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NOx
Monitors for
SCR
Applications
a technical solution to
meet every need…
CEMTEK Instruments Inc.
2013 S. Wood Ave.
Linden, NJ 07036
800-400-0201
www.cemtekinstruments.com
Todays regulations are placing demands on all types
of Combustion sets for tighter control of their
emissions.
No one solution can solve all application demands but
there are several alternate measurements that can
help improve their chances without costly upgrades.
• While manufacturers are striving to find the ultimate
solution for the next generation of turbines, burners
engines, they are still reliant on a combination of
combustion technology & post combustion
technology to achieve the lowest possible
emissions.
• Tighter NOx & CO control, through combustion
improvements and better catalyst efficiency is a
target for many.
Regulatory Constraints.
NOx Monitoring
Emissions variables
NOx can be controlled by various methods and is by
far the largest variable.
CO being a product of combustion conditions is
dependent on the combustor and flame temperature.
By using continuous real time sensors to measure
these variables improvements in their control can be
achieved
SCR NOx Monitoring
How does NOx monitoring help operations?
Better control for transient conditions?
Better control under low load conditions.
Indications of poor combustion.
Catalyst deterioration.
Improve efficiency SCR NH3 injection during above
conditions.
Accurate NOx numbers from sensor with fast
response time, < 10seconds?
SCR NOx Monitoring
How do utilities run their SCR sets?
What are the main criteria for best operating
performance?
Accurate NOx numbers?
Reliable response time?
How are you obtaining this information for control
and optimization?
Continuous monitoring with traditional NEMS NOx
monitoring?
Periodic testing with portable/test trailer?
Close Coupled NOx Probe
SCR NOx Monitoring
SCR NOx Monitoring
Extractive or Dilution NOx measurement:
Response time based on sample line run
Installation can be costly depending on system
location. May be located in CEMS shelter or
designed as stand alone cabinet
Maintenance can be likened to a CEMS since in
effect that is what it is.
CEMTEK NOx – O2 Analyzers
Rack mount Analyzers for standard NEMS applications
Single NOx Analyzer
Dual NOx Analyzer
Single O2 Analyzer
Combination NOx-O2 Analyzer
NOx is typically measured using a
Chemiluminescence sensor
Sensitivity: ppb easily measureable
Oxygen is measured using a Zirconia planar
sensor
CEMTEK NOx – O2 Analyzers
FULLY EXTRACTIVE (DRY BASIS)
DILUTION EXTRACTIVE (WET BASIS)
OTHERS:
•FULLY EXTRACTIVE (HOT/WET)
•IN-SITU (CROSS STACK or PROBE)
•EX-SITU (CLOSE COUPLED EXTRACTIVE)
NEMS TYPES
SCR NOx Monitoring
Sample Gas Dried To A Dew-point Of +2°C
Excellent Performance In Low
Concentrations
Good Performance In High Concentrations
Requires Preventative Maintenance
FULLY EXTRACTIVE - Dry Basis
Standard Extractive NEMS
Extractive Flow Schematic
NOx
O2
Cooler
Probe
Sample Line
CO
Pump
Inst. Air
Cal
Gas
Standard Extractive NEMS
Standard Dilution NEMS
Dilution measurement measures a gas
stream’s properties by extracting a
certain amount of gas sample from the
stack flow then diluting the sample with
instrument grade ambient air to some
exact proportion say 100:1. This makes
for a cleaner gas stream through the
analyzer’s pneumatics eliminating the
need for expensive sample conditioning
and producing less problems which
cause analyzer downtime.
Dilution System Flow Diagram
1
2
3
4 5
6
7
NOx
O2
Probe
Flow Panel
Dilution Air Cleanup
Panel
Filters, Scrubbers, Dryers
1-Dilution Air
2-Diluted Sample
3-Purge
4-Bypass Air
5-Pressure Comp
6-Vacuum
7-Cal Gas
CEMTEK 8000 NOx- Monitor
Chemiluminescense:
Is recognized world wide as best NOx measurement technique
Dilution:
Well proven and accepted in EPA applications
Best technique for particulate laden flue gas applications.
The 8000 Combines proven technology for Coal Fired
Applications into an unconventional analyzer
CEMTEK 8000 NOx - O2 Monitor
This analyzer is specifically
designed for use in combustion
process applications:
SCR inlet/outlet monitoring
applications.
for low NOx burner tuning,
Consisting of 3 Components
1. The Analyzer Controller which
houses the electronics and the
NO Sensor.
2. The Probe which contains the
dilution block and optional
Oxygen Sensor along with the
NO2 converter if required.
