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 Pengfei Group Developed to Utilize Rotary Kiln for Laterite Nickel Calcination
Pengfei Group developed to utilize rotary kiln for laterite nickel calcination
At present, nickel smelting process is basically located in the situation of mainly living on electrolytic nickel. Thus, researching & developing to utilize new technology for produce ferro-nickel from laterite nickel is necessary. Utilizing laterite nickel to produce ferro-nickel is more reasonable on economy, so it is unnecessary to produce electrolytic nickel. In recently years, in order to ensure to meet the nickel demands of national economy development, some Chinese enterprises implemented developing strategy of  "going out", took part in the foreign nickel resources exploitation which played an important role in stable supply of Chinese Nickel. Oxide nickel is widely distributed nearby Equator while the distance for transportation is short, thus the sea freight is not higher. Along with exhaustion of nickel sulfide resources, the utilization of oxide nickel (laterite nickel) has been swiftly developed in the whole world.

1. General Description of oxide nickel smelting process
At present the process utilizing oxide nickel as raw material to produce protosomatic nickel could be divided into pyrometallurgy & we process metallurgy. Nieckel produced through pyrometallurgy still occupies main location. But in recent yers, we process metallurgy process has been developed quickly, meanwhile set up some new factories which utilize HV acid leaching process to produce nickel & cobalt. Wet process metallurgy process could be divided into two types: one is ammonia leaching method, due to the limits of raw material and cost, there is no new factory set up using this method; the other is acid leaching method which is suitable for oxide nickel with low magnesia content. The new developed process of pyrometallurgy & wet process comination shows its advantages: it is suitable for any type oxide nickel with lower cost, but there is some technical problems to be figured out, from the side of resources utilization and energy saving, HV acid leaching process has some advantages & potential which has become important researching subject. But from the side of investment, construction circle & mature technology, it is estimated to set up a new batch of factories utilizing pyrometallurgy process to produce nickel whose product could be ferro-nickel or nickel sulfide.

2. General description of pyrometallrugy process
Pyrometallurgy process could be divided into 2 categories: blast furnace (BF furnace means blast furnace) smelting & rotary kiln - ore furnace - revolving furnace (RKEF) smelting process.

2.1 Process of BF furnace smelting ferro-nickel & blast furnace smelting:
Since 1863 found the laterite nickel, they begin to utilize BFI process to treat this kind of infusible magnesial silicate oxide nickel. Due to the reason of energy consumption, environmental protection, investment & production cost, etc., this kind of process has been eliminated in the world, except China. The Russia Wulaer Nickel Company and Wufali Nickel Facotry which produces ferro-nickel using blast furnace were the last one to stop manufacturing. The process of utilizing blast furnace for smelting, the process flow is: treat the raw material according to its situation (such as pick up the ore block with low nickel by hand, have the treatment of crushing & screening), then utilizes mixing & proportioning equipment of sinter machine to add the reductive & flux into oxide nickel and mix evenly (which could use granulating machine). The mixed material will be distributed on the station of sinter machine through spreader, after sintering; we could get the agglomerate with nickel. The agglomerate will be sent into material pile of blast furnace and go into blast furnace after screening. After smelting via blast furnace, it will produce the pig iron with nickel which has higher impurity and lower nickel, if it is directly used in stainless steel smelting which reduce the nickel value in rough ferro-nickel. Thusit should set us the measure for phosphorous, silicon, coal, sulphur, etc. poisoning element adsorption and precise smelting. These measures could improve the nickel content inside ferro-nickel according to customers' requirements. The reason of the blast furnace elimination:

