Waste concrete reclaimed sand preparation system and process of low-temperature assisted grinding and vertical grinding system

Abstract

The invention discloses a waste concrete reclaimed sand preparation system and process of a low-temperature auxiliary grinding and vertical grinding system, and belongs to the technical field of concrete regeneration. Comprising a pre-crushing unit for pre-crushing a waste concrete raw material, a low-temperature and mechanical force coupling crushing unit for stripping and crushing waste concrete mortar, a dust collector for recovering dust, a dust warehouse for storing dust, a carbon dioxide gas recovery unit for separating and recovering carbon dioxide gas, and a low-temperature grinding aid unit for preparing dry ice, the carbonization reaction unit is used for carbonizing the reclaimed sand; and the finished product warehouse is used for storing the reclaimed sand. According to the waste concrete reclaimed sand preparation system and process of the low-temperature auxiliary grinding cooperating with the vertical grinding system, the problems that in the prior art, reclaimed sand preparation is high in energy consumption, a sand matrix is seriously damaged, and reclaimed sand performance is poor are solved, and efficient resource utilization of waste concrete and industrial production of high-quality reclaimed sand are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete regeneration, and in particular to a system and process for preparing waste concrete regenerated sand using a low-temperature grinding-assisted coordinated vertical mill system. Background Art

[0002] The recycling of waste concrete is a key area of ​​resource utilization for construction waste. Traditional reclaimed sand preparation processes present numerous challenges. The difficulty in stripping the attached mortar, coupled with the tight interface between the mortar and the sand matrix, makes efficient stripping difficult using conventional crushing methods, resulting in high impurity content in the reclaimed sand. Furthermore, the irregular particle shape and lack of precise control during the crushing process result in reclaimed sand particles being angular or flaky, impacting the workability of the concrete mix. Furthermore, the high crushing index significantly damages the sand matrix during the crushing process, leading to a decrease in the mechanical properties of the reclaimed sand and a crushing index exceeding engineering application requirements.

[0003] Although the high-pressure grinding action of the vertical roller mill can effectively strip off the attached mortar, the high pressure will also damage the original sand matrix, resulting in an increase in the mass proportion of recycled powder and a decrease in the utilization rate of sand resources. Traditional research uses high-temperature dehydration to weaken the adhesion of the sand-mortar bonding surface. This requires specific high-temperature conditions, high energy consumption, and does not meet the requirements of green production. Microcracks appear on the surface of the sand matrix due to processing, and the residual attached slurry will cause cracks and other quality problems, resulting in an increase in the water absorption rate of the recycled sand (15% to 20% higher than natural sand), affecting the strength and durability of the concrete.

[0004] Gradient carbonization technology strengthens the interface transition zone through CO2 mineralization, improving the performance of recycled aggregates. The high-pressure grinding action of vertical mills effectively strips away adhering mortar. The combination of these two technologies demonstrates the potential for producing high-quality reclaimed sand. However, ensuring stripping efficiency while reducing energy consumption and minimizing sand matrix damage remains a technical bottleneck that the industry urgently needs to overcome.

[0005] The present invention aims to provide a waste concrete regenerated sand preparation system and process with a low-temperature grinding-assisted coordinated vertical mill system, so as to solve the problems of high energy consumption, serious damage to the sand matrix and poor performance of regenerated sand in the existing technology, and realize the efficient resource utilization of waste concrete and the industrial production of high-quality regenerated sand. To this end, we propose a waste concrete regenerated sand preparation system and process with a low-temperature grinding-assisted coordinated vertical mill system. Summary of the Invention

[0006] The purpose of the present invention is to provide a waste concrete regenerated sand preparation system and process with a low-temperature grinding-assisted vertical mill system to solve the problem of difficult separation of mortar in waste concrete raised in the above background technology and improve the quality of waste concrete regenerated sand.

