(1) Values of steam purity are not given as achievement depends on many
variables, including boiler water total alkalinity and specific
conductance as well as design of boiler, steam drum internals, and
(2) Watertube boilers with relatively large furnaces and firetube boilers
of conservative design with internal chelant, polymer and/or antifoam
treatment can often tolerate higher levels of feedwater impurities
than those in table and still achieve adequate deposition control and
steam purity. Removal of these impurities by external pretreatment is
always a more positive solution. Alternatives must be evaluated as to
practicality and economics used in each individual case.
(3) Values in table assume existence of a deaerator.
(4) Chemical deaeration must be provided in all cases, but especially if
mechanical deaeration is nonexistent or inefficient.
(5) Nonvolatile TOC is that organic carbon not intentionally added as part
of the water treatment regime.
(6) Maximum total alkalinity consistent with acceptable steam purity for
superheaters, turbine drives, and pier side ships. Use of
demineralized water is required.
(7) Alkalinity and total dissolved solid values consistent with steam
purity target. Practical limits above or below tabulated value can be
established for each case by careful steam purity measurements.
Relationship between conductance and steam purity is affected by too
many variables to allow its reduction to a simple list of tabulated
Betz Handbook of Industrial Water Conditioning, 1980.
Boiler Water Makeup. Ion exchange equipment shall be sized to
assure adequate feedwater to the boilers at maximum steam load with no
condensate return, when one unit is being regenerated. If low flows are
expected which could cause channeling through the unit, multiple units of
reduced capacity shall be used. The total capacity of the ion exchange
equipment with one unit being backwashed is from 125 percent of the maximum
steam plant load to 120 percent of the total boiler capacity; this includes 20
percent allowance for blowdown and other plant treated water usage.
Selection of Treatment Process
Methods Available. The choice of treatment depends on many
factors. Selection may be made from the following processes with the choice
usually being a combination of these methods: