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Twisters Used to Clean a Large Crude Tank

Twisters Used to Clean Asphalt Tank

Presentation at ILTA 2015: The Evolution of Black Oil Tank Cleaning: Online Tank Cleaning

Frequently Asked Questions (FAQs)

 ·       How many Twisters do I need on my tank?

The number of Twisters needed depends on the tank size and contents.  A small tank (<60’ D, or 20 m) may only require 1 Twister.  For most tanks, generally between 2 and 4 Twisters may be recommended, but the use of additional Twisters can reduce any “shadowing” behind tank internals.  Being able to refluidize solids that can’t be directly reached by the jet stream of the Twister reduces the amount of time needed for detailed cleaning later.  Often, the number of Twisters installed may be determined by the number of manways available.  In some cases, as many as 7 Twisters have been installed on a 290’ D (88 m) tank in order to turn the tank around as quickly as possible.

·       What size manway do I need to use Twisters?

Twisters have been built on manway covers as small as 20”, and as large as 36”.

·       How long do I have to circulate through the Twisters?

Again, it depends on product, sludge level, heat, chemistry, and diluents, but often 48 hours of circulation is adequate to refluidize the solids.

·       What size pump do I need to power the Twister?

A specific pump recommendation can be made for your application.  In general,  a self-priming high head centrifugal pump from 6” x 4” up to 10” x 8”, powered by 400 – 550 HP, and capable of 1000-2200 gpm (227-500 m3/hr) at 150 psi (10 bar) is adequate.

·       Can I permanently install Twisters on my tank?

Absolutely!  We believe the real value of the Twister is unlocked when Twisters are permanently installed on a tank, allowing “Online Tank Cleaning"...allowing the tank to remain in service….and not just a conventional offline tank cleaning.  The Twister is a unique technology that provides a proactive ability to manage the sludge problem, with the tank in service....not waiting until after the solids have become out of control, and requiring a reactive technology (vacuum trucks, dozers, robots, chemicals, manway cannons, etc).  Provisions are built into Twisters intended for permanent installation to ensure no build up of solids around the swivel mechanism and to provide fail-safe protection against any leaks.

·       How much and what type of diluents do I need?

To help break up and resuspend the solids, it helps to have heat as well as a diluent.  A typical temperature might be 140°F (60 °C), but depends on the flash point of the diluent.  The diluent might be the product itself, or could be a compatible cutter stock such as diesel, VGO, LCO, etc. Often, a lab blend determines an effective level, but cutter-to-sludge ratios of 1:1 to 4:1 are common.

·       Can I use chemicals with the Twister?

The Twister provides an ideal delivery system for chemicals - both an entry point for the chemicals as well as the ability to achieve the intimate mixing and good surface contact needed to distribute the chemical effectively.

·      Can I jet firewater through the Twister?


Yes.  This technique is used to lower LEL levels in the tank after desludging.  Care must be taken to avoid static risk in a high LEL environment, so rates are often limited to <235 gpm (53 m3/hr)

·       Can I take suction for my pump through the Twister?

Waterline builds two basic designs of the Twister.  The first, designed for a permanent installation, has a 3” port intended to provide a means to keep the area around the swivel mechanism clear of solids buildup, by allowing either cutter to be introduced or a vacuum source to be applied, or both.  For a temporary installation for tank cleaning, this feature is not relevant.  So our second basic design has a 6” port in case suction needs to be taken through the manway and circulated through the pump and back into the Twister discharge.  In that case, care must be taken to avoid cavitation on a short circuit.

·       How often do I need to use the Twisters to prevent solids from building up?

That depends on the solids settling characteristic of the product….in some crudes, Twisters may need to be activated every other week to prevent BS&W buildup from causing operational problems downstream.  In other cases, a client may choose to activate every two years, with the express intention of removing any bad actors from the system, through perhaps a 3-phase centrifuge.  And in other cases, a 10-year activation or more may be adequate.

·       What if I can’t open the manway due to sludge?

Waterline offers a version of the Twister that can be inserted into a tank through an 18” fully open gate valve that a third party has hot-tapped onto the manway.  We call this our “Hot Rod” Twister, and invite you to contact us for more details.

·       How do I get the solids out of the tank?

In many cases, frequent activation of the Twister can enable “Online Tank Cleaning”, so that the solids don’t have to be removed from the system because they have not accumulated to a level that will cause operational problems downstream.  In cases where the resuspended solids can cause issues, it is prudent to have some type of material recovery system that can separate the solids and liquids, and the oil and water, so that all hydrocarbon value can be recovered and waste can be minimized.  This system could be a 2- or 3-phase centrifuge.

·       What maintenance do I need on my Twister?

The Twister is designed to be almost maintenance-free for permanent installations.  We do recommend activating the Twister handle to rotate the swivel on a quarterly basis, and using the 3” port to keep the area around the nozzle clear of solids buildup.

·       Can the Twister be automated?

Yes, via air actuation.  However, we find that most clients prefer the simple manual operation, as typical circulation periods are 48 hours or less.

·       Can lights & cameras be added to the Twister?

The Twister is a Submerged Jet Mixer, and shoots its discharge stream below the surface of the product, so you will be unable to see anything.  However, when used for a water wash after desludging, a temporary bank of lights with a camera can be mounted as a separate accessory above the Twister.

·       Can you also supply pumps and ancillary equipment with the Twister?

We would be happy to provide quotes on pumps, strainers, hose, etc., depending on your needs.