Tank Cleaning 101

Tank cleaning can be a very diverse process culminating into disciplines that require experience, mechanical & process engineering, as well as a very good understanding of fluid dynamics. In order to assist in your learning curve the following information is offered in an effort to assist you in selecting the best approach for your cleaning requirement.

 

I. Tank cleaning basically falls into the following categories:

01) Manual Cleaning

Manual cleaning is very common and simply involves a person using a hand held lance or pressure washer or a squeegee or scrub brush and entering the tank to be cleaned and manually using those tools to remove the non-desired material in the tank.

Pro's: Allows for detail attention to certain areas of the tank by the worker.

Con's: The worker is subjected to dirty and hazardous enviroments that can easily result in health degradation or death. Cleaning time is typically longer than other methods and uses more energy resources.

02) Automatic Cleaning Fixed Installed

This category is the process whereby a cleaning design is determined for the tank or process vessel to be cleaned by means of a quick visual inspection and/or a detailed installation analysis using CAD and other fluid dynamics tools and considerations. The cleaning arrangement is permanently installed in the tank and is only removed for periodic maintenance requirements.

Pro's: Allows for a detailed shadow analysis of the tank, therefore optimizing the location of the cleaning device or devices. Pattern matrix development is consistent from one cleaning recipe to the next so that cleaning validation is more readily controlled. Equipment maintenance is much more controlled as the device or devices are not handled by workers except for periodic maintenance. Cleaning is also much faster than portable cleaning methods. This method also allows for multiple tanks to be cleaned and CIP Systems to be designed more effectively.

Con's: Installations are more capital intensive as they will require more cleaning units installed.

03) Automatic Cleaning Portable

This category is the process where by a selected cleaning design is chosen, installed into the tank to be cleaned, and then removed from the tank once the cleaning has been accomplished.. The cleaning device is never left in the tank whilst it is in service.

Pro's: Allows for good impact cleaning and removes the worker from the tank during the cleaning process.

Con's: A worker in most cases will have to enter the tank to set up the cleaning device or at lease expose the tank to the outside atmosphere. Installation location is usually not optimized and the cleaning device must be such that it is easy to be manhandled by the worker(s).

04) Flotation or Fill and Boil

This category is the process of filling a given tank to be cleaned with the required cleaning fluid and then agitating that fluid with mixers and with elevate fluid temperatures to achieve the cleaning desired.

Pro's: Allows for good coverage of the tank and temperature transfer to the surfaces to be cleaned.

Con's: Uses large volumes of fluid compared to other methods and does not utilized the impact values of other methods.

 

II. Tank Cleaning Devices basically fall into these following categories:

01) Hand held lance or pressure washer.

Typically a hand held trigger gun that will release pressure and flow when the trigger is pulled. Predominant applications will use a pressure washer in the range of 1,000 PSIG (69 BAR) to 20,000 PSIG (1,379 BAR).

Pro's: As mentioned in the manual cleaning method above this method does allow for detailed cleaning of certain areas within the tank. Con's: The worker will need to be in the tank to clean the tank internals and equipment maintenance for this type of cleaning setup is typically more than other methods.

02) Dynamic rotating jet-head

Pro's: Excellent technology for the internal cleaning of tanks and process vessels whether on a fixed installed basis or portably. Able to cover tanks >= 200 feet (61 meters)

Con's: Incur's a purchase cost that must be weight against other methods. Typically the cost benefit of using these type of devices far exceeds labor and utility cost associated with other types of cleaning devices.

03) Dynamic rotating spray head

Pro's: Very good cleaning technology for the internal cleaning of tanks and process vessels when the tank size requires jet or spray distances on the radius that are typically under 10 feet (3 meters) per device. Typically a low cost solution for dynamic devices when compared to rotating jet-head technology.

Con's: Tank size is limited compared to other devices and the impact value of these devices are 70% to 80% less than with rotating jet-head technology. These devices are more of a rinsing technology and do offer impact values greater than static spray balls. In many cases that is all that will be required for the cleaning requirement.

04) Static nozzle or spray ball

Pro's: The cost for these type of devices are the lowest of all types and do offer a relatively good rinsing effect for certain size tanks and geometry. Mechanically the require no maintenance if properly installed in either fixed installed applications or when used on a portable basis.

Con's: Limited coverage radius per device compared to other device types. Easily plugged or clogged so the cleaning media must be filtered or you will have void areas in the spray pattern. Relative no impact values compare to other devices and once a certain distance is breached, the spray will atomize into a mist.

 

III. High Pressure Cleaning vs. Lower Pressure Cleaning

For the sake of this writing...

a) High pressure range is typically 500 PSIG (34.5 BAR) to 20,000 PSIG (1,379 BAR)

b) Medium pressure range is typically 60 PSIG (4.14 BAR) to 500 PSIG (34.5 BAR)

c) Low pressure range is typically 0 PSIG (0 BAR) to 60 PSIG (4.14 BAR)

 

High Pressure Tank Cleaners

These type of cleaning devices are available as hand held lances, dynamic rotating jet-heads, and to a certain extent static nozzles. Once you breach 500 PSIG or 34.5 BAR the jet will degrade exponentially relative to the flow and eventually reach a point of diminishing returns relative to energy and maintenance cost vs. benefit. These type of devices however are excellent choices when the cleaning requirements require shorter jet-lengths compared to other device per cleaning unit. The jet-velocities are the highest for these type of devices compared to all others listed in this document. Flow rates are typically much lower for these type of device which will reduce the mass in the jet and hence the jet-length and wetting intensity per square foot/square meters Tolerances within the unit are much tighter than with other cleaning devices so as a result filtration is key to avoid too much maintenance. Maintenance in general on these type of units will be greater than other types.

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This webpage and the material contained within in it is copyrighted to the extend possible as provided by international law. Feel free to use this information in your tank cleaning efforts. However, it is not to be reproduced in any way without the expressed written consent of the writer.

 

Author: Troy R. Humphries

Email: troy@humphries.ws

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