Continuous process and system for the production of high brightness, high surface area calcium hydroxide

Abstract

The application provides a continuous production method and system of calcium hydroxide with high whiteness and high specific surface area, and relates to the technical field of limestone deep processing. The continuous production method comprises the following steps: step one: continuously adding quicklime particles into the inlet of a primary digester, continuously adding digestion water and an additive into the inlet of the primary digester, and carrying out premixing and pre-digestion under stirring conditions; step two: continuously introducing the discharge of the primary digester into a secondary digester, continuously adding digestion water and an additive into the inlet of the secondary digester, and stirring and digesting and aging; step three: the discharge of the secondary digester is sequentially introduced into a tertiary digester, a quaternary digester and a quinary digester for digestion and aging, and the product is obtained after grading by a grader. The method can continuously prepare calcium hydroxide with high whiteness and high specific surface area, and has the characteristics of simple process, short time consumption, remarkable effect and low energy consumption, and has been applied in actual production and has good use effect.

Description

Technical Field

[0001] This invention relates to the field of limestone deep processing technology, and in particular to an energy-efficient and continuous production method and system for producing calcium hydroxide with high whiteness and high specific surface area. Background Technology

[0002] Calcium hydroxide is used in papermaking, coatings, and building materials industries where whiteness and impurities are critically important. High-specific-surface-area calcium hydroxide plays a significant role in flue gas desulfurization, glass manufacturing, and rare earth smelting and extraction. Most mainstream calcium hydroxide products use calcium carbonate calcined in a rotary kiln or vertical kiln with pulverized coal or a burner as raw material, and are produced using dry or semi-dry methods. These methods result in inconsistent ash-to-water ratios, high impurity levels, and low effective calcium hydroxide content. The produced calcium hydroxide also suffers from low specific surface area (≤20 m² / g), low reaction rate, and poor whiteness. High-quality calcium hydroxide in China mainly relies on imports, leading to high operating costs. Against this backdrop, the demand for high-whiteness, high-specific-surface-area calcium hydroxide, especially calcium hydroxide with a specific surface area exceeding 30 m² / g, is increasing in the domestic market due to its low energy consumption, low impurity content, high reaction rate, and good adsorption capacity. Based on process requirements, my country's waste incineration requires 1.5 million tons / year of high specific surface area calcium hydroxide products; rare earth extraction, glass manufacturing, petrochemicals, industrial kiln flue gas desulfurization and denitrification, and heavy metal adsorption require 2.1 million tons / year of high specific surface area calcium hydroxide products. High specific surface area calcium hydroxide products are the best choice to replace sodium-based and amino-based products for absorbing industrial pollutants.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a continuous production method and system for calcium hydroxide with high whiteness and high specific surface area. This method can not only continuously produce calcium hydroxide with high whiteness and high specific surface area, but also the optimized process can achieve the characteristics of simple process, short time, significant effect, and low energy consumption. It is highly efficient and energy-saving, and has been applied in actual production with good results.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a continuous production method for calcium hydroxide with high whiteness and high specific surface area, comprising the following steps:

[0007] Step 1: Quicklime granules are continuously added to the inlet of the primary digester. At the same time, 80-85℃ digestion water and additives are continuously added to the quicklime granules at the inlet of the primary digester according to the set water-to-material ratio. The whole process is carried out under stirring to achieve premixing and predigestion. The inlet temperature of the primary digester is controlled at 85-130℃.

[0008] Step 2: The material that has been premixed and predigested in the primary digester is continuously introduced into the secondary digester. At the same time, 80-85℃ digestion water and additives are continuously added at the inlet of the secondary digester according to the set water-to-material ratio, and the mixture is stirred, digested and aged.

[0009] Step 3: The material from the secondary digester enters the tertiary, quaternary and quinary digesters for digestion and aging, and is then graded by a classifier to obtain the product.

[0010] Furthermore, the quicklime particles are continuously added to the primary digester at a feeding rate set by the feed belt scale, which is 35-50Hz.

[0011] And / or, the water-to-material ratio set in step one is 0.35:1, and the water-to-material ratio set in step two is 0.35:1;

[0012] And / or, the quicklime has an activity of not less than 360 ml, an effective calcium oxide content of ≥90%, and a particle size of ≤3 mm.

[0013] Furthermore, the digestion water mentioned in steps one and two comes from the heat exchanger, which uses the heat from the rotary kiln tail gas and / or the heat generated by the four-stage digester as the heat source.

