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In this paper, a multi-scale Eulerian-Lagrangian CFD model based on OpenFOAM has been constructed, which takes into account heat and mass transfer, pyrolysis, homogeneous and heterogeneous reactions, radiation, as well as the interactions between the continuous gas phase and discrete particles. The proposed model is validated and applied to a lab-scale biomass entrained flow reactor. The operating temperatures are high (1000-1400 °C) and influences of five operating parameters (reactor temperature, steam/carbon molar ratio, excess air ratio, biomass type, and particle size) on the gasification behavior are explored. Results show that an increase in the reactor temperature has positive effect on both the H2 and CO productions; increasing the steam/carbon ratio increases the H2 production but decreases the CO production; increasing the excess air ratio decreases both the H2 and CO productions; the variations in the gas product for the four biomasses studied are not so significant due to similar biomass nature and hence one type can be replaced by another without any major consequences in the gasification performance; and both the CO and H2 productions and carbon conversion decrease with an increase in particle size. Moreover, the predicted results follow the same trend as the experimental data available in the literature. Quantitative comparisons are also made and the agreement is good.

A comprehensive CFD-DEM numerical model has been developed to simulate the biomass gasification process in a fluidized bed reactor. The methodology is based on an Eulerian-Lagrangian concept, which uses an Eulerian method for gas phase and a discrete element method (DEM) for particle phase. Each particle is individually tracked and associated with multiple physical (size, density, composition, and temperature) and thermo-chemical (reactive or inert) properties. Particle collisions, hydrodynamics of dense gas-particle flow in fluidized beds, turbulence, heat and mass transfer, radiation, particle shrinkage, pyrolysis, and homogeneous and heterogeneous chemical reactions are all considered during biomass gasification with steam. A sensitivity analysis is performed to test the integrated model's response to variations in three different operating parameters (reactor temperature, steam/biomass mass ratio, and biomass injection position). Simulation results are analyzed both qualitatively and quantitatively in terms of particle flow pattern, particle mixing and entrainment, bed pressure drop, product gas composition, and carbon conversion. Results show that higher temperatures are favorable for the products in endothermic reactions (e.g. H2 and CO). With the increase of steam/biomass mass ratio, H2 and CO2 concentrations

An experimental investigation was carried out to study the NO x formation and reduction by primary measures for five types of biomass (straw, peat, sewage sludge, forest residues/Grot, and wood pellets) and their mixtures. To minimize the NO x level in biomass-fired boilers, combustion experiments were performed in a laboratory scale multifuel fixed grate reactor using staged air combustion. Flue gas was extracted to measure final levels of CO, CO 2 , C x H y , O 2 , NO, NO 2 , N 2 O, and other species. The fuel gas compositions between the first and second stage were also monitored. The experiments showed good combustion quality with very low concentrations of unburnt species in the flue gas. Under optimum conditions, a NO x reduction of 50-80% was achieved, where the highest reduction represents the case with the highest fuel-N content. The NO x emission levels were very sensitive to the primary excess air ratio and an optimum value for primary excess air ratio was seen at about 0.9. Conversion of fuel nitrogen to NO x showed great dependency on the initial fuel-N content, where the blend with the highest nitrogen content had lowest conversion rate. Between 1-25% of the fuel-N content is converted to NO x depending on the fuel blend and excess air ratio. Sewage sludge is suggested as a favorable fuel to be blended with straw. It resulted in a higher NO x reduction and low fuel-N conversion to NO x . Tops and branches did not show desirable NO x reduction and made the combustion also more unstable. N 2 O emissions were very low, typically below 5 ppm at 11% O 2 in the dry flue gas, except for mixtures with high nitrogen content, where values up to 20 ppm were observed. The presented results are part of a larger study on OPEN ACCESSEnergies 2012, 5 271 problematic fuels, also considering ash content and corrosive compounds which have been discussed elsewhere.

The combustion of biomass, in this case demolition wood, has been investigated in a grate combustion multifuel reactor. In this work a temperature range of 850À1000°C is applied both for staged air combustion and nonstaged combustion of biomass to investigate the effects of these parameters on the emission levels of NOx, N 2 O, CO, hydrocarbons (C x H y ) and different other components. The composition of the flue gas is measured by four advanced continuous gas analyzers including gas chromatograph (GC), two Fourier transform infrared (FTIR) analyzers, and a conventional multispecies gas analyzer with fast response time. The experiments show the effects of staged air combustion, compared to nonstaged combustion, on the emission levels clearly. A NOx reduction of up to 85% is reached with staged air combustion. An optimum primary excess air ratio of 0.8À0.95 is found as a minimizing parameter for the NOx emissions for staged air combustion. Air staging has, however, a negative effect on N 2 O emissions. Even though the trends show a very small reduction in the NOx level as temperature increases in nonstaged combustion, the effect of temperature is not significant for NOx and C x H y , neither in staged air combustion or nonstaged combustion, while it has a great influence on the N 2 O and CO emissions, with decreasing levels with increasing temperature.