Vent gas from crude oil and condensate storage tanks are a significant source of methane (CH4) and volatile organic compound (VOC) emissions. Oil and gas facilities may be required to control storage tank vent gas to comply with air permits and federal and state environmental regulations. The typical emission controls used include vapor recovery units (VRU), flares and enclosure combustion devices (ECD). The emission controls systems used are expected to operate continuously and to maximize the recovery (e.g., VRU) and destruction and removal efficiency (e.g., flares, ECDs).
One way that storage tanks equipped with emission controls may emit appreciable amounts of CH4 and VOCs is malfunctioning (stuck) separator dump valves.
Malfunctioning (Stuck) Separator Dump Valves
Natural gas can be carried through to a storage tank through a separator dump valve that is stuck in the open position (valve failing to reseat and leaking gas into a tank). This excess natural gas will be in addition to the natural gas that “flashes” out of the oil from normal separator operation. This increases the vent gas flowrate from an uncontrolled or controlled storage tank. For a controlled storage tank, this increased volume of gas could overload the control device and cause the storage tank pressure relief device to vent gas directly to the atmosphere.
Venting storage tank vapors to the atmosphere from the pressure relief devices (e.g., thief hatches) increases emissions of CH4 and VOCs.
For storage tanks controlled by a flare or ECD, excess gas from a stuck dump valve will increase CO2 emissions from combustion and to a lesser extent will increase CH4 and VOC emissions.
If a VRU is used as a control device and the VRU is not sized to handle the extra flowrate from the storage tank, venting of CH4 and VOCs can occur. If the VRU uses a flare or ECD as a backup control device, the excess gas could be sent to a flare/ECD will increase CO2, CH4 and VOC emissions.
The GHG reporting regulations in 40 CFR 98 Subpart W require onshore production and onshore petroleum and natural gas gathering and boosting storage tanks to calculate and report emissions from dump valves not closing properly using the method prescribed in 40CFR 98.233(j).
Action Items for Stuck Separator Dump Valves
If operators determine that a stuck dump valve is causing natural gas carry-through to the storage tank, steps should be taken to eliminate such carry-through. This can include:
- Repair or replacement of a stuck dump valve
- Install an appropriately sized separator or maintain liquid levels in the separator above a certain level.
Indications of Stuck Separator Dump Valve
- Increased volume of gas metered to flare or ECD
- Thief hatches open or cycling open/closed
- Pressure relief device cycling open/closed
- Higher Methane concentration in vent gas (requires sampling)
- Flare flame larger than normal
Solutions for Malfunctioning Separator Dump Valves
For companies needing to address the issue of stuck separator dump valves, Cimarron offers its NOVENT™ for smart thief hatch monitoring and IQR services.
NOVENT™ monitors tank thief hatches to detect if they are open and can alert operations through a dashboard displaying alerts as well as cumulative thief hatch leaks duration for a tank battery. This is valuable data for GHG reporting to the USEPA, certain States and for ESG metrics.
In addition, Cimarron can provide the full 360 PERFORMANCE MONITORING of the thief hatches and have fast response service crews address these alerts and minimize the time thief hatches are left open. When on site, the service crews can troubleshoot the reasons why thief hatches will pop open randomly, identify plumping issues or liquid traps causing pressure drops, and remediate the problem.
Cimarron’s IQR services can identify leaking thief hatches using optical gas imaging (OGI) and measure vent gas flowrates from storage tanks to quantify the emission rates.
Summary and Conclusions
Vent gas from crude oil and condensate storage tanks are a significant source of methane (CH4) and volatile organic compound (VOC) emissions. Oil and gas facilities may be required to control vent gas to comply with air permits and federal and state environmental regulations. The typical emission controls used include vapor recovery units (VRU), flares and enclosure combustion devices (ECD).
One way that storage tanks equipped with emission controls may emit appreciable amounts of CH4 and VOCs is malfunctioning (stuck) separator dump valves. Natural gas can be carried through to a storage tank through a separator dump valve that is stuck in the open position. This excess natural gas to the storage tank increases the vent gas flowrate from an uncontrolled or controlled storage tank. For a controlled storage tank, it increases the volume gas that the emission control device (e.g., VRU, flare) must handle or could cause the storage tank pressure relief device to vent gas directly to the atmosphere.
Stuck separator dump valves can be a significant source of CH4 and VOC emissions from oil and gas storage tanks. Operators should take steps to identify and correct malfunctions to reduce emissions and comply with environmental regulations.
Cimarron offers its NOVENT™ for smart thief hatch monitoring and IQR services to address the issue of stuck separator dump valves. NOVENTTM monitors tank thief hatches to detect if they are open and can alert operations through a dashboard displaying alerts as well as cumulative thief hatch leaks duration for a tank battery. Cimarron’s IQR services can identify leaking thief hatches using optical gas imaging (OGI) and measure vent gas flowrates from storage tanks to quantify the emission rates.
Cimarron – Who We Are
Cimarron’s vision is to work with our clients to create a cleaner environment. The company engineers and manufactures environmental, production and process equipment for the upstream, midstream and downstream energy industries, as well as environmental control solutions for biogas at wastewater facilities, digester tanks and landfills. Our flares and ECDs meet all federal and state environmental regulatory requirements for control efficiency and destruction efficiency.
Cimarron offers our customers the know-how and environmental expertise to meet the environmental standards of today and tomorrow. Cimarron is committed to bring value to the Energy industry and their shareholders based on our financial strength, experienced personnel, and engineering capabilities.
As a company, we thrive every day to make a difference through innovation (e.g. ESG), customer focus, and operational efficiency. In addition to being present in all major regions in the US, Cimarron serves more than 45 countries around the world, ranging from offshore to desert. From key operational centers in the United States, Italy and the United Arab Emirates, Cimarron offers ongoing service and support through its own field service personnel and strategic third-party partners, creating a cleaner environment for our customers and their shareholders.
Since its founding in the mid-1970’s in Oklahoma, the company’s product offering has expanded from production equipment to include the largest line of environmental solutions that capture or incinerate fugitive vapors. With the acquisitions of HY-BON/EDI in 2019 and AEREON (including Jordan Technologies) in 2020, Cimarron has added strong brands, products, and services to its portfolio.
Please contact us to learn more about our products and services and about all our ESG solutions at sales@cimarron.com or visit our website cimarron.com.
