Measurement of O2 Concentration in Exhaust Gases from Pulverized Coal-fired Boilers

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Pulverized Coal Boiler

In a pulverized coal-fired boiler of a large power plant, an oxygen analyzer is essential for combustion control. Exhaust gases from the pulverized coal boiler contain a large quantity of dust and flow very fast. Oxygen analyzers that employ a sampling method may be subject to wear or clogging, resulting in increased maintenance workload and cost.

A solution to this problem is the ZR22/ZR402 Direct In-Situ Zirconia Oxygen Analyzer that has no sampling system and utilizes a long-life sensor. A probe protector is attached to protection it against wear.

Expected Benefits

  • Improves combustion efficiency for pulverized coal-fired boilers 
  • Ensures stable, continuous oxygen measurement 
  • Reduces operating cost 
  • Minimizes the need for equipment replacement

Process Overview

While oil is commonly used as a boiler fuel, coal is also used because it is inexpensive and readily available. Unlike oil, coal produces a large quantity of ashes when it is burned, necessitating pulverized coal-fired boilers to be equipped with an ash removal system such as a cyclone. Exhaust gases from these boilers contain a large quantity of dust (10 to 30 g/Nm³) and flow very fast as the result of the large volume of air being blown into the boiler. For oxygen measurement in large ducts, a probe with a long insertion length is used.


  • Improves combustion efficiency for pulverized coal-fired boilers
  • Ensures stable, continuous oxygen measurement
  • Reduces operating costs
  • Minimizes the need for equipment replacement

Field Data

Process Conditions 
Measurement point: economizer outlet
Temperature: 300 to 400°C
Flow rate: ≤ 30 m/s
Pressure: ±1.5 kPa
Dust concentration: approx. 15 g/Nm3 or less
Fuel: pulverized coal

Measurement System

Detector: ZR22G--S-----E-A/CV
Probe protector: ZO21R-L--*B
Converter: ZR402G--E-E-A
Flow setting unit:
Calibration gas unit
Pressure regulator for gas cylinder: P/N G7013XF (inlet W22, outlet Rc1/4) or P/N G7014XF (inlet W22, outlet 1/4NPT)
Case assembly for calibration gas cylinder: P/N E7044KF
Note: the calibration gas cylinder must be purchased locally


Power supply: 85 to 264 V AC, 50/60 Hz
Instrument air (reference gas): pressure, 300 to 700 kPa


  • A probe protector should be attached to the probe for protection against wear or damage. The probe protector should be mounted with the notch of the probe head pointing downstream in the gas flow.
  • It is recommended that the detector be installed with the probe tip pointing downward. As shown in the figure below, it may be installed horizontally, too. The probe head tip should not point upstream in the gas flow.


Related Products & Solutions

Single Channel Oxygen Analyzer System ZR22/ZR402

The ZR probe's in-situ measurement method does not require any process conditioning or extractive sampling. This reduces maintenance costs and allows faster measurement response to changes in the process.

Oxygen Analyzers

Oxygen analyzers provide valuable measurements in combustion control, process quality, safety and environmental applications.


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