Application of low-temperature SCR (Selective Catalytic Reduction) denitration technology in production device for producing cement from carbide slag

Abstract

The invention relates to an application of a low-temperature SCR (Selective Catalytic Reduction) denitration technology in a device for producing cement from carbide slag, which adopts a novel dry cement production technology, comprehensively utilizes industrial waste residues such as carbide slag generated by an acetylene device, limestone slag generated by a calcium carbide device, fly ash generated by a thermoelectric device, desulfurized gypsum and the like as cement raw materials, and adopts an international advanced mature technology as a process technology. Carbide slag, fly ash, sandstone, limestone and iron ore are homogenized, proportioned and metered and then conveyed to a roller press system to be ground, finished raw materials are conveyed to a raw material homogenizing silo to be homogenized and then enter a kiln to be calcined, and clinker discharged out of the kiln is cooled through a fourth-generation grate cooler and then enters a clinker silo to be stored and used. Clinker, desulfurized gypsum and fly ash in cement production are jointly ground by a roller press and a ball mill to prepare cement, and the cement is conveyed to a cement bunker for storage and is delivered in bulk. The SCR low-temperature and low-dust technology is adopted for ultra-low emission, residual heat of smoke is used for emission reduction, heating and heat compensation are not needed in the operation period, and the problems of energy consumption and waste do not exist.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical environmental protection, and in particular relates to the application of a low-temperature SCR desulfurization technology in a cement production device using carbide slag. Background Art

[0002] The original NOx concentration of the flue gas from the existing carbide slag cement production plant is ≤800mg / Nm 3 (dry basis, 10% O2), denitrification adopts SNCR process, and the reducing agent is 20% concentration of ammonia water. There are 6 ammonia water spray guns, which are arranged in two layers (120°) in an alternating manner: the upper layer is located at the root of the gooseneck tube of the main tube of the decomposition furnace, and the lower layer is located in the upper middle part of the decomposition furnace. Under the current operating conditions, the ammonia spraying volume is 350-500L / h, and the NOx emission value is 180~230mg / Nm 3 (dry basis, 10% O2), the amount of ammonia water used is about 4.36kg / ton clinker.

[0003] However, due to the complexity and particularity of the flue gas produced by carbide slag cement making and the limitations of the layout of the transformation equipment, it is difficult to control the pollutants in the flue gas produced by carbide slag cement making (mainly nitrogen oxides and ammonia escape) and control the flue gas stability.

[0004] The difficulty of ultra-low emission transformation of carbide slag cement production line is reflected in:

[0005] (I) The flue gas from cement production with carbide slag has the characteristics of complex composition and large fluctuation in content, which has strict requirements on control process technology and is difficult to control (for example, in addition to conventional pollutants such as nitrogen oxides, sulfur dioxide, and particulate matter, the flue gas also contains special components such as silane, monocyanamide, dicyandiamide, phosphine, and arsine. These flue gas components all have certain reducing properties, and some of them are relatively strong, such as SiH4, PH3, etc., which will compete with the original reducing agent (NH3) for adsorption, thereby partially replacing NH3 to participate in the reaction; in addition, some components will cause catalyst poisoning, such as heavy metals (As, Pt, Pb, etc.), alkali (alkaline earth) metals (Na, K, Ca, Mg), and sulfides and chlorides in the flue gas, which are easy to poison the catalyst, thereby causing the catalyst to deactivate, shorten the life of its chemical properties, and even lose reaction efficiency.

[0006] (II) The flue gas from cement made from carbide slag has the characteristics of high ammonia peak and large peak-to-valley difference, making it difficult to meet the ammonia escape standard. During the drying process, carbide slag releases a large amount of ammonia, ranging from tens of milligrams per cubic meter to hundreds of milligrams per cubic meter, and there will be large fluctuations when the load, process formula, etc. are adjusted. These "passive ammonia" make it extremely difficult to meet the ammonia escape standard.

[0007] (III) The flue gas humidity of cement made from carbide slag is high, which has a great impact on denitrification. The humidity of dry carbide slag flue gas is about 14-19%, and the humidity of wet carbide slag flue gas is about 25-35%. The high humidity in the flue gas causes water vapor to occupy the active sites of the catalyst, resulting in a decrease in the activity of the catalyst, thus affecting the denitrification efficiency and making denitrification difficult.

