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This post was last edited by Blue Point on 2009-7-20 14:24 Contents 1 Literature review 1 1.1 Initial cooling of coke oven gas 1 1.1.1 Brief description of the initial cooling process 1 1.1.2 Initial cooling process of coal gas 1 1.2 Removal process of naphthalene in coke oven gas 2 1.2.1 Naphthalene in coke oven gas and its removal 2 1.2.2 Coke oven gas naphthalene removal technology 3 1.2.3 Good primary purification naphthalene removal process 3 1.3 Gas mist capture process 4 1.3.1 Working principle of electric tar collector 4 1.3.2 Capture mechanism of electric tar collector 4 1.3.3 Formula of electric tar collector 5 1.3.4 Position setting of electric tar collector in gas purification system 6 1.4 Gas transportation and regulation 6 1.4.1 Energy-saving measures for gas blowers 6 1.4.2 Principle of variable frequency speed regulator 7 1.5 Tar ammonia water separation process 7 1.5.1 Separation process with two-stage deslagging 7 1.5.2 Settlement slag removal and static separation process 8 1.5.3 Pressure dehydration tar nitrogen water separation process 8 1.5.4 Mechanized tar ammonia water clarification tank process transformation 8 2 Design plan 10 3 Technical demonstration of process and equipment selection 11 3.1.1 Demonstration of primary cooling process of coal gas 11 3.1.2 Demonstration of staged gas cooling process 12 3.1.3 Demonstration of gas naphthalene removal process 12 3.1.4 Demonstration of gas mist capture process 13 3.1.5 Demonstration of tar ammonia water separation process 14 3.2 Technical demonstration of equipment selection 15 3.2.1 Selection of primary cooler 15 3.2.2 Selection of gas mist capture equipment 15 3.2.3 Selection of gas blower 16 3.2.4 Selection of tar and ammonia water separation equipment 17 4 Process calculation 19 4.1 Material calculation 19 4.2 Calculation of cross tube cooler 19 4.2.1 Calculation of one section of cross tube cooler 19 4.2.2 Calculation of the second section of the cross-tube cooler 21 4.3 Calculation and selection of the electric tar trap 22 4.4 Calculation and selection of the gas blower 24 4.5 Calculation and selection of the ammonia water separator and tar separator 25 4.6 Calculation and selection of various tanks 26 4.7 Calculation and selection of the pump 27 5 Design requirements for other majors 28 5.1 Fire and explosion protection level 28 5.2 Water supply and drainage 28 5.3 Electricity 28 5.4 Civil engineering 28 5.5 Equipment maintenance 29 6 Technical and economic analysis and evaluation 30 Acknowledgments 32 References 33 Appendix 1: English Translation 1 34 Appendix 2: English Translation 2 39 1 Literature Review Coke is the main raw material for ironmaking in the metallurgical industry. China's coke production ranks first in the world, with more than 100 types of coking products. The coking chemical industry is a comprehensive utilization industry of coal. When coal is coked, in addition to about 75% turning into coke, about 25% also generates various chemical products and gas. Recycling these chemical products is of great significance to the comprehensive utilization of coal resources and the development of the national economy. The waste gas from the coke oven needs to be cooled in the chemical recovery workshop and treated with various absorbents. Various chemical products such as tar, ammonia, naphthalene, hydrogen sulfide, hydrogen cyanide and crude benzene can be extracted and the net coke oven gas can be obtained. Because in addition to hydrogen, methane, ethane, ethylene and other components, coal gas also contains other components. Although the content is small, it can have harmful effects. For example, naphthalene precipitates into solid crystals and blocks equipment and gas pipelines. ； Ammonia solution will corrode equipment and pipelines, and the ammonium salt generated can cause blockage ； Hydrogen sulfide and sulfides will corrode equipment, and the generated iron sulfide will cause blockage. Nitric oxide and nitrogen peroxide can polymerize with butadiene, cyclopentadiene, butethylene, etc. in the gas to form complex compounds --- gas glue, which is not conducive to the transportation and use of gas. Therefore, for the above-mentioned harmful components, there should be different removal requirements according to the different uses of coal gas. Therefore, the recovery of chemical products and purification treatment methods from coal gas are also different. The general purification process includes drum cooling, washing, desorption, post-treatment and other main processes. A good process requires each operating unit to be optimized, while also taking into account the actual conditions of the factory. The main principles that new designs should follow are: Advanced and reasonable technology ； Strive to save energy and reduce consumption ； The equipment must be efficient, stable and have a long operating cycle during operation. 