Biomass fuels are increasingly being viewed as viable alternatives for energy production in biomass-fired power plants and coal-fired power plants, which aim to employ co-firing technologies to achieve CO2 emission reductions. In this study, wood pellets (woody biomass) and kenaf (herbaceous biomass) were fully characterized in terms of their elemental compositions, pyrolysis, and char oxidation kinetics. Kinetic parameters were obtained through the application of the multi-Gaussian distributed activation energy model (DAEM) and Kissinger equation. Analyses of the ash indicated that, unlike coal, the biomass fuel is mostly composed of metal oxide ash. The calorific values of wood pellets were slightly higher than those of kenaf. Detailed kinetic analyses are presented so that steps can be taken to combust the biomass fuels in power plants. The kinetic data suggested that the mechanism for the char oxidation of wood pellets may be more complex than that for kenaf. In summary, these torrefied and pyrolyzed materials were found to represent potentially useful biomass fuels.

Abstract:The effect of oxygen-enriched air on low-rank coal char combustion was experimentally investigated. In this work, a coal-heating reactor equipped with a platinum wire mesh in the reaction chamber was used to analyze the combustion temperature, reaction time, and reaction kinetics. Increasing the oxygen content of the primary combustion air increased the combustion temperature and decreased the reaction time. As the oxygen content increased from 21% to 30%, the average temperature increased by 47.72 K at a setup temperature of 1673 K, and the reaction time decreased by 30.22% at the same temperature. The graphite sample exhibited similar trends in temperature and reaction time, although the degree of change was smaller because the pores produced during char devolatilization expanded the active surface available for oxidation of the char sample. A mathematical model was used to define the intrinsic kinetics of the reaction. As the oxygen content increased from 21% to 30%, the reaction rate of the low-rank coal char increased. These results were also compared with those of the graphite sample.

No abstract

To enrich biomass research, particularly for empty fruit bunch (EFB) and kenaf, this study focused on particle size and body structure thickness using a combination of reflected light petrography microscopy and image analysis. Torrefaction was chosen as a prior treatment to upgrade EFB and kenaf fuel properties, and comparisons were made between raw and torrefied samples. Combustibility characteristics were analyzed using a thermogravimetric method. From raw sample combustion characteristics, kenaf shown better combustibility than EFB, while for torrified cases, both were shown the same curve pattern as their raw materials, but with each torrefied case showing shifting phenomena from the previous conditions. These phenomena were in line with the difference in the microstructure properties of both EFB and kenaf. The results indicate that the biomass microstructure properties studied here can be observed using microscopy enhanced with image processing and analysis and that particle size and thickness can affect combustion and kinetic properties in combustion tests.

CO2 emissions are a major contributor to global warming. Biomass combustion is one approach to tackling this issue. Biomass is used with coal combustion in thermal power plants or with blast furnaces (BFs) because it is a carbon-neutral fuel; therefore, biomass provides the advantage of reduced CO2 emissions. To examine the effect of co-firing on pulverized coal injection (PCI) in BFs, two coals of different ranks were blended with the biomass in different proportions, and then their combustion behaviors were examined using a laminar flow reactor (LFR). The PCI combustion primarily functions as a source of heat and CO to supply the upper part of the BF. To create a similar PCI combustion environment, the LFR burner forms a diffusion flat flame with an oxygen concentration of 26% with a flame temperature of ~2000–2250 K at a heating rate of 105 K/s. The combustion characteristics, such as the flame structure, burning coal particle temperature, unburned carbon (UBC), and CO and CO2 emissions were measured to evaluate their effect on PCI combustion. With the increase in the biomass blending ratio, the brightness of the volatile cloud significantly increased, and the particle temperature tended to decrease. The fragmentation phenomenon, which was observed for certain coal samples, decreased with the increase in the biomass blending ratio. In particular, with an increase in the biomass blending ratio, the optimum combustion point occurred, caused by the fragmentation of coal and volatile gas combustion of biomass.