Dongxinyuan overcomes the challenge of zero discharge in coal chemical wastewater treatment

Thread Content

Dongxinyuan Overcomes the Challenge of Zero Discharge of Coal Chemical Industry Wastewater Author/Source: China Chemical Industry News Date: 12-06-2017 Clicks: 25 Last week, news came from Shaanxi Dongxinyuan Chemical Co., Ltd. The company took advantage of its own industrial chain capabilities in lignite carbon, coal tar hydrogenation, metallic magnesium, and power generation to develop innovative methods for treating wastewater at the source, by classifying it and applying appropriate treatment strategies; this approach enabled true zero discharge of wastewater, thus solving the major environmental challenge associated with wastewater treatment in the coal chemical industry. Relying on the abundant local coal resources, Dongxinyuan has established a project for the clean and comprehensive utilization of coal in different forms, producing semi-coke, lightweight coal tar, and magnesium metal, while also generating electricity as a by-product. The project includes 1.2 million tons per year of semi-coke, 500,000 tons per year of coal tar hydrogenation, 20,000 tons per year of metallic magnesium, along with supporting 2×25MW thermal power plants. However, due to numerous defects in the project design and construction, the commissioning process did not progress smoothly, and the process flow was not established by May 2016. In particular, during testing in December 2015, a leakage of industrial wastewater occurred, resulting in pollution of the nearby Shaliang River. In June 2016, Shaanxi Coal Group adjusted the leadership team of Dongxinyuan in light of the prevailing circumstances. After careful consideration, the new leadership team of Dongxinyuan determined that the main reason for the failure to put the facility into operation smoothly was due to \"three errors\": incorrect principles in process design, incorrect design criteria, and improper selection of key equipment. It has been decided to aim to establish the process flow in the shortest possible time, and to carry out wastewater treatment and technical rectification work as soon as possible. It is understood that the industrial wastewater generated from coal pyrolysis for the production of semi-coke has posed a challenge to the development of this industry due to its complex composition. Although coal chemical enterprises in China have also attempted to achieve zero emissions, either the end-stage treatment methods after centralized processing are not effective, or the investment and operating costs of such facilities are too high for companies to bear. In July 2016, Dongxinyuan established a technical task force on its own, and through in-depth analysis and discussions as well as collective brainstorming, it rejected the original plan to invest 93 million yuan in a sewage treatment project with a construction period of over one year. The task force overcame the unscientific traditional approach used by manufacturing enterprises for the centralized treatment of wastewater. By leveraging its unique advantages in the industrial chains related to lignite, coal tar hydrogenation, metallic magnesium, and power generation, it developed a wastewater treatment solution tailored to the characteristics of Dongxinyuan. This solution involves treating wastewater at the source by classifying it according to different qualities and applying appropriate treatment methods, thereby achieving zero emissions. After gas washing in the lignite carbon plant, 20 tons of ammonia-containing wastewater are generated per hour. Due to the high ammonia content in the gas, this has a significant impact on the quality of the adsorbents, the output volume of the product, and the operation of the equipment. Dongxinyuan carries out ammonia removal, oil removal, and phenol removal processes on ammonia-containing wastewater, and the resulting ammonia water is used by power plants for desulfurization and denitrification. The spray washing liquid is recycled and reused, creating a closed-loop system. The oily wastewater generated by delayed coking is highly emulsified, posing a significant treatment challenge in this industry; as a result, it is usually forced to be incinerated at high temperatures. Dongxinyuan has uniquely developed a method for separating oil from oily wastewater through pyrolysis, with the oil being recovered after condensation in a gas-electric tar catcher. For sulfur-containing wastewater, Dongxinyuan cleverly uses a combined acid-base method to recycle it for use in replenishing water in the ammonia tank. The clean water with concentrated salts produced by power plants is generally discharged outside, while Dongxinyuan reuses it for pouring magnesium metal slag. After undergoing renovation through in-house construction, all the industrial wastewater generated by the various units at Dongxinyuan during the production process is reused after preliminary treatment, achieving zero emissions – not a single drop of industrial wastewater is discharged – and 2,000 cubic meters of tap water and softened water are saved each day. The wastewater treatment solution developed by Dongxinyuan Innovation, which features low investment, rapid results, and low costs, has proven effective in practice. It not only resolves the environmental challenges related to wastewater treatment that hinder corporate development but also enables the reuse of wastewater to produce new products such as sulfuric acid an, thereby increasing economic benefits. It not only saves 93 million yuan in funds required for the renovation project and at least one year of construction time, but also reduces wastewater treatment costs by about 60 million yuan per year. The new leadership team at Dongxinyuan adheres to a management philosophy of \"science, diligence, and strictness,\" and upholds the principle that \"emergency repairs must be completed before meals, and machine preparations must be finished within 24 hours.\" By breaking away from conventional practices, they have developed advanced management concepts for chemical production such as \"maintenance without shutting down operations,\" \"inspections without stopping production,\" and \"immediate action in case of shutdowns.\" Since June 2016, Dongxinyuan has carried out more than 700 minor optimization and technical improvement projects, overcame numerous technical challenges, and gradually resolved issues such as wastewater treatment problems, defects in process design, and incorrect equipment selection that were hindering the project’s trial operation. In November 2016, the facilities at Dongxinyuan’s initial light oil production plant entered the commissioning phase; on December 12, the process flow was successfully operationalized to produce qualified oil, achieving a successful first batch of production. Since the trial production began, Dongxinyuan has continuously carried out technical upgrades, fully tapping into its potential and optimizing its production systems in order to keep production costs as low as possible and maximize the capacity of the facilities. This approach not only saved 300–500 million yuan in capital required for startup during trial production but also enabled the company to achieve profitability in a short period of time. The product quality remains stable, and there is a high demand for these products in the market. Apart from a 10-day shutdown for major maintenance, production has remained continuous throughout the year, with a trial production start-up rate of 100%, far exceeding the profit target set at the beginning of the year. It is expected that in 2017, the company will achieve operating revenues of over 1.5 billion yuan, with profits exceeding 100 million yuan.