Mechanical cleaning is to rely on the flow of fluid or mechanical action to provide a greater than the dirt adhesion force and make the dirt from the heat transfer surface off. Advantages of the method: chemical cleaning can be eliminated the cost of chemicals; can remove the chemical method can not remove the carbonized dirt and hard dirt; to avoid the chemical cleaning after cleaning waste liquid emissions and disposal problems; steel loss is small; not easy to cause corrosion of the equipment being cleaned. The disadvantages are: the equipment must be disassembled; cleaning time is long, high cost; some cleaning methods need to interrupt the operation of the system can be carried out.
Mechanical cleaning methods can be divided into two categories: one is a strong cleaning method, such as water jet cleaning, spray vapor cleaning, sandblasting cleaning, high-pressure water jet cleaning, strong cleaning tube. Another category is soft mechanical cleaning, such as scraper, drill or wire brush descaling and sponge rubber ball cleaning. For different dirt should be used in different mechanical cleaning methods, mechanical cleaning is commonly used in industry descaling methods, it can remove carbonized dirt and hard dirt. But the use of mechanical cleaning, often have to dismantle the heat transfer equipment, thus longer time, higher costs.
2. Chemical cleaning technology
Chemical cleaning is added to the fluid descaling agents, acids, enzymes, etc. to reduce the dirt and heat transfer surface of the bonding force, so that it peeled off from the heat transfer surface.
(1) the characteristics of chemical cleaning:
Chemical cleaning can often not have to disassemble the equipment, which is particularly important for the tower and shell and tube equipment.
① chemical cleaning can clean the mechanical cleaning places.
② chemical cleaning uniform, tiny gaps can be washed, and will not be left to deposit particles, the formation of new dirt core.
③ chemical cleaning can avoid damage to the metal surface, such as the formation of sharp corners, and this sharp corners can contribute to corrosion, and the formation of dirt in its vicinity.
④ Rust can be prevented after cleaning due to antirust and passivation treatment.
⑤ The amount of steel corrosion from chemical cleaning is almost negligible. Even if the steel corrosion rate during pickling is taken as 1 mg per square meter, the wall thickness it damages is only below 10 um, and the general situation is lower than that corrosion rate.
(6) chemical cleaning can be completed at the scene, the labor intensity is less than mechanical cleaning.
(2) currently used chemical cleaning methods are categorized as follows:
According to the cleaning method: ① Circulation method: the pump to force the cleaning fluid circulation, cleaning. ② impregnation method: the cleaning solution will be filled with equipment, static for a certain period of time. ③ surge method: the cleaning fluid filled with equipment, every certain period of time to unload a part of the cleaning fluid from the bottom, and then unload the liquid back into the equipment to achieve the purpose of stirring cleaning. ④ Spraying method: It is suitable for cleaning the inner and outer walls of large containers. ⑤ bubble touch method.
According to the cleaning agent used: alkali cleaning, acid cleaning, complex and agent cleaning, polyelectrolyte cleaning, surface-active cleaning, pesticide cleaning and organic solvent cleaning.
According to the cleaning object: single equipment cleaning and system-wide cleaning.
According to the cleaning of production equipment is divided into whether the parking: parking cleaning and non-stop cleaning. Different dirt should be used with different chemical cleaning agents, in the use of chemical cleaning agents should also pay attention to the compatibility of cleaning agents and equipment structure materials. Chemical cleaning should be done before the following preparatory work: understand and check the type of equipment to be cleaned, type, geometry and size; grasp the material of the equipment and should be cleaned to the place; according to the actual situation to determine the type of detergent, cleaning fluid concentration and dosage; proper arrangements for cleaning with the water source, heating cleaning fluid with the source of heat and sewage treatment and discharge; arrangements for cleaning location; dirt check, in representative Structure of the location of the samples taken for analysis and dissolution test will be dirt with a variety of agents to deal with, solubility to determine the varieties of agents, dosage and cleaning time.
(3) commonly used cycle cleaning method of this program
① alkaline washing: phosphate plus a small amount of surfactant prepared aqueous solution cleaning, can remove oil, silicates and loose scale.
② water rinse: wash off the last step of the lye, so that the pH is reduced to 8 ~ 10.
③ acid washing: hydrochloric acid, nitric acid or other acids, plus corrosion inhibitors of the aqueous solution of the cycle cleaning system, so that the surface of the equipment dirt completely removed.
④ Water rinse: wash off the last step of the residual acid, so that the pH rises to 4 ~ 5.
⑤ Neutralization: with 0.1% sodium hydroxide and 0.05% trisodium phosphate, to completely neutralize the residual acid in the equipment, and to promote the formation of a stable protective film on the surface of the equipment.
⑥ passivation: the use of passivation agent to make the surface of the equipment after pickling passivation, not easy to corrode. Commonly used passivation agents are sodium nitrite, trisodium phosphate and so on.
3. Comparison of chemical cleaning and physical cleaning
Chemical cleaning and physical cleaning of the same material to be washed with the same loss of small advantages, but for the complex structure and high surface treatment requirements of the equipment, chemical cleaning is far superior to the physical cleaning; similarly, when removing carbonized scale or dense hard scale, physical cleaning is better than chemical cleaning; physical cleaning is no chemical cleaning of waste acid pollution problems. Cleaning waste acid pollution problems. In chemical production equipment is often complex structure, so often use chemical cleaning.