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I Have Never Made A Steam Boiler/generator Before...help!

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myford1989

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Hi All
Had an idea today to build a steam powered engine which drives a small generator, all powered by a boiler that is heated by the wood fire in my house. Right now here in New Zealand it is Summer so I have a few months to build it before Winter kicks in and the fire will be put in use each night. I have a good lathe and mill in my shop, among a lot of other things. I am no absolutely stranger to metalwork and machining but have zero background/experience with steam/steam engines and generators. I suspect this will be a steep learning curve.
A few questions having never made an engine before, let alone anything steam-related;
Will I be able to generate enough pressure with just a wood-fire?
How much electricity would I be able to produce? I would love to power just a lightbulb but the idea of (relatively) free power is an exciting one.
And the always popular - where to get plans from? If anyone knows of any relatively simple plans for a boiler and motor it would be much appreciated. For the generator - I was planning on modifying an existing solution such as car alternator or small dynamo. Again, if there are any pointers out there they would be greatly appreciated.
 

Jyman

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Hey myford1989,

Ok since no one has given you any advice I will give you some.

I would first look into what rules/laws your country has in place first before you travel down this road. Where I am if you build a high pressure (greater then 15 psi) steam boiler that is over 1 square meter of heating surface it needs to be inspected by the pressure vessel inspector and you have to pay a yearly fee to keep it running.

Well you have a lot of questions, yes you will beable to generate more then enough power from a wood fire. Just depends on how large your fire is.

How much power you will beable to produce will depend on how large your boiler is, as if your steam engine is over sized then it will take a while for your boiler to catch up to how much steam it will use. But if your engine is under sized then you will always be blowing the pressure relef valve on the boiler and wasting energy.

A steam piston engine is the easier engine to make compared to the turbine engine. But the piston engine does move at a much slower rate of speed usually around 400 rpm.

A car alternator is not really the best option for the generator as it takes a really high rpm to generate the 14.4 volts required to charge a battery.

If you want to calulate how much energy a steam piston engine will make its the formula PLAN/33,000 = horse power
P= pressure of the steam
L= length of the piston stroke / 12 (foot)
A= area of the piston ( inches squared)
N= number of rotations a minute

So for example a 1 inch diameter piston with a 4 inch stroke at 100 psi and a rpm of 400 would make:

P= 100 psi
L= 4/12 = .333
A= 0.785 in2
N= 400

10,466.66 / 33,000 would Be about 0.32 real horse power or about 0.32 X 748 watts = 237 watts of power production. Now that 1 inch x 4 inch stroke piston traveling at 400 rpm will use about 3.14 inches cubed of steam in 1 rpm or at 400 rpm would be 1,256 cubic inches of steam that's a lot of steam.

That should get you started on figuring out how much power you need/steam that you need to make.

If you have more questions you can PM me and I will be more then happy to answer any more questions

Oh by the way I'm a Power Engineer (stationary engineer as its called in other country's)

Jon
 
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stupoty

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That's a lot of good info their Jon, as he mentions boiler inspections are/can be an issue , hear in the UK it's inspected at manufacture then re tested every 5 years.

A local live steam club or museum might be a good source of info for that part of it.

Stuart
 

myford1989

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Wow, fantastic information here, thanks Jon. I'll have a read through this and do some maths to figure out my end goal. This is exactly the answer I was looking for! I have found a design(for an engine) that I like the look of, not sure if it is too small or not yet though. The boiler and generator are still to come, I have found a DC motor off a 14V electric drill but again, I need to do some research/maths to determine what sort of power I will be able to achieve, and what exactly it is that I am wanting to achieve.
Does anyone have any tips or recommendations for engine designs?
 

JPigg55

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I have similar aspirations, but to power a boat instead of a generator.
The Engine:
Unless you plan on purchasing a precast engine or can cast yourself, I'd recommend the book "The Steam Engines of Ray HasBrouck".
It contains pictures and plans for 10 different steam engines that were designed to be built with a small lathe and mill. They range in size from small toy sized models to large enough to power a 20 foot boat.
The Boiler:
I've spent countless hours searching for info on them. There are basically 2 types, Fire Tube and Water Tube.
From what I've read, Water Tube seems to be the easiest to build, safest (depending on who you talk to), and fastest to come up to pressure. They, however, tend to not do well with changing steam demand.
As Jyman said, check your local rules and regulations on boilers. Here, due to hobbyists, the yearly pressure test can be done by the individual in certain States/places, but require an ASME Boiler Maker certification.
That said, many people have and do make there own (certified of not). There are liability issues if you make your own.
Also consider, from what I've read, Steam Engine HP vs ICE engine is approximately a 4 to 1 ratio. Meaning a 1 HP steam engine is about the power equivalent to a 4 HP ICE.
This is based on the steam engine is under power on each stroke of the engine for the entire cycle.
For a generator set-up, look at the engine size for a generator that would produce the required power and divide HP/4. This would be a gross approximation and solely based on max output.
Once you have the HP requirement, there are formulas to figure boiler size based on steam flow and pressure. Sizing is generally in heating surface square footage.
 

