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Author Topic: Flash steam plant control.  (Read 95894 times)

flashtwo

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Re: Flash steam plant control.
« Reply #125 on: July 20, 2010, 12:08:10 PM »

Thanks Phil, that's much better.

It looks like one trough behind the bow followed by one crest before the prop, i.e. one wave length.

For those not familiar with the boat, there is a large overhang above the water after the prop (see earlier posts at last year's Guildford Show), which gives the appearance of a much longer hull.

Now, is the hull speed indicated by one wave length or one half wave length?

Ian
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flashtwo

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Re: Flash steam plant control.
« Reply #126 on: August 21, 2010, 02:42:45 PM »

Hi,

Iíve just fitted an oil/water separator and combined feed heater on Vital Byte and tested it with further improved results.

The separator is a vertical brass cylinder 1.75inch diameter by 8.5inch height. Within the cylinder, I've fitted a copper coil 5/32 by 100 inch which gives approx. 50sq.inch of heating area (steam exhaust side).

The exhaust steam /oil enters near the top and condenses on the exposed section of the coil. The drain is located at the bottom and exits above the water-line, the exit height determining the water level in the separation tank. The coil carrying the boiler feed water enters near the cylinder top, passes through the exhaust steam section then into the hot water on top of which lays the separated engine oil.

One problem with the previous exhaust steam collection arrangement was having to manually pump the water/oil out every 20 minutes of running time - with the new arrangement the boat will only be brought in to top up the displacement lubricator having dumped excess (oil free) water overboard.

The unit has been operated on the test pond with the drain water  free from oil and the feed water temperature rising to about 70degC before entering the economiser coil located in the stack.

The economiser outlet temperature is now about 147degC which indicates steam production since it is above the saturation temperature.

The efficiency has improved a lot since the gas valve is only having to open to 48% instead of 100% to achieve an average RPM of 612 over a 18 minute period.

I shall try and take some gas consumption readings on the lake tomorrow.

One thing Iíve got to understand now, is that the inlet temperature to the main boiler coil is 147degC, whereas the boiler outlet steam temperature is 131degC!


Here's a couple of photos.

Ian.
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flashtwo

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Re: Flash steam plant control.
« Reply #127 on: November 24, 2010, 10:30:19 AM »

Hi Mayhemers,

Vital Byte has been performing very well over the past few months with the oil separator / feed heater preventing oil from poluting the lake.

Since there is now no condenstate tank to empty every 20 minutes, extended runs of 40 minutes without returning to shore are a regular feature.

With a view to building a ďproperĒ boat, Iíve started construction of a vertical boiler to match the scale of an Edwardian Steam Launch that I have the plans of.

 The new vertical boiler is unusual (like everything else in this project!), in that the boiler coil extends up through the furnace and into the 2 inch diameter stack. In this way it will have 200sq.inches of copper-to-water surface area plus the 50sq.inches in the feed heater gives a total of 250 sq.inches.

The water will enter the coil at the top of the stack and steam will exit the coil at the connector located at the bottom of the furnace Ė how different is that!

To ease the removal of the boiler, connections have been kept to a minimum. The safety valve (not legally required) and the pressure and temperture tapping points have been removed to their own manifold separate from the boiler. The only connections left are the feed inlet, steam outlet, pilot gas and main burner gas Ė no sight glass or level measurement is required.

The first photo (DVD for scale) shows the skeleton of the boiler prior to attaching the coil and heat shield. The second photo shows the steam outlet to manifold arrangement.

The vertical boiler is in fact the same height of the current horizontal boiler.

After initial trials it is planed to encase the boiler in the traditional wood and brass banding.

Ian.
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steamboatmodel

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Re: Flash steam plant control.
« Reply #128 on: November 24, 2010, 03:50:26 PM »

Hi Ian,
You say "The water will enter the coil at the top of the stack and steam will exit the coil at the connector located at the bottom of the furnace Ė how different is that!"
Would not the steam rise to the top of the coil?
Regards,
Gerald.

