Chemical equipment cleaning technology
In the chemical production process, due to various reasons, such as: polymer, coking, oil grime, scale, sediment, corrosion products and other grime. These seriously affect the use of equipment, so it is very important to carry out chemical equipment cleaning.
Today we have prepared a full dry goods for everyone, wonderful to see:
What are the chemical equipment cleaning technologies?
Why clean chemical equipment?
What are the cleaning processes for chemical equipment?
How to clean heat exchangers, reactors and equipment pipelines?
Chemical equipment cleaning technology
Chemical equipment cleaning includes both online cleaning and offline cleaning.
Use the cool water tower in the circulating water system as a dosing tank to add medicine to the system for natural circulation.
Advantages: The equipment does not need to be shut down, and does not affect normal production and use.
Disadvantages: The cleaning effect is not very good compared to offline cleaning. The cleaning time is long, and the corrosion damage to the equipment is large.
Refers to the process of cleaning the parts to be cleaned after being removed from the equipment or piping and transported to another location (relative to the location of the original parts)
Off-line cleaning can be divided into physical cleaning and chemical cleaning.
Physical cleaning: Clean the equipment with high pressure running water. High pressure cleaning equipment is required.
Chemical cleaning: Take the heat exchanger separately and connect the inlet and outlet pipes of the circulating water to the cleaning car for circulation. Chemical cleaning has the following characteristics:
Advantages: The dosage of the medicament is reduced, and the cleaning effect is good.
Disadvantages: Requires corresponding equipment, such as cleaning car or washing water tank, high pressure pump, connecting valves of various specifications, electric welding equipment, etc.
Chemical cleaning is available in both pickling and alkaline washing.
Alkaline washing: mainly to remove organic matter, microorganisms, oil and other attachments inside the equipment, such as rust inhibitors when the equipment is installed. Alkaline washing can also act to loosen, loosen, emulsify and disperse inorganic salts. Commonly used cleaning agents are sodium hydroxide, sodium carbonate, trisodium phosphate, and the like.
Pickling: mainly to remove the deposition of inorganic salts, such as carbonates, sulfates, silica scales, etc. Commonly used cleaning agents are organic acids such as hydrochloric acid, sulfuric acid and hydrofluoric acid. Organic acids such as citric acid and sulfamic acid.
Why clean chemical equipment?
1. The necessity of cleaning before driving
Chemical cleaning before driving is necessary to improve production efficiency and avoid the impact of dirt on production. Therefore, the new chemical equipment must be cleaned before driving.
A variety of chemical raw materials are involved in the chemical production process and catalysts are used. The purity of certain raw materials and catalysts is extremely high, so there is a high requirement for the cleanliness of the equipment and pipelines in the production process. Any impurity intervention will lead to catalyst poisoning, side reactions, and damage to the entire process. In addition, some of the equipment and accessories in the device are highly sensitive or sensitive to the damage of impurities, so the intervention of any mechanical impurities is very likely to damage the quality of precision components and affect normal production.
2. The necessity of cleaning after starting work
In the case of long-term use of chemical equipment, such as: polymer, coking, oil grime, scale, sediment, corrosion products and other grime, which seriously affect the use of chemical equipment, timely cleaning of chemical equipment, can be extended Reduce equipment life, improve efficiency, ensure safety, and reduce economic loss.
Therefore, whether it is before or after driving, the equipment should be cleaned, which is essential daily maintenance work.
What are the cleaning processes for chemical equipment?
Preparation before cleaning equipment
Before cleaning, the parts of the equipment to be cleaned or damaged by the cleaning liquid, such as regulating valves and flow meters, should be removed, and the filter core (net) and the valve core of the check valve should be removed. And use temporary temporary pipe, bypass or blind plate to ensure that no leakage occurs during the cleaning process, no damage to other components, and the cleaning equipment is separated from the non-cleaning equipment and pipeline.
Cleaning procedures and process conditions
1, cleaning method
According to the specific conditions of the equipment, you can use the soaking cycle cleaning or spray cleaning.
