Kobold was tasked to provide a solution for the problem of phosphate precipitation in wastewater treatment plants. By adding iron(III) chloride (FeCl3) into the aeration basin, the phosphates dissolved in excess wastewater are chemically mixed with sludge flocculants and transferred with sludge to the sludge treatment stage. This process reduces phosphate concentration in waterways and minimises the potential for abnormal algae growth and the detrimental effect on the aquatic ecosystem. Because an overdose of FeCl3 results in badly polluted water that is toxic to humans as well as the environment, a dependable method of process monitoring was sought.
The ideal was a continuous flow measurement of the dosing chemical with a direct data connection to the process control system, which would guarantee water treatment plant owners maximum safety so that possible errors were not discovered only after the event (during sample taking) when it´s too late.
The solution on offer from Kobold is the MIK magnetic-inductive flow meter, an optimal and economical solution for a safe dosage of FeCl3, and specifically developed for this very application. The unit has already proven itself successfully in service, specifically for electric conductivity liquids, acids and caustic solutions, drinking, cooling and wastewater, groundwater, raw water, aggressive or salty solutions, but is unsuitable for oil since it lacks conductivity.
The MIK is housed in polyvinylidene fluoride (PVDF) and the electrodes in contact with the medium are made of tantalum. Both materials have proven to be totally chemically resistant. With the directly mounted transmitter with stainless steel housing, this device forms a very compact yet robust unit ideal for fitting inside cramped control cabinets. It allows detection of very small dosage amounts from 10 ml/min.
The device operates according to the principle of electromagnetic measurement – Faraday's Law of magnetic induction – where a voltage is induced in a conductor moving through a magnetic field. The electrically conductive measuring agent acts as the moved conductor. The voltage induced in the measuring agent is proportional to the flow velocity and is therefore a value for the volumetric flow. The flow rate is calculated on the cross-sectional area of the pipe. The measurement is dependent on the process liquid and its material properties, such as density, viscosity and temperature. The device may be equipped with a switch, frequency or analog output.
With an analog 4-20 mA signal (or optional pulse output) the MIK continuously communicates the measured values to the user’s process control system, allowing for immediate response to the latest process conditions. This results in increased efficiencies and cost savings in the amount of FeCl3 required to achieve phosphate removal, as well as the vitally important environmental protection component.
Areas of application are flow monitoring, flow measuring, dosing and counting for machine building, the chemical industry, paper industry, automobile industry, cement industry and laboratories. Finally, Kobold asserts that automation guarantees high standards of plant safety even at unmanned plants.
Case History 198: Cascade control overcomes valve problems.
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