From Lines on Paper to a Model of Success
What started as a light bulb idea is now trademarked by EnerTech as the SlurryCarb Process and could become the future of biosolids management.
"At that time, all we had was my grandfather's ideas-what we called ‘lines on paper,'" he says. Bolin's career to that point was nonlinear, working as an accountant, then selling television time for a CBS affiliate. In 1992, he left his job selling air time and began a new venture with his grandfather. The basis of the new company was "really just a light bulb," Bolin says. "So what grandpa and I had to do was figure out how to take those ideas and first go into the laboratory and start proving those things out. Then building bench models, pilot- and demo-scale production, all the while trying to figure out how to fund the company." Friends, family and angel investors all helped with the latter. Demonstrating the technology, however, was up to the two founders of EnerTech.
The technology that developed from those "lines on paper" is trademarked the SlurryCarb process, which is short for slurry carbonization. It's a process that converts sewage sludge and other high-moisture organics into what EnerTech calls E-Fuel, which yields 6,500 to 8,000 British thermal units (Btus) per pound. Bolin says the fuel is comparable with lignite coal, but E-Fuel is renewable and carbon neutral.
In early spring, EnerTech is commissioning its first full-scale biosolids treatment plant utilizing the SlurryCarb process. The plant is in Rialto, Calif., and once fully operational later this year, the company will have the capacity to produce 160 tons of E-Fuel per day. EnerTech has made arrangements with five surrounding municipalities-Orange County
Sanitation District, Los Angeles County Sanitation District, the city of Riverside, the city of San Bernardino and the city of Rialto-to supply the new facility with biosolids. Mike Moore, OCSD environmental assessment division manager, says Orange County produces about 700 wet tons of sewer sludge a day, about a third of which the county has contracted with EnerTech for delivery. Moore says in addition to its contractual feedstock arrangement with EnerTech, OCSD takes on an advisory role with the company when needed. "We advise them on a number of issues-outreach and education, marketing-so we provide guidance when asked, and we require them to follow the tenets of our nationally certified biosolid management system," Moore tells Biomass Magazine. Not only does OCSD supply EnerTech's Rialto facility with feedstock, Moore says OCSD is also the recipient of the plant's liquid waste stream.
In addition to EnerTech commissioning its first owned-and-operated plant in Rialto, the company licensed its technology to Mitsubishi Corp. in Japan. "Outside the U.S. we're going to utilize a licensing model," Bolin says. In Abu Dhabi, the first-of-its-kind carbon- and waste-free city is being built and Bolin says EnerTech has been preliminarily selected to provide biosolids treatment.
The SlurryCarb process and E-Fuel
"The process of carbonization-that's been around since the cavemen," Bolin says. "It's basically converting wood to charcoal." But biosolids are delivered at approximately 80 percent moisture, an extremely wet product, which is where the "slurry" in SlurryCarb comes in. After the sewage sludge is run through the SlurryCarb reactor, EnerTech employs centrifugation and drying to remove any excess moisture. The reactor is simply a plug-flow reactor, or a "wide spot in the line," Bolin says, which is a section in the process where pressure and heat can be applied to the biosolids for a 10-minute residence time.
"We don't like to evaporate water," Bolin says. "When you evaporate water, because of the latent heat of evaporation, you lose at least 1,000 Btus per pound. That's clearly a result of changing phase-going from a liquid to a gas or going from water to steam. You lose that energy and it's not recoverable." He says all chemical engineers are familiar with the saturation curve of steam or the liquid-vapor equilibrium. "If you add pressure to a liquid, it actually takes higher temperatures to change phase," he says. Under atmospheric pressure, water boils at 212 degrees Fahrenheit. Add pressure, however, and the boiling temperature of water can increase-depending on how much pressure is added. "With an increase in pressure, you can actually raise the boiling temperature to 300, 400, 500 degrees F and still stay in the liquid phase, and not lose the latent heat of evaporation."
