Application of flue gas PHE in thermal power generation industry

In thermal power plants, flue gas desulfurization (FGD) and flue gas denitrification (SCR/SNCR) are important environmental protection measures to control sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) emissions. Flue gas plate heat exchangers (flue gas plate heat exchangers) mainly play the role of flue gas heat exchange, temperature control, energy saving and consumption reduction in these systems, and optimize the desulfurization and denitrification effects.

1. The role of flue gas plate heat exchanger in the desulfurization system (FGD)

1.1 Reduce flue gas temperature and improve desulfurization efficiency

The desulfurization process (such as the wet limestone-gypsum method) requires the flue gas temperature to be reduced to 45~65℃ to improve the absorption efficiency of the desulfurization absorption tower.

The flue gas plate heat exchanger recovers the heat of the high-temperature flue gas (about 120~180℃) and transfers it to the air or other process gas entering the boiler, so that the flue gas is cooled to a temperature suitable for desulfurization.

1.2. Energy saving and consumption reduction, improving system thermal efficiency

Through the waste heat recovery of the flue gas plate heat exchanger, the air preheater (APH) or boiler inlet air temperature is increased, and the boiler fuel consumption is reduced.

Some systems use a combination of GGH (flue gas heat exchanger) + flue gas plate heat exchanger, first using GGH to initially recover heat, and then using the plate heat exchanger to finely adjust the temperature.

1.3. Prevent low-temperature corrosion and condensation

After wet desulfurization, the water content of the flue gas increases, which is prone to acid dew point corrosion (acid dew point temperature is about 120℃).

The flue gas exchanger reheats the flue gas at the FGD outlet to make the discharge temperature higher than 80~90℃, preventing condensation and corrosion on the chimney and flue inner wall.

1.4.Typical application diagram:

High temperature flue gas (boiler outlet) → flue gas exchanger (cooling to suitable for desulfurization) → desulfurization tower → flue gas exchanger (heating to prevent corrosion) → chimney discharge

2. The role of flue gas exchanger in denitrification system (SCR/SNCR)

Flue gas denitrification is mainly divided into selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). The roles of flue gas exchanger are as follows:

2.1.Control the flue gas temperature at the SCR inlet to improve the denitrification efficiency

The optimal reaction temperature of SCR is 300~400℃. Temperatures above this may damage the catalyst, and temperatures below this will reduce the denitrification efficiency.

The flue gas exchanger is used to heat or cool the flue gas, adjust the temperature to the optimal range, and improve the denitrification efficiency.

2.2.Recover waste heat and improve energy utilization

Flue gas plate heat exchanger can recover the heat of high-temperature flue gas for air preheating, steam heating or boiler feed water preheating, thereby improving energy utilization.

Some SCR systems are equipped with low-temperature economizer (LPE) + flue gas plate heat exchanger to improve boiler efficiency.

2.3. Prevent low-temperature catalyst poisoning and condensation

SCR catalysts are sensitive to dust and sulfides and are prone to clogging or failure at low temperatures. Flue gas plate heat exchanger is used to maintain a suitable temperature to prevent condensation from contaminating the catalyst.

Typical application diagram: high-temperature flue gas (boiler outlet) → flue gas plate heat exchanger (adjusted to the optimal denitrification temperature) → SCR reactor → flue gas plate heat exchanger (recover waste heat) → desulfurization tower

3. The role of flue gas plate heat exchanger in the combined desulfurization + denitrification system

In the combined flue gas treatment system of "SCR denitrification + FGD desulfurization", flue gas plate heat exchanger is usually used at the following key points:

3.1.Before SCR inlet: adjust the flue gas to the optimal denitrification temperature (300~400℃).

3.2.Before the desulfurization tower: cool down to a temperature suitable for desulfurization (45~65℃).

3.3.After the FGD outlet: heat to 80~90℃ to prevent acid dew point corrosion and reduce the "white smoke" phenomenon.

4. Advantages of flue gas plate exchange

Efficient heat exchange: Compared with traditional heat exchangers, plate heat exchangers have higher heat transfer efficiency, which can reach more than 90%.

4.1.Compact structure: small footprint, suitable for power plant transformation and upgrading.

4.2.High temperature corrosion resistance: stainless steel, titanium alloy, nickel-based alloy or anti-corrosion coating can be selected to adapt to high temperature corrosion environment.

4.3.Easy maintenance: detachable structure, easy to clean and replace plates.

5.Summary

In the flue gas desulfurization and denitrification system of thermal power plants, the functions of flue gas plate heat exchangers include:

5.1.Lowering the desulfurization inlet temperature (45~65℃) and improving absorption efficiency

5.2.Raising the flue gas temperature after desulfurization (80~90℃) to prevent acid dew point corrosion

5.3.Optimizing the SCR denitrification temperature (300~400℃) and improving the NOₓ removal rate

5.4.Recovering waste heat, improving boiler efficiency, and reducing energy consumption