The story has become increasingly common in the current economic climate: An organization must address its aging infrastructure and building equipment while trying to manage ever-tightening operating budgets. For Arnot Ogden Medical Center, a not-for-profit, 433,000-sq-ft medical facility in Elmira, N.Y., the answer to this challenge came in the form of a renewable-energy technology- and infrastructure-upgrade program designed to positively impact the environment as well as the hospital's bottom line.

Through a $4 million performance contract, wood chips are being turned into energy savings, thanks in part to a biomass boiler system that handles most of the thermal — heating and non-heating — load for the main medical center. The system shifts more than 60 percent of Arnot Ogden's total energy use to a renewable source, stabilizing operating costs and reducing carbon-dioxide (CO₂) emissions by more than 9.5 million lb a year, equivalent to removing nearly 970 cars from the road.

Combined with more traditional energy-conservation measures, such as building-envelope improvements and motor upgrades, Arnot Ogden is saving more than $535,000 in annual energy and operational costs. The savings pay for the work and are guaranteed for 10 years. As a result, the improvements do not affect the medical center's operating budget.

Biomass-Powered Heat

Arnot Ogden previously relied on three steam boilers in its central utility plant to meet heating needs. The boilers used natural gas as their primary fuel; however, boilers 2 and 3 also were compatible with No. 2 fuel oil (Table 1).

Equipped with an oxygen- (O₂-) trim control system and an economizer for preheating boiler feed water, Boiler 1 was the newest and most efficient boiler and handled 70 percent of the hospital's steam demand. Most of the time, Boiler 2 remained on standby mode when Boiler 1 could meet the hospital's steam load. Boiler 2 operated when Boiler 1 could not meet the hospital's entire steam load, such as during severe weather.

As the oldest and least-efficient boiler, Boiler 3 spent much of its time offline. A 450-hp water-tube boiler, the 35-year-old unit did not have an O₂-trim system or a stack economizer and was beyond its useful life.

In 2006, possible measures to address the hospital's aging infrastructure and equipment, including replacing Boiler 3, were discussed. As the boiler neared the end of its useful life, it required more investment through repairs and maintenance — a tough requirement for any hospital operating on a tight budget.

Ideally, the replacement would provide the base load for the hospital, and Boiler 1 would provide the peak load when needed. (Currently, Boiler 1 functions as the primary backup boiler, operating in “warm standby” mode.) Replacing Boiler 3 with a wood-gasifying boiler or a more conventional fossil-fuel natural-gas-fired boiler was considered. A cost analysis was conducted, and the wood gasifier proved economically superior to the fossil-fuel alternative. Although the installation of fossil-fuel-fired equipment would have been less expensive, the wood-gasifying boiler offered a net benefit of nearly $19 million in operational and capital-investment savings over a 20-year life cycle (Table 2).

Spurred by these findings, the hospital replaced the old boiler with a biomass unit capable of producing 15,000 lb of steam per hour at 125 psig. Although the new boiler can be fired with any organic matter that is approximately 2.5 sq in., wood chips and shavings are preferable because they have a fairly low moisture content and are readily available as waste from local mills and lumberyards. A single load of wood-based fuel produces approximately 1 percent of its volume in ash. Each year, Arnot Ogden fuels the biomass boiler with more than 7,000 tons of wood chips from a local mill. The fuel gives the medical center a U.S. Department of Energy-classified carbon-neutral solution for heating its facilities. Table 3 includes calculated CO₂ data from the installed system.

The two-chamber boiler-system technology, known as close-coupled gasification, heats wood chips in an airtight, O₂-deprived chamber at 1,000°F to 1,400°F until they break down to create a synthetic wood gas — volatile pyrolysis gas — that burns similarly to natural gas (Figure 1). Once released, the gas travels through the burner nozzle where it is superheated at temperatures of up to 2,300°F and mixed with air for complete combustion, leaving little or no waste, such as ash, creosote, or stack effluent. (Any ash residue from the gasifier is non-toxic and suitable for use as compost.) The gas then is treated in a cyclone arrestor to remove any particulate material.

Acceptable Use Policy blog comments powered by Disqus