RU2325956C2 - Spraying device and method of air-fluidized bed granulation - Google Patents

Abstract

FIELD: technological processes, spraying.

SUBSTANCE: invention is related to spraying device for granulation of melt in air-fluidized bed. Device consists of nozzle with supply channel for liquid subject to spraying, at that liquid passes through emulsification agent into internal mixing chamber for gas and liquid, prior to supply into air-fluidized bed. The nozzle has a separate channel for spraying gas, which is installed concentrically around the central channel of liquid supply for liquid subject to spraying or sputtering. The mixing chamber surrounds the zone of sprayed liquid outlet from emulsification agent and gas, providing efficient mixing of high-speed spraying gas and liquid, and is equipped with external gas hood, where fluidizing gas is supplied in the form of jet above spraying device. Invention allows to reduce power consumption, to increase granulation capacity and obtain granules of higher quality.

EFFECT: improvement of quality and capacity of granulation with reduction of power consumption.

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Description

The invention relates to a spray device for use in high-performance granulation of a fluidized bed and to a method for preparing solid granules from a liquid material in a fluidized bed.

In particular, this invention relates to spray nozzles used to supply liquid for growing granules by spraying liquid into a fluidized bed of solid particles, after which microscopic drops of liquid are sprayed.

The fluid bed granulation process, originally developed by Nederlandse Stikstof Maatschappij ⁱ , hereinafter referred to as NSM, is carried out by an HFT granulator (Hydro Fertilizer Technology), which has great advantages over other processes for granulating fertilizer substances such as urea and ammonium nitrate, see, for example, patent US No. 5653781. The HFT granulation process combines very high productivity with good product properties and low energy consumption. For this, a method of spraying the liquid to be granulated into a fluidized bed is very important. The design of liquid atomizing nozzles affects the liquid throughput and thus the granulator throughput, as well as the pressure and volumetric flow rate of the spray gas, necessary to maintain jets with continuous and uniform aerosols without agglomeration and undesired fluidized bed disturbance. Finally, the nozzle design also affects the energy consumption of the granulator through its flow and pressure characteristics.

Spraying devices (nozzles) according to the state of the art are generally double type spray nozzles, where a gas, such as air, is used to spray a liquid to be granulated. In principle, gas and liquid can flow through a nozzle into a single tube or gas and liquid can flow separately through, for example, concentric tubes, so that mixing takes place only at or after the nozzle opening. The principal objectives are the effective mixing of liquid and gas; homogeneous and small particle size of the liquid and suitable geometry of the resulting aerosol or jet, so that the sprayed liquid (microscopic droplets) continuously and uniformly settles on the granules formed in the fluidized bed.

Most existing nozzle designs are not intended for use in high-performance granulation. Granulation nozzles should work with concentrated solutions (up to 99%) or melts without clogging or other problems that disrupt the production process. At the same time, there are noticeable differences between different designs in terms of process energy consumption, productivity (product yield) and the quality of the formed granules. Existing and earlier types of nozzles should work at relatively high levels of atomization gas, at elevated pressures, which again leads to high energy consumption.

The nozzles used in the granulation process are described, for example, in US Pat. No. 4,701,353. They have a central channel through which liquid material is supplied, and a channel concentric with it, providing a powerful gas flow. The fluid passes through the rotation chamber before mixing with the gas stream. The nozzle may also have a concentric external channel to provide a less energetically saturated gas stream. However, this nozzle design has limitations in the fluid throughput and in the energy needed to spray or spray the liquid into suitable droplets and, at the same time, liquefy the droplets into a stream of proper shape where the particles grow. The rotation chamber described in US 4,701,353 serves only to impart a swirling liquid, while the mixing chamber of the present device, described below, provides for thorough mixing of the spray gas and liquid until the aerosol leaves the nozzle outlet. Thus, the kinetic energy of gas and liquid is used in an optimal way. The device and method described herein have high granulation performance and low power consumption; several times better than the values mentioned in US patent No. 4701353. In cases where a second concentric gas tube is installed on the nozzle, such as described in paragraph 5 of US 4701353, this design unnecessarily complicates the device compared to the device described below, since the claimed device and method involve the use of part of the supplied fluidization gas for an additional stream of gas formed around the nozzle.

