technology roadmap: optoelectronic gas sensors in the...

Technology Roadmap: Optoelectronic Gas Sensors in the

Petrochemicals, Gas and Water Industries

R W Bogue Robert Bogue & Partners

Issue: A.2

August 2006

Copyright © OptoCem.Net of 59

Table of Contents 1 INTRODUCTION ......................................................................................4

1.1 DISCLAIMER ................................................................................4 1.2 ABOUT OptoCem.Net.....................................................................4 1.3 SCOPE.........................................................................................4 1.4 OBJECTIVES.................................................................................4 1.5 METHOD AND DATA SOURCES........................................................5

1.5.1 Method .................................................................................5 1.5.2 Data sources .........................................................................6

1.6 ABBREVIATIONS AND TERMINOLOGY ..............................................7 1.7 SUMMARY....................................................................................8 1.8 COMMENTS AND FEEDBACK ...........................................................8 1.9 ACKNOWLEDGEMENTS ..................................................................8

2 OPTOELECTRONIC GAS SENSING: THE PRESENT-DAY SITUATION ......9 2.1 THE SENSOR INDUSTRY: PREAMBLE................................................9 2.2 SENSOR TECHNOLOGIES AND THEIR EXPLOITATION ....................... 10 2.3 GAS SENSING: THE PRESENT STATE OF THE ART............................ 11

2.3.1 GAS DETECTION METHODS ................................................... 11 2.3.2 GAS SENSING TECHNIQUES .................................................. 11 2.3.3 PRINCIPLES......................................................................... 14 2.3.3.1 Optical absorption ............................................................. 14 2.3.3.2 UV fluorescence ................................................................ 16 2.3.3.3 Chemiluminescence........................................................... 16 2.3.3.4 Photoionisation ................................................................. 16 2.3.3.5 DIAL ............................................................................... 17

2.4 PRODUCTS................................................................................. 18 2.5 APPLICATIONS ........................................................................... 19

2.5.1 OVERVIEW .......................................................................... 19 2.5.2 USE BY THE OptoCem.Net INDUSTRIES................................... 20

2.6 MARKETS AND FORECASTS .......................................................... 22 2.6.1 EUROPEAN AND GLOBAL MARKETS ......................................... 22 2.6.2 SOME MARKETS WITHIN THE OptoCem.Net INDUSTRIES........... 23 2.6.3 UK GAS SENSOR PRODUCTION .............................................. 23

2.7 THE SUPPLY SECTOR................................................................... 24 2.7.1 INTRODUCTION ................................................................... 24 2.7.2 SENSOR MANUFACTURING COMPANIES................................... 24 2.7.2.1 Overview ......................................................................... 24 2.7.2.2 OEM sensor supply ............................................................ 25

3 THE FUTURE......................................................................................... 27 3.1 DRIVERS FOR CHANGE ................................................................ 27 3.2 SPECIFIC REQUIREMENTS............................................................ 28 3.3 R&D AND NEW TECHNOLOGIES .................................................... 31

3.3.1 OVERVIEW .......................................................................... 31 3.3.2 SPECIFIC TECHNOLOGIES AND DEVELOPMENTS ....................... 33 3.3.2.1 Introduction ..................................................................... 33 3.3.2.2 Optical sources and detectors ............................................. 33 3.3.2.3 MEMS technology.............................................................. 37

3.3.3 KEY TECHNOLOGIES............................................................. 38 3.3.4 THE UK ACADEMIC ACTIVITY ................................................. 39

3.4 PRODUCT DEVELOPMENT ROADMAPS ............................................ 41 3.4.1 INTRODUCTION ................................................................... 41 3.4.2 DEVELOPMENT ROADMAPS .................................................... 43

3.5 INDUSTRY ROADMAPS................................................................. 54 3.5.1 INTRODUCTION ................................................................... 54 3.5.2 WATER INDUSTRY ................................................................ 55


3.5.3 GAS INDUSTRY .................................................................... 56 3.5.4 PETROCHEMICALS INDUSTRY ................................................ 57

4 References ........................................................................................... 59

Issue History

Date Issue Details 31Aug06 A.2 First public release version


1 INTRODUCTION

1.1 DISCLAIMER The information contained herein is presented in good faith. However, the author, the SOA, the DTI and all other individuals and parties associated with the OptoCem.Net project take no responsibility whatsoever for its accuracy or for any losses or other consequences arising of its interpretation or use.

1.2 ABOUT OptoCem.Net OptoCem.Net is a DTI Knowledge Transfer Network (KTN), beginning in April 2005 and running initially for three years, which aims to stimulate collaborative research, development, commercial exploitation and best use of optoelectronic gas and chemical sensing in the UK. OptoCem.Net is managed by a Consortium comprising the SOA (Scottish Optoelectronics Association), SWIG (Sensors for Water Interest Group), GASG (Gas Analysis and Sensing Group) and Scottish Water. UK organisations and individuals with interests in optoelectronic gas or chemical sensing (and overseas organisations with production or R&D facilities in the UK), are invited to participate. Involvement is free of charge. For further information see www.optocem.net.

1.3 SCOPE This document is concerned with optoelectronic gas sensors which are defined here as sensors that respond to gases and vapours and which operate via optical phenomena such as absorption or fluorescence. The term “sensor” is interpreted broadly to include simple devices such as single point sensors through to more complex products such as ambient air quality analysers and continuous emission monitors. The industries considered are restricted to those covered by the OptoCem.Net KTN, i.e.

• Petrochemicals; • Gas supply; • Water and wastewater.

All applications within these industries are included, e.g. health and safety, environmental monitoring, process control etc. and whilst the emphasis is on the UK, several opportunities and technological developments are relevant in a broader and often global context.

1.4 OBJECTIVES The broad objectives of this document are twofold: to characterise the present status of optoelectronic gas sensing (Chapter 2) and to identify future


technological and product developments and their applications within the OptoCem.Net industries (Chapter 3). Chapter 2 considers:

• The nature of overall sensor industry; • Gas sensing principles and techniques; • Products; • Applications; • The supply companies; • Markets and forecasts.

It should be stressed that a market-led approach has been adopted in considering the future and Chapter 3 is largely centred around needs and opportunities identified by the users. It considers:

• The drivers for change; • Emerging needs and opportunities; • Technological developments; • The UK academic research effort; • Product developments and timescales; • Industry roadmaps.

1.5 METHOD AND DATA SOURCES 1.5.1 Method This document was compiled over a period of many months and was conducted in several stages, as illustrated in Figure 1. The first stage, which was to define the present-day status of optical gas sensing, was largely compiled from data at hand and was supplemented by discussions with sensor manufacturers and users. This was followed by a lengthy data acquisition phase which involved a series of face-to-face meetings and telephone discussions with sensor users and decision makers from the three main industries concerned. The aim was to identify key drivers for change and needs and opportunities for new and improved gas sensing products. (These are considered in detail in a separate OptoCem.Net document: “Needs and opportunities for new and improved gas sensors”). In addition, this project phase quantified, as far as was realistically possible, the size of the potential markets for these products (see the above document). New and emerging technologies were subsequently identified and considered in the context of their potential to meet the previously identified needs and led to a series of product development charts. These were then used to create the three industry roadmaps.


Figure 1 - Methodology

1.5.2 Data sources The information in this document was derived from the following sources.

• Telephone and face-to-face discussions with sensor manufacturers, users, legislators and researchers;

• Company and university web sites; • Product literature; • Technical and commercial reports; • The Micro and Nanotechnology (MNT) Gas Sensors Forum (see:

http://www.gas-sensor-roadmap.com); • Trade and technical press; • Research literature.

Defining present-

day status of optical

gas sensing

Identifying needs and

opportunities for new

sensors and key market

drivers

Review and

appraisal of R&D

and new technology

Information at hand, inputs from sensor users and

manufacturers

Inputs from sensor users

and legislators

etc.

Inputs from academics and sensor

manufacturers

Establishing technological solutions and

product development timescales

Literature review, inputs

from academics and sensor

manufacturers

Creation of three industry

roadmaps showing

adoption of new products and technologies


1.6 ABBREVIATIONS AND TERMINOLOGY The following abbreviations are used: AQ Air quality BTEX Benzene, toluene, ethylbenzene, xylene CEM Continuous emission monitor CHP Combined heat and power CNT Carbon nanotube CRDS Cavity ring-down spectroscopy CW Continuous wave DIAL Differential absorption LIDAR (see below) DOAS Differential optical absorption spectroscopy DUV Deep ultra-violet EC Electrochemical (sensor) FID Flame ionisation detector FTIR Fourier transform infra-red GasFET Gas-responsive field-effect transistor GASG Gas Analysis and Sensing Group GC Gas chromatograph HC Hydrocarbon (unspecified) IMS Ion mobility spectrometry IR Infra-red LED Light emitting diode LEL Lower explosive limit LIDAR Light detection and ranging LNG Liquid natural gas LOD Limit of detection LPG Liquid petroleum gas MEMS Micro-electromechanical systems MNT Micro and Nanotechnology MS Mass spectrometer NDIR Non-dispersive infra-red (absorption) NIR Near infra-red OES Occupational exposure standard OPO Optical parametric oscillator PAS Photoacoustic absorption spectroscopy PID Photo-ionisation detector PMT Photomultiplier tube ppb Parts per billion ppm Parts per million QCL Quantum cascade laser SPR Surface plasmon resonance TDLAS Tuneable diode laser absorption spectroscopy UV Ultra-violet VECSEL Vertical external cavity surface emitting laser VOC Volatile organic compound Well known gases are designated by their chemical formulae (e.g. H2S, CO, NO2). The chemical names of lesser known compounds are written in full (e.g. propylene oxide, dimethyl sulphide). The term NOx is used to designate unspecified or mixed oxides of nitrogen.


