Nitrogen fixation and carbon fixation synergetic waste concrete regeneration method and regenerated concrete

Abstract

The invention provides a nitrogen fixation and carbon fixation synergistic waste concrete regeneration method and recycled concrete, and belongs to the technical field of recycled concrete.The method comprises the following steps that S1, waste concrete is sequentially subjected to coarse crushing, acetic acid solution activation and medium crushing and conveyed to a fluidized bed reactor to be roasted and reconstructed, and activated aggregate is prepared; s2, introducing the industrial flue gas containing nitrogen oxides into the fluidized bed reactor filled with the activated aggregate through a gas input device, and carrying out mineralization reaction at 40-60 DEG C; s3, injecting carbon dioxide into the fluidized bed reactor, and carrying out nitrogen fixation and carbon fixation collaboration to obtain coated aggregate; s4, carrying out water washing and surface modification on the coated aggregate obtained in S3 by using water washing equipment to obtain saturated surface dry aggregate; and S5, preparing the recycled concrete by using the saturated surface dry aggregate. The problem that in the prior art, waste concrete and industrial flue gas do not cooperate, and certain resource waste is caused is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of recycled concrete, and specifically relates to a method for regenerating waste concrete by coordinating nitrogen and carbon fixation and recycled concrete. Background Art

[0002] Traditional recycled aggregate technology only obtains low-quality aggregates through physical means such as crushing, screening, and washing. The aggregates have high porosity and large water absorption, resulting in low strength and poor durability of recycled concrete, making it difficult to use in high-grade structures. At the same time, power plants, cement, steel, building materials and other industries emit large amounts of industrial flue gas containing carbon dioxide and nitrogen oxides. The use of composite flue gas denitrification technology has high energy consumption, large land occupation, and high investment and operating costs.

[0003] At present, whether it is the production line of recycled aggregate from construction waste or the process of co-preparing steel slag concrete by carbonization of steel slag, flue gas treatment is regarded as the end-of-pipe treatment link. After desulfurization, denitrification and dust removal, it is discharged when it meets the standards. The carbon dioxide and nitrogen oxides in the flue gas are not introduced into the aggregates or products of the recycled concrete to participate in the reaction. There is no intersection with the industrial flue gas throughout the whole process. The waste flue gas is not fully utilized, resulting in a certain amount of resource waste. Summary of the Invention

[0004] The embodiments of the present invention provide a method for regenerating waste concrete by synergizing nitrogen and carbon fixation and recycled concrete, which solves the problem in the prior art that waste concrete and industrial flue gas are not synergistically treated, resulting in a certain amount of resource waste.

[0005] In view of the above problems, the technical solution proposed by the present invention is: The present invention provides a method for nitrogen and carbon fixation synergistically regenerating waste concrete, comprising the following steps: S1, the waste concrete is subjected to coarse crushing, acetic acid solution activation, medium crushing, and transported to a fluidized bed reactor for calcination and reconstruction to obtain activated aggregate; S2, introducing the industrial flue gas containing nitrogen oxides into a fluidized bed reactor filled with activated aggregate through a gas input device, and causing a mineralization reaction at 40-60°C; S3, injecting carbon dioxide into the fluidized bed reactor to carry out nitrogen and carbon fixation synergistically to obtain coated aggregate; S4, washing and surface-modifying the coated aggregate obtained in S3 using a water washing device to obtain saturated surface-dry aggregate; S5, preparation of recycled concrete using saturated face-dry aggregate.

[0006] As a preferred technical solution of the present invention, step S1 includes: Acetic acid activation is to spray the coarsely crushed aggregate with 5% acetic acid solution in an acid-resistant spraying device and let it stand for 2 hours; The roasting reconstruction is to roast the aggregate obtained from the medium crushing in the roasting section of the fluidized bed reactor for 2 hours to generate γ-type dicalcium silicate activated aggregate.

[0007] As a preferred technical solution of the present invention, the detailed process of flue gas mineralization and nitrogen fixation in step S2 is as follows: S21, pre-adsorption stage, at 40 °C, a saturated calcium nitrate solution is sprayed into the fluidized bed reactor to activate the aggregate to pre-adsorb nitrogen dioxide; S22, the main reaction stage, the temperature is raised to 60°C, the activated aggregate reacts with the flue gas and completes the nitrogen fixation reaction; S23, monitoring, uses a gas detector to monitor the nitrogen oxides in the flue gas at the gas outlet of the fluidized bed reactor and the content of nitrate ions in the aggregate.

