Calcium Carbide 25-50mm and 50-80mm with 295 L/kg Gas Yield
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Calcium Carbide for Acetylene Production: Sizes, Gas Yield and Specification
Calcium carbide (CaC2) is the feedstock for acetylene generation by hydrolysis, and for a gas plant the single most important commercial number is the acetylene yield per kilogram of carbide. Two crushed size bands dominate the export trade: 25-50 mm, used in medium reactors and portable generators, and 50-80 mm, used in large chemical plants and heavy welding lines. Both bands are supplied here with a guaranteed minimum yield of 295 litres of acetylene per kilogram of carbide, measured at 20 C and 101.3 kPa.
What 295 L/kg Means and How It Is Verified
The gas yield figure states how much acetylene a unit mass of carbide will release under standard conditions, so it is a direct cost driver: at 295 L/kg, a plant needs roughly 3.4 kg of carbide to produce one cubic metre of acetylene. Yield is the result of the CaC2 content of the stone, and it falls when unmelted lime, coke ash or absorbed moisture are present. Verification is done by the standard gas-yield method for calcium carbide, in which a weighed sample is hydrolysed in a closed vessel and the released gas is collected and measured at 20 C and 101.3 kPa; the same test basis is used in GB/T 10665, the Chinese standard for calcium carbide, so buyer laboratory results and producer certificates can be compared on equal terms. Batch testing before shipment is the practical way to keep a reactor running on its designed gas curve.
Typical Specification, Both Size Bands
| Parameter | Specification | Test Basis |
|---|---|---|
| Acetylene gas yield | min 295 L/kg | Hydrolysis, 20 C, 101.3 kPa |
| CaC2 content | min 93% (industrial grade) | Titration |
| CaC2 content | min 96% (high purity grade) | Titration |
| Sulphur (S) | max 0.2% | Wet chemical / instrumental |
| Phosphorus (P) | max 0.15% | Wet chemical / instrumental |
| Moisture | max 0.5% | Drying loss |
| Ash | max 3% | Ignition residue |
Choosing Between 25-50 mm and 50-80 mm
Size governs reaction kinetics and fines generation, not chemistry. A 25-50 mm charge presents more surface area per tonne, so it reacts faster and suits smaller generators, medium-scale steel shops and sites where the acetylene demand curve is sharp. A 50-80 mm charge reacts more slowly and more evenly, produces less fines in the generator and reduces the frequency of sludge removal and screen maintenance, which is why continuous chemical plants and heavy plate cutting lines normally standardise on the coarser band. The practical rule is to match the band to the reactor grate and the water-feed rate: a coarse charge in a small generator leaves unreacted cores in the sludge, while a fine charge in a high-throughput generator can push peak gas pressure above the design point. A mixed charge, such as 70% coarse plus 30% fine, is a used compromise when a plant has an uneven daily demand profile.
Purity Effects Downstream
Sulphur and phosphorus report through hydrolysis to hydrogen sulphide, phosphine and organic sulphur species, which then follow the acetylene into the purification train. Keeping S at max 0.2% and P at max 0.15% limits scrubbing load and protects downstream catalysts used in vinyl chloride monomer and vinyl acetate production. For welding-grade acetylene, low S and P reduce the risk of porosity and of a dirty flame envelope on the cut face. Where the acetylene is intended for sensitive synthesis routes, the min 96% CaC2 grade is normally specified because the higher carbide content translates into a lower inert residue per unit of gas.
Packing, Storage and Moisture Control
Because calcium carbide reacts with water, packing is a moisture-barrier decision as much as a logistics decision. The 25-50 mm band is customarily supplied in 50 kg steel drums or in 1 MT lined bulk bags; the 50-80 mm band ships in 1 MT bulk bags or as bulk cargo on larger orders. Drums must be opened only immediately before charging, and a partially used drum should be resealed. Storage areas should be dry, ventilated and free of water lines and sprinkler discharge; acetylene generation on a wet floor is a safety event, not a quality event. Transit packaging is selected to keep the carbide dry through the loading, sea leg and inland delivery, so the yield guarantee survives the voyage and is still valid when the bag is opened at the plant.
Frequently Asked Questions
Q: Is 295 L/kg the guaranteed minimum or a typical value?
A: It is the guaranteed minimum for the grade. Sample lots are hydrolysed and measured at 20 C and 101.3 kPa before shipment, and the certified figure is reported per batch.
Q: Which size reacts faster, 25-50 mm or 50-80 mm?
A: 25-50 mm reacts faster because it exposes more surface area per tonne; 50-80 mm gives a slower, steadier gas flow with less fines formation in the generator.
Q: Why do sulphur and phosphorus limits matter for acetylene?
A: They hydrolyse into hydrogen sulphide and phosphine, which load the purification train, shorten scrubbing media life and can affect catalyst performance in downstream synthesis units.
Q: What is the gas yield test basis in GB/T 10665?
A: GB/T 10665, the calcium carbide standard, defines yield on the acetylene released per unit mass measured at 20 C and 101.3 kPa, which is the same basis used for the 295 L/kg guarantee.
Q: How is calcium carbide packed for export?
A: The 25-50 mm band normally ships in 50 kg steel drums or 1 MT lined bulk bags, while the 50-80 mm band ships in 1 MT bulk bags or as bulk cargo for larger parcels.
Q: What happens if the carbide absorbs moisture in storage?
A: Part of the yield is consumed before the material reaches the generator and gas pressure becomes unstable, so drums should be opened only just before charging and resealed afterwards.
