| Drum Operating Pressureb, MPa (psig) | ||||||||
|
0-2.07 (0-300) |
2.08-3.10 (301-450) |
3.11-4.14 (451-600) |
4.15-5.17 (601-750) |
5.18-6.21 (751-900) |
6.22-6.89 (901-1000) |
6.90-10.34 (1001-1500) |
10.35-10.79 (1501-2000) |
|
| FEEDWATERh | ||||||||
| Dissolved oxygen (mg/L O2) measured before oxygen scavenger additionj | <0.040 | <0.040 | <0.007 | <0.007 | <0.007 | <0.007 | <0.007 | <0.007 |
| Total iron (mg/L Fe) | 0.100 | 0.050 | 0.030 | 0.025 | 0.020 | 0.020 | 0.010 | 0.010 |
| Total Copper (mg/L Cu) | 0.050 | 0.025 | 0.020 | 0.020 | 0.015 | 0.015 | 0.010 | 0.010 |
| Total Hardness (mg/L CaCO3) | 0.300 | 0.300 | 0.200 | 0.200 | 0.100 | 0.100 | --not detectable-- | |
| pH range at 25° C | 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 |
| Chemicals for preboiler system protection | use only volatile alkaline materials | |||||||
| Nonvolatile TOC (mg/L C)gg |
<1 | <1 | <0.5 | <0.5 | <0.5 | --as low as possible, <0.2-- | ||
| Oily Matter (mg/L) | <1 | <1 | <0.5 | <0.5 | <0.5 | --as low as possible, <0.2-- | ||
| BOILER WATER | ||||||||
| Silica (mg/L SiO2) | £150 | £90 | £40 | £30 | £20 | £8 | £2 | £1 |
| Total alkalinity (mg/L CaCO3) | <350d | <300d | <250d | <200d | <150d | <100d |
--not detectablee-- |
|
| Free Hydroxide alkalinity (mg/L CaCO3)c | --not specified-- |
--not detectablee-- |
||||||
| Specific conductance (µS/cm) (µmho/cm at 25° C without neutralization | <3500f | <3000f | <2500f | <2000f | <1500f | <1000f | £150 | £100 |
a Source: ASME Research Committee on Steam and Water in Thermal Power Systems. Boiler type: industrial water tube, high duty, primary fuel fired, drum type; makeup water percentage: up to 100% of feewater; conditions: includes superheater, turbine drives, or process restriction on steam purity; saturated steam purity target.
b With local heat fluxes >473.2 kW/m2 (>150,000 Btu/hr/ft2), use values for next higher pressure range.
c Minimum level of OH alkalinity in boilers below 6.21MPa (900 psig) must be specified individually with regard to silica solubility and other components of internal treatment.
d Maximum total alkalinity consistent with acceptable steam purity. If necessary override conductance as blowdown control parameter. If makeup is demineralized water at 4.14 MPa (600 psig) to 6.89 MPa (1000 psig), boiler water alkalinity should be that in table for 6.90-10.34 MPa (1001-1500 psig) range.
e Refers to free sodium or potassium hydroxide alkalinity. Some small variable amount of total alkalinity will be present and measurable with the assumed congruent or coordinated phosphate-pH control or volatile treatment employed at these high pressure ranges.
f Maximum values are often not achievable without exceeding suggested maximum alkalinity values, especially in boilers below 6.21 MPa (900 psig) with greater than 20% makeup of water whose total alkalinity is >20% of TDS naturally or after pretreatment by lime-soda or sodium cycle ion exchange softening. Actual permissible conductance values to achieve any desired steam purity must be established for each case by careful steam purity measurement. Relationship between conductance and steam purity is affected by too many variables to allow its reduction to a simple list of tabulated values.
g Nonvolatile TOC is that organic carbon not intentionally added as part of the water treatment regime.
h Boilers below 6.21 MPa (900 psig) with large furnaces, large steam release space, and internal chelant, polymer and/or antifoam treatment can sometimes tolerate higher levels of feedwater impurities than those in the 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 economincs in each individual case.
i Values in table assume existence of a deaerator.
j No value given because steam purity achievable depends on many variables, including boiler water total alkalinity and specific conductance as well as design of boiler, steam drum internals, and operating conditions (see footnote f). Because boilers in this category require a relatively high degree of steam purity, other operating parameters must be set as low as necessary to achieve this high purity for protection of the superheaters and turbines and/or to prevent process contamination.