Mandu Engineering tells you the methods for cleaning heat transfer oil boilers

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　　Heat transfer oil is an organic heat carrier. As a medium for liquid-phase circulation in other equipment systems involving arch replacement, it serves as an excellent new energy-saving technology aimed at heat transfer. It is an excellent heat transfer medium, featuring heat transfer capabilities at high temperatures and low pressures. It offers significant energy savings, high stability, good heat transfer properties, high efficiency, and energy conservation (saving approximately 30%–50% compared to steam-based thermal systems). It has a high boiling point at low pressures, allowing the system to operate at normal pressure at 350°C; it also boasts a large heat capacity, low operation and maintenance costs, and good safety features. Used oil can be reused or burned together with coal. Heat transfer oil furnaces eliminate the investment and operating costs associated with water treatment. 　　Heating with heat transfer oil as a substitute for steam heating holds great potential for widespread use across various industries; it is currently applied in sectors such as wood-based panels, petrochemicals, textiles, chemical fibers, printing and dyeing, light industry, crude oil transportation, food processing, road construction, and building materials. Especially in the fiberglass products industry, switching the heating source for drying from a steam-electric hybrid system to a heat oil furnace yields significant economic benefits; if this technology is adopted in the fiberglass and other industries, it will help **create greater value. This article mainly analyzes and reviews aspects such as the types and physicochemical properties of heat transfer oils, the shortcomings encountered in their application and the reasons for them, as well as the methods to address these shortcomings. 　　Heat transfer oils generally fall into two categories: mineral-based and synthetic. Mineral-based oils are derived from certain high-boiling-point fractions extracted during petroleum refining; after adding antioxidants, they become heat transfer oils. Synthetic heat transfer oils are usually mixtures of several isomers or chemicals with similar properties. The components of heat transfer oils include biphenyl, naphthalene, diphenyl ethers, and their low-melting-point mixtures. Common types include alkylbenzene type, alkylnaphthalene type, alkylbiphenyl type, biphenyl plus diphenyl ether mixture type, hydrogenated terphenyl type, benzyltoluene type, heavy alkylbenzene type, silicone-based types, and mineral oil types. 　　Disadvantages of heat transfer oil Heat transfer oil is prone to oxidation during the heating process; at high temperatures, its acid value increases significantly, with a large rate of change. Its kinematic viscosity gradually increases, due to the thermal cracking and thermopolycondensation reactions of the components in the heat transfer oil at high temperatures. The results of the thermal pyrolysis reaction lead to the formation of small-molecule compounds, reducing its viscosity ； The thermal polycondensation reaction produces polymer products, which increases their viscosity. Small molecular compounds will volatilize in small amounts; as a result, the viscosity of the oil increases, and the amount of residue rises with rising temperature. When the operating temperature is between 300 and 400°C, thermal pyrolysis tends to occur, resulting in the formation of carbon deposits on the inner walls of pipes and equipment. This reduces heat transfer efficiency, accelerates the aging and degradation of the lubricating oil, and also causes localized overheating in the furnace and pipes, thereby compromising their mechanical strength and posing a risk to human safety. Scaling of heat transfer oil in pipelines reduces the flow area of the oil transport lines to varying degrees, increases frictional resistance, raises energy consumption for transportation, lowers the pipeline’s capacity to transport oil, and sometimes even leads to incidents such as initial solidification and flow interruption. Furthermore, the sludge and fouling generated by heat transfer oil can increase the thermal resistance of the pipe walls, leading to higher energy consumption during production and a reduced lifespan of the equipment. The fouling layer also reduces the inner diameter of the equipment, increasing the pressure drop for material flow and thus reducing yield as well as shortening the operational cycle, which severely impacts production. 　　