A method for simultaneously fixing nitrogen and carbon and regenerating waste concrete and regenerated concrete

Abstract

The application provides a nitrogen-fixing and carbon-fixing synergic waste concrete recycling method and recycled concrete, and belongs to the technical field of recycled concrete, and comprises the following steps: S1, waste concrete is sequentially subjected to coarse crushing, acetic acid solution activation, medium crushing, and is transported to a fluidized bed reactor for calcination reconstruction to obtain activated aggregate; S2, industrial flue gas containing nitrogen oxide compounds is introduced into the fluidized bed reactor containing the activated aggregate through a gas input device to cause a mineralization reaction at 40-60 DEG C; S3, carbon dioxide is injected into the fluidized bed reactor to realize nitrogen fixation and carbon fixation synergy, and coated aggregate is obtained; S4, the coated aggregate obtained in S3 is washed and surface modified by using a water washing device to obtain saturated surface dry aggregate; and S5, the saturated surface dry aggregate is used to prepare recycled concrete. The application solves the problem that waste concrete and industrial flue gas are not synergized in the prior art, thereby causing certain resource waste.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of recycled concrete, and particularly relates to a method for recycling waste concrete by fixing nitrogen and carbon and recycled concrete. BACKGROUND

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

[0003] At present, whether it is a construction waste recycled aggregate production line or a process for preparing steel slag concrete by carbonization of steel slag, the flue gas treatment is regarded as an end treatment link. After desulfurization, denitrification, and dust removal, the flue gas is discharged after reaching the standard. Carbon dioxide and nitrogen oxides in the flue gas are not introduced into the aggregate or product of recycled concrete to participate in the reaction. There is no intersection with the industrial flue gas throughout the process. The waste flue gas is not fully utilized, resulting in a certain waste of resources. SUMMARY

[0004] The application provides a method for recycling waste concrete by fixing nitrogen and carbon and recycled concrete, which solves the problem of waste of resources caused by the lack of cooperation between waste concrete and industrial flue gas in the prior art.

[0005] In view of the above problems, the technical scheme provided by the application is as follows:

[0006] The application provides a method for recycling waste concrete by fixing nitrogen and carbon, comprising the following steps:

[0007] S1, waste concrete is sequentially subjected to coarse crushing, activation with an acetic acid solution, and medium crushing, and is then transported to a fluidized bed reactor for calcination and reconstruction to obtain activated aggregate;

[0008] S2, industrial flue gas containing nitrogen oxides is introduced into the fluidized bed reactor containing the activated aggregate through a gas input device to cause a mineralization reaction at 40-60 DEG C;

[0009] S3, carbon dioxide is injected into the fluidized bed reactor to fix nitrogen and carbon cooperatively to obtain coated aggregate;

[0010] S4, the coated aggregate obtained in S3 is washed and surface modified using a water washing device to obtain saturated surface-dry aggregate;

[0011] S5, the saturated surface-dry aggregate is used to prepare recycled concrete.

[0012] As a preferred technical solution of the present application, the step S1 comprises:

[0013] The acetic acid activation is to spray the aggregate obtained by rough crushing with 5% acetic acid solution in an acid-resistant spraying device and stand for 2 hours.

[0014] The calcination reconstruction is to calcine the aggregate obtained by medium crushing in the calcination section of the fluidized bed reactor for 2 hours to generate γ-type dicalcium silicate activated aggregate.

[0015] As a preferred technical solution of the present application, the detailed process of the step S2 of flue gas mineralization of nitrogen fixation is as follows:

[0016] S21, pre-adsorption stage, at 40℃, spray calcium nitrate saturated solution into the fluidized bed reactor to activate the aggregate to pre-adsorb nitrogen dioxide;

[0017] S22, main reaction stage, heat to 60℃, the activated aggregate reacts with the flue gas to complete the nitrogen fixation reaction;

[0018] S23, monitoring, use a gas detector to monitor the content of nitrogen oxides in the flue gas at the gas outlet of the fluidized bed reactor and the content of nitrate ions in the aggregate.