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flashtwo

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Re: Flash steam plant control.
« Reply #129 on: November 24, 2010, 05:29:08 PM »

Hi Gerald,

That's a very good point and well worth the experiment.

One thing with the monutube or flash boiler is that the feed water is continuously pumped in under pressure, which has to be slightly higher than the steam pressure to maintain flow, so hopefully that should discourage the steam from rising to the top.

Another feature is the effective tube gradient.  As you can imagine the tube sprials down from the top over a vertical distance of 405mm. The tube length is in the order of  12 metres and so the effective gradient is about 1 in 30 and as you might have experienced with a steam or air lock in a long pipe they can be difficult to shift by natural circulation.

The reason for pumping water in at the top is to maintain the highest temperature difference between the combustion gases and the water/steam in order to maximise heat transfer.. The coldest part of the boiler is at the top, so that is where the cold feed enters, and the hotest part is near the burner where the steam exits. The water/ steam spirals down from the cold to the hot end.
 
Anyway that's the theory - we'll find out what happens in practice!

Cheers

Ian
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ooyah/2

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Re: Flash steam plant control.
« Reply #130 on: November 24, 2010, 07:56:20 PM »

Hi Ian,
I would have no fear of air locks, your coil is wound in spirals with no sharp corners.
Your coil is similar in construction to my flash steamer with the water going to the cold end and my coil is lying horizontal but in yours with it being vertical the pressure created by the pump and the heat generated will turn any air bubbles into steam along with the air already in the coil.
Any condensate in your cylinders will be shoved out as soon as the valve is opened to the steam.

I am puzzled as to what the large dia tube going up into the funnel is, have you considered making your coil wider to fit into the shell case and then reducing up into the funnel, you could then use a ring burner or a large ceramic one, just a thought.
I look forward to hearing your results, the mechanical ones not the electronic ones !!!

George.
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gondolier88

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Re: Flash steam plant control.
« Reply #131 on: November 24, 2010, 09:30:08 PM »

Hi Ian,

I have to say your idea re. the feed arrangement, though based on sound theory, isn't based on practice, as I'm sure your aware.

The reason the cold water is injected at the base is to make ful use of natural convection- the steam engineers bedfellow, our hobby wouldn't exist without it.

I would suggest you think carefully about your coil arrangement- if you are looking to make the most heating surface in the space available then why not use a 'twin' coil arrangement- an inner and outer coil?

The outer, say 5/16", tube would be a coil of a fairly flat gradient, taking the cold feed from it's base where it would flash and rise to what I would propose is a stainless 'header', which would the connect to an inner steeper coil of say 1/4" tube that takes the now very dry steam back down through the products of combustion, through the flames and the I would really suggest that you again make use of convection and take the steam outlet back up, through the center and have the outlet at the top of the boiler.

This would make a very compact heating exchanger, but very high heating surface and very dry, very hot steam!

The full size monotube boilers I've seen all use this method, along with every twin coil heat exchanger I've come across.

I very much look forward to seeing this launch make progress- what plans are you using- have you found some original Georgian ones or is it one of Selway Fisher's?

Greg
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kno3

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Re: Flash steam plant control.
« Reply #132 on: November 24, 2010, 10:18:24 PM »

This is a really interesting project and I am thinking about building such a coil boiler too. Do you hink it could work on a much smaller scale? In a size of about 10 cm length and 7 cm diameter?
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flashtwo

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Re: Flash steam plant control.
« Reply #133 on: November 24, 2010, 11:45:40 PM »

Hello George,

The centre 15mm copper tube serves two purposes -

1) The feed water connector is located at the bottom diametrically opposite the steam outlet connector and the feed will be directed through a 4mm pipe up inside the 15mm copper pipe to the top of the stack  from whence it spirals back down. Taking this route means it doesn't interfere with the return pipe spriraling down.

