污泥与煤在CO2/O2及N2/O2气氛条件下的混燃特性分析

采集了广州具有代表性的市政污泥,利用热重法对单一污泥、煤及其混合样品在CO_2/O_2及N_2/O_2气氛条件下进行了TG(热重)实验,同时计算了污泥和煤的4个燃烧特性指数,获得了燃烧的动力学参数.实验结果表明,污泥燃烧有4个燃烧阶段,包括水分析出、挥发分析出与燃烧、固定碳的燃烧和无机盐类挥发分解,其中,挥发分析出与燃烧是污泥燃烧的主要阶段;煤掺烧污泥可以提高煤的着火性能.在CO_2/O_2及N_2/O_2燃烧气氛下,增加O_2浓度,污泥与煤混合样的热重曲线整体向低温区移动,微商热重曲线峰值增大,峰宽变小,燃烧性能增强.在CO_2/O_2气氛下,O_2浓度从30%增加到60%时,污泥的挥发分释放特性指数D、可燃性指数C、燃尽指数Cb、综合燃烧特性指数S分别增加了45%、12%、18%、6%.相同O_2浓度条件下,污泥与煤在CO_2/O_2气氛下的着火性能较N_2/O_2气氛滞后,最大峰值变小,高浓度的CO_2抑制其混合样的燃烧.采用Coats-Redfern方程计算得到3个燃烧阶段反应的动力学参数,其中,增加O_2浓度,污泥与煤混合样品的质量平均表观反应活化能Em减小,并且O_2浓度越高越有利于燃烧反应的进行.污泥与煤混合燃烧取n=2可以对挥发分燃烧与固定碳燃尽峰峰前与峰后的反应模型进行描述.

Co-combustion characteristic of sewage sludge and coal under CO2/O2 and N2/O2 atmosphere

Sewage sludge and coal were collected in Guangzhou, both of these materials and their mixtures were estimated by thermogravimetric analysis (TGA) under different CO₂/O₂ and N₂/O₂ atmosphere conditions in this study. Four combustion characteristic indexes and their kinetic parameters were also calculated. Experimental results obtained from TGA tests showed there were four combustion steps for sludge samples including moisture exhalation, volatile exhalation and combustion, fixed carbon combustion and exhalation of inorganic salt. Results found that the process of volatile exhalation and combustion was the control step of the whole combustion. On the other hand, with the increasing of O₂ concentration under CO₂/O₂ and N₂/O₂ atmosphere, TG curves of the mixture samples were tended to migrate into the low temperature area, and combustion performance enhanced while the maximum value of DTG peak increased and also peak width decreased. Nevertheless, volatile combustion characteristic index D, parameters of the flammability index C, burnout index C_b and comprehensive index of combustion characteristics S were all calculated and observed an increasing level of 45%, 12%, 18%, 6%, respectively. With the same concentration of O₂, the combustion performance of mixture samples under CO₂/O₂ atmosphere is lower than those in N₂/O₂ atmosphere according to maximum DTG peak variation. Higher concentrations of CO₂ would inhibit the combustion performance of mixtures. Besides, application of the Coats-Redfern equation in this study achieved the understanding of both reaction equations and the kinetic parameters (E) during various combustion stages. The calculation results found that this model can fit the experimental results of before or after volatile combustion and fixed carbon burnout peaks of the sample combustion when n value is equal to 2.