A circulating fluidized bed solid sulfur ash non-fired brick and its preparation method

Abstract

This invention discloses a circulating fluidized bed desulfurization ash non-fired brick and its preparation method, belonging to the technical field of building material resource utilization from industrial solid waste. Using at least one of circulating fluidized bed desulfurization ash, silicate cement, and carbide slag as a cementing component, the non-fired bricks achieve carbonation hardening through CO2 curing. The cementing components, by weight, are: 50-70 parts circulating fluidized bed desulfurization ash, 10-30 parts silicate cement, and 5-10 parts carbide slag. This invention utilizes widely available raw materials, has low preparation costs, and features a simple and environmentally friendly technical route. It not only solves the problem of large-scale disposal of desulfurization ash but also absorbs CO2, reducing the environmental impact of the greenhouse effect, and offers high economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of building material resource utilization technology of industrial solid waste, specifically relating to a circulating fluidized bed solidified sulfur ash non-fired brick and its preparation method. Background Technology

[0002] Currently, over 30 billion tons of CO2 greenhouse gases are emitted into the atmosphere globally each year. Low-cost, high-energy-efficiency carbon industries based on carbon dioxide-carbonate (CCUS) are key technologies for countries worldwide to achieve carbon neutrality. Mineral carbonation curing technology is based on the principle of rock weathering in nature. It utilizes alkaline metal oxides with high calcium and magnesium content to react with CO2, thereby generating stable carbonates. The advantages of carbonation curing technology have led to its widespread application in concrete, especially in combining solid waste with cement. This not only reduces the use of cement clinker and disposes of solid waste but also absorbs carbon dioxide, resulting in significant benefits. Carbonation-cured concrete technology involves injecting CO2 into fresh concrete. Through mineralization reactions with cementitious components and other alkaline calcium and magnesium components in pre-cured or early-hydrated concrete, carbonate products are formed in the pores and interfacial transition zones within the concrete. Through filling effects, interfacial transition zone elimination effects, and product layer effects, it not only improves the compressive strength and durability of concrete but also permanently binds CO2 within the concrete. my country will continue to adhere to the long-term policy of in-situ capture and utilization of CO2 from direct emissions of major carbon-emitting energy infrastructure such as power plants, cement plants, and steel plants.

[0003] Circulating fluidized bed (CFB) boilers account for a significant proportion of coal-fired power generation in my country. The solid byproducts generated during coal combustion in CFB boilers are desulfurization ash or desulfurization residue, also known as CFB boiler fly ash or bottom ash. Reports indicate that China's annual emissions of CFB desulfurization ash reach 80 million to 150 million tons, with Shanxi Province accounting for nearly 40 million tons per year, ranking first in the country. The large-scale landfilling and stockpiling of CFB desulfurization ash requires land resources and causes environmental damage. The main chemical components of CFB desulfurization ash are SiO2, Al2O3, and SO3, with additional components such as Fe2O3, CaO, MgO, NaO, and K2O; the main mineral components are quartz, anhydrite, hematite, and free calcium oxide. Theoretically, after certain temperature treatment, stable kaolinite in CFB desulfurization ash can be transformed into an unstable, highly active metakaolinite structure, increasing its pozzolanic activity, making it feasible as an active additive and admixture. Due to the unique characteristics of circulating fluidized bed coal combustion technology, the SO3 content in its desulfurization ash is relatively high compared to other solid wastes. SO3 readily reacts with other alkali metal oxides to form expansive products such as ettringite and gypsum, leading to poor volume stability. Limited by strict national and industry standards regarding SO3 content for use in cement concrete admixtures, the current dosage of desulfurization ash in cement concrete is limited, typically not exceeding 30%. Therefore, the high-dosage utilization of circulating fluidized bed desulfurization ash is urgently needed.

[0004] To date, research and practice on the preparation of cementitious materials using desulfurized ash slag both domestically and internationally have mainly focused on using desulfurized ash slag as a cement admixture. However, no practical or research reports have been found regarding the preparation of industrial non-fired bricks based on desulfurized ash slag using carbonation curing circulating fluidized bed boilers. This invention creatively combines the CO2 directly emitted by the building materials industry with the large-scale, difficult-to-dispose-of ash slag emitted by circulating fluidized bed boilers using carbonation curing technology to cure circulating fluidized bed desulfurized ash slag bricks. By using non-fired bricks as a carrier, it achieves high-volume utilization of desulfurized ash slag.

