1. The purpose of volatilization of zinc oxide volatilization kiln
The leaching slag obtained in the production of zinc hydrometallurgy contains more zinc and other valuable metals (such as lead, copper, cadmium, indium, germanium, gold, silver, etc.). In order to make full use of resources, improve the recovery rate of metals and reduce its pollution to the environment, the leach slag must be treated. We currently use the method of rotary kiln volatilization to process the leach slag.
2. Zinc oxide volatilization kiln is used for the treatment of zinc leaching slag
The volatilization rotary kiln process is a new process and new equipment in our company. It is characterized by large equipment, large equipment processing capacity, high degree of automation, and relatively stable product quality, but the overall investment is large. Except for some control instruments, the system all adopts domestic equipment. A large number of automatic or semi-automatic controls are used in the volatilization kiln system, which greatly reduces the labor intensity of operators on the premise of saving investment. The whole system is the most advanced volatilization kiln processing zinc leaching slag system in China at present.
3. Structural components of zinc oxide volatilization kiln
1. Kiln body: The kiln body of a zinc oxide rotary kiln is generally welded (or riveted) into a cylinder by 20 mm thick steel plates.
2. Rolling ring: The rolling ring is not directly set on the kiln body, but is installed on the kiln body through the base plate. Its function is to strengthen the zinc oxide rotary kiln body, and at the same time, it can transfer the weight of the cylinder body to the support. Wheels, zinc oxide rotary kilns used in refractory production, generally have 5 to 8 rolling rings.
3. Supporting wheel and supporting wheel shaft: The supporting wheel is installed on the supporting wheel shaft by hot-loading method, and the supporting wheel shaft is installed in two bearings with bronze bearing bushes. The temperature of the water coming out of the bearings after longitudinal cooling with water should not exceed 25 degrees. .
4. Blocking wheel: The blocking wheel is a limiting device, which limits the position of the zinc oxide rotary kiln body on the supporting wheel, but it cannot stop the nest body from moving up and down.
5. Transmission device: Zinc oxide rotary kiln generally uses gears to drive the rotation.
4. Composition system of zinc oxide volatilization kiln
The zinc oxide volatilization kiln is mainly composed of: batching system, feeding system, rotary kiln system, slag water quenching system, oxidation cooling system, dust collection and bagging system, and flue gas desulfurization system.
1. The main purpose of the batching system is to mix the zinc-containing waste or zinc ore powder and coke powder in proportion and mix them evenly. The system consists of a multi-bin weighing batching machine (optional), a belt conveyor and a mixer;
2. The purpose of the feeding system is to send the stirred mixture into the bin at the end of the kiln, which is composed of a conveyor (belt conveyor or bucket elevator), a bin, and a feeder;
3. Zinc oxide volatilization kiln system is the core equipment of the production line, mainly composed of cylinder body, refractory lining, transmission mechanism, support mechanism, kiln hood, kiln tail material guide mechanism, fan, heat source generating mechanism;
4. The main purpose of the slag water quenching system is to crush the high-temperature waste slag evaporated by high-temperature calcined zinc through water quenching. The system is mainly composed of a cold water pool, a slag removal machine, a water pump, and a circulating water pool;
5. The main purpose of the oxidation cooling system is to fully oxidize the high-temperature zinc vapor to generate zinc oxide and reduce the airflow to a suitable temperature. The system is composed of a herringbone pipe, a pipeline, an air distribution valve, and a collection box;
6. The main purpose of the dust collection and bagging system is to separate the zinc oxide finished product from the air flow and collect it into bags. The system consists of pipelines, pulse dust collectors, air compressors, fans, discharge valves, and weighing and packaging mechanisms. ;
7. The purpose of the flue gas desulfurization system is to remove the sulfur dioxide produced during the calcination process to meet the emission standards; the system is mainly composed of a desulfurization tower, a reaction tank, a regeneration tank, an aerator, a plate and frame filter press, a corrosion-resistant pump, Composition of fans.
