THE EFFECTS OF STACK ON INCREASING THE ODOUR UNIT THRESHOLD
The DEFRA GUIDANCE for Local Authorities includes the following relevant statement:
“A tall dispersion stack, or stacks, provide some in-built safety margin for potential short-term failures or reductions in the performance of abatement plant due to unforeseen circumstances. In effect a tall stack divides odour mitigation effects (from source plant to receptors) into an abatement component and a dispersion component. The enhanced dispersion provided by a stack can allow for some short-term failure or reduction in the performance of an abatement unit without causing a catastrophic increase in perceived off-site odours”
A stack therefore forms a key part of the odour control function, as well as improving flexibility for plant maintenance. The height of the stack itself does not have any real process effect on the adsorber. It simply allows for a greater odour concentration at the stack and hence allows more contaminant to break through the carbon before it is classed as spent.