Energy-efficient melting technology of lead and its alloys

Xiong Jiazheng 1 Zhao Tao 1,2

(Zhuzhou Torch Industrial Furnace Co., Ltd.1, School of Energy Science and Power Engineering, Central South University2)

Abstract : In view of the current situation that lead and its alloys are lagging behind in melting equipment, high energy consumption and serious environmental pollution, two kinds of new melting furnaces, regenerative high-efficiency melting lead furnace and industrial frequency melting lead induction furnace, have been developed. Through experimental research and engineering practice, it is shown that although the heating modes of the two furnaces are different, they all have the characteristics of low energy consumption, fast melting speed, high thermal efficiency and environmental protection. Compared with the domestic lead-zinc smelter, which is commonly used in China, the energy consumption per ton of lead in the two types of furnaces was reduced by 49% and 64% respectively, the thermal efficiency was increased by 9.59% and 62.5% respectively, and the smoke emission was reduced by 49% and respectively. 100%, has achieved good economic and social benefits.

Key words: regenerative high-efficiency lead melting furnace, core frequency melting lead induction furnace, energy saving, environmental protection

Abstract:Due to the fact that the metal lead and its ally melting processes are poorly equipped, high power consumption and environmentally disastrous, including waste gas in metallurgy, a new regenerative type heating furnace and 50Hz twin-channel induction furnaces are researched and developed. These are proved by the research and engineering practice that the two new type melting furnaces are low energy consumption, melting fast, high thermal efficiency and environmental protection, although they are different in heating methods. The energy consumption per ton of lead reduces 49% and 64%, the thermal efficiency increases 9.59% and 62.5%, the emission of waste gas reduces 49% and 100% respectively compared with those melting lead commonly used in a main lead and zinc Smelter. The users have access to a good economic. And social benefits.

Key words: Regenerative efficient lead melter, frequency channel induction lead melter, energy saving, environmental protection

1 Introduction

Main lead smelting processes in the country generally use lead ore smelting to prepare crude lead, crude lead refining to prepare anodes, electrolytic lead to lead, and lead cathode lead to lead ingots. At present, lead smelters use lead melting pots for crude lead refining, cathode lead smelting, cathode plate manufacturing, and lead alloy manufacturing. According to their uses, they can be divided into lead melting pots, electric lead pots, cathode pots, and alloy pots. This is collectively referred to as a melting pot, which heats the steel saggers through the combustion of fuel to achieve the purpose of melting the metal lead in the pot. In the course of use, lead melting pans are generally subject to problems such as high exhaust gas temperature, incomplete combustion of fuels, and high local temperatures, which results in low thermal efficiency, high energy consumption, short lifetime, and large greenhouse gas emissions. Take a large-scale lead-zinc smelter in China as an example: 1 The unit consumption of lead melting gas is 240~260m3/t; 2 The thermal efficiency is only about 10%; 3 The service life of the crucible is generally only 3 to 4 months; 4 The flue gas zone The sensible heat to go is as high as 50% to 60%; 5 The heat loss of incomplete combustion is as high as 20% to 30%. This kind of extensive production not only reduces the market competitiveness of the company's products, but also runs counter to the national industrial policy of energy conservation, consumption reduction and harmonization, especially in the current global economic crisis environment.

For the disadvantages of molten lead pots, Zhuzhou Torch Industrial Furnace Co., Ltd. has systematically investigated and researched the types of equipment, melting methods, heat transfer technology, energy-saving technologies, etc., combined with many years of experience in manufacturing lead-zinc and its alloy melting equipment, combined with Central South University. The School of Energy Science and Power Engineering has developed two types of new lead melting furnaces, regenerative high-efficiency melting lead furnaces and lead-frequency cored lead induction furnaces. Among them, the 85t regenerative high efficiency lead melting furnace has been successfully put into operation at the Zhuzhou Smelter. The practice shows that the furnace has a satisfactory effect in reducing energy consumption, increasing productivity, reducing greenhouse gas and nitrogen oxide emissions, and Reports were made on non-ferrous metal networks and mainstream media in Hunan. The frequency-concentrated melting lead induction furnace has developed a 3t test furnace and successfully conducted nine experiments. The research results show that its advantages in tons of lead energy consumption, thermal efficiency and environmental protection are more prominent. The following will introduce two furnace types and their application effects and experimental results.

2. Regenerative high efficiency melting lead furnace

2.1 High temperature and low oxygen dispersion combustion technology

Regenerative combustion technology is a high technology that has been successfully developed in the field of international fuel utilization and combustion technology since the 1990s. In Japan and the United States, high-temperature air combustion technology HTAC is known, and some countries in Western Europe are known as “flameless combustion” technology. . The principle is to use high-temperature flue gas to preheat the gas and combustion air to achieve the purpose of reducing the temperature and emissions of flue gas and reducing the amount of gas. See Figure 1 for the principle.

