Monitoring catalyst degradation leads to $190.000 savings a year

Case study

The catalyst layers of a Selective Catalytic Reduction (SCR) installation must be timely renewed to ensure proper reduction, avoid ammonia contamination of the fly ash, and prevent unplanned outages. Yet, for economic reasons it is equally important that the catalyst layers are used to their full potential. The case of the Zolling coal-fired power plant illustrates the importance of thorough monitoring and analyzing.

The 502 MW gross/472 MW net capacity power plant at Zolling near Munich, Germany, was built in 1990 and was one of the first coal-fired plants in Europe to be equipped with an SCR deNOx installation. It includes two parallel reactors with three catalyst layers each. No sootblower equipment is needed because exhaust gases and NOx are quite evenly distributed over the reactor layers.

Catalyst potential too low

Nevertheless, some SCR problems occurred during Zolling’s first decade of operation. “In the first 60,000 hours operational, catalyst layers were replaced rather late,” says ENGIE Laborelec Senior Expert Frédéric Mercier, who recently engaged in analyzing and monitoring
the plant’s SCR installation. “Measurements made on catalyst samples showed that the catalyst potential had twice gone below the minimal level. This was a costly affair, because it deteriorated the quality of the resulting fly ash due to ammonia slip and it provoked an unplanned outage at least once.”

Facts and Figures

Saving more than $190.000 per year

The Zolling plant has made a significant saving every year since it cancelled its OEM catalyst layer replacement program and adopted ReNOx Laborelec’s, backed up by monitoring. The three-yearly replacement schedule advised by the OEM would have cost $420.000 each year. ReNOx Laborelec’s monitoring program, which costs about $50.000, allows catalyst layer lifetime to be extended from 4.5 years to 10 years, corresponding to an average annual replacement cost of $180.000. This means that Zolling saves around $190.000 per year.

Not too early, not too late

That’s why ReNOx Laborelec proposed to more closely observe the evolution of the catalyst potential and postpone renewal as close as possible to reaching the minimal potential. “We continue to regularly measure and analyze catalyst samples,” elaborates Mercier. “Based on that, we develop a catalyst degradation curve, which is extrapolated to assess the time the SCR installation will reach the minimal potential. This allows us to carefully plan catalyst renewal activities in line with outage plans. In this Zolling case, we were able to reassure the operator that the current catalyst layers will perform well at least until the next planned outage. Money was saved!”
ReNOx Laborelec performs catalyst sampling, monitoring and analysis at coal, gas, and biomass power plants as well as at glass, cement, and metals production sites and waste treatment facilities.

A waste of money

The plant operator subsequently decided to accelerate the pace of catalyst renewal to always ensure a catalyst potential above the minimal level. Yet out of prudence, they overcompensated. “The measurement data on samples taken at 80,000 hours operational and beyond show much higher catalyst potential levels,” says Mercier.
“The data also show that from that moment on catalyst layers have been replaced long before the minimal potential was reached. Now this is a waste of money, because it is clear that the layers still had great catalytic potential at the time they were replaced.”

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