Reasons for scale formation in heat transfer oil High-temperature heat transfer oil circulates in heat oil boilers to transfer heat, while simultaneously producing gums. The gum is viscous; a high-quality heat transfer oil can keep the gum suspended in the oil. During circulation, some of the gum can be filtered out via a filter. However, if a small amount of gum adheres to the inner wall of the furnace tube, coking is likely to occur. Furthermore, during the circulation of heat transfer oil, if air gets mixed in, degradation and polymerization can occur, resulting in the formation of low-boiling and high-boiling substances. Low-boiling substances can be discharged into the atmosphere through a head tank, while a small amount of high-boiling substances can dissolve in the heat transfer oil. If the solubility of these substances in the heat transfer oil reaches a supersaturated level, they will adhere to the inner walls of the pipes, which is another cause of coking. Furthermore, operating temperatures above their design temperature often lead to autocatalytic thermal decomposition, resulting in coking inside the tubes. Leakage of process materials into the heat transfer oil system leads to the formation of corrosion products that cause rust, while impurities introduced during overhauls further contribute to coking on the inner walls of the pipes. 　　Main components of heat transfer oil fouling Oil fouling is primarily composed of waxes, gums, char, asphalt, carbides, carbonaceous substances, iron sulfide, iron oxide, inorganic salts, organic polymers, catalysts, and other elements. 　　Harm caused by scaling in heat transfer oil A small amount of light components in the heat transfer oil system can be removed through the vent line, but if there are too many light components, it will result in a low pumping flow rate and lead to an automatic shutdown of the furnace. An excessive amount of heavy components will cause coking inside the furnace tubes, resulting in a decrease in their heat transfer rate. The thermal efficiency of hot oil furnaces decreases, leading to energy waste. The temperature difference between the inside and outside of the furnace tubes increases; when the outer wall temperature of these tubes reaches 600–700°C, it is easy for the tubes to be burned through, which can result in fire accidents, equipment damage, and even casualties. Coking is a major threat to hot oil boilers and the root cause of fires; therefore, finding ways to prevent coking in such boilers is a matter that deserves thorough study.
Prerequisites for cleaning heat transfer oil:
Heat transfer oil boilers of any quality will experience quality degradation when used at high temperatures for extended periods. During this degradation process, carbon deposits form on the tube walls, causing six types of hazards:
1. Carbon deposits have insulating properties, which leads to slower temperature rise and affects operational efficiency. 　　2. For every additional millimeter of carbon deposits on the inner wall of the pipe, fuel consumption increases by 20–30%. 　　3. Due to the uneven thickness of carbon deposits on the pipe walls, the temperature at the working surface becomes non-uniform, affecting product quality. 　　4. After carbon contamination and deposits form, the acid value increases, leading to microbattery corrosion and accelerating the aging and damage of the equipment. 　　5. Due to lack of cleaning over a long period, carbon deposits and carbon fouling accumulate in large amounts at the bends in the pipes, leading to localized overheating and gas buildup, which can cause the pipes to crack or fuel to spray out, resulting in a fire and the destruction of the boiler. 　　6. It is beneficial for the regeneration and adjustment of heat transfer oil furnaces, extending their service life and operational period. 　　Type 1: Chemical cleaning (for heating oil boilers) makes use of patented Chinese technology. Taking into account the specific structure of heating oil heating systems and the diversity of materials used, the following cleaning procedure for such boilers is adopted: Discharge of heating oil – Steam flushing – Degreasing – Scaling removal – Rinsing – Neutralization and passivation – Steam flushing – Inspection and acceptance – Nitrogen purging – Restoration to normal operating temperature. (1) Steam flushing involves discharging the heating oil from the pipes, followed by using steam to clean the interior of the pipes and remove surface impurities, rust, and other contaminants. 　　(2) Degreasing: The purpose of degreasing is to remove oily substances from the system and to cause the scale to become moist and transform, thereby creating conditions for the descaling step. Originally, the oil contamination exists on the surface as a spread-out oil film. Under the effect of preferential wetting during washing, it gradually curls up into oil droplets, which are ultimately rinsed away from the surface. 　　