Development ofa3kW Microturbine for CHP Applications Combined heat and power (CHP) concepts for small-scale distributed power generation W. P. J. Visser offer significant potential for saving energy and reducing CO2 emissions. Microturbines e-mail: [email protected] are an interesting candidate for small CHP systems with advantages in terms of perfor- mance, size, noise, and costs. MTT is developinga3kWrecuperated microturbine for S. A. Shakariyants micro CHP applications for large households and for truck combined APU-heating sys- e-mail: [email protected] tems. To minimize costs, off-the-shelf automotive turbocharger technology has been used for the turbomachinery. During recent years, turbocharger turbomachinery performance M. Oostveen and efficiencies have significantly increased, even for very small sizes. At the same time, e-mail: [email protected] efficient high-speed motor-generators have become available at relatively low prices. The development of a concept demonstrator started in May 2008. This program phase in- Micro Turbine Technology MTT b.v., cluded a cycle analysis and component selection study around off-the-shelf turbomachin- De Rondom 1, ery, design of a custom combustor, recuperator and generator, and a test program. In this 5612 AP Eindhoven, The Netherlands paper, results of the cycle definition, conceptual design and component matching study are presented. Next, the development of a detailed performance model is described and performance prediction results are given. Also, results of the test program and test analy- sis work are presented. Finally, from the conclusion of the demonstrator phase an outlook is given on the prototype design and performance, which will be the next phase of the development program. ͓DOI: 10.1115/1.4002156͔ 1 Introduction perated microturbine with a thermal efficiency of at least 16% could be developed. If this concept can be mass produced at low During the last few decades, several attempts have been made prices corresponding to automotive parts, a very competitive op- to develop microturbines with efficiency levels close to those of portunity emerges in small-scale CHP ͑combined heat and power͒ larger gas turbines. Various interesting applications have emerged applications. for both aircraft propulsion and power generation. Particularly for microturbines below 100 kW, many developments have failed to 2 Applications obtain sufficient efficiency, reliability, and cost effectiveness to be successful for the market. The major technical factors that chal- The current development program focuses on a heat demand lenge microturbine development programs are the small-scale ef- driven micro CHP system to replace heating boilers for house- fects: holds and small businesses. During the development, large atten- tion is given to cost price, reliability and low maintenance costs. • low Reynolds numbers in the turbomachinery flow passages Domestic micro CHP offers significant energy saving potential. causing relatively high viscous losses, The system payback time target is 2–4 years depending on the • relatively high tip clearances due to manufacturing toler- user’s profile. Projected CO2 savings per installed system are up ances and bearing limitations to 6 tons per year. • large area-to-volume ratios resulting in high heat losses and While natural gas is the initial fuel of choice for the domestic inadvertent heat transfer to the compressor micro CHP application, liquid fuels such as heating oil or diesel • relatively high auxiliary system losses due to the low power are required for the CAP ͑truck parking heater/APU͒ application output level and for domestic micro CHP at locations without access to a natu- ral gas distribution grid. A separate development program has The turbomachinery dimensions for rated power levels lower started for the development of a clean combustor for liquid fuels than 10 kW become very small. When using the Balje ͓1͔ design that will comply with future emission requirements. rules for characteristic rotor speed and diameter,a3kWgastur- bine optimal radial compressor would have a diameter in the order 3 Conceptual Design of 30–40 mm and a speed of several 100,000 rpm. Off-the-shelf turbocharger technology offers an interesting op- Another factor is costs. Development of efficient turbomachin- portunity to develop low-cost microturbines. The compressor, tur- ery optimized for a particular cycle is very expensive and, in the bine, and sometimes bearing unit can be selected and matched micropower generation market, can only be justified with very without much modification. With the addition of a combustor, fuel large production volumes. An interesting opportunity to get system and control unit, a simple turbojet engine can be built. This around this cost problem is to use small automotive turbocharger concept is used for very small aircraft such as model planes. With