A method for drying wet calcium carbonate particles at room temperature using a fluidized bed

Abstract

The present invention belongs to the technical field of drying chemical products, and specifically relates to a method for fluidized drying of wet calcium carbonate particles at room temperature with controlled humidity. The method for fluidized drying of wet calcium carbonate particles provided by the present invention comprises the following steps: the wet calcium carbonate particles are subjected to a first fluidized drying and a second fluidized drying in sequence to obtain calcium carbonate particles; in the first fluidized drying, the temperature of the drying medium is 20 to 30°C, and the relative humidity is 3% to 10% lower than the relative humidity on the surface of the wet calcium carbonate particles; in the second fluidized drying, the temperature of the drying medium is 50 to 70°C, and the relative humidity is less than 40%. The present invention maintains a normal temperature of the fluidized medium in the first fluidized drying stage, and by controlling the moisture content of the fluidized medium to be 3% to 10% lower than the relative humidity on the surface of the wet calcium carbonate particles, the surface of the wet particles is kept loose, so that the liquid component continuously migrates from the inside of the particles to the surface of the particles, thereby being able to reduce the liquid component content to the required level.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical product drying, and particularly relates to a normal-temperature, humidity-controlled fluidized drying method for wet calcium carbonate particles. Background Art

[0002] Wet granule drying technology mainly involves the process of dehydrating wet granules to obtain dry granules. In this process, the moisture or other liquid components in the wet granules are removed to obtain a dry product. At present, the drying of wet granules is carried out by exchanging heat and mass between hot air and the surface of the wet granules. Specifically, the air is first heated to reduce the relative humidity of the fluidized air, and at the same time, the heat is transferred to the surface of the wet granules. After the liquid components on the surface of the wet granules evaporate into the fluidized hot air, the temperature of the outer layer of the wet granules increases, and the heat is transferred inward. The liquid components inside the wet granules heat up and migrate to the outer layer of the granules, and then evaporate on the surface of the granules, drying the liquid components in the wet granules to the required requirements.

[0003] However, for materials containing calcium carbonate, although increasing the temperature of the hot air will reduce the relative humidity of the hot air, the surface temperature of the wet particles is much lower than that of the hot air, while the relative humidity is much higher than that of the hot air. The combination of these two factors causes the liquid components on the surface of the wet particles to evaporate too quickly, and the rate at which the liquid components inside the wet particles migrate outward is lower than the evaporation rate of the liquid components on the outer surface of the wet particles, causing the outer surface of the wet particles to dry out too quickly and form a compaction, which hinders the migration and evaporation of the liquid components inside the wet particles to the surface of the particles. Even if the hot air temperature continues to increase, the liquid components inside the particles cannot migrate to the surface of the particles, and further increasing the hot air temperature will cause the material to deteriorate due to high temperature. This makes it difficult to dry the liquid components inside the particles to the required requirements during hot air fluidization drying of wet particles containing calcium carbonate. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a normal temperature humidity-controlled fluidized drying method for wet calcium carbonate particles. The normal temperature humidity-controlled fluidized drying method provided by the present invention can fully dry the wet calcium carbonate particles.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for drying wet calcium carbonate particles by fluidized bed drying at room temperature with controlled humidity, comprising the following steps:

[0007] sequentially subjecting the wet calcium carbonate particles to a first fluidized drying step and a second fluidized drying step to obtain calcium carbonate particles;

[0008] In the first fluidized drying, the temperature of the drying medium is 20-30° C., and the relative humidity is 3%-10% lower than the relative humidity of the surface of the wet calcium carbonate particles;

[0009] In the second fluidized drying, the temperature of the drying medium is 50-70° C., and the relative humidity is less than 40%.

[0010] Preferably, the surface relative humidity of the wet calcium carbonate particles is 60% to 90%.

[0011] Preferably, the median particle size of the calcium carbonate wet granules is 120 to 200 μm.

[0012] Preferably, the calcium carbonate wet granules include, by mass, 50-90 parts of calcium carbonate, 10-20 parts of maltodextrin, 1-10 parts of glucose and 5-10 parts of ethanol aqueous solution.

[0013] Preferably, the ethanol content of the ethanol aqueous solution is 65% to 80% by mass.

[0014] Preferably, the drying medium for the first fluidized drying and the second fluidized drying is air.

[0015] Preferably, the frequency of the air inlet motor of the first fluidized drying is 14-20 Hz, and the time is 10-50 minutes.

