One day in June 5438+February 2000, there was no nickel pig iron in this world. In a 36 cubic meter blast furnace in Shanxi Province, hot molten iron is flowing out. Farmer Guang Liu turned worthless low-grade laterite nickel ore powder (less than 2%) into hot nickel-chromium alloy. Products are in short supply, which makes Lao Liu's company develop rapidly. The annual production capacity of nickel-chromium pig iron refined by Zhejiang Huaguang Smelting Group Co., Ltd. once reached 750,000 tons, which was specially supplied to many well-known domestic steel mills such as Baosteel, Taigang and Zhangjiagang Pohang. Nickel-chromium pig iron smelted from laterite ore contains nickel 1.5% to 8%, and even produced by electric furnace can reach 10% to 25%. After refining, it can reach the standard of stainless steel nickel-iron and become a substitute for refined nickel.
Why nickel pig iron? And what is the production process and principle of nickel pig iron?
Nickel sulfide and laterite nickel ore
Nickel ore can be divided into laterite nickel ore (nickel oxide ore) and nickel sulfide ore. Laterite nickel ore is mainly distributed in tropical countries within the Tropic of Cancer, including Cuba, Brazil, Indonesia, Philippines, Australia, New Caledonia, Papua New Guinea and so on. Nickel sulfide ores are mainly distributed in Canada, Russian, Australian, China and South Africa.
According to USGS data, in 20 17 years, the global nickel reserves were about 74 million tons, and the resource reserves were extremely rich. Among them, about 60% is laterite nickel ore and 40% is nickel sulfide ore. In terms of countries, the country with the richest nickel reserves in the world is Australia, with a reserve of190,000 tons in 20 17, accounting for about 25% of the global reserves. Followed by Brazil's120,000 tons and Russia's 7.6 million tons. China's reserves in 20 17 were only 2.9 million tons, mainly nickel sulfide, accounting for less than 4% of the global reserves, and it was heavily dependent on imports.
The main consumers of primary nickel are stainless steel, batteries, electroplating and alloys. Among them, the output of stainless steel crude steel in China showed a blowout growth. In 2000, China's crude stainless steel output was nearly 520,000 tons. By 20 17, China's stainless steel output increased to 23.46 million tons, accounting for more than half of the global stainless steel output. At the same time, more than 80% of primary nickel in China is used for stainless steel production, and the stainless steel industry in China consumes more than 65% of global nickel consumption.
It is the rapid growth of domestic economy brought by China's reform and opening up that not only promotes the vigorous development of stainless steel industry in China, but also promotes the continuous rise of international electrolytic nickel prices. In 2007, the price of LME nickel reached its peak, exceeding $50,000/ton. It is precisely because of the rising price in electrolytic nickel that stainless steel enterprises are facing a high cost burden. Similarly, the supply of nickel sulfide began to lag behind that of China. Over the years, the reserves and grade of nickel sulfide ore have been declining. This leads to the practitioners in our country have to find another way, which also gives nickel pig iron a chance to board the world stage.
It is necessary to know that there is a great difference between the beneficiation and smelting processes of nickel sulfide ore and laterite nickel ore. Nickel sulfide ore should be smelted by different beneficiation methods according to the ore grade. The smelting method of nickel sulfide mainly adopts matte smelting, that is, various nickel sulfide ores are smelted into low-nickel matte through different pyrometallurgical processes, and then the low-nickel matte is blown into high-nickel matte (alloy of nickel sulfide and copper sulfide) through a converter. Nickel refineries use different refining methods to produce high nickel matte to produce different nickel products. Companies such as Jinchuan in Gansu and Xinxin Mining in Xinjiang all adopt this process to produce electrolytic nickel.
Laterite-nickel ore mostly adopts crushing and screening processes, in which large bedrock with weak weathering degree and low nickel content is removed in advance, and then directly smelted. The smelting and enrichment methods of nickel oxide ore can be divided into pyrometallurgical method and wet method. The pyrometallurgical method can be divided into matte smelting method, ferronickel method and granular iron method, and the wet method can be divided into reduction roasting-atmospheric impregnation method and high-pressure pickling method.
Nickel pig iron smelting process
The production process of ferronickel is also varied and complicated. According to the smelting equipment, it can be divided into rotary kiln-electric furnace (RKEF), blast furnace, electric furnace and other processes. At present, RKEF is the mainstream process for smelting laterite nickel ore.
RKEF process, namely rotary kiln-submerged arc furnace process, has the advantages of mature process, simple and controllable equipment and high production efficiency. But its disadvantages are high melting temperature (about 1500℃), high production cost and big dust pollution. In addition, the nickel grade of ore has a great influence on the production cost of pyrometallurgical process. Every 0. 1% decrease in nickel grade of ore will increase the production cost by about 3-4%. This process is suitable for treating magnesium silicate laterite A, intermediate laterite C 1 and C2. And Ni grade >; 1.6%, preferably 1.8%, which is conducive to saving production costs.
The RKEF process flow is as follows: ore batching-rotary kiln drying-rotary kiln roasting-crude ferronickel furnace smelting -LF furnace refining (or mechanical stirring desulfurization)-refined ferronickel water quenching-production of qualified ferronickel particles.
The earliest RKEF process for producing ferronickel by using large rectangular submerged arc furnace in China was Fuan Ding Xin Ferronickel Company invested and constructed by Qingshan Group, which was designed by China Enfei Engineering Technology Co., Ltd. The project adopted two φ5×40m drying kilns, four φ4.8× 100m rotary kilns and four 33000KVA circular submerged arc furnaces. So far, these two RKEF production lines have stable production, good indicators and the lowest cost in China.
