Long-time POWER readers may remember Marmaduke Surfaceblow, a fictional character whose engineering escapades were brilliantly portrayed in hundreds of stories published within POWER magazine’s pages over more than 30 years beginning in 1948. Today, the fictional series continues through Marmy’s granddaughter, Marnie, who is an engineering wiz in her own right.
Don’t fall prey to preconceived notions—investigate all possibilities when searching for an answer to your operations and maintenance problems.
“It’s sodium,” pronounced Marnie Surfaceblow, vice president of Surfaceblow & Associates International.
Maya Sharma, lead field engineer for the firm, shook her head and said, “With respect, I believe it is an operation problem. And, apropos of the subject, isn’t it unusual to be working for a coal power station in America?”
Marnie watched the landscape as they drove, noting the chimney rising above the trees as they neared the power plant. “Transition in the U.S. power industry won’t happen overnight, nor as fast as some might like. Any large country with an underfunded and aging power infrastructure can’t turn on a dime, so large-scale dispatchable generation is needed for backing up the move toward greater renewable power. But not only are these vital plants suffering from lack of investment, too many experienced folks are retiring—and bright young engineers don’t want to enter an industry and become what they see as an expert in a dying field, which is why NO ONE is seeing that this is a fuel sodium problem.”
Maya shook her head and replied, “Or, their operations have failed in some manner. Speaking of retirements, when do you plan on retiring, ma’am?”
Marnie sighed. “Right now, I’m the best in the world at what I do. Maybe not the greatest of all time, but I must be somewhere in the pantheon of engineering goddesses. That ends when I retire—I will diminish and go into the West.”
Noting Maya’s questioning look, Marnie added, “There’s a professorship being held open for me in California where I can teach young engineers about sodium, and its many evil workings.”
Uncovering the Issues
Power plants rarely want external consultants onsite during an outage—especially an unplanned one—but plant manager Staniel Grabowski and his crew were happy for the help. A white-haired “old school” engineer with more than 40 years’ experience at coal plants, Staniel was a friend of Marmaduke’s family. “Little Marnie Surfaceblow, I remember visiting your grandfather one Christmas, and there you were in one of his workshops, barely six years old and using a TIG welder like a pro, making some titanium art-thing. You were so proud of it, but I forget what it was?”
“It was the Christmas Opossum,” replied Marnie while blushing slightly. “I still have it. It was the first thing grandpa ever praised me for.”
Marnie introduced Maya, who received an equally warm greeting, and they decamped to the main conference room. Already populated with a gathering of weary, grim-looking plant staff, introductions and business cards were exchanged. Marnie obtained her customary coffee—raising eyebrows by bringing the entire glass pot with her, and dumping her copious amounts of cream and sweetener into the pot. Noting the amazed looks from the room, Marnie, blushing again, said, “It’s just easier this way. You can start asking them about their sodium problem, Maya.”
Ignoring the plug for sodium, Maya asked Staniel and his team to tell their tale of woe.
“In a word? Catastrophic slagging,” said Staniel.
“That’s two words,” whispered Marnie while Maya, wisely resisting the urge to elbow her boss, asked Staniel to continue.
“Our boiler’s designed for high-sulfur Northern App coal, and that’s all we’ve burned. We take 60% of our deliveries by rail on a long-term contract from the Morganna mine. They haven’t changed operations since we switched to it six years ago—you recommended it, Marnie.” Marnie nodded, and Staniel continued. “We also buy truck coal from four local mom-and-pop mines. We try balancing purchases by taking about 10% from each local mine, but it varies. We’ve been running smooth an’ steady for years, until two months ago. Sal, show our guests what happened.”
Sal Davies, the wizened lead maintenance engineer, plugged her laptop into the room projector. Pausing, she smiled at Marnie. “I’ve met your grandfather and your father. I remember when they solved our coal conveyor bearing problems way on back. And I remember sharing that terrible gin your grandfather drank. What was it called?”
“Sandpaper gin. I think it was banned by treaty, or whatever they made it out of went extinct. It was pretty nightmarish stuff.” Marnie failed to suppress a shudder.
