The Gasification Plant of Shaanxi Shenhua Coal Chemical Group takes multiple measures to successfully overcome the challenges posed by low-temperature methanol washing

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The Gasification Plant of Shaanxi Shenhua Coal Chemical Group Takes Multiple Measures to Successfully Overcome the Challenges Posed by Low-Temperature Methanol Washing Author/Source: Shaanxi Shenhua Coal Chemical Group Co., Ltd. Date: 2019-12-04 Clicks: 45 Some good news came recently from the purification section of the Gasification Plant of Shaanxi Shenhua Coal Chemical Group: the technical problem of high levels of water in the low-temperature methanol washing process, which had plagued them for many years, was successfully resolved after more than three months of intensive efforts by the plant’s staff. The methanol washing process uses low-temperature methanol as the absorption solvent, taking advantage of methanol’s excellent property of having a very high solubility for acidic gases at low temperatures to remove these gases from the feed gas, thereby purifying the syngas. It is a key step in feed gas purification, and the purification units in the gasification plant utilize this process to produce clean feed gas. Purified feed gas is obtained using low-temperature methanol washing, and the methanol-water content is one of the key control parameters; the process requires that the methanol-water content in the system be less than 1.0%. A value higher than the specified limit will accelerate the rate of equipment corrosion, affecting the normal operation of the system. In mild cases, this can lead to high methanol viscosity in the system and liquid accumulation in the scrubber tower, resulting in excessive load on the system; in severe cases, it can cause equipment corrosion, leading to blockages in the coil heat exchangers and preventing the system from functioning properly. Since the initial commissioning of the methanol washing unit in the purification section, the water content in methanol has consistently remained within a high range of 1.5%-2.0%, which has led to frequent liquid accumulation in the system under high load conditions; as a result, it has been impossible to achieve stable and efficient operation at high loads. During that period, in an effort to reduce the water content, the company invited peers and experts for technical guidance on several occasions. Although the water content did decrease, the effect was not significant; it remained above the acceptable level, which had a direct impact on the system’s production and posed a challenge for the company’s manufacturing processes. In June 2019, the gasification plant established a \"Task Force for Reducing Methanol Water Content,\" setting as its goal to \"strengthen process operations, make precise adjustments to the processes, optimize hardware facilities, effectively reduce the methanol water content, and ensure the stable and efficient operation of the system.\" During the pilot phase, the task force conducted numerous on-site investigations and analyses, formulating specific measures to reduce the methanol content in water. It also ensured full alignment with both the process design and actual parameters, carefully verifying the suitability of the process design in practice as well as the accuracy of the process parameters. When problems arose, the team would discuss them together; they were not afraid of the difficulties and would go to the site to identify the root causes, analyze potential solutions, and work together to overcome these challenges. In this way, one technical problem after another was solved, and the specific measures to reduce the methanol content in water were gradually put into practice. To improve process operations, the pressure in tower T2604 was stabilized, and the operation of the methanol-water separation tower T2605 was enhanced to keep its pressure stable ； Secondly, increase the amount of methanol sprayed in the methanol wash to facilitate the capture of more moisture from the process gas. In terms of fine process adjustments, in accordance with the established procedures, the drain valve on the E2601 shell was gradually opened, thereby preventing water-containing methanol from entering the scrubber tower ； The methanol purification efficiency of the system was improved by increasing the flow rate of the S2601 filter. In terms of optimizing hardware facilities, the filter elements used in the system operation were replaced from 60 microns to 2.5 microns filters; this improved the quality of the filtered water and reduced impurities within the system, thereby creating favorable conditions for water removal in subsequent stages and laying the foundation for the long-term operation of the methanol-poor pump ； To address the issues of excessive or insufficient drainage in the steam load drainage system of the methanol dehydration tower, as well as the tendency for steam levels to fluctuate after the steam bypass valve was opened, dual-chamber lever-type high-flow drainage valves were installed in the reboiler drainage system. These valves not only ensured an adequate amount of drainage for the system but also enabled effective separation between steam and condensate once the bypass valve was closed, resulting in a more stable and safer operation of the system. Through the successive implementation of measures aimed at \"reducing the methanol-water content\" by the task force over a period of more than three months, as well as through repeated pilot tests, significant progress was achieved in controlling this indicator. After integrating these measures into the system, the methanol water content was gradually brought within the limits specified by the process requirements. As of November, the methanol water content in System A remained stable at around 0.3%, while that in System B was stable at around 0.6%, both meeting the process requirement of being below 1.0%. The highly problematic issue of the methanol-water content exceeding specified limits has finally been resolved through the joint efforts of the task force. Solving this problem eliminated system fluctuations caused by high water content, removed major risks such as equipment corrosion and heat exchanger blockage resulting therefrom, and laid the foundation for ensuring the stable operation of the system under high loads over extended periods of time.