Environex at CCUG – Is Your SCR / CO System Ready for Turndown?

 
Robert:
Andy is from Environex. He’s worked in the power industry for more than 15 years. He is currently the senior project engineer at Environex. And we welcome him with his presentation, is your SCR/CO system ready for turndown? And the second part of that is how increased NO2/NOx ratios require additional SCR performance. Andy, go ahead. You’re on mute.

Andy:
Thank you, Robert.

Robert:
Yeah.

Andy:
So I guess I’m floored by the participation list. This is fantastic. I’m hoping that all of you enjoy the topic of high NO2 to as much as I do. Thanks to CCUG and Scott for getting this all set up. We’ve been looking at turndown in a lot of different ways over the last couple of years. Most of our focus was on CO, but we had a couple of case studies come up where the challenge was SCR. And one of them I want to talk about today because the end result was very interesting. So for those that don’t know us, Environex started in 1991. And our focus is basically to take the mystery out of your CO and SCR catalyst. And we do that with lifecycle management, testing, design services, troubleshooting, training, AIG tuning. And today is going to be a little bit of all of those, when we talk about some of these case studies.

Andy:
There’s two. So the first one is the high NO2, that’s the teaser for the title of this presentation. The second one is a cool study that another plant did, where they were able to trim their load down in five megawatt increments to 10 megawatts they were able to get down to. And it shows how CO increases exponentially. And how temperature also decreases because you’re in combined cycle, that’s thing that happens. So what they could do to get to low load would me my [inaudible 00:02:37] for that particular case then. But before we get into that, I want to get everyone’s interest in low load and turndown. So my first poll question is, how has your cycling frequency increased? Has it? Or have you been able to run in base load? So that’ll be question number one. This is also to gauge interest. We’re going to get the ball rolling on a softball question here. So if you guys can answer that one. I will go on to my next… This topic, which is a little bit of background.

Andy:
We’ve to talk about competing reactions for SCR reaction chemistry, this blue one on the top is the reaction that everyone knows. This is where we typically say it takes one ppm of ammonia to remove one ppm NOx, that’s this reaction right here. But it’s… Another reaction that occurs on the same catalyst is this skewed ratio here of ammonia and NO2, which is significantly slower than reaction A in blue here. So the takeaway is, while your catalysts can do this reaction, it’s not often… It’s not as fast. So you need either more residence time or a different formula. And I needed everyone to get on board with this background knowledge before we can even get into the case study.

Andy:
And then for the rest to round out what SCR is, you have this potential ammonia oxidation, this occurs a very high temp or if you have an oxidation material on your SCR catalysts, and then you have ammonia salts that form. This is just a refresher slide to get everyone’s mindset ready to talk SCR. And for the second case study. Both of these graphs are also important to keep in mind. So, when you design your catalyst, 10, 15 years ago, he would look at temperature, and it would probably be baseload. And it would probably be high, let’s say in… [inaudible 00:05:09]. In this particular case, you would design to a temperature that’s in the 700s for NOx and CO. And as you can see from this graph, this is where SCR is the highest performing, it’s in the 700 to 750 window you see here, and for CO catalyst over on the right, once you get up over 500, you’re over your light off curve. But your best performance occurs up here at 800, 900 degrees. In combined cycle, you’re just not getting that.

Andy:
And as you turn down, you’re getting lower and lower in temperature. And you also have the problem of sulfur that’s been laying on your catalyst surface in temperatures below 650 F. So the next takeaway here, so we’re all on the same page, is operating temperatures range, not a number. Now we can get into the fun stuff. This first case study, we were asked to investigate why the ammonia flow was significantly higher than design for these combined cycle units. And we were told that this higher ammonia flow is happening at low loads. So we were… If you think about things on a mass basis, that wouldn’t be intuitive. So we went on site, we saw… We looked at operating data, we saw the vaporizer temperature was low at this high ammonia flow, mostly because they were trying to inject more ammonia flow than the vaporizer was designed for. And you were getting… The heat wasn’t vaporizing the liquid well enough. And they had preliminary investigation results that showed high SCR performance. So this is a very interesting mystery. And there was a lot of work done prior to us getting there.

