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.
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.