This post examines the attributes of state based control and the value delivered to manufacturing from the initial design through the operating life of the facility by improving the effectiveness of operators. This is part 4 of a 5 part post and discusses from green and brownfield expectations to instrument justification.
Green and Brown Field Project Expectations
Projects have ever-growing expectations. There is pressure for time lines to be shorter to get to market in a competitive environment, expectations for cutting costs and being efficient with capital, and rising expectations for plant performance when they come on line. Plants need to come up smoothly and safely with no environmental or safety issues while meeting ISA 18.2 alarm loading standards from OSHA as RAGAGEP.
How State Based Control Can Help
The implementation of state based control through standard reusable architecture can improve the profitability and performance of manufacturing from the initial design throughout the operating life of the facility.
Knowledge Capture Through State Based Control
Having a well-designed state based control system is a way to guarantee that the knowledge necessary to operate a facility is captured for future use after the retirement of experienced employees. Capturing the knowledge in state based control gives a complete means of capturing the operating expertise of startup, normal run conditions, shutdown and abnormal conditions. Capturing knowledge into state based control is an efficient way to retain, use and proliferate the knowledge. The time to do it is now, before the knowledge leaves the workforce.
Leverage Reusable Control Technology
State based control has been implemented and standardized for some time through ISA S88. It is often associated with batch processes but works equally well for continuous processes. S88 was written to improve efficiency. It provides a standard way to specify equipment and control modules in an architecture that can be re-used. ISA 106 Procedure Automation for Continuous Process Operations is in development.
Control modules, equipment modules and unit modules are re-usable components for the control design which are designed in a generic form to reuse in specific applications. For instance, one reactor may be charged with a number of things, and a plant may have multiple reactors leading to many charges. Some of the charges may be by weight or others by integrated flow. In the end, one equipment module can be designed using different control modules for all of the charges. The state based control and dynamic alarm rationalization can be designed into the charge equipment module and reused where needed. On a high level, unit modules are made by combining equipment modules, and equipment modules are made by combining control modules. Control modules interface with the instrumentation and many of the differences in the process can be isolated in the control module level. For instance, two reactors in the same service, in different locations, may charge the same component. In one location a weight change is used, and in the other, an integrated flow is use. A control module can be built for each and plugged into the same charge equipment module. That equipment module plugs into the same unit module that can be reused for each application.
One recent project was implemented with this architecture. It took 30% of the time to complete versus a standard architecture.
Instrument and Alarm Justication
Throughout the design process, control engineers, process engineers and equipment subject matter experts should be involved in justifying all instrumentation by its intended purpose. The instrument may be for the safety instrumented system, control, alarming, troubleshooting, regulatory or accounting purposes. Dynamically rationalize alarms in accordance to the corporate alarm philosophy to both determine the correct alarms to have for the process and the instruments required. More of the work may be shifted forward, but I/O creep and the associated costs are eliminated, resulting in improved capital efficiency, lower cost and higher quality.