Andy:
Here’s some of it. GE/Alstom had suspected that NO2 was a potential issue. So they were on site with a stack tester to evaluate the… Terminate the NOx profile, are we above 50% NO2? Because that’s always the standard when you look at replacing your SCR catalysts, if you ever take a look at those bids, that is written in very explicit print where the assumption is that the ratio of NO2 to total NOx is below 50%. And as long as that’s the case, your SCR will not have any problems. But when it’s over, and we’ll get into this more with some actual test data, that’s where the problem lies. So GE/Alstom were on site and they measured NO2 that was higher than 50%. This was not by… This is not designed and it will change what is required of your catalyst.

Andy:
At the stack, they found something very similar, where with no ammonia injection, so this is a backup test, still having the stack tester on site. They also doubled up on their measurement and saw elevated NO2 above 50%. And as high as 70 during startup. And this was one of the conditions where the plant was over injecting ammonia to compensate, which is normal because that’s how your controller works. If your stack NOx is high, it wants more ammonia. It’s a very simple system.

Andy:
So that’s all the data we collected on site. We took a CO sample and a handful of SCR samples and came back to the lab. Here is one of the first tests we performed, a standard CO oxidation light off curve. In both units, the performance was excellent. This plant only needed 85% COO conversion and the chat… catalyst test results were incredible and this is the performance that you want. There are a lot of plants that need 95% conversion and this plant was easily doing it after a year of colder temperature. This is a very good CO catalyst. And on the SCR catalyst side, same opinion. This catalyst also tested very high and if you look at the red line I have here on the graph, this is the minimum required activity at peak load. So we’re at baseload, this is normal operation, this is how the catalyst was designed, the results are great. So, as a catalyst vendor this was well engineered, but yet the plant was having problems.

Robert:
Now, does that get wiped out?

Andy:
Well I could talk through that one. What they found is they put a turbine exit NOx analyzer upstream of the CO catalyst, there was available port there. And the plant… This is just similar to the results from the GE study. The plant also measured high NO2 here’s a case where it was way above 60. But if you look at this concentrated data here and over here, you’re not well above the 50% mark but they’re certainly excursions at low load where they are. So this was the next item to for us to look at. We took that CO catalyst, and put it back in the reactor. Now instead of flowing CO2, we float… We’ve set it up to measure NO to NO2 oxidation. So before the CO catalyst, we were potentially measuring over 50% NO2 and we know the graph has to go across the CO catalyst. How much more NO2 is the CO catalyst making? And we suspected it was going to be high based on the high conversion results that we saw from the normal light off curve and that this is certainly the case.

Andy:
So if you look at this oxidation rate here in percent, the CO catalysts at the plant operating range oxidized an additional 50… Almost 50% No to NO2. So of the 40% measured up to 50% measured in the plot above now you have an extra 40% at this point you are definitely over 50% NO2 to NOx ratio. So then, we loaded some SCR catalyst samples back in the reactor and here we varied the NO2 to NOx ratio at the temperatures that the plant sees, at the space velocity which is just a ratio of the exhaust flow to catalyst volume that’s similar to the plant. So we ran it at plant conditions and we wanted to see what conversion the catalysts can do while altering the NO2 to NOx ratio. And what we found is that over 50% with low temperature, the catalyst performs lower which you would expect.

Andy:
Another interesting result to these curves is they match exactly with every test study for the same conditions. So we were able to recreate this with very similar results. And what this is saying is this makes a lot of sense it’s acting like the catalyst is that end of life because you’re seeing the NO2 slip through and go unreacted and then you’re measuring it together as NOx at the stack and your control logic just wants to spray more ammonia. And then the other part of this mystery was that the NOx in itself was higher than design. So the catalyst manufacturer was given 20 as a design condition and they were seeing excursions during load transition that were up to 25 ppm and then with duct firing significantly lower than that and then duct firing also has the benefit of hotter temperature which the SCR catalyst likes. So there was never a problem at baseload for this particular study. Everything that was… All of the issues were happening at low load and it was a combination of lower temp, higher total NOx, and a higher NO2 to NOx ratio at those conditions.

Andy:
So how do you fix it and that’s where we had ended this study. If you want to… If you use the 70% NO2 to NOx ratio that we had calculated based on the oxidation catalyst test results and the NOx measured before the oxidation catalyst, this particular catalyst would need an additional 20% volume. And with that geometry would have equated to an additional almost three quarters of an inch of water pressure drop. So, here the catalyst again was designed perfectly to do baseload and then the issue of low load caused this chaos. But there’s an alternative to this as well, you can… Both manufacturers have… SCR catalyst in the United States, have a high and NO2 formula. Both have been used in the refinery industry, no one’s really broke into it in natural gas turbines yet, but it is available. And I believe that is the direction this plant was going to go in the last we spoke.

