A system and process for continuously preparing basic magnesium carbonate using kiln exhaust waste heat

Abstract

The application discloses a system and process for continuously preparing basic magnesium carbonate by using kiln tail gas waste heat, comprising a kiln system, a chemical system, a kiln tail and a kiln head resource recovery system. The kiln system is provided with kiln tail flue gas and kiln head waste wind passages, and outputs kiln tail flue gas carrying waste heat, carbon dioxide and magnesium oxide powder, and kiln head waste wind carrying waste heat and powder. Two recovery systems are separately arranged in the corresponding passages to recover the powder, gas and waste heat in the gas flow. The chemical system is sequentially connected with a hydration unit, a carbonization unit, a pyrolysis unit, a solid-liquid separation unit and a drying unit to continuously prepare the basic magnesium carbonate. The kiln is externally connected with the two recovery systems, which are directionally communicated with the chemical units through a conveying pipeline to form a powder, waste heat, carbon dioxide and process water circulation supply structure, so that resource recycling is realized.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization of industrial kiln resources, and in particular to a system and process for continuously preparing basic magnesium carbonate using waste heat from kiln tail gas. Background Technology

[0002] Basic magnesium carbonate is an important inorganic magnesium salt material widely used in flame retardant materials, rubber, plastics, coatings, pharmaceuticals, ceramics, electronics, and environmental protection. Industrially, basic magnesium carbonate is typically produced from lightly calcined magnesium oxide or magnesium hydroxide through processes such as hydration, carbonation, pyrolysis, solid-liquid separation, and drying. With the development of new energy sources, halogen-free flame retardant materials, and high-performance inorganic functional materials, higher demands are being placed on the quality stability and continuous production capacity of basic magnesium carbonate products.

[0003] Light-calcined magnesia is typically produced using high-temperature calcination equipment such as rotary kilns and vertical kilns. During calcination, a large amount of high-temperature exhaust gas and kiln head waste air are generated. This gas contains not only high-grade heat energy but also a certain concentration of carbon dioxide and entrained magnesia powder. In current production processes, these exhaust gases are generally only treated with dust removal before being directly discharged, or only undergo simple waste heat recovery for preheating air or drying materials. The carbon dioxide and powder resources are not effectively utilized, resulting in energy waste and resource loss, while also increasing carbon emissions during the production process.

[0004] On the other hand, existing basic magnesium carbonate production facilities are typically built as independent chemical systems. The heat sources required for their carbonation, pyrolysis, and drying processes mainly rely on external energy sources such as steam, natural gas, or electric heating, resulting in high energy consumption. The carbon dioxide required for the carbonation reaction is mostly obtained from purchased liquid carbon dioxide or specially prepared gas sources, leading to high production costs. Furthermore, the carbon dioxide released during pyrolysis is generally directly discharged or simply treated without being recycled. The process water is also mostly fresh water that is partially discharged and partially replenished, resulting in low resource utilization efficiency.

[0005] Therefore, how to fully utilize the waste heat, carbon dioxide, and magnesium oxide powder in the tail gas and kiln head exhaust air of lightly calcined magnesium oxide kilns, and organically combine them with the continuous production process of basic magnesium carbonate to achieve the recycling of heat energy, materials, and carbon dioxide, while reducing production energy consumption, reducing resource waste, and improving the efficiency of continuous production, and minimizing the impact on the normal operation of the kiln, has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] This invention provides a system and process for continuously preparing basic magnesium carbonate using waste heat from kiln exhaust gas, in order to overcome the above-mentioned problems.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: This invention provides a system for the continuous preparation of basic magnesium carbonate using waste heat from kiln exhaust gas, comprising: A kiln system with a kiln system tail gas outlet and a kiln system waste air outlet; a chemical system for producing basic magnesium carbonate; a kiln tail resource recovery system; and a kiln head resource recovery system. The inlet of the kiln tail resource recovery system is connected to the tail gas outlet of the kiln system, and is used to recover dust and waste heat resources in the kiln tail gas, and send the treated dust and waste heat resources back to the chemical system. The inlet of the kiln head resource recovery system is connected to the exhaust air outlet of the kiln system, and is used to recover dust and waste heat resources in the exhaust air of the kiln, and to send the treated dust and waste heat resources back to the chemical system.

