Applying Automation to Batch Manufacturing Using Industry Standards

By Bruce Jensen & Marcus Tennant Yokogawa Corporation of America Sugarland, TX

Abstract

Batch processes in many industries, including grease manufacturing, are built to achieve very flexible manufacturing requirements. Often, when automating a batch process, that flexibility is lost making it difficult for operators to introduce new products and make process modiἀcations. Developed and reἀned over the past 20 years, the ISA Batch Standard (ISA 88) has become a commonly understood approach to communicate batch system requirements across R&D, process engineering and control disciplines, and has enabled manufactures to build flexible and highly automated batch systems. This presentation will outline the basics of the ISA-88 standard and provide an overview of how it has helped many different companies achieve agile and flexible manufacturing in highly automated batch systems.

Overview of Batch Processing

In the universe of manufacturing, there are two broad ways to produce items for mass markets. On one end of the spectrum, a discrete manufacturer produces things: cars, electronics, appliances and tools. This is where assembly lines with robots and high speed packaging are very prevalent. At the other end, process manufactures make material: gasoline, diesel fuel, paper, and bulk chemicals. Both of these manufacturing worlds share many common traits. They both strive for high levels of automation to help them meet market demands by producing efficiently and at a high rate of speed.

Some products for more specialized markets do not have to be produced in quantities that justify major manufacturing efforts. There are many opportunities for more complex and customized production. For products where the marketplace demands more limited qualities such as pharmaceuticals, food, and many specialty chemicals, including greases and lubricants, manufacturers walk a ἀne line between producing products that are considered commodities on one hand, while still being very specialized to meet customers’ exacting standards.

Issues with Automation in Batch Production Processes

For batch processing, the biggest advantage is often the capability to customize each batch to meet a customer’s requirements. With the advent of computer-based control system technology, the continuous process world quickly adopted the DCS (distributed control system) to automate control functions, replacing pneumatic and single loop analog control. On the discrete manufacturing side, the PLC (programmable logic controller) was developed to replace complicated relaybased machine controls used in many industries.

For batch manufacturers, the introduction of computerbased automation and control technology put them in a quandary. There were certainly recognizable beneἀts to automating a batch process: improved quality, consistency and lower manufacturing costs, but there were downsides as well. In batch manufacturing, procedural control is a major requirement and programming often became very complex to allow users the ability to switch product manufacturing procedures. Typically the systems were coded by very talented control engineers who understood the embedded procedural

control and had to make changes requested by the plant chemist or process engineer. Often the programing was very complex and if the control engineer who designed it originally switched jobs or got promoted, it became difficult to make changes to the batch system.

A Brief History of the ISA-88 Standard.

This kind of frustration was duplicated in many industries such as food and beverage, pharmaceutical and specialty chemical manufacturing. In response, in 1988, the International Society of Automation (ISA) formed standard and practices committee SP88 to provide guidelines for the design and speciἀcations of batch control systems, drawing from existing standards and recommended practices in the industry with the objectives of: 1. Deἀne terminology speciἀc to batch control systems that will encourage understanding between users, equipment vendors and system integrators. 2. Provide a standard structure for data in a batch control language to simplify programming, conἀguration tasks and communication between various components of the system. 3. Provide a standard data structure for batch systems that will simplify data communications within the system architecture. 4. Determine a standard batch control architecture.

After many years of intense work by the committee, the ISA-88 standard was approved in 1995 and was approved by the IEC (International Electrotechnical commission) in 1997 as IEC 61512-1. The standard was reviewed and updated in 2010.

Advantages of the Standard

Since the approval and publication of the standard in 1995, many companies in many different industries saw many beneἀts in ISA 88, including: • A common terminology and set of models for owner operators to discuss system requirements with automation vendors and system integrators. • A conceptual basis for separating the recipe that instructs how the batch is to be made from the equipment that is used to make the batch. This separation enables process specialists, chemists, and formulation scientists to make changes in their recipe procedures without having to make changes to equipment control code. • A modular structural approach that promotes reusable code and procedures. • Scalable models and concepts that are expandable if additional levels are needed and collapsible if all the levels described are not needed. • A structure that can apply to automated and manually-controlled batches. • A methodology that applies to simple batch processes as easily as it does to complex batch processes.

Key Concepts of ISA-88

To introduce the working concepts of ISA-88 we need to examine the primary models and deἀnitions that are the most important components of the standard. Physical model (for equipment) The physical model describes the hierarchy of equipment used in batching operations.

The model describes seven levels shown in Figure 1.

The ἀrst three levels (enterprise, site and area) primarily provide a connection into the business systems of a company and are not used in detail when implementing a batch automation process. The enterprise is the company that owns the plant. It may include multiple production sites. The site is typically the plant where the manufacturing takes place. It may be identiἀed by physical, geographical or a logical segmentation. An area deἀnes a speciἀc location within a site such as a building or other physical layout.

The process cell is the highest level of ISA-88 where batch control boundaries are deἀned when implementing the standard. The process cell contains all of the equipment required to manufacture a batch. A process cell may contain more than one pathway or process train to complete a batch.

A unit is where batch processing occurs, and is typically a vessel such as a reactor or mixing tank that performs some sort of value-added activity such as blending or reaction that adds value to the product being processed. A unit can only contain one batch at a time.