[0008] As a preferred technical solution of the present invention, when the concentration of nitrogen oxides in the flue gas exceeds the standard, it is adjusted by recirculating the tail flue gas or cooling it to 40-45°C; When the nitrate ion content does not meet the standard, the aggregate is returned to the fluidized bed reactor to repeat the nitrogen fixation treatment.

[0009] As a preferred technical solution of the present invention, the detailed process of synergistic nitrogen fixation and carbon fixation in step S3 is as follows: The cooled activated aggregate is placed in a fluidized bed reactor. Through two independent fans, 10% concentration of carbon dioxide and industrial flue gas containing nitrogen oxides are turbulently mixed simultaneously through a 45° symmetrical air flow inlet, and contact and react with the activated aggregate to achieve synergistic carbon fixation and nitrogen fixation to obtain coated aggregate.

[0010] The fluidized bed reactor in steps S1 and S2 is divided from bottom to top into a calcination section for calcination and reconstruction, a spray section for the pre-adsorption stage, and a gas mixing section for coordinated nitrogen and carbon fixation, as well as an aggregate inlet and outlet provided on both sides of the calcination section; The roasting section includes an aggregate support grid arranged at the bottom of the shell of the fluidized bed reactor and an annular air duct for receiving hot air; The spray section includes a spray head array arranged near the middle of the fluidized bed and a heat insulation plate for blocking the hot air from the roasting section below; The gas mixing section includes two gas flow inlets symmetrically arranged at 45 degrees on the top of the fluidized bed reactor, and a honeycomb guide plate is also arranged at the gas mixing section.

[0011] As a preferred technical solution of the present invention, a plurality of air outlets are opened on the inner side of the annular air duct, the annular air duct is externally connected to a hot air blower, the hot air blower is externally connected to a gas hot air furnace that provides a hot air source, and a liquid collecting plate for collecting the solution dripping from the spray section is provided under the aggregate support grid, and the liquid collecting plate is externally connected to a suction pump.

[0012] As a preferred technical solution of the present invention, the spray head array is externally connected to a solution tank filled with a saturated calcium nitrate solution, and a water pump is used for spraying control. The heat insulation plate is arranged near the upper side of the roasting section and higher than the position of the aggregate inlet. The heat insulation plate is corrosion-resistant. Several heat insulation plates are arranged inside the fluidized bed reactor, and an external rotating motor for controlling the rotation of the heat insulation plate is arranged on the outside of the fluidized bed reactor.

[0013] As a preferred technical solution of the present invention, the detailed process of preparing the recycled concrete in step S5 is as follows: The obtained saturated surface dry aggregate is classified into coarse / fine aggregate, and is sequentially mixed with natural sand, cement, water reducing agent and water to obtain recycled concrete.

[0014] On the other hand, a recycled concrete is prepared by a nitrogen and carbon fixation synergistic waste concrete regeneration method, in which the proportions of each component are calculated by mass, including 100 parts of cement, 300 parts of saturated surface dry recycled aggregate, 180 parts of coarse aggregate, 120 parts of fine aggregate, 45 parts of natural sand, 55 parts of water, and 1.0 part of water reducer.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention first utilizes calcium hydroxide / calcium oxide in waste concrete aggregate to rapidly carbonize with carbon dioxide to form a dense inner layer of calcium carbonate, thereby achieving carbon fixation. Nitrogen dioxide is then reacted on the dual active sites of calcium oxide / calcium carbonate to form an outer layer of calcium nitrate, thereby completing nitrogen fixation. By synergistically fixing carbon first and nitrogen later, no additional absorbent is required. By synergistically fixing nitrogen and carbon, industrial waste gas can be captured and solidified, thereby reducing environmental governance costs.