[0014] And / or, the digestive aids mentioned in steps one and two are one or more of ethylene glycol, propylene glycol, butylene glycol, glucose, sodium citrate, sodium pyrophosphate, glycerol, triethanolamine, and sucrose.

[0015] Furthermore, the amount of the additives added in steps one and two is 0.001-0.15% of the mass percentage of the water added in each step;

[0016] And / or, in step one, the average residence time of the material in the primary digester for premixing and predigestion is ≤6 min, and the aging time of the material in the secondary, tertiary, quaternary and quinary digesters is 6-8 min respectively.

[0017] Furthermore, the outlet temperature of the first-stage digester is 150-230℃, the outlet temperature of the second-stage digester is 260-390℃, the outlet temperature of the third-stage digester is 340-390℃, the outlet temperature of the fourth-stage digester is 85-140℃, and the outlet temperature of the fifth-stage digester is 85-130℃.

[0018] And / or, the stirring rate of the first-stage digester is 650-950 r / min, the stirring rate of the second-stage digester is 700-900 r / min, the stirring rate of the third-stage digester is 700-900 r / min, the stirring rate of the fourth-stage digester is 600-850 r / min, and the stirring rate of the fifth-stage digester is 600-850 r / min.

[0019] Secondly, the present invention provides a continuous production system for calcium hydroxide with high whiteness and high specific surface area, comprising:

[0020] The digester water heating device has its heat supply inlet connected to the rotary kiln exhaust outlet and / or the heat outlet generated by the fourth-stage digester.

[0021] The multi-stage digester is connected in series, with the hot water outlet of the digestion water heating device connected to the first and second stage digesters; the first stage digester also includes an auxiliary agent inlet and a calcium oxide raw material inlet, and the second stage digester also includes an auxiliary agent inlet and the calcium oxide raw material inlet connected to the calcium oxide raw material silo;

[0022] A high-efficiency classifier has its inlet connected to the outlet of the last stage digester of the multi-stage digester to classify the semi-finished product from the multi-stage digester to obtain calcium hydroxide product.

[0023] The finished product storage tank has its inlet connected to the finished product outlet of the high-efficiency classifier.

[0024] Furthermore, the multi-stage digester is a five-stage digester, wherein the second-stage digester receives material from the first-stage digester, the third-stage digester receives material from the second-stage digester, the fourth-stage digester receives material from the third-stage digester, and the fifth-stage digester receives material from the fourth-stage digester.

[0025] Furthermore, each of the five stages of digestion is equipped with a spiral reamer device;

[0026] And / or, the five-stage digester is machined from 16mm thick Q345 steel using a CNC lathe;

[0027] And / or, the top of the primary and secondary digesters is provided with a nozzle atomizing device for spraying digestion water onto the calcium oxide raw material.

[0028] Furthermore, the water heating device for digestion includes: an inner tank for holding water; and an outer tank disposed outside the inner tank.

[0029] And / or, all stages of the digesters and heat exchangers in the system are insulated, and the insulation is achieved by setting an insulation layer on their exterior.

[0030] Furthermore, the pores formed by the inner and outer liner are used to transmit heat from the rotary kiln exhaust gas and / or the heat generated by the four-stage digester, which serve as a heat source.

[0031] And / or, the inner liner is made of lithium bromide and the outer liner is made of 304 stainless steel.

[0032] The present invention has the following beneficial effects:

[0033] 1. By controlling the temperature of the digestion water added in the primary and secondary digesters, the whiteness and specific surface area of ​​the final calcium hydroxide product can be significantly improved, with the specific surface area reaching 30m². 2 / g or more. Furthermore, controlling the temperature of the digestion water allows for a more complete hydration reaction of calcium oxide, reducing the amount of additives used. Actual production verification shows that in continuous production of the same yield of calcium hydroxide, the amount of additives used is significantly reduced compared to production processes where the digestion water temperature is lower or higher than that of this invention.

[0034] 2. By controlling the stirring rate of each stage of the reactor, the feed rate of the first-stage digester, the temperature of the digestion water, the multi-stage digestion and aging, and the inlet and outlet temperatures of each stage of the digester, the overall reaction rate is improved, which can ensure continuous production and obtain products with stable quality and small fluctuations.

