Scaling and treatment of heat exchanger cleaning

2019/5/13 3:50:27

Both surface water and groundwater contain minerals, mainly calcium and magnesium carbonate, sulfate, silicate and iron oxide. Most of the circulating cooling water used in heat exchangers in chemical production is treated, and most of the salts have been treated. However, the solubility of some salts decreases with the increase of temperature, and some salts decompose into compounds with lower solubility with the increase of temperature. The circulating water will be continuously evaporated and concentrated as it is used, and the concentration of the unprocessed samples will gradually increase, and crystallization will occur after the saturated concentration is exceeded. In the process of water treatment, due to other reasons, the previous analysis and testing, drug supplement and system sewage discharge are not timely, which will also make the concentration of a substance too high or rise and become silent in the inner wall of the system, forming scale.

Classification of scale:

A. Carbonate scale contains more than 50% carbonate.

B. Sulfate scale contains more than 50% sulfate.

C. Silicate scale contains more than 20% silicate.

D. Mixed scale contains at least the above three components.

B. The formation of rust is mainly rust, which is usually caused by the following reasons: the basic surface of steel is corroded during the rolling process or under natural conditions, and the iron oxide scale formed is mainly FeO, Fe2O3, Fe3O4 and their hydrates; Second, the equipment matrix receives the medium chemical erosion, and divides the acidic environment and the alkaline environment, like the oil refining system produces FeS, FeCl2 and so on; Third, the equipment matrix was corroded by microorganisms in the circulating water system, such as sulfur suan salt reducing bacteria and iron bacteria, whose corrosion products were FeSO4 and FeS.

Classification of rust:

Iron oxides, hydrates, iron fungi, FeS, etc.

C. oil dirties petroleum refining, petrochemical industry, coal chemical industry, fine chemical and other industries, organic materials in the process of production will be more or less deposition to the whole system inside, nature also due to the production process change, formed a variety of oil dirt, such as heavy oil, residual oil, petroleum coke, coal tar, difficult cleaning materials such as kerosene.

D. biological slime biological slime formation of microorganisms living in the water and the number of species, their best incubation temperature of 30-38 ℃, so the cooling water of petrochemical industry is very suitable for microbial growth and reproduction, they not only form gelatinous mass breeding, and gather the inorganic qualitative, such as sand, Fe2O3, Fe (OH) 3, Mn3O4, Al2O3, CaSO4, SiO2, CaCO3 and other solids, make them form a so-called soft mud (slime). This ooze is usually easily mixed with mineral scale.

Classification of biological slime:

It is divided into algae, iron bacteria, sulfur bacteria, fungi, sulfur suan salt, reducing bacteria.

E. During the reflection or flow process of the scale medium of special materials in the system, due to the friction force of the wall and the physical and chemical properties of the medium itself, they will deposit on the inner wall of the system over time to form the scale of special materials of the medium itself.

Classification of special materials scale:

The species may not be the same as the medium species, in the process of its contact with the wall, due to its own physical and chemical properties change. It can also be deposited by forming similar substances.

After introducing the scaling problem of heat exchanger, the following is how to deal with the scaling:

According to the working principle, there are two methods to remove dirt from the heat exchanger surface: physical cleaning method and chemical cleaning method. According to whether the equipment is running online cleaning and non - online cleaning.

1. Physical cleaning method:

It is the flow of fluid or mechanical action to provide a greater than the force of dirt adhesion force from the heat exchange surface off the dirt.

There are two types of physical cleaning methods: one is the strong cleaning method, such as water cleaning, steam cleaning, sand cleaning, scraper or drill descaling; Another kind is soft mechanical cleaning, such as wire brush cleaning and rubber ball cleaning.

