Consequences of CO₂ solubility for hydrate formation from carbon dioxide containing water and other impurities

Abstract

Deciding on the upper bound of water content permissible in a stream of dense carbon dioxide under pipeline transport conditions without facing the risks of hydrate formation is a complex issue. In this work, we outline and analyze ten primary routes of hydrate formation inside a rusty pipeline, with hydrogen sulfide, methane, argon, and nitrogen as additional impurities. A comprehensive treatment of equilibrium absolute thermodynamics as applied to multiple hydrate phase transitions is provided. We also discuss in detail the implications of the Gibbs phase rule that make it necessary to consider non-equilibrium thermodynamics. The analysis of hydrate formation risk has been revised for the dominant routes, including the one traditionally considered in industrial practice and hydrate calculators. The application of absolute thermodynamics with parameters derived from atomistic simulations leads to several important conclusions regarding the impact of hydrogen sulfide. When present at studied concentrations below 5 mol%, the presence of hydrogen sulfide will only support the carbon-dioxide-dominated hydrate formation on the phase interface between liquid water and hydrate formers entering from the carbon dioxide phase. This is in contrast to a homogeneous hydrate nucleation and growth inside the aqueous solution bulk. Our case studies indicate that hydrogen sulfide at higher than 0.1 mol% concentration in carbon dioxide can lead to growth of multiple hydrate phases immediately adjacent to the adsorbed water layers. We conclude that hydrate formation via water adsorption on rusty pipeline walls will be the dominant contributor to the hydrate formation risk, with initial concentration of hydrogen sulfide being the critical factor.

Water-wetting surfaces as hydrate promoters during transport of carbon dioxide with impurities

“…1 At this stage, no attempts have been made to tune the model empirically to fit experimental data available in the open literature. The free energies of CO 2 inclusion can be found in Kvamme et al 18,19 Hydrogen sulfide, a well-known and extremely vigorous hydrate-former was considered to be one of the impurities likely to significantly impact the process of hydrate formation during pipeline transport. Since the molecular interaction model for CO 2 in this work is different from that of Kvamme and Tanaka, 1 new free energy of inclusion function parameters for this model, as well as for the H 2 S model, have been estimated and listed in Table 1 below (complementary to Table 5 of Kvamme and Tanaka 1 ).…”

“…7,8,10,[18][19][20][21] Most hydrate risk evaluation tools are based on liquid water formation through eqn (4) and subsequent hydrate formation together with hydrate formers from the carbon dioxide phase. Further progress towards hydrate can continue both at the interface between water and carbon dioxide and from hydrate formers dissolved in water.…”

Simulation-based techno-economic evaluation for optimal design of CO 2 transport pipeline network

“…The presence of the impurities may result in the formation of gaseous CO 2 or two-phase CO 2 flow inside the pipelines. The water content in the CO 2 stream results in the risk of hydrate, which will pose a complex problem involving phase transient and pipeline blockage [13,[15][16]. Therefore, before the transport, the CO 2 stream has to be conditioned to remove impurities such as water vapour, H 2 S, N 2 , methane, O 2 , hydrocarbons and free water [17][18].…”

PVTx measurements of mixed clathrate hydrates in batch conditions under different crystallization rates: Influence on equilibrium

“…Furthermore, concerns have been raised about the kinetic effects on clathrate hydrates formation and composition. Kvamme et al [22] reported that mixed gas hydrates might not be theoretically reached at equilibrium by reassessing the Gibbs phase rule and the laws of thermodynamics.…”