A Study of Performance on Advanced Humid Air Turbine Systems (2006)

Comparative studies are presented to determine the effect of the turbine blade cooling method on the Advanced Humid Air Turbine (AHAT) system performance. In AHAT systems, two kinds of fluids can be used as a coolant: air extracted from the compressor and humid air. Three types of turbine blade cooling systems are evaluated using the in-house heat cycle simulator. As a result, the thermal efficiency is improved 1.7 percentage points by using the humid air cooling method. The possibility of remodeling a typical mid-size simple cycle gas turbine for use in AHAT systems is examined. A remodeled AHAT system, which can be realized by adjusting the compressor intake flow rate, has 1.3 percentage points higher thermal efficiency than the combined cycle system using the same core gas turbine. NOMENCLATURE nN, nR the n-th stage turbine nozzle, rotor blade AHAT advanced humid air turbine G mass flow rate LHV lower heating value P pressure PR pressure ratio T temperature TET turbine entry temperature (ISO) WAC water atomization cooling Wsp specific work η efficiency or effectiveness Subscripts c cooling or coolant g mainstream gas th thermal INTRODUCTION Gas turbines play a big role in power generation; they may range from small-scale private power generation sources to large-scale combined cycle plants for electric utilities. In combined cycle plants, which are the most efficient of current technologies for power generation, the turbine inlet temperature is increased to enhance the thermal efficiency. However, gas turbines with a turbine inlet temperature of over 1,500°C are difficult to develop because of extensive increases in coolant consumption and NOx emissions. This situation has led to promoting improvement of the heat cycle in recent years. Heat cycle using humid air is one change that can be made. Various novel cycles such as Humid Air Turbine (HAT) (Rao, 1991), Cascaded Humidified Advanced Turbine (CHAT) (Nakhamkin, 1995), REVAP (Ruyck et al., 1996), and TOPHAT (van Liere, 1998) have been proposed for highly effective operation by combining the regenerative cycle with humid air. The concept of the gas turbine system using high humidity air (HAT system) was reported two decades ago. It is thought to be suitable for distributed power supply to a combined cycle because of high efficiency, simplicity of the system, and applicability to co-generation. Many theoretical and practical feasibility studies were made, and a small pilot plant, EvGT in Sweden, has been put tests operation recently (Agren et al., 2000). It seems that developing a new gas turbine with an intercooler would give the highest performance for the HAT cycle. The AHAT system is a system which uses existing mutual technologies and aims at high performance equal to that of the HAT system (Hatamiya et al., 2000). It is suitable for a typical gas turbine, which is widely used for industrial small-size to large-size machines. This paper presents comparative calculation results on the AHAT system performance and especially focuses on the influence of different turbine blade cooling systems. All results are evaluated by the in-house heat cycle simulator, which performs mass and energy balancing based on enthalpy calculations. All blade cooling systems are based on data for a middle-size gas turbine. The basic AHAT system has a conventional turbine blade cooling system which uses compressed air extracted from the compressor as coolant. This system is compared with two other AHAT systems. One uses high humidity air as coolant, which is humidified in the saturator, for all turbine blades, and the other uses high humidity air for turbine nozzle blades and compressed air for turbine rotor blades. Moreover, this paper discusses a remodeling method, which converts a typical gas turbine to the AHAT system. Comparison of performance for typical gas turbines (simple cycle and combined cycle) and the AHAT system are also described. SYSTEM DESCRIPTION Figure 1 shows the conceptual plant scheme of AHAT system. The AHAT system is suitable for a typical gas turbine system, which is widely used from industrial small-size machines to large-size machines for power generation. The compressor does not need to be divided for intercooling. The water atomization cooling (WAC) system is set in the air intake duct of the compressor, and fine droplets of water are sprayed there. Some of the water droplets evaporate at the compressor entrance and cool the intake air. The remainder evaporate while being compressed in the compressor, and they suppress the rise of the air temperature. The compressed air comes in contact directly with hot water in the saturator and it becomes humid air with 100% relative humidity. As a result, the Copyright © 2003 by GTSJ Manuscript Received on July 2, 2003 Proceedings of the International Gas Turbine Congress 2003 Tokyo November 2-7, 2003