Fuel reactivity for steam–carbon gasification (C + H2O → CO + H2): Among the following solid carbonaceous materials used in industry, which one is generally the most reactive toward steam at comparable conditions?

Introduction / Context:
Gasification converts solid carbon (C) and steam (H2O) into synthesis gas (CO + H2). The rate of the steam–carbon reaction is strongly influenced by the reactivity of the solid fuel or char. Understanding which solid carbon materials are more reactive helps in designing gasifiers, optimizing temperature, and selecting feedstocks for efficient syngas production.

Given Data / Assumptions:

• Reaction of interest: C + H2O → CO + H2 (endothermic, steam–carbon reaction).
• Comparative evaluation at similar temperatures where intrinsic carbon reactivity matters.
• Materials compared: blast-furnace coke, low-temperature coke (semi-coke), anthracite, sub-bituminous coal, graphite.

Concept / Approach:

Carbon reactivity correlates with microstructure, surface area, porosity, amount of disordered carbon, and catalytic mineral matter (alkalis, iron, etc.). Lower-rank coals and chars made at lower heat-treatment temperatures retain more functional groups and disorder, making them more reactive toward steam than highly ordered carbons (anthracite, graphite) or strongly carbonized cokes (metallurgical coke).

Step-by-Step Solution:

Verification / Alternative check:

Laboratory thermogravimetric studies and industrial experience in gasifiers show faster conversion rates for low-temperature chars relative to metallurgical coke or anthracite at the same temperature. Catalytic ash constituents in lower-rank materials further promote reactivity.

Why Other Options Are Wrong:

Blast-furnace coke: highly carbonized, dense, and less reactive. Anthracite: very ordered carbon, among the least reactive. Sub-bituminous coal can be reactive, but its raw form must devolatilize first; its resulting char is typically less reactive than dedicated low-temperature coke. Graphite: the least reactive due to high crystallinity.

Common Pitfalls:

Assuming higher fixed carbon always means higher reactivity; ignoring the role of microstructure and ash catalysis; comparing raw coal directly to char without considering devolatilization effects.

Final Answer:

Low-temperature coke (semi-coke/char made at lower coking temperatures)