Influence of CO2 Nucleation Rate towards Cryogenic Separation Technologies in Bulk CO2 Separation from Natural Gas

摘要

Marginal gas field 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 separation methods being studied to develop the field is to use phase separation technique 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 the nucleation of CO2 liquid and solid crystals in order to properly design the separation units. Adiabatic expansion experiments were performed in a pulse expansion chamber(PEC).The CO2 crystal nucleation was induced in a high-pressure expansion chamber,as being reflected by the rapid controlled pressure decrease.The nucleation was 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.As the temperature continues to decrease with the resulting shift in the phase diagram beyond the liqud-solid equilibrium curve,the crystallaization will occur.In this way the experimental setup provided the possibility for the determination of Wilson points,crystallization points,and nucleation rates for multi- component gas mixtures.The onset of nucleation,crystallization,and the measurement of droplet growth were is measured by means of laser light transmission and scattering. In the PEC set-up,temperatures below-100°C could be reached.Experimental results for the CO2 in NG mixture confirmed the theoretical temperature predictions.The results are comparable to the Mean Kinetic Nucleation Theory(MKNT)which predicts the onset of nucleation and nucleation delay.These parameters are then used to design CO2–Natural Gas Separation units.