Chemical equipment cleaning technology Chemical equipment cleaning consists of both online and offline cleaning.
Online cleaning The cooling water tower in the circulating water system is used as a dosing tank to fill the system with chemicals for natural circulation.
Advantages: the equipment does not have to stop, does not affect the normal production use.
Disadvantages: the cleaning effect is not very good compared to offline cleaning. The cleaning time is long and the corrosion hazard to the equipment is high.
Offline cleaning Offline cleaning can be divided into physical cleaning and chemical cleaning.
Physical cleaning: the use of high-pressure water to clean the equipment. High pressure cleaning equipment is required.
Chemical cleaning: the heat exchanger is taken out separately and the inlet and outlet pipes of the circulating water are connected to the cleaning vehicle for circulation.
Advantages: reduces the amount of chemicals used, good cleaning effect.
Disadvantages: corresponding equipment is required, such as cleaning vehicles or cleaning water tanks, high-pressure pumps, various sizes of connection valves, welding equipment, etc.
Chemical cleaning has two forms: acid cleaning and alkaline cleaning.
Alkaline washing: mainly to remove organic matter, micro-organisms, oil and other adhesions inside the equipment, such as rust inhibitors when the equipment is installed. Alkali washing can also play the role of loosening, loosening, emulsifying and dispersing inorganic salts. Commonly used cleaning agents are sodium hydroxide, sodium carbonate, trisodium phosphate, etc.
Acid washing: mainly to remove inorganic salts deposited, such as carbonate, sulfate, silica scale, etc.. Commonly used cleaning agents are hydrochloric acid, sulphuric acid, hydrofluoric acid and other organic acids. Citric acid, sulfamic acid and other organic acids.
Cleaning of Heat Exchangers 1.Mechanical cleaning method
Mechanical cleaning method is to rely on the flow of fluid or mechanical action to provide a force greater than the adhesion force of dirt and dirt from the heat exchanger surface off.
Mechanical cleaning methods have two categories.
One type is a powerful cleaning method, such as water jet cleaning, steam jet cleaning, sand blasting cleaning, scrapers or drill bits to remove scale, etc..
Another category is soft mechanical cleaning, such as wire brush cleaning and rubber ball cleaning.
The following are introduced to these types of methods respectively.
Water jet cleaning, is the use of high-pressure water jetting or mechanical impact of the descaling method. When using this method, the water pressure is generally 20~50MPa. now there is also a higher pressure of 50~70Mpa.
Steam jet cleaning, this cleaner in the design and operation and water jet cleaner similar, with this equipment will be steam sprayed into the tube side of the heat exchanger and shell side, by the impact and heat to remove the dirt.
Sandblast cleaning, is the sieved quartz sand (generally particle size in 3 ~ 5mm) with compressed air (300 ~ 350kPa) through the gun to produce a strong linear velocity, washing the tube wall of the heat exchanger, remove the dirt, so that the tube to restore the original heat transfer characteristics.
Scrapers or drills for descaling, this cleaning machinery is only suitable for dirt inside the tubes or cylinders. The scraper or drill is installed at the top of a flexible rotating shaft and is rotated by compressed air or electricity (also by water or steam).
Gum ball cleaning, which is carried out with a blast cleaner. Shot blasting cleaner is composed of a sponge ball and a fluid gun that pushes the ball inside the tube to be cleaned, the ball is shell-shaped, extruded with a sponge body of semi-hard foam polyurethane, elastic.
2.Chemical cleaning method
Chemical cleaning method, is to add in the fluid descaling agent, acid, enzymes, etc. to reduce the combination of dirt and heat exchange surface force, so that the heat exchange surface from the stripped.
The current chemical cleaning methods used are.
Circulation method: use the pump to force the cleaning fluid circulation, cleaning.
Impregnation method: the cleaning solution will be filled with equipment, standing for a certain period of time.
Surge method: the cleaning fluid will be filled with equipment, every certain 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.
