Corundum castable special for circulating fluidized bed boiler and preparation method thereof

Abstract

The application belongs to the technical field of refractory materials, and particularly relates to a corundum castable special for a circulating fluidized bed boiler and a preparation method thereof. The raw materials of the castable include 20-50 parts of white corundum particles with a size of 3-5 mm, 5-10 parts of alpha-alumina micropowder, 2-5 parts of microsilica, 1-5 parts of a binder, 0.5-1 part of a water reducing agent, and 1-5 parts of SiC-ZrB2 / chitosan quaternary ammonium salt modified graphene composite material. The castable has the properties of low apparent porosity, good mechanical properties, strong corrosion resistance and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of refractory materials, and particularly relates to a corundum castable special for a circulating fluidized bed boiler and a preparation method thereof. BACKGROUND

[0002] The circulating fluidized bed boiler is a thermal equipment used in the metallurgy, power, building material and other industries, and mainly comprises a combustion chamber and a circulating boiler. The circulating fluidized bed boiler needs to burn different materials to continuously supply energy. The materials are collided at high speed in the circulating fluidized bed boiler, and the airflow in the boiler and the materials continuously scour the lining of the boiler. If a good refractory material is not used for the lining of the circulating fluidized bed boiler, the circulating fluidized bed boiler cannot normally operate.

[0003] The corundum castable is an unshaped refractory material prepared by taking corundum as a main raw material and adding binders and admixtures required in preparation. The corundum castable is a widely used refractory material at present. In addition, graphite has the characteristics of poor wetting by molten slag, small thermal expansion coefficient and high thermal conductivity. The introduction of graphite into the refractory material can significantly improve the slag erosion resistance and thermal shock stability of the refractory material. However, the application of graphite in the refractory castable is limited to a certain extent: 1) graphite has poor water wettability and is easy to float and difficult to uniformly disperse in the castable; 2) a large amount of water needs to be added to the carbon-containing castable to achieve appropriate construction fluidity after the graphite is added to the castable, which finally increases the porosity of the castable and deteriorates the use performance of the castable; 3) graphite is easy to oxidize at high temperature. The addition of an antioxidant such as Al powder to prevent oxidation of graphite can easily cause hydration of the castable during construction, resulting in expansion and loose structure of the product. These factors reduce the use performance of the carbon-containing castable to a certain extent and hinder the application of graphite in the castable.

[0004] Therefore, it is urgent to develop a corundum castable special for a circulating fluidized bed boiler, which contains modified graphene and has low apparent porosity, good mechanical properties and corrosion resistance. SUMMARY

[0005] The application aims to provide a corundum castable special for a circulating fluidized bed boiler containing modified graphene and a preparation process thereof, so as to solve the problems of high apparent porosity, poor mechanical properties and poor corrosion resistance in the prior art.

[0006] To solve the above technical problems, the application provides the following technical solutions.

[0007] A corundum castable special for circulating fluidized bed boilers, raw materials of which include, in parts by weight, 20-50 parts of white corundum particles of 3-5 mm, 5-10 parts of alpha-alumina micropowder, 2-5 parts of microsilica, 1-5 parts of a binder, 0.5-1 part of a water reducing agent, and 1-5 parts of SiC-ZrB2 / chitosan quaternary ammonium salt modified graphene composite.

[0008] In some embodiments, the method for preparing the SiC-ZrB2 / chitosan quaternary ammonium salt modified graphene composite comprises the following steps:

[0009] 1) Preparation of chitosan quaternary ammonium salt modified graphene: graphene oxide and deionized water are mixed and ultrasonically dispersed to prepare a graphene oxide solution, and chitosan quaternary ammonium salt is dissolved in deionized water to prepare a chitosan quaternary ammonium salt aqueous solution; the graphene oxide solution and the chitosan quaternary ammonium salt aqueous solution are mixed and stirred uniformly, a prepared NaOH aqueous solution is used to adjust the pH value of the mixed solution to 10, and then a hydrazine hydrate solution is added to react to obtain chitosan quaternary ammonium salt modified graphene.

[0010] 2) Preparation of SiC-ZrB2 composite: KCl and NaCl are used as molten salt, and then SiO2, activated carbon, B4C and ZrO2 are added; the mixture is mixed uniformly in an agate mortar, poured into a corundum crucible, and then placed in a microwave oven to react in an argon environment to obtain a SiC-ZrB2 composite.