When using the soaking cycle cleaning, the low-point liquid inlet and the ammonia return liquid circulation process can be adopted.
When using spray cleaning, high-point liquid inlet and low-point reflux flow can be used.
2, cleaning procedures and the use of pharmacy
The degree of cleaning is generally system water pressure leak detection (water rinse), a skim water rinse, a pickling, a rinse, a rinse, a passivation, a passivation, and a manual treatment.
Each step will be described below.
The purpose of water pressure leak detection (water flushing) is to check the leakage of the temporary system, and at the same time remove dust, sand, falling metal oxides, welding slag and other loose and easy dirt.
The purpose of degreasing cleaning is to remove oil such as mechanical oil, graphite grease, oil coating and fat rust oil in the system to ensure uniform pickling.
The purpose of water washing after degreasing is to remove the alkaline cleaning agent remaining in the system and to remove some of the remaining impurities from the surface. Removed from the object.
The purpose of pickling is to remove the acid by reacting it with a metal oxide to form a soluble substance.
The purpose of water washing after pickling is to remove residual pickling liquid and solid particles falling off in the system for rinsing and passivation treatment.
The purpose of rinsing is to use ammonium citrate and the residual iron ion in the system to remove the floating rust formed during the water rinsing process, so as to reduce the total iron ion concentration of the system to ensure the subsequent passivation effect.
The purpose of the neutralization passivation process is to remove residual acid solution, which is to prevent secondary oxidation of the metal surface in the activated state after pickling.
Cleaning after start-up
Chemical equipment that has been in motion for more than 1 to 2 years often has iron oxide scales or steel-containing scales. Copper scale contains copper oxide (CuO), basic copper carbonate [Cu2(OH)2CO3] and metallic copper. .
Iron scale can generally be removed by pickling. The method and steps of pickling are substantially the same as those of the cleaning device before starting.
When the content of copper in the soil is large, it can be removed only by pickling, and the component of copper is removed by ammonia water, followed by pickling.
Copper and copper oxide scales often form layered deposits with iron oxides, which is troublesome to clean and should be cleaned prior to formation of the layers.
How to clean the heat exchanger?
The cleaning of heat exchangers is generally divided into mechanical cleaning and chemical cleaning.
The mechanical cleaning method relies on the flow or mechanical action of the fluid to provide a force greater than the adhesion of the dirt to cause the dirt to fall off the heat exchange surface.
There are two types of mechanical cleaning methods: one is strong cleaning method, such as water spray cleaning, steam cleaning, sand blast cleaning, scraper or drill bit descaling; the other is soft mechanical cleaning, such as wire brush cleaning and rubber balls. Cleaning, etc. The following describes each of these methods:
Water spray cleaning is a descaling method using high pressure water jet or mechanical shock. When this method is used, the water pressure is generally 20 to 50 MPa. There is also a higher pressure of 50~70Mpa.
Steam cleaning, which is similar in design and operation to a water spray cleaner. This equipment is used to inject steam into the tube side and shell side of the heat exchanger to remove dirt by impact and heat.
Sandblasting cleaning is to sift the quartz sand (generally 3~5mm) with compressed air (300~350kPa) through the spray gun to generate a strong line speed, flush the inner wall of the heat exchanger, remove the dirt, and make the pipe Restore the original heat transfer characteristics.
The scraper or bit is descaled. This cleaning machine is only suitable for dirt inside pipes or cylinders. A descaling scraper or drill bit is mounted on the top end of the flexible rotating shaft to rotate the scraper or drill bit by compressed air or electricity (also using hydraulic or steam).
The rubber ball cleaning is carried out using a shot blasting washer. The shot blasting washer is composed of a sponge ball and a fluid spray gun that pushes the ball into the inside of the pipe to be cleaned. The ball is in the shape of a bullet, which is extruded by a semi-rigid foamed polyurethane sponge and is elastic.
The chemical cleaning method is to add a descaling agent, an acid, an enzyme, etc. to the fluid to reduce the bonding force between the dirt and the heat exchange surface, and to peel off from the heat exchange surface. The current chemical cleaning methods are:
Circulation method: The pump is forced to circulate and wash.
