7 maart 2014

Multiparameter gas analysis with FTIR (Fourier transform infra-red) has become extremely popular for the analysis of emissions, industrial processes and ambient air. However, the capital cost of FTIR is relatively high, so in this article, Antti Heikkilä from Finnish FTIR instrument manufacturer Gasmet, explains why this technology is more effective, easier to use and has a lower lifetime cost than other options.

Emissions monitoring
Historically, continuous emissions monitoring system (CEMS) were used to control combustion processes by monitoring emissions of oxygen, carbon monoxide and carbon dioxide. However, the role of CEMS has been considerably expanded to encompass the measurement of pollutant gases to demonstrate compliance with regulatory requirements. These regulations are continually evolving; some emission limit values have been lowered and new compounds have been added to the list of requirements for certain processes. Every time a new compound is added to the list, process operators with traditional analyzers have to purchase a new monitor, so there is a major financial incentive to employ multiparameter

Multiparameter analysers are generally more expensive than single parameter analysers. However, the cost comparison moves in favour of multiparameter as more gases are measured because the purchase cost of several individual analysers is likely to exceed the cost of a single FTIR analyser. In addition, the cost of ownership for FTIR is much lower because it does not need expensive re-calibration and the requirement for consumables is minimal.

Gasmet’s FTIR CEMS simply require a point calibration with Nitrogen (background), which just takes a few minutes and is required once per day. Water vapour calibration is performed after every major maintenance operation and at least once per year. However, under normal circumstances no other calibration is required, which contrasts greatly with the army of span gas bottles that are required with most other monitoring systems.

The Gasmet CEMS is typically configured for the measurement of H2O, CO2, CO, SO2, NO, NO2, N2O, HCl, HF, NH3, O2 and TOC. However, users can also select from a library of several thousand other species. Many process operators have chosen multiparameter FTIR because it provides them with the option to add further gases at a later stage — 'future proofing' their monitoring capability.

The accuracy of CEMS is particularly important for environmental protection and because monitoring results have major financial implications for process control and abatement efficiency. Rigorous performance requirements for these systems are therefore specified by formal certification systems such as TÜV and MCERTS — Gasmet CEMS are certified to these standards and also fulfil the requirements of the QAL 1 performance test according to EN 14181 and EN ISO 14956.

In addition to fixed CEMS that monitor gases extracted from individual stacks, Gasmet has also developed transportable FTIR CEMS that employ exactly the same measurement technology in a format that can be easily transported from site to site. Benefitting from the same certification, these systems are most commonly employed by test houses to check the performance of installed systems.

A variety of factors affect the choice of analyser, but the regulatory requirement is of course the most significant. A coal fired power station for example, may only be required to monitor SO2, NOx and CO emissions, whereas a municipal waste incineration plant will have to monitor other parameters such as organic compounds, HCl, HF, etc.

FTIR is ideal for process operators that need to:
1) Analyse multiple components, or
2) Analyse hot/wet gas
3) Analyse any gas in complicated gas mixtures

Gasmet has developed an enormous library of reference spectra, each of which contains both quantitative and qualitative information about the components, which means that users are able to analyse their own samples retrospectively if a new parameter becomes of interest.

The flexibility of FTIR to analyse new gases without the need for new hardware is particularly advantageous for manufactured products and processes which often change and necessitate an adjustment to the monitoring strategy. A further benefit of continuous process monitoring is that it provides an opportunity for feedback control of the process and/or the creation of alarms.

Other applications for FTIR Most of the applications mentioned above involve the analysis of hot wet gases. However, Gasmet has developed a unique portable version of the FTIR analyser that has been designed specifically for ambient monitoring. This instrument (Gasmet DX-4040) is able to produce laboratory levels of accuracy in the field, for almost any gas.

The portable ambient FTIR costs more than most portable gas detectors, but with a library containing thousands of compounds it brings laboratory grade analysis into the field and has proved very successful in a variety of applications. For example, the Environment Agency in England has purchased multiple units for the multi-agency air quality cell that was established in 2009 to provide a rapid response to major incidents such as chemical leaks, fires and explosions. SEPA has purchased units for a similar purpose in Scotland, as have regulatory bodies in many other countries around the world.

This ability to detect unknown gases has resulted in the use of FTIR in a wide variety of applications. For example, entry to freight containers at ports represents a significant hazard to staff responsible for inspection, stuffing or destuffing because of the large number of airborne chemicals that can be present. It is therefore necessary to examine containers before entry and FTIR gas analysis has dramatically improved the speed and effectiveness with which containers are assessed, because this technology enables the simultaneous measurement of the 50 gases of most concern.

As governments respond to the challenge of climate change, it has become necessary to measure greenhouse gas (GHG) emissions in order to establish an accurate inventory and so that the effectiveness of mitigation and reduction actions can be measured. As a result, the facility to add GHGs to the parameters monitored by a CEMS is extremely useful and almost cost-free. However, other applications have emerged, such as the measurement of GHG emissions from farm animals. Globally, livestock are responsible for about 15% of GHG emissions so many researchers have employed Gasmet FTIR analysers to measure the emissions from cattle. In other similar applications researchers have employed FTIR to measure GHG flux in soils.

From Gasmet’s perspective it appears that the applications for FTIR are almost limitless, because the company’s staff are constantly surprised and fascinated by the new enquires that are received every day from all over the world. However, the choice of analyser for process, ambient or stack monitoring is dictated by a wide range of factors that can have a substantial effect on the cost, so it is often helpful to obtain expert advice before making an investment in monitoring technology. For this reason Gasmet invests heavily in technical support; which is provided through its own offices and via a worldwide network of highly trained distributors.

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