the Biturbine : concept and use?

How does it work?
Imagine for one moment that you have thousands of small turbines or mini-cylinders which can individually coat 20, 50, 100... grams of fragile or sticky products without the damaging effect of weight. 

Let us assume that these turbines are working in such a pattern as to create a continuous flow.  

This is achieved by associating two parallel helicoïdal screws made of soft fibers. The two screws counter-rotate in a special 8-shaped trough. 

The base product is fed in. Liquid or powder ingredients are metered from top of the oepen trough, at some positions .  Due to the rotation of the screws, the product and the ingredients undergo a transfer and mixing effect which result in a homogeneous coating.

This is the Mini-Turbine-Effect

A complete continuous process can be designed by associating ancillary equipment : feeding hopper, liquid tank and spraying manifold, powder doser... 

How to use it?

Product

 The minimal particle size can be as small as 0.5 mm. The maximal particle size is limited by the space left between the screw shafts and the trough wall. A thumb rule is that the product size should be no more than a third of the distance left. By example, the TB 300 (the trough diameter is 300 mm)  can accomodate tortilla chips without causing damage to them.

The presence of fines should be elminated from the base product. It is the main source of agglomeration  on the screw shafts and trough, and ultimately jamming of the Biturbine.

The temperature of the product should match the temperature of the ingredient applied and vice versa. It is better if the temperature gap is minimal to prevent early setting and crystallization thus hindering an optimal ingredient dispersion and homogeeous coating. A dried RTE cereal should be coated rigth after drying to benefit from the drying temperature.
Liquid ingredients The characteristics of a liquid indredient should be known (melting temperature, concentration, viscosity). The factors are connected. The lower the viscosity, the better the coating. Hence the necessity to work at a temperature above the setting point. The jacketed walls of the Biturbine provide an ideal environment for the application of high temperatrure setting point liquids such as hydrogenated fats or waxes.

A suspension containing particles can be applied ; it is only a matter of transferring and dispersing it properly : cheese slurry, peanut paste...

Application  systems range from the simple infeed tube to airless or air-powered spraying nozzles. For fat or high concentratred sugar syrup, a jacketed transfer pipe and manifold is a must.
Powder ingredients Powder ingredients  dispersion is easy thanks to the mini-turbine-effect. If applied rigth after the liquid addition, the powder is  intimately mixed to the liquid : this is an alternative to the use of a prepared suspension/slurry.

The powder can be used as a dusting. In this case, the base product need only to be ligthly humidified (wated, hydrocolloïd or fat) to stick the powder onto it. There are two solutions. Either the product runs on a "bed" of powder in excess (the excess is recovered through a perforated section att the end of the same Biturbine section). Or the powder is applied with a powder dispenser which distributes it over a given length.

It is  recommended to keep the liquid and powder addition separate in tho individual sections (one  Biturbine after the other). This avoids agglomeration at the liquid/powder phase fronts, generally just under the powder feeder chute.
The Biturbine The Biturbine is made of modular sections : generally one infeed section of 1500 mm where product and liquid ingredients are metered from the top and mixed inside, one or two extra sections of 1000 mm for further mixing or for powder addition.

The Biturbine works generally in a horizontal position. 

It is sometimes tilted backwards to improve the mixing effect with square toffee) or  smooth surface products (jelly, gum, hard-boiled candies) as they tend to glide instead of rollling onto themselves.

The self-cleaning effect of the brushes and the open top make it easy to inspect and clean. Either by flushing it with hot water  (60°C°) or removing the screw brushes (in less than 30 seconds) for thorough cleaning. It is sufficient to sanitize the machine and prevent microbiological growth.

The brush bristles are made of polyamide (Nylon 66). Max. temperature 110°C. They are sealed inside a bore in the shaft to prevent accidental tear and loss.
Process The throughput is given in liters/hour as is depends  of the density of the base product. The TB 100 delivers 1000 l/hr at 60 rpm : 100 kg/h of cereal with 0.1 density. The throughput depends the infeed device (vibrating feeder, elevator, drier outlet...). The screw speed is only used to control the residence time i.e. the volume inside the Biturbine. A mean residence time value  is 30 seconds. It is short compared to a drum  or coating pan : it is a quick process aimed at thin film coating and not dragee-paning or chocolate enrobing.

Jacketed walls are indispensable when fat or syrup are to be applied : just to prevent them to set on the trougth instead of the product  surface. The heat source is water or thermal oil circulation or electrical resistances. It maintains the temperature at its correct value. But the Biturbine is not  an heat exchanger. Nor is it a drier as it is closed, to the exception of the infeed and outlet ports.

Note that many coating applications require a finishing step : polishing (resin), setting (fat), drying (syrup). 
Production The small volume present in  the Biturbine has many advantages : quick adjustement to parameters modification, quick start-up or shut-down. 

It can be stopped or restarted at will under the supervision of a product presence sensor.

It is a continuous process which works best when inserted in a continuously working line (between extruder and drier in RTE cereal coating line). Or it can serve several batch process equipment working alternatively (pre-gumming of dragee centers prior to panning).
Trouble shooting for developpers.!
Agglomeration

Adjust the temperature of the jacketed walls above the setting point

Lower the concentration of the liquid solution

Eliminate fines  from the infeed product.

Separate the liquid and  powder addition in two individual Biturbines. Then feed first the powder in the infeed port then the liquid coated product.
Uneven coating Adjust (increase or lower) the screw speed to fill the troughs up to the shafts level.

Tilt sligthly by 5° the Biturbine body.

Increase the ingredient rate or lower the product infeed rate.

Increase the number of liquid (manifold with more nozzles) or powder addition (use a longitudinal screw dispenser).

Add the ingredient the sooner/closer after the base product infeed point. Or increase the length of the mixing zone after the ingredient addition. 

Lower the concentration of the liquid solution
A few critics at least!
Difficult to clean? Not as it is self-cleaning with the brushes. Use hot (60°C) water. The brushes can be extracted for cleaning separately in less than 30 seconds. A spare set allows for immediate start up.
Microbiologically safe? Made of stainless steel and nylon essentially, it is constantly swept by the processed product. By design, there is no dead spot. Hot water proves to sanitize it satisfactorily. It is used in the diry industry to coat cheese with antisticking oil or talcum. 
Bristle losses? Yes, it happened twice in the very early days of development. This critical problem has been solved by literally clipping the bristles inside the holes drilled in the shaft.
Damage to the product? In the contrary, no. The bristles tend to ply off when in contact with the product avoiding hard contact. The  action of the counter-rotating helicoidal brushes is similar to hands shuffling inside the product mass. If not potatoe chips, tortilla chips are flavoured in a Biturbine.

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