[0007] To achieve the above objectives, the present invention provides the following technical solutions: a system and process for preparing recycled sand from waste concrete using a low-temperature grinding aid coordinated vertical mill system, comprising: a pre-crushing unit, a low-temperature + mechanical force coupled crushing unit, a dust collector, a dust storage, a carbon dioxide gas recovery unit, a low-temperature grinding aid preparation unit, a carbonization reaction unit, and a finished product warehouse;

[0008] The pre-crushing unit is used to perform preliminary crushing of the waste concrete, and includes a jaw vibrating screening device and a pre-cooling bin. The jaw crusher discharges particles with a size of 10 to 30 mm, which then enter the pre-cooling bin.

[0009] The low-temperature + mechanical force coupled crushing unit includes a vertical mill, a low-temperature grinding aid application mechanism and a temperature monitoring mechanism. The low-temperature grinding aid application mechanism is used to spray dry ice particles into the grinding roller area of ​​the vertical mill;

[0010] The dust collector is used to recover dust generated during the crushing process;

[0011] The dust storage is used to store dust generated during the crushing process;

[0012] The carbon dioxide gas recovery unit is used to recover the CO2 gas generated by the sublimation of dry ice during the crushing process;

[0013] The low-temperature grinding aid preparation unit uses system carbon dioxide gas and externally supplied carbon dioxide gas to prepare dry ice grinding aid.

[0014] The carbonization reaction unit is used to perform carbonization treatment on the crushed mortar aggregate;

[0015] The finished product warehouse is used to store carbonized regenerated sand.

[0016] The low-temperature grinding aid preparation unit includes a low-temperature refrigeration device and a grinding aid delivery mechanism. The low-temperature refrigeration device is used to prepare external carbon dioxide into dry ice. The nozzle of the grinding aid delivery mechanism is made of silicon nitride ceramic material.

[0017] Preferably, the temperature monitoring mechanism includes multiple temperature sensors arranged in the vertical mill cavity for real-time monitoring of the temperature of the grinding zone.

[0018] The following steps are involved:

[0019] S100: Pre-crushing and sorting: The waste concrete is crushed to less than 30mm in a jaw vibrating screening device, and then enters the pre-cooling bin, where it is cooled to 0-5℃ by a cold air flow.

[0020] S200: Pre-cooled aggregate is fed into the vertical mill. Dry ice particles are sprayed at a certain mass in the grinding roller area. During the movement of the material layer, the dry ice particles enter the mortar. The dry ice triggers a micro-explosion effect under the grinding pressure. The vertical mill cavity maintains a negative pressure of 0.2-0.5 MPa. The specific low temperature range used is combined with the brittle transformation depth model for calculation:

[0021]

[0022] Among them; d c Aggregate surface crack depth (mm), α thermal expansion coefficient (12×10-6K-1 for siliceous aggregate), σ f Fracture strength (10.3MPa for granite), ΔT actual temperature drop (from 25℃ to -40℃), ΔT crit Critical temperature drop threshold;

[0023] S300: The mortar aggregate enters the subsequent carbonization reaction unit. The carbonization reactor has a positive pressure of 0.2-0.4 MPa, a CO2 concentration of ≥85%, a temperature of 150°C, and the reaction lasts for 8 hours. After the set carbonization reaction time is reached, the regenerated sand is sent to the finished product warehouse.

[0024] Preferably, the spraying mass of the dry ice particles is 20-50 kg / t aggregate.

[0025] Preferably, the temperature of the cold air flow in the pre-cooling chamber is -10°C to 0°C, and the pre-cooling time is 30 minutes.

[0026] Preferably, the S100 includes the following steps:

[0027] S101: The waste concrete is crushed to less than 30mm by a jaw crusher, and the oversized particles are removed by a vibrating screening device;

[0028] S102: The crushed aggregate enters the pre-cooling bin and is pre-cooled to 0-5°C by a cold air flow (temperature -10°C to 0°C) to lower the initial temperature of the aggregate and prepare for subsequent low-temperature grinding.