[0019] As a preferred technical solution of the present application, when the concentration of nitrogen oxides in the flue gas exceeds the standard, adjust by backflow of tail flue gas or cooling to 40-45℃;

[0020] When the content of nitrate ions does not meet the standard, send the aggregate back to the fluidized bed reactor for repeated nitrogen fixation treatment.

[0021] As a preferred technical solution of the present application, the detailed process of the step S3 of simultaneous fixation of nitrogen and carbon is as follows:

[0022] Place the cooled activated aggregate in the fluidized bed reactor, and through two independent air blowers, simultaneously pass 10% concentration of carbon dioxide and industrial flue gas containing nitrogen oxides through the 45° symmetrical air inlet to realize turbulent mixing, contact reaction with the activated aggregate, realize the cooperation of carbon fixation and nitrogen fixation, and obtain the coated aggregate.

[0023] The fluidized bed reactor in the steps S1 and S2 is divided from bottom to top into a calcination section for calcination reconstruction, a spraying section for pre-adsorption stage, and a gas mixing section for simultaneous fixation of nitrogen and carbon, and the aggregate inlet and discharge port are arranged on both sides of the calcination section;

[0024] The calcination section comprises an aggregate support grid arranged at the bottom of the shell of the fluidized bed reactor and an annular air pipe for accessing hot air;

[0025] The spraying section comprises a spray head array arranged near the middle of the fluidized bed and a heat insulation plate for blocking the hot gas from the roasting section below;

[0026] The gas mixing section comprises two gas inlets arranged symmetrically at 45 degrees on the top of the fluidized bed reactor, and a honeycomb guide plate is arranged at the gas mixing section.

[0027] As a preferred technical solution of the present application, a plurality of air inlets are arranged on the inner side of the annular air duct, a hot air fan is arranged outside the annular air duct, a gas hot air furnace providing a hot air source is arranged outside the hot air fan, a liquid collecting plate for collecting the solution dripping from the spraying section is arranged below the aggregate supporting grid, and a suction pump is arranged outside the liquid collecting plate.

[0028] As a preferred technical solution of the present application, a solution tank filled with a saturated calcium nitrate solution is arranged outside the spray head array, and a water pump is used for spraying control, the heat insulation plate is arranged on the upper side near the roasting section and is higher than the aggregate inlet, the heat insulation plate is corrosion-resistant, a plurality of heat insulation plates are arranged inside the fluidized bed reactor, and an external rotary motor for controlling the rotation of the heat insulation plates is arranged outside the fluidized bed reactor.

[0029] As a preferred technical solution of the present application, the preparation process of the recycled concrete in step S5 is as follows:

[0030] The obtained saturated dry surface aggregate is classified into coarse aggregate and fine aggregate, and is sequentially mixed and stirred with natural sand, cement, water reducing agent and water to obtain recycled concrete.

[0031] On the other hand, the recycled concrete prepared by the method for simultaneously fixing nitrogen and carbon and recycling waste concrete comprises cement 100 parts, saturated dry recycled aggregate 300 parts including coarse aggregate 180 parts and fine aggregate 120 parts, natural sand 45 parts, water 55 parts and water reducing agent 1.0 part.

[0032] Compared with the prior art, the present application has the following advantages:

[0033] In the present application, calcium hydroxide / calcium oxide in the waste concrete aggregate is first carbonized with carbon dioxide to form a dense calcium carbonate inner layer, realizing carbon fixation, and then nitrogen dioxide reacts on the calcium oxide / calcium carbonate double active sites to form a calcium nitrate outer layer, completing nitrogen fixation.