[0011] 3) Preparation of SiC-ZrB2 / chitosan quaternary ammonium salt modified graphene composite: the chitosan quaternary ammonium salt modified graphene and the SiC-ZrB2 composite are placed in a stainless steel ball mill jar, and are placed in a planetary ball mill according to a ball-to-material ratio of 1-5:1 for ball milling and uniform mixing to obtain a SiC-ZrB2 / chitosan quaternary ammonium salt modified graphene composite.

[0012] In some embodiments, the mass ratio of graphene oxide to chitosan quaternary ammonium salt is 1:(1-5); the mass ratio of KCl to NaCl is 1:(1-1.2); and the mass ratio of SiO2, activated carbon, B4C and ZrO2 is 1:(1-1.5):(0.5-1):(2-3).

[0013] In some embodiments, the binder is selected from one or more of polyvinyl alcohol, aluminum metaphosphate and magnesium silicate; preferably, the binder is prepared by mixing polyvinyl alcohol, aluminum metaphosphate and magnesium silicate in a weight ratio of 1:1:1.

[0014] In some embodiments, the water reducing agent is selected from one or more of BASF F10, sodium tripolyphosphate and sodium alginate.

[0015] In some embodiments, the Al2O3 content in the alpha-alumina micropowder is greater than or equal to 98%, and the particle size is 1-1.5 microns.

[0016] In some embodiments, the SiO2 content in the microsilica powder is greater than or equal to 95%, and the particle size is 0.5-1.0 microns.

[0017] In another aspect, the application also provides a preparation method of the corundum castable for circulating fluidized bed boilers, characterized in that the method comprises the following steps:

[0018] The raw materials are weighed according to the ratio, the white corundum particles, the alpha-alumina micropowder, the microsilica powder, the binder, the water reducing agent, the SiC-ZrB2 / quaternary ammonium salt of chitosan modified graphene composite material are added into a mixer and uniformly mixed, then 1-3% of water based on the total mass of the materials is added, and the circulating fluidized bed boiler corundum castable is obtained by stirring.

[0019] The application has the following beneficial effects:

[0020] 1) The castable obtained by the application has low apparent porosity, good mechanical properties, and strong corrosion resistance.

[0021] 2) The quaternary ammonium salt of chitosan used in the application is combined with graphene oxide through electrostatic interaction, and then hydrazine hydrate is used for reduction to obtain graphene modified by the quaternary ammonium salt of chitosan. The graphene modified by the quaternary ammonium salt of chitosan has excellent wettability and dispersibility, which can reduce the water demand of the castable, thereby reducing the porosity, improving the compressive and bending strengths, and improving the corrosion resistance.

[0022] 3) SiC-ZrB2 also has excellent high-temperature performance, good water wettability and dispersibility, and its use together with graphene modified by the quaternary ammonium salt of chitosan can maximize the mechanical properties and corrosion resistance of the castable. DETAILED DESCRIPTION

[0023] The technical solutions of the application will be described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0024] Preparation of SiC-ZrB2 / quaternary ammonium salt of chitosan modified graphene composite material

[0025] (1) Preparation of chitosan quaternary ammonium salt modified graphene: graphene oxide (1.0 g) and deionized water (100 mL) were mixed and ultrasonically dispersed to prepare a graphene oxide solution, and chitosan quaternary ammonium salt (HACC) (3.0 g) was dissolved in deionized water (100 mL) to prepare a chitosan quaternary ammonium salt aqueous solution; the above graphene oxide solution and chitosan quaternary ammonium salt aqueous solution were mixed and stirred uniformly, and a prepared NaOH aqueous solution was used to adjust the pH value of the above mixed solution to 10, then a hydrazine hydrate solution (80% by mass, 4.0 g) was added, and the temperature was raised to 100°C for reaction for 5h. After the reaction, filtration was performed, and the obtained filter cake was washed with deionized water for multiple times, and then dried at 100°C for 24h to obtain chitosan quaternary ammonium salt modified graphene.

[0026] (2) Preparation of SiC-ZrB2 composite material: KCl (1.0 g) and NaCl (1.0 g) were used as molten salt, and then SiO2 (1.0 g), activated carbon (1.0 g), B4C (0.5 g) and ZrO2 (1.0 g) were added, and the above mixture was mixed uniformly in an agate mortar, and then poured into a corundum crucible, and then placed in a microwave oven, and then heated at a rate of 10°C·min -1 -1 to 1200°C under an argon atmosphere, and then reacted for 20 min, and then naturally cooled to room temperature. The obtained product was washed with deionized water, and the obtained filter cake was dried at 90°C for 10h to obtain a SiC-ZrB2 composite material.

