I. Introduction

Affected by the economic crisis, nickel prices fell sharply in 2008, the domestic transaction price once fell to 80,000 yuan / t, the price of laterite nickel ore also plummeted, the price of 1.8% grade laterite nickel ore fell to every thousand Tons 180 to 500 yuan. The current price of cement, steel and mechanical and electrical equipment are low, which is building a modern ferro-nickel plant in good time.

Among the apparent consumption of nickel, stainless steel consumption accounts for 50-65% of the total consumption, and the electroplating industry accounts for about 20%. When studying the consumption of nickel, we must first analyze the impact of stainless steel production and consumption.

Second, China's primary nickel market is huge

(1) The rapid growth of stainless steel consumption will boost the consumption of nickel

With the development of China's economy and the improvement of people's living standards, stainless steel production and consumption have grown rapidly. Chromium- nickel stainless steel is the main stainless steel variety that consumes nickel. Due to its excellent comprehensive properties, it is widely used, accounting for 60-75% of the total output of stainless steel. In recent years, nickel prices and chromium prices have risen, and stainless steel companies have made efforts to develop ferritic stainless steel and nickel-saving stainless steel, and have achieved certain results. However, it is widely believed that 300 series stainless steel will still occupy more than 50% of total stainless steel production.

It is estimated that the consumption of stainless steel in China will reach 11 million tons in 2010, of which Cr-Ni stainless steel accounts for more than 6 million tons.

Stainless steel production growth will pull the nickel metal consumption growth. The nickel metal required for stainless steel production is mainly derived from metallic nickel, nickel iron and stainless steel scrap. As the output of stainless steel increases, the situation of China's dependence on imports of nickel metal will not change in the short term.

According to customs statistics, in 2007 China's net import of nickel metal amount 150,000 tons (including nickel in nickel, nickel-iron, stainless steel, etc.), plus domestic nickel metal production of 130,000 tons, nickel-iron 2 million tons, stainless The scrap is 1.82 million tons, and the total supply of nickel metal is about 260,000 tons, and the total nickel supply is about 410,000 tons.

(2) It is expected that in 2010, nickel metal supply will continue to rely on imports.

1, 20l0 will increase production of 1.5 million tons of chrome-nickel grade stainless steel than in 2007, nickel demand will increase by 10 to 150,000 tons.

2, China's stainless steel social accumulation is low, and stainless steel production cycle is long, domestic stainless steel scrap resources are difficult to increase rapidly, stainless steel scrap imports are not likely to increase significantly, the shortage of stainless steel scrap will continue to exist.

3. At present, many domestic enterprises are planning to build nickel (iron) plants at home and abroad, which will increase the supply of nickel. However, in general, due to restrictions in infrastructure, technology, capital, and humanities, progress is slow and the scale is small.

There is no modern ferronickel plant in China. The stainless steel plant consumes about 80,000 tons of low-grade nickel-containing pig iron annually. It is mainly produced from high-pollution small blast furnaces and small-scale ore furnaces with low efficiency and high energy consumption. The product quality does not meet the ISO6501 standard. With the implementation of environmental protection policies and increased market competition, this process will be phased out in recent years.

Third, the national policy actively supports the “development of key technologies for the efficient use of low-grade laterite nickel ore”

For a long time, China's nickel production is mainly based on Jinchuan Company. Its raw material is locally produced nickel sulphide ore, which is a non-renewable resource. The resources are gradually reduced and the mining difficulty is increased. Considering the national strategic reserve, it is worth the Jinchuan nickel mine. Resources for protective development, and the possibility of purchasing nickel-sulphide ore from the international market to solve domestic deficiencies is very small. Therefore, we should learn from international mature nickel-iron smelting technology to develop technologies suitable for domestic raw materials and energy conditions, and make it easy to purchase internationally. The obtained nickel oxide ore produces ferronickel to meet economic development requirements.

In 2008, the Ministry of Development and Reform Office [2008] No. 301, "Notice of the General Office of the National Development Commission on Organizing and Implementing the 2008 Major Industrial Technology Development Special Notice" clearly states: "The key technologies for comprehensive utilization of resources: development is complicated High-efficiency development and utilization technology of metal-associated ore, rare and rare element extraction technology in smelting process, key technology for efficient use of low-grade laterite nickel ore, and efficient collection of valuable elements in secondary resources of metal mines. The key technology for the efficient use of low-grade laterite nickel ore is listed as one of the special contents of national major industrial technology development.

