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A generator which uses wood as a fuel

Discussion in 'Off Grid Living' started by Dolph, Nov 1, 2011.

  1. Dolph

    Dolph Monkey+

    Hi folks,

    Good to see so many people prepping! i only just heard of the word today and thats how i found this site.
    I'm new here(y): 28 years old, ex british Army served in Iraq, now a plumber and a mechanical engineering student. I'm prepping for worse times and I have been building (from scratch) a system for the last 12 months which will hopefully generate electric from heat produced by burning wood fuel or waste.

    It is intended to be simple and constructed mainly out of salvaged car auto parts and junk so that it is easy to maintain and obviously it needs no gasolineor diesel which is a must in a long term survival situation:)

    When finished it will provide heating, electricity and refrigeration from one unit.

    Check out my youtube and website, there is enough free info in the videos for you to build one but i encourage people to buy membership (3.99) to help complete the project.


    It would be good to have some like minded people.

    I'll answer questions here.


    bob_falls@yahoo.com likes this.
  2. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    Welcome aboard. Please contact melbo for authorization to post (potentially) commercial activities, and read the CoC once again, along with the notice http://www.survivalmonkey.com/forum/buy-sell-trade-survival-marketplace/23304-notice-vendors.html

    Pending approval, I've deleted your links.

    You might also do a site search on wood gassification, it has been touched on previously. Might be some useful info for you.

    Congrats on picking the most useful engineering degree that there is on the planet.
  3. Opinionated

    Opinionated Monkey+

    Hi Stuart, and welcome!

    I am thinking out loud here but the first thing that came to mind when I read your thread title was:

    "oh good! Someone has put up plans for a closed loop steam plant!"

    Is that concept impractical? I realize that if not properly constructed (appropriate blow off valves and hardware pressure ratings) it could be potentially . . well, , deadly. But my question is conceptual:

    "if safety was addressed in a practical manner is there some reason a closed loop steam system would be impractical for this purpose (running a current generator)?"
  4. BTPost

    BTPost Old Fart Snow Monkey Moderator

    Closed Loop Steam is a very lossy system, when the sizes are small. (> 20MW)
    that is why you do NOT see anyone messing around with them, much. The losses become more manageable at Power Levels above that lower limit, and become cost effective, at 5-10 times that. ..... YMMV....
  5. Tikka

    Tikka Monkey+++

    Closed loop is the Rankine system as BT said efficiency isn't good meaning 40-45%. Also, it's operating range is small and the pressures are high.
  6. Opinionated

    Opinionated Monkey+

    Thanks guys. I would have guessed it would be more efficient than that. But obviously that would be a mistake.:oops:
  7. Pax Mentis

    Pax Mentis Philosopher King Site Supporter

    I have actually been playing around with adapting one of my hydroelectric setups to a closed loop system...but have recently started looking at using a system like is used to circulate coolant in a (gas) refrigerator to see if there is a way to get convertible enery in addition to cooling. I have succeeded in making the cooling function work with candle flame rather than gas...but have yet to get the kind of power needed to generate electricity.

    Closed loop steam has potential, but it is also a very dangerous system with which to deal...open steam, while less efficient, is much safer.
  8. Dolph

    Dolph Monkey+

    Hi guys thanks for the welcome and interest.

    ghrit: no probs, rules are rules friend.

    Here are some details about my system:

    my system uses the Organic Rankine cycle, so instead of water as the working fluid it uses a refrigerant which boils at a much lower temperature. In this case i am using Butane which boils at -0.5 Degreees C atmospheric pressure. This refrigerant could be substituted for something like HFC 245fa or R123. However, Butane is cheaper and is not covered by F-gas regulations meaning that any Joe can get his hands on it, Butane is also readily available (at least in the UK) which is good news, it may be also be possible to use Propane.

    As you guys have pointed out: In a closed cycle it is obviously best practice to have safety measures to prevent the system pressure from becoming too high. In the case of Butane the critical temp is 150 Degrees C and the critical pressure is 37 bar so as long as the system operates well within these limits there is no problem. A pressure and temperature relief valve along with a high limit thermostat would be sufficient safety measures to make me comfortable but there could always be others added if desired.

