Soot Blowing Basics 5

[dave472005]

I am a seasoned Mechanical Engineer, however, most of my 15 years experience has been on the nuclear side of power generation. I am leading a very small team to evaluate and improve soot blowing performance on a boiler with PRB coal. As you might imagin, I am on a steep learing curve to understand soot blowing, performance measurements and practices. I am also going to a soot blowing symposium by an equipment manufacturer in a couple of weeks.

I am looking for advice on sources of information to help me get up to speed on keeping the boiler tubes clear of ash build-up.

Thanks in advance - Dave

 

[metengr]

Going to the symposium is probably your best introduction into getting the basics of soot blowing. After that, it really comes down to experience. We have been burning 100% PRB for about 10 years in our boilers, and what I have found out is optimization of soot blowing is learned on the job.

As a side note, our thermal performance engineers have been working with software to determine the cleanliness factor before and after soot blowing to optimize the frequency of blowing.

 

[rmw]

If your company will let you travel, the Power Gen conference in Las Vegas later this year will have all the major soot blower and boiler cleaning vendors represented. You can learn a lot from their displays as well as get contacts for the information you need.

There are also companies who don't make soot blowing equipment per se, but who do software for controling cleaning. This link will get you there.

http://www.forry.com/

I assume that you have the ability to google "soot blowers" so I won't go get all those links for you.

rmw

PS, I think this forum is the place for your question, and you should red flag your own double post in the other forum and ask site management to delete it so it can be dealt with here. IMHO only.

 

[dave472005]

To RMW - Thanks for the help. Dave

 

[cub3bead]

Don't forget to evaluate air as a possible soot blowing medium. There is atleast one 750 MW class plant firing PRB coal that uses air soot blowing.

 

[rmw]

You are faced with different scenarios regarding the soot blowing requirements of a PRB fired boiler.

First is the furnace, where water as well as steam is often used to get the slag off the furnace walls with the wall blowers.

Next is the SH/RH/generating tubes/economizer tubes, which can use any combination of steam, air, water, and or sonic methods. I suggest you google "sonic sootblowers" too. While their place is limited, there is a place for them.

Also investigate explosive methods of slag removal. Shotguns fired from obvservation ports is commonly done on PRB coals.

Once, about 25 years ago, while in a PRB fired station, taking a lunch break with the mechanics, they got to spinning yarns about the slag removal exploits that they had experienced. As they described 'dynamiting' one particularly large piece of slag build up, I asked "how big was that piece of slag?" and Bubba answered 'about the size of a school bus.' To which, another mechanic fired up and said "it wasn't that big, it was only about 8' X 10' X 40'....hmmm...well, I guess that is just about the size of a school bus, isn't it?"

In another station larger than 750 MW in my corner of the world some years ago, a large piece of slag build up fell and took out the "Vee" bottom of the furnace. It caused an explosion that remains officially unexplained, but which my personal opinion is that it was a hydrogen explosion caused by the disassociation of water that escaped from the ruptured ash furnace bottom tubes and sprayed onto the red hot ash.

Dave, be thorough in your quest, as it is a big topic you are seeking information on.

rmw

 

[dave472005]

Thanks RMW

I am learning about air soot blowers
- wall and retractable which we have in all of our boilers,
- water lances/cannons (depending on the manufacturer) and
- just found out that we are using sonic soot blowing in our SCR.
- Also came across a dentention type - explosions to cause a pressure wave in a fire box make me a little nervious.

Right now I am working on understanding the typical uses for each type, advantages and disadvantages. My approach is to find the generally accepted soot blowing approaches and applications, then revealuate the current system for improvements - need to understand where I am starting and have an idea of where to go - then draw a line connecting the points.

Any suggestion/thought/comment are always appriciated.

Dave

 

[rmw]

You may be a good one to do this, as you have no preconceived notions, nor axes to grind with respect to what has already been done.

The major soot blower companies that google would find all should have reps in your area. I suggest setting up appointments with each one and letting them come in and do a walk down of your system with you and make recommendations for improvements.

Remember that each will be wanting to supply you with new equipment, that is how they exist, so take it all with a grain of salt, but, that said, those guys live in that world 24/7 and if their proposals have merit, they can give references for locations where their proposed solution has produced results for you to check out.

rmw

 

[eyec]

sorry to be so basic, but an ounce of prevention is worth a pound of cure!

BALANCE YOUR BOILER

you can sootblow 24/7 and not improve or even maintain boiler efficiency if your boiler is not balanced and burning at the most efficient to PREVENT ash buildup.

include water chemistry in the equation to provide better internal heating of your tubes.

once that is done (or atleast underway) then look at you sootblowing procedures/processes.

 

[dave472005]

I am part of a team looking at the overall operation of a coal fired boiler using PRB coal. My portion is sootblowing and the operation of the superheat/reheat spray valves and dampers. There are 6 groups in the overall team that are looking at all parts of the boiler and combustion process.

The more I talk to others about the boiler, it is becoming very clear to me that the overall boiler system/package must be understood.

Of course, this is not unlike how a steam/feed system is designed - number of feedwater heaters is balanced against the amount of steam that is extracted to pre-heat the feedwater - from one standpoint (feedwater) bringing the feedwater to the boiling point before entering the boiler is the most efficient operating point, but the more steam that is diverted from the turbine - this limits the work out of the turbine.

Basically, I think the best process is: just need to have faith in the original boiler designers and understand their intent - then once we are able to meet their original intent - we will probably be at the optimum operating point.

 

[rmw]

Don't forget one thing about the OEM boiler designers. Basically they wanted that thing to make its performance at initial commercial operation testing, and to survive the one year warranty period. Past that; it is your baby.

Other than that, unless someone at your utility prepared a cracker jack specification, what you have there is the best equipment 'low bid' can buy.

You have to look at it from that perspective. This is totally unlike the nuclear side where uh-oh's can get you names like Three Mile Island or Cheyrnoble, and there is a NRC type entity looking over your shoulder for reliability and safety. No gov't entity cares if you melt your boiler or not, and most state's PUC's rules are written so that you can pass your combustion inefficiencies right through to your rate payers.

There are companies out there whose whole existence comprises of making better mouse traps to improve the performance of all types of OEM equipment, including utility boilers. Some call them pirates, and some are no more than pirates in that they are copy cats making inferior stuff. Some, however end up with improvements so significant that the OEMs themselves have to go back and incorporate them into their designs in order to keep the aftermarket people from taking all their business.

Some of the links I gave earlier in this thread are for companies that offer goods and services that vastly improve what the OEM's had to offer. Maybe the OEM's have responded by now with their own offerings, but your boiler may or may not have had some of those features incorporated yet.

Chances are, you can make it into a better mouse trap.

Good luck.

rmw

 

[athomas236]

You may be trying to learn about a dying technology.

A colleague of mine went to a conference in the UK a few weeks ago where a presentation was given by Clyde blowers. The point of the presentation was about non-stick coatings that can with stand temperatures up to 900C and can be applied to the gas side surfaces of both coal and oil fired boilers. Apparently the coating has been so successful in trials that the operators are removing the blowers.

athomas236

 

[dave472005]

rmw/athomas236

Thanks for your inputs. I attended a Boiler Cleaning Symposium sponsored by Clyde Bergemann this week and heard a couple of things that change my perspective somewhat.

* OEM Boiler manufacturers designed for a specific coal not a range of coals - hence todays business drivers to alternate fuel types are a major part of the business plans for companies like Clyde Bergemann and Diamond Power.

* OEM Boiler designers typically applied sootblowing over ~20% of the heat transfer surfaces - I assume in the areas of the boiler that were prone to fouling for the design coal loading.

* In general, the main sources of cleaning medium are water, steam (superheat and saturated), and air. While there advantages and disadvantages to each, there are people that have had good performance from each source and bad performance for the others. No one cleaning medium has proven to be better than the others.

* The main means to really understand fouling in the boiler is not to play with sootblowing sequencing or sootblower locations, rather to instrument the boiler and use current learning technology to build a smart sootblowing cleaning operation. This is the focus of the Clyde Bergemann ISB system and the subject of EPRI research at 3 boilers.

