A First in 20 Years
The majority of the approximate 71 waste-to-energy (WTE) plants still operating in the U.S. at the end of 2015 were built in the late 1970s and ‘80s, at a rapid pace. The desire for new waste disposal solutions and alternative energy were at an all-time high, and the passage of the Public Utility Regulatory Policies Act solidified the financial case for these plants, mandating utilities to long-term contracts at attractive prices.
The fleet of U.S. WTE plants is spread across 20 states, the majority in the Northeast and Florida, collectively capable of generating 2.3 gigawatts of power annually. The U.S. EIA estimates that these facilities combusted 29 million tons of MSW in 2015, 26 million tons of which was used to generate electricity, with the remaining being recycled, composted or landfilled.
While a few have undergone expansions over the years, industry growth has remained stagnant until just recently. Florida’s Palm Beach County just became home to the first WTE plant built and brought online in 20 years, increasing the number of operating plants in the state to 12.
The 95-MW Palm Beach Renewable Energy Facility No. 2, or REF 2, was the result of an extensive investigation regarding the county’s solid waste authority’s (SWA) next 20-year plan would entail, according to design and construction project manager Patrick Carroll. Carroll, who has been with the authority for 21 years, explains that the SWA recently came to the end of a $1 billion capital program. “So, we’ve been very busy,” he says. That’s evidenced by the renewable energy park the SWA has created, consisting of two waste-to-energy plants, a landfill gas facility and a biosolids pelletization operation, all of which is colocated with a bird rookery. The SWA has mapped out what the next two decades of handling the county's waste will look like, and its most recent undertaking—construction of REF 2—has extended the county landfill by 20 years.
REF 1 and REF 2
The first WTE plant built by the SWA, a 62-MW plant known as REF 1, came online in 1989, Carroll says. “Back in the mid- and late ‘80s, there was a pretty big wave of construction of facilities of this type, especially in Florida,” he says. The refuse-derived fuel WTE facility—different from a mass burn facility at which waste is not presorted or treated—is operated by the Palm Beach Resource Recovery Corp., a subsidiary of Babcock and Wilcox Corp. REF 1 processes in excess of 850,000 tons of MSW per year, and without it, the SWA’s landfill would close by 2025.
An on-site biosolids processing facility (BPF) accepts wastewater treatment residuals from six local wastewater treatment facilities, drying the material into saleable fertilizer. Heat required for the drying process is derived from captured landfill gas that is compressed and sent to the BPF, an operation that came online in 2009. “It’s a great use for the landfill gas,” Carroll says.
Finally, there is REF 2. “It’s the first green field project built from scratch in the U.S. in 20 years,” Carroll says. “The genesis of this whole project was long-term planning, which most public agencies do. Back in 2005-’06, we started looking hard at our 20-year plan—one was ending, so we were working on developing our next 20 years. We’ve always prided ourselves being on the cutting-edge, and we looked at a lot of things, including expanding the landfill.”
If nothing had been done, the landfill would reach capacity by 2025. “We looked at a lot of different options—anaerobic digestion, pyrolysis, all of things out there,” Carroll says. “Through that detailed analysis, we decided that we would double down on WTE, and build this new facility.”
REF 1 takes in curbside garbage, but before it’s sent into the boilers, it enters a front-end process that includes chopping, screening and removing noncombustibles. “The idea is that you get a higher Btu value fuel,” Carroll says. “We abandoned that process for the simpler and more efficient mass burn—we throw it all in the boiler and burn it, then sift out the recyclables out of the ash and the noncombustibles. That was one major change with REF 2.”
In a nutshell, at REF 2, MSW collected from homes and businesses in Palm Beach County—as well as a neighboring county—is delivered to transfer stations, and then transported via truck to the renewable energy park, for processing at either REF 1 or REF 2. Once waste is unloaded into a large pit in the refuse building, crane operators manage the waste deliveries from the control room, removing large objects that could potentially jam the processing equipment. MSW is delivered to the boilers through charging hoppers and is fed onto B&W Volund DynaGrate traveling grates, where it is combusted. Process heat is converted into steam, which powers a turbine generate to create power that is sold to Florida Power & Light.
One of the main components that helped move the project forward was installation of the most cutting-edge pollution control system available, according to Carroll. “We have the lowest permit limits of any WTE facility in the country, on REF 2,” he says. “One of the biggest features we incorporated is selective catalytic reduction (SRC) for NOx control. To my knowledge, we’re the only WTE facility in the U.S. that has employed that technology. It’s used extensively in coal-fired plants and in Europe, but as far as the WTE industry in the U.S., it’s the first. Primarily, it allows us to get down to very low NOx limits. The other components of the air pollution control system are fairly standard, but the most up-to-date. All these things in total, allow us to get down to those low permit limits.”
