Ice pigging: a cool concept

Jon Lawson

Greta Eliasson reports on how a new ice pigging machine is set to clean up in the food and FMCG processing sector

Ice pigging is a relatively new process for clearing pipes that uses slush ice instead of water (a common method of purging product from pipes in food processing). Slush ice has unique rheological properties that mean it can pass through variations in pipework such as valves, bends and changes in diameter without becoming stuck in the pipe, yet it has highly effective cleaning properties, similar to a solid ‘pig’ when in the pipe.

For the food and beverage sector, the personal care sector and the paint industry, ice pigging can bring about a step change in the level of production efficiency a plant can reach. Today, during product changeover large quantities of water may have to be used to clear pipes of product, resulting in wastage of high-value product, and at the same time creating large amounts of effluent to treat. Ice pigging can help the recovery of the majority of product left in a pipeline, and in doing so improve the production efficiency of the plant, reduce water consumption and reduce effluent produced.

Suez Advanced Solutions has recently launched what it believes to be the world’s first hygienic ice pigging machine, the AQL500, which is suitable for applications in the food and fast-moving consumer goods (FMCG) sectors.

The launch of the AQL500 factory-ready hygienic ice pigging machine comes as a result of five years of development. The machine is designed for permanent installation into a production facility where it will provide ‘ice pigs’ on an automated basis.

“Much of the development of the machine has been concerned with adapting the technology to be suitable for the stringent hygiene requirements that food producers expect. From top to bottom, the AQL500 uses food-grade components and is fully cleanable itself. The ice produced by one of our machines should be the cleanest ice anywhere in the world,” says Matthew Stephenson, Suez’s head of Ice Pigging.

Suez is already a provider of ice pigging services to the water sector, performing ice pigging on drinking water networks around the world. “We have been offering ice pigging into a number of industries for some years, but the buzz we are feeling in the food and FMCG sector for this technology is very different,” states Stephenson. “We see that there are some clear drivers that are aligned with key benefits that the technique offers, such as product recovery and effluent reduction that aligns well with what many of the major producers tell us they are trying to achieve, and appears to make for a compelling business case.”

How the process works

Ice pigging is proving popular because it is a highly efficient line cleaning and product recovery technique. In the process, ice slurry is pushed through production pipelines to clean and recover product. It differs from conventional solid pigging in that the ice pig is capable of navigating complex pipework that may incorporate changes in pipe diameter, bends, valve systems and other obstructions with no risk of becoming stuck. The ice pig is composed of fine ice crystals and a carrier fluid containing an additive used to maintain the correct fluid characteristics. In most cases the additive can be an ingredient already used in the product.

How the process works in a typical application is that once the factory’s process has completed and the line is ready for either cleaning or push out, the factory calls the AQL500 ice pigging machine to inject ice. The plant automatically pushes ice to the purge valve, with the injection valve closed. This removes any melt that may have occurred to ensure a sharp product interface. Once the purge volume has been delivered the plant stops and alerts the factory that ice is ready for injection.  Once the factory has prepared the line a start signal is sent to the AQL500 machine, which then injects the correct volume of ice for the selected recipe. Upon completion, the factory receives a confirmation signal and can proceed to the ice propulsion stage.  The ice pig must then be propelled to the line end. This task is undertaken by the factory and can be achieved using several methods: water push, CIP liquid push or even using the next product. Finally, to maintain the quality of the product being recovered it is important to detect the product and ice pig interface. Upon detection of this interface a divert valve can be activated to direct the ice pig to a separate collection point. Several options are available for interface detection, where possible sensors present in the system can be used. Suitable measurements include density, brix, conductivity, turbidity and temperature.

What are the benefits?

Ice pigging is such an effective cleaning process that it can reduce or even eradicate the need for a chemical clean-in-place (CIP) flush. The process is also highly flexible, making it suited to a diverse range of products within a number of industries such as food, beverage and personal care. The process can be optimised to efficiently recover and clean products that are normally challenging - such as jam, mayonnaise and face creams. Another key benefit to users is reduced downtime. More effective cleaning considerably decreases cleaning time and fluid volume. Ice pigging is also environmentally friendly as efficient cleaning drastically reduces effluent volume and concentration.

Ice pigging case study

Yeo Valley is the largest organic business in the UK, producing over 2,000 tonnes of yoghurt each week. The current method of flushing dairy products from pipelines is usually done by heating water to around 80°C, then flushing it through the pipes before sending it down the drain, taking the remaining product, wasted heat and energy with it. In a recent project, ice pigging was used to remove a custard product from production machinery. Compared to the usual flushing process, ice pigging was able to recover an additional 50 litres of product per run. The ice pig had a clearly defined interface between the pig and the product, as much as 75% of product in the line is able to be recovered. The amount of mixed product and ice slurry was considerably less than the amount of mixed product and water produced using the existing process. This meant that less effluent was produced for disposal.

“As an engineer myself I was very interested and involved in the project and could see the benefits of ice pigging straight away compared to traditional pigging systems. Ice pigging technology has great potential for the dairy and food industry,” comments Andrew Rimell, general manager of Yeo Valley’s Newton Abbot site.

Greta Eliasson is with Suez