Addendum
Model 3880i
Particulate Matter Continuous
Emissions Monitoring System
Part Number 116969-00
2Sep2016
PM CEMS Isokinetic Sample
Extraction
Many localities require that samples extracted from a stack are performed
using Isokinetic sampling. Isokinetic sampling occurs when the velocity of
the sample being extracted equals that of the velocity of the local gas flow.
Oversampling or undersampling occurs when the sample velocity is less
than or greater than the local gas flow, respectively.
Prior to performing isokinetic sample extraction, a proper sample nozzle
must be selected and installed onto the sampling probe in the stack. This
nozzle must be of the correct diameter so that the velocity of the gas
extracted by the nozzle equals the velocity of the gas in the stack at the
location of the sample extraction. An isokinetic sample nozzle kit is
available (PN:116383-00 ) for this purpose. The local stack gas flow
velocity must be measured, coupled with the information in this
addendum, and the proper sized nozzle selected and installed.
To achieve isokinetic sample extraction, the local stack gas flow velocity
must be continuously measured and this velocity measurement must be
transmitted to the PM CEMS instrument via an analog voltage value. The
measured stack velocity is monitored by the PM CEMS via an analog input
and adjusts the instrument flow rates to maintain the proper sample
extraction velocity.
Isokinetic Sampling – how does it work?
●
The stack velocity input is read through Analog Input #8 scaled to
standard meters per second
●
The Bypass and Sample flows are fixed
●
The Dilution flow will vary which varies the nozzle flow
●
As nozzle flow varies, the nozzle inlet velocity varies to match the stack
velocity signal
●
The system has dilution ratios clamped at 9:1 and 25:1
Figure –1. Proper Isokinetic Sampling
Configuring the PMCEMS for Isokinetic Sampling
●
Using the instructions in this addendum, choose the correct sampling
nozzle, assemble and connect to the PM CEMS probe
●
Configure the PMCEMS monitor:
●
In the Nozzle Selection menu on the PMCEMS, select the nozzle
size that corresponds to the size determined above
●
Configure AIN8 as the stack velocity signal input in units of
standard m/s
●
Connect an analog voltage signal to the AIN8 input on the rear of the
PMCEMS monitor. Be sure to convert the stack full-scale velocity
signal to standard conditions using typical stack temp and pressure data
●
Refer to the PMCEMS manual for details on connecting and
programming the analog input to the PMCEMS
Figure –2. Nozzle with Interchangeable Tips
Thermo Fisher Scientific
Isokinetic Sample Extraction Option Addendum
3
Isokinetic Sampling Example
●
Wet FGD stack
●
(Va) Stack velocity = 55 ft/sec = 16.7 m/sec
●
(Ta) Stack temperature = 52 deg C
●
(Pa) Stack pressure = 29.88 in Hg
●
Convert velocity to standard conditions
●
Vs = 16.7 x (29.88/29.92) x (298.15 / [52.2 + 273.15])
●
Vs = 15.3 m/s
Nominal PM CEMS nozzle flow is 2 slpm (3.33x10-5 m3/s)
●
Divide nozzle flow by stack velocity to get nozzle area.
●
●
Isokinetic Sample Extraction Option Addendum
Vs = Va x (Pa/Ps) x (Ts/Ta)
●
●
4
●
3.33x10-5 / 15.3 = 2.2x10-6 m2
Convert Nozzle area to diameter
●
A = (πD2/4); ([4A/π])0.5 = D (meters)
●
D x 1000 = D (millimeters) = 1.67 mm
Five nozzles to select from; choose closest diameter
●
1.2, 1.6, 1.9, 2.4, and 3.2 mm
●
correct nozzle = 1.6 mm
Thermo Fisher Scientific
Isokinetic Sampling Parts List
Thermo Fisher Scientific
Description
Part Number
Quantity
Nozzle, 1/16 NPT, Wet
37-012045
1
Sample Tip, 1
116363-0468
1
Sample Tip, 2
116363-0625
1
Sample Tip, 3
116363-0781
1
Sample Tip, 4
116363-0938
1
Sample Tip, 5
116363-1250
1
Isokinetic Sample Extraction Option Addendum
5