Classic case analysis of EPC projects for wastewater in the chemical industry

Thread Content

　I. Introduction In recent years, with the rapid development of industrialization in China, the demand for energy and raw materials has increased sharply, which has accelerated the fast growth of chemical industries such as petrochemicals, coal chemicals, and fine chemicals. The chemical industry is a major consumer of water and a significant source of wastewater discharge, which thus presents valuable development opportunities for our water treatment company. Meihua Bobada acts in a timely manner, leveraging advanced technology and R&D capabilities to create comprehensive water system solutions suitable for various industries. By providing services for water treatment projects such as Shenhua Coal-to-Olefins, Shenhua Coal-to-Oil, Shenhua Polyoxymethylene, Jinxin Chemical, and Shandong Zhongsheng Chemical, this demonstrates the further maturity and improvement of Meihua Boda’s comprehensive solutions for coal chemical industry water treatment systems, and it also establishes our position as a leader in this field. At the same time, thanks to our advanced technology, excellent quality, and superior service, we have won the favor of many clients. Examples include winning the contracts for water treatment and wastewater treatment projects at Tenglong Aromatics (Xiamen) Co., Ltd., the 30,000 m3/d comprehensive wastewater treatment plant project for Jiangsu Supor (Group) Co., Ltd., and the water treatment project for Hengli Petrochemical (Dalian) Co., Ltd. 　　As is well known, chemical wastewater is characterized by high concentrations of organic matter, high salt content, high color intensity, and a complex composition; it often contains substances toxic and harmful to microorganisms as well as biodegradably difficult organic compounds, which makes its treatment challenging. The following introduces the application of water treatment technologies in various chemical industries through two engineering cases. 　　II. Water System Solutions for Tenglong Aromatics (Xiamen) Co., Ltd. 1. Project Overview Tenglong Aromatics (Xiamen) Co., Ltd. is a petrochemical enterprise that produces PX, with a designed production capacity of 800,000 tons per year; it is included in the national PX industry plan for the 11th Five-Year Plan period. The water system of the Tenglong Aromatics project is mainly divided into two parts: water treatment works and sewage treatment works. The water treatment systems include: an industrial water treatment system (140,000 m3/d), a domestic water supply system (50 m3/h), a desalinated water system (72,000 m3/d), a steam condensate treatment system (14,400 m3/d), and a fire protection water system (750 L/s). The wastewater treatment project consists of five components: the wastewater treatment system, the rainwater monitoring and fire accident tank system, the odor collection and treatment system for the wastewater treatment plant, the BTX-containing wastewater stripping treatment system (30 m3/h), and the clean wastewater treatment and reuse system (250 m3/h). The wastewater treatment system itself includes an oily wastewater treatment unit (350 m3/h), a saline wastewater treatment unit (250 m3/h, with a recirculation system capable of handling 100 m3/h of water), a sludge dewatering unit (15 m3/h), and an used oil recovery and treatment unit (15 m3/h). The water system involved in the Tenglong Aromatics project is quite comprehensive, covering a wide range of aspects, with complex and diverse process methods; only the circulating cooling water station is not included in it. 　　2. Process Technology and Overcoming Difficulties 　　1) Introduction to three systems in water treatment projects 　　(1) Industrial water treatment system 　　The raw water comes from reservoirs or rivers, and the following traditional processes are used: 　　Raw water → Raw water tank → Coagulation and sedimentation tank → Sand filter (V-type filter) → Disinfection → Clear water tank/firefighting water tank → Pressurized delivery to various users 　　The difficulties in this project lie in the large scale of treatment required and the limited available space. To solve this problem, we replaced the circular mechanically stirred clarifier with a horizontal flow sedimentation tank, and built the coagulation tank and sedimentation tank above the original water tank; since it is difficult to construct a mechanically stirred clarifier above a water tank, this approach resolved the issue of insufficient space. 　　(2) Demineralized water system The demineralization process utilizes ion exchange, with both the anion and cation beds being double-chamber types. This process is mature and reliable; we have extensive experience in implementing it, and filtration rate and exchange capacity are the key factors to control. 　　