脱硝粉煤灰特性对水泥混凝土性能的影响及其机理

The ammonia-nitrogen is remained in coal ash because of denitration applied in thermal power plant, the properties of fly ash as mineral admixtures and itself were changed due to the existence of ammonia-nitrogen, and there are frequent problems due to its qualitative change, which impeded the utilization in building materials and reduced the project quality of concrete materials. Based on the investigation of formation mechanism, existence, properties and content of ammonia-nitrogen in fly ash, and the properties of denitration fly ash and concrete, focusing on the mechanism, behavior, influencing factor, the influence of ammonia release and retained ammonium on the performance of denitration fly ash was systematically investigated. comparing with the effect of normal fly ash on concrete performance, more special is the ammonia releasing of denitration, the effect of the formation rate and release rate of ammonia, the ratio of released and retained ammonium, the properties of pores and its migration rate on concrete performance was firstly investigated in this project, which would ascertain the influence and mechanism of denitration fly ash on cement and concrete performance. This research provided a theoretical reference for the threshold of ammonia-nitrogen and control measure of the denitration fly ash of the utilization in building materials.

燃煤电厂烟气脱硝使粉煤灰含有氨氮物质，氨氮物质的存在使粉煤灰自身和作为水泥混凝土掺合料的性质发生变化，因性质变化的未知而使粉煤灰应用于水泥混凝土中问题频出，阻碍了粉煤灰的资源化利用和严重影响了混凝土材料的工程质量。项目在研究脱硝粉煤灰中氨氮物质（氨或铵盐）的形成机理、存在状态、含量性质及其影响因素的基础上，根据脱硝粉煤灰的特性和水泥混凝土特点，以脱硝粉煤灰中氨氮物质与水泥混凝土作用产生氨气释放与铵盐留存的作用机理、行为规律、影响因素为主线，研究脱硝粉煤灰在水泥混凝土中氨气释放与铵盐留存对其性能的影响；相对于研究混凝土其他原材料对其性能影响更为特殊和重要的，创新地研究氨气释放中氨气反应生成与释放的速率、释放与留存比例、氨气气泡性质和迁移速率对混凝土性能的影响；以此探明脱硝粉煤灰对水泥混凝土性能影响规律和作用机理，为制定粉煤灰在水泥混凝土资源化利用的氨氮含量阈值和调控措施提供理论参考。

脱硝粉煤灰在实际应用生产中出现混凝土塌落度损失加剧，异常凝结和强度下降等问题，为解决其问题，保障工程安全，研究脱硝后粉煤灰性质变化和脱硝粉煤灰对水泥混凝土性能影响，主要包括：脱硝后粉煤灰性质变化、脱硝粉煤灰中氨氮物质的存在形式及检测方法优化、脱硝粉煤灰中氨在水泥中释放行为、脱硝粉煤灰对水泥混凝土水化及性能影响、脱硝粉煤灰中NH4HSO4与碱金属硫酸盐对水泥性能影响对比研究、脱硝粉煤灰中氨的调控措施。.选取15个电厂30种不同粉煤灰，其中脱硝粉煤灰27种，3种未脱硝粉煤灰，发现正常脱硝工艺下，脱硝后的粉煤灰化学成分除SO3外，均在已有统计数据内，脱硝粉煤灰中含有氨氮物质，且pH下降。其中，SO3的含量在0.44%~2.6%，部分超出SO3统计范围（0%~1.1%），脱硝粉煤灰中氨含量为0.016%-0.043%，主要集中在0.02%左右，超细粉煤灰pH值降低至为6，略小于统计值8-12。.根据脱硝工艺和研究结果，脱硝粉煤灰中氨氮物质存在形式是NH4HSO4、(NH4)2SO4和脱硝还原剂氨，其中以NH4HSO4为主。利用蒸馏滴定法和和纳氏试剂分光光度法检测脱硝粉煤灰氨含量，检测效率较低，对上述进行优化，该研究成果已在相应1项国家标准和多部行业标准中应用。同时研发出汽提定氨仪，能更方便且快速检测脱硝粉煤灰中氨含量，已用于实践，并申请专利2项。.脱硝粉煤灰中氨在水泥释放主要集中在水泥水化前48h，持续时间达7d。外掺氨含量2000mg/kg内时，对水泥混凝土性能无明显影响。与碱金属硫酸盐相比，NH4HSO4会降低水泥强度，延长凝结时间等，主要是NH4HSO4中NH4+的作用。为了降低异常脱硝工艺下的脱硝粉煤灰对水泥混凝土性能不利影响，脱硝粉煤灰中氨的调控措施则尤为重要，采用高温灼烧法、加碱-加水-加热法和恒温恒湿处理等方法调控脱硝粉煤灰中氨含量，加碱-加水-加热法中的炒制法调控效果最好，发现升高温度和改善空气流通情况能有效除氨，利用该原理对燃煤电厂提出了输送热空气除氨的技术方案，效果显著。