Batch Control Analysis

Presented at the World Batch Forum European Conference Mechelen, Belgium 14-16 October 2002 107 S. Southgate Drive Chandler, Arizona 85226-3222 480-893-8803 Fax 480-893-7775 E-mail: info@wbf.org www.wbf.org Batch Control Analysis Ferenc Molnár Manager BatchControl Ltd Dugonics u. 11. Budapest, H-1043 Hungary (36)-1-370 0010 (36)-1-370 0020 fmolnar@ batchcontrol.hu Tibor Chován Associate Professor University of Veszprém POB. 158 Veszprém, H-8201 Hungary (36)-88-422 022 x4209 (36)-88-422 022 x4171 chovan@fmt.vein.hu Tibor Nagy Control Engineer Sanofi-Synthelabo CHINOIN Budapest, H-1045 Hungary (36)-1-369-0900 x1565 (36)-1-369-0900 x2561 Tibor.nagy@sanofisynthelabo.com KEY WORDS Batch control, Systematic approach, S88.01 models ABSTRACT Batch control analysis is one of steps in the design of plants executing batch process - an S88- based analysis of batch process from the control point of view. It is between the conceptual design of the batch process (PFD or P&I) and the start of the design of the control system (design of instrumentation, control hardware and software). Its objective is to fill the gap almost always found between the formulation of requirements and the specification of the actual implementation. It transforms user requirements into process-based detailed functional requirements. It has several advantages if these problems are handled, not by software engineers, rather by batch control analysts who are closer to the plant and know the process better. A very important feature of batch control analysis is system-independence. It means that the results of batch control analysis are independent of the actual control system. A good control system will not restrict the implementation of the results. In former batch systems this problem was solved instinctively by the engineers developing control software based on their earlier experience. Systematic design, however, allows finding an optimal or close to optimal solution in an easier and manageable way. The method described in the paper is a new approach in batch engineering practice. Its exact formulation was made possible by the introduction of the S88.01 standard. Copyright 2002 World Batch Forum. All rights reserved. Page 1

Steps of batch control analysis: Analysis of the process a simplified description of the process for control purposes. Structuring Definition of hierarchy levels to be followed in the system (process and physical models). Decomposition of tasks: Choice of control structure at the basic level. Design of elements of procedural control (procedural control model, library of phases and operations). List of instrumentation. Specification of operator requirements. Results: The control solution is optimal with respect to the process. Based on our experience, applying this systematic approach, the software becomes structured and shorter (by 50 % in several cases). Not only are the necessary programming efforts reduced, but the number of software errors is also reduced in the same ratio. The design and installation of the control system is simplified. System reliability increases and, at the same time, the number of abnormal occurrences coming from software is reduced. 1. INTRODUCTION Batch control analysis is the phase in the design of a batch process control installation that covers the analysis of the control problem, the structuring of the process and equipment, the distribution of tasks between control levels (basic control, procedural control, co-ordination control) and the design of the recipe operation library including the control of abnormal situations (exception handling) in order to achieve optimal control. In the plant construction process, batch control analysis is between definition of the user requirements and the design of instrumentation, hardware, and software. It is aimed at filling the gap found between the definition of requirements and the actual implementation in almost every project. For example the user may define only the following: crystallization must be executed automatically. To implement this into the control software, the programmer has to decide whether recipe control (unit approach) or sequential control (equipment module approach) should be used to solve the problem. It is better if these questions are answered, not by software engineers, rather by batch control analysts who are closer to the plant and know the process better. It is even better if the solution can be given in general form that is valid for other equipment as well, i.e. in form of strategies and basic principles, which could provide guidance for the instrumentation engineer as well as the hardware and software designer in other projects as well. Batch control analysis is system independent, which means, that recommendations are defined without any limitations of the actual system. In the following steps such a control system must be chosen that allows implementation of the control strategies elaborated during the batch control analysis. The original name of the method was batch analysis. Since nowadays this term is used for the evaluation of executed batches, we introduced the name batch control analysis in order to emphasize the difference. We feel this name clearly reflects the content, i.e. the analysis of the process and production system for developing an optimal control strategy and control system. Copyright 2002 World Batch Forum. All rights reserved. Page 2

