Reduction Of CO2 Emissions By Carbonation Of
Alkaline Wastewater
Author(s)
M. Uibu, O. Velts, A. Trikkel & R. Kuusik
Abstract
In energy production based on combustion of fossil fuels, particularly the lowgrade
ones (lignite, sulphur-rich coal, oil shale etc.), huge amounts of alkaline
wastewater are formed. This situation is characteristic for the Republic of
Estonia where 59% of the need in primary energy was covered by local oil shale
in 2006. Due to the calcareous origin of the mineral part of oil shale, its
combustion yields lime-containing ashes (5–6 million tons annually, containing
10–25% of lime as free CaO) as well as enhanced amounts of CO2 (up to 29.1 t
C per TJ energy produced) as compared to coal combustion. To transport the ash
into wet open-air deposits, a hydraulic system is used. As a result tens of
millions of cubic meters of alkaline water (pH level 12-13) saturated by Ca2+-
ions is recycling between the plant and sedimentation ponds. Before directing
excessive water to nature it should be neutralized to a pH level accepted by
environmental regulations (< 9). Related to this, the current work was targeted to
develop possibilities for neutralizing wastewater with CO2-containing flue gases,
leading to reduction of CO2 emissions. Intensification of respective
heterogeneous gas–liquid reactions and characterization of calcium carbonate
(PCC) forming were other objectives of the study.
A cycle of laboratory-scale neutralization experiments using industrial
wastewater samples and a model gas of flue gas composition has been carried
out. Two different reactors – barboter-type columns and a dispergator-type phase
mixer – have been comparatively examined. Sedimentation of PCC particles of
rhombohedral crystallic structure has been shown and their main characteristics
have been determined. A neutralization method having up to fifty times higher
specific intensity has been proposed. According to calculations 970–1010 tons of
CO2 can be trapped and 2200–2300 tons of PCC per million cubic meters of
water can be obtained.
Keywords: carbon dioxide, alkaline wastewater, Ca-compounds, carbonation,
precipitated calcium carbonate.
Keywords
carbon dioxide, alkaline wastewater, Ca-compounds, carbonation,
precipitated calcium carbonate.
Related Book
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