Volatiles and char combustion rates of demineralised lignite and wood blends Melek Yilgin * , Dursun Pehlivan Firat University, Chemical Engineering Department, 23279 Elazıg ˘, Turkey article info Article history: Received 15 February 2008 Received in revised form 20 October 2008 Accepted 5 November 2008 Available online 17 December 2008 Keywords: Co-combustion Lignite Poplar wood Volatiles combustion Char combustion abstract Today, much interest is given to the utilisation of materials of plant origin as substitutions of fossil fuels in meeting energy needs to reduce the level of atmospheric pollutant emissions and global warming threat, and emphasis has been placed on the co-combustion of coal and biomass. In this study, volatiles and char combustion behaviour of the fuel pellets composed from demineralised lignite and poplar wood sawdust, were investigated in a cylindrical wire mesh basket placed in a preheated tube furnace. The results have shown that ignition times of the pellets decreased with the burning temperature and short- ened further due to demineralisation of lignite. Volatiles combustion rates of the samples did not corre- late well with combustion times. However, they can be correlated with their respective proximate volatile matter contents. Char burnout times decreased with increasing combustion rates and correlated well with the respective proximate fixed carbon contents of the samples. Deviations were more consid- erable in the case of rate data. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Widespread use of the fossil fuels over the last century has in- creased continually the amount of carbon dioxide and other haz- ardous components in the earth atmosphere [1]. This faced the world to the global warming threat, which may eventually destroy human life on the earth. As an option for preventing this disaster, uses of plant origin (biomass) materials regarded as carbon dioxide neutral fuels have been considered to meet energy needs of today’s societies. In this context, emphasis has been given recently to the co-combustion of coal and biomass. It is predicted that environ- mental, technical and economical advantages could be acquired by the use of biomass in the existing coal combustion systems. By considering a carbon dioxide balance, carbon dioxide emission levels found in the burning of hard coals could be reduced up to 93% by replacing them with the biomass [2]. On the other hand, the coals with high sulphur and mineral matter contents are not suitable for efficient utilisation in gasification, combustion, car- bonisation and liquefaction processes as environmental restric- tions usually implement the use of coals with low sulphur and mineral matter contents. However, it is important to treat low quality coals to become environmentally acceptable fuels [3,4] be- cause reserves of high quality coals are steadily diminishing. Most studies are concentrated on the reduction of sulphur contents or sulphur dioxide emissions during combustion of coals with high sulphur contents [5]. But the costs of these processes are consider- ably high and limit application areas. Because some simple physi- cal operations can eliminate only a limited number of mineral compounds from coal, higher cost chemical cleaning methods such as acid or alkali leaching have been generally applied to remove unwanted minerals or ash precursors of coal more efficiently [6,3]. These methods have not reached widespread commercialisa- tion due to the lack of complete cost analyses yet. Considering to- day’s acid, alkali and high quality fuel prices, however, they may be regarded as viable techniques for preparing clean domestic fuels fulfilling environmental implementations. It has been envisaged that the disposal problem of spent leaching solutions could be overcame by regeneration schemes [3,7]. The main advantages of biomass utilisation in the combustion processes are their low costs, negligible sulphur, nitrogen and mineral matter contents, and renewable nature. Thus, co-combustion of coal and biomass has the potencies of reducing environmentally pollutant emissions and contributing to the solution of solid waste elimination prob- lems, as well as reducing green house gas components [8]. Although this option could help to reduce global carbon dioxide emissions, the choice about utilisation any kind of biomass in en- ergy production as substitute to coal would consequently depend on economical judgements, and individual and co-combustion behaviour of considered biomasses. One of the options for utilising the energy content of biomass in domestic and industrial burners is its densification to form fuel pellets, which appears to be an attractive solution for replacing fos- sil fuels with a reasonable cost because the investment costs for pellet heating systems are also relatively cheap [9–11]. Pellet bio- masses are usually preferred due to their advantage of high energy 0306-2619/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2008.11.002 * Corresponding author. Tel.: +90 424 2370000/5514; fax: +90 424 2415526. E-mail addresses: myilgin@firat.edu.tr (M. Yilgin), dpehlivan@firat.edu.tr (D. Pehlivan). Applied Energy 86 (2009) 1179–1186 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy