Turbine Startup

After the generator is synchronized to the electrical system and is producing a substantial output, the power output is adjusted to meet the system requirements by manual adjustment of control rods, manual or automatic adjustment of reactor recirculation flow, or a combination of fhese two methods. 

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Turbine startup feasible for power recovery strings... 

Branch judiciously. References should not be used to make the writer s life easier. Sending the user to other procedures or documents may make writing the procedure easier, but it makes the procedure very cumbersome. Operators and mechanics often complain that the number of references in a procedure is so great that it makes the procedure impossible to use. For example, a startup procedure refers to a compressor startup procedure which in turn refers to a turbine startup procedure, and so on. If you are just using a step or two from another procedure, copy the step to the procedure you are writing. 

Unlike FPPs, the Super LWR has no superheater. Thus, the main steam conditions during startup of the Super LWR need to be adjusted so that they are suitable for steam turbines. The enthalpy of the core outlet coolant must be high enough to provide the required turbine inlet steam enthalpy. Herein, it is assumed that 5% of the rated power is necessary for turbine startup. The minimum required powers are calculated with various feedwater flow rates and feedwater temperatures. The calculated results at 10 MPa are shown in Fig. 5.16 and those at 20 MPa are shown in Fig. 5.17. It is found that the minimum required power decreases with decreasing flow rate or increasing the feedwater temperature. Figure 5.18 [3] shows the minimum required powers as function of the pressure. 

Pressurization (startup of feedwater pump) Start of nuclear heating Turbine startup Line switching Power raising ... 

Startup and Overcapacity From a design standpoint and also operationally, it is important to remember that pump-turbines not only do not generate power before they attain about 40 percent of design flow but actually consume power in decreasing amounts as the flow is increased from zero to 40 percent. This means that they should... 

When used to eompress air, the axial eompressor may be equipped with adjustable stator blades, either partially (Figure 4-16) or on all stages. In the ease of a motor serving as the assoeiated driver or with a generator eoupled to the train, the adjustable stator blade feature allows more effieient eontrol than suetion throttling. With a steam turbine as the assoeiated driver, stator blade adjustment may be eombined with the obvious shaft speed eontrol. This eombination allows for speeial operating eonditions, sueh as startup, or extreme part-load operation. 

With a steam turbine, the turboeompressors ean be readily matehed to the different plant operating eonditions. Under eontinuous load, this type of installation is powered by the steam resulting from ammonia eombustion. Consequently, an outside steam supply is needed for startup. This may be a separate boiler or another external souree with live-steam properties not neeessarily eorresponding to those obtained from the nitrie aeid plant. The steam turbine must be of robust design beeause of the different pressure and temperature levels. 

Smooth starts are possible with steam turbine installations that include an auxiliary boiler because the startup phases of the turbocompressor can be matched to different plant operating conditions. Aside from process-related timing issues, the time elapse or machinery startup duration is generally determined by the temperature gradients admissible on both steam turbine and expander. These factors are influenced by the relative expansion rates of the fixed and rotating components in these machines. 

A power recovery train—occasionally called a string—(Figure 4-53) employing a turboexpander usually consists of four main elements or casings the expander, a motor-generator, an air blower, and a steam turbine. The steam turbine is used primarily for startup and often to supplement the expander for generation of energy. This topic will be discussed in more detail later in this chapter. 

Step 4. A study of starting characteristics of the train is necessary to select the correct startup driver rating (motor and/or steam turbine). 

Figure 4-70 shows a four-body TPG train (string). As before, the expander supplies power to the generator. The steam turbine supplies power to the generator, provides startup power, and provides control for synchronization. The generator provides electricity, and the gear is used to allow the expander and steam turbine to operate at near optimum efficiency with the generator at its desired speed. 

The typical three-body TPG string is shown in Figure 4-71. With this arrangement the generated electricity is limited by the expander output. Additionally, both startup and synchronization must be accomplished by the expander instead of the steam turbine. 

Ease of installation and commissioning is another reason for gas turbine use. A gas turbine unit can be tested and packaged at the factory. Use of a unit should be carefully planned so as to cause as few start cycles as possible. Frequent startups and shutdowns at commissioning greatly reduce the life of a unit. 

The intent of this standard is to eover the normal requirements of the majority of applieations, reeognizing that eeonomie trade-offs and reliability implieations may differ in some applieations. The user may desire to add, delete, or modify the requirements in this standard to meet his speeifie needs, and he has the option of doing so in his own bid speeifiea-tion. The gas turbine eontrol system shall inelude sequeneing, eontrol, proteetion, and operator information, whieh shall provide for orderly and safe start-up of gas turbine, eontrol of proper loading, and an orderly shutdown proeedure. It shall inelude an emergeney shutdown eapability, whieh ean be operated automatieally by suitable failure deteetors or whieh ean be operated manually. Coordination between gas turbine eontrol and driven equipment must be provided for startup, operation, and shutdown. 

All gas turbines are provided with a eontrol system by the manufaeturer. The eontrol system has three fundamental funetions startup and shutdown sequeneing, steady-state eontrol when the unit is in operation, and protee-tion of the gas turbine. 

The gas turbine control systems are fully automated, and ensure the save and proper startup of the gas turbine. The gas turbine control system is complex and has a number of safety interlocks to ensure the safe startup of the turbine. 

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. 

In gas turbines with multiple eans, the deteetors are mounted in eans not equipped with spark plugs to assure flame propagation between eans during startup. Onee the unit is running, more than one indieator must indieate a loss of flame to trip the maehine, although the loss of flame in only one ean is indieated on the annuneiator panel. 

The startup and shutdown of a typical gas turbine is shown in figures 19-5 and 19-6, respectively. The time and percentages are approximate values and will vary depending upon the turbine design. 

One of the major funetions of the eombined eontrol-proteetion system is to perform the startup sequenee. This sequenee ensures that all subsystems of the gas turbine perform satisfaetorily, and the turbine does not heat too rapidly or overheat during startup. The exaet sequenee will vary for eaeh manufaeturer s engine, and the owner s and operator s manual should be eonsulted for details. 

Table 12-2 shows time intervals for various inspeetions based on fuels and startups. Minor inspeetions should be performed after about 3000-6000 hours of operation, or after approximately 200 starts, whiehever eomes first. This inspeetion requires a shutdown for two to five days, depending on availability of parts and extent of repair work to be done. During this inspeetion, the eombustion system and turbine should be eheeked. 

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