Reliable Flow Measurement Under Demanding Conditions

The long-distance water distribution network of the supraregional drinking water supplier Fernwasser Elbaue-Ostharz (FEO) spans a total length of approximately 800 kilometers. Large-diameter pipelines up to DN 1200 transport approximately 220 million liters of drinking water daily to the central German region. One of the three water treatment plants in the network, the Wienrode Water Treatment Plant, is connected to the Rappbode Dam operated by Talsperrenbetrieb Sachsen-Anhalt AöR. After the raw water is treated at this water treatment plant, it supplies approximately 40% of the drinking water required in Saxony-Anhalt.

Part of the infrastructure at the Wienrode Water Treatment Plant, operated by FEO, is a bypass structure that includes control valves (2x DN 800 ring-piston valves) and the subsequent supply lines to the water treatment plant. Two robust KATflow 150 ultrasonic flow meters are installed in the water treatment plant’s bypass structure to regulate two separate flow rates. These consist of two DN 800 steel pipelines that bypass a turbine operated by Avacon-Natur GmbH in the inflow to the Wienrode Water Treatment Plant.

A key factor for successful measurement using ultrasonic technology is the availability of sufficient inlet and outlet runs to ensure an axisymmetric flow profile. Before deciding on a stationary device from the manufacturer Katronic, FEO conducted three tests with minimum and maximum process peaks at various locations to determine the optimal position for the measurement. The decisive factors in the purchase of the two two-channel flow meters were the successful preliminary tests and the resulting prospect of being able to reliably measure large volumes of water in a turbulent environment using the KATflow 150. 

The primary requirement—“water flow rate”—comes from the dam’s water treatment plant, which supplies drinking water to the region. This pipeline operates around the clock. A typical water flow rate requested by the water treatment plant is approximately 6,000 m³/h. In the bypass lines, this flow rate is typically distributed equally between both pipes at 3,000 m³/h. The bypasses are used whenever the turbine fails or is unable to guarantee the inflow required by the water treatment plant.

Both KATflow 150 units are configured as two-channel measuring devices, each equipped with an analog 4–20 mA process output and a Profibus PA interface. The control system receives four measured values simultaneously, which are processed as part of a plausibility check—a form of quality control. The key criterion is signal redundancy. If one signal fails, the system switches to the remaining available signal. If the current output signal drops to 0 mA, the programmable logic controller (PLC) switches to a substitute value and deactivates the control.

Although the installation conditions for clamp-on flow meters are not ideal due to existing fixtures and butterfly valves, both permanently installed devices have proven reliable in this application within subsequently defined limits.

The volumetric flow rates at both measuring points are turbulent and axially symmetrically offset. Although the control range of the ring-piston valves can be fully utilized, the flow rate can no longer be measured correctly under these conditions. Therefore, the PLC uses software to limit the flow rate and the opening degree of these control valves. Despite the circumstances described, the measurement quality is sufficiently good to allow remote control of both lines via the two ring-piston valves. With these supplementary measures, the measurement data is 98% usable, even under the challenging flow conditions.

Thanks to clamp-on technology, the KATflow 150 flowmeter can be installed while the process is running. Configuration and positioning are performed via the flowmeter’s menu, which can be operated intuitively during operation.