Use Of New Generation Instruments In Measurement Of New Steam Expander
For the past twenty years the Centre for Positive Displacement Compressor Technology, at City University, has employed experimental techniques for the measurement of screw compressors’ performance where both experimental data and predicted mathematical models are found to be in agreement with each other. Some of the experimental measuring techniques involve the use of pressure and temperature transducers installed in the housing to determine the vital thermodynamic process characteristics and functioning performance of compressors. Moreover, as advanced technologies were available, measurements were performed in an optical compressor with a transparent window near the discharge port to allow the application of a laser technique, Laser Doppler Velocimetry (LDV), to investigate the axial mean flow and turbulence characteristics inside the working chamber of the male rotor. Recently a prototype two-phase screw steam expander has been designed and developed as a means of power recovery from liquid geothermal brine. An experimental setup has been designed by using a set of new generation instruments to complement the unit’s numerical modeling, from which predictions of an adiabatic efficiency in the order of 70%, were obtained. The testing includes measurements of instantaneous pressure and temperature in the suction and discharge port, instantaneous torque, speed and flow rate as well as monitoring the temperature and pressure of its lubrication system. Furthermore, four miniature high resolution pressure transducers were installed in the expander unit to measure the main rotor inter lobe temporal pressures with respect to crank angle of the main rotor. The high dynamic characteristics and response of the instrument are captured by a real time processor, National Instrument Compact-RIO, data logger and the programming is done using LabVIEW. The paper presents the measuring method, preparation of the instruments, acquisition and processing of the results obtained during experimental investigation of the two-phase screw expander.
Screw Expanders Increase Output and Decrease the Cost of Geothermal Binary Power Plant Systems
A study has been carried out on the feasibility of using screw expanders, as an alternative to turbines, in three types of binary systems, suitable for recovering power from liquid dominated brines. The maximum power that one machine can generate is of the order of 1-3 MW per unit, depending on the type of system, and the brine and cooling conditions. They are shown to be roughly as efficient as turbines, when expanding dry vapour, and they can be coupled directly to a generator, without an intermediate gearbox. They have similar characteristics as two-phase expanders, when their efficiencies are not much reduced. This latter feature enables improvements to be made in the conversion of heat to power, of the order of 30% over conventional ORC systems, from brines in the 100 – 140C temperature range. The costs of these machines are very competitive and it is shown that in a cycle designed for power recovery from brines in the 170210C range, the cost per unit output of the first expander stage may be less than 50% of that of a radial inflow turbine-generator set.
Development of the Trilateral Flash Cycle System: Part 1: Fundamental Considerations
The world market for systems for power recovery from low-grade heat sources is of the order of £1 billion per annum. Many of these sources are hot liquids or gases from which conventional power systems convert less than 2.5 per cent of the available heat into useful power when the fluid is initially at a temperature of 100° C rising to 8–9 per cent at an initial temperature of 200°C. Consideration of the maximum work recoverable from such single-phase heat sources leads to the concept of an ideal trilateral cycle as the optimum means of power recovery. The trilateral flash cycle (TFC) system is one means of approaching this ideal which involves liquid heating only and two-phase expansion of vapour. Previous work related to this is reviewed and details of analytical studies are given which compare such a system with various types of simple Rankine cycle. It is shown that provided two-phase expanders can be made to attain adiabatic efficiencies of more than 75 per cent, the TFC system can produce outputs of up to 80 per cent more than simple Rankine cycle systems in the recovery of power from hot liquid streams in the 100–200°C temperature range. The estimated cost per unit net output is approximately equal to that of Rankine cycle systems. The preferred working fluids for TFC power plants are light hydrocarbons.