* I listened to the presentation on nano coatings and the encouraging results by Clyde Bergemann, but got the definite impression that Clyde is looking for a test boiler(s) in the US once they have completed the testing in other applications. For now the technology is being tested in non-power boiler applications on a limited basis - specifically in known problem areas. The coatings do wear out - but not sure how long they should last. Also, the coatings don't prevent fouling, rather limit fouling - specifically in areas not covered by soot blowing. The cost of these coatings is still very high.

I am interested in establishing and maintaining contact with people dealing with sootblowing issues and the current trends in their companies.

Dave

 

[rmw]

I had a client that had a waste wood fired boiler, bark, sawdust and planer shavings, who did not have a single soot blower in his boiler. Seems whoever built it for him just didn't put them in. It was a used boiler, and old Springfield, and tough as nails, and had started out its life as a coal fired boiler in Anderson, IN as one of a right hand / left hand boiler set, both with soot blowers.

Both boilers ended up in the same southern state about 90 mi apart each on its fourth owner each about 40 years old when it got there. Both burnt wood, but one burnt hardwood while the other burnt pine waste. One still had its soot blowers, and I could not convince my client, the owner of the one without to add soot blowers. He used the boiler for about 20 years without them, while every other single wood fired boiler in the region that I knew of all had soot blowers, so go figure.

Much as I tried, (it would have been a nice project for me to engineer for him) I could never argue with his years of success without them.

Now, regarding coatings; coatings are extensively (or were) in black liquor chemical recovery furnace wall tubes to reduce corrosion and erosion. They worked well, but they had to be replinished over time.

I'm still from Missouri regarding coatings reducing the need for soot blowers. Now, making the effectiveness of sootblowers better, I can buy that. I can't see how a piece of ash, above its ash fusion temperature would know to say 'oh, that tube is coated, so I can't land and stick there-I'll just keep going and find somewhere else to set down and stick.' I could see it with dry friable ash below the ash fusion temperature.

rmw

 

[ccfowler]

dave472005,

You may want to pay closer attention to details of the combustion process. Even when running with significant amounts of net excess air, a furnace can still have troublesome regions of inadequate available air. Slag formation can be much more severe in regions with inadequate combustion air.

Many years ago, I had some involvement in a research project to reduce slagging in full size utility coal fired boilers, and I recall that substantial reductions in slag formation were realized from cleaning up the air and fuel distribution throughout the furnace while reducing the net excess air. Soot blowing was still necessary, but net fuel savings were available through minimizing the net amount of excess air.

I would attack the problem through optimizing the combustion process for slag minimization first. Then, soot blowing can then be more effectively minimized. As noted previously, soot blowing is a very costly process. By minimizing the need for soot blowing and then optimizing it, compounded benefits are available through energy savings, reduced tube erosion, improved boiler avaliability, etc. You may find that this can be a very profitable project.

Yours should be noth a very interesting and a very rewarding project, and your fresh look at the situation should be highly advantageous. Good luck!

 

[rmw]

One of the costs of sootblowing is erosion damage to boiler tubes done by the moisture in the soot blowing steam. Besides the direct cost of generating steam for soot blowing, this is one of the costs of SB operation.

As you state, dave472005, superheated and saturated steam are both used among the other media that you mention. Superheated steam has less problems with moisture once the piping to the SB and the SB feed tubes and lances are up to temperature.

But, even in a SH steam system, when the blowers are at rest, no matter how good the pipe insulation, the piping cools off, and moisture forms, just to be picked up and carried to and through the SB's when the start, and new moisture forms until the piping comes back up to temperature, wreaking havoc on the SB components and adjacent boiler tubing.

One idea I have had that I never could sell to management was to heat trace the SB supply piping so that the piping was maintained at or above saturation temperature for the steam, and steam entering the SB piping upon initiation of the SB cycle would be running in hot piping, not warming up the piping by giving up its heat to make more moisture.