[0008] Furthermore, the kiln tail resource recovery system includes a kiln tail induced draft fan, a kiln tail heat exchanger, and a kiln tail powder collection device; the kiln tail induced draft fan is connected to the exhaust gas outlet of the kiln system, the kiln tail heat exchanger includes a first heat exchange channel and a second heat exchange channel, the inlet of the first heat exchange channel is connected to the outlet of the kiln tail induced draft fan; the outlet of the first heat exchange channel is connected to the inlet of the kiln tail powder collection device, and the outlet of the second heat exchange channel is connected to the carbonization unit of the chemical system.

[0009] Furthermore, the kiln head resource recovery system includes a kiln head induced draft fan, a kiln head heat exchanger, a kiln head powder collection device, and a clean gas supply unit; the inlet of the kiln head induced draft fan is connected to the exhaust air outlet of the kiln system; the kiln head heat exchanger includes a third heat exchange channel and a fourth heat exchange channel; The inlet of the third heat exchange channel is connected to the outlet of the kiln head induced draft fan, and the outlet of the third heat exchange channel is connected to the inlet of the kiln head powder collection device; the outlet of the kiln head powder collection device is connected to the material inlet of the chemical system; the outlet of the clean gas supply unit is connected to the inlet of the fourth heat exchange channel, and the outlet of the fourth heat exchange channel is connected to the drying unit of the chemical system, for providing the convective purging hot air required for drying.

[0010] Furthermore, the chemical system includes a hydration unit, a carbonization unit, a pyrolysis unit, a solid-liquid separation unit, a drying unit, and a finished product storage unit connected in series.

[0011] Furthermore, a gas outlet is provided at the top of the pyrolysis unit, and the gas outlet is connected to the carbonization unit through a pipeline. A CO2 fan is provided on the pipeline for sending the carbon dioxide generated by pyrolysis back to the interior of the carbonization unit.

[0012] Furthermore, the liquid outlet of the solid-liquid separation unit is connected to the process water storage tank, and the outlet of the process water storage tank is returned to the hydration unit via a water transfer pump.

[0013] Another aspect of the present invention provides a process for continuously preparing basic magnesium carbonate using the system, comprising the following steps: S1. Lightly calcined magnesium oxide is added to the hydration unit, and circulating process water recovered from the solid-liquid separation unit and buffered by the process water storage tank is added to prepare magnesium hydroxide slurry.

[0014] S2. Magnesium hydroxide slurry is continuously transported to the carbonization unit via a carbonization conveying pump, where it reacts countercurrently with the carbon dioxide-containing flue gas recovered and transported by the kiln tail resource recovery system and the high-purity carbon dioxide returned by the CO2 blower to prepare a reaction solution containing magnesium bicarbonate.

[0015] S3. The reaction liquid containing magnesium bicarbonate is transported to the pyrolysis unit through a pyrolysis transfer pump. The high-temperature heat transfer oil waste heat recovered by the kiln tail heat exchanger in the kiln tail resource recovery system is used for heating and pyrolysis to generate basic magnesium carbonate slurry, while carbon dioxide gas is released at the same time.

[0016] S4. The carbon dioxide gas released from the pyrolysis unit is transported back to the auxiliary air inlet at the bottom of the carbonization unit through a pipeline and a CO2 blower. It is mixed with the carbon dioxide-containing clean flue gas transported by the kiln tail resource recovery system to increase the carbon dioxide concentration in the carbonization reaction zone and realize the internal circulation enrichment and utilization of carbon dioxide.

[0017] S5. The pyrolyzed basic magnesium carbonate slurry is sent to the solid-liquid separation unit through a solid-liquid separation pump for solid-liquid separation, and wet basic magnesium carbonate filter cake and filtrate containing trace magnesium ions are obtained respectively.

[0018] S6. The filtrate obtained from solid-liquid separation is introduced into the process water storage tank and then returned to the hydration unit by a water transfer pump to achieve closed-loop recycling of process water.

[0019] S7. The wet basic magnesium carbonate filter cake is conveyed to the drying unit. The basic drying temperature is maintained by indirect heat exchange provided by the heat transfer oil in the kiln tail heat exchanger and the circulating pump in the drying jacket. At the same time, the high-temperature hot air recovered by the kiln head heat exchanger in the kiln head resource recovery system is pressurized by the drying blower and acts on the wet material by convection. The combination of indirect heat exchange and convection drying ensures that the material is fully dried, and finally, a finished basic magnesium carbonate product with a moisture content of ≤1.0% is obtained. The beneficial effects of this invention are: (1) This invention recovers and utilizes the waste heat and carbon dioxide in the kiln tail gas for the production of basic magnesium carbonate, thus solving the problem of resource waste caused by the direct emission of waste heat and carbon dioxide in the kiln tail gas.

