Batch and Continuous Processes
V BATCH PROCESS Dr.Eng. Yulius Deddy Hermawan Department of Chemical Engineering UPN “Veteran” Yogyakarta Outline
1. I ntroduction to Batch Processes
2. Batch Reactor
3. Batch Separation
4. Gantt Chart
5. Production Schedules for Single Products
6. Production Schedules for Multiple Products
7. Equipment Cleaning and Material Transfer
V.1 I NTRODUCTI ON TO BATCH PROCESSES
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY Batch and Continuous Processes
(Smith, R, 2005) However, not all processes operate continuously.
- I n a batch process, the main steps operate discontinuously.
- I n contrast with a continuous process, a batch process does
- not deliver its product continuously but in discrete amounts. This means that heat, mass, temperature, concentration and other properties vary with time. I n practice, most batch processes are made up of a series of
- batch and semicontinuous steps.
runs continuously with periodic start-
- A semicontinuous step ups and shutdowns.
(Smith, R, 2005) Batch Processes:
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY Various modes of operation for batch and semibatch reactors.
( R. Smith)
- are economical for small volumes;
- are flexible in accommodating changes in product formulation;
- are flexible in changing production rate by changing the number of batches made in any period of time;
- allow the use of standardized multipurpose equipment for the production of a variety of products from the same plant;
- are best if equipment needs regular cleaning because of fouling or needs regular sterilization;
- are amenable to direct scale-up from the laboratory and
- allow product identification.
Batch Processes: ( R. Smith) One of the major problems with batch processing is batch to- batch conformity .
Minor changes to the operation can mean slight changes
- in the product from batch to batch. Fine and specialty chemicals are usually manufactured in
- batch processes. Yet, these products often have very tight tolerances for impurities in the final product and demand batch-to-batch variation being minimized.
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY Batch Processes:
(James M. Dauglas) Select batch, if:
1. Production rate
a. Sometimes batch if less than 10million lb/ year
b. Usually batch if 1million lb/ year
c. Multiproduct plant
2. Market forces:
a. Seasonal production
b. Short product lifetime
3. Scale up problems:
a. Very long reaction times
b. Handling slurries at low flowrates
c. Rapidly fouling materials
V.2. BATCH REACTOR
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY Example of parallel reaction Ratio:
Minimize Byproduct: The concentration of both feeds should be minimized
I f a 2 > a 1 and b 2 > b 1 :
and each added progressively as the reaction proceeds. Predilution of the feeds might be considered.
: The concentration of FEED1 should be minimized by I f a 2 > a 1 and b 2 < b 1 charging FEED2 at the beginning of the batch and adding FEED1 progressively as the reaction proceeds. Predilution of FEED1 might be considered.
: The concentration of FEED2 should be minimized by
I f a 2 < a 1 and b 2 > b 1
charging FEED1 at the beginning of the batch and adding FEED2 progressively as the reaction proceeds. Predilution of FEED2 might be considered.
FEED1 and FEED2 should be I f a 2 < a 1 and b 2 < b 1 : The concentration of maximized by rapid addition and mixing.
A temporal superstructure for a w ell- mixed batch reactor.
(Smith, R., 2005)
The greater the number of the time intervals, the closer the model approaches the batch reactor modeled.
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY A temporal superstructure for a multiphase w ell- mixed batch reactor
(Smith, R., 2005) Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY Some examples of mixing compartment netw orks to represent agitated vessels.
V.3. BATCH SEPARATI ON
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY Batch Distillation
Advantages Disadvantages
The same equipment can be used to process High purity products require the careful many different feeds and produce different control of the column because of its dynamic products state There is flexibility to meet different product The mixture is exposed to a high temperature specifications for extended periods One distillation column can separate a Energy requirements are generally higher. multicomponent mixture into relatively pure products
Simple distillation from a batch pot Find other examples of batch separation!
V.4. GANTT CHART
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY Gantt Chart for a simple batch process
Overlapping batches allow s the batch cycle time to be decreased Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
Example 5.4.1: determine reactor capacity
Filling time = 0.25 h Reaction time = 2.5 h
Cycle time = 3 h Reactor emptying = 0.25 h Production capacity = 3000 ton/ year (active: 330 day/ year)
kg 3000 1000
kg ton
Production rate 378 .