Dipping method: Fill the device with the cleaning solution and let it stand for a certain period of time.
Surge method: fill the cleaning liquid with equipment, remove the cleaning liquid from the bottom at regular intervals, and then put the discharged liquid back into the equipment to achieve the purpose of stirring and cleaning.
How to clean the reactor?
The cleaning of the reactor mainly includes three methods: mechanical cleaning, chemical cleaning and manual cleaning.
Mechanical cleaning: a high-pressure cleaning device is used, and a high-pressure water flow is used to wash through the nozzle, and the hard dirt on the inner wall of the reaction vessel and the surface of the agitator is crushed, completely peeled off and removed.
The principle of high pressure water jet cleaning is to compress the water to a high pressure and then release it through a nozzle mounted on the cleaning robot that extends into the kettle. The pressure energy is converted into the kinetic energy of the water flow, and the energy is applied to the wall surface to achieve the effect of cleaning and cleaning.
First of all, it is necessary to know the scale components in the reactor equipment, preferably by sampling analysis. After determining the dirt composition, the test is first carried out, and the cleaning agent is selected and the test is carried out to determine that the metal of the device does not cause corrosion. Then, the cleaning liquid is circulated in the equipment by erecting a temporary circulation device on the spot to wash away the dirt.
Rinse the paddle and the inner wall of the kettle with an appropriate amount of water and let it go.
The solvent was flushed through the press through a pressurizing device.
If the cleaning effect is not achieved, an appropriate amount of solvent is added to the reaction vessel, and the mixture is stirred and refluxed until the cleaning requirement is reached, and then the solvent is discharged.
Finally, the inner wall of the reactor was rinsed with a certain amount of solvent and discharged.
Manual cleaning by hand
The low cost is its greatest advantage, but it takes several hours of ventilation before entering the kettle. During the cleaning process, the oxygen concentration in the kettle must be monitored at any time, and there is a danger of oxygen deficiency. At the same time, the artificial spatula can not be completely cleaned. It will cause slippage on the inner wall of the reactor, which objectively causes further adhesion of the residue. The cleaning of people into the kettle will also cause problems in product hygiene. In general, the time required to clean a kettle is about half a day to one day.
Each of the three methods has its pros and cons:
Mechanical cleaning will not cause corrosion to the equipment, and it can be effectively cleaned for hard scale, but it takes a long time and is labor intensive;
Chemical cleaning has less labor, short cleaning time and thorough cleaning, but it may cause corrosion of equipment;
The manual cleaning of manual steaming is low in cost, but it is dangerous and cannot be completely cleaned up.
Therefore, chemical cleaning is applied to soft and thin working conditions, and mechanical cleaning is applied to hard and thick working conditions.
How to clean the equipment pipeline?
Cleaning chemical production equipment usually uses chemical cleaning or physical cleaning methods.
Different cleaning processes can be used depending on the type of dirt in the pipeline and the purpose of cleaning. Here we introduce the chemical cleaning process used for different cleaning purposes.
The following figure shows the chemical cleaning process used for different cleaning purposes.
Physical or mechanical methods are applied to the dirt on the surface of the pipeline to give a certain impact force to peel off. The methods used include high pressure water jet cleaning, PIG cleaning, sand blast cleaning, rotary mechanical cleaning, suction cleaning and ultrasonic cleaning.
1, high pressure water jet cleaning
The small-caliber nozzle is continuously sprayed with high-pressure water, and the impact of the jet can remove dirt and blockages in the pipeline. The shoulder pressure water jet cleaning device is mainly composed of a high pressure pump power device, a pressure regulating device, a high pressure pipe, various spray guns and nozzles, and can be installed on the engineering vehicle to facilitate on-site construction.
According to the hardness, adhesiveness and oiliness of the inner wall of the pipeline, different pressures and different types of spray guns or nozzles are used. For oily, adhesive scales are generally selected from 20 to 30 MPa pressure, and hard scales are selected from 30 to 70 MPai for special hard scale or nearly blocked pipes. Pressures of 150 MPa or higher can be used.
