HIGH TEMPERATURE SURFACE COMBUSTION BURNER

Abstract: A high temperature surface combustion burner, com­ prises a burner head having an air fuel mixed gas supply inlet, a burner plate secured to said burner head, wherein the burner plate is made of a ceramic porous body having more than 30% by volume of pores of 25 to 500 µ in mean pore diameter; and a plurality of throughholes having 0.05 to 5.0 mm in diameter and provided in said burner plate at intervais of 2 to 30 mm and substantially vertically extending with respect to the combustion surface. Another surface combustion burner comprises a burner head having an air fuel mixed gas supply inlet, a burner element secured to said burner head, said burner element consisting of a ceramic porous body having pores sufficient­ ly communicated from inside to outside for diffusing an air fuel mixed gas, wherein said ceramic porous body has 75 to 95% by volume in total of communicated pores of 0.5 to 5.0 mm in mean pore diameter; and a plurality of throughholes each having hydraulic diameter of 0.05-5.0 mm and sub­ stantially vertically extending with respect to the combustion surface and provided in said burner element at intervals of 2 to 30 mm.

Description: This invention relates to a high temperature surface combustion burner having in use a relatively uniform surface combustion temperature and strong thermal shock resistance for use for industrial furnaces and the like. This invention further relates to a surface combustion burner having a wide combustion range and excellent durability. Hitherto, as surface combustion burners, use has widely been made of a non-permeable ceramic plate provided with a number of throughholes, but said burner cannot be used in the field where uniform heating is required on the surface of ceramic plate, because the combustion only takes place at the outlets of a throughhole. Thus, the surface temperature of intermediate portions between throughholes is low, and it has further such shortcomings that the ceramic plate is liable to break by a thermal shock at the time of igniting the burner, that it takes time to bring the surface of the ceramic plate after ignition to the red hot condition, and that since thermal conductivity of the ceramic plate is high, when the surface combustion temperature is raised to more than 900° C, the temperature in the vicinity of throughholes on the rear of the ceramic plate is raised to ignite fuel gas and to incur the danger of back firing, so that although the desirable surface temperature is more than 900° C in order to improve radiation efficiency, it has to be kept below that. Alternatively, a high surface temperature could be provided with greater injection speed. However, if the injection speed of a mixed gas is increased a blow-off phenomenon is liable to occur. Japanese patent Laid-open No. 56-130,524, shows a surface combustion burner for burning fuel gas with a surface of a metal fiber or ceramic fiber. It has a porous film like body over a shaping body, so that combustion occurs over its surface. This surface combustion burner is advantageous in having a short rising time from ignition to the red heat condition and easy processing but, it is not good at giving large radiation efficiency by raising the surface temperature owing to poor corrosion resistance at high temperature. On the other hand, as shown in Japanese Utility Model Laid-open No. 60-6,933, a surface combustion burner with the use of a ceramic porous body having permeability has been known, which has less problem of back firing due to small thermal conductivity. A mixing and diffusing chamber is behind the permeable body. Gas is introduced into air at an inlet to such chamber. This burner has the disadvantage that soot and dust in combustion air clog it on operation for a long time to lower permeability. Pressure loss rises, and combustion becomes non-uniform. Particularly when using fuel such as coke oven gas containing more than 5 mg/Nm³ of soot and dust in fuel gas, LD gas, blast furnace gas, coal gasification gas and the like, the burner plate is clogged by soot and dust during combustion, so that this burner disadvantageously has durability of only several hundred hours. The prior art also includes Japanese Patent Laid-open No. 55-25773 which employs a film of high conductivity on the surface of a honeycomb ceramic, so as a generate ultraviolet radiation. An object of the present invention is to reduce the above-described shortcomings of the prior art surface combustion burners. According to the present invention there is provided a surface combustion burner, comprising a burner head having an air-fuel mixed gas supply inlet, a burner plate secured