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Hair Brained Idea

Post in 'The Green Room' started by Mr A, Oct 19, 2012.

  1. Mr A

    Mr A Minister of Fire

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    It got a wild idea. I was watching that new TV show "Revolution". There is no electricity in the TV world. Anyway, the bad guys got ahold of an old steam engine locomotive, the 1800's kind with a car full of firewood directly behind the locomotive engine. Steam engine trains were used well into the '70s, but no firewood car required. It is old technology. We all have wood to burn. I wonder if any of that good wood heat we all like so much can be used to make steam and generate your own household electricity with it? Even just a few kilowatts in the winter to run a few lights and the TV in winter, heat water, and maintain comfortable inside temperatures. Any one else thought of something like this? Would it work?

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  2. pen

    pen There are some who call me...mod. Staff Member

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  3. jharkin

    jharkin Minister of Fire

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    Sure you can do it.... But you are going to burn a ridiculous amount of wood to power the average home with a steam piston engine. Wood cars went away when locomotives went over to coal with its vastly superior energy density. Even so the best steam locomotives ever designed never got much over 12% overall thermal efficiency (See Andre Chapelon).

    A better option would be a multi-stage steam turbine setup like used in power stations... those can reach 40% efficiency, but I dont think you are going to be able to piece one together at home scale.

    If you look at Pens link, see that the engine is rated at 3hp. Thats only 2100 watts driving the generator. I doubt it can sustain more than 1,500 watt real power output. I'd like to see the wood consumption at full load.
  4. pdf27

    pdf27 Member

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    Thing is, if you've got a use for heat (warming your house up for instance), the low efficiency isn't a problem - all it means is that you can't generate much electricity before you overheat your house, but most people don't actually need all that much electricity.
    The big problem is cost - there are a couple of natural gas fired combined heat and power boilers on sale in the UK, and the problem is they're 2-3 times the price of a simple gas boiler. You're looking at the same with a wood system, to save very little electricity.

    For a practical design, I'd suggest using some form of gasification boiler. The hot side of the Stirling engine would be put in the hot gas stream, with the cold side being cooled by a heat exchanger and going to heat the house. There will be a secondary heat exchanger downstream of the Stirling engine, so the stack temperature is the same and hence the total efficiency of the system is the same.
    The ultimate problem is that it's a very expensive way to generate a small amount of power. If you're off-grid or trying to live a very low carbon lifestyle it makes sense, or if you're after a shiny new toy. Otherwise the economics just don't work.
  5. peakbagger

    peakbagger Minister of Fire

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    Sure it works but its quite inefficient. If the boiler is over 15 PSI it most likely has to be built to ASME boiler code and inspected on a yearly basis. For small applications a wood gas generator may be a better option. GE bought a company a year ago with a small organic Rankine cycle generator but I havent seen much about this firm lately in the news. ORC is basically a heat pump that runs backwards, The evaporator is heated up and it boils a low temperature heat tranfer fluid which then expands through a compressor which turns a generator. The vapor then is condensed by either outside air or a heat transfer fluid and then heated up again. If you search around for Chena Hot Springs in Alaska they support an entire resort with two large ORC generators that use hot volcanic ground water to run the cycle and a local stream to reject the heat. Of course it was built with lots of state and governemtn money. By the way the Carnot cycle limits still apply so the efficiency is poor.
  6. Mr A

    Mr A Minister of Fire

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    It is intriguing to me that a hot wood fire, partnered with water by the minds of men to produce useful machine power. Use of fire, evolution from a bunch of cave dwellers keeping warm, to cooking meat, to bigger brains, all the way to burning fuel to go to the moon, and beyond. I am in the cave dweller stage,
    I don't know what else to do with my hot fire besides lounge in front of it. Marshmallows, anyone?
  7. EatenByLimestone

    EatenByLimestone Minister of Fire

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    Drinking beer or something mixed with vodka always works well for something to do in front of a fire.

    Matt
    f3cbboy and SmokeyTheBear like this.
  8. hemlock

    hemlock Feeling the Heat

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    I'm with him.
  9. pdf27

    pdf27 Member

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    See http://www.sciencedirect.com/science/article/pii/S0306261904001254 for a suitable Stirling engine design. Real problem is size and cost - a 198cc engine only produced 6W at 1000 deg C gas temperatures. For a useful power generation (say 1kW), you're looking at an engine with 33 litres internal displacement - about the size of a WW2 aero engine. Stirling engines are simpler and lighter than IC engines (this one for instance runs at atmospheric pressure) and should need little maintenence, but you're still looking at a big device. That means expensive.

