Chemical process fired heaters, furnaces or boilers

A chemical process plant incorporating a gas turbine, means for utilising the sensible heat of the gas turbine exhaust (GTE) and a fuel-fired heater including a radiant heating section, fuel being burnt in said radiant section for the purpose of heating therein process-fluid contained in a least one process coil, a heat recovery section being provided in the flue of the heater and containing one or more coils containing heat recovery fluids, wherein the improvement comprises a two-channel heat exchanger (20) having a first channel (21) connected between the gas turbine exhaust (9) and an auxiliary gas exhaust means and having a second channel (22) of the heat exchanger connected between a source of fresh air and the fuel-oxidizing medium input (3) of the radiant section of the heater, said heat exchanger (20) thereby supplying heated fresh air to said radiant section at substantially atmospheric pressure, and including a first burner (26) in said flue (6) and a bypass duct (24) connected between the output of the second channel of the heat exchanger and the first burner (26) for conveying surplus heated air from the heat exchange (20) to the first burner (26) for the purposes of supporting combustion therein, said first burner having a further duel supply, (27) and including controllable valve means (28) in said bypass duct for controlling the flow of fluid therein.