Combined preparation process of cement and biochar

Abstract

The invention relates to the technical field of cement and biochar preparation, and discloses a combined preparation process of cement and biochar, which combines a cement preparation process with a biochar preparation process to fully utilize materials and energy, reduce cost and reduce environmental pollution. The method comprises the specific combined steps that waste gas generated in a rotary kiln of the cement preparation technology is recycled and then conveyed to a drying step of the biochar preparation technology, waste utilization is carried out, gas components and heat in the waste gas are used for optimizing the performance of the prepared biochar, and meanwhile energy is saved; the waste heat in the rotary kiln and the hot material warehouse in the cement preparation process is recovered into the heat exchanger, and then the waste heat is distributed to the drying and carbonization combustion steps of the biochar preparation process for secondary heat utilization, so that energy is fully saved, and external energy consumption in the biochar preparation process is reduced. After combination, the energy utilization rate is high, the cost is low, the material quality is better, and remarkable advantages are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of cement and biochar, and in particular to a combined preparation process of cement and biochar. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] The traditional cement production process requires high-temperature calcination of raw materials, which consumes a lot of energy and produces large carbon emissions. At the same time, byproducts produced during the biochar production process, such as heat and dust, are usually difficult to use effectively. In the prior art, cement production and biochar production are often carried out separately, which fails to achieve efficient utilization of resources and energy. The specific defects are as follows:

[0004] (1) Excessive energy consumption: Traditional cement preparation and biochar preparation are carried out separately, and the thermal energy cannot be effectively shared, resulting in high overall energy consumption.

[0005] (2) High production cost: The traditional separation production process does not reuse resources, resulting in resource waste and increased production costs.

[0006] (3) Waste of by-products and environmental pollution: The dust by-products generated during the preparation of biochar are difficult to utilize effectively and are usually treated as waste. The high carbon emissions during cement production and the emission of dust by-products during biochar production also pose environmental pollution problems.

[0007] (4) Insufficient optimization of product performance: The performance of cement produced by traditional cement preparation process is poor. Even if the separately produced biochar is added to cement, the optimization of cement performance is limited. Summary of the invention

[0008] The purpose of the present invention is to provide a combined preparation process of cement and biochar in response to the defects of the current cement preparation and biochar preparation processes, which cleverly combines the two processes in a linked manner, can not only fully utilize the heat in the two processes, but also can fully utilize the by-products in the two preparation processes.

[0009] The technical solution of the present invention is as follows:

[0010] A combined preparation process of cement and biochar, wherein the cement preparation process and the biochar preparation process respectively comprise the following steps:

[0011] The biochar preparation process specifically includes the following steps:

[0012] Step (1): biomass harvesting;

[0013] Step (2): drying the biomass;

[0014] Step (3): biomass carbonization and combustion;

[0015] Step (4): grinding in a mill;

[0016] Step (5): Harvesting of finished biochar products.

[0017] The cement preparation process specifically includes the following steps:

[0018] Step (1): limestone mining;

[0019] Step (2): limestone enters the rotary kiln;

[0020] Step (3): limestone enters the hot material storage;

[0021] Step (4): Harvesting of finished cement products.

[0022] The specific combination of cement preparation process and biochar preparation process is as follows:

[0023] The first-stage waste gas generated in the rotary kiln of step (2) of the cement preparation process is recovered and filtered through a waste gas treatment device to remove large particles of dust (0.5 microns and above) and then transported to the biomass drying step (2) of the biochar preparation process. The heat carried by the waste gas is used to dry the biomass. At the same time, the carbon dioxide and nitrogen oxides (NO x ) and other gas components react with the biomass during the biomass drying process to achieve waste gas utilization and optimize biochar performance.

[0024] The waste heat of the second-stage exhaust gas of the rotary kiln and the waste heat of the exhaust gas in the hot material storage in steps (2) and (3) of the cement preparation process are recovered to the heat exchanger, and then the heat is redistributed to steps (2) and (3) in the biochar preparation process for heat utilization.

