AT CAD Team/Modular kiln   

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Schematic of the modular kiln

The modular kiln is a design concept of a kiln that can be used for a variety of tasks:

  • Smelting ore to extract metal
  • Smelting metal for casting (ie functionality as a furnace)
  • Heating limestone with clay to make cement
  • Heating lime to make quicklime or calcium oxide
  • Firing of material, such as clay, to form ceramics (pottery or bricks[1])
  • For annealing, fusing and deforming glass, or fusing metallic oxide paints to the surface of glass

[1]

Contents

[edit] Design and implecations of required functionality

A first design requirement, formed quite early into the project was a reduction in energy requirements. One of the most easy ways to accomplish this, without increasing the cost too much is by digging in the entire kiln into the soil. This idea was made after seeing the design of the kilns near www.morwellham quay [2]. The morwellham quay kilns were dug into the soil, meaning that as with earth sheltered buildings, the heat is kept insulated.

Another requirement was the precise control of temperature, which was needed due to the large range of tasks the kiln needs to comply with. Due to this requirement of precise control, the fuel to be used automatically came to electricity. This, since this source of energy is the only one that can be controlled well enough to allow the various tasks/temperature ranges.

By researching the project further, we find that there are different types of electrical furnaces that can be used for the smelting of the metal. See the wikipedia article on furnaces, section "Metallurgical furnaces" The furnaces that seemed most useful aswell as efficient were the electric induction crucible furnace and the electric induction channel furnace.

In the design, the melting furnace was placed in the middle (hottest), and the combined ladle and casting furnace was placed around it. This solution gives a high efficiency due to the fact that the heat is again well contained/insulated. Once the inner furnace has melted the metal, it is transferred to the outer furnace to keep it hot and to pour it into the moulds. Note that a plug is used in the bottom for the pouring, it is not decanted.

Note that due to cost involved of making several tunnels, rather than 1 large tunnel, the design foresees the making of 2 large tunnels, more or less shaped like a half circle, in which the automated system is placed to transport the moulds. Another advantage of the tunnels is that the heat is agin well contained, and if a ventilation system is used that is not connected to the surface, there is again additional energy saving. The downside however is that the tunnels may become so hot that it is impossible to have any personnel running around here. Hence, the entire system needs to be automated, and should be thrustworthy enough to allow it to run without human intervention/inspection. Inspection is only possible once the production of the plant has been halted, or via alternative means.

[edit] Operation of the modular kiln

Temperature range needs to be settable anywhere in between 350 to 1600°C. The firing of a material (ie clay pots, bricks, limestone, ... ) will be done by at a low temperature, and the melting of metals is done at a high temperature, in the electric induction crucible furnace.

Melting points of some common materials:

  • lead-tin (50/50 ratio) --> 183-215°C
  • cupper --> 1083°C
  • iron --> 1535 °C
  • construction steel --> 1400°C

The moulds for the casting can either be (re)made at a green sand regeneration facility, or metal moulds can be used. Another alternative is "Lost Foam" (Replicast CS or Polycast) where the molds can be afterwards burned. Green sand is mostly suitable for large plants, however the metal moulds are most suitable for medium-sized plants, and the lost foam may be suitable to small plants. Keep in mind that a green sand regeneration facility will take time and financial expenses to set up. Options are "Cold recycling with mechanical systems" (mixers, vibrating systems, impact systems, grinding mills, ...), "Cold recycling with pneumatic systems", and "Thermic recycling".[3]

[edit] Advantages/disadvantages over regular kiln/furnace design

Besides the obvious benefit that the modular kiln can double as both a furnace and a kiln, and can also be used in various tasks for the latter, there are additional advantages:

  • First off is the energy saving: one would obviously consider that this would allow for increased financial savings. However, despite that less energy is needed, we still use electricity with this design, which is still expensive; hence in regards to the economics, the modular kiln design mat not be so much better on this issue. If we look at regular kilns and furnaces (see http://www.appropedia.org/Aluminum_recovery_manual ), we see that charcoal is often used in developing countries. Note that it would have been possible to modify existing kiln designs that use charcoal so that they would have been better controllable. This would have been possible by changing the traditional kiln design. This design used a layer of coal followed by a layer of material (ie limestone, ...) and a fireplace at the bottom. This could have been changed to use several smaller ovens, and 1 long fire at the bottom instead. The several smaller ovens then would have a different temperature, and the material could be placed in the most suitable oven/shaft. As a furnace, the loading of the material would be done a bit differently, ie by inserting it at the top, similar to a cupola furnace. Additional heat could have been created by using blow holes and heat recovery. The downside of this whole concept however are that the modularity is still not quite good, the burn can easily fail (still quite bad heat control), the other disadvantages (fumes), and very poor energy efficiency. The upside would have been that the owner could have made his own fuel by means of a clamp (that is, if he had access/free use of a forest ...)

[edit] See also

[edit] References

  1. ↑ http://en.wikipedia.org/wiki/Kiln
  2. ↑ http://www.morwellham-quay.co.uk/Contact_Morwellham/index.php?pagetitle=Contactus
  3. ↑ Sand regeneration equipment
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