Ph-meter calibration method

FIELD: thermal and nuclear power stations; meter calibration in extremely pure water of condensate type and power unit feedwater.

SUBSTANCE: for pH-meter calibration ammonia whose concentration varies by 1.5 - 2 times is dosed in working medium. Electric conductivity and temperature of working-medium H-cationized sample are measured. Measurement results are processed in computer with aid of set of equations characterizing ionic equilibrium in source sample and H-cationized samples. Calculated pH value is compared with measurement results.

EFFECT: enhanced precision and reliability of meter calibration in extremely pure waters.

1 cl, 1 dwg, 1 tbl

 

The invention relates to a method of calibrating pH meters and can be used in thermal and nuclear power stations in ultrapure waters type condensate and feedwater unit.

There is a method of setting and calibration of pH meters on standard buffer solutions [1] (prototype). However, this method of calibration can not be used sufficiently in ultrapure waters due to the fact that the environment buffer solution differs from the operating environment of the unit. It is necessary that the calibration and operation of the instrument was carried out in the same environment. And so the measured pH value cannot be considered as true.

The technical result of the proposed method of calibration is to ensure accurate and reliable calibration of pH meters on ultrapure waters through the use of simultaneous measurements of the conductivity of the source and N-kationirovannykh samples thus produced dosing of ammonia with a known concentration that eliminates the negative impact of carbon dioxide.

A method of calibrating pH meters, using measuring pH value, characterized in that the working environment conduct dosing of ammonia with a variable 1.5-2.0 times the concentration measured conductivity and temperature of the source and H of the acid sample of the working environment measurement results are processed on the computer using a system of equations, characterizing the ionic equilibrium in the original sample and H-acid, calculate the pH value, compare it with the measured pH value and set to a pH-meter calculated value of pH in the conditions of the working environment.

The estimated system of equations for the processing of the results is as follows:

The equations describing the dissociation of weak electrolytes in water analyzed:

The electroneutrality equation for the analyzed water

- Conductivity equation for the analyzed water

The concentration of hydrogen ions in the water analyzed is associated with a pH-value:

The equations describing the dissociation of weak electrolytes in N-filtrate:

The electroneutrality equation for N-filtrate

- The equation of conductivity for N-filtrate

- Balance equation status forms carbonic acid

In equations (1)-(13) are included with ewusie values:

- Input data - the performance of devices ACC:

χCRthat χH-accordingly, the measured specific conductance in the analyzed water and N-filtrate, Cm/cm; pH value in the water analyzed.

- The output is the concentration of ions in water analyzed:

[H+], [N

+
4
], [FNL
-
3
], [
2-
3
], [HE-] is the concentration of the respective ions in the water analyzed, mol/DM3; [Na+]sm- total concentration of cations of sodium, calcium and magnesium in water analyzed in terms of sodium ions, mol/DM3; [Cl-]sm- total concentration of anions of strong acids (chlorides, sulfates and nitrates) in terms of chlorides, mol/DM3; [H+]H, [Na+]H, [FNL
-
3
]H, [td align="left"> 3
2-
]H[HE-]H, [CL-]H- concentration of the respective ions in the filtrate N filter, mol/DM3.

The parameters (internal characteristics of the mathematical model):

Kw, kIToII,- concentration constants of ion equilibria of water, carbon dioxide according to the first and second stages and ammonia;and so the ultimate mobility (or the equivalent conductivity) of the respective ions, Cm·cm2/g-equiv.

To solve equations (1)-(13) it is necessary to adopt the following assumption - the concentration of chlorine ions in N-filtrate equal to its initial concentration:

[CL-]=[CL-]H.

The method of calculation of the above system of equations is used iteratively to Refine the set of assumptions.

To solve equations (1)-(13) there are three parameters: the measured pH in the original sample and specific conductivity in the original sample and its N-filtrate. Optionally set the temperature of the sample and filtrate. Accounting for the temperature of the water samples before and after N-column is an essential feature of this method.

