Comments about technological history, system fractures, and human resilience from James R. Chiles, the author of Inviting Disaster: Lessons from the Edge of Technology (HarperBusiness 2001; paperback 2002) and The God Machine: From Boomerangs to Black Hawks, the Story of the Helicopter (Random House, 2007, paperback 2008)

Thursday, March 10, 2011

Texas Power Grid's Freeze-Up, Five Weeks On

We're waiting for an authoritative report explaining why dozens of generators were unavailable, or tripped, on February 1-4. And we're waiting for a complete list of units involved. The only list on the ERCOT site is a partial one dated February 16. ERCOT might stand on its rights under the law of deregulation and wait until April before releasing a final list. 

I count roughly 60 distinct power stations; most of the entries are multiple units within a single station. An example of a single station having multiple units is Midlothian Energy LP in Ellis County, which according to the ERCOT list had three gas turbines unavailable sometime during the declared emergency. 

See this 2007 power-plant list from the Texas Commission on Environmental Quality for names of power plants along with information about the prime movers, their manufacturers, and the nameplate power output.This makes it a little easier to understand the ERCOT list. 

The majority on ERCOT's list are gas turbines. Many are the more efficient combined-cycle units in which exhaust gases are routed through an HRSG (short for heat recovery steam generator), which uses the heat to boil water to run a steam turbine. 

HRSGs are an important component in today's plants that raise the thermal efficiency of gas-fired units but they can be finicky during ramp up and shutdown, and positively troublesome if not protected from freezing. Among the HRSG components known to be vulnerable if not kept warm heated: condensate drains, water-level sensing lines between steam drums and SCADA transmitters, instrument-air lines, and end-caps of headers.  

Some geek-friendly information about the hard freeze of February is in this document filed with the state Public Utility Commission by El Paso Electric, "Report on Weather Event: February 2-4, 2011."

El Paso Electric (which isn't within the zone covered by ERCOT, by the way) said there was no shortage of fuel gas to its plants. The problem was intense cold that overwhelmed the usual half-measures like electric heat traces. 

Power plants can run fine at much colder temperatures (like ours in Minnesota) but only if they are fully prepared.

On p. 13 of the El Paso report there's a bone-chilling description of how employees and contract workers took up positions on catwalks or ladders 10 to 15 feet apart, wielding blowtorches to heat up a water line between the steam drum and the sensing transmitter. A detailed chronology in Exhibit C describes how units would trip; come on line after much effort; then trip shortly afterward.

Texas households who lost power but are facing higher bills even so are not happy. Said North American Electric Reliability Council (NERC) Chairman Gerry Cauley to a Senate committee's field hearing three weeks ago:
"The events of February 2011 give me cause for significant concern. These are not new issues. We’ve had severe weather before.  We must continue to ensure industry is learning from the past, and must not allow institutional knowledge to fade.  These issues must be kept at the forefront."

1 comment:

  1. As one of those whose power was out that bone chilling day, I appreciate your post. But there have been much colder cold outbreaks in the past without power problems here in Texas, subzero temperatures in Central Texas in 1989, for example. Is the freezing point higher than it used to be?