Clean water for Prague thanks to CHLORINSITU
Changeover to new disinfectant
Around 1.3 million people live in Prague, the capital of the Czech Republic. Supplying such a large city with clean drinking water is a challenging task. For this reason, those responsible at the waterworks decided to switch the post-chlorination from chlorine gas to sodium hypochlorite in the existing water treatment plants. This process step should become safer, as chlorine gas is a toxic gas that has an irritant effect on eyes and skin and is oxidising on contact with oxygen.
Based on former positive experiences from a project, where two electrolysis plants have been installed for drinking water treatment for over 130,000 people, ProMinent Czech Republic was once again assigned. The premise was no transport, no storage and no handling of hazardous chemicals, but the on-site processing of common salt into chlorine, hydrogen and sodium hydroxide solution with modern plant technology.
- Post-chlorination of drinking water for two 100,000 m3 reservoirs for around 800,000 inhabitants of Prague
- Changeover from chlorine gas to sodium hypochlorite as disinfectant
- Post-chlorination of an average of 3,000 litres of water per second with a concentration of free chlorine of 0.2-0.4 ppm
Electrolysis – economical and technically top
The project for this (so far) largest water treatment system in the country, started with an intensive planning phase on the part of ProMinent Czech Republic on behalf of SWECO Hydroprojekt, a.s.. After this, the complete plant has been installed within three months at the end of 2018. The commissioning took place in February 2019 together with the experts from Van den Heuvel Wassertechnologie B.V. The heart of the plant consists of four CHLORINSITU III electrolysis systems with a capacity of 2,500 g/h each. The solution also includes: Seven fully assembled DULCODOS® metering systems, each with two Sigma X motor-driven metering pumps with integrated control and one dosing system with two delta® solenoid-driven diaphragm dosing pumps. In addition, a PE-HD tank for storing 4,000 litres of sodium hypochlorite solution, three chlorine gas warning systems with sensors and one central PLC system. The sodium hypochlorite, that is economically produced in the CHLORINSITU III systems by means of electrolysis, is feed by two metering systems to the two inlets of the two large tanks. Another five metering systems supply five reservoir outlets to the Prague water works, while one system takes over the metering at the outlet to a water works nearby.
Project successfully completed
Thanks to careful planning and execution by experienced companies in the field of water treatment, the new electrolysis plants are running flawlessly since commissioning. The Prague water works benefit from the economical and safe disinfection of drinking water. This is due to the high-purity sodium hypochlorite produced by the CHLORINSITU III systems , that has a concentration of approximately 2.5-3.0% of free chlorine. In addition, there is very little carry-over of common salt from the membrane cell into the end product – a yield of more than 85%. Thus, the complete sodium hypochlorite solution, which is more stable and water-soluble than chlorine gas, can be supplied to the drinking water by means of separate metering pumps.
The customer is again very satisfied with the ProMinent electrolysis systems and the responsiveness of the companies involved in the project. Therefore, the same suppliers were also entrusted with the maintenance and repair of the new systems.
- Supply of clean drinking water to three quarters of Prague's population
- Successful changeover of the disinfectant to sodium hypochlorite
- Economical and safe production of disinfectant by electrolysis
- Reliable system control via Remote Control Engineer for remote diagnosis and troubleshooting
- Long service life of the membrane cells due to constant vacuum
- High operational safety of the CHLORINSITU III systems through design as vacuum systems and equipment with ATEX-95-compliant ventilation system