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5.1.5 Exhaust Gas Sampling
While ZrO2 sensor is capable of in-situ and non-sampling measurement essentially, exhaust gas sampling method should been considered for marine application. It is because diameter of exhaust pipe of large ships is mostly from one to two meters, or more, and difference of gas concentration between at the center and near the pipe wall, where existing sensor can be attached, is not confirmed.
For sample gas handling, there are gas sampling method by suction pump or air/water ejector, and non-sampling method where sensor is installed directly in the sample gas flow. Table 5.1.5.1 shows the comparison of several methods for gas sampling.
Table 5.1.5.1 Comparison of Gas Sampling Methods
| |
Suction pump |
Water ejector |
Air ejector |
Eliminate
Dust |
Filter
- Clean by compression air |
- Filter, clean by
- water Clean by compression air |
- Filter
- Clean by compression air |
Eliminate
Drain |
- Drain trap
- Gas cooler |
- Gas cooler |
- Heat above dew point |
Eliminate
Sox |
- Clean by water
- Activated carbon |
- Clean by water |
- Heat above dew point
- Improved sensor durability |
| Power source |
- Electricity |
- Water |
- Air |
| Measurement |
- Dry |
- Dry |
- Wet |
| Merit |
- No need drain out |
- Maintenance free |
- Maintenance free
- small space
- No need drain out |
| Demerit |
- Frequent maintenance
- Big space
- Need many spare parts
- Heated probe |
- Heated probe
- NO2
- solution Corrosion by sea water
- Need Drain out |
Direct connecting with
sensor and flange |
| Evaluation |
Good |
Fair |
Excellent |
|
From the point of view of space for installing the instrument, restriction of construction work (piping), maintenancebility and operationability, air ejector method is practical for gas sampling. Additionally, exhaust gas measurement with actual wet-base gas is possible by the air ejector method.
Figure 5.1.5.1 is a comparison of gas flow between CLD and ZrO2-type NOx analyzers in block diagrams. One can see that the air ejector method is simple and has excellent maintenancebility utilizing characteristic of ZrO2 sensor.
Figure 5.1.5.1 Gas flow diagrams of CLD and ZrO2-type NOx Sensor
Comparison of flow between CLD and ZrO2 type NOx analyzers
5.2 Example of marine application
5.2.1 Specifications and configuration of on-board NOx monitoring system
Table 5.2.1.1 shows specifications and operating conditions of NOx monitoring systems that were used on-board tests.
Table5.2.1.1 Specifications of NOx monitoring system and operating conditions
| Item |
Category |
Specification |
Note |
| Range |
NOx |
0〜2500 ppm |
|
| O2 |
0〜25 vol% |
|
| Accuracy |
Repeatability |
NOx |
±1 %FS |
|
| O2 |
±1 %FS |
|
| Linearity |
NOx |
±2 %FS |
|
| O2 |
±2 %FS |
|
| Response time |
NOx |
< 10 seconds |
Changing gas |
| O2 |
< 10 seconds |
| Output |
NOx |
DC 0〜1 V |
|
| O2 |
DC 0〜1 V |
|
| Conv. NOx(O2:13%) |
DC 0〜1 V |
|
| Warm-up |
|
30 minutes |
|
| Utility |
Power |
AC 100±10 V、
0.5 kVA |
|
| Compression Air |
0.5〜1MPa |
|
| Operating
conditions |
Transmitter |
-10〜+80degree |
|
| Receiver |
0〜+50degree |
|
| Data logger |
0〜50degree |
|
Gas
measurement
condition |
Temperature |
<550degree |
|
| Pressure |
±5 kPa |
|
| Flow rate |
<20 m/s |
|
|
| Test vessel |
IKOMASAN |
ANTARES |
B |
Condition
of NOx
monitoring
device |
Location of
installation |
Transmitter |
Pre
Economizer |
After
Economizer |
Pre Economizer |
| Receiver |
Control
panel |
Control
panel |
Control panel |
| Cal. Gas |
Under the
control panel |
Under the
control panel |
Under the
control panel |
| Rack |
C floor |
B floor |
- |
| Data logger |
Control
room |
Work
shop |
Control
room |
| Air ejector |
Pressure |
0.035
MPa |
0.1->0.035
MPa |
0.035
MPa |
| Flow rate |
5L/min. |
9->5L/min. |
5L/min. |
| Purge air |
Pressure |
0.2 Mpa |
0.2 MPa |
|
| Probe |
Size |
15 A, 500 mm |
15 A,500 mm |
15 A,500 mm |
| Calibration
gas |
Pressure |
0.1 MPa |
0.1 MPa |
0.1 MPa |
| Flow rate |
1L/min. |
1L/min. |
1L/min. |
| NO sapn |
1899 ppm
NO/N2 |
1906 ppm
NO/N2 |
1886 ppmNO/N2 |
| NO zero |
AIR |
AIR |
AIR |
| O2 span |
AIR |
AIR |
AIR |
| O2 zero |
NO span
gas |
NO span
gas |
NO span
gas |
| Out put |
NOx |
DC 0〜1 V |
DC 0〜1 V |
DC 0〜1 V |
| O2 |
DC 0〜1 V |
DC 0〜1 V |
DC 0〜1 V |
| Conv.NOx |
DC 0〜1 V |
DC 0〜1 V |
DC 0〜1 V |
|
Figures 5.2.1.1 to 5.2.1.3 show outlines and dimensions of NOx monitoring system in use.
Figure 5.2.1.1. Gas Sampling Probe and NOx Sensor
Figure 5.2.1.3 Control Panel with Receiver, and Data Logger
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