“碳达峰”和“碳中和”背景下，了解高碱燃料中碱金属赋存方式及其热化学转化有利于更好地利用高碱固体燃料，减少其使用过程中引起的结焦结渣以及受热面腐蚀等安全问题，增加其适用范围，也可以推动煤炭、生物质等高效和清洁利用工艺的发展。

目前生物质燃烧过程中各种化学形式的钾的异相释放过程的详细反应机制鲜有报道。同时，热工设备中碱金属的原位测量对高碱燃料催化气化的优化控制、颗粒物调控以及结焦结渣控制有着重要意义。为此本文首先利用可调谐半导体激光吸收光谱技术（TDLAS）定量在线测量了在平面火焰燃烧器上麦秸颗粒空气燃烧、富氧燃烧过程中不同赋存形态的钾（水溶态无机钾、可交换态钾、酸溶性有机钾）的释放特征。同时考虑到钾的释放过程与颗粒本身燃烧过程的强耦合关系，在进行钾的在线检测时，还记录了颗粒自身燃烧特性，包括恒温热重曲线、430 nm窄带光谱时序图像、可见光时序录像、颗粒表面附近温度。结果表明：无论是空气燃烧还是富氧燃烧，酸溶态有机钾的释放过程（开始时间、峰值时间、结束时间）几乎与挥发分的燃烧过程完全重合，虽然指前因子可能不同，但酸溶态有机钾的活化能可能与挥发分释放动力学参数相近。无机钾和可交换钾的最大释放速率发生于焦炭燃烧的初期。在燃料干燥过程中，酸溶态有机钾几乎不释放，无机钾释放的持续时间比可交换态钾长，且其释放速率峰值出现在挥发分着火之后。富氧环境对无机钾在干燥阶段的异相释放的抑制作用较大，对无机钾在焦炭燃烧阶段的抑制作用过程次之，而对无机钾在挥发分燃烧阶段的异相释放的影响最弱。结合不同赋存形态钾的释放曲线、生物质颗粒燃烧特性以及不同赋存形态钾的理化特性，本文确定了不同赋存形态钾的详细异相释放动力学参数，并将其结合在生物质单颗粒燃烧模型上，模型预测结果与实验在线检测有良好的匹配性。

除了颗粒状生物质外，粉末状的生物质也有广泛应用场景。为了在更真实的高速、旋流环境下讨论生物质粉体燃料燃烧时钾的释放特性，本文搭建了可视化中心送粉式管状火焰燃烧器系统，结合高速成像和TDLAS技术，深入讨论管状火焰燃烧器中生物质及其焦炭粉末的燃烧特性以及钾的释放特性，为真实场景中生物质粉末状燃料燃烧及其碱金属释放特性提供进一步可靠数据。实验结果发现，去离子水萃取后的麦秸和稻壳的相应着火时间都有所增加。通过实验还发现，生物质粉末在管状火焰燃烧器中的着火模式属于非均相-均相联合着火，生物质焦炭粉末则为非均相着火。在生物质粉末的燃烧进程中只出现了一个K(g)浓度释放峰，且其峰值对应于生物质粉末的均相-非均相联合着火阶段。不论是麦秸粉末还是稻壳粉末燃烧时，释放出来的K(g)峰值位置都要提前于最大自发辐射光强时刻，烘焙后的生物质粉末燃烧时释放出来的K(g)大幅度减少；水洗焦炭燃烧时释放出来的K(g)峰值比对应原始焦炭浓度下降，但峰值出现的位置提前。

