Coking Wastewater Treatment Technology and Process

Industry status and characteristics of coking wastewater

Coking wastewater is industrial wastewater containing volatile phenols, polycyclic aromatic hydrocarbons and heterocyclic compounds such as oxygen, sulfur and nitrogen in the process of high temperature dry distillation, purification and by-product recovery of coking and coal gas. Ammonia nitrogen and difficult to treat an industrial organic wastewater. There are three main sources: one is residual ammonia water, which is the waste water produced in coal dry distillation and gas cooling, and its water volume accounts for more than half of the total coking wastewater, which is the main source of coking wastewater; the other is in the process of gas purification. The generated waste water, such as gas final cold water and crude benzene separation water, etc.; the third is the waste water generated in the refining process of tar, crude benzene, etc. and other occasions.

Coking wastewater contains pollutants including phenols, polycyclic aromatic compounds and heterocyclic compounds containing nitrogen, oxygen and sulfur, etc. It is a typical industrial wastewater containing refractory organic compounds. The easily degradable organic compounds in coking wastewater are mainly phenolic compounds and benzene compounds, and arazoles, naphthalenes, furans, and azoles are degradable organic compounds. Refractory organics mainly include arsenic, carbazole, biphenyl, terphenyl and so on.

The quality of coking wastewater varies greatly due to the large differences in the process flow and production operation methods of each plant. Generally, the quality of ammonia distillation wastewater in coking plant is as follows: CODcr3000-3800mg/L, phenol 600-900mg/L, cyanide 10mg/L, oil 50-70mg/L, ammonia nitrogen 300mg/L. If CODcr is calculated at 3500mg/L and ammonia nitrogen is calculated at 280mg/L, then each ton of coke can produce at least 0.65kg of CODcr and 0.05kg of ammonia nitrogen, and the national machine coke output is 70 million tons, then 45,500 tons of CODcr and 3,500 tons of ammonia nitrogen can be produced every year. If the sewage is not treated, how much pollution will it cause to the environment.

Coking plants use coal as raw material to prepare coke, and fresh water is needed to supplement coal washing, coke quenching, cold drum, and boiler steam, which will produce coking wastewater with complex components and high toxicity.
Coking wastewater mainly includes coal washing wastewater, coke quenching wastewater, ammonia distillation wastewater, tar processing wastewater, gas final cooling circulating water, crude benzene separation water, refined benzene separation water, ammonium sulfate wastewater and other wastewater.
The treatment of coking wastewater is generally a single treatment technology or a combination of several simple process technologies. specifically is:
1. Coke quenching wastewater
Treatment method: microbial treatment technology, etc.
2. Ammonia distillation wastewater
Treatment methods: aerobic biochemical method, GAC adsorption method, Fenton oxidation method, powder activated carbon (PAC) adsorption, etc.
3. Coal washing wastewater
Treatment methods: concentration of coal washing wastewater - filter press, coagulation and sedimentation technology, electric treatment technology, microwave treatment technology, microbial treatment technology, etc.
4. Chemical wastewater
Treatment methods: activated sludge method, biological enhancement technology, supercritical water oxidation, etc.

In addition, there is another method to treat wastewater from the source, so that the production of wastewater is gradually reduced, and finally reaches zero, that is, the reduction technology of coking wastewater. specifically is:
1. Crude benzene separation water
Treatment method: Negative pressure distillation. This reduces the boiling point of benzene and saves heat; but at the same time, the thermal cycle oil is used for heating, which reduces the generation of waste water.
2. Coke quenching wastewater
Treatment method: CDQ technology. Use inert gas instead of water to extinguish red coke, and reduce water by 0.5t/ton of coke.
3. Ammonium sulfate wastewater
Treatment method: recovery and utilization of condensate in the final cooling process of gas in coking plant. The soft water supplemented by the ammonium sulfate process finally exists in the form of residual ammonia water. Using the condensate of the gas final cooling process to replace the saturator to supplement soft water from outside can reduce the disposal load of the residual ammonia water in the coke oven gas.
4. Ammonia distillation wastewater
Treatment method: Ammonia steaming technology with heat transfer oil. Using heat transfer oil at about 270 ℃, heat some waste water discharged from the ammonia distillation tower into steam to steam ammonia instead of direct steam ammonia distillation, and the water reduction is 0.3t/ton of coke.