Author Topic: Developing a Small Steam Plant  (Read 5011 times)

Offline MJM460

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Re: Developing a Small Steam Plant
« Reply #90 on: January 07, 2020, 12:52:56 AM »
Well done on that piping, Gary.  It looks really nice. 

A pity to have to cover it all with insulation, but that is thermodynamics.

Perhaps we have to work out how to cover the insulating material with a metal protective shearing from brass shim.  Or perhaps that is going too far.  Derek makes his look quite nice with white paint or something similar.

MJM460
The more I learn, the more I find that I still have to learn!

Offline gary.a.ayres

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Re: Developing a Small Steam Plant
« Reply #91 on: January 07, 2020, 10:16:53 AM »
Thanks MJM - glad you like it.

Agreed - shiny copper does look great as long as it's kept polished, but it would be sensible to add some insulation.

Derek's does indeed look great, but I'm not planning to do quite as thorough a job as he did.

Currently my aim is to use a tight, thin layer of self-amalgamating tape (your suggestion) and then a layer of string on top of that, then finally paint.

I'm thinking that that may provide a reasonable degree of insulation while not being too involved or too bulky.

Thoughts welcome, of course...

Offline gary.a.ayres

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Re: Developing a Small Steam Plant
« Reply #92 on: January 12, 2020, 09:03:47 PM »
The new tee arrived and this time the machining of it went smoothly as I was on my guard against foulups. Here it is attached to the lubricator:



Once that was installed in the plant it seemed sensible to fire the whole thing up to make sure it worked before going on to the final stages such as lagging the pipes, finishing the base, etc. It may not be the most efficient plant in the world but it certainly works:

<a href="http://www.youtube.com/watch?v=aGtS9f-lxw8" target="_blank">http://www.youtube.com/watch?v=aGtS9f-lxw8</a>

I noticed that with the separator/preheater in the system the engine seems to run more slowly but with more torque. Is that what one would expect?

I was pleased to find that the separator works. I emptied about 100 ml of condensate from the bottom drain cock over the course of just under an hour:



As a novice I have no idea whether or not that is a decent yield of condensate, though I'm sure some of you guys will. What I do know is that this 100 ml of liquid is better in that jar than as condensation all over my lathes, mill and drill press.

 :)


Online crueby

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Re: Developing a Small Steam Plant
« Reply #93 on: January 12, 2020, 09:06:10 PM »
Looking great! Love the layout of it, coming down to the last touchs.   :ThumbsUp: :ThumbsUp: :ThumbsUp:

Online propforward

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Re: Developing a Small Steam Plant
« Reply #94 on: January 12, 2020, 09:28:38 PM »
That's great Gary - really nice work. NIce job on that Tee - looks perfect, and good to see everything working well.  :NotWorthy:
Stuart

Offline gary.a.ayres

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Re: Developing a Small Steam Plant
« Reply #95 on: January 12, 2020, 10:01:18 PM »
Many thanks guys.

Not quite at the end of the journey  yet, but it's in sight...

Offline Johnmcc69

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Re: Developing a Small Steam Plant
« Reply #96 on: January 12, 2020, 11:30:30 PM »
Congratulations Gary! That's a nice set up!

 John

Offline gary.a.ayres

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Re: Developing a Small Steam Plant
« Reply #97 on: January 12, 2020, 11:41:41 PM »
Thank you John.

 :ThumbsUp:

Offline MJM460

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Re: Developing a Small Steam Plant
« Reply #98 on: January 13, 2020, 05:34:46 AM »
Hi Gary, great to see the whole plant running as planned.  You must be feeling very pleased.

Did it take much pumping to maintain the level in the boiler?

You are quite right to feel that condensate is better in the jar than spread though out your workshop where it can only cause harm.  However, I do hope your workshop is well ventilated when you are running that burner.

To understand what that quantity of condensate means, it is necessary to understand what is happening in the plant, and hence why the condensate formed.  More measurements are need to quantify things with more confidence, (I donít think ďexactlyĒ is a relevant concept here), but we can do some basic calculations to give an idea of the magnitude of the quantities, which in turn will indicate which measurements are required if you want to go into more detail.

Initially you will have poured or pumped some cold water into the boiler.  Possible 15 or 20 deg C, or since it is winter there, you may have decided to speed things up using water from a freshly boiled kettle.  Then the heat from your burner heats things up. Initially, everything around the boiler, meaning itís copper shell and tubes, external fittings etc. as well as the water.  Once the boiler reaches steam temperature, the metal parts do not absorb more heat, and further heat goes into evaporating the water.  The steam is then opened to the engine.  Initially it looses some heat to the copper piping, which will result in some condensate forming, then it warms up the engine, even more condensate before it will run without spluttering, and finally your exhaust separator, where even more heat goes into the metal parts before the remaining steam goes up the stack to atmosphere.

