Busted Demin Regeneration Lines

[hillairer]

I work in a power plant as a design engineer, and the cation tanks in the demineralization plant here have run into a few problems: in normal use, the regeneration acid distribution lines in the tank (1"-d 314 SS) have been snapped off the header, and the header inside the tank (6" Schedule 40 314 SS) have been bent downward, as much as 7 inches.

So, currently, I've got a massive part of the water treatment system disabled, and little idea of how it happened. I've got a few ideas:

~ A rapid opening of the 100 psig to ambient causes high velocity flow out of the tank, drawing the laterals and header down with the water

~ after a backwash, when a substantial amount of resin is above the acid regen lines, someone also quickly opens the drain, drawing the header and laterals through the mix like sticks through wet sand

Has this happened to anyone else, and what could have been the cause of this type of damage?

 

[cub3bead]

Please describe the regeneration method (i.e. co-current; countercurrent-water block; countercurrent-air bloc; etc.) used with your equipment.

The forces on the internal distributors can be very large and cause the damage you describe escpcially if you are operating the valves in a very rapid manner. For instance, if you were to rapidly introduce backwash water and lift the bed as a plug rather than fluidizing the individual beads the effect is more like a solid object hitting these distributors rather than the individual resin beads.

Do you have an extreme variation in water temperature or can it get very cold, say less than 40°F?

 

[hillairer]

The regenerant method is co-current, with an air-lance of the unit before a backwash. What you describe is what happened to all 4 anion tanks soon after they were installed. This motivated the plant to implement air-lancing (injecting the unit with air from the bottom of the tank for 20-30 minutes) on both the cation and anion units before a backwash and regeneration. This breaks up the silt and solid particles at the top of the bed, leaving a slurry of broken beads and silt before it's cleaned out in the backwash. The plug concept doesn't explain why the header and laterals were bent *downward* though. I'm open to hear any ideas.

The water can get as cold as 40 degrees in the winter, especially since our untreated water storage comes straight from the city mains and into a poorly sheltered tank.

 

[cub3bead]

When you say air-lance do you actually open the manway and probe the beds or do you introduce air through the underdrain header? Do you introduce the air slowly or all at once? What pressure are you sending into the column at? What is the air flow rate in terms of scfm/sq. ft. of vessel?

When you do this do you drain the water from the vessel to just above the top of the bed first?

I am curious how you are getting silt into an anion column, usually the cation catches all of this good stuff.

I am now confused, your original psot mentioned a damaged acid line so I assumed you were dealing with a cation column. Are you putting acid into an anion column?

 

[hillairer]

Thanks for your prompt responses.

To air lance the unit compressed air (approx. 40 psig) is introduced into a forced air line into the underdrain header, and it is fed to the tank as fast as the operator can open the valve, and it's allowed to bubble up through the bed.

We drain the water from the vesel first from about a foot above the top of the resin to just above the top of the resin, you're right.

The design engineer that was here before me couldn't explain the deposition of silt int he anion tank to me completely, but he was convinced that the silt in the tank was what caused the lines to be bent upward.

When I mentioned the anion tank lines, I was refering to the caustic regeneration lines. I apologize for the mix-up.