[0035] 3. Insulate the digesters and heat exchangers at each stage of the system, such as by setting an external insulation layer, so as to make the calcium hydroxide preparation process more efficient, the preparation cost lower, and the temperature control inside the digester more stable.

[0036] 4. The waste heat from the rotary kiln exhaust gas is used to heat the digestion water, making the calcium hydroxide preparation process energy-saving and efficient.

[0037] 5. In a preferred process or system, the present invention also utilizes the heat generated within the fourth-stage digester, recovers the heat from the fourth-stage digester and uses it in a heat exchanger to heat the water within the heat exchanger, thereby providing digestion water for the first-stage and second-stage digesters.

[0038] 6. Compared with traditional calcium hydroxide production equipment, this equipment uses lower power and has greater versatility.

[0039] 7. The entire process equipment has a simple layout and structure, is easy to install and use, has a long service life, and is widely applicable.

[0040] 8. It can be installed in any location within a limited space, making effective use of existing space, which is of great significance for the fine processing of calcium hydroxide and energy saving. Attached Figure Description

[0041] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of the process flow of a continuous production system provided in an embodiment of the present invention. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0044] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0045] According to a first aspect of the present invention, a continuous production method for calcium hydroxide with high whiteness and high specific surface area includes the following steps:

[0046] Step 1: Quicklime granules are continuously added to the inlet of the primary digester mixer. At the same time, 80-85℃ digestion water and additives are continuously added to the quicklime granules at the inlet of the primary digester according to the set water-to-material ratio. The whole process is carried out under stirring to achieve premixing and predigestion. The inlet temperature of the primary digester is controlled at 85-130℃.

[0047] Step 2: The material that has been premixed and predigested in the primary digester is continuously introduced into the secondary digester. At the same time, 80-85℃ digestion water and additives are continuously added at the inlet of the secondary digester according to the set water-to-material ratio, and the mixture is stirred, digested and aged.

[0048] Step 3: The material from the secondary digester enters the tertiary, quaternary and quinary digesters for digestion and aging, and is then rapidly classified by a classifier to obtain the product.

[0049] In the above-described production method, the main function of the secondary digestion and aging is to increase the digestion reaction time and the degree of complete reaction. The tertiary, quaternary, and quinary digestion and aging mainly serve to ensure thorough stirring and the full growth of calcium hydroxide whiskers. The water-to-material ratio mentioned in step one of this invention refers to the mass ratio of water to quicklime, while the water-to-material ratio mentioned in step two refers to the mass ratio of water to the material entering the secondary digester.

[0050] In the above-mentioned preparation method, as a preferred embodiment, the quicklime in step one has an activity of not less than 360 ml, an effective calcium oxide content of ≥90%, and a particle size of ≤3 mm.

[0051] In the above-described production method, as a preferred embodiment, quicklime is continuously added to the primary digester at a feeding rate set by the feed belt scale (35-50 Hz), with a water-to-lime ratio of 0.35:1; the water-to-lime ratio in step two is also 0.35:1. Controlling the feed rate of quicklime can effectively control the reaction progress and extent in each subsequent digester, which is beneficial for obtaining qualified calcium hydroxide products and improving the purity of the final product.

[0052] In the above manufacturing method, the main function of controlling the inlet temperature of the primary digester in step one is to affect the reaction rate of subsequent processes, control the feed temperature, and avoid excessively high reaction temperatures that could cause blockage in subsequent digestion reactions.

[0053] In the above-mentioned manufacturing method, as a preferred embodiment, the digestion water in steps one and two comes from a heat exchanger. The heat exchanger uses the heat generated by the rotary kiln tail gas and / or the heat generated by the four-stage digester as a heat source. The water temperature of the digestion water is preferably 80-85℃. Below 80℃, the product reaction rate is relatively slow and the amount of additives added is large. Above 85℃, the energy waste is relatively large and it does not help to improve product performance and reduce the amount of additives.

[0054] In the above-described preparation method, as a preferred embodiment, the digestive aids mentioned in steps one and two are one or a mixture of ethylene glycol, propylene glycol, butylene glycol, glucose, sodium citrate, sodium pyrophosphate, glycerol, triethanolamine, and sucrose.

[0055] In the above-mentioned manufacturing method, as a preferred embodiment, the amount of additives added in steps one and two is 0.001-0.15% of the mass percentage of water added in each step; adding the digestion aids in steps can better control the reaction rate, make the utilization rate of the aids higher, and result in relatively less aid residue in the finished product.

