Multiphase flow reactive distillation and de-alkali carbon fixation method for bulk industrial solid waste red mud

Abstract

The present invention provides a method for multiphase flow reactive distillation and de-alkali carbonization of bulk industrial solid waste red mud. The red mud slurry is pumped to the top of a reactive distillation tower, countercurrently contacted with flue gas through multi-stage flow-through tower plates and fillers, and acidic gas in the flue gas is efficiently reactively distilled with alkali in the slurry. The flue gas after dust removal, decarbonization and desulfurization flows out from the top of the reactive distillation tower, and the de-alkali carbonized red mud slurry flows out from the bottom of the reactive distillation tower and the concentrated brine is removed. The dehydrated red mud slurry is diluted again with part of the brine and then pumped to the top of a water washing and desalting tower for countercurrent water washing and desalting. The desalted red mud slurry flowing out from the bottom of the water washing and desalting tower is dehydrated and then discharged for resource utilization. A portion of the brine flowing out from the top of the water washing and desalting tower is used to dilute the dehydrated red mud slurry, and the remaining portion is mixed with the concentrated brine and sent back to the alumina extraction section.

Description

1. Technical Field

[0001] The invention provides a method for multiphase flow reaction distillation de-alkali and carbon fixation of bulk industrial solid waste red mud, belonging to the field of environmental protection. 2. Background technology

[0002] Red mud is a polluting, high-alkali waste residue discharged when the electrolytic aluminum industry extracts alumina. Generally, for every ton of alumina produced, 1.0 to 2.0 tons of red mud are produced. China is the world's fourth largest alumina producer, accounting for 55% of global production. It discharges nearly 100 million tons of red mud each year, and more than 1.3 billion tons of accumulated red mud, which not only occupies a large amount of land, but also causes pollution to the soil, water sources, and air. Resource utilization is an internationally recognized effective means of red mud utilization. Although five major utilization technologies have been developed at home and abroad, namely powder materials, element extraction, cementitious materials, road materials, and ceramic materials, they are currently in the technical growth stage and have not yet been commercialized.

[0003] The comprehensive utilization of red mud has always been difficult to solve. The fundamental reason is that the sodium oxide content in red mud exceeds the standard. Red mud is a highly alkaline solid waste with a pH as high as 11-13. The alkaline substances in red mud are mainly soluble alkali (free alkali) and insoluble alkali (bound alkali). Free alkali mainly includes NaOH, Na2CO3, NaHCO 3、 NaAl(OH)4, Na2SiO3, etc. Insoluble alkali includes calcite, cancrinite, hydrated garnet, sodalite and tricalcium aluminate. Cancrinite is the main alkali-containing substance. Sodium oxide (Na2O) is the main alkaline oxide in its chemical composition, with a content of up to 12.91%, mainly in the form of caustic soda, sodium aluminate and sodium aluminosilicate. Soluble alkali can be removed by passing CO2 or washing at room temperature and pressure, but this part accounts for a small proportion, and most of it is insoluble alkali. In particular, sodium silicate slag accounts for a large proportion of Bayer red mud, accounting for about 35-45%. The removal of this part of alkali is one of the problems that are difficult to solve globally at present, and it is also a key issue affecting the further large-scale utilization of red mud.

[0004] As a high-energy-consuming and high-pollution industry, electrolytic aluminum is equipped with large-scale thermal power generation. With the 3060 dual carbon target proposed, it is currently facing the pressure of carbon emission reduction and ultra-low emissions. Using acidic gases such as CO2, SOx and NOx in flue gas for red mud dealkalization can achieve acid-base neutralization and waste treatment, and at the same time efficiently and low-cost solve the two major problems of red mud dealkalization and flue gas decarbonization and ultra-low emissions. Alcoa in Western Australia has applied CO2 dealkalization on a large scale, adding gaseous and liquid CO2 to thickened red mud slurry, and CO2 reacts with the alkaline components in the slurry to achieve the purpose of dealkalization. However, the gas dispersion method of passing flue gas into the red mud slurry or the red mud slurry spraying method currently used has a dealkalization rate of less than 50%. In addition, since SOx is more acidic than CO2, it is easy to react with insoluble alkaline substances, which can greatly increase the dealkalization rate, but the existing flue gas dealkalization process has not yet achieved flue gas graded utilization, causing insoluble alkaline substances to become a stubborn problem in red mud dealkalization. Therefore, it is urgent to develop red mud flue gas multiphase flow reactive distillation dealkalization and carbon fixation technology and equipment, break through industrial bottlenecks such as efficient utilization of SOx / CO2 by reaction activity classification, slurry blockage, efficient dispersed mass transfer and reaction, and build new technologies for the high-value utilization of red mud resources industry chain to provide guarantees for the sustainable and high-quality development of the electrolytic aluminum industry. 3. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing red mud resource utilization technology and propose a method for multiphase flow reactive distillation de-alkali and carbon fixation of bulk industrial solid waste red mud, which not only solves the problem of cheap and efficient removal of insoluble alkaline substances in red mud, and creates conditions for the high-value utilization of red mud resources; at the same time, it realizes the efficient utilization of acidic gases in flue gas according to reaction activity classification, and solves the problem of decarbonization and ultra-low emission of combustion flue gas with high efficiency and low cost.

