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Nov-2018

Online monitor slashes biocide dosage (TIA)

In many systems, fouling and deposits are a serious problem which results in shutdowns, cleaning actions and unexpected costs for the customer.

Rainer Haug
Kurita
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Article Summary
Proper treatments are available and applied in many systems but changing side conditions still can lead to unexpected and unpredictable fouling or deposit formation. Real time monitoring of these effects, independent of the reason, would give a much better control possibility for the application of the right products at the right time. HydroBio Advance is a monitoring system which fulfils this real time tracking of deposit formation for practically any kind of fouling.

A petrochemical plant wanted to evaluate the real biocide demand of its cooling system during a winter period. With HydroBio Advance, biocide consumption was reduced by 75%.

In this plant the biocide has been dosed throughout the whole year on a constant level. Only in the case of special events or out of spec measurements were additional biocide dosages applied. The main reason behind this approach was the lack of a suitable online monitoring device which could detect fouling occurrence in real time. Indirect measurements using microbiological parameters were used to conclude if serious fouling occurred in the system. So fouling first had to occur, resulting in a serious increase of bacterial count in the cooling water, before counter measures were taken. As the microbiological growth rate depends on various external factors it was impossible to control all of them at the same time.

Microbiological investigations can easily take one week before the results are available. Counter measures consequently are also one week late. Kurita’s HydroBio Advance measures the fouling tendency online when it occurs. Therefore, adequate counter actions can be taken at a much earlier stage avoiding over dosages of products and ensuring smooth plant operation.

The system was installed in January in the cooling water to monitor fouling tendencies by using the approach ‘biofilm elevated’. This programme is using a slightly elevated temperature profile on the sensor surface, making it possible to predict biofilm formation tendency in the system. With this early warning system, corrective actions can be initiated, even before biofilm formation occurs.

Online monitoring of this cooling system with HydroBio Advance indicated no fouling tendency with the biocide dosing programme in place. After stopping the biocide dosage, HydroBio Advance immediately detected that there was a continuous fouling tendency in the recirculation water of the cooling system, even during the cold winter time conditions (see Figure 1).

After stopping the biocide dosage, some extra biocide dosages were applied during a short intermediate phase to remove accumulated biomass from the system.

Following the cleaning, the regular biocide dosage was restarted at one quarter the original dosage. The results showed that this was already enough to keep microbiology and fouling under control during wintertime conditions (see Figure 2).

The HydroBio Advance series of online monitors is available for various applications and with different configurations. The standard sensor is a 1in tube sensor. It is available in stainless steel but also in seawater resistant steel. The tube material itself has practically no impact on the measurement result. Therefore, the sensors can be made from any type of alloy, matching the requirements of each application.

The standard sensors are used at ambient temperatures in cooling water or similar applications. In addition, the tube sensor is available for applications at elevated temperatures up to 110°C. Special strap-on sensors for geothermal applications are currently being developed and will be able to detect deposits at temperatures as high as 250°C.

HydroBio Advance is a robust but sensitive fouling monitor to track fouling occurrences in different applications. As fouling is measured directly all side impacts are taken into account. At the same time, parameters like turbidity or suspended solids have no impact on the measurement.

This short case study originally appeared in PTQ's Technology In Action feature - Q4 2018 issue.

For more information: rainer.haug@kurita.eu

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