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Comparing gassification with steam  RSS feed

 
Garry Hoddinott
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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



 
Len Ovens
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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


Only one quick thought. To do with gensets in general. The engines are often the weak link. Many gasifier gensets start out as gasoline powered gensets. They are cheap to buy and work well. However, the motor is not built for 24/7 running and the materials used may not be compatible with the flue gases in the wood gas either. The gen itself only needs new bearings once in a while. So large, slow turning seems to be the way to go. I don't know anyone who runs a genset all the time though, most people (even with a Lister) run once a week to charge batteries and take the opportunity to wash clothes and do wood work and other high current draw things while it is running.

I agree with the yick factor of batteries and feel there is better ways of storing energy for many things.

Steam? The main thing is that it requires some study to build/operate/maintain, may require certification to run and annual inspection to be legal. I expect they are not quite as dangerous as some people make them out to be, but enough drunks got themselves and worse others killed with lack of care. If they could be used as tractors on the farm, it must be possible to have them be reasonably safe.

Just my two cents.
 
Marcos Buenijo
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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


If your desire is to convert the chemical energy of wood into electricity, then a wood gas engine system is the best prospect. If you desire to make use also of the heat available from the engine system AND hope to minimize the size of a battery system, then a small steam system can be a viable alternative. Unfortunately, there is a serious problem with small scale steam in that the hardware is not readily available. In general, small scale steam is not practical for this reason. I believe strongly that steam power with biomass fuel can be superior to a wood gas engine system for micro scale combined heat and power, but the hardware requires upgrading. That is the main problem.

The best micro combined heat and power system I've seen (with biomass fuel) was devised by Ken Boak in the UK. Google "Ken Boak Lister Powercubes" to find a description of his system. I happen to believe that a small scale piston steam engine could be superior in his application, but again, the lack of hardware is a serious problem. For example, Mr. Boak needs a lot of heat for space heating and water heating in his setting. The engine system he devised also must be loaded down to 5 hp or more to keep the gasifier at sufficiently high temperatures. Therefore, he operates the engine (a single cylinder Lister) to generate ac electricity to (1) charge a battery bank, and (2) while powering space heaters and other electrical loads while the engine is running. He operates for part of each day while heating a large store of water off the engine. After the engine is shut down, then the battery system can provide electricity, and the store of heated water can provide space heating with a hydronic heating system. A good steam system could provide the same, but with the benefits of less fuel processing, quiet operation, and likely longer engine life due to lower speeds and lower peak temperatures. While the thermal efficiency would be lower, the system operated by Mr. Boak uses most of the electricity for space heating in order to load the engine down - so, in a sense, the higher thermal efficiency of the wood gas engine system is wasted in that setting. HOWEVER, again, the problem remains that suitable hardware for steam is just not there.

If a trend toward biomass fuel in the micro scale takes hold, then steam power will almost certainly return with serious work taking place on development of modern systems. Quite simply, physics favors steam power in this setting (micro scale combined heat and power with biomass fuel). If you have more questions on steam power or wood gas engine systems, then feel free to ask whatever you like. I can provide a lot of resources if you're interested.
 
Marcos Buenijo
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Len Ovens wrote:Steam? The main thing is that it requires some study to build/operate/maintain, may require certification to run and annual inspection to be legal. I expect they are not quite as dangerous as some people make them out to be, but enough drunks got themselves and worse others killed with lack of care. If they could be used as tractors on the farm, it must be possible to have them be reasonably safe.


For micro scale combined heat and power, a low power system that sustains output for long periods and within a narrow operating range would be ideal. Under these conditions, a simple monotube steam generator would be perfect. These can be perfectly safe, and they require no certifications as far as I'm aware.
 
Len Ovens
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Marcos Buenijo wrote:
Len Ovens wrote: may require certification to run and annual inspection to be legal.


For micro scale combined heat and power, a low power system that sustains output for long periods and within a narrow operating range would be ideal. Under these conditions, a simple monotube steam generator would be perfect. These can be perfectly safe, and they require no certifications as far as I'm aware.


I have heard some states require the boiler to be inspected annually. I got the idea it was any boiler that was for holding steam. Looking at some pictures of monotube steam generators it does seem like it could be safer... at least there is a lot less water/steam in the system at any one time. Both rocket burner and gasifier burner can be kept pretty constant, I would think.

So where do I get one? from your comment above I get the idea many of the parts are not obtainable right now.

I still don't know that I would want to run it 24/7, but daily during heating season would change battery size needed or maybe allow super caps to fill the night time lighting/entertainment void.... or maybe this would be something to run overnight and let solar panels with a cap bank deal with daytime.
 
Marcos Buenijo
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Len Ovens wrote:I have heard some states require the boiler to be inspected annually. I got the idea it was any boiler that was for holding steam. Looking at some pictures of monotube steam generators it does seem like it could be safer... at least there is a lot less water/steam in the system at any one time. Both rocket burner and gasifier burner can be kept pretty constant, I would think.

So where do I get one? from your comment above I get the idea many of the parts are not obtainable right now.


You would have to make your own steam generator. This is not a serious difficulty for a low power engine. A small unit suitable for powering a one hp steam engine can be had from 50 feet of 1/4" steel tubing (generally one needs on the order of 5 square feet of heat transfer surface area to generate enough steam for a typical small one hp steam engine - the more efficient the system, then the less steam, so a smaller unit will work - also, higher pressure steam requires less surface area due to the higher residence time of the steam in the tube and higher density of the fluid which provides better heat transfer - also, a smaller diameter tube provides better heat transfer due to the higher velocity of the steam for lots of turbulence on the inner wall). Note that there is no need to copy the complicated forms often used for steam cars. Those were engineered for high power/weight and compact form. A unit suitable for an efficient one hp engine could be little more than a simple coil, just have to made sure the very hot furnace exhaust gases make good contact with the tubes for good heat transfer. I also suggest a large recuperator on the furnace exhaust to preheat combustion air. This basic approach should allow high efficiency including higher furnace temps (which in turn allows for higher efficiency). With counter flow heat exchange (water pumped into the coil in the direction opposite the flow of furnace gases), high enough heat transfer surface area (i.e. the tube is large enough for desired output), turbulence (making sure the combustion gases actually impinge on the tube rather than finding the path of least resistance through a large gap), using the furnace gases that leave the coil to preheat combustion air, and getting wicked hot furnace temps will see good results. Might even put a copper water preheating coil that connects to the high temperature steel steam generator for high efficiency - or better yet, use the warm furnace exhaust gases for water heating in the home.

It would be very important to control the furnace output precisely, so I believe a rocket furnace is out of the question unless the volume of the steam generator were much larger (like a larger coil of fatter tubing to provide some energy storage). The system needs at least the primary air to be forced for good control. This is very easy to do with small fans. If you haven't played around with small forced air wood gas furnaces yet, then please do so - it's a lot of fun, and very educational. I was amazed at how precisely I could control the burn rate, and these things get hot! - I had fun melting aluminum cans with pine shavings, and they would melt quickly. I believe the temperature was approaching 2000F.

 
Marcos Buenijo
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Len Ovens wrote:I still don't know that I would want to run it 24/7, but daily during heating season would change battery size needed or maybe allow super caps to fill the night time lighting/entertainment void.... or maybe this would be something to run overnight and let solar panels with a cap bank deal with daytime.


My thinking on this (assuming one has a durable micro steam system available and running) is that the system should be run at the lowest output to meet whatever bottleneck in energy is seen. If it's a cold winter day and space heating is the primary need, then the system should be operated at a rate to provide space heating. An efficient unit will provide all required electricity as well (assuming a modest and efficient home). If it's a hot and humid summer day, then the system can be operated primarily to generate chilled water using adsorption - perhaps a small a/c unit can be placed as an opportunity load on a PV array during the day, and then operate the steam system at night for electricity, chilled water, and water heating as this approach could conserve fuel while also providing air conditioning throughout the evening without relying on battery storage (which would require one helluva battery and PV array). There would be days that require little or no space heating or cooling, and maybe a PV array and modest battery storage can provide all electricity required so no fuel need be consumed - or the steam generator might be operated just to heat water if desired. There are all kinds of possibilities, but the principles that I tend to emphasize with respect to micro steam power is minimizing the output of the system, operating it at a constant output for extended periods, getting decent thermal efficiency, and making the most of the heat from the system. A system like this has no need to exceed one hp output when used to power a modest and efficient home. At this low output, then I believe the prospect for actually constructing a useful system becomes reasonable.
 
Len Ovens
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Marcos Buenijo wrote:
You would have to make your own steam generator. This is not a serious difficulty for a low power engine. A small unit suitable for powering a one hp steam engine can be had from 50 feet of 1/4" steel tubing.

Like brake tubing?


