الطرق الاتوماتيكية لتنظيف خزانات البترول والزيوت والمنتجات البترولية الخام

Automatic Tank Cleaning & Oil Recovery System

by

general.dr

bahaa badr

technolab el-bahaa group

Crude oil and inflammable liquid storage tank owners are required to inspect them at scheduled intervals according to legal regulations or standards. All tanks must be cleaned before they are inspected.

It is not so difficult to clean small capacity storage tanks containing light oils and little sludge.

In contrast ,it is very difficult to clean large-capacity storage tanks, with a diameter of 30 to 100 meters or more, containing a large amount of sludge, such as crude oil storage tanks.

OurS.R.S.(SludgeRecoverySystem), based on the C.O.W.method,is an automated, mobile and modular, non-manned oil tank cleaning system.

Compared to manual cleaning techniques, S.R.S. cleans tanks much more safely and quickly.

A distinctive feature of the S.R.S. is its closed loop cleaning system, which heavily reduces the impact of tank cleaning on the environment and provides near 100% hydrocarbon recovery.

Our systems stems from oil-tanker cleaning methods and it has been adapted and perfectioned to clean above-groundstorage tanks.

The S.R.S. (SludgeRecoverySystem) fluidizes the hydrocarbon phase of the sludge, by injecting the same fluids that generated or, as it often happens in refineries, using cuts compatible with the sludge to be cleaned.

Sludge fluidization is determined by the chemical action of fresh oil, and by the mechanical action of Jet Washers that, properly installed on the tank roof, eject the fresh oil stream at a pressure of 6 bar approx.

This way the hydrocarbon phase, within the sludge, is dissolved in the fluidizing oil, and the inert portion (sand, earth and debris) is left inside the tank. The fresh oil intake and the fluidized phase return can be continuous or discontinuous, according to the cleaning procedure agreed with the Client.

S.R.S TYPICAL LAYOUT

A discontinuous procedure is selected to minimize the use of fluidizing oil, but it requires more time.

A fluidized phase is returned to the Client who can process it accordance with their needs.

For instance, in some operation of ours, it was returned:

To another tank;

To another tank that was feeding the topping tower;

To the line feeding the topping tower, at controlled rates (±0,1 m3/h)
In all cases the stream is filtered by 11 mesh size strainers.

After the oil washing phase, the quantity of residues can be minimized to be disposed to the landfill, through hot-water washing (70-80°C).

During this phase the stream gets thru an oil/water separator. The oil stream is returned to the client, the water stream is returned to the tank.

After water washing, the residue usually has an oil content lower than 20% (by petrol ether extraction 40/70 -IRSA/CNRQ64N21).

At the end of S.R.S.operations, the tank’s man-holes are opened, natural and forced ventilation is applied, and workers can safely enter the tank to take out the final residues.

THE SYSTEM

The S.R.S. mainly consists of:

A –Unit
B –Unit
Separator Tank
Jet Washers
O2 Monitor
A–UNIT

The A-Unit is used to suction oil from the tank being cleaned and transfer it to an oil-receiving tank.

The dissolved sludge and the oil are temporarily suctioned into the ejector vessel and transferred to the receiving tank, through are covery pump(power:75kW,400V@50Hz;flow-rate:180m3/h;head:10bar).

All inflammable gases suctioned by the vacuum pump are returned to the tank being cleaned. This is to keep the area surrounding the workplace safe and to hold the internal pressure of the tank being cleaned, at a positive level.

The liquid level and the degree of vacuum are controlled by automatically starting and stopping the vacuum pump at a signal from a level controller and a vacuum pressure sensor/transmitter.

B–UNIT

The B-Unit is used to feed washing oil to the Jet Washers.

The heat exchanger may be used to heat oil or water for tank washing.

When the A-Unit and the B-Unit are connected the following advantages will result:

Two pumps are available for oil transfer operations.

When dismantling the temporary piping, the oily water left init can be easily recovered into the ejector vessel.

Both the recovery and the washing pump can be used for crude oil cleaning operations.

SEPARATORTANK

A separator tank is used to separate oil from water during water-washing operations.

The separator tank is equipped with a container with a retractable roof.