2. STEPS OF BATCH CONTROL ANALYSIS The batch control analysis consists of the following steps: Process analysis. Structuring. Design of procedural elements (library of recipe operations). List of instruments and manipulated elements. Definition of operator requirements. 2.1. Process analysis The work sets out from a general process description (4-5 pages). It should include the short description of the technological process, the description of the most important operations and process units, the description of the process chemistry, the most important requirements for the process (e.g.: the necessity of high-accuracy temperature control) and the safety, health and environmental protection considerations. It is important in this phase to have a simplified process diagram. It should show all the equipment essential to process control consideration (reactors, dryers, tank park, utilities, shared-use equipment). To avoid misunderstanding a common terminology has to be agreed. Nowadays the usage of the S88.01 standard is a general requirement. 2.2. Structuring Well-considered, well-done structuring makes further work significantly easier. Bad compromises made during structuring will hit back. It is only a question of time and in which phase of the following work the poorly selected hierarchy will become unusable. It is not worthwhile to give up a decomposition justified by system engineering for illusory short-range advantages. If structuring is too difficult to do or involves lots of compromises, it suggests that there are shortcomings in the previous design phase (e.g.: machinery and piping system). The first step of structuring is the definition of the process model (Table 1). The process model as defined by ISA S88 is a four-level hierarchical model composed of process/process stages/process operations/process actions. First the complete process is divided into process stages and then into process operations. Table 1. Example of the process model Process stages: P1: Charging, reaction, evaporation (Unit 01) P2: Extraction, ph setting (Unit 01) P3: Filtering, crystallization (Unit 02) P4: Centrifuging (Unit 03) P5: Drying (Unit 04) P6: 2. Preparation of Toluene solution (Unit 05) P7: 2. Vinyl-ester film-evaporation (Unit 06) P8: Short way distillation (Unit 07 P9: 3. Preparation of extracting solvent (Unit 08) P10: 3. Preparation of Vinyl-ester solution (Unit 02) P11: 3. Preparation of reaction mixture (Unit 01) P12: 3. Dosing, extraction (Unit 01) P13: 3. Vacuum evaporation (Unit 01) P14: 3. Short way distillation (Unit 09) Copyright 2002 World Batch Forum. All rights reserved. Page 3

Table 1 (cont.). Process operations P1: Process stage: 1. Charging, reaction, evaporation (Unit 01) Code Process operation Parameters Process measurement P1_1: P1_2: P1_3: P1_4: P1_5: P1_6: P1_7: P1_8: P1_9: Acetone charging Water charging Temperature setting Solid charging, mixing Solid charging, mixing, cooling Heat up with steam Total reflux and solvent dosing Cool down Solid charging, mixing P1_10: Heat up with steam Critical Important Informative Safety 111 l acetone FIQS aceton Auto W solid TITCA react NTC reactor Process mode Required manipulated element Comments 222 l DEMIwater FIQ water Auto 20 25 ºC TITCA react TTC jack-in PTS jack Auto NTC reactor TT jack-out 333 kg W solid Manual Powder 15 minutes NTC reactor dosing 444 kg KOH TTC jack-in Manual Powder 555 kg NaOH TT jack-out dosing Up to boiling TITCA react TT jack-out TT vapor 5 hours (dosing 3 hours) 666 kg TITCA react TT condensated W solid FITC vapor TT cond TT jack-out TT vapor TI receiver PI receiver LIA receiver 40-45 ºC TITCA react TTC jack-in TT jack-out 777 kg NaOH 15-20 minutes W solid NTC reactor Up to boiling TITCA react TT jack-out TT vapor TT cond PITSA reactor PTS jack PITSA reactor PTS jack PITSA reactor PTS jack Auto Auto Auto Manual Powder dosing Auto Copyright 2000 World Batch Forum. All rights reserved. Page 4

