Boilers play a vital role in industrial production as well as in daily life. However, a problem that has long plagued boiler users is the formation of scale. Boiler scale, in simple terms, is the buildup of dissolved solids in water left behind by the gas-phase process of converting water into steam. It usually appears as a powdery white residue.
The presence of scale has a significant negative impact on boiler performance and service life. It not only reduces the heat transfer efficiency of the boiler and leads to energy wastage, but can also cause a series of serious malfunctions that threaten the safe operation of the equipment. Therefore, understanding how to prevent the formation of boiler scale is of great significance to ensure the efficient and stable operation of boilers and reduce operating costs.
The formation process of boiler scale is not complicated. When the water containing various minerals into the boiler, as the water is heated into steam, the original dissolved solids in the water will gradually precipitate and accumulate in the boiler walls and other parts of the surface, which forms the scale. For example, calcium carbonate (CaCO₃) and magnesium carbonate (MgCO₃) and other compounds commonly found in water, in the process of water being heated, their solubility will be reduced, so that the solid form of the precipitation out of the main components of the scale. In the steam boiler industry, what we call “water hardness” actually refers to the amount of these compounds in the feed water.
The pressure vessel of a steam boiler can be thought of as the heart of the human body, and the buildup of scale is like fat, cholesterol and other substances clogging the arteries of the body. When the arteries are clogged, the heart has to increase its pressure and work harder in order to transport blood through the narrowed vessels. This increased pressure can cause serious damage to the heart and arteries, even risking rupture. Similarly, scale buildup in a boiler can impede the transfer of heat, making the boiler consume more energy to achieve the desired steam production, while excessive temperatures and pressures can also lead to damage to boiler components and safety accidents.
Regular boiler maintenance and servicing is a basic and critical measure to prevent scale buildup. This usually involves a thorough inspection of the boiler and its components by a professional.
- Pressure and Flow Checks: The technician will carefully verify the boiler's pressure and water flow rate to ensure that it is operating within the manufacturer's recommended parameters. This is because abnormal fluctuations in pressure and flow rate may accelerate the formation of scale.
- Cleaning: It's also important to promptly remove any deposits or debris from the inside of the boiler that may catalyze scale formation. For example, some tiny particulate matter may become the core to which scale adheres, accelerating the scale build-up process.
- Safety device testing: Also, make sure that all safety devices, such as relief valves and pressure relief valves, are working properly. These safety devices are not only related to the safe operation of the boiler, but their proper working condition also helps to maintain the stability of the boiler's internal environment and reduces the likelihood of scale formation.
Adding a scale reducer or inhibitor directly to the boiler system is an effective way to prevent scale buildup. The following two types are commonly used today:
- Chemical inhibitors: These additives alter the chemical balance of the water, reducing the likelihood of scale adhering to boiler components. They do this by reacting chemically with minerals in the water, making it difficult for the minerals to form solid deposits, or by changing the nature of the deposits so that they are less likely to adhere to the boiler lining.
- Physical devices: e.g. magnetic or electrolytic scale reducers. Magnetic filters are installed in the piping to attract and trap iron-containing particles and scale, while electrolytic devices use an electrical charge to break the bonds between minerals and change the structure of the minerals, thus preventing them from depositing on the boiler surface. These physical devices require no added chemicals, are relatively environmentally friendly, and are easier to install and maintain.
In addition to the methods described above, there are a number of other measures that can be taken to prevent boiler scale formation.
- Selection of suitable scale inhibitors: There are a variety of scale inhibitors containing phosphonates available on the market, and users can select products with different formulations according to their needs. For example, for boiler systems that come into direct contact with foodstuffs, it is necessary to choose a safe scale inhibitor specifically designed for this purpose.
- Routine water testing: Regular water testing is essential to monitor changes in water hardness. Once abnormal water hardness is detected, measures can be taken in advance, such as adjusting the water treatment process or increasing the dosage of scale inhibitors. At the same time, the measurement of the total dissolved solids (TDS) content of the water is also very important, because the TDS value is too high often means that the water dissolved salts more, these salts is to lead to the formation of boiler scale is an important factor.
- Water pre-treatment: For water with high hardness or high TDS value, equipment such as reverse osmosis, water softener and desalter can be used for pre-treatment to remove calcium, magnesium and other minerals in the water. After pre-treatment of the water into the boiler, can significantly reduce the production of scale.
- Maintain appropriate operating parameters: Strictly maintain the recommended temperature and pressure of the boiler system. Excessive temperatures or unstable pressures can encourage minerals in the water to precipitate more readily and form scale. Therefore, accurate control of operating parameters in accordance with the boiler's operating procedures is one of the most important means of preventing scale.
- Regular sewage operation: According to the use of the boiler, regular sewage operation is carried out, generally every shift or at certain intervals. By discharging, the sludge and dissolved solids accumulated at the bottom of the boiler can be removed in time, preventing these substances from further concentrating in the boiler, thus reducing the source of scale formation.
