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Subtropical Rain Forest Eats Up CO2
Students pass through the tall lush tropical plantings on the Southern California college campus and are oblivious to the unique waste water and carbon dioxide feeding the subtropical rain forest growing on a quarter acre in the heart of the hot and dry San Fernando Valley.
To students not clued in, it may appear as overgrown greenery. In actuality though, this subtropical rain forest, which has been growing exponentially since first planted in May 2009, is the landfill or sink for the byproducts of a sophisticated college physical plant – where backwash or effluent, waste heat and condensate rich in CO2 are recycled.
Eventually, the bamboo growing in the rain forest will be harvested by art students and made into products to permanently sequester the CO2.
California State University, Northridge (CSUN) was lucky to have Tom Brown, a very creative engineer, as the Executive Director of its physical plant management team who imagined how to marry technology and the environment. Tom left in August 2010 but the team he left in place had originally designed the subtropical rain forest, along with teams of engineering, biology and art students. They continue to watch over and maintain the rain forest.
The current physical plant that heats and cools the 356-acre campus was designed as part of an aggressive capital construction campaign. Beginning in 1994, following a January, 1994 earthquake which had damaged a great part of the campus, a new central plant was designed and built.
A 2.3-million-gallon thermal energy storage system was installed to cool the campus buildings during peak afternoon hours. Three electric centrifugal chillers totaling 3600 tons were installed in the central plant and at night, when electric rates are cheap, they cool the water stored in the thermal energy storage system.
In 2001, CSUN received 6, 30 kW Capstone micro turbines through a grant from the South Coast Air Quality Management District. CSUN pays the fuel bills and maintains the equipment. The micro turbines generate power during daytime hours to reduce the electrical peaks. They supply 3% of the campus electricity needs.
Brown then moved on to solar systems. In 2003, the campus installed its first 225 W solar photovoltaic (PV) system in a parking lot – on top of pylons that also creates shade for the cars. A second 467 kW solar system was installed in 2005, along with a public monitoring station where viewers can watch how much electricity is being produced. Together, the two systems supply 2% of the campus electricity needs.
In early 2007, CSUN began operating its 1 MW Direct FuelCell 300MA plant, manufactured by FuelCell Energy. It sits in front of (and adjacent to) the building that houses two new 1000-ton chillers that were installed to cool the two newest campus buildings. The fuel cell plant, made up of four, 250 kW cells, supplies 18% of the campus electrical needs and drives the two chillers.
The fuel cell plant has a rated electrical efficiency of 47%. Its thermal energy is recovered from the plant’s exhaust stream and supplements the campus system that heats the buildings, thereby boosting the estimated overall plant efficiency to about 83%. Brown himself designed the barometric thermal trap to recover the waste heat streaming from each of the four fuel cells. The waste heat is also used to heat the swimming pool water in the nearby student union.
Rebates and incentive payments made the solar systems and fuel cell plant affordable for the campus. The two solar systems, combined, cost US$5.4 million and the school received US$4m in rebates from the local electric and gas utilities. The fuel cell plant cost US$5.26m installed, but US$2.75m in state incentives reduced CSUN’s cost to US$2.5m.
The rain forest is designed
Once the new power plant was up and running, Brown turned his attention to devising a system that could use up all the waste byproducts instead of venting them to the sewer system or atmosphere. He selected a quarter-acre plot next to the fuel cell and chiller plants and set a student design team to work with the campus engineers to design the forest.
Bill Sullivan, CSUN’s Energy Manager filled in the details during a tour of the rain forest. He said Brown, who involved engineering students throughout the development of the fuel cell plant, had biology students research and identify the plants that could grow in the soil – irrigated by water rich in potassium chloride.
A soil amendment, BioChar, was also identified. Originally found in the Amazon, it is extremely fertile and allows the soil to soak up CO2 which becomes sequestered in the growing woody bamboo. Sullivan said BioChar can be purchased locally. Additional green products were located to clean cooling tower water: Organic peroxide breaks down into a benign material and Sanacor Green is used as an erosion inhibitor.
Irrigating and fertilising the rain forest
To provide the moisture needed for tropical forest growth, a system to pipe the waste heat rejected by the nearby chillers was created. 8 cooling towers sit low in the midst of the rain forest and dissipate that heat. Student artists created individually themed dioramas that encircle each cooling tower: pictures of alligators and other swamp creatures encircle one, exotic birds encircle another cooling tower, frogs another and jungle animals yet another cooling tower.
The fuel cell plant requires pure water to convert natural gas to hydrogen. A reverse osmosis process purifies the water but it also produces backwash as contaminants are flushed out. Instead of draining 9000 gallons of water per day into the sewer, it is instead piped to the rain forest to irrigate the soil.
Recall the exhaust heat recovered from the fuel cells? It contains CO2, a byproduct of the natural gas reformer that extracts hydrogen in the fuel-cell cycle. While most CO2 savings are credited to the fuel cells’ non-combustion fuel-reformation process, the exhaust nevertheless is still relatively rich in CO2.