[0056] In the above-mentioned production method, as a preferred embodiment, the average residence time of the material in the primary digester during premixing and predigestion in step one is ≤6 min, preferably ≤6 min, and the digestion and aging times for the secondary, tertiary, quaternary and quinary stages are 6-8 min, respectively.

[0057] In the above manufacturing method, as a preferred embodiment, the outlet temperature of the first-stage digester is 150-230℃, the outlet temperature of the second-stage digester is 260-390℃, the outlet temperature of the third-stage digester is 340-390℃, the outlet temperature of the fourth-stage digester is 85-140℃, and the outlet temperature of the fifth-stage digester is 85-130℃.

[0058] In the above-described manufacturing method, as a preferred embodiment, the stirring rate of the first-stage digester is 650-950 r / min, the stirring rate of the second-stage digester is 700-900 r / min, the stirring rate of the third-stage digester is 700-900 r / min, the stirring rate of the fourth-stage digester is 600-850 r / min, and the stirring rate of the fifth-stage digester is 600-850 r / min.

[0059] The stirring speed of the primary digester is controlled at 650-950 rpm. This is mainly to reasonably control the degree of thorough mixing of the water and materials based on the feed. If the speed of the primary digester is higher than this, the mixture will tumble too quickly, resulting in a short residence time for the material in the primary digester, which may cause blockage at the inlet of the secondary digester. If the speed is lower than this range, the material in the primary digester will react for too long, causing the temperature to rise too high, which may cause material sloshing. The speed of the secondary digester is 700-900 rpm, which is adjusted in real time according to the speed of the primary digester to ensure that the feed material is thoroughly mixed in the secondary digester and that the temperature rise is within a controllable range. The speed of the tertiary digester is 700-900 rpm, which is adjusted according to the real-time reaction temperature in the tertiary digester to ensure that the mixture reacts thoroughly in the tertiary digester and that the material discharged at the end of the digester is basically completely reacted with low moisture content. The speed of the quaternary digester is 600-850 rpm, which is to reduce the speed based on the feed material from the previous primary digester (after reaction, the material is light and fluid), reduce dust in the digester, increase the sufficient aging time in the quaternary digester, and ensure waste heat recovery. The five-stage digester operates at a speed of 600-850 r / min to further increase the aging time.

[0060] Controlling the rotational speed and discharge temperature of the three-, four-, and five-stage digesters is beneficial for controlling product quality.

[0061] Controlling the outlet temperature and stirring speed of each digester stage is mainly to control the residence time and mixing rate of the materials in each digestion stage. The rotation speed of each digester stage is adjusted according to the temperature to control the tumbling speed and dynamic action time of the materials in that digester stage.

[0062] In the above production method, the rapid grading of the classifier in step three is to separate the residue and product from the output of the five-stage digester.

[0063] The hydrated and slaked lime granules prepared through the above steps have a moisture content of 3-10%. After grading, a high-whiteness, high-specific-surface-area calcium hydroxide product is obtained, with a whiteness of 92 degrees or higher, even reaching 95 degrees; a multi-point BET specific surface area of ​​30 m² / g or higher; a total adsorption pore volume of 0.13 m³ / g or higher; an average adsorption pore diameter of 11 nm or higher; and a calcium hydroxide mass content of 96% in the product.

[0064] According to a second aspect of the present invention, a continuous production system for calcium hydroxide with high whiteness and high specific surface area is provided, comprising:

[0065] A digestion water heating device is used to provide digestion water that meets the required temperature.

[0066] The multi-stage digester is connected in series. The hot water outlet of the digestion water heating device is connected to the first-stage and second-stage digesters. The first-stage digester also includes an auxiliary agent inlet and a calcium oxide raw material inlet. The second-stage digester also includes an auxiliary agent inlet and a calcium oxide raw material inlet connected to a calcium oxide raw material silo.

[0067] The high-efficiency classifier has its inlet connected to the outlet of the last stage digester of the multi-stage digester, and classifies the semi-finished products from the multi-stage digester to obtain calcium hydroxide finished product.

[0068] The finished product storage tank has its inlet connected to the finished product outlet of the high-efficiency classifier to collect the finished calcium hydroxide product.