[0016] Preferably, the frequency of the air inlet motor of the second fluidized drying is 15 to 30 Hz, and the time is 10 to 70 minutes.

[0017] Preferably, the first fluidized drying and the second fluidized drying equipment are both fluidized beds.

[0018] The present invention provides a normal-temperature, humidity-controlled fluidized drying method for wet calcium carbonate granules, comprising the following steps: sequentially subjecting the wet calcium carbonate granules to a first fluidized drying step and a second fluidized drying step to obtain the calcium carbonate granules; in the first fluidized drying step, the temperature of the drying medium is 20-30°C, and the relative humidity is 3%-10% lower than the relative humidity on the surface of the wet calcium carbonate granules; in the second fluidized drying step, the temperature of the drying medium is 50-70°C, and the relative humidity is less than 40%. In the first fluidized drying step, while maintaining the fluidized medium at a normal temperature, the moisture content in the fluidized medium is controlled to be 3%-10% lower than the relative humidity on the surface of the wet calcium carbonate granules, thereby maintaining a slow evaporation rate of liquid components on the surface of the wet granules and maintaining a loose surface of the wet granules. Since the liquid content inside the wet granules is higher than that on the granule surface, the resulting concentration difference causes the liquid components to continuously migrate from the granule interior to the granule surface, reducing the liquid content inside and outside the wet granules to a relatively low level. The temperature is then raised and the fluidized drying step is continued, thereby reducing the liquid content to a desired level. DETAILED DESCRIPTION

[0019] The present invention provides a method for drying wet calcium carbonate particles by fluidized bed drying at room temperature with controlled humidity, comprising the following steps:

[0020] sequentially subjecting the wet calcium carbonate particles to a first fluidized drying step and a second fluidized drying step to obtain calcium carbonate particles;

[0021] In the first fluidized drying, the temperature of the drying medium is 20-30° C., and the relative humidity is 3%-10% lower than the relative humidity of the surface of the wet calcium carbonate particles;

[0022] In the second fluidized drying, the temperature of the drying medium is 50-70° C., and the relative humidity is less than 40%.

[0023] In the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art.

[0024] In parts by mass, the calcium carbonate wet granules of the present invention preferably include 50 to 90 parts of calcium carbonate, more preferably 60 to 90 parts, and most preferably 70 to 80 parts.

[0025] Based on the mass fraction of calcium carbonate, the calcium carbonate wet granules of the present invention preferably include 10 to 20 parts of maltodextrin, more preferably 12 to 18 parts, and most preferably 14 to 16 parts.

[0026] Based on the mass fraction of calcium carbonate, the calcium carbonate wet granules of the present invention preferably include 1 to 10 parts of glucose, more preferably 2 to 8 parts, and most preferably 4 to 6 parts.

[0027] Based on the mass fraction of calcium carbonate, the calcium carbonate wet granules of the present invention preferably include 5 to 10 parts of ethanol aqueous solution, more preferably 6 to 8 parts; the ethanol mass percentage of the ethanol aqueous solution is preferably 65% ​​to 80%, more preferably 75% to 80%, and most preferably 75%.

[0028] In the present invention, the relative humidity of the surface of the wet calcium carbonate particles is preferably 60% to 90%, more preferably 70% to 80%.

[0029] In the present invention, the particle size of the calcium carbonate wet granules is preferably 120 to 200 μm, more preferably 130 to 180 μm, and most preferably 150 to 180 μm.

[0030] In the present invention, the equipment for the first fluidized drying is preferably a fluidized bed; the drying medium for the first fluidized drying is preferably air; the temperature of the drying medium is preferably 20-30°C, more preferably 25-30°C; the relative humidity is 50%-87%, more preferably 60%-85%, most preferably 70%-80%, preferably 3%-10% lower than the surface relative humidity of the wet calcium carbonate particles, more preferably 4%-8% lower, most preferably 4%-5% lower; the relative humidity of the drying medium is preferably controlled by a rotary dehumidifier; the frequency of the air inlet motor for the first fluidized drying is preferably 14-20 Hz, more preferably 15-18 Hz; the time is preferably 10-50 min, more preferably 10-40 min; and the first fluidized drying is preferably terminated when the temperature of the wet calcium carbonate particles reaches the temperature of the drying medium.