[0034] The above description is only a summary of the technical solutions of the present application, in order to enable the technical means of the present application to be more clearly understood, and can be implemented according to the content of the specification, and in order to enable the above and other purposes, characteristics and advantages of the present application to be more obvious and easy to understand, the specific embodiments of the present application are described below. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a flow diagram of a method for recycling waste concrete disclosed by the present application;

[0036] Figure 2 is a structural diagram of a fluidized bed reactor of a method for recycling waste concrete disclosed by the present application;

[0037] Figure 3 is a structural diagram of a second fluidized bed reactor of a method for recycling waste concrete disclosed by the present application;

[0038] Reference signs: 1, fluidized bed reactor; 11, calcination section; 111, aggregate support grid; 112, annular air pipe; 113, hot air fan; 114, liquid collection plate; 115, suction pump;

[0039] 12, spraying section; 121, array of spray heads; 122, heat insulation plate; 123, external rotary motor; 13, gas mixing section; 131, gas inlet; 132, honeycomb-shaped flow guide plate;

[0040] 14, aggregate inlet; 15, discharge outlet. DETAILED DESCRIPTION

[0041] In order to make the purposes, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0042] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0043] It should be noted that similar reference numerals and letters refer to like items in the accompanying drawings, and once an item is defined in one drawing, it need not be further defined and explained in subsequent drawings.

[0044] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0045] In addition, the terms "first" and "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first" and "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited. Embodiments

[0046] Referring to the accompanying drawings Figures 1-2 As shown, the present application provides a technical solution: a method for simultaneous nitrogen fixation and carbon sequestration and waste concrete recycling, comprising the following steps:

[0047] S1, the waste concrete is sequentially subjected to coarse crushing, acid solution activation, medium crushing, and is transported to a fluidized bed reactor 1 for calcination and reconstruction to obtain activated aggregate, specifically:

[0048] S11, coarse crushing, using a jaw crusher to crush the waste concrete to a particle size of ≤50mm to obtain coarse aggregate;

[0049] S12, acid activation, the coarse aggregate is transported to an acid-resistant spraying device, and 5% acetic acid solution is sprayed to dissolve the hydration layer on the surface of the coarse aggregate for 2 hours to obtain a demoulded aggregate;

[0050] S13, medium crushing, using an impact crusher to crush the demoulded aggregate for the second time to a particle size of 1-3mm, and using a vibrating screen to sieve and grade to obtain medium aggregate;

[0051] S14, roasting reconstruction, conveying the intermediate aggregate to the roasting section 11 of the fluidized bed reactor 1, removing the volatiles of the intermediate aggregate by hot air fan 113 at 600-800℃, the treatment time is 4-6 hours, then heating to 1250-1350℃, holding for 30 min, then air cooling to below 200℃, obtaining γ-type dicalcium silicate activated aggregate, cooling the activated aggregate to 40-60℃ by air cooling equipment, which is a separate air cooling equipment or uses the hot air fan 113 described in S2 for cooling;

[0052] The detailed process of obtaining γ-type dicalcium silicate activated aggregate: waste concrete is immersed in acetic acid solution, part of calcium ions are dissolved by acetic acid and etched on the surface to form a silicon-rich residue, then crushed to 1-3mm particles in S13, obtaining aggregate with silicon-rich surface and calcium-rich interior, mixing the aggregate with quartz powder according to the stoichiometry of calcium / silicon≈2, granulating, and feeding into the roasting section 11 of the fluidized bed reactor 1, passing 1250-1350℃ hot air through the hot air fan 113, holding for 30 min to generate β-type dicalcium silicate, and then air cooling to <200℃, the β-type dicalcium silicate is transformed into metastable γ-type dicalcium silicate due to the rapid cooling stress, i.e. γ-type dicalcium silicate activated aggregate;

[0053] S2, the industrial flue gas containing nitrogen oxide compounds is introduced into the fluidized bed reactor 1 containing activated aggregate through the gas input device, and the mineralization reaction occurs at 40-60℃, the hot air fan 113 is selected as a variable frequency hot air fan, so that the cold and hot air is switched, such as HWIR900F industrial hot air fan, the temperature of the fluidized bed reactor 1 is detected by the thermometer installed on the fluidized bed reactor 1, so as to master the temperature change in the fluidized bed reactor 1, and the type needs to be resistant to high temperature and low temperature, specifically:

[0054] S21, the industrial flue gas containing nitrogen oxide compounds is introduced into the fluidized bed reactor 1 containing activated aggregate through the precision fan;

[0055] S22, in the pre-adsorption stage, the air volume of the hot air fan 113 is adjusted by the frequency converter to avoid the air temperature rising or falling too fast, and switched to cold air, at a temperature of 40℃, calcium nitrate saturated solution is sprayed into the fluidized bed reactor 1, the calcium nitrate saturated solution provides reaction medium water, so that the activated aggregate pre-adsorbs nitrogen dioxide, the calcium nitrate solution forms a liquid film on the surface of the aggregate, pre-adsorbs nitrogen dioxide in the flue gas, and improves the subsequent nitrogen fixation efficiency;

[0056] In the temperature rising reaction stage, the air volume of the hot air fan 113 is adjusted by the frequency converter, and the hot air channel is switched to perform light heating, which also needs to avoid rapid heating, the temperature of the fluidized bed reactor 1 is raised to 60℃, the activated aggregate reacts with the flue gas, the γ-type dicalcium silicate in the activated aggregate hydrolyzes to generate calcium hydroxide, and the calcium hydroxide reacts with nitrogen dioxide to generate calcium nitrate;

[0057] At the same time, part of the calcium hydroxide reacts with carbon dioxide to generate calcium carbonate;

[0058] S23, using a gas detector to monitor the flue gas of the gas outlet of the fluidized bed reactor 1 in real time, to determine whether the flue gas meets the emission indicators, and if so, to discharge, randomly take out the aggregate sample in the fluidized bed reactor 1, detect the content of nitrate ions, and after the content meets the standard, output by the screw conveyor, and proceed to step S4;

[0059] S3, placing the cooled activated aggregate in the fluidized bed reactor 1, injecting carbon dioxide into the fluidized bed reactor 1, and carrying out nitrogen fixation and carbon fixation cooperation to obtain coated aggregate;

[0060] Specifically, after step S22 ends and before step S23, two independent air blowers are used to inject 10% concentration of carbon dioxide and nitrogen-containing industrial flue gas into the fluidized bed reactor 1, and the inlet of the fluidized bed reactor 1 is symmetrically arranged with gas input ports at an inclination angle of 45° (note that the spacing of the gas input ports should be avoided to avoid airflow interference), and the two gas streams meet at the gas input ports to form a turbulent premixing, ensuring that the carbon dioxide and nitrogen oxides are uniformly distributed and then move downward to contact and react with the activated aggregate, realizing the cooperation of carbon fixation (generating calcium carbonate) and nitrogen fixation (capturing nitrogen oxides), and obtaining coated aggregate;

[0061] It should be noted that the roasting, spraying and carbon fixation and nitrogen fixation cooperation in the fluidized bed reactor 1 are carried out in separate periods, that is, the hot air blower 113 can normally switch between cold and hot air, and the three do not interfere with each other;

[0062] S4, conveying the coated aggregate obtained in S3 to a water washing equipment for water washing and surface modification to obtain saturated surface dry aggregate, specifically:

[0063] S41, water washing, the coated aggregate is conveyed from the discharge port 15 of the fluidized bed reactor 1 to the washing tank through the spiral blade, and the coated aggregate is washed with water at a water pressure of 0.3 MPa until the nitrate ions are leached out, and the sample is taken at the drainage port of the final washing tank, and the content of nitrate ions is analyzed by ion chromatography;

[0064] S42, neutralization, the coated aggregate after water washing is lifted from the washing tank to the stirring tank by the elevator, and the stirring tank is started to stir, and calcium hydroxide solution is added dropwise into the stirring tank to adjust the pH value of the coated aggregate, which is monitored by an online pH meter, and after standing for 20 minutes, the residual nitrate is neutralized to obtain neutral aggregate;