The insert includes a weir that creates an intake area between the weir itself and the side wall;

an inlet gap to introduce the surface oil into the intake area; wherein the weir is positioned in such a way that it induces the influent liquid to flow in a swirling motion within the intake area.

JETWASHERS

This is the core of S.R.S.

It is a washing machine that will dissolve and discharge sludge.

SRS has devoted much attention to the design and construction of Jet Washer type AM-70.

SRS Jet Washer AM-70 is a washing machine with a unique mechanism and an excellent performance standard, it has been developed for the effective cleaning of oil tanks.

The washing liquid passes from 3-inch flange outside the pipe and is injected from the tip of nozzle. Orbital rotation and axial rotation of nozzles are obtained by the rotation force of air motor and gear mechanisms.

Some data about Jet Washer:

Maximum Outer Diameter:70mm(allows installation inside the support guide)

Dispensing Volume:90m3/h @ 7kg/cm2

Driving Force:air motor,maximum pressure 6.1kg/cm2

Repeat Angle:[45-105-45]or[105-140-105] degrees

Main Material:ASTM304; ASTM316;aluminum alloys

ActualLength:1’950mm

Weight:45kg

O2MONITOR

Oxygen concentration within the cleaning tank is held below 8%(vol).

Using an automatic monitoring unit, oxygen concentration is constantly monitored at six locations in side the Tank.

FEATURES OF THE SYSTEM

The reasons why our clients prefer to select S.R.S. tank cleaning are the following:

a. Maximum recovery of hydrocarbon phase contained in the sludge,(upto98%)whose value often pays the overall cleaning operation;

b. Minimum quantity of material to be disposed of,just the inert portion saturated by water and HC(its dryresidue,at 600°C,is approx 35%);

c. Minimum tank downtime, the cleaning operation fluidizes from 200 to 400 t/day of sludge, dependingon sludge quality;

d. Minimum overall cost of tank cleaning operations;

e. Best cost/benefits ratio;

f. Highest possible safety level of operations, according to the most recent CE regulations;

g. Elimination of Health and Safety risks run by the operators; the iraccess, into the tank, is restricted to the final phase, when the tank internal atmosphere is neither flammable nor hazardous;

h. Environmental risks off; e the System operates through a closed cycle.

WHERE S.R.S. WORKS

The S.R.S. can be used to clean whatever type of tank, best results are obtained with:

1.Crude oil tanks

2.Fuel oil tanks:

a.Intermediate cuts (topping and vacuum bottoms);

b. Heavy oil;

c. Light oil;

d. Oil emulsion;

3.Tar and bitumen tanks.

OPERATION

Flow Scheme

MOBILIZATION

Cleaning plans, drawings of temporary piping, schedules, lists of outgoing materials, manpower mobilization schedules, procurement plans, and transportation plans are prepared.

The S.R.S. is installed according to the mobilization plan approved by the customer.

The mobilization process involves the installation of A-Unit, B-Unit,Separator Tank and Jet Washers.

The time required for mobilization of the S.R.S and the auxiliary equipment varies depending on the complexity of the job, but usually it does not take longer than a week.

The auxiliary equipments are setup in accordance with prevailing regulations regarding potentially hazardous zones.

The zones are setup to meet the highest international safety standards and directives when working in potentially hazardous environments.

Depending on the diameter of the tank, the required numbers of nozzles are installed in the roof.

This is either done through existing openings or new, cold tapped openings safely made with the certified safe tap tool.

The nozzles are key to ensuring an optimal cleaning result. Their
unique indexed washing pattern fully covers the tank’s complete surface.

OUTLINE OF S.R.S

The S.R.S. is connected both to the Tank and to a sister tank for the supply of cleaning oil and receipt of dissolved oil.The two are connected by temporary piping.

Temporary piping is connected. Leakage tests are carried out so as to ensure complete connection.

TANK BLANKETING

For the purpose of disaster prevention due to static electricity that may arise from Jet Washer operations, an inertgas(normally nitrogen)is fed into the space.

The purpose is to reduce the oxygen level to below 8 percent, eliminating by so doing the risk of explosion.

This oxygen level is held for the entire cleaning process. When S.R.S is employed for the cleaning of floating-roof storage tanks, the probability for the system to discharge ignitable electrostatic sparks is extremely low.

