Radar technology for continuous level measurement in maceration

Smart TDR with helpful diagnostic capabilities

 

For the cellulose production of a wood manufacturing plant in South America, the guided wave radar was implemented in several water tank constructions within the maceration processes. The modern, high-quality TDR technology ensures a continuous production process of the plant. Uninfluenced by changing process conditions, TDR sensors detect the level reliably and precisely and thus offer optimum support for a smooth process flow.

 

+/-2 mm measuring accuracy & steam compensation

A wood manufacturer who has been operating in the forestry, cellulose and paper industry for 100 years was looking for an innovative and durable solution to modernize the level measurement within his plant processes as part of a stronger strategic focus on sustainability. The company is active in Chile, Argentina, Brazil, Peru, Colombia, Mexico, Ecuador and Uruguay and is considered the fifth largest pulp and paper producer in the world. Main export areas are Asia, USA and Europe. When equipping the main plant near Santiago de Chile, the drying systems including maceration placed special demands on the robustness of the measuring technology to be installed. During the maceration process, the wood in its raw state is exposed for some time to water, which serves as a solvent for certain ingredients. This process is supported by heat input. In the process tank, temperatures of up to 80°C (176°F) and a process pressure of approx. 0.8bar (11.6psi) prevail. The atmospheric conditions place high demands on the sensor to be installed, especially with the high content of steam and moisture.

 

In the field of continuous level measurement, UWT GmbH's solutions were expanded some time ago to include a TDR product line in addition to plumb bobs and non-contact radar technology. In addition to the NivoGuide® NG 8000 which is a classical radar solution in liquid media as well as for interface measurement, a second series with the NivoGuide® NG 3000 for solids applications was implemented. The device versions are each equipped with probe extensions that can be individually adapted to the application. This enables the level measurement technology manufacturer from Germany to configure the appropriate sensor technology from an extensive repertoire for plants depending on the process conditions and the medium to be measured. Functionality, easy handling and long service life of the instruments in accordance with the high requirements and standards of this industry are of utmost importance. Innovative technologies combined with years of industry knowledge enabled UWT GmbH together with the local partner company VESET y Cia. Ltda. to provide a tailor-made solution with the guided wave radar sensor technology of NivoGuide® NG 8000. Microwave pulses are coupled to a cable or rod and guided along the probe. The emitted pulse is reflected by the product surface. The time difference between the emitted and reflected pulse is converted into a level. The low frequency ones are hardly damped even at high moisture content, so that the greatest possible amount of energy is available for the actual level determination. A reliable level determination for a trouble-free process flow is thus guaranteed at all times. For reliable level detection of the water from the heating of the logs in the drying system during maceration, the level is controlled via a pipe with a diameter of 100mm and a height of 600mm. The small diameter of the tube provides a signal bundling that amplifies the measuring signal, which further increases the measuring reliability. Even under these demanding process conditions, NivoGuide® with its 4...20 mA/HART two-wire electronics measures precisely to +-2mm accuracy. Due to the short reaction time even faster changing levels can be reliably detected.

Process pressure or dielectric value fluctuations have no influence on the accuracy of the measuring result, as neither an adjustment to changing process conditions nor a calibration to the measured medium is necessary.

 

Smart TDR with helpful diagnostic capabilities

One of the decisive purchasing reasons for the plant manufacturer was, besides the high precision, the simple and intuitive operation of these devices. The insensitivity to a wide range of process conditions makes the technology a multi-talent and thus facilitates commissioning. The sensor is calibrated in just five steps and delivers a reliable level signal, regardless of whether it is used in water/oil-based media, pastes, foams or slurries. The intelligent software of the guided wave radar sensor technology enables high system availability. Intelligent software algorithms can distinguish between dynamic and static signals. Thus, installations within the vessels can be identified as such and excluded during echo analysis. Faulty level measurements triggered by installations are excluded, minimising the deployment of service technicians and maximising plant availability. However, as failures cannot be excluded one hundred percent, echo curves are automatically recorded and saved. This data is used to speed up fault analysis and keep downtime to a minimum. The programming element with a plug-in indicating and adjustment module as well as a cover with a viewing window enables very user-friendly operation of NivoGuide®. Extensive diagnostic functions ensure quick and safe handling. For example, current measured values and setup parameters are displayed. The parameterised data can be stored and transferred to other guided radar units, which results in a considerable time saving of the installation process.

During the maceration process there are surface movements that exert strong forces on the sensor probe. For this reason, it was decided to install the sensor in a pipe outside the vessel, where the surface movements are significantly reduced. This type of installation in combination with the robust design of the rod version of the NivoGuide® 8000 was the optimal and most durable solution for the customer. The 8mm diameter stainless steel rod design is itself designed to prevent damage even when subjected to strong forces. In liquid devices, the holder of the rod arm is surrounded by a conical sealing element, the so-called condensate cone. This prevents incorrect measurements due to condensate forming at the coupling and facilitates dripping due to its special shape. The material used is extremely durable.

 

Transparency and planning reliability through visualization

Users with a number of scattered storage silos and tank containers also consider it increasingly necessary for their plants to equip them with automated visualization and monitoring of data in addition to continuous level measurement. Detected measuring results of the sensors are quickly and easily displayed by software and can be called up conveniently from the screen at any time. Effective silo logistics then also increases transparency and planning reliability for the plant operator. The TDR series of NivoGuide® has therefore been equipped with the appropriate features, including an analogue 4-20mA signal and a Modbus RTU or Profibus DP interface for the evaluation systems.

The data visualization NivoTec® provides the plant operator with fill levels in height, percentage, weight or volume for a transparent manufacturing process. Trends are stored, e-mails about fill levels or silo full messages can be activated, even the individual fill level sensors can be parameterized. Clean route planning and targeted stockpiling for cost optimization in material delivery can thus be facilitated.