The method is based on consistently pursued the following operations: select and prepare the water samples used for this standard devices the sample preparation measure the conductivity and the pH value of the automatic devices: a conductivity meter and pH meter in the original water sample, and specific conductivity in the sample, passed through the H column (N-filtrate), it also measures the temperature of the water sample and N-filtrate. Data from devices processed on a computer or analytically using the system of equations. Calculated pH value, and then compares the calculated value with the measured and clarification regarding the measured values directly in a controlled environment. In terms of the working environment dosed ammonia with known and periodically changed 1-2 times concentration for a more precise definition of pH. By dosing the ammonia the pH of the sample will increase in proportion to the dosage of ammonia is the more intense, the lower the concentration of carbon dioxide in the sample. The true value of pH of the medium is calculated by solving the system of equations (1)-(13) and is mounted on the measuring of the pH-meter. By the graph (figure 2) on the measured conductivity values are pH value, and corrects the measured value. For accurate calibration of a pH meter, you need to spend a few different doses of ammonia.

Thus, the proposed method allows you to calibrate directly in terms of the working environment; to consider the influence of carbon dioxide on ve is ichino pH dosage in test solutions of known concentration of ammonia and the subsequent calculation of the pH of the sample.

This method of calibration has yielded positive results when used in an industrial environment Ivanovskaya TPP-3 and Kostromskaya GRES. On Ivanovskaya TPP-3 tests were carried out on the unit with boiler TP-87 and turbine PT-80-130, and at Kostromskaya TPP unit 300 MW boiler TGM-114, turbine K-300-240). Some results of measurements and calculations are shown in table 1.

1580
Table 1
The results of the calculation of pH from measurements of the conductivity of the source and H of the acid sample
Dosing of ammoniaΔCNH3g/DM3χ, s/cmχn, s/cmThe estimated value
sample   [NH3], g/DM3pH based on the environment
1. The dosage of ammonia on CHP (drum boiler SVD)
No dosage-6,30,7787909,26
 395to 12.00,7021185to 9.57
Dosage79013,10,719being 9.61
No dosage-6,440,857729a 9.25
Dosage3657,200,8561094of 9.30
 729to 7.320,9401458was 9.33
2. The dosage of ammonia on GRES (once-through boiler ACS)
No dosage-0,4570,180407,49
Dosage200,7040,23260the 7.85
 400,909rate 0.162-8at 8.36
Note: * measured pH value given temperature corrections to the environment [4]

For measurements used instrument set consisting of a device sample preparation (SCP) (1), valve flow switching samples (2, 3, 4), thermometer (5), installed in series sensors conductivity meters (6, 9), H-cationite columns (7) and pH meter (Ref. 8), see figure 1. For carrying out the dosages used the ammonia tank (10) and the pump dispenser of ammonia (11). The proposed computational and analytical method kalibrovki the pH-meter eliminates the negative impact of carbon dioxide, noted above.

The source of information

1. RD-34.37.308-90 guidelines for the determination of pH of feed water once-through boilers ACS within 8 to 10 pH laboratory pH meters.

A method of calibrating pH meters, using measuring pH value, characterized in that the working environment conduct dosing of ammonia with a variable 1.5-2.0 times the concentration measured conductivity and temperature of the source and H of the acid sample of the working environment, the measurement results are processed on the computer using the system of equations describing the ionic equilibrium in the original sample and H-acid, calculate the pH value, compare it with the measured pH value and set to a pH-meter calculated value of pH in the conditions of the working environment.



 

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FIELD: thermal and nuclear power stations; meter calibration in extremely pure water of condensate type and power unit feedwater.

SUBSTANCE: for pH-meter calibration ammonia whose concentration varies by 1.5 - 2 times is dosed in working medium. Electric conductivity and temperature of working-medium H-cationized sample are measured. Measurement results are processed in computer with aid of set of equations characterizing ionic equilibrium in source sample and H-cationized samples. Calculated pH value is compared with measurement results.

EFFECT: enhanced precision and reliability of meter calibration in extremely pure waters.

1 cl, 1 dwg, 1 tbl

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