Coke and 100kg pulverized coal £a leaking 16,000 tons of ore per day to produce blish32! The problem of blowing plastic at the tuyere 1 Introduction The disposal of discarded plastics has become a worldwide problem. From the perspective of saving energy and reducing pollution, countries are studying recycling. Methods. In particular, industrialized countries have invested considerable funds in research and development of recycling technologies for waste plastics. In this respect, Sakamoto Steel Pipe Gyeonggi Steel has undergone extensive basic research to develop a technology for injecting granular plastic into blast furnaces. Since 1996, the injection volume has reached 45,000 tons. In 1999, the amount of coke used has decreased by 50,000 tons per year. The emission of carbon dioxide gas has decreased by 202,000 tons per year, and good economic and social benefits have been received. . Due to the dual effects of this technology in energy conservation and environmental protection, it was rewarded by the 2000 National Energy Conservation Promotion Association of Japan.
During the operation of the blast furnace, it takes a lot of coke to change from ore to molten iron. That is to say, coke is charged from the upper part of the blast furnace, and the raw coal powder is injected from the lower part of the blast furnace, that is, coal is injected. While people are desperately trying to increase the ratio of coal injection, various waste plastics are increasing, and the recycling rate is very low. The plastic has a calorific value of 41,868 kJ/kg, and the hydrogen content is higher than that of coal. Therefore, injecting plastic into the blast furnace can not only reduce the amount of coal used, but also reduce the amount of CO2 emissions. The use of discarded plastics for ironmaking not only saves resources but also protects the environment, it is a good way to do both. At present, this method has been put into practical use abroad, but it is limited to the discussion and research stage in China.
2 Analysis of the status quo 2.1 Current status of the blast furnace The ore and coke are alternately installed in the furnace from the upper part of the blast furnace, and hot air of 1000 ° C or more is blown from the lower tuyere, and the molten iron and the slag are simultaneously discharged. In the swirling zone at the end of the tuyere at the lower part of the blast furnace, the coke is burned to generate high-temperature gas to supply ore for reduction and melting. At this time, most of the coke becomes (1) the gas is reduced with iron ore.
In order to reduce the amount of coke used, coal injection technology has gained popularity.
Take the No. 1 blast furnace of the Gyeonggi Steel Works as an example. 450 kg of 10,000 tons of pig iron is used per ton of pig iron. Fukuyama Iron Works has a coal injection volume of more than 20 Ckg per ton of iron. Gas that is not involved in the reduction reaction is discharged from the top of the furnace, used for the top pressure power generation or supplied to the furnace and generator set as fuel for the gas to be fully effective. Use.
2.2 Recycling of waste plastics Plastics from various sizes of packaging bags, tableware to automobile shock absorbers and other large molded products have penetrated into all aspects of human life, and pollution has become increasingly serious. As the scope of use and usage continue to expand, the amount of waste is increasing year by year. In addition to a small amount of recycling, the treatment method is landfill and the second is incineration. Landfill not only occupies land, but also is difficult to degrade and burn, causing environmental pollution. Governments are promoting resource recycling or recycling and producing a series of policies and regulations to control damage to land and resources and the environment. Japan is a small energy country and attaches great importance to the recycling of waste. Many energy-saving technologies are in the forefront of the world, but the recycling rate of plastics is only 42% (1997), probably because of the complex plastic form and some plastic products. It is a mixture with other materials and is difficult to separate.
3 Problems with the use of plastics in blast furnaces 3.1 Utilization of waste plastics There are two methods for charging plastics into the furnace as follows: (1) loading from the upper part of the blast furnace; (2) blowing from the lower vent of the blast furnace. Regarding the temperature distribution in the blast furnace, the lower part is about 2000 in the upper part of the furnace, and the high temperature gas generated in the lower part is reduced to about 150 ° C by heat exchange with the original, fuel (iron ore, coke). If the plastic is from the upper part of the blast furnace with the ore When coke is put into the furnace together, it will heat up as the raw material falls. Plastics are petrochemical products that melt when the temperature reaches 100~200C. When they reach above 300C, they will decompose into low molecular weight compounds. In the decomposition product, since it contains paraffin and tar components, the inclusion from the upper portion affects the gas permeability of the charge, and it also adheres to the gas purification device, causing malfunction, and it is seen that it is not an ideal method to load from the upper portion. In view of the above situation, the method of blowing from the tuyere is studied intensively... 0-. and the plastic particles below 0mmn in the swirling zone gas 1 oiling blows solid fuel from the tuyere as shown, burning and gasifying in the lower part of the blast furnace The zone (the raceway) is converted into a reducing gas. The hot air blasting from the hot blast stove to the tuyere is about 1000 °q and the speed is about 200 m/s. Due to the impact of the wind, a wind of about 1.5 m in the hot air is rapidly burned and instantaneously generates CO2. At the same time as H2O, the combustion temperature is above 2000 °C. The latter half of the raceway (away from the tuyere portion), 2 disappears, and the resulting C2 and HO react with the coke to convert to reducing gases CO and H2. Eventually the gas composition and temperature profile are shown. The residence time of the solid fuel in the swirl zone is extremely short, about 10 increases the utilization of solid fuel in the blast furnace, and it is necessary to develop a combustion/gasification technique that allows the solid fuel to be used in the shortest time. In the case of pulverized coal injection, the particle size must not exceed 100%!
