Hard-pressed engineers facing mixing and blending challenges should forget traditional models and focus on process goals and the physics involved, suggests Greg Pitcher.
If you’ve ever found yourself allergic to a certain chemical, one used in food or cosmetics perhaps, you will know how difficult it can be to avoid it. Reading the back of product after product seems to yield almost identical lists of ingredients. You wonder how such different outputs can come from the same inputs. The answer is that the magic often happens in the process plant.
“Mixing and blending are often the critical steps in fluid-based production processes and account for a large portion of the added value in manufacturing,” says Peter Brown, managing director at Derbyshire-based Maelstrom Advanced Process Technologies.
“Many of the largest process operators in the world gain their competitive advantage through mixing processes, which is one of the reasons developments are often kept secret.”
Different companies each have their own challenges when it comes to optimising blending processes. Examples range from oil refineries requiring large-scale operation, and compliance with specific safety legislation, to pharmaceutical giants focusing on materials and consistency.
The traditional approach in the mixing and blending market is to place almost all of the responsibility on to the process engineer… [which] usually leads to hasty selection and poor process performance
Peter Brown, managing director, Maelstrom Advanced Process Technologies
In the food and cosmetic industries, as well as for paints and coatings, minimisation of droplet and particle size is often a key factor as firms look to achieve the perfect texture and performance.
These different goals have led to the development of a wide range of mixing and blending technology, often leaving plant managers with an unenviable job of choosing the right gear for their task. This can be a big ask for a generalist charged with a multitude of projects to keep a factory running smoothly.
“The traditional approach in the mixing and blending market is to place almost all of the responsibility for understanding each mixing process, and choosing the right equipment, onto the process engineer,” says Brown. “In practice, this usually leads to hasty selection and poor process performance.”
Hassled process engineers often fall back on what they believe to be industry-standard models, he says.
“A better way would be to look at each mixing and blending problem in terms of the process goals and the physics of what needs to be achieved to deliver these.”
He says this approach could lead to some innovative equipment being trialled and bought. “The final selection may turn out to be quite different to the traditional solution used in the industry and this can offer major competitive advantages.”
Sizing a mixer correctly for a task is important so you don’t waste money on power or have something not effective enough
Chris Ryan technical author at Silverson
Brown says technological advancement in mixing and blending has come in two major guises in recent years.
“Computational fluid dynamics modelling is making rapid progress in optimising vessel and impeller designs to achieve specific process goals, although its usefulness for turbulent flows found in intensive mixing equipment is still limited.
“Process intensification is focused on bottom-up process design to provide smaller, cleaner, more efficient processing, often with a performance advantage in terms of product quality.”
This has led to movement from batch processing to inline operation, says Brown, adding that separation of pumping and mixing actions allows “more efficient and effective mixing with careful control of stress and temperature”.
He adds that mixer performance is always being improved by advances such as higher speed bearings and 3D printing advancements.
Buckinghamshire-based Silverson produces a range of high shear mixers, which inject energy to speed up the process of blending two ingredients together to make a new product.
“We are used across the process industry from pharmaceuticals to chemicals,” says technical author at Silverson, Chris Ryan. “These are multi-purpose machines so they can be used for liquid-and-liquid blending, for high and low viscosity liquid blending; and for powder-and-liquid blending.”
He says that ineffective or inefficient blending can both be problematic for process engineers. Without enough energy into the process, it can take a long time – or an additional process – for lumps to be eradicated. Equally, excessive amounts of a thickening agent, for example, may be used if it is not being distributed properly by a blending process.
“Sizing a mixer correctly for a task is important so you don’t waste money on power or have something not effective enough,” says Ryan.
He adds that a company’s ability to take an innovative process from the laboratory to the factory floor can be dependent on having the right product mixing equipment.
“Scaling up is a major consideration. There are some excellent lab machines out there with no production-scale equivalent. Our lab range is made with the same geometric principles and tolerances as the production machines. So you can scale up and get the same results.”
Silverson has mixers that can blend as little as 1ml of product to as much as 100,000 litres. “It can happen that different people in a company are responsible for lab tests and making processes happen in the factory. We’ve had examples of people buying our production equipment because they want to match results from a lab.”
The supplier recently launched its UHS HV in-line mixer [pictured] and a powder/liquid mixer called Flashmix. These were designed to open up new, thicker products to high shear mixing.
“Rotor stator mixers like ours traditionally become less effective at a certain viscosity,” says Ryan. “An auxiliary pump had to be used, which complicated the process. The more equipment you have in a plant the more maintenance costs, the more risks of downtime and it’s less elegant.
“Our alternative product, an in-line mixer, effectively selfpumps to draw a product through a pipeline and recirculate it around the vessel.”
Flow rate is maintained as viscosity rises, opening up a lot of applications including manufacture of mayonnaise, cosmetic creams, and slurries for the chemical industry.
Ryan says the mixers were the most successful product launches in Silverson’s history. “In the past certain companies couldn’t use high shear mixers, so it’s new territory for us. There are lots of companies looking for better, cheaper, more effective ways to mix and blend to gain a commercial advantage.”
The firm has come up with a number of ways of communicating with process engineers about ways of tackling mixing challenges.
“We’ve launched a series of how-to videos for overcoming common problems and we get increasing numbers of enquiries from those. We also have loan machines so people can test them in their factories free of charge. And we have a large test centre where people can bring in ingredients and try out our equipment in a lab and a production area to get the result they want.”
There is no one-size-fits-all solution, Ryan warns. “Each product has its advantages, different people would take different approaches; it can come down to cost or space in the plant. There can be hi-tech products that take effort out but are more expensive, while other systems may be more simple but better suited for certain applications.”
However, a major common drive is hygiene. “Mixing equipment has to be easy to clean, not just for the food and pharmaceutical industry but for more and more sectors – including cosmetics. Product design can play a big role. A machine needs to be easy to clean: crevasse free, self-draining design is key.”
Raw talent
Rick Earley, national sales manager at Londonderry-headquartered Admix, says adjusting to customer output requirements is a constant challenge for the mixing industry, and as such drives innovation.
“With all-natural labels, there is an increasing demand for raw or minimally processed products,” he says. “This means starting with raw ingredients, rather than powders or purees; like vegetables that must be particle-reduced to meet the product expectation.”
Protein products are also in high demand, providing a new range of challenges as they are often difficult to hydrate at speed.
Earley says demand for natural foods is likely to increase over the next decade and predicts that high-pressure processes will come ever more into vogue.
“Because the high-pressure process uses pressure rather than heat, there is no degradation of food attributes like taste, texture, appearance, or nutritional value.”
