Some standard content:
GB1576—2001
Based on the experience gained since the implementation of GB1576-1996 "Low-pressure Boiler Water Quality" and its inadaptability in the changing environment, this standard has been mainly modified as follows:
1) The name of the standard has been changed from "Low-pressure Boiler Water Quality" to "Industrial Boiler Water Quality". 2) The scope of application of the standard has been expanded to include normal-pressure hot water boilers, and additional water quality indicators for direct-current boilers, normal-pressure hot water boilers and electric boilers have been specified.
3) Table 1, footnote 2), allows for the upper limit of the boiler water alkalinity index of steam boilers and dual-purpose steam-water boilers that use external chemical water treatment to be appropriately relaxed under certain conditions.
4) Table 1, footnote 4), adds that the method of measuring conductivity can be used to indirectly control the dissolved solids in boiler water. 5) Table 1, footnote 5), stipulates that the relative alkalinity of fully welded boilers may not be controlled. 6) Table 1, footnote 6), adds the iron content index for the feed water of oil-fired and gas-fired boilers that use external water treatment methods. 7) The rated power of hot water boilers using the in-boiler dosing treatment method is relaxed from 2.8MW to 4.2MW, and the total hardness index of feed water is relaxed from 4 mmpl/l to 6 mmol/L.
8) Appendix A "Water quality inspection method" adds the determination method of iron content and corrects some errors in the original appendix. Appendix A of this standard is the appendix of the standard.
This standard replaces GB1576-1996 from the date of implementation. This standard is proposed and managed by the Boiler and Pressure Vessel Safety Supervision Bureau of the State Administration of Quality Supervision, Inspection and Quarantine. This standard is drafted by the China Boiler Water Treatment Association. The main drafters of this standard are Zhang Ban and Shen Yuanling. 163
1 Scope
National Standard of the People's Republic of China
Water quality for industrial boilers
Water quality for industrial boilers This standard specifies the water quality requirements for industrial boilers during operation. GH 1576-2001
Replaces GB1576-1996
This standard applies to steam pressure vessels under 2.5 MPa, fixed steam boilers and dual-purpose steam-water boilers with water as the medium, also applicable to fixed pressure hot water boilers and normal pressure hot water boilers with water as the medium, 2 Water quality standards
The feed water of steam boilers and dual-purpose steam-water boilers should generally be treated with external chemical water. The water quality should comply with the provisions of Table 2.1
Rated steam pressure.MPa
Floating matter,mg/L
Total hardness,mmol/l.1)
Total alkalinity,mmol/l.3
pH (25'C)
Dissolved oxygen +mg/L* ||t t||Dissolved solids, tng/L
Free VaOH
Relative alkalinity (
Dissolved solids
Oil content, mg/L
Deficiency mg/L
No superheater
With superheater
No superheater
With superheater
Approved by the State Quality and Technical Supervision Bureau on January 10, 2001 164
10~-12
1{--12
10--30
10-~30
10 -12
2001-10-01 implementation
GB 1576—2001
Table 1 (end)
1) The basic unit of hardness mmol/L is c(1/2Ca2+,1/2Mg*+), the same below.
2) The basic unit of water content mmol/L is c(OHI-,1/2CO-,HCO3, the same below.
For boilers without superheater and with no requirement for steam quality, the user unit may appropriately relax the upper limit of alkalinity index after reporting to the local boiler pressure vessel safety supervision agency for approval.
3) When the boiler is rated evaporation is greater than or equal to 6 t/h, oxygen should be removed. When the rated evaporation is less than 6 t/h, the boiler should be deoxidized. If local corrosion is found in the weak furnace, the feed water should be dehydrogenated. For the boiler feed water supplying steam to the steam turbine, the oxygen content should be less than or equal to 0.05m/L. 4) If it is difficult to determine the dissolved solids, the method of determining the conductivity or chloride ion (C1-) can be used for indirect control. However, the ratio of dissolved solids to medium conductivity or chloride ion (C1-) should be determined based on field tests, and this ratio should be retested and revised regularly: 5) The relative temperature of the fully welded structure boiler can be uncontrolled. 6) Only oil-fired and gas-fired steam boilers with a rated evaporation capacity of less than or equal to 2 1/h and a rated steam pressure of less than or equal to 1. 0 MPa and steam-water dual-purpose boilers (if there is no special requirement for steam and water quality) can also be treated by adding chemicals in the boiler. It is necessary to strengthen supervision of boiler scaling, corrosion and water quality, and do a good job of adding chemicals, draining and cleaning. The water quality should meet the requirements of Table 2. Table 2
Total floating matter·mg/L
Total hardness, ntal/L
Total alkalinity.mml/
PH(25:)
Dissolved solids, mg/I,
2.3 The feed water of pressure hot water boiler shall be treated outside the boiler. For non-tube rack pressure hot water boilers and Changle hot water boilers with rated power less than or equal to 4.2MW, boiler flashover treatment can be adopted. The boiler scaling, corrosion and water quality must be strictly supervised and the dosing work must be done carefully. The water quality composition shall comply with the requirements of Table 3.
