With the continuous advancement of ecological civilization, green development, circular development, and low-carbon development have become social consensus, and the air, water, and soil pollution prevention and control action plans have been comprehensively promoted. The "Technical Guidelines for the Development of Emergency Emission Reduction Measures for Key Industries in Heavy Pollution Weather" (2020 revision) requires ultra-low emission values for Class A enterprises in the glass industry: particulate matter not higher than 10mg/m³, sulfur dioxide not higher than 50mg/m³, nitrogen Oxide is not higher than 200mg/m³. In order to meet the flue gas emission standards, the glass production line must be equipped with desulfurization, denitration, and dust removal facilities, and its investment and operating costs are high.
my country is vigorously promoting the transformation of energy structure. Faced with the pressure of energy saving and emission reduction, electric furnaces with low investment and operating costs, energy saving and environmental protection advantages are becoming more and more widely used.
At present, the melting capacity of all-electric glass melting furnaces at home and abroad is mostly 160t/d. In order to reduce the risk of design, installation and operation of large-scale electric melting furnaces, mathematical simulation research is generally carried out before design. In the process of mathematical simulation, full consideration should be given to furnace life, investment costs, glass melting quality, energy consumption, production flexibility and Adjustability and other factors. Through mathematical simulation research results, the best furnace structure of the electric melting furnace, the best distribution of electrodes and the best configuration range of power are obtained.
1. The 350t/d float glass full electric melting furnace is an approximately circular, deep-pool electric melting furnace. The product category is ordinary soda lime silica glass.
2. Main technical parameters of 350t/d float glass full electric melting furnace
(1) Glass composition: soda lime silica glass;
(2) Type of glass produced: automotive glass with a thickness of 1.8~2.5mm;
(3) Melting capacity: 350t/d;
(4) Melting area: 140m²;
(5) Pool depth: 2450mm;
(6) Width of liquid hole: 600mm;
(7) Ascending track size: 300mmx600mm;
(8) Melting rate: 2.5t/(m²•d);
(9) Glass batch raw and cooked ratio 80:20;
(10) Installed power: 21000kVA;
(11) Normal use power: 17500kVA;
(12) The flow hole and electrode bricks are made of 41# oxidized non-shrinkage zirconia corundum bricks, and the remaining parts are 33# oxidized non-shrinkage zirconia corundum bricks; the thickness of the pool wall brick is 250mm; the thickness of the pool wall insulation layer is 300mm;
(13) A pneumatic level gauge is used to detect liquid level fluctuations; the level gauge is installed on the top of the ascent;
(14) The automatic feeder with the rotary furnace top is adopted; the feeder is interlocked with the liquid level meter, and the feeding amount is automatically adjusted according to the level of the liquid level, and the fluctuation range of the liquid level is controlled within ±0.2mm.
3. Comparison of 350t/d electric melting kiln and 1000t/d flame kiln
3.1 Kiln structure
The flame glass melting furnace is composed of a melting pool, a regenerator, a small furnace, a cooling part, a gate, a flue and a chimney, etc. It has a complex structure and a large area.
The all-electric glass melting furnace has only a melting pool and a flow hole, with a simple structure and a small footprint.
3.2—Investment
The flame furnace is not only an investment in the melting cellar itself, but also an investment in auxiliary equipment such as desulfurization, denitrification, and dust removal.
The electric melting furnace has only refractory materials, electrical appliances and steel structure, and the main melting transformer can directly use 10kV power supply, which reduces the cost of the substation. The exhaust gas produced by the electric melting furnace is mainly carbon dioxide produced by the decomposition of carbonate in the raw materials, which has little environmental pollution. In addition, the dust generated at the feeding port can meet the emission requirements by simply removing dust.
3.3 Operating cost
The 1000t/d float glass melting furnace energy consumption is 5650kJ/kg molten glass. The standard calorific value of natural gas: 33450kJ/m³, the consumption of natural gas is 0.169m³/kg molten glass, and the price of industrial pipeline natural gas is 3.23 yuan/m³, equivalent to 0.546 yuan/kg molten glass.
The melting energy consumption of 350t/d electric melting furnace is generally not more than 1100kWh/t glass. Large power users in industrial enterprises can use direct power purchase. The average price of direct power purchase is 0.298 yuan/kWh, and the ordinary electricity price is 0.5 to 0.8 yuan/kWh. According to the calculation of direct purchase of electricity, the cost of melting glass in electric melting furnace: 0.328 yuan/kg of molten glass, the cost of electric melting furnace is lower than that of flame melting furnace; the cost of melting glass in electric melting furnace is calculated according to the valley value of ordinary electricity: 0.554 yuan/kg The cost of molten glass, electric melting furnace and flame melting furnace are equivalent; the cost of melting glass in electric melting furnace is calculated according to the peak value of ordinary electricity: 0.88 yuan/kg molten glass, and the energy consumption cost of electric melting furnace is higher than that of flame melting furnace.
