Preparation of Blue Tungsten Oxide - Rotary Calciner
Blue tungsten oxide is one of the most important raw materials for the manufacture of tungsten powder. In China, there are three main methods for preparation of the blue tungsten oxide: APT closed calcination method, APT mild hydric reduction method and intrinsic reduction method. And the APT closed calcination method is the most used method.
APT closed calcination method always keeps the furnace system with positive pressure in the heating process, preventing the air from entering the furnace. By this way, ammonia from APT pyrolysis splits into hydrogen and nitrogen. And in the weak reductive atmosphere, the blue tungsten oxide is produced.
The entire process is confined in a rotary calciner. The usage and control of rotary calciner need cautious operation, as it is the main carrier of APT closed calcination process.
The entire process is confined in a rotary calciner. The usage and control of rotary calciner need cautious operation, as it is the main carrier of APT closed calcination process.
Rotary hearth furnace is a rotary calciner with high automation, of which the ring-shaped bottom can be rotated. Generally it is divided into two sections to control the temperature. In different sections, temperature is different due to different configurations of burner. APT is turned from low temperature area to high temperature area by the rotation of the bottom. After a cycle of turning, APT reachs the required temperature and reduce to blue tungsten oxide.
Rotary calciner has simple structure, of which the furnace tube is welded by stainless steel. Baffle in the tube can materials from flowing out to quickly and increase the heat transfer area. Heating cord is embedded in the refractory bricks outside the tube for heating material. The feeding end is connected with the exhaust fan, as the exhaust fan can exhaust away the water vapor and ammonia produced by the decomposition reaction. The recycle of tungsten oxide and APT particles from the exhaust air is carried out by a foam dust collector or an impact dust collector.
In the preparation progress, the temperature in the first section is controlled at about 550℃ and the temperature in the second section zone is controlled at about 600℃. A part of products in the hopper must be retained to seal the discharge screw, preventing air from entering the furnace tube. Throughout the process, the gas pressure is controlled between 49-98Pa greater than the atmospheric pressure. And the positive pressure and the reducing atmosphere are maintained by supplementing a small amount of ammonia and reducing the exhaust air. The product – blue tungsten oxide is Prussian blue. Tungsten recycle rate of rotary furnace can reach 98.5% at the right temperature.
Rotary calciner has simple structure, of which the furnace tube is welded by stainless steel. Baffle in the tube can materials from flowing out to quickly and increase the heat transfer area. Heating cord is embedded in the refractory bricks outside the tube for heating material. The feeding end is connected with the exhaust fan, as the exhaust fan can exhaust away the water vapor and ammonia produced by the decomposition reaction. The recycle of tungsten oxide and APT particles from the exhaust air is carried out by a foam dust collector or an impact dust collector.
In the preparation progress, the temperature in the first section is controlled at about 550℃ and the temperature in the second section zone is controlled at about 600℃. A part of products in the hopper must be retained to seal the discharge screw, preventing air from entering the furnace tube. Throughout the process, the gas pressure is controlled between 49-98Pa greater than the atmospheric pressure. And the positive pressure and the reducing atmosphere are maintained by supplementing a small amount of ammonia and reducing the exhaust air. The product – blue tungsten oxide is Prussian blue. Tungsten recycle rate of rotary furnace can reach 98.5% at the right temperature.
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