Sludge tanks treatment

Arrow Operations and Technologies are capable of treating and recycling sludge from various tank types.

Oil Tank Cleaning and Oil Recycling

Large refineries, petrochemical and energy companies hold heavy oils, as crude oil, in large tanks. With time, heavy sediments accumulate at the bottom of the tanks, partially obstructing the tank & preventing its proper and economical operation. Maintenance teams must shut-down operation & clean the sediments.
They also perform routine maintenance, e.g., welding, that require a gas-free state within the tank.

Cleaning such tanks requires a massive work force & long shut-down periods  of the tank, up to several months. Furthermore, petrochemical companies do not accept the sediments for re-use. Regulations classify these sediments as hazardous waste which requires disposal in special depositories. All this makes tank cleaning a costly operation.

Arrow Operations and Technologies (from the founders of Arrow Ecology, an ISO 9000 certified firm), has developed a unique method for cleaning these tanks: two workers run a thermo-chemical process, cleaning a 15,000 m3 (Fifteen Thousands) tank to near gas-free state within three weeks or less. The treatment unit is mobile; it can reach distant and difficult sites.

Main customer’s benefits are:

Lower direct costs of cleaning.

Recycling of close to 95% (Ninety five percent) of sediments that go back to re-use by customer.

Reduced cost in disposal of only 5% (Five Percent) of sediments which require special post-treatment.

Substantially shorter shut-down time.

Principle of Operation

The aim of the cleaning & recycling operation is to remove the sediments accumulated on the tank bottom in a safe, efficient and time saving manner. This is achieved by the combination of applying mild heating to the sediments while employing a water-based treatment solution. This solution serves as both the heat carrier into the tank and as the separating agent. The solution is environmentally safe. The chemicals used to prepare the treatment solution are a unique combination of absolutely environmentally safe chemicals which are added at very low concentrations. It is important to note that these chemicals have no effect on the quality of the recycled oil and do not enter the oil phase.
Apart from enhancing the separation of valuable oil from the sediments, these chemicals also reduce the formation of an emulsified interface between the recovered oil and the water-based treatment solution. The heating stage forms distinct 3 phases inside the tank. The upper phase contains oil and hydrocarbons, the middle consists of the water-based treatment solution and the bottom carries the heavy residues.

During the heating phase, oil which is released from the sediments is being transported to the upper phase while heavy non-organic sediments which were entrapped inside oil particles sink to the bottom.
The following figure depicts the distribution of the 3 phases formed during the heating phase:

Once the heating phase is finished, the warm oil is pumped to a storage tank and the treatment solution is either transferred to the next tank to be cleaned or neutralized and disposed off.

The Cleaning Process

The cleaning process consists of 10 steps as follows:
1.    Site characterization including field tests on sludge samples
2.   Setup of equipment
3.   Connection of hydro-thermal unit to the tank with injection headers and flexible pipes
4.   Final inspection of system coordinated with the client’s engineers
5.   Heating phase
6.   Oil recovery and transfer to storage tank
7.   Transfer of treatment solution to the next tank to be cleaned or neutralization and disposal
8.   Sediment removal from tank bottom
9.   Inspection of the tank
10. Commissioning of the tank by the client’s engineers

Step 9 is either performed by a remote controlled robot which travels on the
tank’s bottom or, when tank architecture prevents the safe and efficient operation
of the robot, by workers. At this stage, the tank is free of harmful gases and oil,
hence, the risk to the workers is diminished. In any case, the workers are
protected by protective clothing and gas masks. Due to the unique process of
Arrow, the sediments are removed and transferred for post treatment. 

It is important to note the following:
1. No changes what-so-ever are made to the client’s tank or piping.
2. The whole work is carried under explosion proof conditions without any source of open flame or sparks.

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