source monitoring isokinetic stack sampling · 2017. 9. 10. · 1: vocs are collected on sorbent...
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SOURCE MONITORING
An Overview of VOC sampling
methods and reporting in South
Africa
Presented by
Gerald Woollatt
LEVEGO
Stationary Source Emission Measurement
Specialists
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Overview
Volatile Organic Compounds (VOC’s) what are they?
Classification of VOCs – as per UK, EA - TGN: M16
Relevant standards and legislation regarding VOC’s monitoring-for stack gas emissions - a South African perspective
An overview of the sampling methodology /techniques
Reporting criteria
Current challenges in South Africa
Question and answer session
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VOCs what are they?
Volatile organic compounds (VOCs) are organic chemicals that
have a significant vapour pressure at room temperature and as a
result have a low boiling point
Typically classified as organic compounds that have a boiling
point lower than 250oC
They are organic compounds that easily release vapours or gases
into the air we breathe
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VOCs what are they? contd.
Significant build up in the atmosphere can harm
human health and cause damage to the receiving
environment
Common examples of VOCs that may be present in
our daily lives are: benzene, ethylene glycol,
formaldehyde, methylene chloride,
tetrachloroethylene, toluene, xylene, and 1,3-
butadiene.
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Classification of VOCs
Classification of VOCs as per the United Kingdom
Environment Agency, technical guidance note M16 –
Monitoring volatile organic compounds in stack gas emissions
Classified according to potential harmfulness namely:
– Highly harmful – examples; benzene, vinyl chloride. These
substances are known to be carcinogenic, mutagenic or toxic.
– Class A compounds – Carry a lower albeit a significant risk,
suspected carcinogens, contribute substantially to photochemical
ozone. Examples; trichloroethylene, benzyl chloride
– Class B compounds – Remaining majority of VOCs are considered as
having a lower degree of harm examples; butane and ethyl acetate
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Relevant legislation and methods
in South Africa
National Environmental Management: Air Quality Act (Act No. 39 of 2004) sets out the relevant VOC emission limits for new and existing plants under the section 21 regulations for listed activities.
The current limits vary significantly per subcategory described in the regulations
A variety of methods are currently utilised and contained under the section 21 regulations namely:
– US EPA Methods 18, 25A and 25B
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How do we specify the
concentration of VOCs?
There are three commonly used ways of reporting the
concentrations of VOCs:
– The concentration of the individual VOCs – currently defined in
NEMA as the TO14 suite of compounds, USEPA Method 18 as
reference method
– The sum of the concentrations of specific, individual VOCs in the
samples, USEPA Method 18 as reference method
– As total organic carbon (TOC), which is the concentration of
organic carbon in the gas stream, USEPA Method 25A as reference
method
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VOCs vs TOCs
– Volatile organic compounds - speciated
Volatile organic compound (VOC) measurements are typically
determined using sampling and testing procedures as described in US
EPA Method 18 “Measurement of Gaseous Organic Compound
Emissions by Gas Chromatography”
Samples are collected in Tedlar, or similar bags, charcoal tubes or gas
canister's and the major organic components of the gas mixture are
separated by gas chromatography (GC) and individually quantified by
mass spectrometry. The retention times of each separated component
are compared with those of known compounds in the TO14 VOC suite
under identical conditions. Commercially available standard mixtures
are used to calibrate the GC under the same conditions as those of the
samples
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VOCs vs TOCs
– Total organic carbon
Total organic carbon (TOC) concentration measurements are typically
determined using sampling and testing procedures as described in US
EPA Method 25A “Determination of Total Gaseous Organic
Concentration Using a Flame Ionization Analyser”. This method is
applicable for the determination of total gaseous organic concentration
of vapours consisting primarily of alkanes, alkenes, and/or arenes
(aromatic hydrocarbons). The concentration is expressed in terms of
propane (or other appropriate organic calibration gas) or in terms of
carbon
A gas sample is extracted from the source through a heated sample line
and glass fibre filter to a flame ionisation detector (FID). Results are
reported as volume concentration equivalents of the calibration gas or
as carbon equivalents.
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Sampling techniques for
monitoring TOC – FID
Flame Ionisation Detectors – SRM USEPA 25A
• This technique works by a gas being passed into a
measurement chamber which uses a flame to create ions
from VOCs
• FIDs do not differentiate between different compounds
since they respond to the total charge generated from the
ions produced by this technique and will include all
organic compounds reported as total organic carbon as
propane or methane (standard reference/calibration gas)
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Sampling techniques for
monitoring TOC
Other techniques for measuring total organic carbon
include:
Photo Ionisation Detection (PID) and catalytic oxidation
- these techniques have limitations and are not widely
used for compliance monitoring for stack emissions
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Sampling techniques for
monitoring VOCs
1: VOCs are collected on Sorbent tubes (activated carbon)
followed by gas chromatography – SRM USEPA 18
• The GC is calibrated as per the specific suite required, in
the South African context this would be suite TO14 as
defined in the section 21 regulations of NEMA
• Individual species are quantified and a total sum of the
TO14 suite compounds identified can also be reported
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Sampling techniques for
monitoring VOCs1: VOCs are collected on Sorbent tubes (activated carbon)
followed by gas chromatography – SRM USEPA 18
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Sampling techniques for
monitoring VOCs2: Non – dispersive infrared– (NDIR) detection – SRM
USEPA 25B
• All VOCs absorb infrared radiation, different
compounds will absorb energy at different frequencies
• This means that VOCs have an electromagnetic
fingerprint which is known as a spectrum
• VOCs may be identified by quantifying the peak or
peaks in a compounds spectrum
• It should however be noted that if there is a mixture of
VOCs in the gas stream then the spectra may overlap.
This technique is therefore more suitable for identifying
single compounds or simple mixtures where there are no
interferences
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Sampling techniques for
monitoring VOCs
2: Non – dispersive infrared– (NDIR) detection
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Sampling techniques for
monitoring VOCs3: Fourier transform infrared (FTIR) detection
• The FTIR uses the same basic principle as simple infra
red analysers, but resolves interfering spectra by
splitting the beam in two
• A fourier transform calculation is then utilized to
identify distinct compounds
• The technique is not routinely utilized for periodic
monitoring. It is most commonly utilized in fixed
installations for continuous emission monitoring
• Portable units are available but are expensive
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VOC Reporting Criteria
Different requirements for different listed processes
Various reporting requirements:
TOC – as per NEMA
TVOC – as per NEMA
TVOC –Thermal and Non thermal - as per NEMA
Methane and non methane VOCs - as per various
AELs
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Current Challenges Facing South
Africa
Current Legislation does not define VOCs
sufficiently
Different methods / techniques listed in the
regulations will provide potentially different
results which may be misleading or lead to
misinterpretation of results
The licensing authority needs to provide
guidance in this respect
Current legislation specifies TO14 suite which
is out of date and has been replace by TO15
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Current Challenges Facing South
Africa Contd.
South Africa has to establish its own criteria for
sampling and reporting “Reporting needs to be
standardised”
Skilled and qualified sampling personnel are in
short supply
Reporting, sampling and analytical techniques
need to be standardised across the board
The much anticipated norms and standards must
seek to address these regulatory short comings
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Question and Answer Session