为了明晰碱金属在高碱煤中具体化学结合方式，利用¹³C交叉偏振魔角旋转核磁共振（¹³C-NMR）、傅里叶红外光谱（FT-IR）、²³Na交叉偏振魔角旋转核磁共振（²³Na-NMR）、X射线光电子能谱（XPS）和逐级萃取实验结合计算化学阐明准东煤的结构特征和碱金属赋存特性，并进行了分子重构，从微观结构水平上研究了准东煤中碱金属的赋存状态、分布特征。结果显示，绝大部分无机钠以水合离子的形式存在，而小部分以NaCl晶相形式存在。准东煤的无定形晶胞分子式为(C₂₀₈₀H₉₈₀O₃₈₀N₃₀S₁₀Na)_n。典型的五彩湾准东煤中含氧官能团中67.7%为羟基（乙氧基），15.5%为羰基，其余的16.8%为羧基。结合²³Na CP/MAS NMR和逐级萃取实验，有机钠占总钠的18.01%。大多数无机钠（81.99%）以水合离子钠的形式存在（75.08%），而一小部分以氯化钠晶相（3.34%）的形式存在，不溶性钠占3.57%。结合准东煤分子模型表面静电势分布，负静电势区域为有机钠最大概率吸附位点，该位置的钠原子可以与附近的羧基、羰基氧等形成多齿螯合配位键。在所提出的含碱准东煤大分子模型中，靠近羧基的最高负电势区可以归结为有机钠的吸附点，附近的羟基或苯氧基会与钠形成配位键，同时该模型的¹³C-NMR、FT-IR、²³Na-NMR理论计算光谱与实验光谱吻合良好。

采用ReaxFF分子动力学模拟方法，在分子水平上研究了典型五彩湾准东煤恒温热解过程中钠的迁移转化机理，通过对原子运动轨迹以及原子间键的形成和断裂的跟踪，分析了煤分子恒温热解反应过程中的迁移转化机制，结果发现：具有三维网状结构的煤分子上的本征有机钠并不稳定，在热解一次反应阶段，钠原子会与煤分子中的氧原子形成二元配位或多元配位结构，煤分子上化学键较弱的氧原子首先被钠捕获，进而释放出NaOH(g)或Na(g)。在热解的二次反应阶段，这些钠原子、NaOH分子会与煤分子基质不断地“交互”反应，形成络合物。较高热解温度时，有机钠的存在促进了CO的形成，且温度继续升高，这种促进作用更明显，有机钠对水分子的生成有微弱的促进作用；较低热解温度时，有机钠的存在减少了水分子的生成，抑制了CO的生成。较低模拟温度范围内，有机钠会抑制C₂H₂的生成，温度继续升高，钠对C₂H₂的生成几乎没有影响。

Under the goal of "peak carbon dioxide emissions" and "carbon neutrality", understanding the occurrence mode and thermochemical transformation of alkali metals in high-alkali fuels is beneficial to better use of high-alkali solid fuels, reduce the safety problems such as coking and slagging and heating surface corrosion caused by their use, increase their application scope, and promote the development of efficient and clean utilization technologies such as coal and biomass. At present, the detailed reaction mechanism of heterogeneous release of various chemical forms of potassium during biomass combustion is rarely reported. Measuring the alkali metal of in-situ industrial hot standby is of great significance to the optimal control of catalytic gasification, the control of particulate matter and the real-time control of coking and slagging.

The detailed reaction mechanism for the heterogeneous release of potassium in various chemical forms during biomass combustion were rarely reported. In this work, time-resolved release characteristics of different occurrence forms of potassium during the combustion of wheat straw pellet were recorded using the TDLAS (Tunable diode laser absorption spectroscopy) system. Combined with the time-resolved release curves, biomass’s combustion characters, and the physicochemical properties of potassium species, a more detailed solid-phase potassium release model for different occurrence forms of potassium was then developed. The results showed that: peak moment of organic potassium release arrived almost simultaneously with the peak release of volatiles and both stopped at the same time. The maximum emission rates of inorganic and exchangeable potassium occurred at the onset of char combustion. Unlike the release of organic and exchangeable potassium in the drying process, the release process of inorganic potassium is longer and the peak of the release rate occurs after the volatile ignition. The heterogeneous release of inorganic potassium during the drying process is more inhibited by an oxygen-rich environment than it is by the heterogeneous combustion of inorganic potassium during the char combustion process, and the heterogeneous release of K(g) from inorganic potassium during the volatile's combustion is less affected. The simulated potassium release results agree well with online detection experiment, which is useful for providing the initial boundary conditions for the simulation of gas-phase potassium species transformation.