[0025] The exhaust gas entering the heat exchanger is first recovered and filtered to reduce the concentration of particulate matter to 0.01 to 1 mg / m 3 After that, it enters the heat exchanger.

[0026] The dust generated in the biochar preparation process in step (2), step (3) and step (4) is collected and processed, and finally blended into the cement product to optimize the performance of the cement product. Preferably, the dust can also be reused in step (2) of the cement preparation process as a partial alternative fuel.

[0027] Preferably, the dust collection and treatment generated by the biochar preparation specifically includes the following steps:

[0028] Use dust collector to capture dust in the airflow; store in a sealed manner to prevent secondary dusting;

[0029] The airflow after dust capture is processed by a gas purification device until the emission meets environmental protection standards, and the gas is discharged.

[0030] Preferably, the dust collector can be a bag dust collector, which has high efficiency and is suitable for treating fine particles; more preferably, the dust collector can be an electrostatic dust collector, which is suitable for treating high-concentration dust, is energy-saving and has significant effects.

[0031] Preferably, the gas purification device can be a gas washing tower, which absorbs and removes dust through washing liquid and purifies the gas at the same time to ensure that the emissions meet environmental protection standards.

[0032] Preferably, the collected dust can be transported to the cement production line using a screw conveyor or pneumatic conveying system to ensure efficient transfer.

[0033] The prepared biochar product is mixed into the cement product to optimize the performance of the cement product. Preferably, the prepared biochar product can also be reused as a partial alternative fuel in step (2) of the cement preparation process.

[0034] During the biochar preparation process, combustible gases such as carbon monoxide and methane are produced, which can be recycled as a partial alternative fuel in step (2) of the cement preparation process to provide additional heat to support the calcination of cement clinker and replace part of the traditional fossil fuels. The specific replacement ratio depends on the combustible gas output. Generally, the combustible gas produced during the production of 1 t of biochar can replace 30 kg of coal powder.

[0035] Preferably, the first-stage waste gas is the waste gas generated in the first 4 / 5 of the working process of the rotary kiln; and the second-stage waste gas is the waste gas generated in the last 1 / 5 of the working process of the rotary kiln.

[0036] According to a preferred embodiment, the first-stage waste gas of the present application is also subjected to oxygen content detection. When the oxygen content exceeds the permissible threshold of the drying step, a small amount of inert gas is additionally added to the first-stage waste gas to make the oxygen concentration of the first-stage waste gas lower than the permissible threshold of the drying step. Preferably, the permissible threshold is, for example, 5%.

[0037] According to a preferred embodiment, the heat exchanger recovers heat in a manner of only recovering the heat carried by the gas in the rotary kiln and the hot material storage, and only transports the recovered heat to the drying step and the carbonization combustion step of the biochar preparation process.

[0038] According to a preferred embodiment, the heat redistribution method in the heat exchanger is:

[0039] The heat exchanger is divided into a relatively independent drying section and a carbonization section. The heat recovered in the drying section is transported to the drying step of the biochar preparation process, and the heat recovered in the carbonization section is transported to the carbonization and combustion step of the biochar preparation process.

[0040] According to the heat demand of the drying step and the carbonization and combustion step, the total heat recovered by the drying step and the carbonization section is controlled by controlling the amount of exhaust gas entering the drying section and the carbonization section, thereby controlling the heat input into the drying step and the carbonization and combustion step.

[0041] According to a preferred embodiment, the method for controlling the amount of exhaust gas entering the drying section and the carbonization section is: a flow-controllable distribution valve is set on the exhaust gas outlet of the rotary kiln and the hot material storage, and the gas of the rotary kiln or the hot material storage is dynamically diverted to the drying section and the carbonization section according to demand.

[0042] According to a preferred embodiment, when the heat supplied by the heat exchanger is insufficient, energy is supplied to the steps (2) and (3) of the biochar production by auxiliary heating.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1. A combined preparation process of cement and biochar. In this process, the high-temperature gas (300-400°C) emitted by the cement kiln is highly matched with the drying and carbonization temperature requirements (150-600°C) of the biochar carbonization furnace. The heat transfer efficiency can reach 85%. Other processes cannot achieve such a high heat transfer efficiency if they are not within this temperature range.