International patent application WO 02083320 also describes a nozzle for use in fluid bed granulators. It has a central fluid inlet, after which the fluid passes through the vortex device into the internal mixing chamber. Gas enters the mixing chamber through many openings in the wall at the bottom of the mixing chamber. However, the description does not provide examples and there are no figures related to the practical application of the described design, while the claimed device and method described below have such advantages as high performance, high quality products and low power consumption, compared to any other technical previously described decisions.

The objective of the invention is to provide a granulation method with reduced energy consumption and increased granulation productivity, both factors reduce the variable costs per unit of production at the granulation stage. Another task is to obtain granules of higher quality.

To solve these problems, a device and method are provided, described below, defined and characterized by the attached claims.

Thus, the invention relates to a spray device for granulating a melt in a fluidized bed containing a nozzle with a supply channel for a liquid to be sprayed, where the liquid passes through emulsifying means and into an internal mixing chamber for gas and liquid before being supplied to the fluidized bed. The nozzle has a separate channel for atomization gas mounted concentrically around the central channel for supplying liquid for the liquid to be sprayed or sprayed. A mixing chamber surrounds the zone of discharge of the atomized liquid from the emulsifying means and the gas, providing efficient mixing of the high-speed atomizing gas and the liquid, and has an external gas cap where the liquefied gas is drained into the stream above the atomizing device. The mixing chamber may be cylindrical with an upper conical part or conical. The L / D ratio of the mixing chamber should be in the range of 0.5 to 5 and the l / d ratio in the range of 0.1 to 2. Preferably, the L / D ratio of the mixing chamber is in the range of 1 to 4 and l / d ratios ranging from 0.25 to 1.

The gas cap has a conical shape and is fitted concentrically around the nozzle to the perforated bottom plate. The gas cap has a height of from 10 to 200 mm above the bottom plate (3), preferably from 20 to 100 mm. The diameter of the upper opening of the gas cap is 20 to 150 mm and the diameter of the lower opening is 30 to 300 mm, preferably 35 to 100 mm and 40 to 200 mm, respectively.

The invention also relates to a method for preparing solid granules in a fluidized bed, in which a liquid material is atomized by spraying gas and sprayed into a fluidized bed through spray nozzles mounted vertically, and the fluidized bed is supported by a fluidized gas blown upward through a perforated plate below the bed. Part of the liquefied gas must be supplied in a jet through a gas cap surrounding the nozzle to create a gas jet above the spray device.

The invention also relates to a method for preparing solid granules from a liquid material in a fluidized bed using a nozzle with a feed channel for a liquid to be sprayed. The liquid passes through the emulsification means into the internal mixing chamber for gas and liquid until the sprayed liquid is sprayed up into the fluidized bed. Spray gas passes through a channel concentric to the liquid feed channel into the mixing chamber surrounding the liquid and gas outlets, providing efficient mixing of the high-speed atomization gas and liquid. A portion of the liquefied gas is supplied in a jet through a gas cap surrounding the nozzle to create a gas jet above the spray device.

The spraying device can be used to create urea granules and other fertilizer products, for example, ammonium calcium nitrate, ammonium nitrate, ammonium sulfate, and mixtures thereof.

The invention will now be described with reference to the accompanying drawings, figures 1-4, in which:

figure 1 shows the fundamental difference between the design according to the prior art and the claimed design of the nozzle,

figure 2 shows the design of the gas cap and the concentric position of the gas cap outside the nozzle,

figure 3 shows the design of the nozzle with a cylindrical mixing chamber,

figure 4 shows the design of the nozzle with a conical mixing chamber.

During the granulation process, the liquid is sprayed into the fluidized bed through spray nozzles mounted vertically and spraying the sprayed liquid up into the fluidized bed. The fluidized bed is supported by a liquefied gas, blown up through the perforated plate under the bed. The nozzles are placed in the holes of this plate, and their holes are at a certain distance, for example 5-100 mm, above the plate.

