Transcript L15-Batch Processing.pptx

Batch Processing
Optimal Design and Scheduling
Chapter 11
Terry A. Ring
Chemical Engineering
Job Opportunities
• Photogenics, Orem, UT
Neutron detectors
• Crystal Growth
• Polymer Composite Synthesis
• Crystals + polyvinyl toluene
• Icumedical, Salt Lake City, UT
Blood Infusion Therapy
• Chemical Engineer Intern (with full time possibilities)
• Within 2 years of graduation
• ChE lab assistant for senior lab
There may be some work this summer. Fall and spring hours are somewhat
flexible but interested students must be available from 2:00 PM to 5:00 PM
Monday - Friday. Students should contact Bob Cox. The pay is between
$12.00 and $14.00 per/hr.
Schedule
11 21-MarSequential Batch Processing
23-MarSequential Batch Processing
25-MarProject Management
12 28-MarAIChE Contest Problem Kick Off
AIChE Contest Problem for 30
30-Mar Days
HW-7 Assigned Sequential Batch
Processing
Design Contest Problems Assigned
Memo 1 Due - Planning Memo
Memo
1, HW-7
Chemical Processes
• Continuous Processes – AspenPlus
• Large production rates
• Commodity chemicals
• Bulk chemicals, plastics, petroleum, paper
• Batch Processes – Aspen BatchPlus, BatchSep
• Multiple products from a single plant
• Contract Manufacturing
• Small and or intermittent production rates
• Specialty Chemicals, Pharmaceuticals, Drug Fermentations, Electronic Materials, Optical Materials,
Steel/Aluminum parts Mfg.
• Chemicals that are toxic or hazardous
• Very High Purity Chemicals, zone refined materials
• Long residence times, Exothermic Reactions
• Sometimes multiple process steps in the same tank
Batch Processes
• Batch
• Semi-batch
• Semi-continuous
• Fed-Batch
• Feed continuously, then remove, clean
• Batch-product removal
• Mixing and removal are combined
• Optimal operating profiles
• Recipe or sequence of tasks
• Optimal control problems
Batch Reactor – start at t=0
X
• Determine the
temperature profile that
gives min. batch time
given TU.
Batch Reactor – start at t=0
• Determine the
temperature profile that
gives min. batch time
given TU.
As CA decreases CB increases changing Topt
Fed-Batch Reactors
• Reactor Volume increases with
time
• V(t)=Vo+vo*t
• Mass Balance, CA0 = inlet
d C AV 
dC A
dV
 oC Ao  rAV 
V
 CA
dt
dt
dt
First Order Rxn Solution
(t)
Reactor Separator Sequence
• Batch Reactor
• AB (desired) C
• XA=exp(-k1t)
• XB=[exp(-k1t)-exp(-k2t)]*[k1/(k2-k1)]
• XC=1-XA- XB
• tB-opt= [1/(k2-k1)]*ln[k1/k2]
C
Batch Product Removal
• Batch Distillation (Aspen BATCHFRAC)
• Still Charged
• Heat on
• Lights distill out first
• Control needed to Maximize purity
• Reflux ratio increases with time
• Condenser collector changes
• Pressure changes
• Heavies left in reboiler
• Control needed to Maximize
• Reflux control
• Timed Reboiler dumps
Batch Distill Example
• Mixture 1/3 each
• Methanol
• Water
• Propylene glycol
• Steps
• Total Reflux
• R=3, distill 5 lbmole/hr until
xwater=0.001
• R=5, distill until xwater=0.001
• Methanol cut
• Total Reflux
• R=3 distill until xproypylene glycol=0.001
• Propylene glycol cut “slop cut”
• Dump contents of Still
• Also trays
• Water
Reactor Separator Sequence
• Batch Reactor
• ABC
• XA=exp(-k1t)
• XB=[exp(-k1t)-exp(-k2t)]*[k1/(k2-k1)]
• XC=1-XA- XB
• tB-opt= [1/(k2-k1)]*ln[k1/k2]
• tS=VrCAo(1-XC)/Fd
• ttot=tR+tS
A +B
Fd=Distillate Flow Rate
C
Batch Times
• Reactor
• Controlled by kinetics
• Temperature
• Concentration
• Mixing
• Separator
• Controlled by minimum of
• Heating rate or
• Cooling rate
Cases