    The Organic Rankine Cycle is one of the only cheap ways to recover low grade heat <100 degrees C and this gives my system many applications. In my video you notice that the flow temperature is 80 degrees c which is adequate to vapourise enough Butane to power the turbine, even with the very small vapouriser i am using.

    gasoline, diesel, natural gas etc are all "Dangerous" if used in a system which has not been well engineered, build it right and it will work safely though.

    The maximum operating pressure for my system is 10 bar so no stupidly high pressure required, it uses silver soldered (brazed) joints to ensure strength.

    When finished the system will be housed in a sealed box, so any leakage is contained within, a long vent pipe could then be used to discharge Butane away from the boiler.

    In theory the BioGen system could also be used along side a normal liquid cooled diesel generator or internal combustion engine, instead of wasting the heat via the radiator you could recover that energy by sending hot water through BioGen for conversion whilst still achieveing your cooling drop for the return line. So BioGen could be added to an existing generator set to improve its efficiency.

    The pro's of the system are clear: VERY Cheap and easy to build, easy to maintain using salvaged parts (like the turbine which is a car air con compressor which has been modified to work as an expander/turbine by removing the internal check valves). It creates no smoke and is VERY quiet too which is a major help when trying to remain concealed.

    The con's being a fairly low thermal to mechanical conversion efficiency, about 10-15% is the best thermal to mechanical efficiency you could expect. So for every 10kW thermal input you would generate 1.5kW mechanical shaft power with the remaining 8.5 kw as useable heat (dependant on losses) which is fine if you are using the rest of thermal energy to heat water/property/dry wood/greenhouse etc. If you increased the output capacity of the boiler to 200kW then it may be possible to increase efficiency but the ideal is to have a small boiler which can be moved if required.

    Thanks guys,

  9. dewme5

    dewme5 Monkey+

    Some flammability concerns with using butane? Just curious
  10. Dolph

    Dolph Monkey+

    Hi Dewme5,

    I shared those concerns when initially designing the system but they have waned. The way i see it is Butane is flammable and potentially dangerous if used incorrectly. that said, many flammable substances are used in everyday machines without issue, so as long as the machine is built correctly there should be no problem. Gasoline and natural gas are used as fuels in vehicles and boilers, unlike those, the advantage my system has is that the Butane is never ignited and therefore the risks are massively reduced. If there was a leakage then the butane should be vented to a safe area. I am now building my system inside a housing (old washing machine) to contain any leakage, the housing is vented which prevents any build up of vapour. next is the threat of electrics and sparking inside the housing, so i will eventually seal the electrics inside a box.

    The boiler is located seperately to the BioGen and this prevents any ignition. With good maintenance and high build quality there should be no problem. the BioGen system only contains a small quantity of Butane (2-3 litres) so any resulting fire could be extinguished fairly easily.

    Lastly, by locating the BioGen outdoors in a small metal shed one can reduce the damage caused in the event of a fire. Personally, mine is going indoors (once tested) because i'm confident i have covered all angles but it would be easy to build it outdoors, in a metal container like this: Trimetals Sentinel LP Gas Cylinder Storage 1 x 0.6 x 1m | Screwfix.com

    Here is some info for anyone interested in organic Rankine cycle micro generation: http://organicrankine.com/orc_documents/scroll_non_auto/TFE_SQ010607.pdf

    I have also been looking at how my system could be twinned with a gasifier to convert the waste heat instead of dumping it all through a radiator. It would also be possible to connect any water cooled diesel gen Set to my system to extract extra power before dumping the waste heat. As a bolt on to an existing generator my system would improve overall efficiency and output.

    Lots of people understandably have concerns about closed cycles and butane, but with the correct approach to safety there is no reason why it can't be safe. I feel safer with BioGen than i do with the 3 nuclear power plants i have within 50 miles of my house...:(

    Anyway, i'm continuing to make good progress with my system and hope to have a fully working unit come summer time.

    Have a merry christmas,

  11. Dolph

    Dolph Monkey+

  12. Dolph

    Dolph Monkey+

    Hi folks the latest update video has been released on my youtube page.
  13. TnAndy

    TnAndy Senior Member Founding Member

    Without comment on the whether this works or not:

    Packing seals on gate valves DO leak from time to time, and if one of those copper joints comes loose, you're gonna have a heck of a fireball with butane as the working liquid.....
  14. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    There are "packless" diaphragm valves available, often used in refrigeration service that might be useful for the butane side of the system.

