Replacing boiler economiser, demolition phase.

[ttoks]

The current project is to replace the economiser of a recovery boiler at a paper mill, the boiler produces enough steam to produce enough steam to generate around 100 megawatts of electricity, however the steam is often used to also run the paper machines on this site.

For those that are unfamiliar with the boiler design I highly recommend watching this video,, its a little dry but gives the basic idea of what I'm doing.


in the video the economiser runs across from the flow of gas, while the boiler I'm currently working on the economiser hangs vertically but the concept is the same, it pre heats the feed water before it enters the waterwall to be converted to steam increasing the thermal efficiency.

this boiler is a "skin casing" boiler, meaning it is wrapped in a casing os 3-6mm thick steel some boiler are "membrane" type where the waterwall tubes are welded together to do the same job.

this is cutting the skin casing on the top of the economiser separating the headers from the boiler.



my offsider cheering at a job complete.



the boiler hangs from the roof, this allows for the boiler to expand due to heat, here my offsider is cutting two of the 4 hanger's that support the outer wall of the boiler.



Ready to lift



We're using a 500 ton crane with a large jib to lift the old sections out, and new sections into the boiler house, here a rigger is preparing everything to lift the rear wall of the economiser out.



And lifting this 20 ton, 50 foot section of wall out of the boiler house begins.



and up it go's.





the sections of economiser were liften out in a similar way, hooking the crane up then cutting the hangers before lifting the old sections out of the boiler house.

This boiler uses a "cascade" to preheat and dry the fuel, which in this case is a substance called "black liquor" which is a by product of the paper manufacturing, basically a huge vat approximately 50x50x50 feet is filled with the fuel which has an agitator the stir it around driven by this chain drive, the exhaust gasses of the boiler are passed over the fuel in an oxygen depleted environment to heat and dry the fuel without igniting it.



However, the entire cascade is now redundant, the engineer's have determined that completely removing the cascade and replacing the existing economiser as well as the space taken up by the cascade with a new economiser around 4 times the old ones size of the old one will be more efficient.

[ttoks]

So say hello to my little friend, the thermal lance.



the ones we are using are a mixture of alloy steel and aluminium rods inside a mild steel casing, pure oxygen under pressure from a 5000 cubic foot oxygen bank is fed into one end, while the other is heated with an acetylene torch and once red hot the oxygen is turned on, the steel and aluminium burn at somewhere between 2500-4500 degrees C (4500-8000 F) and melt literally melt anything it comes into contact with, be it steel, concrete, diamond or rock.





it also produces ALOT of hazardous smoke.



And the cascade mostly demolished and removed.



another part of this job is modifying the feed water system to cope with the extra capacity of the economiser, which means plumbing extra pipes from the waterwall into the head drum, here is a new nozel we're welding into one of the waterwall headers.



Tig welded root and hot pass, as you can probably tell its a pretty tight spot.



with stick fill and cap.



this picture shows one of the new lines (the off white colour one) running from the waterwall header towards the drum.

[ttoks]

Another scope in this job is replacing the roof tubes of the boiler, although I'll cover this more in the next thread.



this is the very top of the boiler, called the penthouse.



this is the boiler drum, the phase change from liquid to steam happens in the water wall tube's, this is then fed into the drum, the liquid water from the waterwall falls to the bottom and travels down the downcomers back to the bottom of the water wall where it meet's feed water from the economiser, while the steam rises out of the vertical tubes and is fed into the superheater which heats the steam to 600 degrees C (about 1200F), the drum on this boiler is 4 inches thick.



holes for the new feedwater marked out.



holes drilled.



a little more demo work removing a redundant hopper.





and that's all until the next thread, i hope you all enjoy.

[Ky farmer]

Keep the pictures coming, I find it amazing the size of stuff and the quality of work that went into building it
Mike

[gxbxc]

I worked a KC paper mill job back in the seventies I moveed on to power plants but my brother in law stayed and worked his way up to Maintaince forman for the plant. good work if you can keep at it . But dirty as sin.

[snoeproe]

I'm a licensed power/operating engineer myself. I spent several years as an operator in a Kraft mill power and recovery department. Not the nicest place to work. Very dangerous.
We ran a B and W chemical recovery boiler, a gas fired co gen plant with a gas turbine and steam turbine and the mill air systems. We were the power and energy of the mill.
Black liquor is the primary fuel that's fired in the recovery boiler. Its a product of the Kraft pulping process, not the paper making process.
The Kraft liquor system is a never ending loop. Weak black liquor is burned in the recovery boiler at 64% concentration. What's left over runs out the smelt spouts as green liquor. It's then sent to the lime kiln area for recausting by adding hot lime. The liquor is now strong white liquor. Very corrosive and dangerous liquid at this point. This white liquor then goes back into the digesters with wood chips and steam cooks the mixture into Kraft pulp under pressure. Once it leaves the digester, the now weak black liquor is washed out of the pulp and sent back to recovery to start the recaust process over again. The pulp is washed and bleached and sent to the paper mill for paper manufacturing or its dried and processed for shipping.
Lots of years I spent at this facility. Glad I'm doing something different now however.

[Rock knocker]

How are they going to stress relieve the nozzle welds on the drums?