to said burner head and spaced from said gas supply inlet, said burner plate consisting of a ceramic porous body having an inlet side and an outlet combustion side, the pores in said plate communicating said inlet side with said outlet side for passing an air-fuel mixed gas therethrough, characterised in that said ceramic porous body is more than 30% by volume pores of 25 to 500 µmin mean pore diameter and has a plurality of throughholes through the burner plate for passing said air-fuel mixed gas, each throughhole having a hydraulic diameter of 0.05-5.0 mm and extending substantially vertically with respect to the outlet combustion side of the ceramic porous body and provided throughout said burner plate at intervals of 2 to 30 mm, the combination of pores and throughholes being such that combustion occurs both at the outlets of the throughholes and at the surface of the porous body intermediate the throughholes. With the invention, or preferred embodiments thereof, there is provided a high temperature surface combustion burner which can make a surface temperature uniformly high such as more than 900°C, is durable against a high thermal shock, and reaches red heat immediately after ignition. The burner can stably continue the combustion within a wide load range without causing any blow-off or back fire, and also continue the combustion for a period of time without clogging. Preferably, the ceramic porous body contains 2 to 50 % by weight of a heat resisting in organic fibre, which may be a ceramic fibre. In some embodiments the porous body may contain 75 % to 95 % pores by volume. The invention will now be described by way of example with reference to the accompanying drawings, wherein: Fig. 1 is a cross-sectional view showing a first embodiment of the invention; Fig. 2 is a cross-sectional view showing a second embodiment of the invention; and In the drawings, 1 is a burner head, 2 is an air fuel mixed gas supply inlet, 3 is a burner plate, 4 indicates throughholes, 5 is a burner element, 6 is a porous ceramic body, 7 is a throughhole. In the first embodiment shown in Fig. 1, 1 is a burner head provided with an air fuel mixed gas supply inlet 2, and 3 is a burner plate fixed to an opening of the burner head 1. The burner plate 3 is made by a ceramic porous body such as Aℓ₂O₃ group, ZrO₂ group, feldspar group and the like having more than 30 % by volume of pores of 25 to 500 µm in mean pore diameter provided with a number of throughholes 4 having a hydraulic diameter of 0.05 to 5.0 mm at intervals of 2 to 30 mm, which, for example, can be obtained by mixing these ceramic powders with glaze and an inorganic binder, molding the mixture, firing and sintering the molded article at a temperature of more than 1,000°C. Further, if 2 to 50% by weight of a heat-resisting inorganic fiber such as SiO₂-Aℓ₂O₃ ceramic fiber, Aℓ₂O₃ ceramic fiber and the like is added to the raw material, the strength of the ceramic porous body is improved and the thermal shock resistance becomes excellent. The reason why the mean pore diameter of the ceramic porous body is limited to 25 to 500 µ is because less than 25 µm causes great pressure drop of fuel gas passed through the ceramic porous body and more than 500 µ lowers their strength. The reason why the ratio of the pore occupied in the ceramic porous body is more than 30% by volume is because less than 30% by volume makes the thermal conductivity large so as to incur the danger of back fire in the same manner as in the prior Schwank burner. The method of providing throughholes 4 in the ceramic porous body may be attained by molding with a mold at the time of molding or by providing with intervals by a drill after molding. The reason why the hydraulic diameter of the throughhole 4 is made 0.05 to 5.0 mm is because less than 0.05 mm can hardly generate main combustion at the throughhole portion and the combustion becomes incomplete, and more than 5.0 mm generates a blow through phenomenon of combustion flames and the combustion becomes non-uniform. The reason why the interval of the throughhole 4 is made 2 to 30 mm is because less than 2 mm lowers the strength of the burner plane and more than 30 mm cannot make surface temperature uniform. Further, less than 2% of the heat-resisting inorganic fiber is insufficient in addition effect and more than 50% thereof lowers strength, so that the range of 2 to 50% is preferable. In the second embodiment shown in Fig. 2, the burner plate 3 is a convexly curved plate and the same as the first embodiment shown in Fig. 1, except that a combustion area is increased and the high intensity combustion is obtained and that the heat transfer direction of a heat amount generated