焦炭燃烧是燃煤电厂锅炉中煤粉燃烧的主要过程，其燃烧过程由动力燃烧区、扩散/动力区和扩散控制区组成，其中以扩散/动力区的燃烧过程及机理最复杂，影响焦炭燃烧的数值模拟精度。为进一步提高燃煤电厂锅炉侧数值模拟精度，对FLUENT自带模型、改进的随机孔模型及已有的焦炭燃烧改进模型进行了综述与横向对比。结果表明：FLUENT自带模型未考虑实际燃烧时灰分对氧气扩散的影响，造成数值模拟与工程实际差别较大；基于改进的随机孔模型，认为温度是导致扩散区中氧气难以与焦炭接触的原因，但并非根本因素；现有模型普遍未考虑工程实际中燃用劣质煤种时内表面积对反应速率的影响，造成低转化率阶段预测值与实际值偏差较大；考虑灰层扩散阻力缩核模型的应用时，应先比较燃用煤种的软化温度与燃烧温度，且考虑热失活和多孔碳球内表面积；热失活和灰分抑制模型应采用更适宜的灰分抑制模型，提高模型预测精度；目前基于FLUENT对燃煤锅炉其他问题进行数值模拟时，均采用误差很大的扩散/动力模型，后续研究中采用改进后的焦炭燃烧模型是重要研究方向。

Coke combustion is the main process of pulverized coal combustion in coal-fired power plant boilers, and its combustion process consists of power combustion zone, diffusion/dynamic zone and diffusion control zone, among which the combustion process and mechanism in the diffusion/dynamic zone are the most complicated and often affect the accuracy of numerical simulation of coke combustion. To further improve the accuracy of the numerical simulation on the boiler side of coal-fired power plants, the FLUENT self-contained model, the improved random hole model and the existing improved model for coke combustion were reviewed and compared. The results show that the self-contained model of FLUENT does not consider the influence of ash on oxygen diffusion during actual combustion, resulting in large differences between numerical simulation and engineering practice.Based on the improved random pore model, it is considered that temperature is the reason for the difficulty of oxygen contact with coke in the diffusion zone, but it is not the fundamental factor.The existing models generally do not consider the influence of internal surface area on the reaction rate when burning poor quality coal in engineering practice, resulting in large differences between predicted and actual values at the stage of low conversion rate.In the application of nucleation model considering the diffusion resistance of ash layer, the softening temperature of combustion coal with the combustion temperature should be compared first, and the consideration of thermal deactivation and the internal surface area of porous carbon spheres should be considered.The thermal deactivation and ash suppression model should adopt a more suitable ash suppression model to improve the accuracy of model prediction.At present, in the numerical simulation of other problems of coal-fired boiler based on FLUENT, the diffusion/dynamic models with large errors are used, and the adoption of improved coke combustion models in subsequent studies is an important research direction.

0 引言

1 基于扩散/动力区域的研究

   1.1 FLUENT自带扩散/动力模型

   1.2 基于扩散/动力区的随机孔模型

2 考虑灰层扩散阻力的焦炭缩核模型的研究

   2.1 基于灰阻缩核模型的数值模拟研究

   2.2 基于灰阻缩核模型的试验研究

3 基于热失活和灰分抑制修正的焦炭燃烧模型

4 结语与展望