Drying equipment and drying methods

Abstract

The present invention provides drying equipment and a drying method that can reduce the amount of solid particles released into the atmosphere. [Solution] The drying equipment includes a dryer 20 having an inlet 25 for charging solid particles, a hot air supply port 23 for supplying hot air, a gas outlet 24 for discharging the hot air that has been blown onto the solid particles as exhaust gas, and an outlet 26 for extracting the dried solid particles after they have been blown onto the hot air; a dust removal device; and a flue 36 connecting the dryer and the dust removal device. An air introduction section is provided in the middle of the flue 36 to introduce air into the flue, and the air-mixed gas, whose flow rate has increased due to the mixing of air with the exhaust gas, is guided to the dust removal device, where solid particles contained in the air-mixed gas are removed.

Description

Technical Field

[0001] The present invention relates to a drying facility and a drying method. More specifically, the present invention relates to a drying facility and a drying method for drying solid particles such as nickel sulfate crystals by blowing hot air thereon.

Background Art

[0002] When an aqueous nickel sulfate solution is treated in a crystallization can, nickel sulfate crystals precipitate. The slurry discharged from the crystallization can is subjected to solid-liquid separation to recover the nickel sulfate crystals, and then the nickel sulfate crystals to which the mother liquor adheres are dried to obtain a product. Drying of the nickel sulfate crystals is performed by a dryer that blows hot air (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The hot air after being blown onto the nickel sulfate crystals in the dryer is discharged as exhaust gas from the gas outlet of the dryer. In addition, part of the nickel sulfate crystals is scattered by the wind pressure of the hot air, and is discharged from the gas outlet together with the exhaust gas. That is, nickel sulfate crystals are mixed into the exhaust gas of the dryer. The nickel sulfate crystals can be removed by passing the exhaust gas through a dust collector. However, perfect removal is difficult, and extremely trace amounts of nickel sulfate crystals are released into the atmosphere together with the atmospheric discharge gas discharged from the dust collector. When nickel sulfate crystals are released into the atmosphere, nickel loss occurs. As described above, in drying facilities for drying solid particles such as nickel sulfate crystals, it is required to suppress the discharge of solid particles into the atmosphere.

[0005] In view of the above circumstances, the present invention aims to provide a drying facility and a drying method that can reduce the amount of solid particles released into the atmosphere. [Means for solving the problem]

[0006] The drying apparatus of the first embodiment comprises a dryer having an inlet for charging solid particles, a hot air supply port for supplying hot air, a gas outlet for discharging the hot air that has been blown onto the solid particles as exhaust gas, and an outlet for extracting the solid particles after they have been dried by the hot air; a dust removal device having a dry cyclone and / or a wet scrubber; and a flue connecting the gas outlet of the dryer and the dust removal device, wherein an air introduction section is provided in the middle of the flue for introducing air into the flue, and the air-mixed gas, whose flow rate has increased due to the mixing of air with the exhaust gas, is guided to the dust removal device, in which the solid particles contained in the air-mixed gas are removed. The drying equipment of the second embodiment is characterized in that, in the first embodiment, the air intake section is provided in the flue and comprises an air intake port for drawing air into the flue, and a flow control valve for controlling the amount of air drawn in from the air intake port, wherein the air pressure inside the flue is lower than atmospheric pressure. The drying equipment of the third embodiment is characterized in that, in the second embodiment, it comprises a concentration meter for measuring the dust concentration of atmospheric exhaust gas discharged into the atmosphere from the dust removal device, and a control device for controlling the valve opening of the flow control valve and the amount of hot air supplied to the dryer so that the amount of solid particles discharged into the atmosphere, determined from the dust concentration, is less than or equal to a target value. The drying method of the fourth embodiment is a method for drying solid particles using the drying equipment of the second or third embodiment, characterized in that the amount of air intake is 30% to 60% of the flow rate of the exhaust gas at the gas outlet. The fifth aspect of the drying method is a method for drying solid particles using a drying apparatus according to any of the first to third aspects, wherein the dryer has a screen on which the solid particles are supplied to the upper surface and on which the hot air is blown up from below, and the flow velocity of the hot air blown up through the screen is 0.5 to 1.5 m / second. The drying method of the sixth embodiment is a method for drying the solid particles using the drying equipment of the second or third embodiment, characterized in that the flow velocity of the exhaust gas at the time it passes through the gas outlet is 8 to 10 m / sec. The seventh aspect of the drying method is a method of drying the solid particles using any of the drying equipment of the first to third aspects, characterized in that the solid particles are nickel sulfate crystals. [Effects of the Invention]