Andy:
So, before we get into the next case study, I have another question here. And it is essentially how low can you go? So, the next case study is all about trying to see how low the plant can operate. I’d like to know from you guys, how low can you operate? Are you trying to get below 50%, which would be A here, because you’re going to be very interested in what’s coming. And for B, C, you’re just not there yet. It’s coming. The need to offset renewables is heading from west to east, and also from east to west, and those meet in the middle somewhere. But the need to do that is a gift coming. So if we can go to the next slide, we will get into case study number two. So, again, this is a situation where there was work done before we got there and Environex’s role was to interpret the results and give them a real recommendation of how to pull this off. So this one was, how low can we go?

Andy:
The plant measured steady state, CO and NOx emissions incrementally, at loads down to 8%. So every five megawatts or so they would hang there and wait for the emissions to steady out. And you’ll see in the upcoming plots, they did a very good job of doing that. And then see how high the CO goes. That was the goal of this experiment. I want to show some background slides first. So here’s how all these slides are going to look. We’re talking about load in terms of percent, and we’re starting at 50%. So that’s the big… That’s what’s different from all of these slides. That is atypical when disseminating this information. We’re already going to start at 50% and go down. In this particular case, a 50% load here and operating temperatures 675 F, and this goes down as you decrease in load to 605 at 8% load. This is much lower in other combined cycle designs for CO catalyst temperature and the worry here is below 650… Sorry here we go. Below 650, you run the risk of sulfation on top of your CO catalyst, which prematurely the activates your CO catalyst.

Andy:
So this is the first item that Environex took into account when making the recommendation of how to operate. We can’t have an experiment for CO and not measure STR since they’re both right there. In this particular case, there was a section of boiler tubes in between the CO catalyst and the SCR. So you see these temperatures are lower. In this case you only see about a 10 degree drop. So here we get into the exciting part, for NOx, as you came down From 50% load, there was a drop to… In the range of 40 to 30. And then the NOx increases from 35% load down to the 8% for this experiment, so this is interesting. And we would take this into consideration, the design that the catalyst could handle for this catalyst is… Was at the 15% mark, which meant this 45 here, the catalyst, could have… The SCR catalyst had enough performance to do the work that we needed. So, that’s your limiting case for SCR.

Andy:
For CO, much different. Here, we’re looking at emissions that increase from 40% in the hundreds to over 2,000, as you get to closer to 10% load. This ended up being the design limiting case. So, at a conventional CO catalyst designed for 90% conversion, we were limited to 35% load. So right here with a regular CO catalyst, this was what the unit could do for turndown, 35% load. So then we got creative, what if we took out the SCR catalyst and put in a dual function catalyst. Here you have the ability to keep your oxidation catalysts do your 9% conversion there. And then we gave the dual function catalyst a modest 80% conversion. So, if you take both of these into account, you could get down in this case for this turbine to 28% load, that would give you 98% CO removal. As it turns out, well, if you look at this, if this was a 200 megawatt unit, you’re talking about 15 megawatts.

Andy:
So is this the right move? This would be up for the plant to decide in terms of megawatts that the added cost of the dual function catalyst would be something to consider. What ended up happening, which was interesting, is on the [inaudible 00:22:35] side. They were having trouble keeping this operation steady below 35% load if I remember correctly. So the project ended with the combined idea to just stick with the CO catalyst and not pursue the CO and dual function. But if anybody ever puts that in, I’d be very interested to see it. Because I think that’s the answer in how to get what I will call extreme turndown. Feel free to find me, if you are to install that, I’m very interested. But in the interest of saving time, I spoke a little fast there in the middle. We about made it to the end. So the takeaways, I did them individually, are if you have high NO2, it’s something you have to measure. And you also have to make sure to measure the CO catalyst ability to make more NO2 and there are formulations out there.

Andy:
But since the reaction is slow, another way to handle that is to put a large SCR catalyst volume in your duct and the others remember there’s pressure drop penalty to that. So it may behoove you to look into combustor tuning in lieu of doing… Putting all this SCR catalyst then. And then on the CO side, for case study number two, you could go lower in emissions, but your CO increases exponentially. And then there are some creative ways to still meet your stack when that’s and pursue a load that’s far below 40, 50%. I think that’s about good here. I’m very open to questions. I love this topic very much. We’ve been talking about turndown for three or four years now trying to point out all of the mysteries and bring to light the issues that individuals are having to the center stage so that you guys can combat them with less issue.

