Method for measuring the reference oxygen content in electric furnaces using oxygen sensors

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Oxygen content refers to the excess free oxygen present in the flue gases during fuel combustion, and is usually expressed as a volume percentage on a dry basis. Under China’s current emission standards for air pollutants, the concept of baseline oxygen content came into use. At present, most of these emission standards are based on the concentration of pollutants emitted, measured in mg/m³ – where the numerator represents a mass unit and the denominator a volume unit. This means that, with a constant mass, the larger the volume, the lower the concentration. The baseline oxygen content is a reference value for oxygen content specified to convert the emission concentrations of air pollutants from combustion sources. To ensure the comparability of monitoring data, a unified standard has been established based on the principle of achieving complete combustion of the fuel without the emission concentrations being altered by the \"dilution\" effect of excess air. The emission standards for air pollutants in various industries include a provision requiring that the measured emission concentrations be converted to concentrations based on an oxygen content baseline. To ensure complete combustion of the material, an excess of air is usually supplied to guarantee an adequate supply of oxygen. Excess air also has a certain \"dilution\" effect on flue gas emissions; once the pollutants are diluted, their concentration inevitably decreases. In actual production, the amount of air introduced is determined based on the combustion conditions under different operating conditions, and these amounts can vary significantly. If the amount of air supplied is increased arbitrarily to raise the flue gas volume, it will result in a significant decrease in the measured pollutant concentrations. Taking power plants as an example, the benchmark oxygen content requires that the oxygen-based value for the emission concentrations of flue gas pollutants from coal-fired boilers be 6% oxygen. The reason for making such a classification is to standardize the emission values of pollutants through conversion, thereby enabling the values to be compared. The baseline oxygen content is the usual value that maintains a stable oxygen concentration inside the electric furnace during its operation. Generally speaking, the baseline oxygen content is obtained as the oxygen concentration resulting from the steady-state mixing of the gas entering the electric furnace with air at a certain temperature and pressure. The measurement of the baseline oxygen content is primarily aimed at ensuring the stable operation of the electric furnace and controlling the atmosphere inside it, so as to guarantee the quality of the molten material. There are many methods for measuring the reference oxygen content, and the most suitable method should be chosen based on the type of electric furnace and its mode of use during actual measurements. Common methods include: colorimetry, electrochemistry, and infrared spectroscopy, etc. Among them, the electrochemical method is the most common and reliable. An oxygen sensor (O2 sensor) from Gongcainet, the GMS-10 RVS, is a high-precision oxygen sensor suitable for various applications. This product series was initially used in boilers, and later versions were developed for oxygen monitoring in commercial and military aircraft, as well as for use in automotive exhaust testing and medical testing equipment. The Honeywell oxygen sensor uses two ZrO2 disks, with a small airtight sealing chamber between them. The first disc has the function of a reversible oxygen pump, and is used sequentially to fill and evacuate the sealed chamber. The second disc measures the pressure difference ratio and generates a corresponding sensing voltage. The heating element generates the required temperature of 700°C so that ZrO2 can act as an O2 pump. The time it takes for the pump to bring this chamber to the specified level can be used to measure the oxygen partial pressure of the environment. Sensors must operate through electronic measurement circuits that control sensor operation and signal processing. This circuit can either be integrated into the customer’s own electronic device or purchased from Honeywell as a separate electronic device unit.