1.7 SUMMARY Following a general introduction, the first section of this document (Chapter 2) describes in some detail the present state of the optical gas sensing industry by considering the underlying principles and techniques, the major product types and their applications, markets and market forecasts and the nature of the supply companies. This is probably of greatest interest to those who are not presently involved with optical gas sensing. Chapter 3 considers future prospects, with an emphasis on developments that will impact the three main OptoCem.Net industries during the next decade. It firstly identifies the factors driving change within these industries and subsequently lists a number of needs and opportunities for new products, identified by end-users. It then considers key technologies and discusses those that are expected to facilitate the development of the previously identified products. Following a brief discussion of the UK academic research effort, a series of product development charts identify applications, the critical technologies and timescales. Finally, Roadmap Summary Charts show, in graphical form, the anticipated application of new products and technologies by the three OptoCem.Net industries.

1.8 COMMENTS AND FEEDBACK Readers are invited (and encouraged) to comment on this document. All such correspondence should be addressed to the author, Robert Bogue, by e-mail: [email protected].

1.9 ACKNOWLEDGEMENTS The author hereby acknowledges the inputs made by the numerous individuals who kindly contributed to this document.


2 OPTOELECTRONIC GAS SENSING: THE PRESENT-DAY SITUATION

2.1 THE SENSOR INDUSTRY: PREAMBLE Unlike fields such as computers or mobile phones, the sensor industry does not progress in a linear manner with clearly defined product generations, each being more sophisticated and advanced than its predecessors and arising from clear-cut technological developments. There are neither any universal, unsatisfied requirements nor any technologies poised to revolutionise the industry. Oft-quoted “needs” such as those for miniaturisation or improved accuracy are in reality far from universal and are only of genuine benefit in specific instances. Even within the confines of OptoCem.Net, with its emphasis on the optoelectronic sensing of chemical species in a limited number of industries, needs and opportunities vary enormously and are highly application-specific. They can arise from a many factors, as illustrated in Figure 2.

Figure 2 – Factors driving the needs for sensors

Economic Reduced testing

& material costs, process automation,

energy consumption,etc

Political Control of

trans-boundary pollution,

compliance with EU directives,

etc.

Technological Improved

performance, sensing new

variables, new capabilities, etc.

Social Concerns over air and water quality, safety and security

etc.

Legislative Health & safety, environment,

avoiding prosecution etc.

NEEDS FOR

SENSORS


2.2 SENSOR TECHNOLOGIES AND THEIR EXPLOITATION

Today’s sensor markets are served by tens of thousands of products which respond to well over 100 different physical and chemical variables. These are based on a diversity of techniques and technologies and despite recent innovations, several have been in existence for well over half a century. They maintain their market position through an often subtle combination of technical, economic and other application-specific factors. Consequently, new sensor technologies often struggle to exert a significant commercial impact and frequently only satisfy limited applications where particular features confer real benefits; fibre optic sensors and biosensors are good examples. Even much vaunted technologies such as silicon MEMS have only impacted the overall sensor industry to a limited degree. This is even the case in sectors such as the automotive industry, where the requirements are for small, rugged, reliable and very low cost devices where MEMS sensors appear ideally suited, they have only satisfied part of the market. In some instances, a technological development may lie dormant for many years until such time that an application emerges where its features meet that particular requirement. Silicon accelerometers are good examples. First developed in the 1970s, for many years they only satisfied niche applications in the aerospace and defence markets but tens of millions are now used annually as the trigger for vehicle air bags. In other cases, often following decades of research, significant applications for a particular technology with seemingly strong market potential have failed to emerge. Examples include silicon GasFETs and ISFETs and fibre optic gas sensors. In addition to the commercialisation of new technological developments, innovative products can arise as a result of a company identifying a particular market opportunity and addressing it though the use of an existing but hitherto largely unexploited technique or technology. For instance, the ability of oxygen to quench fluorescence in certain organo-metallic compounds has been known for decades but it is only during the last five years that this effect has been exploited in advanced dissolved oxygen sensors.


2.3 GAS SENSING: THE PRESENT STATE OF THE ART 2.3.1 GAS DETECTION METHODS To understand the competitive gas sensing landscape, it is important to recognise that, in addition to sensors, several other techniques are used within the overall gas detection field (Figure 3). This reflects several factors, such as cost, the lack of sensors for some gases or particular operational requirements (resolution, specificity etc.).

Figure 3 – Gas detection techniques

All gas detection

2.3.2 GAS SENSING TECHNIQUES Gas sensors are based on many different techniques and technologies which co-exist in the marketplace due to their particular capabilities; there is some, but relatively little, competition between them. Table 1 and Table 2 list the more important classes of non-optical and optical gas sensors, together with examples of their uses.

Detector

Tubes

Gas Sensors

Analytical Techniques

Exposure Badges


Table 1 – Non-optical gas sensing techniques and their uses

Sensor type

Respond to

Typical applications

Catalytic (pellistors)

All combustible gases (non-selectively)

Fire and explosion prevention

Wet electrolyte (electrochemical)

Oxygen, many toxic species, environnemental pollutants, combustion products

Occupational health and safety, combustion monitoring, medical etc.

Solid electrolyte (zirconia)

Oxygen

Industrial combustion monitoring and control, vehicle exhausts (lambda sensors)

Metal oxide semiconductor

HCs, CO, O3, H2S, organic vapours, aromas etc.

Leak detection, health and safety monitoring, in- vehicle air quality etc.

Paramagnetic

Oxygen

Medical, process control and monitoring etc.

Thermal conductivity

Binary gas mixtures (often a known gas in air)

Leak detection, process control etc.

IMS

Wide range of organic and inorganic compounds

Mainly military uses (detecting chemical warfare agents) etc.

FIDs

Methane, organic vapours (non-selective)

Landfill site monitoring, occupational health and safety, leak detection etc.


Table 2 – Optical gas sensing techniques and their uses

Sensor type

Respond to


NDIR

Many mid-IR absorbing species, e.g. CO2, CO, CH4, H2O, NO etc.

Stack emissions, health and safety, food storage and packaging, medical gas analysis etc.

FTIR

Many IR absorbing species

Stack emissions, trace gas analysis, environmental monitoring, process monitoring etc.

PAS


Trace gas analysis

TDLAS


Emerging uses, e.g. stack emissions, trace gas and moisture analysis etc.

CRDS


Emerging uses, e.g. trace gas and moisture analysis etc.

DIAL

Many species that absorb at IR, visible and UV wavelengths

Remote detection of gases in the atmosphere and around industrial plant etc.

UV absorption

O3, NO, H2S, HCl etc.

Ambient AQ monitoring, stack emissions etc.

UV fluorescence

SO2 (modified variant for H2S)

Ambient AQ monitoring

UV DOAS

O3, H2S, NH3, C6H6, NO2 etc.

Environmental AQ monitoring

Chemiluminescence

NOx (NO, NO2)

Ambient AQ monitoring, stack emissions

Photoionisation

VOCs

Health and safety


2.3.3 PRINCIPLES This sub-section briefly describes the principles that underpin the techniques listed in Table 2, above. 2.3.3.1 Optical absorption Many of the most important optical gas sensing techniques exploit absorption which is, therefore, a critical effect. This is because many combustible and toxic gases have strong fundamental absorption bands in the 2-5 µm (mid-IR) region of the spectrum, as below and shown in Figure 4.

CH4 3.3 µm H2S 2.7 µm CO2 4.2 µm CO 4.6 µm NH3 2.3 µm

Figure 4 – Some fundamental gas absorption peaks in the mid-IR

In the mid-IR, the fundamental absorption is normally measured as this may be several orders of magnitude stronger than the overtone vibrational-rotational bands in the NIR, (although overtones in NIR are starting to be used as a way to employ components from the telecoms industry). Absorption is characterised by the Beer-Lambert gas absorption law which may be written: I(λ) = I0(λ) exp-[Lσ(λ)C] [2.1] Where I(λ) is the light intensity at wavelength λ after it has passed through a layer of gas of thickness (or length) L; I0(λ) is the initial intensity of the transmitted light at wavelength λ; σ(λ) is the gas absorption cross-section at wavelength λ; and C is the gas concentration. Given the values of σ(λ) and L in equation [2.1], the gas concentration can be determined from the measured ratio I0(λ)/I(λ), i.e.

C = log [I0(λ)/I(λ)]/[σ(λ)L] [2.2]


Some of the gases commonly detected by absorption at UV and IR wavelengths are shown in Table 3.

Table 3 – Some gases commonly detected by optical absorption

Spectral region Gas species

IR

CO, CO2, CH4, NO, SF6, NH3, H2O, HCl

UV

O3, H2S, SO2, NO, NO2, NH3, C6H6, Cl2

The more important techniques that exploit absorption are described briefly in Table 4. Note that some of these terms are poorly defined and used somewhat indiscriminately. Whilst DIAL exploits absorption, it also relies on backscatter and is considered separately (see Section 2.3.3.5 below).