[0069] In the above system, as an option, the heat supply inlet of the digestion water heating device is connected to the rotary kiln exhaust outlet to utilize the waste heat of the rotary kiln exhaust gas to heat the digestion water.

[0070] In the above system, as an optional approach, the heat supply inlet of the digestion water heating device is connected to the heat outlet of the fourth-stage digester.

[0071] In the above system, as an optional approach, the top of the primary and secondary digesters is equipped with a nozzle atomizing device for spraying digestion water onto the calcium oxide raw material.

[0072] In the above system, as an optional configuration, the multi-stage digester is a five-stage digester, wherein the second-stage digester receives material from the first-stage digester, the third-stage digester receives material from the second-stage digester, the fourth-stage digester receives material from the third-stage digester, and the fifth-stage digester receives material from the fourth-stage digester. Preferably, each of the five-stage digesters is equipped with a spiral reamer device to thoroughly agitate the mixture during the digestion process, thereby reducing reaction residue. The five-stage digester can be CNC machined from 16mm thick Q345 steel, and all shell supports meet load-bearing capacity requirements.

[0073] In addition, each stage of the digester used in this invention is equipped with a spiral stirrer, which is used for stirring and also for propelling the material forward.

[0074] In the aforementioned system, as an optional embodiment, the water heating device for digestion includes: an inner tank for holding water; and an outer tank disposed outside the inner tank. The pores formed by the inner and outer tanks allow heat to pass through the rotary kiln exhaust gas and / or the heat generated by the four-stage digester, which serves as a heat source. The inner tank can be made of lithium bromide, which has good thermal conductivity. The outer tank can be made of 304 stainless steel.

[0075] The system of this invention mainly includes a rotary kiln tail waste heat recovery heating device, a primary digester for mixing calcium oxide ash water, a secondary digester, a tertiary digester, a quaternary digester, a quinary digester, a high-efficiency classifier, and a finished product storage tank. The rotary kiln waste heat recovery device is made with a lithium bromide inner heat transfer medium and a 304 stainless steel outer liner, using the heat from the 150℃ tail gas of the rotary kiln and / or the heat generated by the quaternary digester to heat the production water in the storage tank. The quinary digester is CNC machined from 16mm thick Q345 steel, and all shell supports meet load-bearing capacity requirements.

[0076] The digester in this invention can also be expressed as a digestive machine.

[0077] like Figure 1 As shown, the system provided in this embodiment of the invention includes a raw material belt conveyor, a raw material elevator, a raw material scraper conveyor, a flow stabilizer reamer, a metering reamer, a primary digester, a secondary digester, a tertiary digester, a quaternary digester, a quinary digester, a digester dust collector, a heat exchanger, a digester water pump, a semi-finished product elevator, a classifier, a finished product elevator, a slag elevator, a finished product silo, a bulk loading machine, tank trucks, and slag tanks.

[0078] The raw material belt conveyor is used to transport the incoming calcium oxide material; the raw material elevator lifts the calcium oxide material from the conveyor belt from the feed hopper to the raw material scraper conveyor; the raw material scraper conveyor horizontally pulls the material conveyed by the elevator to the next equipment, such as the metering buffer silo. The buffer silo can be used to buffer and store the material, facilitating the smooth conveying of the material by the subsequent flow reamer; the flow reamer is used to evenly convey the material transported by the scraper conveyor, facilitating more accurate metering by the subsequent metering reamer; the metering reamer is used to accurately calculate the dynamic weight of the conveyed material; the metering reamer conveys the accurately calculated raw material to the primary digester, and then the output of the primary digester is conveyed to the secondary digester, and so on. The material also passes through the tertiary, quaternary, and quinary digesters in sequence. The primary and secondary digesters are used to fully react the incoming material with water; the tertiary digester is used to fully react and age the material; the quaternary and quinary digesters are used for aging reaction; the digestion dust collector is set in the fourth stage. Above the first-stage digester, a system for separating the mixed gas and dust generated within the fourth-stage digester is used to ensure that the outlet dust meets standards. A heat exchanger connects to the outlet of the digester dust collector, utilizing the heat from the dust collector as a heat source for heat recovery. The hot water outlet of the heat exchanger connects to the digester water pump, which pumps hot water into the first and second-stage digesters. The material outlet of the fifth-stage digester connects to a semi-finished product elevator, which transports the material from the fifth-stage digester to the classifier. The classifier separates and screens the finished material according to specifications (e.g., 325 mesh, 200 mesh, or 400 mesh). The finished product from the classifier enters a finished product elevator, which transports the qualified material to the finished product silo. The slag from the classifier enters a slag elevator, which transports the slag separated by the classifier to the slag tank. The finished product silo stores the qualified material, and the slag tank stores the slag produced during production.

