Energy generation from waste heat using the carbon carrier thermodynamic cycle

Abstract

The invention relates to a method is provided which allows the generation of high temperatures, e.g. above 120° C. and maximum 200° C. and low temperatures, e.g. below minimum minus 20° C., from waste heat or geothermal heat or similar heat sources having a temperature of between 20 and 70° C. The method may use essentially pure carbon dioxide as primary working fluid in an essentially closed loop as described in previous disclosures, alternatively low boiling solvents are employed. The common feature of different embodiments is that the system operates at least partly, specifically in the absorber or cold side of the process, below atmospheric pressure (1 bar). In the method a heat pump or heat transformer is realized within the technical boundaries mentioned above. The invention also relates to the use of the method in combination with a district heating system for elevating the temperature of the district heating medium or for electricity production on demand.

1 . A method for generation of energy where a heat source supplies thermal energy in the range 30-80° C. to a Rankine cycle including a desorber on the hot side, an absorber or liquefier on the cold side, heat exchangers and at least one compressor and at least one pump for working fluid, and at least one of the following product streams is obtained:
 thermal energy in the range +90, +100, +120 and maximum +200° C., 
 thermal energy in the range +15, +10, +5, 0, −5 and minimum −20° C., 
 electricity from the decompression of CO 2  or a working fluid following the extraction of heat, 
 
       wherein the pressure in the absorber or condenser section are always below 1 bar and that the pressures and temperatures in the process are in the following specified ranges:
 Desorber: 0.5-5 bar, 30-80° C. 
 Heat exchanger for heat production: 5-50 bar, 100-250° C., 
 Absorber: 0.01-0.9 bar, 10-50° C. 
 
     
     
         2 . The method according to  claim 1  for co-generation of heat and cold and optionally electrical energy, using a heat source such as geothermal heat or waste heat in the range 30-80° C., comprising the following steps in an essentially closed loop:
 a) condensing and cooling a working fluid such as acetone, ethanol, methanol, isopropanol, ammonia, or water, alone or in any stoichiometric combination, on the cold side of the process (absorber), 
 b) pumping said working fluid to the hot side of the process, 
 c) evaporating said working fluid using said geothermal or other waste heat source and compressing said working fluid from 0.5-5 bar to above 5 bar, or above 10 bar, preferably higher up to 50 bar, 
 d) extracting heat from said compressed working fluid and sending said heat to a point-of-use, 
 e) decompressing said working fluid whereupon cold is optionally extracted and sent to a different point-of-use, 
 f) condensing said working fluid (step a) for the cycle to start again. 
 
     
     
         3 . The method according to  claim 1  for co-generation of heat and cold and optionally electrical energy, using a heat source such as geothermal heat or waste heat in the range 30-80° C., comprising the following steps in an essentially closed loop system:
 a) temporarily absorbing CO 2  as working fluid in a suitable absorbent comprising an alkaline medium such as at least one amine, 
 b) desorbing CO 2  from the absorbent using said geothermal or other waste heat source and compressing CO 2  from 0.3-3 bar to above 5 bar, or above 10 bar, preferably higher, 
 c) extracting heat from said compressed CO 2  and sending heat to a point-of-use, 
 d) decompressing CO 2  whereupon cold is optionally extracted and sent to a different point-of-use, 
 e) re-absorbing CO 2  in said absorbent system, for the cycle to start again. 
 
     
     
         4 . The method according to  claim 1 , whereby a separate device is concentrating and ejecting non-condensable gas such as air from the process which at least partly operates below atmospheric pressure. 
     
     
         5 . The method according to  claim 1 , where more electricity or work is consumed in the compression stage than is generated during the decompression. 
     
     
         6 . The method according to  claim 1 , where the energy consumption of the method is reduced by coupling the gas compression for heat generation with the gas decompression, by mechanical, electrical or other means. 
     
     
         7 . The method according to  claim 1 , in which a heat pump or heat transformer is realized within the technical boundaries of above mentioned claims. 
     
     
         8 . Use of the method according to  claim 1 , in combination with a district heating system for elevating the temperature of the district heating medium or for electricity production on demand.