German facility replaces biocide treatment with ozone treatment
Infraserv Hoechst is a leading company for operating large-scale industrial and chemical production complexes. It is a complete service provider offering services such as purchasing, engineering and facility management, and it has a full supply of products such as compressed air, steam, cooling water, purified water, technical gases and energy.
In Frankfurt, Germany, Infraserv Hoechst operates one of the largest production and research sites for the chemical industry in Europe. The complex is located on 1.5 sq miles and houses more than 80 companies with about 22,000 employees. Clients served on site include Bayer Crop Science, Basell, Clariant, Degussa, Alessa, Dystar and Air Liquide.
Ozone replaces biocides and chlorine
In the early 1990s, Xylem, in collaboration with Hoechst and Messer, investigated in detail the use of ozone for different applications.
After pilot testing—including thorough investigations of relevant water parameters, corrosion measurements, safety and ease of operation—Hoechst changed the former biocide treatment (organic biocides, chlorine gas, hypochlorite) to ozone treatment. The same inhibitor that prevented scaling and corrosion with the chemical treatment was used, with only minor adjustments, when Hoechst changed to ozone cooling water treatment. Between 1995 and 2005, eight WEDECO ozone systems were delivered, and they are operating successfully to prevent biofilm formation inside the cooling loop systems. The cooling loops consist of air-cooled cooling towers that provide chilled water for all the different areas and processes of the chemical production facilities; air separation plants for oxygen and nitrogen supply; and power plants.
The various cooling loops around the facility have circulation rates from 4,500 to more than 70,000 gpm. The WEDECO ozone systems use liquid oxygen available on site or dried, compressed air to produce between 700 and 4,000 grams/hr.
The introduction of small dosages of ozone into the re-circulated cooling water prevents biological growth inside the cooling systems and process heat exchangers, which results in much cleaner cooling water. The cleaner cooling system saves energy due to better heat transfer, reduces maintenance work significantly and increases the lifetimes of components and piping. Since no additional salts are introduced into the cooling loop, less makeup water is consumed, higher concentration cycles can be achieved and thus fewer inhibitors are required.
In addition to the prevention of biological growth, the main motivation was the safe compliance with government thresholds for adsorbable halogens of fewer than 500 μg/cu m and chemical oxygen demand of 40 mg/L in the blow-down (discharge) of the cooling loop, as well as the safe control of Legionella.
Due to the trend toward higher degrees of automation needing less and less manpower to operate the complex systems, the fully automatic operation of the ozone system and the lowest need for maintenance was of the highest priority in choosing an ozone supplier for the client.
Ozone plant details
Seven of the WEDECO SMO/SMA systems installed on site produce ozone from liquid oxygen at typical ozone concentrations of 10 weight percent (wt%), while one unit uses dried and filtered air as feed gas at ozone concentrations of 2.3 wt%.
The systems are complete and operate automatically from remote on/off. The systems consist of an ozone generator, a side-stream pump-injection system, ozone analyzers for the gas phase, an ambient air ozone detection unit and complete process control. Additionally, three of the ozone systems are completely containerized, including all relevant safety features, while five skid-mounted units are installed inside buildings on the premises.