Combustion of peanut and tamarind shells in a conical fluidized-bed combustor: A comparative study Vladimir I. Kuprianov ⇑ , Porametr Arromdee School of Manufacturing Systems and Mechanical Engineering, Sirindhorn International Institute of Technology, Thammasat University, Pathum Thani 12121, Thailand highlights  Morphology and thermogravimetry of peanut and tamarind shells are investigated.  Combustion and emission performance of a conical FBC firing these shells is studied.  Fuel properties and excess air have important effects on the combustor performance.  High (99%) combustion efficiency is achievable for firing peanut and tamarind shells.  Alumina sand can be used to prevent bed agglomeration when burning these biomasses. article info Article history: Received 10 February 2013 Received in revised form 20 April 2013 Accepted 23 April 2013 Available online 30 April 2013 Keywords: Peanut/tamarind shells Fuel morphology and thermogravimetry Conical fluidized-bed combustor Alumina bed material Combustion and emission performance abstract Combustion of peanut and tamarind shells was studied in the conical fluidized-bed combustor using alu- mina sand as the bed material to prevent bed agglomeration. Morphological, thermogravimetric and kinetic characteristics were investigated to compare thermal and combustion reactivity between the bio- mass fuels. The thermogravimetric kinetics of the biomasses was fitted using the Coats–Redfern method. Experimental tests on the combustor were performed at 60 and 45 kg/h fuel feed rates, with excess air within 20–80%. Temperature and gas concentrations were measured along radial and axial directions in the reactor and at stack. The axial temperature and gas concentration profiles inside the combustor exhibited sensible effects of fuel properties and operating conditions on combustion and emission perfor- mance. High (99%) combustion efficiency and acceptable levels of CO, C x H y , and NO emissions are achievable when firing peanut shells at excess air of about 40%, whereas 60% is more preferable for burn- ing tamarind shells. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Peanuts and tamarind are popular food products in Thailand and other Asian countries. Peanut shells and tamarind shells are major residues from processing peanuts and tamarind fruits col- lected in these countries on a large scale. Annually, about 25 million tons of peanuts (or about 70% of the world crop) are produced in Asia, the main suppliers being China and India (USDA, 2013). Taking into account the availability (as about 25 wt.% of total peanut mass) and calorific value (assessed as 16 MJ/kg according to Hanping et al., 2008), the energy potential of peanut shells in Asian countries is estimated to be about 100 PJ per year. Compared to peanuts, the production of tamarind fruits on the Asian continent is much lower, some 400 thousand tons per year, mainly grown in India and Thailand (El-Siddig et al., 2006). Assuming the availability (assessed as 15 wt.% of total fruit mass) and calorific value (about 16 MJ/kg) of tamarind shells, the energy potential of this biomass residue in Asia can be roughly estimated to be 1 PJ per year. As with many other shell-type bio- masses exhibiting excellent combustion properties (high reactivity and substantial calorific value), both peanut and tamarind shells can be considered as potential fuels for small-scale heat and power plants (Demirbas ß, 2004). Grate-firing and fluidized-bed combustion systems (combus- tors and boiler furnaces) are reported to be the main competing options for energy conversion from biomass. Despite some advan- tages of the grate-firing systems, such as (i) ability of handling high-moisture biomasses with large particles sizes, (ii) load flexi- bility, (iii) easy maintenance and (iv) low operational costs, the flu- idized-bed combustion systems seem to be the most effective option for biomass utilization by offering multiple important ben- efits, such as wide fuel flexibility, high combustion efficiency and low emissions (Werther et al., 2000; Van Caneghem et al., 2012). A large number of studies have been devoted to bubbling, vor- texing, and circulating fluidized-bed combustion systems for firing 0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2013.04.086 ⇑ Corresponding author. Tel.: +66 2 986 9009x2208; fax: +66 2 986 9112. E-mail address: ivlaanov@siit.tu.ac.th (V.I. Kuprianov). Bioresource Technology 140 (2013) 199–210 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech