Discharges of treated process water from a carbon capture plant to the Eidangerfjord.

Summary

Norcem in Brevik is selected by Norwegian authorities as test facility for full scale carbon capture. Aker Solution's amine technology is selected for capture and purification of carbon dioxide (CO2). Captured CO2 from the plant will be transported by ships as liquefied gas to facilities in Øygarden. The CO2 will then be piped out for storage in geological formations southeast of the Troll field. Flue gas from the CO2 capture plant will condensate and be purified in a treatment plant before it is mixed with cooling water (sea water from the Eidangerfjord) and discharged via a diffuser at 40 meters depth in the Eidangerfjord. The cooling water will have a volume flow of 3 400 m3/h, while treated condensate will have a volume flow of 6 m3/h. Dilution, neutral buoyancy of the plume (initial dilution), and dispersion of the process water were estimated using the model tool Visual Plumes. The process water contains dust, total organic carbon (TOC), SO2, NOx (mainly NO), metals (including mercury) and dioxins. The volume flow from the treatment plant is significantly less than the volume flow from the cooling water. As a result, the treated condensate is diluted approximately 600x before it reaches the diffuser. The initial dilution is estimated to be at 30- and 40-meters depth, and below the euphotic zone. The probability that the process water will reach the surface is small. At 30- and 40-meters depth (initial dilution), the dilution is 30-50x. At 500 meters from the diffuser, the dilution is estimated to be 50-110x. Elevated concentrations of mercury, dioxins and other pollutants in sediment and biota are the reason why the Eidangerfjord and Langesundsfjord do not achieve good chemical status in accordance with the Water Framework Directive. In the Langesundfjord, moderate ecological status is achieved due to reduced secchi depth and elevated concentration of nitrate. As a result of high dioxin concentrations, warnings on consumption of certain species of seafood have been issued in the Eidangerfjord and Langesundsfjorden. Annual discharges of 271 kg of dust and 632 kg of TOC per year will have a negligible effect on the background concentrations of these substances, and the fluxes (kg/year) in such a large coastal water body as the Eidangerfjord. More information on the chemical composition of the TOC fraction should nevertheless be obtained. Discharges of acidifying substances are assumed to have marginal effects on biota and water chemistry. Expected changes in pH below 0,2 units will be within natural variations. Information on the eutrophic state in the Eidangerfjord is incomplete. It is supposed that the discharges of NOx are converted to NO3 in the water column. The discharge of NOX will not change the background concentrations of NO3-N in the Langesundsfjord, and ecological status is not expected to deteriorate further.