(3) Steam condensate treatment system This system is used to refine and reuse steam condensate, with the aim of removing oil, iron, and salts. The process is as follows: Steam condensate → Heat exchanger → Oil and iron removal filter → Mixed ion exchanger → Water storage tank → Pressurized and sent to the boiler. The key part of this system is the removal of oil and iron; therefore, we choose the oil and iron removal filter carefully and meticulously. We aim to provide our customers with advanced, reliable, safe to operate, easy to use, and cost-effective processing equipment; therefore, we conducted numerous investigations and made comparisons among various options before selecting the supplier for such equipment. 　　2) Introduction to the two systems in the wastewater treatment plant 　　(1) Wastewater treatment system 　　The wastewater treatment system consists of two units: an oil-containing wastewater treatment unit and a salt-containing wastewater treatment unit. 　　A. Process for treating oily wastewater: Oily wastewater → Regulation and oil removal tank → Lift pump → Vortex air flotation → Dissolved air flotation → A/O biological treatment tank → Secondary sedimentation tank → BAF tank → Sand filter → Activated carbon filter → Disinfection → Reuse water tank → Pressurized transmission to various users.
B. Process for treating saline wastewater: Saline wastewater → Regulation and oil removal tank → Lift pump → Vortex air flotation → Dissolved air flotation → A/O biological treatment tank → Secondary sedimentation tank → BAF tank → Discharge after meeting regulatory standards.
Given that the water quality and volume of wastewater in both units are similar, with only a significant difference in salt content, the same pretreatment and biological treatment processes are used; however, the saline wastewater is not reused but is discharged after meeting the required standards. The pool types, capacity sizes, and equipment configurations have been standardized, which facilitates design, results in a more rational layout, and makes operation and maintenance easier. 　　The design of the A/O tank takes into account the characteristics of the water quality as well as ease of operation and maintenance; disc-type jet aerators are used to ensure that the dissolved oxygen level in the water remains at an appropriate level. BAF is a mature process in our company, used in many projects; based on traditional designs, it involves adjustments to the air and water intake for backwashing to make them more uniform. 　　(2) Clean wastewater treatment and reuse system: Clean wastewater → equalization tank → softening, coagulation and sedimentation → sand filter → secondary filtration → ultrafiltration UF → secondary filtration → reverse osmosis RO → reclaimed water tank → pressurized delivery to various users. The clean wastewater is treated using a dual-membrane process, and the treated water can be used as industrial water. The concentrate from reverse osmosis is sent to a saline wastewater treatment system for further processing before being discharged in compliance with regulations. 　　The EPC project for the Tenglong Aromatics water treatment facility is a complex and large-scale water treatment project. Leveraging our extensive technical expertise and management experience, we will ensure high standards in design, procurement, and construction quality to deliver a project that satisfies our clients. This project is not only a test of our comprehensive capabilities but also helps to enhance our experience in managing large-scale projects. 　　III. Engineering Design for a 30,000 m3/d Comprehensive Wastewater Treatment Plant by Jiangsu Supor (Group) Co., Ltd. 1. Project Overview Jiangsu Supor (Group) Co., Ltd. is located in the eastern suburbs of Zhenjiang, a city renowned for its historical and cultural significance in China. It is situated at the confluence of the Yangtze River, an important waterway, and the Beijing-Hangzhou Grand Canal. The company currently has the capacity to produce 600,000 tons of glacial acetic acid, 250,000 tons of ethyl acetate, 120,000 tons of chlor-alkali products, 40,000 tons of ADC foaming agents, 20,000 tons of PVC resins, 10,000 tons of bleaching powder, and 10,000 tons of rubber vulcanization accelerators. Among these, its production capacities for glacial acetic acid, ADC foaming agents, bleaching powder, and rubber vulcanization accelerators rank among the highest in the domestic industry; its glacial acetic acid production capacity is the largest in China and third-largest in the world. 　　