Practical Energy Efficiency Optimization
Presenting basic information for optimizing power plants, this book uses review exercises and practical case studies to provide real-world applications on maintaining optimal efficiency.
TABLE OF CONTENTS Practical Energy Efficiency Optimization
Appendix C: Compressor Theory and Practice
Theory of Compression
Compressors are mechanical devices used to increase the pressure of air/gas mixtures such as fuel gas, ammonia, air, hydrogen, etc., depending on the process requirement. Compressors are also used to transport huge volumes of gas to other sites/countries (transcontinental application). Compressors are either of the dynamic or positive displacement type.
Positive Displacement Compressor
A reciprocating compressor is a positive displacement device. It compresses the gas in a piston. During the suction stroke, gas is sucked into the cylinder. By external energy applied to the crank wheel, the piston pressurizes the gas during discharge stroke. A check valve system prevents the gas from backing up from the cylinder to the suction side. During suction stroke, the gas header pressure will be zero and starts increasing when the gas gets compressed. This results in pressure pulsations/variations. See figures C-l and C-2.
Figure C-1: Reciprocating compressor principle
Figure C-2: Pressure vs. flow reciprocating (double-acting) compressor. Note pressure surges in discharge side. This is minimized by adding more stages.
Centrifugal Compressors
In conventional centrifugal compressors (fig. C-3), kinetic energy is converted into pressure energy. Gas enters axially at the center of the impeller and passes through the tip of the wanes, which are rotating at high speed. The gas picks up the velocity, and high pressure is achieved, when it expands at discharge.
Figure C-3: Centrifugal compressor
Gas Law Applications
In any continuous compression process, the relationship between absolute pressure to volume is given by
where P is absolute pressure of the...
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