The radiant burner is a kind of burner which can make the combustible mixture burn violently on the surface of the burner without light-emitting flame by taking certain measures. The burner itself is in a hot state, and most of the fuel chemical energy is exchanged with the outside in the form of radiation through the wall.
Burner principle
In a radiant burner, most of the energy carried by the fuel is converted into radiant energy. The radiant heat is related to the temperature and material of the radiant surface. Radiation burner is a kind of low pressure premixed burner. When the medium on the burner surface reaches a certain temperature, it radiates infrared rays. When an object receives infrared radiation, it absorbs part of it, reflects part of it, and converts the absorbed part into the energy of the object itself, which makes the thermal movement of the object molecules more intense and achieves the heating effect.
Early research
At the beginning of this century, bone et al. Observed that the mixture of gas and air flowed out of the small holes of the fire-resistant tile and then burned violently on the surface of the tile, making the tile hot, but there was no obvious flame. Boone calls this phenomenon "surface burning", and he believes that the cause of this phenomenon is the catalysis of refractories. Later studies showed that there was no catalysis, and thermal conductivity was more important than surface activity. The mixture flow through the small hole of refractory accelerated combustion due to preheating. There is no obvious evidence of surface activity in the study of multichannel firebrick, but Coles and bagge think that the mechanism of this phenomenon is the combination of gas combustion and surface catalytic combustion according to the experimental study on porous medium burner with small aperture.
Classification of radiant burners
1. Porous medium burner
The mixture flows out of the porous ceramic plate and burns on its surface to produce a uniform radiation surface. Fig. 1 (a)
The surface temperature of the model shown is about 860 ℃, which can be higher when different materials are used. The light-emitting wall design developed from this model (Fig. 2b), most of the surface structure consists of porous refractory bricks. It uses standard porous refractory brick, and the hole is drilled to a place 50 mm away from the brick surface. The mixture from the forced air mixer enters the forced air supply chamber, reaches the back of the refractory brick, and flows out to the surface through the small hole on the refractory brick for uniform combustion. In the process of mixture preheating, refractory bricks are cooled, so only a very thin layer can reach high temperature. In this way, the heat loss on the wall can be minimized and the frequent heating and cooling of the burner structure can be reduced. The heat intensity of the burner is generally 250 kW / m2, and the maximum is 470 kW / m2. The surface temperature is generally limited to 1100 ℃. [3]
2. Burner burning in block duct
The most common is the swank burner (Fig. 1c). The mixture is fed by the atmospheric ejector and burns on the surface through a hole with a diameter of about 1.4mm, with a temperature of about 850 ℃. The radiation surface is composed of 65 × 45mm ceramic plates. When the artificial gas is used, the position of the flame root is about 1.5mm below the plate surface, and the flame surface is at the position where the flow rate and combustion rate are balanced, which is restricted by the diameter of the channel and the pre heat of the mixture. After the conversion of natural gas, the flame surface is no longer lower than the plate surface, which reduces the preheating amount of the mixture and thus intensifies the de fire tendency. The way to solve this problem is to set a metal mesh about 5mm above the block surface, which can reflect the heat back, increase the preheating of the mixture, so as to make the flame stable. [3]
3. Cup type radiation burner and flat flame burner
This type of burner is different from the previous types in that the mixture does not flow through the channel on the radiation block
The radiation surface of the utility model is a cup-shaped or cone-shaped refractory block, from which mixed gas is supplied from the center, or gas and air are respectively supplied to mix in the way of nozzle mouth. The design often includes a guide body which can stabilize the flame. It can distribute the mixture evenly on the fire-resistant surface to form a thin layer for combustion. [3]
4. Radiant tube burner
One way to replace muffle furnace (flameproof furnace) is to use internal combustion type radiant tube when the combustion products need to be separated from the heated workpiece. Because most of the heat is transmitted by radiation, it is also a kind of radiation burner.
5. Mesh burner
In low temperature application, the mesh type burner is often used to replace the porous plate type burner. A Swiss model uses a double-layer mesh, with the inner layer kept at a low temperature to prevent tempering. The surface temperature can reach above 900 ℃, but it is only used in low temperature environment to avoid overheating of burner. Figure 2 (d) shows the application of the burner in the ceiling mounted radiant heater. The utility model comprises an atmospheric Wuhuan type burner, which is used to heat a truncated cone-shaped net cover made of ceramic fiber, and the temperature can reach 1200 ℃. The temperature of the cylindrical stainless steel net cover is 850 ℃, forming a radiation surface.
6. Catalytic burner
On the surface of catalytic material, gas can burn at very low temperature (natural gas is 450 ℃) without visible flame, but it has the same heating capacity as normal high temperature combustion. In Europe, LPG catalytic heating furnace without flue is widely used in home and business, while in the Soviet Union and the United States, LPG and natural gas catalytic burners are used in non home heating occasions. There is no such combustion equipment on sale in the UK market, but Watson Research Institute is still studying its availability in heating.
In principle, the catalytic burner consists of a porous plate full of catalytic substances from which pure gas passes, and the external
——Author：ebico