Scaling occurs when minerals in the water first dissolve, then precipitate and form hard deposits on the inside of the condenser tube. These deposits typically contain calcium carbonate, magnesium hydroxide, calcium sulfate, and silica compounds.
The process begins when water containing dissolved minerals is heated or undergoes pressure changes in the condensing system. As environmental conditions change and the solubility of these minerals decreases, they crystallize on the tube walls and gradually form a thickening layer of scale.
How Does Scale Form in A Condenser?
Formation of Hard Scale
Hard scale is mainly caused by the dissolved calcium and magnesium salts in the cooling water, which are precipitated and deposited on the heat exchange surface after heating. When the hard water with high concentration of calcium and magnesium ions flows through the copper tube in the condenser as a cooling medium.
The solubility of these salts gradually decreases as the water temperature rises, and carbonate and calcium and magnesium ions combine to form insoluble calcium carbonate or magnesium hydroxide and other compounds, which are adhered to the heat exchange surface.
Especially in the heat exchanger tube bend, due to the local flow rate changes, mineral precipitation is easier, thus accelerating the scaling process. Therefore, it is recommended to remove calcium and magnesium from the water by pre-treatment if conditions allow.
Accumulation of Biological Sludge
In addition to chemical components, sediment and microorganisms (e.g. algae) carried by natural water sources may also be part of the fouling. These particulate matter are gradually deposited in areas of slow water flow, forming a biofilm.
Over time, this film will thicken, which not only reduces heat transfer efficiency, but may also trigger pipe clogging or even physical damage. To prevent this from happening, efficient filtration devices can be installed at the inlet end to intercept larger suspended matter, thus reducing the generation of bio-sludge.
Increased Scaling under The Influence of Temperature
High return water temperature is also an important factor in promoting scale generation. According to relevant data, when the cooling water temperature exceeds 40°C, scale formation will become easier. This is because high temperatures reduce the solubility of certain salts in the water, prompting them to precipitate out of solution and adhere to metal surfaces. In addition, high temperatures accelerate the rate of chemical reactions, further exacerbating the scaling phenomenon.
How Does Scale Affect Condenser Performance?
When scale builds up in a condenser, its core performance indicators are negatively impacted in multiple ways. This impact is not only limited to the immediate operation of the equipment, but also triggers a series of chain reactions, posing a threat to the long-term stability and economy of the entire refrigeration system.
Significant Increase in The End Difference
Scale coefficient of thermal conductivity is extremely low, only 1/100 – 1/1000 of the metal material, in the heat transfer surface to form a dense insulation layer. Take the industrial commonly used carbon steel condenser as an example, the metal body thermal conductivity is about 45W/(m・K), while the calcium carbonate scale thermal conductivity is only 0.45W/(m・K).
This layer of “natural thermal insulation blanket” will lead to cooling water outlet temperature and refrigerant condensing temperature of the difference between the sharply expanded. According to professional organizations, every increase of 1mm scale thickness, the end of the difference will rise 3-5 ℃, directly breaking the system design operating conditions.
In the large central air conditioning system, the end difference of every 1 ℃, the annual energy costs will increase by about 3%, this cumulative effect will be more and more significant with the extension of the operating time.
Condensing Pressure Rise
Because of the scale greatly weakened heat transfer efficiency, the refrigerant can not be completed in time to liquefy the heat dissipation. In closed refrigeration circuits, gaseous refrigerant continues to accumulate in the condenser when the condensation process is blocked.
In order to protect the system cycle, the condensing pressure is forced to continue to rise, on average, for every 0.5mm of scale, the pressure increases by 0.1-0.2MPa. This long-term high-pressure operation will force the compressor to overload, which will not only shorten the service life of the equipment, but also exacerbate the risk of lubricating oil carbonization, damage to valves and other failures.
A food refrigeration plant due to condenser fouling led to long-term pressure exceeding the standard, compressor bearing wear increased, and ultimately led to shaft seal leakage accident, resulting in production losses of hundreds of thousands of dollars.
Refrigeration Capacity Decreases Dramatically
Under the influence of scale, the heat dissipation efficiency of the condenser is seriously reduced, which directly leads to a sharp decrease of refrigerant evaporation in the evaporator. In actual operation, when the thickness of scale reaches 1mm, the cooling capacity of the refrigeration system can be reduced by 10%-15%, seriously affecting the cooling effect and production efficiency.
