The most efficient steam turbine power plant in the world is Vattenfalls Nordjylland Power Station Unit 3 in Denmark rated at 400MWe (commissioned in 1998). Higher exhaust moisture is detrimental to expansion efficiency and leads to erosion of LP last stage buckets via impact of microscopic droplets. For the entire plant, TFnet is 0.422/0.571 = 0.74 and the product of TF and CF is 0.74 0.855 = 0.63, which can be considered an overall Carnot Factor of conventional steam cycle technology on a net plant efficiency basis. 2 In modern GTCC power plants, steam is generated at three pressure levels (in the heat recovery steam generator, HRSG) and feed water heating is avoided for maximum combined cycle efficiency. It should be added that the sCO2 technology has its Brayton cycle variant as well. Ferritic and austenitic steels have similar specific heat, but thermal conductivity of ferritic steels is much higher. An additional reheat step can thus bring the expansion end point back to its original place and, in addition to increasing the cycle METH, will increase LP turbine efficiency. 27In 1950s through 1980s, steam turbine startup schemes were devised with thermal stress analysis with the assumption of cylindrical rotor.
Net plant heat rate is 8,730Btu/kWh (HHV), which corresponds to 42.4% in LHV. Very little (if any) can be shaved off of valve, exhaust, and generator losses. In either case, further improvement is unlikelyif nothing else due to limits imposed on flue gas exit temperature based on corrosion (condensation of H2O) and/or plume abatement considerations (stack effect). In their most basic embodiment, both cycles incorporate recuperation of heat from the exhaust stream of the turbine to heat the compressed working fluid from the discharge of the compressor/pump25. Present state-of-the-art in HRSG design with modern gas turbines is three-pressure, reheat (3PRH) with high steam temperatures and pressures. 10th CEPSI, September 1994. Vintage turbine designs (before ca. Cycle studies for similar conditions have shown that the optimal value of is 0.68, which is also the value used herein26. Philo 6 and Eddystone 1 were retired long time ago and no USC plants, single or double reheat steam cycle, are in operation (or planned) in the United States (with the possible exception of John W. Turk). The shaft configuration in Figure 5 is commonly known as tandem compound. This is the end result of sustained engineering achievements over the course of the last century. The impact of steam cycle on net plant efficiency, as a function of METH (i.e., as a function of CE), is illustrated by the chart in Figure 7. A detailed breakdown of auxiliary power consumption is not available. For a plant rated at 600MWe and with 45mbar condenser vacuum, the ideal design is a 4-flow LP turbine (i.e., two double-flow LP turbines) with 16m2 annulus area per end. Development of 700C class steam turbine technology. Another worlds most efficient coal-fired power plant claim was made by the OEM of the 1,050MWe cross-compound steam turbine (250/600/610 single reheat steam cycle) in Electric Power Development Co.s Tachibana-wan Unit 2 in Shikoku, Japan. Operation near the critical point (where fluid properties behave extremely peculiarly), low mass inertia of the turbomachinery, complex turbomachinery configuration and extreme susceptibility to leaks and pressure losses can be counted among them. In the case of steam boiler, it is the feed water temperature around 300C, which is achieved via steam extraction from the turbine to heat the condensate successively in feed water heaters. The reader should be cognizant of the difference between the two Rankine cycles, i.e., sCO2 and steam. It is based on a double-reheat cycle with 290 bara, 582C main steam, and 580C (292/582/580 in short) hot reheat steam conditions. titanium LSB length). Interestingly, for the latter type of starts, superalloys have higher ramp rates than steels. Most of those were built in 1960s and 1970s in Germany, the United States, and Japan. Starting point is fuel exergy (see Kotas (2012) for more on this rather ill-defined aspect of thermal bookkeeping) and ending point is net plant output at transformer high voltage terminals. If there is a demand for power but there is not enough sunshine or wind, dispatchable fossil fuel resources are required to take up the slack. In terms of a Rankine cycle heat engine, it is unlikely that sCO2 cycle can be a panacea. Using this number as a yardstick, the goodness of a given cycle can be determined by how close it can get to it. On the minus side, stage loading in reaction design is limited and, for a given pressure drop, roughly twice the number of impulse stages is necessary in a reaction design. For more in-depth information, refer to the recent monographs by the author and references cited therein (Glen, 2019a; Glen, 2019b). Power Eng. The same is true for the balance of plant (BOP) equipment (i.e., pumps, fans, AQCS, etc.) Due to the different shapes of vanes and buckets and large flow deflection across the buckets, profile and secondary losses are high leading to lower stage efficiency. 26Note that the split-flow recompression improvement can be applied to the basic recuperated Brayton cycle in exactly the same manner with similar thermal efficiency improvement. Due to its much faster dynamic characteristics, the primary response is easier to obtain from the gas turbine via overfire (with some sacrifice in hot gas path component lifeas specified by the OEM), opening of the inlet guide vanes (IGVs) or even activation of compressor on-line wash sprays (extra mass through the machine). The difference between the two lies in the nature of the steam boiler, which in the case of a nuclear power plant is the nuclear reactor. The second law analysis presented above is summarized in Table 1 for quick reference. Instead of trying to reduce cycle losses and irreversibilities, this approach seeks to increase the theoretical potential, i.e., equivalent Carnot efficiency via increasing METH. Bottoming cycle CF is lower than the CF for conventional steam power cycle. Due to their relative positions in the T-s diagram, the former is also referred to as the topping cycle whereas the latter is (not surprisingly) the bottoming cycle.
