High-Temperature Gas Generator with Ceramic Components for Stationary Equipment Gas Turbine Unit

Transcription

1 THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS 345 E. 47 St., New York, N.Y GT The Society shall not be responsible for statements or opinions advanced in papers or in discussion at meetings of the Society or of Its Divisions or Sections, or printed in its publications. Discussion rs printed only If the paper is published in an ASME Journal, Papers are available from ASME for fifteen months after the meeting. Printed in USA Copyright 1991 by ASME High-Temperature Gas Generator with Ceramic Components for Stationary Equipment Gas Turbine Unit G. A. SHISHOV, dr.-ing., director A. V. SUDAREV, dr.tech.sc., prof. V. N. DUBERSHTEIN, dr.-ing. A. N. TSURIKOV, dr.-ing. VNITI EM, Leningrad, USSR Abstract The paper gives description of the systematic analysis algorythm for multi actor matrix of partial solutions, namely, aerodynamic, thermodynamic, strength, processing, design, operation, and other aspects of designing the assemblies and parts of the gas generator with ceramic components. Interrelations between structural ceramics thermophysical and strength parameters, joint techniques (ceramic- -ceramic and ceramic-metal components) has been aetermined at an optimum selection of turbine and compressor types and characteristics. The complex of processing, design, and operation factors influencing the design of the components and assemblies of the gas generator has been studied. The efforts on creation of high -temperature gas turbine unit (GTU) with structural ceramics fabricated assemblies and parts has been exerted in the UuSR since The gas turbine unit is intended for operation on the sites of natural gas and oil production and pumping. n good few of organizations and institutes engagea in the studies of problems related to creation of temperature-resistant non-metallic materials and processing,techniques as well as gaining experience in the field of designing and fabricating the stationary and automotive GTUs has joined the aforesaid project. The all-union Science-Technological Institute of rower Engineering (VNITI EM) in Leningrad has been nominated as the head organization aimed to run the abovementioned complex of operations. VNITI EM is affiliated with the Interbranch state Merger " nergomash". Principal Challenges and Factors of resigning Unlike the transportion gas turbine engines with ceramic components which are nowadays the goal of engineers in Uax, West Germany, Japan, the GTU, which we are pursuing to design, has some essential perculiarities characterized, mainly, by the operation conditions. Among these, the most important issues are an absence of pulsed operation and noticably lesser number of "start-shutdown" cycles during the operation hours, absence of rigid size-mass limitations, operation duty small range, and some others..all this necessitates to carry out a number of computation-analyti- Presented at the International Gas Turbine and Aeroengine Congress and Exposition Orlando, FL June 3-6, 1991

2 cal and test design-technological operations, beginning from a detailed study of the thermodynamic cycles, occurred in the GTU, and including the complete analysis of feasible solutions. Main Characteristics of Gas Generator and GTU rower (by working medium parameters at the outlet of gas generator) is 2.5 Mw; maximum mean-mass temperature of gas in cycle is 1573 K; effeciency of gas turbine unit with high-temperature gas generator is percent (depending on application of the designed GTU). The GTU layoct also envisages two or more gas generators (according to GTU specified power), both running for one common power turbine. Below, some main aspects be considered at designing, are listed. 1)esign when aetermining an optimum (or rational) approach to select the conceptual aspects of designing the gas turbine engine flow part or its cascades (provided the multishaft version is applied), all the variety of factors, characterizing the design features, might be divided into two categories. The first group is the factors which effects upon the design features can be predicted beforehand. The other group is the factors, estimation of effects of which bears a conjunctive imprint. The following factors could be attributed to the first group. 1. Procceding from the fundamental properties of the ceramic materials, and admitting the units to have a considerable specified guaranteed life, one should confine the level of turbine stage loading in accordance with the flowrates, mach numbers, excluding shock waves buildup at all operation duties. 2. It is advisable to admit such a version of the flow part, through which a minimum dynamic effect upon the turbine blading is imposed. 3. The statistical-probabilistic approach to estimate the reliability of the ceramic components demands the design accomplishment of the component shapes be thoroughly conducted to minimize the stresses and "to alleviate" the effects of the probable stress concentrators, since a compromise between the aerodynamic and strength demands can be achieved (the latter being preferable). 4. The abovementioned approach presupposes a certain requirement of minimizing the ceramic components' number in the flow part, i.e., the aesign must include only those ceramic components which are vitally necessary for normal functioning of the uncooled high-temperature flow part. The second group of factors could be determineu in the following manner. 1. Lack of aevelopment of the total solution of the processing procedures and design of the loaded joints of "ceramic-ceramic" and "ceramic-metal" types brings about a practical need to locate in one shaft no more than one ceramic turbine stage. PN

