What are the characteristics of DD furnace in alkaline calciner?

DD furnace-double spouted type was developed by Japan Cement Company and Kobe Iron and Steel Company for 1976. According to the function, the furnace is divided into four structural zones (from bottom to top): reduction zone (denitration), mixing zone (fuel combustion, raw material decomposition), main combustion zone and complete combustion zone. There are two necking areas, which form secondary spouting, prolong the residence time of materials and make the fuel burn more fully. DD calciner is an internationally developed calciner in the mid-1970s, as shown in the figure. It has two characteristics: first, there is a "spouting superposition" flow field in the furnace; Secondly, there is a nozzle for removing nitrogen oxides at the cone of the furnace, which can reduce nitrogen oxides in the kiln gas of the rotary kiln and help reduce the emission of nitrogen oxides in the exhaust gas. The calciner has a second "necking" in the middle of the furnace and a gas-solid "rebound chamber" at the top of the furnace. Because of the secondary injection and rebound chamber, it is beneficial to prevent the partial flow in the furnace. At the same time, because the tertiary air is injected into the furnace at the upper part of the lower cone, that is, the lower part of the cylinder, the spouting airflow can be accelerated; Four combustion nozzles are directly injected into the tertiary air flow of the furnace from both sides of the upper part of the tertiary air inlet on both sides of the furnace, and the flame pre-combustion condition is good; The resistance in the furnace is very low. If sufficient furnace capacity can be maintained according to raw materials and fuel conditions, its working adaptability will be further increased. In 1980s, China, which chose chromium equipment, introduced this furnace type and used it in the construction of new rotary kiln production line. Due to the poor adaptability of this furnace type to low-quality fuel, it is difficult to produce normally. In the 1990s, the long-standing problems were solved through furnace capacity transformation. At present, in many newly developed furnace types, some have added pre-combustion chambers or pre-decomposition chambers and transformed them into ascending flue (or mixing chamber), which has achieved good results as a part of new furnaces. Iron ore dressing equipment, drying equipment, mobile crushing station.