Production process of high-activity calcium oxide

Abstract

The invention relates to the technical field of calcium oxide production, and particularly discloses a production process of high-activity calcium oxide, which comprises the following steps: S1, pretreatment: crushing limestone into limestone fragments; dividing the pulverized coal into biscuiting pulverized coal and salt-fired pulverized coal; s2, biscuit firing: mixing the limestone fragments in the step S1 with biscuit firing coal powder, distributing materials into a shaft kiln after mixing, igniting for calcining, and keeping a firing zone at 1000-1200 DEG C; salt burning: when the unfiring rate of ash discharge of continuous two times of biscuiting is lower than 5%, adding materials again, changing the biscuiting coal powder in the S2 into salt burning coal powder, and adding the salt burning coal powder; and screening: screening out blocky quick lime with the particle size of more than 10mm, and cooling to obtain the high-activity calcium oxide. The technical problems that in the prior art, an additive and a raw material are mixed, the raw material limestone is blocky, the additive is powdery, when the additive and the raw material limestone are mixed, the additive is prone to being accumulated in gaps between the limestone and is not evenly dispersed, and calcium oxide obtained after limestone calcination is high in activity, low in activity and not stable enough in quality are solved.

Description

Technical Field

[0001] The invention relates to the technical field of calcium oxide production, in particular to a production process of highly active calcium oxide. Background Art

[0002] Calcium oxide is an excellent material for absorbing moisture, defoaming, and drying plastics, rubber, and chemical raw materials. It is widely used in metallurgical solvents, chemical raw materials, architectural coatings, papermaking, wastewater purification, food, and pharmaceuticals. Calcium oxide is typically prepared by calcining limestone at high temperatures, causing it to decompose at around 1000°C to produce calcium oxide and carbon dioxide.

[0003] The activity of calcium oxide refers to its ability to chemically react with other substances, primarily reflected in its reaction rate and efficiency. Activated calcium oxide has a high reaction rate and can react quickly with water, acidic substances, etc.

[0004] To increase the activity of calcium oxide, most limestone plants use a gradient heating / cooling technique to avoid agglomeration caused by rapid temperature changes, thereby ensuring the activity of the calcium oxide. For example, publication number CN111454005B discloses a lime kiln calcination process for producing activated calcium oxide. The key technical approach involves preheating the stone in layers before calcining it in layers. This allows for more uniform heating of the limestone, reduces the formation of underfired and overfired lime, and thus ensures the activity of the calcium oxide.

[0005] Although the technology of this mode layered preheating and layered calcining plays a positive role to active calcium oxide, its process layering is too much, and process is complicated, and the activity of calcium oxide is not much improved. Therefore, the technology of adding additives in limestone has appeared in the industry, and additives are utilized to have an impact on the calcium oxide calcining process and crystal generation, so that the activity of the calcium oxide produced is greatly improved, as publication number is: a kind of high-activity calcium oxide and production method thereof are just disclosed in the patent document of CN102225780B, it adds sodium chloride to calcine in raw material calcium carbide slag (calcium hydroxide), thereby improving the activity of calcium oxide, as publication number is CN1023996C discloses a kind of method of producing high-activity calcium oxide, it is at limestone and coke or coal, adds sodium chloride as stimulator, thereby improving the activity of calcium oxide.

[0006] Although the above-mentioned method of adding additives to the calcium oxide production calcination process improves the activity of calcium oxide to a certain extent, the additives are mixed with the raw materials in the process. The raw material limestone is in block form and the additives are in powder form. When the two are mixed, the additives tend to accumulate in the gaps between the limestones and are not dispersed evenly. As a result, some of the calcium oxide after calcining the limestone has high activity and some has low activity, and the quality is not stable. Summary of the Invention

[0007] The object of the present invention is to provide a production process for highly active calcium oxide, so as to solve the technical problem mentioned above that in the prior art, additives are mixed with raw materials, and the raw material limestone is in block form and the additives are in powder form. When the two are mixed, the additives tend to accumulate in the gaps between the limestones, resulting in uneven dispersion, resulting in some calcium oxide having high activity and some having low activity after calcining the limestone, and the quality being unstable.