(3) Coke removal and scale elimination: This process is a key step in chemical cleaning. Its purpose is to use a specially formulated agent for removing coke and scale, which reacts chemically with the scale deposits to form water-soluble substances that are then carried away from the system by the cleaning fluid, thereby achieving the goal of removing coke and scale. 　　The heat transfer oil cokes when heated on the wall tubes, and these coke deposits form hard masses. Over the years, our company has concluded through research on methods for removing this coke that a comprehensive approach is necessary: dissolution – the use of solvents; adsorption – surfactants adsorb dirt and the surface of the components being cleaned (the furnace tubes), thereby altering the properties of various substances at the interface and on the surface (such as mechanical, electrical, and chemical properties); emulsification – the formation of a strong interfacial film that helps to stabilize the emulsion, making it harder for oily particles to settle on the solid surface of the furnace tubes. The addition of detergents further enhances the cleaning effect. It facilitates the suspension of dirt particles, preventing their deposition. Combined with the effects of temperature (thermal motion) and mechanical forces, it achieves an optimized cleaning effect. 　　(4) Rinsing: Rinsing involves using a rinsing solution prepared according to specified guidelines to bind with the free ions remaining in the system, thereby further improving the scale removal efficiency and laying a foundation for the neutralization and passivation process. 　　(5) The neutralization fluid reacts with the residual rinse fluid in the system to bring the pH value throughout the entire thermal oil heating system to the specified level. 　　(6) Passivation: A passivation solution is used to form a complete and dense passivation protective film on the clean metal surface. 　　(7) Rinsing with clean water ensures that all cleaning agents are completely removed, leaving the inside of the pipe walls clean. (8) Nitrogen purging is used to remove as much residual water from the heating pipes filled with heat transfer oil as possible; nitrogen or compressed air can be employed for this purpose. 　　Type 2: Cleaning process flow: Discharge old oil → Pre-washing → Cleaning → Water washing ① → Water washing ② → Water washing ③ → Add new oil → Dehydration → Normal operation. (1) Discharging old oil: Utilize the heating system to heat the heat transfer oil boilers to 70–80°C, and then discharge all the heat transfer oil from the system while it is still hot. Depending on the conditions, try to remove as much residual oil as possible from the system; if some oil remains, add a small amount of cleaning agent to thin it out through processes of penetration, stripping, and dissolution, before discharging it from the system. 　　(2) Pre-washing: Add the cleaning agent specified for this purpose at a rate of 2% of the total circulation volume (70–80 kilograms; one and a half bags of solid form, one and a half barrels of liquid form). The solids are dissolved in hot water before being added, while the liquids are added directly. The agent is introduced into the system at any point in the heating system (usually through a oil pump from a high-level oil tank, in the same way as when adding oil). The system is filled with clean water, and the circulation oil pump is started to facilitate circulation. A heater is used to raise the water temperature to 80°C ± 5°C. The valves associated with each reaction vessel in the system are then adjusted so that all parts of the system can be circulated separately. 　　(3) Cleaning: Add the cleaning agent specifically designed for this purpose at a rate of 6–8% of the total circulation volume (to ensure optimal results, leave 50 kilograms aside; it should be supplied in buckets or bags). Dissolve the solid components in hot water, then add the liquid components as well. As in step (2), introduce these substances into the system. After filling the system with clean water, start the circulation pump to facilitate circulation. Use a heating furnace to heat the cleaning agent to a temperature of 90°C ±5°C. 　　(4) Water washing: Fill the system with clean water, start the circulation pump to enable circulation, use a heating furnace to raise the water temperature to 90°C ± 5°C, and switch the relevant valves in the system so that all parts of it are circulated separately. 　　Type 3: Cleaning plan for hot oil boilers 1) Steam flushing: The heat transfer oil inside the pipes is drained, and steam is used to flush the interior of the pipes in order to remove surface impurities, rust, and other contaminants. 　　2) Degreasing: The purpose of degreasing is to remove oily substances from the system and to cause the scale to become moist and transform, thereby creating conditions for the descaling step. Oil stains originally existed on the surface as a spread oil film; under the effect of preferential wetting during washing, they gradually contracted into oil droplets, and were eventually washed away from the surface. 　　