| Title | Performance of Variable Phase Cycle in Geothermal and Waste Heat Recovery Applications |
|---|---|
| Authors | Boyle, Patrick; Hays, Lance; Kaupert, Kevin; Welch, Phil |
| Year | 2013 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Variable Phase turbine; Flashing Liquid Expander; Triangular Flashing Cycle; Variable Phase cycle; organic Rankine cycle; binary cycle; geothermal utilization; low temperature geothermal; thermodynamic cycle; axial impulse turbine; waste heat recovery |
| Abstract | Previous information has been presented about a method of generating power from low-temperature resources using a cycle called the Variable Phase Cycle [Welch et al 2009, Welch et al 2010, Welch et al 2011) which is similar to the Triangular Flashing Cycle. A typical Variable Phase Cycle uses a single-component fluid which is pumped as a liquid to a heat exchanger where it remains a liquid close to saturation. This liquid then continues to a set of discrete converging-diverging nozzles where it flashes partially or completely to vapor which then passes through a turbine. This cycle uses an axial impulse Variable Phase Turbine (also known as a flashing liquid expander) which by design accepts any vapor fraction from 0-100%. The liquid/vapor is then passed on to a condenser where the cycle is completed. The Variable Phase cycle excels over Organic Rankine and steam cycles at lower temperatures where it can realize a 30-50% power advantage over other approaches. In this paper, two applications of the Variable Phase cycle are discussed. The first application is a geothermal power plant operated in the geothermal field near Coso Junction, California. In this application, the brine separated from the wellheads is sent to the Variable Phase Cycle heat exchanger before being re-injected into the ground as per usual. This approach eliminates the need to drill a new geothermal well by using the sensible heat of the separated brine that was previously being wasted. The turbine is a 1 MW turbine which to date has produced 800 kW. The working fluid in this system is R134a. The second application is a waste heat recovery application. Most diesel engines use a turbocharger to improve power and efficiency. The air output of the turbocharger needs to be cooled before going into the diesel engine and a convenient way to do this and improve overall efficiency at the same time is to use a heat-recovery cycle to cool the air. A Variable Phase Cycle was implemented in lieu of the intercooler for a 10,000HP (7.5MW) diesel ship propulsion engine. The recovered heat was used to generate 150 kW of power using a Variable Phase Turbine (flashing liquid expander). The working fluid in this system is R245fa. |