The structure of the small furnace has a decisive influence on the direction, speed, air-gas mixing degree and flame length of the flame. The preheating temperature of the air-gas and the amount of excess air determine the atmosphere of the flame and the combustion temperature of the flame. Therefore, 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 burning liquid fuels, natural gas and coke oven gas, the structure of the small furnace is relatively simple, with only a small furnace outlet and a horizontal channel. For melting furnaces burning producer gas, in addition to the outlet and horizontal channel, the small furnace also has a pre-combustion chamber, a small furnace tongue, an air riser and a gas riser.
1. Exhaust outlet
The outlet is also called the fire outlet. It is the place where the flame is ejected into the kiln and the place where the exhaust gas is sucked out of 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 outlet determines the speed of the flame ejecting 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 liquid surface.
Too large or too small a flame speed is not conducive to the normal progress of the melting process. If the speed is too large, the fuel will not have time to burn completely and will extend to the opposite small furnace, or even burn in the heat storage chamber, which is not conducive to the melting of the glass in the kiln, and it is easy to burn the opposite small furnace, heat storage chamber and lattice refractory bricks. At the same time, if the flame speed is too large, the powder will be brought into the opposite small furnace, corroding the masonry of various parts of the small furnace and blocking the lattice body. If the flame speed is too small, the flame will float and be weak, which is not conducive to the heat transfer of the glass liquid and the batch material, and it is easy to burn the flat arch 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 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 1#, 2#, and 6# small furnaces are the same, the widths of the nozzles of 3#, 4#, and 5# small furnaces are slightly smaller, and the nozzle of 7# small furnace is the smallest.
The arch on the top of the nozzle is called the front flat arch of the small furnace; the walls on both sides of the nozzle are called the small furnace stacks, and the small furnace hook bricks are below. Since the flame is sprayed into the kiln or the high-temperature gas in the kiln is discharged through the nozzle, the flame scouring and flying material erosion cause a bad use environment, so ordinary cast fused zirconium corundum refractory bricks are used for masonry in various parts of the nozzle.
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 nozzle and the glass liquid surface is 400~600mm.
2. Precombustion chamber
For the melting furnace burning producer gas, the small furnace space from the end of the tongue to the outer edge of the nozzle is called the precombustion chamber. After the preheated air and gas enter from the upper and lower parts of the tongue arch respectively, they meet in front of the tongue, diffuse and collide with each other to mix, burn to a certain extent, and spray into the kiln at a certain angle. In order to ensure that the gas can be completely burned in the kiln, the precombustion chamber plays a great role, so the length of the precombustion chamber (i.e. the distance of the mixed combustion of air and gas) also reflects the time of mixed combustion, which is an important structural indicator.
For a melting furnace that burns on the small furnace through the side insertion, top insertion or bottom insertion of the spray gun, the space in the small furnace is also called the precombustion chamber. For a melting furnace that burns liquid fuel and natural gas through the bottom of the small furnace, the space in the small furnace is called the air channel.
The precombustion chamber is composed of a slope arch, a small furnace side wall and a small furnace bottom plate. The small furnace bottom plate is composed of bottom refractory bricks, cast steel plates or orderly arranged channel steels; the lateral thrust of the slope arch is borne by the tie bars between the I-beam columns on both sides of the small furnace. The structure of the precombustion chamber is an important factor in the organization of the flame of the entire kiln. The brickwork of the pre-combustion chamber is in contact with the high-temperature flame, so the slope arch and side walls use 33# ordinary cast fused zirconium corundum bricks, and the small furnace bottom bricks use 33# oxidation method non-shrinkage fused zirconium corundum bricks. The slope arch and side walls are insulated from the inside to the outside with zirconium sealing materials, high-aluminum insulation bricks and insulation coatings; the small furnace bottom is insulated from the inside to the outside with zirconium sealing materials and high-aluminum bricks; and there is a flat water bag below to reduce the operating environment temperature when checking and replacing the nozzle.