[0020] (2) The present invention utilizes the residual heat at the kiln tail as a heat source for pyrolysis and drying, and uses the residual air at the kiln head as a drying purging air source for the drying process of basic magnesium carbonate, thereby realizing the utilization of thermal energy.

[0021] (3) The present invention uses the kiln tail gas containing carbon dioxide for the carbonization process of basic magnesium carbonate, and returns the carbon dioxide generated during the pyrolysis process to the carbonization process for recycling. The carbonization reaction is accelerated by increasing the reaction concentration of CO2 in the carbonization unit (from the peak concentration of 35% to 55%).

[0022] (4) The present invention reuses the magnesium oxide powder recovered from the kiln tail and kiln head for pulping, thereby reducing powder loss.

[0023] (5) This invention reduces the consumption of fresh water and the discharge of wastewater by recycling process water.

[0024] (6) This invention realizes the combined operation of waste heat and carbon dioxide recovery in kiln tail gas with processes such as hydration, carbonization, pyrolysis, solid-liquid separation and drying, saving the cost of basic magnesium carbonate carbon dioxide raw materials, drying costs, and additional costs of purchasing magnesium raw materials, which total about 20% of the production cost.

[0025] (7) The present invention connects the resource recycling system with the kiln system, so as to realize the comprehensive utilization of kiln resources without changing the main process flow of the kiln, which has little impact on the normal operation of the kiln and is convenient for engineering transformation and promotion. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the overall structure of the system for continuously preparing basic magnesium carbonate using waste heat from kiln exhaust gas as described in this invention. In the diagram, 100 - Kiln system; 101 - Kiln system exhaust gas outlet; 102 - Kiln system waste air outlet; 200 - Chemical system; 600 - Kiln tail resource recovery system; 700 - Kiln head resource recovery system; 210 - Hydration unit; 220 - Carbonization unit; 230 - Pyrolysis unit; 240 - Solid-liquid separation unit; 241 - Process water supply unit; 242 - Process water storage tank; 250 - Drying unit; 251 - Finished product storage unit; 260 - Carbonization conveying pump; 261 - Pyrolysis conveying pump ; 262-Solid-liquid separation pump; 263-Water pump; 264-CO2 fan; 265-Pyrolysis jacket circulation pump; 266-Drying jacket circulation pump; 267-Drying purging fan; 600-Kiln tail resource recovery system; 610-Kiln tail heat exchanger; 630-Kiln tail induced draft fan; 620-Kiln tail powder collection device; 700-Kiln head resource recovery system; 710-Kiln head heat exchanger; 711-Clean gas supply unit; 720-Kiln head powder collection device; 730-Kiln head induced draft fan. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] This embodiment discloses a system for the continuous production of basic magnesium carbonate using waste heat from kiln tail gas. It includes: a kiln system 100 with a kiln system tail gas outlet 101 and a kiln system waste air outlet 102; a chemical system 200 for producing basic magnesium carbonate; a kiln tail resource recovery system 600; and a kiln head resource recovery system 700. The inlet of the kiln tail resource recovery system 600 is connected to the tail gas outlet 101 of the kiln system, and is used to recover dust and waste heat resources in the kiln tail gas, and send the treated dust and waste heat resources back to the chemical system 200. The inlet of the kiln head resource recovery system 700 is connected to the exhaust air outlet 102 of the kiln system, and is used to recover dust and waste heat resources in the exhaust air of the kiln, and send the treated dust and waste heat resources back to the chemical system 200.

[0030] The kiln system 100 serves as the source supply unit for the entire system, outputting kiln tail flue gas (temperature 280–350℃, CO2 volume fraction approximately 25–35%) carrying waste heat, carbon dioxide, and magnesium oxide powder, as well as kiln head exhaust air (temperature 220–250℃) carrying waste heat and magnesium oxide powder. The kiln tail resource recovery system 600 and the kiln head resource recovery system 700 are respectively installed at the kiln tail flue gas outlet 101 and the kiln head exhaust air outlet 102 of the kiln system 100, responsible for recovering magnesium oxide powder, carbon dioxide gas, and waste heat resources from the gas flow. The chemical system 200 serves as the core preparation unit, completing the preparation and processing of basic magnesium carbonate. This system, while ensuring the thermal stability of the kiln system 100, achieves efficient recycling of magnesium oxide powder, carbon dioxide gas, and waste heat resources. The entire system can operate continuously and stably, enabling the large-scale preparation of basic magnesium carbonate.

