What is a threshold?
What are emission limits and why are there different types?
What are stack and fugitive emission limits?
How to convert VOC emissions expressed in VOC into carbon emissions (mg C/Nm³)
What is a threshold?
The threshold is the maximum quantity of solvent (or solvent emission) which a company can use (or emit) within its premises; this varies according to the industry. The threshold for each industry has been stipulated in L.N. 349 of 2010 as transposed form EU Directive EU directive 1999/13/EC.
What are emission limits and why are there different types?
Emission limit values stipulate levels of VOC solvent/s that are tolerated through regulations entrusted within the Directive and National Legislation. Emission limits vary from one industry to another.
The different types of emission limits are to meet the technical requirements of different production processes and the various methods which are available to reduce emissions. For example, if you choose end-of-type abatement, then a stack emission limit will be more convenient than a limit based on the weight of solvent emitted per square metre of material coated. However, if you choose a low solvent option, then the latter may be more appropriate.
There are five basic types of emission limit quoted in the Directive and National Legislation. These are:
- Stack emission limits – as a concentration of solvent in air
- Fugitive emission limits – as a percentage of total solvent input
- Emission limits – as a percentage of total solvent input
- Emission limits relating to a unit of production – per unit produced
- Emission limits set in the Reduction Scheme – per weight of solid coating used
What are stack and fugitive emission limits?
Stack emission limits are given as a concentration of solvent which is emitted through the stack. Such limits are normally quoted in milligrams of solvent per normal metre cubed measured as total carbon. Stack emission limits are normally achieved by using end-of-type abatement equipment. Stack emission limits only apply to those vapours which are captured and treated. In most operations there are emissions which do not get captured and hence are very difficult to assess and/or monitor; these are referred to as fugitive emissions. Where stack emission limits apply, there are also limits on fugitive emissions; these are expressed as a percentage of total solvent inputs. See Solvent Management Plan for calculations of total and fugitive emission values.
How to convert VOC emissions expressed in VOC into carbon emissions (mg C/Nm³)
Emission limits for waste gases, as quoted in VOC Directive, is in mg C (carbon)/Nm3. It is therefore imperative for VOC solvent users to convert volumes or masses of VOC into carbon emissions (in mg C/Nm3) in order to compare their emissions with the waste gas emission limits of the Directive. The carbon content of a solvent can be either supplied by the manufacturer or found on the ESIG web site. The carbon emission from VOC oxygenated solvents and single molecule hydrocarbon solvents can be calculated through the following formula:
(Number of C atoms in the molecular structure x 12/ molecular weight) x 100%.