Pigging technology in the chocolate industry

An alternative to heated pipelines

Nowadays it is almost impossible to think about a chocolate industry without pigging technology. Not only chocolate masses and fillings can be transported through pipelines but also problematic products such as cocoa, nuts or crunchies.

Many confectionery specialists are convinced that piggable pipelines for chocolate have to be heated. However, one of Germany's leading chocolate producers proves that by using pigging technology double walled pipelines are not necessary any more.

Pigging is imperative in the chocolate industry. Without it there would be several problems in chocolate production:

• Chocolate is transported through the pipeline with a temperature of 45-50°C. When the product has a lower temperature than that, there is no possibility to pump and / or store the chocolate. Therefore, up to now very expensive pipelines have been installed and this shows various disadvantages.
• It is not possible to empty the pipeline when production is standing still (e. g. on weekends). Ageing and consequently quality losses of the chocolate occur with permanent heating of the pipeline - especially when handling fillings and white chocolate. There is also the possibility that sediments build up in the pipe. The fructose in diet chocolate can crystallise and thus spoil whole batches.
• It is necessary to use separate pipelines for different products and qualities. This causes high investment expenses.
• Non-piggable pipelines cause long blending phases when changing the product. Large quantities of flushing agent have to be mixed into other products. These residues can reach up to 1,5 t depending on the length and diameter of the pipeline. This means high losses when mixing high quality products into less qualitative ones.
• On production of products for abroad sometimes fats and emulsifying agents are used that are not allowed in products for the domestic sale. A mixture with these local products can easily be detected through the possibilities of analysis.

Many chocolate manufacturers now realize the advantages of using pigging technology for chocolate production: conches and storage containers can be connected with each other by only one piggable pipeline. It is also effective to connect the storage containers with the moulding plant. Moreover, by use of pigging technology the pipeline can be emptied from more than 99% of the product.

Pigging in general

Pigging means that the contents of a pipe is pushed out with a contoured plug - the pig. This pig, made of a flexible elastomer, has a diameter that is a few per cent larger than the inner diameter of the pipe. Thus a good scraping effect and a high cleaning result is guaranteed. This pig is pushed through the pipeline by a propellant (gas, compressed air, N2, water, product etc.).

A product that can be pumped or transported pneumatically (powder or granulate) is also piggable. Almost all industries successfully apply pigging technology - and so does the food industry.

Different systems for different demands

The pigging system has to be adjusted to the large variety of demands. The food industry principally uses closed pigging systems. This means that the pigs stay in special launching stations until they need to be in operation. The system only has to be opened for unloading, control and change. The number of pigs in the system can vary:

• For simple applications a one pig system is recommended. The pig pushes product rests from the initial container to the receiving container. After that the pig is driven back to the launching position by propellant.
• With a two pig system several initial and receiving containers can be connected to each other by just one pipeline. Here the product is "pinned" between the pigs. The containers are equipped with a pig receiving station. The control of the plant can be done manually, by remote control or fully automated.

Pig types

For automated plants the pigs are equipped with a magnetic core. The position of the pigs can be detected by special magnet field switches. These switches pass the position information to the control unit.

Since there are various pig materials it is possible to use pigs in almost every product. For the use in food industry pigs made from the elastomers NBR-L, EPDM-L, silicone and natural rubber are recommended because these are FDA-approved for food application.

The form of the pig is individually chosen for the actual application. The I.S.T. Duo-pig with abrasion proof sealing lips facilitates the passage of elbows and can pass pipe apertures. This "standard pig" is applied for almost all products such as cocoa masses or fillings. For products that are hard to handle (cocoa powder, nuts or crunchies) the jet pig is used. By its special form and function it aerates the product and so avoids a block up of the pipeline.

The stations

I.S.T. Molchtechnik GmbH has constructed a wide range of piggable stations in order to come up to special requirements. In addition to the compulsory launching and receiving stations there are also designs with T-branch, special fittings with lock-up and pig catching function, manifolds, filling equipment as well as pig loading and unloading stations.

With piggable fittings that have a T-branch, T-pieces are often used as launching and receiving stations. By a special construction the T-branch can be passed without bypassing the pig. A T-piece that is equipped with a pig stop can even be installed at a container.

Three way valves are applied as manifolds at a pipeline branch. So it is not only possible to pig from A to B but also to connect various production lines to each other.

There are also multiple-way valves with 1 to 12 or 2 to 12 connections. On request, all piggable fittings can be equipped with heating jacket.

Non-heated pipelines

One of the biggest German chocolate factories (annual output 100,000 t approx.) with 15 years of experience in pigging generally works without heated pipelines - and has got very good experience with it. It is a fact that heated pipelines also cause problems: The cost for installation is very high and additional energy is necessary. Moreover, the large quantity of welding seams and flanges also bears the risk of water entering the product transporting pipeline. It makes no difference whether this intrusion is caused by a leak flange or by corrosion of the pipe - the damage done to the chocolate mass is high. The mass crystallises immediately and blocks the pipeline with a non-dissolvable plug. Consequently, the pipeline has to be cut and replaced at this place. This means a production loss in this line for a certain time.

There is still another danger should the leakage not be discovered through this plug: Since the heating water does not have drinking water quality (because of anticorrosive agent) the product can contaminate easily.

Practical application

The factory in question is working with three piggable pipelines and a fourth one is in the planning phase. This factory uses a Two pig system with pigs made of NBR-L. The propellant is compressed air.

A pigging line is laid from storage containers to moulding plant. Two pigging lines connect 12 conches to 21 storage containers so that two conches with different products can be emptied into two storage tanks at the same time. By integration of three way valves branching of the pigging line to the various storage containers is possible.

The plant is fully automated. Thus operating mistakes are avoided. The control is done by PC from the control room. Immediately on switching off the mass pump the pigging process is started in order to avoid cooling off and solidification.

Every conch and storage container is equipped with two piggable T-pieces - one for each pigging line. The T-pieces at the storage container have an additional pig stop.

The first pig is pushed into the receiving station when pumping chocolate masses. The pig stop of the chosen container is driven down. The second pig is driven by compressed air and so transports the chocolate mass into the container. The pig stop makes sure that the pig can only be driven up to this storage tank. Pig no. 1 transports the product from the receiving station into the container. Now the pig stop is risen and both pigs are driven back into the launching station. The pipeline is free again for the next pumping process. This kind of pigging system facilitates a rational and quality assuring solution for pumping chocolate masses.

Summary

For decades the chocolate industry has used pigging in order to empty the pipelines when changing the product or when production is stopped. More than 99% of the pipeline contents is recovered.

Practical operation has proven that it is possible to abandon heated pipelines. This heating does not only mean high investment and operating expenses but can also cause quality losses of the product.