Fixing the mixing

 

What requirements will blending plant need to fulfil in the future?

 The basic process of blending plays a major role in the manufacture of numerous products. In view of consumers’ partiality for new blended drinks such as alcopops and other “in” drinks (some of which, however, vanish from the scene again within a very short time), blending will become even more important in future. The blending plant of the future will have to allow itself to be judged by the degree of reproducibility it can achieve, and above all by its flexibility.

The blending procedures currently in general use are batch mixing, continuous in-line blending and the tandem blending process developed by GEA Diessel (see also GETRÄNKEINDUSTRIE, issue 04/02).

Batch mixing

The batch mixing procedure is primarily used to manufacture syrup base, a process that takes place in mixing tanks. GEA Diessel’s batch mixing plant, called DIMA, for the mixing of multi-component products (both liquid and solid), is a tried and tested, economical solution for the automation of the syrup room. The plant is positioned between the raw material storage and the mixing tanks.

In the batch mixing plant, components of the most varied kinds can be processed. Dry ingredients, for example, can be introduced manually into starter vessels equipped with agitators, and there liquidised. Very small ingredient packages can be emptied and flushed out using a suction device, so that nothing of the expensive concentrates is wasted. Liquid components in large containers can also be processed.

The control technology enables the DIMA equipment in theory to produce in compliance with any conceivable recipe. If individual components are to be introduced into the mixing tanks in succession, perhaps separated by an intermediate water phase, if the initial water needs to be warmed up for the sake of better dissolution, or if varying agitation times or other special conditions are required by a particular recipe: any such requirements can easily be provided for.

The design (with only one flow meter for all media) and the method of operation (the full hose principle) of the batch mixing plant provide for a high degree of mixing precision. Fluctuations in the Brix value of sugar solution can be determined by a Brix measuring device and compensated for by the control system. Even the few litres of water used to rinse out very small component containers are metered and later compensated for by an equivalent reduction in the volume of water used in final mixing in the mixing tanks.

Continuous in-line blending

Continuous in-line blending is principally used for the blending of finished beverages. The DICON device blends liquid components in constant proportions in the pipe. Thanks to the use of digital regulators, the mixing proportions are kept constant even if the overall throughput fluctuates. The continuously operating plant can convey the beverage directly to the filling unit.

The plant can in theory blend any desired number of liquid components, the limiting factors being first and foremost the additional complexity required and resulting cost of the plant. The equipment consists principally of the main pipe into which the components to be dosed are fed, the dosing line with the introducing pumps and the deaeration vessels, and of course the metering technology, without which precise blending would be impossible. The quality of the flow meters directly influences the accuracy of blending in the continuously operating plant.

To achieve homogenous blending of products with very different or very high viscosities, static or dynamic mixers are integrated into the plant. It is possible to do without such a mixer if, for example, there are pumps further downstream that will ensure a good blend.

Tandem blending procedure

The tandem blending procedure is a combination of the other two mixing processes, with two vessels being placed one above the other in order to reduce the amount of space occupied by the mixing tanks. The syrup base is manufactured in a batch mixer and conveyed to the tandem vessel, which feeds the continuous in-line blending plant downstream.

The tandem vessel functions as follows: when the batch mixing plant has been started up, the mixing vessel (upper vessel) is filled with pre-product and the agitation time required by the recipe is started. When this time is over, the pre-product flows by gravity into the storage vessel (lower vessel). A sensor in the storage vessel detects when there is sufficient product and starts up the continuous in-line blending equipment downstream. Parallel to the feeding of this plant from the storage vessel, the upper vessel can be cleaned or filled with new product. This procedure saves an enormous amount of time when there is a product change.

Since the batch mixing plant produces a starter concentrate without sugar solution (which makes up the greater part of the volume of the syrup base), the emptying time of the storage vessel will always be greater than the starting time and the time it takes to fill the mixing vessel.

Sugar solution is then continuously blended in. If required, a carbonation plant can be installed downstream of the blending plant, enabling carbonated beverages to be added to the diversity of products that can be manufactured.

 

Batch mixing plant with tandem vessel

 

 

Advantages of the batch mixing process: 

  • it is possible to dose with dry ingredients,
  • the widest variety of different ingredient packages can be used, as can emptying by suction,
  • very small batches can be produced,
  • high product diversity,
  • high precision through the use of only one flow meter for all ingredients.

Advantages of continuous in-line blending:

  • direct processing of raw products, resulting in rapid availability of the product,
  • no large mixing tanks required,
  • little space required,
  • fully automatic working,
  • further processes (e.g. filling) can follow on directly,
  • flexibility through rapid product change.

Advantages of the tandem blending process:

  • it is possible to dose with dry ingredients,
  • the widest variety of different ingredient packages can be used, as can emptying by suction,
  • easy and rapid product change,
  • no large mixing tanks required,
  • little space required,
  • easy cleaning,
  • low syrup loss,
  • high product diversity,

 Product quality

In the manufacture of foodstuffs, product quality should always head the list of the specified requirements, so that the consumer can be offered a faultless product.

In the case of blending plant, it is very important to select the correct plant components. Bearing in mind that any measuring errors by flow meters are directly reflected in the blending result, this is not a place where false economies should be made.

Suitable deaeration vessels ensure that no air gets into the flow meter and falsifies the results.

It is equally important to use digital regulators, which work without offset and thus ensure that the recipe is complied with.

If desired, other quality factors such as sugar content, pH value, viscosity, colour and turbidity can also be measured and recorded. If limit values are laid down in the recipes, quality characteristics relating to the individual product can be stored in the device’s memory.

If these limit values are exceeded, an alarm may be given or production interrupted so that suitable countermeasures can be taken. The basic philosophy for defining these limit values should be the motto “as high as possible, as low as necessary”, in order to keep the costs arising out of interruptions to production as low as possible.

Product quality is also dependent upon the design and construction of the plant. Equipment should always to be designed with hygiene in mind, e.g. avoiding dead space, using front-flush O-ring seals for internal parts and making it possible for the plant to largely empty itself by gravity, so that after a CIP cleaning process the cleaning chemicals do not collect in sumps, making them difficult to flush out.

 Selection of the right blending process

The aim of the planning and construction of the blending plant is to produce a faultless product that is constantly reproducible, taking into account so-called life cycle costs. The right blending process is therefore to be determined in an iterative process involving both the plant equipment manufacturer and the operator.

There is unfortunately no set formula for selecting a blending process. Rather, the right selection depends on a multiplicity of parameters, e.g.:

  • type and quantity of the product,
  • product diversity,
  • the space available,
  • availability and type of raw materials,
  • semi-automatic or fully-automatic operation,
  • production management.

 

Summary

The points set out above are of course only a fraction of the many considerations that this topic involves. But they are enough to show that every blending plant must be individually planned and designed.
The constant growth in product diversity and rising quality expectations are a challenge both to the equipment manufacturer and to the operator. However, almost any product can be manufactured with the metering technology and high-performance control systems available today.

The author:
Paul Günther, Born 1967; trained as a toolmaker, studied process engineering at Fachhochschule Hannover (Hanover Polytechnic), obtaining the degree of Dipl.-Ing. (FH). Since 2002 project engineer at GEA Diessel GmbH, Hildesheim, Food and Beverage Division.