A new CHP plant at a US hospital is demonstrating how distributed energy projects can be integrated with conventional heating and cooling equipment – in buildings that never close. Garen Demirchian and Bruce Bennett report.
Eastern Maine Medical Center (EMMC) is a critical regional tertiary hospital facility located in Bangor, Maine, which serves the needs of communities throughout central, eastern, and northern parts of the state. For more than a century, Eastern Maine Medical Center has grown from a five-bed general hospital into a 411-bed medical centre with a staff of 3400 including a medical staff of 373 physicians. The medical centre provides three-quarters of the primary-care hospital services offered in the Bangor area, as well as specialty and intensive services to the northern two-thirds of the state.
With its 24/7 operation, Eastern Maine Medical Center is an excellent candidate for combined heat and power
In June 1997, EMMC determined that it was necessary to evaluate the effectiveness and efficiency of its existing utility and power infrastructure, which consisted of a high-pressure steam boiler plant and distribution system, a 5800 kW (2300 ton refrigeration) electric chilled water plant, two 12.4 kV feeders on overhead poles with primary switchgear and site distribution, and two 1500 kW and one 500 kW diesel emergency generators. As part of this process, EMMC brought in the design/build project team of Vanderweil Engineers and Cianbro Corporation, who determined that the EMMC facility was an excellent candidate for a combined heat and power (CHP) plant.
THE FACILITY NEVER CLOSES
Various factors contributed to the project team’s selection of CHP as the best alternative for the EMMC facility. First, the medical centre serves as the referral hospital for the largest geographical area of any hospital in the Northeast; the facility never closes and it is imperative that it remain operational at all times to continually provide patient care. EMMC’s ability to provide its necessary services is challenged by severe and constantly changing weather conditions that have been known to cause extended electrical outages.
In 1998, an ice storm had a catastrophic effect on this region and on EMMC, which was able to continue operation using on-site generators, but lost dependable power for more than 16 hours. Much of the local utility infrastructure was damaged, causing many homes and businesses to be without power for time periods that ranged from several days to six weeks. The reliability of the gas turbine and the dual-fuel capability (natural gas or oil) will greatly improve the facility’s ability to operate under any condition. EMMC is an economic driver in the region responsible for providing affordable and efficient healthcare services. The CHP project will save EMMC millions of dollars in energy costs over the lifetime of the plant at a rate of approximately one million dollars per year.
The turbine generator set is modular in design. Shown here is EMMC Project Manager Jeff Mylen in front of the enclosure that houses the turbine and generator
Once the CHP project was given final approval, the EMMC/Vanderweil/ Cianbro team determined through a competitive bid process that the plant was to be configured with a dual-fuel 4.6 MWe Centaur 50 gas turbine manufactured by Solar Turbines for power generation, integrated with a Delta heat recovery boiler manufactured by Deltak, LLP. The Centaur 50 provides sufficient heat input to the Delta boiler to produce up to 24,000 lb/hour (10,900 kg/hour) of high-pressure steam. Modular in design, the gas turbine and heat recovery boiler form a compact power island for CHP applications.
Cianbro poured the equipment support slabs in late fall 2005 in time to receive and unload the power modules delivered directly to site, and the building shell was constructed around the power island. In December 2005, the design-build team met with EMMC to value-engineer US$500,000 out of the estimated construction cost to keep the project finances within its target budget range. According to Jeff Mylen, Project Manager of Eastern Maine Medical Center: ‘the team worked very hard to keep construction costs down and were diligent in managing a very tight schedule.’ Design modifications were fast-tracked through winter to keep pace with construction, which was substantially complete by July 2006. At the same time, Bangor Gas completed its high-pressure gas main to the site. Cianbro’s start-up and commissioning team successfully completed performance runs on oil and gas fuels in August 2006.
The new CHP plant is situated adjacent to the old boiler house, which contains five firetube steam boilers ranging in age from 20 to 30+ years. In addition, EMMC has begun decommissioning the three oldest units which will make space for future utility plant expansion. The proximity of the new systems to the old boiler house made process tie-ins easier with minimum disturbance to mechanical and electrical lifelines and the existing de-aerator, boiler feed, and condensate systems were determined to be suitable for integration with CHP. Upgrades were made to the plant’s compressed air system to meet the higher quality and quantity that gas turbines need for cleaning their combustion air inlet filters.
COOLING FROM SPRING TO FALL
The chiller plant for Eastern Maine Medical Center is located across the campus near the hospital’s operating rooms. The existing chiller plant contains three electrical centrifugal chillers, pumps, and a retired absorption unit. The retired unit was removed and replaced with a 500-tonne Trane Horizon unit paired with a two-cell Marley NC Class cooling tower. New piping and pumps were tucked into the mechanical plant and heat traced for winter lay-up (protection from de-watering and freezing). Because operating rooms require cool space temperatures, the absorption unit will run from early spring to late fall.
The new chiller-tower system is controlled by a balance-of-plant control system designed by Honeywell Automation. System automation monitors chilled water production and controls condenser water supply temperature to the new Trane unit. Heat input to the unit is supplied by 110-psig (760 kPa), 345ºF CHP-produced steam fed through the existing campus steam distribution network and let-down (pressure-reducing) station at the chiller plant. Variable-frequency drives are employed on the tower fans and adjustable-frequency drives have been incorporated into the Trane chiller and Solar gas turbine designs to achieve energy savings wherever possible.