[0029] Preferably, the step S200 includes the following steps:

[0030] S201: Pre-cooled aggregate is fed into the vertical mill, and dry ice particles are sprayed at a mass of 0.5-1.0 kg / t in the grinding roller area;

[0031] S202: Dry ice particles enter the mortar during the movement of the material layer, and sublime under the action of grinding pressure (10-30 MPa), causing a micro-explosion effect, which generates micro-cracks inside the mortar and enhances the peeling effect.

[0032] S203: Maintain a negative pressure of 0.2-0.5 MPa in the vertical mill chamber to prevent dust from escaping and promote gas circulation.

[0033] S204: The temperature monitoring mechanism monitors the temperature of the grinding chamber in real time to ensure that the temperature of the grinding area is maintained at -20℃~10℃ to avoid premature sublimation of dry ice due to frictional heat. The specific low temperature range used is combined with the brittle transformation depth model for calculation:

[0034]

[0035] Among them; d c Aggregate surface crack depth (mm), α thermal expansion coefficient (12×10-6K-1 for siliceous aggregate), σ f Fracture strength (10.3MPa for granite), ΔT actual temperature drop (from 25℃ to -40℃), ΔT crit Critical temperature drop threshold.

[0036] Preferably, the S300 includes the following steps:

[0037] S301: The crushed mortar aggregate enters the carbonization reactor, and the reactor is maintained at a positive pressure of 0.2-0.4MPa, a CO2 concentration of ≥85%, and a temperature of 150°C.

[0038] S302: The carbonization reaction lasts for 8 hours, so that calcium carbonate crystals such as vaterite are generated on the surface of the regenerated sand, which strengthens the interface transition zone and improves the activity of the regenerated sand.

[0039] S303: After the reaction is completed, the regenerated sand is cooled and screened and then sent to the finished product warehouse.

[0040] Compared with the existing technology, the beneficial effects of the present invention are as follows: the waste concrete regenerated sand preparation system and process of the low-temperature grinding-assisted collaborative vertical mill system has significantly reduced energy consumption. Through the "low-temperature interface stripping" process, the stripping energy consumption is reduced to 7.2kWh / t, which is more than 50% lower than the traditional high-temperature process; the performance of the regenerated sand is optimized, and the vaterite strengthening makes the activity of the regenerated sand reach 78.5%, which is 30% higher than the traditional process; the crushing index is ≤10%, and the water absorption rate is reduced by 50%, which is close to the performance of natural sand. The number of microcracks is reduced by 40%, and the surface finish is improved. The environmental protection benefits are outstanding, CO2 is recycled, and negative carbon production is achieved (0.1 to 0.15tCO2 can be fixed for every 1t of regenerated sand prepared) and the dust emission is ≤10mg / m 3 , in line with national ultra-low emission standards. It has high industrial feasibility, high system integration, and continuous production capabilities. A single system can produce 100,000 to 200,000 tons of waste per year, providing technical support for the large-scale resource utilization of construction solid waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the waste concrete regenerated sand preparation system of the low-temperature grinding-assisted vertical mill system of the present invention;

[0042] Figure 2 This is a process diagram of the waste concrete regenerated sand preparation process of the low-temperature grinding-assisted vertical mill system of the present invention;

[0043] Figure 3 This is a process diagram of pre-crushing and sorting of waste concrete according to the present invention;

[0044] Figure 4 This is a diagram of the steps of the waste concrete grinding process of the present invention;

[0045] Figure 5 This is a process diagram of carbonization of waste concrete according to the present invention;

[0046] Figure 6 1 is a process step diagram of Example 1 of the present invention;

[0047] Figure 7 1 is a process step diagram of Example 2 of the present invention;

[0048] Figure 8 This is a graph showing the change in water absorption of waste concrete before and after grinding according to Example 2 of the present invention;

[0049] Figure 9 1 is a process step diagram of Example 3 of the present invention;

[0050] Figure 10 This is a graph showing the change in water absorption of waste concrete before and after grinding according to Example 2 of the present invention.