[ttoks]

How are they going to stress relieve the nozzle welds on the drums?

with a 300 kilowatt heat treatment unit, it draw's around 300 amps from a 1000 volt outlet, and a lot of insulation.

[ttoks]

I'm a licensed power/operating engineer myself. I spent several years as an operator in a Kraft mill power and recovery department. Not the nicest place to work. Very dangerous.
We ran a B and W chemical recovery boiler, a gas fired co gen plant with a gas turbine and steam turbine and the mill air systems. We were the power and energy of the mill.
Black liquor is the primary fuel that's fired in the recovery boiler. Its a product of the Kraft pulping process, not the paper making process.
The Kraft liquor system is a never ending loop. Weak black liquor is burned in the recovery boiler at 64% concentration. What's left over runs out the smelt spouts as green liquor. It's then sent to the lime kiln area for recausting by adding hot lime. The liquor is now strong white liquor. Very corrosive and dangerous liquid at this point. This white liquor then goes back into the digesters with wood chips and steam cooks the mixture into Kraft pulp under pressure. Once it leaves the digester, the now weak black liquor is washed out of the pulp and sent back to recovery to start the recaust process over again. The pulp is washed and bleached and sent to the paper mill for paper manufacturing or its dried and processed for shipping.
Lots of years I spent at this facility. Glad I'm doing something different now however.

Very interesting, something I've found a little concerning is the lack of disclosure as to exactly what is in the various shades of liquor beyond being told "if something drips on you dont look up", what exactly is the white liquor and what happens if you get it on you?

[snoeproe]

White liquor is the strongest forum of liquor in a Kraft pulp mill. It's a very strong forum of caustic. It's the liquor that helps cook the wood chips down into pulp in the Kraft digester(s)
If you get white liquor on you, severe skin burns will follow. Any hair is gone. It's very corrosive and will react violently with any acids. You want to just stay away from white liquor in a Kraft pulp mill.

[12V71]

White liquor is the strongest forum of liquor in a Kraft pulp mill. It's a very strong forum of caustic. It's the liquor that helps cook the wood chips down into pulp in the Kraft digester(s)
If you get white liquor on you, severe skin burns will follow. Any hair is gone. It's very corrosive and will react violently with any acids. You want to just stay away from white liquor in a Kraft pulp mill.

Isn't that stuff Sodium Hypochlorite or some such nasty ?

[thegary]

I spent a lot of time in paper mills. We were in the lime kiln area and there was a large tank that we were supposed to go down in the tank to repair the agitator. We opened the hatch about 11;30AM and and put a fiberglass ladder down into the tank. We were waiting for our vessel entry permit we finally went to lunch and came back to find the permit tag on the hatch. We had tied off the ladder at the top to the tank , it was a good thing we did. Evidently the mill had forgot to clean out the tank and there was about 6 inches of liquid in the bottom of the tank. The ladder was hanging by the rope we used to tie it off. The liquid had eaten about 2 ft of the fiberglass ladder while we were gone to lunch. Needless to say no one would go in the tank even after they cleaned it. The mill wound up having to get their own men to do the job.

[snoeproe]

Isn't that stuff Sodium Hypochlorite or some such nasty ?

No
Sodium hypochlorite is a bleaching chemical that's used to bleach the pulp.

[snoeproe]

I spent a lot of time in paper mills. We were in the lime kiln area and there was a large tank that we were supposed to go down in the tank to repair the agitator. We opened the hatch about 11;30AM and and put a fiberglass ladder down into the tank. We were waiting for our vessel entry permit we finally went to lunch and came back to find the permit tag on the hatch. We had tied off the ladder at the top to the tank , it was a good thing we did. Evidently the mill had forgot to clean out the tank and there was about 6 inches of liquid in the bottom of the tank. The ladder was hanging by the rope we used to tie it off. The liquid had eaten about 2 ft of the fiberglass ladder while we were gone to lunch. Needless to say no one would go in the tank even after they cleaned it. The mill wound up having to get their own men to do the job.

That could have been one of a few different tanks in the lime kiln area. White liquor clarifier, green liquor clarifier, lime mud washer etc. They all have a rake in the bottom that pushes the solids towards the centre of the tank. The bottom of these tanks are often sloped down towards the centre.

[snoeproe]

No
Sodium hypochlorite is a bleaching chemical that's used to bleach the pulp.

Hypo is an alkali (low ph). Kraft liquor (caustic) is a base (high ph)

[thegary]

That could have been one of a few different tanks in the lime kiln area. White liquor clarifier, green liquor clarifier, lime mud washer etc. They all have a rake in the bottom that pushes the solids towards the centre of the tank. The bottom of these tanks are often sloped down towards the centre.

Yes , I know it was not one of the clarifiers, it was not that big. The clarifiers were probably 50ft diameter by 3 stories tall. This was probably 12 ft diameter and 20 ft tall. I can not remember what was in it now, that was probably20 years ago when that happened.

[ttoks]

Keep the pictures coming, I find it amazing the size of stuff and the quality of work that went into building it
Mike

funny you mention size, this really is a baby boiler compared to what I'm used to working on, only 10 floor's to the boiler house (normally its 19), the ones I usually work on would fit 8 of this boiler inside of it with room to spare.