Assignment 4 Due: Thursday, February 9, 2017 by 5 pm Bring your assignment to Th

Question

Assignment 4 Due: Thursday, February 9, 2017 by 5 pm Bring your assignment to Thursday's lecture or office D404 before the deadline Problem 1 7 marks Stack gas from a furnace is used to dry barley by the process shown in the figure below. The water content in the barley stream is reduced from 25 wt% to 5 wt%. The gas feed stream has a flow rate of 100 kg/s and a water content of 4.5 wt%. This feed is mixed with a recycle stream. The gas stream leaving the dryer has a water content of 9.0 wt% and 90% of this stream is purged from the process. Determine the mass flow rate and composition of the gas stream entering the dryer. Splitting point 100 kg/s Mixing 0.955 kg gas/kg point 0.045 kg H20/kg ----t- 0.910 kg gas/kg Dryer 0.090 kg H20/kg 0.75 kg barley/kg 0.95 kg barley/kg 0.25 kg H20/kg 0.05 kg H20/kg Problem 2 [10 marks] Nitric acid (HNO cannot be separated from water (H o) by traditional distillation when it is at a

Explanation / Answer

Writing overall balance of the plant

Let P= Purge and B= Product barley

Gas entering the process = 100*0.955=95.5 kg/s

Gas leaving =P*0.91

Hence P*0.91= 95.5

P= 105 kg/s

This is 90% of the recycle.

Hence recycle R =105/0.90 =117 kg/s

Recycle flow rate= 117-105= 12 kg/s

Hence gas entering the dryer contains 95.5 kg/s gas, 4.5 kg/s water

And recycle stream containing 12*9/100 water =1.08 kg/s water and gas = 12-1.08=10.92 kg/s

So mixture of water and gas enterng the dryer = 12+100= 112 kg/s

Water entering = 1.08+4.5=5.58 kg/s and gas = 10.92+95.5 =106.42 kg/s

Composition of gas entering the dryer : water = 5.58/112 =0.0498 and gas = 0.9501

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