is different. The drawing does not show a concavely curved burner plate 3, but the same is applied to such plate. In the thus constructed burner, when the fuel gas is supplied to the inside of a burner head 1, the fuel gas is passed through and combusted on the surface of a burner plate 3 through a number of throughholes 4 having a hydraulic diameter of 0.05 to 5.0 mm, preferably 0.5 to 2.0 mm, provided in the burner plate 3 at intervals in the same manner as in the prior Schwank burner, but the burner plate 3 of the present invention is a ceramic porous body having more than 30% by volume of pores of 25 to 500 µ in mean pore diameter, so that the fuel gas exudes and combusts even at the intermediate portion of the throughhole 4 through these pores, and a uniform surface temperature can be obtained. Further, the burner plate 3 of the present invention is porous and has small inner thermal conductivity, so that there is no possibility of back firing, even if the surface temperature is raised to 900 to 1,200°C, and as a result, the stable combustion can be obtained by making the surface combustion intensity large and the surface of the burner plate 3 can be made red heat immediately after ignition. In order to confirm the properties of the high temperature surface combustion burner according to the invention, four kinds of high temperature surface combustion burner as shown in the following Table 1 were prepared, a propane gas fuel was combusted by the thus prepared burners together with a Schwank burner available on the market, and the surface temperature and combustion conditions were observed. The results are shown in Tables 2, 3 and 4. As shown in Tables 2, 3 and 4, the stable combustion was continued with high surface intensity combustion such as 6,000,000 cal/m²·Hr. The ignition and the extinction were repeated every 1,000 times, but no cracks were generated in the surface combustion burner of the present invention. As apparent from the above explanation, the invention comprises a ceramic porous body having more than 30% by volume of pores of 25 to 500 µ in means pore diameter and a number of throughholes each having hydraulic diameter of 0.05-5.0 mm and substantially vertically extending with respect to the combustion surface and provided in said burner plate at intervals of 2 to 30 mm, wherein the gas fuel exuded through these pores combusts even at the intermediate portion of the throughhole, so that the surface temperature is made uniform and even if the surface temperature is raised to more than 900°C, the stable combustion can be carried out without any danger of back fire. The high temperature surface combustion burner according to the invention is short in rising time from ignition to the red heat condition and excellent in thermal shock resistance, so that the invention is extremely useful in practical value as a solution of disadvantages inherent to the prior surface combustion burner.

Claims: A surface combustion burner, comprising a burner head (1) having an air-fuel mixed gas supply inlet (2), a burner plate (3) secured to said burner head and spaced from said gas supply inlet, said burner plate consisting of a ceramic porous body (3) having an inlet side and an outlet combustion side, the pores in said plate communicating said inlet side with said outlet side for passing an air-fuel mixed gas therethrough, characterised in that said ceramic porous body (3) is more than 30% by volume pores of 25 to 500 µmin mean pore diameter and has a plurality of throughholes (4) through the burner plate for passing said air-fuel mixed gas, each throughhole having a hydraulic diameter of 0.05-5.0 mm and extending substantially vertically with respect to the outlet combustion side of the ceramic porous body and provided throughout said burner plate at intervals of 2 to 30 mm, the combination of pores and throughholes being such that combustion occurs both at the outlets of the throughholes and at the surface of the porous body intermediate the throughholes. A surface combustion burner as defined in claim 1, wherein the ceramic porous body contains 2 to 50% by weight of a heat-resisting inorganic fiber. A surface combustion burner as defined in claim 2, wherein the heat-resisting inorganic fiber is a ceramic fiber. A surface combustion burner as defined in claim 1, 2 or 3, wherein the diameter of the throughholes is 0.5 to 2.0 mm. A surface combustion burner according to any preceding claim, wherein the porous body contains 75 %- to 95 % pores by volume.

Inventors: ABE, FUMIO, FUJITA, TADASHI, HASEGAWA, HIROSHI, MAEDA, MAKOTO
Applicants: NGK INSULATORS, LTD.
Application year: 1985
Main classification: F23D14
IPC codes: F23D14