In addition to granular biomass, powdered biomass has also been widely used. In order to discuss the release characteristics of potassium during the combustion of biomass powder in a more realistic high turbulence environment, a visual tubular burner system with central jet powder feeding mode was constructed, and the combustion characteristics and potassium release characteristics of biomass and char powder under high turbulence are discussed in depth, providing more reliable data for biomass powder combustion and alkali metal release in real scenes. According to the experiment findings, deionized water extraction, the ignition delay of both rice husk and wheat straw powder was increased. In the tubular burner, the biomass powder undergoes a joint hetero-homogeneous ignition, whereas the bio-char powder undergoes a heterogeneous ignition. There is only one K(g) concentration release peak during the combustion of biomass powder, and this peak corresponds to the combined hetero-homogeneous combustion stage of pulverized biomass. Whether it is wheat straw powder or rice husk powder, the peak moment of K(g) released during combustion is ahead of the moment of light intensity of the flame produced by its combustion, and the K(g) released during combustion of the baked biomass powder is substantially reduced. The peak value of K(g) released during the combustion of water-washed char is lower than that of the corresponding original char, but the peak appears earlier.

Detailed intrinsic sodium occurrence for future research on migration, release, and catalyst effect behavior of sodium is necessary. Complementary characterizations, such as ¹³C CP/MAS NMR (¹³C ross-polarization and magic angle pinning nuclear magnetic resonance spectroscopy), FT-IR (Fourier Transform Infrared Spectroscopy), ²³Na CP/MAS NMR, XPS (X-ray Photoelectron Spectroscopy), elemental composition analysis, and sequential extraction experiments, were employed to elucidate the actual compound form of sodium as well as Zhundong coal’s structural features. Thus, a molecular occurrence model of sodium in Zhundong coal was constructed based on its structural characteristics via computational chemistry. The occurrence model of alkali metals in Zhundong coal, including their compound form, relative content, and distribution properties, was investigated at the microstructural level. Preliminary results show that the amorphous cell formula of Zhundong coal is (C₂₀₈₀H₉₈₀O₃₈₀N₃₀S₁₀Na)_n. Organic oxygen in Zhundong coal was 67.7% hydroxyl (ethoxy), 15.5% carbonyl, and the remaining 16.8% was attributed to carboxyl. Combined with the ²³Na CP/MAS NMR and sequential extraction experiment, organic sodium accounts for 18.01% of the total. Most inorganic sodium (81.99%) is present as hydrated sodium ion (75.08%), while a small part is present as NaCl crystal phase (3.34%) insoluble-sodium account for 3.57%. Calculated ¹³C NMR, FT-IR, and ²³Na CP/MAS NMR spectra of the proposed model agree well with the experimental spectra suggesting that the molecular occurrence model of sodium in Zhundong coal is a particularly convincing model in the approximate condition of statistical average. The highest negative electrostatic potential area is near the carboxyl group and may be attributed to organic sodium absorption sites; the hydroxy or phenoxy group nearby may form additional coordination bonds to sodium, indicating the reflection of the complexity of the Na chemical environment as concluded from ²³Na CP/MAS NMR.

The migration and transformation mechanism of intrinsic organic sodium in the thermostatic pyrolysis process of Zhundong coal was investigated at the molecular level by tracking the atomic motion trajectories and the formation and breaking of interatomic bonds using ReaxFF. It has been discovered that the intrinsic organic sodium on coal molecules with three-dimensional mesh structures is unstable. As a result, during pyrolysis, sodium atoms will form binary coordination or multiple coordination structures with oxygen atoms in coal molecules. First, sodium will capture oxygen atoms on coal molecules with weaker chemical bonds, which will then release NaOH(g) or Na(g). Na(g) and NaOH(g) that were produced during the primary reaction stage of pyrolysis would continually "collide" with the coal molecular matrix during the secondary reaction stage. The synthesis of water molecules was inhibited by the presence of organic sodium in the temperature range of 1800 K–3000 K, and it was only marginally promoted at 3200 K by the presence of sodium. When the temperature was between 1800 K and 2800 K, the presence of sodium prevented the creation of CO. However, when the temperature was raised to 3000 K, the presence of sodium encouraged the formation of CO, and this encouragement became more prominent as the temperature rose. When the temperature was simulated to be between 2000 K and 2800 K, organic sodium prevented the synthesis of C₂H₂, and when the temperature was simulated to be between 3000 K and 3200 K, sodium had absolutely little impact.