Exergy Based Analysis of Pneumatic Air Saving Measures

Abstract

Pneumatic linear drives are widely used in manufacturing, mainly for handling tasks. Pneumatic drives are very versatile and reliable. They are easy to install and to maintain as well as economically priced. Due to rising interest in environmental matters and increasing energy costs, energy efficiency has become a major issue in industrial applications. There is a growing competition between pneumatic and electromechanical drives. Pneumatic drives are said to have high operating costs while the purchase of electromechanical drives is more expensive. The operating costs of pneumatics are mainly induced by the energy consumption to provide pressurized air. Therefore many different air saving measures for simple handling tasks are proposed in literature, which offer opportunities for reducing the air consumption in comparison to standard configurations. This paper provides an overview of different approaches for saving air and typical applications for these approaches. The thermodynamic concept of exergy is utilized in the paper. It provides a better standard of comparison between different technologies than common energy analysis because exergy accounts for a system’s ability to conduct work out of different forms of energy. An exergy based analysis and a comparison of different air saving circuits are presented. The approaches described in literature are suitable for different applications. The study includes an analysis of cross flow valves to recuperate parts of the exhaust air during backstroke. Furthermore shut-off-valves using the expansion energy saved in the pressurized air of meter-out controlled cylinders are evaluated. The use of expansion energy is applicable if the entire cylinder force is not required at the end stop. The circuits are simulated based on lumped parameter models (DSHplus). The simulations are validated by experiments. The exergy efficiency of the examined circuits is compared to a meter-out controlled standard drive. Furthermore possible restrictions for the use of these circuits are discussed. This includes stability problems caused by the reduced force in the end stop or influences on the drive dynamics. If these restrictions are considered in the design of the facility, the same level of process quality and reliability compared to a standard setup can be achieved. Large energy savings and therefore reductions of operating costs of the pneumatic drives are possible with limited effort.