Gas composition and temperature distribution in the gyro zone The particle size requirements for the injection of waste plastics are the same as for pulverized coal. However, heat is generated during the pulverization process of the plastic, and the heat generated by the processing causes the plastic to melt. In order to prevent the reflow, it is necessary to adopt a cooling technique, which requires a large amount of energy. In addition, the variety of waste plastics will complicate the pulverization processing system. To this end, the following two questions were studied.
The optimum particle size for the highest utilization of plastic in the blast furnace.
The effect of actual blowing on the operation of the blast furnace.
4 Solution 4.1 Plastic particle size and combustion/gasification characteristics In general incinerators, the combustion/gasification characteristics of solid particles are affected by the particle size. The larger the particle size, the lower the combustion/gasification rate. The size of the particle size is determined by the processing machinery and is therefore critical to the design of the processing machine. From the simulation. For comparison, the situation of coking and coal injection is also indicated. In the case of coal injection, as soon as the coal powder enters the swirling zone, the oxygen is quickly consumed, and the oxygen at the end of the tuyere is completely consumed. In the case of coking, the oxygen consumption is declining and there is a peak of CO2. It can be seen that there is a burning zone in the convoluted zone.
As can be seen, the injection of plastic is similar to the case of coke.
Compared with plastics with a particle size of 0.2-1.0 mm and a particle size of <10 mm, the peak position of CO2 is close to the tuyere, but not as close as pulverized coal. When coke powder is sprayed, the maximum temperature is about 250mm from the tuyere; the situation of coal injection is different, and the highest temperature zone is close to the tuyere. Plastics with a particle size of <10 mm are similar in temperature distribution to coke. Compared with coal injection, since the high temperature zone is slightly far from the tuyere, the heat load on the furnace wall can be reduced, and the heat loss caused by the furnace wall can be alleviated.
Regarding the relationship between the gasification rate of plastic combustion and the particle size, the test results show that the larger the particle size, the higher the gasification rate. Moreover, the gasification rate is higher than that of pulverized coal combustion, the combustion gasification rate of pulverized coal is only 56% to 60%, and the combustion gasification rate of plastic is as high as 90% or more. The reason why the coarse-grained plastic has high combustion gasification rate is that the reason for the analysis is that after blowing into the tuyere, the particles are not immediately ignited by burning, but are temporarily circulated in the swirling zone, when the particle size reaches the degree of scattering (limit particle size). When the reburning gas speed corresponds. The combustion gasification rate in the swirling zone can be expressed by the following formula.
It can be seen that a coarse-grained plastic having a large initial particle size r can ensure a high combustion/gasification rate. The calculation results using the above formula are basically consistent with the measured results, which indicates that the model used in the experiment is appropriate. The reason for the low pulverized coal combustion/gasification rate is that it does not circulate in the swirling zone. Even if the coarse coal powder is sprayed, the effect of circulation retention cannot be received because the coal particles are split by rapid heating and the integrity of the coal particles cannot be controlled. The plastic structure is dense, the heat transfer is slow, and it is not easy to split when heated rapidly. That is to say, as long as the particle size is right, the waste plastic can be used as a reducing agent and a heat source.
4.2 Experiments on plastic injection in blast furnace After repeated analysis and simulation tests, a real furnace experiment was carried out in the blast furnace of Gyeonggi Steel Works. The plastic particle size is divided into two types, one is a particle size of 0.2 to 1.0 mm, and the other particle size is <10 mm. The main measurement items are as follows.
Gas analysis in the blast furnace: The detector is placed at three sampling points in the radial direction of the blast furnace to sample the plastic blast furnace gas.
Analysis of tar in blast furnace dust.