The design of the nozzles in which the liquid is sprayed affects the throughput of the fluid and, thus, the throughput of the granulator. It also affects the pressure and volumetric flow rate of the atomization gas necessary to maintain jets with continuous and uniform aerosols without agglomeration and undesired fluid bed disturbance. Finally, the nozzle design also affects the energy consumption of the granulator through its flow and pressure characteristics. This directly affects the variable costs per unit of output for the operation. The nozzle should spray liquid into droplets of the desired size, approximately 50-100 microns for a single-phase melt. At the same time, the nozzle must ensure the evaporation of a certain amount of water, without creating premature hardening. It should also ensure the distribution and supply of droplets to the layer and at the same time contribute to the movement around the nozzle and mass transfer in the layer.

The novelty of the invention is the use of low energy liquefaction gas to replace a large part of the required high pressure atomization gas. This is achieved by conducting liquefaction through the gas channel through the gas cap of a special design surrounding the nozzle, and thus creating a gas stream. A mixing chamber mounted upstream of the nozzle opening improves the internal mixing of gas and liquid during atomization in the nozzle.

The separation of gas into two specialized functions allows you to freely separate the four main functions during spraying and moving.

Spraying

1) Spraying is carried out with a minimum power consumption, sufficient to create droplets and feed them into the layer.

2) The desired evaporation rate can be adjusted in accordance with the properties of the melt, namely the water content, heat of crystallization, properties of the supercooled state and the crystallization curve.

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3) The transport of droplets and the shape of the jet is adjusted to the geometric dimensions of the layer, and the depth of the layer plays the main role.

4) The impact is also adjustable to ensure mass transfer of seed particles to the jet region.

The present invention allows to maintain and even improve the characteristics of the quality of the granules and the performance of the granulation, and at the same time significantly reduce energy consumption compared to the nozzles that are still used for granulation. Reducing energy consumption is achieved due to the fact that the atomization gas can be used at a lower pressure, without increasing the total amount of liquefied gas. This design also provides high melt throughput and good physical properties of the granules.

Figure 1 shows the fundamental difference between the design according to the prior art, and the design according to the invention. In the construction according to the prior art (case I), the mixing of the fluid (L) and the spray gas (G1) occurs in the fluidized bed by an external impact of the gas (G1) on the fluid (L). In the inventive nozzle design (case II), external mixing of gas (G2) and liquid (L) occurs in the mixing chamber. At the same time, part of the atomization gas is replaced by a fluidization gas (G3) supplied to the stream in a fluidized bed by means of a gas cap mounted concentrically outside the nozzle. Thus, part of the atomization gas is replaced by a fluidization gas (G3) supplied through the gas cap. The required amount of atomization gas is significantly reduced in comparison with the known nozzle design, which will be illustrated by examples (from 80-250 kg / h to 32 kg / h).

On figa shows the design of the gas cap and the position of the gas cap concentrically outside the nozzle. 2B shows a horizontal section along A-A. The gas cap 1 of the conical shape is mounted concentrically around the nozzle 2 of the perforated mesh plate 3 and is open to liquefied gas. The upper diameter of the gas cap device is smaller than the lower diameter, and there is a gap for the passage of gas between the outer wall of the nozzle and the gas cap. The amount of gas passing through the gas hood must be sufficient to create a stable jet into the granulator bed. The speed of the gas passing through the gas cap is determined by the horizontal area between the nozzle and the gas cap, the upper diameter of the gas cap opening and the diameter of the lower gas cap inlet. The mass flow rate of liquefaction gas per square meter of horizontal bed area is almost independent of known designs.

