Gasifier experts can you please tell me this one thing...

GS7 Posted By GS7, Sep 13, 2013 at 4:13 PM

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  1. GS7

    GS7
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    Please tell me the functional differences including the pros and cons of a pressurized or non pressurized gasifier boiler?
     
  2. Floydian

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    Hello GS7,

    I'm sure some folks will give you the basics in this thread but I'd suggest spending some time with the search function. This is one of the "big" subjects here, so of course there is tons of info.

    Happy reading,

    Noah
     
  3. hobbyheater

    hobbyheater
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    [quote="GS7, post: 1516753, member: 25429") pros and cons of a pressurized or non pressurized gasifier boiler?[/quote]

    Non pressured in most cases will require a heat exchanger between the boiler and the rest of the system .
    Non pressured does not have the potential of a catastrophic steam explosion that a pressured boiler has .
     
  4. tom in maine

    tom in maine
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    Manufacturers get around code issues. It is inherently safer. It is potentially less expensive.
     
  5. maple1

    maple1
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    Non-pressurized = more worries about corrosion & more maintenance required (water monitoring & treatment).
     
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  6. GS7

    GS7
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    Thanks for all of the feedback and links, lots of clarity now!
     
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  7. stee6043

    stee6043
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    Hmmm....for some perspective we should all keep in mind that domestic water (city water) systems operate in the 50-75psi range inside our homes. Pressurized boilers will run in the 15-25 psi range. If a pressurized boiler is a time bomb waiting to explode should we consider a domestic hot water heater a potential weapon of mass destruction? Nah...

    Cost between the two is debatable. Performance is also debatable but there is "some" math behind the argument that pressurized should have slightly better performance. I'm not sure relative safety should even be a consideration between the two. Wood burning appliances can have a lot of problems up to and including chimney fires that can indeed be catastrophic. I have yet to know anyone on this board or anyone in my area heating with wood that has had any potentially damaging pressure problems, ever.

    To the OP - before you go to far in trying to figure out which type of system is "better" you may want to see whether or not you can install both in your area. If you can install pressurized, check on the requirements. If you need UL/ASME for your area it will limit your boiler options significantly.
     
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  8. Gasifier

    Gasifier
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    Well said stee6043. And I agree with maple1 as well.
     
  9. hobbyheater

    hobbyheater
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    No comparison between a domestic hot water heater , no real skill involved in its operation .
    Complicated pressurized systems with large storage and an second operator /owner with little or no knowledge of that system ? Nah!
     
  10. maple1

    maple1
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    My boiler runs 5-10 psi, my domestic well water 20-35 psi. I'm more nervous about it springing a leak than my boiler. I will say though that a boiler (not the right name for it given it doesn't boil, but anyway) likely has more danger potential if something were to go really wrong. That would more than likely be due to component failure or very bad installation than operator error, I would think. I had my old one peg the needle to over 240° on a couple of occasions, that was due to a stuck damper motor. It was making a whole bunch of noise inside at that point but no after effects. I don't know what the psi got to, but it didn't blow off. Wouldn't want to get hit by the blow off though if that were to happen, even on booted feet.
     
  11. hobbyheater

    hobbyheater
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    The expansion factor from water to steam at 240 F at 30 Psi is 300,000 to 1. Even if it is only 1,000 to 1, it is still very scary!
     
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  12. flyingcow

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    Keep in mind a oil fired system with baseboard is pressurized, is it not? Millions of these in the country, mine hasn't gone boom. A typical wood boiler will be pressurized about the same psi's?. My first hurdle after deciding on a boiler, was pressurized or non pressurized storage. That question has been debated and still will be when asked.
     
  13. woodsmaster

    woodsmaster
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    I always think of the pressurized school boilers that lasted about a hundred years whenever this question comes up.
    I went pressurized for longevity. lots of these last 25 - 30 years. Look on ebay at old the old Tarms still in working order.
     
  14. Fred61

    Fred61
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    Without pressure don't you need a different pump (circulator) to get the water to the higher heat emitters? Say like on the second floor?
     
  15. heaterman

    heaterman
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    In a nut shell...............

    Unpressurized/Open:
    Pros:
    Inherently safe. The system cannot build pressure and boiler codes do not apply so correct installation requires far less in the line of safety controls and devices such as secondary high limits, low water cut offs, over temperature dump zones.
    Cons:
    Requires diligence in proper maintenance of water chemistry and in certain applications will require the use of a heat exchanger if connected to a sealed system.
    Very close attention must be paid to correct pipe/tube sizing AND pump sizing to ensure required flow rates while not decreasing net "head" at the inlet of the pump. (this is THE major cause of circ failure in an open system and can be a huge waste of electricity)
    A low system head must be designed into the piping plan.

