【Haichuan’s Best Practices】Reducing the outlet pressure of the seal oil pump in catalytic cracking units to enhance control capabilities and achieve energy savings and cost reduction

Thread Content

The seal oil pump in the catalytic cracking unit of Guangdong Petrochemical serves as a key pump in the catalytic process; it is responsible for providing external flushing seal oil for the mechanical seals of other key pumps in the unit, such as the slurry pump, feed oil pump, and reprocessed oil pump. 　　This pump is a high-speed centrifugal pump that uses a gearbox to increase its rotational speed; its rated speed reaches up to 9861 rpm. Due to the high head designed for this pump, the pressure at its outlet is high as well. As a result, the pressure control valve at the pump outlet remains in the 95% position, almost fully open, with little room for adjustment and thus losing its regulatory function. This presents certain safety risks and also leads to significant waste of resources. At the same time, the pump operates away from its optimal flow rate; the Peakvue spectrum of the pump’s high-speed shaft shows a distinct bearing failure frequency at a amplitude of over 40 G’s, requiring the bearings to be replaced almost every month. To address this issue, the department leadership decided to carry out energy-saving modifications to the oil-sealing pump. By replacing the impellers and inducers with those having a smaller diameter, the pump’s head was reduced, thereby lowering the pressure at the pump outlet and providing more room for adjusting this pressure. Since its initiation, this project has received great attention from leaders at all levels in the Second Refining Department as well as from the production teams. 　　On May 27, 2024, once all spare parts such as impellers were ready, energy isolation of the pump was carried out along with pressure release and liquid drainage, in order to complete the preparatory work prior to the modification of the seal oil pump as quickly as possible. Subsequently, personnel from Lanzhou Weida Maintenance Unit carried out operations to open the pump’s equipment and pipelines, and transported the pump to the maintenance workshop for the replacement of the impeller and pump casing. On May 28, the renovated oil-sealing pump was reinstalled and put into official use. 　　After the modification, the adjustment range of the pump outlet pressure control valve **increased**, eliminating the risk of uncontrollable pump outlet pressure. At the same time, the motor current decreased by 10A. The voltage applied to the motor is 380V, and its power factor is 0.89. It is an explosion-proof three-phase asynchronous motor. The power of the motor before the modification was 32.8 KW, while after the modification it became 26.9 KW. This results in a savings of 51,684 kWh of electricity per year. Based on an electricity price of 0.56 yuan per kWh, the operating costs can be reduced by 28,943.04 yuan per year. On June 19, the crew working on the catalytic cracking unit at Guangdong Petrochemical conducted temperature and vibration measurements on the catalytic seal oil pump. The temperature of the high-speed shaft of the pump was 56.3°C, with a maximum vibration value of 6.7 mm/s; the temperature of the low-speed shaft was 49.1°C, with a maximum vibration value of 4.8 mm/s. The current level remained stable at 46 A. Since its modification, this pump has been operating smoothly for 22 days, and calculations show that it has saved 3,115.2 kWh of electricity, resulting in cost savings of 1,744.5 yuan. 　　The relevant personnel from Lanzhou Weida Maintenance Unit used Emerson equipment to monitor and diagnose the oil-sealing pumps before and after the modification. After the modification, the frequency of bearing failures disappeared, and the PK value dropped significantly from 40 to 20. This change greatly contributed to the long-term stable operation of the pump bearings, significantly reducing the frequency of maintenance required for these pumps. For each maintenance session, this pump requires the replacement of 3 sets of 6308-C3 bearings and 1 set of 6306 bearings, with a total cost of 279.52 yuan. Assuming that after the modification the pump needs to be maintained only once a year instead of once a month, the cost associated with bearings can be saved by 3074.72 yuan per year. 　　This renovation project of the seal oil pump effectively addressed issues such as excessive head of the seal oil pump leading to waste of resources, as well as high pressure at the pump outlet resulting in limited control options. It contributed to cost reduction and efficiency improvement for the company, and provided a solid foundation for the stable, continuous, and high-quality operation of its production processes.