Sensitive floating matter.mg/l
Total hardness,mmkl/L
PH(25C:))
Dissolved oxygen.mg/1
Oil content,mg/l.
In-boiler chemical treatment
1) Control the pH of boiler water at 10~12 by adding a reducing agent. Boiler water
10~-12
Out-of-boiler chemical treatment
10--12
2) The feed water of pressure hot water boilers with a rated power of more than 4.2 MW should be deoxygenated, and the feed water of pressure hot water boilers and atmospheric hot water boilers with a rated power of less than 4.2 MW should be deoxygenated as much as possible
2.4 Direct current (high-flow) boiler feed water should be treated with out-of-boiler chemical water. The water quality is based on the rated steam pressure in Table 1, which is greater than 1.6MPa and less than or equal to 2. 5 MPa standard implementation
2.5 The water quality indicators of waste heat boilers and electric boilers shall meet the requirements of boilers of the same type and parameters. 2.6 The water quality inspection method shall be implemented in accordance with Appendix A (Appendix to the standard) 165
A1 General Principles and General Provisions
GB 1576-2001
Appendix A
(Appendix to the standard)
Water Quality Inspection Method
A1.1 This method is used for water quality analysis in industrial boilers and boiler rooms. Each unit can select it according to the specific requirements of this method and chemical analysis and in combination with specific conditions.
A1.2 Requirements for the use of reagents: Unless otherwise specified in this method, analytically pure (AR) or chemically pure (CP) reagents are used. When the reagent (grade) does not meet the requirements, the reagent can be purified or a higher grade reagent can be used. A1.3 The amount of reagent added: In this method, the amount of reagent added is expressed in drops, and it should be calculated based on 20 drops equal to 1 ml. A1.4 Preparation of reagents: The solvents used to prepare the reagents in this method are all aqueous solutions unless otherwise specified. A1.5 Standardization of standard solutions: The standardization of standard solutions should generally be done in parallel in two or more portions. When the relative error of the two portions is within ± (0.2%~0.4%), the average can be taken to calculate its concentration. A1.6 There are several ways to express solution concentration: A1.6.1 Mass percentage concentration and volume percentage concentration: A1.6.1. 1 Mass percentage concentration (%): refers to the number of grams of solute contained in 100 mL of solution. A1.6.1.2 Volume percentage concentration (%): refers to the number of grams of solute contained in 100 mL of solution. This concentration expression method is usually suitable for the preparation of solutions when the solute is solid.
A1.6.2 Volume ratio: Volume ratio refers to the solution of solute X and solvent Y in a volume ratio (e.g., 1:3 mercaptosol, which refers to a sulfuric acid solution made by mixing 1 volume of concentrated sulfuric acid with 3 volumes of water). This method of expressing concentration is usually applicable to the preparation of liquid solutes.
A1.6.3 Molar concentration (cn): refers to the amount of substance ne of substance B divided by the volume V of the mixture. Note: The International System of Units (SI) specifies the unit of amount of substance as millimole (mnl), which is defined as: mole is the amount of substance in a system, the number of basic units contained in the system is equal to the number of atoms in 0.012 kg of carbon-12; when using millimole, the basic unit should be specified, which can be atoms, molecules, ions, electrons and other particles, or a specific combination of these particles. A1.6.4 Titer (T): refers to the mg mass of the component to be tested contained in 1 mL of solution or the mg mass of the solute in the solution.
A1.6.5 Mass concentration (pm): indicates the mass of the solute contained in a unit volume of liquid. The unit is mg/L or \g/L. A1.7 Calibration of instruments: In order to ensure the accuracy of the analysis results, analytical balances, balances and other precision instruments should be calibrated regularly in accordance with relevant national regulations. Analytical instruments such as spectrophotometers should be calibrated according to the instructions, and burettes, pipettes, volumetric flasks, etc. can be calibrated according to the requirements of the test.
A1.8 Blank test: There are two types of blank tests: A1.8.1 In general determination, in order to improve the accuracy of the analysis results, empty water is used instead of water samples, and the determination is carried out using the method and steps for determining water samples. The measured value is called the blank value, and then the water sample determination results are calibrated for blank values. A1.8.2 In the micro-component colorimetric analysis, in order to correct the content of the component to be measured in the blank water, it is necessary to conduct blank tests with single and double reagents. The blank test of single reagent is the same as the general blank test. The blank test of double reagent means that the amount of reagent added is twice the amount of reagent used to measure the water sample. The determination method and steps are the same as those for measuring the water sample. According to the results of the single and double reagent blank tests, the content of the component to be measured in the blank water is calculated, and the blank value correction is performed on the water sample measurement results. A1.9 Requirements for blank water: "blank water" in this method refers to water used to prepare reagents and for blank tests, such as distilled water, demineralized water, commercially pure water, etc. The quality requirements for blank water are as follows: The conductivity of distilled water is less than 0.30005~0.0002S/m25）166
GB1576-2001
The conductivity of salt water is less than 0.000 01~~0. 000 1 5/I(25 The content of Cu, Fe, and Na in high-purity water is less than 0. 002 mg/L; the content of SiO is less than 0. 003 g/l. A1.10 Evaporation and concentration: When the concentration of the solution is low, a quantitative solution can be evaporated on a low-temperature electric furnace or a hot plate first, concentrated to a small volume, and then moved to a water bath for evaporation. During the evaporation process, care should be taken to prevent explosions and splashing. 41.11 Desiccant: Calcium chloride or color-changing silica gel is generally used as a desiccant in a desiccant. When the surface of the calcium chloride desiccant is damp or the color of the color-changing silica gel turns red, it indicates that the desiccant has failed and should be replaced. A1. 12 Constant weight: The constant weight specified in the standard means that under the same burning (drying) and cooling conditions, the difference between two consecutive weighings is not more than 0.4 mg. This is not limited to other provisions in the method. A1. 13 Units for expressing measurement results: The units for expressing measurement results should be based on the provisions of legal measurement units. A1.14 Significant figures Significant figures in analytical work refer to the numbers that can be accurately measured by the analytical method. Therefore, the analytical results should be correctly expressed using significant figures.
A1.15 The main analytical items, representative symbols and units used in this method are summarized in Table A1. Table A1 Water quality analysis items, representative symbols, units Item
Suspended solids
Dissolved solids
Conductivity
Oxides
Sulfites
Phosphates
Dissolved oxygen
Chemical oxygen demand
1) YD mmol/L(1/2Ca2-,1/2Mg+).
2) I ruol/L(HCO-,1/2CO-OH-:
A2 Collection of water samples
A2.1 Sampling device
Chinese unit
milligram/L
milligram/L
cm
milligram/L
millimol/L1
mg/L
mg/L
millimol/L2
mg/L
mg/L
mg/L
mg/L
mg/L
Unit symbol
mmal/L
A2. 1. 1. The installation of the sampler and the arrangement of the sampling points shall be designed, manufactured, installed and arranged according to the type, parameters and water quality supervision requirements (or test requirements) of the boiler to ensure that the collected water samples are fully representative. A2. 1.2 The sampling tubes for deoxygenated water and feed water shall be made of stainless steel pipes as much as possible. A2.1.3 The sampling devices for deoxygenated water, feed water, boiler water and sulfur water must be equipped with coolers. The sampling coolers shall have sufficient cooling area and be connected to a water source that can continuously supply sufficient cooling water to ensure that the water sample flow rate is 500-700ml./min and the water sample temperature is between 30-40℃.
GB 15762001
42.1.4 The sampling cooler shall be regularly inspected and scale removed. When the boiler is repaired, the sampler and its valves shall be inspected and repaired. A2.1.5 The sampling channel shall be flushed regularly (at least once a week). Before sampling for system verification, the relevant sampling pipelines should be flushed, and the flushing time should be appropriately extended. After flushing, sampling should be carried out after 1 to 2 hours to ensure that the water sample is fully representative. A2.1.6 For the determination of dissolved oxygen in deoxygenated water and turbine condensate, the packing and pipeline of the sampling valve should be tight and air should not condense. A2.2 Water sampling method
A2.2. 1 When collecting water samples with a sampling cooler, the cooling water sample valve should be adjusted to make the water sample flow rate within the range of 500~700 mL/min, the temperature within the range of 30~40℃, and the flow rate stable. 42.2.2 When collecting water samples for feed water and boiler water, in principle, it should be continuously flowing water. When collecting other water samples, the accumulated water in the pipeline should be drained and flushed before sampling.
