Device and method for directly curing desulfurized ash-based artificial aggregate using flue gas

Abstract

The present invention discloses a device and method for directly curing desulfurized ash-based artificial aggregate using flue gas, which belongs to the field of waste gas treatment technology. The method comprises the following steps: (1) preparing two portions of flue gas to be treated, one portion being feed flue gas for aggregate curing, and the other portion being heating flue gas; (2) using the feed flue gas to perform gradient curing on the aggregate, and using the heating flue gas as a heat source to regulate the temperature of the flue gas during curing; the gradient curing comprises three staged curing processes, and by changing the temperature and humidity conditions of the curing flue gas, the curing effect of the aggregate at different stages is achieved. The present invention can directly feed the aggregate into the mineralization kettle for mineralization curing using low-pressure flue gas, without the need for pre-curing and pre-drying, thereby enhancing the strength of the aggregate and ensuring the carbonization efficiency of the aggregate. At the same time, the waste heat of the exhaust flue gas itself is used for heat exchange, thereby achieving effective utilization of the heat of the flue gas itself; when the multi-kettle mode is used for gradient curing of the aggregate, the utilization efficiency of CO2 can be increased to more than 50%.

Description

Technical Field

[0001] The invention belongs to the technical field of waste gas treatment, and in particular relates to a device and method for directly curing desulfurized ash-based artificial aggregate using flue gas. Background Art

[0002] Given that coal will remain the main source of energy supply in my country in the medium and long term, it is imperative to control flue gas emissions from coal-fired power plants.

[0003] Power plant flue gas is a CO2-rich gas produced during the combustion of coal in coal-fired power plants. After desulfurization, denitrification and denitrification, it is discharged through the high point of the chimney. The flue gas discharge pressure is close to normal pressure, the CO2 content is 10-20%, the discharge temperature is 75-90℃, the water vapor content is 7-12%, and the relative humidity of the flue gas outlet is 40-60%.

[0004] Since the flue gas concentration of coal-fired power plants is low (CO2 concentration ≤ 20%) and the pressure is low (normal pressure), the current conventional CO2 utilization technologies include membrane separation, chemical absorption, and pressure swing adsorption. However, these treatment methods generally have problems of high investment costs and high energy consumption, and do not yet have the industrial conditions for large-scale flue gas CO2 recovery and utilization.

[0005] Aggregate is an essential raw material for building infrastructure. It plays a major role in the skeleton and filling of concrete. According to the particle size, it can be divided into coarse aggregate (diameter greater than 5mm) and fine aggregate (diameter between 0.16 and 5mm). With the rapid development of society and the acceleration of industrialization and urbanization, the consumption of natural aggregate is increasing. It has become the second largest natural resource consumed by humans. The annual amount of concrete used in the world is about 2 billion cubic meters. 3 The consumption of natural aggregates is approximately 3.4 billion to 4 billion tons. Currently, high-quality sand and gravel resources are becoming increasingly depleted, especially the natural coarse aggregate required for concrete. Artificial aggregate (also known as artificial aggregate) is an industrial product prepared by processes such as compression molding or mixing granulation, and then strengthened by heating, carbonization, or alkali activation. Artificial aggregates prepared from solid wastes such as fly ash, steel slag, mineral powder, red mud, and waste concrete powder can replace natural sand and gravel. On the one hand, this can solve the problem of insufficient coarse aggregate supply, provide a new direction for the sustainable development of aggregates, and on the other hand, it provides new research ideas and application prospects for the treatment of industrial solid waste and construction waste dust.

[0006] The use of flue gas mineralization to cure artificial coarse aggregate can not only realize the recovery and utilization of CO2 in the flue gas and solve the problem of flue gas emissions from power plants, but also use the filling effect of the mineralization reaction to improve the pore structure of the aggregate and thus improve the strength and stability of the artificial aggregate. However, due to the low CO2 content of the flue gas itself (≤20%) and the low pressure (normal pressure), the direct use of flue gas mineralization for curing has a low CO2 utilization rate. At present, the research on flue gas mineralization curing adopts the method of pressurizing the flue gas to normal pressure or even above for utilization, but this method requires a large amount of electricity consumption and increases the cost of flue gas utilization.

[0007] Patent CN116177983 proposes a method for preparing high-performance green building materials using CO2 mineralized from combustion flue gas, using a CO2 concentration of 15-30%. Although this method can produce high-strength artificial aggregates, the combustion flue gas needs to be pressurized to 1-1.5MPa to meet the needs of the mineralization reaction, and this process consumes a large amount of electricity.

