question on thermodynamics I guess.

vince smith · Sep 30, 2011

Hello All, I have a lot of waste heat emitting from my 55gal drum retort when I make charcoal. (and soon wood vinegar)

I would like to convert this to dc power to run my downwell solar pump during the night. I get a burn of between 3 and 7 hours depending on amount of air allowed to the fire.

I thought I could build a monotube boiler to fit atop the retort and produce steam. (not too high a pressure for safety)

My limited understanding is that steam is too fast and too little impact to power a pelton or turgo wheel.

My question is "can I add water to the steam via a venturi to give it more impact or does is just loose all its pressure when the water mixes with it?

I've got to go bush for a few days but will be interested to see if anyone can help when I get back.

Regards Vince Smith.

KTurner · Sep 30, 2011

Check out this place. They sell thermoelectric generators that convert a temperature difference directly into electricity. They have a 15W module for $80. I've never dealt with them, the devices or the company, but was curious one day and did a little reading on it.

Some places also make a fan/TEG in one that you stick on top of your wood stove. The heat from the stove powers the fan.

Keith

Brad_Blazer · Sep 30, 2011

Injecting mass into a high speed flow results in a loss of energy. Conservation of momentum says m1V1 = (m1+m2)V2. Since energy is 1/2 mv^2, the loss of velocity outweighs the gain in mass. This is called an inelastic collision.

Even worse, if the liquid water is not at the boiling point, the steam will rapidly condense, giving it's energy to the water.

A piston type steam engine might be your best bet if you want to produce electricity from steam. Google steam engine. Here is one I found.
Green Steam Engine Home Page

RonMar · Sep 30, 2011

How much fuel is burnt/consumed in that 3-7 hour period? how hot does this drum get?

It is really all about the BTU's Burning wood gives up about 8000 BTU per pound. Knowing the ammount of fuel consumed, you can get an idea about how much work could be performed. No turning those BTU into energy can have quite a few hurdles to overcome.

Steam turbines are not very efficient. A steam reciprocating engine has the edge in efficiency. But, in order to make a steam engine or turbine work you need pressure, so you would have to encase that 55gallon drum inside a boiler/pressure vessel filled with water. But the drum itself is NOT a pressure vessle, so any pressure(and it wouldn't take much) built up in the water surrounding the barrel would crush the barrel... I suppose you could build a purpose built boiler with a large pressure rated inner vessel, but how much cost in materials are you willing to invest in this? You cannot half-*** boilers/pressure vessels. It dosn't take a very large boiler to kill someone... The next issue you would have to overcome is the fuel used. Making charcoal means long, slow burning/smoldering fires right? You put the skin of that barrel in contact with water, and you are going to lower the metal temperature from the many hundred degree range down into the 200's F. This will cause the gasses inside the combustion area to condense and coat the inner wall of the chamber. This will further lower the heat transfer to the water...

Steam boilers run a VERY hot controlled fire to fully consume the products of combustion so they do not foul the heat exchanger tubes thru which the gasses pass to transfer their heat to the boiler. A slow dirty fire would quickly shutdown a boiler...

I like steam engines, but I do not think this is something I would try due to the nature of your heat source. Want steam power? build a purpose built steam boiler and feed it from a fire box that has a smokestack to increase draft and when the engine is running, an engine driven blower to help the fuel in the firebox burn in a superheated violent fashion... With all the work involved in getting wood, I think I would rather tend to a small petrol or diesel powered DC generator to power that DC pump when needed

JohninCT · Oct 1, 2011

Brad_Blazer said:
Injecting mass into a high speed flow results in a loss of energy. Conservation of momentum says m1V1 = (m1+m2)V2. Since energy is 1/2 mv^2, the loss of velocity outweighs the gain in mass. This is called an inelastic collision.

Even worse, if the liquid water is not at the boiling point, the steam will rapidly condense, giving it's energy to the water.

A piston type steam engine might be your best bet if you want to produce electricity from steam. Google steam engine. Here is one I found.
Green Steam Engine Home Page[/quote]

Wow that engine is cool. It has quite an interesting crank mechanism. Although the site says that the exhaust steam is captured, condensed and pumped back to the boiler I couldn't really see how that was accomplished.

vince smith · Oct 1, 2011

Hello All, thanks for the quality reply's. My head is spinning.

Yes I was afraid the "cold" top up water would condense the steam.

I will look closer at the green engines, its a shame they only offer for sale the plans for the 2 piston model. (for a one off buy.)

Hello RonMar, At any one time I burn a 55 gallon drum full of hardwood.
(we call them 44 gallon drums in Australia)

It takes 3 hrs to get to the stage when only but charcoal is left (my objective) thats with an afterburner with an exit dia of 27".