Figure 3 shows the new design of the nozzle with a cylindrical mixing chamber. The length / diameter ratio (L / D) of the mixing chamber may vary as indicated in the drawing. The figure does not show the supply line, the perforated bottom plate of the granulator and the conical cap mounted concentrically with the nozzle on the bottom plate. The nozzle 2 consists of a central channel 4, which is connected at one end A to a liquid supply line not shown in the drawing, and connected to the mixing chamber 5 at the other end B. In the position between openings A and B, a vortex device 6 is installed inside to supply power through A in a spiral motion at point B. In addition, the spray device is provided with a channel 7 placed concentrically around the Central channel 4 of the fluid supply. Channel 7 at one end is connected to a gas supply line not shown in the drawing, and at its other end it is provided with 5-15 round openings 8 extending into the mixing chamber 5. Two continuous flows simultaneously enter the mixing chamber: a liquid for growing granules through openings B and gas flow 8. In this mixing chamber, gas in a liquid emulsion can be generated. The expansion through the nozzle opening 9 turns the emulsion into droplets with a diameter of 50-100 μm, which are suitable for growing granules in a fluidized bed.

Figure 4 shows the nozzle with a conical mixing chamber 5. Other elements of the nozzle are the same as shown in figure 3.

From the literature (Lefebvre AH: Atomization and sprays, Taylor & Francis, 1989, p-214-215 an p-232, (ISBN: 0-89116-603-3), it follows that l / d (length / diameter) of the nozzle and the L / D ratio (length / diameter) of the mixing chamber are important factors for the formation of liquid droplets.Based on these assumptions and our own research, the L / D ratio should be between 0.5 and 5, the l / d ratio should be between 0.1 and 2 in order to efficiently obtain droplets with an average diameter of less than 100 μm , preferably L / D should be in the range of 1 to 4 and l / d should be in the range of 0.25 to 1.

Energy efficiency can also be calculated for the nozzles of this design. For this, standard and well-known equations are used, see Perry: Chemical Engineers' Handbook (chapter “Thermodynamics”).

W = Φ _M · Cp · ΔT [kJ / s],

where ΔT = T ₂ - T ₁ and T ₂ = T ₁ · (P ₂ / P ₁ ) ^{(k-1 / k)} [K];

Φ _M is the mass flow rate of the melt;

Cp - specific heat of gas [kJ / ^K. kg];

T ₁ - external temperature;

T ₂ - temperature after the fan;

P ₁ - gas pressure to the fan;

P ₂ - gas pressure after the fan;

k is the gas constant.

For calculations, we make the following assumptions:

Adiabatic conditions.

Outside temperature: 25 ° C.

Pressure loss: 5000 Pa.

Fan efficiency: 0.80.

According to the calculations, the energy consumption of the liquefaction and atomization air supply can be reduced by about 50%. The energy reduction actually achieved using the inventive spray device is shown below in Example 1.

The parameters of moisture content, density and crushing strength of the urea granules produced using the nozzle of this design have comparable or better values compared to granules created using known designs. This is illustrated in the examples below.

It has been experimentally found that when using a nozzle with an internal gas / liquid mixing chamber instead of a nozzle with an external gas / liquid mixing, granules with higher chemical and physical properties can be produced with lower energy consumption.

In granulation units, especially for urea and ammonium nitrate, it was also important to achieve high performance, in order to avoid the need to have more than one granulation unit per synthesis unit, while at the same time maintaining variable costs per unit of output.

The invention will be further illustrated by the following examples describing urea granulation. The examples demonstrate the values obtained for the product quality parameters, as well as the energy consumption for a number of nozzles based on the claimed design.

Examples were performed under the following conditions.

The granulator was equipped with an experimental nozzle in the center. The conical gas hood had a lower diameter of 105 mm and an upper diameter of 50 mm. It was mounted on a perforated mesh plate with holes occupying 4.5% of its area, containing holes 2 mm in diameter. The amount of air passing through this gas hood was 248 N m ³ / h at a supply pressure equal to the pressure of the gas (air) liquefaction of about 800 mm of water. Art. and temperature 40 ° C. Granulation was carried out under normal standard conditions of granulation of urea with a melt of 96% urea containing 0.55 wt.% Formaldehyde at a temperature of about 132 ° C. the installation was supplied with liquefied gas, necessary to maintain the layer in motion, as well as to create a stream through the "stream opening" of the gas cap. Atomization gas with a flow rate of 32 kg / h and a temperature of 142 ° C was supplied together with the melt into the mixing chamber of the nozzle.

