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Abstract: To meet the urgent environmental targets, substituting coal with biomass has been considered to be an effective and promising method over the last decades. In this paper, a new concept of volumetric combustion is proposed and further developed to achieve 100% fuel switching to biomass in large scale coal-fired boilers. Volumetric combustion not only changes the in-furnace flow but also affects the combustion reactions by the intensive mixing and internal recirculation of the flue gases. Firstly, the volumetric combustion properties of the wood pellets were investigated experimentally. An Aspen model was then used to thermodynamically describe and study the volumetric combustion with three different types of fuel, and the emission properties of CO2 and NOx were compared. Finally, two applications of volumetric combustion were discussed. It is concluded that the wood pellets ignited and combusted much faster than the coal pellets and had a larger combustion volume when combusted under lower oxygen concentration conditions, and the ignition time was almost independent of the oxygen concentration when the oxidizer was preheated to 1000°C. In addition, the NOx emissions decreased as the recirculation ratio of the flue gas increased, and as the percentage of biomass used in co-firing increased, the amount of flue gas that needs to be recycled for reduction of NOx decreased. Thus, the volumetric combustion is beneficial as it reduces the operation cost of NOx reduction. The volumetric combustion would be an attractive technology for co-firing a large proportion of biomass in coal-fired boilers with high boiler efficiency and effective emissions reduction. [Copyright &y& Elsevier]

Abstract: Coconut and cashew nut shells are two typical biomass wastes abundant in most of the tropical countries. However, despite their enormous potential as energy sources, they are hardly studied and their thermal characteristics are still not well known. In this study, both biomasses are thermally degraded through thermogravimetry and their characteristics such as devolatilisation profiles and kinetics are analyzed, from 250 to 900 °C, in an inert atmosphere, at two different heating rates, and compared with wood pellets. The results show that their pyrolysis profiles are different from that of the commonly studied woody biomass. In fact, they present two different peaks instead of the one overlapping peak, for hemicellulose and cellulose. In addition, they present activation energies ranging from that are slightly above the commonly known maximum for biomass. At 10 and 20 °C/min the activation energy varied from about 130 to 174 and 180 to 216 kJ/mol, for cashew and coconut shells, respectively. [Copyright &y& Elsevier]

Abstract: In this work, the high temperature air/steam gasification (HTAG) technique has been tested for a fuel in pellet form made from waste material of woody and plastic origin. The feedstock was gasified in an updraft fixed bed reactor by mixtures of air and steam (102 Nm3/h, 4% to 82% steam) preheated to 1400 °C, a temperature well above the fluid temperature of the feedstock. The produced gas was analyzed with respect to composition, including a detailed characterization of the tar. Lower heating values up to 9.5 MJ/Nm3 and gas yields as high as 3.4 Nm3/kg were reported, indicating the process to be highly efficient for waste-to-energy applications. The composition of the tars, suggested extensive cracking as a result of the high temperatures of the outgoing gas. [Copyright &y& Elsevier]

Secondary pyrolysis in fluidizedbed fast pyrolysis of biomassis the focus of this work. A novel computational fluid dynamics (CFD)model coupled with a comprehensive chemistry scheme (134 species and4169 reactions, in CHEMKIN format) has been developed to investigatethis complex phenomenon. Previous results from a transient three-dimensionalmodel of primary pyrolysis were used for the source terms of primaryproducts in this model. A parametric study of reaction atmospheres(H2O, N2, H2, CO2, CO)has been performed. For the N2and H2O atmosphere,results of the model compared favorably to experimentally obtainedyields after the temperature was adjusted to a value higher than thatused in experiments. One notable deviation versus experiments is pyrolyticwater yield and yield of higher hydrocarbons. The model suggests anot overly strong impact of the reaction atmosphere. However, bothchemical and physical effects were observed. Most notably, effectscould be seen on the yield of various compounds, temperature profilethroughout the reactor system, residence time, radical concentration,and turbulent intensity. At the investigated temperature (873 K),turbulent intensity appeared to have the strongest influence on liquidyield. With the aid of acceleration techniques, most importantly dimensionreduction, chemistry agglomeration, and in-situ tabulation, a convergedsolution could be obtained within a reasonable time (∼30 h).As such, a new potentially useful method has been suggested for numericalanalysis of fast pyrolysis. [ABSTRACT FROM AUTHOR]

Highlights: [•] The performances of torrefaction based co-firing power plant are simulated by using Aspen Plus. [•] Mass loss properties and released gaseous components have been studied during biomass torrefaction processes. [•] Mole fractions of CO2 and CO account for 69–91% and 4–27% in total torrefied gases. [•] The electrical efficiency reduced when increasing either torrefaction temperature or substitution ratio of biomass. [Copyright &y& Elsevier]

Highlights: [•] Biomasses were devolatilized at high temperatures and high heating rates. [•] Biomass decreases its reactivity after torrefaction. [•] The kinetic parameters of torrefied biomasses were determined. [•] CO and H2 are main released volatiles during devolatilization of torrefied biomass. [ABSTRACT FROM AUTHOR]

Abstract: Torrefied biomass has several benefits, such as higher energy density, good grindability, higher flowability and uniformity. The process of torrefaction moves the chemical and physical properties of raw biomass close to that of bituminous coal, which allows co-utilization with high substitution ratios of biomass in the existing coal-fired boilers without major modifications. In this study, a torrefaction based co-firing system was proposed and studied. Devolatilization and char oxidize kinetics of the torrefied biomass have been investigated experimentally. CFD modeling of co-firing with varying substitutions of torrefied biomass in a pulverized coal boiler have been carried out. To figure out the boiler performance when co-firing torrefied biomass, five different cases were involved and simulated, coal only, 25% biomass, 50% biomass, 75% biomass, and 100% biomass on thermal basis, respectively. The results showed torrefaction is able to provide a technical option for high substitution ratios of biomass in the co-firing system. The case-study pulverized coal boiler could be fired 100% torrefied biomass without obvious decreasing of the boiler efficiency and fluctuation of boiler load. More positively, the net CO2 and the NO x emissions significantly reduced with increasing of biomass substitutions in the co-firing system. [Copyright &y& Elsevier]

Abstract: Steam explosion (SE) pretreatment has been implemented for the production of wood pellet. This paper investigated changes in biomass structure due to implication of steam explosion process by its pyrolysis behavior/characteristics. Salix wood chip was treated by SE at different pretreatment conditions, and then pyrolysis characteristic was examined by thermogravimetric analyzer (TGA) at heating rate of 10K/min. Both pyrolysis characteristics and structure of biomass were altered due to SE pretreatment. Hemicellulose decomposition region shifted to low temperature range due to the depolymerization caused by SE pretreatment. The peak intensities of cellulose decreased at mild pretreatment condition while they increased at severe conditions. Lignin reactivity also increased due to SE pretreatment. However, severe pretreatment condition resulted in reduction of lignin reactivity due to condensation and re-polymerization reaction. In summary, higher pretreatment temperature provided more active biomass compared with milder pretreatment conditions. [Copyright &y& Elsevier]