[0008] Patent CN114210692 proposes a device and method for mineralizing low-concentration CO2 from solid waste. Although it can achieve effective capture and utilization of CO2 concentrations in the flue gas within the range of 5-80%, due to the use of a stepped mineralization and curing process, the flue gas pressure needs to meet the condition of ≥0.3MPa. This also means that the flue gas needs to be compressed to be effective, increasing the cost of flue gas utilization.

[0009] Patent CN117510113 proposes an all-solid waste artificial lightweight aggregate based on CO2 mineralization utilization and its preparation method. The pre-cured aggregate is carbonized and cured using CO2 gas with a concentration of 10-30%. The relative humidity of the curing environment is 40-60%. However, the patent does not clearly define the pressure control of the curing process, and pre-curing and wet curing after mineralization are required before and after mineralization curing.

[0010] Patent 202410167395.8 proposes a desulfurized ash-based artificial aggregate, its preparation method, and application. The prepared aggregate is air-cured and then dried, and then subjected to flue gas mineralization curing. The curing conditions are normal pressure, 58-62°C, and 70-90% RH. Although this solution mentions the use of flue gas for mineralization curing, it requires 3-28 days of air curing and drying before curing. Due to the high moisture content of the aggregate, the drying operation also consumes a certain amount of energy. In addition, only the mineralization effect of the aggregate is described, and the utilization efficiency of the flue gas is not introduced. Therefore, it is particularly necessary to develop a method for mineralization and recycling of flue gas under low-pressure conditions. Summary of the Invention

[0011] In response to the above-mentioned deficiencies in the prior art, the present invention provides a device and method for directly curing desulfurized ash-based artificial aggregate using flue gas. The present invention proposes a method and system for directly curing artificial aggregate using flue gas under low pressure. The prepared aggregate can be directly sent into a curing kettle for mineralization curing using low-pressure flue gas, without the need for pre-curing and pre-drying, thereby reducing the investment cost and floor space of the device. Through optimized process design and parameter control, the aggregate strength is enhanced and the aggregate carbonization efficiency is guaranteed. At the same time, a gradient curing treatment is adopted, the heat of the flue gas itself is effectively utilized, and the utilization efficiency of CO2 is improved, which can reach up to more than 50%.

[0012] To achieve the above-mentioned purpose, the technical solution adopted by the present invention to solve the technical problem is:

[0013] A method for directly curing desulfurized ash-based artificial aggregate using flue gas comprises the following steps:

[0014] (1) Prepare two parts of flue gas to be treated, one part is the feed flue gas for aggregate curing, which is pressurized to 1-10kPa; the other part is the flue gas for heating, which is pressurized to 1-5kPa;

[0015] (2) Aggregates are subjected to gradient curing using feed flue gas, and the heating flue gas is used as a heat source to regulate the temperature of the flue gas during curing; wherein, the temperature and humidity of the feed flue gas for gradient curing decrease as the degree of aggregate mineralization increases.

[0016] Furthermore, in step (1), the feed flue gas and the heating flue gas have the same composition.

[0017] Furthermore, during the gradient curing process, part of the flue gas after curing is discharged from the curing kettle, and the other part continues to participate in the curing of the current stage as circulating flue gas.

[0018] Furthermore, gradient curing is divided into three stages. The curing process is controlled by adjusting the feed flue gas conditions at different stages. The specific process is as follows:

[0019] S1. One-stage maintenance

[0020] The temperature of the feed flue gas is adjusted to 55-75°C and the relative humidity is 85-98% by heating the flue gas. The volume ratio of the circulating flue gas to the feed flue gas is 0.5-5, and the curing time is 4-48 hours.

[0021] S2, two-stage maintenance

[0022] The temperature of the flue gas fed by the heating flue gas is 55-70°C, the relative humidity is 70-85%, the volume ratio of the circulating flue gas to the feed flue gas is 1-10, and the curing time is 4-24 hours;

[0023] S3, three-stage maintenance

[0024] The temperature of the feed flue gas is adjusted to 45-65° C. and the relative humidity is adjusted to 30-70% by heating the flue gas. The volume ratio of the circulating flue gas to the feed flue gas is 1-15, and the curing time is 4-48 hours.