“Certainly, it cannot be worse than the whiskey you drink, from that island where everything tastes of smoke and sadness,” teased Maya.
“Islay, and don’t you dare make fun of it—it’s medicinal. I need at least 50 ppm phenols to keep me so well-preserved. Moving on. What do you have to show us, Sal?” Marnie asked.
Bringing up a series of slides, Sal picked up the story. “Almost 60 days ago the night operators reported the slag shedding from our usual nightly second shift load drop wasn’t clearing the upper furnace tubes and the nose upper slope. Normally, this works so well that we barely run the sootblowers up there. Suddenly, we had to switch to blowing every few hours. Then, even continuous blowing would barely keep up. The slag would grow on the west side of the boiler and spread over to the east, until about a month ago, we tripped due to high pressure drop. When we opened it up, we saw the whole front row of secondary superheater tubes was clogged with dirty grey slag.”
“Ma’am, do you know the cause? Were there increased boiler temperatures, excess air control problems, milling difficulty, or problems with the sootblowers?” asked Maya, ignoring Marnie as she dramatically whispered “sooooooodium” to herself.
Sal, acknowledging she’d heard Marnie’s comment, nodded. “We sent the slag for analysis, and it did come back high in sodium. But, we also had a bad boosted overfire air fan, our top mill was way out of spec for pulverized fuel fineness, and we had problems with lower furnace sootblowers, so slag built up above the burners and pushed heat into the upper furnace.”
Marnie, having polished off half the pot of coffee, flipped through some data screens and said, “If troubles were kittens, you’d have a litter.” Folding her arms, she leaned back and narrowed her eyes at the plant manager. “Staniel, didn’t I give you a good fuel specification at least six years ago?”
“Sure Marnie, and we’ve stuck to it. No more than 1.5% sodium in the ash, I got it right here, along with our last six months of coal data.” Staniel scooted a stack of paper over to Marnie and Maya.
“Remember my footnotes,” replied Marnie as she glanced at the coal data. “Consider the boiler sodium loading, not just the percentage in the ash oxide analysis. This 1.5% specification was based on coal with 10% ash content, no more than 20% water-soluble sodium, and a fuel burn rate of 320 ton/hr. In other words, a limit of 960 pounds of sodium oxide per hour, assuming almost none of it is water soluble.”
“We’ve stuck to the same mines we were buying from when you were last here, Marnie. We like the high-sulfur coal because our scrubber is oversized and the coal is still pretty cheap,” Staniel said.
With a nod from Maya, Sal continued, “We used hydro-lances to clean the tubes, repaired the overfire air fan, tuned up the mills, and started running again. Things improved, although pressure drops started to climb again. Then, late last week, just as we were about to trip again from high pressure drop, this happened.” Sal clicked to a slide, showing a grey-white slag boulder laying across the ash hopper opening. It didn’t look so bad, until Marnie and Maya noticed the size relative to two workers in the photo.
“Great Caesar’s ghost! You really buried the lede!” exclaimed Marnie. Maya did a rapid mental calculation and stated, “That is approximately 3,000 cubic feet of slag. Assuming mostly sodium compounds, it weighs greater than 200 short tons, yes?”
Staniel nodded. “Something like that. Why it didn’t tear through the bottom slope tubes, I’ll never know, but removing that slag boxcar and repairing the damage will keep us offline about seven more weeks.”
With uncanny timing, Marnie and Maya gave each other a look, then each nodded.
“Please be at rest,” Maya calmly said. “Based on the data sent when you contacted us, we already prepared an investigation strategy, which Ms. Surfaceblow shall explain.”
Full of energy, Marnie stood and addressed the room. “Right! I have a bet riding on this being a sodium problem, so I’m going to look through your coal data, and with your permission directly contact your fuel buyers and the mines for better data. Maya’s going to review your operations data, interview your staff, and since you’ve got the scaffolding set up already, inspect the boiler inside and out.”
Maya raised a hand. “Mr. Grabowski, I e-mailed you our confined space training certificates, and if someone can show me data from your historian, we can start.” Staniel nodded. “Sal can help you with some of your questions, and our monitoring engineer, Seth, can get the data for you.”