2) The gap between the spiral layers needs to be maintained for good heat circulation, so the 15mm pipe will be drilled to accept 1/8th inch copper pipe sections to act as spacers. The lowest spacers are stainless steel (for strength) rod inserted through copper pipe, which will support the weight of the coil.

When I start the system, I always flood feed right through to the cylinders and, since I have not throttle valve between the boiler and engine, as the steam is raise the feed is blown out of the cylinders (I toggle the reversing gear) and the engine warms up with the boiler, i.e. there is no sudden shock of high temperature steam.

I can see what you mean by having a ceramic burner. The design could be changed so the 15mm pipe terminates higher up and leaves room for a ceramic burner.

Are ceramic burners rated by their gas through put? - I've been aiming for 7 grams/min, though I'm getting very performance at 4 grams/min.

I shall post photos as the construction progresses.


Best regards

Ian.
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ooyah/2

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Re: Flash steam plant control.
« Reply #134 on: November 25, 2010, 12:18:12 AM »

Hi Ian,
Gotcha, as the coil is vertical with the heat being put into it the coils could start to slip down and prevent the heat circulating between the coils, so you St/St rods keep them apart, good idea.
Not sure about the gas consumption with ceramic burners but any that I have made work very well on a No5 jet, here is a pic of one with a No6 jet below a vertical multitube boiler 4.5" dia x 6" between end plates.
I have never been very concerned with the gas consumption as I refill the camping gas cans with Butane fro a 4.5kg bottle, this of course is used in my steam tug not the flash steamer, it has three burners with .025" jets pressure fed from the engine and uses about 3/4 pint of fuel per 4 mins.

Are you going to computerise the boat as the previous one?

George.







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SteamboatPhil

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Re: Flash steam plant control.
« Reply #135 on: November 25, 2010, 09:29:21 AM »

Nice job Ian, can we have than on the stand at Ally Pally as well ?   :-))
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flashtwo

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Re: Flash steam plant control.
« Reply #136 on: November 25, 2010, 09:32:52 AM »

Hi Greg,

The lower part of the coil will be constructed in three layers and the part in the stack will be a single layer in contact with the brass tube. The three layer section is wound with a 3.5mm (on average!) gap between the 22 spirals and with the vertical separation maintained with sections of 1/8th inch copper tube. I have a spread sheet that I can input the heating area required, tube size, gap size etc.,  and it calculates the overall dimensions of the boiler - so I can play around with the numbers to get the boiler shape that I require.

On my steam jet engine project (see the other thread) I used a 5 layered coil and I did achieve steam temperatures in excess of 720degC - yes the silver solder did melt!

I think with the horizontally coiled flash boilers, that Iíve been using, couldn't have had much natural circulation, since any density variation causing circulation must have been cancelled out along the length. In a normal boiler, as you know,  the circulation occurs between the lower headers and the drum and requires lots of relatively large diameter tubes. With the monotube flash boiler with a small diameter tube the flow relies on continuous feed pumping to maintain flow through the narrow tube. Anyway, its all part of experimental fun, which, if it is successful, could be applied to larger vessels Ė all part of modelling I suppose.

I have been wary of using any ďheaderĒ in the system, since it might constitute being a pressure vessel, which is what Iím trying to avoid with all the testing etc.

Yes, Iíve got the Selway Fisher Edwardian 30 foot launch plans and their detailed booklet on strip planking techniques. Iím aiming to use the 5 inch prop thatís currently installed in Vital Byte. The boat is planned to be of  75 inch length  and the boiler is scaled to fit. Iíve never tried strip-planking before, so its back to the bottom of the learning curve!

