MVA Bielefeld-Herford GmbH runs a thermal waste treatment plant with a capacity of approx. 400,000 t/year at the Bielefeld site. Thanks to energy recovery using combined heat and power (CHP), approx. 55,000 households are supplied with electricity and approx. 23,000 with heat in an eco-friendly manner. The plant is continuously being modernised and expanded.
In the grate-firing system, combustion of the raw material takes place in five zones, one after the other. Each zone is supplied with individual primary air flow to regulate the combustion process. There are two air supply lines per zone, left and right. The accurate and continuous regulation of the entire staged process from pyrolysis to combustion has a huge impact on the flue gas amount, the expense incurred during treatment as well as energy efficiency and residual material properties. The air quantity is regulated via the differential pressure flow measurement of the total under-air quantity as well as the minimal differential pressures of the individual zones above and below the grate (approx. 5 mbar / 0.072 psi). The individual dampers for each zone are controlled as a function of these differential pressures.
As part of continuous system modernization, the existing differential pressure transmitters should be renewed. The new measuring instruments had to fit the existing valve connections and have a correspondingly small measuring range. They also had to be stable over the long term as well as easy and quick to configure.
In parallel to the existing pressure transmitters, the OPTIBAR DP 7060 differential pressure transmitter was first installed as a test. The KROHNE device proved itself during a prolonged test phase in this application. After verification with a pressure calibrator, no further adjustment was necessary for the first time. Following the test, the measuring points were fitted with OPTIBAR DP 7060 pressure transmitters for overall measurement of the bottom air quantity and zonal measurement. Thanks to compatible connections and simple operation via the modular, illuminated display, the differential pressure transmitters were swiftly put into service.
To maintain a robust and accurate differential pressure measurement, even under changing process conditions, each OPTIBAR DP 7060 differential pressure transmitter was linearised in all 3 dimensions during calibration: differential pressure, ambient temperature and static pressure were taken into account in all combinations during this "3D linearisation". Since all specified operating ranges are covered, a stable and accurate measurement can be guaranteed under all process conditions.
The OPTIBAR DP 7060 plays a key role in zonal regulation of the incineration plant – and thus for the thermal processing and efficiency of the plant in general. Thanks to differential pressure measurement, the operator can always determine how much lower air needs to be supplied in order for the combustion process to proceed in an optimal manner according to the waste on the grate.
The OPTIBAR DP 7060 units used are extremely reliable, work without interruption and are "unobtrusive" in the best possible way for the customer. The unit has proven itself when it comes to regulating the plant to such an extent that the operator is already planning to retrofit more measuring points, equipping them with the pressure transmitter. The modular design of the differential pressure transmitter facilitates this step. The OPTIBAR DP 7060 offers a flexibly configurable selection of housing variants, process connections and electronics for every application. An all-in-one supplier, KROHNE can also provide a comprehensive range of pressure measurement – including accompanying primary elements, diaphragm seals, manifolds and other accessories – all from the one source.