If the CCUG 2021 Day One roundtable on cold-weather preparation is any guide, winterization continues to vex plant personnel. Many of the issues can be traced to inadequate design bases and insufficient equipment. However, the root cause appears to be building “outdoor” facilities in locations which clearly require far better protection against protracted frigid conditions. Exhibit One: The tragic consequences in Ercot this past February.
For this virtual roundtable, convened in the early afternoon (Eastern time) of July 13, Steve Hilger, plant manager at Dogwood Energy (operated by NAES Corp) and a member of the Combined Cycle User Group’s steering committee, was joined by Mike Armstrong, engineering manager at Competitive Power Ventures’ Woodbridge Energy Center. Hilger’s plant is located south of Kansas City, Armstrong’s 2016-vintage combined cycle is in New Jersey about 20 miles south of New York City and near the shore. Both were designed as outdoor facilities.
Hilger’s first slide notes that the lowest ambient temperature experienced at Dogwood was -23F while the heat-trace design basis was +2F. Dogwood is two decades old and climate disruption is real, but surely this differential is better explained by designer negligence.
Woodbridge, says Armstrong, was designed to -8F but does not account for wind chill. “Most equipment, even our HRSG drums, lack enclosures, and are open to the wind.” Snow breaks and wedges were never installed on the roofs of outbuildings at Woodbridge. “Once we covered 175 valve handles to prepare for a cold weather event,” he lamented (Sidebar). Woodbridge has also added warming sheds on the top of the HRSG to keep personnel warm, and purchased several 120-Vac instrument space heaters wired to plug into outlets. These are used in transmitter boxes and ductwork with failed heaters.
Dig deeper: Heat tracing demands constant attention
Some of these temporary measures have their risks. Portable gas or propane heaters, for example, used in enclosed space elevate CO exposure to workers and present fire hazards.
The impacts aren’t solely on the equipment either. “Operators find reasons to be absent when it is cold outside,” Armstrong said. Woodbridge purchased steel-toed buck boots for winter work and makes space available in nearby motels to keep employees off the highways. We also remind them to look up for icicles in areas which may have leaks, he said, but also review work orders to identify equipment which may be leaking.
Equipment of special interest are drip-pot drains, attemperators, air filters (which can become plugged with ice), and outside air compressors, the last “a problem” at Woodbridge. “We had our heat-tracing contractor do an audit to compare design conditions to actual,” Armstrong said.
An audience member suggested that plants check for clogged drain lines using NDE. He said it takes his plant about three hours to check all HRSG drains in this way. And actions taken in other seasons, like a contractor removing heat tracing for a valve repair in summer, need to be checked.
Users struggling with winterization might spend quality time with the slides, which could be turned into a poster titled “Winter is coming” and hung in the plant’s lunch or common area. Here are a few bullet points:
- Review the 32F action plan (or prepare one if your plant doesn’t have).
- Review alarm points and operational permissives which may be impacted by cold-weather operation.
- Order bulk chemicals and review chemical properties to determine freeze points.
- Stage electric and propane heaters in problem areas.
- Develop HRSG drain procedures with valve identification in case there is only enough fuel to operate one unit.
- Perform a heat-trace audit in August/September and evaluate heat-trace insulation for deficiencies, keeping in mind that heat tracing cannot protect areas with water-soaked insulation.
- Verify calibration of all transmitters suspected of freezing or of over-heating.