We urgently need an air pump, that still has to be developed and produced
The concept of the BrickStove is made up out of two conceptual elements.
- One is a no-cost brick stove made out of everywhere available stones or bricks masoned with mud with freedom to choose shape and finish to once personal liking. This stove should consume to a certain extend low grade fuel, such as garbage.
- Second, this stove can be made superb functional: efficient and nonpolluting by using a commercially distributed, industrially manufactured air pump with drive.
This air pump with drive is not yet on the market, so we have to describe the concept and push firms who could produce it to do so. As there is a demand for millions of these pump-units, the cost of such a unit can be low enough to become general affordable.
To trigger commercial interest, it will help a lot if the concept for this air pump is gradually refined in this Open Source Wiki environment.
Below the concept for this air pump is explained:
Also see the page 'Forced ventilation of Wood Stoves'
We expect the fire box to have a capacity of 10K Watt. This is less than normal kachelovens have, that burn their fuel in a short burst of say half an hour, while the heat produced is stored in the stone mass.
Demotech's brickstove should function in a different way; the fire should be on as long as practical, by using a fuel bin that slowly empties into the firebox. Main reason for the stove to be build from stones and mud is cost and suitability for a local initiative to build one. To use steel for this stove would also be suitable.
Tasks for this air pump
- To provide a first and secondary yet of air into the fire to gasify the wood and to burn this gas-mix. This amount of air to be pumped is small and relatively easy to calculate. Also the pressure difference is low, say 0,01 bar.
- To provide pressure to press or such the gasses from the fire through channels where it transmits all its heat up to the level where water vapor will condense.
- In this way also the condensation heat is recovered
- The condense will also contain tarry substances, thus leaving the exhaust gasses less polluted.
- To provide pressure to clean the smoke even further, by pressing it through filter beds or through fluids in which polluting component of the exhaust gasses will react or dissolve.
How this pump could be driven
The air pump that will perform above task could be conceptualized as:
- Driven electrically from the grid. This is suitable where electricity is guaranteed available at all times, as no electricity means no defense against the cold in the winter. This is similar to the conditions as accepted for high-efficient gas burning central heating units. Without electricity your house becomes an unfriendly location.
- Driven by electricity derived from thermo couples. This is a reliable converter for energy from heat into electric current. We have to find out how much electric energy is needed for driving the most suitable air pump. Only then it can become clear if the cost for the thermo couples needed can be regarded as affordable for the stove we consider.
- Driven by a Stirling engine. As there is plenty of heat available compared to the modest need for energy to pump air, the Stirling engine can be designed with a very low thermal efficiency. This Stirling engine should on the other hand be very reliable. Reliability will be enhanced when the following conditions can be met;
- Low RPM. Low RPM also has the advantage of silent running and lower tolerances in manufacturing. Low RPM asks for an air pump that also can run optimally at the same low RPM. Up-gearing of RPM does not go with this stove concept, because of cost and complexity.
- Only rotating parts, no oscillating parts. Rotary Stirling engines are described at this website. Google search with 'stirling engine principle rotating'.
How this air pump could function
Next the actual air pump has to be considered. An oscillating piston or membrane pump is less likely, because of the long service required. Better is it to consider the below two options:
- A rotating vent. for the air pressure needed for cleaning the smoke, the vent should rotate at a relative high RPM. Driven electrically this seems possible. Driven by thermo couples the amount of energy to be generated by thermo couples may be too high as too costly. Driven by a Stirling engine, the high level of RPM will be hard to realize.
- A rotating air pump such as used to charge large Diesel engines. Different from turbines driven by exhaust gasses, this pump functions according to the principle of the gear pump. A gear pump to pump gasses using two interacting gear wheels with only two teeth each is common. A gearwheel of this type has the shape of the cipher 8. Two of these 'eights' run in an oval space. This set up is engineered in a way that the rotating part do just not touch each other, nor the enveloping oval container. This type of pump could have all the specifications we desire:
- At a given low RPM it can deliver the volume of air as needed at the pressure the flow of exhaust gasses needs to cope with the resistance of the cleansing process. A higher resistance will ask for a higher torc, that the drive will have to deliver. However it will not ask for a higher RPM.
- The two axles of gear pump need to be run perfectly synchronous and therefore are coupled by good quality gears or by a time belt. This set up may go perfectly together with a set up for the Sterling engine. A rotating Stirling engine can be conceived as TWO gear pumps similar as described above. The two pumps run can run on the extension of the two axles for the air pump. The air-intake of one gear pump is connected to the air-outlet of the second gear pump and visa-versa. The two sets of gears do not run in an identical rotary position. One set of gears run a certain angle ahead of the other. Thus it is possible to mimic the compression and the expansion phase of the Sterling engine principle. The ducts through which the air circulates from one gear set to the other have to contain a device for heating or cooling of the circulating air.
As noted before, a low level of thermal efficiency is acceptable as well as to be expected from this set up. But he mechanical setup is simple and robust as it consist of only two rotating units. Each (identical) rotating unit consists out of one axle running in three gear containers in line and on each of them three two lobbed gear pump wheels are fixed.
To Demotech it seems that the above described Stirling powered air pump concept best suits the targets of the BrickStove. Even more so if the little electric current as needed for a very advanced method of governing the process of burning and air cleansing can be generated by thermal couplings.