Marginal gas fields containing large concentrations of CO2 is a technical challenge to develop due to the low CO2 concentration requirement in the sales gas. One of the CO2 - Natural Gas separation methods being studied to develop the field is to use phase separation method in separating CO2 with natural gas. The principle of these gas separations units lies in the cryogenic sciences in the separation unit, causing condensation (and crystallization) of CO2 out of the mixture. Therefore, it is important to understand the concept of nucleation of CO2 to properly design the gas separation units.

An adiabatic expansion experiments is performed in pulse expansion wave tube (PEWT) (1, 2 &3). In this experimental set-up, CO2 nucleation is induced in a high-pressure expansion wave tube, where rapid controlled pressure and temperature decrease is induced. The nucleation is measured by means of laser scattering and extinction signals. Moreover, the onset of crystallization can be measured if the expansion is sufficiently deep for the liquid droplets to evoke liquid-solid transition. Similarly, a new parallel experimental set-up was commissioned to allow for more experimental runs per day. Gas mixture in Expansion Chamber (PEC) is brought into nucleation by subjecting it to a sudden change in temperature and pressure. When temperature continues to decrease, the solid-liquid saturation curve in the phase diagram is passed, and crystallization occurs. In this way the experimental setup open the possibility to determine Wilson points, crystallization points, and nucleation rates for multi-component gas mixtures. The onset of nucleation, crystallization, and the measurement of droplet growth is measured by means of laser light transmission and scattering.

In both set-ups temperatures below -100°C is reached. Experiments in both setups for CO2 in NG mixture confirmed theoretical temperature predictions. The results are comparable to the nucleation theory which predicts the onset of nucleation and nucleation delay. These parameters are then used to design CO2 - Natural Gas Separation devices.

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