Benzene emissions from glycol dehydration units are regulated in Western Canada. In addition, Alberta has initiated a methane emission reduction plan for the oil and gas sector. The major challenge in reducing emissions from dehydration systems is designing systems to capture the gas from the flash tank vent and still column (glycol regenerator) overheads. The still column operates at atmospheric conditions and the vented gas is wet; this leads to additional effort to design a system to handle wet vapour at low pressures.
Several technologies have been proposed to reduce BTEX emissions (benzene, toluene, ethylbenzene, xylenes) from glycol dehydration units, such as combustion flare/incinerator), Kenilworth combustion, SlipStream, JATCO BTEX Eliminator, vapour recovery units (VRU), and condensing tanks (such as TankSafe). GasPro Compression Corp. has recently developed a vapour recovery unit to reduce/eliminate BTEX emissions from glycol dehydration plants. The GasPro BTEX VRU unit addressed in this study has been installed as a trial unit at a dehydration facility in Central Alberta since February 2016. This report presents the results obtained between December 2016 and June 2017 from the data collection, engineering simulation and modelling of the dehydration plant and GasPro BTEX VRU unit as well as a leak survey done by GreenPath Energy. The objective of the study is to determine the GasPro VRU technology emissions reduction efficiency and to investigate the benefits and challenges of the technology.
Aspen HYSYS v7.0 and EPA TANKS 4.0.9d were used for emissions calculations including methane and BTEX emissions from the installed VRU and the facility produced water tank. The leak survey was done by FLIR optical gas imaging camera technology along with a Hi-Flow sampler to detect and estimate volumes of potential leaks from the GasPro VRU and other parts of the facility.
Referring to calculations and observations, we found that the potential BTEX and GHG emissions reduction using the GasPro BTEX VRU is 100%. However, there are two potential sources of emissions which may lead to reductions in the overall efficiency: the emissions from the produced water storage tank and fugitive emissions. The flashing, working and breathing losses from the produced water tank calculated for this project result in zero emissions due to the large amount of produced water collected from the facility. However, fugitive emissions were detected from the GasPro VRU during the site visit due to a leaking PRV (pressure relief valve) with high fugitive emission rate. This led to emissions reduction efficiencies less than 100%: 89.9% for methane and GHGs and 97% for benzene. Subsequent to the initial study, the PRV was replaced with a model from a different manufacturer and the unit was surveyed again, and found to have no leaks and hence zero BTEX and GHG emissions from the dehydration unit and GasPro BTEX VRU.
In general, to establish the reduction efficiency from any VRU system we would recommended taking into account the emissions from condensed water tanks as a result of flashing, working and breathing losses. Alternately, connecting the water tank vent to the VRU system to collect all emissions would ensure complete control. As with other equipment in an upstream facility, we would also recommend scheduled leak surveys for the VRU. VRUs such as the Gas Pro VRU also provide an energy efficiency benefit in addition to reducing emissions, as the recovered gas is compressed and recycled as fuel versus being vented to atmosphere or simply burned in a flare or incinerator. Other emissions reduction technologies such as flaring and incineration do not immediately provide this energy conservation benefit. As per field operators’ feedback, the GasPro technology is simple to understand and reliable compared to alternative technologies and they felt that this GasPro VRU technology was more robust and required virtually no operator intervention.