Abstract
This study analyzes the design and part load performance of a power generation system combining a micro gas turbine (MGT) and an organic Rankine cycle (ORC). Design performances of cycles adopting several different organic fluids are analyzed and compared with performance of the steam based cycle. All of the organic fluids recover greater MGT exhaust heat than the steam cycle (much lower stack temperature), but their bottoming cycle efficiencies are lower. R123 provides higher combined cycle efficiency than steam does. The efficiencies of the combined cycle with organic fluids are maximized when the turbine exhaust heat of the MGT is fully recovered at the MGT recuperator, whereas the efficiency of the combined cycle with steam shows an almost reverse trend. Since organic fluids have much higher density than steam, they allow more compact systems. The efficiency of the combined cycle, based on a MGT with 30 percent efficiency, can reach almost 40 percent. Also, the part load operation of the combined system is analyzed. Two representative power control methods are considered and their performances are compared. The variable speed control of the MGT exhibits far better combined cycle part load efficiency than the fuel only control despite slightly lower bottoming cycle performance.
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Abbreviations
- A:
-
Area [m2]
- BTIT:
-
Turbine inlet temperature of the bottoming cycle [°C]
- EGF:
-
Exhaust gas flow [kg/s]
- EGT:
-
Exhaust gas temperature [°C]
- h:
-
Specific enthalpy [kJ/kg]
- HRU:
-
Heat recovery unit
- LHV:
-
Lower heating value [kJ/kg]
- MGT:
-
Micro gas turbine
- m:
-
Mass flow rate [kg/s]
- ORC:
-
Organic Rankine cycle
- P:
-
Pressure [kPa]
- PHT:
-
Preheater
- PR:
-
Pressure ratio of the micro gas turbine
- REC:
-
Recuperator
- Q:
-
Heat transfer rate [kW]
- T:
-
Temperature [°C]
- TET:
-
Turbine exit temperature [°C]
- TIT:
-
Turbine inlet temperature of the micro gas turbine [°C]
- ΔTlm :
-
Log mean temperature difference [°C]
- U:
-
Overall heat transfer coefficient [kW/m2°C]
- W:
-
Power [kW]
- z:
-
Exponent
- η:
-
Efficiency
- aux:
-
Auxiliary
- BC:
-
Bottoming cycle
- bf:
-
Bottoming cycle fluid
- c:
-
Cold fluid, compressor
- CC:
-
Combined cycle
- d:
-
Design point
- evap:
-
Evaporator
- f:
-
Fuel
- fc:
-
Fuel compressor
- g:
-
Gas
- gen:
-
Generator
- h:
-
Hot fluid
- i:
-
Inlet
- o:
-
Outlet
- p:
-
Pump
- rec:
-
Recuperator
- t:
-
Turbine
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Lee, J.H., Kim, T.S. Analysis of design and part load performance of micro gas turbine/organic Rankine cycle combined systems. J Mech Sci Technol 20, 1502–1513 (2006). https://doi.org/10.1007/BF02915973
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DOI: https://doi.org/10.1007/BF02915973