Gas to Gas Heater (GGH)
Gas gas heater (GGH) is a heat exchanger used in power plants to heat treated flue gas (40-50℃) with raw flue gas (130-150℃) in the FGD system. GGH plays a dual function: flue gas cooling and reheating.
Operation
Raw flue gas is cooled down by the GGH. If hot flue gas enters the FGD tower, it would damage the anti-corrosion coating inside the tower. Lower temperatures also improve the absorption of SO2. Treated flue gas is reheated by the GGH, leaving at a higher temperature (about 80℃).
Benefits
- Enhanced diffusion of contaminants in flue gas.
- Better plume abatement performance with higher plume rise from the stack.
- Fewer droplets falling near the stack.
- Reduced corrosion to downstream equipment.
Types
Gas to Gas Heaters have different designs.
- Rotary GGH: A counter-flow, regenerative heat exchanger. Heating elements rotate and travel through raw gas passage and treated gas passage alternatively. When hot flue gas passes through the rotor, heat is transferred to the heating elements, then released to cold treated gas when elements move to the raw gas passage. It has a similar structure and principle to a rotary APH but works at a much lower temperature.
- The heating elements must resist dew point corrosion. A good sealing system is required to avoid raw flue gas leakage into treated flue gas. Entrained flue gas is replaced with air to ensure leakage is less than 1.0%.
