Turbine nozzles

Larger tubular, or single-can, units usually have more than one nozzle. In many cases a ring of nozzles is placed in the primary zone area. The radial and circumferential distribution of the temperature to the turbine nozzles is not as even as in tubo-annular combustors. In some cases, high stresses are exerted on the turbine casing leading to casing cracks. 

In general terms, the life of a combustor might be reduced by about 30 percent through use of a distillate fuel and by 80 percent through the use of residual fuel. The first stage turbine nozzle life can Be reduced by 20 percent through use of a distillate fuel and by about 6.5 percent when certain residual fuels are used. 

The operating schedule of a gas turbine produces low-frequency thermal fatigue. The number of starts per hours of operating time directly affects the hfe of the hot sections (combustor, turbine nozzles, and blades). The life reduction effect of the number of starts on a combustor liner could be as high as 230 hours/start and on the turbine nozzles as high as 180 hours/start. The effect of full load trips can be nearly 2-3 times as great ... 

Talceislii, K., Matsuura, M., Aoki, S., and Sato, T., 1989, An Experimental Study of Heat Transfer and Film Cooling on Low Aspect Ratio Turbine Nozzles, ASME paper 89-GT-187. 

Power plants in both peaking and standby modes aehieved 30,000 hours between major overhauls. It was during these operations that the deposit problem on the turbine nozzles beeame apparent. Also, deposits developed on the fuel nozzles, a situation that eould eause deviation in the fuel spray angle and related eombustion problems. Therefore, both turbine and fuel nozzles needed frequent eleaning. 

The startup speed and temperature acceleration curves as shown in Figure 19-2 are one such safety measure. If the temperature or speed are not reached in a certain time span from ignition, the turbine will be shutdown. In the early days when these acceleration and temperature curves were not used, the fuel, which was not ignited, was carried from the combustor and then deposited at the first or second turbine nozzle, where the fuel combusted which resulted in the burnout of the turbine nozzles. After an aborted start the turbine must be fully purged of any fuel before the next start is attempted. To achieve the purge of any fuel residual from the turbine, there must be about seven times the turbine volume of air that must be exhausted before combustion is once again attempted. 

The gas turbine eontrol loop eontrols the Inlet Guide Vanes (IGV) and the Gas Turbine Inlet Temperature (TIT). The TIT is defined as the temperature at the inlet of the first stage turbine nozzle. Presently, in 99% of the units, the inlet temperature is eontrolled by an algorithm, whieh relates the turbine exhaust temperature, or the turbine temperature after the gasifier turbine, the eompressor pressure ratio, the eompressor exit temperature, and the air mass flow to the turbine inlet temperature. New teehnologies are being developed to measure the TIT direetly by the use of pyrometers and other speeialized probes, whieh eould last in these harsh environments. The TIT is eontrolled by the fuel flow and the IGV, whieh eontrols the total air mass... 

The gas turbines major limitations on the life are the eombustor eans, first stage turbine nozzles and first stage turbine blades as seen in Figure 21-6. The effeet of dry Low NO eombustors have been very negative on the availability of Combined Cyele Power Plants, espeeially those with dual fuel eapability. Flash baek problems are a very major problem as they tend to ereate burning in the pre-mix seetion of the eombustor, and eause failure of the pre-mix tubes. These pre-mix tubes are also very suseeptible to resonanee vibrations. 

Steam Turbine Nozzle Pa Ming No of Blades RPM Steady... 

Fig. 6.1a shows diagrammatically the steam injection gas turbine (STIG) plant steam. raised in a heat recovery steam generator (HRSG) downstream of the turbine, is injected into the combustion chamber or into the turbine nozzle guide vanes. 

Aircraft engines Ceramic turbine nozzles in the APU (Auxiliary Power Unit Engine). Seals runners installed in different business jets such as Falcon, Citation and Learjet. Ceramic oil pump spacer enhance engine could start capability on APUs on Boeing 777 and 737 and all Airbuses. Cutter pins, which are used as a safety feature for air turbine starters. Ceramic wear indicator on Airbus APU starter brushes since 1997... 

A reversible adiabatic process is isentropic, meaning that a substance will have the same entropy values at the beginning and end of the process. Systems such as pumps, turbines, nozzles, and diffusers are nearly adiabatic operations and are more efficient when irreversibilities, such as friction, are reduced, and hence operated under isentropic conditions. 

The widespread occurrence in process plant of nozzles, intentional and unintentional, means that it is necessary for the control engineer to have an understanding of their physical principles for modelling purposes. We will consider in this chapter the features of an ideal, frictionless nozzle. Results from this simplified model will be put to immediate use in Chapter 6 in order to account for the unavoidable nozzle formed at beginning of a gas pipe. Moreover, the idealized approach provides the groundwork for the more complex models of Chapter 14, where turbine nozzles with friction are considered in some detail. 

Chapter 5 gave a general introduction to nozzles, which were considered to be frictionless and to be supplied with gas at negligible velocity. However, an accurate model of a turbine requires us to consider the inefficiency introduced by frictional effects in nozzles. In addition, the turbine nozzle will be supplied with gas from the previous stage that may have an appreciable velocity, so that we need to develop a method of dealing with non-negligible inlet velocities. 

Velocity and enthalpy relationships in a turbine nozzle nozzle efficiency... 

This equation applies to both incompressible and compressible flow, and no condition of reversibility is implied. Row through a turbine nozzle is adiabatic, so that dq = 0 no work is done (until it reaches the turbine blade downstream of the nozzle), so that dw = 0 and the height difference is zero, so that dz = 0. Accordingly equation (4.7) simplifies to... 

Turbine nozzles 169 just downstream of the nozzle outlet as... 

Keenan, J.H. (1949). Reaction tests of turbine nozzles for supersonic velocities. Transactions of the American Society of Mechanical Engineers, 71, 773-780. 

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