Air Preheating System APH
Air Preheating System APH


Air Preheating System APH

By means of the system the combustion air is preheated and the flue gas temperature is reduced. The efficiency is increased.

  • For increased system efficiency and reduced fuel consumption of up to 2%
  • Prewarming of the combustion air takes over a small portion of the thermal output of the burner
  • Lower investment costs in comparison with conventional solutions, low amortisation time
  • Lower maintenance and servicing costs


  • When installing new steam boiler systems with economisers, air preheating is the ideal solution for increasing efficiency, particularly in cases where the integration of a flue gas condenser is impractical for process reasons.
  • The Bosch air preheating system is available for single or double flame tube boilers with duoblock burners. The system is economically viable from a boiler capacity of around five tonnes of steam per hour. The fan can be installed on the top of the boiler; this means that the compact system requires little space for installation. Return-on-investment (ROI) is generally achieved after 1.5 to 2 years.

In the Bosch system, a part of the heated feed water flow is utilised for increasing the temperature of the combustion air. The hereby cooled feed water increases efficiency by further reducing the flue gas temperature in the downstream economiser.

Equipment level

The air preheating system consists of three-way valve, a combined flue gas heat exchanger and an air-side heat exchanger. In comparison with conventional two-circuit systems, it is now possible to omit the circulation pump, the expansion vessel and various electronic safety and control systems. In turn, this reduces not only investment costs, but also the recurrent costs for maintenance and replacement parts.