Influence of char structure on reactivity and nitric oxide emissions Ana Arenillas, Fernando Rubiera, Jose ´ B. Parra, Jose ´ J. Pis * Department of Energy and Environment, Instituto Nacional del Carbo ´n, CSIC, Apartado 73, 33080 Oviedo, Spain Received 24 January 2002; received in revised form 26 March 2002; accepted 29 March 2002 Abstract The aim of this study was to investigate the influence of coal rank and operating conditions during coal pyrolysis on the resultant char texture properties, morphology and reactivity. A range of bituminous coals were pyrolysed in a fixed bed reactor at different heating rates. It was found that the higher the heating rate and the lower the coal rank, the more microporous chars were obtained. Isothermal (500 jC) gasification in 20% oxygen in argon of the chars was carried out using a differential thermogravimetric system (DTG). The results of this work indicated that the increase in the availability of char-active surface sites led to an increase in char reactivity, not only for oxygen but also for other reactive gases, in particular NO, diminishing emissions during the combustion process. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Coal pyrolysis; Char structure; Texture properties; Reactivity; NO reduction 1. Introduction Most of the coal utilisation processes, such as gasification, liquefaction, coking and production of activated carbon, are influenced by the porosity and pore structure of the intermediate products. Textural development is influenced significantly by the coal- devolatilisation step. Thus, pyrolysis determines the fluidity of coal, which influences processes like softening and swelling, and then affects the porosity and internal surface area of the resultant char [1]. On the other hand, the heterogeneous rate constants are also dependent on textural properties, not only in the reaction between oxygen and carbon, but 0378-3820/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0378-3820(02)00077-2 * Corresponding author. Tel.: +34-985-11-89-71; fax: +34-985-29-76-62. E-mail address: jjpis@incar.csic.es (J.J. Pis). www.elsevier.com/locate/fuproc Fuel Processing Technology 77 – 78 (2002) 103 – 109