Separating Wall Columns Into The Separation Of Liquefied Natural Gas

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A series of articles have been published from the Yeungnam University mainly led by Long and Lee that relates to the incorporation of dividing wall columns into the separation of liquefied natural gas. Each base case had slight variances and the proposed dividing wall column design was also distinctive. 1.5.1.1 First case study Figure 29- Double Dividing Wall Column for Natural Gas separation (Long and Lee 2011) In this natural gas liquid (LNG) separation study conducted by Long and Lee (2011), the base separation system includes a sequence of depropaniser, debutanizer and deisobutanizer which separated a system the includes ethane, propane, n-butane, i-butane and heavies (C5+) (Long and Lee 2011). The demethanizer and deethanizer was…show more content…
This arrangement reduced energy costs by 30.5%, which is a large jump from the previous sequence but there are no logical explanations provides as to how they reached this particular arrangement. The three columns were then integrated into a single Agrawal column (figure 20) with a pressure of 14 bar, but this resulted in the required energy increasing by 13.5% from the conventional sequence showing the unsuitability of integrating the three columns into one (Long and Lee 2011). 1.5.1.2- Second case study In a second study conducted by Long and Lee (2012), they aimed at optimising and integrating a deethanizer and depropaniser, which operate at 30.98 and 17.5 bar respectively. The inspiration of this particular study came from a patented document conducted in 1996 that presented improvements in demethanizing and deethanizing stages of Liquefied Natural Gas separation (Manley 1997). This can be challenging as a balance between a high and low pressure must be found when integrating the two columns into a single dividing wall column. A high pressure will increase the temperature of the top stream and lower refrigerant cost but column and equipment wall thickness will have to be significantly increased. So a balance between the operating and capital cost must be found with the selection of operating pressure. However Long and Lee (2012) opted to go with a low pressure of 17.5bar to minimise capital costs and reboiler duties resulting in a 31.74% decrease in operating
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