Following the combustion process, ash is conveyed to a sizeable ash management building where it is processed indoors. There, a rotary magnet and Eddy current separator removes ferrous and nonferrous metals from the ash to be resold on the scrap metal market. “We have extensive metal recovery,” Carroll says. “The facility is owned by the county, but it’s operated by a B&W subsidiary, and part of the contractual commitment to us is that they have to recover 90 percent of the ferrous mental, and 85 percent of the nonferrous metal.”
Bottom ash and fly ash are combined, and what remains is landfilled, at least for now. “We are currently working with the University of Florida, trying to develop some alternative uses for ash, primarily in areas like road base and concrete supplement aggregate,” Carroll says. “We’re working on those, but still a few years away. There are some research that needs to be done, as well as some convincing that needs to be done with the regulatory authorities before that will be something widely accepted. It’s been done in Europe for many years, and I think it’s just a matter of time before it’s happening in a big way here.”
In another bid to make REF 2 as environmentally friendly as possible, the other major change in REF 2 from REF 1 was its unique water conservation and recycling system. “We wanted to pay particular attention to water usage,” Carroll explains. “Believe it or not, even in south Florida, water is scarce.”
REF 2 employs a rainwater capture system that encompasses 11 buildings and over 270,000 square feet. “There is a lot of rooftop, and we collect all of the rainwater off of them,” Carroll says. “We built a 2 million-gallon storage tank, so the rain water, along with some of the process wastewater from the existing plant, is the primary source for the process water for the new plant, which uses no new groundwater. We also incorporated an air-cooled condensing system, and after the water goes through the turbine as steam, it recondenses back into water and is reused. These three things together supply all of the water needs for the facility, and that’s something I don’t think has been done anywhere.”
Resource, Model for Others
Overall, the facilities collectively process over 6,000 tons of MSW per day. The new facility was built well-over the county’s current capacity, a strategy that not only makes the county money by importing waste from Broward County via tipping fees, but as waste generation in Palm Beach County grows, the facilities will have the ability to take it in, eventually displacing the waste being imported. “It’s a good way to use spare capacity,” Carroll says. “Usually, when these things are built, they’re at capacity at day one. We wanted to look forward a bit, and now we’re in good shape—we’re utilizing all of the capacity, but about 200,000 tons [per year] or so are being imported from outside of the county.”
As for the landfill’s capacity, when REF2 came online, its projected life was extended from 2025 to 2049. “When you’re just putting ash in, it’s a big difference,” Carroll says. “And, we also make money off the electrical generation sales.”
With design, development and construction of a sizeable, monumental project, there are all kinds of associated challenges. Carroll says that one in particular involved siting of the new facility. “We wanted the WTE facilities to be colocated for a number of obvious reasons, but in order for that to happen, we had to reclaim a dredge lake that we had dredged 25 years earlier,” he says. “We actually filled in a 15-acre lake to make the land that we used to build part of the campus on. So that was surely a challenge.”
And on successes, Carroll says, without a doubt, it was putting together the right team [Figure 1]. The amazing thing was that it was the largest project ever untaken in Palm Beach County history, and it came in on time, on budget, with no major technological hurdles. It was just amazing at how well it came together.”
Unsurprisingly, the facility has attracted interest from a stream of other public agencies, from the U.S. and all over the world. “It’s been unbelievable,” Carroll says. “Especially because of all of these facilities that we have in our complex here, it’s fairly unusual. Because of that, we’ve had a lot of visitors from all over the world, and this new facility has amped that up even more.”
Carroll says part of the tremendous U.S. interest is that communities that built WTE plants in the ‘80s are in the same situation the SWA found itself in 10 years ago. “They’re reaching the end of those facilities’ useful lives, so they need to make a decision—refurbish or rebuild the WTE capacity, find new landfill capacity, or do something else. There are a lot of communities that are in that situation. A lot of policymakers, and even professionals, would shy away from pursuing WTE in the past, because there was always ‘you can’t get financing, it’s too expensive, you can’t get permitting, you can’t site one,’ all typical arguments, yet this project proves that you can do that.”
Carroll admits the timing was ripe to develop the project—it was undertaken at the depth of the recession. “Because of that, there wasn’t a lot of lending going on, and we could float a bond at a very favorable rate,” he says. “With no construction going on, we had tremendous pricing, and the permitting part came together because we were willing to implement the SCR, water conservation and some of these other things. It was the perfect storm—it all came together.”
Regardless of the opportune time, Carroll says the new facility shows that these plants can still be built today. “It makes sense for some communities where land isn’t necessarily abundant—there are a host of factors that should be looked at—but it can be done, and it can be done environmentally consciously, and economically.”
Author: Anna Simet
Managing Editor, Biomass Magazine