Experiments were conducted under a hot condition of bituminous coal ignition in a 250 kW pilot-scale bias combustion simulator. The effects of the primary air velocity (PAV) on the ignition characteristics of bias pulverized coal jets in a reducing atmosphere were investigated to develop a better new burner for experimental bituminous coal. Multiple means of measurement and sampling were used for the axial and radial temperatures, flame spectrum, flue gas components, and residual solid inside the furnace. The standoff distance changed nonmonotonically between axial distances of 90 and 330 mm with increasing PAV and was shortest for a PAV of 16 m/s. The radiation heat transfer from the hot environment had more effect on the ignition than the convection heat transfer from high-temperature flue gas in the initial stage, while the convection heat transfer from the high-temperature flue gas played a greater role in the subsequent combustion of the char. At PAVs of 13 and 16 m/s, there was volatile and char homogeneous–heterogeneous combined ignition and one-mode combustion; at PAVs of 20 and 23 m/s, there was volatile-phase homogeneous ignition and two-mode combustion. The ignition of the fuel-rich jet lagged that of the fuel-lean jet at a PAV of 13 m/s. A PAV that is lower could not take advantage of bias pulverized coal combustion technology. The ignition of the fuel-rich jet was ahead of that of the fuel-lean jet at PAVs of 16, 20, and 23 m/s. At a PAV of 13 m/s, the position of stable ignition was the shortest, the temperature of stable ignition the highest, and the boundary of the stable flame the smallest. The PAV of 16 m/s provided the best ignition characteristics for bituminous bias pulverized coal jets, which is suitable to be selected as design PAV for the new burner development.

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Simulation of electronically nonadiabatic dynamics is an important tool for understanding the mechanisms of photochemical and photophysical processes. Two contrasting methods in which the electrons are treated quantum mechanically while the nuclei are treated classically are semiclassical Ehrenfest dynamics and trajectory surface hopping; neither method in its original form includes decoherence. Decoherence in the context of electronically nonadiabatic dynamics refers to the gradual collapse of a coherent quantum mechanical electronic state under the scrutiny of nuclear motion into a mixture of stable pointer states. This is modeled in the coherent switches with decay of mixing (CSDM) method by the decay of the off-diagonal elements of the electronic density matrix. Here, we present an implementation of CSDM in the SHARC program; a key element of the new implementation is the use of a different propagator than that used previously in the ANT program.

Direct dynamics by mixed quantum-classical nonadiabatic methods is an important tool for understanding processes involving multiple electronic states. Very often, the computational bottleneck of such direct simulation comes from electronic structure theory. For example, at every time step of a trajectory, nonadiabatic dynamics requires potential energy surfaces, their gradients, and the matrix elements coupling the surfaces. The need for the couplings can be alleviated by employing the time derivatives of the wave functions, which can be evaluated from overlaps of electronic wave functions at successive time steps. However, evaluation of overlap integrals is still expensive for large systems. In addition, for electronic structure methods for which the wave functions or the coupling matrix elements are not available, nonadiabatic dynamics algorithms become inapplicable. In this work, building on recent work by Baeck and An, we propose new nonadiabatic dynamics algorithms that only require adiabatic potential energies and their gradients. The new methods are named curvature-driven coherent switching with decay of mixing (κCSDM) and curvature-driven trajectory surface hopping (κ TSH). We show how powerful these new methods are in terms of computation time and accuracy as compared to previous mixed quantum-classical nonadiabatic dynamics algorithms. The lowering of the computational cost will allow longer nonadiabatic trajectories and greater ensemble averaging to be affordable, and the ability to calculate the dynamics without electronic structure coupling matrix elements extends the dynamics capability to new classes of electronic structure methods.

Experiments with a small-scale furnace for a down-fired pulverized-coal 300-MWe utility boiler were carried out on a single-phase test facility to investigate the influence of different secondary air distributions on the aerodynamic field in the furnace. When the secondary air flux of tier E increased within a suitable range, it did not reverse the fuel-rich flow or shorten the residence time of coal particles in the furnace. Industrial experiments were also performed on a full-scale boiler. The gas temperature distribution along the primary air and coal mixture flow and in the furnace, and gas components such as O2, CO, CO2, and NO x in the near-wall region, were measured with damper openings of the E-tier secondary air box at 0% and 30%. At 0%, ignition of the primary air and pulverized coal mixture was delayed and the gas temperature peak was above the burner arch, with high NO x emission. Increasing the damper opening to 30% provided the oxygen necessary for the initial combustion. This was advantageous for stable combustion and also lowered NO x emissions and carbon content in the fly ash.