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

Abstract

The invention discloses a device and a method for directly curing desulfurization ash-based artificial aggregates by using flue gas, and belongs to the technical field of waste gas treatment. The method comprises the following steps: (1) preparing two parts of flue gas to be treated, one part of flue gas is feeding flue gas for aggregate maintenance, and the other part of flue gas is flue gas for heating; (2) carrying out gradient curing on the aggregate by adopting feeding flue gas, and adjusting the temperature of the flue gas during curing by taking the flue gas for heating as a heat source; the gradient curing process comprises three stages of curing processes, and the curing effect of the aggregate in different stages is achieved by changing the temperature and humidity conditions of curing flue gas. The aggregate can be directly fed into the mineralization kettle to be subjected to mineralization maintenance through low-pressure flue gas, pre-maintenance and pre-drying are not needed, the strength of the aggregate can be enhanced, the carbonization efficiency of the aggregate can be guaranteed, meanwhile, waste heat of discharged flue gas is used for heat exchange, and effective utilization of heat of the flue gas is achieved; when a multi-kettle mode is adopted for gradient maintenance of the aggregate, the utilization efficiency of CO2 can be improved 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 aggregates by utilizing 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 a coal-fired power plant. It is discharged through the high point of the chimney after desulfurization, denitrification and denitrification. The flue gas emission pressure is close to normal pressure, the CO2 content is 10-20%, the emission 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 implementing large-scale flue gas CO2 recovery and utilization.

[0005] Aggregate is an essential raw material for building infrastructure. It mainly plays the role of skeleton and filling in 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 day by day. It has become the second largest natural resource consumed by humans. The annual amount of concrete used in the world is about 2 billion m 3 , the amount of natural aggregate used is about 3.4 billion to 4 billion tons. At present, high-quality sand and gravel resources are increasingly depleted, especially the natural coarse aggregate required for concrete. Artificial aggregate (also known as artificial aggregate) is an industrial product prepared by pressing or mixing granulation, and strengthened by heating, carbonization or alkali activation. Artificial aggregate prepared from solid waste such as fly ash, steel slag, mineral powder, red mud, and waste concrete powder can replace natural sand and gravel. On the one hand, it can solve the problem of insufficient supply of coarse aggregate and provide a new direction for the sustainable development of aggregates. At the same time, 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 utilize the filling effect of the mineralization reaction to improve the pore structure of the aggregate and thereby improve the strength and stability of the artificial aggregate. However, due to the low CO2 content (≤20%) of the flue gas itself and the low pressure (normal pressure), the utilization rate of CO2 directly using flue gas mineralization for curing is low. 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 consumes a lot of electricity and increases the cost of flue gas utilization.

[0007] Patent CN116177983 proposes a method for preparing high-performance green building materials by mineralizing CO2 based on combustion flue gas, and the CO2 concentration used is 15-30%. Although this method can obtain 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 lot 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 concentration in the range of 5-80% in flue gas, due to the use of a stepped mineralization and maintenance process, the flue gas pressure needs to meet the condition of ≥0.3MPa, which 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, using CO2 gas with a concentration of 10-30% to carbonize the aggregate after pre-curing, and 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 and 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 the scheme mentions the use of flue gas for mineralization curing, air curing and drying treatment for 3-28 days are required before curing. Due to the high moisture content of the aggregate, the drying operation also requires a certain amount of energy consumption; and only the mineralization effect of the aggregate is described, but the utilization efficiency of the flue gas is not introduced. Therefore, it is particularly necessary to develop a method for mineralizing and recycling flue gas under low-pressure conditions. Summary of the invention

[0011] In view of 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 to 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 land occupation of the device. Through optimized process design and parameter control, the strength of the aggregate is enhanced and the carbonization efficiency of the aggregate 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 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 1-10 kPa; the other part is the flue gas for heating, which is pressurized to 1-5 kPa;

[0015] (2) The feed flue gas is used to perform gradient curing on the aggregate, and the heating flue gas is used as a heat source to adjust the temperature of the flue gas during curing; wherein the temperature and humidity of the feed flue gas for gradient curing decrease as the mineralization degree of the aggregate 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 at the current stage as circulating flue gas.

[0018] Furthermore, gradient curing is divided into three stages, and 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 adjusted to 85-98% by heating the flue gas, the volume ratio of the circulating flue gas to the feed flue gas is adjusted to 0.5-5, and the curing time is adjusted to 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 4-24h;

[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 aggregate is carried out in one or more reactors. When a multi-reactor mode is used for the gradient curing of 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, and has a temperature of 75 to 90° C. and a humidity of 20 to 50%.

[0028] A system for directly curing desulfurized ash-based artificial aggregate using flue gas, comprising a booster fan for adjusting the pressure of the flue gas 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, in which the flue gas as a 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 a temperature and humidity sensor for detecting the temperature and relative humidity of the flue gas for maintenance. The equipment used in the above system of the present invention is mature equipment in the field, such as the heat exchanger can choose a shell and tube or plate heat exchanger, the temperature and humidity sensor can choose a DHT11 temperature and humidity sensor, and the booster fan can choose an SDF type pressurized axial flow fan.

