Blast furnace gas burner nozzle: swirl gas and air nozzles sized for a fuel with less than a tenth of the heating value of natural gas

01

Nearly twelve times the volume of natural gas for the same heat: what a 3,270 kJ/Nm³ fuel asks of the nozzle

In tests at an ArcelorMittal experimental furnace in Asturias reported by CIRCE and ArcelorMittal (Processes, 2023), the blast furnace gas burned contained 22.34% CO, 4.13% H2, 48.98% N2, 22.04% CO2, 1.68% H2O and 0.82% O2, with a lower heating value of 3,270 kJ/Nm³ against 38,019 kJ/Nm³ for the natural gas used. The authors give a plant-dependent range for BFG of about 20–30% CO, 2–6% H2, 45–60% N2 and 20–25% CO2. [1]

Fired at 900 kW with combustion air at about 500 °C, BFG held the furnace at about 1,030 °C, compared with about 1,347 °C on 700 kW of natural gas with oxygen injection and about 1,250 °C on a 70/30 BFG and natural gas blend; the authors note that the BFG case ran at 200 kW more power yet 200 to 300 °C lower temperature, and that BFG flow would need to be doubled to approach natural gas temperatures. In the simulations the high BFG flow overrode the swirl, giving straight flames, while the blend's flames rotated and were short. [1]

Editorial calculation: 900 kW ÷ 3,270 kJ/Nm³ = 0.275 Nm³/s, about 990 Nm³/h of BFG, against 700 kW ÷ 38,019 kJ/Nm³ = 0.0184 Nm³/s, about 66 Nm³/h of natural gas; per kilowatt, BFG needs 38,019 ÷ 3,270 ≈ 11.6 times the fuel volume before combustion air is counted. [1]

The authors conclude that burning equipment must be adapted to keep flame geometry when fuels of very different heating value are used, with different nozzles and swirling methods, and that the piping and ports for BFG must be sized for its large volume flows. [1]

Send the supplier your BFG analysis (CO, H2, CO2, N2, H2O), heating value range, supply pressure and temperature, and the firing rate range, so the nozzle area and exit velocity can be calculated for the actual gas.

02

Gas and air openings inclined 30° to 80°: a hot stove swirl burner that halves flame length

Nippon Kokan's patent for a swirling burner in a blast furnace hot stove starts from two older designs. Twisted-blade swirl burners, mainly used on relatively small blast furnaces, developed oscillatory combustion as flow increased; ceramic-grill burners, with a grill about 200 mm thick ejecting air and gas as parallel streams, mixed poorly, so the flame grew long, unburned gas reached the checker bricks and flame length changed strongly with excess air. [2]

Its burner uses an annular blast member below the vertical combustion chamber, with fuel gas passages and air passages stacked alternately around a central cylindrical space and gas and air openings all inclined the same way. The patent selects an inclination of 30° to 80° to the tangent toward the radius and 30° to 90° to the vertical, which builds an upward swirl with a counter-flow region at the centre that acts as a flame holder. [2]

In the combined version with a grill, it sets the ratio of air and gas through the swirl openings to that through the grill at 0.1 to 10 and the degree of swirl S = Pt / (Pt + Pa), swirling flow power over total flow power, at 0.1 to 0.2. The inventors report that in their experiments flame length fell to about half that of the conventional grill nozzle and no longer varied with air-fuel ratio, and that no oscillatory combustion appeared when large gas quantities were burned. [2]

Ask for the opening angles to the tangent and to the vertical, the swirl degree at your firing rate, and test data on flame length and stability across the air-fuel ratio range.

03

Main and auxiliary nozzle rings with 15° to 75° swirl plates: holding flame at low and high load

Zhongye Changtian's patent for a low-calorific-value gas burner on a drying hot gas generator names blast furnace gas and converter gas as the fuels it addresses. It describes the problem with a single large sleeve burner: above 1,500 × 10⁴ kcal/h its outside diameter exceeds 2 m, and with one gas channel and one air channel the outlet velocity is low at low load, inviting flashback, flame-out and burning of the burner head, and high at high load, inviting flame lift-off and incomplete combustion. [3]

Its design splits the burner into an outer main burner and an inner auxiliary burner, each with a ring of gas pipes ending in nozzles with mixing tips, each with its own gas and air control valves. Arc-shaped swirl plates on the inside of each gas pipe and on its outside in the air stream turn the flows; the patent gives three or more plates per pipe with a spiral angle adjustable from 15° to 75°. [3]

For a heat supply of about 2,000 × 10⁴ kcal/h, the patent gives the annular nozzle cross-section diameter as 1,800 mm and states that this is about 30% smaller than an existing burner of the same capacity. [3] Editorial calculation: 2,000 × 10⁴ kcal/h × 4.1868 kJ/kcal ÷ 3,600 s/h ≈ 23,300 kW; at the 3,270 kJ/Nm³ of the CIRCE test gas this is about 7.1 Nm³/s, or roughly 25,600 Nm³/h of BFG (the patent does not state its design gas's heating value). [3] [1]

For a burner that must turn down, ask how many nozzle groups it has, which are shut at minimum load, and the exit velocity at minimum and maximum firing for your gas.

04

Gas, duty and nozzle data for a blast furnace gas burner

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

Gas: [CO, H2, CO2, N2, H2O %; heating value range kJ/Nm³]
Gas supply: [pressure; temperature; dust content]
Enrichment: [natural gas or coke oven gas blend; oxygen]
Duty: [hot stove, hot gas generator, reheating or treatment furnace]
Firing rate: [maximum and minimum kW]
Air: [preheat temperature; excess air]
Nozzle: [opening angles; swirl degree or swirl plate angle; number of nozzle groups]
Flame: [length limit; stability across air-fuel ratio]

See manufacturer records Send an enquiry through CNFX