Mercury Emissions and Removal by Ash in Coal-Fired Oxy-fuel Combustion

Abstract

This paper presents results of experiments performed at a 20 kW once-through combustion rig of the Institute of Combustion and Power Plant Technology (IFK) of the University of Stuttgart. A methodology to investigate oxy-fuel process configurations was used in which impurities were injected to the oxidant gas of the once-through reactor to simulate different extents of oxy-fuel recycle gas treatment. Three Australian coals, which had previously been tested in the Aioi furnace of IHI in Japan, were used in the experiments. A comprehensive set of total (Hg tot ), elemental (Hg 0 ), and oxidized (Hg 2+ ) mercury concentrations was measured for various air and oxy-fuel combustion conditions. These data enable an evaluation of process parameters that influence the Hg emissions of an oxy-fuel combustion process. A theoretical mass balance between Hg fed to the process (fuel and Hg 0 injection) and Hg measured before the filter matched well, indicating that no mercury was captured by fly ash at high temperatures. The capture of Hg 0 and oxidized Hg 2+ by ash in a baghouse filter has been determined for all experiments. Measured Hg concentrations show an increase when switching from air to oxy-fuel operation for all investigated coals and oxy-fuel settings, even when no additional Hg 0 is injected to the oxidant gas. Moreover, the Hg 2+ /Hg tot ratios in the flue gas are higher during oxy-fuel combustion. The Hg capture by ash in the baghouse filter has been found to reduce the Hg emissions considerably. Reduction rates in a range between 18 and 51% for air and between 11 and 29% for oxy-fuel combustion were observed.

Oxyfuel combustion for CO2 capture in power plants

“…in form of HgCl 2 ) and can also be captured with the fly ash in filters and precipitators (Senior et al, 2000;Pavlish, 2009;Sliger et al, 2000;Wilcox et al, 2012). In the past years considerable efforts have been dedicated to clarify how Hg is released, oxidized and captured in air-fired power plants and how this can be influenced to reduce Hg emissions and results have been summarized in a number of reviews and articles (Pavlish et al, 2003(Pavlish et al, , 2010Pavlish, 2009;Wilcox et al, 2012;Scheffknecht et al, 2012;Kolker et al, 2006;Spörl et al, 2014a). The most important factors influencing the concentration levels, speciation and removal of Hg from flue gas in air fired combustion are the content of Hg and Cl (and Br) of the coal, the combustion conditions, the SO x concentrations and speciation, the properties of the generated fly ash (i.e.…”

Sulfur trioxide formation/emissions in coal‐fired air‐ and oxy‐fuel combustion processes: a review

“…However, on a normalized base (mass per energy unit), no difference was found between oxy‐ and air‐firing. Measurements of SO 3 were also undertaken at IFK in a 500 kW oxy‐PC combustor . In these tests, ESP was included along with SCR and the SO 3 sampling was made from the inlets and outlets of ESP and SCR.…”

“…Measurements of SO 3 were also undertaken at IFK in a 500 kW oxy‐PC combustor . In these tests, ESP was included along with SCR and the SO 3 sampling was made from the inlets and outlets of ESP and SCR. Roughly 62% SO 3 capture was noted in the SCR unit.…”

Oxyfuel derived CO2 compression experiments with NO , SO and mercury removal—Experiments involving compression of slip-streams from the Callide Oxyfuel Project (COP)

“…A summary of typical Hg concentrations is given on Table 1. Given that Hg concentrations exiting an oxy-fuel boiler are between 2.7 and 45 g/m 3 (Nelson et al, 2013;Spörl et al, 2014), this suggests that a significant level of cleaning is required prior to CO 2 liquefaction. It has been previously theorised that flue gas bourn mercury (present as Hg 0 ) will be absorbed in the nitric acid formed from compressing the raw CO 2 from an oxyfuel system (Allam et al, 2007).…”