    Pressurized/Sealed:
    Pros:
    Water chemistry requires less maintenance PROVIDED the system is correctly done initially.
    Maintaining positive pressure in the suction side of circulators is not a concern. (the biggest positive in my book)
    Seldom a need for a heat exchanger

    Cons:
    The system must be installed and controlled correctly with appropriate safeties and pressure/temperature operating devices.
    These would include installation of an over temperature zone which will operate without electrical power, a secondary high limit, a low water cut off device which will "disable" the burner should the system lose water.
    Falls under boiler code jurisdictions and in many areas will require ASME rating to be an approved installation.

    There are 2 major dangers introduced to the equation when using a sealed system.
    The first is a very real concern especially if the boiler is installed above the radiation. This would be a low water condition where the system has lost fluid for some reason and the boiler continues to fire. Obviously this will melt things down in short order. The circumstance that leads to the boiler relocating a large portion of your property along with you, onto your neighbors yard, occurs when the water level goes low, the boiler gets extremely hot and then due to control malfunction or operator error, water is reintroduced to the boiler. The water flashes to steam instantly, creating a situation that the relief valve cannot handle and the pressure spike causes the vessel to fail in a spectacular way. You don't want to be within a half mile if this ever happens. Only saw the results of that once. That was enough.
    The second one is a matter of discipline in maintaining the safety equipment. This stuff works so well that people tend to ignore it after a while and fail to test/check the safeties for proper operation. Then when those devices are actually needed they are stuck or don't work for some reason and bad things happen very quickly.
     
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  16. hobbyheater

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    The system that I have is not common to any that I have seen on this site.
    Boiler & storage share the same water with an open to atmosphere expansion tank one story above giving 3.5 PSI at the boiler. On the second circulator for 30+ years of operation.
    Two internal heat exchangers (copper coils) inside the storage with the zones operating at 10 PSI. On my fourth circulator for 30+ years of operation.
    DHW only requires a mixing valve for scald protection and I am on a second mixing valve for 30+ years of operation.
    The system design I cannot take credit for! A commercial boiler inspector became interested in the project and I just followed his suggestions. His major concern was safety! 30+ plus years later The ONLY THING I can remember him saying "at 240 degrees and 30 psi, the expansion factor is 300,000 to one. If a leak was to occur at this temperature, would 300,000 1,000 gallon tanks fit into my basement! "

    IMGP4187.JPG
    This is a Jetstream exchanger and this is the new never used unit. Two years ago when I did a rebuild of the original, I used a Snake Eye Camera and looked inside both heat exchangers. Both looked the same. The unit that had been in operation for 30 years showed little signs of corrosion even after operating in a open system.

    IMGP3657.JPG
    Storage is a steam boiler with its tubes removed; 5/8 riveted plate steel, 1,046 imperial gallons.

    IMGP5459.JPG

    Open to atmosphere expansion tank in the wood shed one floor above the boiler.
     
  17. heaterman

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    That is about as good as can be done on an open system Allan. Nice job whether you take credit for it or not!
    You have covered all the bases from the way it looks to me.
     
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  18. maple1

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    So you've got an electric hot water heater for your expansion tank?

    Nice work & system layout - I would have done something like that too if I had a place above my boiler for it. There is actually a schematic for a similar setup in my boiler manual, I think it's pretty common in Europe. Would also make it a lot easier to incorporate or add a solar drain back system too.
     
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  19. hobbyheater

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    That is correct , the foam insulation prevented heat loss and possible freezing .
    No electric hookup.
     
  20. hobbyheater

    hobbyheater
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    I would like to see that "Schematic" as likely some others on this site . Could you scan and post it?
     
  21. maple1

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  22. heaterman

    heaterman
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    If a system is piped up so it can be purged right there is no need for a second circ to move the water up to a higher "altitude".
    Purging is one thing, circulating is another. When you purge a loop it's always advisable to use a pump suited for that task (think well pump size) in order to get enough velocity to carry all the air out with the water. Do a Google for purge cart or flush cart.
    Once purging is done all the normal circ has to do is just circulate the system. There is no "lifting" involved as the weight of the water coming down pulls the water coming up. ....like a siphon type effect.
     
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  23. maple1

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    Ok, but that brings up a question (or maybe it's where Fed was coming from): it's always recommended, from all I've read about it, to run 'x' amount of PSI in your closed system, and 'x' amount plus some 'y' amount more if you have to go up to a second floor, for the water to circulate properly to the higher zones. i.e., the higher your system water goes the more PSI you need. So where does that leave you with an open system with next to no PSI?

    I run mine pretty low, compared to others, in my two storey system (maxes out at about 10psi when fully hot), and have noticed no issues in the water getting through everything good.
     
  24. BoilerMan

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    X+Y is supposed to be for the elevation so your top floor radiation is not in a vacuum. What Heaterman is saying is that it is ok for them to be in a vacuum in an open system. A drawback to this is that if you are near boiling temps as the water moves higher in the system and the pressure is below atmosphere it will flash to steam and make that radiation non functioning if the circulator is not able to overcome the steam pockets and the look has lost it's syphon effect.

    Alan, do you use any boiler treatment chemicals in your system? Is the water always nice and clear if you drain some out of a low point? I love the simplicity!

    TS
     
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