components. During the last decade, small turbocharger turboma- a generator coupled to the shaft, a turboshaft engine is obtained chinery has become sufficiently efficient for gas turbine cycles for producing electrical power instead of thrust. With a recupera- and cost price is low due to the very large production volumes. tor, the efficiency of a turboshaft engine can be significantly in- At MTT, a conceptual design study indicated that with the creased, especially at the low cycle pressure ratios of smallest off-the-shelf turbocharger turbomachinery,a3kWrecu- turbocharger-based microturbines. This is due to the consequent relatively high turbine exit temperature providing good opportu- nity to recover heat. Off-the-shelf turbochargers are available for ͑ ͒ Contributed by the International Gas Turbine Institute IGTI of ASME for pub- both petrol and diesel engines with rated air flows down to 30 g/s. lication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received April 13, 2010; final manuscript received June 1, 2010; published online Laboratory condition tests have indicated turbine inlet tempera- November 22, 2010. Editor: Dilip R. Ballal. tures up to 1000°C are feasible with the customary Inconel 713 Journal of Engineering for Gas Turbines and Power APRIL 2011, Vol. 133 / 042301-1 Copyright © 2011 by ASME Downloaded 18 Feb 2011 to 131.155.56.82. Redistribution subject to ASME license or copyright; see http://www.asme.org/terms/Terms_Use.cfm material ͓2͔. With advanced materials such as MAR-M247 TIT Table 1 Conceptual design study assumptions for ISA refer- can be raised up to 1050°C ͓3͔. With these TIT levels for a typical ence performance, efficiencies, and losses small turbocharger-based microturbine rated at 35–45 g/s air flow, a power output of 2–3 kW is achievable. The heat input depends Parameter Unit Phase 1—COTS Turbocharger based on the efficiency. For a simple cycle, it would be around 35–40 Air flow g/s 35–45 depending on compressor type kW. With a recuperator, the heat input reduces to around 15 kW Thermal power kW Simple cycle: 35–45 / Recuperated: 10–18 due to the much higher efficiency. Equivalence ratios are around 0.35 ͑simple cycle͒ and 0.15 ͑recuperated͒, respectively. Worst Reference Best A study has been performed on the performance potential of a PLinlet % 1 0.5 0.2 ␩ case with off-the-shelf turbocharger components rated at 45 g/s. is_compressor %607075 Next, a development program has been defined including demon- PRcompressor - 2.0 2.4 3.2 stration of a recuperated microturbine design driving a separate 3 PLcombustor % 2 1 0.5 ␩ kW generator, based on off-the-shelf turbocharger turbomachin- combustor % 99 99.5 99.9 ery. The next phase is the development of a microturbine opti- TIT °C 977 1027 1077 K 1250 1300 1350 mized fora3kWeturbogenerator in a domestic micro CHP sys- ␩ is_turbine %606570 tem, replacing conventional boilers in environments such as larger ␩ mech͑bearings͒ %959798 houses and small offices for which 3 kW of electric power makes Eff - 0.70 0.8 0.9 an optimal business case. At a target turbogenerator efficiency of rec PLrec_hot % Eff.0.7: 3 Eff.0.7: 2 Eff.0.7: 1 16%, about 15 kW is available for the heating system and hot tap Eff.0.8: 4 Eff.0.8: 3 Eff.0.8: 2 water functions. Eff.0.9: 5 Eff.0.9: 4 Eff.0.9: 3 PLrec_cold % Eff.0.7: 2 Eff.0.7: 1 Eff.0.7: 0.5 3.1 Component Efficiencies and Losses. Modern small tur- Eff.0.8: 3 Eff.0.8: 1.5 Eff.0.8: 1 bocharger turbomachinery performance has been significantly im- Eff.0.9: 4 Eff.0.9: 2 Eff.0.9: 1.5 proved over the last decades. A simple survey of performance PLexhaust % 0.8 0.5 0.2 maps publicly available on the internet shows that despite the small-scale, isentropic compressor efficiencies of 75% and turbine efficiencies exceeding 65% are now state of the art. There is room for more improvement by optimizing the turbomachinery for the higher efficiencies and these effects are also included as best case. gas turbine application. The best case is also the starting point for the second phase of the development program with increased efficiencies that are consid- • The compressor impeller and/or diffuser design, which is ered realistic objectives for an optimization program. commonly optimized for a wide flow range ͓4͔ can be Finally, also, a worst case scenario has been defined for the case adapted toward maximum pressure ratio and efficiency. that component efficiencies would be less than expected. Cycle calculations indicate MTT microturbine design point power output and efficiency increase by about 2.5% per per- 3.2 Modeling. For cycle modeling, the gas turbine simulation cent increase in compressor isentropic efficiency at constant program ͑GSP͒ version 11 was used ͓8,9͔. Figure 1 shows the TIT. MTT recuperated cycle model configuration in GSP, including • The turbine design with isentropic efficiency often peaking station numbers.