A2.2.3 The container (sampling bottle) for water samples must be made of hard glass or plastic (plastic containers must be used for samples for the determination of trace components). Before sampling, the sampling container should be thoroughly cleaned. When sampling, rinse it with water three times (unless otherwise specified in the method) before collecting the water sample. After sampling, it should be quickly covered and sealed. A2.2.4 When collecting water samples for on-site supervision and control tests, fixed sampling bottles should generally be used. When collecting water samples for full analysis, labels should be affixed to indicate the name of the water sample, the name of the sampler, the sampling location, time, temperature, and other conditions (such as season, climate conditions, etc.). 42.2.5 When measuring certain unstable components in water (such as dissolved oxygen, free carbon dioxide, etc.), sampling and measurement should be carried out on site, and the collection method should be carried out in accordance with the provisions of each measurement method.
A2.3 Storage and transportation of water samples
A2.3.1 The changes in the composition of water samples after collection are greatly affected by the nature of the water samples, temperature, and storage conditions. In principle, they should be tested in time. In addition, different measurement items have different requirements for the storage time of water samples. Therefore, it is difficult to absolutely stipulate the storage time of water samples. According to general experience, it is advisable to use the time listed in Table A2. Table A2 Storage time of water samples
Types of water samples
Uncontaminated water
Contaminated water
Storage time, h
A2.3.2 When storing and transporting water samples, pay attention to check whether the water sample container is tightly closed. The water sample container should be placed in a cool place that is not directly exposed to sunlight.
A2.3.3 Water samples should be protected from freezing in winter and exposure in summer during transportation. A2.3.4 When testing water samples that have been stored or transported, the storage time and temperature should be noted in the report. A3 Determination of suspended solids
A3-1 Overview
Solids separated from water samples by a certain filter material are called suspended solids. Different filter materials can obtain different measurement results. This method uses a G. glass filter or a Gooch crucible filter covered with a 5 mm thick asbestos layer as the filter material. A3.2 Apparatus
A3. 2. 1 G. glass filter with a pore size of 3~~4 μm or a Gooch crucible with a volume of 30 mL. 43.2.2 Electric vacuum pump or hydraulic aspirator. A3.2.3 Suction filter bottle with a volume of 2000mL
A3.3 Reagents
Nitric acid solution (1:1),
A3.4 Determination method
A3.4.1 When using a G, glass filter, first wash the filter with nitric acid solution, then rinse with distilled water, and then place it in a 105110℃ oven to dry for "h, take it out, put it in a desiccator to cool to room temperature, and weigh it to constant weight. 168
GB15762001
A3.4.2 Install the glass filter (or the Gooch crucible with a layer of acid-washed asbestos) on the filter bottle and start the vacuum system. Note: Acid-washed asbestos can be prepared as follows: Cut high-quality long-fiber asbestos into a length of 0.5cm, pound it with water in a mortar, and then boil it in concentrated hydrochloric acid on a water bath for 12~~18 h,Then wash with hot distilled water until there is no chloride ion in the washing liquid, and then it can be used. 43.4.3 If the acid-washed asbestos layer is used as the filter material, the acid-washed asbestos can be evenly spread on the entire bottom of the Gooch crucible in the following way. A3.4.3.1 Put the acid-washed asbestos into a beaker, add a small amount of distilled water and stir vigorously. A3.4.3.2 Add a large amount of distilled water to the stirred acid-washed asbestos, stir again, and pour the upper turbid liquid containing fine asbestos fiber suspension into one beaker, and pour the longer asbestos fiber suspension that sinks to the bottom of the beaker into another beaker. A3.4.3.3 Place the clean Gooch crucible on the suction filter bottle for suction filtration. A3.4.3.4 Pour the prepared long asbestos fiber suspension into the crucible, slowly filter, pour in gradually, filter gradually, until the acid-washed asbestos layer is about 4 mm thick. A3.4.3.5 Then pour in the fine acid-washed right cotton fiber suspension and filter, so that the thin cover layer is about 1 mm. A3.4.3.6 Wash the prepared acid-washed asbestos layer with distilled water until the washing liquid is transparent. Dry the prepared asbestos layer in an oven at 105~-110℃ for 11. Take it out and put it in the desiccator to cool, weigh it until it is constant weight. 43.4.4 After shaking the water sample, accurately measure the volume of the water sample according to Table A3, and slowly pour it into the glass filter. The first 200mL of filtrate should be filtered again and the filtrate should be reserved for dissolving solids and other analysis. If the filtered water sample is turbid, it should be filtered again. Table A3 Suspended solid content and volume of water sample to be taken De-suspended solid content
Water sample volume
Direct determination
Direct determination
A3.4.5 After filtration, wash the glass filter of the measuring water sample container several times with a small amount of distilled water. Move the glass filter into a 105~110℃ oven and dry it for 1 hour. Take it out and put it in a desiccator. Cool it to room temperature and weigh it. 43.4.6 Dry it again at the same temperature for 0.5 hours, and weigh it. Repeat this operation until constant weight. The content of suspended solids in the water sample (pxc) is calculated according to formula (A1):
Gr=G:×1000 mg/l
Wherein: G:——the total amount of glass filter (or Gooch crucible with asbestos layer) and suspended solids, ig:G
weight of glass filter (or Gooch crucible with asbestos layer), mg, V-volume of water sample, ml.