It is an expensive idea on its face, but when compared with boiler tube replacement, worst case, or pad welding in the zones, every outage, best case, I always thought it was a viable option. It would typically take one of the higher temperature types of heat trace, possibly even the mineral insulated type.

Mull this over as 'out of the box' thinking.

rmw

 

[DougMSOE]

We found a better way to do this than the 3 biggest soot blower mfgs.
In fact 2 of them came here to look at what we had done.
If you want call me.
920.453.2195
Besides I have 30+ years in and only 6 have NOT been in coal fired units.
Doug

 

[dave472005]

DougMSOE

Not to sound like I doubt your claim - but it has been my experience that if the industry is not doing something it is because it doesn't fit the overall application. This is not to say that your application doesn't prove that your approach works, rather that the major manufacturers are not convinenced that the technology will work in all relavent applications - or make economic sense to pursue.

Case in point - heard on NPR that there is a push to use floresent lights inplace of standard light bulbs - claim that you can reduce someting like 25-40% electric consumption (Green technology). However, from my research, the bulbs are ~10 times more expensive (~$15 for 3 new vs ~$2 for 4 standard bulbs) due to a higher manufacturing cost. While the bulb life is advertised as a means to make up for the difference in cost, in my home testing, I didn't see a significant increase in life (about 2-3x longer). Also, look at what part of our household budget makes-up light bulbs, including electricity to burn the bulbs - without doing the math - suspect that it is somewhere around 1-5% - making a change here is not expected to make a significant change in my household budget.

As such - the claim of energy savings is probably verifiable - however, the cost justification does appear to miss the boat - and there maybe an argument that there is more polution produced making an energy efficient light bulb when you account for the manufacturing waste streams and energy usage (just a guess). For me - it doesn't make sence to me to buy and use energy efficient light bulbs.

After all - look at your plant practices. Is it more cost effective to replace components on a computer board - simply replace the computer board? Throwing away a computer board with 99% good components goes against my engieering judgement - however, when you figure in the labor cost, waste cost, lost to production, etc., it becomes very clear that it is more cost effective to through away a malufunctioning computer board - then throwaway the malufunctioning component.

If you would like to describe your sootblowing approach, I suspect that I and others that read this would be interested - and you may find a supporter of your products.

 

[dave472005]

A couple of updates on our plant work and what we are doing. Any other ideas of areas to look at - keeping in mind power plant limited funds, would be appriciated.

* Based on an initial evaluation of the boiler performance and material condition of sootblowers, we have about a 95% availability of the installed sootblowers and we are running them on a continous looping sequence (air is our medium). So the boiler is as clean as the OEM originally intended - maybe better. This does not mean that the cleaning is optimized, just we are meeting/exceeding original cleaning intent.

* Have identified a couple of fouling locations that we seen to have solved by adding a sootblower in the location.

* Have identified evidence of areas for evaluation. One is the review of the maintenace history - the wall blowers appear to have a generic issue that has resulted in a high number of work orders an all the blowers. The retractable blowers appear to have 3 or 4 problem locations. The intent is to use a Pareto approach to identify the most frequent issues to solve.

* Under the assumption that boiler cleanliness (or lack of) can be a contributor to most boiler related problems, I am also going to do a Pareto analysis of the boiler down-powers/forced outages for the last couple of years. This is usually a good tool for plant management in general, but should identify the actual relationship between sootblowers and plant performance.

* On the combustion front - we are balancing the fuel/air flows to the burners, ensuring that the mills are performing as needed, looking at the air flows into the boiler, etc.

 

[DougMSOE]

What I have found over the years and even more so in the last 10 years is that everyone is so willing to "put in new technology" that they have forgot how to think. All of the newer soot blowing controls use time or strain gages. All of this is fine if the fuel supply is VERY consistant. But, what is consistant with coal other than it is black and messy?
We came up with a way to do soot blowing without using time but using the delta T across the various sections of the boiler.
Simple but it works and it has reduced the mumber of tube faiklures by 73.4%. Further, since the different coals all have different fusion temps, the fouling of the boiler can be spotted easily and the control system recognizes this and does its job.
Again, you have my phone number.
Doug