In addition, the City of Bangor has high-quality potable water which simplifies the treatment processes for cooling tower circulating water service and boiler feed make-up water.
In terms of the electrical interface/interconnection of the EMMC campus to the turbine-generator set, EMMC decided to run in parallel with the local utility for increased redundancy and efficiency. An existing 15 kV circuit breaker was retro-fitted and relays added to an existing switchgear line-up to allow for the paralleling mode of operation. This set-up allows the hospital to run on utility power when the turbine is down for maintenance and also allows the system to import utility power when electrical demand is high during the summer months. As a result of this project, EMMC now has two sources of power from the utility, a new CHP plant running in parallel with one of the utility sources, and three emergency diesel generators for life safety redundancy.
A PRISTINE ENVIRONMENT
EMMC is located within a 45-minute drive and about 50 km from Bar Harbor and Acadia National Park, a pristine environment and destination for tourists and hikers. EMMC and its design team met early on in the project with officials of the Maine Department of Environmental Protection – Bureau of Air Quality, to discuss the air emission licence amendment application. The hospital had already amended its licence in January 2003 when it made the decision to change from #6 fuel oil to #2 oil.
The focus now turned to demonstrating that emissions from the proposed CHP plant represented Best Practical Treatment (BPT). BPT for amended applications must demonstrate that emissions are receiving Best Available Control Technology (BACT). To address these requirements, the gas turbine selected for EMMC was capable of firing both natural gas and #2 fuel oil. The dual-fuel design was selected by Vanderweil to provide EMMC with an alternative fuel option in the event that its natural gas supply is interrupted or becomes unfavourable due to market pricing.
A refined air modelling analysis was performed by MacMillian & Donnelly of Falmouth, Maine, to demonstrate that emissions from the new turbine, in conjunction with other area sources, would not cause or contribute to any violations of Maine’s Ambient Air Quality Standards. This issue was addressed by incorporating SoLoNOx combustors on the Centaur 50 gas turbine. The Bureau awarded EMMC’s licence amendment in May 2005. Due to the fact that its CHP project represents a minor modification to a minor source, EMMC has been allowed to operate without any back-end pollution controls.
The CHP project at Eastern Maine Medical Center is particularly note-worthy because many challenges had to be addressed during the process and because its utility systems were designed with the goal of employing innovative technology so that the facility could serve as a model for utility plants at other healthcare facilities. EMMC is the first tertiary hospital in New England to take the lead to fully integrate combined heat and power into its infrastructure.
CHP SYSTEM CONTROL OPTIMIZATION
The control system put in place at EMMC was designed to automatically adjust steam output from the heat recovery boiler while simultaneously meeting the electric demand of the hospital. This distinctive feature was made possible by including a diverter damper in the project design. The concept is simple: divert heat input from the boiler when hospital steam demand is below the boiler’s maximum output by modulating a damper located upstream of the boiler and bypassing hot gas to the main stack. This process allows the turbine to run up to its full load no matter what the steam demand is for the hospital.
Plant operation data are continually monitored, and here Licensed Boiler Operator Timmy Cobb points out some of the data during the plant testing phase.
Bangor, Maine is located above the 45th latitude. Its northern exposure to harsh winters and moderate summers make historical steam loads high in winter and low in summer. To complicate matters, its electric load is just the reverse with peak electric demand occurring in summer. In order to optimize the CHP plant, Vanderweil employed a steam absorption chiller to increase summer steam demand while trimming electric demand by shutting down electric-motor-driven chillers.
The gas turbine can run on natural gas or oil, improving fuel economics in case of natural gas disruptions or price hikes
This method of demand-side management significantly benefits the facility: energy cost savings are initially reaped by the hospital by way of reduced energy costs, and the customers/patients will realize these benefits through their costs for services rendered by the hospital.
Plant metrics are currently being monitored and logged by the Honeywell EBI. In addition, the US Department of Energy’s Oak Ridge National Laboratory (ORNL) has also sponsored a project website which details the technologies used and the progress made through each phase of the project which will be made publicly available by early 2007.
US DEPARTMENT OF ENERGY AWARD
Another facet of the EMMC project that sets it apart is the $3 million energy award granted by ORNL in 2004. The goal of this award was to demonstrate how distributed energy projects utilizing CHP can be integrated with traditional heating and cooling plants at leading hospitals across the United States. Vanderweil and EMMC prepared an outstanding award application which received wide support from state and federal legislators, government agencies and the hospital board. Randy Hudson of ORNL was the guest speaker at the recent commissioning ceremonies, complimenting Jeff Mylen and the EMMC-Vanderweil project management team for their smooth project execution and Nick Bell and Deb Wilson of Cianbro for their day-to-day oversight of the project.
The new CHP plant is currently on-line and run 24/7 by EMMC’s dedicated team of facility engineers.
Garen Demirchian is a Managing Principal and Bruce Bennett is a Senior Corporate Engineer, both at Vanderweil Engineers, Alexandria, Virginia, US.
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