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Thread: Small Scale CHP Steam Engine Project

  1. #1

    Small Scale CHP Steam Engine Project

    I started a long term project late last year to design and build a small scale combined heat and power steam engine system fueled by wood (and other biomass fuels). I've been derelict on the project for several months now, and I am just getting back into it. So, I figured I would start a thread to document any worthwhile progress. Please note this is a LONG TERM project that will advance SLOWLY due to limited resources (including both time and money). I do not expect to actually have a test engine operating until some time in 2022 - if at all.

    PURPOSE: The potential value of this system is in its ability to provide the same amount of heat from the same amount of wood fuel as compared to any highly efficient wood furnace, but ALSO provide all electricity demanded by the home. The primary reasons for selecting a steam system over a wood gas engine system include (1) significantly less fuel processing(*), (2) superior heat recovery, (3) quiet unattended operation.

    PIC OF TEST FURNACE OPERATING: ***https://www.flickr.com/photos/184818...-wkkCBj-ocUDM6***

    (*)I tested the furnace with small wood chunks (about 1" across), large wood chunks (about 4" across), small wood splits, and scrap lumber including 3' lengths of 2x4's dropped into the fire tube. It can't seem to tell the difference. However, the wood must be dry.

    The furnace is the foundation for the entire system, and therefore critical. This crude test unit worked surprisingly well. There was no detectable smoke from the combustion chamber by sight or smell. However, some smoke leaked from the top of the furnace due to poor seals. I estimate the heat output at approximately 10 KW and with peak temperatures approaching 2000F, but I did not get measurements. The basic design of the furnace is sort of a hybrid FEMA gasifier and rocket mass heater. Using a gasifier allows for producing the fuel gas separately. In turn, this makes possible greater control of combustion for higher combustion temperatures, a cleaner burn, and a wider turndown ratio - which I verified by operating the furnace for a long period at a low output (i.e. it still burned hot and clean at the lower output).

    The crude furnace seen in the pic is scrapped. I am now building a new furnace fundamentally identical, but with differences that include (1) it mounts on a heavy steel shelf supported by leveling mounts - this shelf will eventually accommodate the rest of the system, (2) a high quality 24vdc blower fan mounts under the shelf, (3) the combustion chamber is contained inside a insulated steel drum similar to the furnace drum, (4) the furnace fire tube and the combustion chamber are made of a stainless steel alloy, (5) the drums I am using have lever locking lids for a positive seal, (6) the fuel gas and air are directed into the combustion chamber through a slightly different path.

    Anyway, that's all there is for now. I don't expect another installment (if any) for several months.
    Last edited by buenijo; 03-26-2020 at 10:53 AM.
    “The beginning of wisdom is to call things by their proper name.” - Confucius.
    "When plunder becomes a way of life for a group of men living together in society, they create for themselves in the course of time a legal system that authorizes it and a moral code that glorifies it." - Frederic Bastiat
    "Being well adjusted to a sick society is not a measure of health." - Jiddu Krishnamurti



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  3. #2
    Interesting.

    The double use for both steam drive (electric generation) and heat sounds efficient, but will it be able to run the alternator efficiently without heating the house? Or is the firebox too big for that?

    Will this be a reciprocal (piston) steam engine? Are you thinking of using steam pressure to create a draw through the firebox instead of using output electricity on the fan?
    Quote Originally Posted by Swordsmyth View Post
    I don't really care if I happen to be wrong about your positions, you are wrong about mine.
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  4. #3
    Quote Originally Posted by acptulsa View Post
    Interesting.

    The double use for both steam drive (electric generation) and heat sounds efficient, but will it be able to run the alternator efficiently without heating the house? Or is the firebox too big for that?

    Will this be a reciprocal (piston) steam engine? Are you thinking of using steam pressure to create a draw through the firebox instead of using output electricity on the fan?
    Hello acptulsa.

    The system is designed primarily for heating applications. Rather than using a furnace to directly heat water stored for heating applications, this system heats water to generate high pressure superheated steam used to power a small engine. After moving through the expander, the steam moves to an oil separator and finally a condenser to heat the water stored for heating applications. I did not mention this in the OP, but my design also allows for operating the furnace and heating the thermal mass without operating the engine system.

    I have good reason to expect the engine system can convert the lower heating value of wood fuel to DC electricity at an efficiency of 8-10%. The design maximum charging rate is 1 KWe. This corresponds to between 5 and 6 pounds of well seasoned wood consumed per KWh of DC electricity. However, the furnace also is designed with a good turndown ratio. So, the system can be adjusted (by the operator) to a lower output if desired. The output is constant once set, and cycles on/off many times each hour to maintain thermal mass temperature.

    The engine is based on a small single-acting uniflow piston steam engine that operates with superheated steam at medium pressure (300-400 psig and 600-700F) and moderately high speeds (1200 rpm). It is a closed system (fully condensing).
    Last edited by buenijo; 03-25-2020 at 08:45 AM.
    “The beginning of wisdom is to call things by their proper name.” - Confucius.
    "When plunder becomes a way of life for a group of men living together in society, they create for themselves in the course of time a legal system that authorizes it and a moral code that glorifies it." - Frederic Bastiat
    "Being well adjusted to a sick society is not a measure of health." - Jiddu Krishnamurti

  5. #4
    Nice not to waste water. Clearly you don't intend to use steam exhaust to create a flow of exhaust in the flue.

