Anti-Foam Injection Optimization

Habshan-5 & Sulphur Plant consists of two Rich Acid Gas Removal Units (AGRU) designed to process a total of 1340 MMSCFD of sour feed gas. These units utilize MDEA solution to produce close to H2S-free sweet gas. The objective of this study is to minimize the continuous dosing of anti-foam in the AGRUs without increasing the foaming tendencies, while maintaining sweet gas specifications. Consequently, leading to a significant reduction in the operating cost. The method used was the reduction in anti-foam continuous dosing rate in a gradual manner. Each phase lasted for approximately one month, which gave enough time to stabilize the unit and collect sufficient reliable data. Meanwhile, several parameters were monitored on regular basis, such as foam height, foam breakdown time, absorber pressure drop and sweet gas quality. Parameters were gathered using laboratory analysis and PI ProcessBook software. These parameters were then compared against design values and trends analyzed before making decision to go ahead with the next phase or revert to earlier dosing rate. In phase 1, anti-foam dosing rate was reduced from 90 L/hr. to 50 L/hr. Foam height remained below target of 20 cm and even showed slight reduction compared to before. All other parameters were within acceptable limits, and no noticeable changes compared to earlier data. Anti-foam dosing rate in phase 2 was reduced from 50 L/hr. to 40 L/hr. The overall foam breakdown time for both units had a small drop, which indicated a slightly reduced foaming tendency. There were no changes in the other parameters. The anti-foam dosing rate in phase 3 was reduced again from 40 L/hr. to 30 L/hr. All parameters were within the acceptable limits, and there were no changes compared to phase 2. In phase 4, anti-foam dosing rate was reduced from 30 L/hr. to 20 L/hr. Foam height and breakdown time increased significantly to 100 cm and 100 seconds respectively. It was determined that maintaining dosing rate at 20 L/hr. would eventually lead to a foaming event. Thus, dosing rate was increased back to 30L/hr. permanently and trial was completed. Overall anti-foam consumption was reduced by 53%. This initiative shows how decrease in operating costs can be achieved by optimizing chemical injection rate without jeopardizing the safety and integrity of the plant.