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Recently, the China Nitrogen Fertilizer Industry Association organized relevant experts to conduct a scientific and technological achievement appraisal in Xinxiang on the "Methanol Negative Pressure Multi-Effect Coupled Distillation Energy-saving Technology" developed and successfully industrialized by Henan Xinlianxin Chemical Industry Group Co., Ltd. and Tianjin Aozhan Xingda Chemical Technology Co., LTD. The expert group unanimously agreed that this technology can significantly reduce the steam consumption of methanol distillation, improve product quality, and has remarkable economic benefits, reaching the leading level in China. And it is agreed to pass the appraisal, and it is suggested to increase the publicity and application promotion of this technology.

The expert group pointed out that the main innovation of this technological achievement is the introduction of a negative pressure tower in the methanol distillation unit for the first time. Through the "five towers 3+3 effects" thermal coupling process, energy stepwise utilization has been achieved, product quality has been improved, and comprehensive energy consumption has been reduced. Through the application of this technological achievement, the steam consumption has been reduced from 1.05 tons per ton to 0.65 tons per ton of refined alcohol, and the ethanol content in refined methanol is less than 10ppm.

According to Jin Qiming, the project manager of Henan Xinlianxin, the 300,000-ton methanol distillation unit of Xinlianxin has an original crude methanol content of 600ppm and an original steam consumption of approximately 1.05 tons of steam per ton of methanol. Based on the current process flow, through technological transformation, the steam energy consumption has been reduced to below 0.65 tons of steam per ton of methanol, and the ethanol content has been lowered to below 10ppm. The average daily output is 1,142.28 tons, and the load rate is 114.2%. The contract was signed in April 2023, with a production halt period of 20 days. The equipment was started up for commissioning at the end of November 2023. After the renovation, the annual operating cost savings amount to over 19.5 million yuan, and the investment payback period is approximately 10 months.

Gu Zhaohui, the chief engineer of Henan Xinlianxin, introduced that the conventional three-tower two-effect and four-tower two-effect methods are difficult to achieve high-purity product extraction under high load. After in-depth research, Xinlianxin chose the "five-tower 3+ 3-effect" thermal coupling process of Aozhan Xingda. By adding a negative pressure tower and thermal coupling, the excess heat at the top of the pressurized tower is used to heat the pre-tower, and the energy of the methanol vapor at the top of the atmospheric pressure tower is used to heat the reboiler of the negative pressure tower, meeting part of the energy required for distillation in the negative pressure tower. The steam at the top of the pre-tower heats the reboiler of the negative pressure tower, meeting part of the energy required for distillation in the negative pressure tower. Through the above coupling, the "Five towers 3+3 effects" thermal integration is achieved, significantly enhancing the efficiency of thermal energy utilization. The subsequent plan is to continue cooperation to achieve lower energy consumption and even negative carbon goals. The key point of the design lies in control. By rationally allocating the production volume among the pressurized tower, the negative pressure tower and the atmospheric pressure tower, the energy matching requirements of the pressurized tower, the atmospheric pressure tower and the negative pressure tower can be met.

Luo Junjie, the general manager of Jinneng Holding Hubei Jinkong, suggested that multiple towers, multiple indicators for product extraction, multiple intermediate storage tanks and product tanks be utilized to meet the diverse needs of different customers and achieve greater energy efficiency.

Shan Xiuli, the former chief engineer of Hualu Engineering, pointed out that the methanol distillation process is a crucial separation step in the methanol production process. Through the distillation column system, the purity of the product can be effectively improved and energy consumption can be reduced. At present, methanol distillation technology has undergone multiple technological iterations both at home and abroad.

The reason for the improvement of product quality is not only due to the negative pressure tower. After the negative pressure tower takes away 40% of the load, the load of other towers decreases. The hydraulic calculation of the internal components of the pressurized tower and the atmospheric pressure tower can be updated, and the operational flexibility of the internal components can be appropriately increased. Meanwhile, in small-scale (600,000 tons) renovations, the internal components and distributors of the atmospheric pressure tower and the pressurized tower are replaced to match the load changes and prevent leakage problems. If it is a project of several million tons, the tower diameter can reach 6 to 8 meters. In this case, the investment in replacing internal components will increase significantly. The replacement of the internal components of the patented tower from Aozhan Xingda Company accounts for a relatively low proportion of the total investment. After the renovation, the annual savings in steam consumption per unit are significant, and the payback period of the investment is relatively short.

According to Zhang Bing, the general manager of Aozhan Xingda Company, the five-tower multi-effect distillation process has significantly reduced steam consumption to 0.65 tons per ton of methanol by adding a negative pressure tower and adjusting the heat coupling process route to optimize the separation process. The air-cooling power consumption and water consumption have also decreased simultaneously, achieving remarkable energy-saving effects, although the energy-saving process flow is relatively complex. In recent years, the multi-effect thermally coupled distillation process has been widely applied both at home and abroad. By reducing heat exchange between columns and improving heat utilization efficiency, steam consumption has been further reduced to 0.5-0.6 tons per ton of methanol. The 3+3 and 4+3 distillation processes, by coupling the high-pressure tower with the medium-pressure tower and rationally utilizing the waste heat from the pre-tower and atmospheric tower, form a three-stage or higher heat exchange integration, deeply optimizing the heat utilization efficiency. The four-effect and quasi-six-effect processes can reduce the steam consumption per ton of methanol to 0.43-0.65 tons. It has developed into the most advanced methanol energy-saving distillation technology at present.

This technology has broken through the high energy consumption bottleneck of traditional multi-column distillation, providing a new path for the green upgrade of the methanol industry. Its design can be adapted to the renovation of existing facilities, especially suitable for large-scale methanol production enterprises. In the future, by integrating heat pump distillation technology, it is expected to further promote the advancement of methanol distillation towards a "zero-carbon process".

Zhang Bing stated that the technology is currently operating stably in demonstration facilities and is expected to be promoted and applied in multiple domestic methanol production enterprises, contributing to the industry's achievement of the "dual carbon" goals.