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.
As new energy technologies are employed to solve today’s renewable energy challenges, think flexibly while relying upon established safety measures.
“Is this your first time in the Philippines, ma’am?” asked Maya Sharma, lead field engineer for Surfaceblow & Associates International as she frowned at the maps app on her phone. Her phone gave her the equivalent of a Gallic shrug by replying “No Signal.”
“Nope,” replied Marnie Surfaceblow, the firm’s vice president. “Had a mix-up one time with an intern who was handling travel, and before I knew it, a trip to the city of brotherly love—meaning, Philadelphia,” added Marnie as Maya gave her a quizzical look, “became a trip to Manila.”
“That is … a most unfortunate mistake,” Maya replied, knowing full well that unusual adventures are common occurrences for her boss. “Do you know where this facility is, ma’am? My mobile does not have any signal.”
Smiling somewhat smugly, Marnie reached into the laptop bag at her feet and pulled out a stack of printed pages. “Always carry a hard-copy map as a backup when you are going to a new … oh.” Marnie stared at the pages, and then pinched the bridge of her nose and closed her eyes.
“Ma’am?” asked Maya, with a growing sense of unease.
“Don’t worry Maya, I have an excellent map … to Philadelphia.”
A Biomass-Filled Landscape
After a few wrong turns and some directions from a kindly roadside fruit vendor, the jungle-choked road deposited them at the test site. Sitting in the parking lot, they had a quick snack and a brief discussion. Between bites of fresh melon, Marnie asked her assistant, “I know we just got back from the Case of the Errant Hydrogen and hit the road again, so are you ready for this project?”
“My understanding is this is a test facility for torrefaction of biomass that was developed by a research organization with almost no practical experience. Local contractors are building the system, but they have never built a torrefaction facility. They planned on utilizing coconut waste, but there were supply difficulties. Thus, they are trying to change the plant design to use sugar cane waste—bagasse. Based on initial operations, they have … concerns.”
Marnie snorted a laugh. “Your penchant for understatement strikes again. Did you see the photos of the fire last week? Thank goodness no one was hurt, but they’ve lost a conveyor, a storage bin, and an old truck that looked like an antique—the sort of thing Grandpa Marmaduke would’ve loved to tinker with. Now, they’re even further behind in time and money, and what little product they’ve made is so far off the mark that …”
“That it might as well be your carefully printed map to Philadelphia,” Maya chimed in quickly, with a rare smirk.
Site Greetings and Discussions
The pair were met by Angelo Garcia and Frank Ramos, the lead engineer and plant manager, respectively (Figure 1). Frank had the look of a CEO who was visiting the plant for a day trip, but Marnie knew he had extensive operations experience. Angelo was much younger, but experienced as well in fuel handling and preparation systems, although primarily from a coal background.
1. Marnie and Maya are met by Angelo and Frank as they arrive on-site at the torrefaction facility. Source: POWER
Marnie and Maya were welcomed warmly into a conjoined set of mobile homes repurposed as a long and narrow engineering office, and met the rest of the section leaders of the torrefaction facility. After introductions were made, and Marnie carefully mixed together coffee with enough milk and sugar to make pancakes from it, Maya opened the meeting by inviting the group to “tell us your story.”
“It’s simple,” Frank began. “We’re a test site funded by research development from four universities to produce 10,000 tonnes per year of torrefied biomass pellets for pulverized coal plants—mostly located in Luzon. We validated the process at the bench scale in our laboratory, and if this scale-up works and the price is right, we will then increase to 100,000 tonnes within a year. But scaling up and working outside of the laboratory has not been good. Our bench-scale plant was designed for coconut shells and husks left over from food processors, and that was our plan for this facility. But our supplier backed out, so we found a local bagasse source that can supply us with feedstock to prove this pilot plant works and our target customer can perform a test burn.”
“How large was your bench-scale plant you tested this process with?” asked Marnie.
“We ran up to 10 kilograms per hour, and … excuse me Miss Surfaceblow, are you OK?”
“Do not fear,” answered Maya, “that is merely the look of utter horror that is a common expression of my boss. It shall pass.”
Taking a deep breath, Marnie spoke. “Even with double shifts and assuming no unplanned outages, I’m thinking your plant is designed for two to five tonnes per hour, and on coconut, which is absolutely not the same as bagasse. So, this is a 200- to 500-to-one scale-up with a different feedstock,” she suggested. “And you thought this was a good idea … why?”
“The process is very simple. We prepare the biomass, apply heat in a low-oxygen environment for a specific time, and then we make pellets,” replied a slightly cross Angelo. “Our graduate students did this in our laboratory for two years with great success. Because our system is so simple, it was designed to be very flexible, especially because it is a pilot plant.”
Leaning in, Maya noted, “But, sir, according to your messages, your production plant may not be as flexible as you wish.”
“It’s true, we have so many problems we can’t make progress,” replied Angelo. “Carlos, Marisa, could you please describe what’s happening?”
