|Courtesy: Mas Energy|
Owner/operator: Mas Energy
By taking a waste product and converting it into a fuel source, the 6.5-MW Coca-Cola/Mas Energy Facility became the first U.S. operational trigeneration project fueled by landfill gas. Since March, the new system has provided electricity, steam, and chilled water to the adjacent Coca-Cola Syrup Plant, satisfying most of the plant’s energy requirements and reducing its long-term energy costs.
It’s the real thing. The Coca-Cola/Mas Energy Trigeneration Facility in Atlanta is a genuine renewable energy leader that uses treated landfill gas as an energy source for its operations. Using a trigeneration or CCHP (combined cooling, heat, and power) system, the new facility is projected to generate at least 48 million kWh of on-site renewable energy annually. The project also provides Coca-Cola (the “offtaker” or energy user) with the additional economic benefit of leveling its energy costs over an extended period of time.
Landfill gas from Republic Services’ Hickory Ridge Landfill in nearby Conley, Ga., is the primary fuel source for the trigeneration plant. “We anticipate that the plant will use landfill gas as its primary fuel source for the life of the project,” Jason Byars, vice president of business & project development at Mas Energy, told POWER in October. “The plant also was designed and installed with the ability to blend natural gas or use it as a backup fuel when landfill gas is interrupted to ensure relatively constant fuel input to the plant.”
The new facility is gaining attention. For example, the U.S. Environmental Protection Agency’s Green Power Partnership recently recognized the Coca-Cola Co. as the third-largest on-site green power generator in the U.S., and the trigeneration facility was a key factor in that ranking.
The system achieved commercial operation on March 31, 2012, after approximately 15 months of construction and related activities. “This is the first trigen plant built at the offtaker’s site. A significant challenge during the construction phase was coordinating all the construction activities so as not to interfere with or interrupt the offtaker’s existing operations. Coordination of tie-ins to existing site utilities and the controls modifications required to integrate new systems into the existing schemes had to be done with careful attention to detail,” Byars said.
The trigeneration plant has three GE Jenbacher J616 reciprocating engine generators, each rated at 2,175 kW for a gross output of 6,525 kW. The engines use selective catalytic reduction (urea) and selective noncatalytic reduction control technologies to mitigate the plant’s total emissions and thereby keep them below major source thresholds. Fuel gas conditioning equipment (used at the landfill site) was provided by Venture Engineering for removal of siloxane (a chemical potentially harmful to the engines and post-combustion emissions control devices), as were polishing skids. Unison Solutions provided the compression and dehydration equipment. The siloxane regeneration skid was purchased from Abutec.
The engines exhaust into individual heat recovery steam generators (HRSGs) that can each produce up to 3,500 lb/hr of steam at 125 psig, for a total rated steam output of 10,500 lb/hr. The HRSGs have bypass dampers that enable full electrical output to be achieved even when the offtaker’s thermal requirements are relatively low. When in full steam-generation mode, the HRSGs’ steam is dispatched to the offtaker’s facility, where it is primarily used to drive a 1,065-ton steam turbine–driven York YST MaxE chiller. The steam can also be used to offset steam production from the offtaker’s facility boilers via a 125-to-15 psig reducing station. The condensed steam (condensate) produced from each point of use is sent to the facility’s existing feedwater deaerator before being returned to the HRSGs.
Byars explained that the project is unique because it involves landfill treatment and combustion at two different sites interconnected via a dedicated 6-mile pipeline. He said that “this project configuration added significant complexity to the scheme required to automate, monitor, and control the system.” Approximately 2,200 scfm of landfill gas is first processed at the landfill via dehydration, compression, and siloxane removal equipment (Figure 1). Then it is transported to the offtaker’s facility via the pipeline operated and maintained by AGL Resources.
|1. The big squeeze. The gas-conditioning skid dehumidifies and compresses the landfill gas prior to removal of siloxanes. The treated landfill gas is then used as fuel at the Coca-Cola/Mas Energy Trigeneration Facility. Courtesy: Mas Energy|
“The trigeneration plant’s generators operate in parallel with the Georgia Power distribution grid. And because the project has obtained ‘Qualifying Facility’ status, the offtaker is able sell any excess electricity generated by the trigeneration plant and not consumed by the offtaker’s facility back to Georgia Power at avoided cost or better. As a result, Georgia Power gets the benefit of including some incremental renewable generation in their system fleet,” Byars said.
Preparing Landfill Gas for Fuel Use
In order to protect the integrity of the post-combustion environmental controls installed at the offtaker’s site, it was necessary to design and install landfill gas conditioning and cleaning systems at the landfill. Prior to development of this project, all of the gas produced at the landfill (approximately 2,200 scfm) was combusted via an open flare. Now it is delivered from the landfill’s collection system to the treatment system at the landfill. The landfill’s existing flare has remained in service and is available for use when operation of the trigeneration plant is upset or curtailed.
After it is collected in the landfill collection system, the landfill gas is cooled in a heat exchanger to prevent condensation in the oil system. The gas is then compressed to approximately 50 psig and cooled in a gas-to-air heat exchanger. It then flows through a glycol chiller and is cooled to 40F. Next, it passes through a moisture knock-out pot and reenters a regenerative heat exchanger, where it is reheated to 80F. At this point, the landfill gas passes to a siloxane removal skid.
The siloxane removal skid comprises two trains of siloxane removal beds and carbon polishers, each train capable of processing 100% of the landfill gas flow. Only one train operates at any given time while the other side is either in regeneration or standby mode. An auxiliary flare was permitted and installed to accommodate the siloxane removal skid regeneration process. The siloxane removal skid is generally in regeneration mode for six hours each day, during which it regenerates the off-line bed.
Byars explained that during regeneration, a blower and electric heater mix approximately 1,000 scfm of heated ambient air with a slipstream of approximately 120 scfm of landfill gas, which flows in reverse through the regenerating bed before being routed to the auxiliary flare. The two siloxane removal beds operate on an alternating 24-hour adsorption/desorption cycle.
After being in the siloxane removal bed, the gas then flows through a carbon polisher that further removes trace levels of siloxane. The siloxane removal skid’s outlet connects to the inlet of the dedicated landfill gas pipeline, which transports the gas to the trigeneration plant site at the Coca-Cola facility.
Lining up Project Funding
“Mas Energy used a combination of debt and equity to fund construction of the project. One related challenge was the sourcing of debt for a relatively small project such as this. Ultimately, project financing was provided via a bond issuance through the Fulton County Development Authority,” Byars said.
During the planning phase, Mas Energy—which develops, owns, and operates energy systems around the world—spent several weeks analyzing its air permitting options for the trigeneration plant. From one perspective, the permitting process could have taken several months given that the new plant would be a major source of air emissions and the greater Atlanta region is a “severe non-attainment” area for ozone. From another perspective, the project stood to benefit substantially from the U.S. Treasury’s Section 1603 grant program as more fully described in the American Recovery and Reinvestment Act of 2009, provided that it achieved commercial operation prior to the end of 2011 (a deadline since extended by an act of Congress).
To expedite the permitting process and give the project the best chance of achieving commercial operation prior to the deadline, Mas Energy elected to install post-combustion treatment at the plant and permit the project as a synthetic minor source. “By working collaboratively with regulators, we were able to shorten what could have been a ‘several months’ process to one that took approximately 100 days from the date of the air permit application by Mas Energy to the date of air permit issuance by the Georgia Environmental Protection Division,” Byars said.
— Angela Neville, JD is POWER’s senior editor.