Posted by Steve Young on August 27, 2007, 10:09 pm
Nick, here's what I've been using in the heat storage system I built from your
suggestion of using old fuel oil tanks, some years ago. 2 parts to it, a rust
inhibitor, which costs about $5 a gallon and treats 300 gallons and an oxygen
scavenger, at about the same price per gallon. They have a chemical engineer
available, who may be able to answer any questions.
and Stop-Rust #200 oxygen scavenger which is the very last item on the page.
Hope you find this helpful.
Posted by nicksanspam on August 29, 2007, 10:01 am
Steve Young <bowtieATbrightdslDOTnet> wrote:
Thanks. It was.
After talking with Modine and Farwest and Galvotec
this seems very empirical. A Galvotec engineer said they use about 5 mA/ft^2
(a lot) to protect steel in seawater, vs 2 in freshwater. They use more if
the water is flowing fast, as daestrom implied. The engineer didn't have
a value for aluminum.
The current can come from a sacrificial anode "battery" or a DC power supply.
The Farwest site has graphs to predict the lifetime of a pipeline-protection
anode as a function of soil conductivity. This seems to be a simple energy
calc. One of their products is 17 lb of magnesium inside conductive coke
inside bentonite clay inside a cotton bag, which disappears over time. This
can provide 1 amp for 1 year, ie about 1.7Vx1Ax8760h/17lb = 876 Wh/lb...
Galvotec said an anode wouldn't help much in this case (although there's
a 1996 patent for a radiator cap attached to a magnesium anode.) Modine
tried this unsuccessfully. Like chrome plating, it can protect the outside
of a tube, or the inside of a tank with a simple geometry, but it only
protects a few diameters into a tube. This seems to be a matter of water
conductivity and geometry. It might work if the deep insides of the radiator
tubes were directly connected to the anode and the parts closer to the water
hoses were connected via resistors with increasing values :-)
As to oxidation, an oil layer or oxygen getter may be useless if the radiator
is exposed to oxygen every day when it drains down to avoid freezing. STSS
EPDM-lined tank manufacturer Sven Tjernagel said "Don't use oil. That will
destroy the liner." He says just keep the water slightly alkaline. Modine says
their radiators should do fine if dielectrically isolated from other metals,
eg a bronze pump and a pressurized copper pipe DHW coil. The 12V radiator fan
could have an isolated DC supply. They say put a pan under the radiator and
make it inspectable and replaceable, in case it ever leaks.
Davies Chief Chemist Pat Fogerty recommends 0.5-2% of their "ACI 100" Al
corrosion inhibitor, listed in the "industrial" part of their web page.
A 5 gallon pail (0.5%) costs $1.80 + shipping and should last forever.
It's 42% sodium silicate, which may be essentially non-toxic when diluted.
It has a "2 mg/m^3" OSHA TLV (Threshold Limit Value) for human toxicity,
which seems to be a limit for the undiluted solution in a fog, vs a tank.
I wonder if it's still legal to preserve raw eggs in an undiluted solution.
Pat Fogerty says the MSDS says [the undiluted solution?] is non-toxic to
fish and has a "2,0,0" toxicity/flammability/corrosiveness safety rating...
Section P2902.5.2 of the 2006 ICC residential code for 1 and 2 family
Heat exchangers using an essentially toxic transfer fluid shall be
separated from the potable water by double-wall construction [unlike our
copper pipe coil.] An air gap open to the atmosphere shall be provided
between the two walls [which raises the cost and kills efficiency--
where's the GFX air gap?]
Section R202 defines an essentially toxic transfer fluid as
Soil, water, or graywater and fluids having a Gosselin rating of 2 or
more, including ethylene glycol, hydrocarbon oils, ammonia refrigerants
and hydrazine. [The scale runs from 2 (mildly-toxic, meaning 50% of 70 kg
humans would die if they drank 1 quart of it) to 6 (a few drops...)]
If the "2" ACI rating is a Gosselin number for the undiluted solution,
the worst-case toxic dose would be 1 pint, and diluting to 1% makes
the toxic dose 100 pints, well over 1 quart, so it would be fine
with a single wall heat exchanger.
Posted by daestrom on August 31, 2007, 3:01 pm
Gosh that takes me back :-) I worked for an older guy when I was a kid that
kept a couple of cans of 'water glass' around from the depression. Said
they used to dip eggs in it and let them dry. The eggs would last for
months if not years without refrigeration.
Otherwise, thanks for sharing your findings.
I can only surmise that since the tubing is wrapped around the separate
drain pipe and soldered to it, the supply tube wall and the drain pipe wall
are the 'double-wall'construction. I doubt that an 'air gap' is required in
all installations, maybe you better go read that again. Another typical
heat exchanger design is two pressurized coils (one for toxic and one for
potable) mounted in a vented tank filled with non-toxic. If either tubing
leaks, the vented tank overflows and is detected before the opposite tubing
develops a leak. If potable pressure drops while the tubing fails, you
merely syphon the non-toxic water from the tank.
In that regard, the GFX is similar in that since the grey-water is vented to
atmosphere and the potable is pressurized. Any leakage of either will be
detected before a second failure can occur (you either get potable or grey
water all over the floor).
My limited experience in sewage treatment (couple of summers while in school
many years ago) ISTR that all potable to sewage connections had to have a
positive break such that if potable pressure fails and sewage backs up,
there should be no way for sewage to be syphoned into potable.
You could still get contamination with a multiple simultaneous failure of
two walls while the potable pressure fails. But that's pretty remote if you
can be reasonably sure you'd detect a single failure soon after it began
Posted by daestrom on August 27, 2007, 10:47 pm
Quite right. Al forms a nice oxide layer that inhibits further corrosion,
*BUT* that oxide layer can be interrupted by several things. Physical
abrasion is an obvious one, but to a lesser extent erosion from very fast
moving fluids (sometimes called 'flow-accelerated corrosion'). But I don't
think you'll have trouble there.
The minerals in the water can have an affect too. From what I've read, any
with halogens (chlorides, flourides, bromides, etc...) will cause rapid
pitting of the surface. Carbonates (CaCO3, Mg2CO3, et.al.) are not so bad.
But this ends up being you either have 'bad water' or you don't. Oxygen
also plays a part and you're drain down system will have some problems with
that (each night the wet surfaces will be exposed to air, each morning
I've also read that there are dozens of different alloys of Al with
different corrosion resistance. No idea what version a radiator would have.
It may be significant that the interior is protected by anti-freeze with
corrosion inhibitors and the outside (exposed to rain, road salt, and storm
water) is protected by paint.
Posted by dances_with_barkadas on September 2, 2007, 11:16 am
The carbonates combine with the oxygen to form carbonic acid. At
your typical 900 F steam operation, it is a SEVERE headache. This is
why steam plants use active dearation to acheive 7 parts per billion
oxygen in the feedwater.