The invention relates to a total primary combustion burner. More specifically, the invention relates to the total primary combustion burner which utilizes hydrogen gas as a fuel gas.
As a total primary combustion burner of the above species, the one utilizing hydrocarbon gas as the fuel gas has been known in Patent Document No. 1, for example. This burner includes a burner body with an air-fuel mixture chamber, into which a mixture of the fuel gas and primary air is supplied, and a combustion plate portion covering an opening surface, which faces the air-fuel mixture chamber, of the burner body and in which a plurality of aligned flame holes is provided. Inside the air-fuel mixture chamber, a backfire suppressing plate portion is disposed opposite the combustion plate portion with a gap. In the backfire suppressing portion, a plurality of aligned through-holes, passing through in a direction of plate thickness thereof, is provided. The air-fuel mixture supplied into the air-fuel mixture chamber passes from each of the through-holes and between the backfire suppressing plate portion and the combustion plate portion, and is then supplied into each of the flame holes. Subsequently, the air-fuel mixture ejects from each flame hole and undergoes combustion. In this case, a height of the gap is set within a range between 1 mm or more and 4 mm or less, a diameter of each through-hole ranges from 1 mm to 5 mm, and a diameter of each flame hole ranges from 0.5 mm to 3 mm. Thereby, pressure loss is suppressed as the air-fuel mixture passes through both the combustion plate portion and the backfire suppressing plate portion, suppressing backfire that flames propagate within the air-fuel mixture chamber while forming an approximately equal distributed flames across the surface of the combustion plate chamber portion.
Incidentally, hydrogen, which does not emit carbon dioxide, has recently garnered attention as an alternative to hydrocarbon gas for mitigating global warming. However, a combustion speed of an air-fuel mixture of hydrogen and primary air is extremely rapid. When the air-fuel mixture of hydrogen and primary air is combusted in the conventional total primary combustion burner mentioned above, the combustion occurs near the surface of the combustion plate portion, making the combustion plate portion to easily reach high temperatures. Furthermore, because the aforementioned gap is relatively narrow, the backfire suppressing plate portion is excessively heated by radiant heat from the combustion plate portion. Therefore, when the flames propagate within the gap in the air-fuel mixture chamber, there are instances where the flames cannot be extinguished. In addition, due to the relatively long diameter of each through-hole, the flames propagating within the gap become liable to easily extend an upstream side of the air-fuel mixture chamber through the through-hole. As a result, the backfire cannot be effectively suppressed and this may lead to burner breakage. In such a case, it may be considered that the diameter of each through-hole is set to the diameter that is so-called a backfire limit (for example, 0.6 mm). However, this would increase the pressure loss.
In the light of the aforementioned problem, the invention provides a total primary combustion burner which can suppress the backfire as much as possible while suppressing the pressure loss even when hydrogen gas is utilized as the fuel gas.
In order to solve the aforementioned problem, the invention presupposes a total primary combustion burner which includes a burner body with an air-fuel mixture chamber into which an air-fuel mixture of a fuel gas and primary air is supplied; and a combustion plate portion covering an opening surface, which faces the air-fuel mixture chamber, of the burner body, wherein a backfire suppressing plate portion is disposed opposite the combustion plate portion with a gap inside the air-fuel mixture chamber, and wherein the air-fuel mixture passing through the backfire suppressing plate portion is configured to eject from the combustion plate portion and undergoes combustion, and wherein hydrogen gas is utilized as the fuel gas. In the total primary combustion burner, the backfire suppressing plate portion has a sintered sheet formed by sintering an aggregate of metallic fibers or beads.
