Commentaries: Annex 6

(Art. 6 para. 3)

Minimum stack height

1 Scope

The provisions of this Annex apply to installations for which the quantity Q/S exceeds 5, where: Q = mass flow of the emitted air pollutant in grams per hour; S = value calculated in accordance with Number 9.

2 Calculation method

¹The required physical stack height is calculated step by step in accordance with Numbers 3 to 6.

²If more than one air pollutant is emitted, the physical stack height is calculated on the basis of the pollutant for which the quantity Q/S has the highest value.

3 Parameter H0

31 Determination of H0 according to Diagram 1

¹The parameter H0takes account of the short-term effects of the air pollutants emitted from a single installation. It is determined with the aid of Diagram 1.

²The quantities Q and F depend on the emission conditions at the installation. The full load values and the fuel/emission conditions most conducive to air pollution are used to calculate H0.

³The quantity S is used to limit the maximum short-term ambient air pollution levels caused by the installation to a specific value (S value). The S values specified in Number 9 are used to calculate H0.

32 Determination of H0 in individual cases

¹The parameter H0is determined in individual cases according to the recognised rules for calculating the stack height and the dispersion of flue gases if:

the Q/S or F values lie outside Diagram 1; or
the flue gas temperature is less than 55 °C.

²However, where flue gas temperatures are below 55 °C, the parameter H0must not be lower than the value which is obtained according to Diagram 1 for a temperature of 55 °C.

4 Minimum height for flat, obstacle-free terrain

¹The stack height for flat, obstacle-free terrain is:

H1= f x H0

The correction factor f takes account of long-term effects due to wind channelling.

²Values between 1.0 and 1.5 are used for f as follows: f = 1.00 for sites with no prevailing wind direction; f = 1.25 for sites with average conditions; f = 1.50 for valleys with pronounced wind channelling.

³Intermediate values are also possible for f, depending on the site conditions.

5 Height increase for buildings and vegetation

Elevated objects (buildings and vegetation) in the vicinity of the stack are taken into account by means of a height increase I1:

I1= g x I

where: I = Height of the highest significant obstacle area in the region affected by the installation. Values between 0 (no obstacles) and 30 m (e.g. forest) are used for I. g = Correction factor, with values between 0 and 1 according to Diagram 2.

6 Physical stack height

The physical stack height H is calculated according to the following formula:

H = H1+ I1

7 More stringent requirements

In justified cases, the authorities will require taller stacks, for example, in the case of: a. structures with particular shapes; b sites with particularly poor meteorological dispersion conditions; c. particular topographical conditions, such as narrow valleys, hillsides or depressions.

8 Symbols

H (m) = Physical stack height H0(m) = Parameter for determination of H1 H1(m) = Minimum stack height for flat, obstacle-free terrain

I (m) = Height of the highest significant obstacle area

I1(m) = Height increase for buildings and vegetation f (–) = Correction factor for long-term effects due to wind channelling

g (–) = Correction factor for buildings and vegetation

Q (g/h) = Mass flow of the emitted air pollutant; emissions of nitrogen oxides (nitrogen monoxide and nitrogen dioxide) are expressed as nitrogen dioxide Rn(m³/h) = Volume flow of the flue gas under standard conditions (0 °C, 1013 mbar) t (°C) = Flue gas temperature at the stack outlet Δt (°C) = t–10 °C F (m⁴/s³) = Lift flux; F = 3.18 × 10^–6× Rn× Δt S (µg/m³) = S value (cf. Numbers 3 and 9)

9 S values

Pollutant	S (µg/m³)
Suspended particulates (PM10)¹	50
Hydrogen chloride, expressed as HCl	100
Chlorine	150
Hydrogen fluoride and inorganic gaseous fluorine compounds, expressed as HF	1
Carbon monoxide	8000
Sulphur oxides, expressed as sulphur dioxide	100
Hydrogen sulphide	5
Nitrogen oxides, expressed as nitrogen dioxide	100
Substances listed in Annex 1 Number 5:
– Class 1	0.5
– Class 2	2
– Class 3	5
Substances listed in Annex 1 Number 7:
– Class 1	50
– Class 2	200
– Class 3	1000
Substances listed in Annex 1 Number 8:
– Class 1	0.1
– Class 2	1
– Class 3	10
¹ Fine particulate matter with an aerodynamic diameter of less than 10 µm.

Determination of the parameter H0 for stacks

Diagram 1

Determination of the correction factor for buildings and vegetation

Diagram 2

I = Height of the highest significant obstacle area (Number 5) H1 = Minimum stack height for flat, obstacle-free terrain (Number 4)