COW --- Crude Oil Washing
CRUDE OIL TANK CLEANING SYSTEMS
No more manual tank cleaning. Our non-man entry tank cleaning system safely desludges any crude tank in 80% less time, recovering 95% of hydrocarbons. You will save moneyfrom reduced tank downtime and earn money from marketable crude at the same time. Find out all details below.
Zaopin Technologies offers a unique, all-in-one crude oil washing (COW) system for the complete removal and separation of all sludge and sediments from the tank, including the treatment of solid oil waste.
Having a broad scope of application, it is equally suitable for fixed and floating roof tanks and cleans tanks with a storage volume of up to 150,000 m3.
Our system consists of 2 main units:
- Zaopin COW System: A fully automatic no-man-entry crude oil washing (COW) system using powerful high-pressure, high-impact washing cannons to break up the sludge, combined with a sophisticated oil sludge separation system that recovers most of the oil from the sludge.
- Zaopin Dozer: Any remaining non-organic sediments on the tank floor are safely removed with our special cleaning vehicle that can be operated by only one person.
Oil Sludge Causes Trouble
Oil sludge, also called tank bottoms, are sediments forming at the bottom of an oil tank, reducing valuable storage capacity. In crude oil storage tanks, the sludge is a deposition consisting of high-molecular-weight paraffins, asphaltenes, water and inorganic solids.
The sludge needs to be removed periodically, not only to restore storage capacity, but also in order to:
- Comply with inspection policies that require the tank to be free of any sludge.
- Avoid clogged suction lines and damages to downhole refinery equipment.
- Change the product of the storage tank.
Turning Waste into Profit
The Zaopin COW tank washing system turns the slow and risky process of manual sludge removal into a fully automated operation that not only is much faster but also lucrative due to large amounts of valuable hydrocarbons recovered from the sludge.
With sludge volumes reaching several hundred to several thousand cubic meters per tank, the money value of the separated oil can be significant.
Likewise, by removing all tank bottoms, valuable storage capacity is freed up, making the operation of the tank more profitable.
The following key advantages make the Zaopin COW system suitable for even the largest tank cleaning projects:
Cleans Any Storage Tank
- Floating and fixed roof tanks, including old riveted tanks.
- Storage tanks with a volume of up to 150,000 m3.
- Complete desludging, independent of the thickness of the sludge.
Handles Most Hydrocarbons
- Crude oil
- Bunker fuel, heavy fuel oil (HFO)
- Heavy gas oil (HGO)
- Residual oil, wax, bituminous residue, and hard sludge deposits
- Lighter distillates (white oil) are handled by our Product Tank Cleaning System.
- Non-man entry system: No personnel is inside the tank during any cleaning operation.
- Fully automatic tank cleaning and oil separation for maximum safety & efficiency.
- Minimally invasive, damage free installation. No cold-tapping required.
- Inert gas system with constant monitoring of explosive gases (LEL).
- Construction and installation to ATEX 95 (ATEX 114)
- Operation in accordance with ATEX 137.
- Containerized module system for fast installation.
- Streamlined cleaning and separation system reduces tank downtime.
- Complete removal of oil bottom sludge, including non-organic sediments, to fully restore the original storage capacity of the tank.
- Reclaimed oil can be sold as valuable product for profit.
- Nitrogen generator included: Produce cheap nitrogen as needed. No more dependence on external gas providers.
- All-closed cleaning system minimizes emissions.
- Much reduced oil waste that needs to be disposed of.
95% Oil Recovery
Up to 95% of hydrocarbons are reclaimed from the sludge, depending on the amount and particle size of the tank bottoms. The separation process is so precise that the oil recovered is essentially free of impurities and thus of high market value.
Thanks to the high recovery rate of marketable hydrocarbons, the Zaopin tank cleaning literally pays for itself, even at low global oil prices.
How Clean is the Output?
The Zapin COW non-man entry tank cleaning system cleanly separates oil bottom sludge into its oil, water, and solids phase. On average, the following impurities remain after desludging:
|Water||Hydrocarbons||< 100 ppm|
|Solids (cake or dry sludge)||Hydrocarbons||~5%|
80% Waste Reduction
Without further treatment of the oil sludge, as is the case in manual tank cleaning, 100% of tank bottoms end up as hazardous waste. Not only does this waste pose a high impact on the environment, it is also expensive to dispose of and takes up precious space at the tank terminal when stored locally.
This all changes when employing the Zaopin COW system. Due to the clean separation of sludge into its oil, water, and solids phase, only a small amount of solid matter, which also is much less hazardous than the original sludge, needs to be disposed of.
More precisely, by separating the sludge into its components, the total waste volume is reduced by 80%, on average.
