The Culprit Behind “Clogged Arteries” in Thermal Oil Heaters: Causes of Coking and Solutions

In industrial production, thermal oil heaters https://8ruiyan.com/en/all-organic-heat-carrier-boilers/act like the heart of a system, pumping heat to production lines. The thermal oil is the “blood” flowing through it. However, a common and tough problem—”coking”—is like a blood clot in the arteries. It seriously affects system health, leading to surging energy costs, equipment damage, and even safety incidents. Let’s explore the causes of coking in thermal oil heaters and provide a complete set of solutions.

1. What is Coking? What are its Hazards?

Coking refers to a phenomenon where thermal oil undergoes chemical changes at high temperatures. It produces insoluble substances like polymers, gums, and carbides. These substances stick to the inner walls of the heater tubes and the system.

The hazards of coking are serious:

1. Sharp increase in energy consumption: The thermal conductivity of coke scale is much lower than metal pipe walls. It creates an insulating layer, reducing heat transfer efficiency and significantly increasing fuel consumption.
2. Equipment damage from overheating: Heat cannot be carried away by the oil in time. This causes local overheating of the heater tubes, leading to bulging, rupture, leaks, and fire.
3. Blocked system flow: Severe coking reduces the flow area in pipes. This increases the pump’s workload and can even block pipes completely, shutting down the system.
4. Early failure of thermal oil: Coking means the oil has severely degraded. It must be replaced, raising operating costs.
5. Major safety risks: Heater tube rupture is one of the most serious accidents in a thermal oil system.

2. Identifying the Real “Culprits”: Main Causes of Coking

Coking doesn’t happen without cause. It’s usually the result of several factors working together:

1. Poor Quality or Incorrect Selection of Thermal Oil

• Poor thermal stability: Low-quality oil, or oil not rated for the temperature, breaks down and forms polymers easily at high temperatures. This quickly leads to coking.
• Poor oxidation resistance: When exposed to air, the oil oxidizes. This produces organic acids and sludge, which are precursors to coking.

2. Localized Overheating – The “Catalyst” for Coking

• Design flaws: The furnace heat load may be too high. Or the oil flow rate may be too low. This causes the oil to stay in the tubes too long, making its temperature soar.
• Improper operation: Heating up too quickly during startup, or running with low flow (e.g., pump failure, valve mistakenly closed) causes localized overheating.
• High surface load on electric heating elements: In electric heaters, if the surface temperature of the elements is too high, the oil touching them will coke rapidly.

3. Oxidation – The Invisible “Slow Poison”

• No nitrogen blanketing on the expansion tank: The thermal oil in the expansion tank contacts air for a long time. It oxidizes, producing sticky polar substances that eventually form gums and coke.
• Leaks in the system: Air can be drawn into the system at negative pressure points, causing oxidation.

4. Contamination and Impurities – The “Seeds” of Coking

• New oil not properly dehydrated and degassed: New oil or added make-up oil contains water and light components. These vaporize at high temperatures, causing pressure fluctuations. They can also lead to hydrolysis and violent boiling, speeding up oil degradation.
• Internal system contaminants: Residue like welding slag, rust, or sand left from installation or maintenance can act as cores for coking, promoting coke growth.

3. Prevention is Key: Comprehensive Solutions and Preventive Measures

Solving the coking problem requires a principle of “Prevention first, combined with treatment.”

Solution 1: Strict Control of the Oil – Choose Well, Use Well

• Correct selection: Choose high-quality thermal oil with excellent thermal stability and oxidation resistance. Base this on the system’s maximum operating temperature, with a sufficient safety margin.

Solution 2: Optimize Operation and Process – Precise Management

• Strictly control temperature: Avoid operating above the temperature limit. The oil temperature at the heater outlet should be at least 20°C below the oil’s maximum use temperature.
• Ensure safe flow velocity: Maintain turbulent flow in the heater tubes (typically designed for 1.5-3.0 m/s). This provides enough scouring force to prevent impurity deposition and boundary layer overheating.
• Standardize startup/shutdown procedures: Follow the rule “pump first, then heat, warm up slowly” at startup. Let the oil circulate fully before gradually heating. During shutdown, let the oil cool to a safe temperature before stopping the pump.

Solution 3: Eliminate Oxidation Sources – “Mask” the System

• Use a nitrogen blanket system: Purge the expansion tank with nitrogen to隔绝空气. This is the most effective way to prevent oxidation.
• Ensure system tightness: Regularly check the system, especially pump seals and valves, to prevent air ingress.

Solution 4: Keep the System Clean – Start from “New”

• Thorough cleaning and purging: New equipment or equipment after major repair must be rigorously cleaned and purged to remove all contaminants.
• Adequate dehydration and degassing: After adding new oil or a major oil change, follow operating procedures. Heat gradually to two stages: 95-110°C and 210-230°C. This fully removes water and light components.

Solution 5: When Coking Already Exists – Professional Cleaning
If coking is already present, professional cleaning is necessary:

• Chemical cleaning: Use special cleaning agents to circulate and dissolve/remove coke scale. This method is effective but requires technical expertise. Use qualified service providers and dispose of waste properly.
• Physical cleaning: For severely blocked single tubes, methods like high-pressure water jetting or mechanical descaling can be used.

Wnioski

Coking in thermal oil heaters is a systemic problem. It silently erodes profits and safety. By understanding its causes and establishing a complete management system, we can effectively control coking. This system includes correct oil selection, standardized operation, nitrogen blanketing, regular monitoring, and professional maintenance.

This ensures the thermal oil heater system runs long-term, efficiently, and safely. Remember, every bit of careful attention given to the thermal oil heater translates into visible economic benefits and solid safety assurance.

For further consultation, please contact our technical team for expert advice.

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