A thermodynamic analysis of a biogas-fired integrated gasification steam injected gas turbine (BIG/STIG) plant R. Layi Fagbenle a, * , A.B.C. Oguaka b , O.T. Olakoyejo c a Mechanical Engineering Department, University of Ibadan, Ibadan, Nigeria b School of Engineering and Design, Brunel University, Uxbridge, Middlesex UB8 3PH, UK c Mechanical Engineering Department, University of Lagos, Lagos, Nigeria Received 24 February 2005; accepted 25 July 2005 Available online 13 September 2005 Abstract A thermodynamic analysis considering both the first and the second laws of thermodynamics has been made on a 53 MW (net) biogas-fired integrated gasification steam injected gas turbine (BIG/STIG) plant. The energy utilization diagrams (EUDs) for the plant and for the reaction subsystems have also been considered, revealing both problems and potentials for improvement. The anal- ysis indicates a thermal efficiency of about 41% (power based) and 45% (power and recovered heat based) but that the exergy loss in the combustion chamber is largest at about 79% of the total system exergy loss. Ó 2005 Published by Elsevier Ltd. Keywords: EUD; BIG/STIG; BIG/ISTIG; CCGT; Exergy; Biogas; Second law; Availability-factor 1. Introduction Recent heat and power plant improvements have lar- gely been driven by the international imperatives arising from the climate change and the ozone layer issues of the 1997 Kyoto Protocol (United Nations Framework on Climate Change Convention) and the 1987 Montreal Protocol (on ozone layer depleting substances) respec- tively. Quite stringent emission standards and limits are in force for countries of the international community in general in respect of reduction of greenhouse gases and limiting the adverse effects of climate change. The heat and power industry is generally considered a signif- icant stakeholder in the climate change problem, which in turn provides an impetus for improved performance of plant and equipment. In this regard, gas turbine technology in particular has made remarkable progress in the recent past, with the incorporation of the solid (coal and biomass) fuel gasifiers [9]. Gas turbine technologies for the biomass gasifiers are the biomass integrated gasification/gas tur- bines (BIG/GT), the biomass integrated gasification/ steam injected gas turbines (BIG/STIG), and the bio- mass integrated gasification/intercooled steam injected gas turbines (BIG/ISTIG). In its use in the sugar cane milling industry, BIG/STIG and BIG/ISTIG could be fuelled with bagasse during the milling season, palletized or briquetted for a fixed bed gasifier. In the off-season, the systems could use densified barbojo, wood, water hyacinth, etc. Biomass is of particular focus because it has zero net carbon addition to the environment, being a natural car- bon sink originally. Steam injection into the turbine is used to produce more power at a higher efficiency. Water or steam injection was also used earlier in gas turbine 1359-4311/$ - see front matter Ó 2005 Published by Elsevier Ltd. doi:10.1016/j.applthermaleng.2005.07.027 * Corresponding author. Present address: College of Engineering and Technology, Olabisi Onabanjo University, Ibogun Campus, PB5026, Ogun State, Nigeria. E-mail address: layifagbenle@yahoo.com (R.L. Fagbenle). www.elsevier.com/locate/apthermeng Applied Thermal Engineering 27 (2007) 2220–2225