Once the engine is running under roughly constant conditions, all those hot parts that are not really well insulated will continue to loose heat to the atmosphere, the engine will change some of the heat into work, a very small amount unfortunately, and of course, you will have to  start pumping water through the coil in the separator into the boiler.  The fresh water will absorb heat from the exhaust steam in the separator and of course cause more condensate.  This last bit is the condensate that you might call ďdesirable yieldĒ, so the most important when it comes to your question.

You might guess that to proceed further, it would be good to empty and perhaps measure the condensate soon after the engine starts running to determine how much was formed during warming up the system, then resume collecting in a second jar.  Then it would be good to know how much fresh water you pumped into the boiler to maintain the level.  Finally, it would be interesting to know the water temperature into and out of that coil in the separator.  Of course, that might be way over the top for your interest, but to give you an idea of the magnitude of the numbers, we can calculate roughly how much heat was lost by that 100 ml of water in condensing from steam.  From the steam tables assuming relatively low pressure, we can see that the enthalpy of dry saturated steam is about 2676 kJ/kg.  If we assume it had cooled to say 80 C in the separator before run was finished, at this temperature, condensed water has an enthalpy of 250 kJ/kg, so we can estimate the heat lost by the steam to make that condensate was 2426 kJ.  For 100 ml, approximately 0.1 kg, 242.6 kJ or 242600 J.

This is not a figure that would mean much to most of us, including me.  However we can look up the specific heat of the copper, bronze and brass which was heated during your plant run time.  My text book gives slightly different values for each metal, but for our purposes we can assume the average is about 400 J/kg.  If this metal started at say 20 C and was heated to roughly 100 C, we can calculate that this was sufficient heat to raise about 7.7 kg through that temperature range.  Now the boiler is directly heated by the burner, so we need to guess the piping plus engine plus separator, perhaps 2 kg max possibly only 1 kg.  So we can see that heating up the cold metal does not explain all the condensate, indeed, probably only around 20% of it.

We are hoping that coil has heated feed water, so letís see how much it would heat.  Again letís assume the water started at 20 and was heated to 80 in the coil.  The steam is probably close to 100 but you need a temperature difference to cause heat transfer, and we have limited area.  It would be interesting to measure the coil outlet water temperature, but letís continue assuming 80 C.

The specific heat of water in that temperature range is 4184 J/kg, so our 242600 J would heat approximately 1 kg or 1 litre through (80-20 or) 60 deg.  If 20% of the heat was used for warming up the metal, perhaps 800 ml of water.  I wonder how much you actually pumped through the system.  The condensate is not the same as consumed by the engine, of course.  Most of the engine exhaust steam will be going up the stack, so you need several different water measurements to determine the engine steam.

Now either that will excite you, well interest you anyway, and you will want to make more measurements.  Or perhaps you lost interest long ago and did not read this far.  But I hope it will give those interested an idea of how thermodynamics can increase our understanding of how the steam plant works.

Looking forward to the next steps in the development of this plant.  Itís a wonderful demonstration of what it is all about.

MJM460
The more I learn, the more I find that I still have to learn!

Offline Zephyrin

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Re: Developing a Small Steam Plant
« Reply #99 on: January 13, 2020, 09:31:15 AM »
fine development of your steam plan; nice to follow Gary, congratuations !
Thanks for all these input MJM, I greatly appreciate your way to consider our hobby...

Offline MJM460

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Re: Developing a Small Steam Plant
« Reply #100 on: January 13, 2020, 10:42:34 AM »
Hi Zephyrin, I am glad you like it.  I canít add much in the machining area, still a beginner, still striving, but the theory is where I can make a little contribution to this hobby we all enjoy.  I hope I get close to explaining things in a way that most can understand.

MJM460

The more I learn, the more I find that I still have to learn!

Offline gary.a.ayres

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Re: Developing a Small Steam Plant
« Reply #101 on: January 13, 2020, 10:34:46 PM »
Many thanks, Gentlemen.

@ MJM - amazing exposition! When I was at school I never did my maths homework, and every single day I got into trouble for it. I guess that has stuck with me over the years, so to be honest I probably won't be making any calculations. I tend to go more by the general feel of things. However, even to me what you have written makes sense, particularly the point about the initial heatup producing much more condensate (from all parts of the plant) than when the plant is running hot.

Your first question reminded me of what I forgot to include in my prior post, which was that the plant seems to consume a lot less water now that the separator/preheater is in the system. I guess that means that the preheater is doing its job. Cerrtainly, the pipe coming away from the preheater coil was palpably warmer than the one going into it. To reiterate, my sense (albeit not very scientific) is that the engine ran slower but with more torque, and that overall significantly less pumping of water was required. There didn't seeem to be a great deal of steam coming out of the stack, though I guess it must have gone somewhere.

Yes, the kerosene burner does fume somewhat, but I found that keeping the workshop door open cleared it ok. I'm looking forward to trying the vapourising meths burner with this setup!

MJM - please feel free to continue posting on the science of things. Even if I am mathematically challlenged, it's still interesting and educational.

@ Zephyrin - thank you for your kind comments. It feels like I have been on a long journey since you explained to me how to grind off that leaky lump of silver solder at the end of one of the tubes on this boiler and resolder the join. That was advice and encouragement when it was most needed! Much appreciated...


