The structure of the small furnace has a decisive influence on the direction of flame ejection, speed, air-gas mixing degree and flame length. The preheating temperature of air gas and the excess air coefficient determine the atmosphere of the flame and the combustion temperature of the flame. The structure of the small furnace plays an important role in the heat transfer in the kiln and the melting process of the glass.
For melting furnaces that burn liquid fuels, natural gas, and coke oven gas, the small furnace structure is relatively simple, with only small furnace outlets and horizontal channels. For the furnace that burns producer gas, in addition to the spout and horizontal passage, the small furnace also has a pre-combustion chamber, small furnace tongue, air riser, and gas riser.
(1) Ejector
The spout is also called a fire spout (as shown in Figure 1). It is the place where flames are sprayed into the kiln and the exhaust 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 cross-sectional area of ??the spray outlet determines the speed at which the flame is sprayed 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 to the height of the nozzle determines the coverage area of ??the flame on the glass surface.
Too high or too small flame speed is not conducive to the normal progress of the melting process. If the speed is too high, the fuel will extend into the small furnace on the opposite side before it can be completely burned, and it will burn in the regenerator. This is not conducive to the melting of the glass in the kiln, and it is easy to burn the small furnace, regenerator and checker bricks on the opposite side. . At the same time, the flame speed is too high to bring the powder into the opposite small furnace, eroding the masonry of each part of the small furnace and blocking the grid. If the flame speed is too small, the flame will flutter and become weak, which is not conducive to the heat transfer to the molten glass and batch materials, and it is easy to burn the flat chute of 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 spout is often flat to meet the coverage area. Usually according to the requirements of the temperature system in the kiln, the width of the nozzle is different.
The dome at the top of the spout is called a small furnace front flat dome; the walls on both sides of the spout are called small furnace stacks (also called small furnace legs), and below are small furnace hook bricks. Because the flame sprayed into the kiln or the high-temperature gas discharged from the kiln passes through the spray outlet, flame erosion and fly material erosion cause a harsh environment for use, so all parts of the spray outlet are built with ordinary cast fused zirconium corundum bricks by oxidation method.
The distance between the spray outlet and the liquid surface is generally 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 nozzle and the liquid surface of the glass is 400~600mm.
(2) Pre-combustion chamber
For the furnace that burns producer gas, the small furnace space from the end of the tongue to the outer edge of the nozzle is called the pre-combustion chamber. The preheated air and gas enter the tongue from the upper and lower sides of the tongue, meet in front of the tongue, diffuse and collide with each other and mix, burn to a certain extent, 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 very important role, so the length of the pre-combustion chamber (that is, the distance of the air and gas mixed combustion) also reflects the time of mixed combustion, which is an important structural index.
For melting furnaces that burn in the form of side-insertion, top-insertion or bottom-insertion lances on the small furnace, the space in the small furnace is also called the pre-combustion chamber.
For a furnace that burns liquid fuel and natural gas through the bottom of a small furnace, the space in the small furnace is called an air channel.
The pre-combustion chamber (or air channel) is composed of a ramp, side walls of the small furnace and the bottom of the small furnace. The bottom plate of the small furnace is composed of bottom bricks, cast steel plates or ordered channel steel; the lateral thrust of the slope chute is borne by the braces between the I-steel columns on both sides of the small furnace. The structure of the pre-combustion chamber is an important factor for the organization of the entire kiln flame. The brickwork of the pre-combustion chamber is in contact with the high temperature flame, so the slope and side walls use 33# oxidation method ordinary
cast fused zirconia corundum bricks, and the small furnace bottom brick uses 33# oxidation method non-shrinkage fused zirconia corundum bricks. The slope and side walls are insulated with zirconium sealant, high-alumina insulation brick and insulation coating from inside to outside; the small furnace bottom is insulated with zirconium sealant and high-alumina brick in sequence from inside to outside; The water bag is insulated to reduce the operating environment temperature when checking and replacing the nozzle.
