Acid Gas Removal Unit Successful Switch from Silicon to Polyglycol Antifoam to Eliminate Foaming

Abstract

Natural Gas Liquefaction (NGL) plant Acid Gas Removal (AGR) unit successfully switched from silicon based to polyglycol based antifoam. Changing the type of antifoam was to eliminate the repetitive foaming occurrences in the AGR amine absorber, and to avoid the side effects of the excessive silicon deposits in the circulated amine. The polyglycol based antifoam was found to be more effective and required at lower concentration. The AGR unit experienced repetitive amine absorber foaming since the plant commissioning. The foaming events are due to feed quality challenges in the form of liquid hydrocarbon carryover, and suspended solids entrainment. The repetitive foaming led to frequently disturbing the plant operation, reducing the unit throughput and impacting the product quality. To decrease the foaming occurrences the mode of operation for the antifoam injection was changed from intermittent injection to continues injection. However, the unit was so sensitive to the antifoam flow interruptions. The required concentration of the silicon based antifoam was high (110 – 130 PPM compared to 20-25 PPM for the polyglycol based antifoam). This led to the side effects of the excessive silicon deposits in the system, such as the fouling of heating equipment (heat exchangers, reboilers and air coolers), the frequent amine filters clogging, and increasing the circulated amine total suspended solids. The main objective for switching the type of antifoam is to eliminate the foaming events while minimizing the side effects of the silicon deposits. The polyglycol based antifoam was found more effective for continuous injection with concentration of 20-25 PPM. Furthermore, in the case of minor foaming in the amine absorber, increasing the antifoam concentration to 500 PPM was found to be effective in stabilizing the absorber foaming in less than 5 minutes. In addition, the minor antifoam flow interruptions did not result in foaming events unlike the silicon antifoam.