How to select a pH electrode?
In industry, the pH meter is used more frequent as a pH measuring and analyzing instrument rather than the pH test paper and standard colour chart. The digital pH meter can accurately display the pH value on real time, the error is greatly increased by one order of magnitude than that of pH test paper. Moreover, it can also realize the automatic control of pH value and pH value alarm. But due to the service life of pH electrodes, it is easy to break down, as a result, users have to pay much money in replace new pH electrodes. Next we will introduce the selection experience of pH electrode in several typical industries, so as to provide reference for users.
I. Flue Gas Desulfurization
Desulfurization industry is complicated, common methods include the liquid alkali desulphurization (add NaOH solution into the circulating solution), sodium hydroxide desulphurization (add quicklime in the pool to produce lime slurry, a lot of heat will be given out) and double-alkalic process (add both quicklime and NaOH).
Liquid alkali desulphurization is quite common and paying attention to the corrosivity is enough. For strong alkaline, tetrafluoroelectrode can be selected.
Lime slurry is special because it adheres to the glass bulb. In addition, it prevents the full contact between the bulb and the medium, thus resulting in large measurement error. At this time, field temperature and corrosivity shall be considered:
- If the temperature is below 60 ℃ and plastic shell will be not corroded, a common flat pH electrode for Flue Gas Desulfurization can be selected.
- However, if the temperature is high or strong corrosivity, a combination of high temperature pH glass electrode and PTFE sheath can be selected. High temperature glass electrode bulb is rather thicker and has high sensitivity than the flat film electrode. Moreover, it can withstand strong acid and strong alkali, as well as a high temperature of 90℃.
The pH meter is widely used in the FGD industry. In most cases, the pH value will be controlled at 9-12 to ensure the desulphurization effect.
The plating solution directly contacts with the electroplated parts. The composition of the plating solution is relatively the cleanest and the simplest, most compositions exists in the form of mixtures. Its concentration isn’t too high, so the liquid junction would not be blocked, nor poisoning occurs due to reverse osmosis. If the temperature is below 60 ℃ and plastic shell is not corroded, a common combination pH electrode can be selected.
The plating auxiliary is a common chemical formulation, it's generally at room temperature with weak corrosivity, so a common combination pH electrode can be selected.
III. Printing and dyeing factory
Printing and dyeing sewage has a high temperature, the content of heavy metal ions may also be high, so ATO suggest the customers to choose the high temperature pH glass electrode with PTFE sheath. Moreover, the user shall clean the electrode probe regularly, otherwise it's easy to block.
IV. Wastewater treatment plant
The pH electrode is generally used for the wastewater to be discharged after treatment in the wastewater treatment plant. As the wastewater has little corrosivity and a relatively not bad water quality, a common plastic combination pH electrode can be selected.
V. Agricultural irrigation and aquaculture
Water for agricultural irrigation is clean and at normal temperature, so a common plastic combination pH electrode is suitable. Water for aquaculture is dirty, but regular cleaning for the electrode probe is enough, so a common combination pH electrode is also applicable.
VI. Circulating water in refrigeration machinery, condensate water
In this case, pH detection is generally to prevent pipeline leakage or test the refrigeration effect of condensate water, plastic combination pH electrode is often used. Generally, each equipment is equipped with a pH electrode.
VII. Pharmaceutical industry
There are two mediums in the pharmaceutical industry, namely the medical wastewater and the drug pH detection of reactor and sterilizing tank. Drug testing has higher hygienic requirements, choose the pH glass electrode. Sterilizing conditions require special pH electrode for sterilization to adapt to the pasteurization at 120℃.