Evaluation of sub- and supercritical Rankine cycle optimisation criteria

Abstract

The main purpose for this study has been to model an advanced real Rankine cycle for sub and super-critical boilers with all the components as encountered in the industry mathematically and to optimise each cycle. First the Development of the Rankine cycle is illustrated from the most effective theoretical Carnot cycle through to an advanced ideal Rankine cycle with feed water heating and compared to each other by means of the results obtained from EES. After the Ideal Rankine cycle with all the relevant components had been programmed and discussed the Cycle was further developed into an advanced real Rankine cycle. The Advanced real Rankine cycle consists of Superheat, Reheat, two high-pressure feed heaters, a de-aerator, three (super-critical) or four (sub-critical) low-pressure feed heaters, a condenser, a condensate extraction pump and one main feed water pump. The real cycle made provision for pressure losses, efficiencies, steam attemperation and temperature losses. The following were optimised to get the maximum efficiency and net mechanical work for each cycle:  Feed pump maximum pressure  High pressure turbine expansion  Two high pressure feed water heaters  The de-aerator  Three or four low pressure feed water heaters The study touches on low pressure turbine outlet steam quality, but keeps it constant through the optimisation stages. To finish off, a comparison between sub- and super-critical Rankine cycles was done before and after optimisation.