城市干污泥与水葫芦的混燃特性分析

对广州城市干污泥与水葫芦的单一及混合样进行了热重实验,通过TG-DTG曲线计算了不同焚烧条件下其混燃特性指数,建立了其掺烧的动力学方程.结果表明,污泥单独燃烧曲线分为水分析出、挥发分的析出和燃烧、次挥发分及固定碳的燃尽、残留物的燃烧和分解4个过程,其中,挥发分的析出和燃烧是污泥燃烧的主要控制阶段;水葫芦的燃烧则分为水分析出、挥发分析出燃烧、固定碳燃烧、残留物质的燃烧和分解.污泥添加10%~40%水葫芦后,其燃烧性能得到改善,其中,着火点Ti有所升高,挥发特性指数D及综合燃烧特性指数S分别增加了0.22~1.06、0.10~0.92倍.随着水葫芦的添加量增加,污泥挥发分析出及燃烧更加激烈,污泥和水葫芦混燃过程中出现较强的协同交互作用.相对于空气气氛,在富氧(V(CO2)/V(O2)=8/2)条件下,混合试样的燃烧受到抑制.采用积分法(Coats-Redfern方程)计算得到污泥的质量平均表观活化能(Em)在32.09~34.70 k J·mol-1之间,水葫芦的Em在30.56~51.63 k J·mol-1之间,而混合试样的Em在22.44~28.40 k J·mol-1之间,污泥与水葫芦混燃其Em有所降低,与燃烧特性指数的增加是相对应的.第一挥发分峰前取n=0.5、第一挥发分峰后及其他峰取n=2可描述各燃烧阶段的反应机理.

Analysis of co-combustion characteristics of sewage sludge and water hyacinth

The combustion characteristics of dry sludge, water hyacinth and their blends in Guangzhou were investigated under different combustion conditions by thermogravimetric analysis (TGA). The kinetic equation of each sample was established by using the TG-DTG curves. Results obtained from TGA tests indicated that there were four combustion steps for sludge samples, i.e. moisture exhalation, exhalation of main volatile, exhalation of minor volatile and fixed carbon combustion, and residues decomposition. Thermal tests of water hyacinth were corresponding to moisture exhalation, exhalation of main volatile, fixed carbon combustion and residues decomposition. Thus, volatile exhalation stage was considered as the dominating step of the combustion in this experiment. After adding 10%~40% of the water hyacinth, the ignition point T_i of mixed sludge increased slightly.The combustion performance was improved with volatile characteristic index D and comprehensive combustion characteristic index S increased by 0.22~1.06 and 0.10~0.92 times, respectively. Both volatile exhaling and combustion behavior levels in sludge acted intensively with water hyacinth addition, which illustrated a synergistic interaction and co-combustion of sludge and water hyacinth. In comparison with the ambient air, combustion characteristics of mixtures were restrained in the oxy-fuel environment with V(CO₂)/V(O₂) of 8/2. The corresponding kinetics parameter (E_m) was calculated by using Coats-Redfern equation calculations. E_m of the sludge, water hyacinth, and their blends were in the range of 32.09~34.70 kJ·mol^-1, 30.56~51.63 kJ·mol^-1, and 22.44~28.40 kJ·mol^-1, respectively. The activation energy decreased with the addition of water hyacinth as represented by the increase of comprehensive combustion index in the blends. Thus, the reaction orders of pre-peak of the first volatile combustion can be described as n=0.5, while the post-peak and other peaks were both suggested as n=2.