Comparing gassification with steam

It seems a modern steam car would benefit from the development of electric cars. For example, a larger battery system would be required for auxiliary systems since the engine doesn't idle, and DC motor auxiliaries like a/c compressors and regenerative braking systems might be used. I'm not holding my breath on these Cyclone Mark 5 units as I know a lot more development work is necessary. Cyclone is a very small company with limited resources. It's gonna take some serious money to make something ready for commercial application and especially mass production. I'm not knocking the design at all. In fact, I think the thing is brilliant. Feel free to ask questions as I like have same details that are hard to find elsewhere - Harry Schoell himself explained to me by phone how the valve control system works, and that knocked my socks off - it's elegantly simple, effective, and can be precisely controlled with a single push rod.

Their small low temperature waste heat engine seems almost ready to go, but I'm not holding my breath there either (they need to get a real product out there soon or they're sunk as a viable company, in my opinion). That engine was recently modified from its 6 cylinder form to a 3 cylinder radial. So, it seems to have lost its self-starting feature. However, I actually think this is good since it provides an opportunity to increase the expansion that was limited to only 33% cutoff in the previous model. I'm hoping they provide a variable cutoff system or at least set the cutoff for a lot more expansion. The engine could see 15% efficiency with 600F and sufficiently high expansion, even without a vacuum on the condenser. Note that that engine uses a reed valve in the piston to exhaust the steam into a central condenser (the valve is opened by an extension on the piston connecting rod during the up stroke, and there is almost no clearance volume in the cylinder head). It pumps cool water at a high rate in the central block onto which the cylinders are mounted to condense the steam and lubricate the bearings. So, hot saturated water is available directly for heating applications. The condensate stored for the system can be used for this purpose as long as it's cooled beforehand. Personally, I really like this waste heat engine for use in residential scale combined heat and power with biomass fuel. I would like to see a smaller unit dedicated for this application, and simplified for a constant output of 1-2 hp and low speed for longevity.

I have been reading through many things on wood gasification. It is hard to find anything on a wood gasification/furnace combination. That is, most projects are about producing gas (surprise, surprise) and seem to emphasize speed of production. A truck, for example, needs to generate gas at a continuous rate for 30 to 50 hp. These projects are also worried about "clean" gas because of valves etc. The only biomass to heat projects I have seen are small cookers made from tin cans (there are commercial "fireplaces" out there, but not very informative). Again, these are fast burn applications. Get hot fast, cook the food, done, kinds of things. I want the gasification to take a long time, 24 hours would make me happy, 12 hours is ok. So the purpose of using gasification is strictly to slow the burn process down... though it may also provide somewhat better controllability.

I am thinking a top down burn may help. The problem as I see it, is that the fuel has to be heated to 450 for full gasification and that even without air, all the fuel will be heated at the same time releasing gas, the high heat end will have to deal with this gas all the time. Either it will burn it all or not depending on the air supply, but we want it to burn clean so the hot end gets all the air it needs. The gas end therefore has to control the final output (just thinking things though as I go), but the gas end also has to maintain a minimum temperature or it will go out. I am thinking that the primary air can be regulated to control the output heat, but there are two conflicting needs. The primary side has to be hot enough not to go out while at the same time holding enough fuel to last a long time. The "Kimberly" wood stove lasts for 8 hours on a load, which is pretty good... but it does include a catalytic converter so the burn may not be total (or it may just be to keep EPA happy).

To decrease the amount of actual burning in the primary section, insulation would keep the temperature high without burning as much, but mass would keep gas generation faster too. I am thinking that dividing the fuel into zones may be more effective. This is why I am thinking of a top down approach. If the fuel is a well insulated column and only burns/gasifies at the top of that column, as the fuel is used the "top of the column" moves down to fresh fuel. The fuel has some insulating effect so there can be temperature stratification. I don't know if it is best to feed air from the top or bottom in this case, but if the air feed is forced, then I think blowing from the top in a downward direction would be best. I was thinking it would be cooler and heavier, but it may be prewarmed to work best and to make the best use of the heat generated so I don't know if this would be best. In the long run, it may be better to not preheat the air if a longer burn time can be achieved and excess heat at the flue end can always be put into mass for storage. My thought with air introduced at the bottom is that the burn front may move down faster. This may not be a problem if the burn rate can be controlled by the width and depth of the fuel column.

