Waste Heat Recovery System

Abstract

In one embodiment, a waste heat recovery system includes a Rankine cycle system that circulates a working fluid that absorbs heat from exhaust gas. The Rankine cycle system includes an evaporator that may transfer sensible heat from the exhaust gas to the working fluid to produce cooled exhaust gas. The Rankine cycle system also includes an economizer that may transfer latent heat from the exhaust gas to the working fluid. The economizer is a carbon steel heat exchanger with a corrosion resistant coating.

1 . A waste heat recovery system, comprising:
 an exhaust system that generates exhaust gas; and   a Rankine cycle system for circulating a working fluid and comprising:
 an evaporator configured to transfer sensible heat from the exhaust gas to the working fluid to produce cooled exhaust gas; and 
 an economizer configured to transfer latent heat from the exhaust gas to the working fluid, wherein the economizer comprises a carbon steel heat exchanger with a corrosion resistant coating. 
   
     
     
         2 . The waste heat recovery system of  claim 1 , wherein the corrosion resistant coating comprises a silica coating. 
     
     
         3 . The waste heat recovery system of  claim 1 , wherein the corrosion resistant coating exhibits at least one of hydrophobic, oleophobic, or antistatic properties. 
     
     
         4 . The waste heat recovery system of  claim 1 , wherein the working fluid comprises an organic working fluid. 
     
     
         5 . The waste heat recovery system of  claim 1 , wherein the Rankine cycle system comprises an expander configured to expand the working fluid evaporated by the evaporator to drive a generator. 
     
     
         6 . The waste heat recovery system of  claim 1 , wherein the Rankine cycle system comprises a condenser configured to condense the working fluid. 
     
     
         7 . The waste heat recovery system of  claim 1 , wherein the evaporator is configured to at least partially evaporate and/or to superheat the working fluid. 
     
     
         8 . The waste heat recovery system of  claim 1 , comprising an exhaust gas heat exchanger configured to transfer the sensible heat from the exhaust gas to an intermediate fluid in heat transfer communication with the working fluid. 
     
     
         9 . A waste heat recovery system, comprising:
 an exhaust system that generates hot exhaust gas;   a first Rankine cycle system for circulating a first working fluid and comprising:
 an evaporator configured to transfer sensible heat from the hot exhaust gas to the first working fluid to produce cooled exhaust gas; and 
 an economizer configured to transfer latent heat from the cooled exhaust gas to the working fluid, wherein the economizer comprises a carbon steel heat exchanger with a corrosion resistant coating; 
   a second Rankine cycle system for circulating a second working fluid and configured to transfer heat from an engine heat source to the second working fluid; and   a shared heat exchanger common to the first and second Rankine cycle systems and configured to transfer heat from the first working fluid to the second working fluid to condense the first working fluid and to evaporate the second working fluid.   
     
     
         10 . The waste heat recovery system of  claim 9 , wherein the first and second working fluids comprise organic working fluids, and wherein the first working fluid has a condensation temperature above a boiling point of the second working fluid. 
     
     
         11 . The waste heat recovery system of  claim 9 , wherein the engine heat source comprises an engine cooling system. 
     
     
         12 . The waste heat recovery system of  claim 9 , wherein the second Rankine cycle system comprises a preheater configured to transfer heat from the heat source to the second working fluid to at least partially evaporate the second working fluid prior to directing the second working fluid to the shared heat exchanger. 
     
     
         13 . A waste heat recovery system, comprising:
 an exhaust system that generates hot exhaust gas; and   a Rankine cycle system for circulating a working fluid and comprising:
 an evaporator configured to transfer heat from the hot exhaust gas to the working fluid to at least partially vaporize the working fluid and to produce cooled exhaust gas; 
 a condenser configured to receive and to condense the vaporized working fluid; and 
 an economizer configured to transfer heat from the cooled exhaust gas to the condensed working fluid to at least partially condense the cooled exhaust gas, wherein the economizer comprises a carbon steel heat exchanger with a silica coating. 
   
     
     
         14 . The waste heat recovery system of  claim 13 , wherein the working fluid comprises cyclohexane. 
     
     
         15 . The waste heat recovery system of  claim 13 , wherein the silica coating comprises silica nanoparticles disposed on surfaces of the heat exchanger exposed to the cooled exhaust gas. 
     
     
         16 . The waste heat recovery system of  claim 13 , wherein the carbon steel heat exchanger comprises a carbon steel shell configured to receive the cooled exhaust gas and carbon steel tubes configured to receive the working fluid and wherein the corrosion resistant coating is disposed on an interior surface of the carbon steel shell and on an exterior surface of the carbon steel tubes. 
     
     
         17 . The waste heat recovery system of  claim 13 , comprising a thermal oil loop for circulating thermal oil between the evaporator and an exhaust gas heat exchanger configured to receive the hot exhaust gas and transfer heat from the hot exhaust gas to the thermal oil. 
     
     
         18 . The waste heat recovery system of  claim 13 , comprising an exhaust gas heat exchanger configured to receive the hot exhaust gas and transfer heat from the hot exhaust gas to an intermediate fluid in thermal communication with the working fluid. 
     
     
         19 . The waste heat recovery system of  claim 13 , wherein the evaporator is configured to transfer sensible heat from the hot exhaust gas to the working fluid, and wherein the economizer is configured to transfer latent heat from the cooled exhaust gas to the working fluid. 
     
     
         20 . The waste heat recovery system of  claim 13 , comprising a gas engine configured to combust biogas to generate the hot exhaust gas.