[0008] (IV) Limitations in the selection of locations for transformation equipment. Due to the large differences in the production process of carbide slag cement and traditional limestone cement, some ultra-low emission transformation technologies applicable to limestone cement are not applicable to carbide slag cement production lines. For example, the exhaust gas temperature at port C1 of carbide slag cement is high (480°C to 580°C), which can easily cause the denitration catalyst to harden quickly and lose denitration efficiency. Therefore, port C1 is not suitable for arranging denitration equipment; and waste heat boilers or high-temperature fans are not suitable for arrangement because they cannot solve the ammonia released during the drying process of carbide slag. Therefore, excluding the above-mentioned unsuitable transformation locations, only by arranging between the exhaust dust removal and the exhaust draft fan can both nitrogen oxides and ammonia escape be able to meet the emission standards. Therefore, there are very few optional locations, and the process conditions and technical requirements for the arrangement location are stringent. Summary of the invention

[0009] In view of the problems of excessive flue gas at the kiln tail and environmental protection management in the existing carbide slag cement production equipment, the present invention provides an application of low-temperature SCR desulfurization technology in the carbide slag cement production equipment, which solves the technical problem of SCR ultra-low emission transformation of the carbide slag cement production line.

[0010] The technical solution of the present invention is: application of a low-temperature SCR destocking technology in a carbide slag cement production device, and the process is as follows:

[0011] 1. Nitrogen oxides synergistic control of ammonia escape technology

[0012] The SCR low-temperature denitration process is used to selectively react the nitrogen oxides (NOx) in the flue gas with the reducing agent under the action of the catalyst. The nitrogen oxides (NOx) in the flue gas are converted into nitrogen (N2) and water (H2O) through the reducing agent (NH3).

[0013] The main reaction equation is as follows:

[0014] 4NH3+4NO+O2→4N2+6H2O (1)

[0015] 4NH3+2NO+2O2→3N2+6H2O (2)

[0016] 4NH3+6NO→5N2+6H2O (3)

[0017] 8NH3+6NO2→7N2+12H2O (4)

[0018] 2. Low temperature SCR denitrification technology

[0019] Low-temperature SCR technology uses a reducing agent, NH3, to reduce NOx in flue gas to N2 and H2O under the action of a low-temperature catalyst in a temperature window of 150 to 180°C. The main reaction equation is the same as above. The core of low-temperature SCR denitrification technology is the development of low-temperature catalysts and the design of their active components. Low-temperature catalysts are required to have high activity and good resistance to water, sulfur, and alkali metals under a temperature window of 150 to 180°C. After more than ten years of hard work, the Shanghai Hanyu R&D team broke the structure of traditional denitrification catalysts, established a new acidic site and active site structure, and developed an ultra-low temperature SCR denitrification catalyst with rare earth composite transition metals as active components. It has the above characteristics and meets the needs of this project.

[0020] The low-temperature SCR reactor is arranged between the large bag filter and the tail exhaust fan. The flue gas does not need to be heated, and the flue gas passing through the reactor has the characteristics of low temperature, low sulfur and low dust. The denitrification reaction system consists of inlet and outlet flues, guide plates, ammonia spraying grids, rake soot blowers and catalysts. The escaped ammonia from the upstream SNCR or the ammonia released by drying the calcium carbide slag enters the reactor as a reducing agent through the inlet flue, guide plates, and ammonia spraying grids. A catalytic reduction reaction occurs in the low-temperature SCR reactor to efficiently remove NOx from the flue gas.

[0021] 3. Technical indicators

[0022] NOx concentration ≤50mg / Nm 3 (Dry basis, 10% O2).

[0023] 4. Process

[0024] The flue gas is introduced into the ascending flue from the outlet of the dust collector at the tail of the carbide slag cement kiln, and enters the SCR reactor through the equalizing device. Under the pulling force generated by the exhaust draft fan, the flue gas that meets the pollutant standards is discharged into the atmosphere through the chimney.

[0025] Comparison table of energy consumption (heat energy) and carbon emissions of SCR denitrification at different temperatures

[0026]

[0027] The present invention has the following remarkable effects:

[0028] (I) Economic benefits. The SCR denitrification system uses ammonia released by drying carbide slag as a reducing agent, saving about RMB 7 million in ammonia purchase costs annually; after the transformation, it reaches Class A emission standards and can enjoy peak-shifting exemptions according to the policy. Calculated at 30 days per year, it can increase clinker production by 7,500 tons and increase output value by about RMB 20 million.