The secondary burn would still be much the same. Whatever fuel gas reaches would have preheated air introduced in large enough quantity to fully burn the gas cleanly. Insulation would still be important and mass may be helpful too. Mass would be a lot less than used in a mass style heater because the burn rate is being slowed down instead. So this same idea could be used by those who want an efficient wood burning heater for their small cabin, but do not have the room for a cob bench or a ton of bricks.

Anyway, these are some thoughts I had. I don't know how many are valid. Is there something I can look at that deals with long burn times in gasification?

Len Ovens wrote:I have been reading through many things on wood gasification. It is hard to find anything on a wood gasification/furnace combination. That is, most projects are about producing gas (surprise, surprise) and seem to emphasize speed of production. A truck, for example, needs to generate gas at a continuous rate for 30 to 50 hp. These projects are also worried about "clean" gas because of valves etc. The only biomass to heat projects I have seen are small cookers made from tin cans (there are commercial "fireplaces" out there, but not very informative). Again, these are fast burn applications. Get hot fast, cook the food, done, kinds of things. I want the gasification to take a long time, 24 hours would make me happy, 12 hours is ok. So the purpose of using gasification is strictly to slow the burn process down... though it may also provide somewhat better controllability.

I am thinking a top down burn may help. The problem as I see it, is that the fuel has to be heated to 450 for full gasification and that even without air, all the fuel will be heated at the same time releasing gas, the high heat end will have to deal with this gas all the time. Either it will burn it all or not depending on the air supply, but we want it to burn clean so the hot end gets all the air it needs. The gas end therefore has to control the final output (just thinking things though as I go), but the gas end also has to maintain a minimum temperature or it will go out. I am thinking that the primary air can be regulated to control the output heat, but there are two conflicting needs. The primary side has to be hot enough not to go out while at the same time holding enough fuel to last a long time. The "Kimberly" wood stove lasts for 8 hours on a load, which is pretty good... but it does include a catalytic converter so the burn may not be total (or it may just be to keep EPA happy).

To decrease the amount of actual burning in the primary section, insulation would keep the temperature high without burning as much, but mass would keep gas generation faster too. I am thinking that dividing the fuel into zones may be more effective. This is why I am thinking of a top down approach. If the fuel is a well insulated column and only burns/gasifies at the top of that column, as the fuel is used the "top of the column" moves down to fresh fuel. The fuel has some insulating effect so there can be temperature stratification. I don't know if it is best to feed air from the top or bottom in this case, but if the air feed is forced, then I think blowing from the top in a downward direction would be best. I was thinking it would be cooler and heavier, but it may be prewarmed to work best and to make the best use of the heat generated so I don't know if this would be best. In the long run, it may be better to not preheat the air if a longer burn time can be achieved and excess heat at the flue end can always be put into mass for storage. My thought with air introduced at the bottom is that the burn front may move down faster. This may not be a problem if the burn rate can be controlled by the width and depth of the fuel column.

The secondary burn would still be much the same. Whatever fuel gas reaches would have preheated air introduced in large enough quantity to fully burn the gas cleanly. Insulation would still be important and mass may be helpful too. Mass would be a lot less than used in a mass style heater because the burn rate is being slowed down instead. So this same idea could be used by those who want an efficient wood burning heater for their small cabin, but do not have the room for a cob bench or a ton of bricks.

Anyway, these are some thoughts I had. I don't know how many are valid. Is there something I can look at that deals with long burn times in gasification?