[0008] In order to solve the above problems, the technical solution adopted by the present invention is as follows: a production process of highly active calcium oxide, characterized in that it comprises the following steps:

[0009] S1. Pretreatment: crush the limestone into limestone fragments with a particle size of 20 to 90 mm using a crusher; divide the pulverized coal into two parts, one of which is unprocessed to form biscuit-fired pulverized coal, and the other is mixed with additives to form salt-fired pulverized coal;

[0010] S2, biscuit calcination: The limestone fragments from step S1 are mixed with biscuit pulverized coal, and after mixing, the mixture is transported to the distributor located at the top of the vertical furnace, and distributed into the calcination furnace kiln through the distributor. After the distribution is completed, ignition is started for calcination, and the calcination temperature is maintained at 1000°C-1200°C;

[0011] S3, salt burning: When the raw burning rate of biscuit burning is less than 5% for two consecutive times, when charging the shaft furnace again, replace the biscuit burning coal powder in S2 with salt burning coal powder, and then mix it with limestone and add it to the furnace;

[0012] S4, cooling: cooling the quicklime calcined in step 3 to obtain highly active calcium oxide.

[0013] The beneficial effects of this embodiment are:

[0014] 1. In the prior art process of producing calcium oxide by burning salt-burned limestone, the additive is first mixed with the limestone, and then the mixture is calcined. However, the fragments of calcined limestone in the vertical furnace have certain size requirements, which cannot be too small or too large. The size is usually 20 to 90 mm. This results in the raw material limestone being in block form and the additive being in powder form. When the two are mixed, the additive easily accumulates in the gaps between the limestones and is not evenly dispersed. As a result, some calcium oxide after calcining the limestone has high activity, some has low activity, and the quality is not stable enough. However, the present application mixes the salt of the additive with coal powder first. The salt of the additive is evenly dispersed in the coal, and then the coal and limestone fragments are calcined. The use of fuel calcination is to evenly distribute the salt gasification in the vertical furnace, and the mixing with the limestone fragments is more even. Therefore, the activity consistency of the calcium oxide produced is better.

[0015] 2. In traditional technologies, only unglazed limestone fragments were used. After the emergence of the salt-burning process, the temperature control in the furnace body by salt is often more complex. At the initial stage of calcination in the furnace body, it often takes more time to adjust and control to enable the furnace body to enter a stable calcination state. During this adjustment process, a large amount of underburning and overburning occur, resulting in insufficient activity of calcium oxide and failure to meet the quality requirements, causing production waste. This phenomenon is more serious in shaft furnaces. In response to this, after long-term production practice, this application speculates that when salt and limestone are directly mixed and charged for calcination, at the initial stage of calcination, as the furnace body temperature rises, it will first reach the melting and evaporation temperature of salt. And the process of salt being gasified into molecular form at high temperature in the shaft furnace will cause the temperature to stay, resulting in the failure of the temperature in the firing zone of the furnace body to rise, resulting in underburning. In order to raise the temperature of the firing zone to the process design temperature, technicians will increase ventilation or add fuel. However, at this time, the molecules of salt gasified at high temperature have risen to the area with a lower temperature in the preheating zone at the top of the furnace. The salt content in the firing zone is already very small. Without salt, the temperature in the firing zone begins to rise rapidly, resulting in overburning again. Technicians can only adjust ventilation and fuel again. But after adjustment, the salt gas at the upper end of the furnace body will re-condense due to the lower temperature at the furnace top and fall into the firing zone. This process repeats, causing the shaft furnace body to take too long to adjust to a stable calcination state at the initial stage of calcination, resulting in low-quality calcium oxide output and production waste. Therefore, when designing its process, this application first conducts unglazed firing until it is stable (the underburning rate is less than 5%), and then conducts salt-burning. At this time, the temperature in the firing zone has reached the process design temperature and is higher than the sublimation temperature of salt. After starting salt-burning, the salt enters the firing zone and quickly sublimes. Although the temperature in the firing zone will drop somewhat at this time, it is still within the temperature range of the designed process. When the salt sublimes, the temperature in the firing zone rises. When the temperature is about to exceed the process design temperature, the salt gasified into molecular form at high temperature completes cooling and crystallization in the area with a lower temperature in the preheating zone and then drops back into the firing zone again, causing the temperature in the firing zone to drop, forming a small cycle. This enables the temperature in the firing zone to be better controlled within the designed process range. Compared with directly conducting salt-burning in the prior art, by introducing unglazed firing at the initial stage of calcination, this application's process can adjust the firing zone of the furnace body to reach the process design temperature faster when applied in a shaft furnace, enter a stable calcination state of the furnace body, and avoid production waste caused in the initial stage. Secondly, the design of entering salt-burning after unglazed firing is stable can also utilize the characteristics of salt sublimation and condensation to assist in controlling the temperature in the firing zone to be stable within the process design range.

