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High-Efficiency Plate Exchangers: Flue Gas Heat Recovery Made Durable

Release time:

2025-03-03

Through efficient heat transfer structure and corrosion resistance design, the flue gas plate heat exchanger realizes waste heat recovery and precise temperature control of high temperature flue gas.

1. Waste heat recovery mechanism

a. Principle of heat exchange

Convection + conduction heat transfer: high-temperature flue gas (200~600℃) and cold media (such as water, air, process fluid) flow in reverse on both sides of the plate, and turbulent heat transfer is enhanced through the corrugated plate, and the heat recovery efficiency can reach 70%~90%.

Sensible and latent heat recovery:

Sensible heat recovery: directly reduce the temperature of the flue gas (such as from 400 ° C to 150 ° C), and the heat energy is used to preheat the combustion air or the boiler water supply.

Latent heat recovery: If the flue gas contains steam (such as after wet desulfurization), it can be condensed to release the latent heat of vaporization, and increase the energy efficiency by 10% to 15%.

b. Typical process flow

Steel industry:

Sintering machine flue gas (300~450℃) → plate heat exchanger → preheating sinter or power generation (waste heat boiler).

Power industry:

Coal boiler exhaust → heat exchanger heating condensate → reuse to steam turbine thermal system, reducing coal consumption by 1.5%~3%.

c. Technological advantage

High heat transfer coefficient: 5000~8000 W/(m²·K), which is 3~5 times that of shell and tube heat exchanger.

Compact: Unit volume heat exchange area of 250m²/m³, saving more than 50% of installation space.

2. Flue gas temperature regulation method

a. Cooling control (e.g. pre-desulfurization)

Cold medium selection:

Water cooling: The flue gas is reduced from 300 ° C to 160~180 ° C by circulating water (to meet the inlet requirements of the desulfurization tower).

Air cooling: used in water-scarce areas, but the efficiency is low (temperature difference > 100℃).

Multi-process design: The flue gas side is divided into 2 to 3 processes, cooling step by step to avoid thermal stress impact.

b. Temperature control (e.g. flue gas reheating after denitrification)

Anti-corrosion design: After desulfurization, wet flue gas (50~60℃) contains SO₃, HCl, which needs to be fully welded titanium plate or fluoroplastic coated plate.

Heat source selection:

Steam heating: The use of low-pressure steam (0.3~0.5MPa) to heat the flue gas to more than 80 ° C to prevent chimney corrosion.

Hot air mixing: mixed with high temperature bypass gas, high adjustment flexibility but high energy consumption.

c. Dynamic regulation technique

Frequency conversion fan: automatically adjust the flow rate of cold media according to the flue gas flow, and maintain the outlet temperature fluctuation of ±5℃.

Bypass control: Part of the flue gas bypasses the heat exchanger to quickly respond to load changes (adjustment time < 10 minutes).

3. Key design considerations

Ash resistance and ash removal

Flow channel optimization: plate spacing of 8~12mm, flue gas flow rate of 1.5~2.5m/s (lower than the settling speed).

Ash removal device:

Online pulse ash blowing: every 8 hours automatically spray compressed air to remove floating ash on the surface of the plate.

Mechanical vibration: suitable for viscous ash (such as tar), need to stop operation.

Through material innovation, flow path optimization and intelligent control, the flue gas plate heat exchanger realizes efficient recovery of waste heat and accurate temperature regulation, and is the core equipment of industrial energy saving and carbon reduction. When selecting, it is necessary to integrate the change of flue gas composition, heat load and maintenance cost, and prioritize the modular design to adapt to the fluctuations of working conditions.