9 replies to this topic

[rxnarang]

What surprises me is that Blow down is better qulaity than the DM water you produce! That should not be possible in a cloased system. It is only possible in a open system, where you have another source of DM water which is better than 300 ppm TDS DM water you produce. In this case you are actually deteriorating perfectly good Blow down by mixing it with DM water whcih is of poorer quality.

Am I misssing something here?

Rajiv

[Art Montemayor]

Rajiv is correct. What is presented here is a paradox: a seemingly contradictory statement that is, perhaps, true. How can the supposed waste from a boiler be of higher quality than the feed to the same?

Of course, like everything else, there has to be a logical explanation:

1) The feed analysis is wrong;
2) The blowdown analysis is wrong;
3) both analysis are correct; this is what we must fear.

If the analyses are correct and the boiler is tested at steady state, then one conclusion that presents itself as a specter to the operation is that solids' accumulation is taking place inside the boiler! A mental mass balance tells us that if the solids introduced on a steady state are not exiting out with the blowdown, then there must be accumulation of the same solids inside the system. This is the stuff out of which nightmares are created for boiler operators. Tube failure (burn out) and efficiency loss will be the immediate result if the paradox continues. Something is occuring in the operation that may be causing this. Chemical treatment may not be up to specifications. The feed may be too contaminated with dissolved solids. Other treatment methods may not be occuring. But one thing is certain, the operation can't continue the way it is being reported -- not for too long, anyway. Something must be done to remedy this situation or the boiler will be subjected to expensive and possibly hazardous damage.

Does any other reader have any comments on this situation? I'd be interested to know about other experiences and comments.

Art Montemayor
Spring, TX

[rxnarang]

OK, I talked to my expert on Boilers. He said it is unacceptable to recycle boiler blowdown. Total TDS is one thing, but individual ion species is another. He mentioned silica as a typical case. We add phosphate in the feedwater to take out the silica in the blowdown. If one recycles this silica then the DM water plant is bound to fail, as the silica loading continues to increase. It is acceptable to dump the water in the cooling tower basin, but not in the steam cycle.

Please revert back with the DM water specs, DM plant performance specs, blowdown quality and inlet water quality ( reporting individual species) for futher analysis, if desired.

[Technocrat]

dear all,

ashwini is right. we also recycled our waste heat boiler blowdown to cooling tower makeup after cooling. this happened in one of the indian methanol plant.

regards.

[mbeychok]

Are you sure that your TDS values are correct? Unless I misunderstand you, you demineralize raw water and then use the demineralized water as boiler feed water and the boiler blow down, which must have a higher TDS than the boiler feedwater, has a lower TDS than the demineralized boiler feedwater ?? Your raw water demineralizer must be doing an extraordinarily good job of demineralizing the boiler feedwater !!

Before I recycled that water, I would make absolutely sure that your TDS figures are correct.

[bhagat]

Hi
All

If the quality of CBD of Boiler feed water is ok, minimize the blow down and then check again the quality.
In my previous company, still they are using blow down as cooling medium for the Secondary reformer of Ammonia plant and then dumping to cooling water system as make up water.
Thanks and Regard
Bhagat.

[kumaqal.engr]

Assalamoalaykum
in my opnion Rajeev Narang view is absolutely right
The boiler internal treatment is treated with phosphate these days, which removes silica and and other impurities in the boiler by blow down or so, it's not a good idea to blow down limit upto 120 ppm. You must consult your water treatment professional, who ever providing you chemicals, if this is not the case than just check out your TDS level again in CBD, you should also check the various other parameters, like iron, silica, total hardness before making any decision. silica and other impurities filled water is not good for your boiler, most probably it will create problem to your system. However if you still want to use this CBD, than you should pass it through various filteration media, which will depends upon the quality of your water, e.g if it's contains more iron, birm media is used.
with best regards.

ALLAH HAFIZ