If I put a 4"chimney on it it takes 7 hrs.

The effeciency is not too critical as the heat is currently wasted to atmosphere but I plan to improve its effeciency anyway by burying it in the ground.

How hot ? I don't know I would say BLOODY HOT probally about 600 deg.

The drum was never intended to contain any pressure as I will put a monotube boiler into the fire zone.

I'm a cheapscape and intend to use the copper coil out of an old electric hot water heater for the monotube.

I had hoped to keep the pressure under 20 psi for safety reasons.

Thanks again, Ive got something to think about while I'm out bush.

Regards Vince Smith

Egon · Oct 1, 2011

A sterling type engine would work but the return on cost may not be very good.

Forget steam. All kinds of negatives,exspecially cost.

Check out this place. They sell thermoelectric generators that convert a temperature difference directly into electricity./QUOTE]

If you do anything really check this route out.

Pooh_Bear · Oct 2, 2011

Do some research into the Seebeck effect.

Thomas Johann Seebeck - Wikipedia, the free encyclopedia

Pooh Bear

LD1 · Oct 2, 2011

Put the whole setup in your shop and heat it all winter long.:thumbsup:

Egon · Oct 2, 2011

Living Down Under in the OP's location might need an air conditioner during his winter.

vince smith · Oct 7, 2011

Hello All, I've looked at the suggestions, some I'd read about before.

Some are cutting edge but I think too technical for me. I've always liked the stirling engines and thought the gamma the best as its displacer piston is less demanding. (to seal). But it seems to need a high pressuer to realize its potential.

The T.E.G's might be too small to utilize the heat I have available at the smaller size anyway and bigger would be cost prohibitive for me.

I'm thinking still use a monoflow boiler and supply steam to a 2 stroke engine converted to a uniflow steam engine.

There are many examples of these on u tube but none of the makers have answered questions put to them about lubrication and life span. I suspect this is their weakness. I'd like to know for sure if anyone can advise.

Pooh bear, I tried to make one of these (thermocouple) 55 years ago when I was 15.
You would laugh at what I did. One strand of copper, one of lead, one match and a torch bulb. LOL . Of course it didn't work.

Yes EGON winter was on July 2 and 3 here this year and I had to put a shirt on.

Regards to all

Vince Smith.

BHD · Oct 8, 2011

may this would work,
The Tinderbox - Wood Stove Generator - The Fireweaver

Baby Grand · Oct 8, 2011

Have you considered a Newcomen type engine:

Thomas Newcomen - Wikipedia, the free encyclopedia

Uses partial vacuum rather than high pressure steam. If you hitch the output chain to a suitable flywheel via a crank you could drive a dynamo. It's not terribly efficient, but it is seductively simple. Wax up your slide rule, dust off your steam tables, it's time to start calculating your enthalpy.

-Jim

vince smith · Oct 9, 2011

Hello BDH. The tinderbox looks too small and works best with a heat gradient
and here in the tropics thats not going to be very large.Thanks though.

Hello Jim. Yes I find the newcomen very interesting for its safety and low pressure. Its not quite as simple if you use a second chamber for condensation to reduce the hot/cold change issues .

Thats why I'm leaning towards the uniflow engine made from an old 2 stroke engine. I should get an old mower motor for next to nothing, so I will not have much to loose.

Sorry in post 11 I called the monotube boiler a monoflow boiler which was misleading.

Boy oh boy its hot here today, You could fry an egg on a shovel and its not summer yet.

Regards Vince Smith.

Egon · Oct 9, 2011

Could be interesting to design the steam system.

Suggest two coils, one for primary heating and exiting into a smaller coil via a nozzle and drain system. This might condense some of the wet steam allowing the second coil to heat the existing steam to a higher energy value. The secondary coil should be in the hottest heat zone.

Then its on to the prime mover, out to a condensor and into a reheater before becoming feed water again. Add make up water at the condensor as it will be venting a certain amount of wator vapour.

Dream stuff for me.

Are you familiar with Cylesstic type oils ??

vince smith · Oct 9, 2011

Thanks for that Egon, I had not heard of the "cylesstic oils" but after some research I now feel better equiped to try my ideas. This is exactly the information I was needing.I came across a well written piece by a Harry Wade.

Regards Vince Smith.

Brad_Blazer · Oct 10, 2011

Here is an interesting discussion:
Convert gas engine to steam??

The biggest reason for a condensor is to achieve an exhaust pressure far below atmospheric pressure for improved efficiency. A small air ejector (steam powered venturi) prevents the buildup of non-condensing gas. I can't really envision a backyard system operating in a closed loop.