A unit suitable for an efficient one hp engine could be little more than a simple coil, just have to made sure the very hot furnace exhaust gases make good contact with the tubes for good heat transfer.

My first thought is that the steam would be just as likely to push the water back out the input as into the engine. I am guessing there would need to be at least some kind of injector? Would a simple ball valve work for that? (fluid diode) have the steam pulse in time with the piston, or would the pressure need to be continuous? (and need continuous injection)

I am also assuming a piston engine as compared to a turbine? Single stage? Two stage? Double acting I would guess. Would a hydraulic cylinder work? I am guessing that HP would depend on steam pressure/flow as well as engine size (bore and stroke).

Just found some stuff to read.... more questions when I am done.
 
Peter Mckinlay
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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


Hello Gary,

Any piston engine single or multi cylinder easily coverts to steam. A steam pipe goes to the intake port, the rest is left alone. Steam needs be supplied by a boiler, it requires a boiler fill pump, this can be attached to the engine shaft, before the generator is mounted.

Steam is the last energy you should be contemplating, it has huge heat needs for very little energy. My preference is CO2 its active at -40*C , at +50^C it has the same energy of steam at +600*C. +30C will provide all household needs and more, and working on 1 litre per second so the device is very small.

Almost same setup as steam, hot CO2 goes to the intake port, hot CO2 comes out the exhaust manifold into a drum where the CO2 is allowed to cool before being pumped into the heater/boiler.
CO2-Critical.png
[Thumbnail for CO2-Critical.png]
 
Marcos Buenijo
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Len Ovens wrote:Like brake tubing?

My first thought is that the steam would be just as likely to push the water back out the input as into the engine. I am guessing there would need to be at least some kind of injector? Would a simple ball valve work for that? (fluid diode) have the steam pulse in time with the piston, or would the pressure need to be continuous? (and need continuous injection)

I am also assuming a piston engine as compared to a turbine? Single stage? Two stage? Double acting I would guess. Would a hydraulic cylinder work? I am guessing that HP would depend on steam pressure/flow as well as engine size (bore and stroke).

Just found some stuff to read.... more questions when I am done.


See https://archive.org/stream/steamengineprinc00crofrich#page/n0/mode/1up

Brake tubing will work and has been used before in some projects. Steel tubing of all sizes can be had cheaply. You need a check valve (i.e. "ball valve" as you mentioned) on the pump discharge to prevent back flow. The simplest pump for this application is a small plunger or small piston pump (see Hypro brand). You could make this also fairly simply... you need a sealed plunger that reciprocates in the end of a small tube or pipe section with check valves at the end (one to take in water from the collection tank, and one to expel water to the steam generator), and this can be driven by the engine shaft. There are small check valves with compression fittings designed for use with small tubing. The pressure will vary slightly as the pump operates, but the volume of the steam generator and action of the expander (i.e. engine) will keep pressure within a narrow range. You may also require a bypass valve on the pump to set steam generator pressure - generally a relief valve is used, but a small needle valve might serve as a means to set the desired pressure. This can be useful to prevent flooding the steam generator coil. I think you'll find that the most difficult part of this prospect will be feeding water to the steam generator coil at the proper rate. A solution can be had in using a larger steam generator coil and keeping a tight system and low water mass so that most of the water in the system is stored in the coil at all times. Also, a long steam generator coil positioned for good heat transfer can serve to heat excessive water pumped into the coil so that the pressure rises above the limit set by the relief valve on the pump discharge - this will send excess water back to the pump suction and limit the feed rate - a hot furnace operating at a controlled rate will then superheat the steam that is now set at a constant pressure by the relief valve on the pump discharge. This could work well as long as the engine were set for a constant rate and the furnace output were constant. Things get difficult when one desires a highly variable load, and I don't want to even consider it even though I know what's required.

Do not consider a steam turbine for micro scale applications. Very small steam turbines require ridiculously high speeds to see any appreciable efficiency, and even then they won't meet the efficiency of a good piston steam engine. There is also the problem of having to gear down the high speed provided by a turbine. A piston engine is the only way to go for micro scale (meaning less than 10 hp). Good thinking - a hydraulic cylinder will work and has in fact been done before. However, the seals in the hydraulic cylinder are not useful for the project and would have to be replaced. Other projects have converted piston air compressors successfully. Generally, converting a gas engine to a steam engine will not result in a good system because internal combustion engines are designed to radiate heat for cooling, and the steam engine must be highly insulated for good results. It can be done, but select a design that can be properly modified (see White Cliffs steam engine for the best example of an engine conversion I've seen: http://www.rossen.ch/solar/wcengine.html). Personally, I think there is promise in converting a hydraulic cylinder by replacing the piston seals (normally butyl or other high temperature rubbers) with high temperature compression packing like teflon or graphite. In particular, I think the graphite packing can be used successfully, and both have been used in model steam engines with high success. I have not seen them used for larger engines that generate useful power. In my opinion, an engine that operates at a low speed could use this kind of piston sealing with high success as long as a crosshead were provided to prevent all piston side loading. Best of all, a tight system that fully contained the water and steam (condensing for reuse) and prevented all air from entering the system could get away with no oil lubrication under these conditions as there would be no metal to metal contact, just have to keep all oxygen out to prevent corrosion. Double acting could be done if a hydraulic cylinder were used. A single long piston valve might be used to control intake and exhaust for both ports, and the piston could be driven by a single eccentric off the engine shaft - or, poppet valves might be used with uniflow exhaust in the center of the cylinder for both pistons (actually, just a single large piston would be used - I considered this seriously once with a 4" bore hydraulic cylinder by connecting two pistons together in an 8" cylinder with a 4.5" stroke - the large 1.5" dia. piston rod was to be replaced with a much smaller rod and the cylinder end converted to a packing gland for the new piston rod - the rod was to be connected to a crosshead, and used to drive a large flywheel at low speeds on the order of 2-3 hertz - a single port in the bottom of the horizontal cylinder would have provided exhaust to the condenser). There are all kinds of possibilities... even multiple stages (compounding) can be done, and I've considered several unique configurations here.

I tend to emphasize a continual low output at low speeds to simplify the system, extend life, and make things easy to repair and/or cheap to replace when any problems arise. This could also minimize the required energy storage (i.e. battery). Really, this is the main reason I think small scale steam can be useful - if a low speed engine can be made to operate at low power for long periods, and be reliable and easily repaired, and fueled by biomass with little processing, then this seems ideal to me. Throw in the high quality heat from the steam exhaust and it seems like a winner. The main problem beyond getting a reliable system is getting sufficiently high thermal efficiency to make the system worthwhile.

NOTE: I am aware of a small steam engine that used a solid carbon graphite piston and operated at high speeds on the order of 2000 rpm. It was used in a small steam boat. Output was on the order of 1-2 hp. I understand there was no oil lubrication used. I recall that the engine gave good results until the piston finally cracked. I really think experimenting with graphite packing to seal a piston will show good results, especially at low engine speeds. Again, teflon might be worth testing. Teflon is generally rated up to 500F, and the average cylinder temperature should be lower than this in most steam engines. Since the teflon would be in contact with the cylinder wall, then it would be exposed to average cylinder temperatures which should be a lot lower than peak temperatures. There are all kinds of packing (graphite, teflon, graphite teflon, and of various hardness and grades that can be tried - that's my advice, and what I will try when I start my project).

 
Marcos Buenijo
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Peter Mckinlay wrote:Any piston engine single or multi cylinder easily coverts to steam. A steam pipe goes to the intake port, the rest is left alone.

Steam is the last energy you should be contemplating, it has huge heat needs for very little energy. My preference is CO2 its active at -40*C , at +50^C it has the same energy of steam at +600*C. +30C will provide all household needs and more, and working on 1 litre per second so the device is very small.

Almost same setup as steam, hot CO2 goes to the intake port, hot CO2 comes out the exhaust manifold into a drum where the CO2 is allowed to cool before being pumped into the heater/boiler.


Converting any piston engine to steam is a lot more complicated than suggested here. Valves are the main problem. They need a completely new design to achieve anything worthwhile (meaning, anything with decent efficiency). Also, most engines are designed to radiate heat, so the cylinders must be insulated when converting to an expander using high temperature working fluid - and this is not easy for most engine designs. There is also the problem of lubrication. Generally, a different sort of lubricant is required.

Peter, your claim that CO2 at 50C has the same energy as steam at 600C is, well, not quite right. What perhaps you mean to state is that saturated steam at 600C has the same pressure as saturated CO2 vapor at 50C. For example, let us consider saturated steam and saturated CO2 vapor at 1000 psia. Under this condition, steam has a temperature of 545F and CO2 has a temperature of 82.4F. Does the constant pressure of 1000 psia somehow imply that the two substances contain the same energy? Well, it turns out that the specific enthalpy of the saturated CO2 vapor is 164 btu/lbm and the specific enthalpy of the steam is 1193 btu/lbm. Clearly the steam contains a great deal more energy than the CO2 vapor.

