Anup Kumar Sadhukhan

Modelling of pyrolysis of coal–biomass blends using thermogravimetric analysis

The primary objective of this work was to develop an appropriate model to explain the co-pyrolysis behaviour of lignite coal-biomass blends with different proportions using a thermogravimetric analyzer. A new parallel-series kinetic model was proposed to predict the pyrolysis behaviour of biomass over the entire pyrolysis regime, while a kinetic model similar to that of Anthony and Howard [Anthony, D.B., Howard, J.B., 1976. Coal devolatilization and hydrogasification. AIChE Journal 22(4), 625-656] was used for pyrolysis of coal. Analysis of mass loss history of blends showed an absence of synergistic effect between coal and biomass. Co-pyrolysis mass-loss profiles of the blends were predicted using the estimated kinetic parameters of coal and biomass. Excellent agreement was found between the predicted and the experimental results.

Modelling of pyrolysis of large wood particles

A fully transient mathematical model has been developed to describe the pyrolysis of large biomass particles. The kinetic model consists of both primary and secondary reactions. The heat transfer model includes conductive and internal convection within the particle and convective and radiative heat transfer between the external surface and the bulk. An implicit Finite Volume Method (FVM) with Tridiagonal Matrix Algorithm (TDMA) is employed to solve the energy conservation equation. Experimental investigations are carried out for wood fines and large wood cylinder and sphere in an electrically heated furnace under inert atmosphere. The model predictions for temperature and mass loss histories are in excellent agreement with experimental results. The effect of internal convection and particle shrinkage on pyrolysis behaviour is investigated and found to be significant. Finally, simulation studies are carried out to analyze the effect of bulk temperature and particle size on total pyrolysis time and the final yield of char.

An experimental and theoretical investigation on torrefaction of a large wet wood particle

A competitive kinetic scheme representing primary and secondary reactions is proposed for torrefaction of large wet wood particles. Drying and diffusive, convective and radiative mode of heat transfer is considered including particle shrinking during torrefaction. The model prediction compares well with the experimental results of both mass fraction residue and temperature profiles for biomass particles. The effect of temperature, residence time and particle size on torrefaction of cylindrical wood particles is investigated through model simulations. For large biomass particles heat transfer is identified as one of the controlling factor for torrefaction. The optimum torrefaction temperature, residence time and particle size are identified. The model may thus be integrated with CFD analysis to estimate the performance of an existing torrefier for a given feedstock. The performance analysis may also provide useful insight for design and development of an efficient torrefier.

On the data performance in tactical WLAN with signal strength ratio based handoff algorithms

In tactical communication systems, WLANs are very popular options due to their high data rate. Motivated by the work of [1], we investigate performance of newly developed signal strength ratio (SSR) based handoff algorithms in tactical communication systems using WLANs. We obtain better performance in terms of number of handoff, packet loss rate and throughput for SSR based handoff algorithms. Performance of average received signal strength based handoff algorithms has also been investigated for tactical WLAN systems.

Devolatilization and Combustion of Coarse-Sized Coal Particles in Oxy–Fuel Conditions: Experimental and Modeling Studies

A generalized unsteady-state kinetic model, coupled with all modes of heat transfer, was developed to describe the combined coal devolatilization and the subsequent combustion of the residual char under oxy–fuel condition in both O2–CO2 and O2–N2 environments. Experiments were conducted to validate the model, which was also found to predict the experimental data published in the literature well. The effect of coal particle diameter, temperature of the reactor, and oxygen concentration on devolatilization time was investigated. Peaks in devolatilization and char combustion rates and particle center temperature were studied, and the effect of different parameters assessed. Higher reaction time was observed in an O2–CO2 environment compared to that in an O2–N2 environment due to lower particle temperatures resulting from endothermic gasification reaction and the difference in thermo-physical properties. Simulation studies were carried out to generate temperature, carbon, O2, CO, and CO2 contours to understan...

2-D modeling of torrefaction of a large biomass particle

ABSTRACT A two-dimensional (2-D) model is developed to predict the torrefaction behavior of a large wet biomass particle. Although one-dimensional (1-D) model is found to be adequate for L/D ≥ 6, the necessity of using 2-D model at lower L/D ratios and higher torrefaction temperature is established. Errors up to 18% are observed in predicted mass fractions between 1-D and 2-D models. The center temperatures differed more, up to 96%, between z = 0 and z = L/2 in 2-D model which is not captured by the 1-D model. The model predictions agree well with the experimental results of the present authors and others. The evolution of the temperature profile is found to govern the mass fraction profile. At higher reactor temperature, three distinct zones are visible in the contour plots: peripheral fully torrefied zone, intermediate torrefying zone, and core with unreacted virgin biomass zone. Simulation studies show the formation of two symmetric annular hot spots at the ends, which move inward axially and subsequently merge at the center, the rate being faster for smaller L/D ratio. However, 1-D model does not provide such insight. The effects of reactor temperature, particle size, the residence time, and the initial moisture content on the torrefaction behavior are investigated.

Modeling of torrefaction of small biomass particles

ABSTRACT A simple single-step kinetic model consisting of two parallel reactions is proposed for torrefaction of small biomass particles. The model is validated against experimental data on torrefaction of poplar wood fines. Comparison of experimental data and model prediction shows that the results predicted by the proposed simplified model are as accurate as those from the models of Di Blasi and Lanzetta (1997) and Rousset et al. (2006) which involve larger numbers of model parameters – eight and sixteen, respectively – compared to four in the proposed model. This makes it suitable for incorporation into the overall reactor model. At 493 and 553 K, the relative mean errors are found to be 0.056, 0.080, 0.051 and 0.050, 0.100, 0.048 for the proposed model, Rousset et al.’s (2006) model and Blasi and Lanzettas (1997) model, respectively. The effect of particle size, temperature and residence time on torrefaction of biomass is investigated. A transformation of rate-controlling regime from kinetic to heat transfer is identified with an increase in particle size and temperature. Sensitivity analysis shows that the dimensionless groups such as pyrolysis number, dimensionless heat of reaction and dimensionless activation energy have significant influence on the particle temperature and torrefaction behaviour.