Kinetic analysis and modeling of maize straw hydrochar combustion using a multi-Gaussian-distributed activation energy model

Combustion kinetics of the hydrochar was investigated using a multi-Gaussian-distributed activation energy model(DAEM)to ex-pand the knowledge on the combustion mechanisms.The results demonstrated that the kinetic parameters calculated by the multi-Gaussian-DAEM accurately represented the experimental conversion rate curves.Overall,the feedstock combustion could be divided into four stages:the decomposition of hemicellulose,cellulose,lignin,and char combustion.The hydrochar combustion could in turn be divided into three stages:the combustion of cellulose,lignin,and char.The mean activation energy ranges obtained for the cellulose,lignin,and char were 273.7-292.8,315.1-334.5,and 354.4-370 kJ/mol,respectively,with the standard deviations of 2.1-23.1,9.5-27.4,and 12.1-22.9 kJ/mol,re-spectively.The cellulose and lignin contents first increased and then decreased with increasing hydrothermal carbonization(HTC)temperature,while the mass fraction of char gradually increased.

A Model for Agglomeration in Bio-fuel Fired Fluidized Bed

A mathematical model has been developed to describe the agglomeration process in bio-fuel fired fluidized bed combustor. Based on the balance mechanism of the adhesive force caused by liquid bonding between two parti- cles and the breaking force induced by bubbles in the fiuidized bed, the model considers modified Urbain model and chemical equilibrium calculations using FactSage modeling. This model prediction accounts for the evolve- ment of the adhesive and breaking forces, and clearly demonstrates that the different composition of ash, the in- creasing liquid phase matter and the fiuidization velocity cause defluidization in fluidized bed. In this model, it is the first time to hypothesize that the bonding stress between two particles is proportional to mass fraction of liq- uid phase and inversely proportional to the diameter of particles and viscosity of liquid phase. The defluidization time calculated by this model shows good agreement with that from the experimental data.

Elemental mercury (Hg^(0)) removal from coal syngas using magnetic tea-biochar: Experimental and theoretical insights

Mercury is ranked 3^(rd)as a global pollutant because of its long persistence in the environment. Approximately 65% of its anthropogenic emission (Hg^(0)) to the atmosphere is from coal-thermal power plants. Thus, the Hg^(0)emission control from coal-thermal power plants is inevitable. Therefore, multiple sorbent materials were synthesized using a one-step pyrolysis method to capture the Hg^(0)from simulated coal syngas. Results showed, the Hg^(0)removal performance of the sorbents increased by the citric acid/ultrasonic application.T5CUF_(0.3)demonstrated the highest Hg^(0)capturing performance with an adsorption capacity of 106.81 μg/g within 60 min at 200 °C under complex simulated syngas mixture (20% CO,20% H_(2), 10 ppm V HCl, 6% H_(2)O, and 400 ppm V H_(2)S). The Hg^(0)removal mechanism was proposed, revealing that the chemisorption governs the Hg^(0)removal process. Besides, the active Hg^(0)removal performance is attributed to the high dispersion of valence Fe_(3)O_(4)and lattice oxygen (α) contents over the T5CUF_(0.3)surface. In addition, the temperature programmed desorption (TPD) and XPS analysis confirmed that H_(2)S/HCl gases generate active sites over the sorbent surface, facilitating high Hg^(0)adsorption from syngas. This work represented a facile and practical pathway for utilizing cheap and eco-friendly tea waste to control the Hg^(0)emission.

Multi-fluid Eulerian simulation of mixing of binary particles in a gas-solid fluidized bed with a cohesive particle-particle drag model

A particle-particle(p-p)drag model is extended to cohesive particle flow by introducing solid surface energy to characterize cohesive collision energy loss.The effects of the proportion of cohesive particles on the mixing of binary particles were numerically investigated with the use of a Eulerian multiphase flow model incorporating the p-p drag model.The bed expansion,mixing,and segregation of Geldart-A and C particles were simulated with varying superficial velocities and Geldart-C particle proportions,from which we found that the p-p drag model can reasonably predict bed expansion of binary particles.Two segregation types of jetsam-mixture-flotsam and mixture-flotsam processes were observed during the fluidization processes for the Geldart-A and C binary particle system.The mixing processes of the binary particle system can be divided into three scales:macro-scale mixing,meso-scale mixing,and micro-scale mixing.At a constant superficial velocity the optimal mixing was observed for a certain cohesive particle proportion.