Heat Exchanger for Direct Evaporation in Organic Rankine Cycle Systems and Method

Abstract

Systems and methods include heat exchangers using Organic Rankine Cycle (ORC) fluids in power generation systems. The system includes a heat exchanger configured to be mounted inside an exhaust stack that guides hot flue gases and having an inlet and an outlet, the heat exchanger being configured to receive a liquid stream of a first fluid through the inlet and to generate a vapor stream of the first fluid and the heat exchanger is configured to include a double walled pipe, where the first fluid is disposed within an inner wall of the double walled pipe and a second fluid is disposed between the inner wall and an outer wall of the double walled pipe.

1 . A system for power generation using an Organic Rankine Cycle (ORC), the system comprising:
 a heat exchanger configured to be mounted inside an exhaust stack that guides hot flue gases and having an inlet and an outlet, said heat exchanger being configured to receive a liquid stream of a first fluid through said inlet and to generate a vapor stream of said first fluid and said heat exchanger is configured to include a double walled pipe, wherein said first fluid is disposed within an inner wall of said double walled pipe and a second fluid is disposed between said inner wall and an outer wall of said double walled pipe;   an expander fluidly connected to said outlet of said heat exchanger and configured to expand said vapor stream of said first fluid, to generate power;   a condenser fluidly connected to an outlet of said expander and configured to receive and condense an expanded vapor stream; and   a pump fluidly connected to an outlet of said condenser and configured to receive said liquid stream of said first fluid, to pressurize said liquid stream of said first fluid and to circulate said liquid stream of said first fluid to said inlet of said heat exchanger.   
     
     
         2 . The system of  claim 1 , wherein said second fluid is selected from a group comprising water, sodium, thermal oil and a silicon-based thermal oil. 
     
     
         3 . The system of  claim 1 , further comprising:
 a plurality of compartments having a volume between said inner wall and said outer wall, some of said plurality of compartments being adjacent and insulated from each other; and   spacers configured to link said inner wall to said outer wall, wherein each compartment within said plurality of compartments is bounded by said inner wall, said outer wall and one or more of said spacers.   
     
     
         4 . The system of  claim 3 , wherein said spacers are configured to allow fluid communication between selected compartments. 
     
     
         5 . The system of  claim 3 , wherein said second fluid self circulates due to a heat flow within said compartments as said hot flue gasses boil said second fluid next to said outer wall and said first fluid condenses said second fluid next to said inner wall. 
     
     
         6 . The system of  claim 3 , wherein said double walled pipe includes a first pipe that forms said inner wall and has an inner diameter in the range of 12.77-25.4 mm and a second pipe that forms said outer wall and has an inner diameter in the range of 25.4-50.8 mm such that the inner diameter of said second pipe is always greater than the inner diameter of said first pipe, further wherein a distance between said inner wall and said outer wall is between 12.7 mm and 25.4 mm. 
     
     
         7 . The system of  claim 1 , wherein said first fluid is an ORC fluid and selected from a group comprising pentane, propane, cyclohexane, cyclopentane, butane, a fluorohydrocarbon, a ketone, an aromatic, and a combination thereof. 
     
     
         8 . The system of  claim 1 , further comprising:
 said exhaust stack; and   a first baffle provided in said exhaust stack and configured to redirect said hot flue gasses in said exhaust stack such that said hot flue gasses exhaust bypass said heat exchanger when said heat exchanger is in a non-operational condition.   
     
     
         9 . The system of  claim 8 , further comprising:
 a second baffle in said exhaust stack and configured to selectively open to allow air into said exhaust stack to flush gas away from said heat exchanger and into atmosphere when said first baffle is in a closed position.   
     
     
         10 . A method for vaporizing an Organic Rankine Cycle (ORC) fluid in a power generation system, the method comprising:
 transferring heat from a flue gas in an exhaust stack through a first wall of a heat exchanger to a heat pipe medium which changes a first phase of said heat pipe medium from a liquid phase to a gaseous phase inside a compartment of said heat exchanger; and   vaporizing said ORC fluid when transferring heat from said heat pipe medium in said gaseous phase through a second wall to said ORC fluid which is contained inside said heat exchanger within said exhaust stack which changes a second phase of said heat pipe medium from said gaseous phase to said liquid phase, wherein said second wall is provided inside said first wall.   
     
     
         11 . The method of  claim 10 , wherein said heat pipe fluid is selected from a group comprising water, sodium, thermal oil and a silicon-based thermal oil. 
     
     
         12 . The method of  claim 10 , wherein said ORC fluid is selected from a group comprising pentane, propane, cyclohexane, cyclopentane, butane, a fluorohydrocarbon, a ketone, an aromatic, and a combination thereof. 
     
     
         13 . The method of  claim 10 , wherein a temperature of said flue gas is in a temperature range of 350-600 degrees Celsius. 
     
     
         14 . The method of  claim 10 , wherein an average temperature of said ORC fluid is at an average temperature less than or equal to 240 degrees Celsius. 
     
     
         15 . The method of  claim 10 , wherein said heat pipe fluid is self circulating in said compartment. 
     
     
         16 . The method of  claim 10 , wherein said heat pipe fluid is under a higher pressure than said ORC fluid. 
     
     
         17 . The method of  claim 10 , wherein said heat pipe fluid is in a hermetically sealed volume. 
     
     
         18 . A heat exchanger in an exhaust stack directly exposed to hot flue gases, said heat exchanger comprising:
 a first pipe configured to receive a heat pipe fluid and further includes a second pipe, wherein a volume between said first pipe and said second pipe is hermetically sealed and is divided into compartments which are bound by an inner wall of said first pipe, an outer wall of said second pipe and separating walls between said compartments;   said second pipe configured to receive an Organic Rankine Cycle (ORC) fluid; and   said separating walls configured to link said first pipe to said second pipe, said heat exchanger configured to receive heat from said hot flue gases and configured to receive a liquid stream of said ORC fluid through an inlet and to generate a vapor stream of said ORC fluid through an outlet.   
     
     
         19 . The heat exchanger of  claim 18 , wherein said distance between said inner wall of said first pipe and said outer wall of said second pipe is between 12.7 mm and 25.4 mm. 
     
     
         20 . The heat exchanger of  claim 18 , wherein said first and second pipes enter and exit said exhaust stack multiple times.