The alkalinity and chloride levels in the 10-ton gas furnace remain high – what should be done?
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Our unit uses a 10-ton gas furnace; the water hardness after treatment is 0.01 mmol/L, the alkalinity is 6 mmol/L, and the chloride content is 1. Recent tests conducted on water taken from the boiler’s drain showed an alkalinity of 50 mmol/L and a chloride content of 20. The water I use for treatment is of high quality; then why is the water level in the boiler above the standard? May I ask where the problem lies? How should this be solved?
As the water in the pot becomes more concentrated, alkalinity and chloride levels naturally increase； If the water level in the pot exceeds the limit, it must be drained.
Quality standards for water used in industrial boilers Replaces GB1576—1996 I. Scope The standards for boiler water specify the requirements regarding the quality of water used during the operation of industrial boilers. The water quality standards for boilers apply to stationary steam boilers and combined steam-and-hot-water boilers that use water as the medium, with a rated outlet steam pressure of 2.5 MPa or less. They also apply to stationary pressurized hot-water boilers and atmospheric-pressure hot-water boilers that use water as the medium. II. Boiler Water Quality Standards 1. For feedwater in steam boilers and dual-purpose steam and water boilers, external chemical water treatment is generally required, and the water quality should meet the specifications in Table 1. Table 1: Parameters Feedwater Boiler Water >1.0 >1.6 >1.0 >1.6 Rated steam pressure, MPa ≤1.0 ≤1.0 ≤1.6 ≤2.5 Suspended solids, mg/L ≤5 ≤5 ≤5 Total hardness, mmol/L ≤0.03 ≤0.03 ≤0.03 Without superheater: 6–26, 6–24, 6–16 respectively Total alkalinity, mmol/L With superheater: ≤14, ≤12 pH (25°C): ≥7, ≥7, ≥7 respectively; 10–12, 10–12, 10–12 respectively Dissolved oxygen, mg/L: ≤0.1, ≤0.1, ≤0.05 1) The basic unit for hardness in mmol/L is c(1/2Ca2+, 1/2Mg2+); the same applies hereinafter. 2) The basic units for alkalinity in mmol/L are c(OH-), 1/2CO2-3, and HCO3-, the same applies hereafter. For boilers that have low requirements regarding steam quality and do not come equipped with superheaters, the upper limit for the alkalinity value can be appropriately increased, provided that the operating unit obtains approval from the local boiler and pressure vessel safety supervision authority. 3) Deoxidization is required when the rated evaporation capacity of the boiler is 6 t/h or more. For boilers with a rated evaporation capacity of less than 6 t/h, deoxidization measures should be applied to the feedwater in case of local corrosion; the oxygen content in the feedwater for boilers supplying steam to turbines should be less than or equal to 0.05 mg/L. 4) If it is difficult to determine the dissolved solids, conductivity or chloride (Cl-) levels can be used as indirect indicators; however, the ratio between dissolved solids and conductivity, or between dissolved solids and chloride (Cl-), must be determined through experimentation. This ratio should also be rechecked and adjusted regularly. 5) The relative alkalinity of fully welded structure boilers can be left uncontrolled. 6) Only for fuel and gas boilers. 2. Steam boilers and combined steam and water boilers with a rated evaporation capacity of 2 t/h or less, and a rated steam pressure of 1.0 MPa or less (provided that there are no special requirements regarding the quality of steam and water) can also employ internal chemical treatment. However, strict supervision must be exercised over scaling, corrosion, and water quality in the boiler; proper dosing, sludge removal, and cleaning procedures must be carried out, and the water quality must meet the requirements specified in Table 2. Table 2: Parameters for feed water in boilers
Suspensions, mg/L: ≤20
Total hardness, mmol/l: ≤4
Total alkalinity, mmol/l: 8–26
pH (at 25°C): ≥7, 10–12
Dissolved solids, mg/L: <5000
3. For pressure hot water boilers, external water treatment is required. For non-mounted pressure hot water boilers with a rated power of 4.2 MW or less, as well as atmospheric pressure hot water boilers, internal chemical treatment can be used; however, close monitoring of scaling, corrosion, and water quality is necessary, and proper chemical treatment must be carried out. The water quality must meet the requirements specified in Table 3. Table 3: Treatment methods – Chemical treatment inside the boiler vs. chemical treatment outside the boiler. For feed water and boiler water: Suspended solids, mg/L: ≤20, ≤5; Total hardness, mmol/L: ≤6, ≤0.6; pH (at 25°C): ≥7, 10–12, ≥7. Dissolved oxygen, mg/L: ≤0.1. Oil content, mg/L: ≤2, ≤2. 1) The pH value of the boiler water is maintained between 10 and 12 by adding chemicals. 2) The feed water for pressure hot water boilers with a rated power of 4.2 MW or more should be deoxygenated; for pressure hot water boilers with a rated power of less than 4.2 MW and for atmospheric pressure hot water boilers, the feed water should be deoxygenated as much as possible. 4. For DC (through-flow) boiler feed water, external chemical treatment should be employed, and the water quality shall comply with the standards specified in Table 1 for a rated steam pressure of greater than 1.6 Mpa and less than or equal to 2.5 Mpa. 5. The water quality parameters for waste heat boilers and electric heating boilers shall meet the requirements of boilers of the same type and with the same parameters. 6. The water quality testing methods shall be carried out in accordance with Appendix A (the appendix to the standards).
Suspensions, mg/L: ≤20
Total hardness, mmol/l: ≤4
Total alkalinity, mmol/l: 8–26
pH (at 25°C): ≥7, 10–12
Dissolved solids, mg/L: <5000
3. For pressure hot water boilers, external water treatment is required. For non-mounted pressure hot water boilers with a rated power of 4.2 MW or less, as well as atmospheric pressure hot water boilers, internal chemical treatment can be used; however, close monitoring of scaling, corrosion, and water quality is necessary, and proper chemical treatment must be carried out. The water quality must meet the requirements specified in Table 3. Table 3: Treatment methods – Chemical treatment inside the boiler vs. chemical treatment outside the boiler. For feed water and boiler water: Suspended solids, mg/L: ≤20, ≤5; Total hardness, mmol/L: ≤6, ≤0.6; pH (at 25°C): ≥7, 10–12, ≥7. Dissolved oxygen, mg/L: ≤0.1. Oil content, mg/L: ≤2, ≤2. 1) The pH value of the boiler water is maintained between 10 and 12 by adding chemicals. 2) The feed water for pressure hot water boilers with a rated power of 4.2 MW or more should be deoxygenated; for pressure hot water boilers with a rated power of less than 4.2 MW and for atmospheric pressure hot water boilers, the feed water should be deoxygenated as much as possible. 4. For DC (through-flow) boiler feed water, external chemical treatment should be employed, and the water quality shall comply with the standards specified in Table 1 for a rated steam pressure of greater than 1.6 Mpa and less than or equal to 2.5 Mpa. 5. The water quality parameters for waste heat boilers and electric heating boilers shall meet the requirements of boilers of the same type and with the same parameters. 6. The water quality testing methods shall be carried out in accordance with Appendix A (the appendix to the standards).
Alkalinity and chloride content in boiler water are two important parameters in the water quality standards for industrial boilers. An alkalinity of 50 mmol/L is a bit intimidating. 1. Compare the records from the period when the changes occurred. 2. Analyze the alkalinity and chloride levels of the condensate to determine whether there has been a material leak. 3. Replace the boiler water as soon as possible; high levels of alkalinity and chloride can cause severe corrosion in the boiler.