Low pressure turbine

LPG. See gas, liquified petroleum LPIE. See ion exchange, liquid-phase LPM. See methanol, low-pressure LPMEOH. See coal, -to-methanol, liquid-phase methanol LPST. See turbine, low-pressure steam LPT. See turbine, low-pressure LTFT. See Fischer-Tropsch (FT) synthesis, low-temperature... 

Steam costs vary with the price of fuel. If steam is only generated at low pressure and not used for power generation in steam turbines, then the cost can be estimated from local fuel costs assuming a boiler efficiency of around 75 percent (but can be significantly higher) and distribution losses of perhaps another 10 percent, giving an overall efficiency of around 65 percent. 

Exampie A.3.1 The pressures for three steam mains have been set to the conditions given in Table A.l. Medium- and low-pressure steam are generated by expanding high-pressure steam through a steam turbine with an isentropic efficiency of 80 percent. The cost of fuel is 4.00 GJ and the cost of electricity is 0.07 h. Boiler feedwater is available at 100°C with a heat capacity... 

In many large plants, an intermediate pressure (IP) turbine is located on the same shaft as either the HP turbine or the low pressure (LP) turbine. In this arrangement, a common gearbox translates the torque from the high speed turbine shaft to a generator shaft turning at a much lower speed. Unless reheat is used, the steam exiting the HP turbine is typicaHy used directly in the IP turbine. 

Fig. 10. Simple-cycle, two-shaft gas turbine where HP and LP are high and low pressure, respectively.

Some results of the constant-value pricing system are as foUow generation in a central unit at relatively low pressure, <4.24 MPa (600 psig) tremendous economic pressure to use turbines rather than motors for drives lack of incentive for high efficiency turbines excessively high temperature differentials in steam users tremendous incentive to recover waste heat as low pressure steam and a large plume of excess low pressure steam vented to the atmosphere. 

Silica. Sihca is not actually a corrodent of turbines. However, it can deposit on and cause blocking of turbine passages, thus reducing turbine capacity and efficiency. As Httie as 76 pm (3 mils) of deposit can cause measurable loss in turbine efficiency. Severe deposition can also cause imbalance of the turbine and vibration. The solubihty in steam and water is shown in Figure 15, as is a typical steam turbine expansion. Sihca is not a problem except in low pressure turbines unless the concentrations are extraordinarily high. 

The steam balance in the plant shown in Figure 2 enables all pumps and blowers to be turbine-driven by high pressure steam from the boiler. The low pressure exhaust system is used in the reboiler of the recovery system and the condensate returns to the boiler. Although there is generally some excess power capacity in the high pressure steam for driving other equipment, eg, compressors in the carbon dioxide Hquefaction plant, all the steam produced by the boiler is condensed in the recovery system. This provides a weU-balanced plant ia which few external utiUties are required and combustion conditions can be controlled to maintain efficient operation. 

Superheaters and Reheaters A superheater raises the temperature of the steam generated above the saturation level. An important function is to minimize moisture in the last stages of a turbine to avoid blade erosion. With continued increase of evaporation temperatures and pressures, however, a point is reached at which the available superheat temperature is insufficient to prevent excessive moisture from forming in the low-pressure turbine stages. This condition is resolved by removing the vapor for reheat at constant pressure in the... 

Specimen Location Low-pressure turbine condenser inlet just outside tubesheet... 

Figure 1-20 shows multistage high-pressure axial flow turbine rotor. The turbine rotor depicted in this figure has a low-pressure compressor followed by a high-pressure compressor. There are also two turbine sections, and the... 

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