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

(continued)

Isokinetic Sampling

(continued)

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