In my opinion, the answer can be found by examining the operation of TLUDs. I operated two of these to understand the basics of their operation. What I verified is that controlling primary air flow rate can precisely control the combustion rate. Results were improved with insulation. I also verified that combustion will continue indefinitely at this controlled rate as long as fuel is replenished at a rate equal to the rate at which it is consumed (which I did manually by adding a fixed mass of fuel into the top of the stove at regular time intervals). I believe this process can be maintained in the following way: First, imagine a simple updraft gasifier furnace like the Wood Gas Camp Stove (one of the stoves I used). Plug the secondary air holes, add a sealed hopper to the top, insulate the base of the unit heavily, then add an insulated combustion chamber to the side of the unit at about the same level as the primary air holes. Provide an insulated path for the pyrolysis gases to move into the combustion chamber. Secondary air may also be admitted to the combustion chamber through a similar parallel path (also supplied from the single fan unit at the base of the stove), however, it would be best to supply secondary air by another means to better control the primary air flow rate. You can see how this merely redirects the flow of wood gas and preheated secondary air to an adjacent combustion chamber. The wood stored in the hopper above the base cannot be consumed because all primary air is consumed at the base, and all the hot gases are shunted directly over to the combustion chamber since the top of the hopper is sealed. Control the primary air, and you will control the production of wood gas and the resulting burn rate (assuming you provide enough air for secondary combustion).

In order to control this process precisely, a few parameters must be controlled. This includes (1) the rate at which primary air is provided to the pyrolysis chamber, (2) the rate at which heat leaves this chamber (just insulate the hell out of it), (3) the moisture content and type of fuel, and (4) the size of the fuel must present sufficient surface area to react at the required rate - this means a small mass of small pieces, or a larger mass of larger pieces. Tom Kimmel uses large wood splits and even whole logs in his steam buggy. He can do this because the very large pyrolysis chamber he uses allows for loading a lot of wood. A large mass of large pieces of wood presents as much surface area as a small mass of small pieces of wood (which we all know will support high rates of gasification in Imbert downdraft gasifiers), so in either case fairly high combustion rates can be maintained - unfortunately, the thermal losses from the larger pyrolysis chamber will reduce overall efficiency. So, a small chamber is desirable. This can be had with fairly large wood chunks as long as a low burn rate is desired.

Check out the forced air furnaces made by SilverFire (http://www.silverfire.us/silverfire-super-dragon). There is a good review of this stove on YouTube by engineer775. He uses it to heat a pressure cooker for canning, and shows that adjusting the fan speed allows for controlling the pressure cooker.

Marcos Buenijo wrote:

In my opinion, the answer can be found by examining the operation of TLUDs.

I had to look TLUD up, but yes those are the ones I have seen used as cook stoves... that have been natural drafted to burn very quick and were generally less easy to control than the rocket stove, but required less attention than the rocket too. cooking requires lots of attention anyway, so I don't know how bad/good that is.

The forced air furnaces made by SilverFire (http://www.silverfire.us/silverfire-super-dragon) looks like the same thing with fans and control. I like it... for cooking but it would need more attention than I want in a steam genset.

I believe this process can be maintained in the following way: First, imagine a simple updraft gasifier furnace like the Wood Gas Camp Stove (one of the stoves I used). Plug the secondary air holes, add a sealed hopper to the top, insulate the base of the unit heavily, then add an insulated combustion chamber to the side of the unit at about the same level as the primary air holes.
...
The wood stored in the hopper above the base cannot be consumed because all primary air is consumed at the base, and all the hot gases are shunted directly over to the combustion chamber since the top of the hopper is sealed. Control the primary air, and you will control the production of wood gas and the resulting burn rate (assuming you provide enough air for secondary combustion).

I like the idea of a sealed top feeding hopper (after all it is my idea... or at least I have also had it), in fact I used it to feed a rocket. The main thing I don't like about the rocket mass heater is the required attention to the burn process. My findings with this.... are that even with no air, the batch of fuel above the air intake still gets hot (really hot) because the heat from the burn area rises. Mine was not insulated which kept it a little cooler but it was still warm enough that the wood inside, a 4x4 as happens, started to gasify just from the heat. There was tar dripping from the fuel down the inside of the feed hopper (I actually called it a "Cartridge" because I felt I could have more than one prefilled fuel and switch them over when one was empty) The tar was not a problem and just burned up when it fell to the fire, but from my reading about gasification I am guessing I was also producing CH4 and possibly hydrogen gas (though not CO except from the little bit of air that was in there originally, but at least this CO would settle downwards while the ch4 would rise and collect) which while not a problem outside where I was, might be a problem inside if the design is not careful to make sure the seal continues to below the combustion line or at least that all gases end up going through the secondary burner. If this sealed hopper was even opened to add fuel from the top these gases could flash, scorching the person adding fuel.