[0005] CN 111574146B discloses a method for preparing industrial non-fired bricks using various solid wastes, but the carbonation time is long and the strength gain of the mortar cementitious system is slow. CN 104987034A discloses a method for preparing novel slag carbonized bricks using industrial slag, using a single slag as raw material, but the CO2 curing temperature is high, the curing period is long, and the material needs a long hydration time to form strength. CN10311186A discloses a method for strengthening CO2 fixation in steel slag, in which the steel slag needs to be pretreated with a catalyst containing alkali metals before carbonation curing to improve the conversion rate of calcium oxide components. Desulfurization ash slag is significantly different from the above-mentioned solid wastes. Due to the high calcium content of desulfurization ash slag, it naturally has the advantage of combining with CO2 carbonation curing. Summary of the Invention

[0006] The purpose of this invention is to provide a circulating fluidized bed desulfurization ash non-fired brick and its preparation method, which realizes high utilization of desulfurization ash slag and in-situ CO2 capture, and has excellent "low carbon" characteristics and significant social and economic benefits.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A type of non-fired brick based on circulating fluidized bed desulfurization ash using carbonation curing, with circulating fluidized bed desulfurization ash, silicate cement, and carbide slag as cementing components, achieves carbonation hardening and strength generation of the non-fired brick through CO2 curing. The cementing components, by weight, are: 50-70 parts circulating fluidized bed desulfurization ash, 10-30 parts silicate cement, and 5-10 parts carbide slag.

[0009] Furthermore, the cementing component comprises circulating sulfur-fixing ash and an alkaline component, wherein the alkaline component mainly consists of silicate cement and carbide slag. The proportion range of the cementing component and the source of the alkaline component are determined based on the CaO composition of the circulating sulfur-fixing ash. When the CaO content of the undisturbed sulfur-fixing ash is less than 25%, the alkaline component must simultaneously contain silicate cement and carbide slag; when the CaO content of the undisturbed sulfur-fixing ash is greater than 25%, the alkaline component can be one or both of silicate cement and carbide slag.

[0010] Furthermore, in this invention, the fineness range of the circulating fluidized bed desulfurization ash is preferably 280-500 μm. 2 / kg, can be achieved by sieving, mechanical grinding and other measures to solidify sulfur ash slag.

[0011] Furthermore, this invention provides a method for preparing non-fired bricks based on sulfur-fixing ash slag using a circulating fluidized bed curing system. The method involves accurately proportioning the materials according to the aforementioned composition range of the circulating fluidized bed sulfur-fixing ash slag-based cementitious material, mixing it with water to obtain a uniformly mixed brick blank, allowing it to stand for a certain period, and then performing carbonation curing to obtain the sulfur-fixing ash slag-based non-fired bricks.

[0012] Furthermore, brick blanks can be prepared according to the strength grade of the unfired bricks. The cementitious material components mixed with water can be cast or pressed. Among them, a certain amount of concrete chemical admixtures can be introduced to adjust the fluidity when casting. Then, the brick blanks that have been left to stand for a certain period of time are placed into a CO2 reactor.

[0013] Furthermore, the carbonation and hydration hardening of the non-fired bricks are achieved through CO2 carbonation curing. The specific conditions for carbonation curing in the reactor are: temperature 25℃-50℃, reactor pressure 0.5-1.0MPa, curing time 24-48h, and the reaction medium is CO2.

[0014] Furthermore, the CO2 gas source for the reaction medium can be 99% high-purity gas, or it can be a CO2 mixed flue gas with a certain concentration range (30%-90%) obtained from the flue gas capture of coal-fired power plants, rotary kilns in cement plants, and boilers in steel plants.

[0015] The circulating fluidized bed desulfurization ash, as a solid waste, contains a high content of free CaO, meaning it contains a large number of calcium ions. Combined with CO2 mineralization and curing technology, under certain conditions, CO2 is hydrolyzed and ionized in solution to produce CO3. 2- It reacts chemically with calcium ions in the sulfur-fixing ash to form stable calcium carbonate, which is deposited on the surface of the specimen, enhancing its compressive strength and durability. The equation is: Ca 2+ +CO3 2- →CaCO3. This is the scientific basis for the novel non-fired bricks based on sulfur-fixing ash slag in this invention.

