Efforts should be made to maintain boiler systems at peak efficiency to reduce operating costs and environmental impacts. When replacing old equipment or installing new equipment, it is important to consider installing “staged” multiple-boiler systems. One large boiler frequently operating at less than its peak load will be inefficient, while in a staged boiler system, multiple smaller boilers replace the large boiler. This gives the hotel the option of running only some of its boilers at a time, thus reducing the amount of time a given boiler is running at less than peak load. Solar-assisted systems and biomass-fired boilers can serve as alternatives to conventional boiler systems.
Boiler Loading and Efficiency
The maximum efficiency of a boiler does not occur at full load, but at about two-thirds of the full load. If the load on the boiler decreases further, efficiency also tends to decrease.
Steam traps are essential for proper distribution-system performance. During system operation, the traps allow collected condensate to pass into the condensate return system, while minimizing the accompanying loss of steam.
Financial Benefits of Condensate Recovery
Financial reasons - Condensate is a valuable resource, and the recovery of even small quantities is often economically justifiable. The thermal energy in recaptured condensate offsets additional energy purchases. Steam systems with greater operational load factors provide the best opportunities for economical condensate recovery.
Water charges - Any condensate not returned needs to be replaced by fresh water, incurring further water charges from the local water supplier.
Maximizing boiler output - Colder boiler feed water will reduce the steaming rate of the boiler. The lower the feed water temperature, the more heat required, and thus fuel is needed to heat the water. Therefore, it is useful to preheat feed water with waste heat.
Boiler feed water quality - Returning more condensate to the feed tank reduces the need for blowdown and thus reduces the energy lost from the boiler.
A major source of steam and water loss in steam plants is leaking stream traps, although steam loss should be minimized throughout the distribution system. Steam leakage is a visible indicator of waste and must be avoided. It has been estimated that a 3 mm diameter hole on a pipeline carrying 7 kg/cm2 steam would waste 33 KL of fuel oil per year. Steam leaks on high-pressure mains are considerably costlier than on low-pressure mains.
Alliance to Save Energy. Steaming Ahead. www.steamingahead.org
Brecher, Mark L., "Low-Pressure System Gets High Marks from College," Heating/Piping/Air Conditioning, September 1994.
DOE Energy Efficiency and Renewable Energy. Industrial Technologies Program.
Oland, C. B. Review of Orifice Plate Steam Traps. Oak Ridge National Laboratory. January 2001.
Payne, William, Efficient Boiler Operations Sourcebook, 3rd Edition, Fairmont Press, Lilburn, GA, 1991.
U.S. DOE Energy Efficiency and Renewable Energy. Energy Efficiency — Buildings. www.eere.energy.gov