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Ash formation under pressurized pulverized coal combustion conditions.

机译：在加压粉煤燃烧条件下形成灰烬。

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Coal combustion is a source of inorganic particulate matter (ash), which can deposit in boilers and also be emitted into the atmosphere becoming part of ambient fine particulate matter (PM 2.5). In order to decrease coal combustion emissions per unit of power produced, higher efficiency systems have been proposed, including systems operating at elevated pressures. These new operating conditions will affect pollutant formation mechanisms, particularly those associated with the conversion of mineral matter to ash. Ash particle formation mechanisms are particularly sensitive to changes in pressure as they are related to the structure of coal char particles at early stages of combustion.; To assess the importance of pressure on ash particle formation, pyrolyzed chars and ash particles from pressurized pulverized combustion of two bituminous and one subbituminous U.S. coals at operating pressures up to 30 atm were studied. Pressure changes the distribution of char particle types, changing the spatial distribution of the minerals during the combustion process and therefore affecting particle formation mechanisms. Chars were examined by Scanning Electron Microscopy (SEM) and classified into two different types (cenospheric and solid) depending on porosity and wall thickness. A correlation for estimating the amount of these cenospheric char particles was then proposed for bituminous coals based on the operating conditions and coal maceral analysis.; The ash particle size distribution of the coals combusted at different operating pressures was measured using Computer Controlled Scanning Electron Microscopy (CCSEM). The results of the char characterization and ash particle size distribution measurements were then incorporated into an ash particle formation algorithm that was proposed and implemented. The model predicts ash particle size and composition distributions at elevated pressures under conditions of complete char burnout. Ash predictions were calculated by first developing char structure distribution functions based on coal characteristics. To obtain an ash particle size distribution, carbon is then allowed to react away while following coalescence, fragmentation and other transformation processes as combustion proceeds. Particle size distributions calculated with this model showed qualitative agreement with the trends identified in the experimental portion of this research.
机译：燃煤是无机颗粒物（灰分）的一种来源，可以沉积在锅炉中，也可以排放到大气中，成为周围细颗粒物的一部分（PM 2.5）。为了减少单位发电量的燃煤排放，提出了更高效率的系统，包括在高压下运行的系统。这些新的运行条件将影响污染物的形成机制，特别是与矿物物质转化为灰分相关的那些机制。灰分形成机理对压力变化特别敏感，因为它们与燃烧早期的煤焦颗粒的结构有关。为了评估压力对形成灰分颗粒的重要性，研究了在最高30 atm的工作压力下对两种烟煤和一种亚烟煤的加压粉煤燃烧产生的热解焦炭和灰分。压力会改变炭颗粒类型的分布，从而在燃烧过程中改变矿物的空间分布，从而影响颗粒形成机制。通过扫描电子显微镜（SEM）检查炭，并根据孔隙率和壁厚将其分为两种不同的类型（空心和固体）。然后，根据操作条件和煤的宏观分析，提出了一种估计烟气中这些平流层炭颗粒数量的相关性。使用计算机控制扫描电子显微镜（CCSEM）测量在不同工作压力下燃烧的煤的灰分粒径分布。然后将焦炭表征和灰分粒度分布测量的结果合并到提出并实施的灰分形成算法中。该模型可预测在完全烧焦的条件下，在升高的压力下灰分的粒径和组成分布。通过首先根据煤的特性开发炭结构分布函数来计算灰分预测值。为了获得灰分的粒度分布，随着燃烧的进行，碳会发生反应，同时进行聚结，破碎和其他转化过程。用该模型计算出的粒度分布与本研究实验部分确定的趋势显示出定性的一致性。

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