Looking back at the first wave of vapour recovery units (VRUs) installed in Europe some 30 years ago, what was then state-of-the-art would largely be deemed ‘experimental’ today. Focus was on testing and verification of the overall concepts and not always on reliability. Since then, attention on emissions has sharpened considerably and most truck depots and onshore ship terminals are no longer allowed to operate without a functioning VRU.
For the VRU manufacturer, reliability has therefore become the single most important sales parameter. Often, the terms ‘availability’ or ‘up-time’ are used instead of ‘reliability’, since it is easier to quantify (‘availability’ = hours available/hours required [percentage]).
The focus of this article is VRUs based on adsorption on activated carbon followed by regeneration under vacuum. For several decades, this has been the most commonly used process for vapour recovery.
There are many ways of improving the availability of a system. One strategy, often seen in VRU specifications, is to request installed spares (redundancy) of all rotating equipment. While this seems to be a straightforward approach, it is costly in terms of installation and becomes relatively complicated in terms of control, operation and maintenance; equipment cannot be expected to kick in when needed unless it is used frequently. Therefore, the controls must be set up to ensure that the back-up equipment runs regularly, but still less often than the primary equipment. This in turn means uneven service intervals, which can be difficult to arrange in practice. And even if rotating equipment, and perhaps control valves, control systems and instruments, are made in redundant design, then other elements such as on/off valves and solenoid valves are still vulnerable to failure.
In some cases, a degree of redundancy can be obtained at little additional cost by…
Written by Ben Barker, Cool Sorption, Denmark.
Read the article online at: https://www.tanksterminals.com/special-reports/08032019/a-routine-to-rely-on/