A method for recovering energy from a geothermal reservoir in which brine from the reservoir is first employed to heat an immiscible fluid, such as a hydrocarbon in direct heat exchange and the heated hydrocarbon is then utilized in direct heat exchange to heat a second fluid, such as boiler feed water, to raise steam as the actual working fluid in the power cycle.

A method for producing mechanical energy from geothermal brine in which a heat transfer fluid (HTF) is heated by direct contact with the hot geothermal brine in cocurrent flow through a series of flash stages which are maintained at successively lower pressures so that the HTF is vaporized in each stage. A working fluid is countercurrently flowed through the series of flash stages in indirect heat exchange with the vapor produced in each stage so that the vapor is condensed in each stage and the working fluid is progressively heated as it passes through the series of flash stages. The heated working fluid is utilized in a heat engine for the production of mechanical energy.

Hot fluid which may contain salts and other dissolved minerals is passed through a direct contact heat exchanger in heat exchange relationship with a working fluid that has a specific gravity sufficiently below the specific gravity of the fluid so that it may pass from the bottom to the top of the heat exchanger chamber in contact with the fluid. The pressure of the chamber is selected to provide a certain mixture of working fluid and hot fluid at the output of the power extracting device of the system. The working fluid is selected so that the salts and other minerals in the fluid are relatively insoluble therein. The working fluid is vaporized in the exchanger and the vaporized working fluid and any steam mixed therewith are passed through a power extracting gas expansion device. The working fluid is separately condensed and recirculated.

Process and system for recovery of energy from geothermal brines and other hot water sources, which comprises direct contact heat exchange between the brine or hot water, and a hydrocarbon working fluid, e.g. n-butane, in a heat transfer column, the heat transfer column being operated at or above the critical pressure of the working fluid, and the hot brine or hot water feed being at a temperature at or above the critical temperature of the working fluid. The heated working fluid exiting the top of the heat transfer column is expanded through an expander to produce work. The discharge from the expander is cooled to condense working fluid which is separated in an accumulator, from condensed water vapor present in the working fluid, and the condensed working fluid is pressurized and fed back to the heat transfer column. Water from the accumulator can be fed to an H.sub.2 S removal system where good quality water can be recovered. Cooled brine or water from the bottom of the heat transfer column is fed to a flashing device such as a flash drum and the working fluid flashed off is compressed and returned to the cooler at the expander discharge, for condensation and recovery. Such cooled brine or water can be fed to one or more liquid expanders prior to flashing to produce additional work. Also, entrained liquid phase working fluid can be separated from the cooled brine or water prior to flashing, and returned to the system. Uncondensible gases plus some working fluid losses are vented from the accumulator and preferably the system can be operated under conditions to vent a minimum of uncondensible gas from the accumulator, and thereby reduce working fluid losses. Any accumulator vent gas can be fed to the H.sub.2 S removal system. Cold brine or water is discharged from the flash drum. Alternatively, if the flash drum is employed as a stripping column, a portion of the vent gas from the accumulator can be recycled as stripping gas to the stripping column for recovery of working fluids therefrom. Preferably, the uncondensible gases are removed from the feed brine or hot water prior to entry into the heat transfer column, such degassing preferably being carried out by a simple flash followed by energy recovery in a steam expander. The steam from the steam expander can be fed to the H.sub.2 S removal system.

Heat energy from hot geothermal fluids supplied by different temperature wells is transferred by heat exchange into a power fluid cycle, preferably of the dual fluid type, at different points in the cycle, which both enables an increase in peak cycle temperature to be achieved and allows more heat energy to be transferred into lower temperature points in the cycle. The result is an increase in the amount of power which can be developed per unit of geothermal fluid supplied.