Optimising energy management and consumption

October 15th, 2015, Published in Articles: Energize

 

The drying and processing of wood is a process that requires a lot of energy. Holzwerke Weinzierl in Germany nevertheless manages to generate more power than it consumes. The basis for this achievement is a modern energy management system that uses power measurement I/O terminals and embedded PCs to make the plant’s energy use transparent while continually optimising it.

Located on a property spanning 22 hectares in the Bavarian town of Vilshofen, Holzwerke Weinzierl produces roughly 600 000 m3 of round logs and 150 000 t of wood pellets per year. The company’s most important energy transfer medium is electricity, which it distributes via seven transformer stations fed by its own medium-voltage grid.

Fig. 1: The energy management system captures and analyses energy consumption values from all processing systems like this area, for example, where tree trunks enter the plant.

Fig. 1: The energy management system captures and analyses energy consumption values from all processing systems like this area, for example, where tree trunks enter the plant.

The total annual power consumption amounts to roughly 30-million kWh, spread at about one-third each over the lumber production, the pellet plant, and 36 drying kilns. By using three solar panel arrays and burning wood bark in four combined biomass power and heat generation systems, however, Weinzierl produces 35-million kWh of green electricity annually, which enables it to sell roughly 5-million kWh to the public grid.

07-tt-Beckhoff-fig.02

Answering a wide range of energy management and data acquisition requirements

For ecological as well as economic reasons, the company decided in 2011 to implement an energy management system (EMS) according to the DIN 50001 standard, because only a comprehensive energy data acquisition system would provide the transparency needed to exploit all potential for optimisation and maximise the annual power surplus.

For starters, the complete power supply systems were connected, including the seven transformer stations and the low-voltage distribution panels. Over time, the end users will be added, i.e. roughly 40 large drives, until finally all energy data and production performance indicators flow into the system.

Fig. 3: Josef Brauneis, Head of Electrical Engineering at Holzwerke Weinzierl, explains the facility’s power consumption display.

Fig. 3: Josef Brauneis, Head of Electrical Engineering at Holzwerke Weinzierl, explains the facility’s power consumption display.

Selecting the right energy management software was not easy. Josef Brauneis, the company’s head of electrical engineering said that the systems available at the time did not deliver the capabilities, flexibility or price-to-performance ratio the company was looking for. Although the market has improved in the meantime, most systems either facilitate pure data collection with limited interfaces or one must install a powerful building control system. The highly flexible Zenon visualisation system, which the company was already familiar with, and which provides good display, archiving and reporting capabilities, was chosen for the task.

In order to implement such a widely distributed and complex EMS with features that went beyond simply collecting data, Brauneis placed high demands on the process interfaces. For example, the system had to cover all energy-relevant facilities on the large grounds and protect against network problems by storing and analysing the data on site. It also had to handle all current performance indicators and accommodate new ones in a cost-effective manner. Furthermore, it had to be able to use the existing networking infrastructure and keep the control technology as compact as possible, because space was limited.

Fig. 4: The web-based visualisation system provides a rapid overview and diagnostic capabilities.

Fig. 4: The web-based visualisation system provides a rapid overview and diagnostic capabilities.

For Brauneis, having a system with flexible data collection capabilities was also critical for the following reasons. The interface spectrum had to be broad enough to take and accept energy-relevant signals, preferably from all systems controllers. This included, for example, the integration of an interface to the utility company’s feed-in management system, the reliable transmission of signals to the combined power and heat generation systems, and the collection, transmission and linking of all signals from the power distribution facilities such as power switch settings, transformer and room temperatures, and fault signals from compensation systems. The visualisation software also had to be able to read all of this information.

Embedded PCs and EtherCAT terminals provide the best solution

Beckhoff supplied a system consisting of embedded PCs and EtherCAT terminals which enabled the company to import the PLC projects via the visualisation software’s editor. The same applies to the important separation between the production and EMS networks. An Ethernet LAN adapter and appropriate function blocks from the PLC library, enabled the company to easily implement the required data consistency between the EMS and the controllers on the wood processing machines.

Fig. 5: With several biomass boilers and solar power installations, Holzwerke Weinzierl generates “green” electricity that is CO2-neutral.

Fig. 5: With several biomass boilers and solar power installations, Holzwerke Weinzierl generates “green” electricity that is CO2-neutral.

The EMS comprises roughly 200 measurement points for roughly 400 measurement values regarding output, power, voltage, and power factor. Over the medium term, i.e. after integrating the larger single drives, there will be roughly 500 values. In the final stage, when heat output, compressed air consumption and diesel fuel consumption as well as the key production performance indicators are included, the system will comprise roughly 1000 measurement points. The core of the energy data acquisition system is made up of one embedded PC in each transformer station. The embedded PCs are networked via fiber optic cable and Ethernet, and are equipped with 1,1 GHz processors, which provide ample computing power. To collect the energy data, 45 EtherCAT terminals and 30 digital four-channel terminals are used to collect the pulses of various counters. They are supplemented by 20 additional digital input terminals for the signals emitted by the signaling system and numerous analog I/O terminals.

Brauneis says the systems have grown over many years, which is why they differ significantly from each other. In the company’s old building, for example, it collected no energy data at all, while the newer systems it added in 2006 and beyond collected energy data in the form of pulse signals to the next boiler controller, where they were totaled up.

The company built a new power data collection system with power measurement terminals and installed digital I/O terminals so that the interface of the power meters could use existing information.

Since each phase can be analysed separately and the respective converter ratios can also be computed individually in the PLC, the user can measure three asynchronous motors in single-phase mode instead of the three phases of a single drive. The three-phase performance values can then be easily calculated with precision which is sufficient for the power factors and cycle times required for a lumber mill. This approach requires significantly fewer terminals and saves a great deal of space in tight control cabinets. It also contributes to energy savings, because additional terminals and converters would themselves consume additional electricity.

Optimised energy efficiency through better data acquisition

The main benefit of the energy management system is that it makes energy consumption transparent across the entire lumber mill. While the power consumption of the 36 drying kilns with twelve 3 kW drives each had always been tightly controlled, all sorting and wood rounding systems, as well as the pellet systems with their conveyor dryers and boilers, are now integrated as well. Brauneis says that the company added things like a colour-coding system to support the line operator. A red signal indicates that the system’s power consumption needs to be reduced, for example, by cleaning a dirty photo sensor or doing some other maintenance. Another example involves turning on the flue gas fans in the boilers with some delay, because each of them consumes a considerable 160 kW. By taking steps like these the company is able to continuously reduce its power consumption by roughly 150 kW and keep its peak usage unchanged despite the fact that it added another line and two more drying kilns.

Many ideas for improvements came about as a result of receiving all this information about factors such as unexpected usage peaks. For example, the company’s production buildings feature large exhaust systems that now have additional shut-off devices so that we can turn off the energy-intensive ventilation in specific areas when they are not in use. The EMS also enables it to analyse its energy consumption for individual cost centres and product batches.

Contact Michelle Murphy, Beckhoff, Tel 011 795-2898, michellem@beckhoff.co.za

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