Department of Energy, Politecnico di Milano, Via Lambruschini 4, 20156 Milan, Italy.
Waste Manag. 2011 Sep-Oct;31(9-10):2074-84. doi: 10.1016/j.wasman.2011.05.013.
This article is part of a set of six coordinated papers reporting the main findings of a research project carried out by five Italian universities on "Material and energy recovery in Integrated Waste Management Systems (IWMS)". An overview of the project and a summary of the most relevant results can be found in the introductory article of the series. This paper describes the work related to the evaluation of mass and energy balances, which has consisted of three major efforts (i) development of a model for quantifying the energy content and the elemental compositions of the waste streams appearing in a IWMS; (ii) upgrade of an earlier model to predict the performances of Waste-to-Energy (WtE) plants; (iii) evaluation of mass and energy balances of all the scenarios and the recovery paths considered in the project. Results show that not only the amount of material available for energy recovery is significantly higher than the Unsorted Residual Waste (URW) left after Separate Collection (SC), because selection and recycling generate significant amounts of residues, but its heating value is higher than that of the original, gross waste. Therefore, the energy potential of what is left after recycling is always higher than the complement to 100% of the Source Separation Level (SSL). Also, increasing SSL has marginal effects on the potential for energy recovery: nearly doubling SSL (from 35% to 65%) reduces the energy potential only by one fourth. Consequently, even at high SSL energy recovery is a fundamental step of a sustainable waste management system. Variations of SSL do bring about variations of the composition, heating value and moisture content of the material fed to WtE plants, but these variations (i) are smaller than one can expect; (ii) have marginal effects on the performances of the WtE plant. These considerations suggest that the mere value of SSL is not a good indicator of the quality of the waste management system, nor of its energy and environmental outcome. Given the well-known dependence of the efficiency of steam power plants with their power output, the efficiency of energy recovery crucially depends on the size of the IWMS served by the WtE plant. A fivefold increase of the amount of gross waste handled in the IWMS (from 150,000 to 750,000 tons per year of gross waste) allows increasing the electric efficiencies of the WtE plant by about 6-7 percentage points (from 21-23% to 28.5% circa).
本文是一组六篇协调论文的一部分，报告了由意大利五所大学开展的“综合废物管理系统（IWM）中的物质和能量回收”研究项目的主要发现。项目概述和最相关结果的摘要可在该系列的介绍性文章中找到。本文介绍了与评估质量和能量平衡相关的工作，主要包括三个方面：（i） 开发一种模型，以量化 IWMS 中出现的废物流的能量含量和元素组成；（ii） 升级早期模型以预测废物转化能源（WtE）工厂的性能；（iii） 评估项目中考虑的所有情景和回收途径的质量和能量平衡。结果表明，不仅可用于能源回收的物质数量明显高于单独收集（SC）后留下的未分类残余废物（URW），因为选择和回收会产生大量残渣，而且其热值高于原始总废物。因此，回收后剩余物质的能源潜力始终高于 100%源分离水平（SSL）的补充。此外，SSL 的增加对能源回收的潜力影响不大：将 SSL 几乎翻一番（从 35%增加到 65%）只会减少四分之一的能源潜力。因此，即使在 SSL 较高的情况下，能源回收也是可持续废物管理系统的基本步骤。SSL 的变化确实会导致送入 WtE 工厂的物质的组成、热值和水分含量发生变化，但这些变化（i）比预期的要小；（ii）对 WtE 工厂的性能影响不大。这些考虑表明，SSL 的单纯价值不是废物管理系统质量及其能源和环境结果的良好指标。鉴于众所周知的蒸汽动力厂效率与其功率输出的依赖性，能源回收的效率关键取决于为 WtE 厂提供服务的 IWMS 的规模。IWMS 中处理的总废物量增加五倍（从 150,000 吨/年增加到 750,000 吨/年）可使 WtE 厂的电能效率提高约 6-7 个百分点（从 21-23%提高到约 28.5%）。