And now, lagging the pipes. I have done one so far, and I admit it's not wonderfully neat (especially at the ends), but they will improve with practice.

First, a layer of amalgamating tape (thank you again MJM), cut into narrow strips the better to negotiate bends:



Then a layer of string, held with super glue at each end:



And finally, a layer of acrylic paint - brushed into the string straight from the tube, no water:



Yes. Red.


Offline rjconway

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Re: Developing a Small Steam Plant
« Reply #102 on: January 14, 2020, 01:09:50 AM »
Great thread and can plot the progress.   When did you actually start the boiler and engine project,  i think this thread started when you had made the engine & boiler 4 months ago...

I have been 14 months on a similar journey and not had steam yet !

Great to see a video as well

Rob

Offline gary.a.ayres

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Re: Developing a Small Steam Plant
« Reply #103 on: January 14, 2020, 06:51:28 AM »
Hi Rob, and thanks for your comment.

I started with the boiler, which I began in the Spring of 2018, so similar timeframe perhaps.

These things can't be rushed, and life keeps getting in the way too!

Looking forward to seeing a thread on your project if you decide to start one.

gary




Offline MJM460

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Re: Developing a Small Steam Plant
« Reply #104 on: January 14, 2020, 11:53:25 AM »
Hi Gary, I am glad you found my explanation interesting and understandable.  The maths is not for everyone,  but I like to think that just knowing that the maths can be done, and relying only on good data for fluid properties and the basic laws of physics, is worthwhile knowledge.  It is not magic, just the action of the basic laws of the universe.  And our little steam plants demonstrate in an accessible manner so much of the physics.

I am glad you asked again about the engine power and torque.  I gave it quite a bit of thought while writing yesterdayís post, then it slipped my mind.  But not completely, I woke up thinking about it this morning, remembering that I had missed commenting.  Strange how the memory works, or doesnít, as the case may be.

Your plant does add a little length to the exhaust piping, but I donít think enough extra resistance to easy see the effect.  The separator has plenty of internal space for the steam to flow without significant resistance.  So it is hard to see an explanation for your observations.  But in my experience, observations are usually real, so it means we have to look harder for the explanation.

One thing we know is that your engine has now had a bit of running in, so might be spinning much more freely than it did at first.  I am wondering if you actually let the boiler pressure rise quite a bit higher than the engine needs, then use the stop valve to throttle the steam to the engine.  There are good reasons to do this, but letís try and stay on topic.

It may well be running a bit slower than before, but I wonder if the throttle valve is adjusted differently than previously?  However, if, as I am assuming, the boiler pressure is somewhat higher than needed by the unloaded engine, and possibly higher than for earlier tests, when you slow the engine, by holding the flywheel or similar means, there is less pressure drop through the valve (due to the lower steam velocity, so the engine sees more of the steam pressure, and hence produces more torque.  Similarly, the oscillating engine valves are formed by the common area of two partly overlapping circles, usually until about half stroke, where they may be fully overlapping.  At slower speed, there is more time for steam to flow into the cylinder, resulting in higher pressure on the face of the piston.  More pressure means more torque.  Of course if the throttle valve was fully open for each run that explanation evaporates.  Similarly if the boiler pressure was higher than the earlier runs. 

Another thought is that the engine is running much as earlier give or take a bit of variation in boiler pressure or throttle setting, but now with more experience you are observing things you previously did not notice.  After all there is a lot of learning going on in those first runs of your first engine. 

So keep looking and experimenting and see if you can pick up other factors which may offer a better explanation.

Regarding the observation of the quantity of steam from the stack, remember that dry steam is colourless, and the white mist we see and associate with steam is caused by light reflection on the minute water droplets in wet steam.  If your separator is doing its job, those droplets should be coalescing on the inside walls of the vessel, leaving dry steam exiting the stack.

Sometimes there is a clear gap between the top of the stack and where steam starts visibility condensing.  However with a lower velocity of air exiting the stack, there is a lot of air mixing which reduces the partial  pressure of the water in the fluid exiting the stack, and this reduction in partial pressure significantly reduces the dew point temperature or condensing temperature, so that the exhaust stream becomes superheated, and so disappears as higher humidity as it mixes with more air.  I suspect this is why you see less steam exiting the stack.  Of course there may actually be less steam exiting, if as suggested earlier the engine is running freer and requiring less pressure, so that you have throttled the steam flow a bit to get a pleasing speed.

By providing some heat to the feedwater, the preheated reduces the energy necessary to raise the water to boiling point.  Hence, if all else remains constant, particularly the burner fuel consumption, the boiler would operate at a slightly higher pressure.  This would require more  throttling to achieve a similar engine speed, and combined with the free running engine, would indicate a lower steam flow requirement.  But I donít know if the effect would be noticeable.

Not sure if there are some satisfactory explanations in those suggestions, but at least it should prompt some ideas of what to look for or measure in order to identify what is going on.

Looking forward to the next steps

MJM460
The more I learn, the more I find that I still have to learn!