Emission of Organically Bound Elements during the Pyrolysis and Char Oxidation of Lignites in Air and Oxyfuel Combustion Mode

Abstract

This study aims to clarify the abundance of individual elements, particularly those in trace concentrations in lignites, and their emission dynamics during pyrolysis and char oxidation in both air and oxyfuel combustion modes. For this laboratory-scale study, the emission dynamics was represented by element release from the coal/char particle during thermal treatment in a drop-tube furnace. The main coal sample studied is a Victorian brown coal (VBC), which was compared with a Chinese lignite. Irrespective of elemental type, the VBC is rich in organically bound elements, which partly dissociated during the initial flash pyrolysis step. This dissociation extent varied broadly with elemental type. For element release during char oxidation, As release rates in both N 2 and CO 2 bulk gases were slower than char surface consumption rate, because of internal diffusion limitations and scavenging of a portion of As by Ca/Al/Fe-bearing discrete minerals. In contrast, the release rates of Pb from the char surface were faster than the carbon consumption rate. Releases of the remaining elements were simply in linear proportion to the char consumption rate for the two lignites studied, despite their differences in properties with no observable (element release) difference between air and oxyfuel combustion mode.

High-Phosphorus Fuel Combustion: Effect of Oxyfuel Conditions on PM10 Emission from Homo- and Heterogeneous Phases

“…As opposed to volatiles combustion in homogeneous phase, changing from air to oxyfuel combustion leads to substantial decreases of As and Cr in PM 1 formed during char combustion in heterogeneous phase. The observation is consistent with previous reports. , As aforementioned, the particle temperatures are estimated to be similar during air or oxyfuel combustion, so that the particle temperature is unlikely to be a factor responsible for such decreases in As and Cr in PM 1 . A plausible explanation is given as follows.…”

“…During char combustion, volatilized As needs to diffuse through the char structure before being released to the bulk gas phase, allowing it to react with and be stabilized by the ash layer on the char surface . Such reactions (e.g., those between volatilized As and Ca-/Al-/Fe-containing ash compounds) are reported to be enhanced under oxyfuel combustion conditions, hence leading to the reductions of As in PM 1 . Similarly, the reduction of Cr in PM 1 during char oxyfuel combustion can be attributed to the enhanced reactions between Cr and Fe-containing ash species to form FeCr 2 O 4 because such fixation reactions are known to be enhanced during oxyfuel combustion conditions .…”

A Comprehensive Review of Ash Issues in Oxyfuel Combustion of Coal and Biomass: Mineral Matter Transformation, Ash Formation, and Deposition

“…The behavior of organically bound elements during the pyrolysis and char oxidation of lignites in air and oxyfuel combustion was investigated on a drop-tube furnace (DTF) by Low et al 20 It was determined that most of the organically bound elements were only partially released during pyrolysis in pure N 2 , and the extent of their release was element-and coalspecific. During char oxidation in air and oxyfuel combustion (0−5% O 2 ), the release of elements was proportional to the char oxidation rate, which was facilitated by steam addition.…”

Ignitability and Combustibility of Yallourn Pyrolysis Char Blended with Pulverized Coal Injection Coal under Simulated Blast Furnace Conditions

“…A schematic drawing of the DTF setup can be found in previous work 19 . The sample enters the DTF with a low volume primary gas (1.0 L STD /min), while a secondary gas (9.0 L STD /min) is preheated to the furnace temperature and mixes with the coal or char at the injection point.…”