Ian
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flashtwo

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Re: Flash steam plant control.
« Reply #137 on: November 25, 2010, 09:35:43 AM »

Hi Kno3,

I canít see any reason why smaller versions couldnít be made. The required copper-to-water (not combustion gases-to copper) surface area needs to be converted into tube length knowing the tube diameter and wall thickness. The are many ways of coiling the tube:-

1)   Single layer results in a long boiler
2)   Multilayer results in a short boiler
3)   Layering the coils by starting at one end on the inner coil over a former then returning the opposite direction over another former (i.e. a strong plastic tube that slides over the inner coil) and repeating this for the number of layers required. The only problem with this arrangement is that you end up with several very hot spots each time the coil approaches the burner.
4)   Making the layers by spiralling out from the centre to the rim, thus making a spiral ďdiskĒ, then moving up to the next disk and spiral in from the rim to the centre and repeat until the number of disks is achieved. This takes a bit more skill, but it means that the coil gradually moves from the cold end to the hot end without the hot spots of the method 3) above.
5)   Figure of 8 is used a lot by the traditional flash steam tethered boat fraternity.


Ian
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flashtwo

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Re: Flash steam plant control.
« Reply #138 on: November 25, 2010, 09:36:45 AM »

Hi George,

Iím only using copper covered stainless steel supports at the bottom and the rest are copper tube spacers. Iím trying to avoid contact of steel against the copper boiler tube to avoid corrosion.

Blimey! thatís a lot of fuel youíre using on your flash boiler it must go like a rocket. On my steam jet engine Iíve been using 25 grams/min of gas and I thought that was a lot.

Yes, this will also be computerised. The computer based controller will simply unplug from Vital Byte and plug into the new model, though I might have to tweak some of the control settings (via the keyboard) for the new boiler depending on how it raises steam in comparison with the current horizontal boiler.

Thanks for the photos. The stack is a little bit smaller diameter than mine, eh! What device is the V10 driving Ė is it a generator?

Ian.
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flashtwo

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Re: Flash steam plant control.
« Reply #139 on: November 25, 2010, 09:48:33 AM »

Hi Phil,

Yep, it will only be installed in Vital Byte for test purposes come Ally Pally - no sleak mahogany steam launch as yet I'm afraid.

I'm still working on the steam jet boat, though the vertical boiler is the priority at the moment, and I hope to have that at Ally Pally as well, if you can find some extra table space; I've an idea about converting it into a turbo-steam jet that drives the boat's propellor, if the direct water drive doesn't come up with the goodies.

I'll be seeing you at the Model Enigineering Exhibtion Sandown in December - I've not been there before.


All the best
Ian
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ooyah/2

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Re: Flash steam plant control.
« Reply #140 on: November 25, 2010, 11:43:58 AM »

Hi Ian,
Yes my flash steamer can go !!!!!

If you recall I posted some info http://www.modelboatmayhem.co.uk/forum/index.php?topic=24568.0 on my flash steamer OOYAH with some pics of the new engine build. At the time I didn't know how to post pics of the boat in action so here are some.









The speeds of OOYAH in these pics are unknown but 40 mph + isn't far off.
If you look at the wake on the last pic you will see that it takes a hard left and then a hard right followed by a hard left back on course.
This was caused by a radio glich and through that experience I have retired the boat at present as it's becoming a bit dangerous, I keep thinking WHAT IF it shot out of the pond and hit somebody.

The 10V is linked to a reversing gear box which although worked great on the bench once in the boat I couldn't rely on it with the 10V not being self starting it was a pain to get the waders on to rescue it.
I tried extending the shaft on the gearbox to link a geared motor to turn the slip eccentric over when the engine stopped, again not 100% so a D10 will be machined up this winter for the tug.



Keep up the experimentation even if the end result don't work, it only makes one more determined to make it work.
George.
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ooyah/2

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Re: Flash steam plant control.
« Reply #141 on: November 25, 2010, 11:52:28 AM »

Ian,
I forgot to say that to attain these speeds with a steamer you need A LOT OF FUEL  & A LOT OF HEAT and the nerves to hold on to it.
George.
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Patternmaker

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Re: Flash steam plant control.
« Reply #142 on: November 25, 2010, 04:04:14 PM »

Thats very impressive George, I had no idea that you could attain those sort of speeds with steam.

