In addition to the maintenance under special circumstances, the interchangeable plate heat exchanger shall be maintained regularly. As the plate heat exchanger is easy to disassemble and repair, it generally does not need special tools and equipment. According to different conditions, different methods can be adopted. If the equipment does not leak and the heat transfer system K drops, the heat exchanger can not be disassembled, but a closed-circuit system can be used to inject the descaling liquid into the equipment for several hours. If there is no such condition on site, and the equipment is disassembled or the scale is found to be not too serious, the plate can be washed directly with water without taking off the plate, and the soft brush can be used at the same time.
I. normal operation and maintenance
1. For the equipment to be repaired, the heat exchanger shall be disassembled reversely according to the installation sequence.
2. The equipment applied in the petroleum and chemical industry shall be maintained regularly according to the maintenance cycle.
3. If the medium in the equipment is inflammable, explosive or corrosive, it shall be maintained at least once a year.
4. If the plate heat exchanger used in other industries does not leak, it is better to repair it once every three years.
II. Cleaning and protection of plates
Keeping the plate clean is one of the important conditions to keep high heat transfer coefficient. In the plate, the medium moves along the narrow and zigzag channel, even if there is not too thick scale layer, it will also cause the change of channel, significantly affect the movement of fluid, increase the pressure drop, and reduce the heat transfer coefficient. For example, a sugar factory uses plate heat exchanger in heating, the secondary water is not well treated, and the flow channel is blocked only two months in the use process, so it can not continue to operate.
1 chemical cleaning method
This method is to circulate a chemical solution through the heat exchanger to dissolve and discharge the dirt on the surface of the plate. This method does not need to dismantle the heat exchanger, simplifies the cleaning process and reduces the labor level of cleaning. Because the plate ripple can promote the violent turbulence of the cleaning liquid and facilitate the dissolution of the scale layer, the chemical cleaning method is an ideal method
2. Mechanical (physical) cleaning method
This method is to wash the plate manually with a brush, so as to remove the dirt on the surface of the plate. Although this method is direct, it is not easy to clean the hard and thick scale layer.
3. Comprehensive cleaning method
For the case that the dirt layer is hard and thick, it is difficult to clean it simply by using one of the above methods. The comprehensive method is to soften the scale layer with chemical cleaning method and then remove the scale layer with mechanical (physical) cleaning method to keep the plate clean.
4 precautions for cleaning
① during chemical cleaning, the solution should maintain a certain flow rate, generally 0.8-1.2m/s. Its purpose is to increase the turbulence level of the solution.
② different chemical cleaning solutions should be used for different dirt. In addition to the often used dilute soda solution, 5% nitric acid solution can be used for scaling. 5% hydrochloric acid solution can be used for the scale formed in the production of soda ash. But do not use chemical lotion that will cause corrosion to the plate.
③ during mechanical (physical) cleaning, it is not allowed to brush the stainless steel sheet with carbon steel brush to avoid accelerating the corrosion of the sheet. At the same time, the surface of the plate shall not be scratched or deformed.
④ clean and dry the cleaned plates with clear water, and prevent the plates from deforming when placed.
III. characteristics and replacement of gasket
Due to the expanding application of plate heat exchanger, there are different requirements of temperature resistance, pressure resistance and corrosion resistance for different media and processes. It is obviously impossible to use one "universal" gasket to adapt to all situations, but different materials should be used for different situations. The commonly used shape of gasket section is hexagonal row. The commonly used gasket types are natural rubber, neoprene, EPDM, silicone rubber, fluororubber, asbestos fiberboard, etc.
If the gasket of plate heat exchanger leaks, breaks or ages during use, it shall be replaced in time. The replacement shall be carried out in the following order.
① remove the waste gasket. Take care not to scratch the gasket groove during disassembly.
② use acetone, butanone or other ketone solvents to remove the residual glue in the gasket groove.
③ wipe the gasket groove and gasket with clean cloth or cotton yarn.
④ evenly apply the adhesive to the gasket groove.
⑤ stick the clean new gasket on the plate.
⑥ the plate with gasket shall be placed in a flat, cool and ventilated place for natural dry fixation before installation and use.