GER-3705 GE Power Generation GE Steam Turbine Design Philosophy and Technology Programs R.S. Couchman K.E. Robbins P. Schofield GE Company Schenectady, NY GE STEAM TURBINE DESIGN PHILOSOPHY AND TECHNOLOGY PROGRAMS RS. Coucbman, K.E. Robbins and P. Schofield GE Company Schenectady, NY INTRODUCTION The need to provide State-OfTheArt products for a diverse and ever-changing market is the chal- lenge facing steam turbinegenerator manufactur- ers in the ’90s. While GE is uncertain what the industry will need as far as size, steam conditions, and technology mix, we have learned the value of strict adherence to a design philosophy based on ciI,,f ,,,,,,,,, 1 long-term reliability and efficiency measurements. Technology, on the other hand, needs to be I -60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 dynamic and responsive to support the needs of I the power generation industry. Service Year A look back reminds us that change is noth- GT2186( ing new. Figure 2. Growth in MW rating of GE nuclear The market between 1960 and 1990 was every- tits vs. service year thing but constant. The decade of the ’60s was new generation equipment planned and ordered characterized by growth in unit size in both the during the early ’70s created a total market for traditional fossil-fuel market and the newly devel- steam turbines which nearly doubled that of the oping nuclear market (Figures 1 and 2). This ’60s as shown in Figure 3. The drive for improved growth in size was driven by utilities’ strategy of reliability and availability resulted in the industry reducing generation costs by taking advantage of backing away from both the 1050°F steam temper- economy-of-scale to satisfy a constantly increasing atures which were common in the late ’50s and load demand which required power generation early ’60s and the 3500 psig supercritical throttle capability to double every 10 years. pressure which was utilized in the late ’60s and During the 1970s nuclear units continued to grow early ’70s. By 1975 steam conditions of 2400 somewhat in size (Figure 2), but the maximum-size psig/ 1 OOO’F/ 1000°F for utility turbines had fossil unit did not exceed the largest unit installed in become the standard although the performance the ’60s. Bather than being a decade of continually was poorer than the steam conditions which had increasing unit size, the ’70s could be characterized been used previously. as one devoted to reliability and availability improve The ’80s were a period of uncertainty. During ment as it became evident that the large plants the late ’70s and early ’80s load growth virtually installed in the ’60s did not meet expectations. disappeared as the industry coped with the energy During the ’70s load growth continued, but crisis; air, water and environmental concerns; overall only at half the rate of the ’60s. However, nuclear problems; conservation efforts; and a dif- ficult economic environment. Slow load growth 1400 compounded with excess generation capacity B I 1200 installed in the late ’70s created a situation where the new equipment needs of the power genera- P 1000 tion industry were only 30% of that of the ’70s i c 600 (Figure 3), thus manufacturers restructured their 'L .E 600 businesses accordingly. This was also a period 5 E 400 when there was much industry activity and discus- z 1 200 sion regarding what the power generation equip I 0 ment of the future would look like. Substantial 1920 1930 1940 1950 IWO 1970 1960 1990 work was done for advanced steam cycles of 4500 -fear psig, 1050°F and 1 lOO”F, single and double GT21867 reheat, based on pulverized coal boilers. There Figure 1. Growth in MW rating of GE fossil was also an accelerating interest in combined units vs. service year cycles as an operating experience base was rapidly 1 being built on units installed in the ’70s and ’80s and as the promise of advanced combined cycles 3,4pfgzq 120 with very attractive performance levels became a TOM # 01 GE ““its 656 663 363 reality. Much attention was also given to advanced z ‘00 ,. I E ,I 1 .: ::: :: iso ~-;: ‘. : j’, combinedcycle features such as coal gasification >; I, i’,.\~< ,, ,,,t‘^:;.’ and fluidized bed boilers. I ,,:;, .,‘, .y,.,:. $60 .I~1 ‘: ., i ,. : GE’s steam turbine technology programs have 1.; .Q ; .. ,,: Z ,1 ,,-, . always strongly supported industrial and utility E 40 : ,.,1,1 ,;:?