What Is Aeration?
Aeration, (sometimes called aerification), is where air circulates through, becomes mixed with, or dissolves in a liquid. While some processes deliberately aerate liquids, in others, unintentional aeration can cause problems.
When some types of liquids travel through pipelines and suffer from aeration, it can cause foaming. Foaming can be a problem when processing liquids such as detergents, shampoos, shaving foams, some types of gel, and even milk.
Here’s a look at the causes of aeration and foaming during liquid processing, and how pigging, or more precisely double-pig pigging systems can prevent it.
What Causes Foaming
As a liquid travels through the pipeline, the flow is usually turbulent. If there’s air in the pipe, it can mix with the liquid, and the liquid becomes aerated. With certain liquids, for example household detergents and shampoos, even a small amount of air or gas can cause foaming. Obviously, as end products these liquids are deliberately designed to foam. However, if foaming happens during the production process it can cause delays and, in severe cases, render the product unusable.
Wastage and Delays
If a product becomes badly aerated or foams during processing, by the time it gets to the end of the process, sometimes the easiest option is to discard it. The other alternative is to leave the liquid to settle, that is, to wait for the air to escape and the foam and bubbles to disappear. The amount of time this takes depends on the liquid. However, it can cause significant delays (and therefore costs) because production will usually have to stop until the foam or aeration has settled to an acceptable level.
Causes of Aeration in Pipelines
Air or gas can get in to pipes in a variety of ways. Firstly, if no product is being processed, the pipes are not empty; they contain air or gas. This is the case before a process starts, after water flush, Clean In Place (CIP), or between product runs. The pipes may also contain residue from the previous product run, water or cleaning fluids left over from CIP.
When the process pumps liquid through the pipe, unless there’s a system in place to prevent aeration (such as a barrier between the liquid and air), some of this air will inevitably mix with the liquid. What’s more, trapped air tends to migrate to high points in the pipework. As well as aeration, trapped air can also reduce system efficiency and increase operating costs.
Some liquids, such as water, naturally contain a certain amount of air. As the water or other liquid travels through the pipe, it can release this air, which again will tend to gather at the high points of the system. In addition, not all systems are perfectly sealed. Air can get in through pumps, or drawn in through poorly maintained valves, joins, seals and so on.
How to Stop Liquid Foaming in Pipelines
One of the most effective ways to prevent liquid coming in to contact with air before a run, after flush, CIP or product changeover, is to use a double-pig system. Commonly used with products likely to foam, as well as those that would be compromised by coming in to contact with air (such as wine), double-pig systems, as the name suggests, use two pipeline pigs.
How Double Pig Pigging Systems Work
For efficiency, ease of operation and safety, most double-pig solutions are fully automated pigging systems.
In a double-pig system, the first pig is housed after the product destination tank or drop-off. At the start of the process, the system sends the first pig down the ‘empty’ line in the opposite direction of flow to which the liquid is normally processed. This is to expel the air or gas from in front of the product. The pumped product, now protected from air by the pig, then propels the pig back to its housing (the pig acts as a barrier between the product and air in the pipe). With no air in contact with the product, processing continues until product transfer is complete. Then, the second pig, housed close to the product source, transfers the remaining product to its destination while still preventing the product coming in to contact with air.
Gas, air or other suitable propellant propels the second pig. The system then returns the second pig to its housing, and flush wash or CIP (if required) takes place. If necessary the system will then send the first pig back through the pipe to remove residual water or cleaning agents from the CIP, before again returning it to its housing. The process is then ready to begin again.
By sealing the product from air or gas in the pipe, using a double-pig system is a highly effective method of preventing aeration (and hence foaming). It also removes residual water or cleaning fluids (typically up to 99.5%). In addition, HPS can also provide high quality, reliable valves for pigging systems that significantly reduce the the chance of unwanted air entering the system. These include solid seat ball valves (diverter valves which can be pigged), sanitary ball valves, and other specialist valves for hygienic and sanitary pigging.
Find Out More
For more information about preventing aeration, foaming or air contact in your liquid processing operation, then please get in touch.