Gas Turbine Cycle Incorporating Simultaneous, Parallel, Dual-Mode Heat Recovery
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Europaisches Patentamt J European Patent Office 00 Publication number: 0 275 121 Office europeen des brevets A2 EUROPEAN PATENT APPLICATION Application number: 88100532.6 IntCI.*: F 01 K 21/04 F 02 C 3/30 Date of filing: 15.01.88 Priority: 15.01.87 US 3548 ® Applicant: El-Masrl, Maher A. 9 Clubhouse Lane Date of publication of application: Wayland, MA 01778 (US) 20.07.88 Bulletin 88/29 @ Inventor: El-Masrl, Maher A. Designated Contracting States: 9 Clubhouse Lane CH DE FR QB IT LI Wayland, MA 01778 (US) @ Representative: Heidrlch, Udo, Dr. jur., Dipl.-Phys. Franziskanerstrasse 30 D-8000 Miinchen 80 (DE) @ Gas turbine cycle incorporating simultaneous, parallel, dual-mode heat recovery. (g?) The cycle includes water-injection, steam-injection, re- cuperation (or regeneration) and waste-heat boiler heat recovery in an arrangement that provides high thermal efficiency, flexible operation in a cogeneration plant and favorable capital cost in relation to thermodynamic performance when compared to currently practiced cycles. In the present cycle, the sensible enthalpy of the exhaust gases between turbine exit and stack is used to simultaneously and in-parallel heat both air and water/steam. A smaller amount of water is boiled than in the known Cheng cycle, in which the exhaust heat is used only to heat water/steam. Thus, the latent heat exhausted at the stack in the present cycle is lower than that for the Cheng cycle resulting in higher efficiency. CM S CM Si Bundesdruckerei Berlin 1 0 275 121 Description GAS TURBINE CYCLE INCORPORATING SIMULTANEOUS, PARALLEL, DUAL-MODE HEAT RECOVERY bine combustor pressure. The motive fluid is then Background of the Invention mixed with steam from a boiler and the mixture flows This invention relates to an improved gas turbine 5 through a high temperature recuperator before power plant cycle and more particularly to a cyle being conveyed to the combustor. The exhaust wherein both the compressed motive fluid and gases are also used to heat water entering the water/steam are simultaneously and in-parallel aftercooler and boiler. heated by the exhaust gases between the turbine Other embodiments include intercooling between exit and stack. 10 compressor stages. Yet another embodiment of the In current practice, exhaust heat from a gas present invention includes a separate superheater turbine power plant is recaptured for use in the for use in cogeneration applications where super- heat-engine cycle by a single-mode device, i.e., one heated steam is required. In all of these embodi- that heats compressor discharge air only such as a ments, a flow control device may be provided to recuperator or regenerator; or one that heats 15 apportion the flow of hot exhaust gases between water/steam only such as a waste heat boiler, with two parallel paths in the heat recovery system. the steam ultized in the heat-engine either in a separate steam turbine (combined cycle) or by Brief Description of the Drawing direct injection into the gas turbine combustor The invention disclosed herein will be understood (Cheng cycle). The Cheng cycle is disclosed in 20 better with reference to the drawing of which: United States Patent No. 4,128,994. The present Fig. 1a is a schematic diagram of the cycle invention secures significant thermodynamic ad- component layout and flow circuit according to vantages by simultaneously recovering exhaust heat the present invention: by both of the above modes in parallel and across a Figs. 1b and 1c are schematic diagrams of common exhaust gas temperature span. These 25 the present invention including intercooling theremodynamic advantages cannot be realized by between compressor stages; the use of a boiler utilizing exhaust gases exiting Fig. 2 is a Temperature-Entropy diagram from a recuperator, i.e., in a series arrangement, as illustrating the thermodynamic processes in the currently practiced in some cogeneration applica- cycle of Fig. 1a; tions. The advantages also cannot be fully realized 30 Figs. 3a, 3b, 3c and 3d are performance-map solely by evaporative aftercooling followed by re- comparisons between the cycle of the present cuperation (e.g., Lysholm, U.S. Patent No. 2,1 15,338) invention and four other cycles in current or by using staged evaporative water injection along practice; recuperators without aftercooling (e.g., Foote, U.S. Fig. 4 is a diagram of temperature profiles Patent No. 2,869,324). Besides the superior thermo- 35 along the exhaust heat recovery system for a dynamic performance over the latter two systems, typical example of the present cycle; the use of a separate boiler in the present invention Fig. 5 is a diagram of temperature profiles also permits flexible integration into a cogeneration along the exhaust heat recovery system