A3. 4. 7 The filter material used should be indicated in the report of the test result. A4 Determination of dissolved solids (gravimetric method)
A4.1 Overview
A4.1.1 Dissolved solids refer to the residue obtained by evaporating and drying the filtrate after the suspended solids have been separated. A4.2 Apparatus A4.2.1 Water bath or 400 ml beaker, A4.2.2 100~200 ml porcelain evaporator, A4.3 Determination method A4.3.1 Take a certain amount of filtered and fully shaken clear water sample (the volume of the water sample should make the weight of the F residue about 100 mg), gradually inject it into the evaporating liquid that has been dried to constant temperature, and evaporate it in a water bath. Note: In order to prevent the inclusion of foreign matter during the drying process and affect the test results, a glass rack must be placed on the evaporating liquid and covered with a dry surface. A4.3.2 Transfer the evaporated sample and the evaporating liquid to a 105~110°C oven for 2 h. 169
GB 15762001
A4.3.3 Take out the evaporation II and place it in a desiccator to cool to room temperature, and weigh it quickly. A4.3.4 Dry it under the same conditions for 0.5h, weigh it after cooling, and repeat this operation until constant weight. A4.3.5 Calculate the dissolved solid content (ORc:) according to formula (A2): GG×1 000 mg/L
Wherein, Gi—total weight of evaporation residue and evaporation III, mg G2—weight of evaporation, mg,
V-volume of water sample, m.
A5 Determination of conductivity
A5.1 Summary of the method
·(A2)
Acids, alkalis, and salts dissolved in water dissociate into positive and negative ions in the solution, making the electrolyte solution conductive. The conductivity can be expressed by conductivity.
The conductivity of electrolyte solution is usually determined by inserting two metal sheets (i.e. electrodes) into the solution and measuring the resistivity between the two electrodes. Conductivity is the reciprocal of resistivity, and is defined as the conductivity of the liquid when the electrode cross-sectional area is 1 cm and the distance between the electrodes is 1 cm. The unit of conductivity is s/cm (S/cm). In water analysis, its part per million, i.e. microsievert per centimeter (us/cm), is used to represent the conductivity of water.
The conductivity of the solution is related to the properties, concentration and temperature of the electrolyte. In general, the conductivity of the solution refers to the conductivity at 25°C.
A5.2 Instruments
A5.2-1 The measurement range of the conductivity meter (or conductivity meter) is normal and standard, and the DDS11 model can be selected. A5.2.2 Conductivity electrode (referred to as electrode): The conductivity electrode commonly used in experimental space is platinum electrode or platinum electrode. Each electrode has its own conductivity cell constant, which can be divided into the following three categories: (), below 1 cm1, 0.1~-1.0 cm-1 and 1.0~10 cm1. A5.2.3 Thermometer: The accuracy should be higher than 0.5℃. A5.3 Reagents
A5.3.11mol/L potassium chloride standard solution: Weigh 74.5513g of high-grade pure potassium chloride (or reference reagent) dried at 105℃ for 2h, dissolve it in newly prepared T-grade reagent water (20℃+2℃), transfer it into a 1I volumetric flask, dilute to the scale, and mix. A5.3.2 0.1 mol/L potassium chloride standard solution: Weigh 7.4551 g of high-purity potassium chloride (or standard reagent) dried at 105°C for 2 h, dissolve it in freshly prepared Grade 1 reagent water (20°C ± 2°C), transfer it into a 11.5% volumetric flask, dilute to the mark, and mix. A5.3.3 0.01 mol/L potassium oxide standard solution: Weigh 0.7455 g of high-grade pure potassium fluoride (or reference reagent) dried at 105°C for 2 hours. Dissolve it in newly prepared Grade 1 reagent water (20°C ± 2°C). Transfer it to a 1L volumetric flask, dilute to the mark, and mix: A45.3. 4 0.001 mol/L potassium chloride standard solution: Before use, accurately pipette 100 mL of Q. 01 mol/L potassium chloride standard solution, transfer it to a 11L volumetric flask, dilute to the mark with newly prepared Grade 1 reagent water (20°C ± 2°C), and mix. The above potassium oxide standard solutions should be placed in ethylene vinyl plastic bottles (or hard glass bottles) and sealed for storage. The conductivity of these potassium chloride standard solutions at different temperatures are shown in Table A4. Table A4
Solution concentration - mol / L
Conductivity of potassium chloride standard solution
Conductivity.μs/cm
65 176
97 838
111342
Solution concentration, mkl/L.
