If tanks and vessels are to be cleaned effectively, it’s essential to pick the right cleaning head technology, writes Michelle Knott.
An array of static and rotary spray heads and jets can be used to clean tanks and vessels. Knowing which system is right for your particular combination of tank and residue can have a major impact on efficiency in terms of cleaning time and the consumption of water and chemicals.
“There are three forms of cleaning head technology, fixed spray balls, rotary spray heads and rotary jet heads. With today’s massive pressures on CIP [clean-in-place] optimisation/ minimisation of water and chemicals to drain, the focus on the correct choice and use of the right cleaning head technology is very important,” confirms Jacqui Kennedy, marketing manager for inTank Technologies.
“To be able to minimise the cleaning fluid volume requirement and achieve the fastest repeatable cleaning cycles we have to maximise the coverage of the internal surface area of the vessel. If we can maximise coverage as well as impingement values we can reduce flow rates dramatically.”
With today’s massive pressures on CIP [clean-in-place] optimisation/ minimisation of water and chemicals to drain, the focus on the correct choice and use of the right cleaning head technology is very important
Jacqui Kennedy, marketing manager for inTank Technologies
Ivan Zytynski, marketing director for The Spray Nozzle People group, suggests that the key to understanding the pros and cons of different systems is to realise that effective cleaning is a combination of four parameters: time, mechanical action, heat and chemical action. It’s the mechanical action that is primarily affected by the choice of spray head or jet.
“The mechanical action element is effectively a function of how the cleaning fluid is delivered to the cleaning surface. Similar volumes of water will achieve drastically different mechanical actions depending on the nature of the delivery. And delivery of the fluid depends on the pressure it is sprayed at and, most importantly, on the type of tank cleaning head used,” he says.
“At one end of the scale we have a finely atomised spray which delivers almost no mechanical action other than the gentle rinsing as the water runs down the side of the tank. At the other end of the scale the same volume of water delivered in the form of a high-pressure jet will contribute a very high level of mechanical cleaning action.”
The mechanical action element is effectively a function of how the cleaning fluid is delivered to the cleaning surface. Similar volumes of water will achieve drastically different mechanical actions depending on the nature of the delivery
Ivan Zytynski, marketing director for The Spray Nozzle People group
For a fixed spray ball, one issue is that the jets emerging from the ball diverge as they travel. This means that much of the vessel surface experiences no direct impingement at all, as Kennedy explains: “Although the jets on the ball are approximately only 10mm apart, by the time the jets reach the internal surfaces of the tank wall the pattern mesh will be much courser, possibly 100mm-plus, meaning that in between the jet impact hot spots the internal surface of the tank is just rinsed.”
She also notes that any internal tank ‘furniture’ will exacerbate the situation: “The chances that the general 360° spray pattern will target up inside the vessel’s inlet connections, agitator blades, shafts, baffles and fill pipes is minimal.”
The lack of mechanical action may call for more water and chemicals or a longer cycle to achieve effective cleaning. “With spray balls and other static tank cleaning systems we tend to see increased flow rates and cleaning times,” says Zytynski. “In short, static spray balls are very water inefficient.”
At the other end of the scale are impingement cleaners, which use higher-pressure jets to deliver high-impact cleaning. The mechanical action is increased so they can use less water, but the directional jets must work their way through a 3D rotating cycle that enables them to cover the entire tank surface, and that takes time.
“Anything under the minimum time and cleaning will not be complete, so unlike spray balls, there is a hard lower limit on the amount of time rotary jet cleaners need to work for. This can mean that rotary jet cleaners are not suitable for small tanks or residues that only need quick rinse cycles from static nozzles,” says Zytynski [pictured above is the orbitor ECO fast-cycle rotary jet cleaner from The Spray Nozzle People].
“For the larger, harder-to-clean vessels, where the product needs good levels of impingement to remove it, we use the rotary jet head,” says Kennedy. “This technology requires only 50% of the cleaning fluid volume to clean the same sized vessel as compared to the fixed spray ball. During the pre-rinse we would expect the vessel to be 95% clean, which means that the caustic phase will become much less contaminated.”
Caustic fluid is typically reused several times, so a more effective pre-rinse enables it to be recycled many more times before disposal.
Rotary spray heads are the middle option. These rotate to increase the direct coverage provided by the spray but operate at the lower pressure typical of static spray heads, in contrast with impingement cleaners.
Better coverage
Swapping round holes for slots in the head also swaps narrow jets for fans of water, which can further boost the coverage. “This improved coverage enables us to reduce the required flow rate by at least 30% and cleaning cycle times between 30 and 40% [compared with fixed sprays],” confirms Kennedy.
“Rotary spray balls…have the advantage of not needing to conform to a minimum cleaning cycle as complete coverage is achieved within a few seconds,” says Zytynski. “However, given the limited mechanical action of rotary spray balls, considerable time is still required to achieve cleaning, particularly for tougher residues.”
The need to optimise so many different parameters means it’s often worth getting advice from suppliers, especially since some recent developments, such as fast cycle jet cleaners and Burst Rinse technology, could provide a new optimum solution in certain applications.
Until recently, the general rule of thumb has been that impingement cleaners make more sense for bigger tanks and more persistent residues.
With this in mind, they tend to be geared to move slowly around the tank for a thorough clean, making them inefficient in smaller tanks with lighter residues, where the fixed cycle time is wastefully long.
Cleaning cycles
Fast cycle jet cleaners are geared to run faster than conventional impingement systems, enabling them to run through their cycles faster and minimise water use.
“The fast gearing means some mechanical action is lost at further distances because the fast motion of the jets causes them to break up more quickly than on slower geared machines. However, for smaller tanks (below three or four metres in diameter) the fast-moving jets maintain integrity to deliver impact cleaning. This means that these new cleaners can replace spray balls and achieve very significant water savings per cleaning cycle,” says Zytynski.
Burst Rinse technology is a new way of operating CIP to maximise the benefit of the chemical cleaners. Conventional cleaning cycles begin with a pre-rinse before introducing more expensive caustic cleaning fluid
“Of course, any gains in water and time will need to be weighed against the cost of the jet cleaners, as they are more expensive than static spray balls. Furthermore, there might be some increased pumping costs as they may need to run at higher pressures. However, if water consumption per cycle can be reduced by a factor of five or more then these additional costs will quickly be recouped.”
Meanwhile, Burst Rinse technology is a new way of operating CIP to maximise the benefit of the chemical cleaners. Conventional cleaning cycles begin with a pre-rinse before introducing more expensive caustic cleaning fluid.
It’s actually the pre-rinse stage that typically generates the most effluent, but Burst Rinse technology uses modified rotary jet heads to eliminate the vast majority of that effluent.
It’s proving especially popular in the brewing industry, according to Kennedy: “The Burst Rinse CIP cycle uses a short 30-second burst of 2% caustic to totally wet the internal surfaces of the vessel. There can be three or four 30-second bursts with a five minute rest in between, which is then followed by a short rinse. This saves on water volumes to drain, as well as detergent use and overall CIP cycle time.”