[0016] After carbonization, circulating fluidized bed desulfurization ash bricks undergo water curing, which further improves their compressive strength. The desulfurization ash contains SiO, CaO, CaSO3, and Al2O3, which, during the hydration reaction, generate CSH, CaOH2, etc. Carbonation, combined with subsequent hydration curing, does not negatively impact the matrix strength; on the contrary, it improves the matrix's performance. Because the carbonation treatment changes the pH range of the unfired bricks to between 8 and 10.0, the formation of ettringite within this range does not pose a risk of expansion and damage. This is a key technology in this invention that imparts good volume stability to the unfired bricks.

[0017] Circulating fluidized bed desulfurization ash typically contains high levels of SO3, which often causes expansion and cracking in hardened cement concrete, making its use in building materials a risky proposition. This invention, through carbonation curing technology, alters the type of hydration products, transforming the expansive hydration products ettringite and gypsum into calcite, aragonite, or aragonite, etc., thus endowing the unfired bricks with excellent volume stability and eliminating concerns about the stability issues caused by SO3.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] (1) This invention addresses the technical bottleneck that the high SO3 content of circulating fluidized bed desulfurization ash is usually limited in ordinary cement concrete. It proposes to use CO2 to achieve carbonation hardening and strength generation of non-fired bricks with circulating fluidized bed desulfurization ash as the main component, thereby realizing the high utilization of circulating fluidized bed desulfurization ash and making desulfurization ash no longer a "reluctant choice" as a building material.

[0020] (2) The raw materials for this invention are widely available, the preparation cost is low, and the technical route is simple and environmentally friendly. It not only solves the problem of large-scale solid waste disposal, but also utilizes CO2 emitted from the flue gas of my country's energy infrastructure enterprises, reducing the impact of the greenhouse effect on the environment. In addition, it can also bring high economic benefits.

[0021] (3) The non-fired brick proposed in this invention, which uses circulating fluidized bed solid sulfur ash as the main cementing component and absorbs CO2 from flue gas, also has good volume stability and adjustable strength grade, and is highly applicable to existing standards for sintered bricks and non-sintered bricks. Attached Figure Description

[0022] Figure 1 The compressive strength of the specimens before and after carbonation curing in the examples is shown.

[0023] Figure 2 The XRD patterns of the specimens before and after carbonation curing are shown in the examples. Detailed Implementation

[0024] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0025] Example 1

[0026] A circulating fluidized bed desulfurization ash residue from a power plant was mixed with ordinary Portland cement at a ratio of 7:3. Appropriate amounts of water and a water-reducing agent were added and stirred. The mixing process involved slow stirring for 1 minute followed by rapid stirring for 3 minutes. After stirring, bricks measuring 40mm × 40mm × 40mm were formed. The compressive strength before carbonation curing reached 3.5 MPa. After oxidation in a high-pressure reactor with 99% CO2 gas for 24 hours and 48 hours, the compressive strength was tested and found to be 22.63 MPa and 28.5 MPa, respectively. Because the desulfurization ash residue selected in this embodiment has a relatively high CaO content, the compressive strength of the bricks in this embodiment is relatively high.

[0027] Example 2

[0028] The circulating fluidized bed desulfurization ash from a power plant was mixed with ordinary silicate cement at a ratio of 7:3. Appropriate amounts of water and water-reducing agent were added and mixed. The mixture was first stirred slowly for 1 minute, then rapidly for 3 minutes. After mixing, bricks measuring 40mm × 40mm × 40mm were formed. The compressive strength before carbonation curing reached 1.81 MPa. After oxidation in a high-pressure reactor with 99% CO2 gas for 24 hours and 48 hours, the compressive strength was tested and found to be 8.3 MPa and 9.8 MPa, respectively.