[0025] Furthermore, a spray system is used to adjust the relative humidity of the feed flue gas.

[0026] Furthermore, the gradient curing of the aggregate is carried out in one or more reactors. When a multi-reactor mode is used for the gradient curing of the aggregate, efficient utilization of CO2 in the flue gas can be achieved.

[0027] Furthermore, the flue gas in step (1) is flue gas directly discharged from a power plant, with a temperature of 75-90° C. and a humidity of 20-50%.

[0028] A system for directly curing desulfurized ash-based artificial aggregate using flue gas, comprising a booster fan for adjusting the flue gas pressure to 1-10 kPa;

[0029] Curing kettle, used to complete gradient curing;

[0030] The circulating fan transports the circulating flue gas that has completed curing to the curing kettle to continue the curing at the current stage;

[0031] Heat exchanger, where the flue gas as heat source adjusts the temperature of the curing flue gas;

[0032] Spray system to adjust the relative humidity of the flue gas used for maintenance.

[0033] Furthermore, it also includes temperature and humidity sensors for detecting the temperature and relative humidity of the curing flue gas. The equipment used in the above-mentioned system of the present invention is all mature equipment in the field. For example, the heat exchanger can be a shell and tube or plate heat exchanger, the temperature and humidity sensor can be a DHT11 temperature and humidity sensor, and the booster fan can be an SDF type pressurized axial flow fan.

[0034] Beneficial effects of the present invention:

[0035] 1. The present invention employs a gradient aggregate curing method comprising three curing stages. The first stage enhances the aggregate's hydration process and surface mineralization by controlling the temperature and humidity of the flue gas entering the curing apparatus, allowing the aggregate to undergo hydration under high-temperature and high-humidity conditions. This elevated intake air temperature and humidity enhances the aggregate's hydration rate compared to conventional natural curing, rapidly increasing its initial strength. Simultaneously, under the influence of flue gas relative humidity (RH <100%), the aggregate surface slowly loses water, and as this dehydration progresses, the aggregate undergoes surface carbonization.

[0036] The second stage of curing completes the mineralization of the middle layer of aggregate. After the first stage, the humidity of the curing flue gas inlet is appropriately reduced to enhance the rate of aggregate water loss, reduce the moisture content of the middle layer of aggregate, increase the mineralization curing rate, and fully carry out the mineralization process in the middle layer.

[0037] The three-stage curing completes the core mineralization of the aggregate. As the mineralization process proceeds, the surface and middle layer areas of the aggregate are basically mineralized. Due to the filling effect of the mineralization reaction, the porosity of the middle layer area of the aggregate decreases, the internal diffusion channels of the aggregate decrease, and the water evaporation rate decreases. By further reducing the humidity of the inlet flue gas, the moisture in the core area of the aggregate can be effectively evaporated, thereby ensuring the mineralization efficiency of the core.

[0038] 2. This invention uses flue gas to directly cure artificial aggregate, shortening the aggregate curing cycle, reducing equipment footprint, and lowering investment and operating costs. Furthermore, during the treatment process, the flue gas only needs to be pressurized to 1-10 kPa, slightly above atmospheric pressure. This reduces flue gas usage costs, effectively utilizes its own heat, and improves CO2 utilization efficiency to over 50%.

[0039] 3. The present invention ensures the curing effect of the aggregate in the curing vehicle by precisely controlling the flue gas temperature and humidity. In the initial stage of aggregate curing, the aggregate strength is relatively low, and the curing of the aggregate is mainly to strengthen the hydration reaction. The flue gas humidity is controlled at ≥85%, and the temperature is controlled at ≥55°C. As the hydration reaction proceeds fully, the aggregate strength is improved. At the same time, the surface area of the aggregate undergoes a preliminary mineralization reaction as the water content decreases. Subsequently, the temperature and humidity of the flue gas curing area are adjusted by the temperature and humidity control system. The flue gas humidity is controlled at ≥70% and the temperature is ≥55°C. At this time, the aggregate dehydration process is accelerated, and the mineralization reaction process in the middle layer of the aggregate is strengthened. In the later stage of mineralization, by controlling the flue gas humidity at ≥30% and the temperature at ≥45°C, as the flue gas humidity further decreases, the water evaporation efficiency in the core area of the aggregate is enhanced, and the mineralization effect of the core area of the aggregate is guaranteed. DETAILED DESCRIPTION

[0040] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0041] Example 1

[0042] A method for directly curing desulfurized ash-based artificial aggregate using flue gas comprises the following steps:

[0043] (1) Two identical flue gases from the power plant are pressurized to 6 kPa by a booster fan. One of the flue gases is used as the feed flue gas for aggregate curing, and the other is used as the heating flue gas. During the heat exchanger adjustment, the heating flue gas is used to adjust the temperature of the feed flue gas and then adjust its humidity. The aggregate is then subjected to gradient curing.