A rigid spray bar or a flexible spray bar can be used depending on the cleaning object. The former is suitable for cleaning straight pipes, and the latter is suitable for curved pipes. A nozzle is attached to the head of the boom. The nozzle has a porous fixed type and a rotary type (see the related figure in Chapter 10). The cleaning ability can be changed and improved by changing the size, shape, number, spray angle and direction of the nozzle hole.
For the heat exchanger tubes of the curved shape of the heat exchanger, the flexible spray bar is generally used manually, and the work is performed one by one. In recent years, the mechanized boom operating system has also been adopted.
2, mechanical cleaning
It is a method of driving a drill bit at the front end to remove hard or soft dirt in the pipe by using a motor or compressed air or high-pressure water. The low-pressure water sprayed near the drill bit serves to cool the drill bit and remove dirt. For dirt that is not suitable for washing with water or acid, it can be removed by pressurized air. The flammable dirt cannot be removed by nitrogen with pressurized air.
To clean hard dirt, use a drill bit made of super-hard metal, but care should be taken to select a drill bit that is suitable for the inner diameter of the pipe to avoid damage to the inner wall of the pipe. In order to improve the efficiency of cleaning, the cutting edge of the drill has different shapes, and the operation time can reach more than 10000r/mln.
When cleaning soft dirt, the outer diameter of the drill pipe should be relatively thin to ensure sufficient drainage space. In the mechanical cleaning, the rotation of the drill bit is transmitted by the flexible shaft. The center of the shaft is a high-pressure pipe. In this way, the completely blocked U-shaped heat exchanger can be cleaned. It is also possible to use a spike-shaped wire brush instead of a drill bit to clean the pipe, and at the same time drain the removed dirt with water.
3, PIG cleaning
It is a method of cleaning a pipe with a projectile made of plastic. The projectile is pressed into the tube by pressing the water through the reducer (emission device), and the dirt on the inner wall is removed by the friction between the projectile and the tube wall. The removed dirt is transported forward by the leaking back pressure water on the contact surface of the pipe wall and the projectile, and is discharged from the reducer (receiving device) mounted on the other side. Thereafter, the reducer (receiving device) is pressurized, and the projectile is pressed back into the tube and the pipe is cleaned. The projectile is repeatedly moved back and forth in the cleaning tube to clean the dirt; the projectile currently used is a bullet-shaped or spheroid body made of a highly compressible and highly foamable polyurethane material. Abrasives, wire brushes and nails can be embedded on the surface.
4, attract cleaning
This is a cleaning method that is directly attracted by a vacuum pump. It is suitable for cleaning the pipeline blockage caused by the suspension of the liquid in the flow rate fluctuation and the accumulation of the eddy current, and is only suitable for the dirt which is easy to remove. Filters should be installed in the suction system and drained at the same time.
5, ultrasonic cleaning
Suitable for small precision machinery pipes, such as sintered metal pipes or microporous filters. The water is used as a medium to ultrasonically oscillate the cleaning pipeline, and the holes and vibration shock generated by the ultrasonic wave can remove the dirt.
6, electrochemical cleaning
Electrochemical cleaning can be used for pipelines in medical, food, and ultrapure water devices. Immerse the metal tube in an electrolyte of phosphoric acid or sulfuric acid and connect it to the positive or negative electrode of the DC power supply (so that the metal line becomes the anode or cathode of the electrolytic cell), and remove it by the action of oxygen or hydrogen generated on the cleaning surface. Adhesive dirt, this method is only used in special cases.
7, sandblasting cleaning
It is a method of using high-speed injection of quartz sand, steel shot and the like by means of compressed air for high-speed spraying to remove dirt, grease and the like on the inner wall of the pipeline. It has high efficiency for cleaning small-diameter pipelines, and sandblasting large-diameter pipelines. Cleaning requires a large amount of compressed air, which is difficult to achieve on site. It is not suitable for long-distance pipelines due to pressure loss.