In order to protect the local environment and out of a strong sense of social responsibility, Jiangsu Sopco (Group) Co., Ltd. plans to build a comprehensive sewage treatment plant from the perspective of long-term development. The total wastewater treatment capacity is 30,000 m3/day, of which the recycled water capacity is 10,000 m3/day. 　　The project is planned for construction in two phases; the capacity of the wastewater treatment system in phase one is 10,000 m3/day ； The capacity of the secondary wastewater treatment plant is 20,000 m3/day, while the capacity for reclaimed water is 10,000 m3/day. 　　2. Process Technology and Major Issues This project involves a comprehensive wastewater treatment plant designed by the Sop Group to serve long-term production facilities. There is considerable uncertainty in the planning of these production facilities, and the wastewater characteristics are complex; wastewater containing polyvinyl alcohol (PVA), ADC blowing agents, and PVC is particularly difficult to treat. 　　Organic pollutants composed of PVA have high concentrations and are difficult to biodegrade (B/C less than 0.1). When wastewater containing PVA is discharged into water bodies, PVA accumulates in large quantities in these environments, leading to an increase in foam on the water surface and an increase in viscosity. This affects the activity of aerobic microorganisms, thereby causing serious environmental problems. 　　ADC foaming agent wastewater is a type of organic wastewater with high salt and ammonia nitrogen levels, and its organic components are complex. Its pollution indicators mainly include COD, which reflects the combined effect of organic compounds such as urea, hydrazine hydrate, dicyandiamide, and ADC; as well as substances such as NH3-N, SO42‑, Cl‑, and SS, which may be expressed either together with other inorganic components or individually. 　　During the production of polyvinyl chloride (PVC), organic wastewater containing large amounts of PVC is generated. This wastewater consists of three parts: kettle rinsing water, centrifugation mother liquor, and washing water. The water from the kettle is the main source of this wastewater, with the primary pollutants being polyvinyl chloride, emulsifiers, and dispersants. The PVC wastewater is milky white in color, with a large amount of foam on its surface; there are no visible particulate substances. Its CODcr value is approximately 12,000–20,000 mg/L. 　　Since what is to be built is a comprehensive wastewater treatment plant, it is not possible to directly accept the wastewater from various units; such wastewater must undergo separate pretreatment before it can be discharged into the comprehensive wastewater treatment plant. Based on the above analysis, the wastewater entering the integrated sewage treatment plant is an organic wastewater containing substances that are difficult to biodegrade and high levels of ammonia nitrogen; therefore, the treatment process of \"hydrolysis acidification + A/O\" was selected. This process is mature and stable, with numerous successful cases, and its operation is simple. 　　After multiple discussions with the owner, the inlet water quality for the comprehensive sewage treatment plant has been determined as follows: Table of designed inlet water quality for the sewage treatment plant. The outlet water quality shall comply with the first-level standards set out in the \"Emission Standards for Major Water Pollutants in the Chemical Industry\" DB32/939-2006. The designed water quality parameters are as follows: Table of designed effluent quality for the sewage treatment plant. Meanwhile, in accordance with the requirements for controlling the total COD level, when the treatment capacity reaches 30,000 m3/day, 10,000 m3/day of the treated water must be reused in order to maintain a balance in the total COD emissions within the group. The only source of water that can be absorbed by the Thorpe Group in such large quantities is the make-up water for circulating cooling water. We determine that the salt content in the wastewater is high, and desalination is required before it can be reused; therefore, the reclaimed water treatment process employs the \"UF+RO\" method, that is, a dual-membrane process. 　　Other issues to consider in the design: Special attention should be paid to the impact resistance of the wastewater treatment facilities as well as to the margin built into their design, in order to achieve a solution that is both economical and reliable. At the same time, the owner has distinct characteristics in the layout of the factory area, placing great emphasis on landscaping; therefore, close discussions were held with the owner regarding the layout to ensure it matched the overall style of the existing factory area.