“Staniel, Sal, Seth … such superb spontaneous synchronicity,” Marnie muttered, paging through the coal data sheets. “Wait, sodium starts with an ‘s’!”
“So does sootblowing, ma’am,” quipped Maya as she left the room.
Hours later, a smaller group reconvened in the conference room as lunch from a local deli arrived. Halfway through lunch, Marnie looked up from her chilidog and the coal quality data sheets. “Staniel, did you notice anything unusual about this truck coal data?” Marnie asked, returning the stack of coal data sheets to the plant manager (Figure 1).
1. Marnie and Staniel review coal data sheets over lunch. Source: POWER
Flipping through the pages while finishing off his second meatball sub, Staniel replied, “What’s the problem? There’s complete analyses for every delivery.”
Marnie smiled. “They’re complete alright—complete junk. Did you notice that none of the mines provided more data than a proximate analysis, sulfur, chlorine, and grindability?”
Staniel frowned deeply at the coal data sheets, then shrugged. “I guess they stopped testing to cut costs, but each local mine only supplies about 10% of the coal burn. How far off could it be?”
“Now, we come to problem number two. It looks like about three months ago you started buying more of this one coal—Norwich. Interesting etymological factoid, the suffix ‘wich’ often refers to land near brine springs or salt deposits.” Marnie smiled as she saw Maya raise an eyebrow in appreciation. “I’m sure at one time the coal was tested and supposed to be good quality, but did something change? How would you know, when you’re relying on the supplier to provide you with detailed accurate test data—and there isn’t any! I tried to get better data, but the mines refuse to talk to me for contractual reasons. Staniel, would you be so kind as to drop them a little love-note telling them to give me whatever I need?”
Staniel sighed, and started typing emails to get Marnie access to the full coal quality data. Turning to Maya, Marnie asked, “Why don’t you tell everyone what you’ve found?”
Maya frowned. “I admit this could be simply inadvertent high sodium. The overfire air dampers appear to be working, and your latest mill fineness testing was only last month and it exceeds the specifications. I need more time to examine the data.”
A chime from Marnie’s laptop heralded being carbon copied on Staniel’s first email, and Marnie grabbed her phone. “Great! Now I’m going to make some calls and break some … um … hearts. And get coffee—this is a four-pot day, at least.”
Suddenly sitting upright with eyes wide, Maya said, “Excuse me, ma’am, I think I have found something.” Turning to Sal, she continued, “Ms. Davies, can you kindly take me to the control room and then to the boiler? I must inspect some equipment before the day ends!”
Although still convinced of her sodium hypothesis, Marnie could not help but feel pride at the problem-solving passion of her assistant. Good luck, my friend.
A Multi-Faceted Problem
As the day shift ended, Marnie called for a third assembly in the conference room. Maya and Sal were the last ones in, both women covered in coal ash. Maya’s jet-black hair was flecked with so much white ash that Marnie took a quick photo with her phone, joking, “You look great with those sodium highlights, Maya. Very mature.”
Maya smirked, “Thank you, ma’am, but no. As you prove each day, age does not equate to maturity.”
“If you two ladies are done talking about your hair, why don’t you tell us what you found?” It had been a long day for Staniel, and between the outage and the wisecracking he was near his limit.
“Right!” said Marnie. “Issue one! About three months ago, the Norwich mine contacted your corporate fuel buyer and said they were mining a new seam, and asked if your plant wanted to give it a try—and it had a 20% discount. Your fuel buyer checked the specifications, but since the mine only sent minimal data, your own fuel buyer referred to the old ash oxide and ash fusion temperature analyses. In terms of heat content, moisture, ash, sulfur, etc., the coal passed your specifications. And since the ash content was about the same, the calculated sodium loading was about the same. I know, you’re thinking, ‘How dumb could they be?’ But they’re young, and no one trained them properly. A month later, when there weren’t any complaints about the new coal, your fuel buyer tried to help the plant stay economically viable, and started buying most of your truck coal from the Norwich mine. Some weeks, half of your truck coal—20% of your total coal burn—came from this new seam.”
