What are the obstacles facing water conservation and emission reduction in the coal chemical industry”

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What “hurdles” does water conservation and emission reduction face in the coal chemical industry? Author/Source: Date: February 18, 2016. Click rate: 9. “Water conservation and emission reduction are important directions for the development of modern coal chemical industry.” The issue with water, in essence, is a funding problem. Especially for phenol-ammonia wastewater, for a coal-to-natural gas project with an annual production capacity of 4 billion cubic meters, investing in a set of treatment equipment for such wastewater requires 800 million yuan. This puts great pressure on the already struggling modern coal chemical industry. ”Wang Shoujian, chief engineer of China National Chemical Engineering Group Corporation, said recently. 　　In December 2015, the Ministry of Environmental Protection issued the “Environmental Access Conditions for Modern Coal Chemical Industry Construction Projects” (hereinafter referred to as the “Access Conditions”), which stipulates that the modern coal chemical industry must adhere to stricter water conservation standards and wastewater discharge standards. It is necessary not only to strengthen water-saving measures, but also to ensure that wastewater discharges (including saline wastewater) comply with relevant pollutant emission standards. 　　Many industry experts believe that overcoming the bottlenecks in water conservation and emission reduction in China’s modern coal chemical industry through technological innovation and system optimization is an urgent task for the industry’s development during the 13th Five-Year Plan period. Current projects have many problems yet to be resolved. Liu Zhixue, the environmental protection director of the Datang Keqi coal-to-natural gas project who participated in drafting the “Access Conditions”, said: “In accordance with the requirements of the ‘Access Conditions’, there are still numerous issues related to water conservation and emission reduction that need to be addressed in some modern coal chemical projects that are currently in operation.” First, cross-sectoral development is widespread, and there is a lack of specialized management teams ； Second, the improper use of evaporation ponds leads to the release of foul-smelling gases that disturb local residents, and a large amount of solid waste cannot be processed ； Third, there is a general lack of water bodies capable of receiving wastewater in the area surrounding the project; during testing, large amounts of clean wastewater have nowhere to go ； Fourth, wastewater with high COD and high salt content is difficult to treat, and a large amount of miscellaneous salts cannot be utilized effectively; a coal-to-natural gas project with an annual capacity of 4 billion cubic meters generates 50,000 to 80,000 tons of miscellaneous salts per year. ” 　　It is understood that high-concentration organic wastewater mainly originates from wastewater generated in the coal gasification process. It is characterized by low salt content, with COD being the primary pollutant. Generally, the COD level is above 2000 milligrams per liter, and in some sections it even exceeds 10,000 milligrams per liter. In many types of wastewater, the ratio of BOD to COD is less than 0.3; such wastewater remains difficult to treat to meet regulatory standards, thereby causing adverse effects on the surrounding environment. 　　According to Liu Zhixue, currently, the problems related to wastewater treatment in modern coal chemical industry mainly manifest in four aspects. Firstly, the industry does not pay enough attention to wastewater treatment technologies. Some research institutions focus solely on in-depth research of certain individual technologies; there are a lack of institutions capable of conducting comprehensive research across the entire process, which prevents the formation of a unified understanding. Secondly, some projects do not pay enough attention to wastewater treatment; they conduct environmental impact assessments merely to meet the requirements, exaggerating the effectiveness of wastewater treatment in a reckless manner to cover up certain technical shortcomings, which are not in line with the actual conditions of the project. Once again, there is little exchange within the industry regarding wastewater treatment technologies, and some technicians with hands-on experience are reluctant to talk about the difficulties. Finally, some units lack industry standards. Project development often faces a lack of regulatory guidelines, such as product standards for the incineration of biochemical sludge and the purification of mixed salts. 　　“The miscellaneous salts crystallized from coal chemical industry wastewater are classified as hazardous solid waste due to their presence of organic substances and trace heavy metals; these salts must be either utilized or safely disposed of. At present, the technology for the resource utilization of mixed salt materials is still in the research and development phase, and there are also constraints such as the inapplicability of standards for downstream products. Great attention should be paid to the application of effective measures and technologies for the treatment of high-salinity wastewater. ”That’s what Wang Shoujian said. 　　 Treatment of highly saline water lacks systematic optimization and integration. Currently, the treatment processes for coal chemical industry wastewater can be broadly divided into four process units: pretreatment, biological treatment, reuse of saline wastewater, and treatment of highly saline water. The high-salinity water treatment unit poses a technical challenge; although there are many types of technologies available, few operate stably. 　　