Gas flow through packed beds: Identify the furnace/process in which combustion/processing gases are deliberately drawn downward through the stock bed from below the grate or windbox.

Introduction / Context:
Some thermal processes purposefully pull hot gases through a granular or lumpy bed to promote reactions and uniform heating. Recognizing the direction of gas flow is central to diagnosing air distribution, burn-through control, and bed permeability issues.

Given Data / Assumptions:

• We consider classic ore sintering practice on a traveling grate.
• Gas handling involves induced-draft fans drawing gases through the bed.
• We compare this with other furnace types that do not employ strong down-draught through a particulate bed.

Concept / Approach:
On sintering machines, ignition is initiated at the top and powerful suction below the grate draws combustion air and hot gases downward, promoting bed consolidation (sinter). The pressure drop across the bed is an essential control variable. Soaking pits and beehive ovens do not follow this specific down-draught through a particulate bed arrangement.

Step-by-Step Solution:
Identify the process known for induced down-draught through ore/coke/fines: the sintering machine.Relate to equipment layout: windboxes and fans below the grate provide suction.Therefore, select “Sintering machine (down-draught sintering)”.

Verification / Alternative check:
Metallurgical process texts explicitly describe traveling-grate sintering with suction applied beneath the bed to control burn-through and productivity.

Why Other Options Are Wrong:
Soaking pit: heats ingots in a chamber; no downward suction through a loose bed.Beehive oven: coke ovens have different draft and flow patterns, not the sinter down-draught scheme.Rotary kiln: cross-/co-current flow in a rotating tube, not suction through a stationary packed bed.

Common Pitfalls:
Confusing any “draft” with “down-draught through a bed.” The sinter machine’s defining feature is suction through the granular layer.

Final Answer:
Sintering machine (down-draught sintering)