Expansion turbines efficiency

Silica. Sihca is not actually a corrodent of turbines. However, it can deposit on and cause blocking of turbine passages, thus reducing turbine capacity and efficiency. As Httie as 76 pm (3 mils) of deposit can cause measurable loss in turbine efficiency. Severe deposition can also cause imbalance of the turbine and vibration. The solubihty in steam and water is shown in Figure 15, as is a typical steam turbine expansion. Sihca is not a problem except in low pressure turbines unless the concentrations are extraordinarily high. 

The efficiency of expansion turbines (partial admission axial, full admission axial, and radial inflow turbines) is a function of the following four basic parameters. 

For the preliminary estimate of the expected efficiency of expansion turbines, in most cases it is sufficient to neglect Reynolds number effects (Rg > 10 ) and use the efficiency and specific speed correlations shown in Figure 2-12 for partial admission axial impulse, reaction radial inflow and full admission impulse and reaction axial turbines. Due to the economic advantage of the radial turbine, die radial inflow turbine is die best selection when operating in die specific speed range 20 < Nj < 140, whereby die optimum efficiency will be achieved at N, = 80. 

Figure 2-12. Efficiency of various expansion turbine types as a function of specific speed,...

Knowing the turbine efficiency, an approximate condition line for the expansion through the steam turbine can be drawn (to state f at pressure pbO and an estimate made of the steam enthalpy hf. If a fraction of the steam flow is bled at this point then the heat balance for a direct heater raising the water from near the condenser temperature to 7b is approximately... 

Lean burn/dry low-NOx combustors can generate NOx emissions levels as low as 9 ppm (at 15% 02), while those with liquid fuel combustors have NOx emissions limited to approximately 25 ppm (at 15% 02). There is no substantial difference in general performance with either fuel. However, the different heats of combustion result in slightly higher mass flows through the expansion turbine when liquid fuels are used, and thus a very small increase in power and efficiency performance is obtained. Also, the fuel pump work with liquid fuel is less than with the fuel gas booster compressor, thereby further increasing net performance with liquid fuels. 

Determine the effieieney and power output of a reheat Rankine eyele, using steam as the working fluid, in whieh the eondenser pressure is 80 kPa. The boiler pressure is 3 MPa. The steam leaves the boiler at 400°C. The mass flow rate of steam is 1 kg/see. The pump efficiency is 85% and the turbine efficiency is 88%. After expansion in the high-pressure turbine to 800 kPa, the steam is reheated to 400°C and then expanded in the low-pressure turbine to the condenser. 

The shaft work given by Eq. (7.27) is the maximum that can be obtained from an adiabatic turbine with given inlet conditions and given discharge pressure. Actual turbines produce less work, because the actual expansion process is irreversible. We therefore define a turbine efficiency as... 

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 ... 

Real-world efficiencies for liquefaction lie around 30%, which means, about 20% to 30% ofthe energy content ofhydrogen is needed for its liquefaction. In the process, hydrogen is first compressed to about 30 bar. The gas is then cooled with liquid nitrogen to about 80 K. Between 80 and 30 K hydrogen is cooled by expansion turbines, where hydrogen is compressed, cooled and expanded. In this stage also the... 

Multiplying by the turbine efficiency gives the nonisentropic enthalpy of expansion ... 

Propane gas at 300 psia and 150°F is sent to an expansion turbine with an efficiency of 80%. What is the lowest outlet pressure that can be achieved without condensing any of the propane ... 

Valves are often used to reduce the pressure of a gas or liquid process stream. By replacing the valve with a turbine, called an expander, turboexpander, or expansion turbine in the case of a gas and a liquid expander or radial-infiow, power-recovery turbine in the case of a liquid, power can be recovered for use elsewhere. Power recovery from gases is far more common than from liquids because for a given change in pressure and mass flow rate, far more power can be recovered from a gas than from a liquid because of the lower density of the gas. Equations for f.o.b. purchase costs of power recovery devices are included in Table 16.32 in terms of horsepower that can be extracted. Typical efficiencies are 75-85% for gases and 50-60% for liquids. Condensation of gases in expanders up to 20% can be tolerated, but vapor evolution from liquid expansion requires a special design. Whenever more than 100 Hp for a gas and more than 150 Hp for a liquid can be extracted, a power recovery device should be considered. 

The visualisation of the objective function with respect to some of the decision parameters is shown on figure 2. Two situations are presented as a function of the reforming temperature and the steam to carbon ratio. The first (lower surface) represents the turbo-compressor solution where the TiT is such that the expansion turbine will only drive the compressor without net production of electricity (as it is the case in the original design), while the second (upper) assumes a net electricity production by the gas turbine. The optimal efficiency conqruted for the system is of 53%, obtained for a steam to carbon ratio of... 

Expansion turbines have been developed to have high efficiencies of up to 90%. 

The available energy can be converted into mechanical (kinetic) energy only with certain losses because of steam friction and throttling, which increase the entropy of the steam. The end pressure is therefore attained at a higher steam enthalpy h than with isentropic expansion. The internal turbine efficiency then is... 

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