Automated tank-cleaning programs can save time and labor when the solution is tailored to the cleaning environment.
What are the most important factors that make up an oil and gas industry tank or vessel cleaning program? It’s a succinct question and one that many contractors have never asked themselves. In many cases, tanks and vessels are cleaned when they’re no longer functional, using high pressure washing devices and brute human force supplied by workers who must often enter tanks to achieve acceptable results.
“To us, the most important factor in tank cleaning has nothing to do with cleaning the tank,” says Michael Delaney, vice president of business development with automated tank cleaning equipment manufacturer Gamajet. “It has to do with protecting workers and promoting their safety by eliminating the use of confined-space entry for cleaning, when that cleaning could easily be handled by an automated system.”
Gamajet was founded about 60 years ago, offering a cleaning system that applied detergent to the insides of ocean-going oil tankers. About 20 years ago, the company diversified to cover tank cleaning in a number of industries, including oil and gas, using a wide range of cleaning systems and nozzles. The company’s approach to cleaning employs rotary impingement tank-cleaning machines.
“The system combines pressure and flow to create high-impact jets, which clean when the concentrated stream impacts the tank surface,” says Delaney. “This impact and the tangential force that radiates from the point of impact blasts contaminants from the surface, scouring the tank interior. The action of the cleaner is a shearing force, which works more like a putty knife in removing material from the tank walls. The jets rotate in a precise 360-degree pattern to ensure the entire tank interior is cleaned. It’s like a spirograph that eventually covers the entire interior surface of the tank.”
Engineered tank cleaning
Each oil and gas tank cleaning application may be engineered differently, ranging from smaller totes, mud tanks and frac tanks to vacuum trucks, crude oil-carrying rail tank cars, transport tankers and larger refinery tanks.
“Beyond the advantage of getting workers out of the tanks, the goal is to thoroughly clean a tank with cleaning fluids in less time with less labor,” notes Delaney.
Tank owners first need to assess their needs and goals, whether worker safety, reduced labor cost, reduced use of cleaning fluids (either chemicals or water), reduced downtime for vessels and production equipment, the possibility of using tanks to hold more than one substance after cleaning and better tank performance. They next need to describe how the tank is currently cleaned and the type, size and interior layout of the tank.
“Tanks that contain any sort of obstructions, such as baffles and mixing blades can create a shadow that might impede the cleaning jets,” says Delaney. “You can usually clean easily around small obstacles, but for vessels that contain large objects, you might use multiple machines or insertion points.”
The size of the tank is also important. Cleaning jets need to reach the interior surface of the tanks from where the automatic cleaning device is placed. Some tanks may require more than one cleaning machine.
“We have to look at the entry points of the tank as well,” says Delaney. “To a large extent, our market was built around developing products for tanks that offered tiny access ports and weren’t really designed for cleaning. One of the engineering challenges is to create a cleaning unit with a small enough gearbox so that it will fit through a tiny access hole and still provide cleaning power. In a few cases, where access is very controlled, the client may install a permanent cleaning system inside the tank.”
Identifying the grime
Next, clients need to describe the type of material that needs to be cleaned from the tanks – ranging from drilling mud to chemical and oil residues – and the stubbornness of the dirt.
“The type of material that needs to be cleaned from the tank will determine the type of cleaning fluids used,” says Delaney. “Typically, we’ll use hot water for cleaning drilling mud, but on various jobs we use caustic, detergents, brine and other solvents. For some petroleum applications we’ll use diesel. We also need to know what sort of cleaning fluids are going to be used, because although the cleaning equipment is made of stainless steel, we need to make sure that we supply O-ring seals and bushings that are compatible with the cleaning fluid.”
The final consideration will be the actual design of the spray delivery system, including the number of nozzles, the flow rate of the cleaning fluids, the temperature of the fluids and the gear ratio of the equipment that will deliver the necessary cleaning power.
“In some cases, clients provide their own pumps and we can design the system around that,” says Delaney. “We’re often asked how many pounds of pressure our equipment delivers, because many people assume that’s the most important factor in effective tank cleaning. It’s just one factor, but not even the most important one.”
Cleaning fluids are typically delivered to the Gamajet cleaning unit at about 120 psi, enough pressure to get the fluids through the plumbing to the business end of the device. In some cases, more pressure may be required to deliver the fluids to a higher elevation.
“Our equipment includes an impeller that actually reduces the speed of the jets, because we don’t want the cleaning fluid stream to atomize into water droplets at high pressure on the way to the tank wall,” says Delaney. “What we’re looking for is a compact and solid stream of fluid hitting the walls at top impact, delivering a certain number of gallons per minute.”
A safer stream
The stream of cleaning fluid is safer than extremely high pressure washes, Delaney argues, because if a worker is accidentally exposed to the stream, it can’t cut through human flesh. “The worst it would do if you got in the way is give you a bruise,” he says.
Gamajet automatic cleaners offer either two- or three-nozzle machines. Delaney says the choice is a trade-off. A two-nozzle machine operating at 100 pounds per square inch and 100 gallons per minute can deliver 50 gpm per nozzle. A three-nozzle machine operating at 100 psi and 100 gpm will only offer 33 gpm per nozzle and a lower impact force.
“However, the three-nozzle machine has a 33 percent tighter pattern than the two-nozzle machines, so in applications where a quick rinse is the most important factor, a three-nozzle machine has the edge,” he says.
The client also needs to determine how frequently the tank will be cleaned – monthly, weekly, daily or as needed.
Economics of effective cleaning
In many cases, the economic argument for using more effective tank cleaning methods includes reduced capacity of the tank to hold the material for which it was designed.
“A great example involves the rail cars designed to deliver crude oil to refineries,” says Delaney. “We’ve designed systems used to clean out the rail tanks when they’re being decommissioned and by that time they’re filled with 2 feet of sludge. There’s a huge economic cost to running rail cars with that much reduced capacity. Some of the refineries are now saying they’d like to fill the rail cars up with diesel on the way back, but that doesn’t make any sense unless the tanks are clean. If we can make the case that they could clean 100 rail car tanks in 24 hours, then cleaning them regularly and loading them with diesel for the trip back makes a lot more sense.”
Likewise, an improperly cleaned chemical tote can easily destroy high-value contents through contamination, if it’s being used to carry more than one type of material.
Maintenance is another value. Maintaining the Gamajet system largely involves operator replacement of leaking seals and O-rings.
“The preventive maintenance is important here, because the seals and O-rings not only prevent the system from leaking, they also help to control the speed of the machine,” says Delaney. “A machine that’s leaking will operate at a less impact but at a higher flow rate that may accelerate wear on other parts of the equipment.”