Descaling of marine equipment

Chemical descaling of cooling box systems of ships, tugboats and various vessels

Systems in the operation lines of various industries such as power plants, refineries, petrochemicals, drilling and acidizing operations of oil wells, etc., which operate in aqueous and humid environments. Under various conditions such as pressure, temperature and purity of the process water, after a while, deposits form on the inner wall of the layers, which are most often iron oxide layers or adhered carbonate and silicate deposits. The heat transfer surfaces are the hottest point that the cooling water reaches.

The solubility of calcium carbonate present in the device is inversely related to temperature, as a result, the possibility of calcium carbonate settling and precipitation occurs on the heat transfer surfaces. The accumulation of calcium carbonate sediment layers reduces heat transfer, which causes corrosion and creates hot spots that themselves cause thermal stress. All of these will affect the efficiency and life of the device, which will cause a decrease in device efficiency. Therefore, considering the above, the purpose of this article is to select the appropriate corrosion inhibitor.

Seawater is used to cool equipment and heat exchangers in ships. Seawater contains significant amounts of mineral salts, including sulfate, chloride, and carbonate. These substances cause sediment in the exchangers over time. In addition to mineral salts, seawater is a huge source of microorganisms.

 Which, upon entering the cooling heat exchangers and considering the appropriate ambient temperature (about 30 to 35 degrees Celsius), which is very suitable for the growth of bacteria and other microorganisms, quickly grow and multiply on the surfaces of the exchanger. The thermal resistance of a biofilm layer with a certain thickness is greater than a layer of silica sediments with the same thickness. Therefore, the growth of biofilm in seawater systems is the main factor in reducing the efficiency of the exchanger and heat transfer. Ship sedimentation

Sedimentation leads to lower thermal efficiency and pressure drop. Which may also lead to corrosion and cause the exchangers to fail. Most heat exchangers in ships are subject to fouling due to non-compliance with operating instructions or due to poor water quality.

In the event of fouling, fouling should be removed to design conditions close to zero point and achieve the necessary efficiency.

Two types of fouling are proposed, each with its own advantages and disadvantages.

Descaling without stopping the water circulation system

Mechanical descaling requires stopping the system and opening and closing the equipment, resulting in a long stoppage of the ship, which entails costs and possible damages from dismantling the exchangers, tube bundles and ancillary equipment, and a long time, which is almost obsolete or will entail many problems.

The second method is modern chemical fouling, which was invented and used by Abrizan Company.

In this type of operation, the solution produced by Abrizan Industrial Research Company under the trade name Mitreh Kashti is used in a closed system for engines and diesel generators of ships by injecting a sediment removal agent. Sediment removal of cooling box systems or heat exchangers in an open system that have direct contact with seawater is carried out chemically on the dock. In this case, sediment removal operations have been carried out on several ships located in Bandar Abbas, Shahid Rajaee Pier and Bandar Imam Mahshahr.

Pictures before sediment removal operations:

Pictures after sediment removal operation with ship's miter saw:

Conclusion

Deposits on marine equipment, which are mostly calcium and magnesium, act as an insulator between the metal surface and the water and increase the temperature of the metal, resulting in reduced engine cooling. Descaling of marine equipment plays a significant role in reducing costs, including fuel consumption, equipment maintenance, washing, etc. Descaling methods for marine equipment, like other devices, are possible in electronic, mechanical, and chemical forms.