EP3754275A1 - Spray drying apparatus for drying a material to be dried, spray drying method and dried product - Google Patents

Abstract

The invention relates to a spray drying device for drying a material to be dried with an atomizer device, the atomizer device having a rotatable atomizer unit for atomizing the material to be dried in a drying room of the spray drying device, and with a drying gas supply for feeding a drying gas into the drying room and for drying the atomized , material to be dried into dried particles, the atomizing device being set up in such a way that when the particles hit an inner wall of the drying chamber, the particles are dried to such an extent that the particles are prevented from being deposited on the inner wall. The invention also relates to a method for spray drying and a dried product.

Description

The invention relates to a spray drying device for drying a material to be dried with an atomizing device, the atomizing device having a rotatable atomizing unit for atomizing the material to be dried in a drying room of the spray drying device, and with a drying gas supply for feeding a drying gas into the drying room and for drying the atomized , goods to be dried to dried particles. The invention also relates to a method for spray-drying an item to be dried and a dried product.

In atomization drying (also called spray drying), the material to be dried is usually introduced into a stream of hot gas by means of an atomizer and dried to a fine powder in a few seconds. In this case, an inhomogeneous drying process and the settling of components of the goods to be dried and / or the dried particles, both on the atomizer and on the inner walls of the drying chamber, are to be avoided. Despite optimal operational management, it cannot be prevented that the material to be dried and / or the dried-on particles settle on the inner walls of the drying chamber, causing undesirable, potential flame sources (so-called Hotspots) with an increased risk of fire and explosion.

In order to remove deposited material to be dried and / or dried particles on the inner walls of a drying room, blow clearers have been used for more than 20 years, especially in the production of Caramilk®. A blower is, for example, a tube rotating along the inner wall within the drying space, which is closed at the top and has a plurality of vertical slots over its vertical length. Air is blown through these slots at a high speed to the inner wall to remove particles and impurities deposited there.

Particularly in the case of thermoplastic and / or sugar-containing goods to be dried, they have a strong tendency to stick to the inner wall of the drying room, so that they cannot be completely removed by a blower. Thus, despite the use of the blower scraper, deposits on the inner walls of the drying room and thus biofouling occur. In the case of such goods to be dried, the inner wall of the drying room is evenly and permanently occupied by the not completely dried product with increasing time, so that the running time of a spray dryer using a blower is a maximum of one day before the spray dryer has to be taken out of operation and cleaned . The use of blowers has been around since Established for decades without any development in terms of deposit prevention.

In addition, the deposits on the inner wall deteriorate the quality of the dried product because the dried or dried particles in the deposits on the hot inner walls are exposed to an elevated temperature for too long, so that when these particles are removed using a blower scraper and / or the encrustations are broken up , particles that have been dried for too long get into the product withdrawn from the spray dryer. This leads to an undesirable bitter taste in a sugary and / or caramelized product (e.g. Caramilk®).

Consequently, with the spray drying that is currently customary and has been established for years, both non-optimal product properties, in particular in the case of sticky, sugar-containing goods to be dried, are achieved and a high level of cleaning effort is then required in the interior of the spray dryer.

From the DE 6 92 15 212 T2 a method for reducing the deposition of feed liquid on the inner walls of an atomizer chamber is known in which radial auxiliary gas flows with a high flow rate and a low flow rate are aligned on both sides of the atomizer device in such a way that for mechanical cleaning by means of the gas jets a flow rate of the Increased drying gas on the inner walls, thereby preventing substances from settling on the inner walls.

There is also an additional mechanical cleaning device for a spray dryer in the DE 25 35 961 A1 described in which, in addition to the drying gas, a purge gas is introduced into the lower conical section of the spray dryer in order to induce a flow along the inner wall of the conical section and thereby prevent particles from adhering.

In the DE 38 07 543 A1 describes spray drying of aqueous dispersions or pulverulent emulsion polymers, in which water is additionally atomized to prevent the formation of polymerization deposits in the spray unit itself. The water injection only serves to avoid polymer deposition directly in the atomizer unit. In addition, the dilution effect due to the water injection is in principle disadvantageous.

