HYDROCARBON spills are every tank terminal operator’s nightmare
for newly built storage tanks but especially for older storage facilities. Spills can create risks with very high implications, for example:
• Costly loss of hydrocarbon products
• Costly downtime for infrastructure repairs
• Fire and explosion hazard
• Costly clean-up, remediation and restoration
• Long-term environmental damage
• Costly governmental fines and adverse publicity
WHERE TO MONITOR IN A TANK TERMINAL
EARLY LEAK DETECTION
FOR COST SAVINGS
TECHNICAL FEATURE LEAK DETECTION
Even sophisticated tank gauging systems cannot detect small leaks of oil or fuel from large tanks to groundwater. Current health standards allow drinking water to contain less than 1 ppm of hydrocarbons.
This means that an undetected leak of 1 liter/gallon of hydrocarbons can
contaminate more than 1 million liters/ gallons of groundwater.
A Leakwise ID-221 oil sheen detector installed in a groundwater monitoring well near the tank will give a reliable warning on hydrocarbon seepage into groundwater much earlier than any manual sampling. An array of monitoring wells with Leakwise ID-221 sensors in the perimeter of a tank farm will give an indication of leak drifting and layer trend. If the groundwater is already contaminated by a thick oil layer, Leakwise ID-225 sensors can be installed in the monitoring wells to monitor the progress of remediation activity, as these sensors can linearly measure oil layer thickness up to 200 mm.
The presence of an immediate leak warning system on site is crucial as it is the first sentinel before escalation to a disaster. Installing such systems should be the conclusion of a site risk assessment. The optimal solution is
based on installing reliable, field proven and third-party tested systems for detection and monitoring hydrocarbons leaks and spills.
Floating roof drainage
Rainwater accumulated on a storage tank’s concave roof affects its floatation, making it necessary to drain the water. This is usually done through a flexible pipe running from the floating roof down the tank through the oil product, with an outlet above ground near tank base. However, there are several associated risks.
Oil product from the tank can penetrate the flexible pipe through pinholes or cracks and be discharged through the drainage system unnoticed.
Oil product from the tank can run over the roof through the roof’s seal if the floatation of the roof is un-balanced, and then exit through the roof’s water drainage pipe. This can happen also during heavy rain and a partially clogged drainage pipe.
Local regulations may require that drained roof water will be treated. This may be minimised by monitoring
the drained water and diverting it to treatment only if contaminated with oil.
There could be accidental overfill of oil product.
Monitoring the drain exit of each tank is essential for informing management
that leaks have occurred, and which tank needs to be repaired.
Monitoring the drain exit with a Leakwise ID-223 oil sheen detector installed in a sump or retention tank/local separator will reliably indicate any leakage.
Tank bunded (diked) area
Drainage channels and sumps around storage tanks collect and drain storm water. However, they also collect any hydrocarbons from leaking pipes, valves or pumps. Accidental overfill is also contained in the bunded area. These sumps, which can be either wet or dry depending or rains, should be continuously monitored for the following reasons:
• Health and safety – undetected buildup of flammables in the bund area creates harmful vapors and possible fire or explosion
• Environmental – leaks or spills must be detected before they are released from the contained area
• Economic – product loss is a direct cost against the business. However, an additional cost can be incurred when clean storm water from the bunded area is sent for unnecessary treatment
A Leakwise ID-223 oil sheen detector installed in the collecting sump will continuously monitor the water before releasing it to public water. If oily water is detected, an alarm will be set off and
the water outlet valve will be closed. The oily water could then be (manually or automatically) diverted into an
API separator or any other oily water treatment system. Such operation method will reduce the load on the water treatment system, may reduce system size, and eventually cut treatment costs.
Monitoring oil separators and skimmers
In many tanks storage facilities water is collected and sent to a separator, or interceptor, where oil is separated, and water is discharged directly to the sea,
river or public water. In other cases, water from the tank area could be treated by an API separator. A Leakwise ID-225 oil layer thickness monitor will continuously monitor the thickness of the accumulated oil and inform the operator when to skim the oil. Oil skimmers can be automatically controlled by the ID-225 sensor, starting the skimming at a user-set oil thickness and stopping before water is removed with the oil. This can result in considerable savings in treatment and disposal costs.
