Compressed Air Plant by the Numbers

About this book

Compressed air is often called a factory’s most expensive utility, and the reason is in the thermodynamics. A compressor turns electricity into pressure, but most of the electricity becomes heat on the way, and most of the pressure is then thrown away through regulators, leaks and open blowers. The compressor room is where those losses start and where many of them can be fixed.

This book follows the energy and the water through one compressor room. It begins with what “a cubic metre of air” means, calculates the ideal work of compression and compares a real compressor against it, then follows the heat the compressor makes, the water the air carries, the dryers that remove it, the pressure the system runs at, the storage and controls that decide part-load power, and the pipes that take the air to the plant. The last chapter turns the numbers into an assessment.

It serves mechanical and maintenance engineers, energy managers and plant managers who run, audit or extend compressed air plant. You need comfortable algebra, SI units and a spreadsheet. The thermodynamics is introduced as it is used. The Library’s Pneumatics by the Numbers covers the point-of-use side, cylinders, valves and leak hunting; this book stays in the compressor room and the mains.

The running case

Every chapter works on one fictional installation: CA-1, the compressor room of a packaging plant. An oil-injected rotary screw compressor with a 37 kW motor delivers 6.0 m³/min of free air at 750 kPa gauge, drawing about 41 kW at full load. Air at 25 °C and 60 per cent relative humidity enters the intake. An aftercooler cools the compressed air to 35 °C, a refrigerated dryer brings it to a pressure dew point of 3 °C, and a receiver and a main carry it to the plant, which uses an average of 4.2 m³/min over 6,000 hours a year.

This is an illustration. All flows, powers, prices, results and failures are invented for teaching and checked by calculation. They are not KEVOS® work, a real site or a measured compressor, and real compressors’ performance comes from their makers’ test data. Electricity is priced at a teaching A$0.25 per kWh and gas at A$18 per GJ, both excluding GST.

Source limits and professional responsibility

The supplied DOE Fundamentals Handbook informed the subject map and the principles of ideal gases, compression and efficiency. This book develops them in SI units with its own case, figures and exercises, and nothing is copied from the handbook’s text or examples.

This book is educational. Compressed air systems store energy in receivers and pipework, discharge air hot enough to burn and at pressures that can inject air into skin or launch debris, and contain oil that can ignite. Receivers are pressure vessels with design, registration and inspection duties under the model Work Health and Safety Regulations and the Australian Standards named in the references. Changes to pressures, safety valves, controls and receivers need competent review. Use the methods here to understand and question a system, not as authority to alter one.