Texas Power Problems For The Aficionado

[MrTShirt]

From an email discussion between a couple of indivuals:
Note, I removed some quotes to avoid presentation problems.


For those who don't know, I graduated KSU with 2 degrees - Electrical Engineering and Physics.
I spent the first half of my career building power plants and the last half building oil and chemical plants.
I've built 2 power plants in Texas and had 3 oil projects, not refining but gas fractionation - splitting mixed liquid hydrocarbons into their individual components (propane, butane, ethane, C5+).
Specifically, I'm an instrumentation and controls engineer, so all the devices that monitor and control the processes (flow transmitters, pressure transmitters, control valves, distributed control system, etc) are my specific area of knowledge.
Natural gas fired power plants and coal fired power plants basically make steam to run a steam turbine (NG plants also have combustion turbines in them as well, but by adding heat recovery steam generators to them and turning them from simple cycle to combined cycle it greatly increases the plant efficiency).
When you have a 16 inch line of superheated steam - it's not going to freeze.
However, the pressure transmitter connected to that line has to be remote mounted because the electronics can't take the temperature of the steam. When you remote mount it, you're using a 1/2 inch tubing to route the process fluid from the 16 inch line to the transmitter and that loses heat at a rate of 100deg/ft of tubing, which means it will condense to water and can freeze if not adequately freeze protected with electric heat trace.
If the transmitter line freezes, one of two things happens - either the pressure transmitter reading freezes as well (because the line is effectively bottled by the ice) making the pressure reading erroneous and the failure undetected OR the pressure reading fails high/low and the failure is detected by the transmitter.
Scenario 1 is dangerous, because you're essentially flying blind until some other device recognizes there's a problem. Maybe you're just sitting there cranking up the pressure in a steam drum because you're seeing it holding steady while your duct burners (supplemental heating) is cranking up to get more power output until the mechanical pressure relief valves go open.
Scenario 2 the process shuts down because the control system knows there's a problem and is programmed to shut the system down as a safeguard.
When you build a power plant or any facility, the client gives you the parameters to build to and one of them is the design max/min temperatures to account for. In Texas, they might say the 25 year low is 9 degrees, but the average low is 40 degrees. Depending on where the client sets their risk tolerance, that's what the engineer designs for.
My understanding from the ERCOT (Texas grid) numbers is that solar outperformed expectations by about as much as wind turbines underperformed. But it didn't really matter because fossil fuel power plants - which make up the majority of the Texas power grid - drastically underperformed.
Last thing - wind turbines can be relatively easily be retrofitted with de-icing accessories. Relatively, meaning you have to take the wind turbine housing to grade to do the installation of a thin electrical mesh. My area isn't wind, but that's my limited understanding,
  <blockquote> Another guy posted:

</blockquote>    Oh man did I love this post, excellent information. Yes, the Wind Turbines can be retrofitted, but more probable would be cold weather packages installed. The turbines in Texas froze because it was calculated risk that Texas wouldn't be dealing with the type of conditions it faced this past week. These same turbines will be fine during the next extreme weather snap if the energy company chooses to outfit each turbine with a cold weather package, but honestly it wouldn't make sense given the calculated risk. Just remember, all turbines aren't designed the same, they're designed specifically for the geographical location they'll be installed.
  Cxxxxxxxxx said...
The post was already long so I didn't hit on some other points of potential failure - the cooling tower fans icing up (though in cold areas you can put in reversing motors to provide a de-icing effect), cooling water basins icing up, other mechanical type failures from the cold - mainly because those AREN'T my area of expertise.

But just in regards to the instrumentation in conventional power plants - they're so often using much thinner and (potentially) exposed impulse lines and because they're connected to the control system - in fact they're the inputs to the control system - they're a huge potential weak spot if not set up for the weather.

I'm not as adept at nuke plants, but they also operate by making steam to turn a steam turbine (they just use the fissile material to heat a heating media which heats the water to make steam). So you could have similar issues there.
 
I did one project in Illinois where we put 3 Combustion turbines in a chemical plant and the turbine exhaust was used to make steam which was then used by the plant as part of their process.

Part of our design was that if the grid went offline the plant would be able to run in island mode. I set up the logic so when we detected the breakers to the grid opening the plant DCS would send a signal to the turbine controllers to go into island mode.

Well, during startup, once we had our steam generation on line, the owner didn't let us test the island mode logic so it wouldn't jeopardize the plant operation (since our steam was keeping things running on the chemical side).

Sure enough, 3 months later, there was a power outage on the grid, and our island mode lasted exactly 8 minutes before shitting the bed.

The client is pissed, and they call me up to site and they call in the turbine guy too, and I tell him, Man, I've looked at the historical logs, I see that when the breakers tripped we sent the signal to the turbine controllers...

I'll never forget, the turbine guy said, Oh, I know what happened - it was a problem in my programming (the turbine controller).

I said, Wow, that sucks. they're going to be all over you.

And he said, Nope. Because page one of my field summary report 3 months ago stated, At Client direction we did NOT do a functional test of island mode. They can yell all they want, this is what happens when you don't let us test.