Peter, what sort of useful work do you propose can be done with saturated CO2 vapor at 50C? I say it depends on what sort of heat sink one has available. Perhaps NASA showed interest in this working fluid for use in outer space that has access to a heat sink at extremely low temperatures. Under those conditions a heat engine could show an appreciable pressure differential with CO2 as the working fluid and limited to 50C, and it could generate work with an engine at high energy density. I speculate, but perhaps CO2 might make a useful working fluid for a heat engine operated in outer space. However, here on Earth and limited to 50C, I don't suppose it's going to be terribly useful for this purpose. Peter, respectfully, please try to stay tethered to Earth in your considerations, and in particular, when offering advise to others.

 
Len Ovens
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Thank you. I understand the theory quite well, but that gives much of the practical information I lack.


Brake tubing will work and has been used before in some projects. Steel tubing of all sizes can be had cheaply. You need a check valve (i.e. "ball valve" as you mentioned) on the pump discharge to prevent back flow. The simplest pump for this application is a small plunger or small piston pump (see Hypro brand). You could make this also fairly simply... you need a sealed plunger that reciprocates in the end of a small tube or pipe section with check valves at the end (one to take in water from the collection tank, and one to expel water to the steam generator), and this can be driven by the engine shaft. There are small check valves with compression fittings designed for use with small tubing. The pressure will vary slightly as the pump operates, but the volume of the steam generator and action of the expander (i.e. engine) will keep pressure within a narrow range. You may also require a bypass valve on the pump to set steam generator pressure - generally a relief valve is used, but a small needle valve might serve as a means to set the desired pressure. This can be useful to prevent flooding the steam generator coil. I think you'll find that the most difficult part of this prospect will be feeding water to the steam generator coil at the proper rate. A solution can be had in using a larger steam generator coil and keeping a tight system and low water mass so that most of the water in the system is stored in the coil at all times. Also, a long steam generator coil positioned for good heat transfer can serve to heat excessive water pumped into the coil so that the pressure rises above the limit set by the relief valve on the pump discharge - this will send excess water back to the pump suction and limit the feed rate - a hot furnace operating at a controlled rate will then superheat the steam that is now set at a constant pressure by the relief valve on the pump discharge. This could work well as long as the engine were set for a constant rate and the furnace output were constant. Things get difficult when one desires a highly variable load, and I don't want to even consider it even though I know what's required.

Yes check valve was the word I was looking for I had thought a variable stroke pump might work well as an injection pump, run off of a cam (simple eccentric) rather than a crank. The cylinder body could be moved to adjust the water flow and could be manually pumped to prime the steam generator, or moved to an off position. A spring would provide the pump suction. The load should be constant as you say. Changes in speed or load would need to be manually supervised. I am thinking a capacitor buffer to provide motor start peaks and such. With a continuous run application a battery bank could be dispensed with.


Do not consider a steam turbine for micro scale applications. Very small steam turbines require ridiculously high speeds to see any appreciable efficiency, and even then they won't meet the efficiency of a good piston steam engine. There is also the problem of having to gear down the high speed provided by a turbine. A piston engine is the only way to go for micro scale (meaning less than 10 hp).

Good, I don't think I am up to designing/building/working on turbines


Good thinking - a hydraulic cylinder will work and has in fact been done before. However, the seals in the hydraulic cylinder are not useful for the project and would have to be replaced. Other projects have converted piston air compressors successfully. Generally, converting a gas engine to a steam engine will not result in a good system because internal combustion engines are designed to radiate heat for cooling, and the steam engine must be highly insulated for good results. It can be done, but select a design that can be properly modified (see White Cliffs steam engine for the best example of an engine conversion I've seen: http://www.rossen.ch/solar/wcengine.html).

I think if I had a lister(oid) I would use it as is. The amount of work to convert seems as high as a new build and the control and starting seems less than reliable in the long run. Also, lubrication seems more involved. It is certainly not simple.

The hydraulic cylinder seems more promising. I do not have a machine shop beyond a good drill press, so the more expensive off the shelf parts method is for me... though I would be quite happy to acquire a lathe and a mill. (a mill would be a learning experience in itself though as my machining experience did not progress that far)


Personally, I think there is promise in converting a hydraulic cylinder by replacing the piston seals (normally butyl or other high temperature rubbers) with high temperature compression packing like teflon or graphite. In particular, I think the graphite packing can be used successfully, and both have been used in model steam engines with high success. I have not seen them used for larger engines that generate useful power. In my opinion, an engine that operates at a low speed could use this kind of piston sealing with high success as long as a crosshead were provided to prevent all piston side loading. Best of all, a tight system that fully contained the water and steam (condensing for reuse) and prevented all air from entering the system could get away with no oil lubrication under these conditions as there would be no metal to metal contact, just have to keep all oxygen out to prevent corrosion.


This assumes the working cylinder is vertical. It seems to me a horizontal configuration would have gravity adding to wear on one side of the seals. Could the oxygen be purged by use of another gas? Or would water itself work? I am thinking that if the system is at rest, the cylinder needs to be empty and not filled with water. Or would the air be purged from the system at startup? through the condensing setup. A water reservoir with an open top I guess. How would the cylinder be filled with a room temperature gas at shutdown?


Double acting could be done if a hydraulic cylinder were used. A single long piston valve might be used to control intake and exhaust for both ports, and the piston could be driven by a single eccentric off the engine shaft - or, poppet valves might be used with uniflow exhaust in the center of the cylinder for both pistons (actually, just a single large piston would be used - I considered this seriously once with a 4" bore hydraulic cylinder by connecting two pistons together in an 8" cylinder with a 4.5" stroke - the large 1.5" dia. piston rod was to be replaced with a much smaller rod and the cylinder end converted to a packing gland for the new piston rod - the rod was to be connected to a crosshead, and used to drive a large flywheel at low speeds on the order of 2-3 hertz - a single port in the bottom of the horizontal cylinder would have provided exhaust to the condenser). There are all kinds of possibilities... even multiple stages (compounding) can be done, and I've considered several unique configurations here.


I am thinking single stage. It seems best to start simple. I would like to do stages, furnace first, then steam generator and finally the engine. With a single stage, the steam temperature could be lower too. Though a larger piston area would be needed I would guess. It is apparent that the HP rating comes from the steam generator in pressure/flow rate and the HP rating of the engine is the maximum it can handle from the steam generator.


I tend to emphasize a continual low output at low speeds to simplify the system, extend life, and make things easy to repair and/or cheap to replace when any problems arise. This could also minimize the required energy storage (i.e. battery). Really, this is the main reason I think small scale steam can be useful - if a low speed engine can be made to operate at low power for long periods, and be reliable and easily repaired, and fueled by biomass with little processing, then this seems ideal to me. Throw in the high quality heat from the steam exhaust and it seems like a winner. The main problem beyond getting a reliable system is getting sufficiently high thermal efficiency to make the system worthwhile.


This is the one thing that makes it less appealing to me. I have less of a need for extra heat than most people. Cooking, hot water, some space heating... maybe chilling if the energy is wasted otherwise. Then there is the moving of the heat from the steam shed to the house. I guess excess heat could be dumped directly to the ground under the house, heating that mass instead of trying to make everything face south.

Still more to think about and read.
 
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Len Ovens wrote:Thank you. I understand the theory quite well, but that gives much of the practical information I lack.


You're welcome. I just came on that text recently. It took me a long while to acquire the information in that book piecemeal from other sources. That book is probably the best single reference I've come across for the basics. There are a lot of subtleties about piston steam engine systems that may surprise you. My formal education and experience as a steam plant operator has been of only limited value during my research so far.

Len Ovens wrote:Yes check valve was the word I was looking for I had thought a variable stroke pump might work well as an injection pump, run off of a cam (simple eccentric) rather than a crank. The cylinder body could be moved to adjust the water flow and could be manually pumped to prime the steam generator, or moved to an off position. A spring would provide the pump suction. The load should be constant as you say. Changes in speed or load would need to be manually supervised. I am thinking a capacitor buffer to provide motor start peaks and such. With a continuous run application a battery bank could be dispensed with.


I agree on the pump, and I considered the same. Personally, I would go with a small battery system. However, a capacitor could work... just have to keep the electrical loads more constant, and probably use a diversion load regulator (i.e. dump load) much like is used on small wind turbines to keep them loaded after the battery is fully charged. I had also considered a steam engine system designed for two outputs (low or high). This can be done, and would be a lot simpler than trying to follow a load exactly. When the capacitor or battery reaches a high charge, then the unit might switch to low power. However, if heat were the primary need and it were put to good use, then I would use a diversion regulator and just dump the electricity to a load (maybe a small a/c unit during summer months) after the battery were fully charged. Since I intend to make the most of the heat, then this my preference.

