What is the most effective oil tank cleaning method - high pressure or low pressure jetting?
Studies show that low pressure jetting methods (5-15 bar) using high re-circulated cleaning fluid flow rates clean tanks more efficiently than traditional high pressure methods (100-2,500 bar). This is measured in terms of time and cleaning fluid consumption.
Low pressure versus high pressure jetting methods
The graph below illustrates the effect of jetting distance (from nozzle tip to tank wall) on the jet impact pressure on the tank wall (measured in mm water) for high pressure (HP) and low pressure (LP) jetting methods.
At short jetting distances, a high pressure jet exerts greater jet impact pressure on the tank wall. However, this higher impact pressure is quickly lost as jetting distance increases, because the kinetic energy of the HP jet is absorbed by the acceleration of the air molecules surrounding the jet.
As a result, the wall impact pressure of the HP jet drops off very rapidly as it gets further away from the tank wall. Already at a distance of 30 cm (12 inches) from the nozzle, the impact pressure of a LP jet with a fluid flow rate in the range of 250-5000 l/min (60-120 GPM) is 100 times greater than that of HP jet with a fluid flow rate in the range of 75-125 l/min (20-30 GPM).
Note: This graph is a double logaritmic projection.
HP jetting systems are effective for short-distance hydro-blasting applications. Long-distance jetting used for the internal cleaning of larger tanks, such as oil storage tanks, is most effectively accomplished using LP jetting methods.
Benefits of using LP jetting methods for tank cleaning (compared to HP methods)
- Faster cleaning provided by higher impact pressures and higher cleaning fluid flow rates.
- Lower consumption of cleaning fluid resulting as cleaning fluid is re-circulated. (HP systems normally cannot operate with re-circulated cleaning fluid).
- Lower investment costs for cleaning system.
- Lower total operating costs for the cleaning job, due to reduced cleaning time and lower utility consumption.
- Safer cleaning operation, because staff don´t need to enter tanks, eliminating exposure to a hazardous environment.