Problems and Development Trend of Coal Chemical High Salt Wastewater

With the rapid development of industry and the increasing demand for coal resources, it has greatly promoted the development and progress of the coal industry. However, while producing coal and related products, it also brings some pollution problems, which are not conducive to the construction of an ecologically balanced and environmentally friendly society in China. For example, wastewater with high salinity discharged from coal chemical production process needs to be advanced treated by various combined processes. At present, with the increasingly stringent environmental protection requirements, more and more enterprises begin to implement "zero discharge" of wastewater. However, there are still some problems in the related treatment technology. These problems must be paid great attention by the relevant personnel, in order to effectively ensure that the treated product Water and salt meet the corresponding standards.

Coal chemical industry is of great significance to the development and progress of China's industry, but the lack of water resources also limits the progress of the industry to a certain extent. In the daily production of coal chemical industry, a large number of high-salt wastewater will be produced. If it is not treated, it will be discharged, which will cause serious environmental pollution, even pollution of groundwater and soil. Therefore, through reasonable and effective technology, while realizing zero discharge of wastewater and eliminating pollution caused by organic pollutants to the environment, separating Sodium chloride and SODIUM SULFATE from high brine and recycling them are the current trend of high salt wastewater treatment in coal chemical industry. The classification of coal chemical wastewater is

1. The types of wastewater  

For the generated wastewater, they are generally divided into two categories: "process organic wastewater" and "saline wastewater". The former is mainly process wastewater and domestic wastewater, and the pollutants are mainly COD, and the salt content of this kind of wastewater is relatively low, so the treatment process is relatively easy. In the treatment of organic wastewater, the characteristics of water quality should be analyzed first. After pretreatment and biochemical treatment, the wastewater can be reused in the production process. The latter comes from a wide range of sources, such as gas washing wastewater, circulating water system drainage, desalted water system drainage and concentrated water produced in the recycling water treatment system in the process of gas purification.

2. Sources of coal chemical wastewater

In the coal chemical industry, the source of "salt" in salt-containing wastewater is very special. Its generation is closely related to the supplement of fresh water and circulating cooling water, and new high-salt wastewater will be produced in the desalination process. At the same time, in the treatment of organic wastewater, it is often used. Because of the need to add treatment agents, the corresponding high salinity wastewater will also be produced. For example, in a large coal enterprise in China, fresh water is used to supplement the coal-to-natural gas project, and the amount of salt brought in in in this process has exceeded half of the system's salt. At the same time, nearly 30% of the salt will be produced in the production process and in the process of adding chemical agents to the water system. Although the cycle multiple of the circulating cooling system can be optimized and selected, it is difficult to reduce the salt content of wastewater. Generally speaking, TDS of salt-containing wastewater in coal chemical industry is often kept at about 5000mg/L, which is at a high level.

At the present stage, the process of treating high salinity wastewater can be divided into pre-treatment, main process and post-treatment.

In the former stage, the technologies used include chemical softening, catalytic oxidation and membrane concentration, the main purpose of which is to remove calcium ions, magnesium ions and COD, thus laying a good foundation for the subsequent process. In the main process, two methods can be used, i.e., membrane process and thermal process, in order to achieve the removal of monovalent salts in highly saline wastewater. The purpose of separating divalent salts is to prepare sodium chloride crystals with high purity by evaporation crystallization and freezing crystallization. At the same time, the crystallization of sodium sulfate is realized by freezing crystallization, and the corresponding salts are obtained through drying system, thus realizing zero discharge of wastewater.

3. Problems in treatment technology and Countermeasures

Considering the actual production and operation of some enterprises, the main problem of zero discharge of wastewater is the management and control of system risk, which mainly includes the following four aspects. The first is how to strengthen the recycling of water. On the basis of fully understanding the actual water demand of each device and ensuring the rational distribution of water resources, the effective utilization rate of water resources can be effectively improved, so as to realize the quality recovery and reuse of wastewater. It is necessary to find a way to control the discharge of high salinity wastewater and find a suitable solution. Firstly, before the zero discharge design, the water balance and salt balance of the whole process should be calculated, and the data should be analyzed accordingly. At the same time, the water system recycling base should be calculated.