The Thetford power station in UK uses a multiparameter emissions monitor to demonstrate to the Environment Agency that the plant is performing within the conditions of its environmental permit. However, data from the analyzer supplied by Gasmet Technologies UK also performs an important role in helping to manage the plant.“Individual gas readings are displayed in almost real-time in the control room,” says Plant Manager Andrew Corbyn, “which enables our staff to respond quickly to the changes resulting from variations in our feedstock. This ability to continually adjust the process ensures that we operate the plant efficiently; generating the maximum amount of renewable energy whilst maintaining a good clean burn.”

FTIR for emissions monitoring

Thetford Power Station operates under an environmental permit which requires the plant to provide the Environment Agency with continuous monitoring data including half-hour and daily averages for HCl, SO2, and TOC (total organic compounds). Monitoring data for CO, NOx and dust are also reported to the Agency.

Gasmet Technologies UK supplied and installed an MCERTS approved Gasmet FTIR analyzer to continuously monitor all of the gaseous emissions. However, Thetford operates a second Gasmet FTIR analyzer to ensure that there is no possibility of expensive downtime. EPR Group Environmental Manager Kevin Williams says: “We originally purchased the portable DX4000 analyzer as an emergency back-up unit, but the core measurement components of a DX4000 are exactly the same as the Gasmet CEMS, so it made sense to run both analyzers simultaneously so that we always had a ‘hot’ back-up.”

The Gasmet CEMS employs an FTIR spectrometer to obtain infrared spectra from the exhaust gas by first collecting an interferogram of the sample signal with an interferometer, which measures all infrared frequencies simultaneously to produce a spectrum from which qualitative and quantitative data are produced.

FTIR gives flexibility to in-process monitoring

Over several years, Gasmet has established an extensive library of FTIR reference spectra that now extends to the simultaneous quantification of 50 gases or identification of unknowns. This means that it is possible to reanalyze produced spectra with the instrument’s PC-based software (Calcmet) and thereby identify and quantify unknown gases. However, this feature is not particularly important for the Thetford plant because, while the moisture content of the feedstock varies significantly, the chemical composition does not, so the main issue from a monitoring perspective is to measure the parameters that affect process control and those specified in the site’s environmental permit.

Gasmet FTIR technology was chosen for the Thetford plant because of its ability to monitor multiple gases simultaneously.

The system has performed very well, with very little maintenance required. Zero-point calibration with nitrogen (background) just takes a few minutes each day and is fully automated. Water vapor calibration is conducted at least once per year, but under normal circumstances no other calibration is necessary.
-says Operations Team Leader Richard Bloomfield

 

Gas monitoring for process control

Richard says “The Gasmet analyzers are our eyes and ears; providing us with almost real-time information on conditions inside the combustion chamber. We have a display in the control room that displays recent trends in addition to the live data so that we can take steps to ensure optimal combustion efficiency, whilst maintaining compliance with our emission limits.”

There are several ‘tools’ with which the combustion process can be managed. For example, it is possible to adjust the feed rate, the distribution on the grate, the grate speed, and airflow from below (primary air) and from above (secondary air).

The plant operates 24 hours a day, seven days a week, and the control room staff, therefore, work in shifts. Paul Dunthorne has worked at the plant for over 15 years. Initially employed as a part-time night worker, Paul has worked his way up the company and is now highly experienced in managing the process. “I love this job,” he says, “it takes quite a while to learn how to control the process, but with the benefit of the gas measurements, we can make the necessary changes to the process and watch the effects of our actions, which is very rewarding.

 

Every day presents a new challenge

“We also like to make sure that the process is running well when we hand over to the next shift so, with the variability in the feedstock, every day presents a new challenge.”

Nick Gooden is responsible for running the instrumentation. He says: “If the CEMS starts to report unusual figures, it is tempting to blame the analyzer, but with the benefit of a duplicate FTIR system, we usually find that the second analyzer is reading exactly the same, which helps us to identify the true cause of the issue.”

 

The main reason for installing a Gasmet FTIR analyzer at Thetford was to demonstrate compliance with the environmental permit. However, whilst that is certainly being achieved, the major return on investment for multiparameter emissions monitoring has been the process management that it enables.
– sums up Gasmet’s Dominic Duggan

 

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