Table 4 – Absorption-based gas sensing techniques Technique

Principle of operation

NDIR Most simple technique. IR is absorbed by the target gas in path between source and detector. Absorption wavelength is selected by optical filters. Some types employ a second reference beam

Gas filter correlation spectroscopy

Two cells, one containing the target gas the other a non-absorbing gas, are alternately placed in the beam. Difference in detected radiation equates to concentration of the target gas

UV absorption Absorption of UV light at wavelength specific to target gas, e.g. 254 nm for O3. Effectively the UV analogue of NDIR. Can be open-path, i.e. using solar radiation to detect atmospheric O3

UV DOAS Open-path technique, generally using UV/visible wavelengths. Difference in signal intensity for absorbing and non-absorbing wavelengths used to determine gas concentration in optical beam

PAS Pressure waves arising from gas absorbing pulsed IR energy at a particular wavelength within a sealed sample cell are detected by high sensitivity microphones. High resolution technique

TDLAS IR absorption using a tuneable diode laser as the source. High sensitivity technique often using multi-pass cells to increase path-length/resolution

CRDS Measurement of the decay time of the IR light as it is multiply reflected and absorbed between two mirrors within a cell


containing the gas sample. Effective path-length of several km leads to high sensitivity

FTIR Light enters a Michelson interferometer before passing through the gas sample creating an interferogram which is analysed by calculating its Fourier Transform to yield wavelength spectrum. Good for multi-component sensing

2.3.3.2 UV fluorescence UV fluorescence relies on a gas molecule (usually SO2) being excited from its ground state (S0) to an excited state (S*) when illuminated by UV light with a frequency v. On returning to the ground state, the molecule emits light at a characteristic frequency (v1), i.e.

S0 + hv --> S* [2.3]

S* --> S0 + hv1 [2.4]

Where h is Planck’s constant. The intensity of the emitted light is proportional to the gas concentration. The technique can also be used to determine trace levels of H2S. This involves first converting the gas into SO2 with O3, i.e. H2S + O3 � SO2 + H2O and then detecting the SO2 as above. 2.3.3.3 Chemiluminescence To detect NO, an excited NO2 molecule NO2

* is generated by an oxidising reaction between NO and O3. This emits light at a characteristic wavelength/frequency (v) when it returns to the ground state, i.e.

NO + O3 --> NO2* + O2 [2.5]

NO2* --> NO2 + hv [2.6]

The amount of light generated (v) is approximately proportional to the NO concentration. In the case of NO2 detection, this gas is first reduced to NO within the instrument and subsequently detected as above. Many instruments can determine both NO and NO2. 2.3.3.4 Photoionisation This relies on a gas sample entering a chamber with 2 (or sometimes 3) electrodes across which is applied a polarising voltage and which is illuminated with short wavelength light, typically in the DUV (i.e. λ=120 nm). This ionises any gases present whose ionisation potentials are less than the light source’s energy, typically ~10 eV for a 120 nm DUV source. The ionisation causes a current to flow between the electrodes which is proportional to the gas concentration. The technique is non-selective and limited to gases whose ionisation potentials meet the above criteria.


2.3.3.5 DIAL This technique entails a high power, pulsed laser beam which is modulated at two wavelengths – one which will be absorbed by the target gas (the “on” wavelength) and one which will not (the “off” wavelength). The beam is aimed at the target, such as the lower atmosphere or the air above an industrial site, and some is back-scattered by airborne particles or molecules to a high sensitivity detector. On its return the intensity of the on wavelength is attenuated by the target gas whilst the off signal remains unaffected. The difference in intensity between the two signals equates to the gas concentration. By timing the pulses, the distance to the target gas can be determined, thus yielding a range-resolved measure of the gas concentration. Several factors come into play and the equations governing this principle are quite complex.


2.4 PRODUCTS A bewildering number of optical gas sensing products exist, ranging from simple, point sensing devices to large and complex instruments offering analytical capabilities. Further, some manufacturers market bare sensors rather than complete instruments (see Section 2.7.2.2 below). In addition to the differing techniques employed, products can be categorised in several ways, as shown in Table 5.

Table 5 – Some optical gas sensor variants

Portability

Measuring mode

Respond to

Point sensing Open-path sensing

Single point

Multi-point

Non-range-

resolved (e.g.

DOAS)

Range-resolved (DIAL)

Single gas

Multiple gases

Hand portable Transportable

Fixed

Some of the major classes of products are described briefly in Table 6.

Table 6 – Optical gas sensing products and techniques

Product

Techniques

Description

CEMs

NDIR, FTIR, TDLAS, UV absorption etc.

Often complex instruments, making extractive or in situ measurements in hostile stack gas/flue environments. Many can measure several gases simultaneously

Ambient AQ monitors

NDIR, FTIR, UV fluorescence, UV absorption/DOAS, chemiluminescence

Often complex, fixed or transportable instruments. Most are point sensing but open-path devices (e.g. DOAS, FTIR) exist which can monitor several different gases and give a path length-integrated measure of the gas concentration, e.g. in ppm metres

IR sensors and instruments

NDIR

Fixed single and multi-point sensors and portable instruments based on NDIR. Also open-path types (as above)


Trace gas analysers

CRDS, PAS, FTIR, TDLAS etc.

Fixed, often lab-based high resolution instruments, some offering multi-gas sensing capabilities

DIAL systems

Backscatter/absorption (IR, visible, UV)

Large, complex and costly systems, comprising lasers, detectors and signal processing electronics etc., typically housed in a van or articulated truck

Other products

Absorption, backscatter, photo ionisation etc.

Portable PIDs, paper tape analysers (for H2S), gas imaging systems etc.

2.5 APPLICATIONS 2.5.1 OVERVIEW Gas sensors satisfy a diversity of applications in numerous different industries, although the optical sector is somewhat less fragmented. The leading applications for the major optical product types are shown in Table 7 below. The portable and fixed instrument category (based on NDIR) constitutes the most fragmented sector, both in terms of the user-industries and applications.

Table 7 – Applications of the key classes of optical gas sensors

User industries

Product type

Applications Power generation, petrochemicals, chemicals, waste incineration, other process industries (glass, cement, metals etc.)

CEMs

Quantifying gaseous stack emissions to atmosphere, often stipulated by environmental legislation Local authorities, national and regional AQ system operators, environmental consultancies, researchers etc.

Ambient AQ monitors

Quantifying key atmospheric pollutants. Data are often used in regional and national AQ reporting schemes


Petrochemicals, chemicals, offshore, process sector, water/waste, medical, food and drink, horticulture, HVAC, landfill etc.

Portable/fixed instruments (NDIR)

Flammable gas detection (safety), occupational health monitoring, control of atmospheres in food storage and packaging, indoor AQ, monitoring anaesthetic gases etc. Petrochemicals, chemicals, other process industries

PID-based instruments

Occupational health monitoring for toxic VOCs etc. Petrochemicals, chemicals, semiconductors, gas supply, medical, pure gas production etc.

Trace gas analysers

Detecting impurities and contamination in pure or process gases, leak detection, process monitoring etc. Petrochemicals, chemicals, process industries, environmental protection agencies and researchers

DIAL systems

Emission and environmental monitoring, atmospheric research etc.

2.5.2 USE BY THE OptoCem.Net INDUSTRIES The major gas sensing applications for the industries under consideration by OptoCem.Net, together with the more important gases monitored, are shown in Table 8 below. Note than many of these measurements are made by non-optical sensors, e.g. EC and catalytic types.


Table 8 – Gas sensor uses by the OptoCem.Net industries

Industry

Application

Typical gases

sensed

Leak detection (field)

CH4

Processing/distribution

CH4,water vapour, H2S, odours

Gas supply

Safety (plant)

CH4

Safety

CH4, other combustibles

Health

CO, O2 deficiency, Cl2, O3, CO2, H2S

Water/ Wastewater

Other uses

H2S/odours, CH4 (in CHP systems)

Safety

CH4, HCs, H2, other combustibles

Health

CO, CO2, HF, H2S, VOCs, BTEX, HCN, propylene oxide, O2 deficiency etc.

Process monitoring and control

O2, H2, CO, H2S, COS, NH3, arsine, water vapour, ethane, ethylene etc.

Petrochemicals

Environment

NOx, SO2, CO, CO2, NH3 etc.