The National Long-Term Development Plan for Non-Ferrous Metal Industry (2006-2020) also states: "The development of nickel-mineral mines is of great significance due to the shortage of nickel-sulphide resources."

It can be seen that the use of foreign nickel oxide mineral resources, drawing on the internationally advanced, energy-saving and environmentally friendly fire method smelting ferronickel technology, developing high-efficiency utilization technology of laterite nickel ore suitable for national conditions, and building a modern ferronickel plant is supported by national policies and market potential. Large good projects are also an inevitable trend in the development of China's nickel industry.

Fourth, learn from the internationally mature RKEF process, develop high-efficiency utilization technology of low-grade laterite nickel ore

The wet smelting process is suitable for high nickel, high cobalt , low magnesium laterite nickel ore, with liquid acid (or ammonia) as leaching agent to extract Ni and Co, and the rest of the large amount of iron and a small amount of chromium become solid waste. The leaching agent is only partially recycled, and the rest is discharged into the river or waste liquid pool in liquid form after treatment, and a large amount of Co is also produced in the wet smelting. These waste solids, waste liquids and waste gas cannot be recycled, and the environmental hazards are large. At present, we have not mastered the relevant harmless treatment technology.

The process of producing nickel-sulfur by high-pressure acid leaching process using low-grade laterite nickel ore as raw material, and then producing electrolytic nickel has matured in the world, but it is limited by investment, technology introduction and environmental protection measures. The nickel plant also needs technical development and research, and the conditions for the construction of the plant are still immature.

The practical approach is to digest foreign advanced and mature fire method to smelt ferronickel, and to improve this technology according to China's energy conditions. Construct a modern ferronickel plant suitable for China's national conditions.

(1) Current status of nickel (iron) smelting process using lateritic nickel ore as raw material

China's modern ferronickel smelting is still in a blank state. At present, the small blast furnace and small ore furnace technology for producing low-nickel pig iron are gradually withdrawing from the historical stage due to high energy consumption and high pollution.

1. Blast furnace (small blast furnace) process

The blast furnace process is the earliest technology for smelting ferronickel in laterite nickel ore. In 1875, it was applied in the small blast furnace in New Caledonia. It was also used in France, but the method is ill due to the consumption of high quality coke and serious pollution. . In the end, the process stopped under market competition and environmental pressure. In 1985, the last nickel-iron furnace of the Japanese mining company Sagaguan Smelter was turned off, marking the end of the blast furnace smelting ferronickel technology in Europe, America and Japan.

In the past few years, China's rapid development of stainless steel production has driven demand for ferronickel. Under the conditions of high nickel price, low price coke and low environmental protection threshold, some investors have used the iron and steel blast furnaces eliminated by the iron and steel industry policy to smelt ferronickel. However, with the return of coke prices reasonable, the decline in nickel prices and the implementation of environmental protection policies, most of the blast furnace ferronickel plants have been discontinued.

The main reasons why blast furnace smelting ferronickel technology will be eliminated are:

(1) Poor adaptability of raw materials, blast furnace cannot enlarge large red

It is applicable to “high-iron low-magnesium (low-nickel)” laterite nickel ore. When the laterite ore contains 1.5% nickel and 35% iron, it can obtain low-nickel pig iron containing about 4% nickel. If low-iron high-magnesium (high-nickel) ore is used, it is difficult to guarantee that the blast furnace slag is large and the viscosity is high.

Due to the low strength of the charge, only small blast furnaces (dwarf blast furnaces) can be used to produce ferronickel.

(2) Product quality is difficult to meet steelmaking requirements

The blast furnace nickel-containing pig iron has a low grade, generally 2 to 8%, mostly below 5%. When smelting stainless steel, it is necessary to add more nickel plates, which increases the cost per unit of raw material nickel.

The amount of coke and flux in the process is large, and most of P and S enter the product. The nickel-iron grade is low, and the content of ω(S) and ω(P) is high, which increases the burden of stainless smelting.

(3) Unstable production process

The composition of ferronickel is fluctuating and difficult to control, making it difficult to supply large quantities in a stable manner.

