Roll crusher performance: which operating variables primarily affect both the specific power consumption and the production rate in a roll crusher?

Introduction / Context:
Roll crushers are used for intermediate to fine crushing of ores, coal, and industrial minerals. Their economy depends largely on how much energy they draw per ton and how much material they can pass per hour. This question probes the two most influential variables engineers adjust during design and operation.

Given Data / Assumptions:

• Two-roll crusher handling brittle, non-cohesive solids.
• Gap setting establishes target product top size.
• Speeds may be equal or intentionally differential to improve nip and pull-in.

Concept / Approach:
Specific power consumption and throughput are controlled by how much size reduction is imposed (reduction ratio) and by the material transport/biting mechanics at the rolls (influenced by roll speed and especially differential speed). Higher reduction ratios usually require more energy per ton and can lower capacity if the gap is tight. Differential roll speeds improve nip probability and shearing, often raising throughput but also impacting power draw.

Step-by-Step Solution:
Relate energy to size reduction: specific energy increases with increasing reduction ratio.Relate throughput to kinematics: differential speed enhances material draw-in, reducing slippage and increasing capacity.Conclude: both reduction ratio and differential roll speed affect power and rate.

Verification / Alternative check:
Pilot runs commonly show a capacity rise when differential speed is introduced at constant gap, with a corresponding change in kWh/t as the breakage mode shifts from pure compression toward combined compression-shear.

Why Other Options Are Wrong:
Reduction ratio alone (a): ignores strong influence of kinematics.Differential speed alone (b): ignores energy–reduction coupling.Neither (d): contradicted by operating data.

Common Pitfalls:
Assuming only the gap matters; in reality, speed ratio and surface condition also control performance.

Final Answer:
Both (a) and (b).