Power cycle and system for utilizing moderate temperature heat sources
A new thermodynamic cycle is disclosed for converting energy from a moderate temperature stream, external source into useable energy using a working fluid comprising of a mixture of a low boiling component and a higher boiling component and including a higher pressure circuit and a lower pressure circuit. The cycle is designed to improve the efficiency of the energy extraction process by recirculating a portion of a liquid stream prior to further cooling. The new thermodynamic process and system for accomplishing the improved efficiency is especially well-suited for streams from moderate-temperature geothermal sources.
1. A method comprising the steps of:
transforming a portion of thermal energy in a superheated vapor stream into usable energy to produce a spent stream;
transferring thermal energy from an external heat source stream to a first vapor stream to form the superheated vapor stream and a first cooled external heat source stream;
transferring thermal energy from the first cooled external heat source stream to a first mixed stream to form the first vapor stream and a second cooled external heat source stream;
transferring thermal energy from the spent stream to a first pre-heated higher pressure, basic working fluid substream to form a partially condensed spent stream and a first heated, higher pressure, basic working fluid substream;
transferring thermal energy from a third cooled external heat source substream to a second pre-heated higher pressure, basic working fluid substream to form a second heated, higher pressure, basic working fluid substream and a first cooled external heat source substream;
combining the first and second heated, higher pressure basic working fluid substreams to form a combined heated, higher pressure basic working fluid stream;
transferring thermal energy from a first portion of the second cooled external heat source stream to the combined heated, higher pressure basic working fluid stream to form a higher temperature, higher pressure, basic working fluid stream and the third cooled external heat source substream;
separating the partially condensed spent stream into a separated vapor stream and a separated liquid stream;
pressurizing a first portion of the separated liquid stream to a pressure equal to a pressure of the combined higher temperature, higher pressure basic working fluid stream to form a pressurized liquid stream;
transferring thermal energy from a second portion of the second cooled external heat source stream to the pressurized liquid stream to form a second mixed stream and a fourth cooled external heat source substream;
combining the second mixed stream with the combined higher temperature, higher pressure basic working fluid stream to form the first mixed stream;
combining a second portion of the separated liquid stream with the separated vapor stream to from a lower pressure, basic working fluid stream;
transferring thermal energy from the lower pressure, basic working fluid stream to a higher pressure, basic working fluid stream to form a pre-heated, higher pressure, basic working fluid stream and a cooled, lower pressure, basic working fluid stream;
transferring thermal energy from the cooled, lower pressure, basic working fluid stream to an external coolant stream to from a spent external coolant stream and a fully condensed, lower pressure, basic working fluid stream; and
pressurizing the fully condensed, lower pressure, basic working fluid stream to the higher pressure, basic working fluid stream.