Tank Washing Nozzles
Engineering Consideration - Optimising Water and Time Efficiency
Water is money
The true cost of water is often under appreciated.
- Raw utility bill cost per m3
- Cost of filtering and sanitising if recycling wash off
- Cost of caustics or other cleaning fluids
On top of this if we reduce the water needed to clean we can
- Lower Pump running costs (electricity)
- Lower Maintenance cost
- Increase working lifetime for the pump.
-Potentially use a smaller pump (reduced capex)
As the cost of energy and water are both increasing, and likely to continue to increase, reductions in water usage have significant financial benefits to any organisation. Further more the green / environmental benefits are seen a moral imperative by many organisations. Future green legislation is only likely to increase the need for more efficient water usage.
Time is money
The cost of downtime will vary considerably from industry too industry and from application to application. But any down time for cleaning will have a cost associated with it. This cost results from:
- Lost production opportunity
- Potential back logs of orders meaning more overtime required
- Potential lost business as unable to complete orders in time
Any reduction in cleaning times between batches will thus have a value to a business.
The importance of nozzle selection
Correct nozzle selection can dramatically affect the amount of water that is required to clean and or the time required to clean. Efficiency in the context of tank washing is a basically the cleaning power per cubic metre of water used. Whilst water usage is easy to measure “cleaning power” is a somewhat nebulous term. It is perhaps best defined kinetic energy delivered per square meter per minute. This is hard to measure for any given spray set up but the following rules of thumb can be applied:
1- The less the spray is broken apart the more energy is transferred to the target service. This is because the total potential energy of the fluid is used to break apart sprays leaving less for projecting the spray forwards.
2 -The more time a spray dwells on a given area the more energy is delivered.
3- Any over spraying on a given area is wasted water, you can only clean once!
4- The broader the spray pattern is the faster complete coverage can be achieved.
Conclusions
Solid stream jets will be the most efficient in energy transfer. But the fact that the area of impact is very low for solid stream nozzles means that complete cleaning may take longer. Further more solid stream nozzles may result in “over cleaning” if the impact is higher than is actually required then water is being wasted.
Implications
The most water efficient nozzles will be rotary solid stream nozzles followed by rotary flat fan nozzles with static omni-directional nozzles being the least efficient.
Potentially the most time efficient nozzles are omni-directional nozzles as complete coverage will be delivered more or less instantly. But it needs to be remembered that the static nozzle is likely to require a reasonable dwell time before it will clean properly. For many cleaning applications the length of cleaning cycle required may actually be longer than rotary nozzles.
Solid stream rotary nozzles are powerful tank cleaners and may be "overkill" for light washing of small tanks. Over cleaning is a pointless waste of water and time.
For more details on improving efficiency please click on the box below to access a relevant technical article.
Nozzle selection
For very light rinses of smaller tanks static spray nozzles may be the most efficient from a time and water usages perspective.
For tanks with diameters larger than a meter or so a rotary nozzle is almost certainly going to be more water efficient and, with the exception of tanks requiring a quick rinse for a few minutes, will more than likely clean more quickly as well.
For larger tanks or tanks with tough residues rotary solid stream nozzles will be the quickest and most water efficient cleaning system.