Len Ovens wrote:I think if I had a lister(oid) I would use it as is. The amount of work to convert seems as high as a new build and the control and starting seems less than reliable in the long run. Also, lubrication seems more involved. It is certainly not simple.


I agree. Note that I provided the link only as a useful reference. Besides, this size engine would be overkill for the micro scale CHP application. I wanted to emphasize in particular the bash valve system used. I think that is a good model for micro piston engines. It gets beat up pretty good, but I am convinced that a low speed engine will do well. Besides, the White Cliffs engine operated at 1500 rpm for many thousands of hours, so it can be made to work well. Also, it could be easily repaired (replaceable seat and pin, and a tungsten carbide ball would never need replacing - or rarely).

Len Ovens wrote:The hydraulic cylinder seems more promising. I do not have a machine shop beyond a good drill press, so the more expensive off the shelf parts method is for me... though I would be quite happy to acquire a lathe and a mill. (a mill would be a learning experience in itself though as my machining experience did not progress that far)


I agree, and I have considered a complete design and sourced all parts. I'll be starting a project (hopefully later this year) with a good friend who is a master fabricator and has access to all required tools. We're only doing a simple test engine primarily to test valves and seals. If that works out, then we'll continue. If not, then oh well. Actually, I don't expect to require much machining with my design - really I need a very good drill press more than anything else. If you think outside the box, then I bet you can come up with a design that requires little machining. I've done just enough testing with small biomass furnaces to know that this part will work out ok. I have not built a steam generator, so that will be an education. However, the basic principles are straightforward. I'm confident in my ability to build a low power unit. The real unknown for me is the expander. The rest is more or less academic.

Len Ovens wrote:This assumes the working cylinder is vertical. It seems to me a horizontal configuration would have gravity adding to wear on one side of the seals. Could the oxygen be purged by use of another gas? Or would water itself work? I am thinking that if the system is at rest, the cylinder needs to be empty and not filled with water. Or would the air be purged from the system at startup? through the condensing setup. A water reservoir with an open top I guess. How would the cylinder be filled with a room temperature gas at shutdown?


The design I finally considered is vertical and single-acting, but I think a horizontal would work fine. The piston can be rotated periodically to even out wear on the piston seal and these seals are flexible. A vacuum pump can be used to evacuate air, and a tight system can ensure air does not reenter. Once evacuated, then air need not reenter. Steam will displace air also for initial evacuation, and it can also be used as a periodic maintenance procedure to evacuate air that might have entered. This would be done by allowing condenser pressure to rise above atmospheric, then venting the system for a period at a low point since steam is less dense than air (this really works). The kind of system I have considered would have only two places for air to enter the system: pump rod seal, and piston rod seal (assuming positive seals elsewhere like compression fittings and sealed threaded fittings). Also, in my case I intend to operate the condenser at a positive pressure to make better use of the steam exhaust (higher temperature steam), so the system I have considered would be at a positive pressure at all points, and air entry would not occur during operation. The cylinder would never contain water except some during start up when the cool cylinder condenses some incoming steam. Uniflow exhaust ports would drain all condensate in a vertical single acting engine. I think it could work very well.

Len Ovens wrote:I am thinking single stage. It seems best to start simple. I would like to do stages, furnace first, then steam generator and finally the engine. With a single stage, the steam temperature could be lower too. Though a larger piston area would be needed I would guess. It is apparent that the HP rating comes from the steam generator in pressure/flow rate and the HP rating of the engine is the maximum it can handle from the steam generator.


I agree. I'm keeping things very simple and emphasizing the use of the steam exhaust in heating applications. Assuming I finally get a good simple engine going, then I would be interested to experiment with compounding as my particular design could be compounded easily.

There is another idea that you should like. It's possible to place an exhaust valve in the piston itself. There are various engine designs that do this. The approach I considered is to place a spring to unseat this valve when the exhaust port is uncovered. At this point there is no differential pressure across the piston, and the spring will open the valve to eliminate compression on the upstroke. This is good for a small engine to increase mean effective pressure, especially in a system like mine that will maintain high condenser pressure. I want to eliminate all valve operating gear (no cams, eccentrics, or valve rods) by using piston operated steam intake and exhaust valves. In this approach, the exhaust valve (or perhaps decompression valve is the appropriate term) is shut on the upstroke when making contact with the cylinder head, and the valve stays seated after the cylinder is pressurized.

Len Ovens wrote:This is the one thing that makes it less appealing to me. I have less of a need for extra heat than most people. Cooking, hot water, some space heating... maybe chilling if the energy is wasted otherwise. Then there is the moving of the heat from the steam shed to the house. I guess excess heat could be dumped directly to the ground under the house, heating that mass instead of trying to make everything face south.

Still more to think about and read.


In your case it seems getting high thermal efficiency in the engine is important to minimize fuel consumption. It's tough to get anything more than about 10%. Good news is that battery losses could be almost eliminated (and battery costs, of course). A micro steam engine system might be used in tandem with a PV array to further minimize fuel consumption. The steam heat might be used to dry wood quickly whenever it's used. There is also water distillation or pasteurization.
 
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This might interest some - an automotive refrigerant compressor may provide air conditioning efficiently if operated at its most efficient speed (generally around 1000 rpm for piston units) and used to supply refrigerant directly to a fan coil unit much like is done in split ductless a/c units. A combination of low output, excellent condenser cooling, using large tubing to minimize back pressure, and maintaining fairly high evaporator temperature would allow a high Coefficient of Performance of between 4 and 5 (yeah, a little speculation on the figures, but I think it's reasonable). If one compares the fuel consumption required of a micro wood gas engine system operated intermittently to power a small a/c unit and charge a battery to power the unit, then one must consider the many losses seen in the generator, compressor motor, battery, and inverter systems that are avoided in the former configuration. Even if the wood gas engine system were used to operate a compressor directly, then one would have to operate the system intermittently at high power, use much larger heat exchangers, and provide some form of thermal mass to compensate for the intermittent operation. This means lower evaporator temperatures would be required, and more difficulty in cooling the larger condenser - so the COP would be lower in this configuration. Personally, I would consider the steam system preferable for the quieter operation, less fuel processing, and the prospect of having a system simple enough to be fully serviced by the end user.

Sure, I'm speculating here and elsewhere. Still, a lot of interesting things may become possible with a micro heat engine that can operate for long periods at low output. I think steam is the best chance for an individual to pull this off successfully, but getting sufficiently high thermal efficiency would be tough. Personally, I think 10% would justify it.
 
Len Ovens
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Marcos Buenijo wrote:This might interest some - an automotive refrigerant compressor may provide air conditioning efficiently if operated at its most efficient speed (generally around 1000 rpm for piston units) and used to supply refrigerant directly to a fan coil unit much like is done in split ductless a/c units.


The added benefit is that these units have a clutch which could be used to keep the load on the engine more constant by dropping out when more electric power is required. I have not figured out how to tell which are piston units and which are not. All of the cutaway drawings seem to show piston units though, so I would guess they are most common. I don't know if buying used from wrecked cars is a good option or not but new ones are around $200. There seems to be no difference in getting rebuilt or new price wise.
 
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Len Ovens wrote:The added benefit is that these units have a clutch which could be used to keep the load on the engine more constant by dropping out when more electric power is required. I have not figured out how to tell which are piston units and which are not. All of the cutaway drawings seem to show piston units though, so I would guess they are most common. I don't know if buying used from wrecked cars is a good option or not but new ones are around $200. There seems to be no difference in getting rebuilt or new price wise.


Check out the Sanden web site. Their products are among the most common compressors. You can see their model numbers for piston vs. scroll units.

 
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BTW, there is also the prospect of using steam to heat air for regenerating a desiccant wheel (or enthalpy wheel). This can be useful for regions that see high humidity during cool days that also require space heating. For cooling, I prefer either a vapor compression unit or an adsorption chiller that generates chilled water circulated to a fan coil unit. A unit that operates at a low and continual output would do a particularly good job at dehumidifying the air, and under these conditions the dew point need not be below 60F. So, as long as the air moving through a fan coil unit is driven below 60F, then good results can be had (assuming the output of the unit is sufficiently high for the space being cooled). An average evaporator (or chilled water) temperature of about 50F should work.

http://www.dpcalc.org/ In my personal experience, I am comfortable at 75-80F and 50-60% relative humidity. This corresponds to a dew point of 60F. Where I work the conditions are kept at around 40-50% relative humidity and 70-72F, and I often wear a jacket.
 