(4) Coke high

The production of nickel iron containing 2% nickel, the coke consumption per ton of nickel iron is greater than 1.0t; the production of nickel iron containing 5% nickel, the coke consumption per ton of nickel iron is about 2.0t.

(5) Serious pollution

In addition to the traditional blast furnace pollution, fluoride pollution is more serious. In order to keep the blast furnace antegrade, fluorite must be added to improve the slag fluidity. The amount of fluorite added accounts for 8-15% of the total charge. The domestic ferronickel blast furnace has no defluoridation equipment, and all of it is released, which is harmful to people and the environment.

2, cold material into the furnace "sintering machine - ore furnace" nickel-iron process

Due to the price increase of coke and the demand for nickel-iron with high nickel content, some factories have built domestically produced laterite nickel ore sinter with a sintering machine, and smelted ferronickel after cooling. Many of them are retrofitting old ferroalloy electric furnaces to produce ferronickel. The transformer capacity is 6.3MVA, 9MVA and 12.5MVA, and the largest is 25MVA.

The process does not use coke, the material adaptability is better than that of the small blast furnace, and the product has higher nickel content, but there are still defects of high energy consumption and low efficiency. A factory uses 2% grade nickel ore to produce 11~14% nickel-containing nickel iron. The electricity consumption per ton of crude nickel iron is smelting (1~1.2)×104kWh/t, equivalent to 88,000 tons of metal nickel electricity consumption. kWh, more than twice the RKEF process. The reason is that the "sintering machine-mineral furnace" process cannot provide pre-reduced high temperature materials for the submerged arc furnace.

25MVA ore furnace produces iron once every 4h, each time the amount of iron is about 15t, equivalent to lMW power, the annual output of nickel metal is only 140t.

High power consumption and low efficiency are related to the cold charge entering the furnace, and a large amount of time and power are used to heat the charge.

I have seen that the "sintering machine (some also use the soil sintering process and the sintering pot process to prepare the raw materials for the ore furnace) - the smelting furnace of the "mineral furnace" process does not have perfect environmental protection equipment, especially the ore furnace is open or semi-closed type of small hoods, coal gas can not be recycled, not only pollute the environment, also caused a waste of gas. The sintering machines are also not equipped with waste heat recovery facilities. These plants do not have modern, large-scale production conditions for ferronickel.

Some factories use electric arc furnaces to treat sinter, produce ferronickel, and the benefits are even worse. Basically, production has been discontinued.

3. Reduction of ostomy

Initially produced in a blast furnace, it was eliminated due to high energy consumption.

At present, some enterprises carry out smelting and melting in an electric furnace to obtain low-steel ice-nickel. This process is identical to the traditional nickel sulfide process. Due to the low grade of laterite ore, low-ice nickel products contain less nickel, a large amount of slag, and high energy consumption, making the process unable to compete with the traditional process of nickel sulfide ore. There are not many companies using this process.

(II) The RKEF process technology is mature and dominates the field of ferronickel smelting

The RKEF process technology ("Rotary Kiln - Submerged Furnace" method) was started in the 1950s by Elkem in the Donanbo plant in New Caledonia due to its high quality, high productivity and energy efficiency. Environmentally friendly, the RKEF process quickly replaced the blast furnace process. With the development of metallurgical science and technology, RKEF process has also absorbed many of the latest technological achievements including automation and clean production. It has become mature in design, manufacturing, installation, commissioning and production operations, and has become the mainstream process technology for producing ferronickel in the world. , occupying a dominant position. At present, there are more than a dozen companies that use the RKEF process to produce ferronickel. The production plants are located in Europe, America, Japan, Southeast Asia, etc. The largest annual production capacity is 70,000 to 80,000 tons of metal nickel. In the long-term operation, despite the world nickel industry. The price of nickel has risen and fallen, but most of these nickel-iron plants have maintained good performance. In 2005, the American Institute of Metals surveyed the world's laterite nickel ore smelter and annual production, as shown in Table 1.

Table 1 World laterite nickel ore smelter and annual production surveyed by the American Institute of Metals in 2005

The annual output of these 13 nickel smelters totals about 365,000 tons, accounting for 30% of the world's total nickel production, accounting for 8l% of the output of smelting ferronickels in the laterite ore (the world's total nickel production in 2007 was 1.42 million tons, The contribution of nickel oxide ore is 42%, and the amount of metallic nickel produced in the form of nickel iron is about 450,000 tons).

