When does level measurement comes into play?
The production of high quality animal feed and pet food is an important economic growth sector worldwide. As well as livestock feed, this sector also includes pet and sports animal nutrition. Consequently, there is enormous diversity of the end-products: feed for the agricultural sector, livestock such as cattle, horses and poultry; for dairy cattle and feed for breeding animals (e.g. in fisheries) as well as bird and rodent feed. So therefore, the pet food segment can be defined as being made up of nutrition for animals such as dogs, cats or reptiles. Errors that occur in the processing plant during conveying, storing mixing or pelletizing can rarely be offset or rectified at the next processing stage. There the level sensor is an indispensable element of the technical equipment within a modern feed production plant for the detection and monitoring of levels and limit levels. From the large variety of different principles and sensor types the choice of the appropriate measurement instrument is not always an easy job.
KIT solutions allow flexible measurement equipment
The formulation of a compound feed is based on the particular use for which the product is intended. Similarly, the use of appropriate measuring sensors is in accordance with the relevant requirements of the application. The demand to level sensors is defined by their reliable functionality, easy handling and long service life. A major supplier of animal feeds for pets and farm animals in Denmark was modernizing his facility and requested new level limit detection in order to optimize his production processes. The company processes over 200 different grain products. Depending on the medium and application, different measurement techniques should be used. Due to defined customer needs project management had to develop creative ideas and specified solutions that could be implemented efficiently into the plants processes - weather “off the shelf” or tailor-made, had to be defined. Sometimes a quick and easy technology is the effective way to get reliable content and level measurement solutions, sometimes something individualized is needed.
For the milling and grinding processes as found in the crusher and hammer mills of the animal feed producer a continually precise measurement was needed, regardless of material properties - with the ability to detect varying particles and grain sizes as well as abrasive media. The extreme conditions like dust, high temperatures or steam were a challenge for the measurement system. Above, a vibrating system beneath the vessel (in order to prevent deposit build-up in the vessel) was another difficulty within this application. It was taken into consideration to install a rotating paddle switch as simple electromechanical measuring principle that could be adapted for such extreme process conditions. A motor driven shaft causes the vane to rotate. Once the material level reaches the vane, thereby preventing further rotation, this creates a torque, which is converted via a switch to an electric signal. Once the vane is free again of the material, the output signal is reset and the motor driven shaft rotates again. Despite its simplicity the device has a modular design that allowed a flexible configuration even under constantly changing conditions. So called KIT solutions enabled swift, individual equipment configuration and efficient stock-keeping. Sensor, process fitting, electronics and housing can be matched to the specific requirements so that the installation was provided with an effective and reliable measurement technology. Due to the dusty hazardous location the dustproof housing and the ATEX certificated design were indisputable for the installation.
Finally the rotating paddle switch of the series Rotonivo® RN 3000 was chosen with the usage of special high-quality sealing and corrosion resistant materials for the bearings and product tangent parts. For the partial fine grained bulk solids the paddle of the rotating probe was designed with a sensitivity of up to 15g/l and adjustable in 3 grades.
Particularly within the crusher there were a large number of cycles in rapid flow and a quick response time of the sensor helped to support best precision of measurement results.
"Active Shield Technology" supports a smooth process flow
The pelleting of animal feed was one more process throughout the feed manufacturing of the plant to be equipped with modern measurement technology. Within this process steam conditioning played an important role. That meant for the sensor to handle high temperatures in combination with humid/damp environments. Further challenges within this processing stage were dust, vibrations and high load bearing. The required level measurement had to work as reliable backfill detector for the pressed, heated pellets. Due to the demanding conditions it was important to take for the installation a sensor type with a robust, certified design available as high temperature version. Additionally the device needed totally reliable sealing. UWT project management was strongly in favour of the capacitive measuring device RFnivo® RF 3000. The durable measurement technology with different device versions withstands extreme process conditions and is very robust due to the stainless steel components. The sensor measures the capacitance between the probe and container wall. If the probe is covered by the product, the detected capacitance changed and a switching signal is activated. By the integrated "Active Shield Technology" which ensures the probe is insensitive to any material build up or caking, the RF was able to deal with the sticky and heated bulk materials. The probe with ceramic insulators was equipped to cope with process temperature of up to +500°C, because the device does not require temperature limiting components for bulk detection in the application process. After determine the container geometry the installed RF probe was calibrated automatically once the supply voltage has been connected.
