What additional heat is contributed after the economizer in a CFB?

Prepare for the 3rd Class Power Engineering (3B1) Exam. Study with flashcards and multiple choice questions, each question has hints and explanations. Get ready for your exam!

The correct answer relates to the operation of a Circulating Fluidized Bed (CFB) boiler, specifically the role of the economizer and how heat transfer occurs in this type of system. In a CFB boiler, the economizer’s primary function is to recover residual heat from the flue gases before they are discharged into the atmosphere, thus increasing overall efficiency.

After the economizer, the heat contribution from a secondary bed fed from the main cyclone is significant. This secondary bed can utilize tapped-off hot flue gases to enhance the combustion process by raising the temperature of the bed material, which leads to improved combustion efficiency and further heat recovery within the system. This not only optimizes the fuel combustion process but also ensures that more usable heat is extracted from the combustion gases.

The other options do not directly pertain to the additional heat contribution after the economizer. Excess combustion air, while important for achieving complete combustion, does not specifically add heat in the same way that recirculated bed material does. A scrubber system is focused on emissions control rather than heat generation, and a water recirculation system primarily relates to regulating temperatures and maintaining appropriate water levels, thus not directly contributing additional heat in this context.

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