Help: Boiler scaling, how to solve it!

It is normal for scaling to occur after 6 years of operation; for safety reasons, regular maintenance should be carried out in accordance with standards, and professional companies should be hired to remove the scale using chemical methods.

After prolonged operation, scale formation is inevitable. Moreover, the heat exchange equipment should be cleaned regularly every six years, which not only saves energy but also improves the efficiency of heat exchange and production! As for the chemical cleaning method mentioned above, I think it is not as effective as biological agents for cleaning (we use Fositek cleaner); it not only removes scale quickly but also causes no corrosive damage to the equipment or to human health.

The water quality parameters treated by water treatment equipment should comply with the GB1576-2008 standard \"Water Quality for Industrial Boilers\". Water quality testers should communicate promptly with boiler operators to ensure that the water quality parameters are met.

1. Strengthen water quality monitoring to ensure the quality of water supply； 2. Actively adjust the quality of the boiler water and ensure proper waste discharge ； 3. Chemical cleaning, regular inspection and maintenance.

1. Improve water treatment to minimize the salt content in the feed water; this is the fundamental measure to prevent scaling； 2. Strengthen the chemical treatment added to the boiler, so that calcium and magnesium salts prone to scaling are converted into non-adherent, loose sludge; this sludge can then be removed through regular slag discharge ； 3. Enhance boiler blowdown; carry out blowdown properly in accordance with the requirements of chemical monitoring to maintain the quality of the boiler water, and reduce the amount of water and dissolved salts carried in the saturated steam. This is an effective measure to prevent the formation of scale and salt deposits ； 4. Strengthen steam-water separation and steam cleaning to maintain good steam quality ； 5. Regularly clean the interior of the boiler to remove any salt deposits, thereby preventing further buildup of scale.

