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Optimizing process parameters to increase methanol production Zhang Xianbo, Feng Xianfeng (Anyang Chemical Industry Group Company, Anyang 455133, Henan) Abstract: In view of the low methanol production rate in the low-pressure Lurgi process for methanol production, the reasons were analyzed and improvement measures were proposed, resulting in an increase in methanol production from 93.46 t/d to 107.47 t/d. Keywords: Methanol； Yield ； [CLC number] TQ 223.12 [Document code] B [Article ID] 1002-5095(2003)02-0037-01 Anyang Chemical Industry Group Company (formerly Henan Province Anyang Fertilizer Factory) is a large-scale nitrogen fertilizer manufacturer with an annual production capacity of 240,000 tons of synthetic ammonia and 400,000 tons of urea. To expand the company’s scale and strengthen its capabilities, a new methanol production line was put into operation in September 1995. This facility uses coal as raw material and employs the low-pressure Ruhr process for synthesis, with an annual production capacity of 30,000 tons. Back then, it surpassed the limits of design capabilities and became the company’s second most important product line. The synthesis tower in the methanol system began using the NC 306 methanol synthesis catalyst in July 1999. After July 2000, due to a decline in catalyst activity, the methanol production volume dropped significantly under the same process conditions. At that time, the market price of methanol was high; therefore, finding ways to increase production and seize market opportunities to generate substantial profits for the company became an urgent task. 1 Process flow: Raw gas → Desulfurization at atmospheric pressure → Gas holder → Electrostatic precipitation → Compression (1.3 stages) → CO conversion → Desulfurization of the converted gas → CO2 removal → Further desulfurization → Compression (4 stages) → Methanol synthesis → Crude methanol → Distillation → Methanol storage tank. 2 Reasons for low methanol production: 2.1 Insufficient amount of raw gas. The discharge pressure from the compressor is around 1.75 MPa, which is much lower than the required value of 2.05 MPa; this results in a lower volume of gas being sent to the synthesis process, thereby leading to a decrease in production. 2.2 Suboptimal operating conditions of the synthesis tower: The operating pressure and temperature in the synthesis tower are relatively low, which results in a reduced methanol synthesis rate per unit time and thus lower methanol production. 2.3 The raw gas contains a high level of inert gases; the nitrogen content in water gas remains at 3% to 5%, which leads to a decrease in methanol yield. Additionally, due to the good activity of low-temperature shift catalysts, the CO concentration at the outlet is low, at 22%. 2.4 Catalyst aging in the synthesis tower: After 7 months of operation, the electronic NC 306 catalyst underwent natural aging, resulting in a **decrease in its activity, which affected the methanol production rate. 3 Measures to be taken 3.1 We clean the water condensers in each stage of the methanol process to improve heat exchange efficiency; in particular, we lower the inlet temperature of the first stage. We also modify the gas valves to increase the lift height of their valve plates, thereby boosting the compressor’s output. 3.2 By investigating the relationship between the operating pressure and temperature currently used in our company’s methanol system and the production volume, as well as by gathering extensive information on how other companies handle this issue, it was found that our operating pressure and temperature levels are not optimal for the distribution of the catalyst across different stages. The composition of the gas is adjusted promptly, reducing the N2 content in the feed gas to below 2%. Therefore, based on our past operational experience as well as that of other manufacturers, we have established the operating pressures and temperatures that should be followed at each stage of catalyst use, and apply these in production. 3.3 Only when the manufacturing process is stable can consistent and high yields be ensured. To this end, we have adopted work methods that involve strengthening basic management, optimizing process parameters, and enhancing technical oversight: (1) Process engineers must go to the site regularly to inspect and supervise the implementation of process parameters, strengthen the monitoring and management of key process indicators, address any issues that arise promptly, strictly prevent overheating and overpressure, and avoid process accidents, thus ensuring the long-term stable operation of the system. (2) Properly handle various interrelated relationships such as those between humans and equipment, high yield and stable yield, the local and the overall, consumption quotas and output, as well as process parameters and high yield; carry out timely maintenance of the equipment to ensure its proper operation. (3) Carry out in-depth competition on minor indicators among the four major chemical production teams to take the production process to a new level. (4) In response to the problems and contradictions that arose during production, technical solutions and improvements were promptly organized, and a series of issues related to process equipment such as liquid in the circulation machine and the modification of separators were resolved. 3.4 Maintaining the activity of the synthetic catalyst (1) To control the trend of catalyst aging, we have established strict operating parameters under abnormal conditions: the rate of temperature change during start-up and shutdown must be ≤20°C/h, the rate of pressure change must be ≤0.4 MPa/min, and the pressurization time for two units together must be at least 20 minutes; normal operating temperature fluctuations must be ≤1°C. (2) Utilize the parking time to re-reduce the catalyst to improve reaction activity. 4 Effects: Through the implementation of the above measures, the daily methanol production increased from 93.46 t to 107.41 t, resulting in significant economic benefits.