Mathematical modelling of MSW incineration on a travelling bed.
Mathematical modelling of MSW incineration on a travelling bed.
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DOI：
10.1016/s0956-053x(02)00019-3
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发表时间：
2002-07
期刊：
影响因子：
8.1
通讯作者：
Y. Yang;Y. R. Goh;Ridzuan Zakaria;V. Nasserzadeh;J. Swithenbank
中科院分区：
文献类型：
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作者：
Y. Yang;Y. R. Goh;Ridzuan Zakaria;V. Nasserzadeh;J. Swithenbank
城市固体废物（MSW）焚烧的日益普及需要对焚烧过程进行详细的数学建模和理解。本文描述了固体废物焚烧炉移动床中固相和气相的质量、动量和传热的控制方程，并提出了相关的子模型。固体移动床中挥发性碳氢化合物的燃烧速率不仅受到反应动力学的限制，而且还受到挥发性燃料与燃烧空气的混合的限制。混合速率是整个计算单元的平均值，并与许多参数相关，包括床的局部空隙率、气体速度和与床中颗粒尺寸相当的长度尺度。还包括一个相关方程来计算紧邻床面的干舷区域的混合。建造了一个小型固定床垃圾焚烧炉并进行了试运行，测量了床层的总质量损失、沿床层高度不同位置的温度和气体成分。开发了二维床建模程序 (FLIC)，该程序包含各种子过程模型并求解气体和固体的控制方程。热和化学过程主要限制在厚度约为燃烧床平均颗粒尺寸 5-9 倍的层内。在燃烧过程的大部分时间里，总质量损失率保持恒定，直到固体废物完全干燥，随后出现一段二氧化碳排放量大幅上升的时期。最高床温约为1200 K。整个燃烧过程在60分钟内结束。由于沟道和随后当地床层条件的“灾难性”变化，观察到物种浓度的大幅波动。建模和测量之间已经实现了相当好的一致性。然而，由于床内的窜流现象，建模工作变得复杂。不考虑沟道效应的数值模拟与总质量损失的实验非常一致，但温度和气体成分分布存在显着差异。废物焚烧过程中发生的诸如废物颗粒破碎和新燃烧通道“灾难性”产生等瞬态现象是需要在基础层面进行进一步研究的重要领域。床行为的基本理论必须扩展以包括这些瞬态事件。
The rising popularity of incineration of municipal solid waste (MSW) calls for detailed mathematical modelling and understanding of the incineration process. In this paper, governing equations for mass, momentum and heat transfer for both solid and gaseous phases in a moving bed in a solid-waste incineration furnace are described and relevant sub-models are presented. The burning rates of volatile hydrocarbons in the moving bed of solids are limited not only by the reaction kinetics but also the mixing of the volatile fuels with the under-fire air. The mixing rate is averaged across a computation cell and correlated to a number of parameters including local void fraction of the bed, gas velocity and a length scale comparable to the particle size in the bed. A correlation equation is also included to calculate the mixing in the freeboard area immediately next to the bed surface. A small-scale fixed bed waste incinerator was built and test runs were made in which total mass loss from the bed, temperature and gas composition at different locations along the bed height were measured. A 2-D bed-modelling program (FLIC) was developed which incorporates the various sub-process models and solves the governing equations for both gases and solids. Thermal and chemical processes are mainly confined within a layer about 5–9 times in thickness of the averaged particle size in the burning bed. For a large part of the burning process, the total mass loss rate was constant until the solid waste was totally dried out and a period of highly rising CO emission followed. The maximum bed temperature was around 1200 K. The whole burning process ended within 60 min. Big fluctuations in species concentration were observed due to channelling and subsequent ‘catastrophic’ changes in the local bed conditions. Reasonably good agreement between modelling and measurements has been achieved. Yet the modelling work is complicated by the channelling phenomenon in the bed. Numerical simulations without consideration of the channelling effect produced very good agreement with experiments concerning the total mass loss, but significant discrepancy exists for temperature and gas composition profiles. Transient phenomena such as the breaking of waste particles and the “catastrophic” creation of new burning channels occurring during waste incineration is a vital area requiring further investigation at the fundamental level. The underlying theory of bed behaviour must be extended to include these transient events.