n.glasson

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I admire your ambition myford1989! Presumably you will be locating most of the gubbins outside to keep the steam, oil, noise, water etc out of your house. Personally, if I wanted to make a modest amount of power from my wood burner, I'd be looking at a Stirling engine with the hot end coupled to the fire box with a heat pipe. It would need to be reasonably close coupled to the wood burner but it gets you away from all that legal/safety stuff with pressure vessel design. The heat pipe and the Stirling engine are both also pressure containing but volumes can be comparatively small and you don't have to keep on adding water. You could keep it real simple by air cooling the cold end rather than water cooling. Another approach if you only want to power a few LED lamps would be to again use a heat pipe to get the heat out of the firebox but use the heat to drive a thermopile (Peltier module). Using Peltier modules the system would be self starting and you could keep everything inside your house because there would be no moving parts (except a fan to keep air moving over the cold end - all waste heat going into your house). Check out this http://www.biolitestove.com/products/biolite-campstove which uses this principle. This stove uses some power to drive a fan to both cool the cold end and fan the flames. Steam, Stirling or Peltier will all take a lot of expense and effort if your goal is going off grid. But if you just want a fun demo that makes some useful power - go for it.
 

Jyman

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sorry to ask , is that a little typo ?

At least you know it's being read :)

Stuart
Yes Stuart that was a typo, it was early and i was writing it up on my phone this morning . I have made the changes to the formula.
 

Jyman

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If your limited for what size of engine you can make with your lathe and mill you can always make the engine a double acting engine and you will get almost twice the power out of the same single acting engine. Or you can always make it 2 piston engine, by making a little change to the plans you have.

Jpigg55 is correct there are two different main types of boilers a fire tube and water tube. There is also the flash steam boiler but unless you really know what your doing with that one I would stay away from it, basically for a flash steam boiler you heat the boiler then pump just a little bit of water in to it really fast, which flashes to steam to build the pressure. So really there is never any water in the boiler and it's just a red hot tube. but they wear out fast and could blow apart at any moment.

With which ever boiler you end up building I would recomend pressure testing it to twice its working pressure by doing a hydrostatic test, which is just filling it with water and using a small pump to get it up to the pressure. Example if working pressure is 100 psi do a hydro test to 200psi. It tells you that the boiler is safe to operate to a greater pressure/temp incase of a run away
 
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JPigg55

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There is also the flash steam boiler but unless you really know what your doing with that one I would stay away from it, basically for a flash steam boiler you heat the boiler then pump just a little bit of water in to it really fast, which flashes to steam to build the pressure.
For flash boiler, it should be a water tube style. Difference being is having a pressure regulator on the outlet so water heats and pressurizes, but stays in liquid state.
Once pressure is high enough, the pressure regulator releases high temperature/pressure water to a lower pressure steam drum. At the lower pressure, some of the water flashes to steam at a lower pressure.
Think of it like a pressure cooker. Once pressure rises to a point of lifting the weight. it releases (in this case) some of the steam from inside.
Big problem being, for a, let's say, 100 psig steam to run engine, the water (heating side) would have to be at a much higher pressure and temperature. 1 gallon of water at atmospheric pressure turned to steam at atmospheric pressure would occupy about 7,000 cubic feet. At 100 psig, it would drop to about a third of that volume in ideal state, aAll that being at 100% conversion rate. A realistic conversion rate would probably be between something less than 33% (the bigger the pressure drop, the higher the conversion rate, but the lower the steam pressure).
This is why some think a fire tube boiler is much more dangerous. Fire tube boilers heat a much larger volume of water up just below boiling point, thus a catastrophic failure would release all that pressure lowering the boiling point. As you can guess, even a couple gallons of water flashing to steam at atmospheric pressure would expand to 14,000 cubic feet (think of a box 24 feet to a side or a 1400 square foot home with 8 foot walls being filled with scalding steam almost instantaneously). All that from 2 gallons of hot water !!!
 
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