Doing Dew Point Tests and Lowering Expectations

Originally posted May 9, 2014:

There were times when I was working at the Coal-Fired Power Plant in North Central Oklahoma when I wondered if there was anything that we couldn’t do. Surrounded by True Power Plant Men I found that when we were facing a seemingly impossible task, a Power Plant Man would come up with an extremely creative solution to the problem. One such example was during the “We’ve Got The Power” program. I talked about this program in an early post called “Power Plant We’ve Got the Power Program” so I won’t go into detail here about the program itself. I will just say that we broke out into teams to find creative ways to operate more efficiently, and to cut costs.

I was a team leader of our team, and looking back I must have had two criteria in mind when I picked the team members that would be on my team. The first would have been that they were True Power Plant Men (and woman) with a higher than average intelligence. The second criteria would have been that they were friends of mine. I say this, because everyone on my team fit the bill.

During out team meetings, Terry Blevins would often say some bombastic statement that the average person may be inclined to dismiss immediately as being absurd. I say that because I remember more than once thinking that what Terry had just said wouldn’t amount to much. As it turned out, our biggest money saving ideas were those truly bombastic statements that Terry was making. One such idea had to do with the heaters on the precipitators that kept the hoppers and the insulators on the roof too hot to collect moisture.

The Precipitator is a very large box that takes the ash out of the exhaust before it goes out of the smoke stack (how many times have I made that statement in the last two years?). Anyway, the exhaust from the boiler after the coal has been turned to ash in the fireball in the boiler contains a large amount of moisture. The last thing you want to happen is for the temperature of the flue gas to fall below the dew point. When that happens, moisture collects on the structure in a form of… well… of Acid Rain. Basically eating away the precipitator and the duct work from the inside.

Somewhere along the line, it had been determined that the dewpoint of the flue gas was not higher than 250 degrees. So, as long as the structure was at least 250 degrees, no moisture would be collected. Four heaters were mounted on each of the 84 hoppers (on each of the two precipitators) and heaters were mounted on the roof around each of the insulators that held up the wire racks on both ends.

When Terry walked into the office to attend one of our first “We’ve Got The Power” team meetings, he said, I think we could save a lot of money if we did something about the heaters on the precipitator. — He may remember being greeted with blank stares (at least from me). Um. Ok. Heaters on the precipitator. I knew they were everywhere, but I never gave them much thought.

I think Terry could tell right away that I hadn’t taken his idea seriously. I don’t know. Maybe he was bothered by the sound of my eyeballs rolling around in circles as if someone has conked me on the head. So, he explained his idea further. He pointed out that the roof heaters on just one of the precipitators used about 211 kilowatt-hours and the hopper heaters used about 345 kilowatt-hours. Together it more than half a Megawatt of power. — This definitely caught our attention. That meant that between both of the Precipitators (since we had two boilers at our plant), we could possibly save over a Megawatt of electricity every hour we could shut down the heaters.

The plant has a similar electrostatic precipitator, only it is twice as long

The plant has a similar electrostatic precipitator, only ours is twice as long

After discussing all the aspects of the idea, we decided that in order for the idea to have any merit, we had to know if the dew point really was around 250 degrees, or was it possibly a lot lower. 250 degrees seemed high to begin with since the boiling point of water is 212 degrees. If lower, then we could have a workable idea. Originally, I wanted to tackle the task of finding the dew point. So, I went about it in a Science Experiment sort of way.

I figured that if we were able to lower the temperature of the flue gas to a known temperature below the dewpoint, and by knowing the volume of the gas, and the amount of liquid we could condense out of it, we could determine (possibly) the dew point. So, I brought my Graham Condenser to work, and Scott Hubbard and I went up to the 250 foot landing on the smoke stack with the intent of sucking a known amount of exhaust from the smoke stack while the unit was at full load.

Scott Hubbard

Scott Hubbard

We would run it through the condenser while running cool water through it to lower the temperature.

The Exact Graham Condenser used in our experiment Spring 1990

The Exact Graham Condenser used in our experiment Spring 1990 (and that’s my hairy hand in this selfie)

I could measure the output of the vacuum pump by filling up an inverted Erlemeyer flask with water and then letting the flue gas displace the water. — I always loved doing experiments like this in the 9th grade science glass with Mr. Godfrey our Physical Science Teacher (Donna Westhoff, who may sometimes read this blog was in my class and sat right behind me).

An Erlenmeyer Flask (from Google Images, not from my Chemistry Lab)

An Erlenmeyer Flask (from Google Images, not from my Chemistry Lab)

Ok. Side Story, since I mentioned Donna Westhoff from the 9th grade 1974-75 school year.

I knew that Donna’s father was a fire fighter, because one day during a special outing when we were with a group of bicycling Junior High School students and a teacher, we stopped at Donna Westhoff’s house to get a drink of water. On the walls in her house were different types of fire fighting treasures. Donna explained that her father was a fire fighter… That was the Spring of 1975 in Columbia, Missouri

Fast forward 16 years later (1991) at the Power Plant in the middle of nowhere in North Central Oklahoma. Just about a year after the story I’m telling now…. I left the logic room and went to catch the elevator to the Control room. When the doors opened, Tony Mena was in there with a bunch of college age students giving them a tour of the plant. I entered the elevator and turned around to face the door as it closed.

