The structure of the small furnace has a decisive influence on the direction and speed of the flame ejection, the mixing degree of air and gas and the length of the flame. The preheating temperature of the air and gas and the excess air coefficient determine the atmosphere of the flame and the combustion temperature of the flame, so The small furnace structure plays an important role in the heat transfer in the kiln and the glass melting process.
For furnaces that burn liquid fuels, natural gas, and coke oven gas, the structure of the small furnace is relatively simple, with only a small furnace spout and a horizontal channel. For a furnace that burns generator gas, in addition to the spout and horizontal channel, the small furnace also has a pre-combustion chamber, a small furnace tongue, an air rising channel, and a gas rising channel.
1. Spout
The spout, also called the flame outlet, is the place where flames are ejected into the kiln and where waste gas is sucked away from the kiln. When the flow rate of air (and gas) and the combustion temperature of the flame are constant, the size of the cross-sectional area of the nozzle determines the speed of the flame injection into the kiln and also affects the length of the flame. When the cross-sectional area of the nozzle is constant, the ratio of the length and height of the nozzle determines the area covered by the flame on the glass liquid surface.
A flame speed that is too large or too small is not conducive to the normal progress of the melting process. If the speed is too high, the fuel will not have time to burn completely and will extend into the opposite small furnace or even burn in the regenerator. This is not conducive to the melting of the glass in the kiln and will also easily burn out the opposite small furnace, regenerator and checker bricks. At the same time, excessive flame speed will bring the powder into the opposite small furnace, corroding the masonry of various parts of the small furnace and blocking the grid. If the flame speed is too small and the flame is fluttering and weak, it will not be conducive to heat transfer to the glass liquid and batch materials, and it will easily burn out the nozzle of the small furnace. In order to increase the flame coverage area, it is required to increase the width of the nozzle as much as possible. The cross-sectional area of the nozzle is often flat to meet the coverage area. Usually, the width of the nozzle varies according to the requirements of the temperature system in the kiln. For the melting furnace with 7 pairs of small furnaces, the widths of small furnaces 1#, 2#, and 6# are the same, the widths of the spout openings of small furnaces 3#, 4#, and 5# are slightly smaller, and the width of the spouting openings of small furnace #7 is the smallest.
The wall at the top of the spout is called the small furnace stack; the walls on both sides of the spout are called small furnace stacks (also called small furnace legs), and below are the small furnace hook bricks. Since the flame is injected into the kiln or the high-temperature gas in the kiln is discharged through the spout, flame erosion and flying material erosion cause a harsh operating environment. Therefore, all parts of the spout are constructed with ordinary cast fused zirconium corundum bricks.
The distance between the nozzle and the liquid surface is generally expected to be as small as possible, so that the flame is close to the liquid surface, which is beneficial to heat transfer. Generally, the distance between the bottom brick of the spout and the glass liquid level is 400~600mm.
2. Pre-combustion chamber
For a furnace that burns generator gas, the small furnace space from the end of the tongue to the outer edge of the spout is called a pre-combustion chamber. After the preheated air and gas enter respectively from the upper and lower sides of the tongue, they meet in front of the tongue, diffuse and collide with each other to mix, undergo a certain degree of combustion, and are sprayed into the kiln at a certain angle. In order to ensure that the gas can be completely burned in the kiln, the pre-combustion chamber plays a big role, so the length of the pre-combustion chamber (that is, the distance of mixed combustion of air and gas) also reflects the time of mixed combustion and is an important structural index.
For furnaces in which combustion is carried out on a small furnace with side, top or bottom lances, the space inside the small furnace is also called a pre-combustion chamber.
For furnaces that burn liquid fuel and natural gas through the bottom of the furnace, the space within the furnace is called the air passage.
The pre-combustion chamber (or air channel) is composed of a slope, a small furnace side wall and a small furnace bottom plate. The bottom plate of the small furnace is composed of bottom bricks, cast steel plates or orderly arranged channel steel; the lateral thrust of the slope grating is borne by the braces between the I-beam columns on both sides of the small furnace. The structure of the pre-combustion chamber is an important factor in the organization of the entire kiln flame. The brick masonry of the pre-combustion chamber is in contact with high-temperature flames, so 33# ordinary cast fused zirconium corundum bricks are used for the slopes and side walls, and 33# oxidized non-shrinkage fused zirconium corundum bricks are used for the small furnace bottom bricks. The slope vents and side walls are insulated with zirconium sealing material, high-aluminum insulation bricks and thermal insulation coatings from the inside to the outside; the bottom of the small furnace is insulated with zirconium sealing material and high-alumina bricks from the inside to the outside; there is a flat bottom below The water bag is insulated to reduce the operating environment temperature when inspecting and replacing nozzles.