5. Working principle of zinc oxide volatilization kiln
The working principle of zinc oxide volatilization kiln is to use the characteristics of high vapor pressure of metal zinc, cadmium, lead and cadmium sulfide and lead oxide at high temperature, so that zinc, lead, cadmium and other metals can be transformed into The volatiles, copper and precious metals are transferred to the kiln slag, and these metals are recovered from the volatiles and kiln slag with another slag. Generally, zinc oxide rotary kilns are used to process zinc-containing filter cakes. The zinc in the filter cake mainly exists in the form of zinc ferrite, oxide and sulfate. Under the high temperature of the zinc oxide rotary kiln, the zinc ferrite and solid carbon interact to reduce to metal zinc, and the sulfate of zinc, lead and cadmium It is also reduced and volatilized in the form of sulfide and gold. The metals reduced and volatilized from the solid phase are re-oxidized under the action of the kiln atmosphere, and finally are mainly produced in the form of oxides.
Note: The amount of air sent into the zinc oxide rotary kiln should ensure that the dense flue gas has enough oxygen to enable it to re-oxidize all the metal vapors, sulfides and carbon monoxide that have been reduced earlier. Increasing the air volume of the zinc oxide rotary kiln will extend the reduction zone to the inlet end. On the contrary, if the amount of air is reduced, the reduction zone will be shortened, and the initial section of the reduction zone will extend to the discharge end.
6. The processing capacity of zinc oxide volatilization kiln
In order to improve the production efficiency of low-grade zinc ore roasting, under the conditions of maintaining the kiln temperature and zinc utilization rate, and the equipment operating load can withstand the conditions, the feeding rate can be gradually increased experimentally to make it reach a corresponding larger processing capacity. During the trial production of the 45m kiln, the amount of mixed material fed into the kiln was as high as 9 tons per hour. When kiln sticking occurs, the amount of coke added can be appropriately increased to increase the combustion temperature in the kiln, improve the permeability of the kiln material and melt the sticky material from the kiln wall , and then restore the normal charge. When the kiln lining corrodes too fast in the high temperature zone, in addition to strengthening the external forced water cooling of the kiln body at this part, it is mainly necessary to control the reasonable volatilization temperature suitable for the components of the zinc gangue roasting slag to be processed, so that the kiln temperature is slightly lower than its softening point temperature , without affecting the reduction volatilization rate of zinc. In addition, controlling the lead and sulfur content of zinc ore, rational ore blending, appropriately increasing the content of calcium oxide and aluminum oxide in the roasting slag, controlling the blast volume of the kiln head, and preventing the high temperature zone from being too concentrated can also slow down the corrosion rate of the kiln lining and improve the rotation rate. kiln operating rate. The 22-meter section of the high-temperature zone at the head of the 45-meter rotary kiln is built with high-aluminum refractory bricks, and the outside of the kiln is a forced water-cooled kiln body steel shell. In order to adapt to the characteristics of high-silicon zinc oxide ore, the temperature in the high-temperature zone is controlled at 1150-1200°C, and the masonry in the kiln can be operated continuously for more than 3 months.
7. Zinc oxide volatilization kiln to produce secondary zinc oxide from zinc-containing flue ash
The zinc-containing waste and anthracite coal powder (or coke powder) are blended and stirred in a certain proportion to form a uniform mixture, which is transported by belt conveyor or bucket elevator to the mixing silo at the end of the kiln. Below the mixing silo is a disc The feeder, the mixture is metered by the disc feeder and then fed into the rotary kiln. With the rotation of the rotary kiln, the mixture slowly moves from the low temperature area to the high temperature area. In the high temperature area, the coal in the mixture and The air blown into the kiln tail undergoes an oxidation reaction to produce CO, and the CO and C in the coal undergo a reduction reaction with the ZnO in the slag to generate Zn vapor, which is oxidized by O2 in the air to generate ZnO smoke dust, which is discharged in the dust collector The inside is collected, and the remaining slag enters the slag pool after water quenching at the kiln head.
8. The structure and function of the zinc oxide volatilization kiln
The cylinder body is made of welded steel plates, and the kiln head and kiln tail are equipped with retaining rings and lined with kiln bricks. There are three types of kiln bricks: magnesia-aluminum-chrome bricks, high-alumina bricks, and clay bricks. (Oil gun), kiln head sealing device, discharge device, etc. Kiln tail settling chamber: kiln tail seal, feeding pipe, settling chamber Auxiliary facilities: hydraulic station, lubrication station.