[0016] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are specifically listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic flow chart of a method for coordinating waste concrete regeneration with nitrogen and carbon fixation disclosed in the present invention; Figure 2This is a schematic structural diagram of a fluidized bed reactor for a method of nitrogen and carbon fixation and coordinated waste concrete regeneration disclosed in the present invention; Figure 3 This is a schematic structural diagram of a second fluidized bed reactor for a method for nitrogen and carbon fixation and coordinated waste concrete regeneration disclosed in the present invention; Reference numerals: 1, fluidized bed reactor; 11, roasting section; 111, aggregate support grid; 112, annular air duct; 113, hot air blower; 114, liquid collecting plate; 115, suction pump; 12. Spray section; 121. Spray head array; 122. Heat shield; 123. External rotating motor; 13. Gas mixing section; 131. Air flow inlet; 132. Honeycomb guide plate; 14. Aggregate inlet; 15. Discharge outlet. DETAILED DESCRIPTION

[0018] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0019] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are also within the scope of protection of the present invention.

[0020] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0021] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0023] Example 1

[0024] Refer to the attached Figure 1-2 As shown, the present invention provides a technical solution: a method for regenerating waste concrete by coordinating nitrogen and carbon fixation, comprising the following steps: S1, the waste concrete is subjected to coarse crushing, acetic acid solution activation, medium crushing, and transported to the fluidized bed reactor 1 for roasting and reconstruction to obtain activated aggregate, specifically: S11, coarse crushing, using a jaw crusher to crush the waste concrete to a particle size of ≤50 mm to obtain coarse aggregate; S12, acid activation, transporting the coarse aggregate to an acid-resistant spraying device, spraying 5% acetic acid solution, and leaving it for 2 hours to dissolve the hydration layer on the surface of the coarse aggregate to obtain demolded aggregate; S13, medium crushing, uses an impact crusher to perform secondary crushing on the de-molded aggregate to a particle size of 1-3 mm, and uses a vibrating screen to screen and classify to obtain medium aggregate; S14, calcination and reconstruction, the intermediate aggregate is transported to the calcination section 11 of the fluidized bed reactor 1, and hot air at 600-800°C is introduced through the hot air blower 113 to remove volatiles from the intermediate aggregate. The treatment time is 4-6 hours, and then the temperature is raised to 1250-1350°C, kept at this temperature for 30 minutes, and then air-cooled to below 200°C to obtain gamma-type dicalcium silicate activated aggregate. The activated aggregate is cooled to 40-60°C by air cooling equipment, which is a separate external air cooling equipment or uses the hot air blower 113 described in S2 for cooling; The detailed process of obtaining the gamma-type dicalcium silicate activated aggregate is as follows: waste concrete is immersed in an acetic acid solution, the acetic acid dissolves some calcium ions and etches the surface to form a silicon-rich residue, which is then crushed to 1-3 mm particles in S13 to obtain an aggregate with a surface-rich silicon layer and an internally rich calcium layer. The aggregate is mixed with quartz powder according to a stoichiometric ratio of calcium / silicon ≈ 2, granulated, and fed into the roasting section 11 of the fluidized bed reactor 1. Hot air at 1250-1350°C is introduced through the hot air blower 113 and kept warm for 30 minutes to generate beta-type dicalcium silicate. The aggregate is then cooled to <200°C. Due to the rapid cooling stress, the beta-type dicalcium silicate is converted into metastable gamma-type dicalcium silicate, which is the gamma-type dicalcium silicate activated aggregate. S2, the industrial flue gas containing nitrogen oxides is introduced into the fluidized bed reactor 1 filled with activated aggregate through the gas input device, and a mineralization reaction occurs at 40-60°C. The hot air blower 113 uses a variable frequency hot air blower to switch between hot and cold air, such as the HWIR900F industrial hot air blower. The temperature of the fluidized bed reactor 1 is detected by a thermometer installed on the fluidized bed reactor 1 to monitor the temperature change in the fluidized bed reactor 1. The type of hot air blower that is resistant to high and low temperatures is required, specifically: S21, introducing the industrial flue gas containing nitrogen oxides into the fluidized bed reactor 1 filled with activated aggregate through a precision blower; S22, during the pre-adsorption stage, the air volume of the hot air blower 113 is adjusted via a frequency converter to prevent the air temperature from rising or falling too quickly, and the hot air is switched to cold air. At a temperature of 40°C, a saturated calcium nitrate solution