USE OF VACUUM MICROGAS TURBINE PLANTS FOR HEATPOWER SUPPLY OF LOCAL OBJECTS

Consideration subject in article are vacuum cycles of microgas turbine plants (MGTP) for the purpose of studying of their profitability and perspectives of use for heatpower supply of local objects. Vacuum MGTP of a simple cycle and with warmth regeneration is investigated. Optimum parameters of cycles – ratio of turbine expansion and regeneration ratio are found. It is established that profitability of MGTP with regeneration of warmth is higher in comparison with MGTP of a simple cycle almost twice, specific power decreases approximately by 1,35 times. By virtue of profitability and smaller values of compressor pressure ratio increase of the microturbine it is reasonable to apply in MGTP of a vacuum cycle with warmth regeneration.

Inverted Brayton Cycle With Exhaust Gas Condensation

Approximately 30% of the energy from an internal combustion engine is rejected as heat in the exhaust gases. An inverted Brayton cycle (IBC) is one potential means of recovering some of this energy, in order to improve the overall system efficiency. When a fuel is burnt, water and CO2 are produced and expelled as part of the exhaust gases. In an IBC, in order to reduce compression work, the exhaust gases are cooled before compression up to ambient pressure. If coolant with a low enough temperature is available, it is possible to condense some of the water out of the exhaust gases, further reducing compressor work. In this study the condensation of exhaust gas water is studied. The results show that the IBC can produce an improvement of approximately 5% in BSFC at the baseline conditions chosen and for a compressor inlet temperature of 310 K. The main factors that influence the power output are heat exchanger pressure drop, turbine expansion ratio, coolant temperature and turbine inlet temperature. A lower coolant temperature significantly increases power output, particularly when condensation occurs. Larger turbine expansion ratios produce more power and slightly lower the temperature at which condensation onset occurs. The system is very sensitive to heat exchanger pressure drop, as larger pressure drops increase the compressor pressure ratio whilst leaving the turbine expansion ratio unchanged. Higher turbine inlet pressures can also increase net power, but the higher exhaust backpressures may increase engine pumping losses. Finally, for conditions when condensation is possible, the water content of the exhaust gas has a significant influence on power output. The hydrogen to carbon ratio of the fuel has the most potential to vary the water content and hence the power generated by the system. If there is no condensation, water content has a small impact on performance. The effect on power in the condensing region is predominantly due to reduced mass flow in the compressor.

Thermo-Economic Analysis of a Recompression Supercritical CO2 Cycle Combined With a Transcritical CO2 Cycle

The transcritical CO2 cycle (TCO2 cycle) exhibits good performance in low-grade waste heat recovery area. In this study, a TCO2 cycle was employed as a bottoming cycle to recover the waste heat in the topping recompression supercritical CO2 Brayton cycle (SCO2 cycle). A detailed system analysis was performed of a recompression SCO2 cycle combined with a TCO2 cycle to improve the efficiency of energy conversion. Thermodynamic analysis, calculation of heat exchangers’ area and economic analysis were considered. The SCO2 turbine expansion ratio, TCO2 turbine inlet pressure, high temperature recuperator (HTR) effectiveness and condensation temperature were studied to investigate their effect on the system performance. For the basic analysis, SCO2 turbine inlet temperature was conservatively selected to be 550 °C and the compressor outlet pressure set at 20 MPa. For these operating conditions the proposed combined SCO2-TCO2 cycle yielded about 46% thermal efficiency at a SCO2 turbine expansion ratio of 2.7 and TCO2 turbine inlet pressure of 10 MPa. Similarly, the capital cost per net power output of the combined cycle was found as 6.6 k$/kW, which was ∼ 6% more expensive than that of the recompression SCO2 cycle without the bottoming cycle under the same operating condition. An optimum TCO2 turbine inlet pressure and an optimum SCO2 turbine expansion ratio existed where the system thermal efficiency reached the maximum value. Furthermore, the system thermal efficiency was very sensitive to the changes in the condensation temperature and the HTR effectiveness. The HTR effectiveness also had a strong effect on the ratio of heat exchangers’ cost to the plant capital cost. Additionally, increasing SCO2 turbine inlet temperature would significantly improve the cycle overall thermal efficiency and decrease the plant capital cost per net power output.

Design and Off-Design Characteristics of the Alternative Recuperated Gas Turbine Cycle With Divided Turbine Expansion

In order to fully address the characteristics of the alternative recuperated cycle with divided turbine expansion, both design and off-design analyses have been performed. Two types of mechanical design are assumed: two shaft and single shaft. In particular, optimal pressure ratio division between the high- and low-pressure turbines is evaluated for the single-shaft configuration. It is predicted that the alternative recuperated cycle hardly exhibits sensible design efficiency advantage over the conventional recuperated cycle for moderate turbine inlet conditions and with usual component performances. An advantage of the alternative cycle with single-shaft design is that thermal efficiency is less sensitive to compressor pressure ratio compared to other configurations, and we can also have flexibility in the turbine division without much efficiency loss. The part load analyses have been carried out with the aid of realistic component maps and models for off-design operation. In addition to the general fuel only control, a variable speed control is assumed as the part load operating strategy of the single-shaft configuration. Obvious advantage with the alternative cycle is observed in the variable speed operation of the single-shaft design. With this strategy, the part load efficiency of the alternative cycle is far superior to the conventional cycle. Almost constant efficiency is predicted for a wide power range.

Design and Off-Design Characteristics of the Alternative Recuperated Gas Turbine Cycle With Divided Turbine Expansion

In order to fully address the characteristics of the alternative recuperated cycle with divided turbine expansion, both the design and off-design analyses have been performed. Two types of mechanical design are assumed: two-shaft and single-shaft. In particular, optimal pressure ratio division between the high and low pressure turbines is evaluated for the single shaft configuration. It is predicted that the alternative recuperated cycle hardly exhibits sensible design efficiency advantage over the conventional recuperated cycle for moderate turbine inlet conditions and with usual component performances. An advantage of the alternative cycle with single shaft design is that thermal efficiency is less sensitive to compressor pressure ratio compared with other configurations and we can also have flexibility in the turbine division without much efficiency loss. The part load analyses have been carried out with the aid of realistic component maps and models for off-design operation. In addition to the general fuel only control, a variable speed control is assumed as the part load operating strategy of the single shaft configuration. Obvious advantage with the alternative cycle is observed in the variable speed operation of the single shaft design. With this strategy, the part load efficiency of the alternative cycle is far superior to the conventional cycle. Almost constant efficiency is predicted for a wide power range.

Simplified Analyses of Some Vapour Power Cycles

A range of vapour power cycles is analysed, using the assumption originally made by Schaff that along a turbine expansion line the difference between the (local) enthalpy (h) and the liquid enthalpy at the same pressure ( hL) may remain unchanged (β = h – hL is constant). The thermodynamics of the assumption are critically examined and it is found to be valid only over strictly limited ranges of properties (usually low-pressure levels). However, if such limitations are accepted, the analyses provide understanding of the effects of various key parameters on thermal efficiency, and of measures (such as feed heating, reheat, dual pressure boilers, etc.) that are taken to raise that efficiency.