Mick
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ooyah/2

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Re: Flash steam plant control.
« Reply #143 on: November 25, 2010, 04:52:40 PM »

Hi Mick,
If you think my boat is fast have a look at this http://www.youtube.com/watch?v=hVN8iHfQl3s this is the engine that I copied, Bob's hydro is the world record holder at 120 mph, possibly faster since this video clip was made.
George
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gondolier88

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Re: Flash steam plant control.
« Reply #144 on: November 25, 2010, 05:25:35 PM »

I knew someone used a proper monotube full size- you might be interested;

www.steamboat.org.uk/register/html/tani0866.htm

The edwardian 30 is a lovely launch, I prefer the plumb stem to the clipper full size, but it's all personal preferance.

Greg
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rathikrishna

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Re: Flash steam plant control.
« Reply #145 on: December 01, 2010, 09:37:59 AM »

Good evenig, Sir, can we use any EPROM ics for this purpose..?  its amazing work indeed, and i am willing to make a simple one..will you add some good videos here..?  its a request..
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flashtwo

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Re: Flash steam plant control.
« Reply #146 on: December 02, 2010, 06:44:50 PM »

Hi Rathikrishna,

I'm currently using Microchip's 16F877 and 16F819 PIC micro-controllers. These particular ICs contain digital inputs and outputs, analogue inputs, program memory and EEPROM data memory. All of the input and output channels are required to interface with the radio-receiver output, servos, temperature probes and pressure sensors.

Ordinary EEPROMs would, most likely, only contain programming or data memory with no input or output capability.

Ian.
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flashtwo

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Re: Flash steam plant control.
« Reply #147 on: December 02, 2010, 07:20:46 PM »

Hi Mayhemers,

The vertical boiler is progressing with the coil wound and fitted in the main furnace and stack.

The winding started with a single 10 metre length of 5/32 inch, which went well for the first part, but got mildly out of alignment further along. At the base of the stack a joint was made with another 3.3 metres of the same diameter to give me the 200 sq.inch of area. The 3.3 metre was single layer coiled and fitted in the stack (just!).

I managed to fit some copper spacers in the lower section, but realised that pushing the spacers in for the entire height would exceed the height available; oh well, I shall to design some special former to help in the future.

The boiler was temporarily fitted into the boat with feed and steam pipework connections made. The feed pump was ran to pressurise the system and check for leaks. One leaking joint was repaired and the cold hydraulic test past.

The boiler has been removed and had a stainless mesh fitted a short gap from the coils, then 3mm insulation and finally thick tin-foil was wired into place.

When the 2 inches of ice has melted on my test tank, and the 15 inches of snow has been cleared, I shall attempt to make steam and have an engine run.


The attached photos show the supports (copper tube covered stainless) to prevent the coil collapsing into the combustion chamber (please excuse the rather ragged hole , its been tidied up since), the copper coil and the attempted spacers.




Ian
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rathikrishna

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Re: Flash steam plant control.
« Reply #148 on: December 04, 2010, 02:01:10 PM »

Sir..sure you are one too informative...and too sad that you are living far to me...oh..oh...any how i am trying with some ideas, with eprom, but in my country i can only get some PIC controlers for this purpose...any how its amazing that your posts...ah...i need a detailed study about your postings, but its too hard to come here in internet cafe 30 kms from my home...but at any instance i will crawl through your postings and will study some thing to me as i started my steam stuff from put put boat...so god may bless you..and video...?  any hope...with great respect..Rathi
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gondolier88

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Re: Flash steam plant control.
« Reply #149 on: December 04, 2010, 06:06:06 PM »

It's easy to forget how lucky we are in our country sometimes- I think I must echo a lot of members thoughts when I say you are a credit to the hobby Rathi.

Keep it up!

Greg
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