[0016] Further, the additive can be any one of MgCl2, CaCl2, and NaCl.

[0017] Further, in the step: the mass of the additive in the salt-burning pulverized coal accounts for 0.06%-0.12% of the mass of the limestone.

[0018] Further, the green coal powder and salt-baked coal powder in step S1 can be made into coal powder pellets with water and then applied to the processes in steps S2 and S3.

[0019] Further, when making the salt-baked coal powder pellets, first mix the additive with powdered quicklime, then mix it with the coal powder. After mixing evenly, add water to make the coal powder pellets of the salt-baked coal powder. The mixing ratio of quicklime to additive salt is 2:1. After the quicklime is mixed with the additive salt, caking of the additive salt can be avoided. Therefore, when it is mixed with the coal powder, it will be more uniform.

[0020] Further, the calciner in step S2 is a single-chamber vertical furnace. Before step S4, the quicklime calcined in step S3 needs to be sieved to screen out lumpy quicklime with a size of more than 10 mm. This application can also reduce the sulfur content on the surface of calcium oxide. After adding salt, the lime becomes soft, porous and fragile. Its outer surface accounts for 10% of the total surface, but it can capture 80% of the sulfur content in the raw materials, and the remaining 20% is scattered inside the lime. Since the process of this application uses a single-chamber vertical furnace, during calcination, the raw materials will descend vertically in the furnace body. During the descent, the lime will be squeezed and worn against each other, and the lime on the outer surface will become powdery. Therefore, in the lime out of the furnace, the lumpy quicklime has less sulfur content, while the powder ash has more. By screening out lime larger than 10 mm, it is ensured that the sulfur in the calcium oxide produced by this process is 30-50% lower than that of the green-baked lime. Description of the Drawings

[0021] Figure 1 It is the process flow chart of the present invention. Detailed Description of the Invention

[0022] The following is a further detailed description through specific embodiments:

[0023] Example 1

[0024] The production process of highly reactive calcium oxide includes the following steps:

[0025] S1. Pretreatment: Crush the limestone with a crusher to make limestone fragments with a particle size of 20-50 mm; divide the coal powder into two parts, one part is untreated as green coal powder, and the other part is mixed with an additive to form salt-baked coal powder;

[0026] The crushed pieces of limestone used for calcining to produce calcium oxide in the shaft furnace should not be too small or too large. When large pieces of limestone are heated in a rotary kiln or shaft kiln, heat is difficult to quickly transfer to the internal core area, resulting in incomplete decomposition of the central part into calcium oxide and residual calcium carbonate, increasing the unburned rate. The specific surface area of too small crushed pieces is large, and the calcination reaction is too intense, which may lead to local overheating and caking, resulting in overburning and reducing the activity of calcium oxide. Therefore, in this embodiment, the limestone is crushed into limestone crushed pieces of 20 - 25 mm in a crusher. Not too big or too small, which can ensure the calcination quality.

