In the production of dog food pellets, the manufacturer struggled constantly with an unreliable measuring point. After several different measuring principles failed, a breakthrough was achieved with 80-GHz radar level measurement technology, explains Sabine Mühlenkamp, specialised journalist for the chemical industry and general technology – Dipl.-Ing.
The dog is one of man’s favourite companions. Many dog owners spare no effort in care and want only the very best for their pet. Accordingly, a wide range of dog food is available, from puppy food to senior mixes, as well as products for stomach-sensitive and allergic animals. The product range and the variety of recipes has been growing for years.
The South African company RCL Foods knows exactly what dogs like to eat. This leading African food producer, with over 20 000 employees in subsidiaries in South Africa, Swaziland, Namibia, Botswana and Zambia, not only produces various types of pet food, but has also developed and designed its own production equipment for just that purpose. However adding essential oils and fats to the food products has proven to be a very difficult and complex process.
Step by step to the pellet
The basic steps of the pet food process include sourcing raw materials, commingling via a dosing system that involves adding essential vitamins and nutrients, grinding to a specific specification and size, and then mixing. In the next step, the pre-processed product is fed pneumatically via a conveyor line to the extrusion unit. Steam, water and other ingredients are added to produce many different shapes, sizes and mixes of animal feed.
After extrusion, the product must be dried according to moisture specifications. When the product leaves the dryer, it gets coated with essential fats and oils. At this point in the process, however, there have always been difficulties until now. Although this brand new, state-of-the-art facility was designed and built by the company’s own engineering team, one measuring point did not provide readings reliable enough to ensure a smooth, continuous process.
The problem: When the product leaves the batch dryer, the food product is supplied with fats and oils. For this purpose a container for holding the dried pellets was installed. This in turn feeds a belt weigher, which is used to obtain an accurate flow rate for the addition of fats and oils. It is necessary for the filling level in this storage container to be reliably measured to achieve an unvarying flow. Only in this way can the belt weigher operate smoothly and stably. The reason for this is that the four PID loops that control the addition of fats and oils cannot cope well with strongly fluctuating process variables.
A roundabout way to the goal
At first glance, the measuring point does not appear to be especially problematic. The ambient temperature is moderate, and the food pellets are easy to handle. From time-to-time light vibration occurs in the system, but that normally does not affect the measurement. The real difficulty only becomes apparent when you take a closer look. The size, composition and density of the individual pellets vary constantly. What is more, the level itself changes very quickly because the product flows so quickly. That’s why reliable level measurement in the storage container was extremely difficult.
Conclusion and outlook
During installation it was necessary to use the existing mounting sockets, wherever possible without any modifications. This was not optimal, but due to the excellent focusing of the sensor there were hardly any interfering reflections. After installation, the instrument was quickly set up via Bluetooth and smartphone. The measurement engineering team was positively surprised by the high quality of the measuring signals. Now, the level in the pellet container is reliably measured and can be kept constant. The continuous process of coating the food pellets now runs smoothly. Dust deposits from the dog food are also not a problem for VEGAPULS. According to the company, the sensor hasn’t been touched since it was installed two years ago, neither for cleaning nor for maintenance. The level signal is reliable and accurate, ensuring production of a balanced dog food mix.