In the pharmaceutical cold storage and other demanding temperature control scenarios, the decline in refrigeration capacity may lead to the drug storage environment does not meet the standards, triggering quality and safety risks. In addition, insufficient refrigeration capacity will also trigger the system’s self-regulation mechanism, frequent start and stop of the compressor is more prone to mechanical fatigue, shortening the overall life of the equipment.
Sharp Increase in Energy Consumption
In order to make up for the loss of cooling capacity caused by scale and maintain the established cooling effect, the system needs to consume more electricity to drive the compressor. Studies have shown that for every 1mm increase in condenser scale, energy consumption will increase by 10-20%.
Take a medium-sized refrigeration unit with 8000 hours of annual operation as an example, when the scale is 1mm, it will consume about 50,000 kWh of electricity more every year, directly increasing the expenditure on electricity by more than 30,000 yuan. Long-term operation not only significantly increase the cost of electricity, but also exacerbate energy waste and carbon emissions.
From the macro level, if the national industrial refrigeration equipment due to fouling led to an average increase in energy consumption of 15%, will consume nearly 10 billion kWh of electricity per year, equivalent to a new medium-sized thermal power plant’s annual power generation.
Reduction in Heat Transfer Efficiency
As a poor conductor of heat, the presence of scale significantly increases the thermal resistance of the heat transfer path, resulting in a 10%-50% reduction in heat exchange efficiency.
On the one hand, the dirt layer seriously impedes the transfer of heat from the refrigerant to the outside world, forcing the system to consume additional energy to maintain the cooling effect; on the other hand, the thickening of the scale layer reduces the cross-sectional area of the heat transfer tube circulation, increases the resistance to water flow, and further worsens the performance of the cooling water cycle.
In the use of tube condenser chemical plant, when the scale blocked 30% of the pipe cross-section, the cooling water flow will drop 25%, forming a vicious circle. In addition, the rough and uneven microstructure of the scale surface also adsorbs suspended matter and microorganisms in the water, accelerating the formation of biological slime and corrosion products, further reducing heat transfer efficiency and causing equipment corrosion problems.
What is The Best Way to Prevent and Remove Scale?
Prevention
Systematic Water Treatment Program
Implementing a comprehensive water treatment strategy is the first line of defense against scale formation.
Water softening treatment: Through ion exchange resins, reverse osmosis membranes and other specialized equipment, raw water is treated in depth to reduce the concentration of calcium, magnesium and other ions in the water to the desired level.
For example, the use of sodium ion exchange resin softening method can make the hardness ions in the water and the sodium ions on the resin replacement reaction, from the source to reduce the material basis of scale generation. This method is widely used in industrial circulating water systems and can effectively reduce the risk of scale adhesion.
Precise pH value control: The pH value of circulating water directly affects the solubility of minerals and the tendency of deposition, according to the characteristics of water quality and the working conditions of the equipment, the pH value should be strictly controlled in the reasonable interval of 6.5-8.5.
When the pH value is too high, carbonate is easy to precipitate scale; pH value is too low, it may aggravate the corrosion of equipment. The pH value can be dynamically adjusted by installing pH automatic monitor, real-time feedback data and linkage of acid or alkali adding device to avoid mineral deposition caused by imbalance.
Add scale inhibitor and dispersant: Add efficient scale inhibitor and dispersant containing polyphosphate and polyacrylic acid into the water, whose molecular structure can be adsorbed on the surface of mineral crystals, destroying the normal growth of the crystals, and preventing them from aggregating to form a large scale.
At the same time, the dispersant can disperse the tiny particles that have been formed in the water to prevent them from attaching to the condenser tube wall. In practical application, the dosage should be calculated accurately according to water hardness, temperature and other parameters to ensure the best scale inhibition effect.
Regular sewage operation: according to the system design specifications for the development of sewage cycle and sewage volume, generally recommended 1-2 times a day sewage, each time the sewage volume is controlled in the system of the total amount of water 1% -3%.
Through regular sewage, can effectively reduce the concentration of minerals, suspended solids and other impurities in the water, to avoid scale precipitation due to high concentration times. During the sewage process, water conductivity indicators need to be monitored, when the conductivity exceeds the set threshold to start the sewage program in a timely manner.
Constant Monitoring and Maintenance
Ongoing monitoring can help to identify potential scale problems before they worsen, key measures are.