The purpose of the application of each previous column is easily conceivable: Code - for reference (co-ordination links), Process operation - these operations will serve later as the basis for recipe operations, Process measurement - the following groupings: critical (influencing the quality), important for the process, informative and safety provides the requirements for the designer of the instrumentation. Considerable cost reduction can be achieved by choosing suitable types of instruments. Required manipulated element - operations under automatic control require automatic manipulated elements. Other - special requirements, co-ordination requirements, etc. The second step is the definition of the physical model (Table 2). The main function of the physical model is to define the relations of the process equipment unambiguously. The prerequisite for assuring transparency and order is that each element belongs to one and only one higher-level element. Later on, the hierarchy of the control system will follow this model. Every control module will be responsible for handling its own physical elements, therefore it must know which elements of the physical model are allowed to be manipulated directly and which are not. The physical model has an important role in maintaining a clear naming and tagging convention, as well. The notation: process cell / unit / equipment module / control module identifies any element of a system precisely. Table 2. Example of the physical model UNIT 01: Reactor Task: P1: 1: Charging, reaction, evaporation P2: 1: Extraction, ph settings P14: 3 : Preparation of reaction mixture P16: 3 : Vacuum evaporation Central element: No 1 agitated reactor Type: CE glass-lined reactor Producer: Size: 6300 l Equipment modules: Devices: Control modules: TITCA(HL) 01.01 Internal temperature TITCA(HL) 01.11 Bottom valve temperature PITSA(H) 01.04 Pressure inside the reactor FTC 01.05 Vapor flow rate AIT 01.08 Reactor ph NTC 01.10 Stirrer speed control FYC 01.11 Feed rate control LIAS(HH,H,L) 01.12 Feed tank level YITS(H) 01.13 Conductivity NTC 01.25 Dosing pump speed control ES 01.40 Powder dosing feedback FIQ 01.60 De-ionised water charging FIQ 01.61 Potable water charging PI 01.80 Reactor pressure FIQS 01.26 Acetone charging Copyright 2000 World Batch Forum. All rights reserved. Page 5

WI 01.91 Reactor weight Valves: V 01.01 vapor line V 01.02 vent line V 01.04 nitrogen 2,5 bar V 01.05 vacuum V 01.10 nitrogen 80 mbar V 01.11 discharging V 01.19 bottom valve V 01.20 from feeding tank V 01.21 toluene in V 01.22 acetone in V 01.24 HCl in V 01.26 potable water in V 01.27 de-ionised water in V 01.29 from unit 202 V 01.30 from 01.16 weighing vessel V 01.31 from 01.15 separator FY 01.11 dosing control valve 1. Jacket system 01.1 TERMOBLOCK TTCS 01.02 Jacket in (bottom) temperature TTS 01.03 Jacket out (upper) temperature PTS 01.16 Jacket pressure FSA(L) 01.22 Termoblock empty signal LSA(H) 01.23 Termoblock full signal ES 01.28 Termoblock circulation pump feedback V 01.VBE cooling water in V 01.VCS cooling water out V 01.VSB cooling brine in V 01.VSK cooling brine out V 01.VELL circulation V 01.VLE emptiing1 V 01.VLE1 emptiing2 V 01.VLB vent V 01.VKO condensed steam out TY 01.01G steam control valve TY 01.01F liquid control valve 2. Separator system 01.14 Separator vessel LIA(HH,H) 01.30 level 01.15 Separator tank LIH(H) 01.34 level 01.16 Weighting vessel WI 01.90 weight 3. Deflegmator 01.5 Condensator FT 01.05 vapor flow TIT 01.06 vapor pipe temperature TIT 01.07 condensate temperature V 01.06 reflux V 01.07 distillation vent V 01.08 to receiving tank Copyright 2000 World Batch Forum. All rights reserved. Page 6