An equipment module is a group of items that works together to perform a processing activity. Some equipment modules might be ἀxed in place and therefore associated with only on unit. Other items may be more portable and shared among multiple units. Something like a CIP (clean in place) system might be allocated temporarily from one unit to another during processing.

Control modules form the lowest level of the model which includes basic sensors, actuators and other process equipment that can operate as a single entity and typically interfaces with the plant’s control system.

Procedural model (for recipes)

The procedural model (ἀgure 2) deἀnes the equipment actions that occur in a sequence. Like the physical model it is hierarchical in nature and also contains equipment requirements and formulation information.

A procedure is an ordered set of unit procedures and encompasses the overall strategy for manufacturing a batch. It orchestrates the complete control of all the equipment in the process cell.

The next level is the unit procedure, which is an ordered sequence of operations carried out in a single unit. Only one unit procedure can be active in one unit at a time, although two or more unit procedures can be active as long as they are in separate units. An operation is an ordered sequence of phases carried out in a single unit. Operations typically involve taking the batch being processed from one type of physical change to another, such as a reaction, mixing or heating.

The phase is the ἀnal element of the procedural model and performs actions on the process. They are the elements of the procedural model that actually perform processing actions on the batch. The higher

level procedure, unit procedure, and operations are used primarily to group, organize and direct phases

Linking procedures to physical equipment

At some point, a procedure to manufacture a batch must connect the procedural model and physical model to achieve process functionality. The capabilities of the physical model equipment are used to accomplish the desired processing tasks of the procedural control model.

Figure 3 from ISA88 shows an example of the mapping between the procedural control model, physical model, and process model. Note that a one-to-one relationship is not required. In the example shown, unit procedures, operations and phases of the procedural control model can be supported by the units of the physical model.

States and commands

ISA-88 emphasizes the importance of process states and commands. The state speciἀes the current condition of a procedural element. A command is one method for moving the procedural element from one state to another. The standard gives an example of a state diagram, but it is not necessary to follow the example. In the example shown in ἀgure 4, the procedural element in a routine execution would start in an idle state. When issued a run command, the procedural element transitions to a running state performing its normal processing task. Once the procedural element completes its processing task, it transitions from a running state to a complete state and waits for a reset command to cause a transition to an idle state. The commands pause, hold, stop and abort and the corresponding process states paused, held, stopped and aborted represent different levels of exception handling of the procedural element to get it in a condition that is appropriate for efficient and safe operation of the plant.

Example in grease manufacturing

Figure 5 gives an example of how processing equipment may be categorized utilizing the ISA-88 Physical model. In this simple example the Process Cell contains only one Unit, the dispersion vessel. The equipment associated with the dispersion vessel contains two equipment modules material charging and recirculation. There are four control modules deἀned two

of them are organized under the equipment modules pump and material selection. The other two Dispersion and Temperature control are directly associated with the unit- the dispersion vessel.

Figure 6 shows how the procedural model may be applied to a basic grease manufacturing procedure. The overall procedure Make Grease A contains the unit procedure component Make Suspension. The unit procedure contains the operation AIP suspension with one of the phases add oil. Typically it is the phases that would be associated with the control modules in the physical model.

Applying the principles of ISA 88 to other plant applications

Packaging and other discrete manufacturing

ISA-S88 Part 5 (Make2Pack) embraces some of the basic concepts developed for the batch manufacturing industries with the intent of providing the same beneἀts to the machine control industry, speciἀcally packaging machines. An implementation example of ISA-88 became the basis of the packaging standard known as PackML. The OMAC PackML Implementation Guide can be found at the OMAC website. http://www.omac.org/content/ packml

Continuous process applications

Since ISA 88 was adopted, many engineers have informally applied the concepts of ISA 88 to continuous processing control applications such as physical

model, modularization and state operation model. In any continuous process operation there are many procedures that are executed to assure the safe and efficient running of the process such as startup, shutdown, and product grade transition. In 2010 the standards committee was formed (ISA-106) to focus on the procedural operations in continuous process applications. In August of 2013 the committee issued their ἀrst technical report, “Procedure Automation for Continuous Process Operations – Models and Terminology” which is available from the ISA http://www.isa.org/Template.cfm?Section=Standar ds2&template=/ContentManagement/ContentDisplay. cfm&ContentID=94066

Recommended reading

1. The WBF Book Series: Volume 1 ISA-88 Implementation Experiences. Momentum Press 2010 Edited by William Hawkins, Dennis Brandl, and Walt Boyes. 2. http://www.momentumpress.net/books/wbf-seriesisa-88-implementation-experiences 3. This volume is a collection of papers that were presented at the World Batch Forum (Now part of MESA http://www.mesa.org/en/index.asp about several companies experiences in implementing

ISA in different applications and industries. 4. Applying S88: Batch Control from a User’s Perspective by Jim Parshall and Larry Lamb. Published by the ISA(International Society for Automation) 1999. 5. http://www.isa.org/Template. cfm?Section=Books3&Template=/Ecommerce/ ProductDisplay.cfm&ProductID=2967 6. This book is a case history on applying ISA-88 at Ben & Jerry’s St. Albans ice cream plant. The book is informative and entertaining for covering a technical subject.

Bibliography

• ANSI/ISA-88.00.01-2010 Batch Control Part 1: Models and Terminology. Research Triangle Park, NC ISA, 2010 • Ishchuck, Yu. L. Lubricating Grease Manufacturing Technology. New Delhi, India, New Age International Publishers 2005