TDLTech Presentation 14

© TDL Sensors Ltd 2012

Tunable Laser Gas Monitoring


Very high sensitivity - ppt, ppb, ppm concentrations

Measure the gas you want without interference from other gases

Large dynamic range - 5 orders of magnitude

Absolute measurements

– no drift, no calibration, inherently linear

Real-time (10 Hz or faster response)

Very low maintenance

Does not wear out

Advantages of laser based gas analysers:



Based upon high-resolution

laser spectroscopy




Mid IRNear IRUV-Vis Visible


0.7-2.7 µm

Laser diodes, VCSELs

3-5 µm 4.2->12 µm

DFGs

QCLs


We use the IR spectral region for gas measurements

Tunable lasers available within this region



NIR Mid-IR

Each gas

absorbs light in

a characteristic

way.

Hydrogen Fluoride (HF)Carbon Dioxide (CO2)Nitric Oxide (NO)Ammonia (NH3)Carbon Monoxide (CO)Methane (CH4)Water (H2O)

This means that each gas has a unique spectrum or “fingerprint”.



Tunable

laser

PhotodetectorI0

Beer - Lambert Law:

LI

IT )(exp)(

0

Absorption

coefficientPathlengthTransmission

II0

Laser frequency tuned

I

Tra

nsm

issio

nSignal out

Gas

Gas in Gas out

Measurement cell

L


Laser wavelength is tuned rapidly – no photodetector filters

Spectra are recorded 1000s of times per second

Not affected by particulate attenuation or changes in mirror

reflectivity

Full spectrum analysis performed

Powerful pattern recognition signal processing methods used

Absolute concentration measured – no drifting like other

techniques



Full spectrum analysis performed

Powerful pattern recognition signal processing methods used

Absolute concentration measured – no drifting like other

techniques




Extractive gas analyser multipass optical cell


Very long pathlengths can be

achieved using a laser

- 7.6 m standard

- 70 m enhanced


Sample gas stream is often measured at

atmospheric pressure

However, TDL can also measure at

reduced sample pressure


Advantage of measuring at reduced

sample pressure


Reduced sample pressure advantages

•Very specific measurement(s)

•Multi-gas measurements with one laser

•Enhanced stability

•No liquid phase water

•No gas sample stream drying required


Example:

HCl 1 ppm

H2O 30 % Vol

emissions from a stack



1010 mbarA

Pathlength = 760 cm, Temperature = 360 K


-20 -10 0 +10


Peak widths narrow


-20 -10 0 +10

100 mbarA




-20 -10 0 +10

1010 mbarA




-20 -10 0 +10

100 mbarA




-2 -1 0 +1 +2

1010 mbarA



Isolated HCl peak

- even in the

presence of high

humidity

-2 -1 0 +1 +2

100 mbarA




Isolated HCl peak

Can also access H2O peaks to

report dry gas conc


-2 -1 0 +1 +2

100 mbarA



Technology

Contact

TDL Sensors Ltd48 Grafton Street

Manchester M13 9XXUnited Kingdom

Tel: +44 (0)161 606 [email protected]

www.tdlsensors.co.uk

TDLTech Presentation 14

Technology

Transcript of TDLTech Presentation 14