NOx testing to begin March 9-10, 2015 on Unit 1 and March 11-12, 2015 on Unit 2.
Garry, Unit one with 8 pulvs in service NOX @ .581 with 2/3 dmprs @ 40%. Load at 950. I took out 1D pulv out of service. So with 7 pulvs in service at 950MW and 2/3 dampers @40%, NOX went to .444. Time was approximately 20:30 to 20:50
I FOUND THAT ANY MILL O/S THE SECONDARY DAMPER OPENED WILL REDUCE NOX EVEN THE BOTTOM MILLS. ALSO AFTER OPENING THIS O/S DAMPER ALONG WITH LESS OVERFIRED AIR I/S WILL REDUCE THE NOX LEVELS. SOOTBLOWING SEEMS TO CAUSE THE NOX TO INITIALLY TO INCREASE THEN AFTER CLEANING WITH HELP REDUCE NOX. BJ
During our testing it took at least 7 to 10 minutes before the stack NOx point moved. Another 15 minutes before the point stabilized out. CO spikes during ramps and it takes time for O2 to catch up. When using just the out of service pulverizer secondary air (cooling air) the best NOx was around 72% open. This correlates to the highest CO point as well.
Here are additional Directives and Guidelines that should be followed as we strive to demonstrate out lowest possible NOx emission levels:
1) We have experienced several Furnace upsets while removing pulverizers from service at reduced loads (Less than 600 MW) while utilizing the Over Fire Air System. For that reason, we are asking that we remove OFA when in 6 Mill Operation. (Or less) It is vital that we all are aware of potential Unit threatening conditions that can exist if certain emission control techniques are being utilized. That is the very reason for this Blog. PLEASE LOG any concerns that are observed. This Information is vital to the safe and reliable operation of the Units. Let's not hear about these episodes from bystanders.... This information needs to be known by any, and all, who have responsibility of Unit Control.
2) (Reminder) As always, when utilizing the OFA System, return the cooling air on the out of service Mills back to their automated states. We are still observing the utilization of both OFA and Pulverizer Cooling Air together. Be attentive.
Other directives will follow...
Get involved with this Blog. It's pretty sad that we have 2 entries, and 2 are from Garry.
Just to clarify: NOx Reduction- Low Load Operation
Below 600 MWg with 6 pulv operation, take OFA o/s and utilize Simulated OFA (upper pulverizers o/s at cooling air damper 50-75%)
This will help combustion by reducing CO and improving fly ash LOIs.
In the past, we have experienced Furnace fluctuations when Swing Gates are Closed at the conclusion of our Cleaning Cycle (100% PA Flow) when operating at reduced Load. Those fluctuations can be minimized if we allow our PA Control Damper to return to it's normal operating position before Closing the Swing Gates... Something to consider.
FYI......... We need to be aware that moving our OFA Dampers too quickly can cause significant air flow fluctuations. Controlled integration is important.
At full load Unit 2. Overfire air dampers were opened 45% @ 6.7% total OFA and D mill O/S with Sec air Dmprs at 65% CO around 800 PPM and NOx at .29. Going down into the 620-740 Window NOx was down to .271 and CO at 7 PPM. Removed overfire air slowly and 1E Mill from service, NOx landed around .270 and CO around 10 ppm with 1D mill Sec air dmprs still at 65%. Unit load stable at 660mw. Looks like this worked well.
Unit 2 At 790 MW 1D Pulv. o/s cooling air at minimum observed through several changes in OFA damper position from 0 to 90 % that possible best OFA damper position was 40% This is where NOX came below target at .300 lbs. and CO below 200 PPM. As damper position increased, was able to get NOX to .260 lbs. but CO increased significantly. To observe data on PI 3/20/15 10:00 to 17:00
Ramping Down U-2 At 740 mw took 1E mill OOS and over fire air out. Nox was around .31 and Co 200. with 1D and 1E mills out of service I opened the Sec. air dampers on the two top mills to 55% with no change in Nox, at this point, Co had dropped to 2 ppm. Going into the 480-620 window the sec. air dampers on D and E mills were placed back in auto with no change in Nox or Co.
1-27-16 @647 MW we had 10% over-fire air and D and E pulv's
secondary air dmper were @ 70% open. Nox was @.24 tp .25
1-28-16 @ 533MW we had 10% over-fire air and D and E pulv's sec.
air dmper @ 70% open, we were at .233 Nox. @805 MW we had 10% over-fire air in and our Nox was @.318 to .323 We couldn't add anything else due to air requirements. Note also on 1-27-16 we had a -.2 bias on O2 trim. on 1-28 @ 533MW the flame looked at little purple so we couldn't use the bias. These tests were on unit one.
Unit 2, 2/7/2016 0000-0300
On Febuary 7 night shift after reading several memos regarding Nox control and using the Oxygen trim station to lower excess O2 levels to no less than 2%. I attempted to try to achieve the best nox results possible, Here are the results.
480 Mw, 5 mills in service, the nox level at the stack was 0.222 with 60% air on the two top mills.
I took (A) pulverizer O/s which left me with 4 Pulverizers and a Nox level of 0.197, C pulverizer is Dno'd.
I took the Oxygen trim station to manual and started decreasing the setpoint from 60 and ended up at 30 which put the excess o2 at 4.7% from 6.1%. The engineering memo stated that we should be able to reduce to no less than 2% o2 probe indication. The nox result ended up @ 0.189.
This is what we seen. The drum became unstable, the draft was swinging more than usual, and the Reheat temps were at 937degrees. I increased the trim station from 30% to 34% output due to a high vib alarm that come in and cleared on 1A ID fan outboard bearing. I just wanted to pass along the results that we seen with excess air reduction in the boiler.
Barry.... The 2% Excess Air Lower Limit refers to Full Load conditions. It does not mean that we can lower Excess Air to 2% at
Lower Loads. That could cause issues such as those you documented. I will try and provide clarification when answers can be found.
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NOx Reduction Program