Robert:
Okay, well, thank you, Andy. Very good, very informative. Very good information. We’ll go ahead and open it up to questions now. If you have any questions, please enter them into the chat box. And we’ll get those questions over to Andy.

Scott Schwager:
Hey, Andy, this is Scott Schwager. I was just curious if you were surprised by the poll results for your second question. The majority of the respondents chose B, 50 to 75%. And very few chose greater than 75%.

Andy:
I do find that interesting. Thanks, Scott. The… So we rarely see huge issues in that particular window. It’s the quest to go below 50, where we’re getting the calls, because we only get called in on things when there’s a problem. So we’re usually seeing the units that want to go below 50. If any of you guys are having issue between 50 and 75. Most of the time should not be NOx because you don’t really see a NOx increase from 50 to 100. But feel free to share. And maybe I have a quick answer, or maybe it’s a little more convoluted than that.

Robert:
So one of the questions that we have that came in is, can you explain a bit more about the catalysts? I’ve jumped over here, hang on. Can you… I’m sorry. Can you explain a bit more about the catalysts formulation used in other process plants but not for power plant duties?

Andy:
We’re… No, I mean, I wish but there’s a confidentiality agreement there. What I will tell you is I’ve seen it work really well. We haven’t done any aging. But whatever the additive is to a conventional SCR, it works in both cases. So both of your major US manufacturers have a formulation. They’re different. And they both work. And I wish I could have more on that, maybe next year for CCUG. I’ll get my hands on one in the field, and then there wouldn’t be a confidentiality agreement in place.

Robert:
Sounds like a presentation for next year already in the happening. So the next question we have is, do you have any data on how far a Ge7F [inaudible 00:27:54] can turn down to meet nine ppm of NOx and CO?

Andy:
Oh, yeah. So we did this a lot. As a matter of fact, this is the seven F with the VLNs, this is something that I mean, over on the West Coast they’re very actively having to do. Normally, and this is the interesting part about your question. I mean, it’s not a plant, but I’m going to go forever now, you would think that you never had a CO catalyst until you had to turn down in those plants. Your rated emissions for Ge7F were 10, which was an over estimate, they were mostly under two. So if you had a limit of two, and you never had to turn down before, you never had to do any CO conversion.

Andy:
But then once those units began to try to go under 50% load, CO would increase. NOx? Not as high because CO was going to be your limiting factor. And then you would see these Low temp CO catalysts that had software on them not work because they haven’t had to yet. So it wasn’t that they weren’t working before, it was that they didn’t have to do any work before. And now that you needed to see some performance, they didn’t have it. So offline, I can anecdotally share what some of those emissions look like. But you’re… The bigger problem when you go below 50% load in a seven F is CO than SCR. The SCR is… The NOx doesn’t increase near as high and as exponential as your CO.

Robert:
Okay, so the next question is, if we are looking to increase the megawatt output of our combined cycle over the initial design, are there any concerns that we should be aware of on our catalyst system?

Andy:
Oh, we touched on that recently too. So yes, for example, the… I can’t remember the number but that increase from the seven F that went from 175 to 200 megawatts that… GE had… Again because they’re conservative with their estimations they had predicted that your NOx would increase by two or three ppm but your temperature would increase, but your flow would increase. So the temperature increase you like and then your bulk flow and your NOx increased they’re worse for SCR catalysts performance. That’s intuitive.

Andy:
But the NOx increase wasn’t that high in field data and the temperature increase was better than expected but not over the 750 threshold where SCR catalyst performance goes down. So if you’re looking to do a combustor upgrade like that then it may… It would behoove you to look at the operating data afterwards. So take some catalysts testing and then we can predict what we think the emissions are going to be, and if your catalyst is healthy enough for the experiment then you stall the upgrade, look at more data and from there we can change the life projection of the catalyst. Find me offline for this, i have a really great graph that shows what happened with predicted and actual measured emissions on this particular subject to lifecycle, because it wasn’t as grim as design would have made you believe, it was somewhere in the middle of no upgrade at all and what the design was feared to be.

Robert:
Okay, do we have any more questions? I see we have a comment, do we have any more questions? Okay, so one question we have is with a permanent limit of 3.5 ppm how much of an impact will controlling to 2.8 or three ppm have on your catalyst life?