A5.4 Operating steps
GB1576—2001
Table A4 (End)
Temperature, temperature
A5.4.1 The conductivity meter should be operated according to the requirements of the instructions for use. Conductivity, μS/cm
45. 4. 2 The conductivity of water samples is different: electrodes with different conductivity cell constants should be used. For water samples with different conductivity, refer to Table A5 for selecting electrodes with different conductivity cell constants.
Table A5 Selection of electrodes with different conductivity cell bands Conductivity cell constant, cn-1
2>1. 0~-10
Conductivity+μs/cm
3~-100
100～200
Wash the selected electrode with Class I reagent water, then rinse it with reagent water 2~3 times and soak it in 1 A5.4.3 Take 50~[000mI water sample (temperature 25C+5℃) and put it in a plastic cup or a glass cup. Rinse the electrode with the water sample for 2~3 times, and then measure the conductivity in the water sample. Repeat the sampling and measurement for 2~3 times. The relative error of the measurement result reading is within ±3, which is the measured conductivity value (the reading is the conductivity value when using a conductivity meter). At the same time, record the overflow of the water sample. A5.4.4 If the water sample temperature is not 25, the measured value should be converted to the conductivity value of 25C according to formula (A3). DDK
S(25℃) =i+ β(t -25)
Where: S(25℃)
converted to the conductivity of the water sample at 25C: uS/cm; the conductivity measured when the water temperature is t℃, us:
conductivity cell constant.cm-1,
temperature correction coefficient (usually β is approximately equal to 0.02): water sample temperature during measurement, C,
A5.4.5 For the unknown conductivity cell band number or when the conductivity cell constant needs to be calibrated, the electrode can be used to measure the conductivity of a potassium oxide standard solution (temperature 25℃+5C) with a known conductivity (see Table A4), and then the conductivity cell constant of the electrode can be calculated based on the measured results. In order to reduce the error, a potassium chloride standard solution with a conductivity close to that of the water sample to be tested should be used for calibration. The conductivity cell constant of the electrode is calculated according to formula (A4), ss
Formula; K-
—Conductivity cell constant of the electrode, cn--;
S. Conductivity of potassium chloride standard solution, μS/cm; S2: Use an electrode with unknown conductivity cell constant to measure the conductivity of potassium chloride standard solution·uS,. (A4)
A5.4. 6 If the temperature of the chlorinated rivet solution is not 25°C, the measured value should be converted to the conductivity value at 25°C according to formula (A3), and substituted into formula (A4) to calculate the conductivity cell constant.
A5.5 Relationship between conductivity and salt content
For the same type of natural water, at a temperature of 25℃, the conductivity and salt content are roughly proportional, and the ratio is about: 1μS/cm is equivalent to 0.55~~0.90 mg/L. At other temperatures, correction is required, that is, the salt content changes by about 2% for every 1℃ change. When the temperature is higher than 25℃, negative values are used, and vice versa, positive values are used.
Note: At 20℃, the conductivity of a natural water is measured to be 244S/cm. Try to calculate the approximate salt content of this water. Solution: When the conductivity is 1μS/cm, the salt content is equivalent to 0.75mg/L, and the salt content is 244×0.751244x0.75×2%×5=2.0×1nmg/L. According to practical experience, usually in the pH range of 5 to 9, the ratio of the conductivity of natural water to the dissolved substances in the water is about 171
GB 1576—2001
1: (0.6~0. 8), for general boiler water, if the (H- ions with the largest conductivity are neutralized into neutral salt, the ratio of the conductivity of boiler water to dissolved solids is about 1: (0.5~0.6) (i.e. 1μS/cm is equivalent to 0.5~0.6mg/L). Table A6 Conductivity of non-water quality
Water quality name
Fresh hot distilled water
Natural fresh water
Divided salt content water
A6 Determination of pH (electrode method)
A6.1 Overview
Conductivity, S/cm
50--500Www.bzxZ.net
500--1 000
Water samples containing oxidants, reductants, high salt content, pigments, muddy water, and distilled water, demineralized water and other buffered water samples are suitable for this electrode method. When the hydrogen ion is selectively electrode pII When the electrode and the calomel reference electrode are immersed in the solution at the same time, a measuring cell pair is formed. The potential of the pH electrode changes with the activity of hydrogen ions in the solution. The electrode potential corresponding to the activity of hydrogen ions in the aqueous solution can be obtained by measuring with a high impedance input millivoltmeter. It is expressed in pH value, that is, pH = -igau+
The relationship between the potential of the pH electrode and the activity of hydrogen ions in the measured solution conforms to the Nernst formula, that is, RT
nlgag+
F - F. + 2. 306
According to the above formula, it can be obtained that:
0. 058(pH - pH') = AE V
pH pH' +
where E
A6.2 Instrument
The potential generated by the pH electrode, V;
The potential generated by the pH electrode when the hydrogen ion activity is 1, VGas band number;
Faraday constant;
Absolute temperature, K;
The charge valence of the ion being measured:
The activity of oxygen ions in aqueous solution, I101/L; The activity of hydrogen ions in the locating solution, mol/I.1Igam,
The electrode potential difference corresponding to the hydrogen ion concentration of the locating solution. Therefore, at 20°C, when pH1=pH-1, AE---58 mV.
