Abstract: According to the sudden acting of the anti-surge control valve FRC7 and FRC8 in synthetic compressor of ammonia plant, it was determined that the compressor was close to the surge area, which caused fluctuation during the operation process of the unit. Through analysis of the FRC7 and FRC8, it was confirmed that the fluctuation was due to the take-off of 105-F safety valve. This led to the reduction of the FRC8 flowrate and its working point entering the surge area. Then the FRC8 opened automatically until the working point left the surge area and closed gradually. After the FRC7 flowrate increased, the anti-surge working point moved to the right quickly. After the PSV was back to normal, the FRC7 would move to the left and returned to its normal position. Although the working point didn't enter the surge area, the FRC7 still frequently opened because the point was close to the FRC7 spiral point.

Key words: syngas compressor, surge, safety valve