[0027] As fuel, pulverized coal has small particles, is easier to mix and blend with additives, and after being fed into the furnace body, the additives are not easy to accumulate between the crushed pieces of limestone and contact the crushed pieces of limestone more dispersedly. Pulverized coal is divided into two parts. One part is untreated as raw coal for calcination, and the other part is mixed with additives to form salt - burned pulverized coal. Both can be made into spherical coal pellets by mixing with water and then drying. When the salt - burned pulverized coal is made into spherical coal pellets, it is wrapped in the pellets and is less likely to accumulate in the gaps when mixed with limestone. When preparing the pellets, when mixing water with pulverized coal, the water volume needs to be controlled, and it is wetted with water to a total moisture content of 15 - 18%. When the moisture content of the pulverized coal is relatively high, it is adjusted lower; when the pulverized coal is relatively dry, it is adjusted higher. It is necessary to ensure that the pulverized coal can form a viscous state after stirring and can be kneaded into a ball. When preparing the salt - burned pulverized coal, first mix the salt of the additive with powdered quicklime of 0 - 3 mm. The mixing ratio of quicklime to salt is 2:1. After mixing, it is mixed with pulverized coal again, and after mixing evenly, water is added to prepare the pellets.

[0028] The additive can be any one of MgCl2, CaCl2, and NaCl. This application has studied the action effects of MgCl2, CaCl2, and NaCl. In the salt - burning process of the shaft furnace, MgCl2, CaCl2, and NaCl (based on the dosage of Cl) are respectively added. After separate tests, it is found that the above three salts can all increase the activity of calcium oxide to 150 ml. The best effect is CaCl2, followed by MgCl2, and then NaCl.

[0029] The addition amount of salt needs to be explored according to the actual ore. Different limestone ores have different suitable addition amounts. In the long-term practice of this application, it is known that the most suitable addition amount for the Hebei ore is 0.06% of the limestone quality, while that for the Shaanxi limestone ore is 0.08%. The salt addition amount may also be different for different furnaces. Therefore, the salt addition amount needs to be gradually determined after the shaft furnace is rebuilt and ignited for production. The addition amount can be gradually increased to determine the optimal value. For example, the addition amount at the beginning can be lower, such as 0.05%, and then gradually increased to determine the optimal value. It should be noted that there is generally a maximum limit for salt addition in production, which does not exceed 0.12%. If the salt amount is too much, it will have a greater impact on the temperature change in the furnace body, causing the furnace condition to be unstable and being adverse to production instead. In the practice of this application, it is found that for all ores, the salt addition amount is within the range of 0.06% - 0.12%.

[0030] S2. Green firing: Mix the limestone fragments in step S1 with green firing pulverized coal, transport the mixture to the distributor located at the top of the shaft furnace, and distribute the mixture into the calcination furnace through the distributor. After the distribution is completed, ignite for calcination and maintain the calcination at 1000°C - 1200°C in the burning zone;

[0031] After the coal powder pellets prepared from the limestone fragments and the green firing pulverized coal are evenly mixed, direct mixing and calcination with the pulverized coal can also be implemented. However, the pulverized coal particles are relatively small, and the ventilation effect of the furnace body is not ideal enough, which is prone to form smoldering. But after it is prepared into pellets, the overall calcination effect is better.

[0032] S3. Salt firing: When the green firing unburned rate of the green firing ash discharged continuously twice is lower than 5%, when adding materials to the shaft furnace again, replace the green firing pulverized coal in S2 with salt firing pulverized coal for adding materials;

[0033] In actual production, the designed temperature of the burning zone has a certain range. Without overburning, the lower the unburned rate, the closer the temperature of the burning zone is to the upper limit of the designed temperature range of the burning zone. When changing from green firing to salt firing, the temperature in the furnace will drop due to the influence of adding salt. Therefore, when changing from green firing to salt firing, it is necessary to try to make the temperature of the burning zone close to the upper limit of the designed temperature range of the burning zone. When salt is added, the temperature in the furnace cavity drops. Since the amount of salt initially added is small, the temperature drop amplitude is low and will not damage the temperature calcination in the furnace. Then gradually increase the addition amount of the additive salt. On the premise that the temperature drop does not fall below the lower limit of the designed temperature range of the burning zone after the salt is added, adjust the amount of the additive salt to ensure its highest activity.