Product quality parameters, such as moisture content, density, crush strength of granules with a diameter of 2.5-4.5 mm, were analyzed for each nozzle test. During the test, different fluid flow rates were used; l / h, equal to 250, 350 and 450. Each granulation test was performed at least twice.

You can also create nitrate products with 33.5% N and 27% N using this kind of nozzle.

Example 1. Nozzle with a cylindrical mixing chamber L / D = 2.75

In this example, a spray device of type H5, shown in FIG. 3, with a L / D ratio of 2.75 mixing chamber was used. The results were compared with experiments performed in nozzles of a structure according to the prior art.

Table 1
Operating parameters Nozzle HFT design (prior art) New design L / D = 2.75 Example A Example B Example A Example B Urea flow rate kg / h 540 450 540 454 Urea feed pressure bar 1.4 1.3 2.1 1.8 Liquefied gas (air) consumption kg / m ^2. h 7952 7952 8107 8107 Liquefied gas (air) pressure mm water column 800 800 800 800 bar 0.08 0.08 0.08 0.08 Gas (air) flow rate kg / h - - 320 320 Spray gas (air) consumption Nm ³ / h 252 252 32 32 Spray gas (air) pressure bar 0.5 0.5 1.9 1,5

table 2
Obtained product properties, urea Nozzle HFT design (prior art) New design L / D = 2.75 Example A Example B Example A Example B Humidity % 0.26 0.23 0.20 0.19 Density kg / l 1,216 1.23 1,237 1.25 Crushing strength kg 4.40 4.44 4.95 5.03 Abrasion mg / kg 800 650 175 195

Table 3
Power consumption Nozzle HFT design (prior art) New design L / D = 2.75 Experiment A Power consumption (W _T) (kW ^h. Per ton of product) 27 13

Power consumption was calculated as described in the description. Air was used as a liquefaction and spray gas, so k = 1.40 and Cp = 1.04 adjusted for air humidity.

Example 2. Nozzle with a cylindrical mixing chamber L / D = 1

The principle of operation and design, with the exception of the length of the mixing chamber, are the same as described in Example 1. In this design, the length of the mixing chamber is 20 mm instead of 55 mm, so the L / D ratio changed from 2.75 to 1. The results were compared with experiments carried out in nozzles of a design that meets the prior art.

Table 4
Operating parameters Nozzle HFT design (prior art) New design L / D = 1 Example A Example B Urea flow rate kg / h 540 450 450 Urea feed pressure bar 1.4 1.3 1.8 Liquefied gas (air) consumption kg / m ^2. h 7952 7952 8107 Liquefied gas (air) pressure mm of water. Art. 800 800 800 bar 0.08 0.08 0.08 Gas (air) flow rate kg / h - - 320 Spray gas (air) consumption kg / h 252 252 32 Spray gas (air) pressure bar 0.5 0.5 1,5

Table 5
Obtained product properties, urea Nozzle HFT design (prior art) New design L / D = 1 Example A Example B Humidity % 0.26 0.23 0.18 Density kg / l 1,216 1.23 1.24 Crushing strength kg 4.40 4.44 4.75 Abrasion mg / kg 800 650 140

Example 3. Nozzle with a conical mixing chamber

In this example, a spray device with a conical mixing chamber, shown in FIG. 4, was used. The L / D ratio of the nozzle was 2.75. The results were compared with experiments conducted in nozzles of a design that meets the prior art.

This nozzle with a conical mixing chamber also had 12 gas inlet openings (D), which are placed at an angle to the direction of rotation of the fluid vortex. Its design ensures that the atomization gas rotates in the opposite direction with respect to the liquid in order to ensure maximum gas impact into the liquid stream.