is sprayed into the fluidized bed reactor 1. The saturated calcium nitrate solution provides the reaction medium water, causing the activated aggregate to pre-adsorb nitrogen dioxide. The saturated calcium nitrate solution forms a liquid film on the surface of the aggregate, pre-adsorbing nitrogen dioxide in the flue gas and improving the subsequent nitrogen fixation efficiency; During the temperature-raising reaction stage, the air volume of the hot air blower 113 is adjusted by the frequency converter, and the hot air channel is switched to perform light heating. It is also necessary to avoid heating too quickly. The temperature of the fluidized bed reactor 1 is raised to 60°C, and the activated aggregate reacts with the flue gas. The γ-type dicalcium silicate in the activated aggregate is hydrolyzed to form calcium hydroxide, and the calcium hydroxide reacts with nitrogen dioxide to form calcium nitrate. At the same time, part of the calcium hydroxide reacts with carbon dioxide to form calcium carbonate; S23, using a gas detector to monitor the flue gas at the gas outlet of the fluidized bed reactor 1 in real time, to determine whether the flue gas meets the emission standards, and if so, to discharge the flue gas, and randomly taking out aggregate samples from the fluidized bed reactor 1, to detect the nitrate ion content thereof, and if the content meets the standards, to output the aggregate samples via a screw conveyor and proceed to step S4; S3, placing the cooled activated aggregate in a fluidized bed reactor 1, injecting carbon dioxide into the fluidized bed reactor 1 to perform nitrogen and carbon fixation synergistically, thereby obtaining coated aggregate; Specifically, after step S22 and before step S23, 10% carbon dioxide and industrial flue gas containing nitrogen oxides are respectively injected into the fluidized bed reactor 1 through two independent fans. The inlet of the fluidized bed reactor 1 is symmetrically arranged with gas input ports at a 45° inclination angle (it is necessary to pay attention to the spacing of the gas input ports to avoid airflow interference). The two air flows intersect at the gas input ports to form turbulent premixing, ensuring that the carbon dioxide and nitrogen oxides are evenly distributed. The gas flows then move downward to contact and react with the activated aggregate, achieving synergistic carbon fixation (generating calcium carbonate) and nitrogen fixation (capturing nitrogen oxides) to obtain coated aggregate. It should be noted that the coordinated operations of roasting, spraying, and carbon and nitrogen fixation in the fluidized bed reactor 1 are performed in separate time periods. In other words, the hot air blower 113 can normally switch between hot and cold air, and the three do not interfere with each other. S4, conveying the coated aggregate obtained in S3 to a water washing device through a screw conveyor for water washing and surface modification to obtain saturated surface dry aggregate, specifically: S41, water washing: the coated aggregate is conveyed from the discharge port 15 of the fluidized bed reactor 1 to a washing tank via a spiral blade, and the coated aggregate is washed with clean water at a water pressure of 0.3 MPa until nitrate ions are leached. Samples are taken from the outlet of the final washing tank and the nitrate ion content is analyzed using an ion chromatograph; S42, neutralization, lifting the washed coated aggregate from the washing tank to the stirring tank using an elevator, starting the stirring tank for stirring, adding calcium hydroxide solution dropwise to the stirring tank, adjusting the pH value of the coated aggregate, and monitoring it using an online pH meter. After standing for 20 minutes, the residual nitrate is neutralized to obtain neutral aggregate; S43, surface modification: Use the grab bucket of a crane to grab the neutral aggregate and place it in a silane (5%) solution tank. After hydrolysis, the silane reacts with the carboxyl groups on the surface of the aggregate to form a hydrophobic siloxane film, blocking the leaching channel of calcium nitrate and ensuring the durability of the concrete. The immersion is carried out for 10 minutes until the liquid level completely covers the coated aggregate to obtain the modified aggregate. S44, drying, conveying the modified aggregate to a drum dryer using a conveyor, drying it with 80°C hot air, and outputting saturated surface-dry aggregate. The surface of the saturated surface-dry aggregate is dry, and the internal pores remain in a capillary saturated state, so that no additional water is absorbed during subsequent asphalt mixing or concrete mixing; S5, using saturated dry aggregate to prepare recycled concrete, specifically: the obtained saturated dry aggregate is crushed to different degrees to obtain coarse aggregate and fine aggregate, the coarse aggregate and fine aggregate are first added to natural sand in a mixer and mixed and stirred, and then cement is added and stirred, and then a water reducer and water are added and stirred to obtain recycled concrete, and the mixed recycled concrete is sampled and tested.