Compared with mechanical cleaning the advantages of chemical cleaning are
It is not necessary to dismantle the equipment to clean the place where mechanical cleaning is not possible. Chemical cleaning is uniform and consistent, and tiny gaps can be washed to, and there are no particles left to deposit, and the core of new scale formation can avoid damage to the metal surface.
Reactor cleaning methods There are mainly mechanical cleaning, chemical cleaning and manual into the kettle manual removal of three methods.
1.Mechanical cleaning
High-pressure cleaning devices are used to clean the inner wall of the reactor and the surface of the stirrer with a high-pressure water jet, which breaks up the hard scale and removes it completely.
The principle of high-pressure water jet cleaning is to compress the water to high pressure and then release it through the nozzles installed on the kettle cleaning robot that reaches into the kettle. The pressure energy is transformed into kinetic energy of the water flow, and the cleaning and removal effect is achieved by the impact of this energy on the wall dirt.
2. Chemical cleaning
First of all, we need to know the composition of the dirt sample in the reactor equipment, and it is best to take a sample for analysis. After determining the composition of the dirt, first do a test to select the cleaning agent and determine through the test that it will not cause corrosion to the equipment metal. The cleaning solution is then circulated through the equipment by setting up a temporary circulation device on site to wash away the dirt.
The stirring paddle and the kettle wall are first rinsed with an appropriate amount of water and drained.
Flush the reactor with solvent through the pressurised device stream.
If the cleaning effect is not achieved, add an appropriate amount of solvent to the reactor to warm up and stir the reflux until the cleaning requirement is achieved, then release the solvent.
Finally rinse the inner wall of the reactor with a certain amount of solvent and release it.
3.Manually enter the kettle and remove it manually
The low cost is its biggest advantage, but it requires several hours of ventilation before entering the kettle, and the oxygen concentration in the kettle must be monitored at all times during the cleaning process, which may cause the risk of oxygen deficiency; at the same time, manual scraping and shovelling cannot be completely cleaned, but also causes skid marks on the inner wall of the kettle, which objectively causes further adhesion of residues. Cleaning the kettle by hand can also cause problems with product hygiene. Generally speaking, the time required to clean a kettle is about half a day to one day.
Mechanical cleaning does not corrode the equipment and can be effective for hard scales, but it takes a long time and is labour intensive; chemical cleaning uses less labour, has a short cleaning time and is thorough, but may cause the equipment to be corroded; manual cleaning in the kettle is low cost, but is more dangerous and cannot be cleaned completely. Therefore, chemical cleaning is used in the softer, thinner dirt, mechanical cleaning is used in the hard, thick dirt conditions.
Cleaning of equipment pipelines Cleaning chemical production equipment usually uses chemical cleaning or physical cleaning methods.
1.Chemical cleaning process
According to the type of dirt in the pipeline and the purpose of cleaning can use different cleaning processes. Here we introduce the chemical cleaning process according to different cleaning purposes.
2.Physical cleaning process
Through physical or mechanical methods to the surface of the pipeline dirt to give a certain impact to make it peel off. The methods used are high-pressure water jet cleaning, PIG cleaning, sandblasting cleaning, rotating mechanical cleaning, attraction cleaning and ultrasonic cleaning, etc., where only the specific cleaning equipment to do some introduction.
(1) High pressure water jet cleaning
With a small diameter nozzle to high-pressure water continuous spray, by the impact of the jet can remove the dirt and blockage in the pipe. The shoulder pressure water jet cleaning device is mainly composed of a high-pressure pump power unit, pressure regulating device, high-pressure pipe, various spray guns and nozzles, which can be mounted on an engineering vehicle for easy on-site construction.
Depending on the hardness, adhesion, oiliness and other morphological characteristics of the pipe wall, different pressures and different types of lances or nozzles are used. For oily, adhesive adhesion scale generally choose 20 ~ 30MPa pressure, hard scale choose 30 a 70MPai to special hard scale or nearly blocked pipeline can be used 150MPa or higher pressure.