[0031] Furthermore, the kiln tail resource recovery system 600 is integrally assembled on the main flue gas passage of the kiln tail of the kiln system 100. It adopts a bypass parallel pipeline design and relies on the kiln tail induced draft fan 630, preferably a centrifugal fan, to provide continuous airflow power. A portion of the high-temperature flue gas is drawn out from the main flue gas passage of the kiln tail to achieve the stepwise recovery and targeted supply of flue gas waste heat, powder, and carbon dioxide gas. The specific airflow, powder, and flue gas recovery paths are as follows: A dedicated bypass flue gas pipeline is connected in parallel to the main flue gas passage at the kiln tail. Under the traction of the centrifugal fan, the kiln tail flue gas containing waste heat, carbon dioxide, and magnesium oxide powder continuously enters the bypass pipeline and flows sequentially through the kiln tail heat exchanger 610 (preferably a partition wall heat exchanger), the kiln tail powder collection device 620 (preferably a cyclone collector), and a dust collector for step-by-step processing. The partition wall heat exchanger adopts a partition wall heat exchange structure with two major heat exchange channels: one on the flue gas side and one on the heat transfer oil side. The flue gas flows directly through the flue gas side to complete sensible heat exchange, transferring the waste heat of the flue gas to the heat transfer oil side, achieving efficient recovery of the waste heat of the flue gas. The temperature of the flue gas after heat exchange is significantly reduced, and then it flows smoothly into the downstream kiln tail powder collection device 620 (preferably a cyclone collector and a dust collector). The cyclone collector and dust collector integrate a dual gas-solid separation device combining a cyclone separator and a dust collector. This device enables refined gas-solid separation of low-temperature flue gas, completely intercepting magnesium oxide micropowder entrained in the flue gas and completing the separation of powder from the gas phase flue gas. The heat transfer oil circulation pipeline of the waste heat exchanger 610 at the kiln tail is directly connected to the pyrolysis jacket circulation pump 265 of the pyrolysis unit 230, continuously inputting the sensible heat of the kiln tail flue gas into the pyrolysis unit 230 to maintain the pyrolysis temperature at 85±5℃.

[0032] The clean flue gas purified by the dust removal device 620 at the kiln tail is rich in carbon dioxide. Its gas phase clean flue gas outlet is connected to the bottom air inlet of the carbonization unit 220 in the chemical system 200 through a dedicated flue gas pipeline. The purified carbon dioxide-containing flue gas is continuously transported into the carbonization unit 220 to provide a stable reaction gas source for the carbonization reaction and realize the resource utilization of carbon dioxide resources in the kiln tail flue gas.

[0033] The solid discharge port of the kiln tail powder collection device 620 is sealed and connected to the raw material inlet of the chemical system hydration unit 210 through a special screw conveyor. The magnesium oxide micro powder intercepted by gas-solid separation is continuously and quantitatively transported to the hydration unit 210 through the screw conveyor as the core raw material for the preparation of basic magnesium carbonate, realizing the recycling and reuse of waste powder resources at the kiln tail.

[0034] The kiln head resource recovery system 700 is installed on the medium-low temperature waste air passage of the kiln head grate cooler in the kiln system 100. It also adopts a bypass parallel pipeline structure. The kiln head induced draft fan 730, preferably a centrifugal fan, provides the airflow power to recover waste heat and magnesium oxide powder in the kiln head waste air. The recovered products are supplied to the drying unit 250 of the chemical system 200. The specific working path is as follows: A waste heat recovery pipeline is connected in parallel to the main low-temperature waste air passage in the kiln head grate cooler. The kiln head induced draft fan 730 continuously draws in the waste air from the kiln head. The waste airflow first enters the kiln head heat exchanger 710 (indirect heat exchanger) to complete waste heat recovery. The kiln head heat exchanger 710 is an indirect heat exchange device that can efficiently capture the sensible heat in the kiln head waste air, converting the sensible heat of the kiln head waste air into high-temperature hot air, thus completing heat energy enrichment. The waste air after heat exchange then enters the kiln head powder collection device 720. The kiln head powder collection device 720 is equipped with a cyclone separator and a dust collector, which can accurately separate the fine magnesium oxide powder entrained in the waste air, achieving complete gas-solid separation.

