Status of LMMC retrofitting

I’ll start by sharing some preliminary ideas. Sinopec Nanjing Company switched from using oil to coal as a feedstock in 2006, at a pressure of 8.63 MPaG. To ensure that the purified gas exiting unit C1 met the original design specifications, a new process gas pre-washing system was added to pre-wash the gas entering unit C1. A new CO2 desorption tower, Cd2, was also installed; its operating pressure was set to be the same as that of unit C2. One more methanol condenser was added, and the 1# H2S fractionation separator was replaced. Additionally, one more thermal regeneration tower, along with reflux pumps and various instrumentation and valves, were added. The inlet temperature of P4 was reduced, and measures were taken to address the issue of venting CO product gas. During operation, aside from the fact that the CO2 condensation system functioned properly, Cd2 had to be taken out of service after operating for a while, while Cdl was never put into use. Essentially, the system operated on its own. This indicates that this renovation isn’t entirely perfect; there are still some problems.

Is the poster on the 1st floor from a company in Nanjing? There are several papers on the renovation plan for Sinopec Nanjing Company, and I have gained some understanding of it; I would like to contribute my insights here as well. While the Nanjing plant was undergoing upgrades to its raw materials, another coal-based ammonia plant in China was being expanded; its original design capacity was 300,000 tons of NH3 per year, and it was increased to 450,000 tons per year. After the Nanjing plant switched from oil to coal, the volume of reformate gas fed into the low-temperature methanol washing unit increased by 14.3%, while the absolute amount of CO2 gas increased by about 31%. During the renovation, a pre-washing tower, a desorption tower, along with associated equipment such as heat exchangers and pumps, were added. The main issue is whether the absorption tower and the CO2 desorption tower are suitable for the increased gas flow rate after the modification. Since 1990, the development of tray technology in China has kept pace with the expansion of various chemical industries in the country; the oil refining industry has even managed to increase its production capacity by 100% while maintaining unchanged tower diameters, the number of trays, and the fixed components inside the towers. Based on the operational results of another coal-fired plant after renovation, Nanjing Company’s low-temperature methanol washing unit can adapt to the change in feedstock from oil to coal by simply replacing the trays in the original absorption tower and desorption tower. The specific solution is as follows: a absorption tower is used, along with a heat exchanger to fully recover the cooling energy from the CO2 in the desorption tower; this helps to lower the temperature of sulfur-free methanol in the absorption tower, enabling the desulfurization section of the tower to carry out both carbon removal and sulfur removal. At the same time, the temperature of the CO2 gas entering E1 is increased to ensure that CO2 does not condense in V1 ； For the desorption tower, only the trays need to be replaced to accommodate the increased amount of CO2. Calculations show that the load on the desorption tower has increased by 50% compared to the original design, and domestic tray technology is fully sufficient to meet the requirements for this modification.

Is the low-temperature methanol washing unit at the Nanjing plant operating at full capacity? If the gas flow rate specified for the conversion from oil to coal is achieved, the absorption tower and desorption tower of the original system are likely to fail to meet the requirements.

Shanxi Tianji Group (Shanxi Fertilizer Plant) has increased its synthetic ammonia production capacity from 300,000 tons per year to 450,000 tons per year, an increase of 50%. The desulfurization tower of the low-temperature methanol washing unit has also been expanded by 50%; this plant uses Lurgi’s nine-tower process. The modification was carried out without changing the original tower diameter or any fixed components such as the liquid dropping trays and receiving trays inside the tower; instead, the original floating valve trays were replaced with trays invented by a certain university, thereby achieving the goal of expanding production capacity. The unit was successfully put into operation in August 2005, and it has been in operation for nearly 3 years to date. It is the method with the lowest investment and fastest results