Oxygen enriched combustion and co-combustion of lignites and biomass in a 30 kWth circulating fluidized bed Ufuk Kayahan a, b, * , Sibel € Ozdo  gan b, c a TUBITAK Marmara Research Center Energy Institute, p.o.b. 41470, Gebze, Kocaeli, Turkey b Marmara University, Institute of Pure and Applied Sciences, G€ oztepe Campus, 34722, Kadık€ oy, _ Istanbul, Turkey c Faculty of Engineering, Dept. of Mechanical Engineering, G€ oztepe Campus, 34722, Kadık€ oy, _ Istanbul, Turkey article info Article history: Received 7 April 2016 Received in revised form 20 September 2016 Accepted 24 September 2016 Keywords: Combustion Oxygen enriched combustion Fluidized bed Cocombustion abstract Oxygen enriched combustion is a promising retrofitting option for existing power plants to improve CO 2 capture. In this study, the effect of oxygen enrichment of air as oxidant was investigated with a 30kWth fluidized bed combustor. Tests were conducted with two different Turkish lignites, one biomass and their blends. Biomass share was increased up to 20%. The oxygen concentration in the oxidant was kept be- tween 21 and 30%. Oxygen enrichment supports combustion in all cases. Biomass addition to lignites appears to have an increasing synergetic effect on combustion as the oxygen enrichment and biomass portion in the mix increases. It was found that oxygen enrichment increases NO and SO 2 formation in all cases. As the biomass share increases NO emissions increase in all oxygen cases while the opposite is true for SO 2 emissions. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Global energy demand is estimated to increase by one-third from 2011 to 2035. In spite of the rise of the renewable energy usage the share of fossil fuels is expected to reduce from 82% to 75% only [1]. Moreover global coal consumption increase is expected to be more pronounced than that of petroleum because of China. In- crease of fossil fuel consumption in the world, will lead to the in- crease of CO 2 emissions. According to IEA facts, energy related CO 2 emissions are expected to rise 20% by 2035 resulting in 3.6  C temperature rise in the atmosphere. Since the fossil fuels will continue to play a dominant role throughout the world it is of utmost importance to develop technologies that reduce CO 2 emissions while using fossil fuels. Biomass co-combustion and carbon capture and storage (CCS) technologies seem popular so- lutions to reduce CO 2 emissions [2,3]. Biomass co-combustion means partial substitution of biomass for coal in coal power plants. Based on the current worldwide installed coal fired power plant capacity at 800GWe; substitution of each percentage of coal by biomass will reduce annualCO 2 reductions approximately by 60 Mton [4]. Co-combustion approach seems one of the most economic and efficient ways of biomass usage in the existing electricity generation system, because there is no or minor need for extra infrastructure for co-combustion in existing coal power plants [5]. The other major advantages of co- combustion compared to coal firing are related to lower SO 2 and NO x emissions due to biomass' low sulphur and fuel nitrogen content [6]. CCS is also sought to reduce CO 2 emissions. According to IEA scenario CCS will contribute to 14% of the CO 2 emission reductions required in 2050 [7]. Oxy-combustion technology is considered as an appropriate energy and cost efficient CCS technology among others [8]. In oxy-combustion part of the outgoing flue gases are recycled back to the incoming oxygen stream. Further de- velopments in air separation techniques are expected to make this technology economically feasible. While this technology is being developed, an integration concept, oxygen enriched combustion (OEC), can be applied to the existing power plants [9]. Combustion with increased oxygen concentration in the oxidizer atmosphere is called OEC. Pure oxygen is added to the combustion air, and the oxygen concentration is increased in the oxidant stream. The OEC technique was first used in high temperature metallurgy industry [10]. The benefits of the OEC are increased productivity and energy efficiency along with reduced exhaust gas volume and pollutant * Corresponding author. Present address: TUBITAK Marmara Research Center Energy Institute, p.o.b. 2141470, Gebze, Kocaeli, Turkey. E-mail address: ufuk.kayahan@tubitak.gov.tr (U. Kayahan). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy http://dx.doi.org/10.1016/j.energy.2016.09.117 0360-5442/© 2016 Elsevier Ltd. All rights reserved. Energy 116 (2016) 317e328