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I paper I came across entitled "The Regeneration of Silica Gel Desiccant by Air from a Solar Heater with a Compound Parabolic Concentrator" had some promising results. Apparently, good results were had in regenerating silica gel with air heated to as low at 125F. I considered that the steam exhausted from a micro steam steam might be used for this purpose if there were not other uses. Silica gel can be used as a desiccant to dry air and reduce the latent heat load on a vapor compression a/c system, or dry the air in any humid environment. Desiccants can also be used to store thermal energy indirectly, and do so for long periods. If silica gel can be regenerated at such a low temperature, then this would allow a steam condenser to be used while maintaining it under an appreciable vacuum for much better efficiency in the steam system.
 
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Small scale steam could work, but getting a consistent supply of clean water is a problem. 1/4" lines will mineral up or leach away REALLY fast if your water chemistry is a little off. It is a FULL TIME job keeping a steam engine running--that is why they had engineers.

I almost ordered a powerpallet from All Power Labs. The reason I didn't get a gasifier was the fuel prep. I think the APL unit was close enough to what I needed (it is even better now) but the time/money I would have to invest into fuel prep was the deal breaker. If you have a continuous supply of biomass that only needs shovelling into the hopper, you can generate for less than the cost of battery maintenance on a solar system. If you have to process the fuel at all, your costs climb really fast.
 
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R Scott wrote:Small scale steam could work, but getting a consistent supply of clean water is a problem. 1/4" lines will mineral up or leach away REALLY fast if your water chemistry is a little off. It is a FULL TIME job keeping a steam engine running--that is why they had engineers.


Actually, this is not true. First, the high velocity of the water and steam through a 1/4" line would prevent mineral deposits in a noncondensing system. More important, a condensing system is not difficult with a low power stationary unit, and this is what should be done. Second, in principle, there is no reason that a micro steam system cannot be devised for unattended operation for long periods. What's required is a furnace that can maintain a constant output. This is solved with gasifier furnaces. The old systems that required constant attention used large fire tube boilers that would cause massive damage if exploded, and this was the primary concern and the reason engineers were required. This is not a danger with a low power monotube steam generator.

I'm restricting my considerations to a micro piston steam engine system that operates at a constant low output. Note that I fully realize such systems are not commercially available, and I do not consider small scale steam a practical alternative for this reason. In fact, if you check the thread I started called "Practical Alternative Energy" (http://www.permies.com/t/28066/energy/Practical-Alternative-Energy), then you'll see that I did not include steam power on the list. Yet, I discuss this possibility because I understand its potential better than most. Most who look into this option restrict their considerations to very old technology that was killed for good reason. I don't consider those systems, or anything like them, to be a viable prospect.
 
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R Scott wrote:I almost ordered a powerpallet from All Power Labs. The reason I didn't get a gasifier was the fuel prep. I think the APL unit was close enough to what I needed (it is even better now) but the time/money I would have to invest into fuel prep was the deal breaker. If you have a continuous supply of biomass that only needs shovelling into the hopper, you can generate for less than the cost of battery maintenance on a solar system. If you have to process the fuel at all, your costs climb really fast.


I agree on the fuel prep problem. I also consider the Power Pallet to be too large for personal use in most settings. It really is better suited for a small community, and this seems to be the target market (electricity for small communities in remote and/or "third" world settings - most of the APL business is international for this reason). Things only get worse as the power of a gasifier engine system falls. Either the efficiency of the engine drops with decreased output, or the fuel prep problem is aggravated in having to operate an even smaller gasifier to support the efficient operation of a smaller engine. One of the reasons I think more people should take a hard (and modern) look at small scale steam is that less fuel processing is possible as compared to a wood gas engine system (at least at the micro scale). Also, I think a micro steam engine system (properly upgraded) would be superior for stationary heating applications.

Here is one product under development that can help to make more clear some of the benefits of small scale steam: http://www.youtube.com/watch?v=FP8j4e3PzLs . This system is rated at 5 KW electrical. Personally, I would like to see something smaller, and I understand the company is working on a 2 KW model. I think a modest off grid home can do well with a 1 KW system (or even 1/2 KW) if optimized for continual operation at low speeds for long periods, especially if electricity production were augmented with photovoltaics. Also, this is a prototype unit. There remains a lot of work to fully contain the steam system, insulate the components, and enclose the system. The main problem is not so much the engineering, but the capital investment necessary to mass produce units and get the unit cost down. It's particularly difficult when a widespread ignorance of steam power prevails (prospective investors get scared at the word "steam"). I don't blame anyone for this. After all, it's been dead for a long time - it's a lost art, and modern steam engine principles were never adopted in commercial systems. This particular system is a high compression, double acting, uniflow system that should see a thermal efficiency from 10 to 15 percent in final form and with condenser vacuum. I think steam pressure is on the order of 300 psi for this system. Note that it's the nature of this design that efficiency is optimal at a fairly low part load, yet the efficiency does not fall significantly at higher outputs. This is significant since gensets (especially gas engines) get very inefficient at part load operation.
 
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This is a very good site for learning about steam power: www.kimmelsteam.com

 
Len Ovens
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Marcos Buenijo wrote:This is a very good site for learning about steam power: www.kimmelsteam.com



Hmm, not many working things there. Well I shouldn't say that, I guess I haven't read it all, but I did spend some time looking at things and was impressed more by things that failed than things that worked. I do have a pretty good understanding as to why a rocket heater may not be a good thing to use as it heats from the bottom to top. Also, it seems that steam generators need to be heated up slowly by turning the furnace off and on till the steam starts to build. It also seems that the heat needs to be quickly adjustable for other reasons. It does show the steam tube generators fail much more safely than boilers. It talks about how heat changes things... like stiff steel coils that become somewhat rubbery.

The thing to note is that of course his interest seems to be in higher power engines for cars and so the steam generators have to be bigger and more complex to fit in a small space. The steam generator I was looking at had three coils and a pump. A preheat coil (economizer), a primary low pressure steam generator and a high pressure final coil. I found it interesting that this final coil was not the closest one to the flame. It seems that it is very easy to end up with a dry final during startup in which case the tubing can melt.

Anyway, some good reading and lots more reading to do too.

-------------------------------8<-------------------------------

Thinking some more about a small steam genny using gasification furnace. I am assuming the use of a 12v (AKA 15v) Alternator with reasonable pulleys to get the right speed or one rewound for slower speed. Or would you use a permanent rare earth magnet generator? (lots of broken microwave ovens out there) Or the generator from a genset?

It seems to me even a gasifier would need some attention. How often would you see needing to "feed the fire". I would think twice a day would be pretty much the max to make it worthwhile for continuous running. How much unattended running could it do? How easy would it be to make sure it shut down gracefully? (In the case of fuel or water running out)

Buying pellets doesn't make sense (easy auto feed) nor does making pellets or some other easy to feed wood chips. Really I want to start with wood in the same way as a stove. (18inch long by 3 to 6 inch diam.)
 
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Len, yes, the value of that site even according to Mr. Kimmel is learning about what's been done and in particular what doesn't work. Avoiding the mistakes of others is more than half the battle.

The site is definitely biased toward automotive steam to my dismay. I know a modern steam car would be awesome, but it's far beyond the means of mere mortals.

The main problem with the rocket furnace is the inability to precisely control the burn rate. Even if air were admitted at a controlled rate, then this would not guarantee combustion at a controlled rate since most of the air admitted to a rocket furnace is for secondary combustion. A genuine gasifier furnace is necessary where primary air is sharply distinguished from secondary air. A proper gasifier will consume all oxygen in the primary air to generate a combustible gas, and providing this primary air at a controlled rate will generate a combustible gas at a controlled rate. Adding sufficient secondary air to this gas for full combustion will give a furnace with a precisely controlled output.

A steam generator does not have to be heated slowly. However, this is unavoidable with a biomass furnace. Modern compact steam generators have been developed from multiple independent sources to generate pressurized steam within 5 seconds. Steam cars have been developed to start from cold and drive away within 30 seconds. Full power is achieved in under 2 minutes. It's all about the mass that must be heated and the heat transfer surface area available. Small diameter tubing provides a very high surface area/volume ratio with very high pressure ratings. A steam generator suitable for a 1 KW steam engine can be had from less than 100 feet of 1/4" steel tubing that costs about $50. The project is relatively simple when a constant low power is desired. Things get complicated with a highly variable load. Basically, with a constant low power in the stationary setting, then the engine (i.e. expander) is the primary concern... a reliable and efficient unit is desired. Everything else is relatively easy. In the automotive setting it's the steam generator and controls that is the main concern, and the expander is a close second. It's been said that Henry Ford seriously considered steam cars, but abandoned the idea because precise control of a steam generator was not possible at the time. This has since been solved, but it's a non-issue with a constant low power of a simple stationary unit.

