OXYGEN ANALYSER

Oxygen Measurement Problem :
Today's pressing need in many industries is the measurement of the Oxygen, specially with fuel scarcity and its high cost. Conventional Oxygen Analysers suffer from major Limitations; a costly, unreliable & high maintenance sampling system, dry analysis rather than total or wet, long time delay, and inaccurate measurements in stack.

RASKIN Solution :
In a zirconium oxide sensor when two sides are exposed to different oxygen concentrations, it develops a voltage across the two sides. This phenomenon is described by the Nernst equation which states that the voltage generated is a function of absolute temp., Gas constant, Faraday's constant and the logarithm of the ratio of partial pressure of oxygen on the two sides of the sensor.

Nernst Equation :

                                           P1 02
E = 0.0496 T log 10   --------------
 
                                         P2 02
E = Sensor Output, mV
T = Absolute sensor temp. Deg K ( Deg C + 273)
P1 02 = Reference air partial pressure (20.9%)
P2 02 = Sample gas partial pressure

In practice atmospheric air (20.9% O2) is used as reference. The output becomes the inverse logarithm of partial pressure of Oxygen and in direct proportion to temp., of the measured gases. In hot measured gases with temps, above 600°C, a non heated probe is used. In gases with lower temps. a heated probe is used where sensor 2 temp. is held constant with proportional temp. controller. In this case the output voltage becomes proportional to the inverse logarithm of partial pressure of oxygen of the measured gas. As the Oxygen concentration decreases, the voltage increases giving increased sensitivity in low oxygen concentrations.

The Probe :
Many of the Oxygen Analysers even today use sampling systems though gas sample is not to be cooled and conditioned. RASKIN leads the way having patented construction oxygen probes using space age materials and robust common sense.The zirconia sensor is located in the tip of the IN-SITU probe, which is wetted by the flowing gases, unlike other designs where the gas sample is aspirated to the sensor located outside or at the other end of the tip. Thus RASKIN systems do not need pumps, sample probes, cooling / conditioning, in short no sample maintenance / conditioning. Probes are available in lengths 200-1100 mm (longer probes on request).

Instrument Cabinet :
A rugged sheet steel enclosure houses an extremely versatile electronics package
. Where necessary, (in case of heated probe) a separate probe heater control box is provided.
The highly stable, high input impedance amplifiers have been designed to operate over wide measurement ranges. As a standard, probe temperature and O2 mV are also digitally indicated, in addition to volume % (or PPM) oxygen. The oxygen content is continuously calculated and displayed, by programming the Nernst equation, based on actual sensor temperature & O2 mV values. This enhances the accuracy. The electronics is
microprocessor based, where O2 mV, temperature and % (or PPM) oxygen are digitally indicated, with linear, isolated, 4 - 20 mA output, Hi & Lo O2 alarms, probe outside operating temperature range alarm, etc. are provided. Systems equipped with high temperature unheated probes, presence of CO alarm (Hi O2 mV) is provided as a standard.

Oxyprobe Systems :
Using the patented probe and with long varied experience in the field of furnace technology, various systems are built for different applications.

Combustion Optimisation :
In conventional analysers, heated low temperature probe is located in the stack, where flue gas temperatures are much below ignition (< 600°C). Here oxygen is measured not only as left over (excess air) after combustion is complete, but air that has leaked in between combustion chamber and stack. Errors due to reconstitution of gases during cooling also creep in. In case of sampling systems, analysis also is affected due to leaks in sample line, accumulated dust, etc. RASKIN, using a high temperature, unheated probe, have overcome the above limitations. The unheated high temperature probe is positioned downstream of the combustion chamber where combustion is complete, but the temperatures are still above ignition (600°C). This provides true wet analysis - what you really wanted to know - precise Air : Fuel ratio. This enables providing explosive mixture present (presence of Hi CO) alarm.

Features :

  • True wet measurement, eliminates sample system
  • Only requires mains electricity for operation
  • Used with any fuel, high accuracy fast response
  • Solid state, no moving parts
  • Logarithmic sensitivity increases with decreasing oxygen concentration
  • Available with 200-1100mm insertion length Probes
  • Special Explosion-proof executions available.
Specifications :
Measured range 0-21%, 0-10,000 PPM O2
AC voltage options 230/110V ± 10% 50Hz.
Probe length 200-1100mm (longer probes on request)
Ambient Temperature Prob : Upto 100°C Electronics - Upto 45°C
Probe operating
Temperature range
AT :0-600° C
ST : 600-1100°C
HT : 900-1500°C
Overall System accuracy ± 5% of reading or ±0.1% O2, whichever is greater.
Probe speed of response Less than 1 second
Probe reference air Built-in pump (or separate instrument grade air required)
Warm up time 10 minutes (for ST/HT)
Probe Fixing 1" NPT (ST / HT)
Umbilical Cable 10m standard, upto 500 m optional

Dusty Atmospheres :
Equipment such as Cement Kilns / some types of Boilers, have highly dusty atmospheres. High temperature unheated probe is located "IN-SITU" in the combustion gas stream. Since no sampling / aspiration techniques are used, dry dust settling on filter still allows gas to diffuse to the sensor. In addition less dust settles on filters due to high velocity of gases. Therefore, frequency of cleaning is far less. Further, special "IN-SITU" dust cleaning arrangements, by purge air are provided.

Gas Generators :
In most of the gas generators (except endo / exo gas generators), the gas in which oxygen analysis is to be carried out, is at ambient temperatures, a heated zirconia oxygen probe is used. The sensor is maintained at higher temperature with provision of temperature controller, heater power source with tapped transformer. The usual instrument cabinet, with the addition of temperature controller, is provided. Any desired oxygen measurement range is provided to suit the generators.


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