Witzenhausen RDF Plant Meets Limits – Bar One NOx Breach

Key Takeaways

• B+T Energie’s Witzenhausen RDF plant complied with its emission limits during regular operation in 2025.
• NOx exceeded the daily limit once while new limits were being set; 68 half-hourly breaches were also recorded.
• Annual NOx averaged 97.50 mg/m³, just below the 100 mg/m³ limit.
• The plant ran 7,620 hours (87.0% availability), supplying DS Smith’s paper mill with all its steam and power.
• Gross electrical efficiency reached 20.68 per cent and boiler efficiency 90.4 per cent.

The refuse-derived fuel (RDF) power plant in Witzenhausen complied with the emission limits applicable to it during regular operation in 2025, according to the annual report published by its owner, B+T Energie GmbH, under Section 23 of the 17th Federal Immission Control Ordinance (17. BImSchV). The report also lists one exceedance of the daily average limit for nitrogen oxides (NOx). This exceedance occurred while the plant was being adjusted to new limit values. In addition, there were 68 exceedances of permitted half-hourly values.

B+T Energie, based in Alsfeld, owns the plant and operates it together with DS Smith Paper Deutschland GmbH. In 2025, the plant used RDF to supply the paper mill with all of its steam and electricity. Surplus electricity generated in combined heat and power mode was fed into the public grid of Stadtwerke Witzenhausen.

Operating Hours and Plant Availability in 2025

The plant, including its flue gas cleaning system, was in operation for a total of 7,620 hours during the reporting period. This corresponds to an availability of 87.0 per cent of the hours in the year. In addition to the scheduled annual overhaul, which took place from 21 May to 22 June 2025, the plant had two unplanned outages in May and September. Faults during the restart after the overhaul led to further production losses.

According to the report, the daily average limit for NOx was exceeded once while the new limit values were being set. No other daily limits were exceeded. For the half-hourly values, the monitoring data list exceedance rates of 0.03 per cent for mercury and 0.41 per cent for ammonia, and zero for all other parameters. B+T Energie states that targeted countermeasures restored regular operation after a short time in each case. Furthermore, all events were reported to the competent authority immediately.

Continuous Emissions Monitoring: NOx Close to Annual Limit

The continuously monitored emissions are assessed against the plant’s permit of 31 January 2019 and the amended 17th BImSchV of 13 February 2024. The annual average for NOx was 97.50 milligrams per cubic metre, against an annual limit of 100 mg/m³. The daily and half-hourly limits for NOx are 120 mg/m³ and 400 mg/m³.

The annual averages for the other continuously monitored parameters were 6.42 mg/m³ for hydrogen chloride (daily limit 8 mg/m³), 5.79 mg/m³ for sulphur dioxide (daily limit 40 mg/m³), 6.97 mg/m³ for carbon monoxide (daily limit 50 mg/m³), 1.38 mg/m³ for total carbon (daily limit 10 mg/m³), 0.91 mg/m³ for dust (daily limit 5 mg/m³) and 2.92 mg/m³ for ammonia (daily limit 10 mg/m³). Mercury reached an annual average of 0.00025 mg/m³. For mercury, the plant is subject to an annual limit of 0.005 mg/m³, which goes beyond the requirements of the 17th BImSchV, in addition to a daily limit of 0.01 mg/m³.

The values are normalised to the respective reference oxygen content, which averaged 6.6 per cent over the year. They are based on the evaluation of an automatically recording, sealed measuring system. The evaluation covers the period from January to December 2025.

Dioxins, Heavy Metals and Combustion Conditions

Further parameters are monitored through recurring individual measurements, carried out by an independent measuring body under Section 26 of the Federal Immission Control Act (BImSchG) at full load during regular operation with RDF. For hydrogen fluoride, dioxins and furans, cadmium and thallium, the group of antimony, arsenic, lead, chromium, cobalt, copper, manganese, nickel, vanadium and tin, and the group of arsenic, benzo(a)pyrene, cadmium, cobalt and chromium, the report gives the average of the maximum measured values as 0.000 in each case. The corresponding limits are 0.90 mg/m³ for hydrogen fluoride (daily average), 0.08 ng/m³ for dioxins and furans, 0.02 mg/m³ for cadmium and thallium, 0.30 mg/m³ for the first metals group and 0.05 mg/m³ for the second. The values refer to oxygen concentrations of 7.3 to 7.6 per cent. The operator states that the emission limits for individual measurements under Section 19(2) of the 17th BImSchV were complied with.

Under the 17th BImSchV, the minimum temperature after the last supply of combustion air is 850 degrees Celsius. According to the report, the residence time in this temperature zone is more than two seconds, the minimum residence time required by the ordinance. An independent measuring body under Section 26 BImSchG checked the combustion conditions, and the expert confirmed that all requirements of the 17th BImSchV were met in full. The plant’s operational measuring points were calibrated using a water-cooled suction pyrometer. There were no instances of the temperature falling below the minimum.

Electrical Efficiency and Boiler Efficiency

Annex 7 of the amended 17th BImSchV requires operators of waste incineration plants with a rated thermal input of more than 50 megawatts to determine the gross electrical efficiency and the gross energy efficiency of their plant. For 2025, the calculation gave a gross electrical efficiency of 20.68 per cent and a boiler efficiency of 90.4 per cent. According to B+T Energie, this meets the requirements of the 17th BImSchV.

In its assessment of the results, the company states that the limits applicable to the plant were complied with during regular operation and were, as a rule, undercut many times over. It says the level of pollutants in suspended dust was kept low, in particular the concentrations of dioxins and furans and of mercury, and that the plant is operated in an energy-efficient manner.

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