FUNDAMENTALS OF SURVEY SAMPLING - Welcome to IASRI - a premier
AN INTRODUCTION TO SOURCE SAMPLING - Welcome to Levego
Transcript of AN INTRODUCTION TO SOURCE SAMPLING - Welcome to Levego
AN INTRODUCTION TO
SOURCE SAMPLING
Presented by
Gerald Woollatt
LEVEGO
Stationary Source Emission Measurement
Specialists
Particulate Matter vs. Gaseous
Emissions
Source emissions classified broadly into
Isokinetic sampling for particulate matter and
non-isokinetic sampling for gaseous emissions
When do we need to sample?
Emission Data can be used:
Government
To provide data for determining appropriate
emission limits.
To provide data for determining compliance.
To provide data for health risk assessments.
To provide data for dispersion modeling.
Emission Data can be used:
Industry
(continued)
To evaluate air pollution control equipment.
To provide information for design of new process
and control equipment.
To provide information on process operations.
Isokinetic Measurement of Source Emissions:
Particulate emissions from a source are
sampled isokinetically using a recognized
international standard such as US EPA
Method 5 sampling train. The collected
sample is analyzed to determine the
pollutant concentrations.
Isokinetic Sampling
Misconceptions about
Isokinetic Sampling
It is not a quick, simple exercise - fairly involved and complex
Time consuming - setting up equipment, preliminary checks etc.
Specifically used for determining flue gas particulate concentrations in a duct or stack
Equipment specifically designed for Isokinetic Sampling
Isokinetic Sampling
ISOKINETIC
Iso – similar or the same
Kinetic – Moving energy, motion
Isokinetic Sampling
ISOKINETIC SAMPLING
DEFINITION
Sampling at such a rate that the velocity and
the direction of the gas entering the sampling
Nozzle is the same as that of the gas in the
duct/stack at the same sampling point
Isokinetic Sampling
Schematic of Method 5 Sampling
Train
Isokinetic Sampling
Typical sampling location
and equipment
Isokinetic Sampling
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Isokinetic Sampling
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Cross Section of
Measurement Position
Isokinetic Sampling
Purpose of Sampling
Isokinetically
The main objective of Isokinetic sampling is
to acquire a representative sample of flue
gas particulate concentrations
Isokinetic Sampling
Factors that Necessitate the
Need for Isokinetic Sampling
Physical properties of particulates in the
gas stream - density, shape, size etc.
Heterogeneous nature of particulate
mixture in gas stream
Uneven distribution of particles in gas
stream – turbulence, gravity etc.
Isokinetic Sampling
Identifying a Proper Sampling
Location
ISO, EPA, BS etc. provide requirements for selecting proper sample locations
Specific minimum requirements set out by ISO9096- No. of Sampling ports, Distance from fans or bends in system, no. of sampling points required.
Above minimum requirements are dependant on the duct size
Preliminary velocity to determine suitability of sample location
Isokinetic Sampling
Determining Sampling Points
Concept of dividing duct in equal areas
Need to sample at the minimum number of
sampling points set out by the standard in
order to get a proper representative sample
due to uneven distribution of particles in
gas stream
No. of points depends on size of duct
Isokinetic Sampling
Diagrammatic Representation of
Sampling Points in a Duct/Stack
Isokinetic Sampling
Errors Associated with not
Sampling Isokinetically
OVER SAMPLING
Can result in an Increase or decrease in
particulate concentration.
This is due to not sampling Isokinetically by
sampling above the flue gas rate
Isokinetic Sampling
UNDER SAMPLING
Can result in an increase or decrease in
particulate concentration.
This is due to not sampling Isokinetically by
sampling below the flue gas rate
Isokinetic Sampling
(continued)
Under Sampling vs. Over Sampling
UNDER SAMPLING
High pressure created at nozzle
Large particles tend to follow normal path
Small particles will be more easily moved from their original path thus being deflected around the nozzle
Lower percentage of smaller particles collected
Not representative of particulate dust burdens or distribution
OVER SAMPLING
Low pressure created at nozzle
Large particles tend to follow normal path
Small particles will be more easily moved from their original path thus being directed into the nozzle
Higher percentage of smaller particles collected
Not representative of particulate dust burdens or distribution
Isokinetic Sampling
Over Sampling and Under
Sampling
Associated Errors that could
Influence Sampling Accuracy
Moisture
Gas Composition
Nozzle, Probe direction
Leakages on test equipment
Test equipment not calibrated
Non- compliance to minimum requirements of relevant standard
Not collecting enough particulate matter
Unstable Process conditions
Isokinetic Sampling
Theoretical Example
Stack Monitoring – 2 m diameter
– According to ISO 9096 - Two sample ports and twelve points with a minimum sampling time of three minutes per point
– Time required – minimum 36 minutes per test excl. travel, pre-test preparation, set up
– Minimum of three tests required
– Additional analyses could result in an increase in test period e.g particle size analyses, low particulate matter concentrations
Isokinetic Sampling
Gaseous Sampling Principles
Homogenous nature of gases - therefore not necessary to sample Isokinetically - this is because – Flue gases are presumed to mix thoroughly,
– Very small molecules therefore not adversely affected by gravity.
– Properties of gases are such that a sample can be taken at several predetermined points along the diameter of the duct and still be representative with out having to sample Isokinetically
Gaseous Sampling
The sample is taken at a set flow rate, at each point throughout the duct e.g. 1l/min
A Velocity measurement is performed in conjunction with the tests
The velocity measurement is used to calculate the emission rate of the gas sampled
Time, Temperature, Contact time, Surface area, affinity of the gas etc. all effect the sampling time and nature of reagents used when sampling for a specific gas and therefore have to be taken into consideration
Gaseous Sampling
continued
Interferences
Moisture- Many gases are absorbed by moisture,
sample line must be heated in most instances
e.g. HF, Volatile organics etc.
Other gases present in the gas stream may
interfere with sampling reagents.
Certain materials in the sampling line may
interfere with certain gases e.g. acid gases may
react with stainless steel present in the sampling
line
Gaseous Sampling
S
T
A
C
K
Probe
with
filtration
Heated
Line
Heated
Manifold
conditioning
unit /
condenser
VOC’s /
UHC’s
Analyser
(O2, CO2, CO, SO2,
NO, NO2) Non
heated
line
Gaseous Sampling
Relevant Standards used in
South Africa Air Pollution is currently governed by the National
Environmental Management: Air Quality Act (AQA) No. 39 of 2004
AQA: Section 21 regulations detail emission limits for various processes and acceptable methodology – Typically ISO and US-EPA methods are acceptable.
Methods Commonly Used
Environmental Protection Agency
– US EPA Methods
British Standards Institution
– British Standards
International Standards Organisation
– ISO Methods
Current challenges facing the
Source monitoring industry
Shortage of human resources
Shortage of technical expertise
– Lack of training and certification facilities in the country
Lack of infrastructure, e.g. accredited laboratories (air
samples), calibration facilities, etc.
Lack of knowledge by industry with regards to source
sampling requirements e.g. proper sampling locations,
necessity of process info /control parameters.
Question and Answer Session