2.6 MARKETS AND FORECASTS 2.6.1 EUROPEAN AND GLOBAL MARKETS No data are known of which quantify and segment the entire gas sensing instrumentation market in the UK, or elsewhere, let alone the optical sector. However, various figures have been published which cover parts of the whole, as below. Various industry experts have estimated the value of the global gas sensing/detection industry at something in the region of US$ 1 billion per annum. According to Frost & Sullivan, the European “Gas Sensors and Analysers” market was valued at US$ 283.9 million in 2004. IR gas sensors accounted for US$ 112.4 million, 40 percent of the total revenue. Demand for IR sensors is forecast to continue over the next few years as applications for the technology increase, with revenues reaching US$ 133.3 million in 2007. (The UK is generally estimated to constitute around 20% of the Western European total). The report also states: “More demand for infrared gas sensors has kept the gas sensors and analysers market moving upward at a time when there have been few technological advancements in the field. Initially, growth within the IR gas sensors sector was slow due to the size and cost of the technology, but improvements in these areas and performance now outstrips other available technologies”. The report also noted that: “Growth comes at a cost. The advent of smaller, cheaper IR sensors with low power consumption has made the technology more accessible to a wider range of applications. However, much of this growth has come at the cost of declining revenue shares for other technologies, catalytic gas sensors in particular. If market growth is to increase, gas analyser manufacturers must invest more money into research and development so that new technologies and techniques can be exploited”. Further, the report states “The chemicals and pharmaceuticals industries continue to provide growing demand for industrial gas sensors. These industries are extremely lucrative and competition is high”. The petrochemical and oil and gas refinery industries are expected to represent an important area of growth over the next few years. Also according to Frost & Sullivan (report no. 3682), the Western European market for all “Air pollution monitoring equipment” will have reached US$ 300.2 million by 2005. About 50% of this is accounted for by ambient air quality monitors and CEMs, i.e. ~US$ 150 million, and the majority are optical (NDIR, chemiluminescence, UV absorption etc.). The report notes that stack emission monitors are used extensively by the chemicals, petrochemicals and other process industries. An American market study, published in 2005, states that the total worldwide market for “Process Spectroscopy Instrumentation” is expected to rise from US$ 178 million in 2004 to US$ 232 million in 2009, at an average annual growth rate of 5.4%. Europe probably constitutes around one third of this. Another recent American study (McIlvaine Company, 2006) predicts that the global CEM market will rise from its 2005 value of US$ 446 million/annum to US$ 583 million/annum by 2009. It identifies mercury CEMs as a high growth sector.


2.6.2 SOME MARKETS WITHIN THE OptoCem.Net INDUSTRIES The UK water and wastewater industries are believed to consume in the order of 18-24,000 EC sensors annually, broken down between the major gases as below.

Gas Percentage

O2 44%

H2S 28%

CO 17%

Cl2 8%

Others 3%

It is estimated that these industries and their contractors presently employ something in the order of 6-8,000 portable multi-parameter instruments which measure between 3 and 5 different gases, notably CH4/combustibles, O2 deficiency and H2S, with product options on CO2, CO and Cl2 etc. Many applications concern confined space entry into sewers and pumping stations etc. The gas supply industry makes extensive use of portable gas leak detection instruments. It is estimated that NGT (National Grid Transco) and the regional gas network operators have around 12-14,000 of these. In addition, fixed-point detectors and personal monitors for combustible gases are used widely. As illustrated in Table 8, the petrochemicals sector is a major user of gas sensors. For example, the Shell refinery at Stanlow has around 100 fixed-point H2S sensors installed and a medium-sized offshore platform employs around 300-500 optical (and some catalytic) combustible gas sensors. 2.6.3 UK GAS SENSOR PRODUCTION The UK is a major producer of gas sensors and well over two million, probably closer to three million, are manufactured annually. The majority are EC and catalytic and others include NDIR, other optical types, paramagnetic and metal oxide. These are incorporated into instruments produced in the UK which are either sold to domestic users or exported to overseas users, and also exported directly to overseas instrument manufacturers.


2.7 THE SUPPLY SECTOR 2.7.1 INTRODUCTION The UK has had a long and auspicious history in gas sensing and a strong record of developing new and innovative technologies. The ubiquitous catalytic sensor (“pellistor”) was developed in the UK in 1958; Sieger was founded a year later and became a major, international supplier of gas detection equipment; since being founded in 1977, City Technology has pioneered EC sensors and is now the European market leader; e2v (formerly EEV) is Europe’s leading manufacturer of catalytic sensors; Sixth Sense (now part of Honeywell) is the world’s leading supplier of EC CO sensors; Capteur (now part of City) created a generation of advanced metal oxide sensors using technology from London University (UCL) and Harwell; a UMIST spin-off pioneered the commercialisation of the electronic nose in the UK; AMGas is manufacturing IR combustible gas sensors based on advanced LED technology developed at DERA - the list goes on. 2.7.2 SENSOR MANUFACTURING COMPANIES 2.7.2.1 Overview The UK gas detection industry is served by a large number of domestic manufacturers and overseas companies from continental Europe, Japan, the US and elsewhere, some of whom manufacture in the UK. Companies include large, diversified multinationals (e.g. Siemens, ABB, Honeywell, Emerson/Rosemount); the large gas detection specialists (MSA, Draeger); numerous medium-sized and small specialists (UK examples include City Technology, AMGas, Crowcon and many others); and a growing number of university spin-offs. Some of these working on advanced optical techniques are listed in Table 9.

Table 9 – UK university spin-offs involved with advanced optical gas sensing technology

Company

University

Products/Technologies

TDL Sensors www.tdlsensors.co.uk

Manchester

TDL sensors and systems

Oxford Medical Diagnostics

Oxford

Cavity-enhanced laser absorption spectroscopy

Cascade Technologies www.cascade-technologies.com

Strathclyde

Quantum cascade laser systems

OptoSci www.optosci.com

Strathclyde

Fibre optic gas sensors and systems


With the exception of the diversified multinationals, most companies in this business are relatively small, with turnovers of <£100 million. Even Draeger, perhaps the world’s largest gas detection equipment manufacturer, only achieved a 2004 turnover of €510 million for its Safety Division which include all its gas detection and other safety products (total group turnover = €1,523 million). Interestingly, being an SME does not appear to hinder doing business with large users – one such UK company with a mere 20 employees has successfully sold its gas sensing products to most of the big names in the offshore sector. As with much of the sensing and instrumentation sector, recent years have seen the gas sensor supply industry in a highly dynamic state, with many acquisitions and mergers. Equally, several new companies have emerged, often as a result of the above. Some of the most significant recent changes have been:

• The acquisition of City Technology by the First Technology Group (2005 turnover = £163 million), which since acquired Capteur, EnviteC, MST Technology, Sensoric and BW Technologies (an instrument maker rather than a sensor manufacturer);

• Honeywell’s purchase of Zellweger which in the past acquired Sieger,

Neotronics and several other well known names in the business; • Honeywell’s acquisition of the First Technology Group in 2006.

2.7.2.2 OEM sensor supply Some companies just supply bare sensors as there is a large community of gas detection instrument manufacturers who do not produce their own sensors (or all of the types used), in-house. Crowcon is perhaps the best known in the UK. This (optical OEM) market sector is of quite recent origin and whilst the supply of bare sensors for incorporation into finished products has been the norm within the EC, metal oxide and catalytic sensor sectors for several decades, it is only during the last few years that NDIR sensors have been supplied as components in any significant quantities. This reflects a number of factors which illustrate well the complexities associated with, and the application-specific nature of, the adoption of a particular gas sensing technology, i.e. • Growing requirements to monitor CO2 (still impossible with EC or other

inexpensive gas sensors); • Replacement of growing numbers of catalytic sensors by overcoming some of

their operational limitations; • The ability to monitor two gases simultaneously with a single sensor (e.g. CO2

and CH4, ideal for landfill gas monitoring); • Improved designs leading to better performance; • Cost reductions arising from growing sales volumes. (According to a study by

Frost & Sullivan, the average price of an NDIR gas sensor has halved in recent years).

A more recent innovation is City Technology’s launch, in May 2005, of an OEM PID sensor. Whilst PID-based instruments have been used in relatively small numbers for many years, this makes the technique available to a far greater number of instrument manufacturers. This launch again reflects several factors, the most significant being the recognition that several VOCs (benzene, hexane, toluene etc.) are chronically toxic at low ppm levels, well below their LELs, making detection with catalytic sensors of no real value from the health viewpoint. National safety organisations are issuing low occupational exposure


limits for many VOCs, often associated with confined space entry applications. Improved design has also played a role and the City PID features an additional (third) electrode which confers improved performance and a longer operating life from the UV lamp. Further, growing sales volumes will lead to falling prices. The UK is amongst the world leaders in the manufacture and supply of OEM gas sensors (although Japan dominates the metal oxide sector), as illustrated in Table 10. Companies such as these have arisen in recognition of the fact that the sensors have the potential to sell in sufficient volumes to create a profitable business without the need to become involved in complex instrument design and manufacture.

Table 10 – Some UK OEM gas sensor manufacturers

Company

Sensor types

City Technology/ Capteur

EC, catalytic, NDIR, PID, metal oxide

AlphaSense

EC, NDIR, catalytic, solid electrolyte (for CO2)

e2v

NDIR, catalytic

Monox

EC (for CO only)

Sixth Sense

EC, catalytic

Dynament

NDIR

Edinburgh Sensors

NDIR


3 THE FUTURE

3.1 DRIVERS FOR CHANGE The gas sensing industry is in a highly dynamic state: markets are growing, new applications are emerging and the research effort continues to expand in a multitude of directions. Most importantly, gas sensor users are coming under mounting economic, legislative and other pressures (Table 11) which will exert a significant impact on existing and future sensing, monitoring and control practices.

Table 11 – Some pressures facing industry

Pressures

Ever more stringent environmental legislation

Carbon taxes and credit trading schemes

Rising fuel and energy prices

An ever more competitive business environment leading to a need to reduce operating costs

Desire for increased productivity and reduced waste

Reduction in skilled manpower (e.g. instrument and process engineers)

Health and safety legislation

Growing public concern over safety, the environment and business ethics

Discussions with OptoCem.Net industry users led to the identification of a number of factors which will stimulate the development of new and improved gas sensors, some of which relate directly to the issues listed in Table 11. These are listed in Table 12. Many are specific to particular sensor types or applications and none are truly “generic”.