Andy:
This is a great question because all your transient points for many of you are also being limited in terms of compliance. So everyone’s running below what their limit is. What this means is it changes the performance requirement of the catalyst. This is something that whoever is testing your catalyst like us, would love to know in advance. So without knowing where you’re actually running we would project life to the 3 pm… 3.5 ppm limit in your specific case. And that timeline would be longer than what it would be if you’re controlling down to the 2.8 or 3 ppm that you have there. So that’s the difference, we’re talking about maybe a year of catalysts life is different at most but it’s important to have, because the worst thing you could do is over project catalyst life and then you’re scrambling around and paying expedites going to new catalysts in there where testing and end-marrying your test results to your actual operation like your point right here gives you the best end of light projection.

Robert:
Okay so next question… So the question is, is this conclusion correct? The limiting factor in turndown with current combined cycle plant SCR and CO catalyst is operating at sustain loads below 38% as this causes poisoning of the CO catalyst by sulfation deposits.

Andy:
Well, that’s a long one. Unfortunately, it depends on a lot of things. So a lot of your CO catalyst manufacturers are doing a much better job at creating a sulfur tolerant formulation. So if you have something newer then the low temp issue is less of a fear but the other issue that you have is operating at a lower temperature. So you would think at low load you’re running with less mass flow this should be easier to do. But with the extreme increase in your CO emissions before your oxidation catalysts, and the lower temperature, both those things have an impact, but it’s the increase in CO that rules why… That rules where you can run, because if you can only… The catalyst operates in terms of conversion and not if it’s x, your result is y. So if you have 100 ppm, and the catalyst can do 90% conversion, then you’re talking about 10 ppm of CO coming out. But if that number is 500, then you’re talking about 50 at your stack, and if your limit is 10, for example, then you can’t turn down that low with your current catalysts.

Robert:
Okay. The next question we have is, is the catalyst life reduction gradual or some point it falls off the [inaudible 00:36:09]?

Andy:
In terms of your SCR, that is exactly what you’re going to see. You’re going to see a scenario where your ammonia slip exponentially increases past your ammonia slip limit. And the reason why that is, is because of how your NOx is controlled. Your stack NOx is your variable that tells your ammonia to flow more or less. So when your catalyst reaches its end of life, it doesn’t have the ability to meet your stack number and your stack, NOx will increase. Let’s say your limit is three and a half, like the gentleman’s example above, you have… You’re at three and a half ppm. And as your catalyst deactivates the point where it can’t meet that three and a half ppm, your stack sees 3.6, 3.7. And what it wants to do is increase ammonia to reduce that down to three and a half. And if the catalyst doesn’t have the performance to do it, then it just keeps increasing and increasing and increasing until you have a situation where you’re near your design limits for your vaporizer.

Andy:
Then this is all without talking about ammonia slip, I mean, you’re going to go through your ammonia slip first. And then if you’re not measuring that continuously, the number will just keep going higher until it’s a maximum in your controls. Or a temperature limit where your vaporizer can vaporize all the aqueous that it needs to get your additional ammonia in there and you’ll get a low temp vaporizer alone. In your CO catalyst, it is dependent on what the deactivation mechanism is, we’ve seen some non sulfur tolerant CO catalysts deactivate in cold applications like 550 F in a month, we’ve seen them deactivate in six months and we’ve seen them deactivate in 60 years. So the rate of accumulation is important. And the temperature obviously is important and the amount of CO catalyst reduction needs to do. So if it’s somewhere in the 70s, for example, then you have a lot to go for… Because your CO catalyst is typically designed for 90%, it’s just a healthy window in that light off curve.

Andy:
Both of these can be predicted with testing. So I mean, that’s one of the hallmarks of Environex is testing the catalysts, you know where it’s at, you know where its performances, and you marry that up with the operating data. For example, if you’re controlling two eight instead of three five, and then we can hit that… The story I always tell is there was a customer I worked with a couple years ago, he said, “We’re going to go past this life projection, and we’ll see where it ends up.” Because they had the opportunity to do that. And I missed it by two months, I was close enough to two months of a life projection. That was a nice feather in my cap for this career I’m trying to make over here.

Robert:
Okay, thanks, Andy. I don’t see any more questions.

Speaker 4:
Hey Andy, just an easy, easy quick question. When you go in and you start pulling samples out of the catalyst, are you taking them not just off of the test plugs? Are you going in and pulling pieces out of the catalyst and other areas? Or how do you go and map that?