The steam engine system I have considered more than any other is a single acting, single cylinder, bash valve uniflow engine with a sealed piston rod to contain the steam exhaust. The steam is fully condensed and all water is contained. It would be a direct drive single crank with large flywheel coupled to the shaft of a fairly low speed permanent magnet alternator for direct battery charging using a large bridge rectifier. Rated power is only one hp. I am personally interested in operating a system without oil lubrication. If I can do this with sufficiently high efficiency and with the piston and rod seals lasting at least 1000 hours, then I would consider it a success provided the seals are inexpensive and easily replaced. I selected the Windtura 750 PMA (http://www.windynation.com) for its high current rating, high efficiency, and low speed (575 watts at 500 rpm for 24 volt system). It's a fairly large PMA with a particularly massive copper stator.

The gasifier I have considered is an updraft design. I won't consider pellets or even chips for my final version. I'm interested in small wood splits, wood chunks, and stick wood. The principle behind any gasifier stove (updraft type - the downdraft types include reduction reactions) is to contain wood in a highly insulated space where temperature is elevated. This drives the pyrolysis of the wood. The pyrolysis gases are then combusted outside this space. The source of the heat is the combustion of the oxygen in the primary air supplied to the system. Generally, this is admitted to the bottom of a grate. The incoming primary air and water vapor in the air reacts with the charcoal primarily to generate CO and H2 (particularly CO), and some air may combust pyrolysis gas as well. The heat released by this process is what raises the temperature in the hearth region, and excellent insulation like refractory is necessary for good results. Wood breaks down at temperatures approaching 500F (remember the book Fahrenheit 451?) to release combustible gases (called pyrolysis gases). The combination of CO, H2, and pyrolysis gases (including tar vapors and more CO and H2) is kept hot and mixed with secondary air (preferably preheated air) for full combustion. My system shunts the combustible gases over to a combustion chamber connected to the side of the hearth. With this in mind, it's clear that one need only feed fuel into a hearth to keep generating the gas. So, I just put a fuel hopper on top of the hearth that is sealed at the top to prevent gases from escaping - that way, all gases move into the combustion chamber. Eventually, ash would have to be cleaned out, but this is not often with typical wood sources. Also, with air admitted to the system via a shallow ash pan contained in the refractory, then any charcoal that happened to fall through the grate would be consumed by the primary air. There would be only ash remaining. The size of the wood used must be small enough to present enough surface area in the high temperature environment to pyrolyse at the required rate. With a 1 hp engine, then conventional small wood splits will work, but the shape is important to ensure is feeds down into the hearth. Insulation at the hearth is critical, and so is secondary preheating. My system heats secondary air using the flue pipe, and the secondary air is pulled through by draft. Primary air is forced with a small blower fan with variable speed.

As for the steam engine expander, I highly recommend sticking to the bash valve uniflow model. You can find a lot of such projects on YouTube and similar sites, and all of them are junk that I've seen. If you experiment along these lines, then I recommend you try using a ball bearing to seal a single port in the cylinder head and use a hardened pin installed on the piston face to tap the ball open on the order of a millimeter to let in a charge of high pressure steam. The White Cliffs engine is the best example of which I am aware, but others have done it... in fact, I believe the engineers on the White Cliffs project got the idea from Karl Peterson (friend of Tom Kimmel) at the Steam Automobile Club of America (SACA) who built a steam car based on those principles back in the 1970's. Get a really hard ball for the project and hardened pin. I recommend tungsten carbide for the ball and tool steel for the pin. A more sophisticated steam car project used a fairly large valve in the cylinder head that used a combination of cylinder recompression and a pin to tap the valve open about 50 thousands of an inch to let in steam, and that engine was capable of 5000 rpm and 100+ hp. I think the simple ball is the way to go for a low power and low speed engine, but know that a lot of sophisticated projects have been done along these lines.
 
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Len Ovens wrote:It seems to me even a gasifier would need some attention. How often would you see needing to "feed the fire". I would think twice a day would be pretty much the max to make it worthwhile for continuous running. How much unattended running could it do? How easy would it be to make sure it shut down gracefully? (In the case of fuel or water running out)

Buying pellets doesn't make sense (easy auto feed) nor does making pellets or some other easy to feed wood chips. Really I want to start with wood in the same way as a stove. (18inch long by 3 to 6 inch diam.)


Somewhere in the Kimmel steam site you'll find a very crude steam car built by Mr. Kimmel. He fuels the system with fairly large pieces of wood (large wood splits, and even unsplit logs). He's got a long fire box of refractory about 1.5" thick it seems. The wood is shoved in one end on top of iron pipes that serve as the grate. A blower fan admits air into the pipes that are provided with small holes along their lengths for air. I don't recall any provision for secondary air, but I bet it's there. A steam generator is used of a very unusual design. I don't think the vehicle is practical, but I'm sure it's a lot of fun. I do wish to note that if Mr. Kimmel can run even a crude steam car with that kind of furnace and fuel source, then a stationary unit can be had using the same fuel source (rough cut firewood). It's all about insulation, using dry wood, and controlling primary air. Also consider the Uniflow Power unit that uses rough cut firewood and monotube steam generator to power a constant speed genset up to 5 KW (a side issue, but that particular design happens to show peak efficiency at a fairly low part load which is where gensets tend to spend most of their time). I expect a stationary unit would be fed twice daily much like gasifier furnaces used in hydronic heating. I believe strongly that a system can be devised for unattended operation, especially a system that is set to operate at a constant rate. The parameters that should be monitored and/or controlled include steam generator pressure (might be done by using a gage on the feed water side), steam temperature (a probe on the steam line leading to the cylinder head), the output of the primary blower fan. I believe the simplest system would control steam generator pressure by placing a relief valve (adjustable, preferably) on the feed pump discharge. This will limit the pressure in the steam generator during operation, and this will also set the engine speed. If more power (means more speed with a load such as a PMA or compressor) is desired, then the valve must be adjusted to a higher set point while increasing furnace output. This will reduce somewhat the feed that bypasses the pump, and admit water into the steam generator at a slightly higher rate. A combination of the two (adjusting the valve and the primary blower fan speed) will boost steam generator pressure, increase engine torque, and increase engine speed and power. Once the desired output is achieved, then the primary blower fan is tuned to set the best steam temperature. It is possible to devise a system to control the blower fan speed automatically as a function of steam temperature, and if this can be simple and effective, then I think it would be fantastic to do this. This would allow for easily adjusting engine output with the relief valve on the feed pump discharge. Note that this will work only with a system that operates at a more or less constant output. For example, the Doble steam car used pressure to control the furnace and feed water flow to control temperature, and that made sense for a highly variable system - for example, the engine could stop at any moment in a steam car, and keeping the fire on with no steam leaving the tubing would quickly lead to an overpressure condition. In the kind of system I am describing, the steam is leaving the tubing at a constant rate. Now, if the engine stalls for any reason, then there is a problem. The pressure will build and force all feed water and steam out of the relief valve on the water side. The temperature in the furnace flue will start to rise as the tubing coil heats up. The most elegant solution I've considered for this is to place a damper on the flue that will shut on high flue temperature. I suggest using a high temperature wax or similar substance that melts as the temperature rises to allow the damper to fall into place and stop the furnace. Another condition might arise where the engine load is lost and engine overspeed takes place. A simple centrifugal type shut off might be used. Use your imagination - I considered a simple spring loaded plunger on the flyweel that can be used to trip a damper held open by a cable. Stopping the furnace abruptly will stop the engine quickly for a steam generator with very little storage capacity (like 50 feet of 1/4" tubing).
 
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Marcos Buenijo wrote:A few interesting videos I came upon:
...


That gave me some info on why the bash valves work so well. It seems a very small amount of steam injected is most efficient. I expect that this achieves much of what a multi-stage engine does with much less complexity. From the Kimmel page: This one from a compressor seems to be the most likely within my current ability. One of the other pages I saw suggested that in general the the heads will last longer than the compressor parts... but I am not sure. Doesn't matter though. There does not seem to be further info than what is on that page, but the concept is so simple that I can see how to do most of it anyway. The exhaust is very simple. I am not sure why they left the rest of the fins on between the exhaust and the head, I would think insulation would make more sense. I can guess what is inside the head too.

This model here, has what must be a very good exhaust idea, but would not work on the compressor model without remaking the cylinders as well as the pistons. But I do not know that it is worth the trouble for me (and my machining abilities) to try. Maybe as a another step after getting one working first. I question the value of the solenoid keeping the intake open longer though, I see that as something useful for testing and research, but a weak link for long running.

-------------------------

The Windtura 750 PMA Looks like a good unit, for the price, it seems better than building an alternator. Both smaller and I think the DIY model would end up costing close to the same amount even without including my labour.