- Remote monitoring and automated control system: Utilizing modern technology, remote monitoring and automated control systems are used to track water quality changes and boiler operational performance in real time. This can detect potential problems in time, and automatically adjust the relevant parameters or add water treatment chemicals to ensure that the boiler is always in the best operating condition, minimizing the risk of scale formation.
Scale is formed when water is heated, impurities in the water precipitate or precipitate and form deposits inside pipes and on heat transfer surfaces. These deposits accumulate gradually and seriously interfere with the efficiency of heat transfer. In extreme cases, they may even lead to the failure of pipes and the entire system. For example, in some large industrial boilers, heat transfer is impeded due to a large buildup of scale, resulting in a significant increase in boiler energy consumption and a marked decrease in productivity. More seriously, if scale causes localized overheating of pipes, it may trigger pipe rupture, resulting in production interruption and even posing a safety hazard.
Taking power plants that draw water from rivers or lakes as an example, there may be various suspended and colloidal solids in their process water, of which silica is a common one. When feedwater containing silica is heated to produce steam, extremely hard deposits can form on heat transfer surfaces inside the boiler. In addition to silica, common feedwater contaminants that contribute to scale formation include iron, calcium, magnesium, and aluminum.
The extent of scale formation within a boiler depends on the level of these impurities and the pressure at which the boiler is operating. Generally speaking, many high-pressure boilers have higher water quality requirements, because in a high-pressure environment, even a small amount of impurities are more likely to precipitate and form scale, which can have a greater impact on the normal operation of the boiler. In contrast, some low-pressure boilers have a relatively high tolerance for water quality. However, in any case, the quality of the feed water and the level of impurities need to be controlled in strict accordance with the boiler manufacturer's recommendations in order to minimize scale formation.
Many of the problems associated with boiler scale stem in large part from the insulating properties it provides. During boiler operation, heat is generated by the combustion of fuels (e.g., gas, oil, wood, etc.), and ideally, as much of the heat generated by combustion as possible is transferred from the hot combustion gases to the boiler water. However, because scale deposits are insulating, they prevent the efficient transfer of heat to the water through the boiler's metal tubes. In a dirty, scale-built boiler, heat transfer is less efficient, which means that more heat is expelled up the chimney instead of being converted to steam. In order to produce the required amount of steam, more fuel has to be burned, which not only increases energy costs, but also comes with more greenhouse gas emissions.
Different types of scale have different insulating properties. For example, “normal” scale that is only 1/32 of an inch thick can reduce the efficiency of heat transfer by 2%, while the same thickness of high iron and high silica scale can reduce heat transfer efficiency by as much as 7%. This difference is significant in terms of increased fuel costs and increased greenhouse gas emissions. Also, by analyzing the composition of the scale, it is possible to understand the causes of scale formation and thus target preventive measures.
Due to the insulating properties of scale deposits, the metal temperature on the fire/water side is much higher in a dirty boiler than in a clean one. The increased metal temperature, in turn, increases the likelihood of pipe overheating and pipe failure.
In watertube boilers, scale deposits tend to “shed” inside the pipes, which in turn clogs the water flow. Once water circulation is interrupted, pipes can be rapidly damaged by overheating. In firetube boilers, scale can similarly lead to overheating and failure, especially if deposits cause piping to bridge, or if large amounts of scale build up at the bottom of the boiler. Deposit buildup at the tube plate is particularly hazardous because the metal here is not easily cooled. In either case, when it happens, the boiler must be taken out of service for repairs, which can not only bring production to a standstill, but also incur high repair costs.
In short, the end result of boiler scale is often higher fuel and maintenance costs and a real risk of unexpected boiler failure. Preventing scale formation is therefore essential to safeguard stable boiler operation and reduce costs.
Scale is mainly made up of calcium, magnesium and other minerals that build up to form a thick, chalk-like substance on the boiler surface. It dramatically reduces heat transfer efficiency, making the boiler consume more energy to maintain normal operation. More seriously, the presence of scale can also lead to localized overheating of the boiler, which in turn can cause equipment failure and affect the continuity of production. Municipal or well water typically contains high concentrations of dissolved solids and minerals, which are potential sources of scale problems. Therefore, taking effective preventive measures before scale forms is critical to the stable operation and service life of the boiler.
Corrosion is the process by which a metal interacts with an oxidizing agent such as water, hydrogen or hydroxide to form an oxide. In boiler systems, corrosion gradually erodes boiler components, weakening their structural integrity and increasing the risk of leaks and ruptures. Scale and corrosion problems are often interrelated, with scale buildup altering the water flow and electrochemical environment inside the boiler, thereby accelerating the onset of corrosion, while products from corrosion may further contribute to scale formation. Together, the two can lead to not only costly downtime and repairs, but also serious safety hazards.
Traditionally, chemical treatments have been used in industrial boilers to alleviate scale and corrosion problems. These treatments primarily use a variety of inhibitors and dispersants to control scale formation and protect metal surfaces from corrosion. To some extent, chemical treatments are effective, but require careful monitoring and precise dosing of agents to ensure optimal results.