On a cycle-only basis, state-of the-art Carnot Factor range is (0.800.85) 0.855 = 0.68 to 0.73. In other instances, the need can arise unexpectedly, e.g., when there is a sudden drop in wind or cloud cover at a time when there is high demand for power. 7, GT is the gas turbine efficiency, ST is the steam turbine efficiency8 (take note: not the steam cycle), and HRSG is the HRSG effectiveness, i.e., percentage of gas turbine exhaust gas energy utilized in steam production. According to Troyanovskii (2013), the original design [in LMZ] of the nontraditional meridional contours has nothing like it in world steam turbine engineering. Protecting windage heating in IP and LP turbine creates a tug of war between steam flow required to roll the unit (e.g., via IP turbine steam admission) and steam flow required to keep the long last stage buckets cool. Supercritical CO2 Brayton and Rankine cycles with recuperation. Temperature-entropy diagram of Brayton-Rankine combined cycle. Also shown in Figure 1 are three gas temperatures: burner flame temperature, TFLM, boiler flue gas exit temperature, TFGX, and mean-effective average of the two, METFG. Editors D. Y. Goswami, and F. Kreith (Boca Raton, FL: CRC Press), Glen, S. C., Yarinovsky, I., and Ugolini, D. (2017b). Calculated performance data is summarized in Table 8, which indicates that combined cycle performance (including realistic assessment of plant aux load) with 44% efficient gas turbines falls in the range of 6364%. Note that the METL for the Brayton topping cycle of a GTCC given by Eq. Another modern innovation is bowed or leaned stator blades to reduce secondary losses. Considering the very long history of steam turbine technology development, the expectation herein is not more than 1% (if that). The steam turbine in John W. Turk (JWT) power plant has four casings: one single-flow HP turbine, one double-flow IP turbine, and two double-flow LP turbines. Furthermore, due to the axial thrust on the rotor created by the pressure difference across the blades, a dummy balance piston is required in single flow designs (i.e., the HP turbine mainly). Axial steam turbines with variable reaction blading, Proceedings of the 4th international charles parsons turbine conference, advances in turbine materials design and manufacturing, 4660, Steam (2015). Each LP end has an annulus area of 12.5m2. <> titanium LSBs, 303.4C feed water inlet temperature and 45mbar condenser pressure, the projected net efficiency is 45.9% LHV in an inland location (with 0.6% (wt) low sulfur fuel to ensure low flue gas exhaust temperature). Application and development prospects of double-reheat coal-fired power units. His recommendations are the introductory thermodynamics book by Moran and Shapiro (1998)1988 and the proverbial industry bible Steam by The Babcock & Wilcox Company (Steam, 2015). Power Magazine, December 2006, Zrner, W. (1994).
Net efficiency is 45.6% (LHV) with boiler efficiency over 94% (LHV). FIGURE 7.
Depending on site conditions and project economics, it is claimed that 48% is possible with certain modifications. Disappearing thermo-economic sanity in gas turbine combined cycle ratingsa critique, ASME paper GT2019-90883, ASME turbo expo 2019, Phoenix, AZ, June 1721, 2019. doi:10.1115/gt2019-90883, Glen, S. C., and Smith, R. W. (2010). Steam cycle impact on net plant efficiency. Steam turbine/cycle efficiency breakdown (column A: reference to maximum possible efficiency, column B: reference to generator (gross) efficiency. This convention eliminates one design specification from the discussion/analysis, i.e., the condenser pressure (steam turbine backpressure), which is highly dependent on site conditions, project economics, and prevailing regulations. Zachary, J., and Koza, D. (2006). To be precise, the cycle should be called half-Rankine or Rankine-Brayton hybrid. Instead of this awkward phrasing, however, it is referred to as the Rankine cycle.
(See Chapters 4 and 22 in Steam (2015) for detailed boiler combustion calculations.) 14There is some disagreement on the steam temperature delineating SC and USCin some references it is cited as 566C (1,050F), in others as 593C (1,100F). FIGURE 12. The phase change of the working fluid from vapor to liquid is present in the low pressure region of the cycle labeled as Rankine but absent in the high pressure region. The driver of this advantage is high cycle factor (CF) as a result of high cycle METH. This research focuses exclusively on large steam turbines (rated at least at 100 MWe or higher) used in utility-scale electric power generation. (2004). Boss, M. J., Gradoia, M., and Hofer, D. (2005).
In passing, it should be emphasized that the only difference between sCO2 Rankine and Brayton cycles in Figure 10 is in the heat rejection part of the cycles. (Even the more modest simple recuperated cycle has a quite respectable 38% thermal efficiency but better bottoming cycle efficiency.). Combined cycle performance ratings undergo thermodynamic reality check, in Gas turbine world, 2332, Glen, S. C. (2019a). Small and medium steam turbines used in mechanical drive applications in petrochemical and other industries are not included. FIGURE 3. Optimal design point balances the two at a particular steam pressure11. FIGURE 5. Obtaining these numbers requires in-depth boiler thermodynamic and heat transfer analysis. This particular piece of equipment is unique to nuclear power applications [see Chapter 4 in Bowman & Bowman (2020)]. 11This vital RBC design principle will again come up during the discussion of the suitability of supercritical CO2 cycle as the bottoming cycle of an advanced GTCC plant (see sCO2Bottoming Cycle). Due to the relatively short LSB size (39 in.
steam turbine research paper