[0034] Beneficial effects of the present invention:

[0035] 1. The present invention adopts a gradient curing method for aggregates, including three curing stages, wherein the first stage curing strengthens the hydration process and surface mineralization of aggregates. By controlling the temperature and humidity of the flue gas entering the curing device, the aggregates undergo hydration reaction under high temperature and high humidity conditions. Due to the increase in the temperature and humidity of the incoming air, the hydration rate of the aggregates is enhanced compared with conventional natural curing, and the initial strength of the aggregates is rapidly improved. At the same time, under the action of the relative humidity of the flue gas (relative humidity <100%), a slow dehydration process occurs on the surface of the aggregates, and as the dehydration process proceeds, the surface of the aggregates undergoes carbonization.

[0036] The second stage of curing enables the aggregate to complete the mineralization of the middle layer. After the first stage, the humidity of the curing flue gas inlet is appropriately reduced, so that the rate of aggregate water loss is enhanced, the moisture content of the middle layer of the aggregate is reduced, the mineralization curing rate is increased, and the mineralization process in the middle layer can be fully carried out.

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

[0038] 2. The present invention adopts a flue gas direct curing method for artificial aggregates, shortening the curing period of aggregates, reducing the footprint of the device, and reducing the investment and operating costs of the device. At the same time, during the treatment process, the flue gas only needs to be pressurized to 1-10kpa, slightly higher than the normal pressure, which reduces the cost of using the flue gas, and can effectively utilize its own heat, and improve the utilization efficiency of CO2, which can reach more than 50%.

[0039] 3. The present invention ensures the curing effect of aggregates in the curing vehicle by precisely controlling the temperature and humidity of flue gas. In the initial stage of aggregate curing, the strength of aggregates is relatively low, and the curing of aggregates 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 is fully carried out, the strength of aggregates is improved, and at the same time, the surface area of ​​aggregates undergoes a preliminary mineralization reaction as the water content decreases; subsequently, the temperature and humidity of the flue gas curing area are adjusted by a temperature and humidity control system, and 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 of the middle layer of aggregates 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 of the core area of ​​aggregates is strengthened, and the mineralization effect of the core area of ​​aggregates is guaranteed. DETAILED DESCRIPTION

[0040] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept 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 which is used as the feed flue gas for aggregate curing, and the other is used as the heating flue gas. In the heat exchanger regulation, the heating flue gas is used to adjust the temperature of the feed flue gas, and then adjust its humidity, and then the aggregate is gradient cured;

[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 24h, 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 8h, 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 16h, 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 the power plant are pressurized to 10 kPa by a booster fan, one of which 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 adjusts the temperature of the feed flue gas, and then adjusts its humidity, and then the aggregate is gradient cured;

[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 48h, 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 24h, 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 24h, 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 which is used as the feed flue gas for aggregate curing, and the other is used as the heating flue gas. In the heat exchanger regulation, the heating flue gas is used to adjust the temperature of the feed flue gas, and then adjust its humidity, and then the aggregate is gradient cured;

[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 40h, 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 24h, 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 24h, 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, the curing temperature was the same as in Example 1, the temperature during the curing process 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] The fly ash of a power plant is used as the main raw material to prepare aggregate, and the auxiliary raw materials include cement, steel slag and water. The cement type is PO42.5, and the steel slag is ground converter slag. The mass ratio is fly ash: cement: steel slag = 7:1:2. Then the aggregate is granulated into balls through a granulation process for later use.

[0080] 2. Maintenance

[0081] The prepared aggregate was cured by the scheme described in Example 1 and Comparative Examples 1 to 3. After the curing, the strength of the aggregate was tested by 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 fixation 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 cured flue gas enters the curing kettles in the second stage and the second stage in turn for aggregate curing. The specific gradient curing process is shown in Table 2.

[0086] Table 2 Multi-reactor series gradient curing

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

[0088] As shown in Table 2, by operating multiple kettles in series, direct mineralization utilization of flue gas under low pressure conditions is realized. By controlling the flue gas mineralization process in stages, the cascade utilization of CO2 in the 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 solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should 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 1-10 kPa; the other part is the flue gas for heating, which is pressurized to 1-5 kPa; (2) The feed flue gas is used to perform gradient curing on the aggregate, and the heating flue gas is used as a heat source to adjust the temperature of the flue gas during curing; wherein the temperature and humidity of the feed flue gas for gradient curing decrease as the mineralization degree of the aggregate increases.

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 at the current stage as circulating flue gas.

4. The method according to claim 3, characterized in that The gradient curing of aggregate is divided into three stages, the specific process is as follows: S1. One-stage maintenance The temperature of the feed flue gas is adjusted to 55-75°C and the relative humidity is adjusted to 85-98% by heating the flue gas, the volume ratio of the circulating flue gas to the feed flue gas is adjusted to 0.5-5, and the curing time is adjusted to 4-48 hours; S2, two-stage maintenance 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 4-24h; S3, three-stage maintenance 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.

5. The method according to claim 4, characterized in that A spray system is used to adjust the relative humidity of the feed flue gas.

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

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

8. A device for directly curing desulfurized ash-based artificial aggregate using flue gas, characterized in that: Including booster fan, adjusting the flue gas pressure to 1-10kpa; Curing kettle, used to complete gradient curing; The circulating fan transports the circulating flue gas that has completed curing to the curing kettle to continue the curing at the current stage; Heat exchanger, in which the flue gas as a heat source adjusts the temperature of the curing flue gas; Spray system to adjust the relative humidity of the flue gas used for maintenance.

9. The device according to claim 8, characterized in that It also includes temperature and humidity sensors for detecting the temperature and relative humidity of the curing flue gas.