[0079] The continuous production method of the present invention will be further described in detail below with reference to specific embodiments and comparative examples, all of which adopt... Figure 1 The system shown is used to complete this task.

[0080] Example 1

[0081] Step 1: Quicklime granules with an activity of not less than 360 ml, an effective calcium oxide content of 95%, and a particle size of 3 mm are continuously added to the inlet of the primary digester at a feeding rate of 42 Hz set on the feed belt scale. At the same time, digestion water and sodium citrate additive (0.15% of the mass percentage of the water added in this step) are added at a water-to-material ratio of 0.35:1. The mixture is thoroughly stirred and turned at 900 r / min for premixing and predigestion. The total time for premixing and predigestion is 6 min. The temperature of the added digestion water is 80-85℃.

[0082] Step 2: The lime mixture at about 200°C, which has been premixed and predigested in the first digester, is introduced into the second digester. Digestion water at 80-85°C and sodium citrate additive at a water-to-material ratio of 0.35:1 are continuously added at the inlet of the second digester. The mixture is stirred and digested for 8 minutes at a stirring rate of 900 r / min.

[0083] Step 3: The outlet temperature of the secondary digester is approximately 260℃. Its output sequentially enters the tertiary, quaternary, and quinary digesters for further digestion and aging. The residence time in the tertiary digester is 8 minutes, the stirring rate is 900 r / min, and the outlet temperature is approximately 340℃. The residence time in the quaternary digester is 8 minutes, the stirring rate is 850 r / min, and the outlet temperature is approximately 90℃. The residence time in the quinary digester is 8 minutes, the stirring rate is 850 r / min, and the outlet temperature is approximately 90℃. Waste heat recovery is also performed. The semi-finished product discharged from the quinary digester is rapidly classified into 325-mesh particles by a classifier to obtain a finished product with a particle size greater than 325 mesh.

[0084] Example 2

[0085] Step 1: Quicklime granules with an activity of not less than 360 ml, an effective calcium oxide content of 95%, and a particle size of 3 mm are continuously added to the inlet of the primary digester at a feeding rate of 42 Hz set on the feed belt scale. At the same time, digestion water and sodium citrate additive (0.15% of the mass percentage of the water added in this step) are added at a water-to-material ratio of 0.35:1. The mixture is thoroughly stirred and turned at 850 r / min for premixing and predigestion. The total time for premixing and predigestion is 6 min. The temperature of the added digestion water is 80-85℃.

[0086] Step 2: The lime mixture at approximately 200°C, which has been premixed and predigested in the first-stage digester, is introduced into the second-stage digester. Digestion water at 80-85°C and sodium citrate additive at a water-to-material ratio of 0.35:1 are continuously added at the inlet of the second-stage digester. The mixture is stirred and digested for 7 minutes at a stirring rate of 850 r / min.

[0087] Step 3: The outlet temperature of the secondary digester is approximately 260℃. Its output sequentially enters the tertiary, quaternary, and quinary digesters for digestion and aging. The residence time in the tertiary digester is 7 minutes, the stirring rate is 900 r / min, and the outlet temperature is approximately 340℃. The residence time in the quaternary digester is 7 minutes, the stirring rate is 850 r / min, and the outlet temperature is approximately 90℃. The residence time in the quinary digester is 7 minutes, the stirring rate is 850 r / min, and the outlet temperature is approximately 90℃. Waste heat recovery is also performed. The semi-finished product discharged from the quinary digester is rapidly classified into 325-mesh particles by a classifier to obtain a finished product with a particle size greater than 325 mesh.

[0088] Using the above method, calcium hydroxide was continuously produced at a rate of 15 tons / hour. During the production process, the obtained calcium hydroxide product was tested every 60 minutes. Its whiteness, purity, and specific surface area were stable, as detailed below:

[0089]

[0090]

[0091] Comparative Example 1

[0092] Step 1: Quicklime granules with an activity of not less than 360 ml, an effective calcium oxide content of 95%, and a particle size of 3 mm are continuously added to the inlet of the primary digester at a feeding rate of 42 Hz set on the feed belt scale. At the same time, digestion water and sodium citrate additive (0.15% of the mass percentage of the water added in this step) are added at a water-to-material ratio of 0.35:1. The mixture is thoroughly stirred and turned at 900 r / min for premixing and predigestion. The total time for premixing and predigestion is 6 min. The temperature of the added digestion water is 70-75℃.

