|
In the following pages results of computer simulations are shown, based on the
operating options /PAR3/NPE3/DD/SM/SMEQ and on using low pressure purging.
A number of "snap shots" have been taken during a complete cycle of an adsorber,
of its gaseous phase composition profiles over its full height, at start of
adsorption, after having admitted 40, 60, 80 and 100% of the feed charge and further
at the end of depressurization, dumping, purging and repressurization. In addition compostion profiles are given of product gas, product slip gas, secondary product gas, purge gas, dump gas and purge offgas. The numbers in the diagrams refer to the components specified for the adsorber profiles. In this particular example, purging takes place at low pressure, causing a sharper residual loading profile over the adsorber height than if compared to the other case described in the pages B1 through B18, based on high pressure purging. In this respect an interesting phenomenon may be noticed concerning the product slip gas profile, page A11, where a sudden flow increase is shown. At this point a fresh regenerated adsorber is put into adsorption service. Since the initial feed charge passes through a relatively high residual loading less adsorption takes place and the overhead product rate versus the feed rate is temporarily higher than average. In order to maintain a constant net product rate at a constant overall feed rate, more product slip has to be used for repressurization. Proper control measures should be taken to cope with this phenomenon in order to avoid undue pressure and/or product flow fluctuations. |