3. The self-limiting heated
interconnect umbilical which
contains the sample line,
calibration gas line,
thermocouple cables and
power cables.
Difference between PMT & Photo Diode
measurement technique
Most NOx measurements are done using a Photo Multiplier Tube
(PMT).
PMT configuration is complex, more expensive and susceptible to
temperature and moisture changes.
Our analyzer uses a Photo Diode for NOx detection.
Its means of detection consists of a reaction cell and detector, the
photo diode and makes for a much simpler configuration.
Is less susceptible to ambient environmental changes.
Advantages of Photo Diode measurement
technique
Dramatically smaller
Eliminates high voltage power supply
All solid state, much more rugged
Eliminates need for large TE coolers and drivers
Can be close-coupled to reaction, no optics other
than a window needed
Not affected by temperature swings
Linear, accurate, repeatable
Minimal sample conditioning
No air conditioned instrument shelters
The NOx Probe
Highly integrated pneumatics combines analyzer and low flow /
low dilution probe into a single instrument.
Heated to ~350 C to avoid condensation of acid gases before
dilution, also provides orifice temperature control
Heated dual-stage filtration and low flow avoids pluggage.
Through Probe Calibration for full system integrity.
In Stack Dilution block/probe design
The NOx Probe
Fully immersed, temperature
controlled sample orifice
Located at tip of probe for very fast
response and virtually no time lag
Less than 10 seconds combined
Solid state detector for fast accurate
measurement in harsh conditions.
8000 Flow Schematic
NOx Chemiluminescense Sensor
Chemiluminescense NOx
Sensor mounted on main
PCB, input from gas sample
and O3 generator into the
reaction cell, controlled by
exhaust eductor and air
pump
Filter Assembly
This component consists of
the ammonia scrubber and
in-line filter components. The
ammonia scrubber removes
NH3 from the sample gas. As
the in-line filter conditions the
sample gas prior to the NOx
cell. The assembly is located
before the NOx cell in the
controller.
NOx Controller Interface
NOx Controller Interface
Multi-unit Installation
NOx- Monitor Installation
NOx- Monitor Installation
Monitor installation requirements:
All connections between the Probe and the Controller are via the 1.5” Self
Limiting Heated Sample Line, typical length 6-20ft.
Customer Interface for Power, Signal & Pneumatics:
One ¼” Swagelok port for calibration gas, concentration is dependent
on range, xxppm NO in N2
one ¼ Swagelok port for instrument air (2.5 SCFM @ 70 psi). Clean dry
air @ -40F dew point, for dilution air & zero gas.
Air Clean up Panel is available as an option when compressed air is
unavailable
Signals to customer control are isolated 4-20 mA analog,
General Fault alarm – analyzer, System in Calibration alarm- powered
24v dc.
Power consumption of 5A (max on startup) at 120VAC.
SCR PERFORMANCE OPTIMIZATION
Probe install:
13th October 2010, approximately 1/2day work.
1400 MW Coal Fired SCR Application:
Eastern Bituminous High Sulfur
SO2 levels 2000-3000ppm
NH3 Slip 0-5ppm
SCR PERFORMANCE OPTIMIZATION
8000 NOx Probe tracking Dilution Extractive System on Split Outlet of SCR
SCR PERFORMANCE OPTIMIZATION
Expanded graph shows 8000 leading Dilution analyzer by approximately 90sec
SCR Control using CEMTEK 8000
Data taken from SCR NOx-O2 Monitors on a 600 MW power generator, using PRB coal and an SCR with
direct ammonia vaporization. Inlet is located just before ammonia injection grid. Outlet is located just after
SCR and before electrostatic precipitator.
SCR Monitor
Inlet NOx (red)
SCR Monitor
Outlet NOx (blue)
Ammonia Injection (black)
CEMS/Stack
NOx (green)
Control using Inlet
and Outlet Monitors
Control using
CEMS NOx
Target NOx Output Level: about 30 PPM
0 5 10 15 20 25 30 35 40 45 50 55 60
1.2 minutes
2.7 minutes 15.6 minutes
While using the SCR NOx-O2 inlet and outlet monitors, the control system
was able to reduce NOx output to the control level in just over 1 minute
even while NOx input levels remained high. After the combustion excursion
had subsided, the ammonia was quickly returned to “normal” levels and the
NOx output was brought back to the target NOx level in under 3 minutes.
While using the CEMS/Stack NOx, the control system was NOT
able to reduce NOx output before the combustion excursion had
subsided. In fact, the ammonia valve was opened after the excur-
sion subsided and remained open too long, over-injecting ammonia
and pushing NOx well below the target level for over 15 minutes.