Causes, hazards, and removal of boiler scaling (I) Causes of boiler scaling: If water containing hardness enters the boiler without being treated, solid deposits will adhere firmly to the heated surfaces on the water side of the boiler after it has been in operation for some time; this phenomenon is known as scaling. The solid deposits adhering to the heated surface are known as scale. Under certain conditions, solid precipitates can also emerge in the boiler water, existing in a loose suspended state and being referred to as sludge. Slag can be removed along with the wastewater, but if the wastewater is not discharged in a timely manner, some of the slag will deposit on the heated surfaces or in areas where water flow is slow, thereby turning into scale (commonly referred to as \"secondary scale\"). 　　The reasons for boiler scaling are, first of all, the presence of calcium and magnesium hardness or iron ions in the feed water, as well as excessive silicon content ； At the same time, due to the special conditions of high temperature and high pressure in the boiler. The main process of scale formation is as follows: 1. Thermal decomposition – Under high temperature and pressure, certain calcium and magnesium salts that are originally dissolved in water (such as bicarbonates) undergo thermal decomposition, turning into insoluble substances that precipitate out. 　　2. Decreased solubility 　　Under high temperature and pressure, the solubility of certain salts (such as calcium sulfate, silicates, etc.) **decreases** as the temperature rises; once it reaches a certain level, precipitation occurs. 　　3. Evaporation and concentration of water in the boiler 　Under high temperature and pressure, the concentration of salts in the water in the boiler increases as it evaporates and concentrates. When supersaturation is reached, precipitates form on the heated surfaces. 　　4. Interactions and transformations The salts with high solubility in the feed water react with other salts during operation, resulting in the formation of insoluble precipitates. If the reaction occurs on the heated surface, scale is formed directly ； If the reaction occurs in the boiler water, sludge is formed. Some of the water sludge is sticky, and if it is not removed promptly through drainage, it will turn into scale. Furthermore, some corrosion products that adhere to the heated surfaces also tend to transform into metal oxide scale. 　　The aforementioned precipitated deposits adhere to the heating surfaces of the boiler, forming scale; the higher the temperature, the more likely it is that hard scale will form. 　　(II) Hazards of scale 　Scale has very poor thermal conductivity; its thermal conductivity is dozens to hundreds of times lower than that of the boiler steel plates. Therefore, when scale forms in a boiler, it severely hinders heat transfer and causes the following hazards: 　1. Fuel waste and reduced output 　Scale formation in a boiler significantly impairs heat transfer across the heating surfaces, reduces thermal efficiency, lowers steam output, and increases fuel consumption. 　　2. Prone to accidents and affects safe operation 　When scale forms on the heating surfaces, heat from the metal cannot be transferred to the boiler water due to the obstruction caused by the scale, resulting in a sharp increase in the temperature of the metal walls. When this temperature exceeds the limit that the metal can withstand, its strength decreases significantly, leading to overheating and deformation of the metal. In severe cases, this can cause bulging, cracks, or even pipe rupture. 　　3. Clogging of pipes and disruption of water circulation 　If scale forms inside the pipes, it reduces the flow area and increases the resistance to water flow, thereby disrupting normal water circulation. In severe cases, this can lead to complete blockage of the pipes or even pipe bursts. 　　4. Causes under-scale corrosion and shortens the boiler’s lifespan. Scaling in boilers can also lead to hazards such as under-scale corrosion. In some boilers that are compact in structure or have a complex design, once scaling forms on the heating surfaces, it is extremely difficult to remove. In severe cases, repair measures such as patching or replacing tubes must be employed, which not only incurs high costs but also causes serious damage to the heating surfaces. All of the aforementioned hazards will **shorten the boiler’s service life**. 　　Furthermore, when the boiler becomes scaled, it increases the time, cost, and workload required for cleaning and maintenance, which affects production, reduces the effective utilization rate of the boiler, and lowers its economic efficiency. 　　(III) Removal of scale Boilers should prioritize active scale prevention and corrosion protection. However, when the scaling or corrosion deposits in the boiler reach a certain level, they should also be cleaned away promptly to avoid posing risks to the safe operation of the boiler. 　　Methods for cleaning and descaling are mainly divided into two categories: mechanical descaling and chemical cleaning. Chemical cleaning can be further divided into alkali boiling descaling and acid washing descaling. The methods and requirements for descaling boilers are briefly introduced as follows: 1. Mechanical descaling Mechanical descaling is primarily carried out using tools such as electric pipe cleaners, flat shovels, wire brushes, and hammers. This method is relatively simple and low-cost, but it requires a high level of labor effort, has poor descaling efficiency, and can easily damage the metal surface. It is only suitable for small boilers with a small area of scaling, simple structures, and easy access for mechanical tools to reach the scale. In recent years, the use of specialized high-pressure water guns for cleaning has led to rapid development in mechanical descaling methods that utilize hydraulic force. The effectiveness of this high-pressure hydraulic descaling method is significantly higher than that of traditional mechanical tools, and it is also safer and more convenient. However, high-pressure water jet descaling is still limited to industrial boilers with relatively simple structures. 　　