To demonstrate this, imagine 100 tons of biosolids at roughly 80 percent water. "A typical dryer is going to use a lot of muscle and heat in order to evaporate those 80 tons of water," Bolin says. Assuming a theoretical 1,000 Btus per pound necessary for evaporation, it would require 160 million Btus to dry the 80 tons of moisture resident in the 100 tons of biosolids. "That's a lot of energy," Bolin says. In the SlurryCarb process the biosolids are pressurized first and then heated. "In order to get to our reaction temperatures, we add some energy-roughly 32 million Btus as opposed to the 160 million Btus needed to dry down the material," he says. Once reacted, the material still has some moisture-it's about a 50/50 mix of cake and water at this point-so conventional drying methods are used, which takes another 32 million Btus. Added to the previously needed 32 million Btus of energy, the SlurryCarb process requires only 64 million Btus versus the 160 million that would have been necessary to evaporate the water from the sewer sludge.
The pressures and temperatures employed in the SlurryCarb process change the basic molecules of the feedstock, according to EnerTech. "The end result of this reaction we're driving with heat and pressure is that our reactive product, which once had an affinity for water, no longer has an affinity for water because it's become hydrophobic," Bolin says. No catalysts are used in reaction, and approximately 85 percent of the water resident in the incoming biosolids can therefore be removed by mechanical rather than thermal energy. Once the post-reacted sewer sludge comes out of the reactor, it's cooled down to 212 degrees F, then it's depressurized, and finally the remainder of the water is removed via centrifuging or with a filter press. Bolin says, "What's leftover is a nicely isolated carbon product that's conditioned for use as fuel."
The coal-comparable E-Fuel has multiple applications-virtually anywhere a solid fuel is being used, E-Fuel can be substituted in. "In Rialto, we have two cement-kiln customers utilizing E-Fuel," Bolin says. "And as a fuel for gasification, we recently entered into an agreement with a company that is actually going to convert the fuel into liquid transportation fuels. We can also utilize the fuel ourselves in our Rialto facility."
A Sound Model to Follow
Moore says one of the key elements other companies can learn from EnerTech is its ability to get the political backing and to conduct successful public outreach before it began the process of project development. "Too often facilities have failed because they didn't do things right," he says. "Too often projects do the design, build and defend rather than getting the support they need before they even start. We talked with EnerTech early on about developing a relationship with the people in Rialto-and they did."
Conversely, municipalities and municipal agencies like the OCSD should consider an overall approach to managing biosolids, Moore says. "We were one of the early adopters of the environmental management system for biosolids and we were one of the first agencies in the nation to be certified by the National Biosolids Partnership," he adds. "That caused us to rethink the way we manage, to stop thinking of this material as waste and rather think of it as a product you typically don't dispose of, but can if you want to."
There are some benefits to landfilling biosolids. It could help breakdown the landfill trash already being dumped; more so than straight municipal solid waste. In so doing, the methane produced as a result is cleaner, so if landfill gas capture and utilization is to occur, the gas would require less cleanup, and it is higher quality. Also, Moore says some of the landfills where biosolids are dumped have reported higher quality leachate.
Bolin says permitting for the Rialto facility in Southern California-one of the most stringent permitting zones in the U.S.-was completed in a nine-month period. For air, EnerTech's Rialto plant is a minor source for major pollutants-nitrogen oxides, sulfur oxides and particulate matter.
OCSD worked with EnerTech on permits for air emissions, and the liquid effluent, of which OCSD is the recipient. "Since we receive its liquid waste stream that goes through the Rialto treatment facility and then into the Santa Ana River Interceptor line, we talked to them about ammonia and salts that we allow to go into that line, which eventually comes to us," Moore says. When dewatering occurs at the plant, there is a centrate that comes off the centrifuge, which Bolin says is a high-strength wastewater. "We have to pretreat that [before discharge into the Santa Ana River Interceptor line], and in our pretreatment step we actually generate methane gas that goes back into our process," he says.
The most difficult aspect of bringing a biosolids technology to market is not an issue with technology, according to Bolin, but with commercialization-getting a first-of-its-kind commercial plant up and running. "As a company we're very well capitalized, and obviously the Rialto project has been financed," he says. Good technology and teamwork, and working closely with customers, the public and stakeholders to make sure they are all comfortable with the project is extremely important, he says.
Of the EnerTech SlurryCarb process and its approach to business, Moore says, "This will be the full-scale pilot, if you will, and it will be replicated all over the world. I'm sure of it."
Ron Kotrbaa is a Biomass Magazine senior writer. Reach him at firstname.lastname@example.org or (701) 738-4942.