CNOOC Huahoe Coal Chemical creates a new industry benchmark for energy efficiency in closed-loop water systems

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CNOOC Huahe Coal Chemical Creates a New Benchmark for Energy Efficiency in Circulating Water Systems Author/Source: Huahe Company Date: November 30, 2020 Clicks: 20 At 14:48 on April 22, 2020, the dual-electric and steam-driven circulation water pump project of CNOOC Huahe Coal Chemical Co., Ltd. (hereinafter referred to as “Huahe Company”) was successfully tested in conjunction and put into operation. The project was completed 8 days ahead of schedule and entered a 72-hour performance test phase. It became the third contract energy management project following the circulating water system optimization project and the project for generating electricity using the residual pressure from the circulating water return flow, marking the completion of all upgrades aimed at improving the energy efficiency of the circulating water systems. The circulating water system is an important energy-consuming unit in chemical production facilities. Huahoe Company actively pursues the concept of green development. In 2017, it improved the efficiency of water pumps and optimized the volume of circulating water through a project to optimize the circulating water system; in 2018, it implemented a project to generate electricity from the excess pressure energy in the recycled water; and in 2019, it pursued the development of a system that used excess low-pressure steam to drive the circulating water pumps. As a result, the electrical load on the circulating water system decreased from 10,600 kW to 4,600 kW, representing a 56.6% reduction in power consumption ； The electricity consumption per ton of urea decreased from 440 kWh/t in 2017 to 300 kWh/t in 2020, setting a new benchmark for energy efficiency in industry wastewater recycling systems. 01 Adapt measures to local conditions to tap into energy-saving potential and implement the company’s green development philosophy. The original design of Huahe Company’s circulating water system calls for a circulation volume of 50,000 m3/h; the circulating water pump has a rated head of 58 m and a rated flow rate of 10,000 m3/h, with 5 pumps in operation and 1 in standby ； After commissioning and operational adjustments, the actual head achieved by the company’s plant is 48 m, with a considerable surplus in the circulating water volume. The company organized relevant technical personnel to conduct a detailed investigation and evaluation of the operational data of the circulating water system, deciding to adopt an approach tailored to specific conditions in order to improve the compatibility between the circulating water system and the process equipment, reduce the \"useless work\" associated with this system, and ultimately determine energy-saving renovation and optimization plans. First, by optimizing the system’s water distribution, the total amount of circulating water is appropriately reduced ； Secondly, by modifying the water pump impeller, the head of the water pump is reduced and its efficiency is increased, thereby achieving the goal of reducing energy consumption ； Thirdly, while ensuring the system operates properly, by optimizing the flow distribution of the water pumps, the configuration has been changed from \"5 in use and 1 standby\" to \"4 in use and 2 standby\". After the renovation, the circulating water system achieved a power savings of 2,040 kW, resulting in annual energy savings of 17.63 million kWh and economic benefits of 9.16 million yuan. 02 Driven by innovation, overcoming challenges to break through bottlenecks and paving the way for new energy-saving approaches in the industry. The waste pressure power generation renovation project for recycled circulating water: Based on the optimization of circulating water systems, finding effective ways to recover the pressure energy of the recycled water is key to further improving the energy efficiency of such systems. In energy-saving traditional processes, circulating water is often used directly to drive water turbine fans in place of motors, thereby achieving energy savings. However, through continuous practical testing in recent years, it has been found that the performance of turbine fan technologies varies widely, being significantly influenced by factors such as the capabilities of technology patent holders and actual operating conditions ； At the same time, in the extremely cold regions of the northeast, the number of fans in operation during winter is low, so this energy cannot be effectively recovered. Huahoe Company continues to research and explore new technologies for utilizing the residual pressure energy from recycled circulating water. By chance, Jiang Ping, the general manager of the Production Management Center, proposed using this residual pressure to drive turbine-generator sets to generate electricity; this approach not only solves the problem of recovering excess energy throughout the year but also avoids the impact that the operation of these turbine-generators may have on the system. However, after seeking technical service providers from various sources, the company found that either these providers had no relevant experience in this field, or they treated such technology as nothing more than conventional wind turbines driven by water wheels ； Either there have