Duct Burners are usually used in combined cycle and they can work either with fresh air (when gas turbine is turned off) or exhaust gas. For this reason they are made from stainless steel in order to resist to the high temperature inside the duct (up to 500 °C).
Critical conditions at the gas turbine discharge (gas flow rate, temperature, stream vorticity and duct lay – out) often require a CFD study, to provide the best solution and guarantee the best performance in terms of operating, maintenance and expected life of the combustion system.
Duct Burners are generally provided in several rows depending of the thermal power required and the general duct arrangement.
Each row is completely filled by stainless steel baffles, which have a modular design that ensure the mixing between gaseous fuel and flue gas or fresh air; such baffles are fixed on gas distributor by screwed nozzles also made from stainless steel.
Fuel gas is injected through a fuel gas distribution tube, equipped with a set of the above mentioned nozzles. Each “multi jets” nozzle injects the fuel gas inside the combustion chamber.
Each distributor is supported by a carbon steel front plate which is flanged to the duct wall. The front plate has also the support for flame scanner and pilot igniter.
This system guarantee a wide turndown range (10 : 1 for each row) and low pollutants production.