9. Main operation and control of zinc oxide volatilization kiln
What is the effect of rotary kiln operation High metal volatilization rate: zinc, lead, cadmium, indium, germanium and other kiln slags contain low zinc, indium and other valuable metals, low carbon content Zinc oxide good quality: high metal content: zinc, lead, indium etc.; low impurities: carbon, iron, silicon and other kiln bricks have a long service life and low cost: low consumption (coal consumption) and as large a processing capacity as possible.
1. Kiln temperature control The higher the temperature in the kiln, the faster the reduction rate of lead and zinc oxides and the more complete the volatilization. However, if the temperature is too high, the corrosion of the kiln lining will be aggravated, the life of the kiln lining will be greatly shortened, and the furnace charge may be melted to form furnace knots, which will deteriorate the operation and reduce the metal recovery rate. Therefore, the appropriate temperature should be controlled according to the melting point and properties of the charge. The temperature in the kiln can be divided into four temperature zones along the length of the kiln, namely the drying zone, the preheating zone, the reaction zone and the cooling zone. Among them, the reaction zone is the longest and the temperature is the highest. The general reaction temperature is 1100-1300°C, and the temperature of the flue gas at the kiln tail is 650-750°C.
2. Negative pressure control in the kiln The negative pressure in the kiln is generally controlled at -20~50Pa. If the negative pressure is too large, more air will enter the kiln, the reaction zone will move backward, the temperature of the kiln tail will rise, and the feed slide will be easily damaged, even fine. Particles entering the flue affect the quality of zinc oxide. If the negative pressure is too small, the air volume in the kiln will be insufficient, the reaction zone will move forward, the zinc content in the kiln slag will be high, and even the kiln head may burst into flames.
3. Forced air blast Forced air blast is one of the main factors to improve the kiln condition. It can make the kiln temperature uniform, extend the reaction zone, and make the furnace material turn properly to speed up the reaction process. The actual production shows that forced blast can increase the production capacity by 10-25%, and the recovery rate of lead and zinc can be increased by 4-5% and 2-3% respectively. Forced blast pressure is generally 0.1 ~ 0.2MPa.
4. Kiln body rotation The rotational speed of the kiln body has a great influence on the residence time of the furnace material in the kiln, the reaction speed and the completion degree of the reaction. If the rotation speed is too high, the charge stays in the kiln for a short time. Although the turning is good, the reaction is not complete, and the zinc content in the slag increases. If the rotation speed is too slow, the charge stays in the kiln for a long time, and the coke powder (anthracite) burns completely, but the processing capacity is low. Generally speaking, the residence time of the charge in the kiln is 2 to 3 hours, and the kiln body speed is 60 to 120 s/r.
10. Start and stop operation of zinc oxide volatilization kiln
1. Kiln opening operation
1) Move an appropriate amount of firewood into the kiln.
2) Before starting the kiln and igniting, check the preparations for the normal operation of each equipment, and open the direct lift flue. 3) Insert the oil gun and blast pipe, turn on the oil pump, ignite the open flame, and start to heat up the kiln.
3) When heating up the kiln, strictly implement the heating plan, do not increase or decrease the oil volume too rapidly, in order to prevent the refractory bricks from bursting, and adjust the oil volume and air volume in time when the kiln is baked, so that the straight-up flue emits white smoke.
4) If the temperature is lower than 300°C (kiln tail temperature), the kiln should be rotated intermittently, and a quarter of the kiln should be rotated every half hour, and if the temperature is above 300°C, the kiln should be continuously rotated.
5) When the temperature of the kiln tail reaches about 600°C, the material can be fed.
6) When feeding, advance 8~10t of coke powder to help raise the temperature, and then feed the mixture. In the initial stage of feeding, the coke ratio should be appropriately higher. When the material reaches the kiln head, gradually reduce the amount of oil, and stop the oil when the temperature of the kiln tail is stable at about 650°C. You can notify the exhaust fan to open, open the bell valve, and perform forced air blast. normal production.
2. Kiln shutdown operation
1) Before stopping the kiln, all the materials in the silo should be fed in first, and after the zinc in the materials in the kiln is basically volatilized, the air duct is drawn out, the bell valve is closed, and dust collection is stopped. Seal the kiln and let it cool naturally to prevent the kiln lining bricks from bursting
2) After the material is stopped, the kiln must continue to rotate before the kiln cools down, and the kiln can only be shut down when the temperature at the end of the kiln drops below 100°C.
