Liquid product recovery (pigging) is a technology used by manufacturers of liquid products to recover product from pipelines, rather than wasting it. Pigging works by propelling a specialist projectile (called the pig) through the pipeline at a high velocity to push the leftover product to the destination.
There are various mediums that can be used to propel a pig through a pipeline. These include gas, water, and the next batch of product. Depending on your application and product, some of these methods of propelling the pig may be more suited to your company.
So which propellant is best used where and why?
Filtered compressed air is the most used propellant with HPS pigging systems. It is cheap and can be made in-house or bought. Compressed air is a popular alternative to other gases, such as CO2 or nitrogen, largely because of its convenience and price point.
Compressed air can be used in most applications, although products that shouldn’t come into contact with oxygen, such as wine, will be better off using an alternate propellant, such as CO2.
Check out our video showing how compressed air works with a live pigging system!
CO2 is often used in applications that have products that can’t meet oxygen, usually because they will either degrade or be damaged. CO2 is usually used for products such as wine, beer, and certain food stuffs.
Although CO2 is good for preventing product damage and degradation, it can be expensive to purchase, particularly when CO2 supplies run low. There are ways to reduce CO2 use in changeover sequences, including the HPS Double-Pig Pigging System.
For companies that want to ensure their product has minimal risk of degradation or damage, using CO2 as the propellant for the pig is ideal.
As with compressed air and CO2, the use of nitrogen in pigging is down to your company’s needs. Nitrogen is used as an alternative to CO2 for companies that don’t want their product to encounter air and is more frequently used in the pharmaceutical industry.
Nitrogen may be more suitable for use with products that are susceptible to spontaneous combustion, such as chemicals. It may also aid in reducing corrosion in transfer lines.
It is also suitable for use in the food industry as an alternative to compressed air. Nitrogen is useful for preserving freshness, protecting nutrients and preventing microbial growth.
Nitrogen is expensive when compared to compressed air but marginally cheaper than CO2. Nitrogen may also require a more complex venting system to remove the nitrogen from the air. This means it is less frequently used in HPS systems, although it is still an option that can be discussed with one of our engineers.
Water is another propellant that can be used by companies with a pigging system.
Water is often used as an alternative to compressed air and other gas propellants because it enables companies to reduce their water consumption. This works when a company uses washout/sanitisation water to propel the pig, completing an initial wash as part of the pigging process.
Precision of control is also a benefit of using water as a pigging propellant. When using gas, the pig speeds up and slows down with compression, whereas with water the force remains constant allowing for precise control.
There are some applications where water is not suitable for use as a propellant, such as in chocolate manufacturing. Many meat manufacturers also prefer to avoid using water to minimise the risk of listeria contaminating the product.
The final propellant that we’re going to discuss today is product. In some cases, it may be possible for companies to use the next batch of product as their propellant.
For example, in the paint industry the next batch of product can be suitable for use as a propellant if the initial batch and the secondary batch are of a similar shade of colour.
Using the next batch of product as the propellant is great for cost-savings as it reduces the need to make or buy gases or water and it speeds up changeovers significantly by introducing the next batch of product directly into the line.
To see how a product propelled pigging system works, watch our video demonstration on air pigging and product push pigging! This video will show you how pigging with air and pigging with product differ.
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Want to know more about pigging systems and which propellant would suit your application best? Interested in the benefits of pigging systems?
Contact us today to have a chat with one of our engineers about how HPS can help you to decrease your costs and increase your profits.