[0007] According to the first embodiment, since air is introduced into the flue connecting the dryer and the dust removal device, the flow velocity of the air mixed in the dust removal device can be increased while suppressing the flow velocity of the hot air inside the dryer. As a result, the amount of solid particles discharged from the dryer along with the exhaust gas can be reduced, and the dust removal efficiency of the dust removal device can be increased. Consequently, the amount of solid particles discharged into the atmosphere can be reduced. According to the second embodiment, since air is introduced into the flue by utilizing the pressure difference inside and outside the flue, a dedicated power source is not required for introducing air, and the device configuration can be simplified. According to the third embodiment, the amount of air intake is controlled while monitoring the amount of solid particles released into the atmosphere, thereby reliably reducing the amount of solid particles released into the atmosphere. According to the fourth embodiment, compared to the case where air is not introduced into the flue, the amount of solid particles emitted into the atmosphere can be reduced by 25% to 50%. According to the fifth embodiment, since the hot air flow velocity is 0.5 m / sec or more, solid particles can be sufficiently dried. Also, since the hot air flow velocity is 1.5 m / sec or less, the amount of solid particles discharged with the exhaust gas can be reduced. According to the sixth embodiment, since the exhaust gas flow velocity is 8 m / s or more, air can be smoothly introduced into the air intake section. Furthermore, since the exhaust gas flow velocity is 10 m / s or less, the amount of solid particles discharged along with the exhaust gas can be reduced. According to the seventh embodiment, the amount of nickel sulfate crystals released into the atmosphere can be reduced. [Brief explanation of the drawing]

[0008] [Figure 1]This is an explanatory diagram of a crystallization apparatus and a drying apparatus according to one embodiment. [Figure 2] This is an explanatory diagram of a dryer and an air intake unit according to one embodiment. [Figure 3] This graph shows the relationship between atmospheric exhaust gas flow rate and atmospheric emissions of nickel sulfate crystals. [Modes for carrying out the invention]

[0009] Next, embodiments of the present invention will be described based on the drawings. A drying apparatus according to one embodiment of the present invention is incorporated, for example, into a crystallization apparatus for producing nickel sulfate crystals. Therefore, the crystallization apparatus will be described first.

[0010] (Crystalling equipment) As shown in Figure 1, the crystallization equipment CR is a facility that crystallizes using a stock solution to produce crystals as a product. The stock solution is a solution of the component to be crystallized. Examples of components to be crystallized include nickel sulfate, ammonium sulfate, sodium carbonate, caprolactam, and trehalose. If an aqueous solution of nickel sulfate is used as the stock solution, nickel sulfate crystals can be obtained as the product. The following explanation will use the case where an aqueous solution of nickel sulfate is used as the stock solution as an example.

[0011] The crystallization apparatus CR has a mixing tank 11. The stock solution (aqueous nickel sulfate solution) is supplied to the mixing tank 11. The mother liquor, off-spec crystals, and recovered crystals, as described later, are also supplied to the mixing tank 11. The stock solution, mother liquor, off-spec crystals, and recovered crystals are mixed in the mixing tank 11 to obtain a mixed solution. The mixed solution discharged from the mixing tank 11 is supplied to the crystallization vessel 12.

[0012] The crystallizer tank 12 crystallizes nickel sulfate from the mixed solution. The crystallizer tank 12 precipitates nickel sulfate crystals by evaporating the water content of the nickel sulfate aqueous solution under a predetermined pressure. As the crystallizer tank 12, for example, a DTB (Draft Tube Baffle) type continuous crystallizer is used. The internal pressure of the crystallizer tank 12 is adjusted to, for example, 4 to 12 kPa by a vacuum pump or the like. Inside the crystallizer tank 12, a slurry in which the nickel sulfate aqueous solution and nickel sulfate crystals are mixed is held. The crystallizer tank 12 performs crystallization while stirring the internal slurry with a stirring blade.

[0013] The temperature of the slurry in the crystallizer tank 12 decreases as heat is removed by the evaporation of water content. The slurry circulates between the crystallizer tank 12 and a heat exchanger (not shown). By heating the slurry with the heat exchanger, the liquid temperature of the slurry in the crystallizer tank 12 is kept constant. As the heat exchanger, for example, a shell-and-tube heat exchanger is used. Further, the liquid temperature of the slurry in the crystallizer tank 12 is maintained at, for example, 32 to 53°C.

