流化床燃烧稻草床料聚团及灰行为

流化床燃烧生物质发电是生物质能利用的重要技术,但床料聚团影响系统的稳定运行。该文使用石英砂流化床在760℃燃烧稻草,研究床料聚团机理和生物质灰行为。实验结果表明:床料发生了严重的聚团,床层流化状态明显恶化;碱金属在床料颗粒表面富集,在床料颗粒表面形成了约5μm厚的灰层。K2O-CaO-SiO2三元系相图可以有效解释床层中融化物的出现。聚团机理可概括为:由于稻草灰熔点低,燃烧的半焦表面变粘,粘结床料颗粒产生聚团;通过与细灰碰撞、融化的碱金属化合物冷凝,床料颗粒表面形成一层均匀的灰层并融化,当灰层足够厚时,床料颗粒通过有限的点粘结在一起,也会形成聚团。

Bed agglomeration and straw ash behavior during fluidized bed combustion of rice straw

Power generation with biomass through direct combustion in fluidized bed boilers is an important bioenergy utilization technology,but bed agglomeration affects stable operation of the systems.Rice straw was burn in a fluidized bed at 760 ℃,using quartz sand as the bed,to study the bed agglomeration mechanism and biomass ash behavior.The experimental results show that severe bed agglomeration occurs with reduced fluidization with concentrated alkali on the bed particle surfaces and a 5 μm ash coating on the particle surfaces.Melting in the bed can be explained by the phase diagram of the K2O-CaO-SiO2 ternary system.The agglomeration occurs due to the low melting point of the straw ash which causes the surfaces of the burning char to become sticky at high temperatures,so the char bonds with the bed particles to form agglomerates.The melting ash homogeneously coats the bed particles through collisions between the bed particles and the fine ash and condensation of the melting alkali.When the coats are thick enough,adhesion forces cause the quartz particles to bond together at same points,which also results in agglomeration.