System for removing thermal degradation products from heat transfer fluids

Abstract

A system and method removes thermal decomposition components from biphenyl and/or diphenyl oxide-based heat transfer fluids. Light, volatile decomposition components including benzene, water, hydrogen and phenol leave the system for vapor recovery, chemical adsorption or thermal decomposition. Dimerized and polymerized heavy components such as biphenyl phenyl ether, terphenyl and related isomers are concentrated and recovered. The system can be a continuous, semi-continuous or batch operation. Solar electric plants employing the system can use solar field fluids and heating to operate the system during generator operation hours. A wash system operating at or near atmospheric pressure concentrates heavy thermal decomposition components while allowing removal of light, volatile decomposition components for separation from the majority of the thermal fluid components. Temperature-controlled condensation of the majority of the thermal fluid components allows collection of the thermal fluid, while allowing light, volatile decomposition components to be removed prior to vent processing.

What is claimed is: 
     
         1 . A system for removing thermal degradation products from heat transfer fluids comprising:
 A. A wash column with reflux, said wash column generating vapor;   B. A first reboiler for heating said wash column;   C. A tempering condenser in contact with said vapor, said tempering condenser generating condensate;   D. A collection vessel in fluid communication with said tempering condenser; and   E. A second reboiler in fluid communication with said collection vessel, said second reboiler for vaporizing light thermal decomposition components from said condensate.   
     
     
         2 . The system of  claim 1  wherein said first reboiler is selected from the group consisting of a forced circulation evaporator, thin film evaporator, wiped film evaporator, or combinations thereof. 
     
     
         3 . The system of  claim 1  wherein said tempering condenser is selected from the group consisting of a heat exchanger with a tempering fluid as a heat transfer medium, a direct-contact condenser using heat transfer fluid as a condensing medium, and combinations thereof. 
     
     
         4 . The system of  claim 3  wherein said tempering condenser is a heat exchanger with a tempering fluid as a heat transfer medium. 
     
     
         5 . The system of  claim 1  wherein said light thermal decomposition components include constituents selected from the group consisting of phenol, benzene, hydrogen, water and combinations thereof. 
     
     
         6 . The system of  claim 1  wherein said condensate contains heavy component degradation products having constituents selected from the group consisting of biphenyl phenyl ether, terphenyl, dimerized diphenyl oxide, dimerized biphenyl, isomers thereof and combinations thereof. 
     
     
         7 . A method for recovering reusable constituents from heat transfer fluids of high temperature solar electric generator stations comprising the steps of:
 A. Introducing heat transfer fluid into a wash column;   B. Heating said wash column with an evaporator;   C. Maintaining said wash column at or within 10% of atmospheric pressure;   D. Concentrating ullage residue in said wash column;   E. Forcing heavy components into ullage residue; and   F. Vaporizing light components.   
     
     
         8 . The method of  claim 7  wherein said step of concentrating ullage residue in a wash column includes the step of concentrating ullage residue in a wash column having reflux. 
     
     
         9 . The method of  claim 7  further including the step of condensing vaporized light components. 
     
     
         10 . The method of  claim 9  further including the step of transporting vaporized light components to vent collection. 
     
     
         11 . The method of  claim 7  further comprising the step of removing said heavy elements from said ullage reside. 
     
     
         12 . The method of  claim 11  wherein said step of removing said heavy elements from said ullage residue includes the step removing constituents selected from the group consisting of biphenyl phenyl ether, terphenyl, dimerized diphenyl oxide, dimerized biphenyl, isomers thereof and combinations thereof. 
     
     
         13 . The method of  claim 11  wherein said step of introducing heat transfer fluid into a wash column includes the step of introducing an eutectic mixture of biphenyl and diphenyl oxide. 
     
     
         14 . The method of  claim 7  further including the step of maintaining said heat transfer fluid at a temperature within approximately 10° F. of the normal boiling point of said heat transfer fluid. 
     
     
         15 . The method of  claim 7  wherein said step of introducing heat transfer fluid into a wash column further includes the step of introducing heat transfer fluid into a flash tank.