    Of course, your condensers are also a source of radiant heat. Steam radiators work well. Sometimes they work too well.

    Can you create electricity without heating the space? Is it good for power in the summer?
    Last edited by acptulsa; 03-24-2020 at 01:56 PM.
    Quote Originally Posted by Swordsmyth View Post
    I don't really care if I happen to be wrong about your positions, you are wrong about mine.
    Quote Originally Posted by nikcers View Post
    My tax dollars paid to fund ISIS and make fake beheading videos. Are you saying we shouldn't get our monies worth??

  6. #5
    Quote Originally Posted by acptulsa View Post
    Of course, your condensers are also a source of radiant heat. Steam radiators work well. Sometimes they work too well.

    Can you create electricity without heating the space? Is it good for power in the summer?
    My thinking at the moment is to use hydronic heating with readily available (and reliable) small DC magnetic drive circulating pumps to distribute hot water to thermostatically controlled DC fan coil units.

    The unit can be operated without heating the space. I considered this configuration, and determined it would not be difficult. The basic idea is to keep the system operating by providing a heat sink outside the home. This will reduce the thermal mass temperature and keep the system operating. It's a little more involved than this, but not terribly complicated. BTW, everything uses analog controls (with the only exception a readily available and inexpensive voltage sensing relay used as a battery charge controller). This system is designed to be fully serviced by the end user.

    NOTE: This system makes the most sense for a small remote off grid home in a cold region where wood fuel is readily available. Again, heating applications is the primary purpose. The value of my system is in its ability to provide the same amount of heat from the same amount of wood fuel as compared to any highly efficient wood furnace, but ALSO provide all electricity demanded by the home. If I manage to develop a working prototype that works as designed, then I will consider other subsystems to include (1) water distillation, (2) heat regenerative bulk water pasteurization and filtration, and (3) desiccant evaporative space cooling (the only heat powered space cooling system I have determined can be powered efficiently by this system) - however, I remain convinced the most practical cooling system in the off grid setting is conventional vapor compression a/c units powered as opportunity loads on a PV array.
    Last edited by buenijo; 03-25-2020 at 09:58 AM.
    “The beginning of wisdom is to call things by their proper name.” - Confucius.
    "When plunder becomes a way of life for a group of men living together in society, they create for themselves in the course of time a legal system that authorizes it and a moral code that glorifies it." - Frederic Bastiat
    "Being well adjusted to a sick society is not a measure of health." - Jiddu Krishnamurti

  7. #6
    Well it sounds really interesting!
    Quote Originally Posted by Swordsmyth View Post
    I don't really care if I happen to be wrong about your positions, you are wrong about mine.
    Quote Originally Posted by nikcers View Post
    My tax dollars paid to fund ISIS and make fake beheading videos. Are you saying we shouldn't get our monies worth??

  8. #7
    Quote Originally Posted by acptulsa View Post
    Well it sounds really interesting!
    It is surprisingly simple in design - including the control systems - and very few moving parts. However, the devils are in the details - as you know.

    In particular, the system absolutely has to operate at a constant low output to make it feasible. This also makes possible a simple steam generator made from 1/4" steel tubing - which is perfectly safe, but also a lot more efficient than traditional boilers.

    The main headaches I anticipate include the water feed pump, steam admission valve, and the oil separator. These are already designed and parts are sourced. However, those pesky devils are waiting around the corners.
    Last edited by buenijo; 03-25-2020 at 09:59 AM.
    “The beginning of wisdom is to call things by their proper name.” - Confucius.
    "When plunder becomes a way of life for a group of men living together in society, they create for themselves in the course of time a legal system that authorizes it and a moral code that glorifies it." - Frederic Bastiat
    "Being well adjusted to a sick society is not a measure of health." - Jiddu Krishnamurti

  9. #8
    I considered another way to describe some benefits of my system design which might help some to understand my interest. I linked the following video in another thread on this forum. The purpose of my system is fundamentally the same as this "Cobber" system. However, my system is a lot smaller. I estimate the total weight of my system - and this includes the thermal mass and battery system - will come in at approximately 200 pounds and rest on a 1.5' x 4' base. Most of the system will be under 30" in height with the exception of the fuel hopper. My system does this by using a much smaller steam engine system operated at a lower output, then relying on a small thermal mass and battery to meet variable heat and electricity demands. Unfortunately, an inverter is required by my system to provide AC electricity. However, I argue essential electrical loads in the off grid setting should be DC (lighting, electronics are already DC and do not require an inverter generally, pumps, fans, power tools, even a freezer should be DC ideally, etc).

    Last edited by buenijo; 03-25-2020 at 10:05 AM.
    “The beginning of wisdom is to call things by their proper name.” - Confucius.
    "When plunder becomes a way of life for a group of men living together in society, they create for themselves in the course of time a legal system that authorizes it and a moral code that glorifies it." - Frederic Bastiat
    "Being well adjusted to a sick society is not a measure of health." - Jiddu Krishnamurti



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