A6. 2. 1 Laboratory pH A6.2.2 pII electrode, saturated or 3 mol/L potassium chloride electrode. A6.3 Reagents and preparation
A6.3.1 Standard buffer solution with pH equal to 4.00: Accurately weigh 10.12 g of high-grade pure potassium hydrogen phthalate (KHCH2O3) that has been dried at 115°C ± 5°C and cooled to room temperature, dissolve in a small amount of deionized water, and dilute to 1000 mL. A6.3.2 Standard buffer solution with pH equal to 6.86: Accurately weigh 3.390 g of high-grade pure potassium dihydrogen phosphate (KH2PO4) that has been dried at 115°C ± 5°C and cooled to room temperature, and 3.55 g of high-grade pure anhydrous disodium hydrogen phosphate (NaHPO4) that has been dried at 115°C ± 5°C and cooled to room temperature, dissolve in a small amount of deionized water, and dilute to 172
1 000 mL.
GB 1576--2001
A6.3.3 pH standard buffer solution of 9.20: accurately weigh 3.81 g of high-grade pure sodium hydroxide (Na2O·10H2O), dissolve it in a small amount of deionized water, and dilute it to 1000 mL. When storing this solution, use a carbon monoxide absorption tube filled with caustic soda asbestos to prevent the influence of carbon nitride.
The changes in pH of the above standard buffer solutions at different temperatures are listed in Table A7. Table A7 pH values of standard buffer solutions at different temperatures.
A6.4 Determination method
Potassium hydrogen benzoate
Phosphate
A6.4.1 Before using a new electrode or an electrode that has been stored dry for a long time, the electrode should be soaked in distilled water overnight to stabilize its asymmetric position. If it is urgent, the above electrodes can be soaked in (.「n1al/L) hydrochloric acid for at least 1h, and then rinsed repeatedly with distilled water before use.
For contaminated electrodes, cotton soaked in carbon tetrachloride or ether can be used to gently wipe the head of the electrode. If the outer wall of the sensitive membrane is found to have slight rust, the electrode can be soaked in 5%~10% hydrochloric acid and used again after the rust is eliminated. However, it must not be immersed in concentrated acid to prevent the sensitive film from being seriously dehydrated and scrapped.
A6.4.2 Instrument calibration: After the instrument is turned on for half an hour, press the instrument
A6.4.3pH positioning: The standard buffer solution for positioning should be a buffer solution with a pH value close to that of the measured liquid. Before positioning: rinse the electrode and the test beaker with steamed water for more than 2 times, then use a clean filter paper to gently absorb the water droplets remaining at the bottom of the electrode, pour the positioning solution into the test beaker, fill the electrode, adjust the zero point, temperature compensation and full scale calibration of the instrument, and finally adjust the pH value according to the pH value of the positioning buffer used. The pH value is used to locate the pHI, and the location is repeated 1 to 2 times until the error is within the allowable range after relocation. The location solution can be kept for next use. If it is contaminated or used several times, it should be replaced with fresh buffer solution at any time as needed. In order to reduce the measurement error, the pH value of the pH standard buffer solution used for location should be close to that of the water sample to be tested. When the pH value of the water sample is less than ? . (, potassium hydrogen phthalate solution should be used for location, and borax or phosphate mixture should be used for relocation. When the pH value of the water sample is greater than 7.0, borax buffer solution should be used for location, and potassium hydrogen phthalate or phosphate mixture should be used for relocation. When measuring the pH value, the "sodium difference" problem of the glass electrode must also be considered, that is, the concentration of sodium ions in the measured aqueous solution interferes with the oxygen ion test. In particular, when measuring the high pH value of pH greater than 10.5, high-quality high-alkali pHI electrodes must be avoided to reduce errors. Instruments with different precisions can be selected according to different measurement requirements. A6. 4. 4 Repositioning: Rinse the electrode and the test beaker repeatedly with distilled water for more than 2 times. After the last rinse, use a clean filter paper to gently absorb the water droplets at the bottom of the electrode, then pour in the repositioning buffer solution, and continue to measure pH according to the above positioning procedures. If the measured result is within 0.05 of the pII value of the repositioning buffer solution, it can be considered that the instrument and the electrode are normal and the pH measurement can be carried out. The treatment of the repositioning solution should be carried out according to the regulations for the repositioning solution. A6.4.5 Determination of water samples: Rinse the repositioned electrode and the test beaker repeatedly with distilled water for more than 2 times, and then rinse with the water sample to be tested for more than 7 times. After the last rinse, use a clean filter paper to gently absorb the water droplets at the bottom of the electrode, and then immerse the electrode in the test solution, and carry out pH measurement according to the above positioning procedures. After the measurement is completed, the electrode should be repeatedly rinsed with distilled water, and finally the pH should be measured. The electrode is immersed in distilled water for later use.