[0027] (3) Preparation of SiC-ZrB2 / modified graphene composite material: 10.0 g of chitosan quaternary ammonium salt modified graphene and 10.0 g of SiC-ZrB2 composite material were placed in a stainless steel ball mill jar, and then placed in a planetary ball mill according to a ball-to-material ratio of 5:1, and then ball-milled uniformly at a speed of 300 rpm for 5h to obtain a SiC-ZrB2 / modified graphene composite material.

[0028] Example 1

[0029] A corundum castable special for circulating fluidized bed boilers, in terms of weight parts, includes the following raw materials: 30 parts of 5mm white corundum particles, 10 parts of α-alumina micropowder, 5 parts of microsilica, 2 parts of binder, 0.5 parts of water reducing agent, 5 parts of SiC-ZrB2 / chitosan quaternary ammonium salt modified graphene composite material obtained in Preparation Example 1;

[0030] The binder is prepared by mixing polyvinyl alcohol, aluminum metaphosphate and magnesium silicate in a weight ratio of 1:1:1;

[0031] The water reducing agent is sodium tripolyphosphate;

[0032] The α-alumina micropowder contains Al2O3≥98%, and has a particle size of 1-1.5μm.

[0033] The SiO2 content in the micro-silicon powder is ≥95%, and the particle size is 0.5-1.0 μm.

[0034] The corundum castable is prepared by the following steps:

[0035] The raw materials are weighed according to the proportion, the white corundum particles, the α-alumina micro powder, the micro-silicon powder, the binder, the water reducing agent, and the SiC-ZrB2 / chitosan quaternary ammonium salt modified graphene composite material obtained in Preparation Example 1 are added into a stirrer and mixed for 30 min, then 1% of water based on the total mass of the materials is added, and the stirring is continued for 30 min, to obtain the corundum castable special for circulating fluidized bed boilers.

[0036] Example 2

[0037] A corundum castable special for circulating fluidized bed boilers, in terms of weight parts, includes the following raw materials: 4 mm white corundum particles 25 parts, α-alumina micro powder 8 parts, micro-silicon powder 5 parts, binder 5 parts, water reducing agent 1 part, and SiC-ZrB2 / chitosan quaternary ammonium salt modified graphene composite material 2 parts.

[0038] The binder is prepared by mixing polyvinyl alcohol, aluminum metaphosphate, and magnesium silicate in a weight ratio of 1:1:1;

[0039] The water reducing agent is BASF F10 from Germany.

[0040] The Al2O3 content in the α-alumina micro powder is ≥98%, and the particle size is 1-1.5 μm.

[0041] The SiO2 content in the micro-silicon powder is ≥95%, and the particle size is 0.5-1.0 μm.

[0042] The corundum castable is prepared by the following steps:

[0043] The raw materials are weighed according to the proportion, the white corundum particles, the α-alumina micro powder, the micro-silicon powder, the binder, the water reducing agent, and the SiC-ZrB2 / chitosan quaternary ammonium salt modified graphene composite material obtained in Preparation Example 1 are added into a stirrer and mixed for 30 min, then 1% of water based on the total mass of the materials is added, and the stirring is continued for 30 min, to obtain the corundum castable special for circulating fluidized bed boilers.

[0044] Comparative Example 1

[0045] On the basis of Example 1, the SiC-ZrB2 / chitosan quaternary ammonium salt modified graphene composite material is replaced by graphene oxide

[0046] A corundum castable special for circulating fluidized bed boilers, in terms of weight parts, includes the following raw materials: 5 mm white corundum particles 30 parts, α-alumina micro powder 10 parts, micro-silicon powder 5 parts, binder 2 parts, water reducing agent 0.5 parts, and graphene oxide 5 parts.

[0047] The binder is prepared by mixing polyvinyl alcohol, aluminum metaphosphate and magnesium silicate in a weight ratio of 1:1:1;

[0048] The water reducing agent is sodium tripolyphosphate;

[0049] The Al2O3 content of the α-alumina micropowder is ≥98%, and the particle size is 1-1.5 μm.

[0050] The SiO2 content of the microsilica is ≥95%, and the particle size is 0.5-1.0 μm.

[0051] The corundum castable is prepared by the following steps:

[0052] The raw materials are weighed according to the proportion, the white corundum particles, the α-alumina micropowder, the microsilica, the binder, the water reducing agent and the chitosan quaternary ammonium salt modified graphene obtained in step (1) of Preparation Example 1 are mixed in a mixer for 30 min, then 10% of water based on the total mass of the materials is added, and the stirring is continued for 30 min to obtain the special corundum castable for circulating fluidized bed boilers.

