we are experience frequent failure of CO & NOX anlayzer located at the HRSG exhaust stack. Because of the failure we can not predict the actual emmissions from GT exhaust.

Is there any way to calculate manually the CO, NOX & O2 content from the GT exhaust?

Our gas fuel data are as under:

Natural sweet gas data:

Methane MOL % 85.69421387
Ethane MOL % 7.312310219
Propane MOL % 0.829226971
I-BUTANE MOL % 0.184735999
n-Butane MOL % 0.184735999
I-Pentane MOL % 0.057493001
n-Pentane MOL % 0.053213
n-Hexane MOL % 0.076361999
Nitrogen 5.67923975
Carbon Dioxide 0.005658
H2S grains/100scf 0
LHV 936.6845093
HHV btu/SCF 1030.35296
Specific Gravity 0.629812717
Water content
Total sulfur grains/100scf


GT Mass flow# 401 Kg/sec
Inlet Dry air mass flow# 385 Kg/sec

On line analyzer NOX reading# 10.16 PPM
On line analyzer NOX reading# 12.09 PPM
on line analyzer O2 rading # 12.11 %

What are the parameters required to calculate the NOX, CO & O2 content at GT/HRSG exhaust

We are operating GE frame 7FA with DLN 2.6 ( dry low nox) technology for the low nox emmission

 

If it were possible to calculate emissions (manually or automatically), there wouldn't be any need for stack analyzers.

In my experience the biggest causes of CEMS (Continuous Emissions Monitor System) failures are:

--Improper installation (the CEMS vendor should be able to help with analyzing the installation to see if it can be improved or corrected)

--Lack of or improper maintenance, including incorrect procedures for changing reference gases --a propensity for purchasing departments to "source" poor quality gases or gases outside CEMS manufacturer specifications (to "save" money)

--poor quality CEMS monitors (purchased to "save" money); when the operation of the turbine(s) is dependent on emissions monitors and data, the emphasis should be on reliability and quality, <b>not</b> price (as is usually the case).

You can estimate (using calculations) emissions, but if you are required to report actual emissions (as in some parts of the world) these won't do. If your control system requires emissions feedback, calculated estimates aren't going to be very helpful, either.

Get a reputable consultant or a CEMS OEM representative in to review, analyze, and comment on the installation and maintenance practices in use at your site. Listen to this individual, ask questions if you're uncertain. Analyze the recommendations, and then act on them.

If you can't operate your plant because the CEMS isn't operating or isn't reliable it's time for action.

 

I am not at all a specialist on emission monitoring systems but i know there are predictive emission monitoring systems (PEMS) on the market that claim they can accurately predict the NOx and CO emissions. These are generally used for the smaller gas turbines. Even GE provides this for their LM2500 series. For more information concerning this system see the link below:
http://www.gepower.com/prod_serv/products/oc/en/downloads/284015A1.PDF

For more information just google on PEMS.

I do not trust in these systems for gas turbines as you lose an important combustion indicator... Possible problems are overlooked as one relies on a PEMS. A decent CEMS is more expensive than an unreliable CEMS combined with a PEMS but it's worth the price...

 

I agree with the previous coment, and would ask what kind of failures are they?, NOX and CO analizers uses a "cell" to measure, do you use a regular calibration procedure?.

You can buy a portable gas analizer to compare to your field equipment. May be your problem is something as simple as a gas sample line with a leak. May I recomend to try a RCA, root cause analysis, that could give some answers.