It can be seen that in the world, the process technology of smelting ferronickel by RKEF pyrometallurgical method with low-cost laterite nickel ore as raw material has strong applicability and economy.

(III) Introduction to RKEF process

1. Requirements for raw materials

For the “Rotary Kiln (RK) – Ore Heater (EF)” process, the ore composition is important, and there are three indicators that should be of interest to the RKEF process:

(1) Ni grade, hope to be 1.5 or more, preferably 2.0 or more.

(2) Fe/Ni, it is desirable to be 6 to 10, preferably close to 6, and the Ni grade is high; if Fe/Ni>10, it is difficult to smelt 20% of ferronickel because the Fe in the raw material is too high, very It is difficult to control the degree of reduction of iron oxide in a rotary kiln.

(3) MgO/SiO ₂ is suitable for 0.55 to 0.65, and a low melting point slag structure can be obtained by adding a small amount of flux.

The above three conditions are only suitable conditions, not necessary conditions. When the ore conditions do not meet the above requirements, the ferro-nickel with lower product quality can be produced, and the technical and economic indicators will be affected.

Reducing agents (both bituminous or anthracite) and limestone are also required for the RKEF process. These two raw materials are abundant in China and are readily available.

2. Typical process flow and main equipment structure

(1) Production process

Raw material field → screening, crushing and mixing ingredients → rotary kiln → mineral furnace → iron package desulfurization → refining converter → casting. On this basis, the development of raw material pre-drying, raw material ball making, rotary kiln energy saving and waste heat power generation, high efficiency smelting of ore furnace and low melting point slag system, bottom blowing or side blowing refining converter instead of top blowing converter, nickel iron particles Technology, suitable for factories with different conditions.

(2) Typical process equipment composition

2 sets of 5.0×100m rotary kiln, 2 sets of 63MVA closed ore furnace, 40t bottom blowing refining converter, granulation and ingot equipment. The annual output of ferronickel is 101,200 tons (nickel metal 2 to 22,000 tons). In view of the maturity of domestic equipment and transportation conditions, in order to reduce investment, the domestic construction plant with four rotary kiln and two 48MVA submerged arc furnaces will shorten the construction period and receive good economic benefits.

(3) Process overview

After the ore, limestone and reducing agent are sieved and crushed in the raw material field and the preparation material, the mixed ingredients are sent to the rotary kiln.

In the rotary kiln, the raw materials are dried, calcined and pre-reduced to prepare nickel slag at about 1000 ° C. The rotary kiln flue gas is discharged by the waste heat boiler, dust removal and desulfurization, and the dust is mixed with the raw materials and then re-entered into the kiln.

The nickel slag is added to the ore furnace silo (lined refractory brick) in the closed heat insulation state (overhead feeding trolley), and is distributed into the submerged arc furnace through the discharge pipe at different positions according to the process requirements. The submerged arc furnace is a fully enclosed type, self-baking electrode, submerged arc smelting, reduction and melting of crude ferronickel and slag, and at the same time, a coal mine gas containing about 75% of Co is generated, and the waste gas is purified and sent to the rotary kiln for burning. The mouth, together with the pulverized coal as a fuel, is returned to the raw material field after being treated. After the water quenching, the slag of the submerged arc furnace can be used as building materials for road construction and brick making.

The product of the submerged arc furnace is crude ferronickel. Before de-ironing, pre-desulfurization agent is added to the ladle, and the iron is desulfurized at the same time. The crude ferronickel contains Si, C, P and other impurities. It needs to continue to refine. Bessemer, desilication oxygen blowing, while adding nickel scrap iron to prevent high temperature, after the desiliconization slag (slag or iron), blended with a basic converter, dephosphorization oxygen blowing decarburization while adding limestone The alkali slag is made, and the ferronickel water refined by the alkaline converter is sent to the pouring workshop to be cast into a qualified commercial ferronickel or into a granular ferronickel.

(4) Process characteristics

1 The raw material has strong adaptability. It can be applied to magnesia silicate ore and limonite type nickel oxide ore containing no more than 30% iron, and intermediate type ore. It is most suitable for high-magnesium low-iron nickel oxide ore that is difficult to handle using a wet process.

