Condensing turbines

A wide variety of turbine types and arrangements are used in modem power plants. For example, some smaH industrial plants may use only a single condensing turbine. Prepackaged steam/turbine generator systems can be economical for small-to-midsize instaHations. 

Has enough flexibiUty been built into the overall condensing turbine system (The balance changes over the history of a unit as a process evolves, generally in the direction of less condensing demand.)... 

By-product power does not give enough power to match the demand for many processes such as ammonia synthesis, and designs have historically incorporated condensing turbines for incremental power with heat rejection to cooling water. A more effective response is use of the gas turbine combined cycle shown by Figures 5c and 6c. 

The combined cycle is also appHcable to dedicated power production. When the steam from the waste heat boiler is fed to a condensing turbine, overall conversion efficiencies of fuel to electricity in excess of 50% can be achieved. A few pubHc utihty power plants use this cycle, but in general utihties have been slow to convert to gas turbines. Most electricity is generated by the cycle shown in Figures 5d and 6d. 

Straight Condensing Turbine All the steam enters the turbine at one pressure, and all the steam leaves the turbine exhaust at a pressure below atmosphere. 

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. 

The condensing turbine is selected when steam demand for process drivers is greater than the low-pressure process steam requirements. It is also selected when no high pressure steam is available. 

The condensing turbine has several advantages and disadvantages over the back pressure turbine. The advantages are that it requires less change in the live steam for various turbine loads and is therefore easier to control. It also requires less steam because the enthalpy drop is larger. Finally, only one steam level is affected for a change in power requirements. 

The disadvantages are that the condensing turbine has a high capital cost because it is larger than a back-pressure type. It develops high specif-... 

The condensing steam turbine has a relatively low thermal efficiency because about two-thirds of the steam enthalpy is lost to cooling water in the condenser. Expensive boiler feedwater treatment is required to remove chlorides, salts, and silicates, which can be deposited on the blades causing premature failure. The blades are already under erosion conditions because of water drops present in the condensing steam. Even with these disadvantages, the condensing turbine is still selected, especially in a process that requires very large compressor drivers and relatively low amounts of process steam. 

Should a condensing turbine with extraction for process be considered ... 

Concerning condensing turbines, be sure to obtain an adequately sized vacuum breaker for the condenser. There are no words to describe the agony of watching a turbine or the driven compressor tear itself up. 

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

When the steam leaves a condensing turbine, it passes to a surface-type condenser for recovery of the condensate. Vacuum equipment (jets or pumps) are necessary to achieve high vacuums on the condenser. 

A typical axial flow-condensing turbine for industrial application is shown in Figure 15.39. 

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. 

In addition to condensing turbines, manufacturing industries widely use noncondensing (back-pressure) turbines. These back-pressure units are of various designs and are employed for electricity generation, typically within the range 600 to 30,000 KWh at 115 to 1,250 psig, and for a variety of process applications. 

Figure 23.9b shows a condensing turbine. Three types of condensers are used in practice as follows. 

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