Table 12 – Factors driving gas sensor developments

Factors

Requirement for reduced purchase prices

Requirement for reduced ownership costs

More rugged and reliable

Greater specificity/reduced cross-reactivities

Requirement for reduced calibration and maintenance

Improved environmental performance

Reduced response/recovery times

Wider measuring ranges

Requirement for real-time sensing methods

Longer operating/field lives

No sensors exist for certain target gases

3.2 SPECIFIC REQUIREMENTS Further discussions OptoCem.Net industry users led to the identification of a number of specific needs and opportunities for improved gas sensors. These are summarised in Table 13 and full technical and commercial details can be found on the OptoCem.Net web site in a document entitled “Needs and opportunities for new and improved gas sensors”.


Table 13 – Needs and opportunities for new and improved gas sensors

Gas/Concentrations

Application/Industry

Nature of

requirement

Product

type

Hydrogen fluoride at ppm levels

Detecting HF around alkylation units:

• Petrochemicals

Overcoming limitations of EC HF sensors

Sensors for use in fixed multi-point systems

Hydrogen sulphide at ppm levels

Detecting H2S on offshore platforms, around refineries and water/wastewater treatment works:

• Offshore oil and gas

• Petrochemicals • Water and

wastewater

Overcoming limitations of EC H2S sensors

Sensors for use in fixed instruments

Nitric oxide at ppm/sub-ppm levels

Detecting NO in the workplace:

• Petrochemicals • Chemicals etc.

Better LOD (~ 0.1 ppm) than existing EC sensors due to revised OES

Sensors for use in fixed & portable instruments

Toxic organics i.e. BTEX, butadiene etc. at low ppm levels

Detecting BTEX etc. in the workplace:

• Petrochemicals etc.

Requirement for selective, real-time method

Sensors for use in portable instruments

Combustible gases at LEL levels

Detecting combustibles in and around the workplace, plant etc.:


• Petrochemicals

Requirement for reduced maintenance and provision of error alarms

Fixed instruments

Toxic and combustible gases (combined) at ppm and LEL levels respectively

Simultaneous detection of combustible and toxic species in and around the workplace and plant etc.:


• Petrochemicals

Desire for the simultaneous optical detection of combustible and toxic gases, i.e. CH4 and H2S

Fixed instruments


Combustible gas visualisation, at low/sub-LEL levels

Detecting leakage of combustible gases around refineries and offshore platforms etc.:

• Petrochemicals • Offshore oil and

gas

Desire for automated surveillance systems that can visualise and locate gas leaks

Fixed systems

Gas leaks

Detecting high pressure gas leaks around refineries:

• Petrochemicals

Desire to improve on existing (e.g. ultrasonic) methods

Fixed systems

H2S, NH3, mercaptans, ethers, esters, alcohols, ideally at ppb levels

Detection of impurities in process gas (ethylene and propylene) streams:

• Petrochemicals

Requirement for real-time, high sensitivity, on-line alternative to GC

Fixed instruments

Siloxanes at ppm levels

Detecting siloxanes in gases used as feeds in CHP systems:

• Water and wastewater

Requirement for on-line, real-time alternative to lab. analysis

Fixed instruments

Water vapour/moisture content at levels ranging from <1 to >100 ppm

Detecting moisture content during production of LPG, LNG and nitrogen and in natural gas as it enters the transmission system:

• Petrochemicals • Gas supply

Overcoming limitations of existing moisture sensors

Fixed instruments

Methane at concentrations from 10 ppm to 100%

Detecting leaks of town gas:

• Gas supply

Desire to replace existing instruments with a single, wide-range device

Portable instruments

Gas odours, i.e. butyl mercaptan (BM) and dimethyl sulphide (DMS) at low ppm levels

Automated monitoring of odorants in the gas distribution system:

• Gas supply

Desire to replace human operators with automated odour

Fixed instruments


monitoring systems

Toxic and combustible gases at ppm and LEL concentrations

Health and safety monitoring:


• Petrochemicals • Water and

wastewater • Gas supply?

Desire for truly autonomous, self-powered sensors that communicate via a wireless network which can be simply installed without any hard wiring and which will operate un-attended for at least 2 years

Fixed instruments

Some of the above are highly specific to particular user sectors and/or offer limited commercial prospects whilst others represent more general and widespread needs and trends within the gas sensing industry. The individual product development charts (see Section 3.3.3) concentrate on this latter category and also consider certain other well documented requirements.

3.3 R&D AND NEW TECHNOLOGIES 3.3.1 OVERVIEW As noted in Section 2.1, there are no generic technological developments which will revolutionise the industry. However, all manner of technologies and disciplines contribute to the advancement of sensors, including:

• Basic technologies; • Materials; • Components; • Sensing effects and phenomena.

Examples of the above with the potential to impact future generations of optical gas sensors are shown in Table 14.


Table 14 – Technologies and disciplines influencing future generations of

optical gas sensors

Electronics

ASICS, processors, software, chemometrics, data fusion, radio communications etc.

Nanotechnology

Optically-active CNTs, other nano-materials, nano-fibres, quantum dot lasers etc.

Silicon/MEMS

Micro-spectrometers, silicon sources, micro-photoacoustics, optical MEMS etc.

Basic technologies

Integrated optics

Planar waveguides, interferometers, integrated sources etc.

Materials

Silicon, silicon carbide, III-V semiconductors, nano-materials, doped glasses, non-linear optical materials, fluorophores, chromophores, thin films, optically-active polymers etc.

Effects and phenomena

CRDS, TDLAS, FTIR, DOAS, other spectroscopy, SPR, photoacoustics, interferometry, scatter, backscatter, fluorescence, chemiluminescence, photo-ionisation etc.

Sources

QCLs, laser diodes, LEDs, CNTs, fibre lasers, silicon optics, OPOs etc.

Components

Others

Detectors, specialist fibres, gratings, filters etc.


3.3.2 SPECIFIC TECHNOLOGIES AND DEVELOPMENTS 3.3.2.1 Introduction The body of research into optical gas sensors and associated topics is extensive and it is impossible to review it here. As well as the numerous classes of sensors under development, Table 14 illustrates well the wide range of other factors that can influence innovation in this field. To gain an insight into prevailing research, readers are referred to journals such as Sensors & Actuators: B, Spectrochemica Acta, the various optics journals (Applied Optics etc.) and, for a broader and somewhat less academic view, Sensor Review. Two reviews of university gas sensor research, one covering the UK and the other continental Europe, have been published recently by the GASG (Bogue 2003; Bogue 2005). The following sections consider some of the more important developments that are viewed as most likely to impact the industry during the next few years and which are most relevant to the needs and opportunities identified in Table 13. 3.3.2.2 Optical sources and detectors Optical sources are the topic of a major, global research effort, much being driven by the needs of the telecoms and IT industries. A smaller yet widespread activity concerns sources aimed principally at gas detection. Some topics of research include:

• LEDs; • Laser diodes; • QCLs; • Fibre lasers; • UV sources; • OPOs/CWOPOs; • Light emitting CNTs; • Silicon sources.

Although most optical gas sensors operating at mid-IR wavelengths still employ filament lamps as the sources, the use of LEDs and particularly diode lasers is growing. Even though the power of a diode laser is low, being highly mono-chromatic and tuned to the key absorption wavelength, it allows all of the energy to be absorbed by the gas molecules which is not usually the case in non-laser-based devices. These sources are therefore of particular interest to the gas sensing community because of the high sensitivity that can be achieved and the many gases that can de detected in this spectral region, typically 3-15 µm. Thus, lasers and laser diodes are potentially key components within future generations of IR gas sensors and some of the more important types are listed in Table 15.


Table 15 – Solid state laser with the potential to be used in gas sensing

Laser type

Wavelength

Power

Comments

Galium nitride (GaN) lasers

Blue/violet to near UV (400-480 nm)

< 5 mW

-

Aluminium gallium arsenide (AlGaAs) lasers

NIR or visible (750-1,000 nm)

10 mW

Room temperature, low cost

Vertical cavity lasers

NIR or visible (650-1,680 nm)

-

Room temperature, low cost, widely tunable

InGaAsP communications lasers

NIR (1,200-2,000 nm)

10 mW

Room temperature, fiber-optic

Antimonide lasers

NIR to mid-IR (2,000-4,000 nm)

≥1 mW

Room temperature or cooled

QCLs

Mid-IR (3,000- 15,000 nm)

Tens of W pulsed, tens of mW CW

Falling prices, no need now for cryogenic cooling

Lead salt lasers

Mid-IR (3,000- 30,000 nm)

<1 mW

Require cryogenic cooling

Extensive efforts are underway to improve, and extend the wavelength range of, mid-IR diode lasers. Research efforts focus on achieving room temperature operation and single frequency (monochromatic) outputs through the use and development of novel structures and materials, e.g. III-V compounds. Some UK university groups working on IR sources are shown in Table 16.

Table 16 – UK university groups working on optical sources

University Topics of research

Lancaster Room temperature mid-IR laser diodes and LEDs


London, Imperial College Room temperature mid-IR laser diodes and LEDs

St Andrews Mid-IR CWOPOs

Heriot-Watt Mid-IR LEDs

Strathclyde Photonic crystal fibre lasers, VECSELs

Sheffield Mid-IR quantum dot/cascade lasers/photodetectors

The critical requirements for laser diodes for use in gas sensing are shown in Table 17.