“ cu ,: ,^‘<c: g ,,, steam turbine customer needs. Reliability and per- d 20 :. ,,’ ; ‘> formance improvement programs have continued ^\ ~-i. 0 ;” ‘j throughout the three decades discussed above as 19so-1969 1970.1979 well as several earlier ones. During the ’60s Ship emphasis was given to increasing unit size. During LilZlSIO both the ’60s and ’70s heavy emphasis was also Fw 4. Steam turbine shipments - GE Power given to developing cost effective compact Generation unit count designs, primarily through the development of longer laststage buckets. The longer buckets elim- there may be a revival of the market toward the inated the need for cross compound designs for end of the century. the largest ratings and permitted tandem com- A substantial increase in combinedcycle units is pound units to be built in more compact arrange anticipated for the ’90s. For the lO-year period ments with fewer low pressure sections. During 198@1989 about 5% of the MW shipped, corre- the ’70s many programs were aimed at the special sponding to 18% of the number of units, were for areas unique to nuclear applications. The ’80s combinedcycle applications. During the period received heavy emphasis on developing hardware 1990-2000 it is anticipated that combined cycles suitable for retrofitting, particularly in the long- will constitute an increasingly larger share and will bucket area where substantial performance account for 25% of the MW shipped and 45% of improvements were possible through the applica- the number of units as shown in Figures 3 and 4. tion of modem technology. The remaining 55% of the MW and 50% of the As we enter the ’90s we again see a decade of units will be made up of industrial and utility units change although it is anything but clear what using traditional fossil fuels. the exact requirements of the steam turbine Not only was there a change in the robustness market will be. A somewhat increased level of of the market in the ‘6Os, ’70s and ‘8Os, but there shipments compared with the ’80s is anticipat- were significant shifts, ebbs and flows, in the tech- ed as shown in Figures 3 and 4. nology mix, the market segmentation and unit During the ’90s GE expects that about 20% of size. This market required larger, more efficient the MWs shipped will be for nuclear fueled units, units (fossil and nuclear) for the utilities; com- although this represents less than 5% of the num- bined-cycle units for the utilities and industrials; ber of units shipped as shown in Figure 4. These fast-track packaged units for the industrial and units will be for international customers as it is not emerging NUG market; and parts and product anticipated that there will be any new nuclear unit improvements for upgrades and repowering. shipments required domestically prior to the year Design philosophy and technology played a very important role in serving this diversity. 2000, even though there are some indications that As we move through the ’90s one thing seems clear - there will be even greater diversity required in steam turbine designs as the need to serve traditional markets continues and as the need to respond to new applications, particularly in the combinedcycle area, develop. This paper discusses the basic steam turbine design philosophy used by GE and summarizes some of the key technology programs which will support steam turbine designs for the ’90s. OVERALL DESIGN APPROACH bIZltw The design of reliable, efficient steam turbines Figure 3. Steam turbine shipments - GE Power requires the application of many diverse areas of Generation MW count technology. There are many competing design and material requirements that must be thorough- used, rather than simply comparing a single ly evaluated, so that optimum trade-offs can be value of stress to a single value of strength and achieved. As new design requirements are considering the difference between the two as a imposed, and if inset-vice problems occur, the tur- margin of safety. Long ago it was recognized that bine manufacturer must possess the technical this latter approach is quite naive. Regardless of competence to reconcile them quickly and effec- the degree of sophistication employed in calcu- tively. This means a competent, experienced tech- lating or measuring stresses (or strains), there nical staff is required, with adequate supporting remains a considerable amount of uncertainty laboratory facilities to permit keeping current with about their actual magnitude in service under rapidly changing technology and to push back different operating conditions. Similarly, one technological frontiers or barriers, when the need cannot assume a single value of strength (or arises. The overriding objective in all steam tur- strain capability). Heat-to-heat variations and bine design activities is to produce turbine designs even variations within a single large component, which minimize the life-cycle cost of ownership. such as a rotor forging or turbine shell, intro- duce unavoidable uncertainties in material capa- Life-Cycle Cost Objectives bility. Thus, it has become necessary to treat the problem statistically, as illustrated in Figure 5. The total cost of ownership of a steam turbme- The “permissible” probability of failure, or failure generator can be considered to be made up of rate, depends on many factors, including the con- two components.