No abstract

In order to overcome reported failure problems of turbomachinery for the supercritical carbon dioxide power cycle induced by the high rotational speed and axial force, an axial impulse-type turbo-generator with a partial admission nozzle was designed and manufactured to reduce the rotational speed and axial force. The turbine wheel part was separated by carbon ring-type mechanical seals to use conventional oillubricated tilting-pad bearings. A simple transcritical cycle using a liquid CO2 pump was constructed to drive the turbogenerator. A 600,000 kcal/h LNG fired thermal oil boiler and 200 RT chiller were used as a heat source and heat sink. The target turbine inlet temperature and pressure were 200°C and 130 bar, respectively. Two printed circuit heat exchangers were manufactured for both sides of the heater and cooler. A leakage make-up system using a reciprocating CO2 compressor; CO2 supply valve-train to the main loop and mechanical seal; and an oil cooler for the bearings, load bank, and control systems were installed. Prior to the turbine power-generating operation, a turbine bypass loop was operated using an air-driven control valve to determine the system mass flow rate and create turbine inlet conditions. Then, 11 kW of electric power was obtained under 205°C and 100 bar turbine inlet conditions, and the continuous operating time was 45 min.

The development of a 60-kWe turbo generator that uses supercritical carbon dioxide (sCO2) cycle technology at the lab scale is described herein. The design concept for the turbo generator involved using commercially available components to reduce the developmental time and to increase the reliability of the machine. The developed supercritical partial-admission CO2 turbine has a single-stage axial-type design with a 73-mm rotor mean diameter. The design of the sCO2 turbine uses impulse and partial admission to reduce the axial force and rotational speed. We simulated the flow of the designed sCO2 turbine. To increase the simulation accuracy, a real gas property table is coupled with the flow solver. The turbine performance test apparatus and test results are described; then, the turbine is continuously operated for 44 min. The maximum turbine power is 25.4 kW, and the maximum electric power is 10.3 kWe.

Power generation cycle — typically Brayton cycle — to use CO2 at supercritical state as working fluid have been researched many years because this cycle increase thermal efficiency of cycle and decrease turbomachinery size. But small turbomachinery make it difficult to develop proto type Supercritical Carbon dioxide (S-CO2) cycle equipment of lab scale size. KIER (Korea Institute of Energy Research) have been researched S-CO2 cycle since 2013. This paper is about 60kWe scale and sub-kWe class turbo generator development for applying to this S-CO2 cycle at the lab scale. A design concept of this turbo-generator is to use commercially available components so as to reduce development time and increase reliability. Major problem of SCO2 turbine is small volume flow rate and huge axial force. High density S-CO2 was referred as advantage of S-CO2 cycle because it make small turbomachinery possible. But this advantage was not valid in lab-scale cycles under 100kW because small amount volume flow rate means high rotating speed and too small diameter of turbine to manufacture it. Also, high inlet and outlet pressure make huge axial force. To solve these problem, KIER have attempt various turbines. In this paper, these attempts and results are presented and discussed.

KIER (Korea Institute of Energy Research) has developed three supercritical carbon dioxide power cycle test loops since 2013. After developing a 10 kWe-class simple un-recuperated Brayton cycle, a second sub-kWe small-scale experimental test loop was manufactured to investigate the characteristics of the supercritical carbon dioxide power cycle, for which a high speed radial type turbo-generator was also designed and manufactured. Using only one channel of the nozzle, the partial admission method was adopted to reduce the rotational speed of the rotor so that commercial oil-lubricated bearings can be used. This was the world’s first approach to the supercritical carbon dioxide turbo-generator. After several tests, operation of the turbine for power production of up to 670 W was successful. Finally, an 80 kWe-class dual Brayton cycle test loop was designed. Before completion of the full test loop, a 60 kWe axial type turbo-generator was first manufactured and our previous 10 kWe-class test loop was upgraded to drive this turbo-generator. Due to leakage flow through the mechanical seal, a make-up loop was also developed. After assembling all test loops, a cold-run test and a preliminary operation test were conducted. In this paper, the power generating operation results of the sub-kWe-class test loop and the construction of the tens of kWe-class test loop which drives an axial type turbo-generator are described.