“The next key tasks are to screen core technologies, optimize their integration based on experimental verification, and explore new ways to reduce and recycle miscellaneous salts. The wastewater treatment unit is a complex systems engineering project that involves various water treatment technologies. During operation, it is essential to focus on the optimization and coordination of the entire system and its processes, with particular attention paid to maintaining a dynamic balance in water volume in order to avoid disruptions to the system. The key is to focus on source control, reducing the introduction of pollutants through chemical processes; classified collection and treatment of wastewater according to its properties has become a prerequisite for wastewater treatment. ”Liu Zhixue believes that to carry out effective water conservation and emission reduction in coal chemical enterprises, it is necessary to consider the efficient use of water from a systematic perspective. All water-consuming units within such enterprises should be treated as part of an integrated water network, with efforts made to determine how to allocate water volume and quality among these units, so as to maximize the reuse rate of water while minimizing wastewater discharge. 　　It is reported that the systematic engineering approach for water conservation and emission reduction in coal chemical industries consists of: water balance testing—integration and optimization of the water network system—advanced treatment and reuse of wastewater discharged outside the system. The water balance test is the foundation; by improving and refining the measuring instruments, conducting a thorough water balance test across the entire plant, calculating the technical and economic indicators related to water use, and comparing the company’s water usage levels with those of more advanced companies, it is possible to identify and utilize the areas where water savings can be achieved most easily ； Optimization of water network system integration is crucial; by using the \"water pinch point\" method, water quality can be utilized step by step, water sources and sinks can be allocated reasonably, fresh water consumption can be reduced, thereby also significantly decreasing the amount of water distributed ； The advanced treatment and reuse of discharged wastewater is the final step; after the first two stages of treatment, the amount of wastewater discharged has already been significantly reduced. For the wastewater that still must be discharged, it is treated through advanced treatment methods to meet the standards for reuse, after which it can be reintroduced into the system. The characteristic of this step is high equipment investment and a long payback period. Pollutant control: New technologies need to be verified. According to industry experts, China is currently making active efforts to develop modern technologies for controlling pollutants in wastewater from coal chemical industries. However, many new technologies still need further improvement and validation. 　　Taking the Lurgi gasification process as an example, in addition to the light components in coal being converted into gas during the gasification process, substances such as tar, phenols, ammonia, and alkanes are also produced alongside the gas. The majority of these substances end up in the gas water, resulting in typical high-concentration, hard-to-degrade organic wastewater. To address this issue, the EBA process developed by Harbin Institute of Technology is a combined treatment technology designed to handle high-concentration phenol-ammonia wastewater generated by Ruhki reactors, BGL reactors, and low-temperature pyrolysis reactors. By improving the biodegradability of the wastewater, reducing its toxicity, and enhancing the activity of the sludge, this process enables the treated wastewater to meet the standards required for reuse. 　　A chemical company in Hubei has also developed water-saving technology for closed-loop air-cooled circulating cooling water. In a closed air-cooled circulation cooling water system, soft water or demineralized water is used as the cooling water to absorb heat from the heat exchange equipment. Soft water is circulated in a closed-loop system, without coming into contact with the outside air, thereby carrying out the heat transfer process of heat absorption and release. This process replaces traditional industrial circulating cooling water systems, using water-film air coolers or combined air coolers in place of cooling towers. It ensures that the temperature of the cooling water meets all process requirements, while also saving water, reducing scaling in piping and equipment, and extending the service life of the equipment. 　　Furthermore, the comprehensive utilization technology of concentrated brine desalination and crystallization may provide a pathway for the comprehensive utilization of highly concentrated brine. The technology of multi-stage evaporation crystallization of high-concentration brine to produce mixed salts has been validated in the fertilizer project of China Coal Tuoke, but there are still issues regarding the comprehensive utilization of these mixed salts. 　　“Crystallization salt separation and comprehensive utilization technologies involve the separation of sodium chloride and sodium sulfate through stepwise crystallization, as well as methods for dealing with impurities such as organic substances in concentrated brine; however, there is no experimental data to verify the effectiveness of this stepwise crystallization process. Furthermore, the current quality standards for sodium chloride and sodium sulfate in our country are not suitable for salt production from industrial wastewater, and further validation as well as pilot tests are required. ”Wang Shoujian explained.