2 Nickel iron has a high grade and less harmful elements. The same ore, the RKEF process produces nickel-iron grades higher than the blast furnace process and the “sinter-mineral furnace” process. The desulfurization and converter refining processes of this process can reduce the harmful elements of ferronickel to the extent required by the ISO6501 standard and are welcomed by steel users.

3 energy saving and environmental protection, recycling. The raw material has more moisture, and no dust is generated during the process of crushing and transporting the material yard and the screen. The waste heat of the rotary kiln flue gas can be used for power generation. After the flue gas desulfurization meets the environmental protection requirements, it is discharged into the atmosphere, and the rotary kiln and the submerged arc furnace Return to the stockyard; after the dust removal, the ore furnace gas is sent to the rotary kiln for fuel, and the slag becomes the raw material for the construction industry after water quenching. Converter flue gas waste heat recovery steam, gas recycling, slag magnetic separation back to furnace, tail slag can be paved or cement. From the entry of the water-containing charge into the rotary kiln until the discharge of the slag from the ore furnace, the charge is completely enclosed, environmentally friendly and energy-saving.

4 nickel slag hot material into the mine furnace. The nickel slag produced in the rotary kiln enters the furnace at a high temperature above 900 °C. Compared with the cold material of the "sinter-mineral furnace", it saves a lot of physical heat and chemical heat, and significantly reduces the electrical energy and reducing agent. Consumption increases production efficiency.

China is a big country in the production and consumption of stainless steel. The demand for ferronickel is huge. It is very necessary to master the application of RKEF technology to produce ferronickel at low cost and high efficiency to meet the development needs of the national society while creating good economic benefits. Most of the equipment in this process is commonly used in the metallurgical industry. With the manufacturing capacity of China's metallurgical equipment, it can be localized and greatly reduce investment.

RKEF nickel oxide ore pyrometallurgical technology is owned by Japan, Canada and the former Soviet Union. Since 2005, he has been in contact with experts from the former Soviet Union to explore the possibility of cooperation and to inspect the Pabush nickel iron plant built by the former Soviet Union and located in Ukraine. At present, Sinosteel Binhai Company, Fujian Desheng Nickel Industry and Tianjin Rongcheng Iron and Steel Company have purchased the technology. These projects are in progress and are expected to be completed and put into operation within one to two years.

V. Improvement and innovation of RKEF technology

Although RKEF is a mature technology, it will affect production costs due to different external conditions, such as electricity and energy structures.

Domestic adoption of this technology must be improved. The first thing to do is to study the ingredient model. Domestic nickel oxide ore resources are scarce, relying on imports, imported mineral sources are complex, and lack of stable raw material bases, making the development of ingredient models more important. After the batching model is determined, small industrial experiments are also carried out to obtain data such as slag melting point, slag iron melting characteristics and suitable sintering temperature to guide production.

Secondly, research on waste heat utilization and flue gas desulfurization of rotary kiln is carried out. Due to the shortage of natural gas resources, the rotary kiln of domestic construction projects mostly uses pulverized coal as fuel. To protect the environment, it is necessary to clarify the characteristics of rotary kiln flue gas, remove soot and sulfur, and study the utilization of low temperature waste heat in rotary kiln.

Once again, the submerged arc furnace is the largest investment in nickel-iron smelting investment. It is necessary to study the furnace type, refractory material, electrode diameter, diameter of the center circle, electrode current density and voltage adjustment to determine the most suitable parameters to achieve power saving and Extend the life of the lining.

Finally, the problem with the converter. Several nickel-iron refining converters seen in China have adopted the design of top-blown converters for steelmaking. The splashing is serious because the slag volume of the ferronickel refining converter is about 10 times that of the steelmaking converter slag. In addition, the crude ferronickel is high-silicon ferronickel, which is difficult to handle in ordinary steelmaking converters. The use of an oxygen bottom-blown converter in a nickel-iron plant under construction in the country will solve the above problems well.

Converter slag recycling and nickel iron granulation process are also important research contents.

6. Investment and main technical and economic indicators of a typical RKEF process plant

1. Investment estimate

Project settings:

Construct a nickel-iron plant with an annual output of 100,000 tons of ferronickel (20% nickel content and 20,000 tons of nickel metal). The product meets the ISO650l standard.

