The integration of steam from a central-receiver solar field into a combined cycle power plant (CCPP) provides an option to convert solar energy into electricity at the highest possible efficiency, because of the high pressure and temperature conditions of the solar steam, and at the lowest capital investment, because the water-steam cycle of the CCPP is in shared use with the solar field. From the operational point of view, the plant operator has the option to compensate the variability of the solar energy with fossil fuel electricity production, to use the solar energy to save fuel and to boost the plant power output, while reducing the environmental footprint of the plant operation. Alstom is able to integrate very large amounts of solar energy in its new combined-cycle power plants, in the range of the largest solar field ever built (Ivanpah Solar Power Facility, California, 3 units, total 392 MWel). The performance potential of such integration is analyzed both at base load and at part load operation of the plant. Additionally, the potential for solar retrofit of existing combined-cycle power plants is assessed. In this case, other types of concentrating solar power technologies than central receiver (linear Fresnel and trough) may be best suited to the specific conditions. Alstom is able to integrate any of these technologies into existing combined-cycle power plants.
Over the past years, Alstom gas turbines have been protected against icing based on a set of ambient temperature and relative humidity limits. These limits were derived mainly from operational and fleet experience. In recent times, the potential for optimizing these limits arose as they were observed to be too conservative. It is recognized that lowering the icing limits by a better understanding of the formation of condensate ice offers an opportunity for engine performance optimization while simultaneously ensuring adequate protection of the engine hardware. However, the level to which the original limits could be extended has not been known and this necessitated the setting up of a dedicated project to address the issue. This paper presents part of the results of the work done within this project and addresses how the new limits have been derived based on the thermodynamics of ice accretion at stationary and rotating surfaces of the compressor. The theory of ice accretion on the variable inlet guide vane (VIGV) and compressor blade surfaces as the intake air is expanded through the GT inlet system presented in this paper covers the process of condensation of moist air, the solidification of the condensate and the accumulation of the sub-cooled water condensate on surfaces with temperatures below 0°C. Using a state-of-the-art gas turbine modelling environment, relevant thermodynamic quantities including static and velocity components up to the first rotating plane of the compressor have been used to quantify the amount of condensate in the intake air at the first compressor rotating plane at various ambient conditions of temperature and humidity and at various engine operation modes (base load and part load operation). Empirical in-house relations for surface temperatures have been used to estimate the VIGV and the surface temperature of the first blade of the compressor. The theoretical results obtained have been validated on a heavy-duty gas turbine engine. Based on the confirmation of the theoretical results with engine data, the presented method can accurately be used to determine the anti-icing limits for a gas turbine. The approach is a generic one and is therefore applicable to all compressor designs for stationary gas turbines.
Geothermal power is becoming more and more significant in the renewable power mix of several countries in the world. The thermal conditions of the geothermal fluids exhausting from geothermal power plants shows additional potential for improved heat utilization through the integration of a low heat recovery system. This paper addresses the optimum integration of an Organic Rankine Cycle (ORC) as bottoming cycle with a geothermal steam power plant as topping cycle over a range of geothermal fluid interface temperatures. A reference geothermal based steam turbine power plant of 50MW capacity with indirect cycle configuration has been chosen for the study. At design point of the reference plant, optimized Organic Rankine Cycles based on three working fluids n-pentane, R123, and R245fa have been integrated at the exhaust of the geothermal fluid leaving the geothermal plant. An overall optimization of the power plant has been carried out by downsizing and over sizing the topping cycle with the integration of the bottoming cycle. One of the optimization variables for the overall plant is the interface temperature, which is a consequence of the resizing of the topping cycle. The procedure is repeated for the three different organic working fluids. By applying this procedure, it is then possible to know within a given interface temperature range, the organic working fluid that will give optimum plant performance. The choice of ORC integration option is not only driven by the best techno-economic solution but additionally by environmental, health and safety compliance.
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