Removal of mineral matter and trace elements by chemical coal cleaning, and use of the reaction product as desulfurization agent

为了抑制煤燃烧过程中有毒杂原子的排放，重要的是要了解杂原子在燃烧过程中的存在方式和行为。在本项目中，我们的目标是提出抑制硫氧化物和有毒微量元素排放的方法。该项目的具体目标如下：1）通过简单的方法负载钙进行脱硫，2）使用石灰进行化学清洗以去除微量元素和矿物质，3）开发抑制微量元素排放的方法。研究结果表明：1）在煤中负载水合钙能有效地抑制燃烧过程中SOx的排放。与煤与石灰石的物理混合物的燃烧相比，SOx的排放水平低得多。2）石灰化学净化煤对B、F、Cd、As等微量元素的去除率可达70%左右。结果表明，微量元素的溶出率低于矿物质溶出率，表明存在有机伴生的微量元素。3）通过综合淋滤实验，对微量元素的赋存状态有了一些认识。本文提出了一种新的方法，即用HNO_3和HCl浸取煤焦和原煤，以阐明微量元素的赋存状态。结果表明，Pb、Cr和As在1100℃时挥发，且挥发行为强烈依赖于升温速率。升温速率对挥发的依赖性与高温区未燃碳的存在有关。最后，我们提出了一种方法来捕获的As通过其挥发行为的理解。

To suppress emission of toxic heteroatoms during coal combustion, it is important to understand the mode of occurrence and behavior of heteroatoms during combustion. In this project, we aim to propose the methods to suppress the emission of sulfur oxide and toxic trace elements. Detailed objectives of this project are as follow : 1) desulfurization by loading calcium with simple methods, 2) chemical cleaning using lime for removal of trace elements as well as mineral matter, And 3) development of method for suppression of trace elements emission. The following results were obtained from this project.1) SOx emission during combustion was effectively suppressed by loading hydrated calcium on coal. The level of SOx emission was much lower when compared with the combustion of the physical mixture of coal with limestone. Furthermore, desulfurization yield was increased when loading calcium under ultrasonic irradiation.2) Removal yields of trace elements such as B, F, Cd, and As by chemical coal cleaning with lime were attained to about 70%. The yield was not so high in comparison with that of mineral matter, indicating the presence of organically associated trace elements.3) Several insights on the mode of occurrence of trace elements were obtained by the comprehensive leaching experiments. We proposed a novel method, leaching of coal char as well as raw coal with HNO_3 and HCl, to elucidate the mode of occurrence of trace elements. We found that Pb, Cr and As were volatilized by heating up to 1100℃ and the volatilization behavior strongly depended on the heating rate. The heating rate dependency on the volatilization was related to the presence of unburnt carbon at high temperature region. Finally, we proposed a method for capture of As through the understanding of its volatilization behavior.