[0053] Comparative Example 2

[0054] On the basis of Example 1, the SiC-ZrB2 / chitosan quaternary ammonium salt modified graphene composite material is replaced by chitosan quaternary ammonium salt modified graphene

[0055] A special corundum castable for circulating fluidized bed boilers, in terms of weight parts, includes the following raw materials: 30 parts of 5mm white corundum particles, 10 parts of α-alumina micropowder, 5 parts of microsilica, 2 parts of binder, 0.5 parts of water reducing agent, and 5 parts of chitosan quaternary ammonium salt modified graphene obtained in step (1) of Preparation Example 1.

[0056] The binder is prepared by mixing polyvinyl alcohol, aluminum metaphosphate and magnesium silicate in a weight ratio of 1:1:1;

[0057] The water reducing agent is sodium tripolyphosphate;

[0058] The Al2O3 content of the α-alumina micropowder is ≥98%, and the particle size is 1-1.5 μm.

[0059] The SiO2 content of the microsilica is ≥95%, and the particle size is 0.5-1.0 μm.

[0060] The corundum castable is prepared by the following steps:

[0061] The raw materials are weighed according to the proportion, the white corundum particles, the α-alumina micropowder, the microsilica, the binder, the water reducing agent and the chitosan quaternary ammonium salt modified graphene obtained in step (1) of Preparation Example 1 are mixed in a mixer for 30 min, then 10% of water based on the total mass of the materials is added, and the stirring is continued for 30 min to obtain the special corundum castable for circulating fluidized bed boilers.

[0062] Comparative Example 3

[0063] On the basis of Example 1, the SiC-ZrB2 / chitosan quaternary ammonium salt modified graphene composite material is replaced by SiC-ZrB2 composite material

[0064] A corundum castable special for circulating fluidized bed boiler, raw materials of which include, by weight: 30 parts of 5mm white corundum particles, 10 parts of α-alumina micropowder, 5 parts of microsilica, 2 parts of binder, 0.5 parts of water reducing agent, 5 parts of SiC-ZrB2 composite material obtained in step (2) of Preparation Example 1;

[0065] The binder is prepared by mixing polyvinyl alcohol, aluminum metaphosphate and magnesium silicate in a weight ratio of 1:1:1;

[0066] The water reducing agent is sodium tripolyphosphate;

[0067] The α-alumina micropowder contains ≥98% Al2O3 and has a particle size of 1-1.5 μm.

[0068] The microsilica contains ≥95% SiO2 and has a particle size of 0.5-1.0 μm.

[0069] The above corundum castable is prepared by the following steps:

[0070] The raw materials are weighed according to the proportions, the white corundum particles, α-alumina micropowder, microsilica, binder, water reducing agent and chitosan quaternary ammonium salt modified graphene obtained in step (2) of Preparation Example 1 are mixed in a mixer for 30 min, then 1% of water based on the total mass of the materials is added, and the stirring is continued for 30 min to obtain the corundum castable special for circulating fluidized bed boiler.

[0071] Performance test

[0072] The castables of Examples 1-2 and Comparative Examples 1-3 are subjected to performance test, and the test process is as follows: the castables are injected into a mold, then vibration forming is carried out on a vibration table, demolding is carried out after 2 days of curing, drying is carried out at 120℃ for 24h, then cooling to room temperature, and the related properties are tested, and the results are shown in Table 1.

[0073] The apparent porosity is tested in accordance with the standard GB / T 2997-2015;

[0074] The high temperature compressive strength is tested in accordance with GB / T 34218-2017 “Test method for high temperature compressive strength of refractory materials”, wherein the test temperature is 1400℃, the holding time is 3h, the heating rate is 10℃ / min, and the loading rate is 1.0MPa / s;

[0075] The high-temperature bending strength is tested according to GB / T 3002-2017 'Method for testing high-temperature bending strength of refractory materials', wherein the test temperature is 1400 DEG C, the holding time is 3h, the heating rate is 5 DEG C / min, and the loading rate is 0.15 MPa / s;

[0076] Corrosion resistance test: the weight loss after 24h of immersion in 10% sulfuric acid and 10% sodium hydroxide is tested.

