INFLUENCE OF HEAT DEMAND ON TECHNO-ECONOMIC PERFORMANCE OF A BIOMASS/NATURAL GAS MICRO GAS TURBINE AND BOTTOMING ORC FOR COGENERATION

asme-orc2015 Tracking Number 182

This paper presents a thermo-economic analysis of small scale Combined Heat and Power (CHP) plants composed by a micro gas turbine (MGT) and a bottoming Organic Rankine Cycle (ORC). The focus is to improve the flexibility of the plant through a bottoming ORC that can increase the electric power production despite reducing the useful heat for cogeneration. For the topping cycle three different configurations are examined: 1) a simple recuperative micro gas turbine fuelled by natural gas, 2) an externally fired gas turbine (EFGT) with direct combustion of biomass, and 3) a dual fuel EFGT cycle, fuelled by biomass and natural gas. For the bottoming cycle, a saturated recuperative Rankine cycle is examined under two different condensation temperatures for applications of heat and power generation. The simulation results show that, at low condensation temperature, higher electric efficiency can be obtained but heat rejected by the ORC cycle cannot be used for cogeneration while, with high condensation temperature, lower electric efficiency but higher plant cogeneration efficiency can be obtained. The research assesses the global energy efficiency and profitability of the different schemes, as a function of the thermal energy demand intensity, represented by the annual equivalent heat demand hours. For this purpose, the following factors are considered: (i) lower energy conversion efficiency, higher investment cost and lower fuel costs of biomass vs natural gas fuel; (ii) revenues from feed-in tariff available for biomass electricity fed into the grid; (iii) revenues from heat distribution to end users.