Estimation of CO2 emission in reservoir coupling floating chamber and thin boundary layer methods

Abstract

With the growing development of hydropower projects all over the world, the excessive greenhouse gas (GHG) emissions from increasing reservoirs have drawn public concern. While precise evaluations of GHG emissions are urgently needed, the widely applied methods including floating chamber (FC) method and thin boundary layer (TBL) method are unsatisfactory. In this paper, a new methodology of estimating CO₂ emission coupling FC and TBL methods was proposed. Three efforts were achieved stepwise:1) the CO₂ transfer coefficient was determined combining the measurements of FC method and TBL model; 2) a semi-empirical model connecting gas-water transfer coefficient and near-surface water turbulence in reservoir was proposed; 3) finally, since surface turbulence in the reservoir could be describe in detail by numerical simulation, integration thousands of discrete cells of local fluxes could be applied to estimate the total CO₂ emission with an improved precision. Nine locations in Xiangjiaba Reservoir were selected as a demo study for applying the method, the CO₂ emission in the whole reservoir was about 1.37 kg/s. With a deeper insight into the law of gas transfer and an elaborate consideration of the whole reservoir, this study is expected to provide a new approach and technical support to estimate the CO₂ emissions accurately in reservoirs.

Keywords: Gas transfer; Greenhouse gas emission; Integration; Numerical simulation; Surface turbulence.