3 2. A quite explicable intention to obtain a higher power on the turbine- -wheel let it possible, when estimating the alternatives (axial or axiradial flow part), to give preference to the latter one. 3. The evident desire to reduce (to zero, if possible) the cooling agent flow for provision of the support servicability within the turbine zone results in a conclusion in relation to advisability to use the gas or magnet bearings of non-conventional, though found in service types. This leads to additional higher requirements for improving the procedure of the rotor balancing, and causes a need to obtain quite certain dynamic characteristics which actually excludes a possibility to use the axial compressor. 4. Availability of the ceramic components and assemblies makes the structure maintanability, as it is cor..monly understood, a rather problematic ussue. The preferance is given to the block-module version of the unit, where the maintanability must be provided at the expense of replacing the totally undismountable turbo-compressor blocks characteri - zed by comparatively low fubrication expenditures. At the fabrication of structu - res having more shafts than one, it is extremely desirable to minimize the gas path length in the benefits of both the design reliability and reduction of heat losses from the cycle. This analysis permits to formulate the basic features of an optimum solution of the gas generator with components made from structural ceramics for a stationary type GTU, which operation duties are characterized by absence of impulse loads, This solution can be exemplified by the design where each rotor in manufactured by the simplest schematic, i.e., double-support shaft, including one centrifugal compressor impeller and one centripetal turbine (with subsonic flow saris ). The turbine flow part, which experiences the greatest thermal loading, consists of the intake scroll and the turbine-wheel, The distinctive feature is the absence of the nozzle set. The rotor equipped with the appropriate stator parts, i.e., intake and outlet arrangements of turbine and compressor, and the bearing assemblies as well, constitutes a unique undismountable block. The turbocuenressor blocks, interconnected with air and gas pipelines, form a spatial multishaft structure. Thereat, the axes of blocks are positioned in the co-perpendicular planes which promote to minimizing the lengths of the "hot" branch-pipes, thus to the utmost simplifying the diagram of the module components' thermal expansions (Fig.1). Thermal Cycle The technology's peculiarties indicating the effects of the scale factor on the turbine-wheel's reliability characteristics, determine (at the selection of thermal cycle) the dominant effect of parameter characterizing the servicability of the working medium flowrate unit. 3

4 B) z T3 Y x C) 9{!D f 8f T Fig.1. Gas generator gas-air path diagram a - thermodynamic diagram of gas generator; 8 - version of spatial layout of turbocompressor shaft axes positions; C - diagram of gas path length minimization; 1, 2, 3 - shafts of turbocompressors of low, mean, and high pressures, relatively; 4 - combustion chamber; 5 - intermediate air cooler between compressors of low and mean pressures; 6 - atmospheric air; 7 - gas from gas generator low pressure turbine to power turbine; 8, 9, 10 - turbine of high, mean, and low pressure, relatively. 60 fide ^7 Sao #a8 yy ^id zoo f 2 3 y 5 36! 2 3 ^/ 5 Fig.2. Comparative characteristics of ti rmal cycles for gas turbine units ( t mqj( 1300 C) r I - Bryton cycle,eopt--30); 2 - cycle intermediate cooling (9.t, % 55) ; 3- cycle with end reg:neration 0.85,fi t = ; 4 - cycle with intermediate regeneration (Z016/...18, = 0.85;) 5 - cycle with intermediate cooling and end regeneration (V T 12, ( =

5 ^2 - specific servicability of workin medium;?e- cycle maximum efficiency; 40MAW - maximum mean-mass temperature of gas; tvat- optimum level of pressure increase; - regeneration level. The thermal cycle, providing a maximum specific power per flowrate unit, should be considered as optimum for GTU of the specified power. Fig.2 shows the comparative characteristics of the most widely applied thermal cycles. It results from this analysis that the intermediate cooling cycle is the most desirable one. This selection permits (when other conditions are similar) to obtain a minimum size for turbine-wheels and, therefore, better characteristics for GTU reliability. The abovementioned reasons are valid for gas turbine units of more than 1 MW power. When gas generator power is less than 1 NW, minimization of turbine-wheels on the basis of the principles abovecited can result in augmentation of thickness of edges, clearances etc., as for both turbine and compressor, i.e., for small (up to 1 MW) powers, it is reasonable to have a cycle which would promote to optimization (not minimization) of she turbine-wheels' sizes. One should not overlook a by- -work, though rather essential positive effect of the intermediate cooling thermal cycle for high temperature GTU. At a relevant distribution of pressure rise stages among sections upstream and downstream of the air cooler and at an appropriate selection of its characteristics in the diagram 5 one can obtain water steam condensate from atmospheric air which could be used to reduce the intensity of nitrogen oxides' formation in the combustion products; this is a fairly important ussue for high-temperature GI U with ceramic components. Kinematic Aspects of Gas Generator Turbomachines ran approach to optimize and design the kinematics diagrams of the turbo-wheels and compressor impellers considering their level reactivity differs from the conventional "metallic" solutions, bide by side with the reasons taking into account their economic efficiency, it is necessary to consider a number of factors illustra -'Uing the specific features of the plants of the type under discussion. Thus, the operation conditions and reliability of characteristics of the bearing assemly positioned between the compressor impeller and the turbine-wheel are, to a considerable extent, determined by the temperature factors, which "governing" can be conducted mostly reliably at a positive differential of the static pressures between the sections behind the compressor impeller and prior to the turbine-wheel. This differential is a function, in particular, of the levels of reactivities of impellers and wheels. Minimization of the total axial ro. rce acting upon the rotor can be achieved through changing the reactivity of the impeller and wheel and the design of both the turbine and compressor main discs, and the compressor cover disc. Furthermore, when selecting

6 the compressor reactivity level, it is advisable to consider a rather important consequences, i.e., at similar conditions concerning the pre$sure ratio and the working medium flowrate the reactivity increase results in an increase of the rotor speed which, in its turn, leads (at expansion ratio in the turbine, working medium flowrate, speed value being constant) to a reduction of the turbine-wheel outer diameter. Conclusions The concept of designing the gas turbine units for drive of the stationary equipment with uncooled high-temperature flow part designed on the basis of the structural ceramics application has been formulated. The discussed GTU must include single turbocompressor blocks positioned in train along the gas and air pathes and made as simple as possible, i.e., consisting of single shaft, single centrifugal compressor, and single centripetal turbine. It was illustrated that the current level of structural ceramics development stipulates to give preference to the intermediate air cooling cycle (for gas turbine units of more than 1 Mw power). The solutions presented in the paper can find a further development through utilization of the exhaust gas heat which would promote to obtaining the economic efficiency of the plant not less than that obtained through application of the combined cycle co-generation plants. 6