Jet condenser

[87gn@tahoe]

Now here's one to ponder;

A jet condenser takes water from the body which the vessel is in, and injects in a spray into the exhaust causing the exhaust steam to colapse and condense back into water. Used primarily on fresh-water going multiple-expansion vessels, such as say a 80ft steam tug with a compound.

Now, could one theoretically forgoe using the body of water for the "jet" and instead use a makeup water tank to supply the water? Then any excess water in the hotwell ould be pumped back into the makeup tank? Am I missing something?

[gondolier88]

That would mean you would need to have means of cooling the make-up tank down to a low temperature in order to make the jet as efficient as possible- whether you would still get it as cold as straight from the wet stuff on the other side of the hull is questionable.

It would also require more plumbing, and would require a larger pump to work the extra resistance making more maintanance and more weight in the ship.

To answer your question however, in theory, yes you could.

Just as an aside- would a tug of that size, on what would probably be a lake or large freshwater estuary, need/have a make-up tank, surely the hotwell would be topped up from the lake/estuary?

Greg

[87gn@tahoe]

The question was brought up with the idea to possibly take said "jet condensing vessel",if it is indeed jet condensing, into salt water.

I am sure the end condensate teperature would have a great effect on the needed makeup tank "cooling provisions". I guess it all depends on how effecient the jet condenser was at creating condensate.

[gondolier88]

I see, perhaps you would be able to adapt it into a contra-flow surface condenser which would stop the jet hitting hot surfaces and leaving salt deposits by providing a constant cold surface to the exhaust steam.

It wouldn't be pretty, but it might work.

Have you pic's of the condenser?

Greg

[87gn@tahoe]

no pictures as of yet, just an assumption that it is jet condensing because it was quite common practice on the great lakes.

[fredrosse]

As stated previously, the jet of cooling water gets heated by the
condensing steam, so you would need a big heat exchanger to cool your
onboard water tank. Better to just use a steam surface condenser to
directly condense the steam with lake or sea or river water.

Jet condensers are simple and effective, but there are some problems:

1. The jet condenser water mixes with the condensate, and contaminates it
with the impurities, a bad problem with sea water jet condensing, although
it was used on low pressure ocean-going ships 150 years ago.

2. The jet condensing water, many many times the flow-rate of the steam, has
to be pumped from the condenser vacuum up to atmospheric pressure, with a
good vacuum you have to pump against 10 -15 PSI. With a surface condenser,
you only have to pump against the pressure drop through the condenser tubes.
This is only a small fraction of the pumping power needed for a jet
condenser, assuming a properly sized condenser.

3. If the jet condensing water is not constantly removed from the
condensing zone, the jet water will completely flood the condenser, and may
flood the steam engine cylinder, with potentially disastrous results. A
float mechanism is required to assure that this will not happen, shutting
off the jet condensing water if the pump fails, or stops for any reason.
But then, float valves can also fail, and it would only take a short time
to fill the condenser and flood the engine's cylinder.

[steamboatjack]

The Steamer "Sir Walter Scott" has a jet condenser but using the lake of course. The only advantage I could see on a boat is that properly designed you could get a really good vacuum with these but the extra power would be absorbed in needing a more powerful air pump as explained above.
As a matter of interest the old salt feed steam ships had a connection from the bilges called the "bilge injection" this was an emergency suction using the condenser and air pump for when the water was up to your knees.
Fifth Engineer " chief the waters going up the steps!" Chief Engineer "let me know when the waters going down the steps son"

Yes I know its not funny but engine room humor was usually a bit black, the favorite greeting on taking over the watch with Mobil was "the job's a nightmare!"

Regards
Jack

[SailorHarry]

no pictures as of yet, just an assumption that it is jet condensing because it was quite common practice on the great lakes.

Hello,

This is my first post here, though I have been lurking for a while. I'm a merchant mariner with experience working in the engine rooms of large steam ships, from a 3000hp Skinner Unaflow to a 120,000hp twin turbine. A year or two ago I had the pleasure of working on the <i>St. Mary's Challenger</i>, the oldest working steamer on the Great Lakes...perhaps in the world. She was repowered in 1950 with a 4 cylinder Skinner Unaflow but still has the original steering engine and anchor windlass from 1906. It's a working boat that earns her keep hauling cement, sort of a living museum. I've got some pictures I could post a link to if anyone is interested.