Regular water quality testing: Full water quality analysis is conducted at least once a week, using professional instruments such as Inductively Coupled Plasma Mass Spectrometer (ICP-MS) and Ion Chromatography to accurately determine the content of metal ions such as calcium, magnesium and iron in the water, as well as key indicators such as acidity and alkalinity, turbidity, and Total Dissolved Solids (TDS). By establishing a water quality database and comparing historical data, we can analyze the trend of water quality changes and adjust the water treatment program in time.
Routine inspection of condenser piping: Conduct a visual inspection of condenser piping once a month. An industrial endoscope can be used to penetrate deep into the piping to observe whether there are signs of white or yellowish scaling on the wall of the piping or whether there is any local color abnormality or increase in roughness. For the slight scaling area found, localized cleaning treatment is carried out in time to prevent the problem from expanding.
Temperature and pressure difference monitoring: Install high-precision temperature sensors and pressure sensors in the condenser inlet and outlet to monitor the temperature and pressure difference changes in real time.
Under normal circumstances, the temperature difference between the condenser inlet and outlet should be kept within a certain range (e.g., 5-8℃), when the temperature difference decreases significantly, it may mean that the pipe wall scaling affects the heat exchange efficiency; and the system pressure difference increases, it may be the scale clogging the pipeline resulting in increased resistance. Once abnormal fluctuations in data are monitored, it is necessary to immediately investigate the causes and take countermeasures.
Formulate a preventive maintenance program: Based on the operating hours of the equipment, load conditions and monitoring data, formulate a detailed preventive maintenance program. For example, a chemical pre-film treatment is carried out on the condenser every 1,000 hours of operation, and a comprehensive equipment inspection and maintenance is carried out once a quarter, including cleaning filters and checking valve sealing. Through regular maintenance, the equipment is kept in good operating condition and its service life is prolonged.
Installation of Automated Cleaning System
Installation of automated cleaning systems can realize the continuous protection of the condenser, common types include.
Online brush cleaning system: the system consists of a driving device, a brush carrier and a control system. During the operation of the condenser, the brush carrier carries the brushes in reciprocating motion inside the pipes and removes the adhering dirt through the friction between the bristles and the pipe wall.
The system can automatically adjust the cleaning frequency and speed according to the set program, and the cleaning work can be completed without stopping the machine, which is especially suitable for the scenarios with high requirements for production continuity.
Ball Cleaning System: Adopting elastic sponge ball or rubber ball as the cleaning medium, the cleaning ball is injected into the condenser pipe through the ball dispenser. Under the impetus of the water flow, the cleaning ball is in full contact with the inner wall of the pipe, and utilizes its own elastic deformation and friction to remove the dirt on the pipe wall. After the cleaning ball completes one cycle, it is recovered by the ball collector and can be reused. The system can be set to send the ball function at regular intervals to clean the pipe and keep the inner wall of the pipe in a clean state.
Automated chemical dosing system: It consists of dosing pump, controller and chemical storage tank. Through the real-time feedback data from the online water quality monitoring instrument, it automatically calculates and accurately controls the dosage and time of chemical agents such as scale inhibitor, corrosion inhibitor and biocide.
For example, when the hardness ion concentration in the water is monitored to increase, the system automatically increases the dosage of scale inhibitor; when the water temperature rises, the frequency of corrosion inhibitor is appropriately adjusted to ensure the effectiveness of pharmaceutical treatment while avoiding the waste of pharmaceuticals and environmental pollution.
Cleaning
Chemical Cleaning
Chemical cleaning involves the use of specific acidic or alkaline solutions to dissolve and remove dirt. For example, an appropriate amount of acidic cleaning solution can be added to the cooling water system, and a circulating pump is activated to keep the cleaning solution flowing for 12 to 24 hours, during which time the pipe walls are continuously flushed until the dirt is completely removed.
The solution is then neutralized with an alkaline solution to ensure that all residual chemicals are rinsed away. Although chemical cleaning is effective in removing stubborn stains, it may cause minor corrosion of copper tubes and the resulting waste solution needs to be disposed of properly to avoid environmental contamination.
Physical Cleaning
Physical cleaning is the use of mechanical means of direct action on the surface of the dirt, such as the use of flexible shaft brush cleaning technology. The method relies on high-speed rotating nylon brushes deep inside the condenser copper tube, through friction to strip the adhesion, and finally rinsed with water.