According to the different cleaning objects can be used rigid spray rod or flexible spray rod, the former is suitable for cleaning straight pipe, the latter is suitable for curved pipe. The nozzle is attached to the head of the spray bar. Nozzle has a multi-hole fixed type and rotary type, by changing the size of the nozzle hole, shape, number, spray angle, direction can change and improve the cleaning capacity.
The bent shape of the heat exchanger heat transfer tube, generally rely on manual use of flexible spray rod, one after the other ten to work, in recent years, also use mechanized spray rod operating system.
(2) mechanical cleaning
Is the use of electric motors or compressed air, high-pressure water driven to make the front end of the drill bit rotation to remove hard or soft dirt inside the tube method. The low pressure water sprayed near the drill bit plays a role in cooling the bit and removing dirt. For dirt that should not be cleaned with water or acid, pressurised air can be used to remove it, while combustible dirt cannot be removed with pressurised air or nitrogen.
To clean hard dirt, use a drill made of super-hard metal, but be careful to choose a drill bit that is suitable for the internal diameter of the pipe so as not to cause damage to the inner wall of the pipe. To increase the efficiency of cleaning, the drill has different shapes of cutting edges and the operating time can be 10,000r/mln or more.
When cleaning soft dirt, the outer diameter of the drill pipe should be relatively thin to ensure that there is sufficient drainage space. The rotation of the drill bit in mechanical cleaning is transmitted by a flexible shaft, the centre of which is a high-pressure tube. A completely blocked U-shaped heat exchanger can be cleaned by this method. The pipe can also be cleaned with a spike wire brush instead of a drill, while water is used to drain off the dislodged dirt.
(3) PIG cleaning
This is a method of cleaning pipes with a projectile made of plastic. The projectile with water pressure through the gradual shrinkage tube (launch device) pressed into the cleaned pipe, the use of the projectile and the friction of the pipe wall to remove the inner wall of the dirt. Then use the wall of the tube and the projectile contact surface of the leakage back pressure water to remove the dirt forward, and from the other side of the installation of the retractable tube (receiving device) discharge. Afterwards, the tube is pressurised and the pellets are pressed back into the tube and the tube is cleaned. The pellets are repeatedly moved back and forth in the cleaning tube to clean the dirt; the pellets currently used are elastic and compressible high foaming polyurethane materials made of shells or spherical bodies. In its surface can be embedded with abrasives, wire brushes and iron nails.
(4) Suction cleaning
This is the use of vacuum pump direct attraction cleaning method, it is suitable for cleaning due to the liquid in suspension in the flow rate changes and vortex occurs in the part of the accumulation of sludge caused by the blockage of the pipe, only suitable for easier to remove the dirt. The attraction system should be set up in the filter, while making good drainage treatment.
(5) Ultrasonic cleaning
Suitable for small precision machinery pipeline, such as sintered metal pipe or microporous filter cleaning. The use of water as the media to clean the pipeline for ultrasonic oscillation processing, ultrasound generated by the cavity and vibration impact can remove dirt.
(6) electrochemical cleaning
For medicine, food, ultra-pure water devices in the pipeline can be used for electrochemical cleaning. The metal pipe - immersed in phosphoric acid or sulfuric acid electrolyte, and with the positive or negative DC power supply is connected (so that the metal pipeline becomes the anode or cathode of the electrolytic tank), relying on the oxygen or hydrogen produced on the cleaning surface to remove the attached dirt, this method is only used in special circumstances.
(7) sandblasting cleaning
Is the use of quartz sand, steel shot and other abrasives by compressed air for high-speed spraying, to remove the inner wall of the pipeline rust scale, grease and other dirt methods, it is a small diameter of the shorter pipeline cleaning has a high efficiency, while the large diameter pipeline for sandblasting cleaning requires a lot of compressed air, on-site construction is difficult to achieve, the long distance pipeline due to pressure loss is too large for this method.
Source: Reproduced
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