Halogens and Halides (HBr, Br₂, Cl₂)
Description
Halogens and Halides are gaseous pollutants with chemical formulas such as HBr for halides and Br₂ or Cl₂ for halogens. HBr is a colourless gas with a pungent irritating odour. Br₂ is dark reddish-brown fuming liquid with a pungent odour. Cl₂ is yellow-green gas with a bleach odour. All the above are not flammable..
Sources
Halogens and Halides occur naturally in the environment. The sea contains most of the chlorine and bromine in the natural environment, but some is also found in the earth’s crust. Chlorine is mainly used for swimming pools and bromine can be used as a substitute. Emissions of halogens and halides are produced from combustion processes and chemical manufacturing processes, amongst others.
Environmental Impact
Halogens and Halides can interact with greenhouse gases in the atmosphere and remain stable for longer. Inhalation of high concentrations of halogens and halides can be fatal to humans..
Control
Control is commonly by the use of gas scrubbers where the polluted air is injected with a highly alkaline material which acts either to neutralise, absorb or otherwise react with the hydrogen halides to form a waste eluent which is collected as waste and not exhausted into the atmosphere. Halogens may be more readily collected in acidic scrubbing solutions.
Measurement
Alkali Environmental perform periodic measurements of halogens and halides in gaseous streams from stationary sources in line with the standard reference method US EPA M26/M26a. The method measures total inorganic chlorides, including hydrogen chloride, with the reported result expressed as HCl. The reported results carry UKAS and MCERTS accreditation where the method can be performed to the standard.
These measurements are taken using a manual sampling train whereby a single result is obtained for a gas sample taken from the duct. In combustion gases the reported results are often corrected for oxygen concentration to avoid the affect of dilution air on the result.
Emission Limits
Some examples of common sulphur dioxide emission limits:
30mg/m³ at 11% O₂ – Crematoria
100mg/m³ at 11% O₂ – Combustion of Coated Wood (0.4-3MWth)