Novel, cost-effective configurations of combined power plants for small-scale cogeneration from biomass
CHALLENGE - The aim of this paper was to demonstrate the feasibility of small combined cycles for Combined Heat and Power generation from biomass by proposing novel configurations that are cost-effective and highly efficient. In the small combined cycle proposed, a commercially available micro-steam turbine is utilized as the steam expander of the bottoming cycle, while the conventional micro turbine of the topping cycle is replaced by a cheaper automotive turbocharger.
SOLUTION - Two design optimizations are performed: the first one makes use of the innovative Immersed Particle heat exchanger (IPHE), whilst a Nickel Alloy heat exchanger (NAHE) is used in the other one. An optimization procedure, based on a genetic algorithm combined with a computing code, is utilized to analyze the trade-off between the maximization of the electrical and thermal efficiency. After selecting the optimum combination of the design parameters, the operation in load following mode is also assessed for both configurations.
BENEFITS - The optimization process was implemented in modeFRONTIER, in which a calculation code was coupled with a genetic algorithm, MOGAII. Results have shown that configurations with the IPHE and with the NAHE have the potential to reach a maximum electrical efficiency of about 0.25 and 0.22, respectively. This is level is higher than that of a typical biomass-fuelled ORC system, whose electrical efficiency is usually well below 0.2. Concerning maximum overall efficiency, a value of 0.7 can be achieved with the IPHE and 0.65 with the NAHE.