for a system. typical Cheng cycle of the same power and It is therefore an object of the present invention to 40 engine technology as for the example of Fig. 4; provide a novel configuration for the turbine Figs. 6a and 6b are diagrams of the stack exhaust heat recovery system in a gas turbine power temperatures and "pinch-point" temperature plant cycle that provides high thermal efficiency. differences for eight Cheng cycle examples and Yet another object of the invention is a gas turbine eight examples of the present cycle as given on power plant cycle resulting in flexible operation in a 45 the performance maps of Fig. 3a; cogeneration plant having additional degrees of Fig. 7 is a graph comparing the water freedom for variable heat and power loads in comsumption per unit power output of the cogeneration applications. present cycle examples of Fig. 6 to that for the Cheng cycle examples of Fig. 6; Summary of the Invention 50 Fig. 8 is a graph comparing the total required These and other objects and advantages of the heat-exchanger capacity per unit power output invention are achieved in a gas turbine power plant for the present cycle examples of Fig. 6 to that cycle that includes water-injection, steam-injection, for the Cheng cycle examples of Fig. 6; and recuperation and waste-heat boiler heat recovery. Fig. 9 is a schematic diagram of an alternate All of the motive fluid entering the combustor in the 55 arrangement of the heat-recovery system of the present cycle has been heated. In particular, the present invention including a steam super- exhaust gases are used to simultaneously and heater. in-parallel heat both air and water/steam. In one embodiment, the compressor output is evapora- Description of the Preferred Embodiments tively cooled by water injection in an aftercooler. The 60 Figs. 1a and 2 show the cycle processes of the motive fluid is then heated in a low temperature present invention for the non-intercooled case. In recuperator where it is heated to a temperature the text square brackets are used to designate close to the saturation temperature at the gas-tur- thermodynamic state points and numbers without 0 275 121 brackets to designate component nomenclature as ical friction, auxiliary power requirements or electric indicated on Fig. 1a. Motive fluid, typically ambient losses. The calculations for all cycles in these figures is air, compressed from state [1] to state [CD] in a are based upon identical turbomachinery compo- compressor 1. The compressed air then enters nent assumptions. The effect of turbine cooling aftercooler la where it is evaporatively cooled by 5 flows upon the cycle thermodynamics has been water injection thereby reducing its temperature and computed and included for all cycles based upon increasing the mass flow rate of motive fluid, which identical cooling technology assumptions. The set of exits the aftercooler at state [2B] and flows into a common assumptions used is representive of low-temperature recuperator (LTR) 2 where it is current idustrial gas-turbine engines. In the calcula- heated to a temperature close to the saturation 10 tions presented, the minimum "pinch-point" tem- temperature at the gas turbine combustor pressure, perature difference allowed was 25° F, the minimum state [2C]. The motive fluid is then mixed with steam stack temperature allowed was 200° F, and the and the mixture flows through a high temperature temperature difference between exhaust gases at recuperator (HTR) 3 where it is heated to state [2] [4] and motive fluid at [2] was 75° F. In the before being conveyed to the combustor 3a. In most 15 calculations whose results are presented for this cases the combustor 3a will be a directly fired design cycle in Fig 3, it was assumed that all the aftercooler as commonly used in gas turbine engines but could water was extracted through valve 9 and that also be an indirectly fired heat exchanger. Heated valves 8 and 10 were shut. It was also assumed that motive fluid leaves the combustort at state [3] and the aftercooler water injection rate was such as to enters a gas turbine 3b, where it is expanded to 20 result in 95O/o relative humidity of the motive fluid at close-to-ambient pressure, state [4], thereby pro- its exit, state [2B]. In the calculations presented for ducing work to drive the compressor 1 and external this cycle with evaporative intercooling (Fig. 1b) on load. The hot exhaust motive fluid as state [4] is then Fig. 3b it was assumed that intercooler and conveyed to the heat recovery system where it flows aftercooler both saturate the air to 80% relative in counterflow heat exchange relationship against 25 humidity at their outlet and that valves 8, 10, 14, and the cooler compressed motive fluid. A damper 7 (or 16 of Fig. 1b were shut. For the results with surface other flow control device) is used to apportion the intercooling shown in Fig.