Analytical Instrumentation

Exploring Zirconia Oxygen Analyzers in Industrial Applications

  • Zirconia oxygen analyzers are devices that are utilized for the purpose of determining the amount of oxygen present in a gas mixture. They employ a zirconia-based solid electrolyte as the key sensing element.
  • Zirconia oxygen analyzers are widely used in various industries where accurate measurement and control of oxygen concentration are critical, such as in combustion processes, industrial furnaces, power plants, and environmental monitoring. 
  • They are preferred for their high accuracy, reliability, and ability to operate in harsh environments with high temperatures and potentially corrosive gasses. 
  • Additionally, they offer fast response times and minimal maintenance requirements compared to other types of oxygen analyzers.
Working Principle of Zirconia Type Oxygen Analyzers
  • Oxygen analyzers of the zirconia type are a common family of instruments used to measure the concentration of oxygen in different gas mixtures. 
  • For the purpose of manufacturing, environmental monitoring, and combustion processes, among other industries, it is necessary to understand their basic principles of operation. 
  • These analyzers are dependent on the basic characteristics of zirconia, a ceramic substance that has the ability to conduct oxygen ions at high temperatures.
  • The core principle involves a zirconia element with platinum electrodes bonded to both sides. When this zirconia element is heated and exposed to gasses that have different partial oxygen pressures on either side, it acts similarly to a concentration cell. 
  • The side in contact with the gas with higher partial oxygen pressure acts as the negative electrode. 
  • Here, oxygen molecules in the gas gain electrons and transform into oxygen ions upon interaction with the zirconia element. 
  • These oxygen ions then migrate through the zirconia element towards the positive electrode on the opposite side. 
  • At the positive electrode, electrons are released, and the ions revert to oxygen molecules.
  • This ion migration generates an electromotive force (EMF) between the two electrodes, which is governed by Nernst’s equation.
  • This equation accounts for factors like gas constant, Faraday’s constant, absolute temperature, and the oxygen concentrations of the gas samples in contact with the positive and negative electrodes. 
  • Typically, the sensor (zirconia element) is heated to around 750°C to facilitate this process effectively.
  • The zirconia oxygen analyzer’s construction comprises the zirconia element, platinum electrodes, a probe for gas measurement, and a voltmeter to measure the generated EMF. 
  • In the context of air being used as the reference gas on the negative electrode side, the relationship between oxygen concentration in the measurement gas and the EMF of the sensor (cell) is established. 
  • However, practical implementations may exhibit slight deviations from theoretical values, which are corrected through calibration using calibration gasses.
Construction and Configuration of Zirconia Type Oxygen Analyzers
Construction and Configuration of Zirconia Type Oxygen Analyzers 2
  • The construction of zirconia type oxygen analyzers encompasses several key components tailored to facilitate precise oxygen concentration measurements. 
  • The zirconia element serves as the central sensing unit, with platinum electrodes facilitating ion migration and EMF generation. 
  • The probe allows for gas sampling, while the voltmeter quantifies the EMF for analysis.
  • System configurations of zirconia type oxygen analyzers can vary based on intended applications and environmental conditions. 
  • These configurations are broadly categorized into two main types: those equipped with general-purpose detectors and those with high-temperature detectors.
  •  Each type is further subdivided into three subtypes, resulting in six distinct configurations.
Construction and Configuration of Zirconia Type Oxygen Analyzers 3
  • The differentiation among these configurations primarily lies in the calibration methods employed and the temperature ranges in which they operate. 
  • For instance, general-purpose detectors are suitable for measurement gas temperatures up to 700°C, while high-temperature detectors extend this capability up to 1400°C.
  • In terms of calibration methods, the simpler types utilize standard gas units, while more sophisticated options involve instrumentation air and zero gas.
  • The selection of a calibration technique is frequently determined by a number of criteria, including the needs for accuracy, the availability of calibration resources, and the preferences of the operating staff.
  • The introduction of reference air into the system can be accomplished through natural convection or instrument air. 
  • Natural convection involves allowing air to flow near the detector spontaneously, while instrument air refers to air that has been treated to remove moisture, oil mist, and dust. 
  • The latter method is preferred for its reliability and ability to maintain consistent measurement conditions, especially in environments prone to humidity fluctuations and airborne contaminants.
  • The construction and configuration of zirconia type oxygen analyzers are designed to ensure robust performance and accurate measurements across diverse operating conditions. 