[0025] The embodiment of the present invention is also implemented through the following technical solutions.

[0026] In the embodiment of the present invention, the fluidized bed reactor 1 in steps S1 and S2 is divided from bottom to top into a calcination section 11 for calcination and reconstruction, a spraying section 12 for the pre-adsorption stage, and a gas mixing section 13 for coordinated nitrogen and carbon fixation, as well as an aggregate inlet 14 and an outlet 15 provided on both sides of the calcination section 11; The roasting section 11 includes an aggregate support grid 111 provided at the bottom of the shell of the fluidized bed reactor 1 and an annular air duct 112 for receiving hot air; The spray section 12 includes a spray head array 121 located near the middle of the fluidized bed and a heat shield 122 for blocking the hot air from the roasting section 11 below. The gas mixing section 13 includes two gas flow inlets 131 symmetrically arranged at 45° on the top of the fluidized bed reactor 1 , and a honeycomb guide plate 132 is also provided at the gas mixing section 13 .

[0027] In an embodiment of the present invention, a plurality of air outlets are provided on the inner side of the annular air duct 112, the annular air duct 112 is externally connected to a hot air blower 113, the hot air blower 113 is externally connected to a gas hot air furnace that provides a hot air source, and a liquid collecting plate 114 for collecting the solution dripping from the spray section 12 is provided below the aggregate support grid 111, and the liquid collecting plate 114 is externally connected to a suction pump 115.

[0028] Specifically, hot air is introduced through the hot air blower 113 to statically roast the aggregate. At this time, the spraying section 12 and the gas mixing section 13 are not working, and the aggregate is intercepted by the aggregate support grid 111 and will not fall. The solution in the liquid collecting plate 114 is pumped to the external storage tank through the external suction pump 115.

[0029] It should be noted that, considering that the aggregates are piled together and have a certain height, multiple annular air ducts 112 can be set to match aggregates with a certain height, and the wind force of the hot air blower 113 can be adjusted to fully roast the aggregates.

[0030] In an embodiment of the present invention, the spray head array 121 is externally connected to a solution tank filled with a saturated calcium nitrate solution, and a water pump is used for spraying control. The heat insulation plate 122 is arranged near the upper side of the roasting section 11, higher than the aggregate inlet 14. The heat insulation plate 122 is made of corrosion-resistant material. Several heat insulation plates 122 are arranged inside the fluidized bed reactor 1. An external rotating motor 123 for controlling the rotation of the heat insulation plate 122 is arranged on the outside of the fluidized bed reactor 1. The output end of the external rotating motor 123 passes through the outer wall of the fluidized bed reactor 1 and is screwed to one side of the heat insulation plate 122, thereby controlling the rotation of the heat insulation plate 122. The other end of the heat insulation plate is fixed to a rotating column for rotating on the inner wall of the fluidized bed reactor 1, thereby realizing rotation inside the fluidized bed reactor 1.

[0031] Specifically, a corrosion-resistant hydrophobic coating is added to the outside of the heat partition to prevent droplets from being retained. When the spray section 12 is not working, the heat insulation board 122 is in a horizontal state to isolate the upwelling of hot air. When the spray section 12 is working, the external rotating motor 123 is synchronously turned on to flip the heat insulation board 122 to a vertical state to provide space for the dripping of the saturated calcium nitrate solution. The saturated calcium nitrate solution is sprayed out from the spray head array 121 and drips onto the activated aggregate below. When the gas mixing section 13 is working, the heat insulation board 122 also needs to be in a vertical state.

[0032] In addition, if Figure 3 As shown, considering that the vertical heat insulation plate 122 blocks part of the airflow, the setting positions of the spray section 12 and the gas mixing section 13 can be replaced according to actual conditions, and the air flow inlet 131 can be set on the side wall of the fluidized bed reactor 1. The height position is set to leave mixing space for the gas, thereby reducing conflicts. At this time, after the spray section 12 is fully operational, the heat insulation plate 122 can be rotated to keep it horizontal.

