Putting WFI to Work in Juncos

Automation and control

Amgen’s WFI unit is completely automated. “There’s no routine operator interaction,” says Cope. “We send a signal to turn on and start producing WFI, and tell it to turn off.” Mueller MES run on Allen-Bradley programmable-logic controllers (PLCs), and include an operator-interface terminal (OIT) for monitoring and configuration of set points, delay times, and PID (for “Proportional-Integral-Derivative”) loop parameters.

The WFI control is integrated with the process control system — Rockwell’s RS Batch — which is connected to a plant information system for data archiving. Integrating the WFI control with the batch system was fairly standard, Cope notes. “The biggest problem I’ve noticed between our system and any vendor PLC system was the ControlNet communication between the two,” says Cope. “We had some problems getting it set up and configured between the various skids. It was a little rocky at first, but once we figured it out, it went smoothly.

Design concerns

Both Jarvis and Cope were instrumental in designing WFI distribution at the site. The greatest challenge, Cope says, was accounting for the size of the facility and the numerous WFI applications throughout. “We have so many users spread over such a wide area that we ended up with some pretty long loops,” he says. “This presents a problem in maintaining a constant pressure.”

With long loops, it is best to keep flow rates low in order to keep loop pressure low, but this can lead to control issues. “Overall flow rates and back-pressures tend to fluctuate widely and make it difficult to control constant pressure,” says Cope. The solution, in one situation, was to make the loop with a larger diameter so that more fluid could be pumped to keep pressures constant.

In another instance, a control valve that could handle both high and low flow rates was placed on the end of the loop. This has been a “mixed success,” Cope notes, because the valve controls can not be tuned to easily accommodate the differing needs of the many WFI users. “The control valve doesn’t necessarily like to be tuned to handle many different scenarios because they all require it to respond differently,” he adds. “Essentially, you can tune the valve for one or two scenarios and see if it can respond reasonably to the dozens of other situations that arise.”

The results are “tolerable” since pressure requirements are not strict, Cope says, but the company will search for better solutions as it continues to expand. “I’ve only seen loops handled in a few different ways — with a back-pressure control valve, a spray-ball, or with a VFD [variable-frequency drive],” says Cope. “If you have no control valve at the end of the loop, you can use your VFD to maintain a constant pressure, but it increases the flow rate more than with just using a control valve.”

Science and sampling

Some would say that WFI is overused in most facilities, and that in many instances high-quality purified water would suffice. Jarvis agrees. “I’ve worked in successful plants where we’ve used high-quality purified water for upstream process steps,” he says. “It wasn’t until we got into purification, where we had unit operations that were designed to remove endotoxin, that we wanted to make sure we had low-endotoxin water downstream. Even then, the highly-purified water that we used upstream met WFI requirements for endotoxins.”

So why do it, then? Better safe than sorry, Jarvis says. “We have to be conservative.” As the WFI implementation in Juncos becomes more established, Jarvis and Cope plan to put more science behind their water choices.

The Juncos team samples its WFI water daily for conductivity, TOC, colony forming units and endotoxins. Most of this is done by analyzing samples in the laboratory. It also measures conductivity and temperature on-line using standard set points. In some Amgen plants, Jarvis notes, on-line TOC measurements are taken as well to back up lab data.

The entire science of WFI distribution needs upgrading, Jarvis and Cope believe. The subject of rouge discoloration on internal surfaces is a case in point. WFI systems should be re-passivated and checked for rouge every few years, and Juncos has a regular passivation regimen. “But it’s really not science-based,” Jarvis says. “We need to get better knowledge of whether or not rouge is a bad thing. We tend to think, ‘We’ve got rouge, we’ve got to get rid of it.’ But it’s possible that you could be doing more harm than good by doing this. You could be tearing your system up, so we’ve got to get some more science behind it.”