Combustion Process Of Pulverized Coal Research Articles

Numerical investigation using two different CFD codes of pulverized-coal combustion process characteristic in an industrial power plant boiler

Steam boilers using the coal as a basic fuel are still one of the most important techniques used to generate electricity in Power Plants. Many activities connected with optimization of steam boilers operation, investigation of combustion efficiency using different fuels, control and reducing pollutants emission are observed. Numerical modeling of large steam boilers using Computational Fluid Dynamic method can be a very way to develop and verify effects of all activities regarding combustion process optimization. Numerical modeling results of the coal combustion process in the front wall coal-fired boiler are presented in the paper. The behavior of the flow of pulverized coal through the burners was analyzed, and the temperature and velocity distribution in the combustion chamber were reproduced in the simulation. Despite the fact that the attention has been focused on boiler simulation at nominal load, it is possible to perform numerical studies concerning the analysis of coal combustion at different boiler loads (minimum load and flexible boiler operation). Analysis of different fuels and their impact on the combustion process, as well as analysis of coal mills operation, coal particles size distribution and they impact on boiler operation can be performed using developed models.

The dynamic model of pulverized coal and waste plastic bonded together in flight combustion process

A mathematical model was established which describes the co-combustion of pulverized coal (PC) and polyethylene particles (PEP) in this study. The model was designed to be incorporated into an overall model simulating PC and PEP process. The combustion model of PC and PEP takes into account the principal physical and chemical phenomena occurring during the pyrolysis and combustion of PC and PEP blend combustion, namely, mass transfer toward and exterior the grain, volatile combustion of PC and PEP, combustion of fixed carbon. Particular care has been taken in the determination of the thermophysical and kinetic parameters necessary for the model. Thus the pyrolysis and combustion kinetics for PC and PEP were determined by thermogravimetry. In order to simulate the flight co-combustion process of PC and PEP blend, the true conversion rates during combustion process of PC and PEP were measured as a function of temperature. The numerical model, calculates the temperature, composition, and mass flow rates of the PC and particles evolved at each point in the grain at any instant of time. In the end, the combustion model has proved to be valid by the comparison between calculated and measured data of the co-combustion process of PC and PEP.

Numerical investigation on the flow, combustion, and NOX emission characteristics in a 660 MWe tangential firing ultra-supercritical boiler

A three-dimensional numerical simulation was carried out to study the pulverized-coal combustion process in a tangentially fired ultra-supercritical boiler. The realizable k- ε model for gas coupled with discrete phase model for coal particles, P-1 radiation model for radiation, two-competing-rates model for devolatilization, and kinetics/diffusion-limited model for combustion process are considered. The characteristics of the flow field, particle motion, temperature distribution, species components, and NOx emissions were numerically investigated. The good agreement of the measurements and predictions implies that the applied simulation models are appropriate for modeling commercial-scale coal boilers. It is found that an ideal turbulent flow and particle trajectory can be observed in this unconventional pulverized-coal furnace. With the application of over-fire air and additional air, lean-oxygen combustion takes place near the burner sets region and higher temperature at furnace exit is acquired for better heat transfer. Within the limits of secondary air, more steady combustion process is achieved as well as the reduction of NOx. Furthermore, the influences of the secondary air, over-fire air, and additional air on the NOx emissions are obtained. The numerical results reveal that NOx formation attenuates with the decrease in the secondary air ratio ( γ2nd) and the ratio of the additional air to the over-fire air ( γAA/ γOFA) was within the limits.

Development of Advanced Simulator for Desulfurization in the Pulverized Coal Combustion Process

An advanced simulator is newly developed to predict desulfurization behavior by direct injection of Ca fine particles in coal combustion furnaces. The Ca fine particles, the main component of which is CaCO3, are a byproduct of cement manufacturing process. This simulator is built on the coal combustion/gasification module based on the commercial computational fluid dynamics (CFD) software of STAR-CD V3.26. Regarding the desulfurization reaction model, it is based on two physical models of thermal decomposition reaction of CaCO3 and of desulfurization reaction by CaO. We improve both models in order to simulate desulfurization behavior of Ca fine particles in coal combustion furnaces. A case study is carried out with a bench scale experimental furnace. According to the comparison between calculated result and experimental one, this simulator can predict the tendency of the increase of desulfurization ratio with an increase of feeding rate of Ca fine particles and the influence of the temperature at injection part of Ca fine particles. Moreover, the calculated result shows that the desulfurization reaction does not finish in the boiler and it continues at the exhaust pipe, since the Ca fine particle’s temperature in the pipe is still higher than 1073 K. As a consequence, this simulator well predicts the tendency of the desulfurization process successfully and can be used for improvement of the operation condition of the furnaces.

Numerical Simulations of Combustion Characteristics and NO x Emissions for Two Configurations of Swirl Coal Burners in a 300 MWe Wall-Fired Boiler

We studied both experimentally and numerically the pulverized-coal combustion process and NO x emissions in a 300 MWe wall-fired boiler burning bituminous coal. In simulations of an enhanced ignition-dual register (EI-DR) burner arrangement, results gave values of 6.39% and 861.43 mg/m3 at 6% O2 for combustible material content in the fly ash and NO x concentration at the furnace outlet, respectively. Meanwhile, simulations with a centrally fuel rich (CFR) swirl burner arrangement gave similar results of 3.63% and 695.36 mg/m3 at 6% O2. Comparing the two, the NO x concentration of the latter had decreased by 19.28%.

Improving Combustion Characteristics and NOx Emissions of a Down-Fired 350 MWe Utility Boiler with Multiple Injection and Multiple Staging

Within a Mitsui Babcock Energy Limited down-fired pulverized-coal 350 MW(e) utility boiler, in situ experiments were performed, with measurements taken of gas temperatures in the burner and near the right-wall regions, and of gas concentrations (O(2) and NO) from the near-wall region. Large combustion differences between zones near the front and rear walls and particularly high NO(x) emissions were found in the boiler. With focus on minimizing these problems, a new technology based on multiple-injection and multiple-staging has been developed. Combustion improvements and NO(x) reductions were validated by investigating three aspects. First, numerical simulations of the pulverized-coal combustion process and NO(x) emissions were compared in both the original and new technologies. Good agreement was found between simulations and in situ measurements with the original technology. Second, with the new technology, gas temperature and concentration distributions were found to be symmetric near the front and rear walls. A relatively low-temperature and high-oxygen-concentration zone formed in the near-wall region that helps mitigate slagging in the lower furnace. Third, NO(x) emissions were found to have decreased by as much as 50%, yielding a slight decrease in the levels of unburnt carbon in the fly ash.

Numerical Simulation of Combustion Characteristics and NOx Emissions in a 300 MWe Utility Boiler with Different Outer Secondary-Air Vane Angles

We experimentally and numerically studied the pulverized-coal combustion process and NOx emissions for a 300 MWe wall-fired boiler burning bituminous coal. Measurements of the polar components of t...