For over two decades, select US states and non-attainment areas have required the degassing of stationary storage tanks that most recently contained volatile organic compounds (VOCs) with vapour pressures of greater than 0.5 psi.
Significant VOC emissions are generated during maintenance start-up and shutdown (MSS) activities (cleaning, repair, inspection and change of cargo), and generally when landing or floating a roof. Several US states have specific regulations covering these activities and the American Petroleum Institute (API) has developed generic language in API RP 2016. These requirements should be familiar to anyone operating a terminal or refinery in the US. Some terminals in Texas and California have been utilising ‘degassing’ contractors since the mid-1990s. Most of the cargos subject to these regulations are flammable and as such a common technology for degassing has been combustion based – trailer mounted thermal oxidisers and flare units are brought on site and flammable vapours are pulled from the vessel and destroyed. This satisfies environmental regulations in many applicable tank locations and cargos. However, there are times when a portable combustion device is not the best choice or not an appropriate choice at all.
Refrigerated vapour recovery systems (RVRUs) have seen a steady increase in use at storage tank degassing in refineries, chemical plants, and barge terminals since 2010. At least four separate tank degassing groups have a RVRU offering. This article will highlight the safety and operational incentives for this new approach.
Alternative to flaring
Prior to the development of RVRUs, the most common vapour control system used in refineries and tank terminals for hydrocarbon degassing was combustion based. Portable, skid-mounted flaring units and thermal oxidation units allow operators to comply with degassing regulations established by….
Written by Townsend Hilliard, Purgit, USA.
Read the article online at: https://www.tanksterminals.com/special-reports/12032019/emissions-cutting/