Figure 1 - Original Dryer Steam Control Valve

SMI did not recommend the same method of flow indication for the steam vat control valves due to the mixed phase nature of the heating medium (steam/condensate/boiler blowdown). Instead, SMI advised at 30% design that a flow transmitter be included in the steam header upgrade project (performed by others). That project was completed before this installation.

Valve power, valve position feedback, transmitters feedback and transmitter power wiring were all new circuits that had to be routed within new conduit and terminated at the valves and appropriate I/O points.

Controls Engineering & Programming

Steam Management, with it’s system integration partner Cross Company (www.crossco.com), executed the PLC programming and controls commissioning required for this project.

The project included PLC programming to calculate steam flows across the dryer and press steam valves. The program uses saturated steam properties, based on the readout of the valve’s upstream pressure transmitter. The program then calculates flow across each valve based on the valve’s position vs. Cv flow curve and the differential pressure reading across the valve, measured between the two transmitters.

For the vat valves’ flow estimate, the new flowmeter value is proportioned across the valves based on each valve’s position feedback.

During project design, extra functionality was added to the programming to override valve position based on an upstream pressure setpoint at each valve. This function serves to protect the steam header pressure from being depleted. If the steam pressure drops too far, the valve enters “holdback” mode, and the PLC limits the valve until header pressure is restored. This pressure set point can be set strategically for each location to prioritize users (i.e., if dryer 1 is the priority over the presses, dryer one pressure protection set point could be set lower so that holdback mode for that piece of equipment activates later).

Additionally, a “flow holdback” mode was programmed for the vat valves to limit the total flow to the vats.

The following controls engineering deliverables were provided for the project:

• Network diagram showing design concept and controls scope
• I/O list with 40 data points, including 26 new feedback signals, terminated in 3 separate PLCs
• Functional Design Specification (FDS) and Detailed Design Specification (DDS) documents
• System testing plan
• Factory Acceptance Test (FAT) performed using an in-house created process data simulator
• PLC program modifications, uploads, and troubleshooting to incorporate all new features and calculations for 4 separate PLCs.
• Coordination of all new data points and collaboration with Weyerhaeuser controls engineers on new HMI screens to communicate the new data. These screens are shown below.

Figure 3 - Steam monitoring screen for dryers and presses valves

Key Actions

The limited availability of plant-wide steam outages and the long lead-time of critical components complicated this design/build effort. To facilitate both limitations, the design effort included accelerating the material selection process ahead of the 100% design, with customer buy-in, to ensure materials would be available and on-site for the January outage.

Three-phase project approach:

Phase I – Performed 100% design engineering including new PLC programming

Phase II – Purchased long-lead time equipment

Phase III – Installed and commissioned new equipment and PLC programming during mill outage. Collaborated with plant controls personnel on new HMI screen designs.

Phase IIII – Was executed through a collaborative 30%-90%-100% stage-gate design process.