[0034] However, there are errors in the temperature monitoring inside the calciner. Using electronic temperature monitoring cannot actually reflect the temperature of the sintering zone inside the calciner. However, in the limestone calcination process, when the calcination temperature is insufficient, the limestone cannot be fully calcined, and the underburning rate is higher. According to this characteristic, without overburning, the lower the underburning rate, the closer the temperature of the sintering zone is to the upper limit of the designed temperature range of the sintering zone. Therefore, in this application, an underburning rate lower than 5% is used as the key point for the conversion between green firing and salt firing, which can ensure that when salt is added, the temperature inside the furnace will not drop below the lower limit of the designed temperature range of the sintering zone, ensuring the stability of the furnace body calcination.

[0035] S4. Cooling: Cool the quicklime obtained by calcination in step 3 to obtain highly active calcium oxide.

[0036] After adding salt, the lime becomes soft, porous and brittle. Its outer surface accounts for 10% of the total surface area, but it can capture 80% of the S content in the raw materials. The remaining 20% is distributed inside the lime. Since the process of this application uses a single-chamber vertical furnace, during calcination, the raw materials will descend vertically inside the furnace body. During the descent process, the lime will be squeezed and worn against each other, and the lime on the outer surface will become powdery. Therefore, in the lime taken out of the furnace, the lumpy quicklime has a lower S content, while the powder ash has a higher S content. By screening out lime larger than 10 mm, it is ensured that the S in the calcium oxide produced by this process is 30 - 50% lower than that of the green-fired lime.

[0037] The above are only the embodiments of the present invention. Common knowledge such as specific structures and characteristics known in the solution is not described in detail here. It should be noted that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can still be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application should be based on the content of its claims, and the specific implementation manners described in the specification can be used to explain the content of the claims.

Claims

1. The production process of highly active calcium oxide is characterized in that: It includes the following steps: S1. Pretreatment: Crush limestone with a crusher to produce limestone fragments with a particle size of 20 - 50 mm; divide the pulverized coal into two parts, one part remains untreated as plain-burned pulverized coal, and the other part is mixed with an additive to form salt-burned pulverized coal; S2. Plain burning: Mix the limestone fragments in step S1 with the plain-burned pulverized coal, transport the mixture to the distributor at the top of the shaft furnace after mixing, and distribute the mixture into the calcination furnace kiln through the distributor. After the distribution is completed, ignite for calcination and maintain the calcination at 1000 °C - 1200 °C in the burning zone; S3. Salt burning: When the green burning rate of the plain-burned ash discharged continuously twice is less than 5%, when adding materials to the shaft furnace again, replace the plain-burned pulverized coal in S2 with salt-burned pulverized coal and then mix it with limestone for feeding; S4. Cooling: Cool the quicklime calcined in step 3 to obtain highly active calcium oxide.

2. The production process of highly active calcium oxide according to claim 1, characterized in that: The additive can be any one of salts such as MgCl2, CaCl2, and NaCl.

3. The production process of highly active calcium oxide according to claim 2, characterized in that: In the step: The mass of the additive in the salt-burned pulverized coal accounts for 0.06% - 0.12% of the mass of the limestone.

4. The production process of highly active calcium oxide according to claim 1, characterized in that: The plain-burned pulverized coal and the salt-burned pulverized coal in step S1 can be made into pulverized coal pellets with water and then the pulverized coal is applied in the processes of steps S2 and S3.

5. The production process of highly active calcium oxide according to claim 3, characterized in that: When making the pulverized coal pellets of the salt-burned pulverized coal, first mix the additive with powdered quicklime, then mix it with the pulverized coal, and add water after mixing evenly to make the pulverized coal pellets of the salt-burned pulverized coal.

6. The production process of highly active calcium oxide according to claim 2, characterized in that: The calcination furnace in step S2 is a single-chamber shaft furnace. Before step S4, the quicklime calcined in step S3 needs to be sieved to screen out the massive quicklime with a size of more than 10 mm, and the mixing ratio of the quicklime to the salt is 2:1.

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