Control of a metering and mixing system with entry and exit in a brine facility
Founded in 1947, Stephan Schmidt Gruppe is one of the world's leading manufacturers of specialty clays and mineral products. The group's headquarters, Stephan Schmidt KG, is located in Dornburg. The group also includes the companies Marx Bergbau GmbH & Co. KG, Müllenbach & Thewald GmbH, Stephan Schmidt Meissen GmbH, MTG Mittelhessische Tonbergbau GmbH & Co. KG, the Italian-based Ceramat s.r.l. and Progind International s.r.l., and the Spanish Cerargillum S.L..
In its 20 clay pits, 18 of which are located in the Westerwald region, the company extracts raw materials for the manufacture of clay products, prepares them and makes them available for further processing in consistently high quality. In addition to the pits, the group of companies includes 9 homogenization plants, 3 grinding and preparation plants, 2 laboratories for "research and development" and "quality control".
At the Maienburg processing plant, the control system for the existing clay mixing and batching plant was to be modernized. This also included the connection of the silo plant for the storage of the clays. On the plant, other dry components and/or water are added in doses to the ground clay and mixed together. The clay is then either stored in silos or transported to the wet clay boxes. The task was to ensure that the clays are transported in a purely graded manner so that no mixing of the different types of clay is possible.
To implement the task, the old weighing control system was replaced. The old system comprised a Siemens S5 with a special computer, via which both the control of the scales and the evaluation of recipe data was possible. Now, two Siemens S7-300 controllers are in use (one for the mixing/dosing system and another for the silo system). WinCC 7 with dual monitor support was set up as the control system on a highly available server (Microsoft Windows 2003 Server as the operating system). The entire recipe management and logging was realized via the WinCC application by connecting to an MSSQL database. This makes it possible to evaluate dosing times, daily quantities and other recipe-specific data. With the help of diagrams, this data is graphically processed in order to be able to trace previous or currently running batches. The recipe management system is also designed to allow the system to be linked to SAP at a later stage.
The former weighing technology for the mixing and dosing system was replaced by Siwarex components from Siemens, which are coupled to the control system via decentralized peripherals (SIMA-TIC ET200S). The automation for loading and unloading the silos was also designed by focus. The silos are filled via screws on two different lines. The important thing here is to ensure that the two lines are conveyed by the same type of material so that they do not mix. The silos are unloaded either back into the blending plant or for truck loading. The new control technology was put into operation in a very short time. Just 4 working days were required for the conversion of the weighing technology, the replacement of the controls and the commissioning of the new control system. The plant was thus able to resume operation after a relatively short downtime.
Control of a dosing and mixing plant with storage and retrieval in a silo plant