The Application of Helical Screw Expanding Technology for Geothermal Power Generation

Abstract

The Helical Screw Expander (HSE) is a unique reciprocating positive displacement machine used to compress air, nitrogen, hydrocarbons and a variety of refrigerants. As expanders, these machines are used as prime movers, accessory power drives and for temperature reduction in gas cycle refrigeration systems. They have been demonstrated to have adiabatic efficiencies in excess of 70-75% over a wide operating range. Widely deployed in China for waste heat recovery, current installed capacity is estimated at approximately 500MW in industries such as; iron and steel, petroleum, chemicals, non-ferrous metal smelting and waste incineration.
Its application for geothermal power production is however relatively recent, with much of the development in this field occurring within China. In this paper we describe Chinese experience; from the early stages of technical development as a waste heat recovery unit through to deployment of the 1st HSE geothermal power generation unit in 2007 in Yangbajing, Tibet. Commercial development of the technology continues with currently 6 operating units generating 6.8MW installed in the Tibet area, further capacity under way in Yunnan province and a first enhanced geothermal system (EGS) project commencing in Zhengzhou.
In New Zealand, an unsuccessful trial of an early-stage version of the HSE technology by the MWD at the Broadlands in 1982 has tended to colour industry attitude in respect of the technology in this country. Chinese experience, however, has demonstrated the potential of HSE technology to extract more power than competing technologies from strongly mineralized low enthalpy geothermal fluids.
To this end, Demeter New Energy Technology Ltd. has proposed a first demonstration project within the Te Mihi geothermal field. If approvals are given the project will initially involve a 2MW single stage, containerized wellhead unit to evaluate mechanical and thermodynamic performance of the technology and its reliability in a NZ geothermal field condition.