[0045] 2. A combined preparation process of cement and biochar. In a cement kiln, the high-temperature gas produced by calcination contains not only a large amount of heat energy, but also special gas components, such as carbon dioxide (main component) and a small amount of nitrogen oxides.

[0046] 1) After proper dust removal, these gases enter the biochar preparation process, which can promote the pyrolysis reaction of biomass, making the biochar have a higher specific surface area and a more developed pore structure. This reaction requires the participation of specific gas components, and the gas produced in cement production can significantly optimize the biochar preparation.

[0047] 2) At the same time, carbon dioxide can react with the active sites on the surface of biochar to generate various oxygen-containing functional groups, such as carboxyl and carbonyl. The presence of these functional groups can affect the surface properties of biochar, making it have better adsorption performance. It will also significantly improve the hydrophilicity of the generated biochar, increase the rate of later hydration reactions, and enhance the early strength of biochar-doped concrete.

[0048] 3) Furthermore, the carbon dioxide in the high-temperature gas produced by calcination will also significantly inhibit the production of methane during the biochar preparation process.

[0049] 4) At high temperatures, carbon dioxide can react with carbon in biochar to produce carbon monoxide, helping the carbonization reaction process to be self-sustaining.

[0050] 5) Biomass contains alkali metal or alkaline earth metal elements. At high temperatures, these elements can react with carbon dioxide to generate corresponding carbonates, thereby achieving carbon fixation.

[0051] 6) The exhaust gas contains a small amount of nitrogen oxides (NO x ), nitrogen oxides can promote the formation of nitrogen-containing functional groups on the surface of biochar. These nitrogen-containing functional groups can increase the adsorption capacity and reaction activity of biochar in cement, thereby improving the anti-cracking performance of cement. Experimental data show that in NO x At a concentration of 200ppm, the nitrogen content on the surface of biochar increased by 30%. The role of biochar particles treated with waste heat from cement kilns in cement paste is not only physical filling, but also the formation of weak chemical bonds with calcium ions in cement through their surface oxygen-containing functional groups. This bonding method can significantly enhance the mechanical properties of cement, increasing the compressive strength by about 10% and the flexural strength by 15%.

[0052] 7) Through microscopic analysis and rheological tests, it was found that the dispersion of biochar particles treated with waste heat from cement kilns was 25% higher than that of untreated biochar in cement. This evenly distributed biochar can more effectively act as a microporous template, promote the uniform distribution of cement hydration products, and ultimately improve the compressive strength of cement. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a schematic diagram of a process for the combined preparation of cement and biochar;

[0054] Figure 2 This is a cross-sectional SEM image of the biochar prepared in Example 3;

[0055] Figure 3 This is the surface SEM image of the biochar prepared in Example 3;

[0056] Figure 4 A schematic diagram of the surface contact angle of the biochar prepared in Example 3;

[0057] Figure 5 Schematic diagram of the surface contact angle of the biochar prepared in Example 1;

[0058] Figure 6 A schematic diagram showing the variation of the adsorption and desorption performance of the biochar prepared in Example 3 with pressure;

[0059] Figure 7 This is the EDS image of the biochar prepared in Example 3. DETAILED DESCRIPTION

[0060] The specific embodiments listed in the present invention are only examples of the present invention, and the present invention is not limited to the specific embodiments described below. For those skilled in the art, any equivalent modifications and substitutions to the embodiments described below are also within the scope of the present invention. Therefore, the equal transformations and modifications made without departing from the spirit and scope of the present invention should be included in the scope of the present invention. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturers are not specified for all reagents or instruments, they are all conventional products that can be purchased commercially. In order to better illustrate the present invention, numerous specific details are given in the specific embodiments below. It should be understood by those skilled in the art that the present invention can also be implemented without certain specific details. In other embodiments, the methods, means, equipment and steps well known to those skilled in the art are not described in detail to highlight the purport of the present invention.