[0093] Step 2: The lime mixture at approximately 200°C, which has been premixed and predigested in the first-stage digester, is introduced into the second-stage digester. Digestion water at 70-75°C and sodium citrate additive (0.15% by mass of the water added in this step) are continuously added at the inlet of the second-stage digester at a water-to-material ratio of 0.35:1. The mixture is stirred and digested for 8 minutes at a stirring rate of 900 r / min.

[0094] Step 3: The outlet temperature of the secondary digester is approximately 260℃. Its output sequentially enters the tertiary, quaternary, and quinary digesters for further digestion and aging. The residence time in the tertiary digester is 8 minutes, the stirring rate is 900 r / min, and the outlet temperature is approximately 340℃. The residence time in the quaternary digester is 8 minutes, the stirring rate is 850 r / min, and the outlet temperature is approximately 90℃. The residence time in the quinary digester is 8 minutes, the stirring rate is 850 r / min, and the outlet temperature is approximately 90℃. Waste heat recovery is also performed. The semi-finished product discharged from the quinary digester is rapidly classified into 325-mesh particles by a classifier to obtain a finished product with a particle size greater than 325 mesh.

[0095] Comparative Example 2

[0096] Step 1: Quicklime granules with an activity of not less than 360 ml, an effective calcium oxide content of 95%, and a particle size of 3 mm are continuously added to the inlet of the primary digester at a feeding rate of 42 Hz set on the feed belt scale. At the same time, digestion water and sodium citrate additive at a water-to-material ratio of 0.35:1 and a mass percentage of the water added in this step are added. The mixture is thoroughly stirred and turned at 900 r / min for premixing and predigestion. The total time for premixing and predigestion is 6 min. The temperature of the added digestion water is 90-100℃.

[0097] Step 2: The lime mixture at approximately 200°C, which has been premixed and predigested in the first-stage digester, is introduced into the second-stage digester. Digestion water at 90-100°C and sodium citrate additive (0.15% by mass of the water added in this step) are continuously added at the inlet of the second-stage digester at a water-to-material ratio of 0.35:1. The mixture is stirred and digested for 8 minutes at a stirring rate of 900 r / min.

[0098] Step 3: The outlet temperature of the secondary digester is approximately 260℃. Its output sequentially enters the tertiary, quaternary, and quinary digesters for further digestion and aging. The residence time in the tertiary digester is 8 minutes, the stirring rate is 900 r / min, and the outlet temperature is approximately 340℃. The residence time in the quaternary digester is 8 minutes, the stirring rate is 850 r / min, and the outlet temperature is approximately 90℃. The residence time in the quinary digester is 8 minutes, the stirring rate is 850 r / min, and the outlet temperature is approximately 90℃. Waste heat recovery is also performed. The semi-finished product discharged from the quinary digester is rapidly classified into 325-mesh particles by a classifier to obtain a finished product with a particle size greater than 325 mesh.

[0099] Comparative Example 3

[0100] Step 1: Quicklime granules with an activity of not less than 360 ml, an effective calcium oxide content of 95%, and a particle size of 3 mm are continuously added to the inlet of the primary digester at a feeding rate of 42 Hz set on the feed belt scale. At the same time, digestion water and sodium citrate additive (0.15% of the mass percentage of the water added in this step) are added at a water-to-material ratio of 0.35:1. The mixture is thoroughly stirred and turned at 850 r / min for premixing and predigestion. The total time for premixing and predigestion is 6 min. The temperature of the added digestion water is 80-85℃.

[0101] Step 2: The 200℃ lime mixture, which has been premixed and pre-digested in the primary digester, is introduced into the secondary digester. Digestion water at 80-85℃ and sodium citrate additive (0.15% by mass of the water added in this step) are continuously added at the inlet of the secondary digester at a water-to-material ratio of 0.35:1. The mixture is stirred and digested for 7 minutes at a stirring rate of 850 r / min. The outlet temperature of the secondary digester is 260℃. The semi-finished product discharged from the secondary digester is rapidly classified by a classifier according to a particle size of 325 mesh to obtain a finished product with a particle size greater than 325 mesh.