[0077] Table 1: Performance test results of castable

[0078]

[0079]

[0080] As shown in Table 1, the castable material obtained by the application has low apparent porosity, good mechanical properties, and strong corrosion resistance. The main reason is that graphite has poor performance in castable due to its low density, poor wettability and dispersibility. The chitosan quaternary ammonium salt (HACC) used in the application is combined with graphene oxide through electrostatic interaction, and then reduced by hydrazine hydrate to obtain chitosan quaternary ammonium salt modified graphene. The chitosan quaternary ammonium salt modified graphene has excellent wettability and dispersibility, which can reduce the water demand of the castable (as shown in Examples 1-2, the water demand is only 1%), thereby reducing the porosity, improving the compressive and bending strength, and improving the corrosion resistance. In addition, SiC-ZrB2 also has excellent high-temperature performance, good water wettability and dispersibility, and its use with chitosan quaternary ammonium salt modified graphene can maximize the improvement of the mechanical properties and corrosion resistance of the castable.

[0081] The above examples are preferred embodiments of the application, but the embodiments of the application are not limited by the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the application are equivalent replacement methods and are included in the protection scope of the application.

Claims

1. A corundum castable for circulating fluidized bed boilers, characterized in that, By weight, the raw materials include: 20-50 parts of 3-5mm white corundum particles, 5-10 parts of α-alumina micro powder, 2-5 parts of microsilica powder, 1-5 parts of binder, 0.5-1 parts of water-reducing agent, and 1-5 parts of SiC-ZrB2 / chitosan quaternary ammonium salt modified graphene composite material. The preparation method of the SiC-ZrB2 / chitosan quaternary ammonium salt modified graphene composite material includes the following steps: 1) Preparation of chitosan quaternary ammonium salt modified graphene: graphene oxide and deionized water were mixed and ultrasonically dispersed to obtain a graphene oxide solution. Chitosan quaternary ammonium salt was dissolved in deionized water to obtain a chitosan quaternary ammonium salt aqueous solution. The above graphene oxide solution and chitosan quaternary ammonium salt aqueous solution were mixed and stirred evenly. The pH value of the above mixed solution was adjusted to 10 with a prepared NaOH aqueous solution. Then, hydrazine hydrate solution was added to react and obtain chitosan quaternary ammonium salt modified graphene. 2) Preparation of SiC-ZrB2 composite material: KCl and NaCl were used as molten salts, and then SiO2, activated carbon, B4C and ZrO2 were added. The mixture was mixed evenly in an agate mortar, poured into a corundum crucible and placed in a microwave oven. The reaction was carried out in an argon atmosphere to obtain SiC-ZrB2 composite material. 3) Preparation of SiC-ZrB2 / chitosan quaternary ammonium salt modified graphene composite material: Chitosan quaternary ammonium salt modified graphene and SiC-ZrB2 composite material were placed in a stainless steel ball mill jar and ball milled in a planetary ball mill at a ball-to-material ratio of (1-5):1 to obtain SiC-ZrB2 / chitosan quaternary ammonium salt modified graphene composite material.

2. The corundum castable for circulating fluidized bed boilers according to claim 1, characterized in that, The mass ratio of graphene oxide to chitosan quaternary ammonium salt is 1:(1-5); the mass ratio of KCl to NaCl is 1:(1-1.2); and the mass ratio of SiO2, activated carbon, B4C to ZrO2 is 1:(1-1.5):(0.5-1):(2-3).

3. The corundum castable for circulating fluidized bed boilers according to claim 1, characterized in that, The adhesive is selected from one or more of polyvinyl alcohol, aluminum metaphosphate, and magnesium silicate.

4. The corundum castable for circulating fluidized bed boilers according to claim 3, characterized in that, The adhesive is prepared by mixing polyvinyl alcohol, aluminum metaphosphate and magnesium silicate in a weight ratio of 1:1:

1.

5. The corundum castable for circulating fluidized bed boilers according to claim 1, characterized in that, The water-reducing agent is selected from one or more of BASF F10, sodium tripolyphosphate, and sodium alginate.

6. The corundum castable for circulating fluidized bed boilers according to claim 1, characterized in that, The α-alumina micro powder has an Al2O3 content of ≥98% and a particle size of 1-1.5μm.

7. The corundum castable for circulating fluidized bed boilers according to claim 1, characterized in that, The microsilica powder contains ≥95% SiO2 and has a particle size of 0.5–1.0 μm.

8. The preparation method of the corundum castable for circulating fluidized bed boilers according to any one of claims 1-7, characterized in that, Includes the following steps: Weigh each raw material according to the formula, add white corundum particles, α-alumina micro powder, silica powder, binder, water-reducing agent, and SiC-ZrB2 / chitosan quaternary ammonium salt modified graphene composite material to a mixer and mix evenly. Then add water accounting for 1% to 3% of the total mass of the materials and stir to obtain corundum castable for circulating fluidized bed boilers.

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