A. FD fanB. Steam air warmerC ScrubberD. Air heater
A...FD fan. I've worked with boilers and furnaces for many years. An air preheater has never been included with air intake heated by flue gas. Air and flue gases are controlled by Four methods... 1...Natural Draft...air intake for both Primary combustion air and air flow through the furnace controlled by air inlet 'doors' around the burner 'Throat' and flue gas dampers to the stack maintaining a slight positive pressure (Inches of water gauge draft) within the furnace. 2...Forced draft where air is fed by a fan into the system and flue gases controlled by a damper. 3...Induced Draft. flue gases are pulled out by a fan and exhausted to the stack. Air inlet doors or dampers control the draft and combustion air at the burner end. 4...Balanced Draft. Here, an air inlet and a flue gas exhaust fan are incorporated. Draft and Combustion air are controlled by dampers to 'Balance' the draft. In each case, air supply to the burners and the draft through the furnace are carefully controlled for optimum performance and combustion profiles. Keep your thumb where it belongs...!!
Air preheater. This takes the hot flue gas and uses a heat exchanger to heat up the fresh air to the burner before combustion. Therefore less fuel is required to make the same heat output. Also less emissions. Typical eff improvement of 6-10 percent.
