Boiler feed water costs are associated with the following parameters
■ pH
■ Hardness
■ Oxygen and carbon dioxide concentration
■ Silicates
■ Dissolved solids
■ Suspended solids
■ Concentration organics
Usual treatments include:
Water softening for hardness. Ca and Mg are exchanged for sodium ions on an ion exchange resin. Hardness in water causes scale. Scale is usually Calcium and/o
r Magnesium carbonate that precipitates out as the ions are concentrated in the boiler. Chemicals can be added to control scale but they can be reduced to a very small quantity if a softener is used. Pervaporation, a membrane process or deaerator can be used to remove Oxygen and CO2 down to very low levels for high pressure boilers. Only small amounts of chemical oxygen scavengers are required after oxygen removal. Silicates cause another type of scaling and can be removed with ion exchange or a membrane process. Membrane systems are preferred where dissolved ion concentrations are high because of operating cost considerations. High silicate levels are difficult and may require co-precipitation with other ions or high temperature caustic regeneration of ion exchange system. Dissolved solids can be removed by ion exchange or Reverse Osmosis membrane processes. The results are similar with ion exchange able to remove practically all the ions and RO able to get very close with lower operating and maintenance costs. With high TDS concentrating, a combination of the two can be very cost effective. The advantage of removing dissolved solids is that you can greatly increase the time between blow downs as the makeup water is almost void of solids. It takes much longer to get to the concentration when the boiler should be blown. Suspended solids are removed by filtration. Normally, you would want a backwashing filter followed by a fine cartridge filter for the best results. The backwashing filter can take high solids loading before flows are reduced and is self cleaning. The polishing filter makes sure any residual material does not get through. Concentration of organics are less of a problem in a properly designed feedwater system because much less chemistry is required to maintain the boiler. It is much easier to balance the system, and in some systems, no oxygen scavenger is required. Remember, a good water analysis is you best friend. We will ask you for a water analysis. Print out the attached form if you don't know what you need to measure.
