Class 30 - Modeling of a Batch Reactor

System Modeling Coursework

P.R. VENKATESWARANFaculty, Instrumentation and Control Engineering,

Manipal Institute of Technology, ManipalKarnataka 576 104 INDIAPh: 0820 2925154, 2925152

Fax: 0820 2571071Email: [email protected], [email protected]

Web address: http://www.esnips.com/web/SystemModelingClassNotes

Class 30: Modeling of Batch reactor

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http://www.esnips.com/web/SystemModelingClassNotes

July – December 2008 prv/System Modeling Coursework/MIT-Manipal 2

WARNING!

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I claim no originality in all these notes. These are the compilation from various sources for the purpose of delivering lectures. I humbly acknowledge the wonderful help provided by the original sources in this compilation.

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For best results, it is always suggested you read the source material.

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Refer to Class 14: Modeling of Chemical Systems for more material and proper perspective


Contents

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Batch process definition•

Batch process nomenclature

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Batch formalism•

Batch Procedure

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Control loop suggested•

References


Introduction

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Prior to the late 1930s practically all chemical and petroleum production processes essentially were of the batch mode.

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When crude oil, for example, was first cracked into lighter hydrocarbon fractions, thermal cracking was of the batch mode.

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Where inherently suited (chemically or physically) andwhere a large and continuous market demand for a single product

existed, manufacturers found that continuous production warranted the costs of scaling up equipment and integrating the flow to and from various unit operations in a continuous production system.


What could be a batch process?

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Every process is a batch process; the difference is how long the process runs between startup and shutdown. (While this may be true

theoretically, it is indeed an oversimplification.)•

A batch process is discontinuous, in which ingredients are sequentially prepared, mixed, reacted, cooked, heated, or cooled, finished, and packed—all in accordance with a time-sequenced schedule worked out by a process engineer.

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A batch process seldom is purely batch; a continuous process seldom is purely continuous. Most batch processes require continuous control over one or more variables throughout the entire schedule, and thus the overall batch control system must be a form of hybrid. Many products made continuously will, at the end of the line, require

batch

packaging, inspection, handling, storing, and shipping.


Speaking in general…

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A batch process usually is completed within a matter of minutes to a few hours, as contrasted with a few seconds for what may be termed a discrete operation or weeks or months for a continuous process from start-up to shutdown.

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However, in the latter case, for any given molecule of substance entering the process, the interval of time within the process (residence time or throughput rate) before it exits as part of a finished product usually can be measured in seconds to very few minutes.


Batch Nomenclature

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Recipe: A list of ingredients, amounts, or proportions of each ingredient. Depending on the product, the recipe may be created by a chemist or other specialist as the result of formulating the desired product in a laboratory (possibly pilot plant) environment.

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Grade: A variation in a recipe or formula, usually achieved through the use of different product data parameters such as temperature, times, and amounts. This may constitute a new recipe.

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Unit: A vessel and its associated process equipment that acts independently of other process units


Batch Nomenclature

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Operation: A time-

and event-based sequence that defines the actions of a process unit in performing a process function. A typical operation may be the sequence to charge, heat, or dump a given unit.

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Procedure: A sequence of unit operations with specific product data that constitutes the batch cycle; also commonly referred to as a recipe or formula.

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Discrete Control Device: An on-off device, such as a solenoid valve, pump, or motor.

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Regulatory Control: A general term encompassing PID (proportional plus integral plus derivative) loops and continuous control functionality.


Batch Nomenclature

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Sequenced Batch: The most basic type of batching control. This can become quite complex because of the large number of operations in some cases. It may be considered as logic planning and incorporates all on–off functions and control of other discrete devices. In the pure

form, sequence control involves no process feedback or regulatory control. It is quite amenable to ladder-logic-based programmable logic controllers (PLCs).

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Programmed Batch: Elements of sequenced batch plus the addition of some regulatory control. This system requires little operator

intervention. Sophisticated regulatory controls (beyond PID) seldom are needed.

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High-Level Batch: Elements of programmed batching with external and process feedback. Optimization routines may be used as, for example, in the production of polyvinylchloride (PVC) and other polymeric emulsions.


Process type characteristics


Batch formalism


Step 1.

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The starting point is that of defining the control elements from the piping and instrumentation drawings (P&IDs).

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Using the P&ID, an equipment tag list can be constructed, including various regulatory and discrete devices


Step 2.

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Following the identification of the control elements, the individual strategies must be defined.

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Regulatory control strategies may be specified, using ISA symbology, or, for complex interactive loops, the Scientific Apparatus Makers Association (SAMA) standard RC22-11 may be useful.

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Due to the nature of batch control processes, attention should be given to loop mode changes, alarm status changes, and adaptive tuning requirements.


Step 3.

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Individual sets of time and event sequences are called operations. The actions within an operation include sequencing, interlocking, profiling, failure monitoring with emergency shutdown, calculations, integrators and timers, and parallel operations in addition to the discrete and regulatory functions.

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In addition the operation provides for manual operator entry and convenient entry and reentry points, all for coordinated control of the total unit


Step 4: Procedure Definition

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The procedure consists of a sequence of operations and sets of product parameters, because most batch processes are characterized by a series of small batches flowing sequentially through multiple units.

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Each batch follows some path, using some or all of the units or operations along that path.

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By treating each operation as a single control action in the procedure, a time-sequence-type diagram can be designed for the procedure


Step 5: Defining Failure Conditions.

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After the first four steps of the formalism are complete, the designer should pass through the hierarchy once again to establish an analysis of the failure conditions of the process. Time sequences should then be defined for the application-

dependent failure steps.•

These failure sequences should be incorporated by operation and should allow for reentry into the operation at a position that does not jeopardize personnel, equipment, or product.


Step 6: Optimization and Reports.

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Finally, once all phases of the definition are complete, optimization of the performance of equipment and data measurement should be done and the determination of end report and batch history data completed.

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The format of batch end data should also be considered for printed reports.


Batch reactor and associated Instrumentation


Model Proposed


To complete the picture …

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Refer to class 14: modeling of chemical process


References

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Handbook of Process Control –

Liptak


And, before we break…

I laugh not at another’s loss;I grudge not at another’s gain;

No worldly waves my mind can toss;My state at one doth still remain.I fear no foe, I fawn no friend;

I loathe not life, nor dread my end.-

Sir Edward Dyer

Thanks for listening…

Class 30 - Modeling of a Batch Reactor

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