[0051] In the figure: 1. Pre-crushing unit; 2. Low-temperature + mechanical force coupled crushing unit; 201. Vertical mill; 202. Low-temperature grinding aid application mechanism; 203. Temperature monitoring mechanism; 3. Dust collector; 4. Dust storage; 5. Carbon dioxide gas recovery unit; 6. Low-temperature grinding aid preparation unit; 601. Low-temperature refrigeration equipment; 602. Grinding aid conveying mechanism; 7. Carbonization reaction unit; 8. Finished product warehouse. DETAILED DESCRIPTION

[0052] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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.

[0053] Reference Figure 1A waste concrete recycled sand preparation system and process of a low-temperature grinding aid coordinated vertical mill system. The waste concrete recycled sand preparation system of the dry ice grinding aid coordinated vertical mill system includes: a pre-crushing unit 1, a low-temperature + mechanical force coupling crushing unit 2, a dust collector 3, a dust storage 4, a carbon dioxide recovery unit 5, a low-temperature grinding aid preparation unit 6, a carbonization reaction unit 7 and a finished product warehouse 8.

[0054] Furthermore, the pre-crushing unit 1 includes a jaw crusher with a discharge particle size of 10 to 30 mm and is equipped with a vibrating screening device; the low-temperature + mechanical force coupling crushing unit 2 includes a vertical mill 201, a low-temperature grinding aid application mechanism 202, and a temperature monitoring mechanism 203; the low-temperature grinding aid preparation unit 6 includes a low-temperature refrigeration device 601 to prepare external carbon dioxide into dry ice, and the nozzle in the grinding aid delivery mechanism 602 is made of silicon nitride ceramic material; the carbon dioxide gas recovery unit 5, the dust collector 3, and the dust bin 4 together constitute the dust gas recovery and separation function;

[0055] The regenerated sand preparation process according to claims 1-4 is characterized in that it comprises the following steps:

[0056] S100: Pre-crushing and sorting: The waste concrete is crushed to less than 30mm in the pre-crushing unit 1, and then enters the pre-cooling chamber 102, where it is pre-cooled to 0-5℃ by a cold air flow;

[0057] S200: Pre-cooled aggregate is fed into the vertical mill 201. A nozzle in the grinding aid delivery mechanism 602 in the grinding roller area sprays dry ice particles at a certain mass. During the movement of the material layer, the dry ice particles enter the slurry. Under the grinding pressure, the dry ice triggers a micro-explosion effect. A negative pressure of 0.2-0.5 MPa is maintained in the vertical mill chamber. The ground material is separated by air separation in the vertical mill 201. Regenerated fine powder enters the dust collector 3. CO2 gas is recovered through a membrane separation device as the gas feedstock for the carbonization reaction unit 7. The specific low-temperature range used is combined with the brittle conversion depth model for calculation:

[0058]

[0059] Among them; d c Aggregate surface crack depth (mm), α thermal expansion coefficient (12×10-6K-1 for siliceous aggregate), σ f Fracture strength (10.3MPa for granite), ΔT actual temperature drop (from 25℃ to -40℃), ΔT crit Critical temperature drop threshold;

[0060] S300: The regenerated sand enters the subsequent carbonization reaction unit 7. The carbonization reactor has a positive pressure of 0.2-0.4 MPa, a CO2 concentration of ≥85%, a temperature of 150°C, and the reaction lasts for 8 hours. After the set carbonization reaction time is reached, the regenerated sand is sent to the finished product warehouse 8.

[0061] Example 1

[0062] See also Figure 2 、 Figure 3 、 Figure 4 and Figure 5 , pre-crushing unit 1 runs:

[0063] The waste concrete is fed by a loader into a jaw vibrating screening device 101, where it is crushed to less than 30 mm, with a processing capacity of 80-100 t / h. The crushed material is screened by a vibrating screen. The oversize (>30 mm) is returned to the crusher for further crushing, and the undersize enters the pre-cooling bin.