2. Alkaline cleaning (boiling) for scale removal The purpose of boiling a boiler with an alkaline solution is mainly to transform the scale and at the same time help it loosen and fall off. Simple alkali boiling has poor descaling effects and often needs to be combined with mechanical descaling. Alkali boiling descaling is effective against scale primarily composed of sulfates and silicates, but it is far less effective than acid cleaning for carbonate scale. Alkali washing furnaces are also commonly used for rust and oil removal from newly installed boilers; sometimes they are employed for oil cleaning or scale transformation prior to acid washing. 　　The amount of alkali cleaning agent used should be determined based on the degree of scaling and fouling in the boiler. The typical dosage used for descaling (per ton of water) is as follows: 5–10 kg of sodium tripolyphosphate for industrial use, 3–6 kg of sodium carbonate, or 2–4 kg of sodium hydroxide. These alkali cleaning agents should first be prepared to a certain concentration in a solution tank, and then pumped into the boiler via a pump to ensure uniform distribution. 　　The method of descaling by alkali boiling is essentially the same as that used for boiler sterilization of new boilers; however, after the sterilization process is complete, the various inspection holes in the boiler should be opened to carry out mechanical (or high-pressure hydraulic) assistance in removing scale, so as to prevent the softened scale from hardening again. 　　3. Acid cleaning for descaling 　　Among the various descaling methods available today, acid cleaning yields the best results. However, if the acid cleaning process is not appropriate or not properly controlled, it can affect the descaling efficiency or cause metal corrosion; in some cases, it may even seriously compromise the safe operation of the boiler. To ensure the safety and quality of boiler acid cleaning, the **Quality and Technical Supervision Bureau has specifically formulated and issued the ‘Rules for Chemical Cleaning of Boilers’. These rules stipulate that entities engaged in the chemical cleaning of boilers must obtain accreditation from provincial or higher-level supervision agencies responsible for the safety of boilers and pressure vessels in order to carry out such cleaning operations at the corresponding level. Any unit or individual without the appropriate qualifications (including units that use boilers) shall not carry out boiler pickling without permission. 　　Before acid cleaning, representative scale samples from the boiler should be taken for testing in order to develop a cleaning plan ； At the start of acid introduction, corrosion indicator tablets must be placed inside the boiler and the acid tank (to be removed when the acid is removed) ； The pickling process flow, as well as the temperature, concentration, flow rate of the pickling solution and the pickling time, should be implemented and controlled in accordance with the cleaning plan ； During the cleaning process, samples should be taken for testing continuously, and records should be kept accurately. After the cleaning is completed, the furnace management unit, the cleaning unit, and the boiler safety supervision department shall conduct an inspection to assess the quality of the cleaning. The quality requirements for pickling industrial boilers are as follows: 　　(1) Scale removal rate 　　1) When removing scale that is primarily carbonate-based, the area cleared of scale should be at least 80% of the original area covered by the scale. 　　2) Clean silicate or sulfate scale, with the descaling area covering more than 60% of the original scale coverage area. 　　If the scale removal rate is below the specified value, or although the requirements are met the main heating surfaces of the boiler are still covered with scale that is difficult to remove, the boiler should be operated for about a month while maintaining the alkalinity of the boiler water at the upper limit of the quality standards, after which it should be shut down to remove the detached scale and residual deposits by manual means or with a high-pressure water gun. Since the hard deposits remaining after acid cleaning are usually already loosened, they will gradually fall off as the boiler starts operating. If no further cleaning is carried out, accidents are likely to occur; therefore, when there is a large amount of residual scale, it must be removed. 　　(2) Passivation film: A good passivation protective film should be formed on the surface of the boiler after cleaning, so that no secondary rust appears on the metal surface and there is no pitting. 　　(3) Corrosion rate: The average value of the metal’s corrosion rate measured using corrosion indicator sheets should be less than 6 g/(m2·h), and the total amount of corrosion should not exceed 72 g/m2. 　　(4) Unobstructed furnace tubes: After cleaning, all the water wall tubes and convection tubes, etc., within the boiler should allow smooth flow without any obstructions. For pipes that were already blocked before cleaning and remain clogged even after cleaning, they should be repaired or replaced by a qualified repair unit.

Chemical cleaning is possible at present, but care should be taken to use corrosion inhibitors that inhibit hydrogen infiltration in order to prevent hydrogen embrittlement； It is best to strengthen efforts in routine operation and management; the water quality parameters should meet the standards specified in GB1576-2008 \"Water Quality for Industrial Boilers\", and boiler scale inhibitors should be used during daily operation.

“During regular maintenance, it was also found that there was a large amount of water sludge accumulated in the lower collection box. What’s going on? ” Make sure that the drain valve used is a \"quick drain valve\"; if you are concerned about potential problems, you can connect a gate valve in series. Do not use a globe valve for leak prevention (as there are specific regulations regarding this). By quickly opening and closing the sewage valve at scheduled times, the sludge can be flushed away as effectively as possible. In addition to ensuring the parameters of the boiler feedwater, it is necessary to pay attention to controlling the pH value and alkalinity of the boiler water during operation; if control proves difficult, improve the management of chemical dosing. (Avoid conditions that facilitate scale formation) During the annual inspection of the boiler, make sure to open the boiler drum and blind plates for inspection. When serious problems are detected, clean the system promptly or adjust the regulations for water quality monitoring and chemical dosing.