Two younger engineers at the end of the table hooked up a laptop to a projector and then stepped through slides on a large monitor. Marisa, the elder of the two, spoke as Carlos ran the slides. “Product quality depends on some factors we control. As you know, we heat biomass in a low-oxygen process for a certain time and certain temperature. Not only does this remove moisture and some volatiles, but it transforms the lignin fibers in the biomass, making it crush just like coal.”
“Not … so much. It does make it more friable—crushable—but not like coal. Especially after you add the binders during the pelletizing process, because they can be softer and sticky under coal plant milling conditions.” Marnie shook her head. “So, tell us why we’re here.”
“Well ma’am, choosing the correct combination of conditions is very difficult, and we are constantly searching for the right combination, but our yield is less than 20% of what enters. Often, we make product like this.” A slide was displayed showing light tan-colored biomass. “Or like this.” Another slide was displayed showing jet-black and smoking biomass. “Rarely do we find a good balance, so most of our lightly cooked product is blended with the over-cooked product,” explained Marisa.
“We sometimes send the less-cooked biomass through a second time, but still our yield is very low,” added Carlos. ”Ma’am? Are you unwell?”
“Oh, nothing much, just my brain hurts. I think I need some fresh air, so let’s go for a walk,” Marnie said.
A Stroll Through Paradise
The test facility was running, but not very well. A conveyor laden with sugarcane leaves, stems, and miscellaneous roots complete with dirt clods (Figure 2) was steadily dumping its cargo into a bin with a large set of vibrating sifting screens at the bottom. Angelo pointed to the waste bin, and said, “We try to screen as much debris as possible, but still dirt goes into the torrefier. An electromagnet sorts ferrous metals, but we rarely find any.”
2. The feedstock for the test facility contained sugarcane leaves, stems, and miscellaneous roots, including dirt clods. Source: POWER
“What sort of preparation is conducted on the bagasse?” asked Maya, as Marnie looked in dismay at the cloud of dust rising from the sifter.
“It’s delivered by truck, then stocked into 100 tonne piles,” Angelo replied. “We don’t cover it, since it already seems very wet. We chop and grate it, but our capacity is reduced because the system was designed for coconut. Everything is sized to 25 millimeters before going on the feed belt.”
“That may be so,” Marnie noted, as she reached out a gloved hand and snatched a long sugarcane leaf hanging from the conveyor belt. “But, this is about 25 millimeters by 400 millimeters. You are only sizing in one axis, so you have a feedstock that is very inconsistent.” Angelo shrugged. “It’s the best we can do,” he said.
“And sir, what is the moisture content of the bagasse when you reclaim it?” Maya asked, taking notes on her tablet.
Angelo shrugged again, which was becoming a regular habit. “It is of course variable. If it is aged and dry, maybe 10%, if it is new and wet, maybe 60%. It rains here every two days on average, so there is that,” Angelo sputtered as he saw the look on Marnie’s face. Maya cleared her throat and headed off a pending outburst by asking, “And what about the quality of the fuel? Is it from the same plantation or producer?”
“Yes, it is from one source, and we receive up to 15 trucks each day.” Angelo pointed toward five awkwardly arranged rows of bagasse.
“That pile is on fire,” Marnie commented resignedly. “I am seeing that, correct?”
Angelo shrugged again. “It is just spontaneous combustion, from mixing wet and dry bagasse. It’s not a problem.”
“Except, of course, for the fire that melted your conveyor,” Marnie retorted.
“Oh, that was in the finished product area,” replied Angelo. “Come see the rest of the system.”
“Must we?” asked Marnie before she received a gentle but firm elbow from her assistant.
The Finishing Area
The torrefier was a standard rotary type, looking like a large tumble-dryer. It turned slowly, and radiated heat and occasional wisps of steam and smoke. A screw feeder slowly fed biomass on one side, while natural gas burners added hot exhaust gas to start the drying process. On the other end, smoking black biomass char was dumped out, and quenched by a water mist.
“The drum is specially modified with an internal spiral liner to turn the biomass constantly while moving it toward the outlet. We control the feed rate, heat input, rotation speed, and oxygen level in the system. But the ideal control points always change, and we cannot get the needed product quality,” Angelo explained.
“How do you dispose of volatiles and steam released from the process?” frowned Maya, looking around, then noticing a vertical pipe with a flame at the top near the end of the drum. “Oh, you flare it into the atmosphere, with no scrubbing and no re-use of the heat. How unfortunate.”
“Hey,” exclaimed Marnie, “that’s my phrase!”
“Yes ma’am, and I am using it to good effect,” Maya replied deadpan.
A Hot Mess
“Your fuel product storage is just … well … a steaming pile,” said Marnie, watching the water-quenched biomass char falling off the outlet conveyor into a heap. “What are those workers doing near the end of the torrefier? That’s a pretty hazardous area, I mean, they’re exposed to hot biomass, potential burns, an explosion risk, carbon monoxide—please show me your CO monitors, Angelo.”