[0065] S43, surface modification, using the grab bucket of the crane to grab the neutral aggregate into the silane (5%) solution tank, after the hydrolysis of silane, the silane reacts with the carboxyl group on the surface of the aggregate to form a hydrophobic siloxane film, which blocks the calcium nitrate leaching channel and ensures the durability of the concrete, and the modified aggregate is immersed for 10 minutes, the liquid level completely covers the coated aggregate, and the modified aggregate is obtained;

[0066] S44, drying, the modified aggregate is conveyed to the drum dryer using the conveyor, and the saturated surface dry aggregate is output after drying by 80 DEG C hot air, the surface of the saturated surface dry aggregate is dry, and the internal pores still maintain the capillary saturation state, and no additional water is absorbed during subsequent asphalt mixing or concrete mixing;

[0067] S5, the preparation of recycled concrete using saturated surface dry aggregate, specifically: the obtained saturated surface dry aggregate is crushed to different degrees to obtain coarse aggregate and fine aggregate, the coarse aggregate and fine aggregate are first mixed and stirred with natural sand in a mixer, then cement is added and stirred, and then water reducing agent and water are added and stirred to obtain recycled concrete, and the mixed recycled concrete is sampled and detected.

[0068] The embodiment of the application is also realized by the following technical solutions.

[0069] In the embodiment of the application, the fluidized bed reactor 1 in steps S1 and S2 is divided into a roasting section 11 for roasting reconstruction, a spraying section 12 for a pre-adsorption stage, and a gas mixing section 13 for nitrogen fixation and carbon fixation cooperation from bottom to top, and the aggregate inlet 14 and the discharge port 15 are arranged on both sides of the roasting section 11;

[0070] The roasting section 11 includes an aggregate support grid 111 arranged at the bottom of the outer shell of the fluidized bed reactor 1 and an annular air pipe 112 for accessing hot air;

[0071] The spraying section 12 includes a spraying head array 121 arranged near the middle position of the fluidized bed and a heat insulation plate 122 for blocking the hot air of the roasting section 11 below;

[0072] The gas mixing section 13 includes two gas inlets 131 symmetrically arranged at the top of the fluidized bed reactor 1 at an angle of 45 degrees, and a honeycomb guide plate 132 is arranged at the gas mixing section 13.

[0073] In the embodiment of the application, a plurality of air openings are formed in the inner side of the annular air pipe 112, the annular air pipe 112 is connected with a hot air fan 113, the hot air fan 113 is connected with a gas hot air furnace providing a hot air source, and the lower side of the aggregate support grid 111 is provided with a liquid collecting plate 114 for collecting the solution dripping from the spraying section 12, and the liquid collecting plate 114 is connected with a suction pump 115.

[0074] Specifically, the hot air is introduced by the hot air blower 113 to perform static roasting on 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 supporting grid 111 and cannot fall, and the solution in the liquid collecting plate 114 is pumped to the external storage tank by the external suction pump 115.

[0075] It should be noted that, considering that the aggregate is piled together and has a certain height, the annular air pipe 112 can be provided in multiple to match the aggregate with a certain height, and the air volume of the hot air blower 113 can be adjusted to fully roast the aggregate.

[0076] In the embodiment of the present application, the solution tank of the calcium nitrate saturated solution is externally connected to the spray head array 121, and a water pump is used for spraying control, the heat insulation plate 122 is arranged on the upper side close to the roasting section 11 and is higher than the position of the aggregate inlet 14, the heat insulation plate 122 is made of corrosion-resistant material, the inside of the fluidized bed reactor 1 is provided with a plurality of heat insulation plates 122, the outside of the fluidized bed reactor 1 is provided with an external rotary motor 123 for controlling the rotation of the heat insulation plate 122, the output end of the external rotary motor 123 penetrates the outer wall of the fluidized bed reactor 1 and is screw-connected with one side of the heat insulation plate 122, so as to control the rotation of the heat insulation plate 122, and the other end of the heat insulation plate is fixed with a rotating column for rotating in the inner wall of the fluidized bed reactor 1, so as to realize the rotation in the fluidized bed reactor 1.