Sintering-blast furnace reduction smelting process is a laterite smelting process developed in China in recent years. There are great technical differences between ferronickel and pig iron produced by blast furnace. At present, there are many low-nickel pig iron produced by domestic blast furnaces. The raw material is generally laterite nickel ore containing about nickel 1%, and low-nickel pig iron containing 2% nickel is produced. The barrier-free coke ratio is about 0.8 (800 kg coke/ton nickel pig iron). Technically speaking, the sintering-blast furnace reduction smelting process has some shortcomings, such as low volume utilization rate of blast furnace, high coke consumption, serious sintering pollution, high phosphorus content in nickel pig iron and low nickel recovery rate.
The technological process of producing ferronickel in blast furnace mainly includes: ore drying and screening (massive crushing)-batching-sintering-adding coke and flux (Shi Ying) to the sintered ore to be smelted in blast furnace-ferronickel ingot and slag water quenching-producing ferronickel ingot and slag water quenching.
With the adjustment of national industrial policy, a large number of ironmaking blast furnaces below 500m have been eliminated. However, due to the shortage of nickel for stainless steel in China, a large number of laterite nickel ores are imported. In order to solve the employment problem and create tax revenue, these eliminated blast furnaces are used to treat laterite nickel ores and produce ferronickel containing 3-5% nickel.
Rotary kiln-electric furnace reduction process is a common pyrometallurgical process in China, and the process is simply divided into the following procedures; 1. Dry roasting: in a rotary kiln with a diameter of 3m and a length of 80m, the ore is heated to 650-700℃ with hot gas to remove all the attached water and 60%-70% bound water. 2. Smelting and reduction, that is, the hot ore is melted in the electric furnace into a metallogenic melt, and then the crude ferronickel and iron slag are reduced and separated. 3. Refining, generally using ladle refining, desulfurization and phosphorus.
Rotary kiln-magnetic separation process is also called direct reduction process. At present, only Dajiangshan Smelter, a Japanese metallurgical company, adopts this process in the world. At present, this process is recognized as the most economical method to treat laterite nickel ore. Its biggest feature is low production cost, 85% of energy consumption is provided by coal, and the coal consumption per ton of ore is 160- 180kg. However, more than 80% of the energy consumption of ferronickel smelting in electric furnace is provided by electric energy, and the power consumption per ton of ore is 560-600kwh. However, the main problems of this process are rotary kiln ring formation and recovery rate. Although Dajiangshan Smelter has been improved many times, the process technology is still not stable enough.
Distribution of Nickel Pig Iron Industry in China
At present, there are more than 50 ferronickel production enterprises in China, mostly distributed in Shandong, Jiangsu, Inner Mongolia, Liaoning, Fujian and other places. Among them, blast furnace manufacturers are the main ones in Shandong, and electric furnace manufacturers are few in number but large in scale, representing Xinhai. Shanxi, Jiangsu, Henan and other places also have a certain number of blast furnace enterprises; Inner Mongolia and Ningxia are basically submerged arc furnace enterprises, among which Inner Mongolia has a large number of enterprises in production but small production capacity.
At present, there are more and more self-built ferronickel projects in stainless steel plants, such as Qingpu Alloy, a joint venture between Qingshan Holdings and South Korea's Pohang, and Bao Zhong Binhai Nickel Industry, a joint venture between Baosteel and Sinosteel. In addition, many manufacturers in Shandong, Jiangsu and other places are also actively planning to expand production capacity and form scale advantages. Qingshan Group, Jiangsu Delong and Shandong Xinhai are the three major ferronickel smelting enterprises in China.
In the future, domestic enterprises will gradually lay out overseas ferronickel and stainless steel industries. Among them, the representative enterprise is Qingshan Group. As for the domestic ferronickel industry, the focus of the market is environmental protection. The continuous tightening of environmental supervision in China will limit the growth of domestic ferronickel production. In other words, the peak of domestic ferronickel has passed, and the scenery of more than 300 ferronickel plants is no longer there. After the reshuffle of industry losses and the closure of small and medium-sized enterprises, it will be impacted by Indonesia's low-priced ferronickel, and domestic ferronickel factories will usher in a wave of closure.
Cost calculation of nickel pig iron
1. laterite nickel ore-the main raw material ore for smelting high-nickel iron. Three kinds of laterite nickel ores with nickel content of 0.9- 1.0%, 1.4- 1.6% and 1.9-2.0% are mainly used in industry, and we choose the one with relatively low nickel content. Let's first take a look at the nickel content of the high-nickel iron we want to produce: 10%- 15%. The theoretical calculation takes the median value of 12.5% as the accounting value, so the wet laterite nickel ore per ton of nickel-chromium-iron products is 9. 16 tons.
2. Power cost-the main energy consumption cost of smelting high-nickel iron. It is reported that each dry ton of laterite nickel ore in the industry needs 700kwh of electricity. According to this demand, the power consumption per ton of products is 4488 kWh/h.
3. Fuel consumption: it takes about 1 ton of coal to produce one ton of ferronickel products.
4. Reducing coke: reducing iron needs coke, and reducing agent needs 450kg coke.
5. The total cost of lime, electrodes and other raw materials is 654.38 million yuan/ton.
6. Salary, depreciation, maintenance and other expenses are 2500 yuan/ton.
From this, the cost of smelting high nickel pig iron by RKEF can be calculated.