New technology requires new ways of thinking, especially because safety is paramount. This is even more true for any situation where an established industry experience base is lacking.
“Did you have a good time on your extended holiday, my young apprentice?” asked Marnie Surfaceblow, vice president of Surfaceblow & Associates International.
Maya Sharma, lead field engineer for Marnie, replied, “Yes, ma’am,” as she steered the rental car to the plant guard shack and rolled down her window. “My family is very proud of me, but it was difficult to relax as so many came to visit. My aunties especially fussed over my traveling. Am I eating enough? Am I doing puja? And always giving a multitude of warnings to be safe. Every day it was something new.”
While handing their identification and business cards to the plant guard, Marnie asked, “Just how many aunties do you have? You’ve mentioned aunties Komal, Meghana, Rohini, Natasha, Uma, Pratibha, Sonal, Tara—forgive me if I missed any?”
Leaning over the steering wheel and staring into the distance, Maya replied simply, “In India, there are many aunties—many.”
“Someday I’ll introduce you to a literary character named Bertie Wooster; he also had problems with aunties … well, I think he rather deserved them. Anyhow, I’m certain they’ll be very proud of our next three projects—each one working to decarbonize fossil power plants. It’s a nice corporate buzzword you know, ‘decarbonize.’ Do you remember when everything was about ‘leaning in to synergize holistic pivots from greenwashing?’ ” Maya shook her head. Marnie continued.
“Like I explained in the project briefing, this municipality has a 40-MW pulverized coal power plant that, for contingency reasons, they need to keep operating. They converted it to run in dual-fuel mode with up to 100% natural gas a decade back. I helped with that, thank you very much. Then, their city council decided to see if they could be greener, and a local agriculture company said they could supply up to 20% of the total plant heat input with blue hydrogen. Believe it or not, they have a use for the carbon that’s stripped out. They called me up and knowledge-mined me, and then went with a cheaper contractor. Now, surprise, they have some problems,” Marnie explained.
“ ‘Knowledge mined?’ ” inquired Maya with a raised eyebrow. “Did you just invent your own corporate buzzword?”
“Nope, I’m pretty sure Grandpa Marmaduke used it a few times. Usually with much more colorful adverbs surrounding it. Our contact at this plant is notorious for doing that with our firm, and sometimes, it gets him—and others—into trouble. And given what they’re messing with, it really worries me,” said Marnie.
They received visitor badges from the guard, a map of the plant site, and some cursory safety pointers. The two women checked each other’s personal protective equipment, and headed to the plant.
1. The dynamic engineering duo of Maya and Marnie arrive on-site, ready to problem-solve. Source: POWER
The Adventure Begins
They were met and greeted by the lead plant engineer, Gary Hallidar, who led them to the plant conference room, where many adventures both start and finish. “I told them we should have hired you all from the start for this project, but as a municipality, they lean on us to always go with the lowest bidder that can safely do the job.” Having worked with Gary before and found him to be someone who put cost-cutting way over quality, Marnie wasn’t completely convinced, but nodded her head politely nonetheless. “I remembered the advice you gave me when I called you up, but the contractors we used had some different ideas, and one thing led to another…” Gary trailed off as they entered an already crowded conference room.
Introductions and business cards were exchanged, with Marnie relying on Maya to keep the names and faces straight. In small meetings, she could arrange the business cards in front of her in seating order, but with so many people, it became a blur. Sitting down and taking a large drink of truly terrible power plant coffee, she thought, “Well, they certainly went with the lowest bidder on their coffee. Korean War surplus?”
“OK, Gary, tell me what’s going on,” said Marnie. Gary scratched the back of his neck and looked slightly embarrassed. “Well, Marnie, we took the advice you gave us …” Gary began.
“Let’s be careful here,” Marnie interjected. “I didn’t give you any official advice. I’m a professional engineer and what I told you on the phone were general rules and recommendations, and you never hired me.” Marnie’s eyes flashed WARNING. “I don’t mind telling people generalities about technical solutions, but that’s all they were.”
“I’m sorry, and it doesn’t matter much anyhow since we told the contractors your adv … your general recommendations, and they had different ideas,” Gary replied, flushing more red.
Marnie choked down another sip of coffee. “OK, spill it.”
“Well, you said we ought to put the hydrogen in at the top part of the furnace, although I’m not sure I remember why, but the contractors thought it would be better in the middle of the burner zone,” said Gary.
Maya started at this. “So, very hot combustion gas enters the furnace at the hottest part of the furnace.”
“Yeah, and it’s overheating the boiler tubes. We had six forced outages in the first year alone in that area. Even with the burners tilted up 30 degrees, it’s still too hot. But there’s more than just that,” noted Gary.
