The smoke extraction system is an important link in the design of industrial furnace and a prerequisite to ensure the normal operation of heat treatment furnace. In larger heat treatment furnace designs, the chimney diameter calculated based on parameters such as flue gas flow rate and flue gas temperature is large and the chimney height will be very high. This brings problems to the installation and selection of the control valve in the chimney. The general practice is to divide a large chimney into several smaller chimney diameters to avoid this problem.
In the actual working process, the heat treatment furnace may not always exhaust smoke according to the envisaged channel. To simplify the analysis, the number of chimneys is reduced to 2 below and further simplified. Because in the design, the chimney is usually designed according to the loading capacity and the maximum heating speed, and there is a margin, so the chimney is too large for the furnace in about 98% of the time.
As the root cause of the smoke exhaust phenomenon is the imbalance of temperature, the hot air is lighter and tends to move upward, which makes the temperature reach equilibrium through air convection. When there is only one chimney in the heat treatment furnace, there is only one passage for hot air. The hot air constantly burning in the furnace generates pressure and forces the hot air to move upward. At the same time, the positive pressure in the furnace also prevents the cold air outside the furnace from settling down along the chimney. But that changes when stoves have two or more chimneys. The fundamental driving force behind the phenomenon is the difference in air density. For example, when the temperature inside the furnace is 300℃, according to the law of thermodynamics, the density of hot air inside the furnace is half of the ambient air density outside the furnace.
If the hot air has a tendency to move up, it also means that the cold air has a tendency to move down. When there is only one chimney, the cold air does not settle because the furnace continuously produces hot air, and the pressure from the spout prevents the cold air from sinking. When the system has two or more than two root smoke exhaust passage of time, as a result of the chimney smoke is full of excess capacity in the vast majority of time, the process of rising hot air can easily along a chimney, due to the imbalance in furnace pressure, another root pressure is not enough to hold back the settlement of the cold air, chimney then settling down another chimney. Observing the situation of a furnace with 4 chimneys, it is found that the number of settling chimneys and discharging chimneys is uncertain, and even the order of settling chimneys and discharging chimneys will change at different stages of operation. Usually there is one settling chimney, 3 discharging chimney, or 2 settling chimney and 2 discharging smoke. The position of the settling chimney can also be changed by the time the next furnace is reached.
On 2018-08-08 11:45:46