Click here for 9 Step Zirconia Oxygen Analyzer Calibration Procedure

Pressure Compensation Method - Zirconia Type Oxygen Analyzers
  • The pressure compensation method is employed to ensure accurate measurement of oxygen concentration in environments with high in- combustion area pressures or pressure variations.
  • When such conditions disrupt the pressure balance between the furnace interior and the reference air, accurate readings become challenging. 
  • To address this, the detector’s pressure compensation function returns reference air to the furnace, restoring the pressure equilibrium. 
  • This enables reliable measurements, accommodating in-furnace pressures of up to 250 kPa. 
  • By maintaining consistent pressure conditions, this method enhances the accuracy and reliability of oxygen concentration measurements in diverse industrial settings.
  • Reliability in crucial industrial processes is ensured by the accurate measurements of oxygen concentrations in gas mixtures provided by zirconia type oxygen analyzers.
  • Zirconia sensors typically provide rapid response times, allowing for quick adjustments in processes requiring immediate oxygen concentration control.
  • With durable zirconia elements and platinum electrodes, these analyzers withstand harsh environments, ensuring longevity and minimal maintenance requirements.
  • Zirconia sensors can function at elevated temperatures, making them ideal for applications involving combustion processes and high-temperature environments.
  • These analyzers exhibit minimal drift over time, maintaining consistent accuracy and reliability throughout prolonged operation periods.
  • The span side (air) is the only one that needs calibration.
  • Measurement error arises if the sample gas contains a combustible gas (combustion exhaust gas creates nearly no difficulty because it is totally burnt).
  • At lower temperatures, zirconia sensors may exhibit a slower response time, which could impact the efficiency of processes requiring rapid oxygen concentration adjustments.
  • Zirconia sensors may not be suitable for measuring oxygen concentrations in certain gas mixtures or environments with specific chemical compositions.

Zirconia type oxygen analyzers find extensive applications across various industries where precise measurement and control of oxygen concentration are paramount. Some notable industries and their specific applications include:

  • Monitoring oxygen levels in boiler combustion gases to optimize fuel efficiency and reduce emissions.
  • Ensuring proper air-fuel ratio for combustion processes in power plants to enhance energy production.
  • Monitoring oxygen levels in refinery processes to prevent explosions and ensure safe operation.
  • Controlling oxygen concentrations in chemical reactors to optimize production processes and maintain product quality.
  • Monitoring oxygen levels in blast furnaces and converters to optimize steelmaking processes and reduce energy consumption.
  • Controlling oxygen concentrations in heat treatment furnaces to enhance the quality and properties of steel products.
  • Zirconia oxygen sensors measure oxygen concentration by detecting the voltage generated when oxygen ions migrate through a heated zirconia electrolyte, creating an electromotive force.
  • The output of a zirconia oxygen sensor is typically a voltage signal proportional to the oxygen concentration in the gas sample being measured. This voltage signal is generated due to the ion conductivity of the heated zirconia electrolyte.
  • The operating temperature of zirconia oxygen sensors typically ranges from around 600°C to 900°C . This elevated temperature is necessary to facilitate the ion conductivity of the zirconia electrolyte for accurate oxygen concentration measurements.
  • The application of zirconia oxygen analyzers spans across various industries, including power generation, petrochemical refining, steel production, automotive manufacturing, environmental monitoring, medical devices, aerospace, food and beverage production, and research laboratories. 
  • They are primarily used for measuring and controlling oxygen levels in processes to optimize efficiency, ensure safety, and maintain product quality.

Click here to know more about Analytical Instruments in process industries

Sundareswaran Iyalunaidu

With over 24 years of dedicated experience, I am a seasoned professional specializing in the commissioning, maintenance, and installation of Electrical, Instrumentation and Control systems. My expertise extends across a spectrum of industries, including Power stations, Oil and Gas, Aluminium, Utilities, Steel and Continuous process industries. Tweet me @sundareshinfohe

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