Operation | Rasert™
PRINCIPLES of OPERATION When the combustion air enters the 4748 RASERT™ burner, it is split into primary and secondary air streams. The primary air, which is approximately 25% of the total air, is combined with all of the fuel and is used to induce FGR (flue gas recirculation) from the flue. This air/fuel/FGR mix then travels down a tube in the center of the burner‘s integrated recuperator towards the flame stabilizer. The secondary air stream also induces and mixes with FGR in the burner body. It travels down the outside of the recuperator towards the flame stabilizer. The integrated recuperator preheats the combustion air, fuel and FGR with heat recovered from the waste flue gas as it travels in the annular gap between the primary air tube and the outer wall of the recuperator casting. The actual secondary air preheat achieved is dependent on the application, but it is generally over 1100°F in furnaces running at 1600°F. When the primary air (with added fuel and FGR) and second- ary air reach the stabilizer they are reintroduced and ignited in the annular space around the combustion tube and inside the stabilizer can. The stabilizer is designed to delay some of the combustion so the flame can be spread out along the length of the radiant tube, which helps provide uniform temperature distribution. When the products of combustion reach the end of the radiant tube they enter the center combustion tube and travel back towards the recuperator and burner. When the flue gas reaches the burner body some of it is used as FGR and the rest exits through the flue outlet. PREHEATED AIR The level of preheated combustion air is a major determining factor in the overall efficiency of a radiant tube combustion process. The higher the combustion air preheat the higher the efficiency and the greater the fuel savings. At the combustion air preheat levels in the figure below, the combustion efficiency ranges from 62-69% based on the higher heating value of the fuel. This increased efficiency results in fuel savings of up to 50% compared to conventionally fired ambient air burners.
The temperature of the preheated air generated by an internal recuperator is dependent on the flue gas temperature and flow, and the design of the heat exchanger element. The air in the 4748 RASERT burner is split into primary and secondary streams, that travel in separate paths through the heat exchanger elements. Approximately 75% of the air travels around the outside of the heat exchanger in the secondary air stream. The graph below shows a typical relationship of the secondary air temperature to the average radiant tube temperature, where the burner is operating at 16 osi air pressure with approximately 3% O 2 in the flue gas exiting the burner.
1050 1100 1150 1200 1250 1300
1500
1600
1700
1800
1400
Average Radiant Tube Temperature °F
CONSTRUCTION The burner body is constructed of sturdy ductile iron, and in- cludes a built-in V-port fuel adjustment plug, observation ports, a flanged air connection, and built-in air and gas meters. The recuperator is made from a series of high temperature alloy investment castings, as is the stabilizer.
Bulletin 4748 Page 3
Made with FlippingBook flipbook maker