Investment estimate:

(1) Raw material field. Including the grabber, tape conveyor, feeder, iron remover, etc., the storage capacity is determined by the raw material supply conditions, which can meet the normal production of materials for one month.

(2) Screening and crushing section. Including tape conveyor, plate feeder, hammer crusher , grid sieve, hook bridge crane and so on.

(3) Preparation section. Disc feeders, metering belts, overhead cranes, etc.

(4) Rotary kiln section. Rotary kiln, self-discharging trolleys, etc.

(5) Mine furnace section. Closed ore electric furnace.

(6) Refinement section. The desulfurization device is sprayed and the converter is refined.

(7) Casting section. Cast iron machine or ring casting machine.

(8) Public and auxiliary facilities, plant roads: total drop, oxygen production, energy center, safe power supply facilities, flue gas purification, waste heat (gas) recovery equipment, slag treatment, injection coal preparation, water treatment, machine repair, finished product warehouse, etc. .

The estimated cost of investment is shown in Table 2.

Table 2 Investment Estimation Table (Unit: 10,000 yuan)

The above estimates are rough and there will be some changes in the location of the project.

2. Main technical and economic indicators and cost calculation

After the nickel ore is transferred to the factory yard, the water content is 25-30% (physical water). After the natural storage of the stockpiles, the water content in the rotary kiln is 22-25%. 1.7% in Table 3 refers to the nickel content of the nickel base of the dry basis.

Table 3 Main technical and economic indicators

Under the above conditions, the RKEF process cost calculation is shown in Table 4.

Table 4 Estimation of ferronickel costs

3. Analysis of cost and profitability

It can be seen from Table 4 that the cost of producing ferronickel by the RKEF process in China is low and the profit margin is large.

The cost of the RKEF process is most sensitive to changes in the price of laterite nickel ore and electricity, followed by the price of reducing agents and fuel (coal). The impact of mine price, electricity bill and coal price on production costs is shown in Figure 1.

Figure 1 Production costs of the RKEF process under domestic conditions

The price fluctuation of laterite nickel ore is 200-1600 yuan/t dry ore. The electricity price considers 0.4 yuan/kWh, 0.6 yuan/kWh, 0.8 yuan/kWh. The coal price considers 700 yuan/t, 1000 yuan/t, 1300 yuan/t, and is typical under the conditions of the raw materials. Production cost curve for the RKEF plant.

When electricity price and coal price fluctuate by 20-30%, the production cost of nickel fluctuates by about 1000 US dollars. When raw materials and energy are expensive, the production cost of RKEF process is about 11,000 US dollars/t metal nickel. When raw materials and energy are cheap, RKEF The production cost of the process is less than $10/t metal nickel.

The logarithmic trend analysis is carried out by counting the domestic nickel price from 2001 to 2007 and the laterite nickel ore price between 1.8 and 1.9%, and the arc in Figure 1 is obtained. It can be seen that when the nickel price is less than 10,000 USD/t, RKEF The method of producing ferronickel is uneconomical. When the nickel price is between 10,000 and 11,000 US dollars, the RKEF method produces ferronickel at a low profit. When the nickel price is higher than 11,000 US dollars, the RKEF method produces ferronickel which is profitable.

Conclusion

Through the above analysis, it is believed that the supply of domestic nickel will still be less than demand in the short term. National policies support the development of high-efficiency utilization technologies for low-grade laterite nickel ore, creating opportunities for the development of China's ferronickel industry.

The domestic small blast furnace ferronickel process and the "sintering machine-mineral furnace" ferronickel process all have high energy consumption, high pollution and poor quality, and are being phased out.

The RKEF process is widely used in smelting of nickel-iron, with mature technology, energy saving and environmental protection. It is the most important method for the production of ferronickel in the world. Study China's specific raw material conditions and energy structure, break through the batching model, rotary kiln with pulverized coal as fuel for roasting and reduction, bottom blowing oxygen converter smelting and other key technologies, develop RKEF process suitable for China's national conditions will be the development of China's ferronickel industry make a contribution.

Although nickel prices are historically low, cost analysis shows that the use of advanced nickel-iron smelting processes to make full use of the advantages of low-cost equipment and building materials, the construction of modern nickel-iron plants, still have good economic benefits.

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