      A.  This kind of process don't have effective method for treating the problem of environmental pollution, besides the traditional blast furnace pollution factor, in order to improve the flow-ability of slag and reduce dross of furnace body, it should add fluorite into material, in order to avoid fluoride pollution, this operation has been forbidden. For oxide nickel with higher A1:O, the percent of fluorite is larger, thus the problem will be much series. As the strength of agglomerate produced using laterite nickel is weaker, it is not suitable for large blast furnace smelting, and normally it will take use small smelting blast furnace and small sintering machine to produce ferro-nickel. The volume of blast furnace which are used to produce ferro-nickel is 50m3 to 380m3 (according to the reports, there are smaller blast furnace, their volume is mainly less than 150m3), while the volume of sintering machine is 18m3. However, some ferro-nickel factories are lack of necessary environmental protection measures, carbon oxide, sulfur oxide, fluoride and powder has heavily polluted neighboring environmental. Utilizing eliminated equipment of black metallurgy to produce nonferrous is unacceptable.

      B. Low recovery percent of nickel. The recovery percent of ore is normally lower than 90% using this kind of ferro-nickel production process. Some factories stop in the primary production stage of rough ferro-nickel production, they don't have precise ferro-nickel smelting workshop. Thus, this recovery percent is different with that in foreign documents.

      C.  Higher power consumption and higher cost coke. For sintering process, it is based on characteristics of power wasting of small blast furnace and adds the power wasting factor of higher sinter return ratio. For blast furnace process, the important factor for small blast furnace elimination is power wasting however now it adds large slag quantity factory. The coal gas and excessive heat of some factories hasn't been used sufficiently and precious power has been wasted meanwhile the environment has been polluted.  

      D. Product don't been refined, the impurity percent is higher which don't meets the international nickel product trade standards. We request higher nickel percent in ferro-nickel and lower coal, silicon, sulfur and phosphorus percent. However the ferro-nickel produced by blast furnace in China normally is the product with higher coal content, lower nickel content and higher silicon percent and the phosphorus content is decided by raw material while now raw material with lower phosphorus content is short supply. The nickel value in this kind of intermediate is much lower than that in qualified ferro-nickel; meanwhile the ferrum is basically given to customers for freely.
E. The investment on unit nickel production is large: The investment on mechanical material pile, sintering machine and blast furnace is higher than that of RKEF process. Of course utilizing current eliminated small equipment requested by industrial policies to produce ferro-nickel could save the investment. This process has been developed in the situation of low cost laterite nickel, much higher nickel, bad execution of environmental policies and power policies. We believe that the price of laterite nickel will keep increasing, the nickel price will return to reasonable price and the national environmental and energy-saving policies will be well executed, thus this process will quit the marketing competition automatically.

2.2 RKEF process of pytometallurgy
RKEF process is developed in 50s of last century, at present, it replaces blast furnace to produce ferro-nickel. This process crease a new situation of ferro-nickel production via pytometallurgy. According to incomplete statistics, at present there are 17 factories utilizing this process for smelting ferro-nickel in the world. The basic process flow is: Ore treatment and preparation of reductive - rotary kiln calcination - loaded into ore furnace for smelting - rough ferro - nickel desulfuration out of furnace - silicon, phosphorus, coal, sulfur, manganese, etc. impurity desorption - refining ferro-nickel water block casting, others, it need to set ups the workshop which could recover and utilize iron & nickel in the slag of converter.
( 1 ) Ore treatment and preparation of reductive
After the ore is sent into raw material pile, they will be crushed, mixed and proportioned with reductive, and they are sent into rotary kiln. Some factories have the pre-drying treatment before the material entering into rotary kiln, some others add the granulating process of the material. Material proportioning is very important which has the decisive function of avoiding ring of rotary kiln (material cohered inside of liner), controlling electrical conductivity of material, detaching slag and metal (nickel & iron) in ore furnace.