[0033] In an embodiment of the present invention, in step S23, when the flue gas does not meet the emission index, the tail flue gas is refluxed to the inlet of the fluidized bed reactor 1 through the induced draft fan and mixed with the fresh flue gas to reduce the inlet nitrogen oxide concentration and prolong the residence time, or the temperature of the fluidized bed reactor 1 is adjusted from 60°C to 40-45°C (by spraying water or steam) to inhibit the secondary release of carbon dioxide by calcium carbonate and improve the nitrogen fixation efficiency of nitrogen dioxide and calcium oxide / calcium carbonate; When the nitrate ion content does not meet the standard, the activated aggregate that does not meet the standard is returned to the top of the fluidized bed reactor 1 using a screw conveyor, and steps S21-S22 are repeated and sampling is performed again until the nitrate ion content meets the standard.

[0034] It should be noted that a dual-control valve of "proportion-oxygen content" must be installed for flue gas recirculation to prevent the oxygen partial pressure from being too low, thereby inhibiting the oxidation reaction of nitrogen dioxide and nitrate ions; The number of secondary circulations of aggregates should be limited (≤3 times), otherwise excessive thickening of calcium carbonate will block pores, reduce fluidization quality, and increase energy consumption.

[0035] In an embodiment of the present invention, the synergistic reaction process of nitrogen fixation and carbon fixation in step S3 includes: carbon dioxide in the mixed gas reacts with calcium hydroxide in the aggregate to produce calcium carbonate, which is in situ deposited on the outer surface and pores of the aggregate to form a first dense calcium carbonate coating layer; nitrogen dioxide in the mixed gas reacts with calcium oxide in the aggregate to produce calcium nitrate, which is again deposited on the calcium carbonate layer to form a second calcium nitrate coating layer; the obtained calcium carbonate further reacts with nitrogen dioxide to produce calcium nitrate and release carbon dioxide gas; and under the continuous fluidization and tumbling action in the fluidized bed reactor 1, the aggregate surface eventually obtains a shell composed of a double-layer nano-coating of calcium carbonate / calcium nitrate, forming a composite coated aggregate; Among them, the concentration of carbon dioxide needs to be higher than that of nitrogen oxides. The partial pressure of carbon dioxide is high and the mass transfer driving force is large. Carbon dioxide will preferentially occupy the active sites on the surface of the aggregate and carbonize quickly, so that the mixed gas formed by the two comes into contact with the aggregate. Carbon dioxide also reacts before the aggregate, and nitrogen oxides then react with the calcium oxide in the aggregate to achieve carbon fixation first and then nitrogen fixation.

[0036] In an embodiment of the present invention, after the preparation of the recycled concrete in step S5 is completed, samples are taken at the mixer outlet on site to measure the slump and apparent density. After confirming the pumpability and uniformity, the sample is placed in a 150 mm cubic test mold, three pieces per group, and standard curing is carried out for 28 days. The laboratory measures the compressive strength of the 28-day specimens, and simultaneously checks the splitting tensile strength, elastic modulus and shrinkage. The impermeability grade is determined by the step-by-step pressurization method of the frustum specimen. When all the measured values ​​reach the design strength and the specification limit, the batch of recycled concrete can be judged as qualified. Small batches are first adapted. After being judged as qualified, formal production is carried out according to the regeneration method of steps S1-S5.

[0037] It should be noted that the model parameters of the above-mentioned processing equipment, including the size / gas flow rate and other parameters of the fluidized bed reactor 1, need to be determined according to the actual preparation situation.

[0038] An embodiment of the present invention further provides a method for fixing nitrogen and carbon in a coordinated manner to regenerate waste concrete, wherein the proportion of each component, calculated by mass, includes 100 parts of cement, 300 parts of saturated surface dry recycled aggregate, 180 parts of coarse aggregate, 120 parts of fine aggregate, 45 parts of natural sand, 55 parts of water, and 1.0 part of a water reducer (accounting for 1% of the mass of the cement).

[0039] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

[0040] It should be understood that the specific order or hierarchy of steps in the disclosed processes is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process can be rearranged without departing from the scope of the present disclosure. The accompanying method claims present elements of the various steps in an exemplary order and are not intended to be limited to a specific order or hierarchy.