[0029] (II) Environmental benefits. Enterprises should not only focus on economic benefits, but also shoulder social responsibilities. As we all know, nitrogen oxides are the culprit of environmental pollution such as smog, acid rain, ozone layer depletion, and global warming. Therefore, nitrogen oxides are the most important pollutants that need to be solved urgently. After adopting SCR low-temperature and low-dust technology for ultra-low emission transformation, nitrogen oxide emissions will be reduced by more than 620,000 tons, making a real and outstanding contribution to improving the environment.

[0030] (III) Operation and maintenance benefits. There is no production equipment behind the low-temperature SCR system, and it will not affect the production equipment at the front end, so it will not interfere with the operation of the production line and has good operation stability; the device is arranged after the dust collector, the dust content is extremely low, the catalyst has no risk of wear, blockage, or poisoning, and the catalyst has a relatively long service life.

[0031] (IV) Energy-saving benefits. Low-temperature and low-dust SCR technology uses the remaining heat of the flue gas itself to reduce emissions. No heating or supplementary heat is required during operation, and there is no problem of energy consumption or waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the production device of cement made from carbide slag of the present invention.

[0033] In the figure: 1. Kiln tail dust collector; 2. Low temperature SCR reactor; 3. Low temperature SCR catalyst; 4. Kiln tail exhaust fan; 5. Chimney; 6. Compressed air storage tank; 7. Rake soot blower; 8. Hot air furnace; 9. Compensator; 10. Flue gas damper door; 11. Flue gas diversion device; 12. Flue gas rectification device; 13. Valve A; 14. Valve B; 15. Valve C; 16. Valve D; 17. Valve E; 18. Valve F; 19. Temperature meter Table A; 20. Pressure instrument A; 21. Temperature instrument B; 22. Pressure instrument B; 23. Temperature instrument C; 24. Pressure instrument C; 25. NOx online monitor; 26. NH3 online monitor; 27. Oxygen online monitor; 28. SO2 online monitor; 29. ​​Particulate matter online monitor; 30. Temperature instrument D; 31. Pressure instrument D; 32. Humidity monitoring instrument; 33. Air volume monitor; 34. Pressure instrument E. DETAILED DESCRIPTION

[0034] A low-temperature SCR destocking technology is applied in a carbide slag cement production device, and the process is as follows:

[0035] 1. Nitrogen oxides synergistic control of ammonia escape technology

[0036] The SCR low-temperature denitration process is used to selectively react the nitrogen oxides (NOx) in the flue gas with the reducing agent under the action of the catalyst. The nitrogen oxides (NOx) in the flue gas are converted into nitrogen (N2) and water (H2O) through the reducing agent (NH3).

[0037] The main reaction equation is as follows:

[0038] 4NH3+4NO+O2→4N2+6H2O (1)

[0039] 4NH3+2NO+2O2→3N2+6H2O (2)

[0040] 4NH3+6NO→5N2+6H2O (3)

[0041] 8NH3+6NO2→7N2+12H2O (4)

[0042] 2. Low temperature SCR denitrification technology

[0043] Low-temperature SCR technology uses the reducing agent NH3 to reduce NOx in the flue gas to N2 and H2O under the action of a low-temperature catalyst in a temperature window of 150-180°C. The main reaction equation is the same as above.

[0044] The core of low-temperature SCR denitration technology is the development of low-temperature catalysts and the design of their active components, which requires low-temperature catalysts to have high activity and good resistance to water, sulfur and alkali metals under the working condition of the temperature window of 150-180°C. After more than ten years of hard work, the Shanghai Hanyu R&D team broke the structure of traditional denitration catalysts, established a new acid site and active site structure, and developed an ultra-low temperature SCR denitration catalyst with rare earth composite transition metals as active components. It has the above characteristics and meets the needs of this project.

[0045] The low-temperature SCR reactor is arranged between the large bag filter and the tail exhaust fan. The flue gas does not need to be heated, and the flue gas passing through the reactor has the characteristics of low temperature, low sulfur and low dust. The denitrification reaction system consists of inlet and outlet flues, guide plates, ammonia spraying grids, rake soot blowers and catalysts. The escaped ammonia from the upstream SNCR or the ammonia released by drying the calcium carbide slag enters the reactor as a reducing agent through the inlet flue, guide plates and ammonia spraying grids. A catalytic reduction reaction occurs in the low-temperature SCR reactor to efficiently remove NOx from the flue gas.

[0046] 3. Technical indicators

[0047] NOx concentration ≤50mg / Nm 3 (Dry basis, 10% O2).

