Marginal gas field containing large concentrations of CO 2 is a technical challenge to develop due to the low CO 2 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 CO 2 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 CO 2 liquid and solid crystals in order to properly design the separation units.Adiabatic expansion experiments were performed in a pulse expansion chamber (PEC). The CO 2 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 multicomponent 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 CO 2 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 CO 2 -Natural Gas Separation units.
Application of nozzle supersonic expansion has been used for dehydration and hydrocarbon dew pointing. Recently, the potential of the supersonic expansion technology in bulk CO2 separation from natural gas has been studied. The proof of concept testing of the nozzle prototype is being validated via a 15 MMSCFD flow loop at 36 bar and -19°C at KEMA, Groningen. The setup consists of a multiphase pump, gas-liquid separators and heat exchangers. Pressure transducer has been installed along the nozzle tube prototype and the pressure reading is recorded through the data acquisition system. Besides pressure, the temperature inlet, primary and secondary outlet of the tube has been monitored. Two vibration sensors have been installed to monitor the effect of the high vibration to the prototype. For quality check, an on-line gas chromatography has been installed at the inlet and the outlet. Several challenges had been faced during the start-up of the test in order to achieve the test condition. The pressure profile plotted along the prototype will be compared with the CFD simulation with various parameters evaluated. The shockwave predicted via simulation has been observed at the pressure profile and significant flow of liquid CO2 has been produced during the initial test. Reduction of temperature at the outlet of the tube gives an indication of separation has been occurred in the process. The preliminary results from the experiment will provide the improvements for the CFD simulation numerical modelling as well as the in-house coding for CO2 separation efficiency.
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