The turbine stage

The boundary conditions we can expect when modelling a turbine stage will be 

We may apply the steady-state flow equation (4.7) to the complete turbine stage  

Dropping the terms dq and gdz because the flow is adiabatic and experiences no or negligible height change, we may integrate between stage inlet (station 0 ) and outlet (station 2 ) to obtain  

Introducing a double-subscript notation, with the second subscript identifying the stage, the inlet velocity to the first stage of a turbine will be essentially zero, i.e. 

For subsequent stages, the inlet velocity will be equal to the outlet velocity of the previous stage  

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Superheaters and Reheaters A superheater raises the temperature of the steam generated above the saturation level. An important function is to minimize moisture in the last stages of a turbine to avoid blade erosion. With continued increase of evaporation temperatures and pressures, however, a point is reached at which the available superheat temperature is insufficient to prevent excessive moisture from forming in the low-pressure turbine stages. This condition is resolved by removing the vapor for reheat at constant pressure in the... 

Reheat Turbine After the steam has expanded through several stages, it leaves the turbine and passes through a sec tiou of the boiler, where superheat is added. The superheated steam is then returned to the turbine for further expansion. 

In general terms, the life of a combustor might be reduced by about 30 percent through use of a distillate fuel and by 80 percent through the use of residual fuel. The first stage turbine nozzle life can Be reduced by 20 percent through use of a distillate fuel and by about 6.5 percent when certain residual fuels are used. 

In the case of nitrous acid plants, application of integrally geared process gas radial turbines and compressors are used in plants with capacities ranging from 120-600 t/day and higher. For air compression, up to three compressor stages are connected in series. To increase efficiency, the inlet temperature of the individual stages is reduced by using two external intermediate coolers. 

Maintenanee expenses are estimated at 3% for the required equipment. Spare wearing parts are allowed for the steam turbine. Every three years spare wearing parts and a rotor should be expensed for the power reeovery eases. Expensing a rotor every three years is eonsidered eonservative espeeially for the two-stage alternative. 

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