Effect of Acid Gases on Elemental Mercury Removal in an Oxy-fuel CO₂ Compression Process

Abstract

Oxy-fuel combustion is considered as one of the most promising options for capturing CO2 from coal-fired power plants. Oxy-fuel flue gas contains traces of gaseous elemental mercury (Hg0) impurity, which accumulate in the CO2 compression units, causing severe damage to the aluminum heat exchangers. It is of great interest that the co-capture of flue gas impurities, such as nitrogen oxide (NO x ) and elemental mercury, could be achieved in a CO2 compression system at a high pressure. Currently, most of the studies associated with Hg0 removal were conducted on traditional gas-cleaning devices at atmospheric pressure. It has been demonstrated that both NO x and SO2 from flue gas played a significant role in Hg0 reactions at atmospheric pressure in O2/CO2 (oxy-combustion) or O2/N2 (air-fired) conditions. However, the effect of those acidic gases on elemental mercury removal in the oxy-fuel compression system at high pressures was unclear. In this work, gas-phase Hg0 oxidation by NO x and SO2 was experimentally performed at the simulated O2/N2 and O2/CO2 atmospheres at pressures up to 2.5 MPa. It was found that Hg0 removal was dependent upon the concentration of NO2 in flue gas and primarily achieved by gas-phase reactions between Hg0 and NO2. High pressure dramatically enhanced the oxidation of NO to NO2. Thus, the flue gas impurity Hg0 could be efficiently removed through reacting with NO2 in the CO2 compression purification units. SO2 hardly reacted with Hg0 but affected the reaction of Hg0 and NO2. The presence of SO2 inhibited mercury removal especially at high pressures because of the decreased NO2 concentration through the reaction with SO2 and the decomposition of HgO to Hg0 by SO2. The presence of CO2 made the Hg0 removal rate less dependent upon the pressure. The removal behavior of Hg0 in the O2/CO2 atmosphere was similar to that in the O2/N2 atmosphere at pressures lower than 1.0 MPa. With the increasing pressure, the removal rate of Hg0 in the O2/CO2 atmosphere was lower than that in the O2/N2 atmosphere.

Potential Synergy of Chlorine and Potassium and Sodium Elements in Carbonation Enhancement of CaO-Based Sorbents

“…Absorption, , adsorption, , chemical looping combustion (CLC), , membranes separation, , and cryogenic distillation are well considered as effective methods to isolate CO 2 from the atmosphere. Among them calcium looping (CaL), a typical absorption technique, has been considered as one of the most important technologies for CO 2 isolation.…”

NH4Br-Modified Biomass Char for Mercury Removal in a Simulated Oxy-fuel Atmosphere: Mechanism Analysis by X-ray Photoelectron Spectroscopy

“…However, Hg 0 is very difficult to be removed by current air pollution control devices (APCDs), because it has high volatility and low water solubility . Thus, the development of Hg 0 control technology is the essential problem to solve, especially for an oxy-fuel combustion system …”

Synergistic effect between H2O and SO2 on mercury removal by activated carbon in O2/CO2 conditions

“…also summarized recent work on mercury removal by modified adsorbents with a literature review. However, research into mercury control by activated carbon under oxy‐fuel combustion is still lacking in published reports . Note that H 2 O and SO 2 are much higher than those in air combustion due to the recycled flue gas, but there is little reported research into this.…”

“…However, research into mercury control by activated carbon under oxy-fuel combustion is still lacking in published reports. [17][18][19] Note that H 2 O and SO 2 are much higher than those in air combustion due to the recycled flue gas, 20 21 investigated the impact of H 2 O and other flue gases on mercury removal performance by sulfur-modified activated carbon under laboratory conditions. The results indicated that the sulfur-modified sorbent had greater mercury capacity than the raw sorbent, and the mechanism of Hg removal performance without H 2 O was different from that with H 2 O.…”

“…However, research into mercury control by activated carbon under oxy-fuel combustion is still lacking in published reports. [17][18][19] Note that H 2 O and SO 2 are much higher than those in air combustion due to the recycled flue gas, 20 but there is little reported research into this. Thus, it is important to www.soci.org H Wang et al…”