Most industrial sites have cooling towers. Those located in urbanised areas are faced, beyond the objectives of productivity and sanitary compliance of the produced goods, with crucial public health issues inherent to the risk of legionellosis.
Discover how Veolia helps one of these industrialists of the F&B industry meet its challenges and focus on its core business while also benefiting from expert advice tailored to its needs.
An article by Thomas Le Boursicot , Veolia Water Technologies Hydrex product manager cooling applications.
For 14 years, Veolia Water Technologies has managed the water treatment of cooling towers at a leading industrial site producing yeasts and yeast extracts near Paris. This historic site, established in 1872, is in a densely populated urban area of about 15,000 inhabitants/km2. Over the years, technological innovations have kept the site competitive, including with cooling towers essential for process cooling and air conditioning.
Legionella: A Major Challenge for Cooling Towers
Increased medical knowledge has highlighted the major public health issues related to the risk of development and proliferation of Legionella Pneumophila especially in the cooling systems.
This bacterium can cause legionellosis, a respiratory infection with a 10% lethality rate, resulting in thousands of deaths annually.
Despite drift eliminators which limit its extent, the operation of cooling towers induces the projection of microdroplets, a consequence of the dispersion of cooling water in an air flow. These droplets can potentially spread Legionella over several kilometers and put the nearby population at risk if the cooling water is contaminated.
Our treatment approach
To protect our industrial client in Paris from this risk, Veolia Water STI has developed a robust and innovative Hydrex strategy combining equipment, the necessary and optimal dosage of products and services.
The treatment strategy leverages an oxidising biocide treatment with Hydrex Chemical solutions provided online by a salt electrolysis technology (OSG Hydrex).
Associated with a monitoring tool (Hydrex Controller range) it orchestrates the treatment implementation while alerting in real time the site’s owner and the operator of any drift.
On-site expertise needed to adjust the program
Through the monitoring and site visits by Veolia Water STI Hydrex teams, it was identified that the site was still facing certain instabilities, particularly on one of the applications using two evaporative condensers. These independent 3 m³ galvanised steel cooling towers, operating intermittently, had the following operating and treatment characteristics:
Hydrex Mix Oxidant Solution (MOS) injection into the makeup water, controlled by a flow meter
- Difficulties in maintaining a stable chlorine content in the cooling towers, linked to a lack of online measurement, as well as the intermittent operation of these towers ⇒ lack of water additions causing a continuous and inevitable decrease of the residual chlorine in the towers when stopped and not drained.
Finding the complementary solution
The installation of a new Hydrex Controller in 2023 allowed us to remedy this problem. Thus, several control and management elements of the biocide treatment could be implemented using this new technology:
Distinct measurements of free chlorine residuals on each of the cooling towers, using amperometric sensors
- Maintaining the dosage of oxidising biocide on the common make-up water line
- Triggering, by means of a program output on the Hydrex Controller, a forced opening of the blowdown solenoid valve in case of insufficient residual free chlorine content (less than 0.3 ppm) in one or the other of the two towers, in order to generate a forced water make-up for a few seconds, and thus allow the maintenance of a satisfactory free chlorine residual in the cooling systems.
Benefits achieved
This innovation has thus provided the following benefits :
Maintaining a minimum residual free chlorine content at all times in the cooling towers
⇒ Increased security of the facilities against the risk of legionellosis
Figure: Measured value of residual free chlorine in the cooling tower |
Refined alarm thresholds allowing for a quick readjustment of the oxidising biocide dosage rate in case of excessive free chlorine content measured in the TAR
⇒ reduction of the corrosion rate on steel by an average of 20 µm/year
Forced deconcentration allowing to secure the cooling towers with a minimum water loss, preventing the operator from having to drain the entire circuit in case of prolonged absence of thermal load
⇒ average water savings of 300 m³/year.
Conclusion
The benefits we have reached for this F&B site, we, at Veolia, can deliver them to you as well, for your performance and sustainability without compromise.
We understand that each industrial site’s situation is unique and we will work with you to design the best cooling tower treatment and monitoring program to meet your needs.
If you want to learn more, contact our experts.
