Sewage sludge must not be used any longer as fertilizer in agriculture due to nitrate contamination. In dried form, however, it can be used as fuel, for example, for energy generation. For this reason, Stadtentwässerung Mannheim (urban drainage) modernizes the sewage sludge drying plant of its sewage treatment plant. Three belt dryers replace two existing drum dryers and thus at the same time expand the drying capacities.

The first drying line was put into operation in July 2020, the other two should follow after dismantling of the drum dryer by the end of 2021, respectively summer 2022.

Performance for permanent availability

By order of HUBER SE, SPANGLER Automation planned, programmed and produced the switch and control system for all three drying streets, including conveyor system and exhaust air treatment. A redundantly designed process control system ensures that the processes are permanently monitored, and the plant is permanently available.

High operational reliability

The main control, a Siemens PLC S7-400, is also redundantly designed as the process control system Siemens SIMATIC PCS7, with which the plants are operated per HMI. A generously dimensioned power supply buffers so much electrical energy that all required PCs can continue their operation without any interruption in case of voltage breakdown. Furthermore, a low voltage main distribution takes care that the power supply plant in case of failure automatically switches to the second power supply to avoid any interruptions. For control of all drying streets, forty control cabinet fields, ten sub-distribution boxes directly at the machines, four control cabinets for the low voltage main distribution, and two IT panels were installed. Compliance with the machine safety directive is ensured by a
PROFIsafe bus system (210 nodes) to which all frequency converters are connected.

“The Siemens PCS7 and the redundant systems are highly available equipment and in connection with the bus system provide a very high safety level, “ Spangler project manager Anton Höcker describes the result of the high effort.

Spangler Automation has supported the Upper Bavarian municipality Burgkirchen on the Alz with the expansion and modernisation of its sewage treatment plant for more than 20 years. The latest project was about the exchange of the mimic diagram for the control of the plant stations by a video wall consisting of four LED screens. “With the existing static execution, new plants such as a combined heat and power plant or a sludge dewatering plant, cannot be added anymore “, Martin Müller, Sales Manager, reports.

Flexible Alternative

To comply with the limit values for a high water quality, the operator must identify critical plant conditions as early as possible and correct faults immediately. For a fast and reliable fault reporting, a clear presentation of the plant technology and thus of all processes is essential. In Burgkirchen this has been done so far via an aluminium plate with foil printing that has represented the circuit diagram and via small lamps in traffic light colours which has shown faults in the system.

This mimic diagram is established and has been common for a long time, the presentation of the plant, however, was inflexible. For this reason, it was now replaced in Burgkirchen by a video wall with a size of 410 x 232 cm, which is dynamically alterable and thus applicable on a long-term basis. It switches on in the presence of the sewage works operators and immediately visualizes the current operating conditions and possible faults. If required, it is even possible to switch from the control system to the video surveillance of the premises. Thanks to LED screens and a targeted operation, the energy consumption is negligible.

Technical precision and solid programming performance

The video wall exists of four 46-inch LED screens, which were mounted on a rail construction and recessed in the wall of the operation building. Using the existing constructions for mounting the new technology, the installation costs turned out to be very cost-effective. A PC system programmed by Spangler, consisting of a main computer and four small PCs, now clearly displays the control system and links the four screens into one large display. The complete hardware as well was hidden in the wall, however, is easily accessible.

“For planning, programming, assembly and start-up we needed just one week”, says Martin Müller. It is no wonder that such an optimisation also found favour with other customers and will be installed there soon.

Actually, it is already well equipped, the sewage treatment plant of Bad Tölz: it has several PLC controls and a control system, a screen plant and a sludge dewatering with subsequent solar drying. However, most of the components, among them the control units, are already between 15 and 20 years old – therefore, it is time to bring the plant up to the current technical standard, especially since spare parts are not available anymore.

With its retrofit programme Spangler Automation has a suitable package in its portfolio to bring the entire automation technology up to date. Therefore, the possibilities for remote control have to be extended, the speed and stability of the system must be improved and the application of the control software and the training of the employees must be simplified. Last but not least, a secure supply of spare parts also plays a decisive role.

Extensive modification of the control technology

“Due to its size we have divided this project in six steps“, reports Maximilian Mayer, deputy manager of the department Service & Installation at Spangler. As a first step, the previous main control Siemens S7-400 was replaced by a S7-1516. It already controls the plant technology (pumps, blower, etc) in the main building; for the time being the old hardware supports it only as regards communication. As soon as the controls will be changed in the adjoining building and the communication to the process control system is completely changed to ethernet in further steps, the old plant will be switched offline.

For this, Spangler uses fiber optic cables to create the basis for the set-up of the ethernet network. Every component includes a central switch, which are connected in ring topology. „As fiber optic cables are particularly characterized by long transmission paths, they are ideal for covering the extensive area in terms of network technology “, says Mayer. Even under rough circumstances a reliable data transfer is guaranteed.

Changeover from Profibus to Ethernet

Before the final transition to ethernet can be completed, Spangler experts firstly split up the existing Profibus system into segments. To connect such a segment then to the new network they first renew the respective control and subsequently all associated peripheries. Assemblies of Siemens S7-1500 and ET200SP series as well as products from Siemens SCALANCE family will be applied.

During the changeover all programmes will be migrated to the TIA Portal which is cross-sectoral applicable or will be installed anew there. An exchange of more control units and the final conversion from Profibus to ethernet will be completed by end of 2023.

The Software SEMA (Spangler Electronic Material Request) has already facilitated Spangler’s goods logistics for some years. The software has now been supplemented by the SEMA App for mobile devices to enable the electricians on the installation site to have access to our material supply. The development took just a couple of weeks; currently the employees are testing the app in the operative application.

Ordered by smartphone

The handling is very simple: when required only the QR code of the material needed is scanned; the same applies for all other order data, such as place of delivery or project number. After that, the delivery is initiated per e-mail or via VPN. „The limited process steps reduce the error rate and make the order process quick and safe, “says programmer Daniel Rengnath. Furthermore, all data are archived and can be retrieved as often as required.

Focusing on the future

Currently, Spangler is working on a SEMA App for Windows tablets to make it usable for manufacturing employees as well. „As a next step, we would like to handle the inventory of our assembly material via this app, too. “, the programmer looks further into the future. A welcome side effect: the Spangler team has intensely dealt with the
MAUI-platform in this connection
This is a code base for the programming of the app, which is used for all mobile operation systems, such as Android, Apple IOS or even for MacOS. This is another advantage for our customers who we can offer the programming of apps and QR codes with the latest state of the art.