Assignment
byereturns
project_description.pdf
CHE212- Process Engineering and Analysis 2014
29 August 2014 Page 1
Project 1 -‐ Bentley campus Required submissions (15 marks): one hardcopy to Assignment Office and one softcopy to BB (one member per group).
Presentation (5 marks): Check BB for the group presentation time.
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General description
Consider a UV-based micro-reactor system in Figure 1. The feed contains aqueous solution of component A. The desire product is B. Under UV radiation, three chemical reactions can occur simultaneously:
𝐴 !! 𝐵
𝐵 !! 𝐶
𝐶 !! 𝐴
The kinetics constants are specified in the Appendix. The micro-reactor consists of series of parallel circular channels, with diameter of 100 µm. The length, L, of the channels can be any distance between 1 and 6 cm. The velocity, v, in each channel is fixed at 1 mm/s. The process is assumed isothermal. Molecular weight of three molecules (A, B and C) is 280 gmol/mol.
Within the micro-channels, the changes of reactants can be modelled as with a plug flow reactor:
𝑑𝐶! 𝑑𝑙
= 1 𝑣 (− 𝑘!𝐶! + 𝑘!𝐶!)
𝑑𝐶! 𝑑𝑙
= 1 𝑣 ( 𝑘!𝐶! − 𝑘!𝐶!)
𝑑𝐶! 𝑑𝑙
= 1 𝑣 ( 𝑘!𝐶! − 𝑘!𝐶!)
Where CA,CB, CC are the concentrations of the three component, respectively (mol/L).
Figure 1. Process without recycling.
water
Feed U1 U2 P1
U3
U4 P2
U5 water
Vaporization
Reactor Separation Vaporization
Separation
CHE212- Process Engineering and Analysis 2014
29 August 2014 Page 2
After the reactor, the outflow goes through separation processes:
1. Stream U1 is separated into U2 and U3. Stream U2 consists of 50% water and 50% B by weight (none of A and C). The amount of B in U2 equals to 40% B from U1. Consequently, U2 is completely dehydrated to produce the powder product P1 (which contains B only).
2. Stream U3 is separated by crystallization and centrifugal separation. During the crystallization, the percentages of precipitation follow a general rule:
o pB = pC+ 20 % o pC = pA + 20%
where pA, pB and pC are ratio of precipitated amount over the total amount in U3 for each components).
The above rules are not applicable when components reach the limits, for example at the beginning or near the end of the process. The crystallization stops when a certain percentage, X, of total mass (of all three component) are precipitated. The value of X is specified in the Appendix. The mixture is then separated into two streams: U4 (containing all solid phase and 10% aqueous phase) and U5 (90% aqueous phase). The composition of aqueous portion in U4 is the same as in aqueous solution U5.
3. Stream U4 is dehydrated to obtain a dry product P2 (water is removed completely). 4. The fresh feed is 60 L/min, containing 0.5 mol/L of A.
Questions.
Question 1. Without recycling.
a. Calculate the chemical concentrations in reactor as function of reactor length. Plot the results. b. What is the optimal length to maximize P1?
(2 marks)
Question 2. Stream U5 is recycled into the reactor (mixed with feed).
Figure 2. Process with recycling
water
Feed U1 U2 P1
U3
U4 P2
U5 water
Reactor Separation Vaporization
VaporizationSeparation
CHE212- Process Engineering and Analysis 2014
29 August 2014 Page 3
Assuming steady process:
a. Determine the optimal reactor length to maximize P1. b. Based on the prices and operation costs, determine the optimal length to maximize the profit.
(4 marks)
Question 3. Considering the new setup:
Figure 3. Alternative process.
The 2nd vaporizer can remove some water in U3 before recycling. Can the new process be more profitable than the previous one? (3 marks)
Question 4. There are several ways you could have solved this problem in Excel. Outline some of the possibilities you considered and briefly explain why you chose the approach you did.
(2 marks)
Notes:
• The reactor length should be accurate to 1 mm. • You need to state your model assumptions. • The presentation/formatting of the report worth 4 marks.
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water
Feed U1 U2 P1
U3
water
Reactor Separation Vaporization
Vaporization
CHE212- Process Engineering and Analysis 2014
29 August 2014 Page 4
Appendix. Data
1. The feed solution costs $200/L. 2. The costs of the separation and vaporization processes are assumed negligible. 3. The cost variations with the reactor size (length and number of channels) are assumed negligible.
Table 1. The reaction constants, prices and cost for your group are specified below:
Group #
Market prices and cost ($) X
Reaction rates
P2 (/g) P1 (/g) Reactor (/L) 𝒌𝟏 (min-1)
𝒌𝟐 (min-1)
𝒌𝟑 (min-1)
1,11,21,31 2 80 15 70% 3 2.5 0.8 2,12,22,32 1 70 13 60% 3 2 0.5 3,13,23,33, 2 70 14 70% 3 2.5 0.8 4,14,24,34 2 80 17 70% 2.5 1.8 0.8 5,15,25,35 2 80 18 80% 3 2.5 0.7 6,16,26 2 80 14 80% 3 2 0.5 7,17,27 2 70 14 70% 2.5 1.8 0.7 8,18,28 2 80 14 60% 3 2 0.6 9,19,29 1 60 13 80% 3 2.5 0.7 10,20,30 2 80 16 60% 2.5 1.8 0.8