[0048] 4. Process

[0049] The flue gas is introduced into the ascending flue from the outlet of the dust collector at the tail of the carbide slag cement kiln, and enters the SCR reactor through the equalizing device. Under the pulling force generated by the exhaust draft fan, the flue gas that meets the pollutant standards is discharged into the atmosphere through the chimney.

[0050] The carbide slag cement production device of the present invention adopts a new dry cement production technology, comprehensively utilizes carbide slag produced by acetylene devices, limestone slag produced by carbide devices, fly ash produced by thermoelectric devices, desulfurized gypsum and other industrial waste slag as cement raw materials, and the process technology adopts internationally advanced and mature technology (five-stage suspension preheater). The main process is: after homogenization and batching, carbide slag, fly ash, sandstone, limestone, and iron ore are transported to the roller press system for grinding, and the finished raw materials are transported to the raw material homogenization warehouse for homogenization and then calcined in the kiln. The clinker discharged from the kiln is cooled by the fourth-generation grate cooler and then stored in the clinker warehouse for use. In cement production, clinker, desulfurized gypsum, and fly ash are ground by roller press and ball mill to make cement, which is transported to the cement warehouse for storage and shipped in bulk.

[0051] like Figure 1 As shown, the production device of cement made from calcium carbide slag of the present invention: the production device includes a tail kiln dust collector 1, a low-temperature SCR reactor 2, a low-temperature SCR catalyst 3, a tail kiln exhaust fan 4, a chimney 5, a compressed air storage tank 6, a hot air furnace 8, a compensator 9, a flue gas diversion device 11 and a flue gas rectification device 12. The flue gas after grinding or drying and crushing of the cement kiln tail raw materials enters the tail kiln dust collector, reaches the flue gas diversion device through the compensator 9, and then enters the flue gas rectification device 12 and the low-temperature SCR reactor 2. A rake-type soot blower 7 is arranged in the low-temperature SCR reactor 2, and a temperature meter B21 and a pressure meter B22 are installed on the wall of the low-temperature SCR reactor. The flue gas treated by the low-temperature SCR catalyst 3 enters the chimney 6 through the tail kiln exhaust fan 5.

Claims

1. The application of low-temperature SCR destocking technology in carbide slag cement production equipment is characterized by: The application process is as follows: (1) Nitrogen oxides and ammonia escape synergistic control technology The SCR low-temperature denitrification process is used to selectively react the nitrogen oxides (NOx) in the flue gas with the reducing agent under the action of the catalyst, and the nitrogen oxides (NOx) in the flue gas are converted into nitrogen (N2) and water (H2O) through the reducing agent (NH3); The main reaction equation is as follows: 4NH3+4NO+O2→4N2+6H2O (1) 4NH3+2NO+2O2→3N2+6H2O (2) 4NH3+6NO→5N2+6H2O (3) 8NH3+6NO2→7N2+12H2O (4) (2) Low-temperature SCR denitrification technology Low-temperature SCR technology is to reduce NOx in flue gas to N2 and H2O using the reducing agent NH3 under the action of low-temperature catalyst in the temperature window of 150-180℃. The main reaction equation is the same as above. The core of low-temperature SCR denitrification technology is the development of low-temperature catalyst and the design of its active components. The low-temperature catalyst is required to have high activity and good resistance to water, sulfur and alkali metals under the working condition of the temperature window of 150-180℃. The low-temperature SCR reactor is arranged between the large bag filter and the tail exhaust fan. The flue gas does not need to be heated. The flue gas passing through the reactor has the characteristics of low temperature, low sulfur and low dust. The denitrification reaction system consists of inlet and outlet flues, guide plates, ammonia spraying grids, rake soot blowers and catalysts. The escaped ammonia from the upstream SNCR or the ammonia released by drying the calcium carbide slag enters the reactor as a reducing agent through the inlet flue, guide plates and ammonia spraying grids. A catalytic reduction reaction occurs in the low-temperature SCR reactor to efficiently remove NOx from the flue gas. (3) Technical indicators NOx concentration ≤50mg / Nm 3 (dry basis, 10%O2); (4) Process flow The flue gas is introduced into the ascending flue from the outlet of the dust collector at the tail of the carbide slag cement kiln, and enters the SCR reactor through the equalizing device. Under the pulling force generated by the exhaust draft fan, the flue gas that meets the pollutant standards is discharged into the atmosphere through the chimney.

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