1.1 Primary cooling of coke oven gas 1.1.1 Brief description of the primary cooling process The raw coal gas from the coke oven gas collector with a temperature of 80°C to 85°C is condensed and cooled through the gas primary cooler, and most of the tar gas and water vapor are condensed. According to different purification and recovery process requirements, the gas is cooled to 21°C~23°C or 25°C~30°C and then sent to the next process. While cooling, tar, naphthalene and other corrosive media should be removed as much as possible to purify the gas to the greatest extent. 1.1.2 The primary cooling process of gas There are currently three methods of primary cooling of gas widely used at home and abroad: indirect cooling, direct cooling and indirect-direct mixed cooling. Different cooling methods can be selected according to different production scales, process requirements and other conditions during design. (1) Direct cooling of gas The direct cooling of gas is accomplished by direct heat and mass transfer between gas and cold ammonia in the direct cooling tower. While cooling the gas, some corrosive media, tar mist, and naphthalene are taken away by the spray ammonia. In the low-temperature cooling stage, since the water vapor content in the gas has been greatly reduced, the gas layer will limit the cooling of the steam-gas mixture, and the condensation of naphthalene is also prone to cause blockage. Therefore, direct cooling should be used at this stage. There are two types of direct cooling tower: empty spray tower and packed tower. At present, the most commonly used one is the temperature-resistant polypropylene rosette packing tower. Direct cooling has the advantages of high cooling efficiency, small gas pressure loss, difficulty in clogging, and low construction investment. However, it also has the disadvantages of complex process flow, high gas outlet temperature, large power consumption, large liquid-to-gas ratio, large number of ammonia water coolers, easy blockage, and large floor space. Therefore, it is currently only used in the initial construction of some small coking plants. (2) Indirect primary cooling of gas Indirect cooling of gas is to achieve the purpose of condensation cooling by indirect heat exchange between gas and cooling water, and to separate most of the tar, water and naphthalene in the gas. There are two types of gas intercoolers: vertical tube type and horizontal tube type. The vertical tube cooler has shortcomings such as small heat transfer coefficient, low thermal efficiency, high naphthalene content in the gas outlet, easy blockage of naphthalene in the rear section of the cooler, increased resistance, and frequent cleaning. Especially in recent years, with the continuous improvement and development of horizontal tube coolers, vertical tube coolers are rarely used anymore. Since the horizontal tube cooler increases the spraying of ammonia and light tar between the tubes, it can not only form a liquid film outside the tube to improve the heat and mass transfer effect, but also flush the heat transfer tube from top to bottom to prevent the deposition of naphthalene and tar. The naphthalene removal effect is also better than that of the vertical tube type. In addition, the horizontal tube cooler increases the flow rate of cooling water, which can generally reach lm/s. ~2m/s, the gas flow rate can also reach 0.5m/s~0.7m/s, and the flow direction of gas and condensate is the same, so the total heat transfer coefficient can be as high as 836kJ/(m2·h·℃) ~1627kJ/(m2·h·℃), which is almost twice as high as the heat transfer coefficient of the vertical tube cooler (heat transfer coefficient is 418kJ/(m2·h·℃)~627kJ/(m2·h·℃)), which can greatly reduce the heat exchange area of the cooler. In addition, the dense cooling tube bundle can also act as a baffle to separate tar mist and water mist, and can cause turbulence and impact of the gas to achieve uniform cooling and improve heat and mass transfer efficiency. At the same time, since the lower section indirectly exchanges heat with low-temperature water, the outlet gas temperature can be reduced to 21°C~22°C, which is 5°C~7°C lower than the direct cooling type. (3) Indirect-direct mixed cooling The indirect-direct mixed cooling process is a combination of indirect cooling and direct cooling. That is, an indirect cooler is used to cool the gas from 80°C~85°C to 50°C~55°C, and then a direct cooler is used for further cooling. In the intercooling stage, due to the large temperature difference, large amount of condensate and relatively small amount of naphthalene, the heat transfer coefficient is high, which can greatly reduce the required heat transfer area; while in the direct cooling stage, the effect of gas purification can be fully exerted, and the naphthalene content and corrosive media in the gas can be reduced, making it less likely to be blocked. However, there are also shortcomings such as complex processes, multiple equipment, high energy consumption, and large floor space. Therefore, this process is rarely used in China. 