Vapor Recovery System Design


Example of Vapor Recovery System Design Project:

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.


Other Vapor Control Engineering Studies include:

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