Southworth 12" Vertical pumps

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Re: Southworth 12" Vertical pumps

Post by JonRiley56 » Thu Feb 21, 2013 3:03 am

Hey Guys

Are you suggesting that I could use the exhaust from the little pump to preheat the boiler feed water ? I was planning on using the main exhaust to preheat the water.

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Re: Southworth 12" Vertical pumps

Post by fredrosse » Thu Feb 21, 2013 5:00 am

In general, with a condensing steam plant, you want to have the highest vacuum available for the main engine. That means the lowest absolute exhaust pressure, which implies the lowest condensing temperature. If you have sea water cooling the condenser at, say 70F, and a relatively tight system, you could maintain perhaps 26 inches mercury vacuum, with an exhaust steam condensing temperature of 125F. In this case, the highest possible temperature that your engine exhaust could heat feedwater is around 115F, somewhat less than the saturated steam temperature of 125F.

On the Liberty ships, the main engine ran with good vacuum exhaust, and the auxiliary steam system had all the little engines, winches, electric generators, and steam pumps, etc. exhausting at something above atmospheric pressure (10 PSIG, condensing temperature 240F). This auxiliary steam flow, although a much smaller quantity of steam, could heat all the main feedwater to about 220F.

Of course, if the main engine exhaust is at atmospheric pressure, you could just use that to heat feedwater to about 205F, but you want to maintain a good vacuum for the main engine. The small steam feed pump uses enough steam that it is almost ideal to produce the first stage of feedwater heating, easily getting all the feedwater fairly hot, raising the temperature about 80 degrees above whatever your condenser outlet temperature is.
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Re: Southworth 12" Vertical pumps

Post by Lopez Mike » Thu Feb 21, 2013 2:23 pm

I don't get it, Fred. Why would it make any difference whether the main engine exhaust was at atmospheric pressure or at a vacuum? Either way I should be able to run it though a feed water heater and get some of that energy back? Seems as though both the main engine AND the recip feed water pump could both be plumbed into the input of the same heat exchanger. Seems as though any source of heat could be used heat up the feed water.

I can see it now. Big ugly old solar hot water heaters on the cabin top. What have I done?

I'll go back and read all of this over again. Maybe I missed something (That's never happened before! Snort!)

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Re: Southworth 12" Vertical pumps

Post by fredrosse » Thu Feb 21, 2013 9:07 pm

"Why would it make any difference whether the main engine exhaust was at atmospheric pressure or at a vacuum?"

The main engine produces more power, more efficiently, with a good vacuum, but a lower condensing temperature (saturation temperature) comes along with that good vacuum. In a feedwater heater, the maximum theoretical temperature that can be found is the saturation temperature of the steam providing the heat duty. A heat exchanger with whatever surface area you like cannot heat even one drop of feedwater above the saturation temperature of the exhaust steam.

"Either way I should be able to run it though a feed water heater and get some of that energy back?"

Yes, but the main engine exhaust could not possibly heat any feedwater above 125F, wheras the aux pump exhaust line (at atmospheric pressure, with a saturation temperature corresponding to 212F), can heat feedwater up to approach 212F.

"Seems as though both the main engine AND the recip feed water pump could both be plumbed into the input of the same heat exchanger. Seems as though any source of heat could be used heat up the feed water."

To do heating, two conditions must be met, A: ENERGY AVAILABLE: there has to be enough energy available to heat the feedwater, and either stream meets this requirement. B: HEAT TRANSFER: The energy source to heat the feedwater must be available at a temperature somewhat higher than the final outlet feedwater temperature. Fundamentals tell us that heat will naturally only flow from a higher temperature substance to a lower temperature substance, and this is where the high vacuum main engine exhaust falls short, it cannot heat feedwater over 125F, while the little steam pump exhaust can heat feedwater up to almost 212F, the saturation temperature corresponding to atmospheric pressure.
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Re: Southworth 12" Vertical pumps

Post by Lopez Mike » Thu Feb 21, 2013 9:52 pm

Thanks. I have a much better feel for it all.

Now my boat with a single cylinder engine has no vacuum pump. The engine exhaust is likely at 212F. The engine exhaust pressure just pushes the condensate back into the hot well. So I should get significant benefit from an exhaust feed water heater. Right?

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Re: Southworth 12" Vertical pumps

Post by DetroiTug » Thu Feb 21, 2013 11:43 pm

Here is the heat exchanger I picked up. It has 5/8" barb fitting on the ends and 3/8" on the sides. Now the question is, would it be better to run the feedwater in the ends or the sides, or will it matter?

Image

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Re: Southworth 12" Vertical pumps

Post by Lopez Mike » Fri Feb 22, 2013 12:42 am

Mine looks pretty much like that. It was a transmission oil cooler for a power boat engine.

I'm going to run the steam through the ends as that way there is much more area for the steam to pass. I calculated the area of the internal tubes. There are 43 of them with an I.D. of .200". That adds up to 1.35 square inches. The existing end fittings have an I.D. of .64" which figures out to only .3 square inches. A lot of restriction since my exhaust hose is about 1" diameter with an area of .78 square inches.

I'm cutting off the ends and boring them to fit a couple of copper fittings that are about 1" diameter. Not quite so restrictive. A little fooling around flaring my new end tubes to get some area to solder them onto the end cones.

The feed water flow is so low that the smaller side fittings should handle it without a problem.

Another doodad to insulate. No moving parts though.
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Re: Southworth 12" Vertical pumps

Post by DetroiTug » Fri Feb 22, 2013 4:19 am

As I was looking around for one of these, most of them appear to have 1.25" ends.

Also, it's becoming apparent with running and testing (on my setup anyways), the closer I can get the feedwater temperature to the boiler temperature, the better. So yes, I would use an exhaust heat exchanger- plus an economizer, anything that raises the feedwater temp is going to help, especially on a VFT where water is admitted right in to the steam generation area.

My theory again, but I don't think it is, as critical on a Roberts type where feedwater is admitted in to a mud drum prior to entering the steam generation tubes.

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Re: Southworth 12" Vertical pumps

Post by fredrosse » Fri Feb 22, 2013 6:52 am

When heating feedwater with engine exhaust steam, the feedwater heater does not have to accept all of the engine's exhaust steam, only a fraction of it, about 10% or less. So the exhaust steam line can have a tee, with a small steam line (1/2 inch or 5/8 inch) going into the feedwater heat exchanger, and the rest of the exhaust going to atmosphere, the stack, or condenser through a much larger main exhaust pipe.

It would be OK to send all the exhaust steam thru the feedwater heater, but the small size would probably restrict the exhaust flow, so that is why a tee is recommended, to avoid excessive back pressure on the engine.
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Re: Southworth 12" Vertical pumps

Post by Lopez Mike » Fri Feb 22, 2013 7:14 am

In this case, the area of the 'flues' in the heat exchanger is larger than the regular exhaust piping so there won't be much, if any, restriction on the steam flow.

Besides, I already started modifying it for the larger fittings!

The feed water piping in my boat is 3/8" copper. I wish there was an easier way to insulate it than gooping stuff on it. The smallest plastic foam stuff from a box store is made for 1/2" cpvc and fits kinda loose. I suppose that really won't matter and it is water proof. Just trying to keep that precious energy trapped in there.

All of this working to save energy reminds me of the old hack about trying to get to the moon by climbing a tree. It will only get me a teeny part of the way to big power plant efficiency but it's fun anyway.

Mike
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