INTRODUCTION OF THE IES 7000B
AND DEVELOPMENT OF THE 7MW
KAWASAKI GAS TURBINE

International Energy Systems (1983) Limited is now able to  offer a new, 7 megawatt baseload gas turbine generator set package, designated the 7000B. Oil companies, utilities, governments, and institutions such as hospitals and universities will be able to take advantage of the increased power offered by the 7000B. The 7000B is driven by Kawasaki's new M7A-02 gas turbine engine.

The 7MW-class M7A-02 gas turbine from Kawasaki Heavy Industries Ltd., Akashi, Japan, is a single-shaft, high-efficiency gas turbine designed for electric power generation, especially for cogeneration and combined-cycle power generation systems, configurations that contribute to environmental protection and energy savings. The new engine is based on the company's 6 MW-class M7A-01 gas turbine and its abundant operating experience. The M7A-02 has, however, adopted new technologies, such as an 11-stage transonic axial compressor and transonic turbine, as well as attaining greater output and higher thermal efficiency.

The M7A-02 has a thermal efficiency of 32% after the speed reducing gearbox. In addition, the high exhaust gas temperature of 520°C increases the heat recovery efficiency, making the total thermal efficiency higher when utilized in a cogeneration or combined-cycle system.

More than 80% of the parts used in the M7A-02 gas turbine are in common with the M7A-01, an engine that has over 1 million hours of on-site operating experience. This includes the combustor and turbine hot section, which have proven their reliability over time.

The structure of the M7A-02 gas turbine—adopting the horizontal split and light casing—enables easy maintenance and inspection at site. In addition, the detachable annular type combustor and borescope inspection holes further reduce the maintenance and inspection time.

Based on the multiple-stage axial flow compressor of the M7A-01 gas turbine, the M7A-02 gas turbine establishes a higher pressure ratio and a larger amount of airflow than the M7A-01. By adopting transonic stages with the characteristics of high pressure ratio, the airflow rate and pressure ratio are increased by about 20%, despite a decreased number of stages from 12 to 11.

The first to sixth compressor rotor blades are made from the Ti-6A1-4V material, which has high strength and high corrosion resistance. From the seventh to eleventh stages, rotor blades and all stages of vanes use stainless steel designed for high strength against creep.

At the first and second stages, the rotor blades have adopted a multicircular arc (MCA) airfoil type blade developed with Kawasaki's own technologies. As a result, a 1.6 pressure ratio is achieved at the first stage and a high pressure ratio and a large amount of air flow are established. Wide chord airfoils are adopted in the front stages, establishing advanced performance of hydrodynamics, strength and characteristics of erosion resistance.

The angle of the vanes, including the inlet guide vanes at the front four stages of the eleven-stage compressor, are variable in order to run with sufficient surge margin in starting operation. During continuous operation, a high efficiency can be maintained and airflow rate controlled by changing vane angles.

The axial flow turbine consists of four stages. The first to third stages are subject to high temperatures as with the M7A-01 gas turbine. The comparatively high turbine inlet temperature in this class realizes high thermal efficiency and also increased heat recovery by raising the exhaust gas temperature.

The turbine blades are made from a nickel-based alloy, designed for high strength against creep at high temperature. The turbine vanes are made from a cobalt-based heat-resisting alloy, which demonstrates characteristics against thermal impact and oxidation. Blades and vanes are both produced by precision casting.

The blades and vanes at the first and second stages have an internal cooling air channel, and the first stage blades and vanes also adopt a film cooling system, forming a film of cooling air on the surface of an airfoil in order to tolerate the high inlet temperature. A ceramic thermal barrier coating is also applied on the surface of the stator vanes at the first stage for effective cooling.

The airfoil height of the blades and vanes at the fourth stage are higher than of the M7A-01 gas turbine by about 9% due to the increase of gas flow rate. At this stage, since the velocity of gas increases to near supersonic levels, a new airfoil section has been adopted.

Borescope inspection holes are provided in the turbine casing, enabling hot section inspections without removing the horizontal split casing. This is a major improvement for field inspection and maintenance.

The combustor of the M7A-02 gas turbine is designed as a conventional cannular type with six cans. This combustor is common with the M7A-01 and, as with other common components, has abundant operating experience. By shortening the length of the transition section leading to the turbine inlet, the required cooling air volume for the section is decreased. As a result, the flame temperature is lowered and NO_x emissions can be kept to a low level despite the high turbine inlet temperature.

The double wall structure of the combustor lining achieves effective cooling. In addition, a thermal barrier coating of the inner wall has resulted in long operating life by keeping the temperature of the nickel-based alloy low. Separate external combustor casings enable easy inspection without requiring detachment of the horizontal split casing.

The casing and rotor design has also been adopted from the M7A-01 machine. Detaching the upper portion of the horizontally split casing enables on-site inspection and maintenance. In addition, the light casing is advantageous when assembling, disassembling, and lifting. Each casing is also split vertically, which enables partial inspection and maintenance by detaching necessary parts. The casing is supported on both the air inlet side and the exhaust side; the former is a fixed support and the latter is a trunnion support, designed to allow for casing thermal expansion.

The compressor part of the rotor is welded together by the electronic beam method, which helps minimize imbalance and achieve stability of rotor motion. Six discs make up the turbine portion, which are bolted by spindle bolts and assembled with curvic couplings. The curvic couplings enable precise alignment and allow for thermal expansion of the turbine rotor, which in turn keeps rotor vibration low regardless of a change in turbine temperatures.

The design for bearings to support the rotor features two tilting pad-type journal bearings, each located on both ends of the rotor and a tilting pad type thrust bearing located on the inlet side. Supported by two points, alignment problems are eased. Also, the tilting pad-type bearings produce vibration reduction by oil film, resulting in low rotor vibration at critical speeds. Output power is transmitted to a gearbox through a flexible coupling that in turn drives a generator.

The M7A-02 gas turbine adopts a high-speed digital control system, governed by a 32-bit CPU. This system controls the: start and stop sequences of the gas turbine, generation system, protective alarm and trip system, fuel supply system, compressor variable stator vane angle. In addition, a separately installed monitoring system allows data logging and remote monitoring via telecommunication lines.