In addition to maintenance during special circumstances, plate heat exchangers should also undergo regular maintenance. Due to the ease of disassembly and simple maintenance of plate heat exchangers, special tools and equipment are generally not required. Different methods can be employed based on different situations. If there is no leakage in the equipment and only a decrease in the heat transfer system K, the heat exchanger does not need to be disassembled; instead, a closed-loop system can be used to circulate descaling liquid into the equipment for several hours. If such conditions are not available on-site, and if the equipment is not severely scaled, it can be rinsed directly with water without removing the plates, while using a soft brush for scrubbing.
1. Normal Operation Maintenance
① Equipment that needs maintenance should be disassembled in reverse order of installation.
② Equipment used in the petroleum and chemical industries should undergo regular maintenance according to the maintenance cycle.
③ If the medium inside the equipment is flammable, explosive, or highly corrosive, maintenance should be performed at least once a year.
④ For plate heat exchangers used in other industries, if no leakage has occurred, it is best to perform maintenance once every three years.
2. Cleaning and Protection of Plates
Keeping the plates clean is one of the important conditions for maintaining a high heat transfer coefficient. The medium moves through narrow and tortuous flow paths between the plates. Even a not very thick layer of scale can cause changes in the flow path, significantly affecting fluid movement, increasing pressure drop, and decreasing heat transfer coefficient. For example, a sugar factory used a plate heat exchanger for heating, and due to poor treatment of secondary water, the flow path was blocked within just two months of use, making it unable to continue operation.
1. Chemical Cleaning Method
This method involves circulating a chemical solution through the heat exchanger to dissolve and discharge the dirt on the surface of the plates. This method does not require disassembly of the heat exchanger, simplifying the cleaning process and reducing the labor intensity of cleaning. Since the corrugation of the plates can promote intense turbulence of the cleaning liquid, which is beneficial for dissolving scale, the chemical cleaning method is considered an ideal method.
2. Mechanical (Physical) Cleaning Method
This method involves manually scrubbing the plates with a brush to remove dirt from the surface of the plates. Although this method is more direct, it is not easy to clean hard and thick scale thoroughly.
3. Comprehensive Cleaning Method
For cases where the scale is hard and thick, it is difficult to clean thoroughly using only one of the above methods. The comprehensive method first uses the chemical cleaning method to soften the scale, and then uses the mechanical (physical) cleaning method to remove the scale, in order to keep the plates clean.
4. Precautions During Cleaning
① During chemical cleaning, the solution should maintain a certain flow rate, generally between 0.8 and 1.2 m/s. The purpose is to increase the turbulence of the solution.
② Different cleaning solutions should be used for different types of dirt. In addition to the commonly used diluted soda solution, a 5% nitric acid solution can be used for water scale. For scale generated during soda production, a 5% hydrochloric acid solution can be used. However, chemical agents that can corrode the plates must not be used.
③ During mechanical (physical) cleaning, it is not allowed to use carbon steel brushes to scrub stainless steel plates to avoid accelerating the corrosion of the plates. At the same time, care should be taken to avoid scratches or deformation on the surface of the plates.
④ After cleaning, the plates should be rinsed thoroughly with clean water and dried, and care should be taken to prevent deformation of the plates during storage.
3. Characteristics of Gaskets and Their Replacement
As the application fields of plate heat exchangers continue to expand, there are different requirements for temperature resistance, pressure resistance, and corrosion resistance for different media and processes. It is obviously impossible to use a "universal" gasket to adapt to all situations; instead, different materials of gaskets should be used for different situations. The commonly used gasket cross-section shape is hexagonal. Common types of gaskets include natural rubber, neoprene rubber, EPDM rubber, silicone rubber, fluorine rubber, and asbestos fiber boards.
If the gaskets of the plate heat exchanger show signs of leakage, breakage, or aging during use, they should be replaced in a timely manner. The replacement should be carried out in the following order.
① Remove the old gaskets. Care should be taken during disassembly to avoid scratches in the gasket groove.
② Use acetone, butanone, or other ketone solvents to remove residual glue from the gasket groove.
③ Wipe the gasket groove and gaskets clean with a clean cloth or cotton yarn.
④ Evenly apply adhesive in the gasket groove.
⑤ Attach the clean new gasket to the plate.
⑥ The plate with the properly attached gasket should be placed in a flat, cool, and ventilated area to dry naturally before it can be installed and used.