[0044] (2) During the gradient curing process, part of the flue gas after curing is discharged from the curing kettle, and the other part continues to participate in the curing of the current stage as circulating flue gas. The flue gas control conditions of aggregates at different curing stages are as follows:

[0045] S1. One-stage maintenance

[0046] The temperature of the feed flue gas is 65°C, the relative humidity is 95%, the curing time is 24 hours, and the volume ratio of the circulating gas volume to the feed flue gas is: 1.

[0047] S2, two-stage maintenance

[0048] The temperature of the feed flue gas is 60°C, the relative humidity is 80%, the curing time is 8 hours, and the volume ratio of the circulating gas volume to the feed flue gas is: 4.

[0049] S3, three-stage maintenance

[0050] The temperature of the feed flue gas is 55°C, the relative humidity is 45%, the curing time is 16 hours, and the volume ratio of the circulating gas volume to the feed flue gas is: 6.

[0051] Example 2

[0052] A method for directly curing desulfurized ash-based artificial aggregate using flue gas comprises the following steps:

[0053] (1) Two identical flue gases from a power plant are pressurized to 10 kPa by a booster fan. One of the flue gases is used as feed flue gas for aggregate curing, and the other is used as heating flue gas. During heat exchanger regulation, the heating flue gas adjusts the temperature of the feed flue gas and then adjusts its humidity. Gradual curing of the aggregate is then performed.

[0054] (2) During the gradient curing process, part of the flue gas after curing is discharged from the curing kettle, and the other part continues to participate in the curing of the current stage as circulating flue gas. The flue gas control conditions of aggregates at different curing stages are as follows:

[0055] S1. One-stage maintenance

[0056] The temperature of the feed flue gas is 75°C, the relative humidity is 98%, the curing time is 48 hours, and the volume ratio of the circulating gas volume to the feed flue gas is 0.5.

[0057] S2, two-stage maintenance

[0058] The temperature of the feed flue gas is 55°C, the relative humidity is 85%, the curing time is 24 hours, and the volume ratio of the circulating gas volume to the feed flue gas is: 3.

[0059] S3, three-stage maintenance

[0060] The temperature of the feed flue gas is 45°C, the relative humidity is 70%, the curing time is 24 hours, and the volume ratio of the circulating gas volume to the feed flue gas is: 8.

[0061] Example 3

[0062] A method for directly curing desulfurized ash-based artificial aggregate using flue gas comprises the following steps:

[0063] (1) Two identical flue gases from the power plant are pressurized to 5 kPa by a booster fan. One of the flue gases is used as the feed flue gas for aggregate curing, and the other is used as the heating flue gas. In the heat exchanger, the heating flue gas is used to adjust the temperature of the feed flue gas and then adjust its humidity. The aggregate is then subjected to gradient curing.

[0064] (2) During the gradient curing process, part of the flue gas after curing is discharged from the curing kettle, and the other part continues to participate in the curing of the current stage as circulating flue gas. The flue gas control conditions of aggregates at different curing stages are as follows:

[0065] S1. One-stage maintenance

[0066] The temperature of the feed flue gas is 55°C, the relative humidity is 85%, the curing time is 40 hours, and the volume ratio of the circulating gas volume to the feed flue gas is: 2.

[0067] S2, two-stage maintenance

[0068] The temperature of the feed flue gas is 55°C, the relative humidity is 70%, the curing time is 24 hours, and the volume ratio of the circulating gas volume to the feed flue gas is: 5.

[0069] S3, three-stage maintenance

[0070] The temperature of the feed flue gas is 45°C, the relative humidity is 30%, the curing time is 24 hours, and the volume ratio of the circulating gas volume to the feed flue gas is: 8.

[0071] Comparative Example 1

[0072] No gradient curing was performed, and the curing temperature was the same as in Example 1. During the curing process, the temperature was controlled at 60° C., the humidity was controlled at 90%, and the curing time was 48 h.

