Division 1.5.2.5 Emissions of mercury

United Kingdom

BAT 31. In order to reduce channelled mercury emissions to air (including mercury emission peaks) from the incineration of waste, BAT is to use one or a combination of the techniques given below.

	Technique	Description	Applicability
(a)	Wet scrubber (low pH)	See Section 2.2. A wet scrubber operated at a pH value around 1. The mercury removal rate of the technique can be enhanced by adding reagents and/or adsorbents to the scrubbing liquor, e.g.: oxidants such as hydrogen peroxide to transform elemental mercury to a water-soluble oxidised form; sulphur compounds to form stable complexes or salts with mercury; carbon sorbent to adsorb mercury, including elemental mercury. When designed for a sufficiently high buffer capacity for mercury capture, the technique effectively prevents the occurrence of mercury emission peaks.	There may be applicability restrictions due to low water availability, e.g. in arid areas.
(b)	Dry sorbent injection	See Section 2.2. Adsorption by injection of activated carbon or other reagents, generally combined with a bag filter where a reaction layer is created in the filter cake and the solids generated are removed.	Generally applicable.
(c)	Injection of special, highly reactive activated carbon	Injection of highly reactive activated carbon doped with sulphur or other reagents to enhance the reactivity with mercury. Usually, the injection of this special activated carbon is not continuous but only takes place when a mercury peak is detected. For this purpose, the technique can be used in combination with the continuous monitoring of mercury in the raw flue-gas.	May not be applicable to plants dedicated to the incineration of sewage sludge.
(d)	Boiler bromine addition	Bromide added to the waste or injected into the furnace is converted at high temperatures to elemental bromine, which oxidises elemental mercury to the water-soluble and highly adsorbable HgBr₂. The technique is used in combination with a downstream abatement technique such as a wet scrubber or an activated carbon injection system. Usually, the injection of bromide is not continuous but only takes place when a mercury peak is detected. For this purpose, the technique can be used in combination with the continuous monitoring of mercury in the raw flue-gas.	Generally applicable.
(e)	Fixed- or moving-bed adsorption	See Section 2.2. When designed for a sufficiently high adsorption capacity, the technique effectively prevents the occurrence of mercury emission peaks.	The applicability may be limited by the overall pressure drop associated with the FGC system. In the case of existing plants, the applicability may be limited by a lack of space.

Table 8

BAT-associated emission levels (BAT-AELs) for channelled mercury emissions to air from the incineration of waste

Parameter	BAT-AEL^f1		Averaging period
Either the BAT-AEL for daily average or average over the sampling period or the BAT-AEL for long-term sampling period applies. The BAT-AEL for long-term sampling may apply in the case of plants incinerating waste with a proven low and stable mercury content (e.g. mono-streams of waste of a controlled composition).
The lower end of the BAT-AEL ranges may be achieved when: incinerating wastes with a proven low and stable mercury content (e.g. mono-streams of waste of a controlled composition), or using specific techniques to prevent or reduce the occurrence of mercury peak emissions while incinerating non-hazardous waste. The higher end of the BAT-AEL ranges may be associated with the use of dry sorbent injection.
(µg/Nm³)
Parameter	New plant	Existing plant	Averaging period
Hg	< 5–20 ^f2	< 5–20	Daily average or average over the sampling period
Hg	1–10	1–10	Long-term sampling period

As an indication, the half-hourly average mercury emission levels will generally be:

< 15–40 µg/Nm³ for existing plants;
< 15–35 µg/Nm³ for new plants.

The associated monitoring is in BAT 4.

Annotations

Footnotes

f1

Either the BAT-AEL for daily average or average over the sampling period or the BAT-AEL for long-term sampling period applies. The BAT-AEL for long-term sampling may apply in the case of plants incinerating waste with a proven low and stable mercury content (e.g. mono-streams of waste of a controlled composition).

f2

The lower end of the BAT-AEL ranges may be achieved when:

incinerating wastes with a proven low and stable mercury content (e.g. mono-streams of waste of a controlled composition), or
using specific techniques to prevent or reduce the occurrence of mercury peak emissions while incinerating non-hazardous waste.

The higher end of the BAT-AEL ranges may be associated with the use of dry sorbent injection.