This is why I felt having the fuel at the bottom and burning just the top of the fuel at any one time would be better, though I said bring the forced air in from the top, I was still thinking updraft operation. My problem was how to have the air supply follow the gassing part (the top) of the fuel as it burned down. The obvious solution of feeding air from the bottom would move the burn front down faster too. I really do want a long burn time on one load. You may be right that big wood chunks is the way to go. Certainly all of the demos I have seen have used relatively small wood pieces... even the Kimerly has only a small firebox for 8 hours and expects smaller wood (3in dia max or so). Also their fire box is not very deep, they want the secondary burner to take most of the unit so the flame can be fully contained and the heat up the flue is minimized.

Len Ovens wrote:I had to look TLUD up, but yes those are the ones I have seen used as cook stoves... that have been natural drafted to burn very quick and were generally less easy to control than the rocket stove, but required less attention than the rocket too. cooking requires lots of attention anyway, so I don't know how bad/good that is.

The forced air furnaces made by SilverFire (http://www.silverfire.us/silverfire-super-dragon) looks like the same thing with fans and control. I like it... for cooking but it would need more attention than I want in a steam genset.

The reason I linked the SilverFire is because it shows that the combustion rate of a biomass furnace can be precisely controlled by controlling primary air flow rate. Actually, the design uses the fan to supply both primary and secondary air. Even better results can be seen by forcing only primary air, or by forcing primary air and secondary air separately. I don't suggest this product be used to support a steam generator. The message I want to emphasize is that a properly configured gasifier furnace will see all primary air consumed - therefore, controlling the primary air flow rate will control the combustion rate by proxy.... and the size of the fuel doesn't matter as long as there is enough surface area, and as long as the fuel is not too small to obstruct air flow.

Len Ovens wrote:I like the idea of a sealed top feeding hopper (after all it is my idea... or at least I have also had it), in fact I used it to feed a rocket. The main thing I don't like about the rocket mass heater is the required attention to the burn process. My findings with this.... are that even with no air, the batch of fuel above the air intake still gets hot (really hot) because the heat from the burn area rises. Mine was not insulated which kept it a little cooler but it was still warm enough that the wood inside, a 4x4 as happens, started to gasify just from the heat. There was tar dripping from the fuel down the inside of the feed hopper (I actually called it a "Cartridge" because I felt I could have more than one prefilled fuel and switch them over when one was empty) The tar was not a problem and just burned up when it fell to the fire, but from my reading about gasification I am guessing I was also producing CH4 and possibly hydrogen gas (though not CO except from the little bit of air that was in there originally, but at least this CO would settle downwards while the ch4 would rise and collect) which while not a problem outside where I was, might be a problem inside if the design is not careful to make sure the seal continues to below the combustion line or at least that all gases end up going through the secondary burner. If this sealed hopper was even opened to add fuel from the top these gases could flash, scorching the person adding fuel.

The tars would have been vaporized in a gasifier design. The combination of no insulation and high air flow rate (rocket furnaces supply both primary and secondary air via the same path) allowed a cool area to condense the tars.

The primary fuel gas in a wood gasifier is CO. H2 is second. There are various hydrocarbons and alcohols, and very little is methane.

The design I considered would keep the sealed hopper under a slight negative pressure since the flue of the combustion chamber provides draft. So, one could safely open the hopper during operation without getting a face full of wood gas. The purpose of the blower fan is primary to meter the primarily air keeping it constant under all conditions.

Len Ovens wrote:This is why I felt having the fuel at the bottom and burning just the top of the fuel at any one time would be better, though I said bring the forced air in from the top, I was still thinking updraft operation. My problem was how to have the air supply follow the gassing part (the top) of the fuel as it burned down. The obvious solution of feeding air from the bottom would move the burn front down faster too. I really do want a long burn time on one load. You may be right that big wood chunks is the way to go. Certainly all of the demos I have seen have used relatively small wood pieces... even the Kimerly has only a small firebox for 8 hours and expects smaller wood (3in dia max or so). Also their fire box is not very deep, they want the secondary burner to take most of the unit so the flame can be fully contained and the heat up the flue is minimized.

