Method for conversion of low temperature heat to electricity and cooling, and system therefore

Abstract

A method for producing electrical energy is disclosed which uses a heat source, such as solar heat, geothermal heat, industrial waste heat or heat from power production processes, providing heat of 150° C. or below, further comprising an absorber system in which a working gas, primarily carbon dioxide CO2, is absorbed into an absorbent, typically an amine, further comprising a reactor which receives heat from said heat source and in which the absorbent-CO2 mixture is split into CO2 and absorbent, further comprising an expansion machine, an electricity generator and auxiliary equipment such as pumps, pipes and heat exchangers. The system according to the method allows the cost-efficient production of electrical energy and cooling using low value heat source.

1 . A method for producing energy using an essentially closed loop system comprising:
 using thermal energy from a heat source ( 1 ) to heat a pressurized gas-absorbent mix in a reactor ( 7 );   causing the gas-absorbent mix to split into heated and pressurized C02 gas and a heated absorbent liquid that are output from the reactor;   transforming the heated and pressurized CO2 gas into low temperature CO2 gas in a transition machine ( 15 );   piping the heated absorbent liquid exiting the reactor and the low temperature C02 gas exiting the transition machine to an absorber system ( 3 ); and   causing the C02 gas to be chemically re-absorbed into the heated absorbent liquid by the absorber system creating the gas-absorbent mix for the process to start over in a reversible reaction between the C02 gas and the heated absorbent liquid.   
     
     
         2 . The method according to  claim 1  wherein the transforming step is carried out using an expansion machine ( 15 ) as the transition machine. 
     
     
         3 . The method according to  claim 2 , further comprising the step of:
 providing a booster system ( 19 ) for heating the heated and pressurized gas by said heat source or a secondary heat source, operating at least at the same temperature as the gas-absorbent mix, after or at a downstream section of the reactor ( 7 ) and before entering the expansion machine ( 15 ).   
     
     
         4 . The method according to  claim 2 , further comprising:
 providing the expansion machine ( 15 ) with a generator ( 23 ) for producing electricity by expanding the heated and pressurized CO 2  gas from the said reactor ( 7 ) into the low temperature CO 2  gas by using a low pressure generated in the said absorber system ( 3 ).   
     
     
         5 . A method according to  claim 2  further comprising using the expansion machine ( 15 ) for production of electrical energy. 
     
     
         6 . The method according to  claim 2 , comprising at least one of the following:
 the low temperature CO 2  exiting the expansion machine ( 15 ) is used for condensing water or making ice to produce fresh water or supply cooling for freezer applications; and   using any excess heat generated to provide residential hot water or to preheat a thermal fluid from the heat source ( 1 ), the heat source comprising a solar heat source to achieve a faster start-up.   
     
     
         7 . A method according to  claim 1 , wherein the thermal energy using step is carried out with thermal energy from the heat source at up to 150° C. 
     
     
         8 . The method according to  claim 1 , wherein the CO2 gas is chemically re-absorbed into the heated absorbent liquid in an exothermic reaction. 
     
     
         9 . The method according to  claim 1 , further comprising the steps of:
 transferring heat using a heat exchange system ( 12 ) from the heated absorbent liquid from the reactor ( 7 ) to the gas-absorbent mix before the gas-absorbent mix enters the reactor ( 7 ); and   providing a thermal energy storage unit ( 2 ) for storing the gas-absorbent mix to provide thermal energy to supplement or replace heat from the heat source.   
     
     
         10 . The method according to  claim 1 , wherein the gas-absorbent mix is subjected to a separation step selected from phase separation, decanting and centrifuging, and wherein the gas-absorbent mix is split into at least two fractions of which the fraction which is richest in CO 2  is transferred to the reactor for splitting into CO 2  gas and lean absorbent. 
     
     
         11 . The method according to  claim 1 , wherein the using thermal energy step comprises transferring thermal energy from the heat source directly to the reactor ( 7 ). 
     
     
         12 . The method according to  claim 1 , further comprising: separating said gas-absorbent mix from the absorber system and recycling part of said gas-absorbent mix to said absorber system. 
     
     
         13 . A method for producing energy using an essentially closed loop system comprising:
 using thermal energy from a heat source ( 1 ) to heat a pressurized gas-absorbent mix in a reactor ( 7 );   the thermal energy using step being carried out with thermal energy from the heat source at up to 150° C.;   causing the gas-absorbent mix to split into heated and pressurized C02 gas and a heated absorbent liquid that are output from the reactor;   transforming the heated and pressurized CO2 gas into low temperature CO2 gas in an expansion machine ( 15 );   piping the heated absorbent liquid exiting the reactor and the low temperature C02 gas exiting the transition machine to an absorber system ( 3 ); and   causing the C02 gas to be chemically re-absorbed into the heated absorbent liquid by the absorber system creating the gas-absorbent mix for the process to start over in a reversible reaction between the C02 gas and the heated absorbent liquid; and   separating said gas-absorbent mix from the absorber system and recycling part of said gas-absorbent mix to said absorber system.   
     
     
         14 . The method according to  claim 13 , further comprising the steps of:
 transferring heat using a heat exchange system ( 12 ) from the heated absorbent liquid from the reactor ( 7 ) to the gas-absorbent mix before the gas-absorbent mix enters the reactor ( 7 ); and   providing a thermal energy storage unit ( 2 ) for storing the gas-absorbent mix to provide thermal energy to supplement or replace heat from the heat source.