Treated fresh water is mixed with condensate-return water, which contains natural carbon dioxide (CO₂). If this CO₂ were left in the boiler feedwater, carbonic acid would form, resulting in a lower pH. The carbonic acid not only would cause severe corrosion of the condensate-return piping, but be carried over in the steam and corrode the supply and return piping throughout the system. Furthermore, the cold-water supply would contain a significant amount of free oxygen, which would exacerbate the corrosive properties of the liquid in the boiler. While CO₂ and free oxygen can be removed chemically, mechanical removal, called deaerification, is much more efficient.

Mechanical removal is possible because as the temperature of the water/condensate mixture rises, the solubility of the CO₂, as well as that of any dissolved oxygen, is reduced. A deaerating feedwater heater (Photo B) removes these gasses and, thus, considerably reduces the corrosive nature of the feedwater. In the heater, feedwater is sprayed into a steam atmosphere. The spraying is done in such a manner that the water has the maximum possible surface area so that the temperature rise is as rapid as possible. As the water reaches the saturation temperature, non-condensable gasses are released and vented to the atmosphere.

Treated feedwater is transferred from the deaerating feedwater heater to the boiler by the main feedwater pumps, which deliver 200 gal. of water per minute at a pressure of 150 psig to the boiler drum.

Further boiler-system-efficiency improvement is accomplished with a stack economizer (Photo C). This "coil" is constructed of non-corrosive materials and positioned in the boiler flue. Feedwater is circulated through the economizer, where its temperature is increased by 56 F, on its way to the boiler. This increase in makeup-water supply temperature results in an approximately 4.75-percent improvement in the efficiency of the steam-production process.

Flue Gas
Current air-pollution standards typically are not a concern with heating boilers in Northeast Ohio, which is considered a "non-attainment zone." U.S. Environmental Protection Agency (EPA) emission requirements for gas-fired boilers, which are permitted under Title V of the Clean Air Act, are met if the "best available technology" is utilized in burner control. The Cleveland Clinic, however, operates five boilers—two at 135,000 PPH, two at 70,000 PPH, and the new boiler at 100,000 PPH. The total production of 510,000 lb of steam per hour puts the Clinic in the category of large producer, which requires maintenance of an annual emissions limit, established as a certain number of tons of NOx discharged per year. It was determined that total plant emissions would remain below the EPA-dictated limit if the new boiler were operated with average NOx emissions of 30 ppm. Construction of the boiler in conjunction with the operation of the burner controls enabled the boiler/burner manufacturers to provide a guarantee that NOx emissions would not exceed 30 ppm.

A NOx-monitoring system provides a continuous record of emissions for annual verification of compliance with EPA requirements and confirmation of boiler operation within manufacturer-guaranteed limits. If the flue-gas NOx levelwere to exceed 30 ppm, the system would send an alarm to the continuously occupied operator station. This would let the operator know that permissible limits had been exceeded, giving him or her the opportunity to determine if it would be preferable to tweak the burner manually or to shut down the boiler until the reason for the excessive emission levels were known.

Boiler Installation
Construction of the boiler plant was complicated by the large physical size of the new boiler and associated equipment. Approximately the size of a railroad car and weighing 110,500 lb, the boiler had to be delivered by rail (Photo D). Prior to installation, it was stored on a rail siding approximately 3 miles from the construction site. Before the boiler could be installed, the surge tank (Photo E) and deaerating feedwater heater had to be put in place.

The surge tank and deaerating feedwater heater are located at the lowest level of the boiler plant, beneath the new boiler. They had to be dropped through the first floor onto their concrete pads, with the concrete floor then poured in place. Once offloaded from the railcar and placed on a flatbed trailer, the boiler had to be transported through downtown city streets. This required a full-time police escort and significant planning with regard to traffic lights and other suspended wiring, which had to be protected or moved out of the path of the boiler. Furthermore, normal downtown traffic had to be stopped and/or rerouted to avoid conflict. Upon arrival at the hospital campus, the boiler was lifted off of the trailer and over a pedestrian bridge and placed on a specially constructed structural steel platform, from which it was slid into the plant (Photo F).

Conclusion
The successful completion of the Cleveland Clinic's new steam-production facility was the result of significant commitment by, and coordination among, the members of the design, construction, manufacturing, expediting, and facilities teams. Through the hard work and dedication of many people working very long hours, the Cleveland Clinic was able to obtain the steam capacity necessary to supply the new heart hospital on time and within budget. Furthermore, the successful operation of the new steam-production system provides one small part of the reason for the Cleveland Clinic's continued status as one of the world's leading hospitals.

About the Authors
A longtime member of HPAC Engineering's Editorial Advisory Board, Dennis J. Wessel, PE, LEED AP, is senior vice president of, and director of marketing for, Cleveland-based Karpinski Engineering Inc. An American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Fellow and Distinguished Service Award recipient, he chairs the ASHRAE technical committee on large-building air-conditioning systems, is a member and former chair of the ASHRAE technical committee on tall buildings, and is a member of the ASHRAE Program Committee.

R. Wayne Thomas is a senior project engineer for Karpinski Engineering Inc. A member of ASHRAE and the American Society of Plumbing Engineers, he has 30 years of experience in commercial, institutional, and industrial design.

Frank A. Eisenhower, PE, LEED AP, is a mechanical associate for Karpinski Engineering Inc. A 1994 graduate of The Pennsylvania State University's architectural-engineering program, he has more than 12 years of HVAC experience, with emphasis on infrastructure projects within the health-care industry. In 2000, he received a master-of-business-administration degree from Case Western Reserve University.

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