ZrO₂-Probes for the Measurement of Oxygen in Flue Gases

High-temperature probe AMS 3211-700, electronic controller AMS 3220 (EEx-version).

Content

Technical description of the measuring system
ZrO₂-probes for the measurement of Oxygen in flue gases
Applications
System features
System components

The Probes
Standard probe AMS 3211-500
High-temperature probe AMS 3211-700, up to 1100°C
High-temperature probe AMS 3211-600, up to 1750°C
EEx-approved probe, up to 400°C
EEEx-approved probe, up to 1100°C
Probe AMS 3211-500L
AMS Screw-in probe

The system components
Pneumatic unit and automatic calibration
Electronic controller AMS 3220
Extended application areas for the AMS ZrO2-probes using the electronic controller AMS 3220

Technical Data
Probes
Cabinets
Electronic controller AMS 3220

Data Sheet
Certifications

Back to the product program

ZrO₂-probes for the measurement of Oxygen in flue gases
The wide range of applications of ZrO₂-probes for the measurement of Oxygen requires the adaptation of this measuring system to varying process conditions like temperature, aggressive flue gas and even hazardous areas. A short response time and durability of the sensor are further major customer demands. But also ease of use, reliability and minimum maintenance of the analysis system are important design features.
Twenty years of experience in system technology enable AMS Analysen-, Mess- und Systemtechnik to provide ZrO₂-probes with these features already built-in while still keeping an attractive price.
The European Directive 2000/76/EC governs the operation of waste incinerators.
For the approval and for the certification of measuring and analytical instruments to be used at incinerators, it requires an extension of the ( TUEV )-approval and certificate with respect to the quality assurance of the measurements.
TUEV Rheinland (Köln) have issued the appropriate confirmation as extension to the report 936/807023/A, dated 2000-08-14.

Applications
The Oxygen measuring units are used for the determination of the Oxygen concentration in flue gases of incinerators or in pure industrial gases covering the temperature range from 20°C to 1750°C.
Since the Zirconia measuring cell is located in the flue gas flow the measurement takes place directly (in-situ) allowing the sample extraction and conditioning system to be omitted.
Specific applications demand probes aligned to the particular process environment: e.g. to hazardous areas classified as zone 1 or 2 (ATEX approved), to residue free combustion processes using Natural Gas or to flue gas ducts with small diameters.

System features

• Specially AMS designed sensor for flue gas applications, operator replaceable TÜV-approval for large boilers in power plants, industrial furnaces and for waste incenerators and for crematoria
• Gas wetted parts made of stainless steel, other materials are available
• Range of probe lengths from 150 mm to 3000 mm
• Gas temperatures up to 1750°C
• TÜV-approved in compliance with European Directive 2000/76/EC for waste incinerators
• EEx-ATEX-approved probes for zone 1 and zone 2
• EEx-ATEX-approved high temperature probes (1100°C) zone 2
• EEx d II B + H₂-probe for zone 1
• Electronic controller:
  Self diagnostics with fault signals
  Automatic calibration
  Plausibility check of the correction data

Certicates for waste incinerators and ATEX

System components
The oxygen measuring system consists of the ZrO₂-probe with temperature controlled measuring cell, the electronic controller as well as of the pneumatic unit for the air supply. The measuring procedure is based on the galvanic oxygen concentration cell with solid electrolyte.
To match the varying application areas seven different probe models can be supplied. The electronic controller is the same for all probes. The latter is installed separately but can be built into the pneumatic cabinet as well.

Standard probe AMS 3211-500
The in-situ probe AMS 3211-500 for flue gas temperatures up to 600°C (temporarily up to 800°C) is manufactured in three standard lengths (500mm, 1000mm, 1500mm) using stainless steel; other lengths (150mm to 1800mm) are available. Probes made of special materials like INCONEL or Hastelloy C are supplied on demand.
The ZrO₂-sensor is located directly in the flue gas duct mounted on the probe tip. The specially designed sensor regularely employed in all probes has a life-time of at least two years due to the low operating temperature of less than 500°C.
The replacement of the O₂-sensor is easily done: only 2x4 screws are to be removed for this purpose.
The 6mm Swagelok gas inlets for calibration gas and reference gas (instrument air) are fixed on the mounting flange of the probe.

High temperature probe AMS 3211-700, up to 1100°C
The semi-extractive probe AMS 3211-700 gives the user some operating advantages, additional to the high-temperature feature:

• Neither aspirator pump air nor reference air lines are needed
• The aspirator pump, usually flange integrated, can be omitted The sensor life is substantially increased

The introduction of a Venturi gas jet at the top of the probe is the basic innovation: The probe gas flow through the Venturi generates a reduced pressure in the inner tube of the probe thus sucking flue gas through the perforated bottom plate of the outer probe tube. That´s why the aspirator pump is not necessary anymore.
Being flange mounted outside the flue gas duct the thermal load of the sensor is remarkably reduced, thus increasing its life time to the customer´s benefit.

High temperature probe AMS 3211-600, up to 1750°C
The semi-extractive probe AMS 3211-600 can be utilized at temperatures up to 1750°C employing a sample tube made of ceramic. Vertical set-up of the probe will be provided in this case.
Given a maximum flue gas temperature of 900°C the fitting position may be freely chosen when special materials have been used in making the probe.
The standard length of the probe is 1000 mm, other lengths (150 mm to 1000 mm) can be supplied on demand.
The Zirconia measuring cell is built into the mounting flange of the probe. The measuring gas passes the sensor via an aspirator pump integrated into the flange and will be fed back into the process: This arrangement keeps the dew point fixed while avoiding blockage of the measuring system.