“There always is,” sighed Marnie. “Alright, let me guess, they bought hydrogen burners off of Wish?”
Maya was forced to smile. “If they did that, ma’am, they’d still be waiting for them. How long have you waited for that Dragon Maid cosplay outfit?”
While Marnie desperately waved at Maya to change the subject, Gary replied, “No, they re-used the existing natural gas burners and …”
Maya stood up suddenly. “What? Did they re-use the gas lines, regulators, valves, and fittings?”
Gary rubbed the back of his neck again, as he and the plant staff looked even more embarrassed. “Well, yeah, because it was cheaper that way, and so, they tied into the natural gas lines at the distribution block on that burner level. But they built a nice monitoring shed to isolate the system from the rest of the plant in case there was a leak.”
“And you followed the API, ASME, and NFPA codes, of course? Who certified this? Who was your AHJ?” Maya asked, with a serious calm hiding a growing sense of fear.
“AHJ?” asked one of the plant operators.
“Authority having jurisdiction,” Maya explained, as Marnie nodded approval. “NFPA code enforcement is not required by law in this state, but someone in government, an insurance inspector, someone must be certain the work is proper.”
“And using hydrogen in existing natural gas lines, shoot, using it at all, can make the area classified as hazardous, hence, the term ‘Hazardous Area Classification,’ ” Marnie added. “By the way, your coffeemaker could probably fall under that category. Seriously though, Gary, you need to check all potential leak points, perform testing, ensure materials are suitable for alternative use from their original design, that you have proper leak monitoring, fire detection and suppression, and emergency response equipment.”
“Well, we’re self-insured, so we don’t have an inspector that does that. And there was leak testing done before commissioning,” Gary balked.
“I read that section of the report,” replied Maya. “It was exceedingly easy. It said simply, ‘No leaks detected.’ ”
Marnie laughed despite the seriousness of the situation. “It sounds like how my mother used to cook—the ‘by gosh and by golly’ method, where every single recipe was a new experience in culinary adventure. I told you about the time she tried cooking a turkey for two days at 180F, didn’t I Maya?”
“Yes, ma’am. A horror story you have relayed to me on many an occasion, validating my choice to be vegetarian,” Maya replied.
“We haven’t had any problems with the fuel system, the issue is our boiler tubes. The city keeps this plant running because we’ve always had really high reliability, but with one forced outage every two months, and being pressured to use this hydrogen so the city can say it’s cutting carbon emissions,” Gary stopped and shook his head in exasperation. “We should have had you all do this in the first place, but we can’t undo that, so how can you help us now?”
Marnie gripped the bridge of her nose and closed her eyes in deliberately exaggerated anguish. “Is there a coffee shop nearby? I need a quad-quad delivered. If they don’t know what that is, abandon all hope.”
Getting to the Heart of the Matter
“Problem number one, your plant uses a corner-fired tilting-burner design, with one burner at each corner and 4 levels total. All other things being equal, using all the burners should require 25% heat input per level, right?” Marnie quizzed Gary while looking over the current boiler drawings.
“Yeah, and we figured only using 20% hydrogen on one level we’d cut down the heat, and if things got too hot, we could use the tilts,” Gary replied.
“But you were already having to tilt the burners 10 to 15 degrees after your coal to gas conversion to make steam temperatures, so you weren’t starting from a ‘zero point,’ you were starting from halfway through your tilt range,” Marnie noted. “Maya, tell our audience what other unwanted prizes they have received.”
“Gas flames burn quickly, but hydrogen is much more rapid. Under stoichiometric conditions, natural gas flames move approximately 0.4 meters per second, but hydrogen flames move approximately 2.7 to 3.2 meters per second. So, even with your burners tilted at 30 degrees, the heat is still being released in a small area, and closer to the burners and walls than normal. Thus, higher boiler tube temperatures.” Maya paused. Gary asked, “So, what do we do about it? Just cut the gas flow down?”
“There are methods to mitigate this problem, but we will need to study which is best,” replied Maya. “Ms. Surfaceblow, do you have some suggestions?”
“Ones I can say in mixed company?” Marnie asked. Receiving a nonplussed look from her assistant, Marnie continued, “Your gas burners were designed for a high flow rate, but hydrogen is much less dense than natural gas, otherwise, I’d suggest using some of the flow margin and mixing in a small amount of flue gas—sort of an in-burner flue gas recirculation. You could also inject some flue gas into the boiler near the burners, but that could be more complicated depending on your spacing. Both of these methods are expensive, by the way.”
“Ma’am, could they not coat the tubes with a refractory overlay?” Maya asked.
