An operator of a municipal sewage system in southern Germany uses a mixed water drainage system. In this system, household water loads as well as rainwater transfer to a municipal treatment plant via a mixed water collection system. The influent to the sewage treatment plant requires flow monitoring. This is especially important when the rainwater load is high. It also needs regulating because if the plant floods the peripheral areas, the wastewater can cause a great deal of environmental damage. However, the pipeline is not always full, so a device that can measure partially filled pipes is necessary.
The municipal operator relies on several rainwater retention basins (RRB) for intermediate storage. This allows the operator to drain off excess precipitation loads as necessary. In addition, the respective water authority requires that the discharge from the rainwater basin into the mixed water system does not exceed a specific flow rate (m3/h). This requirement prevents the sewage treatment plant from hydraulic overload. However, documentation for the storage capacity of the RRB requires evidence to verify the discharge.
In this case, an operator requires a new flow meter to verify the discharge. This allows the operator to check the quantity of precipitation flowing into the mixed water duct precisely. Gate valves must control the discharge quantity so that both the rainwater and the dry weather flow does not exceed an upper limit of 40 l/s.
The rainwater basin discharge is an unpressurized, gravity pipeline (DN 250 / 10″). Because of this, there are limited options for measuring flow in these partially filled pipelines. Moreover, because fermentation processes can produce flammable methane (CH4) and easily ignitable hydrogen sulphide (H2S) in the wastewater. So, both the flow sensor and the converter need approval in accordance with ATEX for use in Ex zone 1.
Due to the high requirements for the measurement and the explosion protection, the only measuring device suitable for this application is the TIDALFLUX 2300 F. The TIDALFLUX is an electromagnetic flow meter, or magmeter, that installs in the discharge line of the RRB by means of a flange connection. This magmeter offers a patented level measuring system.
For this reason, the TIDALFLUX can perform reliable measurements, even in partially filled pipelines, starting at a level of 10 percent. Furthermore, the capacitive level sensors in the liner of the measuring device do not come into contact with the wastewater. Therefore, the measurement has no effect by grease and oil floating on the surface. In addition, the polyurethane liner of the TIDALFLUX protects the instrument from abrasion and chemicals. All of the components of the measuring device have approval in accordance with ATEX for use in Ex zone 1.
With the TIDALFLUX 2300 F, the operator can comply with the maximum upper limit for dry weather and rainwater discharge into the mixed water drainage system. The measuring results can transfer directly to a gate valve. Or, they can transfer to an electrical gate valve in the structure with overflow whereby the customer can control the flow automatically before and after the measuring device. In this way, the magmeter can perform reliable measurements in partially filled pipelines. The TIDALFLUX is currently the only device on the market that meets the requirements for use in Ex zone 1 with respect to both the sensor and the converter.
In addition, the TIDALFLUX allows the municipal operator to check the storage volume of the RRB. Therefore, the operator can demonstrate efficiency to the water authority. In contrast to a rain overflow basin, the RRB does not overflow into a body of water. So it must be able to store the entire amount of precipitation when it rains. For this reason, the investment in the TIDALFLUX pays off. With flow measurement, the operator can regularly prove that the size of the basin is sufficient. Furthermore, it proves that an expensive expansion or even the construction of another RRB is not necessary.
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