Material Handling in Agro Industries Questions and Answers

Answer: A

Correct answer: Statement I is incorrect but Statement II is correct

Statement I is incorrect. Relief panels do not prevent explosions at all - they take no part until an explosion has already begun.

Statement II is correct and states what they actually do: they fail at a low pressure and vent the explosion in a controlled direction, so the pressure inside never reaches the level that would destroy the structure. Prevention is a separate line of defence - dust extraction, housekeeping and the elimination of ignition sources - and the two are used together.

Answer: B

Correct answer: Both Statement I and Statement II are correct

Both statements are correct and the second explains the first. Breakage accumulates at impacts, and each transfer point and each free fall costs a further small percentage of whole kernels.

Because the losses compound through a plant, a layout with six transfers does markedly more damage than one with three, and the difference shows in the proportion of brokens at the end. Reducing transfers, shortening drops and fitting retarding chutes where a fall is unavoidable are the standard measures.

Answer: C

Correct answer: 2, 1, 4, 3

The path follows the grain. The truck discharges into the intake pit (2), the lowest point of the plant. A bucket elevator lifts it to the top of the silo (1), since that is the only economical way to gain height.

A drag conveyor then carries it horizontally across the top of the bins (4), and a distributor directs it into the chosen bin (3). The order reflects a general principle: lift once, as early as possible, and distribute by gravity thereafter.

Answer: D

Correct answer: 2, 4, 1, 3

The sequence runs from requirement to hardware. First establish the capacity required and the geometry of the run (2) - how much, how far, and through what rise. Then characterise the material for bulk density, angle of repose and fragility (4), since those govern what will handle it.

Only with both in hand can a conveyor type be chosen that suits them (1). Finally the drive is sized and the power per tonne checked (3), which may send the designer back a step if the figure is unacceptable.

Answer: A

A belt lets the material ride untouched, a drag moves it as a bed, a screw shears it against the trough and pneumatic conveying flings it against bends at high speed. The order is essentially the order of relative motion between grain and machine.

Answer: B

Correct answer: 1, 2, 3, 4

The elements must come together in this order. Combustible dust is generated at a transfer point (1); it is then dispersed as a suspended cloud (2), since settled dust cannot explode.

The cloud must be confined within an elevator leg or bin (3), because without confinement the pressure cannot build and the result is a flash fire rather than an explosion. Finally an ignition source such as a hot bearing initiates it (4). Removing any one element breaks the chain, which is why control works on several at once.

Answer: C

Correct answer: 1, 2, 3, 4

The chain begins with moisture content rising in the material (1), which increases the cohesion between particles as liquid bridges form at their contact points (2).

A cohesive material can support an arch across the outlet (3), and once that arch is stable the flow stops and the hopper must be rodded or vibrated to clear it (4). The permanent cure is an outlet larger than the material's critical arching dimension, since the arch then cannot form at all.

Answer: D

Correct answer: Only three

Three pairs are right. A belt conveyor excels at long horizontal runs with low power per tonne; a bucket elevator at vertical lift with high capacity; and a pneumatic conveyor at flexible routing, since the pipe can go anywhere.

The fourth is wrong. A screw conveyor causes high product damage, dragging the material against the trough along the whole run. Its strengths are compactness, enclosure and low cost, not gentleness - a belt is far kinder to the product.

Answer: A

Correct answer: Only three

Three pairs are right. Bridging is a self-supporting arch across the outlet; ratholing is a stable channel that empties through otherwise static material; and funnel flow is the pattern in which only a central core moves on withdrawal.

The fourth is wrong, and describes funnel flow rather than mass flow. In mass flow all the material moves whenever any is withdrawn, so there is no stagnant material at the walls - the absence of stagnant regions being the whole point of the design.

Answer: B

Correct answer: Only three

Three pairs are right. Bulk density converts a volumetric rate into tonnes per hour; angle of repose governs chute slope and the surcharge profile on a belt; and fragility governs the choice between a gentle belt and an abrasive screw.

The fourth is wrong. Saltation velocity depends on particle size, shape and density - the aerodynamic properties that determine when a particle drops out of suspension. Abrasiveness governs pipe and bend wear, and materials of construction, but not the velocity required.