The conference room was filled with muttered recriminations. “I guess you’re going to tell us the new seam was high in sodium,” Sal stated resignedly.
“Just a wee bit. From the data the mine gave me by phone, it looks like sodium averaged about 5.9%. Given an average ash content of 13.6% with the new coal, and adjusting the coal burn rate by its estimated change in heat content, moisture, carbon-to-hydrogen ratio, and accounting for the amount of coal received over the last month, I figure your overall weighted average boiler sodium loading increased from about 903 pounds per hour to, oh, about 1,700 pounds per hour.”
Staniel was stunned. “Of all the boneheaded stupid things, I’m going to barbecue that fuel buyer.”
“Then save some space on the grill for yourself, Staniel,” Marnie’s voice was hard and her green eyes flashed warning. “You had all the data—you should have seen this. The life of your boiler depended on verifying the fuel data, and you didn’t. If the mine says they want to cut costs by scrimping on testing, remind them who the customer is, and the definition of ‘the cost of doing business.’ What I recommend you do is have your fuel buyer properly train them. Bring them out to the plant and show them the slagging situation so they get a direct, visual understanding.”
Sheepishly, Staniel nodded. “You’re right, Marnie. I got too busy and took the coal quality for granted. We’ll make those changes at once, and for now we’ll stop buying any coal that doesn’t have good data. We’ll start validating the data too with our own testing.”
2. Maya and Sal inspect the long retractable sootblowers on the west side of the boiler. Source: POWER
“That is a good start, sir,” Maya added, “but there is another factor to consider. When I examined your plant operations, I saw there are eight long retractable sootblowers directly in the region of highest slag formation—four on each side of the boiler [Figure 2]. I know this model of sootblower and it should have been possible to properly clean your tubes. The slag has grown from the west, so we examined those sootblowers and they appeared functional. But examining your steam consumption during sootblowing, I discovered that when that region is cleaned, you are only using half the normal quantity of steam. Sal and her team just examined the west-side sootblowers and discovered their steam header has a blocked valve.”
Sal spoke up. “I checked the records Staniel, and it looks like the valve was flagged for replacement last year, but it never got added to the maintenance schedule due to lack of budget. Seems like it was mostly working then, just sticking once in a while. Tracking the steam flow in the historian, it looks like the valve failed completely just over two months ago.”
The conference room came alive with chatter over the second revelation, until Staniel motioned for silence. “So, between folks trying to save money on the coal and trying to save money on maintenance budgets, we ended up losing at least a couple million dollars.”
“Sir,” replied Maya, “Ms. Surfaceblow sometimes says, it is the stingy person who pays the most, and I think in this case, she is correct.”
Win-Win (or Lose-Lose)—You Make the Call
Staniel and Sal walked Marnie and Maya to their car, and arrangements were made for the duo to help with slag removal and boiler repair the next morning. “I know some boys from Alabama that are artistes nonpareil with dynamite that can shave about a week off your outage, and a father-daughter welding team that have performed so many welding miracles that they’re both up for canonization. We might be able to get you back online in just a month—if we don’t scrimp too much.”
Thanking both ladies again, Staniel said, “I have to ask—what was that you said about some sort of bet?”
Maya answered, “Based on your description of the situation upon contacting us, Ms. Surfaceblow wagered sodium was the sole cause. I wagered it was operations. The loser must cook the other one dinner.”
“But like many plant problems, there wasn’t just one cause, and we both lost—or won. So, Maya is going to try my special vegetarian take on the Marmaduke family haggis,” Marnie said with a diabolical grin. “And, it’s just as reekin’, even without the sheep guts.”
“Very well, ma’am. For you, I shall make my auntie Indira’s Naga tindaloo,” Maya replied with a smirk.
“Huh. I never heard of that. Is it, um, hot?” asked Marnie hesitantly.
Deftly dodging the question, Maya shrugged, “It is low in sodium.”
—Una Nowling, PE is an adjunct professor of mechanical engineering at the University of Missouri-Kansas City.