Ingenieria

Fuel 88 (2009) 424–430

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Fuel
journal homepage: www.elsevier.com/locate/fuel

Co-gasification of Colombian coal and biomass in fluidized bed: An experimental study
Jhon F. Vélez, Farid Chejne *, Carlos F. Valdés, Eder J. Emery, Carlos A. Londoño
Grupo de Termodinámica Aplicada y Energías Alternativas, Escuela de Procesos y Energía, UniversidadNacional de Colombia, Carr. 80 No. 65–223, Facultad de Minas, Medellín, Antioquia, Colombia

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a b s t r a c t
The main results of an experimental work on co-gasification of Colombian biomass/coal blends in a fluidized bed working at atmospheric pressure are reported in this paper. Several samples of blends were prepared by mixing 6–15wt% biomass (sawdust, rice or coffeehusk) with coal. Experimental assays were carried out by using mixtures of different steams/blends (Rvc) and air/blend (Rac) ratios showing the feasibility to implement co-gasification as energetic alternative to produce fuel gas to heat and to generate electricity and the possibility of converting clean and efficiently the refuse coal to a low-heating value gas. Ó 2008 Elsevier Ltd. All rightsreserved.

Article history: Received 11 March 2008 Received in revised form 26 August 2008 Accepted 7 October 2008 Available online 6 November 2008 Keywords: Co-gasification Biomass Coal Energy efficiency

1. Introduction Reduced availability of fossil fuels and increased public concern on pollution and climate change has caused a renewed interest on environmentally friendly technologies forconversion of fossil fuels in energy. One of these technologies is the co-gasification of coal and biomass [1–6] in which a mixture of both fuels are converted into a gas that can be used as a fuel or as a chemical precursor. A reduction of green-house emission when coal and biomass are co-gasified becomes evident given the renewable character of biomass and the higher efficiency that gasification has whencompared to coal combustion. Additional environmental benefits of co-gasification include a reduction on nitrogen oxides and sulfur emissions. Colombia has the largest coal reserves (around 6700 Mt) in South America [7]. At the same time, residual biomass, particularly sawdust, rice and coffee husks are abundant given the ample distribution of woodshops and the extensive agricultural exploitationof rice and coffee. The study of the co-gasification of coal and residual biomass applied to the Colombian case seems, therefore, relevant. The co-gasification of coal and biomass has been extensively studied [1–6,8–11]. The biomass traditionally used in gasification include pine [1,3,6], olive oil wastes [3,12], wood [5,8,9] and rice husk (e.g. [13]). Some authors [14] have studied gasificationcharacteristics of coffee related products, however, in the reviewed lit* Corresponding author. Tel.: +57 4 4255333; fax: +57 4 2341002. E-mail address: fchejne@unalmed.edu.co (F. Chejne). 0016-2361/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2008.10.018

erature there was no study dedicated neither to the gasification of coffee husk nor to the co-gasification ofcoffee or rice husks with coal. The possibility of feeding solids of different size distribution makes fluidized beds [15–19] one of the most studied technologies for biomass gasification. Gasification in fluidized beds yields gases with heating values varying from 1.6 to 4.2 MJ mÀ3 [15–19]. One drawback of biomass gasification in fluidized beds is that the low ash melting point of sawdust can lead toagglomeration and loose of fluidizability [20]. This paper presents results obtained during the co-gasification of a Colombian coal and sawdust, rice and coffee husks in a fluidized-bed pilot plant at atmospheric pressure with air/steam mixtures. In the experiments, the steam/fuel ratio (Rvc) was varied between 0.1 and 0.8 kg/kg and the air/fuel ratio (Rac) from 2.0 to 3.0 kg/kg with the goal of...