Steam turbines extraction

A rule of thumb Select an extraction steam turbine when 15 to 20 i of the driver power requirements can be supplied by the extracted steam. 

Steam extracted from one or more controlled pressure points on an extraction steam turbine and used for various process applications. Extraction steam may be delivered to an extraction heater. 

Extraction steam turbines will have minimum and maximum flows in each section of the turbine. This leads to minimum and maximum flows at each extraction level. 

Back-pressui-e, or condensing, extraction steam turbine/ alternator systems are widely used in the chemical process industries to meet electrical-power and process-steam requirements. These turbines employ superheated steam at high temperatures and pressures. 

In a condensing-extraction steam turbine used in a process plant, steam at 850 psi and 000°F is expanded to 2 in. Hg back-pressure, and process steam is extracted at 40 psi. The turbine operates at a combined efficiency of 72.5%. If 300,000 Ib/h of steam is condensed and 200,000 Ib/h of steam is extracted from the turbine, what is the total power developed at the alternator terminals ... 

Pressure rise point In an automatic-extraction steam turbine the maximum exhaust flow with zero extraction flow. 

FIGURE 6.82 Performance curve of a single automatic-extraction steam turbine. 

When automatic-extraction steam turbines have a condensing exhaust, the control system can control pressure as well as power generation by varying flow to the condenser. The amount of power called for by the steam turbine unit control system can be continuously modulated by the plant control system. 

Fossil Fuel-Fired Plants. In modem, fossil fuel-fired power plants, the Rankine cycle typically operates as a closed loop. In describing the steam—water cycle of a modem Rankine cycle plant, it is easiest to start with the condensate system (see Fig. 1). Condensate is the water that remains after the steam employed by the plant s steam turbines exhausts into the plant s condenser, where it is collected for reuse in the cycle. Many modem power plants employ a series of heat exchangers to boost efficiency. As a first step, the condensate is heated in a series of heat exchangers, usually sheU-and-tube heat exchangers, by steam extracted from strategic locations on the plant s steam turbines (see HeaT-EXCHANGETECHNOLOGy). 

Automatic-Extraction Turbine, Condensing or Noncondensing Steam is extracted from one or more stages with means for con-troUing the pressures of the extracted steam. 

When an extraction-condensing turbine is decided upon, it may be specified in three different ways, depending upon process steam and power demand. Referring to Fig. 29-24, the usualpurchase is a unit in which rated capability can be carried either straight-... 

Electric motors may be considered in cases where it is considered advantageous to export surplus steam outside the nitric acid plant. Condensing steam turbines are normally used to bridge the power deficit. Extraction-condensing turbines make it possible to use some of the available steam for heating purposes. 

This design has a number of tubes embedded inside the turbine biade to provide ehanneis for steam. In most cases these tubes are constructed from copper for good heat-transfer conditions. Steam injection is becoming the prime source of cooiing for gas turbines in a combined cycie appiication. The steam, which is extracted from the exit of the HP Turbine, is sent through the nozzie biades, where the steam is heated, and the biade metai temperature decreased. The steam is then injected into the flow stream entering the IP steam turbine. This increases the overaii efficiency of the combined cycie. 

Steam turbine, 53, 146, 282-92, 179 back pressure, 282 blade deposits, 479 condensing, 282 efficiency, 288 extraction, 282 induction-type, 282 paitial admission, 288 rating, 290 reliability, 478 selecuon variable, 275, 285 speed, 278 stage losses, 286 steam temperatures, 284 steam velocity, 288 trip and throttle valve. 479 Step unloading system, 80 Stiffness coefficients, 385 Stodola slip, 153, 155 Stonewall, 186 Straight labyrinth. seal leakage, 532... 

Most steam turbines operate in the condensing (of steam on exhaust from turbine) mode or noncondensing or backpressure mode. (Steam is exhausted or extracted from the turbine at preselected exhaust pressure for other uses.) See Figures 14-17A-C, 14-18A, 14-18B, 14-19A, 14-19B, 14-20A, and 14-20B. 

The turbine applied to driving mechanical equipment is not operated (very often) with extraction or bleed streams. Here again, this depends upon the plant steam balance, and this is one of the fine features of steam turbine drive. The flexibility of design and application allow it to be set in the proper place for the economic balance of a system. The decision as to condensing or noncondensing should not be... 

TEST FDR A CONTROLLED EXTRACTION CONDENSING TURBINE mechanical drive (SUPERHEATED INLET AND EXTRACTION STEAM)... 

Figure 14-18A. Condensing, extraction mechanical drive steam turbine. (Used by permission Lamberson, J. and Moll, R. Technology Report ST 18.6. Dresser-Rand Company.

Manufacturing industries often utilize condensing extraction turbines and employ the extracted steam for staged FW heating and industrial process applications. 

Generally, the efficiency of steam turbines decreases with decreasing load. The overall turbine efficiency can be represented by two components the isentropic efficiency and the mechanical efficiency. The mechanical efficiency reflects the efficiency with which the energy that is extracted from steam is transformed into useful power and accounts for mechanical frictional losses, heat losses, and so on. The mechanical efficiency is high (typically 0.95 to 0.99)6. However, the mechanical efficiency does not reflect the efficiency with which energy is extracted from steam. This is characterized by the isentropic efficiency introduced in Figure 2.1 and Equation 2.3, defined as ... 

As described in the methodology, the curve starts from an optimized operation for the initial process steam demands (Figure 23.54b). At this initial point, the HP extraction of Turbine T4 is set to its minimum of 15 th-1. The first HP segment saves steam by reducing the HP extraction of Turbine T6. Part of this saving is realized by reduction in steam generation in Boiler 2 and the remainder by increasing the LP exhaust of Turbine T6 and the LP... 

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