Boiler maintenace costs

[tomrabe]

We have a couple of Cleaver Brooks 250hp boilers. They are fire backs dating from about 1969. We spend about $5000. per year for each boiler on major repairs, ie. tube replacement, crack repair, refractory. From the aspect of justifying replacement of these boilers, does anyone have a feel for what this type of maintenace should cost?

 

[rmw]

You don't say what type of fuel you are firing, nor what type of service they are in such as continuous, intermittent, etc.

Some more information that would help us answer your question would be helpful.

rmw

 

[tomrabe]

Sorry. They are natural gas fired boilers operating on a continuous basis.

 

[kenvlach]

I think you already know the answer, just want some support.
It seems high (unless putting crappy water into a high pressure; then kind of low).

Have you ever installed new high efficiency burners?
Your savings on natural gas might be more than on maintanence. May also be able to use a slightly smaller, higher efficiency replacement boiler.

 

[spector]

It doesn't take much to reach 5K when it comes to hiring boiler repairs, especially when you consider it involves tube replacement and repairing cracks.

Repeat cracks and tube leaks make me concerned with the conditions of your watersides....I suspect that your boiler is overfiring due to scale buildup. The scale will be thicker at the back where the metal tends to get hottest...That is most likely where the cracks and tubes fail also on your boiler, am I right?

Once you have insured the watersides are descaled, then look at your operational practices. Make sure your operators allow for a slow and gradual warm up...examine your loads to look for large swings in demand and how often and for how long the boiler must operate at high fire.

 

[metengr]

Yes, for the amount of maintenance dollars you spend, this appears typical. You didn't mention about current operating conditions - base load versus cycling. I would be willing to bet, that if you cycle these Cleaver Brooks boilers, your annual costs will increase and you will be replacing major boiler components because of thermal/corrosion fatigue damage, and refractory.

 

[tomrabe]

Thanks everyone... Kenvlach is right, I was looking for support. Spector, also right on the money. To fill out the description of how we operate the boilers: We run continuously but we are a farm and we have a season. So the boilers do get shut down for weeks at a time. Our owner is also an economist who loves to dabble with engineering problems. He favors operating the boilers at low pressures (60 psi vs 125 psi design pressure) and shutting them off on weekends. Also, our water comes from a well and is loaded with all the good minerals that entails. Have I got anyone feeling sorry for me yet?

 

[spector]

You nailed the overheating problem when you revealed that you operate the boiler at less than half it's designed MAWP. Your boiler actually fires harder and longer because of it....Sounds to me like the boiler was sized correctly for the process requirements and expected load, but he shot himself in the foot when he decided to lower op press. The lower pressure allows much large steam bubbles to form inside the tubes and against the tube sheets...Those larger bubbles don't provide enough surface area exposure to water to cool the metal

Tell the boss he ain't saving any money operating at less than 1/2 design pressure.

Your shutdown cycle is fine as long as you take care to slowly warm the boiler on start up.

Next chance you get, remove a rear handhole and examine the waterside of the rear tube sheet at first pass position. If you see scale there on the tube sheet and tubes, then you need to remove the scale and take measures to prevent it. Scale buildup also causes the boiler metal to overheat.