“May…be. Refractory in the middle of a pulverized coal or gas burner zone isn’t the most reliable solution. I doubt it would last. Installing hydrogen burners with better jetting and a wider heat distribution would help, as would tuning the windbox for a much lower combustion stoichiometry on that level. This is why I suggested new hydrogen burners on the very top level, where you could potentially better tune the heat flux.” Marnie paused as one of the plant staff brought in her coffee order. “Well, I’ll be … they did know what a quad-quad was,” she said. “Cheer up, since that worked out for us, maybe there is hope! Now, let’s inspect what your contractors did.”
Danger, Will Robinson!
The contractors had built a rather nice-looking shed to separate the hydrogen distribution block from the rest of the plant, complete with a small air conditioning system, but it was only large enough inside for Marnie, Maya, Gary, and one of the plant maintenance technicians. Maya examined the equipment carefully with a penlight, sharp dark eyes noting something that bothered her. “Sir, did they not replace the seals and gaskets when they switched the lines to transport hydrogen? These appear to have been untouched,” she said.
2. Portions of the plant’s hydrogen distribution block were enclosed within a small shack where Marnie found leaks. Source: POWER
“I honestly don’t know,” replied Gary, and the maintenance technician shrugged. “We’ve never taken them apart ourselves.”
“Where is the ventilation system?” asked Maya. Gary replied, “The air conditioner runs all the time and the shack is well-insulated, so it stays cool. Neat system, and sometimes it’s nice to take a break …”
“I see no flammable gas monitor. Does someone have a portable one?” Maya asked. She could tell by the looks she received, the answer was no. “Get one please!” Maya exclaimed. Suddenly, they heard a sound—a single note, sung loudly by Marnie for a couple of seconds—followed by an order, “DON’T TOUCH ANYTHING! EVERYONE OUT NOW! THERE’S A HYDROGEN LEAK! SHUT THE SYSTEM DOWN!”
Code Is Code for a Reason
Back in the conference room, there was silence as Marnie stalked back and forth in front of the whiteboard, muttering softly to herself. One of the plant staff came in and said, “Just like she said, there was a leak from a union on the distribution block. We’re tearing it apart now to …”
“NO!” Marnie shocked the room. “You’re replacing the entire system with new equipment certified for hydrogen use, you’re replacing the burners with proper hydrogen burners, and you’re having continuous flammable gas monitoring put in, or so help me, I will shut you down!”
There was silence, and Gary nodded his head. “Just write up everything we need to do and I’ll get it approved. And note whatever you think we should do about the boiler tube problem too. What I want to know is how you knew there was a leak?” he queried Marnie.
“Several things made me suspicious. Hydrogen is much lighter than air, so it pools by the ceiling, and your air conditioner was only at knee-height. Your shack was so well-insulated that I knew any hydrogen that reached the ceiling would likely stay there and build up—or downwards rather. And, in the 80s, I played in a Goth band called ‘The Sisters of Hopelessness.’ One thing I do have is perfect pitch, so I sang a middle-C note, and what I heard instead was definitely much higher, like a G.”
Seeing the confused looks, Maya added, “Just as when one inhales from a balloon of helium and speaks, the speed of sound increases and the frequency is higher. Hydrogen has an even higher speed of sound than helium, and deep sea divers that use heliox, hydrox, and other gas mixtures experience this as well.”
“When we discovered there was no installed leak monitor and a portable one was not immediately handy, I thought, ‘Why not try sounding the note quickly while someone is getting a flammable gas monitor?’ To be honest, I didn’t actually expect it would work, and the fact that it did surprised me, but it confirmed there was a lot of hydrogen in a small area,” Marnie explained.
“Hydrogen has an explosive range of approximately 5% to 75% in atmospheric air, whereas, natural gas has a range of approximately 5% to 15% under the same conditions,” Maya added. “This is why the NFPA gives hydrogen one of the highest flammability danger ratings. Amongst gases encountered at power stations, only carbon monoxide is close to hydrogen in terms of flammability. And it, of course, possesses its own hazards, which I need not mention.”
Gary and the rest of the crew looked chastised but grateful. With a deep sigh, he said, “You both saved us a lot of trouble today, and hopefully in the future, after we follow your instructions.”
Marnie, in the middle of using a brush to untangle her hopelessly hard-hatted hair, replied, “New fuels mean new opportunities. Your basic goal was good, and you and your team know your plant better than anyone else, but when you enter unknown territory, you need an experienced guide to lend a hand—especially for something as new as this. You can make this work and make it work well, but let’s help you get a plan together and do it right.”
—Una Nowling, PE is an adjunct professor of mechanical engineering at the University of Missouri-Kansas City.