This method eliminates the need to add chemicals, reducing the impact on the environment while avoiding the risk of potential metal corrosion. However, for particularly hard or tightly adhered layers of scale, it may be difficult to achieve the desired results by relying on physical cleaning alone. At this point, you can consider implementing chemical pretreatment before following up with physical cleaning steps to improve the overall cleaning efficiency.
Electronic Descaling
Electronic descaling method is the use of electronic equipment generated by the high-frequency electromagnetic field or electrostatic field, change the water calcium, magnesium and other ions of the crystallization habit, so that it can not form a hard scale, but with tiny particles suspended in the water, along with the water discharge.
After the installation of electronic descaling device, no downtime can continue to work, does not affect the normal operation of the condenser, and no chemical pollution, no corrosion of the equipment. However, the electronic descaling method is more focused on the prevention of scale generation, for the formation of thicker scale, the removal effect is limited, usually as an auxiliary means with other cleaning methods used in conjunction.
Ultrasonic Cleaning
Ultrasonic cleaning is the ultrasonic transducer generated by high-frequency vibration energy transferred to the water, the formation of countless tiny cavitation bubbles in the water, these bubbles in the instantaneous rupture of a strong impact, can break the condenser surface scale, so that it is detached from the surface of the equipment, discharged with the water flow.
Ultrasonic cleaning can realize non-contact cleaning, no damage to the equipment, especially suitable for cleaning complex structures, difficult to reach parts of the scale. However, the cost of ultrasonic cleaning equipment is relatively high, and requires specialized personnel to operate and maintain.
Other Common Problems and Solutions in Condenser
Air Leakage
In addition to the common sources of leakage such as turbine seals, expansion joints and penetrations, the complex internal structure makes it often time-consuming and costly to pinpoint leaks. It is important to note that excessive air intrusion not only directly pushes up the condensing pressure, but may also have a compounding effect on the condenser’s own defective configuration, increasing the burden on the system’s operation.
At this point, with the help of professional instruments that can directly measure the gas parameters of the exhaust pipe, the precise quantification of air leakage becomes a prerequisite for the formulation of an effective response.
High Condensing Pressure
High condensing pressures are one of the central causes of reduced plant efficiency and increased risk of downtime, and can be caused by a combination of air leakage, areas of air blockage in the system, underperformance of the vacuum equipment, or fouling of the heat exchanger surfaces. This problem is directly manifested by a reduction in power generation or a surge in fuel consumption, resulting in significant economic losses.
In this case, it is wise to seek professional services to conduct a comprehensive analysis of the condenser configuration, optimize the design and adjust the parameters to restore the system’s load capacity and reduce the back pressure for efficient operation and maintenance.
Dissolved Gas and Corrosion
Corrosion caused by dissolved gases should not be ignored. Oxygen and other gases dissolved in the water will continue to erode the condenser tube, tube plate and related components, affecting the service life of the equipment and operational safety.
It is important to note that high dissolved oxygen levels are not always directly related to severe air leakage. Inadequate degassing due to defective condenser configuration design can also be a significant contributing factor, and therefore structural modifications and functional optimization are required.
Maintenance, Cleaning and Operation
During routine maintenance and operation management, the overall performance of the plant may be affected by low heat transfer efficiency, even after routine overhauls. This can occur in the case of small air leakage and normal pumping capacity, and is often due to the system being operated at high back pressure for a long period of time and low heat transfer coefficients.
To solve this problem, a step-by-step condenser performance assessment is required: first, the design parameters are verified and compared with the original configuration to pinpoint the problem; at the same time, the condenser tubes must be cleaned on a regular basis, and the cleanliness of the surface is quantitatively assessed by calculating the cleanliness coefficient (i.e., the ratio of the actual heat transfer coefficient to the percentage of the HEI-specified design coefficient), which provides a scientific basis for the maintenance work and ensures that the system is always operating efficiently.
Conclusion
Condenser scale is formed by mineral deposits in water, accumulation of biological sludge and temperature changes, and is mainly composed of calcium carbonate and magnesium hydroxide. It seriously affects the performance of the equipment, leading to the rise of the end difference, increase in condensing pressure, decrease in refrigeration capacity, increase in energy consumption and decrease in heat transfer efficiency, resulting in economic losses and energy waste.
In daily maintenance, regular cleaning, performance evaluation and preventive measures are the key to ensure efficient and stable operation of the condenser, prolong life and reduce costs.
