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Coking wastewater is produced by high-temperature carbonization of raw coal, gas purification, and chemical product refining. The composition of wastewater is complex, and its water quality varies with raw coal composition and coking process. Nuclear magnetic resonance chromatograms show that the coking wastewater contains dozens of inorganic and organic compounds. Among them, inorganic compounds are mainly a large amount of ammonia salts, thiocyanides, sulfides, cyanides, etc. In addition to phenols, organic compounds include monocyclic and polycyclic aromatic compounds, heterocyclic compounds containing nitrogen, sulfur, and oxygen, etc. . In short, the serious pollution of coking wastewater is a prominent environmental problem in the discharge of industrial wastewater. In-depth study of advanced treatment technology for coking wastewater is not only a realistic problem facing the current economic construction, but also the focus of technical research in the future. We should seek both efficient and economical treatment technologies, improve environmental quality, and realize the recycling of water resources.
A large amount of waste water containing toxic, harmful substances such as phenol, cyanide, oil, and ammonia nitrogen was discharged during the coking production process. Coking wastewater mainly comes from coking and gas purification processes and the refining process of chemical products, and the remaining ammonia produced in the process of helium evaporation is the main source. Distilled ammonia waste water is the waste water discharged after mixing the remaining ammonia water for distillation. Residual ammonia water is the most important phenol cyanide wastewater source of the coking plant. It is a high-concentration phenol water containing ammonia, which is discharged by the circulating ammonia water pump in the condensing blast section and sent to the remaining ammonia water storage tank. The remaining ammonia water is mainly composed of three parts: the wet storage water on the surface of the loaded coal, the combined water produced by the carbonization of the loaded coal, and the oily process wastewater added to the gas suction pipe and the collector oxygen circulating water pump. The total amount of remaining ammonia can be calculated based on 14% of the coal in the furnace. After the remaining ammonia is mixed with the process wastewater sent by other production units in the storage tank, it is called mixed residual ammonia. Where the remaining ammonia is mixed, some are directly steamed ammonia, some are dephenolized first, then ammonia are distilled, some are combined with ammonia-rich water to steam ammonia, and some are desulfurized and rich ammonia together with desulfurized rich liquid. Filtering and degreasing before deacidification . The coking plant also contains some other wastewater, the proportion of which is not large, and the pollution index is also low, so it will not be introduced here.
废水特点 Characteristics of coking wastewater
Coking wastewater contains pollutants including phenols, polycyclic aromatic compounds and heterocyclic compounds containing nitrogen, oxygen, and sulfur. It is a typical industrial wastewater containing difficult-to-degrade organic compounds. The easily degradable organic compounds in coking wastewater are mainly phenolic compounds and benzene compounds, and pyrrole, naphthalene, furan, and oxazole are degradable organic compounds. The hardly degradable organic substances are pyridine, carbazole, biphenyl, terphenyl and the like.
The water quality of coking wastewater varies greatly depending on the process and production operation methods of each plant. The quality of the steamed ammonia wastewater from the coking plant is as follows: CODcr 3000mg / L, phenol 600-900mg / L, cyanide 10mg / L, oil 50-100mg / L, ammonia nitrogen 100-300mg / L. If CODcr is calculated as 3500mg / L and ammonia nitrogen is calculated as 280mg / L, each ton of coke can produce at least 0.65kg CODcr and 0.05kg ammonia nitrogen.
Hazards of coking wastewater
If coking wastewater is directly discharged without treatment, it will cause serious pollution to the environment.
Coking wastewater is also called phenol cyanide wastewater. In addition to containing a large amount of phenol, cyanide, and ammonia nitrogen, there are also small amounts such as indole, benzofluorene (a), naphthalene, and indene. Some of these trace organic substances have been identified as Carcinogens, and not easily biodegradable, this high concentration of toxic wastewater is the focus of sewage treatment in coking plants.
1. Harm to water bodies and aquatic organisms.
Coking sewage mainly contains organic matter. Most organic matter is biodegradable and can consume dissolved oxygen in water. When the oxygen concentration in the water is below a certain limit, the survival of aquatic animals will be affected. When the oxygen in the water is depleted, the water quality deteriorates severely. Other substances in the sewage such as oil, suspended matter, cyanide, etc. are also harmful to water bodies and fish, and nitrogen compounds can cause eutrophication of water bodies.
2. Toxic effect on human body.
The phenolic compounds contained in the sewage are prototype toxicants, which can inhale through the skin and mucous membranes and inhale through the oral cavity to invade the human body, causing the human cells to lose vitality. In addition, they can penetrate deeper, causing deep tissue damage or necrosis; Low-grade phenol can also cause skin irritation. Long-term drinking of phenol-containing sewage can cause dizziness, anemia, and various nervous system disorders.
3. Harm to agriculture.
4. Directly irrigating farmland with untreated coking sewage will reduce crop yields and wither; oily substances in sewage will block soil pores, make the soil high in salt content, and soil salinization.
Coking wastewater treatment equipment
Domestically, the physical and chemical + biochemical treatment process is used to treat coking wastewater. Firstly, oil particles are removed through an oil trap and air flotation, and then harmful substances such as phenol, ammonia, and cyanide sulfide are removed through a stripping tower. The biochemical method is used for detreatment, and the biochemical effluent enters the coagulation reactor to further remove COD and oil. Finally, phenols and COD are removed through secondary filtration to ensure that the system effluent meets the standard discharge.
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