Figure 1 Schematic diagram of the working principle of HTAC technology

Regenerative burners work in pairs, alternating with combustion and exhaust. As shown in FIG. 1 , when burner A burns, the regenerators A and B at the front end of the burner are correspondingly in a state of heat release and heat absorption, and the air flows through the regenerator A which has been accumulated, and is preheated to 800° C. After participating in the above combustion, while the B burner smoke, 1000 °C flue gas heating and regenerative body B, the flue gas temperature decreases through the flue exhaust; reversing valve after reversing, B burner combustion, burner front end corresponding The regenerators B and A are in an exothermic and endothermic state, respectively. Repeatedly, the waste heat of the flue gas is recovered by the regenerator, the air is preheated to above 800° C., and the temperature of the flue gas is reduced to about 150-200° C. Japan, the United States, Europe and other countries in the steel industry applied the technology to achieve an average of 30 to 50% energy savings, CO2 emissions reduction by more than 30%.

Zhuzhou Torch Industrial Furnace Co., Ltd. and the School of Energy of Central South University began to research the application of HTAC technology in non-ferrous metal furnaces from the early 90s of last century. On the basis of learning from the overseas HTAC technology, it has successfully developed suitable low melting point characteristics for non-ferrous metals. The high-temperature, low-oxygen dispersion combustion technology achieves the effect of saving energy in large amounts, reducing greenhouse gas emissions, and reducing the content of nitrogen oxides in flue gas from several hundred or thousands of ppm to 30 to 50 ppm.

2.2 Regenerative high-efficiency melting lead furnace

The regenerative high-efficiency melting lead furnace adopts many technical measures such as optimized combustion, enhanced heat transfer, waste heat recovery, and low-oxygen dispersion combustion. 1 Furnace is equipped with a guide wall to efficiently organize airflow in the furnace and enhance the heat transfer between the flue gas and the boiler body. Effect; 2 Two independent combustion chambers to ensure full combustion of gas while avoiding the direct contact of the flame with the boiler; 3 Optimize the burner structure by means of computer simulation optimization through combustion dynamics criteria to make combustion more fully and save fuel to the maximum extent. 4Use the flue gas return and ejector technology to reduce the oxygen content in the combustion zone to achieve diffuse combustion—that is, the furnace temperature is uniform, the flame is full, and there is no local high-temperature zone; 5 The heat transfer efficiency and resistance that are prepared by the company The two-parameter optimization design calculation program of the function repeatedly calculates and optimizes the structure of the heat storage body and related parameters. The heat storage efficiency is high, the commutation cycle is moderate, and the resistance loss is appropriate. 6 The control system adopts S7-300 series programmable controllers produced by Germany SIEMENS ( PLC) implements logic control, configures upper computer, establishes configuration screen of furnace, and intuitively reacts furnace operation Status and remote operation. See Table 1 for main technical parameters and Figure 2 for device configuration and structure.

Table 1 Main technical parameters of regenerative high efficiency lead melting furnace

Figure 2 Regenerative high efficiency melting lead furnace structure

2.3 Project Example and Benefit Analysis

The 85t regenerative lead melting furnace of the Zhuzhou Smelter was completed and put into operation in late 2008. After nearly 8 months of production practice, the performance of the 85t regenerative lead melting furnace proved to have many advantages in comparison with the performance of the lead melting pot: 1 ton of lead melting energy was reduced by an average of 49%; 2 melting 21.43% increase in speed; 3 increase in average furnace temperature around 115°C; 4 increase in thermal efficiency by 9.59%; 5 decrease in smoke emission by 49%; 6 decrease in chemical incomplete combustion rate by nearly 13.36%; 7 decrease in oxygen content in smoke by approximately 5.8% 8 The service life of lead pots has been extended by an average of 4 months or more. See Table 2 for statistical data.

Table 2 Comparison of performance of regenerative lead melting furnace and lead melting pot

Due to the excellent performance of the regenerative high-efficiency melting lead furnace, it brings significant economic and social benefits: 1 5 million Nm3 reduction of gas consumption annually, energy-saving benefits of more than 1.5 million yuan; 2 annual reduction of greenhouse gas CO2 emissions of 4000 tons; 3 annual reduction of NOx emissions of 2,500 Nm3 The above; 4 reduce the consumption of 2 to 3; 5 greatly improve the worker's operating environment and reduce labor intensity.

3. Frequent-frequency melting lead induction furnace

3.1 Induction Melting Technology

Industrial frequency induction furnaces are widely used for metal melting and heat preservation because of their high thermal efficiency, good melt exhaustability, uniform melt temperature, and low oxidation loss. Compared with coal, oil, gas and other fuel melting methods have the following characteristics: 1 high thermal efficiency and energy conservation. The fuel furnace produces a lot of heat due to the combustion of flue gas, the thermal efficiency is far lower than that of the induction furnace; 2 The heating speed is fast, the vortex is directly heated inside the material, and the melting efficiency is high; 3 The heating quality is high, the burning loss is small, the metal melt The composition is stable and easy to adjust; 4 induction heating is a pollution-free heating method, does not produce fuel combustion flue gas; 5 easier to achieve mechanization and automation.

