University of Bergen, Norway
Title: Impact of solid surface adsorption on hydrate formation risk evaluation
Biography: Bjørn Kvamme
Hydrocarbons being transported in pipelines will always contain some dissolved water. High pressures and low temperature involves a risk of hydrate (ice-like crystals contain up to 14% CH4) formation. The traditional way to calculate the risk of hydrate formation and the corresponding level of water content that can be permitted before transport has been to calculate water dew-point and the checking if presence of liquid water would lead to hydrate formation at the conditions of temperatures and pressures at these conditions. Pipelines being used for hydrocarbon are, however, normally covered by rust even before they are placed out. One of the most stable iron oxide in rust is Fe2O3. This mineral is a very good adsorption material for water and will as such represent another route for the water to drop out from hydrocarbon mixtures. The chemical potential of water adsorbed on rust can be 3.4 kJ/mole lower than chemical potential of liquid water at relevant conditions. In this study we have examined maximum water content which can be permitted in mixtures of CH4 and C2H6 when considering adsorption drop out versus drop out as liquid water. For CH4 contacting water the tolerance limit based on liquid water drop out is found to be in the order of 26 times higher than corresponding limit based on rust adsorption, for temperature 275 K and pressures between 50 and 250 bars. Similar ratios are also found for pure C2H6 and a mixture of CH4 with 20% C2H6. As a consequence the hydrate risk analysis needs to be revised in order to reflect the most preferred routes for water drop out from gas.