[0077] Specifically, a corrosion-resistant and water-repellent coating is additionally provided on the outside of the heat insulation plate to prevent liquid droplets from being retained, when the spraying section 12 is not working, the heat insulation plate 122 is in a horizontal state to prevent hot air from flowing upwards, when the spraying section 12 is working, the external rotary motor 123 is opened synchronously to overturn the heat insulation plate 122 to a vertical state to provide space for the falling of the calcium nitrate saturated solution, the calcium nitrate saturated solution is sprayed from the spray head array 121 and falls on the activated aggregate below, and when the gas mixing section 13 is working, the heat insulation plate 122 also needs to be in a vertical state.

[0078] In addition, as shown in Figure 3 , considering that the vertical heat insulation plate 122 may block part of the airflow, the setting positions of the spraying section 12 and the gas mixing section 13 can be replaced according to the actual situation, and the airflow inlet 131 is arranged on the side wall of the fluidized bed reactor 1 at a proper height position to provide mixing space for the gas, so as to reduce the conflict, at this time, after the spraying section 12 is completely working, the heat insulation plate 122 can be rotated back to be horizontal.

[0079] In the embodiment of the present application, when the flue gas does not meet the emission index in step S23, the tail flue gas is returned to the inlet of the fluidized bed reactor 1 through the induced draft fan to mix with the fresh flue gas, reduce the concentration of nitrogen oxides at the inlet, and prolong the residence time, or the temperature of the fluidized bed reactor 1 is lowered from 60°C to 40-45°C (using spray water or steam) to inhibit the secondary release of carbon dioxide by calcium carbonate reaction, while improving the nitrogen fixation efficiency of nitrogen dioxide and calcium oxide / calcium carbonate.

[0080] When the content of nitrate ions does not meet the standard, the non-standard activated aggregate is sent back to the top of the fluidized bed reactor 1 using a screw conveyor, and steps S21-S22 are repeated for sampling again until the content of nitrate ions meets the standard.

[0081] It should be noted that the flue gas return must be provided with a "proportion-oxygen content" double control valve to prevent the oxygen partial pressure from being too low and inhibit the oxidation reaction of nitrogen dioxide-nitrate ions.

[0082] The secondary circulation of aggregate should be limited in number (≤3 times), otherwise the excessive thickening of calcium carbonate will block the pores, reduce the fluidization quality, and increase the energy consumption.

[0083] In the embodiment of the present application, the reaction process of nitrogen fixation and carbon fixation in step S3 includes that the carbon dioxide in the mixed gas reacts with the calcium hydroxide of the aggregate to obtain calcium carbonate, the calcium carbonate is deposited in situ on the outer surface of the aggregate and in the pores to form a first layer of dense calcium carbonate coating, the nitrogen dioxide in the mixed gas reacts with the calcium oxide of the aggregate to obtain calcium nitrate, the generated calcium nitrate is deposited on the calcium carbonate layer to form a second layer of calcium nitrate coating, the obtained calcium carbonate further reacts with nitrogen dioxide to generate calcium nitrate and release carbon dioxide gas, and under the continuous fluidization and rolling action in the fluidized bed reactor 1, the surface of the aggregate finally obtains an outer shell composed of a double-layer nano-coating of calcium carbonate / calcium nitrate, forming a composite coated aggregate.

[0084] Among them, the concentration of carbon dioxide needs to be higher than that of nitrogen oxides, the partial pressure of carbon dioxide is high, 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 contacts with the aggregate, and carbon dioxide reacts first, and then nitrogen oxides react with calcium oxide of the aggregate to realize carbon fixation first and nitrogen fixation later.