[0006] The technical solution of the present invention:

[0007] The present invention provides a method for multiphase flow reactive distillation dealkalization and carbon fixation of bulk industrial solid waste red mud, which is characterized in that a red mud slurry at 10-100°C is pumped to the top of a reactive distillation tower, and is countercurrently contacted with a combustion flue gas at 30-180°C introduced from the bottom of the tower through a flow-through tower plate or filler with 1-30 theoretical plates, and the feed ratio of the flue gas to the red mud slurry is 500-3000:1 (volume ratio); in the reactive distillation tower, the CO2, SOx and NOx acidic gases in the flue gas are efficiently reactively distilled with Na2O, K2O and alkaline salts thereof in the slurry, and SOx and NOx are mainly reacted with insoluble alkaline gases in the lower part of the tower. Material reaction, CO2 mainly reacts with soluble alkaline substances in the upper part of the tower to reduce the pH value of the red mud slurry from 11-14 to no more than 8, the dust-removed, decarbonized and desulfurized flue gas flows out from the top of the reaction distillation tower, and the alkali-free and carbon-fixed red mud slurry flows out from the bottom of the reaction distillation tower and the concentrated brine is removed; the dehydrated red mud slurry is diluted with part of the washing brine again, and then pumped to the top of the water washing and desalting tower for countercurrent water washing and desalination. The desalted red mud slurry flowing out of the bottom of the water washing and desalting tower is dehydrated and discharged for resource utilization. Part of the washing brine flowing out of the top of the water washing and desalting tower is used to dilute the dehydrated red mud slurry, and the remaining part is mixed with concentrated brine and sent back to the alumina extraction section.

[0008] The reactive distillation tower is a flow-through structure without a downcomer. A red mud slurry distributor is arranged at the top of the tower. The plate spacing of the flow-through tower plates is 250-900mm. A combustion flue gas distributor is arranged at the bottom of the tower. The top of the tower is a flue gas outlet, and a red mud slurry outlet is arranged at the bottom of the tower.

[0009] The CO2 content in the combustion flue gas is 12%-25%, the SOx content is 0-50000PPm, the NOx content is 0-3000PPm, and the flow rate in the flue gas tower is 0.5-3.0m / s.

[0010] The concentration of red mud slurry is 5%-60% and the spray density in the tower is 5-120m 3 / m 2 ·h.

[0011] The water washing desalination tower is a flow-through plate tower, a packed tower or an empty tower.

[0012] The present invention will be described in detail with reference to embodiments. 4. Description of the drawings

[0013] The accompanying drawings are schematic diagrams of the present invention. The drawings of the accompanying drawings are as follows:

[0014] 1. Mud pump 2. Flue gas distributor 3. Reaction distillation tower 4. Filter press 5. Mixed mud pump 6. Water washing and desalination tower 7. Soft water distributor 8. Dehydration filter press.

[0015] The process characteristics of the present invention are described in detail below in conjunction with the accompanying drawings and embodiments. 5. Specific implementation methods

[0016] In the embodiment, red mud at 10-100° C. is delivered to the top of a reaction distillation tower (3) through a slurry pump (1), and is countercurrently contacted with combustion flue gas at 30-180° C. introduced from a flue gas distributor (2) at the bottom of the tower through a flow-through tower plate or a filler with 1-30 theoretical plates, and the feed ratio of flue gas to red mud slurry is 500-3000:1 (volume ratio); in the reaction distillation tower (3), the acidic gases CO2, SOx and NOx in the flue gas are subjected to efficient reaction distillation with Na2O, K2O and alkaline salts thereof in the slurry, SOx and NOx mainly react with insoluble alkaline substances in the lower part of the tower, and CO2 mainly reacts with soluble alkaline substances in the upper part of the tower, thereby reducing the pH value of the red mud slurry. The value decreases from 11-14 to no more than 8, the flue gas with dust removal, decarbonization and desulfurization flows out from the top of the reaction distillation tower (3), the red mud slurry with dealkali and carbon fixation flows out from the bottom of the reaction distillation tower, and the concentrated brine is removed by the filter press (4); the dehydrated red mud slurry is diluted again with part of the water washing brine, and then pumped to the top of the water washing and desalting tower (6) by the mixed mud pump (5), and is washed and desalted in the countercurrent with the soft water introduced by the soft water distributor (7); the desalted red mud slurry flowing out of the bottom of the water washing and desalting tower (6) is dehydrated by the dehydration filter press (8) and then discharged for resource utilization; the water washing brine flowing out of the top of the water washing and desalting tower (6) is partially used to dilute the dehydrated red mud slurry, and the remaining part is mixed with the concentrated brine and sent back to the alumina extraction section.

