Fly Ash Erosion

[ggrindle]

I have a boiler burning lignite with 29% ash. As you can imagine the flyash erosion is mind boggling.

Ducts, Boiler tubes, economizer, precip, etc. all take a beating.

What type of materials have proven to be cost effective solutions in this severe application?

 

[davefitz]

refer to thread794-147547. This includes a link to the mitsui babcock report that provides test data and theoretical basis for predicting flyash erosion.

Basically, the erosion rate is proportional to the 3.5 power of the velocity of the impinging flyash particles, but only for those particles that are larger than ( 20 um ?) and for ash constituents that are harder than normal piping steel. Particles smaller than ( 20 um) will not impact the wall, as per the "law of the wall" they will follow the gluegas streamlines and miss impaction of the wall.

 

[EdStainless]

You will find many Ni and Co alloys in your search. These various metal overlay solutions are not cost effective, not to be confused with being reasonable. They are expensive, but they do work.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[arunmrao]

metengr is perhaps on a holiday. Else he would be the first to reply this thread. Ceramic tiles can be a solution at other sites high chrome irons have been used. For a more detailed reply please wait.You are sure to get a better response.

 

[rmw]

Go here for some interesting reading. This company has make a mint resisting coal ash erosion.

http://www.surealloy.com/products_abrasion_resistant_materials.asp

rmw

 

[metengr]

Unfortunately, there are always trade-offs in the power boiler business especially when you burn the lower BTU content (and lower price) fuels. I would bet that you don’t have a budget big enough to handle full replacement of these large boiler components.

Instead, you need to decide on a preventative maintenance strategy. The top priority, in my opinion, is to maintain boiler reliability because this generates revenue. So, tackle the boiler tube circuit first by using stainless steel tube shields (310 ss) and/or weld overlays (309 ss) to reduce tube wastage. To prioritize where the needed tube shields and weld overlays are necessary, you need to obtain tube wall thickness data as baseline information and map the areas over time to trend the data.

In my opinion, the precip internals and boiler flue ducts that you mentioned are not an immediate threat to forced outage rate so here you can plan over time to selectively repair high wear areas during scheduled overhauls. There is no magic material that one can use to suddenly eliminate susceptibility to fly ash erosion. One can, however, make deliberate attempts to apply weld hardfacing (Stellite) or utilize wear noses for turning vanes in flue ducts or use ceramic tiles at areas where flue gas impinges on the steel.

You would be surprised that the appearance of fly ash erosion looks much worse than the actual amount of metal lost. Your key is to perform thickness testing during short outages so that you can selectively repair high wastage areas during longer planned overhauls. This is your best bet to assure unit availability at least cost.

 

[ggrindle]

Thanks for the input.

metengr. Thanks for the input. I am doing much of what you mention. We use 625 overlay on the boiler furnace walls for wastage. We shield tubes with SS shields and in some areas have to reshield them again in 6 months.

You are right that ducts are a minor issue until the leakage because so much that the plant is derated due to ID fan amps. We were limited 50 MW limping into last outage due to duct leaks.

As for the problem looking worst than it really is...When you have holes in your turning vanes big enough to drive a school bus thru then there is no need to UT check the thickness!

I have experimented with weld overlay, AR plate, Chome carbide cladding, Tungsten Carbide clading, ceramics, Gunnite, Envelope shields, white iron, vanadium alloys, denzit, trowlable ceramic, conforma clad etc. I don't think we are anywhere near finding the optimum solution. Some work good but are outrageously expensive, some are cheap and don't work.

My question to the community is are there optimum solutions and lots of bang for the buck that have been found in similar abrasive type applications.

Thanks for the responses