Facilities Quality Service
BOILER PLANT MAKE-UP WATER ALKALINITY CONTROL
ISSUE
High quality make-up water is necessary in boiler plants to replace water lost in the
steam generation and distribution process. Reverse osmosis systems should be
considered when it is necessary to reduce make-up water alkalinity.
BACKGROUND
A relatively small number of VA boiler plants have a make-up water supply, which has
excessive alkalinity. Excessive alkalinity adversely affects boiler performance and may
result in damage to the boilers. The decision on whether a reduction in make-up water
alkalinity is necessary should be based on the recommendations of a water treatment
consultant. Generally, dealkalizing equipment is recommended when make-up water
alkalinity exceeds 50 parts per million (ppm). In most cases, chloride ion-exchange
dealkalizers have been applied. Reverse osmosis should be considered as an
alternative to ion-exchange.
DISCUSSION
Compared to chloride ion-exchange systems, reverse osmosis systems have the
benefit of reducing the total dissolved solids content of the make-up water, which
reduces the amount of boiler blowdown energy loss. Also, the amount of boiler water
treatment chemicals is reduced. These cost savings are somewhat offset by the
electric power costs of the reverse osmosis pumps and the cost of periodic
replacement of reverse osmosis membranes. Another option is acid ion-exchange
systems but these have been avoided because of the hazards associated with the
handling of the acid. Acid systems reduce the solids content of the make-up water.
Because of the limited application, VA has no Master Specification on reverse osmosis
systems.
RECOMMENDATIONS/CONCLUSIONS:
If the boiler plant make-up water alkalinity is too high, it is recommended that reverse
osmosis and chloride ion-exchange systems be compared and evaluated. A life cycle
cost analysis should be performed before a decision is made on which type of
dealkalizing system to choose.
FOR ADDITIONAL INFORMATION
Contact Jim Shoemaker (183) at 202-565-5176.
12 April 2000
FM-181A-DA104
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