秸秆类生物质基添加剂在粉煤气流床气化中的作用机制

Entrained-flow gasifiers are all slagging gasifiers. To meet the need of slagging, a large number of coals with high ash fusion temperature are usually either added the addition of flux or blended with low ash fusion temperature coals during gasification, which not only increases the consumption of raw materials but also may result in equipment block-up. Biomass has higher reaction activity and lower ash fusion temperature because of the high content of alkali metals like potassium and natrium and alkali earth metals like calcium and magnesium. Making full use of this feature of biomass, it is proposed that biomass is used as additive of entrained-flow pulverized coal gasification, which not only efficiently reduces gasification temperature and promotes slagging but also provides a new technical approach for large scale, high efficient, clean and economic utilization of biomass. Combining characteristics of entrained-flow pulverized coal gasification and physicochemical properties of biomass, the research focuses on the following contents: dense-phase pneumatic conveying laws of large difference binary mixed particles, ash-forming mechanism and slag characteristic during co-gasification. Based on above researches, the action mechanism of straw biomass-based additives used in entrained-flow pulverized coal gasification was elucidated. The researches are of obvious innovation, and they have positive significance for enrichment and improvement of entrained-flow gasification technology and gas-solid phase theory. Moreover, preliminary works have laid a solid foundation for completion of the project.

气流床煤气化技术普遍采用液态排渣，为满足此要求，大量高灰熔点煤在实际气化应用中常需添加钙基等助熔剂或配入低灰熔点煤，不仅在一定程度上增加了原料和能量消耗，甚至可能因为灰分量的增大而导致气化后续设备的堵塞。秸秆类生物质因富含碱金属和碱土金属，气化活性高、灰熔融温度低，本项目充分利用这一特点，将其作为粉煤气流床气化的添加剂，不仅可有效降低煤气化温度、促进气化炉液态排渣，而且也为生物质的大规模、高效、清洁、经济利用提供了一条新的技术途径。本项目围绕粉煤气流床气化的特点和秸秆类生物质的物理化学特性，重点研究煤与秸秆类生物质混合颗粒密相气力输送规律；煤与秸秆类生物质在气流床共气化过程中的成灰机理及熔渣特性，揭示秸秆类生物质基添加剂在粉煤气流床气化中的作用机制。这些研究创新性明显，对丰富和完善气流床气化和气固两相流领域的基础理论有重要意义。前期工作已为完成项目打下坚实基础。

本项目充分利用生物质与煤在物理特性和气化性能方面的互补性，从资源可持续发展、能源清洁高效利用、环境保护的角度出发，提出在粉煤中掺入秸秆类生物质基添加剂以实现气流床共气化的工艺思想，对拓展气流床气化原料煤的适应性、实现生物质的清洁高效利用具有重要意义。项目围绕生物质与煤干法气流床共气化所涉及的关键科学问题，重点研究了生物质与煤混合颗粒的密相气力输送规律，煤与秸秆类生物质在气流床共气化过程中的成灰机理及熔渣特性。这些研究创新性明显，对丰富和完善气流床气化和气固两相流领域的基础理论有重要意义。. 研究结果表明：(1)随着掺混稻草质量分数的增大，混合颗粒松装密度与振实密度均减小，混合颗粒的休止角变大，混合颗粒的空隙率减小，混合颗粒基本流动能增加，混合颗粒的稳定性都较好，流动速率指数先增大后减小，通气比增大。(2)毫米级秸秆类生物质颗粒加入煤粉等粘性颗粒后，可有效改善其流动性，基于此提出了“针状颗粒效应”，并建立了预测生物质与煤混合颗粒重力下料速率的经验模型；当生物质颗粒的添加比例小于25%时，可有效提高煤等粘性颗粒的下料流率和下料稳定性。(3)当秸秆类生物质掺混比例≤10%时，可实现生物质与煤混合颗粒的稳定输送，并且输送过程中二者未发生明显离析。(4) 添加秸秆类生物质均能有效地降低高灰熔点煤的灰熔融温度；碱酸比在0.5-3.0时煤和生物质的混合灰具有较低的流动温度。(5)添加稻草明显促进了神府煤的灰沉积效率，气化温度越低，促进作用越明显；气化温度相同时，随着稻草添加量的增加，共气化灰的沉积效率先增大后降低。(6) 稻草的添加明显促进了煤的转化；稻草掺混比例达10%时，生物质与煤气流床共气化运行稳定，对气化结果无明显影响，但气化灰渣中钾、钙和氯等元素的含量明显增加。. 项目研究达到了既定的研究目标，取得了预期的研究结果，为生物质的大规模、高效、清洁、经济利用探索了一条新的技术途径。项目发表SCI收录论文4篇，申请专利1项，培养研究生3名。