[0014] The slurry discharged from the crystallizer tank 12 is supplied to the solid-liquid separation device 13. The solid-liquid separation device 13 performs solid-liquid separation of the slurry into nickel sulfate crystals and a mother liquor. The mother liquor discharged from the solid-liquid separation device 13 is supplied to the mixing tank 11. The mother liquor adheres to the nickel sulfate crystals discharged from the solid-liquid separation device 13. The nickel sulfate crystals are supplied to the dryer 20 to remove moisture. The dried nickel sulfate crystals are supplied to the classification device 14.

[0015] For nickel sulfate crystals produced by the crystallization equipment CR, a proper particle size is set for the product. The classifier 14 classifies the supplied nickel sulfate crystals into in-spec crystals having a particle size within the specification and out-of-spec crystals having a particle size outside the specification. Here, crystals with a proper particle size that is equal to or greater than the lower limit and equal to or less than the upper limit are defined as in-spec crystals, and small-particle-size crystals with a particle size less than the lower limit and large-particle-size crystals with a particle size exceeding the upper limit are defined as out-of-spec crystals. For example, the particle size of the in-spec crystals is adjusted such that crystals of 0.4 to 2.0 mm account for more than 90% by weight. The in-spec crystals obtained by the classifier 14 are shipped as products after being packed. On the other hand, the out-of-spec crystals obtained by the classifier 14 are returned to the mixing tank 11.

[0016] (Drying equipment, drying method) Next, a drying equipment AA according to an embodiment of the present invention and a drying method using the drying equipment AA will be described. The drying equipment AA of the present embodiment is used for drying nickel sulfate crystals to which mother liquor adheres. However, the object to be dried only needs to be solid particles. The object to be dried is not limited to nickel sulfate crystals, and may be crystals of other components to be crystallized. Further, the object to be dried is not limited to crystals obtained by crystallization, and may be other solid particles.

[0017] The drying equipment AA includes a dryer 20. A hot air generator 31 is connected to the dryer 20. The hot air generator 31 is composed of a fan for sending atmospheric air and a heater for heating the atmospheric air. Hot air is supplied from the hot air generator 31 to the dryer 20.

[0018] The dryer 20 blows hot air onto the solid particles to remove moisture from the solid particles. The hot air after being blown onto the solid particles is discharged from the dryer 20 as exhaust gas. The configuration of the dryer 20 will be described later.

[0019] When hot air is blown onto solid particles, some of the solid particles are scattered and discharged from the dryer 20 along with the exhaust gas. In other words, solid particles are mixed into the exhaust gas from the dryer 20. The exhaust gas is then led to a dust removal device, where the solid particles contained in the exhaust gas are removed. In this embodiment, the dust removal device consists of a dry cyclone 32 and a wet scrubber 33. Nickel sulfate crystals recovered by the dry cyclone 32 are supplied to the mixing tank 11 as recovered crystals.

[0020] Furthermore, the wet scrubber 33 used is one that has higher dust removal efficiency as the gas flow velocity increases. Examples of this type of wet scrubber 33 include venturi scrubbers, jet scrubbers, and wet cyclones. Alternatively, a dry cyclone 32 may be installed upstream of the gas flow, and a wet scrubber 33 downstream. Alternatively, a wet scrubber 33 may be installed upstream of the gas flow, and a dry cyclone 32 downstream. Moreover, the dust removal device may consist of either a dry cyclone 32 or a wet scrubber 33. The following explanation will use the case where the dry cyclone 32 and the wet scrubber 33 are connected in this order along the gas flow as an example.

[0021] Downstream of the dust removal device (wet scrubber 33), an exhaust fan 34 is provided to draw gas from the dust removal device. The operation of the exhaust fan 34 causes the exhaust gas generated in the dryer 20 to pass through the dry cyclone 32 and the wet scrubber 33 and be discharged into the atmosphere. Hereinafter, the gas discharged from the dust removal device into the atmosphere will be referred to as atmospheric exhaust gas.

[0022] A chimney is provided on the exhaust side of the exhaust fan 34. A concentration meter 35 for measuring the dust concentration of the exhaust gas can be installed in this chimney. A soot concentration meter can be used as the concentration meter 35. The concentration meter 35 can be used to measure the dust concentration of the exhaust gas. Furthermore, by multiplying the dust concentration of the exhaust gas by the flow rate of the exhaust gas, the amount of solid particles released into the atmosphere can be determined. The flow rate of the exhaust gas can be measured with a flow meter installed in the chimney, or it can be determined from the rotation speed of the exhaust fan 34.