A6.4.6 When measuring pH,The difference between the overflow of the water sample and the positioning temperature cannot exceed 5℃, otherwise, it will directly affect the accuracy of the pH value. A7 Determination of fluoride (silver nitrate volumetric method) 47.1 Overview
Applicable to water samples with a chloride content of 5-109 mg in a neutral or weakly alkaline solution. Chloride reacts with silver chromate to form a white silver chloride precipitate. Excess silver nitrate reacts with potassium chromate to form a brick-red silver chromate precipitate, making the solution appear orange, which is the titration end point. A7.2 Reagents and preparation
A7.2.1 Sodium nitride standard solution (1 mL contains 1 mg chloride ion): Take 3-4 ml of standard reagent or high-purity sodium chloride and place it in a glass. Heat it to 500'C in a high-temperature furnace: burn for 10 min, then put it in a desiccator and cool it to room temperature. Accurately weigh 1.648 g of sodium fluoride, first add it to a small amount of distilled water, and then dilute it to 1 000 mL. A7.2.2 Silver nitrate standard solution (1 ml is equivalent to 1 mz Cl-) Weigh 5.0 g of silver nitrate and dissolve it in 1 000 mL of distilled water. Standardize it with sodium chloride standard solution. The calibration method is as follows: In two conical flasks, use a pipette to inject 10 mL of platinum chloride standard solution into each flask, then add 90 mL of distilled water and 1.0 mL of 10% potassium chromate indicator. Titrate with silver nitrate standard solution until it turns orange. Record the consumption of silver nitrate standard solution V and calculate it with the average value. However, the relative error between the three test values should be less than 0.25. Take 100 InL distilled water for blank test. Except for not adding sodium fluoride standard solution, other steps are the same as above. Record the consumption of silver nitrate standard solution V1. The titer (T) of silver nitrate standard solution is calculated according to formula (A8): 10X1.0
Where: V, the volume of silver nitrate standard solution consumed in blank test, mL; the volume of sodium chloride standard solution consumed, mL; 10 - the volume of sodium chloride standard solution, ml.1.0 -
- the concentration of sodium chloride standard solution, tmg/mE. Finally, adjust the concentration of silver nitrate solution so that 1 mL is equivalent to 1 mg Cl= standard solution. A7.2.3 10% potassium hydroxide indicator.
A7.2.4 1% phenol indicator (using ethanol as solvent). A7.2. 5cnGH: 0. 1 mol/L.
A7.2-6 c1/2H,s0, +0. 1 mol/L.A7.3 Determination method
A7. 3. 1 Measure 10U ml of water sample into a conical flask, add 2-3 drops of 1% phenolic acid indicator, if it turns red, neutralize with acid solution until colorless, if it does not turn red, neutralize with sodium hydroxide solution until slightly red, then add sulfuric acid solution until colorless, then add 1.0 mL of 10% potassium chromate indicator,
A7.3.2 Titrate with silver nitrate standard solution until it turns white, record the volume V1 of the silver nitrate standard solution consumed, and at the same time perform a blank test (same method as A7.2.2), record the volume V1 of the silver nitrate standard solution consumed. The chloride (C1-) content is calculated according to formula (A9): (V1-Ve) × 1.0 × 1 000 mg/L:
In the formula: -
-The volume of silver nitrate solution consumed by titrating the water sample.ml.; V——The volume of silver nitrate solution consumed by titrating the blank water sample,mL:1.0
-The titer of the silver nitrate standard solution, 1 mL is equivalent to 1mg Cl-; 174
(A9)
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