However, in order to ensure safety in the event of emergency, explosion-proof measures are taken.

This device measures oxygen density thanks an automatic change over mechanism through both
indications and records.

It is composed of an O2 sampler and an O2 density monitor.

A mixture of inflammable gas and oxygen (air)causes an explosive combustion whenever the mixing ratio of gas to oxygen is reaches a certain level. No explosive combustion occurs when the mixing ratio is out side the explosive combustion limits

Our gas sampler is explosion proof.

DESLUDGING & CLEANING

SRS Jet Washers are installed on the roof (floating or fixed)of the tank and play a basic role in thecleaning process.

Generally Jet Washers are assembled in the centre of some roof supports, there fore avoiding the need to cut through the roof.

Clean crude oil is used as cleaning oil.

The cleaning oil is ejected through SRS Jet Washers toward the sludge deposited within the Tank in order to break,dissolve,disperse and fluidize the sludge.

The fluidized sludge is then flushed out of the Tank.

The cleaning process consists basically of oil wash

Desludging is the first process of tank cleaning and it is also where most of the oily sludge from the tank is removed.

The desludging process may begin after the oxygen level has fallen below 8 percent.

The nozzles are operated alternately.

Since the sludge may contain solids, water and trapped liquefied oil it may be necessary to add cutter stock to re-liquefy the sludge.

The cleaning process consists basically of oil wash. The nozzles use re-circulated oil as their primary cleaning media and their effectiveness is due to their far-reaching, low pressure high impact jets. The nozzles are compressed air driven and they can be operated two at a time.

After oil cleaning, there are cases in which the Tank is further cleaned with hot water. Such cleaning operation removes almost all oil components from inside the Tank facilitating there fore the manual finish-cleaning. The nozzles can be programmed to focus on areas that require more intensive desludging.

CONTROL

The system is easily operated and monitored by a few trained operators via user-friendly controlpanels.

In addition to this, personnel must undergo a comprehensive training programme to operate the S.R.S. as well as a safety-procedure training.

The panels, provided with explosion-proof start and stop switches, are used to control pumps and air compressor.

SRS Research & Development department is planning and testing an S.R.S.remote monitoring; the picture shows a prototype of the Digital Monitoring

OILTRANSFER

Before SRS’ Jet Washers are started, all fluidic oil remaining in the Tank is transferred through the drain nozzle at the bottom of the Tank to a receiving tank.

After the floating roof deck support reaches the tank bottom, space is formed inside the Tank.

S.R.S. operations remove almost all the deposited sludge. However, in order to ensure complete removal of oil, there are cases when hot-water cleaning is performed after S.R.S. operations.

HOT-WATER CLEANING

The Tank is filled with a quantity of hot water, which is made to circulate through an oils eparating tank to recover oil.

Hot-water cleaning is more effective in the removal of greasy matter but it is likely to emulsify the remaining sludge and for moisture-containing sludge as by-product.

INTERNAL FINISH-CLEANING

The portions of the tank that are not completely cleaned and rusty are scraped and brushed.

All mud, sand and rust deposits, solid matter and sludge, within the Tank, are removed. All the work is done manually.

The Tank is required to be finish-cleaned to the extent that the use of fire is allowed inside it.

When a Tank is to be cleaned for the storage of a different kind of oil, then it will require a cleaning based on different standards.

DISMANTLING OF TEMPORARY INSTALLATION

Finally demobilization and de-installation of the tank cleaning system takes place. As soon as the tank atmosphere has been approved by a safety officer, personnel will be free to enter.

Temporary piping is disconnected, and all materials are removed from the location of the cleaned Tank.To facilitate transportation S.R.S. is built into standard 20'flat rack containers..

BENEFITS OF S.R.S.

VALUE OF RECOVERED OIL

The hydrocarbon recovered through an S.R.S.cleaning,is 95%of hydrocarbon in the sludge.

These will be dissolved in the fluidizing oil and carried to the production, thus becoming a true recovery.

The hydrocarbon recovered through manual cleaning is“zero”, because hydrocarbons transferred by the manual cleaning to the receiving tank, will settle in side it, and will never go back to production.

This situation will generate a further cost when the receiving tank will need to be cleaned.

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