By Joe Zwers
Starting out as the University Farm in 1905, the University of California at Davis has become a research leader in biology, agriculture and environmental science. In 1961 the university started the first environmental toxicology department outside of a medical school. And in 2010 Reuters reported that UC-Davis had more papers published in environment/ecology journals over the past five years than any other American research body, beating No. 2 UC-Berkeley by 15 percent.
So it’s not surprising that when UC-Davis needed to boost its steam output to meet campus expansion plans, it wanted to meet the lowest possible emissions levels.
The university chose a RENTECH boiler with a Coen QLN burner and selective catalytic reduction (SCR) technology from Combustion and Energy Systems Ltd. UC-Davis attained NOx levels of 3 PPM, well below the 5 PPM required by the Yolo-Solano Air Quality Management District.
The Need for Steam
About 15 miles west of Sacramento, UC-Davis is a leading university in biological sciences. In addition to the usual need for steam for heating and cooling buildings, the university uses steam for everything from cleaning out animal cages to sterilizing medical equipment and providing process steam for experiments, some of which require a continuous source of steam over several years.
“If you lose steam for an hour,” Louis G. Brizzolara, PE, said. “experiments may need to be scrubbed, wasting a lot of money and effort.” Brizzolara is president of AHM Associates, Inc., a manufacturer’s representative in Hayward, Calif., who represented RENTECH, Coen and Combustion and Energy Systems on these projects.
With campus enrollment expected to grow from 27,300 full-time equivalent students in the 2006-07 school year to 32,000 in 2015-16, the university embarked on a five-year, $800 million program to ensure it had the educational and housing facilities necessary to serve this increase. In addition to adding classrooms, dormitories and dining facilities, the program called for upgrading or expanding parts of the infrastructure, including steam generation.
“Steam is considered a critical system for us, and reliability is essential,” John Larsen, manager of the university’s Central Heating and Cooling Plant (CHCP) plant, said.
The CHCP had three aging boilers dating back to the 1950s and 1960s.
“The university hired us to do a steam and condensate master plan study to determine how much their steam load would grow, what equipment to install to best meet those increased steam load requirements, and at what point they should be adding the new boilers,” Quindi Guiseppe III, PE, from the consulting engineering firm Syska Hennessy Group, said.
CHCP had four buildings; Plant A housed the existing boilers, and Plants B, C and D housed chillers. Since there was no room in Plant A to install another boiler, the plan called for the construction of Plant E to house a 150,000 lb/hr 150 psig condensing boiler together with balance of plant (BoP) equipment to support all four boilers. Once the new ancillary equipment was installed and tested, the old BoP equipment in Plant A could be decommissioned. But due to the critical nature of the steam, service could not be interrupted. CHCP was located in the middle of the campus so Plant E had to fit onto a gardening easement next to the existing CHCP buildings.
Guiseppe specified the necessary boiler parameters and assisted in evaluating the proposals submitted based on cost, efficiency, emissions and reliability were among the criteria.
The boiler selected was an 180MMBTU D-Type unit with a Coen QLN Ultra LoNox burner. The QLN burner has the ability to meet low emissions – 30 PPM NOx – without the mass flow and parasitic losses of flue gas recirculation. As a result, it doesn’t need as much reactant and allows the use of a more compact SCR since it doesn’t need to deal with the higher mass flow or higher NOx levels. The SCR uses a compact bottled anhydrous ammonia system. The boiler can reach an 8-to-1 turndown ratio while still meeting the NOx requirements.
“8-to-1 is spectacular in today’s world of Ultra Lo NOx,” Brizzolarra said.
In addition to the boiler, the new building included the replacement of much of the BoP equipment.
“The existing equipment was failing miserably,” Larsen said. “Maintenance costs were tremendous, efficiencies were terrible; our deaerator was undersized for the capacity the campus requires, and the pumps were falling apart.”
So the project included installing dual reverse osmosis pretreatment systems for the raw water, a prefeed water makeup holding tank, a 400,000 lb/hr deaerator and feed pump, and a condensate polisher. All of the motorized equipment came with variable speed drives to save electricity. There was also a 35,000-gallon fuel oil tank to act as a backup when the natural gas supply is constrained.
“The occasions where we need to use diesel are very rare, but when needed, we can switch, and production is pretty seamless,” Larsen said.
The university has invested about $20 million in the last five years on the steam distribution piping around the campus, consisting of upgrades to the old infrastructure as well as running pipes to the new buildings.
Efficient and Reliable
Once it started, the $14.5 million project took about a year and a half to complete, including construction of the 5,200-square-foot building. “Since the project was completed, we haven’t had an interruption of service,” Larsen said.
The boiler is controlled through a Coen touch screen, and UC-Davis is in the process of tying all the boilers into a common Allen-Bradley control system. The new boiler has a Continuous Emissions Monitoring System so running the quarterly report required by the air district takes Larsen about a minute. To get more value out of the steam system, the university is in the process of installing a ConDex condensing economizer from Combustion and Energy Systems to turn waste heat from the boiler into hot water for domestic and process use. Next will be replacing the oldest boilers.
“We have two existing boilers that will need replacement in the near future,” Pablo Orozco, UC-Davis’ assistant director of engineering who developed and managed the project, said. “We are waiting for the air district to make the call on the emission reductions.”
A new building would have to be built to house the new boilers. But the BoP equipment that was installed in Plant 5 with the new RENTECH boiler will be adequate to support replacement boilers. Depending on growth in demand, additional boilers will be added perhaps over the next decade. However, steam growth has not kept up with the original projections from Syska. The Western Area Power Authority gave the university a good electricity rate, so UC-Davis replaced the steam absorption chillers at the two chiller plants with electric centrifugal chillers, cutting some of the steam demand.
“They have also been very aggressive with load curtailment using building insulation and lighting retrofits, and due to the economy have cancelled a couple of buildings that were on the master plan,” Guiseppe said. “But the old boilers are in line to be replaced due to age before the next one is needed due to load growth.”