Treatment equipment and furnaces
FIB Combustion Technology: a unique solution out of the box!
Air/gas separated or nozzle mixed burners: limitation in the control of air / gas ratio
Nozzle mixed burners, eventually combined with self recuperation system, have been applied since many years.
However, these burners are limited to work on “on-off” mode when the control of the air/gas becomes an issue.
Indeed, if the regime of this type of burner needs to be modulated, the factor related to the difference of pressure drop in the nozzle between the air pipe and the gas pipe will disturb the air/gas ratio.
This means that the final atmosphere in the furnace will change depending on the level of modulation of the burners of the zone.
The recovery of a correct air/gas ratio can be tuned only by adapting manually and per burner, the pressure drop of both the air and gas conducts. This manual adjustment (usually made with a screw) will be a substantial job if several burners are heating the same zone and is only valid for the specific air/gas ratio at that moment as it will vary with the modulation of the zone.
On top of that, if one burner of the zone is stopped, the readjustment of each burner of the zone has to be considered.
The importance of this adjustment of the air/gas ratio is strongly related to both the efficiency of the combustion and the composition of the burned fume gas in contact with the products processed in the thermal equipment.
The curves here below show the combustion efficiency depending on the air/gas ratio and the exit temperature of the fume gas.
Specifically, nozzle mixed burners have the tendency to go to reducing conditions on low fire.
This means that any change in the air/gas ratio has substantial consequences on the running costs of the thermal equipment especially for nozzle mixed burners that go to reducing combustion on low firing (see examples in the table).
For instance, for a useful power of 835 kW with a temperature of 1.100°C, and in case of excess of air, a 1940 kW is needed and in stoichiometric conditions, only 1.740 kW, i.e. 11,6 % of energy saving.
Temperature
[°C]
Lack of air (10%)
efficiency [%]
Stoichiometric
efficiency [%]
Excess of air (10%)
efficiency [%]
700
60
69
67
900
50
58.5
55
1100
40
48
43
The reducing (lack of air) or oxidizing (excess of air) atmosphere can also have consequences on the treated product or on the aging of the insulation materials.
As a conclusion, there is a substantial advantage to consider a system to keep the chosen air/gas ratio constant at any regime of the burners of the zone even if one of the burners is totally switched off.
Principle of a premix combustion piping
Such a system can be obtained while mixing air and gas according to the ratio required upstream the burners. The combustible mix that is perfectly homogeneous is then going to be equally distributed to all burners, independently from their number or size.
The obtained combustion will then be optimal, stable and identical for all burners: either stoichiometric for a maximum efficiency, or in excess or air default if the process is requiring it.
In opposition to the separated air/gas system, the power modulation for a whole series of burners is made via a single actuator on the air inlet. If well designed, the system will automatically adapt the quantity of gas to the variations of air quantity in order to keep the ratio constant.
The control of backfire, particularly in case of high counter-pressure beyond the burners is assured by placing some pressure relief valves at appropriate places.
This technology is successfully used in many fields such as the glass industry (fore hearths, lehrs, melting furnaces, feeders), the ceramic industry, brickworks, Heat treatment wire furnaces, Lauders in the Copper industry…
FIB typical premix combustion system
The “heart” of the system is the CONSTAN® dosing-mixer that, being coupled with a zero governor, can guarantee the stability of the air/gas ratio.
This dosing-mixer is “multi-gas” and able to feed a variable number of burners at a variable power, insensitive to counter-pressure variations, and while keeping at the same time the air/gas ratio programmed by its user. A motorized version exists when remote control of the atmosphere is required.
It is then inside the burners that the combustion takes place, without flames being in contact with the product in order to avoid any alteration, and with very high fumes velocity for high convection.
FIB Belgium is offering a whole range of burners for all types of applications as well as a wide range of powers.
Lastly, the only wealth being man, the safety of the operators is our main concern. In this aim, FIB has developed on the one hand the TESE pressure relief valve that allows immediately absorbing a sudden overpressure due to an incidental backfire and, on the other hand, the GORGON® flame detector with UV detection, equipped with a auto-selfcheck double electronic circuit
The combustion system and their accessories are designed following the Major Safety standards: EN 746-2:2010, GOST R, GOSPROMNADZOR and in the US following OSHA requirements.