[0023] As the dryer 20, a fluidized bed dryer as shown in Figure 2 can be used. The dryer 20 has a sealed container 21. A screen 22 is provided at the bottom of the container 21, dividing the internal space of the container 21 into upper and lower sections. A hot air supply port 23 is provided at the bottom of the container 21, located below the screen 22. Hot air is supplied to the hot air supply port 23 from a hot air generator 31. A gas outlet 24 is provided at the top of the container 21, located above the screen 22. The hot air rises inside the container 21, passes through the screen 22, and is then discharged as exhaust gas from the gas outlet 24.

[0024] The container 21 is provided with an inlet 25. Solid particles with liquid attached are charged in through the inlet 25 and supplied to the upper surface of the screen 22. The solid particles form a fluidized bed due to the hot air blown up from below the screen 22. After being exposed to the hot air and dried, the solid particles are removed from the outlet 26.

[0025] The exhaust gas from dryer 20 is led to a dust removal device, where solid particles contained in the exhaust gas are removed. However, complete removal is difficult, and a very small amount of solid particles are released into the atmosphere along with the exhaust gas. It is possible to improve the dust removal efficiency by modifying or upgrading the dust removal device, but this would increase the equipment cost.

[0026] One way to reduce the amount of solid particles released into the atmosphere is to increase the flow rate of the gas supplied to the dust removal device to improve dust removal efficiency. Increasing the flow rate of the gas supplied to the dry cyclone 32 increases the swirling speed of the airflow within the cyclone, resulting in a stronger centrifugal force. This makes it easier to remove solid particles, especially those with larger particle sizes. In addition, with the wet scrubber 33, particularly the venturi scrubber, increasing the gas flow rate promotes the atomization of the liquid in the venturi section, increasing the contact area between the solid particles and the liquid, thus capturing more solid particles.

[0027] On the other hand, if the flow rate of hot air in the dryer 20 is made too fast, solid particles will be more easily scattered, and the amount of solid particles discharged with the exhaust gas will increase. In order to reduce the amount of solid particles discharged from the dryer 20 with the exhaust gas, it is necessary to reduce the flow rate of hot air. Also, if the flow rate of hot air is increased, the energy consumption of the fan and heater of the hot air generator 31 will increase, and energy costs will rise.

[0028] In contrast, if the flow rate of hot air in the dryer 20 can be reduced while increasing the flow rate of gas supplied to the dust removal device, the amount of solid particles discharged into the atmosphere can be reduced.

[0029] As shown in Figure 1, the dryer 20 and the dust removal device (dry cyclone 32) are connected by a flue 36. Exhaust gas is guided from the dryer 20 to the dust removal device (dry cyclone 32) via the flue 36. An air inlet 40 is provided in the middle of the flue 36 to introduce air into the flue 36. That is, air is mixed with the exhaust gas discharged from the dryer 20, and the gas with increased flow rate is supplied to the dust removal device. Hereinafter, the gas in which air has been mixed with exhaust gas will be referred to as air-mixed gas.

[0030] In this way, since air is introduced into the flue 36 connecting the dryer 20 and the dust removal device, the flow velocity of the hot air inside the dryer 20 can be suppressed while the flow velocity of the air-mixed gas inside the dust removal device can be increased. By suppressing the flow velocity of the hot air, the amount of solid particles discharged from the dryer 20 along with the exhaust gas can be reduced. In addition, by increasing the flow velocity of the air-mixed gas, the dust removal efficiency of the dust removal device can be improved. As a result, the amount of solid particles released into the atmosphere can be reduced. When the material to be dried is nickel sulfate crystals, the amount of nickel sulfate crystals released into the atmosphere can be reduced. Furthermore, since there is no need to increase the flow rate of the hot air, the energy cost of the hot air generator 31 does not increase.

[0031] An example of the air intake section 40 is shown in Figure 2. A flue 36 is connected to the gas outlet 24 of the dryer 20. The exhaust gas is guided to the dust removal device through the flue 36. The flue 36 is made of duct pipe. An air intake port 41 is provided in the middle of the flue 36. If the inside of the flue 36 is under negative pressure (atmospheric pressure), air can be drawn into the inside of the flue 36 from the air intake port 41. A flow control valve 42 is provided at the air intake port 41 to control the amount of air drawn in. A damper can be used as the flow control valve 42. The air intake port 41 and the flow control valve 42 constitute the air intake section 40.

