Design and layout of a new liquid piping system
required to supply gasoline to a vapor recovery unit from a new product tank.
Through acquisition and sale of various assets, a
small terminal company lost the use of a tank previously used for the
absorbant circulation to its activated carbon vapor recovery unit. The tank
had previously been used during the loading of marine vessels with
reformulated fuel oxygenate additives. In this case, the liquid absorbant used
during operation was slip-stream of the cargo being loaded. Once the marine
vessel had been loaded, the vapor recovery unit was required to run for a
short period, roughly two complete regeneration cycles. This allows the
activated carbon beds to be regenerated prior to shutting down the vapor
recovery unit.
However, during this after loading period they had no
liquid absorbent to be circulated. (Liquid absorbant is used to remove the
recovered volatile organic compounds (VOCs) from the recycle stream and to
cool the seal fluid used by the vacuum system. For a complete explanation of
how activated carbon based vapor recovery units function, please go to
Activated Carbon Adsorption Vapor Recovery Equipment
page. In this situation after a short time, the
vapor recovery unit's activated carbon became saturated and emissions, greater
than permitted, were being vented to the atmosphere.
WNEC was contracted to study the problem and to
develop a least cost alternative allowing the activated carbon based vapor
recovery unit from exceeding the emissions limits during loading of the
oxygenate additive. WNEC arrived at two different operations scenarios, one of
which was chosen by the terminal management as the option they would
implement.
The solution involved the use of an existing
refrigeration package to chill the circulating liquid absorbant and a number
of piping modifications. The piping modifications allowed the utilization of a
considerable amount of unused large diameter piping to act as a reservoir for
the circulating absorbant liquid. The operations scenario allowed the loading
operation to continue as normal. Once the loading cycle had been completed and
the after-loading cycle begun, a series of valves repositioned the flow of the
absorbant and the refrigeration package chilled the absorbant liquid. This
chilling of the static volume of absorbant providing enough extra absorption
capacity in the absorbant that the carbon beds could be regenerated
thoroughly.
When the after-loading operation was completed, the
now saturated absorbant remained in the piping until the next marine vessel
loading at which time it was flushed from the lines to the marine vessel using
fresh product. The complete cycle was again repeated after each loading
operation was completed. The design of the process revisions included the use
of existing equipment, a small surge tank and abandoned large diameter piping.
New valves and fittings required for the piping revisions were the major new
equipment items needed to be purchased.