From the WO 97/21477 A1 An atomization dryer for the production of detergents and / or cleaning agents is known, in which at least part of the inner wall of the drying container is lined with an air-permeable textile spaced from the container wall and at least one outlet for compressed air is arranged between the container wall and the textile, so that on the textile adhering particles can be cleaned off by applying compressed air to the back of the textile.

The object of the invention is to improve the state of the art.

The object is achieved by a spray drying device for drying goods to be dried with an atomizer device, the atomizer device having a rotatable atomizer unit for atomizing the goods to be dried in a drying room of the spray drying device, and with a drying gas supply for feeding a drying gas into the drying room and for drying of the atomized material to be dried into dried particles, the atomizing device being set up such that when the particles hit an inner wall of the drying room, the particles are dried to such an extent that the particles are prevented from being deposited on the inner wall.

The fact that the atomizer device is set up in such a way that at the time of the impact of the particles on the inner wall of the drying room the particles are already so largely dried that they only have a low level of residual moisture and / or stickiness, the particles will deposit on the inner wall avoided or there are only very small deposits compared to the prior art.

Even if blow cleaners have been used in spray drying devices for decades, it has surprisingly been found that the particles which are still deposited when a blower is used and the deposits are relatively moist and in particular the particles on impact the inner wall has dried on, but has not dried through sufficiently quickly, so that due to the moisture remaining in the particles there is adhesion and / or sticking to the inner wall of the drying room.

When the particles hit the inner wall of the drying room, the particles have, in particular, a moisture content of <10.0%, in particular <1.0%, preferably <4.8%. On the other hand, in deposits in a spray dryer which works with a rotating blower, a moisture content of> 3% was found in the deposits.

Another disadvantage of the known prior art could be that only slightly heated air or cold air is often used to blow off the deposits in order to avoid thermal damage to the hot inner wall by adhering particles in addition to blowing off the deposits. Here, the only slightly heated air or cold air can in turn cause locally increased humidity of the particles.

In addition, with the spray drying device according to the invention there are no safety concerns with regard to the risk of fire and explosion, since there is no deposit of particles on the inner wall of the drying chamber or, in the case of very sticky particles, only slight deposits.

Since the particles do not adhere to and / or deposit on the inner wall, there is consequently no thermal either Damage to the particles due to excessive dwell time on the hot inner wall, so that consequently a loss of quality in the dried product is prevented.

Thus, a spray drying device is provided which has a long running time and a low risk of fire and / or explosion during drying as well as a low maintenance and / or cleaning intensity.

An essential idea of the invention is based on the fact that the spray drying according to the invention does not have a blower or any other mechanical cleaning device and, by means of the atomizer device, directly achieves optimal drying and movement of the particles in the drying gas, so that when they hit the inner wall of the drying room they already have such a have low humidity that the particles do not adhere and / or deposit on the inner wall.

The following terms are explained:

A “spray drying device” (also called “spray dryer” or “drying tower”) is in particular a device for drying solutions, suspensions or emulsions. In a spray drying device, in particular by means of an atomizer device, the material to be dried is introduced into a drying gas stream which dries to fine powder particles in a very short time, usually a few seconds to fractions of a second. A spray drying device has in particular at least one atomizer device, a feed for the goods to be dried and for the drying gas and a drying room.

An "item to be dried" is in particular a liquid, such as a solution, suspension or emulsion, which is sprayed and / or atomized in a drying gas for drying and forming dry particles (individual particles, agglomerates and / or granulates).

An "atomizer device" is in particular a device for dividing a liquid, a suspension or emulsion into fine droplets and / or fine moist particles in a gas. As a result of the "atomization" (also called "spraying"), the material to be dried is in particular in the form of an aerosol (mist). As a result of the atomization, there is in particular a strong increase in the free reactive surface of the material to be dried. An atomizer device is in particular a rotary atomizer (also called a rotary atomizer), for example with a rotary atomizer disk and / or cup. The atomizing device can, for example, also be one or more rotating spray nozzles. The rotatable atomizer unit of the atomizer device is used in particular to generate a very large reactive liquid surface and / or moist particle surface through atomization and to ensure a homogeneous distribution of the fine droplets and / or moist particles within the drying chamber.