-------------------------

The updraft tube steam generators seem to be two coil parts, a bottom cylinder shaped coil that should have preheating water and a pancake shaped steam generator, though I have seen just the pancake part used too. When you say 50ft of 1/4in tubing, is that the preheat as well or just the pancake part?

------------------------

The explanation of how this works and why was very interesting.

 
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Len Ovens wrote:That gave me some info on why the bash valves work so well. It seems a very small amount of steam injected is most efficient. I expect that this achieves much of what a multi-stage engine does with much less complexity. From the Kimmel page: This one from a compressor seems to be the most likely within my current ability. One of the other pages I saw suggested that in general the the heads will last longer than the compressor parts... but I am not sure. Doesn't matter though. There does not seem to be further info than what is on that page, but the concept is so simple that I can see how to do most of it anyway. The exhaust is very simple. I am not sure why they left the rest of the fins on between the exhaust and the head, I would think insulation would make more sense. I can guess what is inside the head too.

The updraft tube steam generators seem to be two coil parts, a bottom cylinder shaped coil that should have preheating water and a pancake shaped steam generator, though I have seen just the pancake part used too. When you say 50ft of 1/4in tubing, is that the preheat as well or just the pancake part?


Getting high efficiency in a steam engine is all about achieving the highest possible expansion while minimizing the losses along the way. However in practice too high an expansion can drop mean effective pressure so low that diminishing returns result due to friction. Therefore, any high expansion should be used with correspondingly high steam pressure. Also, it's not possible to expand steam at very high ratios without superheating and/or reheating... so, very high expansion also means a lot of superheat should be used. Whenever steam expands, then any superheat is first used up... then some of the saturated steam will condense as it expands, and pressure starts to drop more quickly at this point. At the very least, one desires enough superheat in the steam supplied to the engine to overcome clearance volume losses or thermal losses from the cylinder or thermal losses from cylinder head cooling so that, at the very least, the steam is dry when expansion begins. There are some unavoidable clearance volume losses and cylinder head cooling in the bump valve system, but I say the simple design makes up for it.

I like the decompression valve in the piston idea, but I don't think it's worth it unless one desires to maintain a fairly high condenser pressure (might be used in the automotive setting to allow higher condenser pressure so it will condense at a higher temperature, or the stationary setting to allow for higher temperature in the steam for more efficient or a wider range of heating applications). However, if the condenser has a fairly high vacuum, then the straight uniflow model seems best.

I say a steam generator for an efficient 1 hp steam engine can be had from nothing more than 50 feet of 1/4" tubing. Place most of the tubing to pick up heat from combustion gases, and a small section is coiled above and around the fire for superheat. Add a recuperator that preheats combustion air, and it can be efficient. There is more than enough heat transfer surface area there for 1 hp, just gotta shape the coils for good heat transfer.

I am totally sold on the bump valve model with uniflow exhaust and vacuum on the condenser. I am interested in a few twists here and there, but I'm convinced the basic bump valve uniflow is the best combination of simplicity and performance. On that I say stick to a design similar in principle to the White Cliffs engine, and emphasize a very hard ball (harder than the seat), and a hard pin well mounted on the piston. All parts should be easily accessed and replaced if necessary. A spring on the ball is likely required. Also, no need to open the valve more than a millimeter or even less, and personally, I will be using low speeds with a heavy flywheel to try and emphasize longevity.
 
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Len Ovens wrote:
From the Kimmel page: This one from a compressor seems to be the most likely within my current ability. One of the other pages I saw suggested that in general the the heads will last longer than the compressor parts... but I am not sure. Doesn't matter though. There does not seem to be further info than what is on that page, but the concept is so simple that I can see how to do most of it anyway. The exhaust is very simple. I am not sure why they left the rest of the fins on between the exhaust and the head, I would think insulation would make more sense. I can guess what is inside the head too.


I agree. I came across that page recently also, and considered the same. Yeah, for best results the cylinders must be well insulated. I don't think this engine would allow for very high steam pressures or temps due to the use of a reed valve in the head, but I bet it's quite efficient with a condenser vacuum and high expansion. I did look into that compressor design and other nonlubricated (i.e. dry) type compressors, and all I came up with were very expensive. So, I considered other possibilities. HOWEVER, if anyone knows where to get such a unit (rugged oil free piston compressor at a good price and with rebuild kits), then please let me know.

Also, I believe some conventional air compressor models are very good candidates for converting to a steam engine. Single stage units should make good bump valve conversions, but I also like the prospect of converting a good two stage unit to a compounded expander. I'm convinced such a unit can last a very long time at low speed while delivering useful power with modest steam pressures. There are very rugged cast iron two stage compressors available for reasonable pricing. One would have to fashion suitable valves (some form of poppet valve seems best). Compounding would provide an opportunity to place a reheat between the two cylinders, and this could provide high efficiency even at fairly low steam pressures. There is a problem of water collecting in the crankcase, so a means to separate this water is necessary (however, excellent insulation and superheated steam with a reheat stage might minimize this). I am aware of the practice of placing a heat exchanger in the crank case heated with steam exhausted from the engine to evaporate water from the oil, and it was claimed to work well. A combination of heating oil in some way while keeping the crank case under vacuum should keep out all water. This means connecting the crankcase to a vacuum vessel that collects all steam blow by in the form of condensate - OR, the oil might be pumped to a small heated vacuum vessel for this separation to take place. I have verified that small magnetic drive impeller pumps work well under high vacuum, so these might be used - and they are very efficient (however, a small plunger pump driven by the engine seems preferable). Yeah, it's elaborate, but it might be worth it if these air compressor units were to prove super reliable as a stationary steam power plant. I haven't discounted the prospect. If it could be devised to require little more than shoving wood splits into a furnace and cleaning out ash every few days, and nothing beyond simple routine maintenance and periodic engine overhaul, then it seems interesting prospect. Oh, also, it may be possible to separate water effectively from the crank case using small centrifugal separators designed for separating cream from milk - that is also an interesting prospect.

http://www.surpluscenter.com/Air-Pneumatics/Air-Compressors-Vacuum-Pumps/Belt-Driven-Compressors/23-CFM-AIR-COMPRESSOR-TWO-STAGE-5-HP-CAST-IRON-4-1066.axd An expander this size would generate one hp at only 3 hertz with steam pressure well under 200 psig, and assuming high expansion on the order of 8 fold... this means about 50% cutoff in the first stage since the second cylinder has four times the volume of the first. Shunting the exhaust from the first stage through a long reheat in the furnace will boost temperature for higher steam quality and added work in the second stage. If the steam exhausted from the second stage remains superheated, then this superheat can be regenerated back into the system with combustion air preheating thereby boosting efficiency further. Poppet valves should be used since these do not require lubrication, and low speed will allow good results from fairly small valves. Good compound engines with condenser vacuum were known to achieve 50% Carnot efficiency, so 500F steam could show north of 15% net thermal efficiency even with steam generator losses. Throw in reheat and regeneration, and 20% seems possible with a very good system that gets aggressive with higher expansion.
 
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Marcos Buenijo wrote:
Also, I believe some conventional air compressor models are very good candidates for converting to a steam engine. Single stage units should make good bump valve conversions, but I also like the prospect of converting a good two stage unit to a compounded expander. I'm convinced such a unit can last a very long time at low speed while delivering useful power with modest steam pressures. There are very rugged cast iron two stage compressors available for reasonable pricing. One would have to fashion suitable valves (some form of poppet valve seems best). Compounding would provide an opportunity to place a reheat between the two cylinders, and this could provide high efficiency even at fairly low steam pressures. There is a problem of water collecting in the crankcase, so a means to separate this water is necessary (however, excellent insulation and superheated steam with a reheat stage might prevent this altogether). I am aware of the practice of placing a heat exchanger in the crank case heated with steam exhausted from the engine to evaporate water from the oil, and it was claimed to work well. A combination of heating oil in some way while keeping the crank case under vacuum should keep out all water. This means connecting the crankcase to a vacuum vessel that collects all steam blow by in the form of condensate - OR, the oil might be pumped to a small heated vacuum vessel for this separation to take place. I have verified that small magnetic drive impeller pumps work well under high vacuum, so these might be used - and they are very efficient. Yeah, it's elaborate, but it might be worth it if these air compressor units were to prove super reliable as a stationary steam power plant. I haven't discounted the prospect. If it could be devised to require little more than shoving wood splits into a furnace and cleaning out ash every few days, and nothing beyond simple routine maintenance and periodic engine overhaul, then it seems interesting prospect. Oh, also, it may be possible to separate water effectively from the crank case using small centrifugal separators designed for separating cream from milk - that is also an interesting prospect.

http://www.surpluscenter.com/Air-Pneumatics/Air-Compressors-Vacuum-Pumps/Belt-Driven-Compressors/23-CFM-AIR-COMPRESSOR-TWO-STAGE-5-HP-CAST-IRON-4-1066.axd An expander this size would generate one hp at only 3 hertz with steam pressure well under 200 psig, and assuming high expansion on the order of 8 fold...