[0017] The reaction distillation tower (3) is a flow-through structure without a downcomer. A red mud slurry distributor is arranged at the top of the tower. The plate spacing of the flow-through tower plate is 250-900 mm. A combustion flue gas distributor (2) is arranged at the bottom of the tower. The top of the tower is a flue gas outlet, and the bottom of the tower is provided with a red mud slurry outlet. The CO2 content in the combustion flue gas is 12%-25%, and the flow rate of the flue gas in the reaction distillation tower (3) is 0.5-3.0 m / s. The mass concentration of the red mud slurry is 5%-60%, and the spray density in the reaction distillation tower (3) is 5-120 m / s. 3 / m 2 ·h.

[0018] The water washing desalination tower (6) is a flow-through plate tower, a packed tower or an empty tower.

[0019] The method for multiphase flow reactive distillation dealkalization and carbon fixation of bulk industrial solid waste red mud provided by the present invention realizes graded utilization of acidic gases in flue gas according to reaction activity through a reactive distillation tower, thereby solving the problem of decarbonization and ultra-low emission of combustion flue gas with high efficiency and low cost, and solves the problem of cheap and efficient removal of insoluble alkaline substances in red mud. The dealkalization rate is increased from the usual 50% to 98%, and the carbon fixation amount is increased from less than 40KgCO2 / ton of 30% red mud to more than 150KgCO2 / ton of 30% red mud, creating conditions for high-value utilization of red mud resources.

Claims

1. A method for de-alkali and carbon fixation of bulk industrial solid waste red mud by multiphase flow reactive distillation, characterized by: The red mud slurry at 10-100°C is pumped to the top of the reaction distillation tower, and is countercurrently contacted with the 30-180°C combustion flue gas introduced from the bottom of the tower through 1-30 theoretical plates of flow-through trays or fillers. The volume ratio of the flue gas to the red mud slurry feed is 500-3000:

1. CO2 and SO X and NO X The acid gas reacts with Na2O, K2O and their alkaline salts in the slurry for efficient reaction distillation, SO X and NO X It mainly reacts with insoluble alkaline substances in the lower part of the tower, and CO2 mainly reacts with soluble alkaline substances in the upper part of the tower to reduce the pH value of the red mud slurry from 11-14 to no more than 8. The flue gas with dust removal, decarbonization and desulfurization flows out from the top of the reaction distillation tower, and the red mud slurry with dealkali and carbon fixation flows out from the bottom of the reaction distillation tower and the concentrated brine is removed; the dehydrated red mud slurry is diluted with part of the washing brine again, and then pumped to the top of the water washing and desalting tower, and the countercurrent water washing and desalting are carried out. The desalted red mud slurry flowing out of the bottom of the water washing and desalting tower is dehydrated and discharged for resource utilization. The washing brine flowing out of the top of the water washing and desalting tower is partially used to dilute the dehydrated red mud slurry, and the remaining part is mixed with the concentrated brine and sent back to the alumina extraction section; the CO2 content in the combustion flue gas is 12%-25%, SO X Content is 0-50000ppm, NO X The content is 0-3000ppm, among which SO X and NO X The content is not taken as 0ppm, and the flow rate in the flue gas tower is 0.5-3.0m / s.

2. The method for dealkalization and carbon fixation of bulk industrial solid waste red mud by multiphase flow reactive distillation according to claim 1 is characterized in that The reactive distillation tower is a flow-through structure without a downcomer. A red mud slurry distributor is arranged at the top of the tower. The plate spacing of the flow-through tower plates is 250-900mm. A combustion flue gas distributor is arranged at the bottom of the tower. The top of the tower is a flue gas outlet, and a red mud slurry outlet is arranged at the bottom of the tower.

3. The method for dealkalization and carbon fixation of bulk industrial solid waste red mud by multiphase flow reactive distillation according to claim 1, characterized in that The concentration of red mud slurry is 5%-60% and the spray density in the tower is 5-120m 3 / m 2 ·h.

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