The "drying room" is in particular the room in which the drying of the goods to be dried takes place. In the drying room, in particular, the material to be dried is atomized and the material to be atomized and the drying gas supplied meet one another.

An "inner wall" is in particular a wall in the interior of the drying room. The inner wall is in particular the inner delimitation of the wall of the drying room, which separates the interior of the drying room from the external environment. The inner wall can also be the inner wall of a jacket as the inner lining of the drying room, the wall of a duct, for example a ventilation and / or hot duct, and the like. In particular, the inner wall comes into physical contact both with the material to be dried and / or atomized and with the drying gas.

A "drying gas supply" is in particular a device for supplying a drying gas into the drying room. The drying gas supply can, for example, be a supply line into the drying room. The drying gas supply can also be arranged as a gas distributor base, for example on the underside of the drying room.

A "drying gas" is, in particular, a gas which causes the liquid in the material to be dried to evaporate and thus dries the moist material into fine powder particles. It is a drying gas especially air and / or an inert gas such as nitrogen. The drying gas is in particular passed as a gas stream through the spray drying device in order to dry the atomized material to be dried. The drying gas is in particular a hot gas. The drying gas has, in particular, a temperature in a range from 100 ° C. to 350 ° C., preferably between 150 ° C. and 250 ° C. The drying gas is introduced into the spray drying device in countercurrent and / or cocurrent or at different points.

An “impact” is understood to mean, in particular, the impact of a dried particle accelerated by the atomizing device on the inner wall of the drying chamber. An impact is in particular the first time a particle hits the inner wall.

In a further embodiment, the spray drying device is free from a mechanical cleaning device, in particular from a blower, for removing deposited particles.

A mechanical cleaning device, in particular a blower scraper, is therefore specifically dispensed with in the spray drying device according to the invention and the corresponding method.

A "mechanical cleaning device" is, in particular, a device which mechanically removes particles deposited on an inner wall of a drying room. With a mechanical The cleaning device can in particular be a blower, as already described above, a pneumatic knocker, a jacket through which gas flows and / or the targeted application of a gas flow on and / or along the inner wall, for example as a downwardly directed cold air curtain.

In order to achieve sufficient drying of the material to be dried and an early formation of the dried particles before the first impact on the inner wall, the rotating atomizer unit has a speed in a range from 15,300 rpm to 19,000 rpm, in particular from 16,000 rpm min to 18,000 rpm, preferably from 16,500 rpm to 17,000 rpm.

The speed of the rotatable atomizer unit in the spray drying device according to the invention is significantly higher than the speed of 12,000 rpm to 15,000 rpm of a conventional spray dryer with a blower according to the prior art.

Due to the high speed of the rotating atomizer unit, a very large reactive surface area of the generated droplets and / or the moist material is achieved on the one hand and the droplets and / or moist particles are optimally brought into contact in an atomizer flow with the drying gas flow so that the forming dried particles are already so largely dried before impact on the inner wall that the particles do not adhere to and / or deposit on the inner wall. It Surprisingly, it has been shown that although dried particles make contact with the side walls more quickly, they were, however, unexpectedly "completely dry".

The "speed" indicates in particular the number of revolutions of the rotatable atomizer unit per time. The speed is specified in particular in rpm.

In a further embodiment of the spray drying device, the drying gas supply has a drying gas flow rate in a range from 1,800 kg / (m ^{2 ∗} h) to 5,000 kg / (m ^{2 ∗} h), in particular from 2,500 kg / (m ^{2 ∗} h) to 4,500 kg / (m ^{2 ∗} h), preferably from 3,000 kg / (m ^{2 ∗} h) to 4,000 kg / (m ^{2 ∗} h).

The flow rate of the drying gas in the spray drying device according to the invention is significantly higher than the maximum flow rate of 1,500 kg / (m ^{2 *} h) usually used for a conventional spray dryer with a blower according to the prior art.