been attempts to use relevant technologies, but these were not successful; for example, Shanghai Foster Company’s attempts to apply such technologies in Linggu, Jiangsu, failed because issues such as water entering the bearings within the turbines prevented the systems from operating properly. Leveraging the technical strengths of Xi’an University of Technology in the field of water resources and hydropower, the company carried out in-depth research and exchanges on the application of turbines in circulating water systems. As a result, a through-flow turbine generator set was developed and successfully tested; these 10 units are capable of generating 1,800 kW of electricity per hour, resulting in an annual electricity production of 15.55 million kWh and generating economic benefits of 8.08 million yuan. 03 Coordinate all aspects and optimize resource allocation to help enterprises reduce costs and increase efficiency. Since the installation came online, part of the low-pressure steam from the process system has been vented, resulting in serious heat waste as well as increased noise pollution. The steam-electric dual-drive project for circulation water pumps recovers 20 tons per hour of low-pressure vent steam generated by the process equipment, using it to drive a turbine to perform work equivalent to that of a 1920 kW circulation water pump motor; at the same time, this system also drives a generator to produce 240 kW of electricity. As a result, it is possible to save 17.28 million kWh of electricity per year, generating an economic benefit of 8.9856 million yuan. Huahe Company has conducted extensive research and analysis on solutions for recovering low-pressure vent steam. While turbine generation can operate independently of the process system, issues such as whether policies permit this approach, whether turbine units can function stably given the frequent fluctuations in the volume of low-pressure steam produced – which ranges from a few tons per hour to over a dozen tons per hour – and how to determine the volume of vent steam in the absence of flow meters to select the optimal load for the turbines, all pose challenges for the technical staff. Turbine and generator manufacturers who came for technical exchanges also shook their heads at such large fluctuations in steam volume. Using the available tools, the technical staff at Huahe Company utilized the data extraction functions of MES to retrieve the average values over time for the relief valves. By analyzing the corresponding flow rate curves, they were able to determine the accurate range of steam flow variations as well as the intervals during which the flow rate remained stable ； To address the impact of steam flow fluctuations on the turbine as well as the constraints imposed by power generation policies, Huahoe Company adopted a new approach and used a turbine instead of an electric motor to drive the circulation water pump. By utilizing the work done by the motor, it was possible to compensate for the effects of steam fluctuations on the turbine, thereby circumventing the requirements set by power generation regulations and achieving the goal of recovering excess low-pressure steam that would otherwise be wasted. Circulation pump steam-electric dual-drive renovation project: The contract for this circulation pump steam-electric dual-drive project was signed in June 2019; the equipment and construction materials ordered in December arrived one after another. Installation work had been underway for less than a month when the Spring Festival holiday came, and subsequently, due to the impact of the COVID-19 pandemic, construction activities could not resume. Key technical personnel from outside the province, as well as those responsible for equipment maintenance and installation, were unable to arrive at the site in time to provide guidance on the installation process. To avoid affecting the overall schedule, some workers from areas not affected by the epidemic have resumed work gradually. However, as temperatures rise and more steam needs to be vented, Huahe Company incurs a loss of nearly 25,000 yuan for every day it delays operations. The company’s Party committee has decided that efforts to prevent and control the epidemic must not be relaxed, and project construction must not be delayed. Huahe Company’s technical capabilities need to be strengthened; the sooner operations resume, the sooner Huahe will benefit. Miao Zhongjian, the secretary of the Public Works Department Party branch at Huahe Company, led the party branch committee to stay on site around the clock to identify problems and potential hazards, providing timely support and guidance for the on-site construction work ； The party committee members of the Company’s Production and Logistics Center Party Branch, as well as the party members of the Production Management Center Party Branch, took the initiative to carry out the on-site installation and debugging of electrical and instrumentation equipment. During this period, we overcame difficulties such as a shortage of maintenance personnel for the “two furnaces” and excessively long working hours. By making continuous efforts and pooling resources and technical expertise from across the company, we managed to complete the unit’s integrated trial run 8 days ahead of the schedule set after the impact of the pandemic, and the unit was officially put into operation.