Combustion – Porous – capillary – particulate or sievelike flame holder,... – Means supplying fuel for passage through the flame holding...
Patent
1993-06-28
1994-12-27
Dority, Carroll B.
Combustion
Porous, capillary, particulate or sievelike flame holder,...
Means supplying fuel for passage through the flame holding...
F23D 1412
Patent
active
053759982
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a premix gas burner with a predetermined regulation range, provided with an air feed and a gas feed, a mixing device for forming from gas and air a mixture, which may be under stoichiometric, stoichiometric or over stoichiometric and a gas pervious body with a feed side, openings to let pass the mixture and a flame side, the body having a sufficient overall heat conductivity to transfer heat to the mixture flowing through its openings in order to maintain the feed side of said body at a sufficient low temperature to prevent back firing.
Such a premix gas burner has been described in U.S. Pat. No. 3 947 233. This known burner has a gas pervious body in the shape of a burner plate of porous metal, preferably a sintered body of metal particles. The pressure of the mixture fed to the burner plate is called stated to be fairly high. The high exit velocity of the mixture causes the flame to be "free burning", which means that the flame does not contact the plate. The exit direction of the mixture is said to be random. This causes turbulence, which enhances mixing and leads to a flame which is short and stable.
This known burner has, however, some disadvantages, which the invention aims to eliminate or at least to reduce.
The first of these disadvantages is, that a plate of sintered particles is rather expensive.
The second is, that it is very difficult to manufacture a sintered plate which is so homogeneous, that nowhere a small gas stream occurs with a relatively low velocity.
The third is, that the overall heat conductivity of a body consisting of sintered particles is considerably reduced in comparison with that of a body of a solid metal. Consequently any slowly moving stream which burns in direct contact with the plate causes a hot spot. Because of the low neat conductivity of the sintered material, such a hot spot will not only be stable, but also may reach a temperature which is so high, that the metal locally is burned. This may lead to growth of the hot spot.
The fourth disadvantage is, that, due to the low heat conductivity, a hot spot will transmit only little heat to its surroundings, so that the location below it at the feed side of the pervious body may become a hot spot too, causing important temperature differences at said feed side.
A fifth disadvantage is, that high velocities of the burning mixture will lead to a flame, which is completely separated from the burner plate and due to good mixing is very hot, without loosing much heat, such as by radiation of the plate or an incomplete burned yellow flame, so that NOx forming may be considerable.
The invention aims to provide a burner of the indicated type, which eliminates or reduces the above indicated disadvantages.
Accordingly the invention provides that the pervious body is of massive solid material and that the openings are manufactured with a well defined cross-sectional shape run regularly from the feed side to the flame side, the heat conductivity of the body material and the pattern of openings being such, that even with the highest body temperatures occurring within said range the highest temperature at the feed side will be below 500.degree. C.
Because with the invention, due to the high cooling of the pervious body, very low flames are allowable, whereas the blow-off point of the flame is almost the same as with the known burners, a very large regulation range or region is possible. This range may go down to 20 Kcal/cm.sup.2 hr. With the known construction it is thought that difficulties will occur below 100 Kcal/cm.sup.2 hr.
It is remarked that with the invention the openings running regularly between both sides of the pervious body may have a constant cross-sectional shape and may be directed perpendicularly to the surfaces of the pervious body, but that some deviation, for instance tapered holes or bevelled slits are also possible. The pattern of the openings should be such that sufficient heat transfer from the flame side of the body toward the walls of the openings is present to give off sufficient heat
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