Agro Processing Plant Design Questions and Answers

Answer: A

Correct answer: Cost scales to a power near 0.6, not linearly

By the six-tenths rule, \(C_2 = C_1 (Q_2/Q_1)^{0.6}\), so doubling the capacity multiplies cost by \(2^{0.6} = 1.52\) - about half again. The economy of scale arises because a vessel’s cost follows its surface while its capacity follows its volume.

Answer: B

Correct answer: A year's raw material is bought in one season

Ten per cent is a reasonable figure for a plant buying raw material steadily through the year. A seasonal plant must buy a year’s supply in one season and then hold the product as stock until it sells - so its working capital is far higher, and underestimating it is a common way for such projects to run out of money in their first year.

Answer: C

Correct answer: The boiler will be oversized and inefficient

The sum of individual peaks overstates the real maximum, because the consumers do not all peak together - which is what the diversity factor corrects. A boiler sized on the raw sum costs more to buy and runs at part load, where efficiency is poorer and cycling losses are higher.

Answer: D

Correct answer: line balancing

Line balancing. The object is to match the capacities of successive stages so that none of them limits the rest - because throughput is set by the slowest, and capacity installed anywhere else is idle capital.

Answer: A

Correct answer: breakeven

The breakeven point:

Below it the plant loses money; above it, each additional tonne adds its contribution to profit.

Answer: B

Correct answer: Lang

The Lang factor multiplies delivered equipment cost to give the total fixed capital - typically 3 for a solids plant, 4 to 5 for a mixed one, above 5 for fluids. The factor covers installation, piping, instrumentation, electrical work, buildings and engineering.

Answer: C

Correct answer: six-tenths

The six-tenths rule: \(C_2 = C_1 (Q_2/Q_1)^{0.6}\). The exponent below unity is the economy of scale, and it is the reason large plants have lower capital cost per tonne of capacity than small ones.

Answer: D

Correct answer: utilisation

The utilisation factor is actual annual output over rated annual output. It is inherently low in a seasonal plant, whose capacity is set by the peak arrival rate rather than the average.

Answer: A

Correct answer: 4.5 t/h now, rising to 5.5 t/h

Peeling, at 4.5 t/h, is at 100 per cent utilisation - it is the bottleneck, and the line runs at 4.5 t/h. Raising it to 6.5 t/h leaves stages of 6.0, 6.5, 7.0 and 5.5, so filling becomes the new constraint at 5.5 t/h. The gain is 1.0 t/h, not the 2.0 the new machine’s rating suggests - which is what makes debottlenecking iterative.

Answer: B

Correct answer: It falls steadily as capacity rises

Divide cost by capacity in each row: 2.50, 2.14, 1.90 and 1.61 million per t/h. Because the cost factor grows more slowly than the capacity ratio, the cost per tonne of capacity falls throughout - not only above some threshold. That continuous economy of scale is the whole content of the six-tenths rule.