[0035] Furthermore, the solid discharge port of the kiln head powder collection device 720 is connected to the raw material inlet of the hydration unit 210 via a screw conveyor, where it merges with the magnesium oxide micro powder recovered by the kiln tail resource recovery system and serves as the raw material for hydration slurry preparation, maximizing the recovery of magnesium oxide powder waste generated during the kiln production process and improving the raw material utilization rate.

[0036] Furthermore, the high-temperature hot air produced by the kiln head heat exchanger 710 is connected to the hot air purging channel of the drying unit 250 of the chemical system 200 through the hot air pipeline. The high-temperature hot air acts directly on the wet material in the drying unit 250 in the form of convection purging. Through convection heat exchange, the moisture of the material is quickly removed, which helps to improve the material drying efficiency and realize the direct resource utilization of the waste air and waste heat of the kiln head.

[0037] Furthermore, the chemical system 200 is the core unit for the continuous preparation of basic magnesium carbonate. It consists of a hydration unit 210, preferably a hydration tank; a carbonation unit 220, preferably a gas-liquid countercurrent carbonation tower; a pyrolysis unit 230, preferably a pyrolysis reactor; a solid-liquid separation unit 240, preferably a filter press; and a drying unit 250, preferably a drying chamber, connected in series via sealed pipelines. Each unit is equipped with a dedicated delivery pump, fan, and storage tank, forming four closed-loop circuits: continuous slurry delivery, internal carbon dioxide circulation and lifting, full process water circulation, and cascade utilization of waste heat. This achieves continuous preparation process and maximizes resource utilization. The specific implementation methods of each circuit are as follows: The hydration tank is an atmospheric pressure hydration tank with a mechanical stirring device, which can fully stir and slurry the recovered magnesium oxide powder and circulating process water to ensure uniform dispersion of the powder. The slurry outlet of the hydration tank is connected to the top spray port of the gas-liquid countercurrent carbonization tower via a suspension pump 260, preferably a slurry pump. The stirred magnesium oxide slurry is quantitatively transported into the gas-liquid countercurrent carbonization tower by the slurry pump. The gas-liquid countercurrent carbonization tower is a gas-liquid countercurrent packed carbonization tower, which can achieve full countercurrent contact reaction between gaseous carbon dioxide and liquid magnesium oxide slurry to complete the carbonization synthesis process. The overflow port at the bottom of the gas-liquid countercurrent carbonization tower is connected to the feed port of the pyrolysis reactor via a magnesium bicarbonate transfer pump 261, preferably a centrifugal pump. The mixed slurry after the reaction is stably transported to the pyrolysis reactor. The pyrolysis reactor is a jacketed reactor, which provides a stable reaction environment for the pyrolysis reaction of basic magnesium carbonate. Its bottom discharge port is connected to the inlet of the filter press through a slurry pump. The filter press can achieve efficient separation of solid and liquid materials. The separated solid filter cake is accurately transported to the material inlet of the drying room by a scraper conveyor. The entire process realizes automated and continuous material transportation and completes the connection between each process without interruption.

[0038] During the pyrolysis reaction, the pyrolysis reactor continuously releases high-purity carbon dioxide gas, with a purity exceeding 95%. A gas outlet is located at the top of the pyrolysis reactor. This outlet is connected to the auxiliary inlet at the bottom of the gas-liquid countercurrent carbonization tower via a CO2 blower 264, preferably a centrifugal blower. The high-concentration carbon dioxide generated during pyrolysis is continuously returned to the interior of the carbonization tower via the centrifugal blower, where it is thoroughly mixed with the kiln tail flue gas supplied by the kiln tail resource recovery system 600. This internal circulation structure increases the volume concentration of carbon dioxide in the carbonization reaction zone from the original 25-35% to 35-55%, effectively improving the carbonization reaction rate and reaction sufficiency, reducing carbon dioxide raw material loss, and achieving the recycling and reuse of high-purity carbon dioxide.