As I was standing there, I suddenly became aware that the person standing next to me was staring right at me. So, I turned to see who it was. Standing next to me was someone that looked very familiar wearing a big grin as if she knew who I was. I recognized her, and while my mind was going through filing cabinets of memories trying to index this particular person, I asked her, “Don’t I know you?” She shook her head and said, “I’m Donna Westhoff!”

A High School picture of Donna Westhoff  who is on the Lower Left

A High School picture of Donna Westhoff who is on the Lower Left

As the elevator door opened and we stepped out, Donna and I began talking about what we were both doing there. She was surprised to find that I had become an electrician at a power plant instead of some kind of scientist in a lab somewhere. Donna was going to school in Stillwater where one of the best Fire Fighting Schools in the country is found. Following in her father’s footsteps, I thought. After a while I could tell that Tony was getting a little perturbed that the wisdom he was imparting about the fire protection system on the Turbine Generator wasn’t being absorbed by Donna, so I cut our conversation short. It turned out that a very good friend of hers lived just two houses from where we lived, and her friend’s mother was my landlord. Peggy Pickens.

Ok. End of the side story, and another example of how I occasionally run into friends from my childhood in the most unexpected places (see the post: “Relay Tests and Radio Quizzes with Ben Davis“).

So. Scott Hubbard and I tried using the Graham Condenser and the Erlenmeyer Flask, but we quickly found out that this wasn’t big enough, to capture a large enough quantity. So, we increased the size of the condenser by winding a garden hose around inside of a water bucket and filling it with ice. Then we captured all the water that condensed in the hose.

A 5 gallon water bucket we used as our condenser with a garden hose and ice

A 5 gallon water bucket we used as our condenser with a garden hose and ice

When it finally came down to it. Even though it was fun trying to do this experiment halfway up the 500 foot smoke stack, I never was able to figure out how to calculate the dew point given the data I had collected.

That’s when we decided to look at dew point sensors in the parts catalogs. If we could stick a probe down into the precipitator and measure the dew point directly in the flue gas, that would be best. After looking at a few in the catalog, Terry Blevins said he thought he could make one. So, he went to work.

Terry Blevins

Terry Blevins

The next day he came in with an inch and a half conduit with hoses hanging out the back and a homemade sensor on the other end. I won’t go into detail how the sensor was built because some day Terry may want to patent this thing because, as it turned out, it was so sensitive that it could detect my breathe from about a foot away. If I breathed out of my mouth toward the sensor, it would detect the moisture in my breath. This was perfect!

We went to work on the roof of the precipitator sticking the probe down into different sections of the precipitator. It not only measured the moisture, it also had thermocouples on it that we used to accurately measure the temperature of the sensor as we varied the temperature by blowing cold air through the conduit using the same ice bucket and hose from before.

I could go into a lot of detail about how we performed our experiments, but it would only excite me and bore you. So, let me just say that we came up with two very important results. First of all, at full load when the humidity outside was at 100% the dew point was around 150 degrees! A full 100 degrees below what the plant had originally assumed. This was very important, because a lot of energy was spent trying to keep the flue gas above 250 degrees, and just by lowering it down to 210 degrees, still a safe amount above the dew point, that extra energy could be used to create electricity.

The second thing that we discovered was that the middle sections of the precipitator was a lot cooler inside than the outer fields. We realized that this was caused by the air preheater coils that rotated between the flue gas and the Primary Air intake duct. This took the last amount of heat safely possible from the exhaust and transferred it to the air going into the boiler so that it was already hot when it was used to burn the coal. Because of the way the air preheater coils rotated, the part of the duct toward the middle of the precipitator was a lot cooler than the air on the outside.

Diagram of a boiler

Diagram of a boiler. See the Air Preheater? Flue Gas on one side and ambient air on the other

Lower temperatures in the precipitator increased the performance, so we decided that if we could mix the air around as it was going into the precipitator so that the outer edges were cooler, then it would increase the overall performance. One suggestion was to put a mobile home in the duct work because in Oklahoma it was a known fact that mobile homes attracted tornadoes and it would probably cause a tornadic reaction that would mix up the flue gases. — We just couldn’t figure out how to convince management to put a mobile home in the duct between the economizer and the precipitator.

Thanks to Terry’s handy dandy Dew Point Sensor, we were able to prove that the hopper and roof heaters could be lowered to where we set the thermostat at 180 degrees. At that setting the heaters that used to always run at 250 degrees would remain off anytime the ambient temperature was above 45 degrees. In Oklahoma, that is most of the year. This turned out to save over $350,000 per year in energy savings at a cost of about 1.5 cents per kilowatt-hour. Not to mention the unknown savings from being able to lower the flue gas temperature by 40 degrees.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: