Mixed facts in mechanical operations: Pick out the WRONG statement from the list below (assume ordinary industrial practice).
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ARecycled coarse material returned by a classifier to a grinder is termed the circulating load.
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BWear and tear in wet crushing is more than in dry crushing of similar materials.
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CSize enlargement (agglomeration, pelletizing) is a mechanical operation.
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DA dust catcher is an enlargement in a pipeline where solids settle due to reduced gas velocity.
Answer
Correct Answer: Wear and tear in wet crushing is more than in dry crushing of similar materials.
Explanation
Introduction / Context:Mechanical operations span crushing, grinding, classification, dust collection, and size enlargement. Understanding what is and is not true in common plant practice helps avoid design and operating errors.
Given Data / Assumptions:
- Comparison of wet versus dry crushing conditions for similar materials and machines.
- Standard terminology for circulating load and dust catcher geometry.
- Size enlargement is recognized as a mechanical unit operation.
Concept / Approach:
Water in wet crushing lubricates and cushions contacts, often reducing liner and media wear compared with dry crushing, where abrasion is more severe and dust is generated. Circulating load and dust catcher definitions are standard. Size enlargement uses mechanical force to form larger agglomerates and is indeed a mechanical operation.
Step-by-Step Solution:
Evaluate each statement against practice and textbooks.(a) Correct: circulating load is the coarse fraction looped back.(b) Incorrect: wet crushing typically reduces wear relative to dry service.(c) Correct: agglomeration/pelletizing/briquetting are mechanical operations.(d) Correct: dust catchers slow gas to let particles settle by gravity.Verification / Alternative check:
Mining/mineral processing references consistently note lower wear and dust in wet grinding/crushing versus dry conditions, other factors equal.
Why Other Options Are Wrong:
They are accurate descriptions of standard terminology and unit operation categories.
Common Pitfalls:
Overgeneralizing: special slurries can be corrosive, but the typical wear comparison still favors wet crushing for abrasion reduction.
Final Answer:
Wear and tear in wet crushing is more than in dry crushing of similar materials.