    For a situation like this efficiency really isn't a big deal - you're generating heat with electricity as a convenient by-product. That means that your electricity generation is effectively at 100% efficiency as there is no additional waste heat.
  10. Slow1

    Slow1 Minister of Fire

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    If you want to use wood to generate electricity, consider doing it by way of feeding wood gas into a slightly modified but otherwise standard gas burning generator. Yes it is a bit complicated on the surface but once operational it would be far more efficient than steam power.
  11. oldspark

    oldspark Guest

    Where's the doobie?;)
  12. Delta-T

    Delta-T Minister of Fire

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    NO Michael MacDonald! any other Doobie is fine, but there must be standards.....I draw the line at Mike.
    PapaDave likes this.
  13. Dune

    Dune Minister of Fire

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    As far as I know (correct me if I am wrong) any boiler over 15 P.S.I. must be operated by a licensed engineer.
    Micro turbine tech (homeowner size) isn't quite there yet, but is being worked on by some.

    Check out the Victory wood gassifiers. Combined with a water cooled generator, an extremely efficient Co-Gen system for home is do-able.
  14. peakbagger

    peakbagger Minister of Fire

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    Operators with boiler licenses are only required in some states and there are usually exemptions for small residential units
    Dune likes this.
  15. blades

    blades Minister of Fire

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    there are bio-gas gen sets available about the same cost as any other diesel gen set. But, as they say, the devil is in the details, in this case the bio gas generation system and storage that will set you pocket book back a fair share.
  16. renewablejohn

    renewablejohn Member

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    My two girls both generate 250kw electric using wood and solar. We use thermal oil and a steam evaporator instead of a boiler as it is far safer and not restricted to employing a boiler engineer. For those wanting to know the technical stuff the steam engines are 1937 vintage bellies and morcom upright high speed twin cylinder engines.
  17. begreen

    begreen Mooderator Staff Member

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    Fascinating, we need pictures if possible. 250kw is a lot of electricity. Are you powering a large facility? I have seen pictures of these units still running in SE Asia, mostly in rice mills. What fuels your units, regular cord wood. What is consumption like and do you run them continuously or just for show?
  18. begreen

    begreen Mooderator Staff Member

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    More modern steam engines still have a tender, it just isn't storing wood. Some are sleekly designed to look integrated with the engine, but they still are needed to haul fuel and water. Some are for coal storage with a stoker and some are oil storage.
  19. renewablejohn

    renewablejohn Member

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    Fuel is mainly forest brash turned into G30 spec woodchip with additional arb waste from tree surgeons. Solar element from evacuated tubes all heating thermal oil which is then turned into steam by a thermal oil steam evaporator. Power is just supplying the National Grid 24/7 and our own farm requirements.

    Attached Files:

    jatoxico likes this.
  20. begreen

    begreen Mooderator Staff Member

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    Wowser! That is a twin beauty. I don't suppose there is a video of it running posted? Tell us more about the farm.
  21. renewablejohn

    renewablejohn Member

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    If there was a video it would be the most boring video ever. Bellis steam engines are totally enclosed so the only thing you will see is a silent spinning generator. As for the farm we used to grow herbs and perennials under polytunnels but with the recession we have diversified into forestry and biomass power generation.
  22. begreen

    begreen Mooderator Staff Member

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    Bore me please. This was quite a nice design. Are your engines with enclosed sumps and self lubricating?
  23. renewablejohn

    renewablejohn Member

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    You do really want to be bored

    Here is a video of an engine similar to mine although mine is a lot newer so even the exciter is enclosed. We also dont have the pretty perspex cover so you cant see into the engine. Yes it is a fully enclosed sump with high pressure self lubricating which Bellis was famous for and allowed the engine to be "high" speed to allow direct connection of the generator.

  24. begreen

    begreen Mooderator Staff Member

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    I caught that one, thanks. Unfortunately it's not running.
  25. renewablejohn

    renewablejohn Member

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    Maybe this is more boring for you as it is actually running

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