Table 17 – Critical requirements for mid-IR laser diodes

Characteristics

Operate at room temperature

Low cost

Cover the spectral range ~2-20 µm

Readily tuneable within this range

Exhibit high wavelength and thermal stability

QCLs, in particular, are attracting a great deal of interest. In these, electrons cascade down a series of quantum wells which result from the growth of very thin layers of semiconductor materials. Whereas a single electron-hole recombination can only ever produce a single photon, the QCL electrons can cascade down between 20 and 100 quantum wells producing a photon at each step. This yields a major increase in lasing efficiency, enabling QCLs to emit several watts of peak power in pulsed mode and tens of mW in CW mode. A QCL’s lasing wavelength is determined not by the choice of semiconductor material as with conventional solid-state lasers but by adjusting the physical thickness of the layers themselves. This removes the material barriers commonly associated with conventional semiconductor lasers and opens up the possibility of NIR through to THz spectral coverage. Wavelength-tuneable devices are now available which offer prospects for multi-gas sensing applications. Until very recently, the major limitations were the need for cryogenic cooling and high prices but room-temperature devices are now available and prices have fallen and further price reductions are expected during the next 12 months or so, as volume applications emerge. The degree of interest in this technology is well illustrated by the recent announcement (May 2006) that the US National Science Foundation has agreed to fund a research centre at Princeton University to the tune of $15 million over five years. Dubbed MIRTHE, for Mid-Infrared Technologies for Health and the Environment, the centre aims to develop gas and chemical sensing products based on mid-IR QCLs.


Whilst the emphasis of most optical gas sensing is on the IR region of the electromagnetic spectrum, UV wavelengths are attracting growing interest. As with IR, UV radiation is characterised by subdivision into various regions: Near UV (λ = 380–200 nm); Far or vacuum UV (λ = 200–10 nm, abbreviated as FUV or VUV); Extreme UV (λ = 1–31 nm, EUV or XUV). When considering the effect of UV on human health or the environment, UV wavelengths are often subdivided into: UVA (λ = 380–315 nm), also called “long wave” or “blacklight”; UVB (λ = 315–280 nm), also called “medium wave”; UVC (λ <280 nm), also called “short wave” or “germicidal”, due to its use in water sterilisation. As yet, relatively few gas measurements are made at UV wavelengths, reflecting in part the lack of small, ideally tuneable, and inexpensive sources and also, perhaps, that UV spectra are less rich in features than their IR counterparts, requiring more complex signal analysis and data processing. Many UV measurements involve relatively large and costly instruments, e.g. open-path DOAS systems and ambient O3 and SO2 analysers. The characteristics and uses of some UV sources are shown in Table 18.

Table 18 – Characteristics and uses of UV sources

Lamp type

Wavelength range


Hg vapour 253.7 nm (peak) and weaker lines in the near-UV and visible

DOAS systems, ambient O3 analysers

Deuterium ~200-370 nm DOAS systems, PIDs

Xenon arc ~300-1300 nm Ambient SO2 analysers, PIDs

Zinc 213.9 nm (peak), plus other weaker lines in the UV

Ambient SO2 analysers

Deuterium lamps have the advantages of being relatively small and inexpensive and cover a wide spectral range. Further, recent developments which eliminate the need for internal electrodes (i.e. RF powered) have extended the operating lives of these devices to well beyond 1000 hours. However, the availability of small and low cost UV sources such as laser diodes and LEDs will invariably extend the capabilities of detecting gases at these wavelengths. UV LEDs covering the spectral range 250-430 nm are now commercially available (e.g. from Roither Lasertechnik, Austria, www.roither-laser.com) and an LED fabricated from magnesium-doped aluminium nitride (AlN) has recently been reported which operates down at 210 nm. As yet, however, there is little evidence of UV LEDs being applied to gas sensing, although detectors, fabricated from SiC and which cover the spectral range ~200-380 nm, already exist (e.g. from Cree Research in


the US, see also Table 19, below). UV laser diodes are anticipated in the near future and blue/violet devices operating at 405 nm are now available. Detector technology is also developing rapidly and some detector types are shown in Table 19.

Table 19 – Some detectors used in gas sensing and related fields

Detector

type

Wavelength range

(nm)

SiC 200-400

Si 200/400-1000/1150

Ge 800-1800

InGaAs 800-1700

Extended InGaAs 800-2300/2700

PbS 1000-3000

PbSe 1000-4700

PC-HgCdTe 1000-3000/6500

PV-HgCdTe 2000-10,000/20,000

As with sources, the main thrust of research is to develop low cost detectors that operate at room temperature and which cover the wavelengths of interest within the mid-IR. Sensitivity is also a critical consideration. Within the UK, the Lancaster group is particularly active and has developed uncooled detectors based on materials such as InAsSb and InGaAs which operate at 6.4 µm and 2-3 µm respectively (see: www.lancs.ac.uk/depts/physics/research/condmatt/mid-ir/gas-sen5.htm). For many high sensitivity optical sensing instruments, PMTs are used to detect light but whilst highly sensitive they are bulky and costly and require high operating voltages. Recent developments by the Irish company SensL have yielded a family of silicon photomultiplier devices which are essentially arrays of around 1000 photon counting photodiodes connected in parallel. These offer high gains (106) yet operate at <100 volts (see www.sensl.com). 3.3.2.3 MEMS technology Being something of a “high profile” technology, MEMS warrants mention. It has been outstandingly successful in the physical sensing context (accelerometers, pressure sensors etc.) and more recently the various techniques have been used to fabricate miniaturised analytical instruments such as GCs and MSs.


In the optical context, the main application has been the development of micro-spectrometers which offer the benefits of small size, potentially low prices and rugged construction. Their availability is expected to allow techniques such as FTIR and perhaps UV absorption spectroscopy to be more widely deployed. Given price and size reductions, prospects exist for small, hand-held instruments based on these techniques. Some other optical gas sensing uses of MEMS include:

• Miniaturised silicon photoacoustic sensors. Limited LODs; • MEMS integrated NDIR sensors. Limited LODs; • Miniaturised IMS (arguably an optical technique if a UV ionisation source is

used). Mostly still at the research stage; • IR lasing in silicon. (Observed in nanoporous silicon for the first time in

2005); Although the first two, above, have enjoyed a limited degree of commercialisation, their performance lags behind that of their conventional counterparts and MEMS technology has yet to make a significant impact on optical gas sensing practices. A recent report (Anon., 2004), predicts that, by 2008, the global market for optical MEMS-based spectrometers will reach a relatively modest $96 million/annum. The report notes that the “Spectrometer market appeared in 2000 and is growing slowly because current applications volumes are small and new high volume applications have to be found”. 3.3.3 KEY TECHNOLOGIES Table 20 lists the key technological developments that will facilitate many of the new product opportunities considered above and in Section 3.4, below. A number are likely to contribute also to progress in other sectors of the optical gas sensing industry. Novel mid-IR sources, in particular, are expected by many to exert a significant impact in all manner of gas sensing applications and could result in something of an “optical gas sensing revolution”.

Table 20 – Key technological developments Components/developments

Leading to:

Low cost, room temperature, tuneable mid-IR sources (~2-20 µm) Improved room temperature mid-IR detectors New means of increasing the effective path-length in absorption-based sensors

Low cost, optical high sensitivity toxic and combustible gas sensors Low cost, optical water vapour sensors Combined optical toxic and combustible gas sensors Low cost CRDS (trace gases and water vapour)


Batteries/other power sources Power management techniques Low cost, low power gas sensors Radio communications and associated standards

Autonomous toxic and combustible gas sensors

Low cost, room temperature, tuneable UV sources Advanced spectral analysis techniques MEMS spectrometers (UV)

Sensors for toxic VOCs (portable instruments, personal monitors)

MEMS spectrometers (mid-IR)

Low cost FTIR (hand-portable instruments for gas mixtures?)

High power, eye-safe laser diodes (e.g. at 3.3 µm for CH4) Improved mid-IR detector arrays with on-chip signal processing?

Hand-held gas leak/cloud imagers

3.3.4 THE UK ACADEMIC ACTIVITY The UK has one of the strongest academic gas sensor research activities in Europe, second only to that in Germany. During the period 1999-2002 (latest quantitative data available), 52 groups from 36 universities were actively engaged in this highly fragmented endeavour. “Groups” ranged in size from just 2 to a maximum of around 15. Some statistics are reproduced in Table 21, below, and are taken from a GASG report (Bogue, 2003), which also provides details of the activities of the 52 groups.


Table 21 – Gas sensing research at UK universities

Statistics

Number of universities active or publishing (1999-2002) 36

Number of individual groups active or publishing (1999-2002) 52

Approximate number of workers active in 2002 200

Mean number of workers per group 4

Number of groups with 10 or more workers 6

Number of publications located (1999-2002) >180

Published in >50 journals

The UK has national strength in the overall optics field and in gas sensing in particular. Around 30 groups worked on optical gas sensing during 1999-2002. Some of the technologies and techniques concerned are listed in Table 22.

Table 22 –Optical gas sensing research at UK universities

Topics

Optically-active polymers and organo-metallic compounds

CRDS, THz-frequency CRDS, e-CRDS

TDLAS, FTIR, correlation spectroscopy, other spectroscopic techniques

Interferometry

Photoionisation

Fluorescence, fluorescence decay/quenching

UV and IR absorption

Fibre optic gas sensors (intrinsic, extrinsic, distributed, multi-point)

SPR sensors

Gas-responsive optical biosensors

Optical sources (lasers, LEDs, laser diodes, CWOPOs) and detectors

Integrated optics


UK academics have a good record of working with industry and exploiting the fruits of their research and almost all of the UK’s major gas sensor manufacturers have, at one time or another, collaborated with them. Around 77% of the groups mentioned in Table 21 reported some form of industrial collaboration. In total, this involved working with over 80 UK and overseas sensor manufacturers, users and other non-academic organisations and took the form of both directly funded research and government-supported collaborative projects such as the former LINK schemes. Further, a number of optical (and other) gas sensing university spin-off companies have been set up in recent years (Table 9 above).