01.6 Drop separator V 01.09 vent through drop trap 4. Receiving tanks 01.7 Receiving tank LIA(HH,H) 01.31 receiving tank level TI 01.71 receiving tank temperature PI 01.81 receiving tank pressure V 01.32 receiving tank inlet V 01.33 receiving tank vent V 01.34 receiving tank vacuum 01.8 Receiving tank LIA(HH,H) 01.32 receiving tank level TI 01.72 receiving tank temperature PI 01.82 receiving tank pressure V 01.35 receiving tank inlet V 01.36 receiving tank vent V 01.37 receiving tank vacuum 5. Vacuum system 01.9 Trap LIA 01.33 Level in trap 01.10 Vacuum pump PI 01.83 Vacuum pump pressure During the whole course of the installation of the system all of the structuring and grouping steps should follow some of these models. For example, the process graphics can be organized according to the process model. The support system for maintenance tasks should follow the physical model, etc. 2.3. Design of procedural elements The recipe operation is an element of ISA S88 recipe model (recipe procedure/unitprocedure/operation/phase). The recipe operation is a more generalized form of process operation, which can be used for a number of different processes. The library of recipe operations has to be developed during the batch control analysis. At this time required recipe operations have to be generated from the process operations in a way that allows the production task to be defined by compiling a recipe. A few points of view for the development a recipe operation are the following: Any process operation (phase) can be generated by assembling one or more recipe operations (phases) serially or parallel. Functions used more than once have to be identified. The fewer and the simpler recipe operations required to cover the problem, the better the implementation will be. The simpler available recipe operations are, the more difficult is to build a recipe, however, the system will be more flexible. An optimum has to be found to reach the necessary flexibility with the most complex operations. The tool for fitting recipe operations to the actual process application is the use of recipe parameters. The more the available parameters there are, the more flexible the system will be, however at the same time, the more difficult it is to build a recipe and understand and explain an operation and its parameters. Copyright 2000 World Batch Forum. All rights reserved. Page 7

Table 3. Relationship of process and recipe operations Process operation Recipe operation RO No Quick heat up Quick cool down Linear heat up Linear cool down Temperature hold Thermal operations 01 Refluxing Reflux 09 Solvent removal Evaporation Solvent removal in vacuum Evaporation in vacuum Solvent charging Water charging Atmospheric distillation 04 Vacuum distillation 05 Liquid charging 16 Solid charging Solid charging 17 Inertization Inertization 10 Filling from drum Filling 12 Discharging into drum Discharging to incinerator Discharging by pump Circulation Discharging Transfer into other unit Transfer 18 2.4. List of instruments and manipulated elements After defining the operations and the basic control requirements for the instrumentation (i.e. what kind of measurements and manipulating elements are necessary) and the importance with respect to the process (critical, important, informative, safety, etc.), each instrument can be defined. Therefore the necessary elements of the loops can be designed and selected optimally considering functionality and cost aspects. 2.5. Definition of operator requirements Based on the ratio of Automatic and Manual modes (given in the Mode column of the process model definition) the operator requirements and the corresponding human-machine interface for the field and control-room operations can be designed. The more manual activities are involved the more complex field HMI is required. 13 Copyright 2000 World Batch Forum. All rights reserved. Page 8

3. SUMMARY Engineering activities similar to that of batch control analysis were necessary in the past as well, of course. Engineers developing the control system did this work instinctively based on their earlier experience. Systematic design, however, makes it simpler and more straightforward to achieve an optimal or close to optimal solution. According to our experience, in many cases the control software of systematically structured systems is shorter by 50 % than that of instinctively structured solutions. The method reduces not only programming efforts but also the number of software errors by the same ratio, and it results in a system which is simpler to start-up and is more reliable. It is not negligible that batch control analysis provides control engineers with very deep knowledge of the process. That has an advantageous effect throughout the whole project. 4. LITERATURE 1. ISA-S88.01-1995 Batch Control. Part 1: Models and Terminology, Internal Society for Measurement and Control, 1995. 2. Thomas G. Fisher: Batch Control System: Design, Application, and Implementation, ISA, 1990 3. Liptak B. (Ed.): Instrument Engineer's Handbook, Process Control Volume, Chilton Book Company, 1995. 4. Molnar F.: Batch Analysis (in Hungarian), Magyar Elektronika, OMIKK, Hungary, 1999. Copyright 2000 World Batch Forum. All rights reserved. Page 9