[0085] In the embodiment of the present application, after the recycled concrete is prepared in step S5, the sample is taken at the outlet of the mixer on site, the slump and apparent density are measured, and the pumpability and uniformity are confirmed, then the sample is loaded into 150mm cubic test mold, three pieces per group, standard curing for 28 days, the compressive strength of the 28-day test piece is measured in the laboratory, and the splitting tensile, elastic modulus and dry shrinkage are synchronously sampled and tested, the impermeability grade is measured by the circular platform test piece step-by-step pressure method, when all the measured values reach the design strength and the specification limit, the batch of recycled concrete is determined to be qualified, a small batch is first adapted, and after being determined to be qualified, the recycled method of steps S1-S5 is used for formal production.

[0086] It should be noted that the size / gas flow rate and other model parameters of the fluidized bed reactor 1 in the above processing device need to be determined according to the actual preparation situation.

[0087] The embodiment of the present application further provides a recycled concrete prepared by the nitrogen-fixing and carbon-fixing collaborative waste concrete recycling method, and the proportion of each component is 100 parts of cement, 300 parts of saturated surface-dry recycled aggregate including 180 parts of coarse aggregate and 120 parts of fine aggregate, 45 parts of natural sand, 55 parts of water, and 1.0 part of water reducing agent (1% of the mass of cement).

[0088] The above is only a preferred embodiment of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for simultaneous nitrogen fixation and carbon sequestration and waste concrete recycling, characterized in that, The method comprises the following steps: S1, the waste concrete is sequentially subjected to coarse crushing, acetic acid solution activation, medium crushing, and is transported to a fluidized bed reactor (1) to perform calcination reconstruction, so as to obtain activated aggregate; Step S1 comprises: The acetic acid activation is that the aggregate obtained by coarse crushing is treated by spraying 5% acetic acid solution in an acid-resistant spraying device, and is placed for 2 hours; The calcination reconstruction is that the aggregate obtained by medium crushing is calcined in a calcination section (11) of the fluidized bed reactor (1) for 2 hours, so as to generate γ-type dicalcium silicate activated aggregate; S2, the industrial flue gas containing nitrogen oxide compounds is introduced into the fluidized bed reactor (1) filled with the activated aggregate through a gas input device, and a mineralization reaction occurs at 40-60 DEG C; The detailed process of the flue gas mineralization nitrogen fixation is as follows: S21, the industrial flue gas containing nitrogen oxide compounds is introduced into the fluidized bed reactor (1) filled with the activated aggregate through a precision fan; S22, in the pre-adsorption stage, the air volume of the hot air fan (113) is adjusted by a frequency converter to avoid the air temperature from rising or falling too fast, and is switched to cold air, the calcium nitrate saturated solution is sprayed into the fluidized bed reactor (1) at a temperature of 40 DEG C, the calcium nitrate saturated solution provides the reaction medium water, the activated aggregate pre-adsorbs the nitrogen dioxide, the calcium nitrate solution forms a liquid film on the surface of the aggregate, pre-adsorbs the nitrogen dioxide in the flue gas, and the subsequent nitrogen fixation efficiency is improved; In the temperature rising reaction stage, the air volume of the hot air fan (113) is adjusted by the frequency converter, and is switched to the hot air channel for light temperature rising, and it is also necessary to avoid the temperature rising too fast, the temperature of the fluidized bed reactor (1) is raised to 60 DEG C, the activated aggregate reacts with the flue gas, the γ-type dicalcium silicate in the activated aggregate is hydrolyzed to generate calcium hydroxide, and the calcium hydroxide reacts with the nitrogen dioxide to generate calcium nitrate; At the same time, part of the calcium hydroxide reacts with carbon dioxide to generate calcium carbonate; S23, monitoring, the content of the nitrogen oxide compounds in the flue gas at the gas outlet of the fluidized bed reactor (1) and the nitrate ions in the aggregate is monitored by using a gas detector; S3, after step S22 is completed and before step S23, carbon dioxide is injected into the fluidized bed reactor (1), the concentration of the carbon dioxide needs to be higher than that of the nitrogen oxide compounds, nitrogen fixation and carbon sequestration are cooperated, and coated aggregate is obtained; S4, the coated aggregate obtained in S3 is washed by using a water washing device, surface modification is performed, and saturated surface dry aggregate is obtained; S5, the saturated surface dry aggregate is used to prepare recycled concrete.

