Emerson Process Management (www.emersonprocess.com) is supplying Rosemount Analytical X-STREAM process gas analyzers to Roplex Engineering, a provider of Vapor Recovery Units (VRUs) and services to petroleum distribution terminals. The explosion-proof, dual-channel X-STREAM infrared analyzers are being used to measure carbon monoxide and butane, monitoring the effectiveness of the VRU in removing all the hydrocarbons, and thereby adding additional levels of safety at terminals.

VRU’s have long been installed on petroleum tanker loading terminals in response to legislation limiting the amount of hydrocarbon vapors being emitted to the atmosphere. When tankers arrive at the refuelling points they are empty of fuel, but full of air saturated with vapor, up to 40 percent by volume. As the tanker is filled, the expelled vapor is collected and fed to a VRU where the hydrocarbons are removed before the air is vented to atmosphere.

A typical VRU has two scrubbers both containing activated carbon. Installed in parallel, the scrubbers are routinely switched. One adsorbs the hydrocarbons and then, once saturated, the beds switch and the hydrocarbons are removed and returned to liquid form. The X-STREAM analyzers detect carbon monoxide in the gas exiting the absorber bed — a presence of the gas provides an early indication of an upset condition that has the potential to become a hazard. The second measurement, butane, is made on the final vent-to-atmosphere to ensure that the VRU is working effectively.