    1) What is the expander? Sounds like a piston machine.
    2) What is the static pressure on the butane side when shut down?
    3) Is there a level measuring means on the reservoir?
    4) A filter dehydrator might be useful for further crud and water removal from the butane side.
    5) Have you load tested it over and above self sustaining? I.e., what is the net available power to run other "stuff"?

    So far, so good.
  15. ColtCarbine

    ColtCarbine Monkey+++ Founding Member

    Is there a nomenclature difference between regions? The joints I see in the video of your prototype look soldered not brazed/welded. Not nit picking, cool project and one I am going to see how this progresses.

    Your prototype looks easy enough to build, for a minimal cost. Waiting to see if you are going to build a larger unit that produces more power. I see there are companies producing much larger units.

    Interested to see if the resident Engineer gives it a seal of approval.
  16. TnAndy

    TnAndy Senior Member Founding Member

    Looking at a joint with silver solder versus regular solder, you'd be hard pressed to tell the difference, but silver solder is a lot stronger.
  17. Dolph

    Dolph Monkey+

    Thanks guys some good points there,

    I appologise for use of the term "fire it up" in the video, i roast myself every time i use it because it is incorrect, there is nothing being fired up, no combustion.

    TnAndy, the gate valves are not in the refrigerant circuit so it does'nt really matter if they pass a bit of water. there are no valves in the refrigerant circuit for that very reason, they almost always leak.

    Even if a joint was to come loose it does'nt neccessarily mean it will ignite the butane, once the alternator (possible sparking) is replaced with a motor generator and the wiring and switches are insulated it will be as safe as a gas boiler if not safer due to there being no combustion

    hi Ghrit, the expander is a scroll type, cold pressure is under 1 bar gauge. Hot vapour pressure never exceeds 7-8 bar at 80 degrees. no refrigeratant charge meter can't afford it. A line strainer would be useful and as you say a means of clearing water. Net electrical power has been 45 watts due to inefficiency of alternator, that will climb to 120 watts when 85% efficient generator fitted.

    gunbunny, ColtCarbine and BTPost like this.
  18. Dolph

    Dolph Monkey+

    A silver soldered pipe joint looks exactly the same as a lead/tin or lead free joint until you get in close. However, I was so strapped for cash that some of the pipe joints in the low pressure zone ended up with standard solder as i could'nt afford any more silver solder, the weaker joints in high pressure/temp zones are silver soldered including the expander manifold. I would obviously recommend that silver solder or copper braze is used on all refrigerant joints if available. The system was performance tested before i filled it with refrigerant so that i knew it could easily hold the pressure.

    this is the vapour pressure curve: http://encyclopedia.airliquide.com/images_encyclopedie/VaporPressureGraph/Butane_Vapor_Pressure.GIF

    There have been some compromises in my system due to lack of funding but the concept is firmly proven, with more money one could easily improve on what i've already built.

    Building a larger unit is exactly what i want to do, however, i've no more pennies to do it with.

    This project is now totally reliant on those guys who are interested in it, joining it, so that some funds can be ploghed back in. If everyone sits back and waits then there will be no more project!

    I'll need at least 100 members to get to the next stage (a 1 kW net electrical output at 80 degrees C flow) without severely compromising the engineering to the extent it becomes really dangerous.

  19. ColtCarbine

    ColtCarbine Monkey+++ Founding Member

    When I saw you reference silver solder as brazed, I was like that is soldering not brazing. To me a silver soldered joint is a hard soldered joint and lead/tin alloy as a soft solder joint. It's interesting to hear other plumbers from different regions refer to the same processes differently.

    It's just a terminology/nomenclature difference between us.

    Around here I still here some guys refer to silver brazing as silver soldering.

    Cool project, keep us informed of your progress. Thank you for sharing.
  20. Dolph

    Dolph Monkey+

    Thanks, glad to see you're enjoying it

    I've given my website a good update today and hopefully explained the project intentions a bit better.

    I'll keep you posted on any developments

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