The Steamboating Forum

Ok, this question is sure to get opinions and advise coming my way. With the soon to arrive steamboat of my dreams, I am faced with having to decide where I will get the water for her boiler. What recommendations would the experienced boat owners have on what source of raw water I should use to put in to my boiler.

The previous owner used municipal water with some sort of an additive (which he included with the sale of the boat) put in to eliminate/reduce scaling in the Bryan CL-90, 21hp, WT boiler. Guess I'll do the same to start. But, municipal water rates in W. Texas are at a premium and will cost me. The lake water is clear enough, but not sure if best for this application. I'd like to know what quality standard is the best for boilers. Or, should I try collecting rain water which would seem to have the lowest possible ph levels in theory. Indicating that I was considering using "distilled" water when I get her - he said, don't.

He's had her for 17 yrs and has had good success with her. I suspect I will do the same. But, I was interested in what other Captains were using for their boiler water protocols.

Thanks.

I Pull right out of whatever freshwater body I'm in. Not running any additives. But, I trailer the boat and it is either blown down and dry when I haul out or it is completely full from over night condensing/vacuum when I leave it in the water. When I blow down, I see no rust and there is no scale floating in the glass. And When I remove a fitting all I see is a fine brown silt.

If it were me, I would do what he's been doing. If it works, don't change it. That is an expensive boiler to replace. Mine? I can make another if needed.

The worst thing to do to a boiler is leave it half full. Empty and dry or completely full for storage.

-Ron

I guess I don't get why your water rates would be an issue. If you only fill it once in a while (and use a little TSP to keep the boiler from rusting), your water consumption should be minimal.

As an example, when I'm not showing off in the harbor with the whistle or using the stack blower for impromptu races, my water consumption is nearly zero. I went twelve miles in a straight line a week ago and the level in the glass never moved.

Does the boat have a steam atomizer. That might use a bit more.

Buy a TDS Meter (Total Dissolved Solids) to check water quality, about $30-$40 USD. Also use Pet Store Ph Test Strips (used to check fish tank Ph) to monitor the alkalinity. These are about $5 for 100 test strips. Boiler Ph to be maintained at 9 - 10.

I use ordinary lake water for feed, runs about 115 PPM (Parts Per Million) TDS. City water in Phila is about 230 PPM. In Texas I understand the TDS levels run as high as 500 PPM for municipal water. Without condensing (and condensate recycling to the boiler), water TDS rapidly increases, and should be kept below 1000 PPM with blowdown as required. Condensing systems with condensate recovery build up TDS far more slowly. Either way TDS is lowered with blowdown.

Collected rainwater is best, running about 1 or 2 PPM TDS if collected after the roof (assuming you get the water from a roof drain) has had about 15-20 minutes of wash-off before collecting rainwater. Rainwater however is usually acid (Ph 6-7), so chemical additive is required to control Ph. If you run condensing with condensate recovery, then enough makeup water can be produced with low TDS from city water, with a small Reverse Osmosis (RO) unit if you run out of rainwater. The very low TDS of rainwater is not really needed in a conventional boiler running at less than 250 PSI. A flash boiler needs this low TDS water, as all dissolved solids are immediately deposited inside the boiler tubes while steaming.

Tri-Sodium Phosphate (TSP) is used to increase Ph of boiler water, I usually put in about a tablespoon for a 15 gallon reserve feed tank. The TSP protects the boiler from corrosion, keeps sludge in suspension rather than allowing hard scale to buildup inside the boiler. Other boiler treatments may work OK, but I work for a company that has built literally millions of horsepower in steam-electric plants, and the water quality chemists here at work are always doubtful of ready-made boiler water additives that nobody can figure out what they contain. There is no good universal water treatment chemicals, except TSP in 75 - 250 PSI pressure boilers as far as I know, but I am not a water treatment engineer. If you can, consult with real local boiler water treatment chemist, there may be other specifics for your location. What treatment chemical did the previous owner use?

One important issue is oil in the feedwater, Be sure your condensing system supplies feedwater that is free of oil. 10 PPM oil is considered the maximum allowable for boiler pressures below 250 PSI. A lightly loaded boiler can often survive some oil, but whenever high boiler heat/output occurs, the oil will bake on to heat transfer surfaces, form an insulating brown film, and the boiler metal will begin to overheat, very bad.

One other issue is un-dissolved solids in the water, easily controlled with ordinary water filters for makeup water, and routine blowdown.

When I shutdown and the boiler cools off, a vacuum is formed and feedwater is sucked into the boiler till it is entirely liquid filled. The feedwater that is sucked into the boiler is usually deaerated before it enters the boiler, so very little Oxygen is present. This is a good layup practice if the boiler will not be used for a day, a week, a month, etc.