[0031] In the present invention, the equipment for the second fluidized drying is preferably a fluidized bed; the drying medium for the second fluidized drying is preferably air; the temperature of the drying medium is preferably 50-70°C, more preferably 55-65°C, and most preferably 60°C; the relative humidity is preferably <40%, more preferably <35%, and most preferably <30%; the relative humidity of the drying medium is preferably the normal relative humidity of air, that is, there is no need to control the relative humidity; the frequency of the air inlet motor for the second fluidized drying is preferably 15-30 Hz, more preferably 16-26 Hz, and most preferably 17-25 Hz; the time is preferably 10-70 min, more preferably 15-60 min, and most preferably 20-60 min; and the second fluidized drying is preferably terminated when the moisture content in the calcium carbonate particles is as low as 1%.

[0032] The method for fluidized drying of wet calcium carbonate particles at a constant temperature provided by the present invention comprises the following steps: in a first fluidized drying process, the fluidized medium is kept at a normal temperature, and the moisture content in the fluidized medium is controlled to be 3% to 10% lower than the relative humidity on the surface of the wet calcium carbonate particles, so that the evaporation rate of the liquid components on the surface of the wet particles is maintained at a relatively slow rate, and the surface of the wet particles is kept loose. Since the liquid component content inside the wet particles is higher than that on the particle surface, the resulting concentration difference causes the liquid components to continuously migrate from the particle interior to the particle surface, so that the liquid component content inside and outside the wet particles reaches a relatively low level. The temperature is then raised to continue fluidized drying, thereby reducing the liquid component content to a desired level.

[0033] To further illustrate the present invention, the method for drying wet calcium carbonate granules at room temperature by fluidized bed drying according to the present invention is described in detail below with reference to the following examples. However, these examples should not be construed as limiting the scope of protection of the present invention.

[0034] Example 1

[0035] Calcium carbonate wet granules with a median particle size of 170 μm were prepared by combining 80 parts by mass of calcium carbonate, 15 parts by mass of maltodextrin, 5 parts by mass of glucose, and 7 parts by mass of a 75% ethanol aqueous solution. The relative humidity of the granules was 80% at 25°C.

[0036] The calcium carbonate wet granules were placed in a fluidized bed for drying, with air as the drying medium. The inlet air temperature was set at 25°C, the inlet air motor frequency was 15Hz, and the inlet air relative humidity was controlled at 70% to 75% by a rotary dehumidifier. After drying for 30 minutes, the temperature of the wet granules reached 25°C.

[0037] The inlet air temperature was increased to 60°C, the inlet motor frequency was 18 Hz, the relative humidity was 25%, and the temperature of the wet particles reached 60°C after drying for 20 minutes. The moisture content of the dry particles was measured by an infrared moisture meter and was less than 1%. The drying was terminated to obtain calcium carbonate particles.

[0038] The residual ethanol content in the dry calcium carbonate particles was determined by the loss on drying method. The calcium carbonate particles were dried at 105° C. to a constant weight, and the calculated weight loss was no more than 0.5 wt %, indicating that the residual ethanol content in the dry calcium carbonate particles was no more than 0.5 wt %.

[0039] Comparative Example 1

[0040] Calcium carbonate wet granules with a median particle size of 180 μm were prepared by combining 80 parts by mass of calcium carbonate, 15 parts by mass of maltodextrin, 5 parts by mass of glucose, and 7 parts by mass of a 75% ethanol aqueous solution. The relative humidity on the surface of the granules was 80% at 25°C.

[0041] The wet calcium carbonate particles were placed in a fluidized bed for drying, with air as the drying medium, the inlet air temperature set to 60°C, the inlet air motor frequency to 18 Hz, and the relative humidity to less than 30%. After drying for 30 minutes, the temperature of the wet particles reached 60 degrees. The moisture content of the dry particles was measured by an infrared moisture meter and was less than 1 wt%. The drying was completed to obtain calcium carbonate particles.

[0042] The residual ethanol content in the dry calcium carbonate particles was determined by the loss on drying method. The calcium carbonate particles were dried to a constant weight at 105° C. The calculated weight loss was 1.3 wt %, exceeding the drying limit requirement of 0.5 wt %.

[0043] Example 2

[0044] Calcium carbonate wet granules with a median particle size of 180 μm were prepared by combining 80 parts of calcium carbonate, 15 parts of maltodextrin, 5 parts of glucose and 8 parts of a 75% ethanol aqueous solution in parts by mass. The relative humidity on the surface of the granules was 75% at 30°C.

