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rocket stove steam boiler.  RSS feed

 
richard orr
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O.K. it's been some time since last posting here.. Never the less, a 36 foot sidewheel steamboat sits outside my door, 85% done and waiting for life. The second generation shop is going being built, probably be up and running in about two more months. Then the rocket stove monotube boiler begins. I haven't done enough research ...never enough I suppose and yet I have a definate idea about what I'm going to do... Screw it, it's go time!. Where ignorance resides, I will simply make an adjustable everything. The deviation from rocket stove design is that I will be using a modified type of riser. It will be elongated ...(rectangular) rather then tubeular. The reason for this rout is that I will be using off the shelf, screw-together piping in a hairpin configuration. I will be using extreemly low pressure steam and supplying a large 12" x 11" double acting steam engine. Not effecient, but durable and easy on gaskets and packing...what ever. More about that later.
Pipes will be arranged on top of and outside of the riser and dump into an outside circulation drum. Don't expect anything solid for the next two but then, .....stay tuned.
 
Gerrit Jan Brethouwer
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richard orr wrote: O.K. it's been some time since last posting here.. Never the less, a 36 foot sidewheel steamboat sits outside my door, 85% done and waiting for life. The second generation shop is going being built, probably be up and running in about two more months. Then the rocket stove monotube boiler begins. I haven't done enough research ...never enough I suppose and yet I have a definate idea about what I'm going to do... Screw it, it's go time!. Where ignorance resides, I will simply make an adjustable everything. The deviation from rocket stove design is that I will be using a modified type of riser. It will be elongated ...(rectangular) rather then tubeular. The reason for this rout is that I will be using off the shelf, screw-together piping in a hairpin configuration. I will be using extreemly low pressure steam and supplying a large 12" x 11" double acting steam engine. Not effecient, but durable and easy on gaskets and packing...what ever. More about that later.
Pipes will be arranged on top of and outside of the riser and dump into an outside circulation drum. Don't expect anything solid for the next two but then, .....stay tuned.


Please keep us posted.
At the moment I am studying possibilities for a power + heat generator.
I would be interested in a small steam engine boiler that can be heated with a rocket stove mass heater.
 
Marcos Buenijo
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http://www.douglas-self.com/MUSEUM/LOCOLOCO/soda/soda.htm

The link describes a means to generate steam with sodium hydroxide and other highly hygroscopic salts like calcium chloride. It may be possible to regenerate the solution while the system operates an engine thereby allowing a small furnace operating at a continual output to fuel a steam engine over a wide power range. It might operate much like a large fire tube boiler with a lot of reserve capacity. This seems to be ideal for your application, especially since you desire to use a monotube steam generator. In this case the vessel containing the salt solution is not pressurized.

 
Marcos Buenijo
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On another note, Richard, have you considered scrapping the steam engine idea and going with a wood gas engine system? I understand completely the allure of a steam engine, especially a steam boat. However, if the primary reason for the steam engine system here is to use biomass (primarily wood) to fuel the boat, then a wood gas engine system will be a great deal more efficient, and most likely a great deal less expensive. I expect the fuel to require more processing for the wood gasifier, but being able to reduce fuel consumption by a factor of 4 or 5 should more than compensate.
 
Marcos Buenijo
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I'm posting another description on the use of hygroscopic salts for steam generation. This may have some potential in this application, and I'm mildly curious that perhaps it's not fully understood by the readers (which would explain the lack of replies).

PROBLEM: A steam engine in this steam boat application will require the ability to vary the output over a wide range. If the steam generator does not have a good reserve capacity, then it will be necessary to vary the furnace output over a wide range and to precisely match the output with engine demands. This would be very difficult with the combination of monotube steam generator and rocket furnace.

TRADITIONAL SOLUTION: A large fire tube boiler would solve the problem. This approach would store saturated water and steam in the pressure vessel, and the furnace output does not require precise control, and it can operate at a much lower average rate while providing the ability to operate the engine at a high rate for limited time - and this would be a lot simpler. Unfortunately, a large fire tube boiler is an expensive and potentially dangerous system that requires regular maintenance.

PROPOSED SOLUTION: The use of a hygroscopic salt to generate steam provides the reserve capacity of a fire tube boiler with the simplicity and safety of a monotube boiler. It also allows for the use of copper tubing in the steam generator which is easy to work with and provides superior heat transfer characteristics. Also, the temperatures achieved by the solution will never rise beyond the limits of the copper boiler, so there is an inherent safety factor. There is no pressure vessel other than small diameter copper tubing to carry the steam. Note that since the solution system is not pressurized and the temperatures are limited to the boiling point of the solution, then copper could be used to heat the solution.

BASIC CONFIGURATION AND OPERATION: There are many ways to configure such a system. I suggest setting up a furnace to heat the salt solution in a thermosiphon that transfers the solution to an insulated vessel containing the steam generator tubing coil. The temperature of the solution is proportional to the concentration, and this temperature is used to determine the conditions of the system. Pressure in the solution system will never rise above ambient as it would be vented at all times. This vent emits superheated steam at atmospheric pressure at the same temperature as the solution. This heat should be regenerated into the system by using the superheated steam to preheat feed water just before it enters the copper tubing. This will also eliminate thermal shock in the boiler tubing while increasing efficiency.

The system is operated by sending the steam exhaust from the engine into the base of the insulated solution vessel where it bubbles up through the solution and is absorbed by the solution to generate heat. The copper tubing coil in the solution carries the feed water that is used to produce steam. The flow path is as follows: water storage tank => feed pump => inside of feed water preheater => steam generator tubing coil => engine => base of solution vessel => vented from the solution vessel in the form of superheated steam at atmospheric pressure => outside of feed water preheater => condenser => water storage tank. All the while the furnace operates at a more or less constant rate equal to the overall average engine output to heat the solution heat exchanger that is adjacent to the insulation solution vessel that contains the steam generator coil. The system can actually be quite efficient for a low pressure steam engine, particularly if a large air preheater (recuperator) is added to the furnace exhaust to heat combustion air. NOTE: The solution is partially vaporized when heated, and this will provide excellent thermosiphon since the density of the solution is very low under this condition. This causes the solution surrounding the steam generator coil to be at a much higher density than the partially vaporized solution in the heater coil, and the more dense solution flows quickly into the heater coil (similar to a coffee percolator). The feed water is provided to the copper tubing coil at the bottom since the solution flows from top to bottom and is hotter at the top (counterflow heat exchange), and this provides a head of steam at the top of the coil.

A PROBLEM TO FIX: When cold, the solution is likely to crystallize, and this will make start up a problem. A way around this can be as simple as providing a small steel coil in the furnace that can be filled with water and capped. A line near the top of coil extends to the steam engine exhaust header which in turn leads to the line that provides steam to the solution. So, when first starting up the water that is added to the coil will flash to steam in the furnace, and this will penetrate the solution to heat and liquify it. The system is sized so that by the time the water in this system is fully vaporized, then all the solution is liquid, and flow is normal. At this point you have steam to start warming up the engine.
 
J.D. Ray
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I'm interested in your progress because of an interest in developing an external-combustion CHP system. The most straightforward implementation, and the most known and reliable technology, seems to be using steam to convert thermal to mechanical energy, then the mechanical to electric. Waste heat would be captured and distributed to home heating.
 
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