Depending on the composition of the sludge, the solid waste returned by Zaopin COW contains about 5% of hydrocarbons.
In cases where a further reduction is required, our Zaopin SOR slop oil recovery system can be used to further treat the cake or dry sludge. Specifically designed to treat oily waste, Zaopin SOR reclaims close to 100% of the contained hydrocarbons. The discharged solids are considered non-hazardous and safe for landfill disposal.
80% Reduced Tank Downtime
Desludging your tank with the Zaopin Tank Cleaning System is very fast. In fact, compared to manual tank cleaning, the tank downtime can be reduced by over 80%.
Thanks to a highly standardized operation process, the cleaning schedule is very precise, allowing you to reliably estimate the amount of time needed for desludging any given tank:
|Cleaning Step||50,000 m3 Tank||100,000 m3 Tank||150,000 m3 Tank|
|Installation||1 day||1 day||1 day|
|Nitrogen blanketing||2 days||2 days||2 days|
5 days 
+12-14 days 
|Water wash||2 days||2 days||2 days|
|Inspection||1 day||1 day||1 day|
|Disassembly||1 day||1 day||1 day|
 Sludge height below the bottom manhole (up to 60 cm).
 Each additional meter of sludge.
How The Equipment Works
The COW system combines non-man entry tank cleaning and oil recovery into a single operation.
How does it do that?
The following step-by-step description of the cleaning and oil separation process provides all the answers.
Tank Cleaning Process Overview
- Preparation: Transportation of our mobile cleaning unit on-site, installation of the high-pressure washing cannons, and nitrogen blanketing of the tank.
- Oil wash (desludging): Automatic liquefaction of the sludge, removal from the tank, and separation of its oil, water, and solids in a closed-loop system.
- Water Wash: Automatic cleaning of the tank from any oil residue on the walls and bottom of the tank and recovery of the oil from the water.
- Sediment Removal (optional): Complete removal of any residual sediments that might be left on the tank bottom using our specialized cleaning dozer.
- Disassembly: Removal of the cleaning equipment from the tank.
First of all the tank is drained, but a small amount of crude—about 15 cm above the sludge—is left to be used as the washing medium during the first cleaning step (oil wash). Alternatively, if the tank is already empty, oil from an adjacent tank can be used instead.
Next, high impact cleaning cannons are securely mounted to pre existing manways at the top or bottom, depending on the type of tank and the height of the sludge. Each cannon comprises of the following major components:
- A large cleaning nozzle, movable 180 degrees horizontally and vertically that flushes the tank with a pressure of 27 bar at a flow rate of 50 m3/h.
- A video camera and headlamp for easy monitoring and recording of the cleaning process.
Less is More
Because of their superior performance, only 1-4 cleaning cannons need to be installed per tank (compared to up to 15 jet guns required in traditional tank flushing systems), thus significantly cutting back on installation time and costs.
Finally, the empty space of the tank is filled with nitrogen gas produced by the Zaopin N2generator module until the oxygen content is below 8%. Throughout the cleaning process the amount of oxygen and presence of explosive gases (LEL) is automatically monitored and regulated.
The actual cleaning process is divided into two parts, an oil wash, followed by a water wash.
Oil Wash (Desludging)
The first and main washing step is the oil wash, which uses the oil left inside the storage tank for desludging.
The oil is heated and pumped through the cleaning cannons under high pressure, breaking up and liquefying the sludge. The movement of the cleaning cannons is computer-controlled to ensure there won't be any blind spots left.
Dissolved sludge is constantly pumped from the tank to the separation modules where it is separated into its oil, water, and solids components:
- Part of the separated oil is re-heated and re-circulated to the manhole cannons to be reused for washing.
- The water is clean enough to be fed directly into a waste water line.
- The separated solids are suited for incineration or special landfill disposal.
Throughout the oil washing phase, the flushing medium is re-circulated inside a closed loop until all sludge has been removed and processed. This closed system has the advantage of sealing the cleaning process from the environment and minimizing the amount of washing medium required to clean the tank.
In a separate washing step, water is used as the flushing medium to remove any oil residue from the bottom and walls of the tank.
Oil-contaminated fluid from the tank is constantly pumped to the separation modules, where the oil is separated from the water. The treated water is then recirculated to the manhole cannons and re-used for washing in a closed loop until the tank is completely clean.
The whole cleaning process is fully automated and safely monitored from the control room inside the monitoring container.
After the last cleaning step—depending on the composition of the sludge—sometimes a thin layer of high-density inorganic sediments remains on the tank floor. Those sediments are easily removed using the Zaopin extractor, a small, hydraulically-powered cleaning dozer that can be assembled inside the tank in less than 2 hours.