Turbines, steam power output from

A steam power plant employs two adiabatic turbines in series. Steam enters the first turbine at 600°C and 6,500kPa and discharges from the second turbine at lOkPa. The system is designed for equal power outputs from the two turbines, based on a turbine efficiency of 76 percent for each turbine. Determine the temperature and pressure of the steam in its intermediate state between the two turbines. What is the overall efficiency of the two turbines together with respect to isentropic expansion of the steam from the initial to the final state ... 

Many industrial processes require electrical power and heat. This heat is often provided from large quantities of low-pressure steam. In this section, it is demonstrated that a thermal power station gives up very large quantities of heat to the cooling water in the condenser. For this purpose, the steam pressure in the condenser is usually at the lowest practical pressure (around 0.05 bar-absolute) to achieve maximum work output from the turbine. 

The electrical and heat analysis, as discussed in Section 15.3, will show the relationship between power and heat and how this varies over time. It may be necessary to use steam bypass and stations or dump condenser, as discussed in Section 15.2. The uses of dump condensers for meeting part-load requirement is inefficient and should be avoided. It is more acceptable to reduce turbine power output accordingly and import or top-up from an alternative supply. 

Determine the efficiency and power output of a regenerative Rankine cycle using steam as the working fluid and a condenser pressure of 80 kPa. The boiler pressure is 3 MPa. The steam leaves the boiler at 400° C. The mass rate of steam flow is 1 kg/sec. The pump efficiency is 85% and the turbine efficiency is 88%. After expansion in the high-pressure turbine to 400 kPa, some of the steam is extracted from the turbine exit for the purpose of heating the feed-water in an open feed-water heater, the rest of the steam is reheated to 400°C and then expanded in the low-pressure turbine to the condenser. The water leaves the open feed-water heater at 400 kPa as saturated liquid. Determine the steam fraction extracted from the turbine exit, cycle efficiency, and net power output of the cycle. 

Determine the steam fraction extracted from the turbine exit, cycle efficiency, and net power output of the cycle. 

It provides an increase in both power output and overall efficiency. For a given temperature at inlet to the gas turbine, extra fuel has to be supplied in order to heat the injected steam to that temperature, but the additional power arising from the expansion of the injected steam as it passes through the gas turbine more than offsets the otherwise adverse effect on the overall efficiency of the cycle of the increase in fuel supply. 

Figure 8.1 shows a simple steady-state flow process in which steam generated in a boiler is expanded in an adiabatic turbine to produce work. The discharge stream from the turbine passes to a condenser from which it is pumped adiabati-cally back to the boiler. The power produced by the turbine is much greater than that required by the pump, and the net power output is equal to the difference between the rate of heat input in the boiler QH and the rate of heat rejection in the condenser Qc-... 

Example 4.13 Simple reheat Rankine cycle in a steam power plant A simple ideal reheat Rankine cycle is used in a steam power plant (see Figure 4.19). Steam enters the turbine at 9000kPa and 823.15 K and leaves at 4350kPa. The steam is reheated at constant pressure to 823.15K. The discharged steam from the low-pressure turbine is at 10 kPa. The net power output of the turbine is 65 MW. Determine the thermal efficiency and the work loss at each unit. 

Example 4.17 Ideal reheat regenerative cycle A steam power plant is using an ideal reheat regenerative Rankine cycle (see Figure 4.23). Steam enters the high-pressure turbine at 9000 kPa and 773.15 K and leaves at 850 kPa. The condenser operates at 10 kPa. Part of the steam is extracted from the turbine at 850 kPa to heat the water in an open heater, where the steam and liquid water from the condenser mix and direct contact heat transfer takes place. The rest of the steam is reheated to 723.15 K, and expanded in the low-pressure turbine section to the condenser pressure. The water is a saturated liquid after passing through the water heater and is at the heater pressure. The work output of the turbine is 75 MW. Determine the work loss at each unit. 

Example 4.20 Energy dissipation in an actual cogeneration plant A cogeneration plant uses steam at 900 psia and 1000°F to produce power and process heat (see Figure 4.26). The steam flow rate from the boiler is 16 lb/s. The process requires steam at 70 psia at a rate of 3.2 lb/s supplied by the expanding steam in the turbine. The extracted steam is condensed and mixed with the water output of the condenser. The remaining steam expands from 70 psia to the condenser pressure of 3.2 psia. If the turbine operates with an efficiency of 80% and pumps with an efficiency of 85%, determine the work loss at each unit. 

A steam turbine operates adiabatically with a steam rate of 30 kgs. The steam is supplied all 1,050 kPa and 37S°C and discharges at 20 kPa and 7S°C. Determine tthe power output of the turbine and the efficiency of its operation in comparison with a turbine that operates isentropically from the same initial conditions to the same final pressure. 

Your company produces small power plants that generate electricity by expanding waste process steam in a turbine. One way to ensure good efficiency in turbine operation is to operate adiabatically. For one turbine, measurements showed that for 1000 Ib/hr steam at the inlet conditions of 500 F and 250 psia, the work output from the turbine was 86.5 hp and the exit steam leaving the turbine was at 14.7 psia with 15% wetness (i.e., with a quality of 85%). 

Rate of loss of availability. In the scheme of Fig. 13.4 for reboUing a tower with low-pressure exhaust steam from a turbine, factors that reduce the power output of the turbine are (l)the temperature difference across the reboiler, which causes the turbine exhaust pressure to be higher than the tower bottom pressure, and (2) the steam pressure drop through the tower, which causes the tower bottom pressure to be higher than the tower top. We shall focus attention on the second of these inefficiencies and shall derive an expression for the reduction in turbine power caused by steam pressure drop through the tower. 

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