Table 6
Operating parameters Nozzle HFT design (prior art) New design, cone Example A Example B Urea flow rate kg / h 540 450 375 Urea feed pressure bar 1.4 1.4 1.9 Liquefied gas (air) consumption kg / m ^2. h 7952 7952 8107 Liquefied gas (air) pressure mm of water. Art. 800 800 800 bar 0.08 0.08 0.08 Gas (air) flow rate kg / h - - 320 Spray gas (air) consumption kg / h 252 252 32 Spray gas (air) pressure bar 0.5 0.5 1.7

Table 7
Obtained product properties, urea Nozzle HFT design (prior art) New design, cone Example A Example B Humidity % 0.26 0.23 0.21 Density kg / l 1,216 1.23 1.20 Crushing strength kg 4.40 4.44 4,51 Abrasion mg / kg 800 650 1430

Thanks to the use of the nozzle design in the granulation process, it is possible to create granules with lower energy consumption, with better quality and higher productivity.

Claims (11)

1. A spray device for granulating a melt in a fluidized bed containing a nozzle (2) with a feed channel (4) for the liquid to be sprayed, where the liquid passes through emulsifying means (6) into the internal mixing chamber (5) for gas and liquid, up to supply to the fluidized bed, characterized in that the nozzle (2) has a separate channel (7) for the spray gas, mounted concentrically around the Central channel of the fluid supply (4) for the liquid to be sprayed or sprayed, while the mixing chamber (5) o it circles the zone of discharge of the sprayed liquid from the emulsification means and the gas, providing efficient mixing of the high-speed spraying gas and the liquid, and has an external gas cap (1), where the liquefied gas is supplied in the form of a jet over the spraying device. 2. A spray device according to claim 1, characterized in that the mixing chamber (5) is cylindrical with a conical upper part. 3. A spray device according to claim 2, characterized in that the ratio of the length (L) and diameter (D) of the mixing chamber (5) is in the range from 0.5 to 5 and the ratio of the length (1) and diameter (d) of the hole ( 9) is in the range from 0.1 to 2. 4. A spray device according to claim 2, characterized in that the ratio of the length (L) and diameter (D) of the mixing chamber (5) is in the range from 1 to 4 and the ratio of the length (1) and diameter (d) of the hole (9) ranges from 0.25 to 1. 5. The spray device according to claim 1, characterized in that the mixing chamber (5) is made conical. 6. A spray device according to claim 1, characterized in that the gas cap (1) is made conical and fitted to a perforated bottom plate (3) concentrically around the nozzle (2). 7. A spray device according to claim 6, characterized in that the gas cap (1) has a height of 10 to 200 mm above the bottom plate (3), preferably 20 to 100 mm. 8. The spray device according to claim 6, characterized in that the gas cap (1) has a diameter of the upper hole from 20 to 150 mm and a diameter of the lower hole from 30 to 300 mm, preferably from 35 to 100 mm and from 40 to 200 mm , respectively. 9. A method of preparing solid granules in a fluidized bed, in which a liquid material is sprayed by spraying gas and sprayed into the fluidized bed through spray nozzles (2) mounted vertically, the fluidized bed being supported by a fluidized gas being blown upward through a perforated plate below the bed, characterized the fact that part of the liquefaction gas is supplied in the form of a jet through a gas cap (1) surrounding the nozzle to create a gas stream above the spray device. 10. A method of preparing solid granules from a liquid material in a fluidized bed using a nozzle (2) with a feed channel (4) for the liquid to be sprayed, in which the liquid passes through the emulsification means into the internal mixing chamber (5) for gas and liquid before spraying sprayed liquid up into the fluidized bed, characterized in that the spray gas is fed into the mixing chamber (5) through a channel (7), a concentric channel for supplying liquid to the mixing chamber surrounding the liquid outlet and gas, providing efficient mixing of high velocity gas and spraying liquid, wherein a portion of fluidization gas fed as a jet through the gas cap (1) surrounding the nozzle (2) for creating a jet of gas above the spraying device. 11. The use of a spray device according to one of claims 1 to 8 in the process of preparing granules from urea and other melts suitable for the production of fertilizer products, for example, calcium ammonium nitrate, ammonium nitrate, ammonium sulfate and mixtures thereof.

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