EEx-approved probes, up to 400°C
The EEx-probe feature a flameproof enclosure for the sensors with flame barriers to separate safely the sensors from the flue gas and the electrical connections from the ambient area.
The probe is certified for hazardous areas zone 1 and zone 2 at surface temperatures up to 160°C (T3) and ambient temperatures until 40°C. The installation lengths may vary from 150 mm to 860 mm. The probe is designed for flue gas temperatures up to 400°C (short time 500°C).

EEx-approved probes, up to 1100°C
This particular design combines the characteristic features of both the EEx-approved probe and the semi-extractive high-temperature probe 3211-600. Flue gas temperatures up to 1100°C as well as hazardous zone 2 (ATEX 3G-approved) applications proof the outstanding capability of this specific ZrO2-probe.

Probe AMS 3211-500L
For applications in combustion processes producing no residues,e.g. natural gas heating, we recommend the probe AMS 3211-500L, properly fitted to this application.
Ambient air is used as reference gas. As flue gas ducts operate under pressure conditions slightly below ambient, this low pressure will continuously suck air into the stach via a capillary tube. This air passes by the reference side ot the Zirkonia sensor and thereby provides the reference air required.
The probe will be delivered with a mounting flange DN65 PN6 and lenghts up to 500 mm, the weight is approximately 3 kg. The other technical data correspond to the probe AMS 3211-500.

Small diameter ducts: AMS Screw-in probe
The ZrO2-sensor is to be fixed directly to the exhaust duct with the flange featuring a metric M40x2 thread, and likewise as all other AMS probes too, shielded against dust particles from exhaust gas by a filter head made from stainless steel. The weight is approximately 0,45 kg.
The flue gas temperature may amount up to 450°C at most, the stack´s diameter should be about 100 mm to 250 mm. As for the gas supply ambient air will be used as reference gas. A connector for calibration gas or air can be added on demand.

Pneumatic unit and automatic calibration
To operate the ZrO₂-probes, a reference gas as well as a test gas for calibration is required. The corresponding tubing includes pressure controller (or diaphragm pump), filter, switching valves and flow meter, all parts being mounted in a special sample cabinet. For the gas supply,
6 mm Schott terminals have been chosen. Power and signal connections are fitted to a row of terminals located in the sample cabinet. As reference gas ambient air or instrument air can be used.
Furthermore the automatic calibration of all AMS ZrO₂-probes within preselectable time periods is feasible while using the electronic unit AMS 3220.
Alternatively to the separate assembly of electronic controller and pneumatic unit both systems may be delivered installed in a single sample cabinet.

Electronic controller AMS 3220
The electronic controller AMS 3220 is the supply-control- and evaluation
unit for all AMS ZrO₂-probes; the unit can be delivered in several housing models. The measuring range for flue gas applications covers
0,1 - 25 vol-% Oxygen permitting the operator to adjust to the process values.
Considering process applications measuring ranges from 1 ppm to 100 vol-% O₂ can be applied. The calibration limits will be laid down in the E-PROM of the controller correspondingly.
Programming and controlling the entire measuring system will be executed with only three push buttons: one for the operation mode, two for the cursor. A display featuring two LCD rows indicates the measuring value and user fed data as well as the operation directions in plain text messages. A key operated switch locks The usually locked programming level is, if required, accessible via an specific service mode.
The self diagnostics of the controller with the corresponding fault signals reduce the usually time consuming monitoring to a reasonable extent.
All instrument parameters, e.g. the calibration and alarm data, the assignment of the display lines, and of the two analogue outputs can be comfortably set at the control unit.
Particularly important regarding the reliability of the O₂ measurement is of course the identification and hence the error message while calibrating: The stability of the measuring signal during calibration and the plausibility of the calculated correction data are subject to the continuous check from the electronic controller.

Extended application areas for the AMS ZrO₂-probes using the electronic controller AMS 3220
The electronioc controller AMS 3220 succeeds the model AMS 3211. While keeping the well known features some innovative functions have been integrated into the controller AMS 3220:

• TÜV-approval for large boilers in power plants, for industrial boilers and furnaces, for waste incinerators and for crematoria.
• TÜV-approved in compliance with European Directive 2000/76/EC for waste incinerators
• In connection with the appropriate pneumatic units for automatic calibration, it offers the AUTOCAL routine.
• For the EEx-d-probe, also an EEx-d-housing for the electronic unit can be offered. Depending upon the application, either an EEx-IIC- or an EEx-d-IIB-housing is available.
• The housing of the electronic unit is made from painted steel sheet; the enclosure complies with IP65 and warrants an improved dissipation of the heat produced.
• Signal from the sensor and heating power are galvanically isolated to keep away wandering signals.
• Galvanic separation of two 0/4 ... 20 mA outputs is standard as well as the digital interface RS232.
• An improved A/D-converter provides better resolution and the continuous measurement from 25 vol-% down to 1 ppm Oxygen.

Technical Data
Probes
Cabinets
Electronic controller AMS 3220