to achieve zero discharge of coking wastewater (1) Treated wastewater is reused as wet coke quenching supplementary water (2) Plant-wide circulating water supplementary water (3) Desulfurization liquid for solvent dephenolization and extraction solvent (4) Liquid preparation water and dilution water for each process (5) Coal yard dust-proof spray liquid, etc. 10. The application of the "Gerui" new process in Chengdu, Sichuan, achieves "zero discharge of ammonia evaporated wastewater" from coking (1) "Gerui" process: Ammonia evaporation wastewater → "Gray" method treatment → supplementary water for converter flue gas wet dust removal, or supplementary water for sintering, or supplementary water for ironmaking slag washing, or supplementary water for wet coke quenching. Ultimately, “zero discharge” of coking wastewater will be achieved. (2) Characteristics of the "Gray" method: 1. Cancel the "biochemical treatment" device ； 2. No dilution water is added, and the amount of wastewater treated is small. ； 3. Simple process and low operating cost ； 4. As a user of supplementary water, it will not scale or corrode, and the operation will be stable and normal. (3) Core technology of "Gray" method: 1. Coking wastewater is treated with special ammonia evaporation technology ； 2. Ammonia evaporation wastewater undergoes special physical and chemical treatment technology using the "Gray" method ； 3. Stabilization technology for reusing dust removal water from converter steelmaking plants, blast furnace slag washing water, coke quenching water from coking plants, and batching water from sintering plants, etc. 11. Evaluation of the "Gray" process (1) The "Gray" method uses evaporated ammonia wastewater as the starting material, without biological dephenolization, and can be directly used for circulating supplementary water for coke quenching, converter steelmaking dust washing, blast furnace slag washing, and batching water for sintering pellets, etc. It can not only save the investment cost of biological dephenolization equipment, but also achieve "zero discharge" of coking wastewater. It is especially suitable for coking plants that have not yet built biological dephenolization. (2) The "Gray" method uses biochemical wastewater as the starting material and is directly used for circulating supplementary water for coke quenching, converter steelmaking dust washing, blast furnace slag washing, and batching water for sintering pellets, etc., to achieve "zero discharge" of coking wastewater. To be sure, the requirements for biological dephenolization can be relaxed and the cost of biological dephenolization can be reduced. For cases where a biological dephenolization device has been built but the external drainage water quality does not meet the * * Standard coking plants are particularly suitable. (3) Since the coking plant of Chuanwei Iron and Steel Group has not built a solvent dephenolization device, nor a fixed ammonium salt decomposition device, the operation of the ammonia evaporation device of the remaining ammonia water must add more alkali liquid to fix the phenol (forming phenol sodium salt) and decompose the fixed ammonium salt into volatile ammonia. For coking plants that have built solvent dephenolization and fixed ammonium salt decomposition devices, there is no need to add alkali liquid during ammonia evaporation operation. (4) In order to improve the ammonia evaporation efficiency of the remaining ammonia ammonia evaporation device and reduce steam consumption, * Suggestions: (1) Add a steam injection device to save steam consumption and reduce the ammonia content of ammonia evaporation wastewater. (2) Use high-efficiency ammonia evaporation tower, etc. * Purpose: Lay a solid foundation for the promotion and application of "Gray" technology. The quality of ammonia evaporated wastewater has been improved, and the processing load of the "Gray" process unit has been reduced. It can be seen that the "Gray" technology still needs to be perfected to facilitate promotion and application. * Prospects for promotion and application: (1) In the first step, coking plants that have already built solvent dephenolization and biological dephenolization devices, such as: Panzhihua Iron and Steel Coking Plant applies "Gray" technology to treat qualified or unqualified discharged wastewater after biological dephenolization to achieve "zero discharge" of coking wastewater. This technology has great practical significance for existing metallurgical enterprises. (2) In the second step, for coking plants that have not built a biological dephenolization device but have built a solvent dephenolization device, such as: The Panzhihua Iron and Steel Coking Plant Expansion Project directly applies the perfected "Gray" process to treat ammonia evaporated wastewater to achieve "zero discharge" of coking wastewater. This technology eliminates the biological dephenolization device, so it is more superior, more economical, more energy-saving, and more valuable for promotion. (3) In the third step, for independent coking plants that have not (already) built a solvent dephenolization device and a biological dephenolization device, if they only need to undergo special ammonia evaporation treatment and then apply the "Gray" technology to directly mix the ammonia evaporation wastewater into the clean circulating water system and use it as coke quenching supplementary water to achieve "zero discharge" of coking wastewater, then the "Gray" process will have more universal promotion value. In short, the "Gray" process is an advanced environmentally friendly technology, the first of its kind in China. There are no application reports abroad. If improved, it will reach the international leading level. In particular, the realization of "zero discharge" of coking wastewater is of great practical significance and social and economic value.