Fin tube preheater in the urea chemical industry

In urea chemical production, the energy consumption of granulators mainly focuses on air heating, atomization of urea molten liquid and fluidized bed operation, etc. The finned tube preheater can significantly reduce energy consumption and improve energy utilization efficiency by optimizing the heat exchange process. The following are the specific mechanisms of action and optimization directions:

1. Efficiently recover waste heat and reduce primary energy consumption

There is a large amount of waste heat in the urea production process (such as boiler flue gas, residual heat from process condensate, steam condensate water, etc.). The finned tube preheater can efficiently recover these low-grade heat energies and be used to preheat the air or process medium required for the granulator.

1.1. Utilization of Waste heat from Boiler Flue gas

1.1.1.The flue gas temperature discharged from the coal-fired/gas-fired boilers that are part of the urea plant is usually between 150 and 250° C. In traditional processes, this part of the heat is directly discharged, resulting in waste.

1.1.2.By using finned tube air preheaters (such as H-shaped finned tubes or spiral finned tubes), the residual heat of the flue gas can be transferred to the air entering the granulator, preheating it from room temperature (20~30°C) to 80~100°C, reducing the load of subsequent electric heating or steam heating.

1.1.3.Case data: After a certain urea factory adopted the finned tube flue gas waste heat recovery system, the steam consumption for air heating in the granulator was reduced by 15% to 20%.

1.2. Recovery of waste heat from process condensate

1.2.1.The condensate produced in the urea evaporation section (~90°C) is usually directly cooled, but the granulation air can be preheated through a finned tube heat exchanger to improve the utilization rate of thermal energy.

1.2.2. Optimization effect: If the initial air temperature is raised to 60°C, the energy consumption for subsequent heating to the granulation temperature (130°C) can be reduced by more than 30%.

2. Enhance heat exchange efficiency and reduce steam or electrical energy consumption

The core advantage of the finned tube preheater lies in expanding the heat exchange area and enhancing heat transfer, thereby reducing the consumption of the heating medium.

2.1. Comparison with traditional smooth tube heat exchangers

Parameters	Smooth tube heat exchanger	finned tube heat exchanger (Spiral/Sawtooth fin)
The heat exchange area ratio  (of the same volume)	1×	5 ~10×
Heat transfer coefficient (W/m²·K)	30-50	80-150
The increase in air preheating temperature	low (~50°C)	high (~100°C)

• Energy-saving effect: Under the same heat load, the finned tube preheater can reduce steam or electricity consumption by 20% to 30%.

2.2. Specific calculation for reducing steam consumption

2.2.1. Air heating requirements for urea granulation:

Air flow rate: 10,000 Nm³/h

Heating temperature: 20°C → 130°C

The heat required: Q = m·Cp·ΔT ≈ 1.3 MW

2.2.2. After adopting the finned tube preheater:

If waste heat is used to preheat the air to 80°C, then only 50°C (80→130°C) is required for subsequent heating, the heat load is reduced to 0.5 MW, and energy is saved by 61.5%.

If steam heating (0.4 MPa saturated steam with a calorific value of ~2100 kJ/kg) is adopted, the steam consumption decreases from 2.23 t/h to 0.86 t/h, and the annual steam savings are ~10,000 tons (calculated based on 8,000 hours per year).

3. Optimize the fluidized bed granulation process to reduce ineffective energy consumption

The fluidized bed of the urea granulator requires a stable temperature (~130°C) to ensure uniform particle formation. The finned tube preheater can reduce temperature fluctuations and lower the additional energy consumption caused by unstable processes.

3.1. Reduce the "supercooling - reheating" cycle

• Problem: Unpreheated cold air entering the granulator may cause local cooling of urea droplets, forming fine powder or lumps, which requires additional heating for adjustment.

Solution: The finned tube preheater ensures that the air temperature remains stable above 100°C, reduces temperature fluctuations within the granulation bed, and lowers the energy consumption for repeated heating by 5% to 10%.

3.2. Reduce the power consumption of the fluidizing fan

After preheating, the density of the air decreases (volume expands), and the power of the fan can be reduced by 3% to 5% under the same mass flow rate (according to the ideal gas law, PV=nRT).

4. Future optimization direction: Further enhance energy efficiency

4.1. Adopt an efficient fin structure

• Spiral finned tubes: Increase turbulence and enhance the heat transfer coefficient.

• Corrugated finned tubes: Enhance airflow disturbance, reduce ash accumulation, and are suitable for recovering waste heat from dusty flue gas.

4.2. Intelligent temperature Control system

Combined with the PLC/DCS control system, the preheating temperature is dynamically adjusted to match different granulation loads and avoid excessive heating that wastes energy.

4.3. Multi-stage heat recovery system

• First stage: Preheat the flue gas from the boiler to 80°C.

• Second stage: The process condensate is further heated to 100°C.

The final electric/steam heating only requires a 30°C temperature difference to be supplemented, maximizing the utilization of waste heat.

5. Conclusion

The finned tube preheater significantly improves the energy utilization efficiency of the urea granulator through a triple mechanism of waste heat recovery, enhanced heat exchange and process optimization. The typical energy-saving effect can reach 20% to 40%. In the future, by integrating intelligent control with new fin technology, its energy-saving potential will be further unleashed, helping the urea industry achieve its carbon neutrality goal.

Related Links:

The Application of Finned Tube Heat Exchangers in Granulation enterprises

Finned tube heat exchangers in the power industry

Finned tube heat exchangers in the petrochemical industry