Brown had a distribution system designed in which side-stream flows of condensate are pumped from the fuel cell plant at selected volumes to the rain forest and on through diffuser rings surrounding each cooling tower. When the chiller load is low, usually in the morning, cooling tower fans run backward to pump the condensate containing CO2 through holes in the diffuser rings and into the microclimate, thereby enhancing photosynthesis.
Sullivan explained, as we stood beside a cooling tower with condensate spraying gently out, variable speed drives automatically control the forward/backward operation of the cooling tower fans, based on the surrounding temperatures and the need for cooling.
Additional work is continuing. Students are now designing a system to use cooling tower effluent for additional irrigation water.
Tom Pepe, Assistant Director of the Environmental Health and Safety Department at CSUN, explained that an irrigation storage permit was required to satisfy a general waste water discharge requirement set by the Los Angeles Regional Water Quality Control Board. That agency, like many, is bureaucratic and took its time, but Pepe said the people were cooperative and the permit was granted in about 6 months.
Chloride is the main element of interest to the Water Quality Control Board and has to be monitored to avoid it contaminating the water table. Recall that it is present in the irrigation water since it is washed out in the reverse osmosis process to purify the water for the fuel cells. Pepe said the irrigation water is tested quarterly. If the level of chloride increases, brine is diverted from one of the four fuel cells.
Brown, before he left CSUN, explained that the next phase is to make use of the bamboo growing in the rain forest before it dies and releases the CO2 back into the atmosphere. Art students will cull the bamboo once it matures and manufacture sustainable green products from it, using hand tools.
A manufacturing process, for example one that uses power tools, he said, would generate carbon and defeat the sequestration effort.
Fuel cell plants, digester gas to cut GHG emissions
A small company, BioFuels Energy LLC, headquartered in Encinitas, California, is designing a major project that once completed will capture approximately 1.3 million ft3 per day of methane currently being flared at a waste water treatment facility, clean it up and pipe it on to three separate fuel cell plants where it will be burned to generate electricity.
The project will reduce CO2 greenhouse gas emissions by approximately 30.8 million pounds/year, equivalent to removing 3000 cars per year off the road – according to the company.
Announced in summer 2009, BioFuels Energy signed a 10-year agreement with the City of San Diego to install a 1.4 MW fuel cell at the city’s South Bay Water Reclamation Plant. The company will design, permit, install, own and operate the project. It will also build a 300 kW fuel cell plant at the Point Loma Waste Water Treatment Plant to provide the power for a facility it will have built to purify and compress the 1.3 million ft3 per day of methane.
The clean biogas will then be inserted into San Diego Gas & Electric’s gas line where it will mix with natural gas and then be piped to South Bay and the University California, San Diego where the third fuel cell plant will be built. An agent will be hired to schedule and coordinate gas deliveries from Point Loma to the two other fuel cell plants, according to Frank Mazanec, Managing Director at BioFuels Energy.
BioFuels Energy has already signed a power purchase agreement with UCSD where it will design, install, own and operate a 2.8 MW fuel cell facility. Mazanec said the US$45m project, including all three fuel cell plants and the methane cleanup facility, is expected to be completed in the fourth quarter of 2011.
Mazanec said the company was originally planning to truck the biogas to each location, but following protests from local residents and with the help of the California Public Utilities Commission (CPUC) and SDG&E, it decided to pipe the biofuel through utility gas lines. As a result, Mazanec said, it is a better project.
To make the piping possible, the CPUC in late 2009 approved a concept called Directed Biogas which made it legal to combine biogas in a pipeline with natural gas. SDG&E then created guidelines that established the criteria, 990 Btu/ft3, for insertion of biogas into natural gas pipelines.
Mazanec said all the permits and contracts are now in place. Equipment will be ordered once approximately US$12.5m in bonds authorised by the California Pollution Control Financing Authority are in place in October.
Another US$14.4m in Self Generation Incentive Program funding from the CPUC has already been awarded.
BioFuels Energy will pay San Diego’s Metropolitan Wastewater Department about US$2.6m over the initial 10-year term of the contract with the city for the digester gas. The city, in turn, will save approximately US$78,000 per year for the power it buys from BioFuels Energy under the South Bay power purchase agreement.
UCSD microgrid will grow
University of California, San Diego (UCSD) has already created an infrastructure that includes 26 MW of cogeneration, 1 MW of solar PV and 60 generator sets totaling 32 MW, allowing it to operate its own microgrid and using the local utility as a backup system. Once BioFuels Energy installs the 2.8 MW fuel cell system, the waste heat generated by the fuel cell will power 320 tons of chilling capacity to cool campus buildings.
UCSD is now in contract negotiations with a company to add a 2.8 MW advanced energy storage system to its microgrid system. It is to be paired with and installed in tandem with the fuel cell plant, to qualify for CPUC self generation incentive funds.
Byron Washom, UCSD’s Director of Strategic Energy Initiatives, said he could not talk about the details of the energy storage system nor how much it will cost while negotiations are underway. He did say it has to be capable of four-hour storage at rated capacity, and will be used on a daily basis for permanent load shifting. Both systems will be in operation by the end of 2011.
About the author:
Lyn Corum is a freelance western U.S. correspondent for Renewable Energy Focus magazine.