[0029] Example 3

[0030] The circulating fluidized bed desulfurization ash from a power plant was mixed with ordinary silicate cement at a ratio of 7:3. Appropriate amounts of water and water-reducing agent were added and mixed. The mixture was first stirred slowly for 1 minute, then rapidly for 3 minutes. After mixing, bricks measuring 40mm × 40mm × 40mm were formed. The compressive strength before carbonation curing reached 1.81 MPa. After oxidation in a high-pressure reactor with 99% CO2 gas for 24 hours and 48 hours, the compressive strength was tested and found to be 9.7 MPa and 11.7 MPa, respectively.

[0031] Table 1. Main oxide content (%) of circulating fluidized bed desulfurization ash.

[0032] OPC 62.66 20.74 4.79 3.45 3.29 0.26 3 0.85 0.267 Example 1 29.09 27.44 14.55 14.36 7.57 1.79 1.7 0.799 0.767 Example 2 4.57 43.416 40.261 3.739 3.83 0.469 1.173 0.68 1.332 Example 3 21.82 36.88 22.38 6.57 6.96 0.79 0.75 1.11 1.34

[0033] Table 1 lists the circulating fluidized bed desulfurization ash from different power plants used in this invention, outlining the content of the main oxides in the ash.

[0034] Figure 1 The figures show the compressive strength of specimens before and after carbonation curing in this example. As can be seen from the figures, the compressive strength of the carbonated specimens is significantly higher than that of the control experiment, and the compressive strength gradually increases with the extension of carbonation time.

[0035] Figure 2 The figures show the XRD patterns of the specimens before and after carbonation curing in this example. As can be seen from the figures, after carbonation curing, the gypsum content gradually decreases and gradually transforms into calcium carbonate. Notably, not only calcite is present after carbonation curing, but aragonite is also formed.

[0036] Example 4

[0037] One hundred portions of circulating fluidized bed desulfurization ash from a power plant were selected, mixed with 20% water, and pressed into bricks with dimensions of 25mm×25mm×25mm using a pressure of 30MPa. The compressive strength before carbonation curing reached 1.41MPa. After oxidation in a high-pressure reactor with 99% CO2 gas for 24h and 48h, the compressive strength was tested and found to be 9.43MPa and 11.42MPa, respectively.

[0038] Example 5

[0039] 85 parts of circulating fluidized bed desulfurization ash from a power plant were mixed with 5 parts of ordinary silicate cement and 10 parts of carbide slag. Appropriate amounts of water and water-reducing agent were added and stirred. The mixture was first stirred slowly for 1 minute, then rapidly for 3 minutes. After stirring, bricks of 40mm×40mm×40mm were formed. The compressive strength before carbonation curing reached 1.77MPa. After oxidation in a high-pressure reactor with 99% CO2 gas for 24 hours and 48 hours, the compressive strength was tested and found to be 9.23MPa and 11.75MPa, respectively.

[0040] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A circulating fluidized bed solid sulfur ash non-fired brick, characterized in that: The cementing component is at least one of circulating fluidized bed desulfurization ash, silicate cement, and carbide slag; the cementing component, by weight, is: 50-70 parts circulating fluidized bed desulfurization ash, 10-30 parts silicate cement, and 5-10 parts carbide slag; the unfired bricks are carbonated and hardened through CO2 curing.

2. The circulating fluidized bed desulfurization ash non-fired brick according to claim 1, characterized in that: The fineness of the circulating fluidized bed desulfurization ash is 300-500 μm. 2 / kg.

3. A method for preparing circulating fluidized bed desulfurized ash non-fired bricks as described in claim 1: characterized in that: Includes the following steps: (1) Dry and sieve the circulating fluidized bed desulfurization ash to obtain circulating fluidized bed desulfurization ash with a particle size of less than 0.075 mm. Mix it with at least one of silicate cement and carbide slag, add water and water-reducing agent and mix evenly to make brick blanks. (2) The brick blanks are subjected to CO2 carbonation curing to obtain the circulating fluidized bed solid sulfur ash non-fired bricks.

4. The method according to claim 3, characterized in that: The brick blanks are formed by casting or pressing.

5. The method according to claim 3, characterized in that: The CO2 carbonation curing conditions are as follows: temperature 25℃-50℃, reactor pressure 0.5-1.0MPa, and curing time 2-48h.

6. The method according to claim 5, characterized in that: The CO2 gas concentration in the reactor is greater than 50%.

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