According to the invention, the air-fuel mixture supplied into the air-fuel mixture chamber passes through numerous micro-porosities of the sintered sheet. These micro-porosities, formed by random intertwining and combination (welding) of the metallic fibers or beads during sintering, are intricate and smaller than a hole diameter of the so-called backfire limit. Subsequently, the air-fuel mixture is supplied to the combustion plate portion. At this time, temperature rise of the sintered sheet, i.e., the backfire suppressing plate portion itself, can be suppressed by large contact areas with the air-fuel mixture at normal temperature. In addition, pressure loss can also be suppressed by the numerous micro-porosities. Furthermore, the air-fuel mixture passing through the sintered sheet of the backfire suppressing plate portion passes through the gap between the backfire suppressing plate portion and the combustion plate portion, ejects from the combustion plate portion and undergoes combustion. At this time, even if flames propagate within the gap between the combustion plate portion and the backfire suppressing plate portion, the temperature rise of the backfire suppressing plate portion is suppressed, allowing the flames to be extinguished by the backfire suppressing plate portion. Also, if the flames propagating within the gap are not extinguished and persist on a surface of the backfire suppressing plate portion facing the gap, presence of only the micro-porosities helps suppress propagation of the flames to an upstream side of the backfire suppressing plate portion. Thus, in the invention, since the backfire suppressing plate portion has the sintered sheet, even when utilizing hydrogen gas as the fuel gas, the backfire can be suppressed as much as possible while suppressing the pressure loss. Meanwhile, the metallic fibers or beads in the invention contain a semimetal as a constituent element.
In the invention, it is preferable that the metallic fibers or beads are composed of Fe (iron) and at least one element selected from the group consisting of Al (aluminum), Cr (chromium), Mn (manganese), and Si (silicon), or a carbide(s) thereof. In this case, it is preferable that weight per unit area during sintering the sintered sheet is set within a range of 1,200 g/m2 to 1,800 g/m2. If the weight per unit area is less than 1,200 g/m2, each of the micro-porosities may become excessively large, resulting in a risk that the backfire cannot be effectively suppressed. On the other hand, if the weight per unit area is more than 1,800 g/m2, passing resistance of the air-fuel mixture will increase.
In addition, in the invention, it is preferable that a temperature sensor is disposed at a portion of the air-fuel mixture chamber, which is positioned between the combustion plate portion and the backfire suppressing plate portion. Thereby, in the case where the flames propagating within the gap are not extinguished and combustion occurs on the surface of the backfire suppressing portion facing the gap, any temperature rise can be detected by the temperature sensor. This enables swift action such as halting the air-fuel mixture supply, suppressing combustion that could bring about burner damage.
Furthermore, in the invention, it is preferable that the gap between the combustion plate portion and the backfire suppressing plate portion is set within a range of 5 mm to 30 mm. If the gap is shorter than 5 mm, there may be a risk of overheating the backfire suppressing plate portion due to excessive radiant heat from the combustion plate portion. On the other hand, if the gap is longer than 30 mm, a larger amount of air-fuel mixture may accumulate within the gap between the combustion plate portion and the backfire suppressing portion. This leads to the occurrence of loud noises when flames propagate within the gap.
In addition, in the invention, it is preferable that the combustion plate portion is configured by a sintered sheet formed by sintering an aggregate of metallic fibers or beads. This allows for large contact areas with the air-fuel mixture, resulting in suppressed temperature rise of the combustion plate portion itself, which is advantageous.
Now, referring to figures, an embodiment of a total primary combustion burner CB utilizing hydrogen gas as a fuel gas will be described. This embodiment includes a backfire suppressing plate portion includes a sintered sheet made by sintering an aggregate of metallic fibers. Meanwhile, the term ‘hydrogen’ as defined by the invention is not limited to pure hydrogen, but encompasses hydrogen mixtures with small amounts of a foul-smelling agent added for flavoring purposes, for example.
As shown in
Referring also to
Referring also to
The sintered sheet 33 is made by sintering an aggregate in which metallic fibers 33a are stacked. The aggregate could be a laminate, for example. The metallic fibers are composed of Fe (iron) and at least one element selected from the group consisting of Al (aluminum), Cr (chromium), Mn (manganese), and Si (silicon), or carbide(s) thereof. For example, stainless steel, which primarily contains Fe as a main component element, may be utilized for the metallic fibers. A diameter of each metallic fiber falls in a range from 50 μm to 100 μm. Well-known methods such as hot pressing (hot press working) in which pressure molding and sintering are simultaneously performed, and HIP (Hot Isostatic Pressing), can be utilized for making the sintered sheet 33. For example, in the case of the hot pressing, although there is no specific explanation with any figure, the metallic fibers 33a are stacked or laminated and formed into an aggregate within a cavity in a die, without weaving or knitting. At this time, weight per unit area is set within a range from 1,200 g/m2 to 1,800 g/m2. Subsequently, the aggregate is pressurized from one axis direction by a punch, and then the aggregate is heated and held at a predetermined temperature through the die.