[0032] The amount of air drawn in from the air intake port 41 is preferably 30% to 60% of the exhaust gas flow rate at the point where it passes through the gas outlet 24 of the dryer 20. In this way, the amount of solid particles discharged into the atmosphere can be reduced by 25% to 50% compared to when air is not introduced into the flue 36.

[0033] The amount of air intake from the air intake port 41 may be controlled manually by an operator. For example, an operator may check the measurement value of the concentration meter 35 (dust concentration of exhaust gas) and adjust the valve opening of the flow control valve 42 so that the dust concentration is reduced. Alternatively, the amount of air intake may be automatically controlled using a control device. In this case, the control device determines the amount of solid particles released into the atmosphere from the dust concentration measured by the concentration meter 35. The control device also controls the valve opening of the flow control valve 42 so that the amount of particles released into the atmosphere is below a predetermined target value. The control device then controls the amount of hot air supplied to the dryer 20 in conjunction with the valve opening of the flow control valve 42. In this way, by controlling the amount of air intake while monitoring the amount of solid particles released into the atmosphere, the amount of solid particles released into the atmosphere can be reliably reduced.

[0034] Furthermore, in order to maintain negative pressure inside the flue 36, for example, the following configuration can be adopted. The flue 36 is equipped with a pressure gauge 37 that measures the atmospheric pressure inside it. The measurement value from the pressure gauge 37 is input to a control device such as an inverter. The control device controls the exhaust volume of the exhaust fan 34 so that the measured pressure value becomes a predetermined pressure set value. If the pressure set value is set to a value lower than atmospheric pressure, the atmospheric pressure inside the flue 36 can be made lower than atmospheric pressure. Since negative pressure is maintained inside the flue 36 by controlling the exhaust volume, exhaust gas can be prevented from being discharged from the atmospheric intake port 41.

[0035] The atmospheric intake section 40 is not limited to a configuration consisting of an atmospheric intake port 41 and a flow control valve 42. The atmospheric intake section 40 may also be configured to draw in air using an ejector. Alternatively, the atmospheric intake section 40 may be configured to push air into the flue 36 using a pump. In this case, the air pressure inside the flue 36 may be higher than atmospheric pressure. However, with the configuration shown in Figure 2, air is introduced into the flue 36 by utilizing the pressure difference between the inside and outside of the flue 36, so a dedicated power source for air introduction is not required, and the device configuration can be simplified.

[0036] If the hot air flow rate in the dryer 20 is too slow, the solid particles will not dry sufficiently, and if it is too fast, a large amount of solid particles will be discharged along with the exhaust gas. The hot air flow rate blown up through the screen 22 is preferably 0.5 to 1.5 m / sec. If the hot air flow rate is 0.5 m / sec or higher, the solid particles can be dried sufficiently. Also, if the hot air flow rate is 1.5 m / sec or lower, the amount of solid particles discharged along with the exhaust gas can be reduced.

[0037] Alternatively, the exhaust gas flow velocity at the point of passing through the gas outlet 24 is preferably 8 to 10 m / sec. If the exhaust gas flow velocity is 8 m / sec or higher, air can be smoothly introduced into the air intake section 40. Furthermore, if the exhaust gas flow velocity is 10 m / sec or lower, the amount of solid particles discharged along with the exhaust gas can be reduced. [Examples]

[0038] Next, we will describe some examples. Nickel sulfate crystals were dried using the drying equipment AA shown in Figures 1 and 2. The temperature of the hot air supplied to the dryer 20 was set to 40-46°C. The amount of hot air supplied to the dryer 20 was 8,500-13,000 Nm³. 3 The flow rate was increased or decreased between / h. The valve opening of the flow control valve 42 was adjusted to control the amount of air intake from the air intake port 41 from 0 to 5,000 Nm³. 3 The value was increased or decreased using / h.

[0039] A concentration meter 35 was installed in the chimney connected to the exhaust fan 34 to measure the dust concentration of the exhaust gas. The amount of nickel sulfate crystals released into the atmosphere was determined from the flow rate of the exhaust gas and the dust concentration.

