RO Water use in Boilers

[jisita]

Hello,

I'm José Isita, an engineer from Mexico. In the plant we have 2 RO Units, the first unit produces permeated water that we use in our product, and the second, treat the reject from the first unit for reusing it in other areas of the plant.

Since this water is softened and has lower conductivity, silica and minerals than our well water. I want to use it in the boilers of the plant. So I want to know if somebody has done that? And is you think that I will have savings on water, chemicals and diesel?

Here is some info about the situation:

Boiler Operating Pressure: 106 PSI
Steam Production: 10,000,000 lb/month

Well Water RO Water
Conductivity 850 400
Silica 80 50
Hardness 240 0

 

[metengr]

The RO concept is an excellent idea. Not exactly your situation, but we have replaced our aging demineralizers at several of our Fossil Plants with RO units. The RO units were justified based on significant cost savings in chemicals and water availability. The internal rate of return was about 30% for each RO.

 

[EdStainless]

It should work, and reduce your chemical usage. Why is your conductivity still so high? What is your control range for the boiler water?

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[jisita]

Thanks for your answers,

EdStainless:

Teh conductivity is so high because the water that enters to the 2nd RO unit, is the reject from the 1st one, so that water has a conductivity of 3000 microsiemens.

The boilers purge when water reaches a conductivity of 3000 microsiemens...

Are there going to be also savings in fuel? Because since water will last longer, I will need to heat less water, I am right?

 

[TBP]

Fuel savings will depend on how much blow down can eliminated from the boiler. The amount of blow down will largely be a function of how much condensate gets returned to the boiler. If you have 100% condensate return, then the make-up water requirements will be pretty much zero. Not much payback on any kind of pre-treatment system. On the other hand, if you have a plant with 100% make-up, then the blow down rate will be high - maybe 10% or so of the steam actually generated by the boiler. If you can cut that number, then that's where the savings show up.

 

[jisita]

Thanks for your answers,

TBP:

We have condensates return, but anyways, we are feeding 55 m3/day to our boilers (19,800 m3/yr). We didn't know the amount of blowdown... Can somebody aproximate the amount of blowdown that we could have? We recirculate part of the blowdown to the condensates tank.

According my estimates, sending to the boilers the RO water will allow us to double the concentration cycles, thus reducing the blowdown from 1147 lbs/hr to 842 lbs/hr, and that will gave us savings of 23 m3 of diesel pero year.

This by reducing the blowdown from 8 to 6%

 

[GenB]

RO water is a bit corrossive and balanced chemicals will be required GB

 

[daldoula]

it appears to me that your second stage RO system is more of a softener than it is a full demineralization.

This explains the value of zero hardness but still high conduvtivity.

This water can be used in a low pressure boiler because it will not have scaling abilities, however you should check the pH and chloride contents for the materials suitability of piping and the boiler..