(3) Lower inclination angle of small furnace
For a furnace that burns producer gas, the angle between the small furnace slope and the horizontal plane constitutes the downward inclination angle of the air stream, and the angle between the small furnace floor and the horizontal plane constitutes the upward inclination angle of the gas stream. The upward and downward inclination angles constitute the intersection angle where the gas and the air stream meet. The greater the angle of intersection between the two streams, the stronger the mixing. The distance from the end of the tongue to the outlet section of the spout is the length of the pre-chamber. The longer the pre-chamber, the higher the degree of gas and air mixing. At the same time, when the air, gas flow and temperature are constant, the mixture is The degree is related to the cross-sectional ratio of the air and gas horizontal channels. The mixing degree of gas and air in the pre-combustion chamber is also related to the gas contact area, that is, in the case of intersecting air and gas horizontal passage cross-sectional ratios, the flat-form pre-combustion chamber has a lower degree of mixing of streams. For flat glass melting furnaces that burn producer gas, the pre-combustion chamber of small furnaces mostly adopts a "small angle" that has tongues out, the flame is stable and long, the temperature difference between the root and the tip of the flame is small, and it is easy to control and convenient for maintenance. Long pre-combustion chamber. The long pre-chamber generally has an air downward inclination angle of 20°~26°, and a gas upward inclination angle of 0°~5°, that is, the intersection angle of air and gas is 20°~30°.
In the structure of the bottom-burning small furnace that burns liquid and natural gas, the inclination angle of the slope of the air passage is an important parameter. In order to make the air and oil mist mix uniformly and quickly, and to make the flame close to the liquid surface, the downward inclination angle is generally 20°~25°. The allowable upward tilt angle of the nozzle is 5°~12°. The bottom plate of the small furnace has no upward inclination, and is generally built into a flat or stepped shape, so that the combustion-supporting air mixes with the oil mist as quickly as possible when entering the kiln through the small furnace door, and ensures that there is enough air near the nozzle for the gradual diffusion of the oil mist. Burn, and make the flame just pass the glass surface. The downward inclination angle must be matched with other conditions, such as the aspect ratio of the small furnace, the distance between the small furnace and the burner, the height between the small furnace and the liquid level, etc., so as to select the most suitable angle.
(4) Small furnace horizontal channel
For fuel oil, natural gas, and coke oven gas furnaces, the air is preheated through the regenerator, rises to the top and turns into the horizontal channel of the small furnace, changes the airflow angle under the action of the slope, and is sprayed into the furnace through the spray outlet. The horizontal passage of the small furnace serves as a passage for introducing preheated air and a passage for exhaust gas.
The air rises through the regenerator to the turning point of the horizontal channel. After the flow direction changes, the airflow is relatively unstable. In order to stabilize the airflow, the horizontal channel must have a certain length. The increase in length is conducive to the stability of the airflow. In addition, the extended horizontal channel expands into the operating space under the small furnace, which brings greater convenience to adjustment, assembly and disassembly, and maintenance of the spray gun.
Due to the large temperature fluctuation at the turning point and the airflow to the refractory material to a certain extent, here (the back flat and stack bricks between the regenerator and the ramp), the more corrosion-resistant 33# oxidation method ordinary casting electric Masonry of fused zirconia corundum bricks.
(5) Little furnace tongue
The "small furnace tongue" is only for the furnace that burns producer gas, and mainly forms a horizontal channel separating air and gas. The structure and size of the tongue is another important structural factor that affects the degree of air and gas mixing and the flame entering the kiln. The length, thickness and shape of the tongue have an effect on the length, angle, temperature distribution and erosion of the jet outlet.
The length of the tongue: After the other dimensions of the small furnace are fixed, the longer the tongue, the closer the air and gas meet point to the outlet. The horizontal flame furnace requires the flame to have sufficient length, direction and rigidity, and the tongue of zirconium corundum brick is generally used.
Tongue thickness: When the size of the small furnace is determined, the thickness of the tongue is related to the distance of the intersection of air and gas, and it affects the mixing degree of air and gas and the flame angle. From the perspective of structural strength, the tongue should also have a certain thickness. Too thin will cause serious fire penetration and aggravate burn damage. Generally, the tongue slug is 250mm thick.
