Multi-Stage High-Efficiency Adiabatic Compressor/Expander Uses Covered Liquid Pistons

Abstract

A machine for near-adiabatic compression/expansion of gas comprises two or more stages. Each stage utilises the oscillatory motion of liquid through a set of tubes to transfer power between a displacer part and a converter part. In the converter part, each of several vertical gas compression/expansion cylinders admits an oscillating column of liquid which rises and falls to act as a liquid piston. The surface of said liquid piston is thermally isolated from the gas above it by a cover-block floating atop the liquid. The cover-block also acts to minimise the transport of gas molecules into the liquid or liquid molecules into the gas. The displacer part transforms power between the oscillatory motion of the liquid and mechanical shaft power. The machine is suited to converting slow speed mechanical power into the form of (near-) adiabatically compressed gas and has potential applications in wind wave and tidal generation.

1 . A machine for gas compression or expansion has multiple stages in series coupled to a single common shaft with each individual stage comprising: (a) a displacer part providing positive displacement coupling between the rotation of the shaft and oscillatory flow of liquid through several ports, (b) a convertor part which comprises a set of cylinders with substantially-vertical axes in each of which oscillatory liquid flow acts as a reciprocating liquid piston acting to change the volume of the gas-containing space above that liquid piston with said liquid piston being separated thermally from the gas above it by a floating cover-block, and (c) a set of tubes coupling each one port of the displacer part to a corresponding single port of the convertor part. 
     
     
         2 . A machine as described in claim I wherein the displacer part of one or more of the stages comprises a set of cylinders within which pistons are caused to reciprocate so that the changing volume above each piston drives the oscillatory flow of liquid through one corresponding port and the one common volume beneath all of the pistons holds the same liquid at a pressure between the lowest and the highest pressure above the pistons. 
     
     
         3 . A machine as described in  claim 2  in which controllable valves for gas inlet and exhaust are situated at the tops of some or all of the cylinders of the convertor part. 
     
     
         4 . A machine as described in  claim 3  which can be operated at part load by keeping open either the inlet or exhaust valves on two or more of the cylinders of the convertor part such that the pressure above the liquid piston in that cylinder does not change significantly through the cycle. 
     
     
         5 . A machine as described in claim I where plenum chambers are provided between successive stages of the machine to reduce the effect of alternating pressures from the output of one stage on the input of an adjacent stage. 
     
     
         6 . A machine as described in  claim 1  in which the displacer of one or more of the stages comprises a set of deformable closed spaces whose internal volumes change with rotation of the shaft. 
     
     
         7 . A machine as described in  claim 6  in which controllable valves for gas inlet and exhaust are situated at the tops of some or all of the cylinders of the convertor part. 
     
     
         8 . A machine as described in  claim 7  which can be operated at part load by keeping open either the inlet or exhaust valves on two or more of the cylinders of the convertor part such that the pressure above the liquid piston in that cylinder does not change significantly through the cycle.