[0102] Example 1, Comparative Examples 1 and 2 were digested with water at different temperatures. The indicators of the final products obtained after stable operation are compared in Table 1.

[0103] Table 1

[0104]

[0105] The unit for whiteness is degrees; the unit for specific surface area is m². 2 / g.

[0106] Example 2 and Comparative Example 3 employed multi-stage digestion and two-stage digester treatments, respectively. The comparison of their performance indicators after stable operation is shown in Table 2.

[0107] Table 2

[0108]

[0109] The unit for whiteness is degrees; the unit for specific surface area is m². 2 / g.

[0110] Performance testing

[0111] The method for determining the specific surface area of ​​solid materials adopts the national standard GB / T 19587-2017.

[0112] Whiteness testing was performed using ISO P277:2010.

[0113] Results data

[0114] Based on the data in the table above, a comparison of the examples shows that, with the digestion aid water temperature as a single variable, the product whiteness and specific surface area are optimal at the recommended temperature. Analysis was conducted with the number of digester stages as a single variable. The use of a two-stage digester versus a five-stage digester significantly impacted the finished product's indicators, greatly affecting the final product's whiteness, specific surface area, and the rate of complete reaction of raw materials during the preparation process. Data collection and analysis revealed that a five-stage digestion process resulted in complete reaction and high equipment utilization, leading to excellent final product performance and stable product quality.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A continuous production method for calcium hydroxide with high whiteness and high specific surface area, characterized in that, Includes the following steps: Step 1: Quicklime granules are continuously added to the inlet of the primary digester. At the same time, 80-85℃ digestion water and additives are continuously added to the quicklime granules at the inlet of the primary digester according to the set water-to-material ratio. The whole process is carried out under stirring to achieve premixing and predigestion. The inlet temperature of the primary digester is controlled at 85-130℃. Step 2: The material that has been premixed and predigested in the primary digester is continuously introduced into the secondary digester. At the same time, 80-85℃ digestion water and additives are continuously added at the inlet of the secondary digester according to the set water-to-material ratio, and the mixture is stirred, digested and aged. Step 3: The material from the secondary digester enters the tertiary, quaternary and quinary digesters for digestion and aging, and is then graded by a classifier to obtain the product; The water-to-material ratio set in step one is 0.35:1, and the water-to-material ratio set in step two is also 0.35:

1. The digestive aids mentioned in Step 1 and Step 2 are one or more of the following: ethylene glycol, propylene glycol, butylene glycol, glucose, sodium citrate, sodium pyrophosphate, glycerol, triethanolamine, and sucrose. The amount of additives added in steps one and two is 0.001-0.15% of the mass percentage of water added in each step; In step one, the average residence time of the material in the primary digester for premixing and predigestion is ≤6 min, and the aging time of the material in the secondary, tertiary, quaternary and quinary digesters is 6-8 min, respectively.

2. The continuous production method of high-whiteness, high-specific-surface-area calcium hydroxide according to claim 1, characterized in that, In step one, the quicklime particles are continuously added to the primary digester at a feeding rate set by the feed belt scale, which is 35-50Hz. And / or, the quicklime has an activity of not less than 360 ml, an effective calcium oxide content of ≥90%, and a particle size of ≤3 mm.

3. The continuous production method of high-whiteness, high-specific-surface-area calcium hydroxide according to claim 1, characterized in that, The water used for digestion in Step 1 and Step 2 comes from a heat exchanger, which uses heat from the rotary kiln exhaust gas and / or the heat generated by the four-stage digester as a heat source.

4. The continuous production method of high-whiteness, high-specific-surface-area calcium hydroxide according to claim 1, characterized in that, The outlet temperature of the first-stage digester is 150-230℃, the outlet temperature of the second-stage digester is 260-390℃, the outlet temperature of the third-stage digester is 340-390℃, the outlet temperature of the fourth-stage digester is 85-140℃, and the outlet temperature of the fifth-stage digester is 85-130℃. And / or, the stirring rate of the first-stage digester is 650-950 r / min, the stirring rate of the second-stage digester is 700-900 r / min, the stirring rate of the third-stage digester is 700-900 r / min, the stirring rate of the fourth-stage digester is 600-850 r / min, and the stirring rate of the fifth-stage digester is 600-850 r / min.

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