The "drying gas flow rate" indicates in particular the amount of drying gas which is fed into the drying room per area and unit of time. The area in square meters relates in particular to the maximum cross-sectional area of the drying room.

The drying space of the spray drying device preferably has a volume which is 30% larger than the volume of a conventional spray dryer with a blower scraper. In particular, the inventive The drying space has a volume of 1.5 to 1000 m ³ , while a conventional spray dryer with a blower according to the prior art uses a volume of 1.2 to 900 m ³ . In order to dry in a continuous process or a batch process, the spray drying device has a continuous or discontinuous product discharge.

A “product withdrawal” is, in particular, a targeted discharge of the dried product and / or powder from the drying chamber of the spray drying device. After the product has been discharged, the powdery material to be dried is usually separated from the drying gas flow by a cyclone separator.

• Zuführen des Trocknungsgases in den Trocknungsraum der Sprühtrocknungsvorrichtung,
• Zerstäuben des zu trocknenden Gutes mittels der drehbaren Zerstäubereinheit, und
• Trocknen des zerstäubten, zu trocknenden Gutes zu getrockneten Partikeln,

wobei die Partikel derart getrocknet werden, dass eine Ablagerung der Partikel auf einer Innenwand der Sprühtrocknungsvorrichtung vermieden wird.In an additional aspect of the invention, the object is achieved by a method for spray drying an item to be dried, in particular Caramilk®, using a previously described spray drying device, with the following steps:

• Feeding the drying gas into the drying chamber of the spray drying device,
• Atomizing the material to be dried by means of the rotatable atomizing unit, and
• Drying the atomized material to be dried into dried particles,

wherein the particles are dried in such a way that deposition of the particles on an inner wall of the spray drying device is avoided.

A method is thus provided in which the dried particles are conditioned simply by supplying the drying gas and atomizing the goods to be dried in the drying room in such a way that they have such a low level of residual moisture when they hit the inner wall of the drying room that they stick and / or deposit the dried particles on the inner wall is largely avoided.

It is particularly advantageous here that the method according to the invention is carried out free of the use of a mechanical cleaning device, in particular a blower, to remove deposited particles.

In a further embodiment of the method, a speed of the rotatable atomizer unit is or are in a range from 15,300 rpm to 19,000 rpm, in particular from 16,000 rpm to 18,000 rpm, preferably from 16,500 rpm to 17,000 rpm. min, and / or a drying gas flow rate in a range from 1,800 kg / (m ^{2 ∗} h) to 5,000 kg / (m ^{2 ∗} h), in particular from 2,500 kg / (m ^{2 ∗} h) to 4,500 kg / (m ^{2 ∗} h) ), preferably from 3,000 kg / (m ^{2 ∗} h) to 4,000 kg / (m ^{2 ∗} h).

As a result, optimal atomization of the material to be dried and / or optimal feeding of the drying gas into the is or will be in the method according to the invention Drying room carried out. As a result, the atomizer flow of the atomized material to be dried and the drying gas flow are optimally brought into contact with one another, so that the moist material is dried quickly before it can hit the inner wall of the drying room.

In a further embodiment of the method, the drying gas is supplied in countercurrent and / or cocurrent for atomization.

“Countercurrent” is understood in particular to mean that the material flow of the atomized material to be dried and the material flow of the drying gas are guided and / or meet one another in opposite directions. “Direct current” is understood in particular to mean that the atomization and the supply of the drying gas take place from the same direction into the drying chamber.

In order to make optimum use of the method according to the invention, a sugar-containing milk product is used as the item to be dried.

In this way, a sugar-containing and / or caramelized milk product is also optimally converted into a homogeneous, finely powdered, dried product.

It is particularly advantageous that the spray drying device according to the invention and the method according to the invention are suitable and used for drying thermoplastic materials and / or sticky goods to be dried.