[0039] After the filter press completes solid-liquid separation, it produces a process filtrate containing trace amounts of magnesium ions. The filtrate outlet is connected to the process water storage tank through a pipeline. The separated process filtrate is collected and stored in the process water storage tank 242. The outlet of the process water storage tank is connected to the inlet of the hydration tank through a magnesium ion water transfer pump 263. The collected process water can be transferred back to the hydration tank for magnesium oxide powder slurry production. There is no process wastewater discharge throughout the process, realizing closed-loop recycling of process water, significantly reducing production water consumption, and recovering the trace amounts of magnesium ions remaining in the process water, thereby improving the raw material recovery rate.

[0040] This system utilizes the waste heat from the high-temperature thermal oil recovered by the kiln tail heat exchanger 610 and the waste heat from the hot air recovered by the kiln head heat exchanger 710 to achieve precise cascade utilization of thermal energy, respectively matching the temperature requirements of the pyrolysis and drying processes. Specifically, in the pyrolysis unit heating loop: the thermal oil outlet of the kiln tail heat exchanger 610 (preferably a partition wall heat exchanger) is connected to the heating jacket of the pyrolysis unit 230 (preferably a pyrolysis reactor) via a pyrolysis jacket circulation pump 265 (preferably a centrifugal pump), forming a closed thermal oil circulation heating loop. Through continuous heat exchange via the circulating thermal oil, a stable heat source is provided to the pyrolysis unit 230 (preferably a pyrolysis reactor), precisely maintaining the pyrolysis reaction temperature at a constant 85±5℃, ensuring the smooth progress of the pyrolysis reaction. The heat transfer oil outlet of the kiln tail heat exchanger 610 (preferably a partition wall heat exchanger) is connected to the heating jacket and heat exchange coil of the drying unit 250 (preferably a drying chamber) through the drying jacket circulation pump 266 (preferably a centrifugal pump). This provides a basic drying heat source for the drying unit 250 through indirect heat exchange, maintaining the drying temperature at a stable 200-280℃. At the same time, the high-temperature hot air produced by the kiln head heat exchanger 710 (preferably a partition wall heat exchanger) is pressurized and transported by the drying purge fan 267 (preferably a centrifugal fan). It is then connected to the hot air purging channel of the drying unit 250 through pipelines, directly acting on the wet material in a convective purging manner. The combination of indirect heat exchange and convective drying doubles the drying efficiency, realizing the tiered, efficient, and graded utilization of kiln exhaust gas, waste air, and waste heat.

[0041] The entire system, through precise pipeline matching of the kiln system 100, chemical system 200, kiln tail resource recovery system 600, and kiln head resource recovery system 700, and the coordinated operation of various dedicated pumps and fans, constructs a complete circulating supply system for powder, waste heat, carbon dioxide, and process water, realizing the full-component resource utilization of kiln tail gas and waste air. Simultaneously, the hydration tank, process water storage tank 242, and finished product storage unit 251 in the chemical system 200 possess excellent buffering and adjustment capabilities. The finished product storage unit 251 receives and temporarily stores the finished basic magnesium carbonate produced by the drying unit 250 for transfer, and can autonomously balance fluctuations in materials, water volume, and concentration during the chemical preparation process. All fluctuations are confined within the chemical system 200 and will not interfere with the thermal stability regime of the kiln system 100. Under the premise of ensuring normal kiln production, it achieves continuous, stable, and energy-efficient preparation of basic magnesium carbonate, significantly improving resource utilization and reducing production energy consumption and waste emissions.

[0042] This embodiment describes a rotary kiln system for producing 300 tons of light-burned magnesia per day. The specific process steps are as follows: S1, hydration unit 210 is an atmospheric pressure hydration tank with a mechanical stirring device. Lightly calcined magnesium oxide and magnesium oxide powder recovered from the kiln tail and kiln head are continuously added into it. The water delivery pump 263 is turned on to continuously inject circulating process water at a solid-liquid mass ratio of 1:8 to 1:12. Hydration is carried out at room temperature for 1.5 to 2.5 hours to obtain magnesium hydroxide slurry with constant fluidity.

[0043] S2, carbonization unit 220 is a gas-liquid countercurrent packed carbonization tower. Magnesium hydroxide slurry is pumped to the top of the tower and sprayed downwards by carbonization delivery pump 260; CO2-containing clean flue gas filtered by kiln tail powder collection device 620 is introduced countercurrently upwards from the bottom of the tower, and mixed with high-purity carbon dioxide returned from the pyrolysis unit by CO2 blower 264, so that the CO2 volume concentration in the carbonization reaction zone is increased from 25-35% to 35-55%, and the gas and liquid phases are fully in contact on the packing surface to prepare a reaction liquid containing magnesium bicarbonate.