One potential problem with a fully drained boiler layup is residual moisture. If the boiler is not completely dry, then a little water remaining will promote quick corrosion. How to insure no moisture residual is the issue. Keeping a small fire to dry out the boiler is generally not recommended, as thermal distortions can damage the boiler, depending on how the fire is arranged. A moderate heat source and good ventilation might be used. A good vacuum pump on a tight system (reducing the boiler pressure to well under one inch of Mercury Absolute) will properly dry a boiler internals using ambient temperature of only 90F. I would recommend, for the very best setup, a 1/2 PSIG nitrogen blanket, which securely keeps Oxygen out of the system, but with the complication of a Nitrogen regulator and gas bottle.

We use a three stage process:

A - feedwater makeup
This is done with deionized water provided by a filter cartrigde, it gives pure water in the range of appr. 2 µS/cm.
One cartridge (3" dia. by 12" length) gives appr. 1/2 m³ pure water which is enough for half or 2/3 a season.
Initial filling of the boiler (0.25 m³) is done with clean drinking water.

B - Trisodiumphosphate
for controlling scaling, corrosion inhibitor and adjusting pH, should be 10-20 mg/l.

C - Sodium Sulfite
as an oxygen scavenger, there should be an excess of appr. 10-20 mg/l Na2SO3 in the boilerwater to avoid any free oxygen.

One scotch type boiler is now in its 25th year of operation without any corrosion on the waterside.

Of course such a system is only to be used with a closed circuit, the most loss comes from the use of blowers.

Scotty

A few questions please:
"A - feedwater makeup
This is done with deionized water provided by a filter cartrigde, it gives pure water in the range of appr. 2 µS/cm.
One cartridge (3" dia. by 12" length) gives appr. 1/2 m³ pure water which is enough for half or 2/3 a season.
Initial filling of the boiler (0.25 m³) is done with clean drinking water."

O; Is this cartridge a demineralizing cartridge? 2 µS/cm, do you have any idea of the resulting TDS in Parts Per Million, or mg/liter? How much does a cartridge cost, and what is the maximum flow rate allowed. Thinking here of the cost if used for a system without condensate recovery.

"B - Trisodiumphosphate
for controlling scaling, corrosion inhibitor and adjusting pH, should be 10-20 mg/l."

Q; 10-20 mg/l, this is the concentration of TSP to be maintained in makeup water, or the concentration to be maintained in the boiler?

"C - Sodium Sulfite
as an oxygen scavenger, there should be an excess of appr. 10-20 mg/l Na2SO3 in the boiler water to avoid any free oxygen."

Q; How is this concentration measured? I assume the concentration goes down as the chemical is consumed in scavenging Oxygen?

As a comparison to the above;

On SY Gondola we evaporate fresh water straight from the lake. Very soft water (low calcifying mineral content). We have a strum box immediately after the sea cock and a strainer immediately before the injector.

One low pressure blowdown at the start of the day and one high pressure blowdown in the middle of the day ensures we don't get a build up of scale.

The boiler is 35 years old and had it's first set of tubes last year, due to erosion on the fire side, the water side was perfect other than the odd spot of localised pitting.

During the summer the boiler never goes cold, and we try not to inject water after the engine has finished for the day to reduce oxygen content as far as possible.

During the winter it is bone dry with all openings vented and a small tubular heater installed in the firebox.

Greg

fredrosse wrote:A few questions please:
"A - feedwater makeup ...
O; Is this cartridge a demineralizing cartridge? 2 µS/cm, do you have any idea of the resulting TDS in Parts Per Million, or mg/liter? How much does a cartridge cost, and what is the maximum flow rate allowed. Thinking here of the cost if used for a system without condensate recovery.

"B - Trisodiumphosphate ...
Q; 10-20 mg/l, this is the concentration of TSP to be maintained in makeup water, or the concentration to be maintained in the boiler?

"C - Sodium Sulfite ...
Q; How is this concentration measured? I assume the concentration goes down as the chemical is consumed in scavenging Oxygen?

A - yes, it is an ion exchange filter, TDS depends on blowdown frequency.
We do not measure TDS, we measure hardness of the boiler water instead. ***
Cost appr. 50,- € per cartridge, max. flow rate appr. 5 l/min.
This is only practicable for the makeup for a closed system!!
Of course the consumption depends on the quality of the raw water, this should have drinking water quality.
This system is used on Lake Constance, which is rather clean, but with much higher hardness than
Lake Windermere or Lake Coniston for example.

B - concentration in the boiler.

C - done by titration for colour change (after adding two reagents), this takes maybe two minutes.
Yes, concentration will be slowly getting lower. After shutdown it will keep fairly constant
if there is no air leakage into the boiler.

Scotty


*** edit:
one indication for the pureness of the boiler water is the fact, that it slowly dissolves
the glass (borosilicate) of the water gages, app. 2 mm in 15 years.