Winterization

[Volkonski]

NBC DFW
@NBCDFW
WATCH LIVE: ERCOT leaders are convening in their first meeting since the winter storm disaster left millions of Texans without power for days.

What is important here is the photo.

This is a counter flow water cooling tower such as is used in coal fired power plants and the petrochemical industry (which is why I know about them). Hot water is pumped into distribution trays at the top of the tower and then falls down against a flow of cool air pulled up by fans. The water cools and then is pumped to heat exchangers to remove heat from the process.

This type of cooling tower has an inherent vulnerability. When the air temperature drops below freezing, drift (small water droplets) from the tower will freeze on nearby surfaces including the tower itself. In the photo ice has begun to build up at the air inlet to the tower. If nothing is done ice can build up so much that the tower may collapse under the weight.

That happened to a cooling tower in Canada at a plant owned by my employer which is one the the things that caused me to learn about cooling towers in addition to worrying about the cooling water chemistry at a time when traditional water treatments (chromates mostly) were facing bans.

So how do you prevent a wooden water cooling tower from icing?

1- Shut down the operation entirely. This was a popular option along the Gulf Coast last week.

2- Shut off the fans or even reverse them. This makes the tower less efficient so the cooled water is warmer. This is not a long term solution but it might get you thru and day or so. (Note, the air leaving the tower via the stacks must be above freezing temperature otherwise ice will build up on the fan blades.)

3- Use steam to warm the tower. Of course the steam pipes and valves must be in place ahead of time. My employer had plants in Alberta that used this type of cooling tower. Their towers were covered with steam pipes intended to prevent freezing during winter.

What do you not do (that inexperienced plant operators are likely to do).

1- Turn off the water flow to some of the tower cells (in the photo each fan pulls air thru a single cell). Yes, this will make the cooling water warmer but the cells that are dry will cool quickly and ice will build up on them from the drift from the still operating cells. This is a good way of insuring a collapse.

2- Turn off the water flow entirely. Unless the pipes and pumps are drained this risks freezing the pipes and pump which may cause bursting.

Other issues.

1- Drift. All water cooling towers produce drift. In the winter this drift builds up as ice on nearby surfaces. A local ice storm in effect. It is a good plan to located such towers well away from other structures, parking lots and so forth.

[Reality Check]

I worked in refineries. In the olden days we used two speed reversing motors on the fans on cooling towers. Of course you would run them in reverse to prevent icing. They were a controls nightmare however. Now you can use a normal induction motor with a variable frequency drive. They worked great in that application.

[filly]

I rely on you guys for the mechanical explanation here. My question (as someone who almost froze to death in their own home) is: what did the plants that did not fail, that continued to operate do?

[Volkonski]

Heat tracing and lagging.

If ever you have seen process plants or even just photos of then you might have noticed that they contain a lot of pipes and lines. Sometimes miles of them.

Often these pipes are insulated either to keep process heat in them or in the case of cold lines to keep ambient heat out of them.

In addition to insulation, pipes and lines are often heat traced using electric heaters or steam. (Or cold traced if the liquid in the pipe must be kept cool.)

When extreme cold or hot air temperatures occur these can exceed the capability of the insulation and/or tracing to maintain the required pipe temperature and so force a shutdown.

Here we come to the design issue. How much insulation and heating capacity do you install on a given line located in a given place? The short answer is as little as possible based on likely ambient temperatures.

(It is the same with wind loads. On the Gulf Coast you might design for continuous 175 MPH winds. In Singapore where the worst wind gusts since records have been kept rarely go above 80 MPH you would design for maybe 100 MPH winds.)

Plant designers look at the data and design to keep plants operating over a range of likely temperature accepting the fact that once in a while the plant will shut down. High reliability is no good if your less reliable competitors can undersell you most of the time because they spend less on reliability.

Our modern world is very interconnected and very dependent on electricity.. As seen last week a cold weather event became an electric power outage event both of which caused a municipal water outage event and then all three combined closed schools, businesses, churches, etc. (Oh, there was also a snow and ice event which became the least of our problems.)

So how reliable should the electric power system be? How much will electric customers be willing to pay for reliability enhancements that are only needed for a few days every 10 to 20 years? Should critical electric power users have their own backup electrical power systems? Should home owners insulate and trace their water pipes? (Heat tracing won't do much good without power so maybe they should keep a generator too.)

Do we need more warming centers? Last week part of the problem seemed to be that people who needed them didn't know they were there or had no way to get to them.

Should plumbing codes be revised to keep pipes out of exterior walls? Some houses that never lose electricity still suffer from frozen pipes.

It is complicated and therefore I suspect we will continue to muddle along.

[Reality Check]

Heat tracing and lagging.
:snip:

Yes for sure. I think fuel type also played a role. Wasn't natural gas either not available or outrageously expensive when the freeze hit? I would say location made a difference. Plants not in the coldest areas had a better chance of staying on line. Finally luck. If the wrong instruments freeze up you are probably going down.

