de-scaling steel boilers

[Ian S CParticipant @iansc]

Chris, if you have a fridge/freezer that needs defrosting, there is another good pure water source.

Ian S C

[frank brownParticipant @frankbrown22225]

Very OT but of some interest?

De-ionised water is water that has no extra ions, ie. dissolved salts. Distilled water as de-ionised and contains no non-ionic substances i.e. sand.

I worked with steam cooled transmitters for some years. It dealt with extremely high heat flux, 100 KW coming out of the anode which had a surface area of 3,600 sq cms. The temperature drop was that the outside was 120 degs C and the inside was 600+. Any surface contaminents caused the internal temperature to rise and the copper anode to melt which was the end of a £25,000 valve. So purity of the water system was paramount. We used to buy the de-ionised water from power stations and checked its conductivity (1/ resistance), which was in the region of 2 micro MHos.

Searching around for data wrt pump materials/couplers etc. it seems tha de-ionised water is just about the most aggressive liquid you can get (because it wants to dissolve everything in sight?).

One reason for the low conductivity (high resistance) of the water is the thermo-electric effect, if you have a pond of water, heating one end you get an voltage generated of 250 microvolts/degree. i.e. it acts as a battery. So if the water has a high conductance (low resistance) a large current will flow and electro- erosion and deposition will occur (like electro plating), which will thin some parts giving rise to leaks.

The main problems we had in real life was an accumulation of copper oxide, by the kilogram and the fact that soft soldered joints were just dissolved away. Hard soldering seemed to improve this.

After about 15 years running I used some stuff called MOR 75 (?) , which was magic. Clear liquid we tipped into the header tank. After about 5 minutes the tank (and system) took on a greenish colour, then after 15 minutes of so , it was all black as ink. After another 30 minutes it went green, and finally it all went clear!!!. This "water" was dumped, and the system was flushed again and again, and finally the water was back to 2 micro mhos. Doing nothing else it dropped the pump pressure by a factor of 5 and increased the flow by at least double.

Apparently the chemical action is called "chellation", worked brilliantly !

Frank

[Bob Brown 1Participant @bobbrown1]

Rain water or water from a dehumidifier is not as clean as one would think, particles in the air be they dust or salts will be in the water. In the marine environment we used to produce our own water and aimed at less than 7ppm salt from sea water (35,000 ppm) for boiler use amongst others. This with chemical dosing to remove dissolved oxygen and maintain PH levels ensured there was no build up of solids or corrosion of the boiler internals. As for cleaning things like the evaporators we used SAF-ACID descaling compound which is a blend of sulfamic acid, wetting agent and colour indicator.

Bob

[Chris Pattison 1Participant @chrispattison1]

In NZ, during winter we run a dehumidifier to keep the air in the house dry and easier to keep warm. The water resulting from this we use in the iron, as it is free of minerals. I have not checked the pH, but I reckon this water could be used in boilers as well.

Chris

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