[0040] In the comparative example, the flow control valve 42 was kept closed to prevent air intake. In the embodiment, the valve opening of the flow control valve 42 was adjusted to allow air intake. The results are shown in Table 1. Figure 3 shows the relationship between the atmospheric exhaust gas flow rate and the atmospheric nickel sulfate crystal discharge rate. Note that the dryer exhaust gas flow rate refers to the flow rate of exhaust gas at the point where it passes through the gas outlet 24 of the dryer 20. The atmospheric intake rate refers to the flow rate of air drawn in from the atmospheric intake 41. The atmospheric exhaust gas flow rate refers to the flow rate of atmospheric exhaust gas discharged into the atmosphere by the exhaust fan 34. The atmospheric nickel sulfate crystal discharge rate refers to the discharge of nickel sulfate crystals into the atmosphere. The atmospheric nickel sulfate crystal discharge rate is shown as a ratio with the case of Comparative Example 1 set to 100%.

[0041] [Table 1]

[0042] Regardless of whether or not air intake is performed, the higher the flow rate of the exhaust gas, the lower the amount of nickel sulfate crystals emitted into the air. This is thought to be because the dust removal efficiency of the dust removal device increases with higher gas flow rates. The example in which air intake was performed showed lower emissions of nickel sulfate crystals compared to the comparative example in which air intake was not performed. This is thought to be because, in the example, the flow rate of hot air in the dryer 20 was suppressed while the flow rate of gas supplied to the dust removal device was increased.

[0043] Air intake volume in Example 1 (2,700 Nm³) 3 / h) is the dryer exhaust gas flow rate (8,600 Nm³ 3 This is 31% of the air intake volume (4,500 Nm³ / h) in Example 2. 3 ( / h) is the dryer exhaust gas flow rate (8,500 Nm³ 3 This is 53% of the air intake volume (5,000 Nm³ / h) in Example 3. 3 ( / h) is the dryer exhaust gas flow rate (8,500 Nm³ 3 This is 59% of ( / h). If the amount of air intake is set to 30% to 60% of the dryer exhaust gas flow rate, the amount of nickel sulfate crystals emitted into the air can be reduced to 25% to 50% of that in Comparative Example 1. [Explanation of symbols]

[0044] CR crystallization equipment AA drying equipment 20...Dryer 21…Container 22…Screen 23... Hot air supply port 24...Gas outlet 25…Charging port 26…Exit 36…Flute 40...Atmospheric intake section 41... Air intake 42…Flow control valve

Claims

1. A dryer having an inlet for loading solid particles, a hot air supply port for supplying hot air, a gas outlet for discharging the hot air that has been blown onto the solid particles as exhaust gas, and an outlet for removing the solid particles after they have been dried by the hot air, A dust removal device having a dry cyclone and / or a wet scrubber, The dryer comprises a flue connecting the gas outlet and the dust removal device, An air intake section is provided in the middle of the flue to introduce air into the interior of the flue. The exhaust gas, with its increased flow rate due to the mixing of air, is then guided to the dust removal device. In the dust removal device, the solid particles contained in the atmospheric gas are removed. A drying apparatus characterized by the following features.

2. The aforementioned atmospheric inlet section is, An air intake port is provided in the flue and draws air into the interior of the flue, The system includes a flow control valve that controls the amount of air intake from the aforementioned air intake port, The air pressure inside the aforementioned flue is lower than atmospheric pressure. The drying apparatus according to claim 1, characterized by its features.

3. A concentration meter for measuring the dust concentration of atmospheric exhaust gas discharged into the atmosphere from the dust removal device, The system includes a control device that controls the valve opening of the flow control valve and the amount of hot air supplied to the dryer so that the amount of solid particles discharged into the atmosphere, determined from the dust concentration, is below a target value. The drying apparatus according to claim 2, characterized by its features.

4. A method for drying the solid particles using the drying equipment described in claim 2, The amount of air intake is 30% to 60% of the flow rate of the exhaust gas at the gas outlet. A drying method characterized by the following.

5. A method for drying the solid particles using the drying equipment described in claim 1, The dryer has a screen on which the solid particles are supplied to the upper surface and on which the hot air is blown up from below. The flow velocity of the warm air blown upward through the screen is 0.5 to 1.5 m / second. A drying method characterized by the following.

6. A method for drying the solid particles using the drying equipment described in claim 2, The flow velocity of the exhaust gas at the point where it passes through the gas outlet is 8 to 10 m / s. A drying method characterized by the following.

7. A method for drying the solid particles using the drying equipment described in claim 1, The solid particles are nickel sulfate crystals. A drying method characterized by the following.

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