( 2 ) Rotary Kiln Calcination
The working area of rotary kiln could be divided into 3 sections which is drying section, heating section and calcining section. Inside of rotary kiln, ore are roasted for water desorption and the weight will be reduced in 30%. Meanwhile, oxide nickel and part iron are restored by reductive inside of furnace. The discharging side of rotary kiln is set up sealed discharging device, nickel slag will be sent into material supply silo of ore furnace in 6 00
9 0 0 centi-degree under heat insulation stage, then they will be evenly distributed inside of ore furnace via a sealed tubular distributing device. According to different material treating method, the rotary kiln has different ratio between diameter and length. The burner structure of rotary kiln is very important, which effectively adjusts the length and rigidity of fire and ensure the temperature of three working areas to be in the range of process requested. Others, it should sufficiently consider using smoke of rotary kiln to dry material for energy saving.


( 3 ) Ore furnace smelting
The material discharged from rotary kiln will be sent into ore furnace after weighing. The material supplying system of ore furnace should comply with the demands of hot material loading. Hot loading is very important which besides recover the physical heat power; it should ensure no secondary oxide during transportation. In order to protect the environment, keep the industrial health, recovery the powder & coal gas, the ore furnace is sealed. Inside ore furnace, material separates the ferro-nickel and slag of electrical furnace via arc smelting, meanwhile they could produce 75% CO reducibility, after the gas is cleaned, it will be used as fuel of rotary kiln which occupies 30% of rotary kiln fuel. According to different raw material, one ton raw material ore could get 650-700kg nickel slag after calcination of rotary kiln which could get 110-150kg rough ferro-nickel after smelting in ore furnace. The nickel content in rough ferro-nickel is normally 10%-18%.

( 4 ) During the process of iron produced from ore furnace to liquid iron, add the soda ash meanwhile the percentage should be 5-15kg per ton liquid nickel-iron, the sulfur content in liquid nickel-iron could decrease to 0.015%-0.08%. It also could spout magnesia granulator into liquid iron which need special steamer to spout magnesia granulator into 1.0m deep of liquid iron, this process could reduce the sulfur content to less than 0.015%.
Eliminate the dreg on the surface of rough liquid nickel-iron, put into acid converter and oxidize via blowing silicon-oxygen. In order to control the temperature of weld puddle, add the metal waste or waste material with nickel inside of furnace. 


Liquid nickel-iron will be sent into basic converter after silicon desorption and the coal, phosphorus and part of iron will be eliminated from liquid nickel-iron. During smelting process add the limestone into converter. If there is enough waste with nickel, utilize lime instead of limestone. The liquid nickel-iron discharged from basic converter has met the requirements of commodity nickel-iron standard which could be sold as commodity nickel-iron. Other, two step refining method of rough ferro-nickel is to replace acid converter with basic converter, utilizes new process to implement silicon desorption and desulfuration in first converter. The liquid nickel-iron discharged from first converter will be sent into 2nd basic converter for phosphorus and coal desorption. During smelting process, add lime and limestone into the furnace to ensure the suitable smelting temperature. Two step methods could get the qualified refining liquid nickel-iron.
2.3 The process of smelting stainless steel directly from rough ferro-nickel (in developing)
According to the two step method smelting process, replace the second converter with the refining converter using argon & oxygen which could directly produce 300eries stainless steel. This process don't need to set up electric furnace for wasted steel fusion, sufficiently utilizes heat power of oxidation of silicon, saves investment and power, adequately uses Ferrum in rough ferro-nickel. This technology has tantalizing foreground but it is under developing. 


3. The factors which need to consider while setting up ferro-nickel factory
Start from the strategic target of integrative utilization of resources, long-range development & programming of nonferrous industry, it is necessary to choose suitable area to set up large-scale ferro-nickel production base in China. But, avoid rushing headlong into action. The conditions of setting up ferro-nickel production base: commitment the resource of ore: different ore is suitable for different smelting process. Pytometallurgical process should preferentially choose the garnierite as raw material, thus before deciding to set up ferro-nickel factory, the oxide nickel ore resource should be commitment. At present, the price os nickel ore has been fixed, thus the recourse difficulties of nickel ore will come.
 

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