2. The method according to claim 1, wherein, In the step S23, when the concentration of the nitrogen oxide compounds in the flue gas exceeds the standard, the tail flue gas is adjusted by backflow or is cooled to 40-45 DEG C; When the content of the nitrate ions does not reach the standard, the aggregate is sent back to the fluidized bed reactor (1) to repeat the nitrogen fixation treatment.

3. The method according to claim 2, wherein the method is characterized by, The detailed process of the nitrogen fixation and carbon sequestration cooperation in the step S3 is as follows: The cooled activated aggregate is placed in the fluidized bed reactor (1), 10% carbon dioxide and industrial flue gas containing nitrogen oxide compounds are simultaneously introduced into the fluidized bed reactor (1) through the 45 DEG symmetric air inlet (131) by two independent fans, and are tumbled to mix with the activated aggregate, so that the carbon sequestration and nitrogen fixation are cooperated, and the coated aggregate is obtained.

4. The method according to claim 3, wherein the method is characterized by, The fluidized bed reactor (1) in the steps S1 and S2 is divided into a calcination section (11) for calcination of the reconstructed aggregate, a spraying section (12) for a pre-adsorption stage, and a gas mixing section (13) for nitrogen fixation and carbon fixation cooperation from bottom to top, and the aggregate inlet (14) and the discharge outlet (15) are arranged on both sides of the calcination section (11); The calcination 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 pipe (112) for accessing hot air; The spraying section (12) comprises a spray head array (121) arranged near the middle position of the fluidized bed, and a heat insulation plate (122) for blocking the hot air of the calcination section (11) below; The gas mixing section (13) comprises two air inlets (131) arranged symmetrically at 45° at the top of the fluidized bed reactor (1), and a honeycomb guide plate (132) is arranged at the gas mixing section (13).

5. The method according to claim 4, wherein the method is characterized by, The annular air pipe (112) is provided with a plurality of air openings on the inner side, and the annular air pipe (112) is provided with a hot air fan (113) outside, the hot air fan (113) is provided with a gas hot air furnace outside to provide a hot air source, and the aggregate support grid (111) is provided with a liquid collecting plate (114) below for collecting the solution dripping from the spraying section (12), and the liquid collecting plate (114) is provided with a suction pump (115) outside.

6. The method according to claim 5, wherein the method is characterized by, The spray head array (121) is provided with a solution tank filled with calcium nitrate saturated solution, and a water pump is used for spraying control, the heat insulation plate (122) is arranged on the upper side close to the calcination section (11) and higher than the aggregate inlet (14), the heat insulation plate (122) is corrosion-resistant, a plurality of heat insulation plates (122) are arranged inside the fluidized bed reactor (1), and an external rotary motor (123) is arranged outside the fluidized bed reactor (1) for controlling the rotation of the heat insulation plate (122).

7. The method according to claim 6, wherein the method is characterized by, The preparation process of the recycled concrete in step S5 is as follows: The obtained saturated dry aggregate is graded into coarse / fine aggregate, and is sequentially mixed with natural sand, cement, water reducing agent and water to obtain recycled concrete.

8. The recycled concrete prepared by the method for recycling waste concrete in conjunction with nitrogen fixation and carbon sequestration according to any one of claims 1-7, characterized in that, The proportions of the components are by mass fraction, including cement 100 parts, total saturated dry aggregate 300 parts including coarse aggregate 180 parts and fine aggregate 120 parts, natural sand 45 parts, water 55 parts, and water reducing agent 1.0 parts.

Images