Combustion
Excursions
2 minute delay
Time (minutes)
3 to 4 PPM
450 PPM
300 PPM
100 PPM
CT Performance Optimization
SCR INLET
CT OUTLET
CT Trial for GE. 7FNB DLN 150MW
Testing a new Fast Response Close Coupled
NOx / O2 probe:
Comparative measurements to Utility Test
Trailer with conventional CEMS:
Prove accuracy, availability, speed of
response.
Usefulness of real-time continuous monitoring
for feed back.
CT Trial for GE. 7FB DLN 150MW
Testing of CEMTEK 8000 NOx/O2 Probe:
Outlet of 150 mw GE Turbine prior to HRSG.
Gas Temp- 1200F, Duct Pressure - 20”wc.
PROBE length 20”, with 10” extension.
Sample Line 12ft.
Response time < 10 sec
CT Trial for GE. Frame 7 150MW
Testing for CEMTEK 8000 NOx/O2 Probe:
During initial burn in ( 2 wks) daily calibration
checks to prove RA.
NOx values corrected to 15% O2 using
analyzer measurement.
Corrected to dry number using trailer test
data for moisture.
Calibration Drift logged every 24 hours.
NOx Raw Signal WET vs. Dry
CT Outlet Corrected to 15% O2
CT Trial for GE. Frame 7 150MW
Resultant average values between Test trailer
and Fast Response Close Coupled NOx / O2
probe:
Relative Accuracy shown:
Trailer @ 15% O2 = 15.86ppm
8000 Probe @ 15% = 15.4ppm
RA differential 0.46ppm
Response differential 60 seconds
Daily Cal Check Response
NOx Calibration Gas = 25.17ppm Nox Range = 0-50ppm
O2 Gas = 20.9% O2 Range = 0-25%
Sytem Responses Date Day NOx Zero NOx Span O2 Zero O2 Span
9/9/2011 1 0.67 26.09 0.03 20.82
9/10/2011 2 0.60 25.30 0.00 20.80
9/11/2011 3 0.90 26.70 0.00 20.80
9/12/2011 4 0.60 25.40 0.00 20.80
9/13/2011 5 0.40 25.30 0.00 20.80
9/14/2011 6 0.70 24.40 0.00 20.80
9/15/2011 7 0.20 24.90 0.00 20.80
9/16/2011 8 -0.10 24.40 0.00 20.90
9/17/2011 9 0.50 25.50 0.00 21.00
9/18/2011 10 0.20 25.80 0.00 20.70
9/19/2011 11 0.60 25.40 0.00 20.70
9/20/2011 12 0.50 25.00 0.00 20.60
9/21/2011 13 0.40 24.50 0.00 20.80
9/22/2011 14 0.30 24.30 0.00 20.80
9/23/2011 15 1.10 24.00 0.00 20.90
9/24/2011 16 0.30 23.50 0.00 20.80
9/25/2011 17 0.40 23.20 0.00 20.70
9/26/2011 18 0.20 23.50 0.00 20.70
Analyzer Zero Drift
Drift Calculations (Difference From Bottle)
Date Day NOx Zero NOx Span O2 Zero O2 Span
9/9/2011 1 0.67 26.09 0.03 -20.82
9/10/2011 2 0.60 25.30 0.00 -20.80
9/11/2011 3 0.90 26.70 0.00 -20.80
9/12/2011 4 0.60 25.40 0.00 -20.80
9/13/2011 5 0.40 25.30 0.00 -20.80
9/14/2011 6 0.70 24.40 0.00 -20.80
9/15/2011 7 0.20 24.90 0.00 -20.80
9/16/2011 8 -0.10 24.40 0.00 -20.90
9/17/2011 9 0.50 25.50 0.00 -21.00
9/18/2011 10 0.20 25.80 0.00 -20.70
9/19/2011 11 0.60 25.40 0.00 -20.70
9/20/2011 12 0.50 25.00 0.00 -20.60
9/21/2011 13 0.40 24.50 0.00 -20.80
9/22/2011 14 0.30 24.30 0.00 -20.80
9/23/2011 15 1.10 24.00 0.00 -20.90
9/24/2011 16 0.30 23.50 0.00 -20.80
9/25/2011 17 0.40 23.20 0.00 -20.70
9/26/2011 18 0.20 23.50 0.00 -20.70
Target Drift Rates Not to Exceed
NOx = 2.5 ppm
O2 = 0.5 %