Determination of dissolved oxygen in deaerated water for boilers

Take a look at the standard GB/T 12157-2007 for the determination of dissolved oxygen in industrial circulating cooling water and boiler water

The dissolved oxygen level in water used for boilers is strictly regulated, with an allowable level that is quite low. It is difficult to determine accurately using conventional laboratory methods; generally, an online dissolved oxygen analyzer should be used. Manufacturers of such dissolved oxygen analyzers include Japanese companies such as DKK, American companies like HACH and Yokogawa Electric, as well as companies such as E+H and MeterLab. If you need information related to DKK, you can contact me.

Regarding the issue raised by LZ, our laboratory has not yet been asked to conduct any tests; at present, we are only required to test the hardness, alkalinity, and chloride levels of the boiler water. It’s likely that tests for dissolved oxygen in boiler water will be introduced soon, so let’s learn about it first. I also wish that LZ can find a suitable approach for their own organization as soon as possible

A portable dissolved oxygen meter can also be used; it’s best to opt for one from Mettler or Hach, as they offer high precision

We have an HDY-2110 dissolved oxygen monitor, and calibrating it presents significant challenges due to complex errors.

Currently, there are mainly two principles for measuring dissolved oxygen: fluorescence measurement and polarography measurement. When it comes to measuring very low levels of dissolved oxygen, especially those below 10 ppb, the polarography method, which is based on more advanced technology and offers higher precision, should be chosen. In applications such as measuring dissolved oxygen in nuclear power plant steam (where the concentration is less than 3 ppb) and in ultra-pure water used in semiconductors (where the concentration is less than 1 ppb; SMIC’s final wastewater contains less than 0.3 ppb of dissolved oxygen), the Hach Orbisphere brand has held a monopoly in these areas for many years. It is clear that, in terms of measurement accuracy, polarography is generally considered to be more accurate than optical methods. Products related to polarography have been on the market for over 20 years; as a result, many high-precision products such as Orbisphere, which have been around for decades, remain unchanged. Their shortcomings are quite obvious: they have a slow measurement speed and require highly specialized maintenance. As for Mettler and Hamilton, which are primarily used in the biofermentation industry, their polarographic electrodes also have a slow measurement speed; moreover, after a power outage of more than 5 minutes, they require over 15 minutes of polarization, which poses significant difficulties for field measurements. Their optical dissolved oxygen readings are below 5 ppb, rendering them completely inaccurate. According to national standards for industrial boilers, the dissolved oxygen level should be less than 15 ppb, while for power plant boilers it should be less than 7 ppb. For accurate measurement, optical detection methods are not recommended; moreover, optical instruments are relatively expensive. Therefore, how to measure trace dissolved oxygen at the ppb level quickly and accurately, while minimizing the complexity and cost of instrument maintenance, has been a problem plaguing the industry for many years. Currently, there are companies in China (such as Yu Yan Technology) that are capable of developing polarographic dissolved oxygen sensors with precision comparable to that of the world’s best Orbisphere sensors; moreover, their measurement speed is close to that of optical dissolved oxygen sensors. This approach eliminates all the drawbacks associated with traditional dissolved oxygen measurement methods, while also offering easy maintenance and low costs. Currently, the product is used in nuclear power, the five major power groups, China Resources Microelectronics, and other fields.