At the same time, chemical treatments have some drawbacks. Firstly, the use of chemicals is costly, especially for large industrial boiler systems, where long-term consumption of chemicals can be a significant expense. Secondly, environmental problems can be caused by the potentially hazardous nature of the chemicals used. For example, some chemicals may cause contamination to water or soil after discharge, and therefore need to be treated and discharged in strict compliance with environmental regulations.
In addition, cathodic protection methods can be used to prevent corrosion. This method reduces corrosion of metals by using the metal surface of the boiler as the cathode of an electrochemical cell. Cathodic protection is often used in conjunction with chemical treatments to provide a more comprehensive corrosion prevention strategy. However, cathodic protection has its drawbacks, such as higher initial installation costs and the need for ongoing maintenance and monitoring to ensure proper system operation. If not managed properly, cathodic protection can also lead to hydrogen embrittlement, which makes metals brittle and increases the risk of equipment failure.
Reverse osmosis systems utilize semi-permeable membranes to remove dissolved minerals and impurities from water, thereby effectively preventing scale formation and reducing the potential for corrosion. By treating boiler feedwater with reverse osmosis, industrial facilities are able to significantly improve boiler operating performance, reduce maintenance costs and extend equipment life. Reverse osmosis technology is not only efficient, but also reduces the amount of chemicals used in the production process and is more environmentally friendly.
In practice, reverse osmosis systems are able to accurately filter out tiny particles and ions from the water, ensuring that the water entering the boiler is virtually free of substances that cause scale and corrosion. This not only improves the heat transfer efficiency of the boiler, but also reduces equipment failures due to scale and corrosion, which saves companies a lot of operating costs.
Boiler water treatment can prevent a wide range of problems in the boiler system, from minor to serious. First, it is critical to initially treat the water entering the boiler, which includes filtration, monitoring water quality, and adding chemicals as needed to maintain the water's chemical balance. To facilitate this process, appropriate equipment should be installed on the boiler to monitor the water chemistry in real time and automatically add treatment chemicals to ensure that the newly replenished water does not cause an imbalance in the system.
- Boiler Probe: The boiler probe is used to measure various parameters of the boiler water, such as tank level and pH. The information collected by the probe is transmitted to the controller so that chemical additions can be adjusted in a timely manner to maintain stable water quality.
- Contact water meter: A contact water meter is a mechanical device used to measure water flow. When a certain volume of water flows through it, it sends an electrical signal, thus monitoring the use of boiler water. Through the monitoring of water flow, you can better grasp the operating status of the boiler, providing a basis for water treatment.
- Corrosion Test Piece Holder: The Corrosion Test Piece Holder measures the corrosion rate of a boiler system without opening the piping. It evaluates the corrosion of the system by measuring the weight loss of the test piece over a certain period of time, and provides data to support the adoption of appropriate anti-corrosion measures.
In addition, the boiler equipment includes controllers for precise control of boiler water treatment chemical dosing. These devices make it easier to measure and add water treatment products, keeping the boiler system cleaner for longer periods of time.
- Chemical Mixing Tanks: These tanks are used to safely store and mix chemicals with boiler water. They ensure that the chemicals are well mixed before entering the boiler for optimum treatment.
- Chemical Pumps: Chemical pumps are responsible for transferring the chemicals from the mixing tanks to the boiler. Their precise delivery capacity ensures that the chemicals are added in the set dosage, avoiding the effects of too much or too little chemicals on the water treatment.
- Drain valves and solenoid valves: These valves are used to regulate the flow of chemicals or water. By precisely controlling the flow rate, the intensity of the water treatment can be flexibly adjusted according to the actual operating conditions of the boiler.
- Automated controller: The automated controller automatically adjusts the amount of chemicals added according to the information coming from the probe. This intelligent control greatly improves the accuracy and efficiency of water treatment and reduces the errors that can be caused by manual intervention.
Having the right equipment is vital to maintaining water quality, but it is important to note that it is the chemicals added to the water for treatment that have the greatest impact on boiler life and water quality. Different boilers may require different compositions of water treatment chemicals due to differences in their materials and operating methods. Therefore, it's important to rely on a water treatment professional to select the right chemicals for your boiler and determine the correct amount to add to ensure that your boiler system is always running cleanly and efficiently.
Boiler scale formation is a complex and serious problem, but with a thorough understanding of the mechanisms, hazards, prevention methods and effective treatments, we can take targeted action to combat it. Regular maintenance, the rational use of scale inhibitors, water quality testing and pretreatment, the use of appropriate water treatment equipment, etc., are effective means of preventing the formation of boiler scale. At the same time, it is necessary to fully recognize the interconnectedness of scale and corrosion problems, as well as the advantages and disadvantages of chemical treatment and membrane separation and other solutions, and choose the most suitable treatment method according to the actual situation.
Only by paying attention to the prevention and treatment of boiler scale can we ensure the long-term stable and efficient operation of the boiler, reduce operating costs, minimize safety risks, and provide reliable energy support for industrial production and daily life. In the future boiler operation and management, continuous attention and optimization of scale prevention measures will be the key to safeguard the performance of the boiler system.