1.2 Removal process of naphthalene in coke oven gas 1.2.1 Naphthalene in Coke Oven Gas and Its Removal Crude gas contains about 10g/m3 of naphthalene, most of which is condensed in the primary cooler and dissolved in tar. After primary cooling, the naphthalene content of about 2g/m3 is in a supersaturated state. When the primary-cooled gas flows along the pipeline to the subsequent purification equipment, once the flow rate is slow or the temperature drops further, naphthalene will precipitate and cause blockage, so further denaphthalene removal of the gas is necessary. At present, there are two main ways to remove naphthalene, water washing method and oil washing method. The so-called water washing method uses the reverse contact between cold water and hot gas in the final cooling tower to reduce the temperature of the gas to precipitate naphthalene, and then uses hot tar to absorb naphthalene in the water to achieve cold water circulation washing of naphthalene. Oil-washed naphthalene uses washing oil to wash the gas and absorb the naphthalene in it. The separation of naphthalene from the washing oil can be carried out at the same time as the debenzene removal of the rich oil. This method is more efficient than the water washing method and can generally reduce the naphthalene content in the gas to less than 0.5g/m3. Water-washed naphthalene was once a widely used technology. Later, washing oil was used as a detergent to wash gas with hot or cold methods. However, there are problems of low efficiency or difficulties caused by conflicts, such as corrosion of equipment, resource constraints, environmental pollution, regeneration, and reuse difficulties, etc., which have not been affirmed. And completely removing naphthalene, even in the front part of gas refining, such as removing it all at once in the preliminary cooling process, is still the goal pursued by people. 1.2.2 Naphthalene removal technology from coke oven gas Only by mastering the behavior of naphthalene in coal gas, adopting effective and scientific steps, and using technology step by step can the purpose of removing naphthalene be achieved. Research and experience tell us that the technical logic of naphthalene removal is: cooling is the basis, washing is the key, and negative pressure (in front of the blower) capture of tar mist particles is the guarantee. Only when it is cooled to a specified temperature can naphthalene be fully sublimated, and the naphthalene content in the gas can be reduced to a level that can be achieved by economical methods. But this alone does not mean that the task of separating naphthalene from coal gas has been completed, but it can only be said that this is the first step, which is the foundation. Very high temperatures make it impossible to remove naphthalene from the gas phase. The crucial key is washing. It is necessary to find the appropriate detergent and appropriate process conditions to dissolve and absorb naphthalene, further reduce the naphthalene in the gas, and remove all the removed naphthalene from the equipment. Finally, there must be safeguard measures to prevent the naphthalene content in the gas from increasing, which is to remove all the tar mist particles (generally 5-8g/m3) contained in the gas (as low as less than 20 mg/m3 in the gas). Tar mist particles can contain up to 40% naphthalene. When the temperature rises, naphthalene will sublimate and then escape into the gas phase (gas). Since the tar mist is removed, the possibility of naphthalene sublimation is eliminated, which will consolidate the existing results to ensure the degree of gas purification. When gas processing is carried out according to this logical step, the residual naphthalene will be low enough to be harmless, and there is no need to worry about naphthalene desublimation in subsequent processes. 1.2.3 A good one-time purification process for naphthalene removal. Starting from the above logic, a good one-time purification process for naphthalene removal does exist. The key point lies in the key parts of the above three links of low-temperature cooling, detergent washing, and tar mist capture, that is, the detergent and lotion technology are proposed. After years of research and practice, Chinese engineers have completed the technology of scrubbing gas-phase naphthalene in coal gas at low temperatures (20~22°C). It can achieve the good effect that the naphthalene dew point in the gas is 5~6℃ lower than the temperature reached by cooling. The source of detergent is stable and reliable, the resources are sufficient, the preparation is easy, and the washing is efficient. There are no problems such as corrosion prevention, detergent regeneration, reuse post-processing, pollution prevention, etc. This cooling-washing absorption technology has obtained Chinese technology patents and has been used in more than 30 factories with good results. The possibility of increased naphthalene content in coal gas does exist. The source is tar droplets, which contain nearly 40% naphthalene. Once the gas temperature rises, this part of naphthalene immediately sublimates and escapes into the gas. Therefore, there is still one missing link in the perfect process, which is to remove the tar mist in front of the blower and cut off the only source of naphthalene. The best technology (practical, cheap and advanced) that can be provided now is the application of electric tar collector. After the gas passes through the electric tar collector, the coal tar mist particles can even be