Parking
When stopping for maintenance, the fluid valves on both sides of the heat exchanger should be closed slowly first, so that the pressure on both sides will drop slowly at the same time, and the tension nut will be loosened after emptying the residual liquid. When disassembling the tie rod, the temperature must be reduced to room temperature and try to empty the residual liquid before proceeding.
Plate cleaning
Clean and oxide-free plate surface is necessary to ensure tightness. Plate heat exchanger thermal efficiency significantly lower, the pressure drop of significant changes in serious fouling, should be disassembled, put flat brush. Steam bubble tank with chemical cleaning method is an effective way to obtain high quality surface quality. Cleaning, the first plate on the temperature of 57-60oC (if the temperature of 70-80oC better) in the lye tank soak 48h, the use of lye in the high temperature so that the sealant pasted on the plate and scaling softened. Then, the plate sheet is soaked in the acid tank for 2h, so that the scale reacts fully with the acid. After the end of the soaking of the plate sheet, clean the brush with a soft brush on the platform, and prohibit the use of steel brushes.
When cleaning the sealing groove, use a screwdriver to cock the gasket, gently remove it (or gently bake it on the backside with fire, but avoid discolouration of the metal), and then tear it off. Use acetone methyl liquid or other ketone organic solvents to clean the sealing groove.
After cleaning and brushing the plate first rinse with water, and then dry with a clean cloth, the plate surface is not allowed to leave foreign particles and fibres and such things. The chlorine ion content of the cleaning water is ≤25pp.
After checking and determining the workload has been cleaned, the plates are carefully inspected. There are three methods of inspection.
1, colouring method: checking with a colouring agent.
2, translucent method: one side of the plate piece put a light source, people on the other side of the check.
3, unilateral pressure test method: unilateral test pressure through the water to 0. 35MPa (gauge pressure), if the other side of the lowest place of water, quickly check the wet place of the plate. We choose to check the transmittance method, the advantages of this method is convenient, low cost, new and old plate sheet inspection are applicable. However, it requires a high degree of responsibility on the part of the inspection personnel.
According to the plate sheet inspection, to determine the workload, there are three main types.
1, plate sheet and gasket all replacement.
2, only the replacement of the gasket.
3, the replacement of gaskets and part of the damage, deformation of serious plate.
Gasket paste
With adhesive or strong adhesive, uniformly in the bottom of the sealing groove coated layer, and then the gasket will be placed in the sealing groove, fit evenly, pressurised, natural drying, or heating to 100 ℃ -120 ℃ two hours after drying. Check whether it fits evenly sheet by sheet, and remove the excess adhesive.
Assembly
Plate heat exchanger process combination is characterised by:If the fluid comes in from the left corner hole of the plate, it always comes out from the left corner hole of the plate, and vice versa. Assembly, to correctly distinguish between A plate, B plate, that is: to the plate sheet adhesive pads for the front side, according to the direction of the guide groove distinction, the guide groove for a certain direction of the plate as A plate, the guide groove for the other direction of the plate that is the B plate, but in the plate and do not hit the mark.
Hydraulic test
According to take over the flange size to do four blind plate, welded to the import and export, welded pipe on the plate to make the compressor and heat exchanger connected. In the import and export at the installation of a certified, and in the validity of the pressure gauge, the pressure gauge range to double the test pressure is appropriate. Test pressure is 1.5 times the working pressure.
1, strictly in accordance with the above requirements for overhaul, the quality fully meets the design requirements, load test 72 hours without leakage. Heat exchange liquid temperature measurement results: alumina mother liquor import 45.2oC, export 84.6oC; alumina concentrate import 97.0oC, export 78oC, to meet the normal operating requirements.
2, cost savings. Due to the plate material for ultra-thin Crl7Nil3Mo2Ti stainless steel, the gasket is also special, all replace the new plate cost is very high. Through cleaning and inspection, reuse, single plate heat exchanger can save costs 25-45 million yuan.
