The key words for minimising operational down time due to fouling (build up of impurities) are prevention and maintenance. It is very important to ensure that the cooling fluid of heat exchanger is treated regularly to prevent to a certain extend the build up of impurities. Large-scale operations like open circuit cooling systems in the Mining and Petrochemical industries use water treatment such as purification, addition of chemicals to water and water testing to minimise fouling in heat exchangers.
Heat exchangers require dissembling and cleaning periodically. Methods of cleaning tubular heat exchangers include:
- Chemical cleaning - Close circuit chemical cleaning is used to pump chemical through the heat exchanger which dissolves the build up of impurities.
- Sandblasting - This method is used for removing corrosion impurities which generally build up on the inside of the heat exchanger shell.
- High-pressure water jet - The method is used to remove the build up of impurities for example lime scale builds on the inner tube where water is generally used as the cooling fluid.
- Drill rods - This method is used to clrill through the lime scale build up in tubes where the High-pressure water jet did not provide the required results. It is important to take exceptional care when using this method as the tube wall could easily be damaged with the Drill rods especially where the lime scale build up is highly concentrated and very hard to drill through. In such instances it is often more beneficial in the long term to re-tube the tube bundle and Cooler Engineering will always take the responsibility to inform and advise our clients if we deem it necessary to re-tube the heat exchanger.
Fouling occurs when a fluid which flows through or over the heat exchanger tubes contain impurities that over time precipitate onto the surface of the tubes.
- Precipitation of these impurities can be caused by:
- Frequent use of the heat exchanger
- Not cleaning the heat exchanger regularly
- Reducing the velocity of the fluids moving through the heat exchanger
- Over-sizing of the heat exchanger
Effects of fouling are more abundant in the cold tubes of the heat exchanger than in the hot tubes. This is because impurities are less likely to be dissolved in a cold fluid. This is because, for most substances, solubility increases as temperature increases. A notable exception is hard water where the opposite is true.
The conventional approach to fouling control combines the “blind” application of biocides and anti-scale chemicals with periodic lab testing. This often results in the excessive use of chemicals with the inherent side effects of accelerating system corrosion and increasing toxic waste- not to mention the incremental cost of unnecessary treatments. There are however solutions for continuous fouling monitoring In liquid environments, such as the Neosens FS sensor, measuring both fouling thickness and temperature, allowing to optimize the use of chemicals and control the efficiency of cleanings.
General Engineering services
- Fabrications and assembly according to drawings
- Cutting and bending
Heat Exchanger services