New breakthroughs in energy and water savings for coal chemical industry: Hubei Zhongsheng Co., Ltd.’s \"closed-air cooling and recycled cooling water system\"”

Thread Content

1. Application Background: In 2012, the State Council’s Guidelines on Implementing the Strictest Water Resources Management System placed the total amount of water used and the efficiency of its utilization at the core of development in various industries. **The 12th Five-Year Plan explicitly set water consumption targets for the coal chemical industry, stipulating that the water usage per ton of standard coal should not exceed 3 tons. At present, the water consumption rate for domestic coal chemical enterprises is generally no less than 5 tons of water per ton of standard coal used. By analyzing the water consumption metrics of various units in coal chemical enterprises, it is found that the circulating cooling water system is the largest consumer of water, accounting for around 60% of the total water usage. The cooling method employed is mainly an open-type circulating cooling water system; this method provides good cooling effects but requires a large amount of water. With the acceleration of the development of the western region, there are more and more coal chemical projects in the northwestern area, which in turn increases the demand for water resources. However, the northwest region suffers from a water shortage, and the operating costs of using open-type cooling towers are too high. On the other hand, the low temperatures and strong winds in this region make it very suitable for using air coolers for cooling. Studying water-saving technologies for circulating cooling water systems is one of the key approaches to meeting the water consumption targets set out in the 12th Five-Year Plan for the coal chemical industry. Ensuring rational and efficient water use is an important task for coal chemical enterprises in order to save energy, reduce consumption, cut emissions, and improve efficiency. At the same time, water conservation holds great strategic significance for alleviating water shortages and ensuring the sustainable development of the national economy. The outline of China’s water-saving technology policy states that \"water conservation and efficient use of water are the fundamental ways to address the imbalance between water supply and demand.\" The key to water conservation is improving water use efficiency and effectiveness. **Practice strict water conservation. Adhere to a scientific view of development and give greater emphasis to water conservation. **Encourage the research, development, and application of new water-saving technologies, processes, and major equipment. It also clearly states in the outline to \"develop efficient closed-loop cooling water treatment technologies and promote closed-cycle cooling technologies.\" 2. Closed-air-cooled circulating cooling water system: In response to **energy-saving and emission-reduction policies and to support the development of water-intensive enterprises in arid regions, Hubei Zhongsheng Co., Ltd. (formerly Wuhan Zhongsheng Energy; hereinafter referred to as “Hubei Zhongsheng Co.”) has developed its own closed-air-cooled circulating cooling water system. Replacing the traditional \"industrial circulating cooling water system\" with an innovative \"closed-air-cooled circulation cooling water system\", and substituting chillers with energy-efficient air-cooled film coolers or combined air-cooled units, not only ensures that the temperature of the cooling water meets the requirements of various processes, but also enables long-term stable operation. It also helps to save water and energy, reduce emissions, prevent scaling in process equipment, and extend the lifespan of such equipment. The closed air-cooled circulating cooling water system integrates water cooling and air cooling, as well as heat transfer and mass transfer processes, and is a new type of efficient and energy-saving circulating cooling water system. 2.1. Process Characteristics: The closed air-cooled circulating cooling water system uses soft water or deionized water as the cooling medium to absorb heat from the process heat exchange equipment. After heating up, this water enters the tubes of an energy-saving water film air cooler or a combined air cooler (see figure below; referred to as air cooler). It first passes through the finned tube section (present in combined air coolers) for pre-cooling, and then enters the spray tube section where it further loses heat to the air outside the tubes and the spray water. Once cooled, it is pressurized by a circulation pump and sent back to the process 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. Since the quality of water used in closed-loop softening or desalination remains stable with little loss, only a small