Gross vs. net calorific value (GCV vs. NCV): For which of the following gaseous fuels are the gross and net calorific values practically the same?

Introduction / Context:
Gross calorific value (GCV) includes the latent heat of water vapor formed during combustion, assuming complete condensation of products. Net calorific value (NCV) excludes this latent heat. Fuels with significant hydrogen content produce more water and hence a larger gap between GCV and NCV.

Given Data / Assumptions:

• Composition trends: blast furnace gas (BFG) is mainly CO, CO2, N2 with very little H2.
• Coke oven gas (COG) contains a high fraction of H2 and light hydrocarbons.
• Basic oxygen furnace (L.D.) gas is rich in CO with low H2.

Concept / Approach:
The GCV–NCV difference is dominated by the water formed from hydrogen combustion. If hydrogen content is negligible, little water forms and the two values converge. BFG, with minimal hydrogen, therefore shows almost identical GCV and NCV, whereas COG shows a large difference because of high H2 and hydrocarbons.

Step-by-Step Solution:
Assess hydrogen content: BFG ≪ LDG < COG (approximate trend).Infer latent heat penalty: smallest for BFG → GCV ≈ NCV.Select the fuel where the two values are practically the same: blast furnace gas.

Verification / Alternative check:
Typical analyses: BFG ~ 20–28% CO, 2–5% H2; COG ~ 45–60% H2, hydrocarbons present; LD gas mainly CO with low H2. The GCV–NCV gap mirrors hydrogen level.

Why Other Options Are Wrong:
COG has high hydrogen, so NCV is appreciably lower than GCV. LD converter gas also shows some difference but again greater than BFG.

Common Pitfalls:

• Confusing CO-derived energy (no water produced) with H2-derived energy (water produced).
• Assuming GCV and NCV differ equally for all gaseous fuels.

Final Answer:
blast furnace gas