The economizer is an energy-saving device that preheats boiler feedwater by recovering waste heat from the tail flue gas of the boiler. Its working principle and function are as follows:
1、 Working principle
1. Heat exchange process
High temperature flue gas (usually 250-350 ℃) flows outside the serpentine tube bundle of the economizer, and boiler feedwater flows in the opposite direction inside the tube, absorbing heat from the flue gas through the tube wall and raising the water temperature to near saturation temperature (some designs allow partial boiling of water). The flue gas temperature drops to 100-150 ℃ before being discharged.
  •  Reverse flow design: Smoke and water flow in reverse to maximize heat transfer temperature difference.
  •  Material selection: commonly used carbon steel pipes (with fins for enhanced heat transfer) or cast iron pipes (for low-pressure boilers).
2. Operation protection mechanism
During the start-up phase, the water flow is maintained through a recirculation pipeline to prevent local overheating and vaporization; Automatically cut off the water flow during shutdown to avoid dry burning of the empty pipe.
2、 Core role
1. Energy saving and efficiency improvement
  •  Reduce the exhaust temperature by more than 100 ℃, reduce heat loss by 5% -15%, and save more than 10% of fuel consumption.
  •  After preheating the feedwater, the load on the evaporation heating surface is reduced, and the boiler thermal efficiency is increased to over 90%.
2. Equipment protection and optimization
  •  Reduce the temperature difference between the inlet water of the steam drum, lower thermal stress, and extend the service life of the equipment.
  •  Replace some evaporative heating surfaces (such as convection tube bundles) to reduce manufacturing costs.
3. Environmental protection and emission reduction
  •  Low temperature flue gas reduces the generation of nitrogen oxides and improves the subsequent desulfurization and denitrification efficiency.
  •  Ash content is partially retained in the tube bundle, reducing the burden on purification facilities.
4. Operational stability
The recirculation system and anti ash design (such as finned tubes) ensure continuous operation and avoid local overheating or blockage.
5. Expand application scenarios
In addition to coal-fired boilers, it has been promoted to power plants, pharmaceuticals, petrochemicals and other fields, becoming a key component for waste heat recovery.