3) Carbon removal and scale elimination: This process is a key step in chemical cleaning. Its purpose is to use a specially formulated agent for removing carbon and scale, which reacts chemically with the scale deposits to form water-soluble substances that are then carried away from the system by the cleaning solution, thereby achieving the goal of removing carbon and scale. 　　4) Rinsing: Rinsing involves using a rinsing solution prepared according to specified criteria to bind with the free ions remaining in the system, thereby further improving the scale removal efficiency and laying a foundation for the neutralization and passivation process. 　　5) The neutralizing solution is used to react with the residual rinsing liquid in the system, thereby bringing the pH value throughout the system to the specified level. 　　6) Passivation: A passivation solution is used to form a complete and dense passivation protective film on the clean metal surface. 　　7) Rinsing with clean water ensures that all cleaning agents are completely removed, leaving the inside of the pipe walls clean. 　　8) After the cleaning is completed, the contractor first conducts a self-inspection of the cleaning quality. Once the self-inspection shows that the quality is satisfactory, the contractor and the user unit jointly organize an inspection and acceptance process. Upon successful completion of this inspection, both parties sign a cleaning acceptance report. 　　9) Nitrogen purging is used to remove as much residual washing water as possible from the pipes; nitrogen or compressed air can be employed for this purpose. 　　The water-based chemical cleaner, a specialized cleaning agent for heat transfer oil boilers, is used to remove heavy oil residues, oil coke, sludge, as well as oil stains on metal surfaces in heat transfer oil equipment. Composed of a mixture of high-quality surfactants and organic additives, it possesses excellent penetration, emulsification, and oil residue removal capabilities. It has great solubility in water, is easy to use, and can be applied through various cleaning methods such as soaking, spraying, or circulation. It is safe and non-corrosive, and can be discharged directly after use. 　　Features of water-based chemical cleaners: 1. They have a strong ability to remove oil residues and heavy oil deposits, cleaning the oil stains in equipment thoroughly and leaving no residue behind. 　　2. It has a wide range of applications: it can remove oil stains from metal objects as well as be used for cleaning non-metallic objects. 　　3. Safe to use: This product is odorless, non-toxic, non-flammable, and does not corrode the surfaces being cleaned. It has low irritancy, does not damage the skin, and is safe for all types of surfaces without causing corrosion. It also provides short-term rust prevention for metal surfaces. 　　4. It is simple to use; this product can be applied at room temperature directly or diluted with water, and it can meet the requirements for soaking, scrubbing, spraying, wiping, and ultrasonic cleaning. 　　High-temperature synthetic heat transfer oil – This oil is formulated by adding functional additives to a base oil that has undergone three stages of high-pressure hydrogenation; in Europe and the United States, it is classified as Type III synthetic oil, and its performance is comparable to that of PAO synthetic oils! Its good thermal stability and excellent anti-oxidation properties ensure that this oil has a longer service life compared to ordinary mineral oils! A high flash point, as well as a high ignition point and auto-ignition point, ensure safety during handling. Online cleaning agent for heat transfer oil furnaces: no need to shut down production ； No water required ； Short cleaning time ； Cleaning efficiency 98% ； Extend the lifespan of heat transfer oil by 1-3 years ； As proven by users, the results are highly satisfactory. 　　Precautions for cleaning thermal oil boilers 1. Dilute the descaling agent with water in a ratio of 1:10 and inject it into the boiler’s water inlet ； 　　2. Fill with water up to the maximum level, and wait for 4 hours to allow the descaling solution to fully react with the scale ； 　　3. Open the drain outlet to drain the cleaning solution ； 　　4. Pour in clean water and rinse until the water is clear; the descaling process is then complete. 　　Tip: 1. For a 0.5-ton boiler, it is recommended to use 10 kilograms of descaling agent. 2. If the boiler has not been cleaned for over 2 years, please extend the cleaning time or increase the amount of cleaning agent used. 3. Cleaning with water at around 50 degrees yields better results.