[0044] S3, pyrolysis unit 230 is a jacketed reactor. The reaction liquid containing magnesium bicarbonate is sent in by pyrolysis transfer pump 261, and the heat transfer oil of kiln tail heat exchanger 610 is connected to the heating jacket by pyrolysis jacket circulation pump 265 to maintain the temperature inside the jacket at 85±5℃ for heating and pyrolysis, continuously generating basic magnesium carbonate slurry and high-purity carbon dioxide (purity ≥95%) is released from the top of the reactor.

[0045] S4. The gas outlet at the top of the pyrolysis unit 230 is connected to the auxiliary gas inlet at the bottom of the carbonization unit 220 via the CO2 blower 264. The high-purity carbon dioxide released is continuously fed back to the carbonization tower to mix with the kiln tail flue gas, thereby realizing the internal circulation enrichment and utilization of carbon dioxide.

[0046] S5. The pyrolyzed basic magnesium carbonate slurry is sent to the solid-liquid separation unit 240 (filter press) via solid-liquid separation pump 262 to separate wet basic magnesium carbonate filter cake (moisture content 35-45%) and filtrate containing trace magnesium ions.

[0047] S6. The filtrate flows into the process water storage tank 242 via pipeline, and then flows back to the hydration unit 210 via the water transfer pump 263 to participate in the pulping of S1, realizing the closed-loop recycling of process water and the complete process without the discharge of process wastewater.

[0048] S7. The wet filter cake is conveyed into the drying unit 250 (drying chamber) via a scraper conveyor. The heat transfer oil in the kiln tail heat exchanger 610 is maintained at 200-280℃ by the drying jacket circulation pump 266 to provide the basic drying heat source through indirect heat exchange. The high-temperature hot air produced by the kiln head heat exchanger 710 is pressurized by the drying purge fan 267 and connected to the hot air purging channel to directly act on the wet material through convection purging. The material stays for 30-50 minutes, and finally, a finished product of basic magnesium carbonate with a moisture content of ≤1.0% is obtained, which is then collected and temporarily stored in the finished product storage unit 251.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A system for continuously preparing basic magnesium carbonate using waste heat from kiln exhaust gas, characterized in that, include: A kiln system (100) having a kiln system tail gas outlet (101) and a kiln system waste air outlet (102), a chemical system (200) for generating basic magnesium carbonate, a kiln tail resource recovery system (600) and a kiln head resource recovery system (700). The inlet of the kiln tail resource recovery system (600) is connected to the tail gas outlet (101) of the kiln system, and is used to recover dust and waste heat resources in the kiln tail gas, and send the treated dust and waste heat resources back to the chemical system (200). The inlet of the kiln head resource recovery system (700) is connected to the exhaust air outlet (102) of the kiln system, and is used to recover dust and waste heat resources in the kiln exhaust air, and send the treated dust and waste heat resources back to the chemical system (200).

2. The system for continuously preparing basic magnesium carbonate using waste heat from kiln tail gas according to claim 1, characterized in that, The kiln tail resource recovery system (600) includes a kiln tail induced draft fan (630), a kiln tail heat exchanger (610), and a kiln tail powder collection device (620). The kiln tail induced draft fan (630) is connected to the tail gas outlet (101) of the kiln system. The kiln tail heat exchanger (610) includes a first heat exchange channel and a second heat exchange channel. The inlet of the first heat exchange channel is connected to the outlet of the kiln tail induced draft fan (630). The outlet of the first heat exchange channel is connected to the inlet of the kiln tail powder collection device (620), and the outlet of the second heat exchange channel is connected to the chemical system (200).

3. The system for continuously preparing basic magnesium carbonate using waste heat from kiln tail gas according to claim 2, characterized in that, The kiln tail powder collection device (620) includes a dust outlet and a gas outlet. The dust outlet is connected to the material inlet of the chemical system (200) through a pipeline and is used to return the collected dust to the chemical system (200) to participate in the reaction. The gas outlet is connected to the bottom air inlet of the chemical system (200) through a flue gas pipeline.

