Condensation problem at the top of the liquefied gas tower
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For a current natural gas processing plant project, there is an issue regarding the condensation method at the top of the liquefied gas tower; if a full condensation approach is used, all the product at the top of the tower will be in the form of liquefied gas； If partial condensation is used, with some of the product being in the form of liquefied gas, I have a question for the experts: which is better, full condensation at the top of the liquefied gas tower or partial condensation? What are the characteristics of each of these two methods?
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I mean, that type of condensation method yields a higher recovery rate for liquefied gas; which one is more widely used?
Full condensation, with periodic discharge of non-condensable gases.
Is the non-condensable gas discharged regularly through a pressure control valve or a safety valve? Is the pipeline connected to the top of the liquefied gas tower or to the condenser?
Reply to 5# Snail Walk: This can be achieved using a pressure control valve, or a switch valve – either works. This gas can enter the fuel gas system and be released from the top of the reflux tank.
Reply to 1# Snail Walk: A fully condensing type condenser is generally used, along with a pipeline for venting non-condensable gases. These non-condensable gases are usually routed to the highest point after condensation or to the top of the reflux tank. The pipeline for venting non-condensable gases can be operated manually; it suffices to open it slightly when pressure is high. A DN25 pipeline is usually sufficient for this purpose. If the pressure of the natural gas being processed is low, the non-condensable gases can be sent back before the gas is pressurized; if the gas pressure is high, they are sent directly into the fuel gas network
There should be at least two operating modes for the top condenser. First, there is the internal condenser at the top of the liquefied gas column: the liquefied gas formed at the top is condensed to serve as reflux (which cannot be adjusted), while the remaining gaseous phase goes to the liquefied gas condenser to be used as a product. This design needs to take into account the overall design of the distillation column, such as the processing capacity, reflux volume, and top temperature, among other factors. Another option is the one discussed above, where all products are cooled, along with a recirculation pump that allows for adjustment of the recirculation volume.