[0041] In the foregoing detailed description, various features are grouped together in a single embodiment to simplify the disclosure. This method of disclosure should not be interpreted as reflecting an intention that embodiments of the claimed subject matter require more features than are expressly recited in each claim. On the contrary, as reflected in the appended claims, the invention comprises less than all the features of any individual disclosed embodiment. The appended claims are therefore hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

[0042] Those skilled in the art will also appreciate that the various illustrative logic blocks, modules, circuits, and algorithmic steps described in conjunction with the embodiments herein may be implemented as electronic hardware, computer software, or a combination thereof. In order to clearly illustrate the interchangeability between hardware and software, the various illustrative components, blocks, modules, circuits, and steps described above are generally described around their functions. Whether such functions are implemented as hardware or software depends on the specific application and the design constraints imposed on the entire system. A skilled person may implement the described functions in an adaptable manner for each specific application, but such implementation decisions should not be interpreted as departing from the scope of protection of this disclosure.

[0043] The steps of the methods or algorithms described in conjunction with the embodiments herein may be directly embodied as hardware, software modules executed by a processor, or a combination thereof. The software module may be located in a RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, register, hard disk, removable disk, CD-ROM, or any other form of storage medium well known in the art. An exemplary storage medium is connected to the processor so that the processor can read information from the storage medium and write information to the storage medium. Of course, the storage medium may also be an integral part of the processor. The processor and storage medium may be located in an ASIC. The ASIC may be located in a user terminal. Of course, the processor and storage medium may also be present in a user terminal as discrete components.

[0044] For software implementation, the techniques described in this application can be implemented using modules (e.g., procedures, functions, etc.) that perform the functions described in this application. These software codes can be stored in a memory unit and executed by a processor. The memory unit can be implemented within the processor or external to the processor. In the latter case, it is communicatively coupled to the processor via various means, which are well known in the art.

[0045] The foregoing description includes examples of one or more embodiments. Of course, it is not possible to describe all possible combinations of components or methods for the purposes of describing the above embodiments, but one of ordinary skill in the art will recognize that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to encompass all such changes, modifications and variations that fall within the scope of the appended claims. Furthermore, to the extent the term "comprising" is used in the specification or claims, the term is intended to be encompassed in a manner similar to the term "including," as explained in terms of "including," used as a transitional word in the claims. Furthermore, any use of the term "or" in the specification of the claims is intended to mean a "non-exclusive or."

Claims

1. A method for nitrogen and carbon fixation synergistically regenerating waste concrete, characterized in that: The following steps are involved: S1, the waste concrete is subjected to coarse crushing, acetic acid solution activation, medium crushing in sequence, and transported to a fluidized bed reactor (1) for roasting and reconstruction to obtain activated aggregate; S2, introducing the industrial flue gas containing nitrogen oxides into a fluidized bed reactor (1) filled with activated aggregate through a gas input device, and causing a mineralization reaction at 40-60°C; S3, injecting carbon dioxide into the fluidized bed reactor (1) to carry out nitrogen and carbon fixation synergistically to obtain coated aggregate; S4, washing and surface-modifying the coated aggregate obtained in S3 using a water washing device to obtain saturated surface-dry aggregate; S5, preparation of recycled concrete using saturated face-dry aggregate.

2. The method for nitrogen and carbon fixation synergistically regenerating waste concrete according to claim 1, characterized in that: The step S1 comprises: Acetic acid activation is to spray the coarsely crushed aggregate with 5% acetic acid solution in an acid-resistant spraying device and let it stand for 2 hours; The roasting and reconstructing step is to roast the aggregate obtained by the medium crushing in the roasting section (11) of the fluidized bed reactor (1) for 2 hours to generate gamma-type dicalcium silicate activated aggregate.

3. The method for nitrogen and carbon fixation synergistically regenerating waste concrete according to claim 2, characterized in that: The detailed process of the flue gas mineralization and nitrogen fixation in step S2 is as follows: S21, pre-adsorption stage, at 40°C, a saturated calcium nitrate solution is sprayed into the fluidized bed reactor (1) to activate the aggregate to pre-adsorb nitrogen dioxide; S22, the main reaction stage, the temperature is raised to 60°C, the activated aggregate reacts with the flue gas and completes the nitrogen fixation reaction; S23, monitoring, using a gas detector to monitor the nitrogen oxides in the flue gas at the gas outlet of the fluidized bed reactor (1) and the content of nitrate ions in the aggregate.