3. Downward inclination angle of small furnace
For a furnace that burns furnace gas, the angle between the slope of the small furnace and the horizontal plane constitutes the downward angle of the air flow, and the angle between the bottom plate of the small furnace and the horizontal plane constitutes the upward angle of the gas flow. The upper and lower inclination angles constitute the intersection angle where the gas and air streams meet. The larger the angle between the two streams, the more intense the mixing. The distance from the end of the tongue to the outlet section of the spout is the length of the pre-combustion chamber. The longer the pre-combustion chamber, the higher the degree of mixing of gas and air. At the same time, when the air and gas flow rates and temperatures are constant, the mixing The degree is related to the cross-section ratio of the air and gas horizontal channels. The degree of mixing of gas and air in the pre-combustion chamber is also related to the gas contact area, that is, given the relative air and gas horizontal channel section ratio, the mixing degree of the streams in the flat-type pre-combustion chamber is relatively large. For flat glass furnaces that burn generator gas, the pre-combustion chamber of small furnaces usually adopts a “small intersection angle” with a protruding tongue, a stable and long flame, a small temperature difference between the fire root and the fire tip, and easy control and maintenance. Long pre-combustion chamber. The general downward inclination angle of air in a long pre-combustion chamber is 20°~26°, and the upward inclination angle of gas is 0°~5°, that is, the intersection angle of air and gas is 20°~30°.
In the structure of bottom-fired small furnaces burning liquid and natural gas, the slope down angle of the air channel is an important parameter. In order to mix the air and oil mist evenly and quickly, and to keep the flame close to the liquid surface, the downtilt angle is generally 20°~25°. The allowed upward tilt angle of the nozzle is 5°~12°. The bottom plate of the small furnace has no upward inclination angle and is generally built in a flat or stepped manner. This allows the combustion air to mix with the oil mist as quickly as possible when it enters the kiln through the small furnace door, ensuring that there is enough air near the nozzle for the gradually spreading oil mist to be separated. Burn and let the flame just skim the surface of the glass. The downtilt angle must match other conditions, such as the height-to-width ratio of the furnace, the distance between the furnace and the burner, the height of the furnace and the liquid level, etc., so as to select the most appropriate angle.
4. Small furnace horizontal passage
For furnaces using fuel oil, natural gas, and coke oven gas, the air is preheated by the regenerator, rises to the top, turns and enters the horizontal channel of the small furnace. It changes the airflow angle under the action of the slope roller and then is sprayed into the furnace through the spout. The horizontal channel of the small furnace serves as both a channel for introducing preheated air and a channel for exhausting exhaust gas.
The air rises through the regenerator to the turning point of the horizontal channel. After the flow direction changes, the air flow becomes unstable. In order to stabilize the air flow, the horizontal channel must have a certain length. The increase in length is conducive to the stability of the air flow. In addition, the lengthened horizontal passage has expanded the operating space under the small furnace, which brings greater convenience to the adjustment, assembly, disassembly and maintenance of the spray gun.
Due to the large temperature fluctuations at the corners and the erosion of the refractory materials by the airflow, 33# ordinary cast fused zirconium, which is more resistant to corrosion, is used here (the rear flat bed and stacking bricks between the regenerator and the slope wall). Corundum brick masonry.
5. Small stove tongue
“Small furnace tongue” is only for furnaces that burn generator gas. It mainly forms a horizontal channel that separates air and gas. The structure and size of the tongue is another important structural factor that affects the mixing degree of air and gas and the flame entering the kiln. The length, thickness and shape of the tongue have an impact on the length, angle, temperature distribution and erosion of the ejection port of the flame.
Length of the tongue: After other dimensions of the small stove are fixed, the longer the tongue, the closer the point where the air and gas meet is to the outlet. The horizontal flame furnace requires the flame to have sufficient length, direction and rigidity, and generally uses the tongue of zirconium corundum bricks.
Tongue thickness: When the outer dimensions of the small furnace are determined, the thickness of the tongue is related to the distance between the intersection of air and gas. It affects the mixing degree of air and gas and the flame angle. Considering the structural strength, the tongue should also have a certain thickness. If it is too thin, it will cause serious fire penetration and aggravate the burn damage. Generally, the tongue thickness is 250mm.