[0064] Operation of low temperature + mechanical force coupling crushing unit 2:

[0065] A cold air flow at -10°C is introduced into pre-cooling chamber 102, lowering the aggregate temperature to approximately 3°C. The pre-cooling time is 30 minutes, and the pre-cooling chamber 102 has a capacity of 50 tons. The pre-cooled aggregate is fed to vertical mill 201 via a belt conveyor at a feed rate of 60-70 tons / hour. A low-temperature refrigeration unit 601 converts industrial-grade CO2 (purity ≥99%) into dry ice pellets (1-3 mm in diameter), which are then sprayed onto the grinding roller area at a rate of 0.8 kg / t via a grinding aid delivery mechanism 602. The grinding pressure in vertical mill 201 is set at 20 MPa, with the negative pressure in the chamber maintained at 0.3 MPa. The grinding zone temperature is controlled between -10°C and 5°C by adjusting the dry ice spray volume. The ground material is separated by an air separation system. Qualified fine powder (≤4.75 mm) enters dust collector 3 and then dust storage 4, while coarse powder returns to vertical mill 201 for further grinding.

[0066] Operation of the carbon dioxide gas recovery unit 5:

[0067] The dust-laden gas is first removed by dust collector 3 (bag filter). The collected dust can be used as a concrete admixture. The dust-free gas enters the membrane separation device, where the separated CO2 (purity ≥ 90%) is compressed and stored, then returned to the carbonization reaction unit 7 for recycling. The remaining gas meets emission standards.

[0068] Carbonization reaction unit 7 operation:

[0069] Ground mortar aggregate (moisture content ≤ 5%) is fed into the carbonization reaction unit 7 via a screw conveyor, with a feed rate of 20 tons per time. CO2 gas (purity ≥ 99%) is introduced into the reactor to raise the pressure to 0.3 MPa. Simultaneously, the heating device is activated, raising the temperature to 150°C. The reaction continues for 8 hours, during which time a stirring device (30 rpm) is used to ensure uniform reaction of the materials.

[0070] After the reaction is completed, the pressure is released and the temperature is lowered, and the regenerated sand is sent to the finished product warehouse 8 after screening (sieve hole 0.6mm).

[0071] Example 2

[0072] See also Figure 2 、 Figure 3 、 Figure 4 and Figure 5 The difference between Example 2 and Example 1 is that the waste concrete raw materials do not enter the pre-cooling bin 102 after being crushed. When the ambient temperature of the waste concrete raw materials is 0-10°C, the waste concrete is directly fed into the vertical mill 101 after being crushed to 30 mm in the pre-crushing unit 1.

[0073] Except for the above steps, the remaining steps are exactly the same as those in Example 1.

[0074] Application Example 1

[0075] See also Figure 6 , using C40 strength waste concrete raw materials (siliceous aggregate accounts for 40%) and dry ice mass ratio of 5% to produce medium-quality regenerated sand, the main process parameters are: low temperature + mechanical force coupling crushing unit 2 dry ice mass ratio of 5%, temperature -20℃, vertical mill 201 grinding roller pressure 4MPa; carbonization reaction unit 7, CO2 gas supply volume 80m3 / ton regenerated sand, temperature 150℃, air pressure 0.5MPa, after 8h carbonization, the quality of regenerated sand, 28d activity index 82.5%, carbon fixation amount 86kg / ton regenerated sand, crushing index 12.5%.

[0076] Application Example 2

[0077] See also Figure 7 and Figure 8 , using C50 high-strength waste concrete raw materials (silicon content 60%) and a dry ice mass ratio of 8% to produce high-quality regenerated sand. The main process parameters are: low temperature + mechanical force coupling crushing unit 2 dry ice mass ratio 8%, temperature is -30℃, vertical mill 201 grinding roller pressure 5.5MPa; carbonization reaction unit 7, CO2 gas supply volume 90m3 / ton regenerated sand, temperature 150℃, air pressure 0.5MPa, after 8h carbonization, the quality of regenerated sand, vaterite conversion rate 91%, 28d activity index 88%, carbon fixation 120kg / ton regenerated sand, crushing index 9.5%, and water absorption rate reduced by 50%.

