Uwe Ruedel

Development of an Annular Combustor Chamber

To accommodate the customer’s expectations for operational flexibility and low power generation costs, a gas turbine has to be robust, flexible and cost effective. Since its introduction in 1993 and with its more than 7.5 million operating hours and over 54’000 starts, the GT13E2 gas turbine has already demonstrated to be a most flexible and reliable engine. It is being used in connection with many different applications, and meets a very broad range of environment and operation conditions. The GT13E2 upgrade 2012 described in this paper further improves these capabilities.The next generation of GT13E2 combustors is improved for increased lifetime, reduced total life cycle cost and implementation of a low emission dual fuel AEV burner system. The basic design philosophy for the lifetime improvement is adapted from the well-proven GT24 and GT26 annular combustors. The liner segments represent Alstom’s proven technology of sealed TBC coated metallic combustor liners that can expand in their fixations. The application of a thermal barrier coating onto the segments is simple and cost-effective. The design is robust so that the liners have to be checked only at major inspections and are not subject to reconditioning/replacement at hot gas part inspections. The closed-loop cooling arrangement is used for the backside cooling of the hot gas liner segments and to maintain the large structural components at a constant temperature. This combustion segment improvement is combined with the AEV (Advanced EnVironmental) burner. All the mentioned features result in a marked improvement of the operating and cyclic lifetime of the GT13E2 combustor.This paper describes the development and validation process for the implementation of the combustion liner segment technology of the GT13E2. The various design phases from concept development to validation including the generic tests and final engine implementation are described and substantiated.Copyright

Experimental Study of Advanced Convective Cooling Techniques for Combustor Liners

An experimental study was conducted to determine the heat transfer performance of advanced convective cooling techniques at the typical conditions found in a backside cooled combustion chamber. For these internal cooling channels, the Reynolds number is usually found to be above the Reynolds number range covered by available databases in the open literature. As possible candidates for an improved convective cooling configuration in terms of heat transfer augmentation and acceptable pressure drops, W-shaped and WW-shaped ribs were considered for channels with a rectangular cross section. Additionally, uniformly distributed hemispheres were investigated. Here, four different roughness spacings were studied to identify the influence on friction factors and the heat transfer enhancement. The ribs and the hemispheres were placed on one channel wall only. Pressure losses and heat transfer enhancement data for all test cases are reported. To resolve the heat transfer coefficient, a transient thermocromic liquid crystal technique was applied. Additionally, the area-averaged heat transfer coefficient on the W-shaped rib itself was observed using the so-called lumped-heat capacitance method. To gain insight into the flow field and to reveal the important flow field structures, numerical computations were conducted with the commercial code FLUENT™.Copyright

Alstom Gas Turbine Technology Overview: Status 2014

Market requirements for the heavy duty gas turbine power generation business have significantly changed over the last few years. With high gas prices in former times, all users have been mainly focusing on efficiency in addition to overall life cycle costs. Today individual countries see different requirements, which is easily explainable picking three typical trends. In the United States, with the exploitation of shale gas, gas prices are at a very low level. Hence, many gas turbines are used as base load engines, i.e. nearly constant loads for extended times. For these engines reliability is of main importance and efficiency somewhat less. In Japan gas prices are extremely high, and therefore the need for efficiency is significantly higher. Due to the challenge to partly replace nuclear plants, these engines as well are mainly intended for base load operation. In Europe, with the mid and long term carbon reduction strategy, heavy duty gas turbines is mainly used to compensate for intermittent renewable power generation. As a consequence, very high cyclic operation including fast and reliable start-up, very high loading gradients, including frequency response, and extended minimum and maximum operating ranges are required.Additionally, there are other features that are frequently requested. Fuel flexibility is a major demand, reaching from fuels of lower purity, i.e. with higher carbon (C2+), content up to possible combustion of gases generated by electrolysis (H2). Lifecycle optimization, as another important request, relies on new technologies for reconditioning, lifetime monitoring, and improved lifetime prediction methods.Out of Alstom’s recent research and development activities the following items are specifically addressed in this paper. Thermodynamic engine modelling and associated tasks are discussed, as well as the improvement and introduction of new operating concepts. Furthermore extended applications of design methodologies are shown. An additional focus is set ono improve emission behaviour understanding and increased fuel flexibility.Finally, some applications of the new technologies in Alstom products are given, indicating the focus on market requirements and customer care.Copyright

Heat Transfer and Pressure Drop in Combustor Cooling Channels With Combinations of Geometrical Elements

An investigation was conducted to assess the thermal performance of 90° ribs, low and high W-shaped ribs, and combinations of low W-shaped ribs with high W-shaped ribs and with dimples in a rectangular channel with an aspect ratio (W/H) of 2:1. The blockage ratios (e/Dh ) were 0.02 with the 90° ribs and the low W-shaped ribs and 0.06 with high W-shaped ribs. The rib pitch-to-height ratio (P/e) were 10 and 20. The channel height-to-dimple diameter (H/D) was 16.67; the dimple depth-to-dimple diameter (δ/D) was 0.3. The ribs and the dimples were located on one channel wall (side W). Furthermore, W-shaped ribs and 90° ribs with e/Dh = 0.027 and P/e = 10 were also individually investigated in a test channel with 1/4 of its cross section blocked. The Reynolds numbers investigated (Re > 100k) are typical for combustor liner cooling configurations in gas turbines. Local heat transfer coefficients using the transient thermochromic liquid crystal technique and overall pressure losses were measured. The different configurations were investigated numerically to visualize the flow pattern in the channel and to support the understanding of the experimental data. The results show that the highest heat transfer enhancement rates are obtained by a combination of W-shaped ribs with P/e = 10 and e/Dh = 0.06 and W-shaped ribs with P/e = 10 and e/Dh = 0.02. The best thermal performance is achieved by regularly spaced lower W-shaped ribs and by a compound roughness of regularly spaced W-shaped ribs and dimples at Re below and above 300,000, respectively.Copyright