4. The method for nitrogen and carbon fixation synergistically regenerating waste concrete according to claim 3, characterized in that: When the concentration of nitrogen oxides in the flue gas exceeds the standard, it can be adjusted by recirculating the tail flue gas or cooling it to 40-45°C; When the nitrate ion content does not meet the standard, the aggregate is returned to the fluidized bed reactor (1) to repeat the nitrogen fixation treatment.

5. The method for nitrogen and carbon fixation synergistically regenerating waste concrete according to claim 4, characterized in that: The detailed process of nitrogen fixation and carbon fixation synergistically in step S3 is as follows: The cooled activated aggregate is placed in a fluidized bed reactor (1). Two independent fans are used to simultaneously mix 10% carbon dioxide and industrial flue gas containing nitrogen oxides through a 45° symmetrical air flow inlet (131) for turbulent mixing, and the mixed gas contacts and reacts with the activated aggregate to achieve synergistic carbon fixation and nitrogen fixation, thereby obtaining coated aggregate.

6. The method for nitrogen and carbon fixation synergistically regenerating waste concrete according to claim 5, characterized in that: The fluidized bed reactor (1) in steps S1 and S2 is divided from bottom to top into a calcination section (11) for calcination reconstruction, a spraying section (12) for the pre-adsorption stage, and a gas mixing section (13) for coordinated nitrogen fixation and carbon fixation, as well as an aggregate inlet (14) and an outlet (15) provided on both sides of the calcination section (11); The roasting section (11) comprises an aggregate support grid (111) arranged at the bottom of the shell of the fluidized bed reactor (1) and an annular air duct (112) for receiving hot air; The spray section (12) includes a spray head array (121) arranged near the middle of the fluidized bed and a heat insulation plate (122) for blocking hot air from the roasting section (11) below. The gas mixing section (13) comprises two gas flow inlets (131) symmetrically arranged at 45 degrees on the top of the fluidized bed reactor (1), and a honeycomb guide plate (132) is also provided at the gas mixing section (13).

7. The method for nitrogen and carbon fixation synergistically regenerating waste concrete according to claim 6, characterized in that: A plurality of air vents are provided on the inner side of the annular air duct (112). The annular air duct (112) is externally connected to a hot air blower (113). The hot air blower (113) is externally connected to a gas hot air furnace that provides a hot air source. A liquid collecting plate (114) for collecting solution dripping from the spray section (12) is provided below the aggregate support grid (111). The liquid collecting plate (114) is externally connected to a suction pump (115).

8. The method for nitrogen and carbon fixation synergistically regenerating waste concrete according to claim 7, characterized in that: The spray head array (121) is externally connected to a solution tank filled with a saturated calcium nitrate solution, and a water pump is used for spraying control. The heat insulation board (122) is arranged near the upper side of the roasting section (11) and higher than the position of the aggregate inlet (14). The heat insulation board (122) is corrosion-resistant. A plurality of the heat insulation boards (122) are arranged inside the fluidized bed reactor (1), and an external rotating motor (123) for controlling the rotation of the heat insulation board (122) is arranged outside the fluidized bed reactor (1).

9. The method for nitrogen and carbon fixation synergistically regenerating waste concrete according to claim 8, characterized in that: The detailed process of preparing the recycled concrete in step S5 is as follows: The obtained saturated surface dry aggregate is classified into coarse / fine aggregate, and is sequentially mixed with natural sand, cement, water reducing agent and water to obtain recycled concrete.

10. A recycled concrete prepared by a nitrogen and carbon fixation synergistic waste concrete regeneration method, applied to a nitrogen and carbon fixation synergistic waste concrete regeneration method according to any one of claims 1 to 9, characterized in that: The proportion of each component is calculated by mass, including 100 parts of cement, 300 parts of saturated surface dry recycled aggregate, 180 parts of coarse aggregate, 120 parts of fine aggregate, 45 parts of natural sand, 55 parts of water, and 1.0 part of water reducer.

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