[0073] Comparative Example 2

[0074] No gradient curing was performed, the curing temperature and curing time were the same as those in Comparative Example 1, and the curing humidity was adjusted to 80%.

[0075] Comparative Example 3

[0076] No gradient curing was performed, the curing temperature and curing time were the same as those in Comparative Example 1, and the curing humidity was adjusted to 60%.

[0077] Experimental example

[0078] 1. Aggregate preparation

[0079] Aggregate was prepared using fly ash from a power plant as the main raw material, and auxiliary raw materials included cement, steel slag, and water. The cement type was PO42.5, and the steel slag was ground converter slag. The mass ratio of fly ash:cement:slag was 7:1:2. The aggregate was then pelletized into balls for later use.

[0080] 2. Maintenance

[0081] The prepared aggregate was cured using the scheme described in Example 1 and Comparative Examples 1 to 3. After curing, the aggregate strength was tested using a strength tester, and the carbon fixation rate of the aggregate after curing was determined by the loss on ignition. The results are shown in Table 1.

[0082] Table 1 Strength and carbon fixation rate of aggregates after different curing methods

[0083] Test items Particle strength Carbon sequestration rate Example 1 4.15 5.72％ Comparative Example 1 4.38 2.67％ Comparative Example 2 3.4 4.63％ Comparative Example 3 1.83 5.82％

[0084] 3. Flue gas utilization rate detection

[0085] The multi-kettle series mode is adopted for mineralization curing. Each curing kettle is equipped with an independent circulation fan, heat exchanger and spray system. When gradient curing is carried out, the flue gas first enters the curing kettle in the three-stage curing state to carry out mineralization curing with the aggregate. The flue gas after curing enters the curing kettles in the second and second stages in turn to cure the aggregate. The specific gradient curing process is shown in Table 2.

[0086] Table 2 Multi-reactor series gradient curing

[0087] Maintenance stage Phase 1 Phase II Three stages Number of curing kettles 2 1 3 Curing time h 16 8 24 Flue gas outlet concentration 6.72％ 7.21％ 7.65％

[0088] As shown in Table 2, by operating multiple reactors in series, direct mineralization utilization of flue gas under low-pressure conditions is achieved. By controlling the staged process of flue gas mineralization, the cascade utilization of CO2 in flue gas is achieved, and the utilization rate can reach more than 55%.

[0089] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for directly curing desulfurized ash-based artificial aggregate using flue gas, characterized in that: The following steps are involved: (1) Prepare two parts of flue gas to be treated, one part is the feed flue gas for aggregate curing, which is pressurized to 1~10kPa; the other part is the flue gas for heating, which is pressurized to 1~5kPa; the flue gas is the flue gas from the power plant; (2) Gradual curing of aggregates using feed flue gas, with heating flue gas used as a heat source to regulate the temperature of the flue gas during curing; wherein, the temperature and humidity of the feed flue gas for gradient curing decrease as the degree of aggregate mineralization increases; The process of gradient curing is: S1. One-stage maintenance The temperature of the feed flue gas is adjusted to 65-75°C and the relative humidity is 85-98% by heating the flue gas. The volume ratio of the circulating flue gas to the feed flue gas is 0.5-5, and the curing time is 4-48 hours. S2, two-stage maintenance The temperature of the flue gas fed by the heating flue gas is 55~70℃, the relative humidity is 70~85%, the volume ratio of the circulating flue gas to the feed flue gas is 1~10, and the curing time is 4~24h; S3, three-stage maintenance The temperature of the feed flue gas is adjusted to 45~65℃ and the relative humidity is 30~70% by heating the flue gas. The volume ratio of the circulating flue gas to the feed flue gas is 1~15, and the curing time is 4~48h.

2. The method according to claim 1, characterized in that In step (1), the feed flue gas and the heating flue gas have the same composition.

3. The method according to claim 1, characterized in that During the gradient curing process, part of the feed flue gas after curing is discharged from the curing kettle, and the other part continues to participate in the curing of the current stage as circulating flue gas.

4. The method according to claim 1, wherein A spray system is used to adjust the relative humidity of the feed flue gas.

5. The method according to any one of claims 1 to 4, characterized in that Gradient curing of aggregates is carried out in one or more curing tanks.

6. The method according to claim 1, characterized in that The flue gas in step (1) is the flue gas directly discharged from the power plant, with a temperature of 75-90°C and a humidity of 20-50%.