4. The system for continuously preparing basic magnesium carbonate using waste heat from kiln tail gas according to claim 1, characterized in that, The kiln head resource recovery system (700) includes: a kiln head induced draft fan (730), a kiln head heat exchanger (710), a kiln head powder collection device (720), and a clean gas supply unit (711); the inlet of the kiln head induced draft fan (730) is connected to the waste air outlet (102) of the kiln system; the kiln head heat exchanger (710) includes a third heat exchange channel and a fourth heat exchange channel; The inlet of the third heat exchange channel is connected to the outlet of the kiln head induced draft fan (730), and the outlet of the third heat exchange channel is connected to the inlet of the kiln head powder collection device (720); the outlet of the kiln head powder collection device (720) is connected to the material inlet of the chemical system (200); the outlet of the clean gas supply unit (711) is connected to the inlet of the fourth heat exchange channel, and the outlet of the fourth heat exchange channel is connected to the drying unit (250) of the chemical system (200), for providing convective purging hot air required for drying.

5. The system for continuously preparing basic magnesium carbonate using waste heat from kiln tail gas according to claim 1, characterized in that, The chemical system (200) includes a hydration unit (210), a carbonization unit (220), a pyrolysis unit (230), a solid-liquid separation unit (240), a drying unit (250), and a finished product storage unit (251) connected in series.

6. The system for continuously preparing basic magnesium carbonate using waste heat from kiln tail gas according to claim 5, characterized in that, The pyrolysis unit (230) is provided with a gas outlet at the top. The gas outlet is connected to the carbonization unit (220) through a pipeline. A CO2 fan (264) is provided on the pipeline to send the carbon dioxide generated by pyrolysis back to the interior of the carbonization unit (220).

7. The system for continuously preparing basic magnesium carbonate using waste heat from kiln tail gas according to claim 5, characterized in that, The liquid outlet of the solid-liquid separation unit (240) is connected to the process water storage tank (242), and the water outlet of the process water storage tank (242) is returned to the hydration unit (210) through the water transfer pump (263).

8. A process for continuously preparing basic magnesium carbonate using the system described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Lightly calcined magnesium oxide is added to the hydration unit (210), and circulating process water recovered by the solid-liquid separation unit (240) and buffered by the process water storage tank (242) is added to prepare magnesium hydroxide slurry. S2. Magnesium hydroxide slurry is continuously transported to carbonization unit (220) via carbonization transfer pump (260) and reacted countercurrently with carbon dioxide-containing clean flue gas recovered and transported by kiln tail resource recovery system (600) and carbon dioxide returned by CO2 blower (264) to prepare reaction liquid containing magnesium bicarbonate. S3. The reaction liquid containing magnesium bicarbonate is transported to the pyrolysis unit (230) through the pyrolysis transfer pump (261). The residual heat of the heat transfer oil recovered by the kiln tail heat exchanger (610) in the kiln tail resource recovery system (600) is used for heating and pyrolysis to generate basic magnesium carbonate slurry, while carbon dioxide gas is released. S4. The carbon dioxide gas released from the pyrolysis unit (230) is transported back to the bottom auxiliary air inlet of the carbonization unit (220) through the pipeline via the CO2 blower (264) and mixed with the carbon dioxide-containing clean flue gas transported by the kiln tail resource recovery system (600) to increase the carbon dioxide concentration in the carbonization reaction zone and realize the internal circulation enrichment and utilization of carbon dioxide. S5. The pyrolyzed basic magnesium carbonate slurry is sent to the solid-liquid separation unit (240) through the solid-liquid separation pump (262) for solid-liquid separation, and wet basic magnesium carbonate filter cake and filtrate containing trace magnesium ions are obtained respectively. S6. The filtrate obtained from solid-liquid separation is introduced into the process water storage tank (242) and returned to the hydration unit (210) by the water transfer pump (263) to realize the closed-loop recycling of process water. S7. The wet basic magnesium carbonate filter cake is transported to the drying unit (250). The heat transfer oil of the kiln tail heat exchanger (610) is used to maintain the basic drying temperature through indirect heat exchange provided by the drying jacket circulation pump (266). At the same time, the high-temperature hot air recovered by the kiln head heat exchanger (710) in the kiln head resource recovery system (700) is pressurized by the drying blower (267) and acts on the wet material in a convective blowing manner. The combination of indirect heat exchange and convective drying makes the material fully dry and finally obtains the finished basic magnesium carbonate with a moisture content of ≤1.0%.

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