The off-gas from submerged arc furnaces (closed‑system furnace raw gas) is a by‑product of smelting ferrosilicon, silicomanganese, ferrochrome, and industrial silicon. Its main combustible component is CO, and it is utilized in applications such as rotary kilns, drying processes, hot‑air furnaces, waste‑heat boilers, and incinerators.

I. Characteristics of the smelting furnace off-gas (raw coal gas):

1. Composition and Heating Value

CO: 60%–80% (the primary combustible component, highly toxic); H₂: 2%–4%; CH₄ in small amounts; N₂ and CO₂ are inert components.

Lower heating value: 1,450–2,200 kcal/Nm³ (6–7.5 MJ/Nm³), classified as medium‑low calorific gas; combustion conditions are unstable.

2. Dust and Impurities

Dust content in raw coal gas: 15–250 g/Nm³; includes silica fume, carbon black, and metal oxides—fine particles with extremely strong adhesion, readily clogging nozzles and pipelines.

It contains trace corrosive components such as tar, sulfur, fluorine, and arsenic; as the temperature drops, the tar condenses and forms coke, which clogs the burner passages.

Dust removal and purification must be performed upstream of use; typically, the dust concentration entering the burner is required to be ≤100 mg/Nm³, with an ideal range of ≤20–50 mg/Nm³.

3. Temperature and pressure:

Coke oven gas temperature at the furnace outlet: 500–850°C; after cooling and purification, it typically enters the burner at 40–180°C.

Pressure: Slightly positive pressure; the pipeline network experiences significant pressure fluctuations, ranging from 0 to 5 kPa, necessitating a pressure‑stabilizing device.

4. Security Features

Highly toxic CO; significant risk of poisoning in the event of a leak.

The explosion range is wide, making backfire and explosions extremely likely.

It contains a small amount of H₂, resulting in rapid flame propagation and a higher risk of flashback compared to ordinary town gas.

Key point: It is not recommended to feed raw coke oven gas directly to the burner without dust removal, as this can easily clog the burner nozzles and cause coking, leading to premature failure.

II. Design Considerations for the Off-Gas Burner of a Submerged Arc Furnace:

Low calorific value and significant compositional fluctuations make it prone to flameout and extinguishment, necessitating a robust flame‑stabilization structure.

Dust and tar tend to clog the nozzle; therefore, it must be resistant to coking and easy to clean.

A CO–H₂ gas mixture poses a high risk of backfire; the outlet velocity at the nozzle must exceed the flame propagation speed.

The medium is toxic and explosive, so the entire system must be equipped with a comprehensive safety interlock.

III. Main Types and Structures of Specialized Burners for Mine‑Heating Furnace Exhaust Gas

1. Swirl‑diffusion type (most commonly used)

Structure: A multi‑channel swirl nozzle for coal gas, with staged swirl mixing of combustion air; comprising a central ignition channel, a coal‑gas channel, and multi‑stage combustion‑air channels.

Applicable to: hot-air furnaces, drying kilns, rotary kilns, waste-heat boilers, and baking equipment.

Features: Strong resistance to fluctuations, preventing flameout and flashback; can be equipped with a small amount of natural gas or liquefied petroleum gas as an auxiliary fuel for stable ignition and combustion.

2. Multi-channel, high-intensity mixing burner (used for the main burner of a rotary kiln)

Multi‑channel configuration: furnace gas, auxiliary fuel, primary air, and secondary air; capable of co-firing with pulverized coal.

Wide modulation ratio of 1:5 to 1:8, accommodating significant fluctuations in gas flow.

IV. Key Technical Parameters and Configuration of the Mine‑Heating Furnace Flue Gas Burner

Stable combustion structure: swirl‑type flame stabilizer / refractory flame‑stabilizing flue, ensuring no flameout even with low calorific value.

Nozzle flow velocity: The outlet velocity of the gas nozzle shall be ≥25–40 m/s to prevent flashback.

Material: Gas-contacting head—310S stainless steel and heat-resistant cast steel, resistant to high-temperature erosion and minor corrosion.

Ignition System: Built-in ignition burner (using natural gas or liquefied petroleum gas as auxiliary fuel); direct ignition using the tail gas from the smelting furnace is prohibited.

Flame Monitoring: Ionization Flame Detection / Ultraviolet (UV) Flame Detector; gas supply is immediately shut off upon flameout.

Safety interlocks: low-pressure, high-pressure, flameout, fan failure, and purging interlocks; gas pipeline emergency shut-off valve and venting valve.

Air–fuel ratio control: PLC‑based automatic proportional regulation, adaptable to fluctuations in calorific value; excess air coefficient α = 1.05–1.2.

Preventive measures: the nozzle features a large flow cross-section and is detachable; pipeline insulation prevents tar condensation; a purging port is provided.

V. Supporting Process Route:

Blast furnace off-gas → Cooling → Cyclone dust removal / High‑temperature baghouse filtration → Pressure stabilization and regulation → Pipeline insulation → Blast furnace tail‑gas burner → Kiln / Boiler / Incinerator

VI. Common Application Scenarios

Main or auxiliary fuel for the rotary kiln

Raw Material Drying and Mineral Material Hot-Air Drying Furnace

Steam generation through combustion in a waste heat boiler

Flaring of furnace gas from the smelting furnace

Ladle / Hot Metal Ladle Heater (using purified, qualified gas)

Additional comparison: The flue gases from a submerged‑arc furnace and those from a calcium carbide furnace have similar compositions, allowing for a common burner design; however, the flue gas from the submerged‑arc furnace contains silicon micropowder with higher adhesion, necessitating more stringent dust‑removal requirements than those for calcium carbide furnace flue gas.

Characteristics of Mine‑Heating Furnace Offgas, Combustion and Applications of Offgas Burners, and Related Information

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