3-E analyses of a natural gas fired multi-generation plant with back pressure steam turbine

Abstract

Abstract Energetic, exergetic and environmental (3-E) analyses of a natural gas fired multigeneration (NGFMG) plant is carried out in this study. The plant is consisting of a topping gas turbine (GT) block with fixed 30 MWe output, bottoming back pressure steam turbine (ST) block with variable electrical output and utility hot water generation block with variable generation capacity. Variation of topping cycle pressure ratio (rp=2-18) and gas turbine inlet temperature (TIT=750-850 °C) as plant operational parameters on the 3-E performance of the plant of are reported here. Base case performance (at rp=4 & TIT=800°C) of the plant shows that the plant is about 33% electrically efficient at base case with fuel energy savings ratio (FESR) value of 40 %. Electrical efficiency of the plant along with FESR increases with either increase in rp or in TIT. However ST output and hot water production rate decreases with increase in the value of plant operational parameters. Exergy analysis of the plant shows that maximum exergy destruction occurs at the combustion chamber. Exergy analysis also signifies that isentropic efficiency of the GT can also be a plant influencing parameter. From emission point of view it is observed that electrical specific CO2 emission is 0.6 kg/kWeh at base case. Specific CO2 emission rate gets lowered with either increase in rp or in TIT.