[0045] The calcium carbonate wet granules were placed in a fluidized bed for drying, with air as the drying medium, the air inlet temperature set at 30°C, the air inlet motor frequency at 15Hz, and the relative humidity controlled at 65% to 70% by a rotary dehumidifier. After drying for 20 minutes, the temperature of the wet granules reached 30°C.

[0046] The inlet air temperature was increased to 60°C, the inlet motor frequency was 20 Hz, the relative humidity was 25%, and the temperature of the wet particles reached 60°C after drying for 30 minutes. The moisture content of the dry particles was measured by an infrared moisture meter and was less than 1%. The drying was terminated to obtain calcium carbonate particles.

[0047] The residual ethanol content in the dry calcium carbonate particles was determined by the loss on drying method. The calcium carbonate particles were dried at 105° C. to a constant weight, and the calculated weight loss was no more than 0.5 wt %, indicating that the residual ethanol content in the dry calcium carbonate particles was no more than 0.5 wt %.

[0048] Comparative Example 2

[0049] Calcium carbonate wet granules with a particle size of 180 μm were prepared by combining 80 parts by mass of calcium carbonate, 15 parts by mass of maltodextrin, 5 parts by mass of glucose, and 8 parts by mass of a 75% ethanol aqueous solution. The relative humidity on the surface of the granules was 75% at 30°C.

[0050] The wet calcium carbonate particles are placed in a fluidized bed for drying, with air as the drying medium, the air inlet temperature set to 60°C, the air inlet motor frequency to 20Hz, and the relative humidity to 25%. After drying for 30 minutes, the temperature of the wet particles reaches 60 degrees. The moisture content of the dry particles is measured by an infrared moisture meter and is less than 1%. The drying is completed to obtain calcium carbonate particles.

[0051] The residual ethanol content in the dry calcium carbonate particles was determined by the loss on drying method. The calcium carbonate particles were dried to a constant weight at 105° C. The calculated weight loss was 1.4 wt %, exceeding the drying limit requirement of 0.5 wt %.

[0052] As can be seen from the above embodiment, the two-stage fluidized drying process of the present invention can ensure that the moisture and ethanol content of the wet particles containing calcium carbonate meet the process requirements after the second stage fluidized drying by controlling the temperature and humidity of the inlet air to be close to the particle surface in the first stage.

[0053] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for drying wet calcium carbonate particles by fluidized bed drying at room temperature with controlled humidity, characterized in that: The following steps are involved: sequentially subjecting the wet calcium carbonate particles to a first fluidized drying step and a second fluidized drying step to obtain calcium carbonate particles; During the first fluidized drying, the temperature of the drying medium is 20-30° C., and the relative humidity is 3%-10% lower than the relative humidity of the surface of the wet calcium carbonate particles; the first fluidized drying ends when the temperature of the wet calcium carbonate particles reaches the temperature of the drying medium; the relative humidity of the surface of the wet calcium carbonate particles is 60%-90%; In the second fluidized drying, the temperature of the drying medium is 50-70° C., and the relative humidity is less than 40%.

2. The normal temperature humidity controlled fluidized bed drying method according to claim 1, characterized in that: The median particle size of the calcium carbonate wet particles is 120 to 200 μm.

3. The normal temperature humidity controlled fluidized bed drying method according to claim 1, characterized in that: Calculated by mass, the calcium carbonate wet granules include 50-90 parts of calcium carbonate, 10-20 parts of maltodextrin, 1-10 parts of glucose and 5-10 parts of ethanol aqueous solution.

4. The normal temperature humidity controlled fluidized bed drying method according to claim 3, characterized in that: The ethanol mass percentage of the ethanol aqueous solution is 65-80%.

5. The normal temperature humidity controlled fluidized bed drying method according to claim 1, characterized in that: The drying medium of the first fluidized drying and the second fluidized drying is air.

6. The normal temperature humidity controlled fluidized bed drying method according to claim 1 or 5, characterized in that: The frequency of the air inlet motor of the first fluidized drying is 14-20 Hz, and the drying time is 10-50 minutes.

7. The normal temperature humidity controlled fluidized bed drying method according to claim 1 or 5, characterized in that: The frequency of the air inlet motor of the second fluidized drying is 15 to 30 Hz, and the drying time is 10 to 70 minutes.

8. The normal temperature humidity controlled fluidized bed drying method according to claim 1, characterized in that: The equipment for the first fluidized drying and the second fluidized drying are both fluidized beds.