According to the analysis of the H2 content in the center, middle and peripheral gas in the radial direction of the blast furnace, it is known that when the plastic is sprayed, the H2 content is increased compared with the non-spraying plastic regardless of the particle size. In particular, the plastic which is sprayed with 0. ~ 1.0 mm has a higher H2 content in the middle and the periphery than in the center of the furnace. When the plastic particles having a particle size of <10 mm are sprayed, the H2 content in the middle and the center portion is high. That is to say, when the coarse-grained plastic of <10 mm is sprayed, it is circulated in the depth of the swirling zone, and the generated reducing gas is effectively infiltrated into the interior of the blast furnace.
Regarding the tar problem in the blast furnace, the experimental results show that the tar content in the blast furnace dust is the same as when the plastic is not sprayed, which eliminates the original concern. It can be seen that there is no problem in the injection of plastic, and the H2 content in the blast furnace gas increases, indicating that the emission of blast furnace carbonic acid gas will be reduced.
4.3 Simulation calculation effect Compared with coal injection and plastic injection, the consumption of coke is less than that of coal injection when plastic is sprayed. This is because the heat of plastic is higher than that of coal powder. It can be calculated that if the amount of plastic sprayed is 10 kg/t, the amount of iron 7 water coke can be reduced by 12.1 kg/t of molten iron.
The rate has also received the desired results. The plastic is converted into reduced gas in the blast furnace for the reduction of iron ore. The amount of coke used is determined by the thermal equilibrium and material balance of the blast furnace. The research results show that when the plastic injection volume is 50kg/t hot metal, the utilization rate of reducing gas is 51%, indicating that plastic is effectively used as a reducing agent. Gas that has not been discharged outside the furnace is used for hot blast stoves and power generation. When the plastic is blown, the heat recovery rate of the blast furnace as a whole system can reach 80%, which is much more efficient than the heat recovery for urban waste heat generation.
5 Economic benefits obtained by blowing plastics 5.1 Plastics and furnaces The plastics injected into the blast furnace must have a certain particle size. In October 1996, the plastic used in the Gyeonggi No. 1 blast furnace in Japan was industrial waste plastics other than polyethylene. It is divided into two types, film and block, and is processed in two systems. The film-like plastic is granulated in a granulator, and the bulk plastic is pulverized in a pulverizer, and must be processed to a predetermined particle size. The annual processing capacity is more than 40,000 tons. The results show that after the spray molding system is set, the coke ratio is reduced and the furnace condition is stable.
5.2 Energy-saving effect Table 1 blows plastic to save energy. Comparison of resources Name unit (unsprayed) (spraying) increase or decrease of coke oven coal loading kg/t hot metal spray: a 24.7 increase coal dry distillation heat MJ / t hot water high coke kg / t iron water increase coal injection : A 13.8 furnace coal powder kg / t hot metal plastic kg / t hot metal plastic heat: 35588kJ / kg; pulverized coal heat: 30982k | / kg energy efficiency of spraying waste plastics into the blast furnace is mainly reflected in the reduction of the coke ratio. Table 1 shows the energy saving and resource saving effects including the coke oven. Coal injection and injection molding reduce the coke ratio and also reduce the coal consumption during coking. The effect of blowing plastic can be calculated from the respective blowing amount and heat generation amount. In 1999, 45,000 tons of plastic was injected, equivalent to 13. 3kg per ton of molten iron. According to this calculation, the amount of coke reduction was 14.3kg, and the annual reduction was about 50,000 tons. Calculated according to the average calorific value of coke 29726kJ/kg. The energy saving is 1.475X106GJ. It can be seen from Table 1 that due to the reduction of coke-burning plastic coke ratio, coke oven coking consumes less than 24.7kg/t of molten iron, and the coal consumption can be reduced by 85,000 tons per year (the output of iron is 9500t/d). In addition, the calorie consumption can be reduced by 339 MJ/:t//iron water during the recovery and retorting of Huiyuan in the process of coking with less coal. Meng, 1 energy-saving annual energy saving 46473GJ. The annual energy saving of coke oven and blast furnace is 1.521X106GJ, which is equivalent to 1.47 5.3 of the annual energy consumption of Gyeongsang Steel. The reduction of carbon dioxide emissions is comprehensive, as the plastic injection is reduced. The amount of coke used, thus reducing the amount of carbon dioxide emissions. According to the above-mentioned reduction of 50,000 tons of coke, the annual emission of carbonic acid gas can be reduced by 158,000 tons (according to 0.86).
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