In one steady state process, a wet starchy food has to be dried. This is achieve
ID: 484397 • Letter: I
Question
In one steady state process, a wet starchy food has to be dried. This is achieved by using a rotary dryer to dry remove only water (W) from the input to the dryer. A fresh feed (Flof wet material enters the process at a fixed rate of37 MTPD with mass fraction of water z 0.31. This wet material has to be dried to give a final product (P) containing a mass fraction water However, dryer cannot handle an input containing significant moisture and therefore, some of the product is recycled back to mix with the fresh feed before the combined stream (M) enters the dryer. The mass fraction of water in this mixed stream is fixed to be y 0.253. For setting operating parameters such as x, the mass fraction of water in product, the relative impact oftwo the product and the recycle is considered in a rudimentary economic analysis. The selling price of the product is fixed at s600 per metric ton of product and the cost of pumping the recycle is S250 metric ton of recycle. A simple objective function based on the profit i.e. sales minus the cost can then be used. Evaluate each option below and mark all that are correct. Credit will be given only ifall the correctnns wers are chosen, (20% mass flow of P does not change with x more information is needed to determine changes in W with x mass flow of recycle decreases as x increases more information is needed to determine changes in recycle with xExplanation / Answer
1.
(i) Mass flow rate of P does not change with X.
For real world applications wherein the moisture of product is critical, it is a false statement.
But in the given problem, it only crucial that X<Y, therefore the statement is Correct. As under least drier efficiencies, X will always be lesser than Y.
(ii) Yes, more information is required to analyze changes in W with X. It required to know the amount of water in the output product or the efficiency of the drier operating. Correct
(iii) Correct. It is required to maintain a constant input water content in the feed.
(iv) Incorrect. It can be calculated from the given data.
(v) Incorrect. It will decrease as X increases.
(vi) Incorrect. As soon as X increases, the mass flow of recycle will be reduced to keep Y constant. Therefore W is supposed to be constant as long as drier efficiency remains constant.
(viii) Correct. Drier efficiency is required to calculate the output product rate.
(ix) Correct. As W decreases, the amount of water in product will increase, i.e W will increase.
(x) Incorrect. W and X are interdependent.
(xi) Incorrect. Mass flow of P will increase as X increases as the mass flow of recycle stream will reduce as soon as X increases thus increasing P.
(xii) Incorrect. Mass flow of recycle will decrease as X increases.
(xiii) Correct.
P.S: All the remaining question are not from chemistry.
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