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Organic
Water Treatment Chemicals
Steam Boilers, Cooling Towers,
Hot And Chilled Closed Systems
Fuel Oil Treatment
(Home of D.M Concentrate)
Boiler Water Carryover and its Causes
Carryover is the term applied to the presence of contaminants in steam leaving a boiler.
These contaminants can be in the form of a solid, liquid or vapor. Carryover can create
problems in plant equipment such as turbines or may represent a potential violation where
steam purity is a requirement, such as in food plants. Below we have listed the most
common causes of carryover broken into two categories – chemical and mechanical.
Chemical Causes of Carryover
Excessive dissolved and suspended solids in the boiler water. Additionally, high alkalinity
levels or the presence of a surfactant can lead to foaming which results in carryover.
The immediate solution for this type of carryover is additional
blowdown. Additionally, any
contamination should be located and the application of a boiler antifoam considered.
Selective vaporous carryover. In boilers operating above 400 psig, silica can be present in
the steam as a result of vaporization. This condition is usually only a problem when turbines
are present and can be prevented by restricting silica concentrations to the maximum allowable
limit for the operating pressure.
ASME
Guidelines
Feedwater
- ASME Consensus on Operating
Practices
| Drum
Operating Pressure
(psig) |
| Feedwater |
0-300 |
301-450 |
451-600 |
601-750 |
751-900 |
901-1000 |
1001-1500 |
1501-2000 |
| Diss.
Oxygen
| <40ppb |
<40ppb |
<7ppb |
<7ppb |
<7ppb |
<7ppb |
<7ppb |
<7ppb |
| Total
Iron |
<100ppb |
<50ppb |
<30ppb |
<25ppb |
<20ppb |
<20ppb |
<10ppb |
<10ppb |
| Total
Copper |
<50ppb |
<25ppb |
<20ppb |
<20ppb |
<15ppb |
<15ppb |
<10ppb |
<10ppb |
| Hardness |
<300ppb |
<300ppb |
<200ppb |
<200ppb |
<100ppb |
<50ppb |
-
Not Detectable- |
| pH |
7.5-10.0 |
7.5-10.0 |
7.5-10.0 |
7.5-10.0 |
7.5-10.0 |
8.5-9.5 |
9.0-9.6 |
9.0-9.6 |
Note:
These feedwater guidelines are
based on achieving steam purity
required for superheaters,
turbines, or process
restrictions. Many plants
operate outside of these
criteria. For specific
recommendations ask
our water treatment experts
online.
Boiler
Water - ASME Consensus on
Operating Practices
| Drum
Operating Pressure
(psig) |
| Boiler
Water |
0-300 |
301-450 |
451-600 |
601-750 |
751-900 |
901-1000 |
1001-1500 |
1501-2000 |
| Silica |
<150ppm |
<90ppm |
<40ppm |
<30ppm |
<20ppm |
<8ppm |
<2ppm |
<1ppm |
| Total
Alkalinity |
<350ppm |
<300ppm |
<250ppm |
<200ppm |
<150ppm |
<100ppm |
--Not
Specified-- |
| Conductivity |
<3500 |
<3000 |
<2500 |
<2000 |
<1500 |
<1000 |
<150 |
<100 |
| Free
Hydroxide |
-----------------Not
Specified----------------- |
---Not
Detectable--- |
Note:
These Boiler water guidelines
are based on achieving steam
purity required for superheaters,
turbines, or process
restrictions. Many plants
operate outside of these
criteria.
Mechanical Causes of Carryover
In today’s steam systems the most common factor in carryover is load changes. These usually
involve very sudden and excessive increases in steam demand. In such cases, the drop in pressure
in the steam header is of such magnitude that boiler water is "pulled" through the steam purifying
equipment.
Water level can also have an impact on carryover and steam purity. The higher the level of water
in the steam drum, the less disengaging space, and the greater the chance that water level will be
a mechanical factor in increased carryover.
Carryover can also occur due to damaged or defective steam separation equipment.
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Boiler
Carryover 