amount of softened water lost due to leaks in the system equipment needs to be replenished. Energy-saving water film air coolers, combined air coolers: When the air temperature is high, both the fan and the spray water pump are turned on simultaneously. The spray water pump delivers the spray water to the spray water distribution system located above the heat exchange tubes; the spray water is then sprayed downward onto these tubes, forming a uniform water film on their exterior. This water film absorbs the heat from inside the tubes and evaporates into vapor. The latent heat of vaporization of water **exceeds the sensible heat required to raise the temperature of water, thereby greatly enhancing the overall heat transfer process and reducing the required heat exchange area. As the vaporized water enters the air, it passes through the finned tubes and is discharged into the atmosphere after the entrained water droplets are removed by a dehydrator at the outlet. Most of the spray water falls back down into the water tank for reuse, and as it falls, it is cooled by air. As the temperature drops, it is possible to reduce the number of fans and spray pumps, or lower the fan speed using variable frequency control in order to adjust the heat exchange rate and maintain a stable outlet water temperature. Through heat exchange design, the spray water can be stopped at 0°C, 5°C, 10°C, and 15°C. At this time, the air cooler functions as a draft-type dry air cooler. In the coal-to-methanol project of Datong Tongmei Group, when the ambient temperature is below 0°C, there is no need to spray water, **which saves water consumption. 2.2. Technical Advantages Compared with traditional industrial circulating cooling water systems, the closed-air-cooled circulating cooling water system has many advantages, as shown in the table below. Advantages of closed-air-cooled circulating cooling water systems; Disadvantages of traditional industrial circulating cooling water systems. Site selection is not restricted; Site selection is highly dependent on water sources. The combination of air cooling and water cooling helps to reduce water consumption. Relying solely on water cooling results in high water consumption. Closed-loop circulation ensures stable water quality, thereby improving the heat transfer efficiency and lifespan of process heat exchange equipment. Unstable water quality in the circulating water can lead to scaling and corrosion in heat exchange equipment. Simple maintenance and low operating costs; Complex maintenance and high operating costs. Low wastewater volume, which is beneficial for environmental protection; High wastewater volume, requiring significant investment in wastewater treatment. Some cooling capacity remains even after the power supply is cut off; Production must stop completely once the power is interrupted. 2.3. Economic advantages: According to conventional design, a circulating water station with a capacity of 20,000 m3/h that uses a closed-air-cooled circulating cooling water system offers clear advantages over open-loop circulating water systems as well as conventional closed-loop systems, in terms of design capacity, equipment investment, and consumption levels. See the table below. Project Equipment Investment (10,000 yuan) Chemical Consumption (kg/h) Power Consumption (kW) Average Water Consumption (m3/h) Operating Cost* (10,000 yuan/year) Traditional Open-Circuit Cooling Water System: 3700 6.2 4350 410 5726 Closed-Circuit Air-Cooled Cooling Water System: 6900 3.1 5550 205 4213 Note*: Operating cost = cost of chemicals + electricity cost + water cost; the values used are 10 yuan/kg for chemicals, 0.5 yuan/kWh for electricity, and 12 yuan/m3 for water (based on data from a company in Inner Mongolia). Compared to traditional open-loop circulating water systems, closed-loop air-cooled circulating water systems can save 15.13 million yuan in operating costs per year, with the investment being recovered within 2-3 years. 3. Company’s research achievements: Over the years, Hubei Zhongsheng Co., Ltd. has continued to pursue innovation. Through the joint efforts of its design and R&D personnel, the closed-air-cooled circulating cooling water system has been continuously improved, yielding the following technical achievements. 