In the drug industry process of using the gasket plate heat exchanger
, the calcium, magnesium and carbonate in the water will be decomposed into calcium carbonate and calcium hydroxide precipitates on the heating surface of the heat exchanger, forming a hard scale. Due to the poor thermal conductivity of scale, the heat exchange efficiency of heat exchanger is reduced and the heat energy is wasted seriously.
Here are some ethods for cleaning fouling on gasket plate heat exchanger
1.Mechanical cleaning is the simplest cleaning method, but the disadvantages are:
A.There are scratches on the plate, and it is easier to hang scale after brushing.
B.Workers work in cold water with poor working conditions.
C. When cleaning, the heat exchanger must be dismantled, which is easy to damage the plate and gasket and result in high labor intensity.
2. Chemical cleaning: It is found through experiments that formic acid and oxalic acid are better cleaning solutions without corroding the heat exchanger plates.
A.Formic acid cleaning. Adding buffer and surfactant in formic acid cleaning solution can improve the cleaning effect and reduce the corrosion of cleaning solution to plate.
The technological requirements for cleaning scale
1.Pickling temperature: raising pickling temperature is beneficial to improve the scale removal effect. If the temperature is too high, it will aggravate the corrosion of pickling solution to heat exchanger plate. It is advisable to keep pickling temperature at 60 ℃.
2.Concentration of pickling solution: According to the test, the pickling solution should be prepared according to the concentration of formic acid 81.0%, water 17.0%, buffer 1.2%, surfactant 0.8%, and the cleaning effect is excellent.
3.Pickling method and time: pickling time is static soaking for 2 hours, then dynamic cycling for 3-4 hours.
4.Passivation treatment: After pickling, most of the scale and metal oxide on the surface of plate heat exchanger are dissolved and peeled off, which exposes brand- new metals and is very easy to corrode. Therefore, after pickling, the plate of heat exchanger should be passivated.
Specific steps for cleaning scale
1.Flushing: before pickling, the heat exchanger should be flushed open-style, so that there is no mud, dirt and other impurities in the heat exchanger.
2.Pour the cleaning fluid into the cleaning facility and then inject it into the heat exchanger.
3.Pickling: the heat exchanger filled with acid solution is immersed in static state for 2 hours, and then continuously circulated for 3-4 hours, during which positive and negative alternating cleaning is carried out every 0.15 hours. After pickling, if the pH value of acid is greater than 2, the acid can be reused. Otherwise, the acid should be diluted and neutralized and discharged.
4.Alkali washing: After pickling, the heat exchanger is alkali washed with trisodium phosphate and softened water in a certain proportion. The heat exchanger is neutralized by acid and alkali by means of dynamic circulation, so that the plate of the heat exchanger is no longer corroded.
5.Washing: After alkali washing, rinse the heat exchanger repeatedly with clean softened water for 0.15h, and rinse the residue in the heat exchanger thoroughly.
Oxalic acid cleaning
Oxalic acid can react with scale and has no corrosion to plate. Cleaning process：
1.Without dismantling the heat exchanger, water injection valves are installed in the inlet and outlet valves of the secondary network of the heat exchanger, and 3%-5% oxalic acid solution in the water tank is injected into the heat exchanger. The oxalic acid solution is forced to circulate between the heat exchanger and the water tank by a circulating pump to achieve the purpose of cleaning.
2.Clean twice, three or four hours each time. After dismantling the heat exchanger, the plate is as clean as new and the test is successful.
3.Wash with 2% trisodium phosphate and rinse with clean water twice.
Oxalic acid should be used to clean the plates. The following operating procedures must be followed：
I.The water temperature must be < 16 C.
II.Oxalic acid concentration < 5%, soaking time should not exceed 6 hours;
III.Solution tank must be protected from light;
IV.After washing with oxalic acid, it must be washed with 2% trisodium phosphate and rinsed twice with clean water.
V.The valves for inlet and outlet must be strict, and the solution must not enter the system.
VI.Cleaning fluid must not be put into pump pit, but into sewage.