[0078] Application Example 3

[0079] See also Figure 9 and Figure 10 Economical reclaimed sand is produced using C30 strength waste concrete (30% silica content) and a 3% dry ice mass fraction. Key process parameters include: low-temperature + mechanically coupled crushing unit 2, 3% dry ice mass fraction, -15°C temperature, vertical mill 201 roller pressure of 3.5 MPa; carbonization reaction unit 7, CO2 supply of 75 m³ / ton of reclaimed sand, temperature of 150°C, and pressure of 0.5 MPa. After 8 hours of carbonization, the reclaimed sand achieved a vaterite conversion rate of 65%, a 28-day activity index of 79.5%, a carbon fixation capacity of 70 kg / ton of reclaimed sand, a crushing index of 14.5%, and a 30% reduction in water absorption. The change in water absorption is a key indicator.

[0080] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0081] Although the present invention has been described above with reference to exemplary embodiments, various modifications may be made thereto and equivalent components may be substituted without departing from the scope of the present invention. In particular, the various features of the embodiments disclosed herein may be combined with one another in any manner, provided no structural conflicts exist. The omission of an exhaustive description of these combinations in this specification is solely for the sake of space and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. A waste concrete regenerated sand preparation system using a low-temperature grinding aid and vertical mill system, characterized by: include: Pre-crushing unit 1, low temperature + mechanical force coupled crushing unit 2, dust collector 3, dust storage 4, carbon dioxide gas recovery unit 5, low temperature grinding aid preparation unit 6, carbonization reaction unit 7 and finished product warehouse 8; The pre-crushing unit 1 is used for preliminary crushing of waste concrete, and includes a jaw vibrating screening device 101 and a pre-cooling bin 102. The jaw crusher discharges particles with a size of 10 to 30 mm, which then enter the pre-cooling bin 102. The low-temperature + mechanical force coupled crushing unit 2 includes a vertical mill 201, a low-temperature grinding aid application mechanism 202 and a temperature monitoring mechanism 203. The low-temperature grinding aid application mechanism 202 is used to spray dry ice particles into the grinding roller area of ​​the vertical mill 201. The dust collector 3 is used to recover the dust generated during the crushing process; The dust storage 4 is used to store the dust generated during the crushing process; The carbon dioxide gas recovery unit 5 is used to recover the CO2 gas generated by the sublimation of dry ice during the crushing process; The low-temperature grinding aid preparation unit 6 uses system carbon dioxide gas and externally supplied carbon dioxide gas to prepare dry ice grinding aid. The carbonization reaction unit 7 is used to perform carbonization treatment on the crushed mortar aggregate; The finished product warehouse 8 is used to store the carbonized regenerated sand.

2. The waste concrete regenerated sand preparation system of the low-temperature grinding-assisted vertical mill system according to claim 1 is characterized by: The low-temperature grinding aid preparation unit 6 includes a low-temperature refrigeration device 601 and a grinding aid delivery mechanism 602. The low-temperature refrigeration device 601 is used to prepare external carbon dioxide into dry ice. The nozzle of the grinding aid delivery mechanism 602 is made of silicon nitride ceramic material.

3. The waste concrete regenerated sand preparation system of the low-temperature grinding-assisted vertical mill system according to claim 1 is characterized by: The temperature monitoring mechanism 203 includes multiple temperature sensors disposed in the vertical mill cavity for real-time monitoring of the temperature of the grinding zone.