The animal feed producer used also expanders integrated into the pelleting process, where the material is heated within 5 sec from 100°C up to 120°C. Afterwards, the product is pressed and kneaded. Thus, bacteria, salmonellae and mold are killed but the same time nutrients and agents are not damaged. In the end, the animal feed is easily digested. The main challenge of this application was the corrosion resulting from the aggressive oils. Further expanding influences were humidity, temperature and pressure of the material. Referring to these conditions UWT installed the heavy duty model of the RF 3000 series with a design that could withstand high container pressures up to 25bar (363 psi) and further offered a high torque setting of 525Nm. Besides he coped with tension forces of up to 40kN. Of course the device also had the "Active Shield Technology" to handle adhesive components.
Stress-free process flow through safe overfill protection
In accordance with the high standards found in the food industry sector solutions have to be customer-oriented planning comprehensive support for your requirements and technical needs. During production, the free-flowing bulk goods were transported either mechanically using chain conveyors, elevators, screw or pneumatic conveyors by one manufacturing process to another. Here, controlled material flow is essential to ensure an effective production process. Faults in conveyor systems for raw material, pellets and other bulk materials had to be detected early through the use of appropriate measurement principles thus any consequential damage is reliably avoided.
In order to ensure a continuous supply chain, both the raw and the finished product must be clearly and properly stored. It all starts with the raw materials to be transported and stored in raw cells (silos) once delivered, weighed and cleaned. The materials remain there until further processing. The end products such as the pelleted and other finished feeds are stored in finished feed cells until delivery. The sensor demanded during these warehouse processes should cover contents level measurement with reliable overfill protection. Conditions including silo and tank geometry, installation position of the sensor, properties of the medium such as flow ability, bulk density, conductivity, moisture, dust and adhesion had to be taken into consideration when configuring the measurement solution; plus the required approvals such as explosion protection.
The series of plumb bob sensors NivoBob® has proven itself in practice as a full detector for continuous level measurement several times. With the NivoBob® NB 4000 even a very cost-effective solution within the durable technology of the electromechanical measuring system could be found for the plant operator. The sensor weight, made of a suitable material, attached to either a tape or rope is electromechanically lowered from the top into the vessel. Once the sensor weight rests on the material, the winding direction of the motor changes and the sensor weight is rewound to the upper stop position. The device was working fluently within the measuring range of up to 30m and was used also during the filling process. The integrated aiming flange was mounted on top of the silo roofs and could be exactly aligned. In combination a visualization system was used within the storage silos to detect the levels remotely, analyze trends and round off the logistics management system.
The requirements of animals in terms of nutrition are diverse and so a variety of mixed feed formulations is needed to be manufactured. Accordingly, the focus of the measuring technology equipment in the manufacturing plant is on the ability to easily and quickly adapt to the varying processing conditions.
New equipment development
More often the project management has been asked for a single rod probe working with the vibrating principle and having universally valid technical structures. The design of this measurement instrumentation has established during the last years on the international markets. Especially due to its high compatibility (already through the standard version) it is very favored by plant operators. UWT has responded to the wishes of their customers with a new product series that uses the vibration measurement principle in the form of a single rod probe. The device called Mononivo® MN 4000 can be used in silos and tanks as a full, demand or empty detector. The unit is also appropriate as an overfill detector within pipes and shafts and is suitable for all bulk materials. Electronically stimulated piezos cause the probe to vibrate. As soon as the sensor is covered with material, the vibration is dampened and the resulting electrical current change causes the output signal to switch. Due to its compact construction including the threads from 1" available the sensor is very appropriate for different bulk applications all around the globe - no matter if powdery material with strong caking properties or coarse-grained granulate. With the adjustable sensitivity the device handles also light bulk solids from 20 g/l.