Angelo shrugged yet again. “We don’t have them. This is outdoors, and the wind surely takes it away before …”
“Imbecile!” exploded Maya, shocking even Marnie into silence. “It does not matter where I travel, what the situation, people are not caring about the safety of their colleagues! Ammonia, hydrogen, lost ionizing radiation sources—I have had enough!” Maya turned and stomped off, yelling back at a still shocked Marnie and Angelo, “Ma’am! Sir! Forgiveness please, I am retrieving our portable gas tester from our vehicle!”
Angelo started to say something, but Marnie put a hand on his shoulder in almost a motherly gesture. “She knows what she’s doing. Trust me on this. Get those workers out of that area, NOW. Then, let’s examine your biomass feedstock and torrefied product analysis trends.”
“Um … yes, of course, ma’am.” Angelo thought for a second. “Do you wish to see the pelletizing plant? We have many pellet consistency problems with the binders, and the pellet dies last only half of their expected life.”
“The binders don’t bind, the dies are dying, and so is your plant. When Cyclone Maya is done with her testing, let’s have a meeting and go over the high points.” Marnie headed back to the engineering trailers with Angelo in tow. Ten minutes later, sipping her coffee and looking over laboratory test reports of the feedstock and product, Marnie was not surprised in the least to hear loud cursing in Marathi, followed by the torrefaction system’s emergency manual trip claxon. “Good job, my perceptive protégé,” she said softly to herself.
Setting the Stage for Success
Standing at the front of the meeting room next to a still-fuming Maya, Marnie opened the debriefing. “There’s … just a lot to unpack here. Let me explain why your simple system is, well, simply dreadful. Your laboratory reports were the only good part. They were comprehensive and complete. After that, however, your efforts to scale up your bench model by more than 200 to 1 are just … bad.”
“Allow me to assist,” said Maya. “Bagasse is not coconut. People think coal quality impacts are difficult to manage at traditional power stations, but they are not close in comparison to biomass. And then you add torrefaction? Torrefaction is not a simple process. It is, in fact, very complex, and biomass quality differs from source to source, dependent upon the soil, how it is harvested, the age it’s harvested at, how it’s stored, everything up to and including the phase of the moon. But one of the simplest factors is what is causing the greatest problem—feedstock moisture. In the laboratory you performed some moisture sensitivity analyses on the coconut shells and husks, but bagasse has much greater moisture variability, both inherently and from environmental factors, such as storing it uncovered in the rain.”
As Maya shook her head, Marnie took over. “Even if the dry fuel quality is different, you could greatly improve your product quality by installing a pre-dryer upstream of the torrefier. One design uses a low-temperature drum with humidity sensors to pre-dry the product without losing your volatile matter or carbonizing the feedstock. Sure, it costs more, but it could potentially double your yield,” she said. “And pretty please, with sugar on it, cover your biomass piles. Here, again, your investment will pay off.”
Maya quickly added, “And you must do what is needed to better remove the soil, rock, and other materials from the bagasse before it enters the system. Because you have not operated long, you have not seen that these contaminants can build up inside your torrefier, leading to increasing unplanned maintenance and poorer product quality.”
Continuing the foray, Marnie said, “Bagasse and coconut both have low inorganic content, so adding even small amounts of dirt and rock will significantly change your product quality—and you’d better believe, it’s almost always for the worse. Also, for goodness’ sake, find a way to size your product better. You should not be sending leaves and stems nearly half-a-meter long into your pelletizer. Which, by the way, was designed for torrefied coconut, which can be less abrasive than bagasse, depending upon the inorganic minerals within and without it.”
“But, most of all,” Maya returned, in the intellectual tennis match of the presentation, “let me ask you this: Do you hate your employees? Of course not!” she emphasized, cutting off Frank in mid-protest. “Then, why do you not have carbon monoxide sensors at the outlet of a process predestined to predominantly produce poisonous pollutants?”
“She’s really mirrored my tendency for creative alliteration,” thought Marnie, as Maya continued.
“I measured the CO at the torrefier outlet area, and found levels from 200 to more than 600 ppm!” Maya exclaimed. “That is enough to kill in three hours, maybe less. Even with shorter exposure time, workers will have long-term health effects being in that environment for just one hour a day!”
The silence in the room spoke volumes, and while Marnie sat in admiration, Maya softened her speech. “There is a saying from my Auntie Komal that applies. ‘Making mistakes is common, accepting mistakes is sacrament, and learning from mistakes is progress.’ Meaning, take the same academic problem-solving you used with your tests on the bench and apply them to fix this plant, make it safe, make it efficient, and help your coal power stations reduce their pollution as well.”
“In other words, folks, when the real world meets academia, one of two things can happen: Utter disaster or brilliant success,” Marnie supposed. “Let’s try for option two, shall we?”
As general discussion and debate broke out, with Maya answering several pointed questions. Marnie, while prepared to provide backup, simply drank her coffee and thought, “We did good work today, so all things considered, I’m glad we’re not in Philadelphia.”
—Una Nowling, PE is an adjunct professor of mechanical engineering at the University of Missouri-Kansas City.