基于矩阵描述的燃烧温度对秸秆灰肥性影响的平衡和动力学研究

Potassium fertilizer import costs billions of yuan in our country annually due to the 50% shortage of them. The large amount of potassium (10-30%) and a certain amount of various nutrients in straw ash make it of great significance for the recirculation of the ash as fertilizer to maintain the agro-ecosystem and to reduce the cost of agricultural production. However, the lack of the evaluation and measurement methods of the fertilizer property and the little knowledge on the effect of combustion temperature would hinder the development of the recirculation technology. In this project, the effect of combustion temperature on fertilizer property of straw ash based on matrix description is proposed to be investigated according to the characteristics of straw ash and the adoption of the concepts of equilibrium and kinetics in the relative fields. A fertilizer property matrix will be developed using the water-soluble, weak acid-soluble and strong acid-soluble content of nutrients as matrix elements. And a fast accurate measurement method will be established in line with the modern detection techniques of ash and the norms of fertilizer detection. Full factorial experiments of ashes from corn stover, wheat straw and rice stalk will be performed and equilibrium and kinetics correlations matrix will be established. The microstructure, chemical composition and element content of ash from different conditions will be analyzed to study the mechanisms the transformation of the fertilizer property. The application of the transformation kinetics of the fertilizer property will be explored by the modeling and experiments of corn-stover-pellet combustion in a vertical tube reactor. The project will lay a theoretical foundation for the sustainable application of straw as energy and fertilizer.

我国50%的钾肥依赖进口，年耗资数十亿元。秸秆灰含有钾(10-30%)及多种营养元素，用作肥料对生态保护和农业生产成本降低意义重大。针对灰肥应用目前缺乏肥性表征体系和肥性受燃烧温度影响规律不明确等问题，本项目根据秸秆灰肥特点、参考相关领域平衡和动力学概念，提出采用矩阵描述来研究燃烧温度对秸秆灰肥性影响的平衡和动力学规律。将建立以秸秆灰各营养元素的水溶、弱酸溶、强酸溶含量为矩阵元素的矩阵式肥性表征方法，并结合秸秆灰现代分析手段和化肥标准，建立矩阵参数快速准确的测定方法。将通过对玉米秸、麦秸、稻秸灰的完全要因实验，构建3种灰肥性变化的平衡和动力学方程式矩阵。并通过研究肥性变化与灰微观尺寸、营养元素赋存形态变化等的关系，探索肥性变化机理。将通过玉米秸成型燃料在管式炉燃烧后肥性的模拟和实验，研究肥性动力学方程矩阵在燃烧过程分析上的应用。项目成果为秸秆作为能源和肥料应用的可持续技术开发奠定理论基础。

经济清洁地应处理秸秆等农林废弃物和供给农村生产生活分布式用热是我国农村面临的两大问题。应用分散燃烧秸秆技术进行分布式供热，并实施灰肥还田，能同时解决这两个问题并实现农业生态可持续。然而，秸秆灰和灰中钾含量高，目前借鉴煤燃烧所用的高温(>800°C)锅炉技术，常使秸秆灰成分变化和逸出，导致灰肥失效产生固渣，设备粘污降低热效率，故障多增加维护费用。.为解决该问题，本项目研究了燃烧温度对秸秆灰化肥特性影响的规律和机理。首先，参考分析生物质灰使用的浸出试剂和检测化肥使用的溶出试剂等，建立了以生物质灰肥中主要营养元素的去离子水、0.5mol/L的乙酸铵和乙酸混合液和2%的柠檬酸溶解含量为矩阵元素的肥性矩阵，表征含量大于1%的营养元素及其总量和速效、缓效、长效释放量。其次，测定了秸秆粉体、秸秆成型颗粒在管式炉（500-900°C）燃烧灰化肥特性随燃烧温度的变化，发现粉体燃烧所得灰在600-700°C间，肥性下降显著。成型颗粒燃烧时内部温度和炉膛温度差异明显。通过对生物质及灰中钾赋存状态和变化的实验，发现秸秆中氯化钾和硫酸钾在680°C共熔，以及低温燃烧产生灰中的氯化钾在700-900°C的蒸发逸出是灰肥失效和设备粘污的主要原因。通过对氯化钾、氯化钾+二氧化硅、氯化钾+生物质灰，氯化钾+硫酸钾，生物质水溶物的热分析，结合拉瓦尔定律建立了灰中氯化钾逸出过程的物理数学描述，建立了集中熔化和分散熔化后蒸发模型，编程计算并实验验证了钾逸出规律。另外，实验和理论分析了灰成型时成型尺寸及压强对其营养元素释放的影响。发现成型后释放速率降低一个数量级，玉米秸灰初始释放速率高于麦秸灰。.在上述研究基础上，提出秸秆固相低温、气相高温燃烧技术，固相低温由堆积阴燃实现。该技术可实现气体排放高于欧洲生物质锅炉标准，供暖价格低于传统煤供暖价格，灰肥100%还田，实现秸秆经济、清洁、可靠、生态可持续供热。