3.4 PRODUCT DEVELOPMENT ROADMAPS 3.4.1 INTRODUCTION The following section comprises product development roadmaps, in tabular form, for the more important needs and opportunities shown in Table 13 and as listed below. Note that siloxanes, gas odours and trace impurities in process gas streams all represent needs for sensors to determine hitherto unmonitored species and are considered collectively (“Monitoring new gas species”).

• Optical toxic gas sensors and combined toxic/combustible gas sensors; • Sensors for monitoring toxic organic vapours; • Improved moisture sensors; • Autonomous gas sensors; • Gas cloud/leak imaging; • Monitoring new gas species.

A development roadmap on CEMs was planned but it transpires that many of the technological innovations will be associated with industries outside the present remit (power generation, incineration etc.). However, Table 23 provides brief details of some of these.

Table 23 – Some innovations in CEM technology Analyte

Present monitoring technique

Future technological prospects

Mercury

Catalysis followed by UV atomic absorption photometry, with detection typically at 253.7 nm. Some systems can resolve ≤1 ng/m3 Hg

More simple and less costly techniques required. Legislatively driven high growth market

Other toxic metals

Sampling plus lab analysis, e.g. AAS

Laser induced breakdown spectroscopy (LIBS), for the selective determination of As, Pb, Cd, Zn, Cu etc.


Dioxins

Sampling plus lab analysis (e.g. GC/MS). Continuous dioxin samplers recently developed

SRI (US) has demonstrated a real-time CEM technique termed Jet-REMPI, based on supersonic jet expansion and cooling* followed by resonantly enhanced, multiphoton ionisation (REMPI) and a mass spectrometer

*The supersonic cooling results in low sample temperatures, increasing the electronic ground state population and narrowing the resonance line-widths through a reduction in the molecular velocities and transition-perturbing collisions. The reduced line-widths eliminate the ionisation of other molecular species leading to improved selectivity and make the peak absorption larger, leading to improved sensitivity. (For details of the Jet-REMPI technique, see Oser et al., 2001).


3.4.2 DEVELOPMENT ROADMAPS

Optical toxic gas sensors and combined optical toxic/combustible gas sensors

Market drivers/needs

Desire to overcome certain limitations of EC toxic gas sensors, principally in fixed systems, e.g. limited field lives, limited environmental performance, cost of ownership and cross-reactivities.

• Petrochemicals; • Chemicals; • Gas; • Water.

User industries and applications

• Health and safety monitoring; • Process monitoring.

Present practices

Widespread use of EC toxic gas sensors. Small but growing use of high cost optical systems based on TDLAS in some critical applications.

Anticipated products

• Low cost optical toxic gas sensors for use in fixed

detectors and systems (e.g. for H2S, CO, HF, NOx etc.);

• Similar devices for the simultaneous detection of

methane and toxic species.

Sensing technique

• Mid-IR absorption.

Critical technologies and developments

• Low cost tuneable mid-IR sources (e.g. laser

diodes, QCLs), operating in the ~2-12 µm region. • Novel detectors (in some instances) e.g. for sensing

H2S at 7-8 µm with QCLs.

Comments

Until such time when widely tuneable sources become available, simultaneous toxic and combustible gas detection will probably require two separate sources, e.g. one at 3.3 µm for methane and another at 2.3 µm for NH3.

Likely timescale for development

• Low cost optical toxic gas sensors 2-4 years • Optical toxic/combustible gas sensors 3-5 years


Sensors for monitoring toxic organic vapours


Desire for real-time techniques to monitor toxic VOCs, notably BTEX, in the workplace, selectively and at low ppm concentrations. Benzene is a known carcinogen.

• Petrochemicals (refineries); • Chemicals.


• Health and safety monitoring.

Present practices

Limited use of non-real-time methods, e.g. sampling followed by GC or (cumulative) exposure badges. Also some non-selective detection with PIDs.


• Portable instruments that can selectively determine

BTEX compounds at low ppm levels;

• Longer term: small personal BTEX monitors.

Sensing techniques

Several techniques potentially offer prospects, i.e.

• UV absorption spectroscopy, perhaps combined with advanced signal processing techniques;

• UV TDLAS; • High resolution FTIR spectroscopy*; • Longer term possibility: absorption spectroscopy at

THz frequencies (gas absorption spectra at these wavelengths are yet to be fully characterised).

*Sigrist (1994) has shown that BTEX compounds can be readily identified and discriminated from their IR absorption spectra; even the three isomers of xylene (o-, m- and p-) can be distinguished, albeit with long path lengths.



• Low cost, possibly MEMS-based, UV spectrometers; • Advanced signal processing techniques to separate

the key (UV) spectral characteristics; • UV sources, i.e. laser diodes, emitting at ~220-260

nm. These are viewed as critical for the development of small, personal UV-based BTEX monitors;

• Low cost, tuneable IR sources; • Means of achieving high sensitivity without

physically long path-lengths.

Comments

VOC detection is a major theme of academic gas sensor research; between 1999 and 2002, 16 UK university groups reported work on this topic.

A non-optical alternative might be a MEMS-based micro-GC or GC/MS. IMS also offers prospects. There is also a significant body of research concerning various solid-state techniques such as nano-particulate metal oxides, etc.


• Portable instruments 2-4 years • Low cost personal monitors 3-5 years


Improved Moisture Sensors


Desire to overcome limitations of existing (non-optical) moisture sensing techniques, i.e. slow response and recovery times, effects of contaminants, high ownership costs (calibration etc.), limited range and resolution.

• Natural gas (entry into the transmission system, LNG production etc.);

• Petrochemicals (LPG production etc.); • Chemicals (pure gas production); • Semiconductor processing.


• Process monitoring and control; • Product quality monitoring; • Fiscal transfer.

Present practices

Use of a variety of electrochemical technologies, e.g. Al2O3, P2O5 etc. Some limited use of high cost TDLAS and CRDS systems in critical applications.


Sensors for use in fixed systems (single and multi-point) with wide operating ranges and low/sub-ppb LODs. Fast response/recovery times (i.e. <1 sec.) are critical in several applications, as is immunity to contaminants such as CO2, H2S and glycol etc. In some applications there is a desire to monitor water vapour, CO2 and H2S simultaneously and optical products offering this capability are under development.

Sensing techniques

• TDLAS; • CRDS.


• Low cost, tuneable optical sources (TDLAS and

CRDS); • Lower cost means of extending the path-length (L)

in TDLAS systems (i.e. alternatives to Herriott cells)*;

• Lower cost high finess mirrors or other means of beam reflection.

*Perhaps L could be extended using guided wave technology, e.g. gas-filled hollow optical fibres (see Fetzer et al., 2002)


Nano-fibres, where the light is guided around the outside of the fibre and could thus interact with a gas, may offer prospects in the longer term.

Comments

Cost reductions are vital if these high sensitivity, optical techniques are to gain more widespread use.


• Lower cost TDLAS 2-3 years • Lower cost CRDS 2-3 years • Multi-sensing of H2O, H2S and CO2 2-4 years


Autonomous gas sensors


Requirement for fully autonomous, battery-powered gas sensors with radio communications which will operate unattended for at least two years. These will result in greatly simplified installation and reduced ownership costs, allowing larger numbers of measuring points to be deployed.

• Petrochemicals (refineries and offshore); • Gas processing; • Water industry.


• Conventional gas sensor applications (i.e. health and

safety monitoring); • New uses (longer term), e.g. in inaccessible locations

and/or where no external power is available.

Present practices

Use of conventional fixed-point gas sensors which require hard wiring, mains power and often regular maintenance.


Fixed, wire-free, battery-powered toxic and combustible gas sensors with radio communications.

Sensing techniques

Toxic and combustible gas sensors need to be low power, low cost and offer operating lives of at least 2 years. Possible technologies might include low-power optics (NDIR) or perhaps nano-sensors and MEMS-based devices. In the short term it may be possible to use conventional sensors, given the availability of suitable batteries and power management techniques, although the life/ownership cost issues would remain.


• Battery/other power sources; • Power management techniques; • Low cost, low power gas sensors; • Establishment of a widely-accepted wireless protocol

(e.g. Mesh and ZigBee, see below); • Chip sets for the above.

Comments

The Wireless Sensing Interest Group (WiSIG) has recently been established “To explore the opportunities, applications and successful deployment of wireless technologies and subsequently inform and advise the UK sensing community


on its uses and benefits”. WiSIG is supported by the Sensors KTN. Presently, there are more than 70 competing schemes for routing data packets across Mesh networks. The IEEE is developing a set of standards under the title 802.11s to define an architecture and protocol for Mesh networking. ZigBee is a specification for a suite of high-level communication protocols using small, low-power digital radios based on the IEEE 802.15.4 standard for wireless personal area networks. The ZigBee Alliance is an association of companies working together to enable reliable, cost-effective, low-power, wirelessly networked, monitoring and control products based on an open global standard, see www.zigbee.org.