• Available equipment sizes determine the batch volumes and times
• Vr>>Vc multiple distillation batches
• Storage Tank for Reactor Product = Vr
• Storage Tank for Products
• Vc>>Vr  multiple reactor batches
• Storage Tank for Reactor Product = Vc
• Storage Tank for Products
• tr>tc  Reactor is idle
• Add more reactors to balance the unit times
• tc>tr  Distillation column is idle
• Add more distillation columns or a larger column to balance unit times
Processing Sequences – see articles for
reading materials
• Optimal Batch Times
• Recipe of Tasks
• Numerous Batch Steps
• Each with a program and tasks to follow
• Each with a given batch size
• Task Integration
• Sequence of steps that take place in one piece of equipment
• Gives batch time determined by batch size and processing time
• Optimum Cycle times for Recipe (sequence of batch steps)
• Using rates of production & yields, vessel sizes are determined to minimize the cost of the
plant and determine the cycle times for a given recipe
Production Line
• Set list of equipment items assigned to tasks
• Tanks, mixers, reactors, separators
• Equipment can be used for two or more tasks, if free
• Prevents contamination
• Cycle time = time between the completion of batches
• Schedule of Production = Gantt Chart of the flow of material from start to finish
showing times for each task in recipe
• Bottleneck = unit having longest batch time
• Zero-wait strategy = no intermediate storage tanks
Example
• Distillation Task – Many Steps
•
•
•
•
•
Charge Still
Heat and Condense (may include heat up)
Empty the Reflux Accumulator
Empty Reboiler
Clean (may include cool down)
Cycle Time (CT)
No parallel Tasks with batch times, tj
CT= max {tj} = max {2,6,4,3}=6
Max{2,6,4,3} =6
Parallel Tasks (nj in parallel)
CT= max {tj/nj} = max{2,6/2=3,4,3}=4
Multi-Product Processing Sequences
• Re Purposing the Plant
• Product A
• Task 1 –U1
• Task 2 –U2, U3
• Product B
• Task 1 –U1, U2
• Task 2 – U2
Multi-Purpose Plant –general use equipment
• Product A
• Task 1–U1, U2, U3
• Task 2–U1,U2, U3
• Product B
• Task 1–U1, U2, U3
• Task 2–U1, U2, U3
Costing a Sequential Batch Plant
Equipment
Cost EQ.
• min(𝐸𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝐶𝑜𝑠𝑡) =
τ𝑖𝑗
• 𝐶𝑇𝑖 ≥
•
𝑛𝑗
𝑁 𝑄𝑖
𝑖=1 𝐵
𝑖
𝑀
𝑗=1 𝑛𝑗
𝑎𝑗 𝑉𝑗
α𝑗
product i cycle time
𝐶𝑇𝑖 ≤ 𝑃𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝐻𝑜𝑢𝑟𝑠/𝑦𝑟
• Qi= annual demand for product i.
• nj= number of identical units.
• Bi = product batch size (plant can produce several products, i’s)
What you need to know.
• Know about process units executed in batch mode and approaches for
optimization of their design and operation
• Know how to determine the optimial reaction for a batch reactorseparator process.
• Be able to schedule recipes for the production of a single chemical
product.
• Understand how to scheudle batch plants for the production of
multiple products.
• Determine the cost of total plant equipment and profitability measures
HW 7-1
Unit/Hour
U1 (3 hr)
U2 (5 hr)
1
x
2
x
3
x
4
5
6
Y`
Y`
Y`
x
x
x
7
8
y
x
U3 (4 hr)
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
y
x
x
U4-A (7 hr)
y
x
y
y
x
x
y
x
U5 (2 hr)
Bottleneck is U4
y
x
y
x
Y
y
y
y
x
x
x
x
y
y
x
x
y
y
y
y
y
y
*
y
*
*
y – Zero Wait
Y` - intermediate storage in U1 until U2 is ready
Intermediate storage for the product of U4-A is possible but only if U5 can not handle the total volume of the U4 batch
or you can design the plant to have a much smaller and less costly U5 and have it operate 6 of 7 hrs.