The balance between safe efficient process control and low instrumentation cost is quite hard to achieve. It was found that design of process control systems plays an important role for achieving the optimum process safety and efficiency beside the minimum required instrumentation costs. This paper is mainly intended to describe a new approach to compressor control aimed principally at achieving increased controllability during start-up which optimizes safety and control of a multistage gas compressor. It highlights the importance of the proper compressor control, introduces some recommendations for compressor control to facilitate the development of optimum process control and also stresses on the factors that improve the safety and efficiency of compressor control for already existed systems. Surge phenomenon causes and effects on compressors were explained together with Universal Performance Curve anti-surge control method and the Minimum Flow Strategy used to compensate for pressure transmitters failure. A detailed study was performed on a specific common problem that occurs in petrochemical plants, gas compressor first stage suction pressure measurement. Conventional solutions were discussed and disadvantages were highlighted. The main contribution of this paper is a novel idea to overcome the problem without affecting either safety or efficiency of operation and absolutely no extra instrumentation cost. A new dimensionless parameter was invented, Ratio of Pressure Ratios. Relation between ratio of pressure ratios and compressor speed is being investigated experimentally and numerically. Experimental results show that there is a relation between ratio of pressure ratios, the results were fitted to second order polynomial trend lines using least squares method. The numerical calculations are compared with experimental data and good agreement is found. The results also suggest direction for further investigations. Ratio of Pressure Ratios method was implemented for a propylene gas compressor turbine train, the results of calculation were collected and compared to actual measurements, and it was found that calculation error is less than 1%.

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