4. The process for preparing recycled sand from waste concrete using a low-temperature grinding-assisted vertical mill system according to claims 1-3, characterized in that: The following steps are involved: S100: Pre-crushing and sorting: The waste concrete is crushed to less than 30 mm in the jaw vibrating screening device 101, and then enters the pre-cooling bin 102, where it is pre-cooled to 0-5°C by a cold air flow; S200: Pre-cooled aggregate is fed into the vertical mill 201. Dry ice particles are sprayed at a certain mass in the grinding roller area. During the movement of the material layer, the dry ice particles enter the mortar. The dry ice triggers a micro-explosion effect under the grinding pressure, and the vertical mill cavity maintains a negative pressure of 0.2-0.5 MPa. The specific low temperature range used is combined with the brittle transformation depth model for calculation: in; d c Aggregate surface crack depth (mm), α thermal expansion coefficient (12×10-6K-1 for siliceous aggregate), σ f Fracture strength (10.3MPa for granite), ΔT actual temperature drop (from 25℃ to -40℃), ΔT crit Critical temperature drop threshold; S300: The mortar aggregate enters the subsequent carbonization reaction unit 7. The carbonization reactor has a positive pressure of 0.2-0.4 MPa, a CO2 concentration of ≥85%, a temperature of 150°C, and the reaction lasts for 8 hours. After the set carbonization reaction time is reached, the regenerated sand is sent to the finished product warehouse 8.

5. The process for preparing recycled sand from waste concrete using a low-temperature grinding-assisted vertical mill system according to claim 1, characterized in that: The spraying mass of the dry ice particles is 20-50 kg / t aggregate.

6. The process for preparing recycled sand from waste concrete using a low-temperature grinding-assisted vertical mill system according to claim 1, characterized in that: The temperature of the cold air flow in the pre-cooling chamber 102 is -10°C to 0°C, and the pre-cooling time is 30 minutes.

7. The process for preparing recycled sand from waste concrete using a low-temperature grinding-assisted vertical mill system according to claim 4, characterized in that: The S100 includes the following steps: S101: The waste concrete is crushed to less than 30mm by a jaw crusher, and the oversized particles are removed by a vibrating screening device; S102: The crushed aggregate enters the pre-cooling bin 102 and is pre-cooled to 0-5°C by a cold air flow (temperature -10°C to 0°C) to lower the initial temperature of the aggregate and prepare for subsequent low-temperature grinding.

8. The system and process for preparing recycled sand from waste concrete using a low-temperature grinding-assisted vertical mill system according to claim 4, characterized in that: The S200 includes the following steps: S201: Pre-cooled aggregate is fed into the vertical mill 201, and dry ice particles are sprayed at a mass of 0.5-1.0 kg / t in the grinding roller area; S202: Dry ice particles enter the mortar during the movement of the material layer, and sublime under the action of grinding pressure (10-30 MPa), causing a micro-explosion effect, which generates micro-cracks inside the mortar and enhances the peeling effect. S203: Maintain a negative pressure of 0.2-0.5 MPa in the vertical mill chamber to prevent dust from escaping and promote gas circulation. S204: The temperature monitoring mechanism 203 monitors the temperature of the grinding chamber in real time to ensure that the temperature of the grinding area is maintained at -20°C to 10°C to avoid premature sublimation of dry ice due to frictional heat. The specific low temperature range used is combined with the brittle transformation depth model for calculation: Among them; d c Aggregate surface crack depth (mm), α thermal expansion coefficient (12×10-6K-1 for siliceous aggregate), σ f Fracture strength (10.3MPa for granite), ΔT actual temperature drop (from 25℃ to -40℃), ΔT crit Critical temperature drop threshold.

9. The system and process for preparing recycled sand from waste concrete using a low-temperature grinding-assisted vertical mill system according to claim 4, characterized in that: The S300 includes the following steps: S301: The crushed mortar aggregate enters the carbonization reactor, and the reactor is maintained at a positive pressure of 0.2-0.4 MPa, a CO2 concentration of ≥85%, and a temperature of 150°C. S302: The carbonization reaction lasts for 8 hours, so that calcium carbonate crystals such as vaterite are generated on the surface of the regenerated sand, which strengthens the interface transition zone and improves the activity of the regenerated sand. S303: After the reaction is completed, the regenerated sand is cooled, screened, and then sent to the finished product warehouse 8.

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