Energy Nexus (Mar 2022)
An integrated CCHP system based on biomass and natural gas co-firing: Exergetic and thermo-economic assessments in the framework of energy nexus
Abstract
Agriculture and energy are inextricably connected; many energy systems can be driven by biomass supplied from agricultural waste products. In this study, a combined biomass/natural gas fed multi-generation system, prodcuing cooling, heating, and power is investigated from exergetic and thermo-economic standpoints. The system consists of four susbsystems, encompassing a gasification cycle, a gas cycle, a Rankine steam cycle, and a double effect absorption refrigeration cycle. To increase the lower heating value of the fuel injected into the combustion chamber, natural gas is mixed with syngas. Also, to exploit the exhaust gas from the stack of the gas turbine, the flue gas is divided into two streams by a spliter,providing the required heat for the Rankine steam and absorption refrigeration cycles. The effects of parameters such as the gas turbine inlet temperature , combustion chamber inlet pressure, the amount of natural gas mixed with syngas, and split ratio of the exhaust gas from the gas turbine on the thermodynamic and thermo-economic outputs are studied. The results show that the gas cycle with 61% and the double-effect absorption refrigeration cycle with 6% exergy destruction rates have the largest and lowest shares of the total exergy destruction rate, respectively. By changing the mixing ratio of the natural gas injected into the cycle from 0.5 to 1, the system's net work is seen to increase by 90.77%, while the modified ecological coefficient of the system performance boosts by 9.49%. In addition, such a change leads to 53.45% increase in the net present value of the total cost over the defined economic life, and also an increase of 90.25% in the net present value of the total output of the cycle equivalent to electricity over the economic life. Moreover, it brings about 19.36% decrease in the system's levelized cost of energy.