• Devices based on conventional sensors 2-4 years • Devices based on novel sensors 3-6 years


Combustible gas cloud and leak imaging


Desire for improved real-time detection of flammable gases by overcoming the shortcomings of point and open-path detectors, i.e. limited spatial coverage.

• Petrochemicals (refineries, offshore); • Natural gas (terminals, offshore, tankers, town gas

leak detection); • Environment? (landfill etc.).


• Safety monitoring (combustible gases); • Surveillance of greenhouse gas emissions (landfill

sites etc.).

Present practices

Catalytic sensors, point and open-path NDIR sensors, FIDs (portable detectors). Limited uses of first generation, fixed passive imaging systems (see below).


• Fixed imaging systems (active and passive – see

below); • Hand-portable instruments (active).

Both would generate real-time images of combustible gas clouds and leaks at concentrations below the LELs. The advantage of active systems is that they are fail-safe; passive systems can fail to detect a leak if the difference in temperature between the gas and the background is insufficient.

Sensing techniques

• IR absorption on scanned laser light, backscattered

from a remote target (active technique); • IR absorption on reflected ambient thermal IR

(passive technique, needs a significant temperature difference between target gas and background to operate).


Key technologies for detecting methane both actively and passively in fixed systems already exist, i.e. 1.65 µm laser diodes (active) and InGaAs detectors (both). For some uses, systems should ideally respond to a range of combustible gases (e.g. methane, propane, propylene etc.). For (active) hand-portable systems, a critical issue to be resolved is the weight and size of the collecting lens (diameter ~15 cm) and the drive motor. The lens size is


necessary as the amount of incident light is very low (source power typically 10 mW). Several possibilities exist:

• Higher power laser diode sources but these must operate in another part of the methane absorption spectrum which is eye-safe (i.e. ~3.3 µm);

• Higher sensitivity detectors; • Eliminate scanning through the use of detector

arrays.

All of these approaches presently remain problematic.

Comments

The UK has a long history of involvement with this type of technology. An active, transportable, prototype system has recently been developed and evaluated in the UK (see Gibson et al., 2006). OTIM was another, earlier MOD-funded project. A fixed, passive system with a range of up to 150 m and which arose from research at the University of Lund has recently been commercialised by Gas Optics (Sweden), see www.gasoptics.com


• Fixed imaging systems 1-4 years • Hand-portable instruments 5-8 years


Monitoring new gas species


Desire to monitor certain gas species in real-time that are presently determined by sampling and lab analysis or which remain largely unmonitored. This would confer various application-specific economic and operational benefits.

• Gas supply; • Water; • Petrochemicals.


• Automated gas odour monitoring and control (gas); • Protection of CHP systems by real-time monitoring of

siloxanes (water); • Real-time monitoring of impurities in feed gas

streams (petrochemicals).

Present practices

Case_1. Gas odours: Trained human operators; Case_2. Siloxanes: Sampling and lab analysis; Case_3. Feed gas impurities: Sampling and lab analysis.


Case_1. Fixed instruments that can determine butyl mercaptan and dimethyl sulphide (gas odorants) at low ppm levels in town gas. Case_2. On-line instruments that can determine siloxanes at ppm levels in CHP feed gases. Case_3. Probably extractive instruments that can determine H2S, NH3, mercaptans, ethers, esters and alcohols, ideally at ppb levels, in process gas (ethylene and propylene) streams.

Sensing techniques

Case_1. TDLAS using a QCL? This approach (rather than NDIR) is probably necessary to achieve the required resolution and to overcome interference from other species present. Electronic noses might offer a less costly, non-optical solution. Case_2. Same approach as in Case_1 above, except that electronic noses are not used. Case_3. Uncertain, high resolution FTIR?



Low cost QCLs or other tuneable sources operating in the mid-IR would allow the cost-effective application of TDLAS to Case_1 and Case_2, above. The multi-sensing and resolution requirements of 3 suggest a high resolution spectroscopic technique. TDLAS, using a separate laser for each compound, is a possibility but at present the cost would be excessive. An alternative might be high resolution FTIR or other spectroscopic methods such as CRDS or PAS, using broadly tuneable sources such as CWOPOs.

Comments

In the first two instances, available technology (i.e. TDLAS) could probably meet these requirements but presently the costs might well preclude its use.


Case_1. Gas odour monitors 3-5 years Case_2. Siloxane monitors 3-5 years Case_3. Feed gas impurity monitor Unclear, perhaps 4-6 years


3.5 INDUSTRY ROADMAPS 3.5.1 INTRODUCTION Roadmaps covering anticipated product developments for the three major OptoCem.Net industries are shown in the following sections. Certain products that might subsequently arise from those identified in Table 13 but which are not considered therein are also included. Timescales are very approximate. Further, even though a new product may be developed, there is no guarantee that a particular industry will immediately use it (or even use it at all) – very often there is first an evaluation/trial period, e.g. as we are presently seeing with TDLAS systems in the petrochemicals industry. The UK water industry is subject to all manner of economic pressures and not expected to be a major user of advanced optical gas sensors during the next decade. However, it is likely to adopt a limited range of new products than can confer real economic benefits. Conversely, the UK gas industry has a long history of technological innovations and stands to benefit from several novel gas sensing products, some of which are, or have recently been, the subject of industry-supported R&D. The petrochemicals sector operates on a global rather than national basis and will be the largest user of innovative gas sensors. It is the most technologically aware of the three industries under consideration and is exploring the capabilities of various novel optical gas sensors, both via supported R&D and through on-going field trials.


3.5.2 WATER INDUSTRY

WATER INDUSTRY GAS SENSING ROADMAP

Timescale (years) 2 4 6 8 10 Longer term

Market drivers Optical H2S: Reduced ownership costs, improved performanceAutonomous sensors: Reduced installation and ownership costsOn-line siloxane sensing: Real-time protection of CHP systems,

reduced costs

Technologicaldevelopments

Products

Optical H2S sensors with

improved performance

Optical combined toxic & combustible gas sensors

Batteries, radio comms, standards, low

power sensors and electronics

Combined on-line CH4 and

siloxane sensing

Low cost TDLAS

On-line siloxane sensors for CHP

systems

New/improved mid-IR sources

(QCLs?)

Autonomous toxic/combustible

gas sensors


3.5.3 GAS INDUSTRY

GAS INDUSTRY GAS SENSING ROADMAP

Timescale (years) 2 4 6 8 10 Longer term

Market drivers Wide range leak detector: Requirement to replace multiple, limited range instruments with single instrumentImproved moisture sensors:To overcome operational limitations and ownership costs of existing sensorsGas odour monitor: Desire to automate process leading to reduced costsHand-held gas imagers: Improved leak detection/locationAutonomous sensors: Reduced installation and ownership costs


Products

Autonomous toxic &combustible gas

sensors

Hand-held gas leak imagers

Batteries, radio comms, standards, low power sensors

Low cost TDLAS and/or

CRDS

Improved moisture sensors

Automated gas odour monitors

Laser diodes (technology

exists)

New/improved, low cost mid-IR sources

Detectors, eye-safe laser diodes etc.

Portable wide-range leak detectors


3.5.4 PETROCHEMICALS INDUSTRY


PETROCHEMICALS INDUSTRY GAS SENSING ROADMAP

Timescale (years) 2 4 6 8 10

Improved moisture sensors:To overcome operational limitations Market drivers and ownership costs of existing sensors

Autonomous sensors: Reduced installation and ownership costsOptical toxic gas sensors: Reduced ownership costs, improvedperformance Monitors for toxic organics: Real-time detectionFeed gas impurity monitors: Real-time protection of processHand-held gas leak imagers: improved safety/leak detection


Products

Optical toxic gas sensors

with improved performance

Combined optical toxic &

combustible gas sensors

Batteries, radio comms, standards, low power sensors

and electronics

Hand-held gas leak imagers

Low cost TDLAS

and/or CRDS

Improved moisture sensors

New/improved mid-IR sources

(QCLs?)

Autonomous toxic/combustible

gas sensors

Monitors for toxic organics (BTEX)

UV sources, low costUV spectrometers

Detectors, eye-safe laser diodes

etc.

On-line feed gas impurity monitors

Broadly tunable sources plus high resolution mid-IR

spectroscopy?

Active, fixed gas leak imagers


4 References Anon., 2004. “OMEMS”: Analysis of Optical MEMS applications for non telecom markets. Yole Développement, France. Bogue, R.W., 2003. A directory of gas sensor research at UK universities, edition 2, Gas Analysis & Sensing Group, Swansea. Bogue, R.W., 2005. A directory of gas sensor research at continental European universities. Gas Analysis & Sensing Group, Swansea. Fetzer, G.J., Pittner, A.S., Ryder, W.L. and Brown, D.A., 2002. Tunable diode laser absorption spectroscopy in coiled hollow optical waveguides. Appl. Opt. 41, 3613-3621. Gibson, G., van Wel, B., Hodgkinson, J., Pride, R., Strzoda, R., Murray, S., Bishton, S. and Padgett, M., 2006. Imaging of methane gas using a scanning, open-path laser system. New Journal of Physics, published on-line Feb 15th 2006. Oser, H., Coggiola, M.J., Faris, G.W., Young, S.E., Volquardsen, B. and Crosley, D.R., 2001. Development of a jet-REMPI continuous monitor for environmental applications, Appl. Opt. 40, 859-865. Sigrist, M.W., ed., 1994. Air monitoring by spectroscopic techniques. Wiley.


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