FTIR provides flexible Emissions Monitoring
Multi-component FTIR gas analysers from specialist instrumentation company Quantitech are helping the UK’s leading producers of dolomitic products for the steel industry go from strength-to-strength.
The FTIR Gasmet DX-4000 analysers are operated at Steetley Dolomite’s Whitwell Works, in Nottinghamshire, which is situated on one of the best quality Dolomite limestone deposits in the UK.
The magnesium limestone on the site provides raw material for a range of specialist burnt Dolomite products, including Dolomet, Dolofrit and Dolopel. These are used in the steel industry for fluxes, furnace repairs and high quality refractory brick.
The materials are produced in two large rotary kilns, with each product requiring different firing temperatures and kiln residence times so accurate process control information is essential to maintain product quality. Steetley use a mix of fuels in the rotary kilns, mainly petroleum coke and up to 40% of solvent derived fuel.
The CEMS system must be able to differentiate between a wide range of analytes, many at trace levels in the presence of up to 18% CO2. Recent legislation means there is a legal requirement to measure CO2, CO, SO2, HCL, HF and nitrogen oxides as well as a range of hydrocarbons as indicators of total organic compounds emissions.
The involvement of Quantitech began with the provision of a hired Gasmet DX-3000 analyser from the Milton Keynes-based firm for trials in 2000.
After a successful trial period, Steetley decided to install a continuous system on one of its main kilns. The sampling system incorporated a heated probe, a 30metre heated sample line and a heated filter/pump assembly.
Currently, Steetley is using two DX-4000 analysers at its Whitwell site, using Gasmet’s Calcmet software integrated into its own SCADA system. The package produces summary reports on a daily basis as well as reports to enable compliance with the WID Directive.
A further DX4000 analyser was also purchased for its Thrislington Works, in County Durham.
John Collins, Steetley’s Senior Electrotech, who has overall responsibility for maintaining the CEMS systems, said: “We have had a long and interesting journey with Quantitech going back almost 10 years right up to where we are now. Due to the legal requirements we have to ensure that levels of gases such as CO2,SO2 and NOX are measured and so in this case, the DX-4000 has proved to be ideal.
“Each product needs a different firing temperature and so conditions are variable which means that a versatile instrument is needed. We looked at other systems but the FTIR from Quantitech offered the versatility and high-performance which was absolutely vital. I am pleased to report that over the years we have received excellent reliability and availability from the analysers, using Quantitech for a twice yearly service and thorough technical support.”
Analysis by infrared spectroscopy involves the passing of IR radiation through a sample of gaseous molecules. Some of this radiation is absorbed by the sample and the remainder is transmitted. This produces an infrared spectrum, or “molecular fingerprint”. A unique infrared spectrum is generated because each molecular structure has a unique combination of atoms. As a result, both qualitative and quantitative analysis of the gas is possible.
FTIR stands for Fourier Transform Infrared, the preferred method for infrared spectroscopy. An FTIR spectrometer obtains infrared spectra by first collecting an ‘interferogram’ of a sample signal with an interferometer, which measures all infrared frequencies simultaneously to produce a spectrum.
Sample identification is possible because chemical functional groups absorb light at specific frequencies. In addition, through calibration of the spectrometer, it is possible to determine the intensity of the absorption (relative to the component concentration).
The Gasmet™ FTIR gas analyser from Quantitech can measure any gas, with the exception of the following:
• Noble (or Inert) gases
• Homonuclear diatomic gases (e.g., N2, Cl2, H2, F2, etc)
• H2S (detection limit too high)
The majority of FTIR analysers are used for process control, exhaust monitoring, emissions monitoring, workplace/industrial hygiene monitoring and research.
As a multicomponent gas analyser, the Gasmet™ FTIR from Quantitech is ideal for customers that need to:
1) Analyse multiple components, or
2) Analyse hot/wet gas (e.g., hot humid applications for HCN, NH3 or HCl etc)
3) Analyse any gas in complicated gas mixtures
The Gasmet™ library of reference spectra consists of reference files of gas spectra measured to date with different Gasmet™ gas analysers. The library contains hundreds of spectra and each reference spectrum contains both quantitative and qualitative information about the component.
High levels of accuracy and low levels of maintenance are achieved as a result of continuous calibration with a He-Ne laser, which provides a stable wavenumber scale. In addition, high spectral signal to noise ratio and high wavenumber precision are characteristic of the FTIR method. This yields high analytical sensitivity, accuracy and precision.
Quantitech’s Dominic Duggan says that in comparison with multiple analyser CEMS, the FTIR is “Extremely easy to operate”, adding “Zero point calibration with Nitrogen (background) just takes a few minutes and is required once a day. Under normal circumstances no other calibration is required which saves our customers a great deal of time, effort and money. However, water vapour calibration must be performed after every major maintenance operation and at least once per year.
“At Quantitech we are able to add measurement parameters to installed CEMS as and when required. This is because absorptivity is a physical constant specific to each gas, and the reference spectra (or calibrations) can be easily transferred from analyser to analyser. This means that customers can buy an instrument for today’s requirements and then upgrade to include other parameters at any point in the future at no extra cost.”