Combustion air blower for industrial furnace burners

01

Size the airflow from the firing rate and excess air

The US Department of Energy's process heating tip sheet on burner air-to-fuel ratios states that for natural gas, propane and fuel oils about one cubic foot of air is needed to release about 100 Btu in complete combustion. It gives about 10% to 20% excess combustion air at high fire as the operating level of high-temperature direct-fired furnaces, radiant tubes and boilers, to prevent carbon monoxide and soot, and gives 2% to 3% oxygen in the flue gas with only 10 to 50 ppm of combustibles as indicating ideal operating conditions. [1]

Editorial calculation: a furnace fired at 10 MMBtu/h, the size used in DOE's preheated-air example, needs about 10,000,000 / 100 = 100,000 ft³/h of stoichiometric air, or about 1,667 CFM; with 20% excess air that becomes about 2,000 CFM (roughly 3,400 m³/h). [1] [2] Size the blower for the high-fire air of all burners it serves, plus the margin the burner maker requires.

DOE notes that drying ovens that evaporate moisture or solvents need large amounts of excess air to dilute solvent vapour to non-combustible levels, and that cutting excess air there can create an explosion hazard; it also warns that efficiency falls considerably when air is well above or below the theoretical requirement. [1] Editorial note: on solvent ovens the blower may be sized by the dilution air, not by combustion, so give the supplier the solvent load as well as the firing rate.

Give the supplier the burner type, number and firing rate, fuel, excess air at high and low fire, required air pressure at the burner inlet including the air valve train, air temperature (ambient or preheated), altitude, turndown method (damper, inlet vanes or variable-speed drive), installation indoors or outdoors, and the electrical supply.

02

Pick the pressure blower and allow for air temperature

Cincinnati Fan's pressure blower range spans models from 1,200 CFM at 30 in. wg to 180,000 CFM at 36 in. wg; its Model PB cast-aluminium blower covers up to 4,500 CFM and 20 in. wg, the fabricated steel PBS up to 4,462 CFM and 20 in. wg, and the HP-II up to 7,000 CFM and 78 in. wg. [3]

The Model PB page lists combustion air among its applications, with eight housing sizes, radial self-cleaning wheels, round inlets and discharges for pipe or duct, AMCA Type B spark resistance as standard, direct-drive Arrangement 8 with a shaft and coupling guard or belt-driven Arrangement 9, and standard air-stream temperatures to 150° with optional high-temperature construction to 400° (scale as listed by the maker). [4] Editorial calculation: 20 in. wg is about 20 × 249 ≈ 5.0 kPa. [4]

DOE's preheated combustion air tip sheet describes recuperators and regenerators that transfer exhaust heat to the incoming combustion air; in its example, preheating air to 800 °F on a 1,600 °F furnace firing 10 MMBtu/h saves 22% of fuel. [2] Editorial calculation: if a blower has to move air already heated to 800 °F rather than 70 °F, the same mass flow occupies (800 + 460) / (70 + 460) ≈ 2.4 times the volume, so state whether the blower sits on the cold side of the preheater and what temperature it will see.

03

A forced-draft fan maker, and the curve, wheel and damper data to ask for

The linked maker lists forced-draft blowers for burner systems among its industrial fan applications. Ask for the performance curve at your air temperature and altitude, the wheel type and material, the drive arrangement and the inlet damper or variable-speed option.

04

Impeller, housing and inlet, motor drive, inlet damper, air preheater and flue O2 check

05

Air flow per burner, static pressure, air temperature and wheel material for a pressure blower

Start the flow figure from the burners: about 1 ft³ of air per 100 Btu released, plus 10–20% excess air at high fire. [1]

06

Send the burners, air and site together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Burners: [number; firing rate; fuel; excess air]
Air: [flow at high fire; pressure at burner inlet; temperature]
Control: [damper; inlet vanes; variable-speed drive]
Blower: [wheel type; material; spark resistance; arrangement]
Site: [altitude; indoor or outdoor; noise limit]
Electrical: [voltage; frequency; motor IP]
Documents: [performance curve; sound data]

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