I'll describe some details of the design I considered. It's not a TLUD. The reason I referenced the TLUD is because a forced air TLUD shows that combustion rate in a gasifier furnace is determined by primary air flow rate. What I want to do is provide a highly insulated furnace base with a sealed hopper. A grate and shallow ash pan is provided. I would start my system by igniting the fuel at the grate by placing starter material (like paper) in the ash pan, starting the blower fan, igniting the paper, then shutting the access port to the ash pan. The grate is to be made of multiple parallel lengths of black iron pipe capped at one end and connected to a header at the other. The blower fan supplies air into the header, and the bottom of the pipes have small holes drilled along their lengths. The purpose of putting the holes at the bottom is to keep ash and char out of the holes and prevent blockage, and to admit air directly to the ash pan to consume any char that falls through. Admitting air into the pipes serves to (1) preheat the primary air, and (2) cool the grate. Preheating the primary air helps ensure the full combustion of primary air (since hot oxygen is more reactive), and it helps to keep the reaction close to the grate for the same reason (hot char on grate plus hot primary air equals serious temperature). The wood fuel on top of the charcoal will be pyrolysed and any air the gets past the charcoal will be consumed in pyrolysis gas combustion to add more heat for the pyrolysis process... but the main point is that no free oxygen from primary air is going to get to the combustion chamber. The resulting wood gas then moves a short distance to the adjacent combustion chamber to mix with preheating secondary air for combustion (this secondary air is preheated by the walls of the combustion chamber before it moves down into the base to mix with the incoming hot wood gas).

A benefit of this configuration is that the conditions between the grate and the plenum where wood gas moves into the combustion chamber (on the order of 6-8 inches in height) are constant as long as the space below this plenum is filled with wood fuel. So, the furnace can be operated at a constant low rate for a long period after the hopper is filled without fear of conditions changing to affect combustion rate. A problem with combustion at the top of a fuel mass is that the conditions change as the fuel is consumed, and the pyrolysis gases move through the fuel mass to cool down. Any tars that condense would be combusted as the fuel is consumed, but the wood gas that moves into a combustion chamber is cool, and this is not good for combustion. You want hot wood gas mixing with plenty of hot air for good combustion.

Marcos Buenijo wrote:

Len Ovens wrote:I like the idea of a sealed top feeding hopper (after all it is my idea... or at least I have also had it), in fact I used it to feed a rocket. The main thing I don't like about the rocket mass heater is the required attention to the burn process. My findings with this.... are that even with no air, the batch of fuel above the air intake still gets hot (really hot) because the heat from the burn area rises. Mine was not insulated which kept it a little cooler but it was still warm enough that the wood inside, a 4x4 as happens, started to gasify just from the heat. There was tar dripping from the fuel down the inside of the feed hopper (I actually called it a "Cartridge" because I felt I could have more than one prefilled fuel and switch them over when one was empty) The tar was not a problem and just burned up when it fell to the fire, but from my reading about gasification I am guessing I was also producing CH4 and possibly hydrogen gas (though not CO except from the little bit of air that was in there originally, but at least this CO would settle downwards while the ch4 would rise and collect) which while not a problem outside where I was, might be a problem inside if the design is not careful to make sure the seal continues to below the combustion line or at least that all gases end up going through the secondary burner. If this sealed hopper was even opened to add fuel from the top these gases could flash, scorching the person adding fuel.

The tars would have been vaporized in a gasifier design. The combination of no insulation and high air flow rate (rocket furnaces supply both primary and secondary air via the same path) allowed a cool area to condense the tars.

