Extraction turbines

Nonautomatic-Extraction Turbine, Condensing or Noncondensing Steam is extracted from one or more stages, but without means for controlling the pressures of the extrac ted steam. 

FIG. 29-22 Three -arm lever/mechanism for extraction-turbine-pressure control. 

Sometimes, conventional techniques do not produce a satisfactory steam balance for all operating modes. Options are available for steam drives for flexibility, such as extraction and induction turbines. Extraction turbines are widely used. In these, an intermediate pressure steam is removed or extracted from an intermediate turbine stage with the extraction flow varying as required over preset limits. Induction turbines are not as widely used as extraction turbines, but are a very satisfactory application... 

The extraction turbine is selected when there is a demand for intermediate-pressure steam and, in particular, when there is a variation in the amount of steam required. The extraction turbine generally falls into two classes... 

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. 

Where extraction turbines are employed, it is most efficient to operate at the lowest level of condensing possible (the highest level of extraction). This occurs when steam from the turbine is extracted and directed by various takeoffs, either to air or water heaters or to industrial processes requiring steam. This practice occurs because no heat is lost from the steam flowing from the throttle to the extraction takeoff (whence it can be delivered for beneficial use by the industrial process), whereas over two-thirds of the heat flowing from the throttle to the surface condenser is ultimately rejected, so efficiency suffers. 

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

The inlet steam to an extraction turbine is 30 bara and 400°C. The extraction steam is at 10 bara and the exhaust is condensed at 0.12 bara. The steam turbine is fully loaded with a throttle flow of 40 kg s-1 to the inlet, 15 kg s-1 going to extraction and the remaining 25 kg s-1 going to condensation. Using the Willans Line Model with parameters for large back-pressure and condensing turbines from Table 23.1 and an intercept ratio of 0.05, calculate the power production. 

Most of the turbines you will encounter in your work are called topping, or extraction, turbines. The idea of such a turbine is to extract much of the potential work from the motive steam, and then use the exhaust steam to reboil towers. Typically, the energy content of the exhaust steam is only 10 to 20 percent less than that of the motive steam. That is the calculation we just did with the Mollier diagram. The rest of the energy of the steam may then be used as the steam condensers, to reboil towers. This sounds pretty efficient. It is the basis for the new cogeneration projects you may have heard about. Of course, this system was used by the British Navy in the nineteenth century. 

Extraction turbines are two-stage turbines that can provide steam at a pressure between that of the supply and that of the exhaust, while meeting their... 

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. 

Steam output Steam quality Boiler mfr. Extraction turbine Turbine mfr. Generator ... 

Steam turbines. In modern plants the centrifugal synthesis gas compressors, including recycle, are almost exclusively driven by a steam turbines. These are generally extraction turbines with a condensing section. Steam is extracted at suitable pressure levels (e.g. 45-55 bar) to provide, for example, the process steam in steam reforming plants, and for other drivers, e.g., air compressor, ammonia compressor, boiler feed water pumps, and blowers. 

Extraction Turbines discharge some of the steam from between pressure... 

EXTRACTION TURBINE - are turbines where steam is extracted at one or more points at constant pressure. Extraction turbines may be single or double-extraction-condensing turbines or single-or doubleextraction back-pressure turbines. The extracted steam is used for... 

There are two kinds of steam turbines. In a condensing turbine, the exhaust steam is condensed using cooling water, at a pressure determined by the temperature of the cooling water. In an extraction turbine, the exhaust steam is not condensed, rather it is exhausted at an intermediate pressure to be reheated and used in a condensing turbine. 

In another process plant, the steam system operates with a large amount of LP vent. To prevent loss of valuable condensate due to LP vent, a condenser was installed to cool down the LP steam and return LP condensate back to the deaerator. Although this solution saves condensate, it did not resolve the LP long issue. It was later identified that a driver switch could help to reduce the LP vent In the boiler house, there are three forced draft (FD) fans currently run by MP-LP extraction turbines but fans have spare motor drivers. The operation policy acceptable to the plant was to use steam turbines for reliability reasons. The engineer wanted to establish the value of the driver switch to minimize the LP dump. 

There are three boiler forced draft (FD) fans, which are run by medium-pressme to low-pressure (MP-LP) extraction turbines currently with motors in spare. It was identified that motor driving is more economical than turbine due to relatively low electricity price. Based on steam marginal pricing, it is estimated that if one fan can be switched to motor, the benefit would be 738,144 per year. The cost savings would be 2.2MM/year if three fans could be switched to motors. 

The incremental effects on steam balance are shown in Figure 20.6. This steam balance is better than the base steam balance in Figure 20.1 in that boiler load is reduced by 23%. In addition, HP letdown is shifted to MP letdown. However, there is still a large MP letdown and LP dump, which are the sources of inefficiency. The potential solution for reducing the LP dump is to consider a driver switch to motor for HP-LP extraction turbines in process units. Such opportunities should be the tasks for further investigation. 

In the VPBER-600 nuclear power plant, either a condensing turbine of the K-600-5 9/500 type for a power station or an extraction turbine of the T-600-5 9/500 type for a co-generation plant are used... 

In the design with a steam-extraction turbine the heat output is up to 645 GCal/hr (with reduction of the electric output down to 430 MW)... 

Except for the BN GT 300 (17), all sodium and lead-bismuth cooled reactor concepts use a Rankine superheated steam cycle, and a number of them provide options for the extraction turbines to support seawater desalination, district heating, or process heat cogeneration. The BN GT 300 (17) uses a gas-turbine cycle. 

A power and desalination complex (a cogeneration plant) based on a distillation desalinating plant (DDP) includes the reactor installation the extraction turbine the intermediate loop and the desalination plant (see Fig. IV-11). Heat and part of the electric power generated by the floating power unit are used for desalination the rest of the electric power is supplied to the consumers. 

Automatic-extraction turbine A steam turbine with the capacity to extract steam. The pressure of the extracted steam is controlled by a valve gear at that opening, as with an automatic-admission turbine. Note Steam turbines can be fnmished with antomatic extraction and admission capability at the same opening. 

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