Application of Electrochemical Gas Sensors in Flue Gas Analyzers
With the advancement of global industrialization, the massive consumption of fossil energy has exerted a considerable impact on the environment. In the 12th Five-Year Plan for Energy Conservation and Emission Reduction issued by the State Council, China refined and quantified energy conservation and emission reduction measures and targets for key industries and fields. Against this backdrop, the market for emission monitoring instruments and meters related to flue gas emission and combustion efficiency monitoring is poised for explosive growth. To meet the business demands and development trends of the Chinese market, British company DDS has launched the S+4OXLF, a long-life lead-free oxygen sensor suitable for both industrial scenarios and flue gas analysis.
I. Traditional Lead-containing Oxygen Sensors in Flue Gas Analyzers
Traditional oxygen sensors for exhaust gas detection are essentially two-electrode metal-air batteries, consisting of an air cathode, a lead anode, and alkaline electrolyte. The cathode is a polytetrafluoroethylene membrane coated with active catalyst, while the anode is a lead block, both encapsulated in a sealed metal or plastic housing. Air enters the sensor through a capillary tube at the top, and the cathode and anode are connected to the sensor’s two pins via current collection wires. When oxygen reaches the working electrode, a reduction reaction occurs to generate hydroxide ions, which migrate through the electrolyte to the lead electrode. An oxidation reaction then takes place at the lead electrode, producing lead oxide. By converting current into voltage through an external fixed resistor, the oxygen concentration can be calculated. Despite a development history of over 30 years, lead-containing oxygen sensors still have inherent limitations:
Combustion by-products shorten service life.Combustion products generally contain acidic gases such as carbon dioxide (CO₂), nitrogen oxides (NOₓ), and sulfur dioxide (SO₂). The sensor is filled with alkaline electrolyte internally. With prolonged use, the pH value of the alkaline solution decreases, and the lead anode is consumed at an accelerated rate, shortening the sensor’s service life.
Failure to meet lead-free standards.Although lead-containing sensors currently enjoy exemptions under RoHS and WEEE regulations, the replacement of lead-containing sensors by lead-free alternatives has become an irreversible environmental trend.
Excessive weight and bulky size.To extend service life, a larger amount of lead material is required, resulting in increased weight and volume.
II. Technical Features of the Long-Life Lead-Free Oxygen Sensor
Addressing the shortcomings of traditional lead-containing oxygen sensors, the three-electrode long-life lead-free oxygen sensor S+4OXLF has been developed.
Extended Service LifeThroughout the chemical reaction process, the high-activity electrodes only serve as catalysts for oxidation and reduction without being consumed, eliminating the issue of anode fuel depletion in traditional lead oxygen sensors. The unique structural design of the S+4OXLF effectively suppresses electrolyte volatilization inside the sensor, delivering a service life far exceeding conventional oxygen sensors. It can operate stably for more than 5 years within a temperature range of -40℃ to 60℃ and a relative humidity range of 15% to 90%.
Resistance to Acidic GasesThe S+4OXLF adopts acidic electrolyte internally, which effectively resists interference from acidic gases generated by the combustion of natural gas, petroleum, wood, biomass and other fuels, ensuring adaptability across various fuel application environments.
Lightweight DesignCommon lead-containing oxygen sensors for emission monitoring, such as the S+5OX/5FO, weigh approximately 40g, while the S+4OXLF weighs only 5g, offering a distinct weight advantage. It creates favorable conditions for the development of compact, lightweight combustion efficiency meters.
Compliance with RoHS and WEEE StandardsBeing completely lead-free, the S+4OXLF enables monitoring instruments to easily pass RoHS and WEEE certification.
Complete Technical DocumentationWe provide users with sensor characteristic specifications, operating principles and reference circuit diagrams, fully supporting customers’ application development.
Market Applications
With its advantages of miniaturization, strong resistance to acidic gas interference and long service life, the sensor has gained high recognition from end customers. Its key application scenarios are as follows:
Online Flue Gas AnalyzersDomestic online oxygen monitoring mostly uses zirconia sensors or partial-pressure lead oxygen sensors. The latter has a theoretical service life of nearly 5 years, yet temperature and humidity fluctuations in intake air often reduce its actual lifespan to around one year. Additionally, its weak resistance to high-concentration acidic gas interference limits its application scope. The S+4OXLF operates stably for 5 years unaffected by intake air temperature and humidity, even under high-concentration acidic gas conditions. It also helps users save substantial maintenance costs incurred by sensor failure within the warranty period, including product replacement and travel expenses.
Combustion Efficiency AnalyzersCombustion efficiency analyzers are widely used for efficiency testing of industrial boilers. As civil boilers gradually enter household use—especially with the popularization of condensing boilers—the home heating market will see explosive growth, driving rising market demand for combustion efficiency analyzers and improving monitoring systems. Boiler manufacturers and maintenance service providers are increasingly equipped with such analyzers.
Flue Gas AnalyzersMost domestic flue gas analyzers adopt a box-type structure, internally equipped with lead oxygen sensors and large-sized Series 3 toxic gas sensors. The S+4OXLF can serve as an ideal replacement, enabling instrument manufacturers to develop thinner, lighter, smaller and more compact devices.
