Industry:  Petroleum Refinery
Project Type:  StackVision Software-Only DAS Implementation
Scope:  7 Units: 2 FCCUs, 2 Charge Heaters, 3 SRUs
Driver:  Refinery Sector Rule (RSR) deadline for non-flare units
Regulation(s):  Refinery Sector Rule (RSR)
Parameter(s):  Temperature, O2-Dry, CO2, CO
Location:  Texas
Year:  2018

Project Description

The units configured in this project had an accelerated compliance deadline, so they were broken out of the larger RSR DAS requirements and used as the initial project. The RSR Flares and Part 60 reporting configurations were handled in a separate mixed-DAS project following this one.

For these units the plant personnel felt that they could handle operational data validity, one-minute averages and QA/QC activities. They wanted to use StackVision as a system of record, for documenting data validity, building extended averages, trending, alarming limits, dashboards, reporting and so on. Since they did not install Data Controllers or re-wire most existing equipment, they were able to expedite the project to meet their deadline, but there are some trade-offs they needed to consider.

Problems or Requirements

They chose to implement a controller-less DAS
In a standard ESC DAS the 8864 Data Controllers would handle data acquisition, validation, and averaging and provide complex communications capabilities as well as a storage buffer of up to one year of data. A software-only DAS lacks any 8864s and Pi data from the historian is pulled into StackVison through an OPC UA Server.
Daily validations (calibration checks) are an important consideration
The controls group decided they would continue to handle the daily validations for this group of analyzers, rather than take advantage of the automated calibrations and test management that the 8864 provides. The plan was to pass the calibration and maintenance Pi tags to StackVision.
Removing the controller removes a safeguard
Following a break in network communications, data in the 8864 can be quickly back-polled into StackVision. With Pi as the delivery channel, any interruptions in the OPC or StackVision services will cause missing data, and all data for that time period will be missing.

Solutions and Outcomes

Data scans every 30 seconds
The StackVision OPC UA Server has an associated Data Mapper tool that we provide for easy setup. The last reading in a minute is written to the 1-minute average in StackVision. Once there, normal data processing moves forward.
Using Event Lab to manually load calibration/ maintenance tag values
The planned-for calibration/maintenance tags were not yet setup for us to use at the time of installation. So, until they were available the time-online/SUSD/Hot Standby conditions and calibration results were all manually loaded through Event Lab, a powerful data management tool in StackVision. The tags were added in a later project.
Lack of a data buffer is an irritant, but workable
Plant personnel must manually export any missing data from the historian and import it into StackVision. Since the minute data originates in the DCS and StackVision’s validations are for the purposes of recordkeeping, the short delay in retrieving the missing data is not critical and StackVison alarms and reports keep everyone aware of any gaps.

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