[0061] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art. Unless otherwise specified, the units used in this specification are all international standard units, and the numerical values ​​and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0062] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0063] Example 1 Biochar Preparation Process

[0064] This embodiment provides a separate biochar preparation process.

[0065] The preparation process specifically comprises the following steps:

[0066] Step (1): harvesting biomass; the type of biomass is rice husk;

[0067] Step (2): Biomass drying: After the pretreatment, the biomass raw material is dried at 200° C. to remove moisture, thereby obtaining a dry raw material with a moisture content of less than 10%;

[0068] Step (3): Biomass carbonization and combustion: the dried biomass raw material is fed into a carbonization furnace, and the biochar carbonization temperature is 500° C. for carbonization reaction to generate biochar and gas by-products.

[0069] Step (4): grinding in a mill to a particle size of 5-7 μm;

[0070] Step (5): Harvesting of finished biochar products.

[0071] The properties of the biochar prepared in this example are as follows:

[0072] Biochar specific surface area: 37.7982m 2 / g;

[0073] Biochar pore structure: mesoporous structure: 12.5123-13.6459nm;

[0074] Hydrophilic properties of biochar: It is highly hydrophilic, with a surface contact angle of 10.2 degrees.

[0075] The biochar prepared in this example was added to cement slurry and was evenly dispersed in the cement slurry. The rheological test results of the cement slurry after addition were as follows: the slurry viscosity was 200 mPa·s, and the slurry yield stress was 65 Pa.

[0076] Example 2 Cement Preparation Process

[0077] This embodiment provides a separate preparation process for cement:

[0078] The preparation process specifically comprises the following steps:

[0079] Step (1): limestone mining;

[0080] Step (2): Limestone enters the rotary kiln: After the limestone, clay and other raw materials are crushed and mixed, they are calcined in a rotary kiln at a high temperature of 1400-1450°C to produce clinker.

[0081] Step (3): limestone enters the hot material storage;

[0082] Step (4): Harvesting of finished cement products.

[0083] After the finished cement product was prepared into cement slurry in the same manner as in Example 1, the rheological test results of the cement slurry were as follows: the compressive strength was 40.1 MPa (28 days); the flexural strength was 8.1 MPa (28 days).

[0084] Example 3 Combined preparation process of cement and biochar

[0085] The preparation process specifically adopts Figure 1 The joint method shown:

[0086] The biochar preparation process specifically includes the following steps:

[0087] Step (1): biomass harvesting; rice husk is used as raw material for preparing biochar, and 1 t of biochar is prepared.

[0088] Step (2): Biomass drying: After the biomass raw material is pretreated, moisture is removed during a drying process at 200° C. to obtain a dry raw material with a moisture content of less than 10%.

[0089] Step (3): Biomass carbonization and combustion: The dried biomass raw material is fed into a carbonization furnace, and the biochar carbonization temperature is 500° C. for carbonization reaction to generate biochar and gas by-products.

[0090] Step (4): grinding in a mill to a particle size of 5-7 μm;

[0091] Step (5): Harvesting of finished biochar products.

[0092] The cement preparation process specifically includes the following steps:

[0093] Step (1): limestone mining;

[0094] Step (2): Limestone enters the rotary kiln; limestone and clay are used to prepare cement clinker. Cement kiln calcination temperature: 1450℃.

[0095] Step (3): limestone enters the hot material storage;

[0096] Step (4): Harvesting of finished cement products.

[0097] Taking the production of 1 ton of cement clinker as an example, the first-stage waste gas generated in the rotary kiln of step (2) of the cement preparation process is recovered and filtered through the waste gas treatment device to remove large particles of dust (0.5 microns and above), and then transported to the biomass drying step (2) of the biochar preparation process to reduce the carbon dioxide and nitrogen oxides (NO x ) and other gas components react with the biomass during the biomass drying process to achieve waste gas utilization and optimize biochar performance; at the same time, the heat carried by the waste gas is used to dry the biomass.

