Feasibility Study of Optimisation of Scroll Air Motors and Energy Recovery from Exhaust Compressed Air

Although renewable resources are immense, it seems far-fetched to use all the renewable supply to satisfy our power requirement. The renewable sources, such as solar and wind power, are diffuse and intermittent. So energy storage is very important for obtaining a stable power supply. Compressed air energy storage is a well known controllable and affordable approach nowadays. The energy stored in compressed air will be used to generate electricity when required. However, the commonly used air motor (air transformer) is a cost effective traditional vane type air motor but the energy efficiency of vane type air motors is rather low, less than 30%. This is a big drawback in adopting compressed air energy storage system in the renewable resources power supply. Pneumatic actuators provide solutions through motion technology in a range of applications. In the UK, a massive amount of energy, over 10% of the National Grid output, is used to generate compressed air. Also, around 20% of electricity supplied to manufacturers/factories has been employed to generate compressed air. However, the energy efficiency of pneumatic actuator systems remains low. In European countries, an energy efficiency of between 23%-30% is achieved in working systems. It is considered that such low energy efficiencies are mainly due to the open-circuit structure of pneumatic actuator systems. Although much effort has been made, it is considered that there are no suitable mechanisms to recover energy lost through the exhaust. Therefore, there is considerable scope for research in the subject of reusing the exhaust air. A scroll air motor is a relatively new concept to pneumatic actuators. Its unique structure features its higher ability of energy conversion than conventional pneumatic actuators. The scroll technique is now mainly implemented in air conditioner and refrigeration compressors. Recently, the concept was re-invented to build scroll air motors, which are immediately adopted to drive generators for electric power generation. They have been successfully used in Micro Combined Heat and Power systems by a number of companies, such as Energetix Group Plc, Honda and Climate Energy. Scroll type air motors provide a possibly suitable actuator for recovering the energy loss at the exhaust and generating electricity efficiently for renewable power sources. It is anticipated that scroll air motors as a new type of energy efficient pneumatic actuator will be found in wide industrial and domestic applications in the near future. However, a number of fundamental problems need to be addressed before substantial progresses can be made in this area. This proposal is to seek the EPSRC support to set up a link between mathematicians and engineers to conduct the feasibility study of solving a number of fundamental issues associated with the structure of scrolls and their applications. The tasks of the project are:- to develop a complete mathematical model of scrolls based on the current scroll structure and a software program in Matlab/Simulink;- to set up a novel system to recycle pneumatic actuator exhaust air to improve energy efficiency in the laboratory at Birmingham;- to investigate the dynamic behaviour of scroll air motors while they are working at a low pressure of compressed air supply with variable air flow rates;- to investigate how the recycling equipment at down stream affects the behaviour of the pneumatic actuators;- to investigate a feasible control strategy for generating a stable electrical power at a variable pressure of compressed air supply with uncertain flow rates;- to investigate different shapes of scrolls which will lead to high energy efficiency using a differential geometry method;- to investigate how the design parameters affect the energy efficiency of scroll air motors through madelling and simulation study - optimisation;- to verify mathematical model and simulation results.