Some CHP Options for Wood-Fired Fuel Cells

Abstract

The possibility of integrating biomass gasifiers with fuel cells has already been explored and shown to offer a method for using renewable energy to generate electricity at a small scale. A preliminary study of applying such a system for use in an isolated community and for several selected buildings has been made and the results of these studies reported earlier. In this study wood gasification integrated with fuel cell (WGIFC) systems in CHP configurations for five building systems with different energy demand profiles, are assessed. These are a hospital, a hotel, a leisure centre, a multi-residential community and a university hall of residence. Heat and electricity use profiles for typical examples of these buildings were obtained and the WGIFC system scaled to the power demand. Detailed technical, environmental and economic analyses of each version are made, using the ECLIPSE process simulation package. Various factors influencing the economic viability of each application are examined and a sensitivity analysis for each system produced. The WGIFC system was modelled for two different types of fuel cell, the Molten Carbonate and the Phosphoric Acid. In each case an oxygen-fired gasification system is proposed, in order to eliminate the need for a methane reformer. Technical, environmental and economic analyses of each version were made, using ECLIPSE. Since fuel cell lifetimes are not yet precisely known, economics for a range of fuel cell lifetimes have been produced. While the wood-fired Phosphoric Acid Fuel Cell (WFPAFC) system was found to have low electrical efficiency (13–16%), the wood-fired Molten Carbonate Fuel Cell (WFMCFC) system was found to be quite efficient for electricity generation (24 to 27%). Much of the waste heat could be recovered for the WFPAFC, so that the overall efficiency was 64 to 67%, and some waste heat, but potentially of higher grade, could be recovered by the WFMCFC to give an overall energy efficiency of 60 to 63%. The capital costs of both systems are still expected to be very high, but the examination of wood fuel prices, fuel cell costs, fuel cell lifetime and waste heat selling prices on the break-even selling price for electricity, as well as comparative sensitivity analyses, can help identify which other factors would have the main impacts on the system economics.