By Matt Hale, International Sales & Marketing Director, HRS Heat Exchangers
Moving products around during processing is an inherent need for most medium and large-scale food manufacturers. The texture and viscosity of food is not only an important quality parameter, but it also influences how it behaves during production and processing. Therefore, it should influence the choice of handling and treatment equipment used in the manufacturing process.
The exact requirements obviously depend on many factors, including the nature of the product itself and the processes involved. However, they tend to fall into two types, those which can be pumped and transported in pipes and those which need to conveyed, usually by mechanical belts or similar systems.
Many problems can arise because the pumps used have not been specifically designed for the applications or conditions which they are being used for. It is also worth remembering that it is not just simple liquids which can be pumped. With the right equipment a range of products including powders, pastes and mixtures of liquids and solids can also be pumped through suitable pipe work and equipment. There are a number of advantages to this approach, in particular the ability to avoid contamination of products during processing, as well as being able to maintain processing temperatures, viscosity, etc.
Assessing difficult products
One of the issues with pumping is the potential to damage product. This is particularly important when handling high value viscous products such as honey, treacle, custards and creams, where any loses of product can be financially damaging. The viscosity of different fluids can be affected, resulting in issues such as runny or separated sauces or unwanted churning of dairy products. For materials containing solids, for example fruit mixtures, the wrong type of pump can easily damage the solid fraction reducing quality or, at worst, removing the very aspect of your product which you are trying to preserve in your product.
Although the physical and behavioural properties of many foods are well documented, in more complex cases it is necessary to fully understand the foodstuff to be handled in order to specify the right pump for both the product and the process. It may be possible to do this with simple measurements taken in situ, or laboratory analysis may be required. The temperature of the product is important as physical properties will vary with temperature. Viscosity is a measurement of resistance to flow and is therefore is an important consideration, and information on particle size is also required.
These could include anything from ground spices to whole fruits or pieces of meat, and everything in between. The chemical composition, for example is the material acidic, will also need to be known so that the most cost effective materials can be used to produce the pump. Amongst other things, the shear sensitivity of the fluid reflects how likely it is to be damaged by the impeller of the pump. The physical characteristics of some products will change after exposure to high shear stresses, and while this may be beneficial in some circumstances (such as turning cream into butter) but not others (for example when wanting to produce cream). Vapour pressure will also need to be considered to prevent issues such as flashing or cavitation.
As viscosity is a key part of the texture of food and drink, processing operations should not have an adverse effect on it. Factors such as pumping, heating, cooling and passing through pipe work all have the potential to affect viscosity, with the exact effects depending both on the liquid itself and the way it is handled.
Types of pump
As well as being designed to handle your product, it needs to fulfil the normal requirements of food handling equipment, such as Clean-in-Place (CIP) and Sterilise-in-Place (SIP). Depending on the range of products handled and product complexity this may be required several times a day between production batches. There are many different types of sanitary pump which are suitable for use in the food industry, including rotary lobe, rotary piston, reciprocating positive displacement, progressing cavity, peristaltic hose and air-operated double diaphragm designs. Problems arise not only because of the high costs of traditional pumps, but also because lobular pumps have low flow rates. In addition, using progressive cavity pumps can break the produce, while double diaphragm pumps result in a low pressure drop.
Centrifugal pumps are typically used for materials such as batters, oils and beverages. Common uses for positive displacement pumps include icing, dough, fruit fillings & purees, baby food, tomato paste & sauces, cream, cheese, dressings, mayonnaise, meat emulsions and many more. Over many years of providing solutions to difficult heat transfer challenges in the food industry showed us that pumping products without destroying their integrity is as important as developing heat exchange solutions which maintain product quality.
More recently, new purpose designed reciprocating positive-displacement pumps have been developed to handle very delicate and viscous food stuffs without damage while working at high pressure in heavy duty applications in the food and pharmaceutical industries.
Positive displacement pumps have an expanding cavity on the suction side of the pump and a decreasing cavity on the discharge side. Liquid flows into the pump as the cavity on the suction side expands and is forced out of the discharge side as the cavity collapses. These pumps feature a hygienic design which incorporates a separator fitted between the piston and the hydraulic chamber to ensure that there is no contact between the product chamber and the hydraulic oil. Once the pump is in operation, no part which comes into contact with oil comes into contact with the product.
With an adjustable flow, which can range from a minimum of 300 litres/hour to a maximum of 20,000litres/hour, and a high pressure drop of up to 30 bar, positive displacement pumps suitable for a wide range of high viscosity, shear sensitive and large particle containing fluids. Clap valves allow pumping of whole fruits or vegetables, and an Alternative piston pump with a pneumatic cylinder can be supplied for low pressure applications of less than 5 bar.
Whatever foodstuff you are looking to pump, understanding its viscosity properties is the first step to specifying a system which will not result in adverse effects on the quality of your product. The good news is that the processing and packaging part of the food chain is already the most efficient, accounting for just 4% of overall food losses according to the UN Food and Agriculture Organisation(FAO)1. However, there is always room for improvement and management processes and equipment design are the two biggest tools food manufactures have at their disposal.