Thermodynamic analysis of rankine cycle with generalisation of feed water heaters

The use of feed water heaters reduces the amount of heat required to generate the superheated steam in the boiler. Thermodynamic analyses (ie, both first law and second law analyses) have been carried out for analysing the effect of number of feed water heaters and bled temperature ratio on over all performance of the Rankine cycle. A computer code has been developed for the evaluation of first law efficiency, irreversibilities and second law efficiency of Rankine cycle with different number of feed water heaters and the concept of generalisation of the problem. For single feed water heater, with the increase of bled steam temperature ratio, the first law efficiency increases first and later decreases. There is an optimum ratio, ie, 0.5, where the efficiency of the cycle is maximum. The effect of boiler pressure, steam inlet temperature and flue gas inlet temperature for different number of feed water heaters has also been discussed. With the increase of number of feed water heaters, both energetic and exergetic efficiencies are found to be increasing. This is due to reduction in irreversibility in the boiler with the increase of number of feed water heaters. The maximum increment in efficiency is observed with first heater and the increment is diminishing with the addition of number of heaters further.