Installing a Leakwise ID-223 sensor in the final retention pond will continuously monitor the discharged water and ensure that the treatment process is running smoothly. An oil overflow to the exit chamber will be detected and the operator notified, or the system can automatically stop the discharge and contain the oil, allowing the operator to take an appropriate corrective action.
Monitoring water treatment discharge
Monitoring loading terminals
Oil distribution terminals are used for
loading truck-containers with refined oil products to be distributed to gas stations. These terminals are prone to oil leaks
during the filling process. The area of the terminal is drained to a sump that collects rainwater but also the potential oil spills. A Leakwise ID-223 sensor installed in the
sump will give an early warning as soon as an oil sheen is detected. Water release will then be stopped until the water is treated.
Leakwise technology was verified by several third-party tests and has a huge global installed base.
A Leakwise system is comprised of a sensor and a controller.
The sensor is a floating device that sits flat and accurately on water surface.
It uses a proprietary high-frequency low-power Electromagnetic Energy Absorption Technique. The energy is introduced to the upper layer
of the water. Since water absorbs more electromagnetic energy than
hydrocarbons, changes in the absorption rate of the water indicate the presence or buildup of a hydrocarbon layer.
The sensor continuously sends the measured signal to the processor, which analyses it and determines if there is a presence of a hydrocarbon layer and evaluates its’ thickness. The processor then activates the alarms and controls according to easily adjustable sensitivity settings.
This technology is optimised for detection and monitoring the buildup of separated or emulsified non-soluble hydrocarbons on water and other aqueous solutions. The technology is sensitive enough for differentiating between hydrocarbons and no liquids at all, which allows also hydrocarbons detection in containment areas that may be continuously or occasionally dry. Leakwise sensors can detect the
presence of as little as 0.3 mm of hydrocarbon on water. Detection is immediate upon contact of the hydrocarbons with the sensor. The immediate detection fully complies with the 30 seconds detection response requirement of FM Class 7745 standard. After detection, the system continues to monitor the oil layer buildup and trend up to 25 mm.
Leakwise oil thickness special sensors are
optimized for linear measurement of thick oil layers on water, up to 200 mm. Leakwise controllers display system status on the front panel, and interface to user’s control center via relay contacts, 4-20mA, Modbus and wireless messaging.
Adding fuel leaks and spills monitoring systems can be challenging for existing large fuel storage facilities, where the wiring infrastructure was not prepared in advance to accept such systems. One solution is to use a battery-operated system with a small solar panel, and a wireless communication to the control room. Wireless can be either a point-to- point radio link or a cellular link.
For example, Leakwise ID-223/2000 sensors were installed in 23 tank bunded areas in a European tank facility. Outside the dike a battery-operated controller was installed for each sensor, with point-to- point wireless link at 869.4 - 869.65 MHz, fixed channel, 500mW transmit power, and line-of-sight range up to 5km.
A point-to-point receiver was installed in the control room with a receiving antenna installed on a mast on the roof. The communication from all
transmitters was verified at the receiver to have a success of 99.9 % (during a test period of two months and more than 17,000 transmissions, with several thunderstorms during this period).
Communication security is achieved by digital encryption of transmissions.
The customer previously had a bad experience with other leak detection systems that had reliability issues. Prior to purchase, the customer wanted to be sure that Leakwise technology would work reliably on a range of insoluble hydrocarbons including crude oil. They commissioned a third-party consulting company to test the Leakwise technology. Tests with crude oil and diesel, both at ambient and chilled temperatures, clearly showed that the technology reliably detected these types of oils. In addition, the tests established that the technology continued to work reliably even when the sensor was coated by crude oil, and oil layer thickness continued to be reported while increasing or decreasing.
For more information
This article was written by Shimon David, technical director, Agar Environmental.
01 Leakwise ID-223/500 oil sheen detector
installed in a sump 02 Leakwise ID-223/2000 oil sheen detector
installed in a bunded area 03 Leakwise ID-223/500 oil sheen detector
installed in a water collection pond of a tank farm