[0098] The waste heat of the second-stage exhaust gas of the rotary kiln and the waste heat of the exhaust gas in the hot material storage in steps (2) and (3) of the cement preparation process are recovered to the heat exchanger, and then the heat is redistributed to steps (2) and (3) in the biochar preparation process for heat utilization.

[0099] The total amount of waste gas generated in the rotary kiln is 2000m 3 The temperature of the first-stage exhaust gas is 300-400℃, and the first-stage exhaust gas volume generated in the rotary kiln is 1600m 3 , the oxygen content is 2-4%, and 70-80% of the waste gas in the first stage is input into step (2) of the biochar preparation process, saving 20%-30% of heat for biomass drying.

[0100] The total amount of waste gas generated in the hot material warehouse is 1300m3 The second stage waste gas volume generated in the rotary kiln is 400m 3 20-30% of the second-stage waste gas generated in the rotary kiln and the waste gas in the hot material storage are input into the heat exchanger for heat recovery, and then provided to the biochar drying and carbonization process, saving a total of 30% of external energy consumption.

[0101] The dust generated by the biochar preparation in step (2), step (3) and step (4) of the biochar preparation process is collected and processed, and finally mixed into the cement product to optimize the performance of the cement product. Preferably, the dust can also be used as an alternative fuel for the thermal process in the rotary kiln. The dust generated during the carbonization process is collected by a high-efficiency filtering device (such as a bag filter), and the dust particle size is usually less than 20 microns. 300 kg of biochar is generated, and 10 kg of dust is produced as a by-product.

[0102] The carbon content of biochar dust was determined to be about 70-90%. After being added to cement, the amount of carbon stored was proportional to the mixing ratio, and the amount of biochar added was controlled at 10-30 kg of carbon per ton of cement. The biochar dust of this embodiment was added to cement clinker at a weight ratio of 7%. The 28-day compressive strength test results showed that the compressive strength of the cement mixed with the dust reached 43.2 MPa, which was better than conventional cement.

[0103] The properties of the biochar prepared in this application were measured:

[0104] Surface properties of biochar: Curves showing changes in adsorption and desorption properties with pressure Figure 6 As shown, from Figure 6 It can be seen that the adsorption performance of the biochar prepared in Example 1 is stronger.

[0105] Biochar pore structure: Mesoporous structure: The average pore size (4V / A) is 7.1591nm-7.9979nm; The cross-sectional SEM image and surface SEM image of the biochar prepared in this example are as follows Figure 2 and Figure 3 shown.

[0106] Hydrophilicity of biochar: The surface contact angle of biochar is as follows: Figure 4 As shown, Figure 5 Compared with the surface contact angle of the biochar prepared in Example 1 shown, the hydrophilic property is stronger, which can increase the later hydration reaction rate and enhance the early strength of biochar-doped concrete.

[0107] The nitrogen content on the surface of biochar increased by 30%. Figure 7 As shown, from Figure 7 A peak of N element can be seen in the graph.

[0108] The biochar product prepared in this embodiment is mixed into the cement product to optimize the performance of the cement product.

[0109] The dispersion of the added biochar in the cement paste was analyzed by microscope, and the dispersion was improved by 25% compared with Example 1; rheological test: the paste viscosity was 150 mPa·s, and the paste yield stress was 50 Pa.

[0110] The cement paste doped with the biochar prepared in Example 3 exhibited lower viscosity and yield stress, indicating that the biochar was more evenly dispersed in the paste, reducing the interaction force between particles.

[0111] For the cement paste doped with the biochar prepared in Example 3, the compressive strength was increased by about 10% and the flexural strength was increased by 15%.

[0112] Carbon emissions: The carbon emissions in this embodiment are: 0.65t / ton of cement. Compared with the traditional cement production in Example 2, this linkage preparation process can reduce carbon emissions by 15-20%, significantly improving the environmental friendliness of the process.

