RSPA proposal encourages industry to develop purging system for wetlines
Feb 1, 2005 12:00 PM
A RECENT Research and Special Programs Administration (RSPA) proposal to reduce the amount of flammable product in tank trailer individual wetlines to one liter (.26 gallon) or less has prompted the industry to develop new products to handle the requirement.
Information about some of the products was presented at the National Tank Truck Carriers (NTTC) Cargo Tank Maintenance Seminar October 18-20, 2004, in Chicago, Illinois.
RSPA proposed December 30, 2004, that comments had to be submitted no later than February 28, 2005. NTTC has voiced concerns about the rule and its impact on the tank truck industry and asked for a 180-day delay. However, RSPA denied the request and extended the comment period for 60 days to April 28.
At the NTTC meeting in Chicago, Jack Rademacher of Brenner Tank Inc, Bryan VanDeVyvere of Civacon, David Ball of EBW Inc, and Roger Beames of Gardner Denver/Drum/Emco Wheaton discussed their companies' products.
One of the reasons causing RSPA to investigate wetlines is that, per RSPA's own regulation, the piping beneath a petroleum tanker is designed to break via a shear section to protect the cargo tank and prevent the entire contents of the cargo tank from being released, Rademacher said.
If the gasoline retained in the piping is released in an accident, the hot exhaust system from the colliding vehicle can set the spilled gasoline on fire, which in-turn can cause the cargo tank contents (8,000 gallons) to ignite.
The Brenner wetline solution is a valve designed with two closures; one to retain product in the cargo tank as is currently regulated and one to retain product in the piping in the event of an underride incident. Both closures are self closing and linked to open and close simultaneously. The DOT required shear section is located between the two closures. If, in the event of an impact, the shear section fails as intended, the upper closure remains with the cargo tank to retain the product in the cargo tank and the lower closure remains with the piping, retaining all but about .25 liters (one cup) of product in the piping.
The idea behind the valve is that product retained in the pipe is not necessarily a hazard. The true hazard is when product spills to the ground. The Brenner wetline valve is designed to retain product in the pipe in the event of a collision.
One of the advantages of the solution is its simplicity, he said. There are no circuit boards, no electronics, no probes, and the valve technology in a single poppet arrangement has been proven and in use for many years.
Rademacher pointed out that Brenner has partnered with Fort Vale to develop the prototype valve to be dimensionally in compliance with TTMA RP-28 insuring that installing the valves requires no hot work to the trailer. Since the poppets rotate completely out of the product flow path, the valve has a high flow rate comparable to current industry four-inch valves. In addition, the linkage between the two poppets can be easily removed to test for leakage. The valve is also equipped with an O-ring gasket instead of a flat-seat gasket, adding to easy maintenance.
Civacon has had its wetline purging system in place for three years, VanDeVyvere said. The two-compartment automated system is self-contained and requires no interface with the driver. It is a closed system and no air is introduced. The purging system using a pump is one of several concepts that Civacon is considering at this time.
“The new proposed rule has just recently been released and we are still digesting the requirements and re-evaluating our design(s),” he told Modern Bulk Transporter in January 2005.
Optic sensors are used to determine the wet or dry condition in the loading lines. When a wet condition is sensed, a microprocessor controls the purging by communicating with an electric-driven, high-performance, 12-volt pump that will purge the liquid from the line and send it into the tank compartment. Civacon is currently considering different types of pumps to improve on the efficiency and performance of the purging system.
In addition, a check valve prevents liquid from draining back into the loading lines. The liquid is replaced with vapor from the vapor space in the tank shell.
The optic-sensing and control circuit system, the same type as is used in overfill protection, is equipped with LED lights that communicate operation. A blinking light on the pumping assembly indicates a wet situation, and then communicates with the pump where a blue light will come on indicating the pump is working.
Electronic circuits are mounted on a board underneath the pump in the cast housing. The pump assembly communicates with the loading lines by a mounting ring that is mounted between the API unloading adapter and the TTMA flange on the end of the loading lines. The pump housing is attached to this mounting ring.
The vapor control system is located inside the tank. A check valve is installed to prevent leakage and a shutoff valve is available for annual leak testing.
Liquid and vapor lines are plumbed through the emergency valve and the sump, which means there is no need to weld any couplings in the tank shell.
There also is short-circuit protection on the electronics in the event of a power surge. Pump and electronics are contained in a metal housing with no exposed electrical connections. Pumps can be wired to run at the same time on multiple compartment tanks, or they can be sequenced.
Civacon recommends that the wiring for the pump be wired into an ignition control circuit.
The wetline evacuation system from EBW utilizes an air-operated Versa-Matic Pump Co diaphragm pump that runs off the trailer compressor, Ball said.
The pump is activated by an Allen-Bradley controller that is powered with 12 volts direct current from the truck. The controller has analog or digital inputs, which are liquid sensors located at the base of each loading adapter for petroleum loading lines.
If the liquid sensor reacts in any loading adapter, then the controller will issue an analog output to energize the corresponding control valve, which in turn will activate the evacuation pump for a specific petroleum delivery line.
When pump activation occurs, the product will be pumped from the loading line to the corresponding tank trailer compartment via a half-inch line installed in the interior of the compartment.
The liquid in the loading line will be replaced by saturated vapor present in the corresponding non-liquid area of the compartment. The controller sequentially evacuates product lines due to the limited air supply available from the tractor.
A utility cabinet on the tank trailer can house up to five of the pumps, depending on number of compartments. The system adds about 80 pounds to the trailer, excluding the cabinet weight.
Emco Wheaton is offering the Cargo Tank Concepts (CTC) onboard wetline purging system that uses patented technology to evacuate product from the wetlines by forcing it out of the product piping and into the cargo tank body by using compressed air, said Beames.
After loading, the main cargo compartment valves are closed when the system introduces compressed air from an auxiliary tank into the piping under low pressure and low flow rate. Lading in the piping is displaced by air and flows through separate purging lines into the tank. The system completely drains the contents of the loading lines and the product transfer lines will also be empty. The wetline purging system is equipped with a time-out feature should the line not be purged due to a problem with an emergency valve poppet leaking or a damaged check valve. In addition, the system is automated and does not require the driver to operate it manually. The purging process is controlled automatically and the purging time is relative to the longest wetline that needs to be purged. The system also is capable of detecting and automatically purging any product leakage through the tank's internal shutoff valve into the piping, thereby eliminating a potential wetline condition during transportation.
Purging the product into the tank raises load height incrementally so that the system is integrated into the overspill protection system. A warning LED on the control panel indicates high liquid level if the probe is ever made wet.
The main components required include a control box with LED feedback, liquid sensor for API adaptors, emergency valve sump check valves, product transfer lines manufactured from stainless steel braided hose, air-operated emergency valve or actuating cylinder for mechanical valves, pneumatic airline and fittings. Emco Wheaton has been producing four-inch emergency valves and F5002 API adaptors with tapped and plugged ports suitable for retrofit to this system since early 2001 to simplify the retrofit process.
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