Low-grade coal and biomass co-combustion on fluidized bed: exergy analysis Carmen Martı ´n a , Miguel A. Villaman ˜a ´n a , Ce ´sar R. Chamorro a , Juan Otero b , Andre ´s Cabanillas b , Jose ´ J. Segovia a, * a Laboratory of Thermodynamic and Calibration TERMOCAL, Department of Energy, School of Engineering, University of Valladolid, E-47011 Valladolid, Spain b Department of Fossil Fuels, Research Centre for Energy, Environment and Technology Ciemat, E-28040 Madrid, Spain Received 31 July 2003 Abstract The purpose of this work is to prove the technical feasibility of the bubbling fluidized bed co-combustion, using biomass and low-grade coal mixtures and applying the exergy method. The pilot plant modelled is an atmospheric bubbling fluidized bed combustion chamber with a nominal capacity of 1 MWth. We have applied the mass balance, the energy balance and the exergy balance to the plant in nine experiments, which have been performed at different operation conditions. The exergy analysis includes the calculation of the exergy destruction and the exergetic efficiency of the plant for these experiments. An estimation of the irreversibility cost is also evaluated. q 2005 Elsevier Ltd. All rights reserved. 1. Introduction Low coal rank or coal waste and biomass co-combustion in coal fired power plants is a good technique that contributes to the reduction of greenhouse gases. It is also a solution to the waste disposal problem. Co-firing biomass with coal has the capability to reduce both NO x and SO x levels from coal fired power plants. It also reduces CO 2 emissions, and soil and water pollution [1]. Energy 31 (2006) 330–344 www.elsevier.com/locate/energy 0360-5442/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2005.01.008 * Corresponding author. Tel./fax: C34 983 423 420.