Enrichment of inorganic trace pollutants in re-circulated water streams from a wet limestone flue gas desulphurisation system in two coal power plants

Control of Hg0 re-emission from gypsum slurries by means of additives in typical wet scrubber conditions

“…In the first case, oxidized mercury may be reduced by the aqueous S(IV) species (sulfite and/or bisulfite) resulting from the absorption of SO 2 in the slurry [17]. In the second case, if the liquid fraction of the limestone slurry is recirculated, high concentrations of mercury may accumulate throughout the system giving rise to a new risk [18]. The last option appears to be the most suitable for desulphurization system which dispose of solid products at landfill sites if the spread of mercury is to be avoided.…”

Evaluation of a Flue Gas Desulphurisation (FGD)-Gypsum from a Wet Limestone FGD as Adsorbent for Removal of Selenium in Water Streams

“…Because coal-combustion processes are well evaluated, general trends in trace element behaviour during combustion have been identified [1][2][3][4][5][6][7][8][9]. It is common knowledge that many of the trace elements from coal are partially or totally vaporised during combustion.…”

“…The degree of vaporisation determines how each element is partitioned between various solid residues and the flue gas [1]. Selenium during Pulverised Coal Combustion (PCC) can be released as gas SeO 2 and/ or as particulate Se [7][8][9]. However, when the flue gas cools down some of gas SeO 2 may condense on the finest particle surfaces of Fly Ashes (FAs).…”

“…Most of FAs are captured in cleaning systems by high-efficiency particulate collector devices, though some particulate Se may escape from controls and reach Flue Gas Desulphurisation (FGD) system. Once in FGD, gas SeO 2 and particulate Se may be dissolved in the aqueous phase of absorber slurries and/or concentrated in the gypsum sludge [7][8][9]. Depending on the abatement capacity of FGDs, a given proportion of Se can be released in a gaseous and/or PM form [8,9].…”

“…In FGD systems under operational conditions of water recirculation to the scrubber, inorganic trace pollutants initially in subsaturation in FGD waters may reach equilibrium and a subsequent saturation in the water stream after a number of water re-circulations in the scrubber [7]. The gradual increase in the concentration of inorganic trace pollutants from the sub-saturation to equilibrium and/or saturation because of continuous water re-circulation in the scrubber, accounts for enriched inorganic trace pollutants in the recirculated water [7] which could result in environmental (pollution of soil and groundwater) and technical problems (fouling of scrubber and pipes of the FGD), especially, if the re-circulation of the water streams is interrupted and/or a water treatment is necessary for hypothetical and eventual discharges to the environment.…”