One of the more commonly used is high pressure water jet cleaning, it is the use of liquid pressurization principle, through the high pressure pump, the power source (motor) system energy into pressure energy, water with great pressure energy through the orifice nozzle (another energy changing device), and then the pressure energy into kinetic energy, thus forming a high-speed jet (WJ). It has the following advantages:

A. High cleaning quality

When cleaning the inner hole of the pipe and heat exchanger, it can remove all the structure dirt and plug in the pipe, and can see the metal body, but there is no corrosion and damage to the metal and pipe, so as to achieve high quality cleaning. Cleaning rate up to 100%, cleaning rate up to 95%, greatly improve the efficiency of the cleaning equipment. And it is easy to check the construction effect after the completion of construction. Because the water jet pressure is adjustable, so. The pressure and flow of the water jet can be conveniently adjusted so as not to damage the substrate being cleaned.

B. Fast cleaning speed

As a result of water jet (also known as water bomb abroad) scouring, wedge and grinding, etc., the structure can be immediately broken off. It is several to dozens of times faster than traditional chemical methods, sand blasting, simple mechanical and manual cleaning methods. Set the jet medium is tap water, in the cleaning process because of the strong energy, do not need to add any filler and cleaning agent can be cleaned, so the cost is very low.

C. Low cleaning cost

It also USES very little water, 2 cubic meters per hour. Only about 1/3 of chemical cleaning, namely high pressure water jet cleaning belongs to fine jet, in the case of continuous uninterrupted, low water consumption, small power, belongs to energy-saving equipment.

D. wide application

Flexible and convenient to use in company inspection and maintenance operation. All water jet can direct to the part of the pipeline and vessel lumen, or the equipment surface, whether also hard scale, or explain a blockage, all can make it quickly fall off matrix, thoroughly cleaned, the cleaning method of equipment material, characteristics, shape and GouWu types are no special requirements, can only ask point-blank, so its application is very extensive.

E. no secondary pollution

After cleaning if there is no special requirements, do not need to carry out cleaning treatment, water jet cleaning does not want to sandblasting shot blasting and simple machinery as, produce a lot of dust, pollution of the atmosphere, damage to the human body and health. Also do not want chemical methods, produce a large number of acid and alkali waste liquid, pollution of the city, river, soil, water quality. Water jet is cleaned a method to be able to make atmospheric dust by other every cubic metre 80 milligram reduce the safety standard that sets to the country every cubic metre the following 2 milligram, eradicative silicosis disease source, eliminate acid base waste fluid to flow poisonous, it is a major move of cause of our country environmental protection.

F. high security

The water jet cleaning method is adopted to ensure the safety of no spark, and the operation can be carried out under the condition of oil storage in oil tanks, which reduces the cleaning process and saves money. High pressure water jet cleaning has incomparable advantages in cleaning effect and power, cleaning cost and environmental protection, and its popularization and application is an inevitable trend.

2. Chemical cleaning method: chemical cleaning method is to add scale remover, acid and enzyme in the fluid to reduce the binding force of dirt and heat exchange surface, so that it will peel off from the heat exchange surface. Currently, the following chemical cleaning methods are adopted:

Circulation method: the pump forced circulation of cleaning fluid, cleaning.

Impregnation method: fill the cleaning liquid into the equipment and let it sit for a certain time.

Surge method: fill the equipment with cleaning liquid, discharge part of the cleaning liquid from the bottom at regular intervals, and then put the discharged liquid back into the equipment to achieve the purpose of mixing and cleaning.

Compared with mechanical cleaning, chemical cleaning has the following advantages:

Don't have to open device can clean the reach of the mechanical cleaning chemical cleaning uniform, small clearance can wash, and won't rest deposited particles, formed the core of the new scale can avoid the damage of the metal surface, such as mechanical cleaning of Angle can promote the corrosion and dirt from forming on the nearby rust and passivation treatment can prevent rust after cleaning chemical cleaning can be done at the scene, the intensity of labor is smaller than mechanical cleaning.

In order to save the labor and cost of shutdown cleaning, prolong the operation cycle, and save the maintenance cost, a variety of on-line mechanical cleaning and on-line chemical cleaning devices have been developed.

On-line chemical cleaning is developed on the basis of chemical cleaning in recent decades. At the beginning, this method is only suitable for the removal of the fouling in the cooling water side of the condenser and the cooler, and has been successfully used in the hydrocarbon processing heat exchanger.

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