Method and device for converting thermal energy into mechanical energy

Abstract

When converting thermal into mechanical energy by a working medium containing a mixture of at least two materials having different boiling and condensation points, which is fed to a condenser, and is condensed therein, the condenser condensation pressure may increase and the efficiency for generating the mechanical energy thus decreases because the mixture of materials is separated into a liquid phase and a vapor phase upstream of the condenser. To prevent this, the liquid phase of the working medium is mixed with the vapor phase of the working medium before or while the working medium is condensed, thus once again creating a homogeneous mixture of materials which condenses at a lower pressure than the separated working medium, thereby preventing loss of efficiency. This can be applied to the use of thermal energy from low-temperature sources such as geothermal fluids, industrial waste heat, or waste heat from internal combustion engines.

1 . A method for conversion of thermal energy to mechanical energy using an agent which comprises a substance mixture having at least two substances which have different boiling and condensation temperatures, the method comprising the steps of:
 supplying the agent which is expanded in an expansion device as a two-phase flow with a liquid phase and a vapor phase to a condenser, in which it is condensed, and   mixing the liquid phase with the vapor phase in the two-phase flow before or during the condensation of the agent in the condenser.   
     
     
         2 . The method according to  claim 1 , wherein
 for mixing in the two-phase flow, the liquid phase is separated from the vapor phase, and the separated liquid phase is then combined with the vapor phase again, wherein the separated liquid phase is preferably sprayed into the vapor phase for combination.   
     
     
         3 . The method according to  claim 2 , wherein
 before being sprayed in, the pressure of the separated liquid phase is increased to a value which is higher than the pressure of the vapor phase.   
     
     
         4 . The method according to  claim 2 , wherein
 the separation of the liquid phase from the vapor phase is carried out immediately before the condenser.   
     
     
         5 . The method according to  claim 1 , wherein
 the mixing process is carried out immediately before or in the condenser.   
     
     
         6 . The method according to  claim 1 , wherein
 the agent passes through at least the following method steps in a closed circuit after the condensation:
 increasing the pressure of the agent, 
 producing a vapor phase of the agent by heat transfer from an external heat source, and 
 expanding the vapor phase and converting its thermal energy to mechanical energy. 
   
     
     
         7 . The method according to  claim 6 , wherein
 before the expansion of the vapor phase of the agent, a liquid phase of the agent is separated from the vapor phase, and the vapor phase is supplied again after it has been expanded.   
     
     
         8 . The method according to  claim 6 , wherein
 a geothermal fluid, industrial waste heat or waste heat from an internal combustion engine is used as the external heat source.   
     
     
         9 . The method according to  claim 1 , wherein
 a mixture of ammonia and water is used as the agent.   
     
     
         10 . An apparatus for conversion of thermal energy to mechanical energy using an agent which comprises a substance mixture with at least two substances which have different boiling and condensation temperatures, having a condenser for condensation of the agent, wherein the agent, which is expanded in an expansion device, is in the form of a two-phase flow with a liquid phase and a vapor phase before it is supplied to the condenser, the apparatus comprising a mixing device for mixing the liquid phase of the two-phase flow with the vapor phase of the two-phase flow before or during the condensation of the agent in the condenser. 
     
     
         11 . The apparatus according to  claim 10 , wherein
 the mixing device has a separator for separation of the liquid phase from the vapor phase, and has at least one nozzle for spraying the separated liquid phase into the vapor phase.   
     
     
         12 . The apparatus according to  claim 11 , wherein
 the mixing device has a pump, by means of which the pressure of the separated liquid phase can be increased to a value which is higher than the pressure of the vapor phase.   
     
     
         13 . The apparatus according to  claim 11 , wherein
 the separator is arranged immediately before the condenser in the flow direction of the agent.   
     
     
         14 . The apparatus according to  claim 11 , wherein
 the at least one nozzle is arranged immediately before or in the condenser in the flow direction of the agent.   
     
     
         15 . The apparatus according to  claim 10 , wherein
 the agent can be carried in a closed circuit in the apparatus, which closed circuit has at least the following components after the condenser in the flow direction of the agent:
 a pump for increasing the pressure of the agent 
 a heat exchanger for producing a vapor phase of the agent by heat transfer from an external heat source, and 
 an expansion device for expansion of the vapor phase and conversion of its thermal energy to mechanical energy. 
   
     
     
         16 . The apparatus according to  claim 15 , wherein
 the circuit additionally comprises a separator, which is arranged between the heat exchanger and the expansion device, for separation of a liquid phase of the agent from a vapor phase, and a combination means, which is arranged between the expansion device and the mixing device, for combination of the separated liquid phase and the expanded vapor phase.   
     
     
         17 . The apparatus according to  claim 15 , wherein
 the external heat source is a geothermal flow, industrial waste heat or waste heat from an internal combustion engine.   
     
     
         18 . The apparatus according to  claim 10 , wherein
 the agent is a mixture of ammonia and water.   
     
     
         19 . The apparatus according to  claim 15 , wherein the expansion device is a turbine. 
     
     
         20 . A method for conversion of thermal energy to mechanical energy, comprising the steps of:
 providing an agent which comprises a substance mixture having at least two substances which have different boiling and condensation temperatures,   supplying the agent which is expanded in an expansion device as a two-phase flow with a liquid phase and a vapor phase to a condenser, in which it is condensed, and   mixing the liquid phase with the vapor phase in the two-phase flow before or during the condensation of the agent in the condenser.