Andy:
Well, one of the most interesting things that we do is bring our own fresh catalyst and a core drill so that we’re not married to the sample location. If there’s, let’s say, you have a tube leak, and it’s on the… In the middle of your duct and towards maybe the east side, and your sample tray is on the ground on the west side, that wouldn’t be a very light… That wouldn’t be a good candidate to see if you have any alkali metals on your SCR catalysts. So what we’d do is we’d scaffold or sky climb and get up to where the potential damage is, and take a core sample right from there, and then plug that up with some fresh catalysts that we bring on site.

Andy:
And then we have the ability to… We have the complete flexibility to test anywhere. And with SCR catalyst you want to. So everyone here has a unit that has at least two batches of SCR catalyst in their duct because of volume. I mean, it’s… The process is very interesting, but it starts out like a dough and it’s extruded like a pasta and the batches that they use you can’t fill one of the units that you guys all have because they’re all big, you can’t fill that with one batch. So getting more than one sample and determining if… Where your bulk catalyst activity is, is also something that you’d want to consider. I’m going to use my presentation here, hope no one gets seasick. But I just want to show the variation in these SCR catalyst tests. So when you’re near end of life, this, almost 10% difference between these eight samples that we tested from one unit is important. So if you measure this guy, for example, and I’ll tell you that knowing my… Because I did this project, knowing that it’s sample A it’s towards the top.

Andy:
So if you were to take this top sample, you could overestimate how long your catalyst life is. And if you take this guy here, which would be towards the middle of the back, this sample would underestimate how much catalyst life you have. Now, is this difference huge? No. But taking all of these samples gave us a better appreciation for where the average is. And we would project the catalyst life accordingly. Those two are the difference between, probably, three quarters of a year, maybe a year, that we would project.

Robert:
So Andy, this is Robert, I have a question for you. So most of the plants that I worked at, were built in that early 2000 bubble. So then, we weren’t testing catalysts on an annual basis, but a lot of those plants are 20 years old now. So you could be testing every other year on both SCR and CO catalyst to try to figure out where you’re at so you can project end of life. So with… So an example is we’ve installed a new SCR catalyst and a new CO catalyst. CO this past year and SCR a couple years ago. So what would be a good testing frequency other than testing for baseline when they were installed? What would be your recommendation as far as… Moving forward as far as testing I mean, you don’t need to do it every year, but should that really be based on operating profile changes or hardware changes, or it was… It deserves a methodology to the testing frequency that you will do now if you do have new catalysts installed?

Andy:
Absolutely. The catalysts that you have installed in 2001 at the time everyone over designed. So result, unless you got a direct in-kind replacement, catalyst volumes are more competitive. And I’m sure that you took pressure drop into account, and your catalyst volume is also going to be lower to lower pressure drop, those two things are intuitive. That being the case, you can’t bank on getting the same life as you did with those catalysts that you did with the old one. So with test frequency, I like baseline, that’s great, where you’re starting, and then somewhere towards the end of warranty or a year after the warranty. Let’s get in there and take multiple samples and marry it up to your operating data.

Andy:
So when you talked about hardware changes and operation profile, turndowns, up firing rate, et cetera. Those are all things that your catalyst tester would need to know. Because it changes where your bottleneck condition would be. Or even just how, in some units, especially those older GE units, the cold weather affects how much mass gets sucked through those things. And that changes the performance of the SCR. So knowing all those things with hourly averages of your operating data really gives us a lot of information. And then that would dictate your test frequency. So I was getting around to answering your question, I just… I had to preamble that a little bit.

Andy:
So where your performance is, based on where it needs to be, would be how I would recommend the next catalyst test in your cycle. If you have barely any CO conversion to do and your CO catalyst is in good shape, maybe that thing can go five years. But your SCR maybe you need a tight 92% removal, then… And you maybe only have a 5% excess margin, maybe you’re going to want to test that every two years or every three. And it all… The first test after baseline really sets up a schedule that we would help you with to determine where you want to test and where you want to monitor for the other aspects of prolonging catalysts life like cleaning, or AIG cleaning, to blast that… All of those other things. Plugging in your CO catalyst will affect your SCR catalysts downstream. Because here you’re changing the bulk flow that your AIG was designed to and your SCR catalyst isn’t aware of that. So you have a skewed ammonia to NOx ratio. So if you have a fouling issue with insulation that would also want me to increase the frequency of both maintenance and testing.

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