Abstract:
Sri Lanka has to rely on thermal power generation for reliability of the national electricity
grid, especially during droughts or dry seasons, due to frequently changing climatic
patterns. For thermal power generation, the country is entirely dependent on imported fuels
and therefore, it is vital that the thermal power plants of Sri Lanka should be operated in a
cost effective manner. The exhaust gas temperatures of thermal power plants are usually
in the range of 290 C – 320 C which indicates that a considerable amount of thermal
energy is wasted without being used. This study was undertaken at a power station where
a part of this energy is recovered and used to produce saturated steam using waste heat
boilers, which are used for heating heavy fuel oil used for gas turbines in order to increase
the efficiency. The practical limitation of recoverable heat from exhaust gasses can be
determined by the sulfur dew point of the fuel which is usually 135 oC.The study was
conducted with the objective of recovering the maximum possible heat from the exhaust of
a diesel engine and utilizing the recovered heat to operate a power plant based on the
Organic Rankine Cycle, with the working fluid being toluene, which is best suited for low
temperature heat sources. The Organic Rankine Cycle was optimized using Engineering
Equation Solve Software based on the constraints imposed by the sulfur dew point of the
fuel and the pinch point temperature difference. The study established the parameters of
the Organic Rankine Cycle as: pinch point temperature difference - 2.011 oC, turbine power
- 570.6 kW, condenser pressure -0.07 bar, mass flow rate of toluene - 3.298 kg/s and
thermal efficiency - 20.95% for optimum conditions.
