CO2 recovery is an important part of CCUS, among which low-temperature separation technology is widely used in high-concentration CO2 recovery occasions. NEWTEK designed the process flow of CO2 cryogenic liquefaction unit, built the unit model using HYSYS software, determined the optimal design parameters of the unit, and selected and calculated the equipment based on the optimal design parameters.
The total amount of CO2 emitted by China each year is about 10 billion tons, accounting for about 1/4 of the global total emissions, which has brought great pressure to the realization of my country's "carbon neutrality" and "carbon peak" goals. Carbon capture, utilization and storage technology (CCUS) is one of the important technical means to achieve the "dual carbon" goal.
CO 2 purification and liquefaction plants process principle
The phase change characteristics of CO2 are the theoretical basis for the liquefaction of carbon dioxide gas. The triple point temperature of carbon dioxide is -56.6℃, and the pressure is 0.52MPa; the critical temperature is 31.2℃, and the critical pressure is 7.38MPa. It can be seen that pure CO2 will present 5 states during the phase change process, namely solid phase, liquid phase, gas phase, dense phase and supercritical phase, as well as triple point and critical point. CO2 can be liquefied by pressurized cooling at any temperature between these two points, which is the theoretical basis for industrial liquefaction of carbon dioxide.
CO 2 purification and liquefaction plants process flow design
The raw gas from the upstream first enters the bottom reboiler to provide heat for it, then enters the precooler, exchanges heat with the non-condensable gas returned from the top condenser, and then enters the liquefier for further condensation and liquefaction. After the raw gas passes through the liquefier, about 80% of the gas is condensed into liquid, and then the mixed fluid enters the flash tank for flash separation. The separated liquid enters the purification tower for purification, and a liquid product with a CO2 concentration of more than 99% is obtained. After being supercooled and throttled by the cooler, it is transported to the injection system. The non-condensable gas obtained at the top of the tower enters the top condenser (built-in type), and after cooling, enters the top separator (using the top space of the tower) for gas-liquid separation. The separated liquid returns to the top of the tower for reflux, and after gas throttling, it is mixed with the throttled gas from the flash tank to provide cooling capacity for the top condenser. After the non-condensable gas recovers cooling capacity, it enters the precooler to provide cooling capacity for the raw gas precooling again. The non-condensable gas after the second cooling capacity recovery enters the venting system for venting.
In the entire device, the cooling capacity required by the liquefier and subcooler is provided by the ammonia refrigeration system, the cooling capacity required by the top condenser is provided by the non-condensable gas after throttling, and the heat required by the bottom reboiler is provided by the latent heat of vaporization carried by the raw gas itself. The process flow is modeled using Aspen HYSYS software. The unit modules used in the simulation process and their functions are briefly introduced.
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