The influence of air flow on the reaction of raw fuel in the decomposing furnace
In the decomposing furnace, the three processes of fuel combustion heat release, suspension heat transfer, and material decomposing heat absorption are closely combined. Only when the combustion heat release rate is compatible with the decomposing heat absorption rate, the decomposing furnace can play its due role. Therefore, the size of the calciner should first ensure that the carbonate decomposing rate of raw material meets the requirements (generally in the 85%-95%) and the fuel is completely burnt out. And by the experiment that when preheat to 600 ℃ with uncooked materials into the inner state of suspension, the decomposing furnace at 900 ℃ takes about 0.8 seconds, carbonate decomposing rate can reach 85%, and volatile divided into 25%, fineness of pulverized coal is 15% (more than 0.08 mm sieve sieve) at 850 ℃, 900 ℃ decomposing furnace burning, after 0.8 seconds without fuel, to 1.5 seconds, 2 seconds to complete combustion, state the time needed for pulverized coal fuel is completely is much longer than the time needed for carbonate decomposing, it is to decompose the movement of airflow in furnace and decomposing furnace put forward special requirements, To meet the needs of material endothermic decomposing and fuel combustion heat release.
On the one hand, it can be solved by increasing the volume of calcination furnace and reducing the wind speed inside the furnace. However, for modern large-scale dry kiln calcination system, unilateral increase of furnace volume increases the difficulty of manufacturing and installation, which is also economically unreasonable. Reducing the wind speed reduces the ability of the air flow to suspend conveying materials and restricts the increase of production.
On the other hand, we can also use the cyclone or spout effect of the air flow to make the cyclone or spout movement in the decomposing furnace, so that the material lags behind the air flow, in order to meet the thermal process of the decomposing furnace. The so-called cyclone or spout effect is to make the air flow in the preheater or the decomposing furnace swirling or spout motion, because of the centrifugal force, so that the material lags behind the effect of the air flow.
The air flow in the decomposing furnace has multiple functions of oxygen combustion, material floating and heat transfer medium. In order to obtain good combustion conditions and heat transfer effect, it is required that each part of the decomposing furnace maintain a certain wind speed, so as to make combustion stable and material suspension uniform. While under the same section of wind speed, flow directly through the decomposing furnace and the vortex or the time needed for spouting movement by decomposing furnace is the same, but for raw material and coal powder, as a result of the airflow coanda effect formed by the influence of centrifugal force, the journey taken in the furnace and air taken away is very different, making it in the retention period of furnace greatly extended, so to make in certain inside the furnace volume of material and fuel longer retention time, insist on airflow in furnace cyclone or spouting shaped or a combination of both, the relative motion between airflow and material, so that the powder lag. The airflow in the furnace depends on the wall effect so that its dust content increases greatly and does not produce the falling-off phenomenon, so that the material powder in the furnace to obtain a proper length of endothermic decomposing time. In order to improve the heat transfer efficiency and production efficiency at the same time, the required airflow with appropriate powder floating to send, the quantity of heat decomposing of the same material, to reduce the decomposing furnace volume, and high effective utilization, on the premise of meet the above conditions, requirements decomposing furnace has a small fluid resistance, to reduce the power consumption of the system.
In the same way, due to the cyclone furnace or spouting effect, pulverized coal was lagging behind the airflow, the pulverized coal particles stay in the oven for a significantly longer time, caused by furnace pulverized coal concentration increases, it increase the decomposing furnace combustion particles in unit volume, the total area make the overall combustion rate increases, thus raising the heat load of unit volume of decomposing furnace.
Vortex or spouting effect in a great influence on the retention period of pulverized coal in the furnace, if control is not good, will greatly affect the pulverized coal and raw materials in the furnace combustion decomposing time, probably doesn't make the pulverized coal in the furnace combustion and to continue to burn after furnace system, the decomposing rate of decline of material, overtemperature after furnace system.
On 2018-08-08 11:45:46