8 300 24 h h
1 kg of FEED produces 0.8 of main product
378 . 8 kg Reactor capacity 3 h 1420 . 5 kg
. 8 h
Single Step – Single Reactor
1 time
STEP Hour
FILLING0.25 REACTION
2.50 EMPTYING
0.25
3.00 Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY total 2 1 Single Step – 3 Parallel Reactors
3 time FILLING STEP Hour REACTION
0.25 1 EMPTYING
2.50 total
0.25 3 2
3.00 1 time 3
2 time Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY V.5.
PRODUCTI ON SCHEDULE FOR SI NGLE PRODUCTS Production schedules for a three- step process. Subsequent batches are only started once the previous batch has been completely finished. For this sequential production schedule, the cycle time is 20 h. This clearly leads to very poor utilization of equipment. Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY I t has already been noted that overlapping batches can reduce the cycle time.
Subsequent batches are started as soon as the appropriate equipment becomes available. Cycle time decreases to 10 h for overlapping batches (the length of the longest step). I f a specified volume of production needs to be achieved over a given period of time, then the equipment in the process that uses overlapping batches in Figure
( b) can in principle be half the size of the equipment for sequential production in
Figure ( a) .Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY There are two items of equipment operating Step A, but in parallel.
This allows both Step B and Step C to be carried out with complete utilization. I f the sizes of the equipment are compared to the sequential production schedule, then each of the two Steps A1 and A2 in Figure ( c) can in principle be one-quarter the size of the equipment for Step A for sequential production in Figure ( a) .
The size of the equipment for Steps B and C in Figure ( c) will also be one-quarter the size of those in the sequential production schedule in Figure ( a) .
The final option shown in Figure ( d) is to use intermediate storage for the limiting step. Material from Step A is sent to storage, from which Step B draws its feed. Material is still passed directly from Step B to Step C. Now all three steps are fully utilized. For the same rate of production over a period of time, the size of Step A can in principle be half that relative to the sequential production in
Figure ( a) and the
sizes of Steps B and C can in principle be one-quarter those for sequential production. However, this is at the cost of introducing intermediate storage.
V.6. PRODUCTI ON SCHEDULE FOR MULTI PLE PRODUCTS
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY Production schedule for tw o products w ith a three- step process. Figure (a) shows a production cycle involving a sequential
production schedule.
Production alternates between Product 1 and Product 2.
The cycle time to produce a batch each of Product 1 and 2 is 30 h. Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY The first thing that can be considered in order to reduce the
cycle time and increase equipment utilization is to overlap the batches as shown in Figure (b). This reduces the cycle time to 18 h.
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
All of the schedules considered so far involved transferring material from one step to another, from a step to storage or from storage to a step without any time delay. This is known as zero-wait transfer. An alternative is to exploit the equipment in which a production step has taken place to provide hold-up. In this situation, material is held in the equipment until it is required by the production schedule. A schedule using equipment hold-up is shown in Figure ( c) . This reduces the cycle time to 15 h.
Finally, Figure ( d) shows the use of intermediate storage. The use of storage is only necessary for Product 2. Use of intermediate storage in this way reduces the cycle timeto14 h.
Single versus mixed- product campaigns for three batches each of tw o products.
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY The production cycle for three batches each of Product 1 and Product 2.
The batches have been overlapped to increase equipment utilization. I n order to produce three products each of Product 1 and Product 2, the schedule involves single-product campaigns.
Three batches of Product 1 and three batches of Product 2 follow directly from each other. The cycle time is 47 h. The total time required to produce a given number of batches, in this case
three batches of each Product 1 and Product 2, is known as the
makespan, it is 53 h.An alternative production schedule can be suggested by
following a mixed-product campaign. Alternating between batches of Product 1 and Product 2 in
allows the cycle time to be reduced to 45 h and the makespan to be reduced to 51 h. Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
V.7. EQUPI MENT CLEANI NG AND MATERI AL TRANSFER
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY Cleaning betw een product changes extends the cycle times.
Once cleaning is introduced, the mixed-product campaigns are seen to be less efficient than single-product campaigns Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY Transfer times extend the cycle times.
Compare to the the schedule without transfer time, Cycle time increases from 10 h to 12 h.
Compare to the the schedule without transfer time, Cycle time increases from 20 h to 24 h.
Good luck