The metallic fibers 33a, made in the aforementioned manner, randomly intertwine and combine (weld) during the sintering. As a result, numerous micro-porosities 33b which are complex and smaller than a hole diameter of so-called a backfire limit are formed in the sintered sheet 33. This is partially enlarged as shown in
In the aforementioned total primary combustion burner CB, the air-fuel mixture supplied from the inlet port 14 of the burner body 1 into the air-fuel mixture chamber 11 is supplied to the combustion plate portion 2 after passing through numerous micro-porosities 33b in the sintered sheet 33. At this time, temperature rise of the sintered sheet 33, i.e., the backfire suppressing plate portion 3 itself, can be suppressed by large contact areas with the air-fuel mixture at normal temperature. In addition, pressure loss can also be suppressed by the numerous micro-porosities 33b. Furthermore, the air-fuel mixture passing through the sintered sheet 33 of the backfire suppressing plate portion 3 passes through the gap Gp between the combustion plate portion 2 and the backfire suppressing plate portion 3, ejects from the main body portion 23 of the combustion plate portion 2 and undergoes combustion (combustion without secondary air). At this time, even if flames propagate within the gap Gp between the combustion plate portion 2 and the backfire suppressing plate portion 3, the temperature rise of the backfire suppressing plate portion 3 is suppressed, allowing the flames to be extinguished by the backfire suppressing plate portion 3. Also, if the flames propagating within the gap Gp are not extinguished and persist, presence of only the micro-porosities 33b in the backfire suppressing plate portion 3 helps to suppress propagation of the flames to an upstream side of the backfire suppressing plate portion 3. Thus, in the total primary combustion burner CB, due to disposition of the backfire suppressing plate portion 3 having the sintered sheet 33, even when utilizing hydrogen gas as the fuel gas, the backfire can be suppressed as much as possible while suppressing the pressure loss.
In addition, in the total primary combustion burner CB, a temperature sensor 4 is disposed at a portion of the air-fuel mixture chamber 11, which is positioned between the combustion plate portion 2 and the backfire suppressing plate portion 3. Well-known detecting devices such as a thermocouple or a bimetal switch are utilized as the temperature sensor 4. Thereby, in the case where the flames propagating within the gap Gp are not extinguished and combustion occurs on the surface (lower surface) of the sintered sheet 33 facing the gap Gp, any temperature rise can be detected by the temperature sensor 4. This enables swift action such as halting the air-fuel mixture supply, suppressing combustion that could bring about damage of the total primary combustion burner CB.
Although the embodiment of the invention is described above, various modifications are possible as long as the modifications adhere to the technical concept of the invention. In the aforementioned embodiment, the sintered sheet 33 is configured by the sintered aggregate of the metallic fibers 33a. However, as long as numerous micro-porosities, which are complex and smaller than the hole diameter of the backfire limit, can be formed after the sintering, the sintered sheet is not restricted to the sintered sheet 33. As shown in
In addition, although, in the aforementioned embodiment, the knitted material made from the metallic fibers is described as the main body portion 23 of the combustion plate portion 2, it should be noted that the main body portion 23 is not exclusively limited to the knitted material. Instead of the knitted material, the sintered sheet 33 produced in accordance with the aforementioned manner can be utilized as the main body portion 23 of the combustion plate portion 2. Similarly, due to increase of the contact areas with the air-fuel mixture, the temperature rise of the combustion plate portion itself is suppressed, which is advantageous.
Number | Date | Country | Kind |
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2022-086442 | May 2022 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2022/042075 | 11/11/2022 | WO |