Meeting the challenge
The Crailsheim Dairy to date has used considerable amounts of fresh water. It was used, among other applications, as a cleaning agent additive, for control water, for rinsing the centrifuges, for the mould washing machines, for the cooling towers returning coolant and for interim rinsing of all tanks and pipe cleaning. The consumption of peracetic acid as a disinfectant was around 800 liters a month. The goal was to reduce the costs of fresh and wastewater, as well as costs for chemicals used in disinfecting by re-using the water vapour produced during the production process.
Solution
To achieve this goal, chlorine dioxide, in the form of a disinfecting vapor, from ProMinent was used. Chlorine dioxide has long been known as an unstable but very reactive disinfectant. The importance of chlorine dioxide to disinfect water has grown enormously in the last few years. One reason being that it does not produce any undesirable by-products from the reaction process, such as chlorophenols, trihalomethanes or chloramines. Chlorine dioxide is a very effective disinfectant that works on cell proteins and nucleic acids. It also promotes the breakdown of bioflims in piping systems and is effective protection against reinfection.
 | BelloZon® chlorine dioxide system with receiver module and 2 dosage modules |  | cooling water 1.000 l |
 | hot condensed vapours 80.000 l |  | whey condensators |
 | cold condensed vapours 160.000 l |  | milk heater |
 | cooling tower
| | |
 | condensed vapours to ClO2 dosing system |  | fresh water supply |
 | condensed vapours from ClO2 dosing system |  | condensed vapours from ClO2 dosing system |
Water is extracted in an evaporation plant from the whey which is produced during the manufacture of cheese. This is how the whey concentrate and what are known as ‘vapours’ arise. The Crailsheim Diary differentiates between hot and cold vapors. On average, 200,000 litres of hot and cold vapors are collected each day, with the cold vapours making up the greater part with 160,000 – 170,000 liters. They run at approximately 14 m3/h into a 160,000-litre capacity capture tank and the hot vapours into an 80,000-liters tank. The cold vapors have a temperature of approximately 18°C, and the hot vapours 50°C.
Water is extracted in an evaporation plant from the whey which is produced during the manufacture of cheese. This is how the whey concentrate and what are known as ‘vapours’ arise. The Crailsheim Diary differentiates between hot and cold vapors. On average, 200,000 litres of hot and cold vapors are collected each day, with the cold vapours making up the greater part with 160,000 – 170,000 liters. They run at approximately 14 m3/h into a 160,000-litre capacity capture tank and the hot vapours into an 80,000-liters tank. The cold vapors have a temperature of approximately 18°C, and the hot vapours 50°C.
At the outlet of both tanks, the vapour flows are extracted using the bypass lines and fed to the chlorine dioxide dosing system. At this point, the hot and cold vapors, which are separated from each other, are charged with chlorine dioxide in one of the two ClO2 dosing modules. To do this, the bypass flow is split in the dosing module into two streams. The main stream, which is later fed at a height of approximately one metre back into the tank, is charged to around 1.5 ppm, dependent on measured value. Beforehand, the concentration of ClO2 is measured using the ClO2 and Redox control unit. This determines the ClO2 quantity to be added corresponding to the main load dosage. The secondary stream, which feeds into the tank’s vapor intake pipe, is charged in proportion to volume with approximately 1.0 ppm corresponding the basic load dosage. The intake of vapor into the tanks occurs in the upper section. The basic load dosing serves to prevent a layer of ClO2 concentration and therefore, any possible formation of biofilm in the upper area.
The vapors treated in this way then go for intermediate storage in the respective tanks. Even the energy from the hot and cold vapors is utilised using a heat exchanger before being used elsewhere in the plant. From here they can be fed to other areas of application. For instance, as an additive to the cleaning agent, as control water and for rinsing the centrifuges and sometimes for the mould washing machines. The majority is used however by the cooling towers for the return of coolant and for intermediate rinsing of all tank and pipe cleaning agents. The vaporiser itself is likewise supplied with vapor. Once these applications are finished, the vapors are discarded.
The chlorine dioxide plant itself is washed with fresh water in proportion to volume. A stock solution is made from the diluted chemicals of hydrochloric acid (9%) and Sodium Chlorite (7.5%) of up to 1000 ppm and stored in the interim in the supply container of the feeding module. The feeding module is controlled using a Siemens SPS control unit, which controls the fill level of the chemicals’ storage tank and has different safety devices, that, for example, block the supply of water to the chlorine dioxide plant if there is a fault. The stock solution is then fed from the feeding module to the individual dosing modules at a constant rate via the compressed air diaphragm pump. The diaphragm valves needed for dosing are opened and closed using ClO2 measurement and control technology and the controls of the dosing modules. The equipment parts are fitted in series in stainless steel cabinets, and therefore make a compact unit.
Customer advantage
The use of chlorine dioxide as a disinfectant and the reuse and further use of the vapors produced, result in considerable cost savings for the plant operator. Before the conversion, the areas of application mentioned always used fresh water. Peracetic acid was used as a disinfectant. The consumption of peracetic acid was around 800 litres a month at a dosage of 30 – 50 ppm. The Chlorine Dioxide plant consumption of chemicals is around 250 litres for each chemical, with an average dosage of 1.25 ppm. Cost savings of up to 40% are made on chemicals where the average price is approximately 1.50€ per kg of peracetic acid and approximately 1.00€ per kg of acid/alkali for chlorine dioxide. There are savings of up to 40% on fresh water consumption where the vapour is fully utilised. The picture on the microbiological front is also very good. The treated vapours meet all requirements in this respect.