isa ad2015 adami mettler toledo v01.0

Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015

Session 10 / Paper No.2Maintaining TDL measurement accuracy in high temperature

applications

Jean-Nic Adami, Mettler-Toledo AG


Slide 2

Outline

TDL technology benefits

Path lengths effects

Influence of process temperature

External Temperature error

Spectral Temperature

Experimental setup

Conclusion


Slide 3

TDL's now fully established

High selectivity for the target gas species

In-situ analysis

Non-contacting

Fast response time

Dynamic measurement of process

Minimal calibration/validation requirements

Zero drift free


Slide 4

Cross-stack TDL's

Originally designed for long path length applications, i.e. combustion, DeNOx

Process Applications tend to be more challenging

Installation requirements in small pipes can be detrimental to measurement quality

• Challenge to keep alignment with varying temperatures


Slide 5

Effect of long path lengths

Concentration measurement over path length is averaged

Combustion control: ability to exclude leakage errors with over-the-burner location

Higher impact of dust load in process gas

Beam steering effects can lead to loss of transmission

But: what is the effective gas temperature over whole path? Temperature sensor is a point measurement Location of sensor very relevant for accuracy


Slide 6

Folded path probe design

Single-port installation

No alignment user-side

Suitable for small pipes (2" and above)

Concept is expandable to different process interfaces

More adapted to control applications in process


Slide 7

Effect of short effective path lengths

Wider choice of installation points

Collimated beam Improved SNR Dust tolerant

Detrimental to detection limit

Purge flow and process gas speed must be balanced

Possible T gradients over pipe length


Slide 8

Lambert Beer

• I0 : Initial intensity

• I : Signal intensity after crossing the gas

• S : Line strength

• L : Optical path length

• G : Line profile

• n : density concentration

][exp ),,()( nLGS TPT ×××−= νoI

I=τ


Slide 9

Temperature influence


Slide 10

Temperature influence


Slide 11

Sources of temperature errors

External temperature sensor too far away

Varying process gas temperature over path length Wall effects on small ID

pipes

Over the burner location

Filter on probe type process adaptions


Slide 12

Probe style TDL with filter

No process side purging

Filter for dust prevention

Automated filter blow-back

Low beam steering

Fixed path length


Slide 13

Probe style TDL with filter

Measurement-free zone (wall thickness) -100mm (standard)-200mm-300mm

Process window

Optical path lengths (effective) -200mm-400mm-800mm

Instrument side purge

Exchangeable metal filter -40 microns-100 microns-200 microns


Slide 14

Impact of temperature error

(% Relative error on % Oxygen in air reading at ambient pressure and 1m OPL)

T∆T= -3°C

∆T= -5°C

∆T= -15°C

∆T= -30°C

20°C 1.39 2.34 7.22 15.12100°C 1.24 2.08 6.4 13.38200°C 1.07 1.79 5.52 11.47300°C 0.94 1.58 4.83 9.99500°C 0.76 1.27 3.88 7.96


Slide 15

External temperature error

(Oxygen concentration in air measured in DN100 pipe with filter probe during temperature ramp to 225°C)

30% error on measurement ∆T approx. 40°C


Slide 16

Spectral temperature

S1 S2

( )( )

( )( ) ( )

−−

−=

0

0

2

0

102

01

2

1 11exp

TTk

hc

TS

TS

TS

TSEE


Slide 17

Spectral temperature measurement


Slide 18

Conclusion

Best measurement performance with TDL's can be obtained when effective process gas temperature is taken into account External temperature sensor location

Expected temperature gradients over long path lengths

Expected wall effects on short path TDL's

Best option is to use spectral temperature measurement to achieve full freedom from above sources of error

isa ad2015 adami mettler toledo v01.0

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