Biomass and Bioenergy 19 (2000) 199–208 Modelling and experiments of straw combustion in a grate furnace R.P. van der Lans ∗ , L.T. Pedersen, A. Jensen, P. Glarborg, K. Dam-Johansen Department of Chemical Engineering, Technical University of Denmark, Building 229, DK-2800, Lyngby, Denmark Received 29 December 1999; accepted 9 May 2000 Abstract A two-dimensional mathematical model for the combustion of straw in a cross-current, moving bed was developed as part of a tool for optimizing operating conditions and design parameters. To verify the model and to increase the understanding of straw bed combustion, laboratory xed-bed experiments were performed in a 15 cm diameter and 137 cm long vertical reactor. Air was introduced through the bottom plate and the straw was ignited from the top with an electrical radiation source. The temperature was measured at eight positions within the bed and gas analysis was performed for O 2, CO2, CO, Cx Hy , NOx , NH3 and SO2. The inlet air ow rate and air preheat temperature were varied. The experimental data for ignition front temperatures and front propagation velocity compared reasonably well with the modelling results. A higher air inlet temperature resulted in lower maximum bed temperatures, which was successfully modelled. A limited parameter analysis study was performed. Measurement of NO from the bed showed that, within the air inlet ow rates investigated, the conversion of fuel nitrogen to NO decreased with increasing air ow rate during ignition front propagation, while the conversion increased during the char burnout phase. c  2000 Elsevier Science Ltd. All rights reserved. Keywords: Biomass; Straw; Grate; Combustion; Modelling; Experimental 1. Introduction In order to reduce CO 2 emissions from fossil fuel combustion, Danish power plants are obliged to uti- lize annually at least 1.0 million tonnes of straw by the year 2004. To this purpose grate boilers are be- ing installed with capacities up to about 100 MW th . Since the combustion of straw for power generation is a relatively new concept, the design and operating conditions are not fully optimized yet. Lower NO and * Corresponding author. Tel.: +45-4525-2800; fax: +45-4588- 2258. E-mail address: chec@kt.dtu.dk (R.P. van der Lans). CO emissions may be achieved, as well as improved design and control. Modelling may help increase the understanding of the combustion processes occurring in grate boilers. Modelling of grate boilers involves both combustion of the fuel bed and gas-phase reac- tions above the bed. The chemical species leaving the bed and entering the freeboard depend completely on the reactions inside the fuel bed. Therefore, a reliable bed model is a prerequisite for a good model of a grate furnace. During combustion of a fuel bed in a hot fur- nace with air entering through the grate, an ignition front moves downward (i.e. underfeed combustion). Important parameters for this process are: the ignition front propagation velocity and the gas species leaving 0961-9534/00/$ - see front matter c  2000 Elsevier Science Ltd. All rights reserved. PII:S0961-9534(00)00033-7