[0113] The specific comparison table of the properties of the biochar prepared in Examples 1-3 and the corresponding biochar-doped cement paste is as follows:

[0114]

[0115] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. A combined preparation process of cement and biochar, characterized in that: Combine the cement preparation process with the biochar preparation process to synergistically prepare cement and biochar; The combined steps include: The first-stage waste gas generated in the rotary kiln of the cement production process is recovered and transported to the drying step of the biochar production process; The waste heat of the second-stage exhaust gas of the rotary kiln in the cement production process and the waste heat of the exhaust gas in the hot material storage are recovered into the heat exchanger, and then the heat in the heat exchanger is redistributed to the drying and carbonization combustion steps in the biochar production process for secondary heat utilization; The dust generated during the biochar preparation process is collected and then mixed into cement to optimize the performance of the finished cement product.

2. A combined preparation process of cement and biochar according to claim 1, characterized in that: The exhaust gas from the first stage of the rotary kiln is recovered and filtered by the exhaust gas treatment device, and then input into the biochar preparation process after removing large particles of dust; The second-stage waste gas of the rotary kiln and the waste gas in the hot material storehouse are recovered and filtered through the waste gas treatment device, and then input into the heat exchanger after reducing the concentration of particulate matter.

3. A combined preparation process of cement and biochar according to claim 2, characterized in that: The first-stage waste gas is the waste gas generated in the first 4 / 5 of the working process of the rotary kiln; the second-stage waste gas is the waste gas generated in the last 1 / 5 of the working process of the rotary kiln.

4. The combined preparation process of cement and biochar according to claim 1, characterized in that: The heat exchanger recovers heat in a manner of only recovering the heat carried by the gas in the rotary kiln and the hot material store, and only transports the recovered heat to the drying step and the carbonization step of the biochar preparation process.

5. A combined preparation process of cement and biochar according to claim 4, characterized in that: The heat redistribution in the heat exchanger is as follows: The heat exchanger is divided into a relatively independent drying section and a carbonization section. The heat recovered in the drying section is transported to the drying step of the biochar preparation process, and the heat recovered in the carbonization section is transported to the carbonization step of the biochar preparation process. According to the heat demand of the drying step and the carbonization and combustion step, the total heat recovered by the drying section and the carbonization section is controlled by controlling the amount of exhaust gas entering the drying section and the carbonization section, thereby controlling the heat input into the drying step and the carbonization and combustion step.

6. A combined preparation process of cement and biochar according to claim 5, characterized in that: The method for controlling the amount of exhaust gas entering the drying section and the carbonization section is as follows: a flow-controllable distribution valve is set on the exhaust gas outlet of the rotary kiln and the hot material storage, and the gas of the rotary kiln or the hot material storage is dynamically diverted to the drying section and the carbonization section of the heat exchanger according to the requirements of the drying step and the carbonization combustion step.

7. The combined preparation process of cement and biochar according to claim 1, characterized in that: The combined preparation process also includes: when the heat supplied by the heat exchanger is insufficient, energy is provided for the drying step and the carbonization and combustion step of the biochar preparation process through auxiliary heating.

8. The combined preparation process of cement and biochar according to claim 1, characterized in that: The combined step also includes: conveying dust generated in the biochar preparation process to the rotary kiln as an alternative fuel for the cement preparation process.

9. The combined preparation process of cement and biochar according to claim 1, characterized in that: The combined step also includes: conveying the combustible gas generated in the biochar preparation process to the rotary kiln as an alternative fuel for the cement preparation process.

10. The combined preparation process of cement and biochar according to claim 1, characterized in that: The biochar preparation process specifically comprises the following steps: Step (1): biomass harvesting; Step (2): drying the biomass; Step (3): biomass carbonization and combustion; Step (4): grinding in a mill; Step (5): harvesting of finished biochar; The cement preparation process specifically comprises the following steps: Step (1): limestone mining; Step (2): limestone enters the rotary kiln; Step (3): limestone enters the hot material storage; Step (4): Harvesting of finished cement products.

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