[Chilidog]

This was one of the schools that I do managing environmental consulting work for.



Notice in the picture there are actually two buildings. On the right is the original structure, built in 1881, when it's namesake was still alive. The left building is the modern addition, built in 1893. Yes. The fire escapes are iced over.

Here are a couple shots of the alley side





These older buildings have exterior roof drains.

When the downspouts freeze up, the water flows out the overflow sump.

And freezes itself.

Meanwhile melt water ponds on the roof and eventually finds a hole.

[noblepa]

High reliability is no good if your less reliable competitors can undersell you most of the time because they spend less on reliability.

This is precisely why state or federal regulation is required. That way, the playing field is level, if all providers are required to spend the same amounts on this type of reliability.

But Texas chose to build an isolated power grid that does not cross any state borders, so that they could avoid federal regulation. Then the legislators in Austin, thinking that all regulation of business is the work of the devil, chose not to implement regulations calling for weatherization.

[filly]

Heat tracing and lagging.
:snip:

Yes for sure. I think fuel type also played a role. Wasn't natural gas either not available or outrageously expensive when the freeze hit? I would say location made a difference. Plants not in the coldest areas had a better chance of staying on line. Finally luck. If the wrong instruments freeze up you are probably going down.

I've "heard" some of the natural gas pipe valves froze too. I don't know where "not in the coldest areas" would be last week. McAllen, 13 miles from the Mexican border, where it's always warm, was frozen too.

Note also that a good swath of NE Texas (including Beaumont) opted out of the Texas grid and is part of the East grid of the US. Wonder why they made that decision?

[AndyinPA]

Heat tracing and lagging.
:snip:

Yes for sure. I think fuel type also played a role. Wasn't natural gas either not available or outrageously expensive when the freeze hit? I would say location made a difference. Plants not in the coldest areas had a better chance of staying on line. Finally luck. If the wrong instruments freeze up you are probably going down.

I've "heard" some of the natural gas pipe valves froze too. I don't know where "not in the coldest areas" would be last week. McAllen, 13 miles from the Mexican border, where it's always warm, was frozen too.

Note also that a good swath of NE Texas (including Beaumont) opted out of the Texas grid and is part of the East grid of the US. Wonder why they made that decision?

Maybe they remember the last time this happened.

[Volkonski]

Heat tracing and lagging.
:snip:

Yes for sure. I think fuel type also played a role. Wasn't natural gas either not available or outrageously expensive when the freeze hit? I would say location made a difference. Plants not in the coldest areas had a better chance of staying on line. Finally luck. If the wrong instruments freeze up you are probably going down.

When the big freeze hit demand for natural gas for heating and electrical power generation skyrocketed. That was why the PUC increased the wholesale price of electricity. Operators of gas-fired power plants were reducing electricity production so as to not lose money paying for high priced gas.

There were also reports of gas lines freezing.

Years ago Texas law was such that gas produced in Texas was sold very cheaply inside Texas. "Cheap intrastate gas". The result was that gas was used for many applications in Texas. Gas powered clothes driers. Gas powered air conditioners. Gas home heat. Gas powered utility electric generators. Oil never got much of a start start here for home heating or power generation. Inertia being what it is, Texans still use a lot of gas.

Oil is a liquid and can easily be stored in tanks. Natural gas is a gas and, short of liquifying it at very cold temperatures, it is hard to store lots of it. So when demand for gas goes up you can't just draw down on stored gas for very long. Pretty soon you are constrained by what the gas wells can produce. That is why Gov. Abbot ordered TX gas producers to stop shipping gas out of the state during the worst of the cold weather. This of course created problems for Mexico and some other US states.

Soon the air temperatures went up. Demand for gas (and electricity) fell.

[Chilidog]

In illinois we have a gelogical formation in the middle of the state where we pump the gas back into the ground for storage.

Also, I've been to a gas transmission station.

The compressors are turbine engines and they have to be cooled down and the water extracted before the gas can go into the pipeline. My bet is that there is a ton of water in the gas lines in Texas and that's what froze.

And stay out of the methyl mercsptan room.

[tek]

This is one of the reasons grid interconnection is important. Mutual aid.

But too also: when you are part of an interconnection you have to abide by the reliability rules... the Northeast blackout of 2003, for example, was basically caused by First Energy playing fast and loose with the NERC/FERC reliability rules -- simultaneously in many areas, from vegetation clearing to alarm supervision..

Every time something like this happens on an interconnection, EVERY company works to make sure it doesn't happen again - and to clean up everything else laid bare by the failures.
Because no company wants some jerk (company) to take down THEIR network. This is another important reason for interconnection.

Texas, however, seems to believe in magic energy fairies.. they don't have to listen to the people who know their shit when it comes to grid reliability.