Process-photometer for online determination and control of inhibitor concentration in cooling systems

Introduction
Prolonged operation times and maximum operational safety are essential requirements expected from cooling systems these days. The application of especially selected corrosion- and hardness-inhibitors will allow high retention times and high numbers of cycles in the system. The chemicals in use are generally combined products based on phosphorous compounds and polyacrylic acid derivates.
Continuous determination and automatic dosage of these treatment products is more and more important. In many cases this is the only way to avoid an overdose or underdose of inhibitors and to ensure operation of the system in an ecological and economical way.



Fig. 1: Analyser type KURIAUTO IDC 20

The analysers of the KURIAUTO product series have been developed based on two aspects:

• superior reliability and accuracy of measurement
• simple to operate

The process analyzer runs a discontinuous photometric determination of the inhibitor concentration in cooling water according to an adjustable time interval. The measurement is based on a turbidity reaction of poly-acrylic acid based polymers with the reagent Hyamine 1622. The intensity of the turbidity is directly proportional to the polymer content in the adjusted pH-range.

A special reagent, tuned for the specific water-system, is dosed into the measurement-chamber with a peristaltic pump and mixed with the cooling-water. The turbidity is then determined by the photometric system after the specified reaction time has elapsed. The result of the analysis is displayed in milligrams per litre. The entire analytical process including filling and rinsing of the measuring cell is controlled by a microprocessor. Limit values and sampling intervals can be entered manually via the operator menu. Users have access to a limiting value relay, an alarm relay and a scaleable 20mA measurement signal. The entire analysis unit is mounted on a PVC-plate which should be fixed to a wall. A compatible FRP-cabinet (IP65) is also available as an option.

Installation

The hydraulic connection should be installed as a bypass from the cooling-water supply line. The discharge of tested water from the unit has to pass through an unrestricted outlet. Control of the dosage pump is carried out via a potential-free relay or the 0/4-20 mA measuring signal.



Fig. 2: Installation of the measuring device

Application example
In an open cooling system in Germany (circulation = 1100 m3/h) strong fluctuations of inhibitor concentration were recorded. By manually adjusting the dosage pump based on lab measurements taken, it was impossible to achieve stable product concentration in the system. For this reason a KURIAUTO IDC 20 device for online measurement and control of product concentration was installed in early 2000. The dosage pump was controlled via the potential-free relay of the measuring device. As soon as it went into service the previously strong fluctuations in product concentration were stabilised within the intended range of 80 mg/l.



Fig. 3: Product concentration in the cooling water

The KURIAUTO system, unlike online measurements, which only determine tracer concentration and not product content, is not adversely affected by organic contamination.

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