A 500 kg aluminum ladle treated for 10 minutes at 6–12 L/min consumes 60–120 L of nitrogen, equivalent to 0.06–0.12 m³ per 0.5 tonne of metal [S1].
At $0.80–$1.50/m³ for purchased industrial nitrogen, the modeled consumption cost is $48–$180 per tonne of aluminum, before equipment, labor, and gas-delivery losses [S1].
Working Cost per Tonne of Treated Aluminum
The direct gas-cost formula is nitrogen consumption in Nm³ per tonne multiplied by the delivered price per Nm³. A process using 120–240 Nm³ per tonne therefore costs $96–$360 per tonne with industrial nitrogen at $0.80–$1.50/m³ [S1].
The cited 10-minute treatment at 6–12 L/min uses 60–120 L for a 500 kg ladle. The same recipe applied across 1 tonne of aluminum doubles consumption to 120–240 L, or 0.12–0.24 m³, producing $96–$360 per tonne at the stated gas price [S1].
That calculation is a process-model benchmark, not a universal purchase rate. Actual consumption depends on ladle fill weight, treatment time, flow rate, alloy, starting hydrogen level, and the efficiency of the degassing unit [S1].
Purchased Nitrogen versus Onsite PSA
Onsite PSA nitrogen generation has an operating cost of $0.01–$0.03/Nm³ after capital recovery, compared with $0.80–$1.50/m³ for industrial nitrogen in most markets [S1][S2]. At the benchmark treatment of 120–240 Nm³ per tonne, this produces an operating gas cost of $1.20–$7.20 per tonne [S1][S2].
A higher-consumption case at 20–40 L/min for 10 minutes applied to 500 kg would use 200–400 L, or 0.2–0.4 m³, and a 1–2 tonne batch would use 0.4–0.8 m³. These figures are useful for comparing gas-supply economics, but the operating recipe still requires validation for the alloy and quality target [S1].
Rotary Treatment Parameters and Consumption
A typical nitrogen treatment for 300–800 kg ladles uses 8–12 minutes, 300–450 RPM, and 6–12 L/min. These parameters generate 48–144 L of gas per treatment, while a rotary head shears and disperses bubbles at approximately 1–3 mm [S1].
Small bubbles matter because they increase the gas-metal contact area and carry dissolved hydrogen and solid inclusions toward the surface. The cited operating range also lowers gas consumption by reducing treatment time compared with inefficient large-bubble heads, but exact savings depend on the selected rotor, flow meter, and alloy [S1][S5].
For a 500 kg ladle, 8–12 minutes at 6–12 L/min means 48–144 L of nitrogen, equal to 0.096–0.288 Nm³ and 0.48–1.44 Nm³ per tonne of metal. At $0.80–$1.50/m³, that translates to $77–$432 per tonne [S1].
Why Nitrogen and Argon Deliver Different Economics
Argon is priced at $8–$12/m³, versus $0.80–$1.50/m³ for industrial nitrogen, so argon is approximately 5.3 to 15 times more expensive per unit volume [S1]. A separate comparison places nitrogen at 60%–80% below argon on a cubic-meter basis [S2].
The comparison in the 2026-05-13 analysis gives argon the metallurgical advantage in sensitive applications, including lower final hydrogen content, fewer inclusions, and better surface finish. Nitrogen remains widely used in high-volume commercial casting where the operating-cost advantage dominates [S2].
Gas Consumption Is Not the Full Operating Cost
The cheapest gas per cubic meter does not always produce the lowest total cost per tonne. An onsite PSA system adds capital recovery, electricity, maintenance, air preparation, and backup or buffer capacity to the calculation [S2]. A rotary treatment also consumes labor and affects downstream scrap, rework, and rejection exposure [S1][S5].
The 2026 comparison states that onsite PSA operating cost includes electricity only after capital recovery, while the broader 2015 generator reference describes a typical 24-month payback period for its nitrogen-generation package [S2][S4]. These figures are not universal project guarantees because duty cycle, electricity tariff, equipment size, and local nitrogen pricing determine the result [S2][S4].
Installation quality also affects the delivered cost. An aluminum melting furnace and furnace refractories can introduce hydrogen when damp, while wet charge material and atmospheric moisture add to the hydrogen load that the degassing cycle must remove [S1][S2].
Alloy and Quality Constraints
A well-executed nitrogen or argon cycle can reduce hydrogen from a typical pretreatment level of 0.30–0.50 cm³/100 g to 0.08–0.15 cm³/100 g, depending on gas purity, rotor speed, flow rate, and treatment duration [S2]. The outcome depends on the alloy and the required casting quality, not only on the lowest gas price [S2].
Below 0.10 cm³/100 g is identified as suitable for aerospace and pressure-tight castings, 0.10–0.15 cm³/100 g for structural automotive castings, 0.15–0.20 cm³/100 g for non-critical applications, and above 0.30 cm³/100 g as unacceptable because of significant macro-porosity and rejection risk [S2].
Nitrogen can react with certain aluminum alloys at elevated temperature to form aluminum nitride inclusions, while argon is chemically inert. Therefore, nitrogen is not the automatic choice for pressure-tight or defect-sensitive products, and an argon system may justify its higher gas price where nitrogen risks inclusion formation or misses the target hydrogen level [S2].
Procurement and Operating Envelope
The strongest procurement case for onsite nitrogen is a high-duty rotary system with stable gas demand, access to economical electricity, and local delivered nitrogen above the modeled $0.80–$1.50/m³ benchmark. At 120–240 L per tonne, the published price comparison can indicate an operating saving versus purchased nitrogen, but the saving depends on the onsite operating cost and other project costs [S1][S2].
Lower consumption cases still show a meaningful difference. At 48–144 L per 500 kg ladle, or 0.096–0.144 m³ per tonne, purchased nitrogen at $0.80–$1.50/m³ costs $76.80–$216 per tonne, while the onsite PSA operating cost is not established by the supplied excerpts [S1][S2].
Foundries should track Nm³ per tonne, cost per degassed tonne, residual hydrogen in cm³/100 g, inclusion rate, and treatment time. If the rotary impeller versus porous-plug comparison shows that the selected dispersion method cannot hold flow and treatment time, gas cost per tonne will not represent the true refining economics.