Steam boilers are commonly used in large heating systems, institutional kitchens, or in facilities where large amounts of process steam are used. This equipment consumes varying amounts of water depending on system size and the amount of condensate returned.
Operations and Maintenance Options
To maintain water efficiency in operations and maintenance, federal agencies should do the following.
Develop and implement a routine inspection and maintenance program to check steam traps and steam lines for leaks. Repair leaks and replace faulty steam traps as soon as possible.
Develop and implement a boiler tuning program to be completed a minimum of once per operating year.
Provide proper insulation on steam and condensate return piping, as well as, on the central storage tank.
Blowdown is the periodic or continuous removal of water from a boiler to remove accumulated dissolved solids and/or sludge. Proper control of blowdown is critical to boiler operation. Insufficient blowdown may lead to deposits or carryover. Excessive blowdown wastes water, energy, and chemicals.
Obtain the services of a water treatment specialist to prevent system scale and corrosion and to optimize cycles of concentration. Treatment programs should include routine checks of boiler water chemistry.
Develop and implement routine inspections and maintenance programs on condensate pumps.
Regularly inspect both the water side and fire side of the boiler. If needed, clean the tube surfaces to ensure optimal heat transfer thereby maximizing system energy efficiency.
Employ an expansion flash tank to temper boiler blowdown rather than using cold water mixing.
Install meters on boiler system make-up lines.
Install meters on make-up lines to recirculating closed water loop heating systems so that leaks can be accounted for.
Consider summer shutdown, especially for those systems primarily used for space comfort heating.
The following retrofit options help federal agencies maintain water efficiency across facilities:
Install and maintain a condensate return system. Water use, chemical use, and operating costs can be significantly reduced by capturing and reusing steam system condensate. A condensate return system also lowers energy costs as the condensate water is already hot and needs less heating to produce steam than water from other make-up sources.
Install an automatic blowdown system based on boiler water quality to better manage the treatment of boiler make-up water.
Add an automatic chemical feed system controlled by make-up water flow or real-time monitoring of boiler chemical residuals.
To optimize cycles of concentration and reduce the frequency of blowdown, an inert ion like silica or chloride can be measured in the boiler and the concentration compared to the amount in the boiler feedwater. For example, a boiler with a silica concentration of 100 parts per million (ppm) and a feedwater silica concentration of 10 ppm is considered to be carrying 10 cycles of concentration. Monitoring the ion continuously can allow better control and adjustment of the chemical feed rate to optimize the number of blowdown cycles.
Blowdown heat exchangers are a useful technology to consider because they allow some of the heat contained in the boiler blowdown to be transferred to the boiler feed water. This also allows for the production of low pressure steam, which can be returned to the steam system or used in the de-aeration of boiler feed water.
The following replacement options help federal agencies maintain water efficiency across facilities.
Replacement options vary depending on the size of the facility and existing equipment. Consider performing an energy audit to reduce heating loads and ensure that the system is sized appropriately. Reducing the size of the boiler system can reduce water requirements.
Always purchase the most life cycle cost-effective boiler available for new installations or major renovations
Consider installing a small summer boiler, distributed system, or heat-capture system for reheat or dehumidification requirements instead of running a large boiler at part load. Also consider alternative technologies such as heat pumps
Consult with experts in the field. Your first resource should be local or headquarters engineers, but do not overlook input from experienced contractors or other government agencies.
For more information, read the U.S. Environmental Protection Agency's WaterSense at Work BMP on boiler and steam systems and the Council of Industrial Boiler Owners Energy Efficiency Handbook.