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Significant improvements achieved in the anti-surge modification of ammonia compressors at Shaanxi Chemical Industry Company. Author/Source: Shaanxi Chemical Industry Company. Date: 2022-07-09. Clicks: 14. The ammonia compressor units in the synthesis unit area of Shaanxi Chemical Industry Company’s urea production plant are equipped with centrifugal compressors manufactured by MAN Turbo, driven by steam turbines. Since their installation, the control systems’ software and hardware have functioned well. However, over time, abnormal conditions have arisen in the operation of these ammonia compressors, preventing them from achieving their optimal performance in terms of energy savings and automated control. The anti-surge valve cannot be closed completely; about 20% of the flow remains in circulation, resulting in energy waste. This renovation focuses on optimizing the unit’s energy-saving and consumption-reduction measures as well as the fully automatic operation control system. It aims to achieve decoupled automatic control for adjusting the process load, implementing cascade speed control based on inlet pressure, and carrying out anti-surge control, thereby ensuring optimal unit performance, energy savings, and operation in a fully automatic manner. Liu Di, the deputy director of the branch plant, Zhang Pan, the process technician, and the operators conducted on-site tests of the ammonia compressor’s surge curve in accordance with the \"Ammonia Compressor Surge Testing Plan\", based on the actual conditions of the compressor. During the testing process, it was found that the anti-surge setting was incorrect; the reason why one section of the anti-surge valve could not be fully closed was identified, and the anti-surge setting was revised accordingly. The original ammonia compressor was also modified to be controlled by the speed regulation of a turbine; now, the operation of the ammonia compressor is controlled through an inlet pressure, resulting in an updated and optimized control method. Currently, since the #2 ammonia compressor, which has been modified for anti-surge protection, was put into operation, the anti-surge valve in that section can be fully closed, eliminating waste in air intake volume and resulting in a significant improvement in efficiency.