Anyway the point of mentioning that is that the <i>Challenger</i> uses a jet condenser. She has make-up tanks for use while navigating the rivers but draws feed water from the lake when possible (treated with a water-softening system). The jet condenser is surprisingly small for the size of the engine. There is a steam turbine-driven centrifigal pump that removes the water and two air ejectors for maintaining the vacuum. A portion of the warm water from the condensor tops off the hot well and the rest goes overboard. It works very well in practice.

I was inspired by my experience with the <i>Challenger</i> to built myself a steamboat and have spent a great deal of time thinking about different plant configurations. Because I live on the Gulf Coast where most of the water is brakish at best a condensing plant would be preferred. One design I have mulled over is exactly what you describe: a closed-loop jet condensor using makeup water instead of seawater. There is no need to cool the entire makeup tank, just run the water thru a cooler on its way to the jet condensor. I would construct the jet condensor from a medium size fire extinguisher. A small electric pump would fit in the bottom for dewatering, many of which come with a float switch for level control. The only issue there is finding one powerful enough to pump out of the vacuum. By using a small air ejector to create an initial vacuum the cooling water will be pushed into the condensor by atmospheric pressure alone. I would like an electric system for lighting, etc. anyway so using it for something as relatively non-vital as a condensate pump would be okay. You can always exhaust to atmosphere if something goes wrong with the condensor but I imagine an electric pump would be more reliable in the long run than a mechanical air pump.

Now, is this simpler or better than a traditional surface condensor and air pump arrangement? I'm not really sure. There's a million ways to skin a cat...its just amusing to consider different alternatives.

[fredrosse]

There are two large walking beam sidewheel steamers in the USA, one in SanFransisco, I think named Eureka, a ferry with a steam Surface Condenser (due to the high salt content of the bay), and one in Vermont, the Ticonderoga, with a Jet Condenser (very popular in the great lakes, and freash water rivers.

When designing the steam plant for my sidewheeler, I considered both types of condensers. The design has to condense about 80 pounds per hour (PPH) of steam for a one horsepower engine. My pumps are driven off the engine beam, at a slow 90 RPM, which makes for reasonably efficient pumping with an ordinary piston pump. The feedwater pump needs about 0.025 Horsepower (HP), and the injection pump about 0.1 HP, almost 10% of the engine output.

A steam surface condenser, consisting of 14 tubes, 1/2 inch outside diameter x 3 feet long each, will fit in a 3 inch diameter heat exchanger shell. The pressure loss in the cooling water circuit is about 1/10 the power required for a jet condenser pump. To this must be added the wet vacuum pump to maintain vacuum and remove the condensate, only about 80 PPH. This arrangement can use a condensate pump of only about 0.01 HP. The circulating water can be pumped, but I only plan to use scoops to force circulation thru the condenser while underway. A keel condenser, always submerged underwater, also requires no circulating pump, and has been proven as the probable best choice for typical steam launches.

Considering the potential problems with a dangerously flooded jet condenser, plus the rather high pumping power required, I will definately be using a surface condenser. The only reason I am not using a keel condenser is because I plan to run aground often.

One other point is the probable efficiency of a small electric pump for injection water service. This would probably be a flexable rubber impeller pump, to get enough pressure to force the injection water out of the condenser under vacuum conditions. This type of pump generally has very low efficiency, under 50% in small sizes.

[artemis]

The USS Monitor, built in 1862 used standard practice for the time: water from "over-the-side" was introduced to the jet condenser, the condensate (both air and water) then pumped to the hotwell which had an overflow directly over the side, and the water was pumped to the boiler. This was all done in a single unit driven off the engine crankshaft. Creating a partial vacuum in the condenser to induce the "sea water jet" also helped to turn the engine over for starting (well, a two cylinder, double acting, horizontal engine of 44" bore and - as I recall - 24" stroke needs a little help). The Ericsson "vibrating lever" engine operated quite reliably and was very efficient with no dead center. Unfortunately the rapid increase in marine operating pressure from 30psi to 100psi over about 5-6 years made "compounding" workable and spelled the death of "simple" marine engines for anything but "small boats". The jet condenser, two feedwater pumps, air/condensate pump, condensing chamber, and hot well made a rectangular package about 4' x 4' x 6' and maintained a vacuum of 26" using uncooled, raw sea water. Would a jet condenser work? Probably very well. Such devices were being used by Bolton & Watt for Robert Fulton's several steamboats as well as many others.