Turbines, steam extraction type

In extraction turbines, in addition to the governor valve, a second "valve" is required (Figure 2.134), which controls the steam flow rate that is extracted from the first stage of the turbine and is sent to the second stage. The extraction rate can be controlled either to keep the shaft speed or the pressure of the LP header constant, or a combination of the two. If the turbine incorporates the controls as a built-in feature, the turbine is referred to as an "automatic-extraction" type. Such turbines are generally designed to deliver 100% shaft power and to provide extraction steam only if the load requirements permit. This is the most common type of extraction machine. 

A sulfuric acid plant generally produces more steam than it can consume internally. The excess steam can be used for generating power or for driving certain equipment like the main air blower, boiler feed water pump, etc., by steam turbines. The turbines could be condensing, backpressure, or extraction types. 

The steam from backpressure or extraction type turbines can be used in-house for process heating or for export to nearby industries. 

Extraction-type turbine—It may be used if different process units require steam at different pressures. But there could be operational difficulties if too many extractions are taken at different pressures. 

When steam is required at the process plant at different pressmes, the extraction-type steam turbine may be considered, wherein steam is extracted out from different stages, and the last stage exhausts at a pressme corresponding to the lowest pressure required in the plant. An accurate estimate of the consirmption pattern of steam is necessary for procitring the turbine with the right design and to operate it efficiently. 

The SMART and MED-TVC units are connected through the steam transformer. The steam transformer produces the motive steam using steam extracted from the turbine and supplies process steam to the desalination plant. A steam transformer also prevents contamination of the produced water by hydrazine and radioactive material of the primary steam. The steam transformer is made of horizontal tube bundles the primary steam flow is condensed inside the tubes at its saturation temperature. The feed brine is sprayed outside of the tube bundles by the recycling pump. Part of the sprayed water is evaporated and the produced steam is used as the motive steam for the thermo-compressor of the evaporator. Part of the condensate in the first cell of the evaporator is used as make-up for the steam transformer and this makeup water is preheated by the condensate of the primary steam before being fed into the steam transformer. The pre-heater is a plate-type heat exchanger made of welded titanium. 

There are two ways of presenting steam balance data, schematically or tabulady. For both presentation types, a balance is made at each pressure level. In a schematic balance, such as that shown in Figure 9, horizontal lines are drawn for each pressure. The steam-using equipment is shown between the lines, and individual flows are shown vertically. Table 3 contains the same data as shown in Figure 9. In both cases the steam balance has been simplified to show only mass flows. A separate balance should be developed that identifies energy flows, including heat losses and power extraction from the turbines. 

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... 

Utility plants primarily employ reheat condensing turbines, whereas cogeneration plants and larger process industries that produce their own electrical power tend to employ extraction turbines. Both types of turbine rely on a surface condenser to receive exhaust steam from the LP turbine stage and condense it to liquid for reuse. 

There are two general types of steam turbines extraction and condensing. The most common turbine with which the process operator comes into contact is used to spare an electric-motor-driven centrifugal pump. The three-phase, AC motors used in the United States and South America are either 1800 or 3600 rpm. The motors used in Europe are 1500 or 3000 rpm. Small steam turbines (20 to 500 hp) used to drive centrifugal pumps, are rated for the same speed as the electric motors that are used in that particular service. 

Steam turbine generation of electricity for example, via condensate-type steam turbine with simple automatic extraction and two-pole synchronous generators with a cylindrical rotor and brushless exciter system. 

A combination of small capacity turbines (extraction and backpressure type) may be considered with the balance amount steam sent to a condensing-type turbine for power generation. Cost of steam and power shall also be taken into account before the final decision is taken. 

The condenser is of the surface, twin pass type. It is of a twin shell construction. There are two deaerators that utilize extraction steam from the low pressure turbines, five low pressure feedwater heaters that utilize extraction steam from the low pressure turbines, three high pressure heaters that utilize extraction and exhaust steam from the high pressure turbine, three one-half-sized condensate pumps and condensate booster pumps, and three one-half-sized feedwater pumps. Heater drains from the three high pressure feedwater heaths are cascaded to the deaerator, drains from the five low pressure heaters are cascaded to the condenser. 

Many industrial plants requiring various quantities of process steam combined with a certain electric power load make use of extraction turbines. It is possible to adapt the extraction turbine to a great variety of plant conditions, and many different types are built, among them noncondensing and condensing extraction turbines with one or more extraction points and automatic and nonautomatic extractior additionally, in certain urban areas, extraction turbines are used by the utility company to supply steam to buildings in the neighborhood of the plant. 

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