Actually, the rocket burner I used had two air supplies and did not get any of it's air, even primary, from through the unburned fuel. The primary air was regulated at less than 1/4 riser CSA and secondary air (preheated) was added just before the riser. Sort of side draft gasification. It was not a classic RMH design at all. The only condensing of tar was in the sealed fuel cartridge where no combustion was supposed to take place. However, the cartridge acted as a bell collecting heat from the primary burn area. I do not believe (I could of course be wrong) the tar in the feed cartridge came from the primary burn area as the flame was properly sideways and the tar in the flue gas would be heavier anyway. However, any heat at the mouth of the cartridge would rise to the top and collect in classic bell fashion (and did). This would apply to a sealed fuel hopper as well. Even if the hot gases are being pulled away from the feed area, radiation would add heat in this area. The fuel in the cartridge did not have an oxygen supply and so would not produce CO, but did (even with no insulation) get wood hot enough for it to start to break down... thus the tar. If the sealed feed hopper is uninsulated then the tar will condense on it's surfaces. If the feed hopper is insulated then more gasification will take place making for an extra source of fuel for the secondary burner, but the tar will at least remain as a gas. I do not know which parts of gasification happen in the absence of oxygen, but these are the ones to think about. I mention H2 and CH4 not because they are produced in quantity, but because they are lighter than other gases and most likely to collect at the very top of the feed hopper and of course would be kept hot as well. So long as the hopper remains sealed, there is no problem. However, opening the top of the hopper with this gas sitting at or beyond it's flash point, even with a partial vacuum seems to mean instant combustion and the rapid expansion that creates may be more than that vacuum could handle. Experimentation will of course prove me right or wrong. My experimentation has proven to me that a space above a burning process will collect heat. So I am very sure an overhead sealed fuel hopper will get hot and with any amount of insulation/mass in the walls will over time equalize to the same temperature as the primary burn, or higher.

I'll describe some details of the design I considered. It's not a TLUD. The reason I referenced the TLUD is because a forced air TLUD shows that combustion rate in a gasifier furnace is determined by primary air flow rate. What I want to do is provide a highly insulated furnace base with a sealed hopper. A grate and shallow ash pan is provided. I would start my system by igniting the fuel at the grate by placing starter material (like paper) in the ash pan, starting the blower fan, igniting the paper, then shutting the access port to the ash pan. The grate is to be made of multiple parallel lengths of black iron pipe capped at one end and connected to a header at the other. The blower fan supplies air into the header, and the bottom of the pipes have small holes drilled along their lengths. The purpose of putting the holes at the bottom is to keep ash and char out of the holes and prevent blockage, and to admit air directly to the ash pan to consume any char that falls through. Admitting air into the pipes serves to (1) preheat the primary air, and (2) cool the grate. Preheating the primary air helps ensure the full combustion of primary air (since hot oxygen is more reactive), and it helps to keep the reaction close to the grate for the same reason (hot char on grate plus hot primary air equals serious temperature). The wood fuel on top of the charcoal will be pyrolysed and any air the gets past the charcoal will be consumed in pyrolysis gas combustion to add more heat for the pyrolysis process... but the main point is that no free oxygen from primary air is going to get to the combustion chamber. The resulting wood gas then moves a short distance to the adjacent combustion chamber to mix with preheating secondary air for combustion (this secondary air is preheated by the walls of the combustion chamber before it moves down into the base to mix with the incoming hot wood gas).

This part made sense to me and I agree it should work well. I had that part figured out way back from your first description and it has only been the feeding for a long burn part I have wondered about. In my case, the cartridge was filled with pieces that were the whole length of the cartridge because I felt smaller pieces might end up sideways and jam. This means that any one piece of fuel will have one end in the primary burn and one end in the cartridge/hopper. I am assuming you would do the same or use small enough fuel that the feed area is larger than the longest fuel piece. I personally want to stay away from having to prepare the fuel at all beyond cutting to length (three feet in this case, but maybe longer for a genset) and drying. I think I will mostly do the same, but maybe try more than one feed style in a smaller unit to verify operation. The only way to learn is try things that don't work or watch someone else try them. But this doesn't seem to be an area that is hot in experimentation right now.

When? well, I find this interesting enough to back burner any RMH experimenting. For heater only, I have pretty much decided a masonry heater would fit better than a RMH anyway... in a non-permit setting, they are both the same price and in a permit setting the masonry heater may be cheaper... or at least possible. A gasifier heater would be experimental, but outside of the dwelling anyway and could be run without permit even in a picky place so long as no smoke/noise is evident. I am sure I would have complaints in this area if I ran a gasifier IC genset, just because of the noise... in fact I might be the one complaining if someone else did. I would not have to worry about house insurance with a wood burner not too close to the house either. So even from a heating steam to heat water (or heating water directly) the burner design is interesting. Making power at the same time, even a little, in a quiet power plant is a bonus even in the city. Power outages are rare, but mostly happen at least once a season due to wind off the ocean. Supplying heating and minimal power would mean I am just paying for power to cook and do laundry (I would switch hot water over too). Having power for lighting, food chilling and entertainment should be well within the capability of a small steam setup. Cooking with steam may come in time too, but for most off grid setups a wood stove would make more sense.