It sounds overly complex at my stage of the game. My thought is that I need to have something that "turns" to play with first. First I turn it with compressed air then I make a steam gen, then I worry about collecting exhaust and oil separation etc. If I can get something that can run two speed... or two power levels, I have a 3.5kw gen... for wash days? To keep constant load when running that would require a switchable load. Then run at 1 hp with a small alternator the rest of the time. I think though, for learning, just the alternator would be best.
 
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Len Ovens wrote:It sounds overly complex at my stage of the game. My thought is that I need to have something that "turns" to play with first. First I turn it with compressed air then I make a steam gen, then I worry about collecting exhaust and oil separation etc. If I can get something that can run two speed... or two power levels, I have a 3.5kw gen... for wash days? To keep constant load when running that would require a switchable load. Then run at 1 hp with a small alternator the rest of the time. I think though, for learning, just the alternator would be best.


Oh yes, it's just food for thought. Of course, I'm thinking a totally off grid set up with a steam power plant operating almost 24/7 here. A more sophisticated system like this would not be justified for backup power. Still, I prefer the bump/bash valve configuration. Anything else I discuss is mainly for interest/education.
 
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I have been looking through the cyclone site. The main differences seem to be the water lubrication which allows much higher pressure/temperature and no oil/water mixing problems. They seem also to use a tappet valve with variable timing. Aside from efficiency, this means it self starts (with the 6 cylinder model. not so sure about the 2 in lawn mowers). The bash valve will not self start... except by accident and then there is no surety of direction.

Another thing I noticed both with the cyclone site as well as others, is that the speed is obviously not that stable. I am not sure if this is just because they always show the startup stage and the speed settles as the steam generator does or if this is an inherent problem. I would think it would be fine for motive power, but if used as rotation for AC power it could be a problem. Unless an inverter is used. I would guess that because the the steam generation is somewhat disconnected there is a delay in control. A big flywheel can only help so much. On the other hand, have you ever heard a Hammond organ being run from a gas genset? They wander quite a bit too.

Anyway, I think that because of the infancy of this old tech stuff.... there is a lot that can be done. I am realizing that steam is actually "cool" compared to IC flue gas. I could see myself making a simple crankshaft with a disk and a normal rubber seal roller bearing... Talking lower pressure than the Cyclone of course. In fact almost no real milling.
 
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Is there a way to do steam without building an engine your self?
I skimmed this thread, but every thing steam seems to require a lot of modifications or out right fabrication.
The gasifiers can be very simple, simpler still if they are charcoal gasifiers.
I know fuel processing can be prohibitively labor intensive, but adressing that seems easier than building a steam engine.
 
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Len Ovens wrote:I have been looking through the cyclone site. The main differences seem to be the water lubrication which allows much higher pressure/temperature and no oil/water mixing problems. They seem also to use a tappet valve with variable timing. Aside from efficiency, this means it self starts (with the 6 cylinder model. not so sure about the 2 in lawn mowers). The bash valve will not self start... except by accident and then there is no surety of direction.

Another thing I noticed both with the cyclone site as well as others, is that the speed is obviously not that stable. I am not sure if this is just because they always show the startup stage and the speed settles as the steam generator does or if this is an inherent problem. I would think it would be fine for motive power, but if used as rotation for AC power it could be a problem. Unless an inverter is used. I would guess that because the the steam generation is somewhat disconnected there is a delay in control. A big flywheel can only help so much. On the other hand, have you ever heard a Hammond organ being run from a gas genset? They wander quite a bit too.

Anyway, I think that because of the infancy of this old tech stuff.... there is a lot that can be done. I am realizing that steam is actually "cool" compared to IC flue gas. I could see myself making a simple crankshaft with a disk and a normal rubber seal roller bearing... Talking lower pressure than the Cyclone of course. In fact almost no real milling.


Yes, getting away from oil made it possible to use higher temperatures, and that made higher efficiencies possible. There is no reason that a steam engine cannot be controlled precisely with respect to speed. The engines can do this by controlling steam pressure to the steam intake valve (using a throttle) or by controlling the cutoff to these valves as is done in the automotive version. In fact, the reserve capacity of the steam generator or boiler allows for better speed control than internal combustion engines (all else equal like flywheel energy).

The exhaust temperature of the Cyclone engines is about 350F. I think they're getting steam generator efficiencies from 85-90%, which is amazing for such a compact and high power unit. The experimental SES steam car of the 1970's showed similar results and also used a very compact steam generator. A compact stationary steam generator for a low power engine could do better since one can be more generous with tubing, even putting a large copper preheater, use flue gases to preheat combustion air, and get really aggressive with insulation. Really, 95% efficiency is achievable under these circumstances. That's interesting when one considers that fairly simple steam engines can use steam very efficiently. When losses from the steam generator are extremely low, then the overall efficiency of the system is boosted substantially.

http://cyclonepower.com/PDF/Cyclone%20Engine%20White%20Paper.pdf This is an interesting read. I can't say I agree with everything, but there is no doubt some opinions are expressed in this paper. James Crank is retired mechanical engineer and world recognized authority on steam car technology.
 
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William Bronson wrote:Is there a way to do steam without building an engine your self?
I skimmed this thread, but every thing steam seems to require a lot of modifications or out right fabrication.
The gasifiers can be very simple, simpler still if they are charcoal gasifiers.
I know fuel processing can be prohibitively labor intensive, but adressing that seems easier than building a steam engine.


There are no turn key systems for steam power. For this reason, a wood gas engine system is the only practical alternative to convert biomass energy to shaft power/electricity. My discussion of steam power is primarily for education purposes. However, please note that education is sorely needed in small scale steam power. I believe that a modern wood fueled steam engine system can be so much better than a wood gas engine system in the micro scale combined heat and power setting that I see education into this possibility as worthwhile.

Charcoal gasifiers are particularly simple, and I've studied those as well. Unfortunately, the fuel processing is a great deal worse there and the net efficiency in shaft power generation dramatically lower due to the heat lost in charcoal production. I've discussed the possibility of harvesting this heat, but in my opinion the prospect is too work intensive for the micro scale.

I researched wood gas engine systems intensively believing there to be a way around the problems present in the micro scale setting, but I left that research convinced again that steam power is the better prospect.The 'holy grail' wood fueled system would be a slow moving engine that sustains a low power for long periods and fueled by rough cut firewood, and where the heat is put to full use whenever possible. I happen to believe that a steam engine has the best chance of pulling this off. It's possible, and therefore worth the education in my opinion.
 
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Marcos Buenijo wrote:
http://cyclonepower.com/PDF/Cyclone%20Engine%20White%20Paper.pdf This is an interesting read. I can't say I agree with everything, but there is no doubt some opinions are expressed in this paper. James Crank is retired mechanical engineer and world recognized authority on steam car technology.


Ya, I had read that. It repeats itself a lot I was just rereading some of it and think I have figured out one of the things that puzzled me... They talk about the "Schoell cycle engine" like this some new style of cycle, but then never really described what it was. I am realizing that it is still a Rankine cycle engine. It's just his name for the Cyclone way of doing the same thing. It is not fundamentally different, but incrementally different. It is still a uniflow steam expander with an intake of variable opening degrees running at higher than normal temp/pressure. It would be interesting to see that in a car, but, I think it will still need some cold weather engineering, even here, to be viable. The idea of using power to keep the water from freezing misses the mark. Vehicles may be parked away from power for an indefinite time. There may need to be a burner at the reservoir as well that can thaw the ice in reasonable time. I don't think there is another working fluid that could easily be substituted. The battery would be different because it does not need to "start" the engine. It does need to start the burner and run the car when it is not moving. Battery charging would rely on car movement with the engine connected directly to the axle. The alternator would need to be redesigned to run at much lower RPM. Not a drop-in replacement for an IC... at least not if it's full potential is to be realized.

I would love to get one of the 100hp models and put it in a car. It would be fun... better than building an electric car.

With the form factor of that engine, it would be interesting to have one engine that might be used for more than one purpose, Car, truck, tractor or generator (or boat). Have four "quick release" mounts and a hoist to lift it out. Great for a homestead. There would of course need to be power and control disconnects... Maybe only control. The unit could have a small battery for burner starting as part of it. The powered unit could have it's own gen/battery that stayed with it. So two controls... on/off and how much (edit, I forgot direction). Assuming manual controls (safer in my mind than electronic), I am sure that just setting the unit in could connect these three controls with no help from the operator.

Ya, I can dream.
 
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