Burners for fired heaters can be generally divided into two categories, natural draft and forced draft. The natural draft type burner requires less pressure differential to provide the required air for combustion then the forced draft burner. Air pressure differential, or pressure drop, across a natural draft burner would normally fall in the 0.1 to 1.0 in H2O range, where the forced draft burner would normally require 0.3 to 4.0 in H2O. Burner combustion air can also be induced by the fuel gas flowing through a venturi section. Also burners have different air registers for primary and secondary air intake. The air may be delivered to the registers by an air plenum.
In addition to burners being classified by the draft requirements, they are also described by the fuel they burn such as oil or gas or combination. There are numerous fuels which may be burned including:
|Refinery Gas||Propane or Heavier Gas|
|Natural Gas||High Hydrogen Gas|
|Waste Gas||No. 2 Fuel Oil|
|No. 6 Fuel Oil||Other Liquids|
Burners may be of the low NOx which may incorporate staged air or fuel designs. These burner types have become almost standard in the developed world where environmental air standards demand the best combustion technology available.
Burners may be designed for mounting in the heater floor, side walls, or end walls. The burner tips can be designed for various shapes or flame patterns.
In conclusion, there is such a wide variety of types and configurations of burners available from the many manufacturers, that selecting a particular burner for a design requires that the designer work closely with the burner manufacturer to assure the correct selection. But, for many furnaces, the burner(s) can be selected and sized using the standard data provided in the manufacturer's catalog.
This data might consist of a graph similar to that shown below for a sizing standard burners for natural draft:
Heat Release = Design Release * AirCorr * AltCorr * TempCorr
AirCorr = (1 + ExcessAir%/100)/1.15
AltCorr = 1 + (Altitude/1000)*0.02
TempCorr = ((Temp+460)/520)0.5
As an example of how this data may be used, we will set up the following data:
Natural draft, cylindrical fired heater :
Tube circle = 7.25 feet
Radiant height = 18.4 feet
Heat Release = 14.24 MM Btu/hr
Excess Air = 15%
Air temperature = 80 °F
Altitude = 1200 feet
Flue Gas Temperature = 1630 °F