3.2 Numerical Simulation Analysis of Power-frequency Concentric Melting Lead Induction Furnace

Because lead metal has the characteristics of low melting point, low specific heat, small electrical conductivity, high density, good fluidity, and strong permeability, three major difficulties must be solved by adopting frequency-frequency induction heating and melting. ; 2 lead liquid leakage; 3 melting groove wall superheat control. To this end, the following technical measures are taken: (1) Using a metal material with a higher melting point than lead, better thermal stability, and no reaction with the lead liquid, a closed-type trench cavity mold is used instead of a refractory material. This new structure prevents the leakage of lead. 2 The “W” sensor is used to enhance the flow of lead.

Based on this, a numerical model of the center frequency melting lead sensing body is established (see Figure 3). The performance of the power frequency melting lead sensing body is analyzed by using the numerical simulation and equivalent circuit model (see Figure 4). Simulation and optimization.

Fig. 3 Calculated area and mesh of molten lead induction model Fig. 4 Equivalent circuit model of molten lead induction body

Through simulation and optimization calculations, the lead-inducing inductor has the characteristics of high voltage, high natural power factor, and low compensation capacitance, ie, "two high and one low" impedance characteristics. Numerical simulation analysis verifies theoretically the feasibility of melting metal lead using a power frequency centered induction body, and finds the optimal parameters of the relevant structure of the induction body, and predicts the working conditions at the same time. The simulation calculation data of the 300kW power frequency cored lead lead induction body is shown in Table 3.

Table 3 Simulation results of molten lead induction

3.3 Hot-frequency experiment of center frequency melting lead induction furnace

In order to further verify the feasibility and technical performance indicators of lead melting in induction furnaces, the company produced a 3 t pilot-scale cored lead melting induction furnace at the end of 2008 based on data obtained from simulation optimization calculations. Hot lead test, see Table 4 for experimental results.

Table 4 Experimental measurement data and calculation data

Experiments show that: 1 It is feasible to use the frequency-frequency induction furnace to heat and melt lead and its alloys; 2 The flow of liquid lead during heating is obvious, which is conducive to heat transfer and mass transfer. See Figure 5; 3 The surface temperature of the metal frit cavity wall is relatively uniform , There is no serious wall overheating. After the terminal voltage reaches 300V, the temperature difference between the lead temperature and the surface of the metal bath cavity wall remains stable within 50°C. See Figure 6; 4 The design of the induction body and the metal melting trench die Reasonable, no damage after multiple destructive tests.

Fig. 5 Flow of mass transfer at the side of the trench

Fig. 6 The temperature of the measuring point on the surface of the melting groove changes with time

AB: U=100V; BC: U=200V; CDE: U=300V

Table 5 compares the performance of the electric furnace with the core frequency melting lead induction experiment and the performance data of the regenerative high-efficiency melting lead furnace and the molten lead pot. It can be seen that the technical performance of the frequency-frequency cored lead-induction furnace is superior, the lead-lead energy consumption of the lead-conducted lead-cooker is reduced by 64%, the thermal efficiency is increased by 62.5%, and the emission of flue gas is expected to be reduced by 100%.

Table 5 Performance Data Sheets of Frequency-Concentrated Melting Lead Induction Furnace, Regenerative High-Efficiency Melting Lead Furnace, and Melting Lead Pot

At present, the Zhuzhou smelter has purchased a 6t frequency-concentrated lead-lead induction alloy electric furnace, which is in the production phase and will be put into use in August.

4 Conclusion

Through engineering practice and experimental research, it is shown that although the two new melting furnaces have different heating methods, they all have the characteristics of low energy consumption, fast melting speed, high thermal efficiency, and environmental protection; the lead melting pots commonly used in large-scale lead-zinc plants in China, The energy consumption per ton of lead was reduced by 49% and 64% respectively, the melting rate was greatly increased, the thermal efficiency was increased by 9.59% and 62.5%, and the smoke emission was reduced by 49% and 100%, respectively, achieving good economic and social benefits. Although the initial investment of the new furnace is larger than that of the lead melting pot, it has a high cost performance and has a high promotion value in the melting of lead and its alloys.

The selection of the two furnace types will depend on local conditions, such as the operating habits of the workers, local coal prices and electricity prices, whether or not there are existing gas generators, and whether or not power addition is required. At present, domestic lead and its alloys are lagging behind in the level of melting equipment. Zhuzhou Torch Industrial Furnace Co., Ltd. intends to work with the majority of its colleagues to contribute to the improvement of industry equipment and the promotion of industry development.