3.4 Environmental protection investment
Flame glass melting furnaces inevitably produce sulfur oxides, nitrogen oxides and dust during the production process. In order to meet environmental protection requirements for flue gas emissions, additional desulfurization, denitrification, and dust removal equipment must be installed.
3.5 Control accuracy
The temperature of the flame glass melting furnace is interlocked with the combustion-supporting wind and gas (or fuel oil). Adjust the opening degree of combustion air and gas (or fuel oil) through temperature feedback, generally using thermocouple to measure temperature. The thermocouple detects the temperature of the combustion space and cannot directly reflect the temperature of the molten glass. The reaction lags behind and causes large fluctuations in the temperature of the molten glass.
The electric melting furnace indirectly controls the temperature of the molten glass through constant current control.
P——The input power of electric melting furnace, W;
I——current between electrodes, A;
R——Resistance between electrodes, Ω.
The resistance of the molten glass is inversely proportional to the temperature of the molten glass, that is, when the temperature of the molten glass increases, the resistance of the molten glass decreases; on the contrary, the resistance of the molten glass increases. If the temperature of the molten glass increases, the resistance of the molten glass decreases. It can be seen from equation (1) that the applied power decreases and the temperature of the molten glass decreases; on the contrary, if the temperature of the molten glass decreases, the resistance of the molten glass increases, which is applied to the molten glass. The increase in power increases the temperature of the molten glass.
In theory, the temperature of the molten glass can be constant. Through the use of advanced power forecasting system, the melting power is corrected in time according to weather changes to ensure the stability of the melting temperature.
3.6 Thermal efficiency
The energy consumption of a 1000t/d flame float glass melting furnace is 5650kJ/kg molten glass, which is 1.568kWh/kg molten glass. The useful energy consumption of float glass is 0.756kWh/kg molten glass, and the thermal efficiency is 48.21%.
The melting energy consumption of 350t/d float glass full electric melting furnace is 1.1kWh/kg molten glass, and the thermal efficiency is 68.73%, which is higher than that of flame melting furnace.
3.7 Furnace service life
Due to the improvement of the quality of refractory materials and the scientific design of the furnace, the service life of the flame furnace is generally more than 8 years, and the electric melting furnace must be cold repaired at least once within 8 years, and the 350t/d float glass electric melting furnace is cold repaired. The materials that need to be replaced are: zirconium corundum bricks, ordinary refractory materials, molybdenum electrodes, etc. The total investment in cold repair including labor costs is about 22 million yuan.
The service life of an electric melting furnace depends on three aspects: electrode, refractory life and melting rate. Molybdenum electrodes are commonly used in soda-lime-silica glass electric melting furnaces. With reasonable design and proper use, the life of the furnace can reach the design age. The fastest erosion in the electric melting furnace is the liquid hole brick and the electrode brick. The design life of these two places is generally not less than 3 years. In actual production, the life of the soda lime silica glass melting furnace is more than 4 years. Temperature is the main factor that affects the life of refractory materials. Increasing the melting rate will inevitably increase the melting temperature, and the life of the furnace will decrease accordingly.
If the direct purchase of electricity is used, compared with the 1000t/d flame furnace, the melting cost of the electric melting furnace is saved: (0.546-0.328)×1000×1000=21.8 (ten thousand yuan/d). Converted into 8 years of savings: 21.8 × 350 × 8 = 610.4 million yuan, cold repair costs: 2200 × 3 = 66 million yuan (The melting capacity of a 1000t/d flame furnace is equivalent to three 350t/d all-electric furnaces Melting capacity). If the high price of ordinary electricity is used, the flame furnace has advantages only from an economic point of view (without considering environmental protection). If the low-cost electricity of ordinary electricity is used, the comprehensive cost of the two melting methods (considering the age of the kiln and environmental protection) is equivalent, and the specific needs to be accurately calculated according to the actual situation.
4. Conclusion
Compared with flame glass melting furnaces, all-electric glass melting furnaces have the characteristics of low investment, low environmental pollution, low operating costs and high thermal efficiency. At the same time, the electric melting furnace has realized fully automated control. In the fierce market competition, more and more float glass manufacturers will consider the application of electric melting furnaces.
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