I am thinking a steam engine (expander) even made from compressor parts could easily be quieter than the compressor was. The compressor has almost open intake and the cylinder itself has noise amplifying fins. An expander would (should) not have fins but rather insulation and both intake and exhaust would be covered and the pipes insulated. There is no exhaust pipe like an IC engine has and so the whole unit can be in a well sound proofed box/shed.

To me, it seems crucial to ensure all free oxygen in the primary air is consumed in combustion, and that this heat from combustion is transferred to the fuel to drive pyrolysis. There must be enough surface area of fuel available, sufficient residence time of the gases, and excellent insulation. The simplistic model that I use is to control primary air flow rate, combust all oxygen in the primary air, transfer all heat from this primary combustion to the fuel mass contained in a highly insulated space to drive pyrolysis, transfer the hot pyrolysis gases to a combustion chamber, then mix with sufficient preheated secondary air for full combustion.

A similar process occurs in downdraft gasifiers. In both cases the fuel gas production rate is proportional to the primary air flow rate in a properly designed system:

DOWNDRAFT GASIFIER: Most of the primary oxygen is consumed by combustion with pyrolysis gases. The heat generated by this combustion (1) generates the pyrolysis gases required to keep the process going, (2) is used to drive reduction reactions with charcoal to generate the fuel gas, and (3) is carried out of the hearth with the fuel gas at elevated temperature.

UPDRAFT GASIFIER: By contrast, the updraft unit sees most of the primary oxygen consumed in charcoal combustion. The heat generated by this combustion (1) generates the pyrolysis gases that is fuel gas in this case, and (2) generates the charcoal required to keep the process going (charcoal being generated by the pyrolysis of wood).

These observations are what led me to my design. Really, it's nothing new. I'll be simply trying to achieve dimensions that are ideal for generating hot pyrolysis gas (fuel gas) at my desired rate with the widest possible fuel conditions. I think insulation and the use of highly preheated primary air is the key (hence the grate design that preheats the air), along with controlling primary air flow rate of course.

Garry Hoddinott wrote:My need is a modest output energy system. My beef with solar is batteries. They are too short lived to be sustainable and just a bit toxic (am interested in capacitor banks).

My property (which I wish to share (grafton NSW Australia)) has ample wood supply - stored solar! What is the best way to convert that to electricity? Gassification seems do-able, but steam??? We don't hear too much about steam. Is it really just too hard?

I met a wonderful old guy in Australia who told me of his dad's very large hot air machine. Umm - his hand guestures indicated it was bedroom sized and used 2 chimneys as monster pistons, and used a very large flywheel. Seems like it turned a crankshaft and powered a stationary sawmill and ran on sawdust from the mill itself.

That sounds funky - any thoughts???

Gary

I have just about given up posting on permies but dont be afraid of steam yes it can be dangerous but with the right kit and safety valves its pretty foolproof. Thankfully in UK we have a history of steam and a dedicated steam industry keeping the technology alive. Have a look on the Prestons website they have systems for every budget and have even started doing packaged systems. If you really get into steam then I would recommend the Bellis & Morcom generating sets as my two girls are very reliable.

http://www.prestonservices.co.uk/generators.html#turbines

R John, I'm interested to learn more about the operation you have going. Please provide any web resources that describe your operation including pictures. In particular, I'm curious to know how you are making use of such a large steam engine. Are these large steam engines your personal property? Are you involved in a business venture with this engine system and other systems (such as the Jenbacher you mentioned elsewhere)? Is the system generating electricity and revenue? Details please.

