Process Flow Diagrams
A process flow diagram is used for a plant with many processes. These diagrams contain the basic plant topology and the connections to model the data into a production plant model. Peter instructed the team that they would be using process flow diagrams to build the context necessary for EIDI data.
"To gather the required information for each of the process units, we need to build a process flow diagram, which includes references to the sensor tags or identifiers from the control system," said Peter. The process flow diagram represents a quantum step up from the block flow diagram in terms of the amount of information that it contains.
Peter explained, "Process flow diagrams describe the physical plant, and we can use them to develop process simulation models." These diagrams are usually developed when the plant is constructed, and they are similar to the architectural drawings used when building a house.
For the South Texas refinery, the process flow diagram contains the bulk of the process and maintenance engineering data necessary for the design of a metallurgical or chemical process. In addition, process engineers use the process flow diagram to abstract events in the plant.
For plant information management, the objective is to capture the necessary information for performance monitoring of the process (production quality, equipment reliability, and environmental monitoring). The process information is used to predict quality variables or to define when the system should alert engineers to assets that fall below quality levels set in target plans. "While most process flow diagrams include similar information, the process flow diagrams from one company vary from those describing the same process at another company," offered Peter.
A typical commercial process flow diagram contains the following information:
- • All the major pieces of equipment in the process are represented on the diagram along with a description of the equipment. Each piece of equipment is assigned a unique equipment number and a descriptive name.
- • All process flow streams are shown and identified by a number.
A description of the process conditions and chemical compositions of each stream are included. These data are displayed either directly on the process flow diagram or included in an accompanying flow summary table.
- • All utility streams supplied to major processing equipment are shown. Each piece of equipment has its own description of the process variable that should be included. The diagram also should note the unique sensor tags associated with each piece of equipment. Doing this provides information to build the contextual asset object model and the associated physical description.
- • Basic control loops are displayed, illustrating the control strategy used to operate the process unit during normal operations.
The same principles used to draw block flow or process flow diagrams can be used to develop powerful information linked to real-time and historical data. The elements making up the process flow diagram are created from templates whose additional properties and attributes can have data references to external databases. For example, the template attributes can store the equipment numbers and physical descriptions of equipment.
Peter announced that he wanted the digital transformation team to use process flow diagrams to start organizing the data generated in the process units (a process unit is composed of several pieces of equipment and components and includes details about individual devices or pieces of equipment).
Peter said that Monica Armstrong (planning and economics coordinator) could build on the foundation established by the process flow diagrams. She offered to provide a plant unit block flow diagram to organize the basic data necessary to integrate requirements for the plant schedule she prepares daily. This would add data definitions for products, maintenance, quality, and inventory. Combining these elements will make it possible to report the performance of all units based on a daily schedule.
Peter observed, "The process flow diagram provides all of the information we need to establish process-control protocols and prepare cost estimates to determine economic viability for the continuous process improvements. Using process flow diagrams with real-time data and events will help create processing plant optimization."
"Process flow diagrams are a key ingredient in digitizing the refinery," explained Peter. "In conjunction with the EIDI, the process flow diagram is used to proactively estimate equipment conditions and resources used in the refinery. It can help pinpoint issues, such as the efficiency of the pumps and compressors. It can be used for preparing estimates for inventories, and by using online process analytics, it can be used for predicting product quality."
Peter continued, "In addition, it is the basis for developing process simulators for mass and heat balances. It is also regularly used to diagnose operating problems that arise and to predict effects of process changes. Moreover, the process flow diagram is used to train operators and new engineers" (Bascur 2019; Steyn et al. 2018).