1. Combined air cooling is used to achieve optimal water savings (ZL200910062950.6). Given China’s climate characteristics of cold winters and hot summers, in order to achieve the best water-saving results, the patented combined air cooler developed by Hubei Zhongsheng Co., Ltd. is employed to reduce the consumption of spray water. During summer, both dry air cooling and wet air cooling operate simultaneously with the spray water in use; in winter, only dry air cooling is used. In spring and autumn, the spray water is used either not at all or to a limited extent, while the air volume and direction are adjusted as needed. Actual operational experience with the products of this project shows that the water consumption rate of this system is only 0.9%, whereas the average water consumption rate for traditional industrial cooling water systems of similar scale is 2.5%. System products can save 30%-70% water compared to traditional industrial cooling water systems. At present, this innovation has been successfully applied in the northwestern and northeastern regions of China. In the coalbed methane power generation projects of China National Coal Group in Yulin, Shaanxi, and Kaijia, Shanxi, as well as in the closed-loop cooling water system of Hubei Zhongsheng Co., Ltd., the water supply can be stopped at 0°C. In the upcoming demonstration project for deep coal processing in Ordos, Inner Mongolia, carried out by Zhongtian Hechuang, Hubei Zhongsheng Co., Ltd. will be the first to adopt the new technology that allows the water supply to be stopped at temperatures below 15°C. 2. Flow regulation of the spraying system (ZL201420522388.7): The spraying pipes in the existing spraying system of the evaporation air cooler use a main pipe plus branch pipes distribution scheme, with nozzles installed on the branch pipes. The spray water piping is installed above the tube bundle of the evaporative air cooler, with air and water flowing in counterflow outside the tube bundle. In the upper tube bundle, water comes into uniform contact with the tubes, resulting in good heat exchange efficiency. In the lowest section of the tube bundle, due to the flow of water, the contact between the water and the tubes is uneven. As a result of air unsaturation and high airflow rates, the water distribution in the lower part of the tube bundle becomes uneven, leading to dry spots. Moreover, as water flows from the upper tube bundle to the lower one, it absorbs heat and its temperature rises, increasing the likelihood of scaling; in actual operation, severe scaling can also be observed in the lower tube bundle. Hubei Zhongsheng Co., Ltd. adds a spray pipe system below the tube bundle, based on the existing design; this system sprays water directly onto the lower heat exchange tubes, preventing dry spots from forming on the outer walls of those tubes. It also helps to reduce scaling in the lower tube bundle. The flow rate of the lower spray pipe system can be adjusted using a flow control valve ； A pressure stabilizing tank is added at the outlet of the spray water pump to stabilize the pressure in the spraying system, thereby effectively mitigating the fluctuations in system pressure caused by flow rate adjustments in the upper and lower spray pipes. 3. Introduction of fillers to improve heat exchange efficiency (ZL201420522389.1). Closed-type cooling towers rely primarily on air as the heat exchange medium, making it difficult to reduce the temperature of the cooling fluid below the ambient temperature. To address this issue, Hubei Zhongsheng Co., Ltd. designed a system that incorporates cooling tower fillers into closed-type cooling towers, thereby increasing heat exchange efficiency by reducing the temperature of the spray water. By using this method, the temperature of the cooling medium can be reduced by 2–3°C compared to conventional closed-loop air-cooled cooling water systems, achieving the same cooling effect as open-loop cooling water systems. At present, Hubei Zhongsheng Co., Ltd. is using this system in the clean utilization project of high-sulfur coal at Shanxi Lu’an. 4. Application Performance: The closed air-cooled circulating cooling water systems designed and manufactured by Hubei Zhongsheng Co., Ltd. are currently widely used in the metallurgy, petrochemical, power, and chemical industries. There are also numerous successful applications in the coal chemical sector; some of these performance metrics are shown in the table below. Serial Number Customer Device Name Quantity 1 China Coal Shanxi Yuheng Coal Chemical Industry Closed-loop air-cooled circulating water system 2 2 Tongmei Guangfa Chemical Industry Co., Ltd. Closed-loop air-cooled circulating water system 38 3 Shanxi Kaijia Coalbed Methane Power Generation Co., Ltd. Closed-loop air-cooled circulating water system 2 4 Shanxi Lu’an Coal-based Oil Closed-type cooling tower 3 5 Shanxi Lu’an Group’s Clean Utilization of High-sulfur Coal Closed-type cooling tower 63 6 Zhongtian Hechuang Ordos Coal Deep Processing Closed-loop air-cooled circulating water system 38 Address: 4F, Building A, Juxian Building, International Enterprise Center, Guanggu Avenue, East Lake Development Zone, Wuhan City, Hubei Province Phone: 027-87526852 / 027-87526979 / 027-87797047 Fax: 027-67845121 Postal Code: 430074 Website: www.whzseco.com E-mail: whzsco@163.com (Source: Hubei Zhongsheng Shares)