Marcos Buenijo wrote:R John, I'm interested to learn more about the operation you have going. Please provide any web resources that describe your operation including pictures. In particular, I'm curious to know how you are making use of such a large steam engine. Are these large steam engines your personal property? Are you involved in a business venture with this engine system and other systems (such as the Jenbacher you mentioned elsewhere)? Is the system generating electricity and revenue? Details please.

Already described on previous thread just do a search for Bellis & Morcom.

r john wrote:

Already described on previous thread just do a search for Bellis & Morcom.

I've noted several posts where you mentioned it, and I did a search. I find no resources and no details. If there is available a resource such as a web site that describes your operation, then please provide link. I would like to get as many details as are available. In particular, I'm interested to know if the system is generating useful power and profit... or are these engine part of a museum? Either way, myself and likely others would like to see details of such an impressive operation. Thank you John.

Purely commercial generating electric using woodchip and thermal solar via a thermal oil steam evaporator hence no need for explosive boilers.

Similar technology to my commercial scale operation will soon be available for the domestic market.

http://www.vdg.no/index.php?articleid=12

Small Steam System

I am adding this link and discussion to the thread as it's relevant to the topic. Those who have read through the thread will understand the relevance.

The link describes a small steam system used to power a small boat. The system uses a small monotube steam generator. The steam generator is made from 40 feet of roughly 1/4" diameter stainless steel tubing. While the system is crude and inefficient (the builder stated elsewhere that he was all about K.I.S.S. and didn't give a damn about efficiency or cosmetics), it shows clearly that a simple length of small diameter tubing can generate quality steam at a surprising rate.

The control system is interesting to me as it's similar in some respects to a configuration I considered independently. The system in the link uses a bimetallic strip exposed to the peak steam temperature supplied to the engine (it's in thermal contact with the steam supply line by mounting the strip to a small copper block clamped onto the steam line). The strip bends in response to the steam temperature changes, and this bending actuates the potentiometer of a Pulse Width Modulating (PWM) controller for a small DC motor. The motor drives the water feed pump for the steam generator. As the steam temperature approaches 600F, then the water is pumped into the coil at the max rate and this cools the coil. Since the the system uses a more or less uncontrolled wood furnace, then this would also increase steam pressure and increase engine output. A simple means to control engine output was devised: an adjustable steam relief valve is placed to manually vent excess steam and drop the steam pressure as required to lower engine output. While wasteful, it does make some sense in this case (uncontrolled wood furnace). The builder states that the steam temperature stays between 550F and 600F during operation, and the pressure is 150-200 psig during normal operation (pressure would be determined primarily by the load on the engine).

More than anything else I just wanted to show that a simple and surprisingly small coil of 1/4" steel tubing can in fact generate steam to run a useful steam engine. In fact, since this system has high thermal losses from the flue (due to the less than ideal shape and placement of the tubing coil), and since the engine design shows low efficiency (simple small counterflow slide valve unit), then it's clear that an efficient system could produce a lot more power with the same steam consumption rate. The engine in the link is described as having an output that corresponds to about 2/3 hp. A good single acting bump valve uniflow engine exhausting to a vacuum (fully condensing) could show twice the efficiency. Add to this a highly efficient steam generator coil and excellent insulation, and the output could approach 2 hp with the same size tubing coil. In any case, the steam generator required for a 1-2 hp steam engine system can be a great deal more compact than most people understand.

Now, the control system I considered also called for using a bimetallic strip to govern steam temperature. However, I considered using it to (1) control a PWM for the small blower fan of a gasification furnace, or (2) control a damper for the air supplied to a rocket furnace. The water feed pump in these cases would be driven mechanically by the engine, and there would be a relief valve on the pump discharge to limit the pressure in the system (this relief should also be able to handle steam just in case). The system would be operating at a constant output that might be adjusted up or down as desired by adjusting the relief valve. An alternative approach would be to set the relief valve at a constant setting, then throttle the steam supply to the engine to vary its output. Other features might include a high flue temperature thermostat to stop the blower fan of a gasification furnace, and a thermostatic damper shut off for high flue temperature in a rocket furnace (both these high flue temp conditions would occur if the engine were to stall while the furnace is putting out).

Hopefully this shows how small scale steam does not require dangerous pressure vessels - and it's not quite rocket science when kept simple.