A “milk product” is in particular a food or a food precursor whose ingredients consist predominantly of milk or milk components such as milk protein, milk fat and / or milk sugar. In addition to the lactose already contained, a "sugar-containing milk product" is additionally enriched with lactose or another type of sugar, such as refined sugar, sucrose solution, inverted sugar, glucose syrup, dextrose and / or fructose or artificial sweeteners.

In a further aspect of the invention, the object is achieved by a dried product, in particular milk caramel powder (Caramilk®), produced by a method described above.

This provides a dried product, in particular a sugar-containing and / or caramelized milk powder, which does not have a bitter taste due to thermal damage to the powder due to deposits during drying.

To produce milk caramel powder, milk in particular is caramelized in a known, traditional manner and then dried according to the method according to the invention and / or in the spray-drying device according to the invention. Since no auxiliary devices for removing deposits on the inner wall of the drying room, such as blowers, are used, and no or only very little particle deposits are used during drying take place, thermal damage during drying to the milk caramel powder and in particular a bitter taste of the milk caramel powder does not occur.

"Milk caramel powder" is known, for example, under the trade name Caramilk® and is used in confectionery, chocolate, milk products, ice cream and / or cereals, among other things.

Figur 1

eine stark schematische Schnittdarstellung eines Sprühturms mit einem Drehzerstäuber und einem Trocknungsraum.

The invention is explained in more detail below using an exemplary embodiment. It shows the only one

Figure 1

a highly schematic sectional view of a spray tower with a rotary atomizer and a drying room.

A spray tower 101 has a drying room 103 and a rotary atomizer 107. A caramel milk supply line 113 leads into the rotary atomizer 107. The rotary atomizer 107 has a rotary atomizer disk 109 with a direction of rotation 111, which is arranged within the drying space 103.

On a side opposite the rotary atomizer 107, a hot air supply 117 is arranged on the spray tower 101, by means of which a hot air stream 119 is slid into the drying room 103.

Furthermore, the drying space 103 has an inner wall 105 and a milk caramel powder and air vent 121.

The following operations are carried out with the spray tower 101 and the rotary atomizer 107:

A pre-caramelized milk is continuously fed to the rotary atomizer 107 via the caramel milk supply line 113 and atomized into very fine droplets within the drying space 103 via the rotary atomizer disk 109. The rotary atomizer disk 109 rotates at a speed of 16,800 rpm in the direction of rotation 111. At the same time, hot air at a temperature of 180 ° C is continuously countercurrent via the hot air supply 117 as a hot air stream 119 with a hot air quantity of 3,500 kg / (m ^{2 ∗} h) introduced into the drying chamber 103, whereby the caramel milk, which is atomized into very fine droplets, is dried and milk caramel powder is formed within one second. The milk caramel powder is heated to a temperature of 50 ° C.

Here, the atomizer stream 115 of the finest droplets is designed in such a way that the droplets are completely converted into caramel powder particles before they strike the inner wall 105 of the drying room 103 for the first time. The dried milk caramel powder is continuously led out of the drying room 103 via the milk caramel powder and air vent 121 and the milk caramel powder is separated from the air flow by means of a cyclone (not shown).

Since the milk caramel powder particles have already dried so far when they hit the inner wall 105 that they have reached their predetermined residual moisture content of 3.8%, the milk caramel powder particles do not adhere and / or deposit on the inner wall 105.

List of reference symbols

101

Spray tower

103

Drying room

105

Inner wall

107

Rotary atomizer

109

Rotary atomizer disc

111

Direction of rotation

113

Caramel milk supply line

115

Atomizer stream

117

Hot air supply

119

Hot air flow

121

Milk caramel powder and air exhaust

Claims (10)

Spray drying device (101) for drying goods to be dried with an atomizer device (107), the atomizer device having a rotatable atomizer unit (109) for atomizing the goods to be dried in a drying room (103) of the spray drying device, and with a drying gas supply (117) to the Feeding a drying gas into the drying room and for drying the atomized material to be dried to form dried particles, characterized in that the atomizing device is set up in such a way that when the particles hit an inner wall (105) of the drying room, the particles are dried to such an extent that a deposition of the particles on the inner wall is avoided. Spray drying device according to claim 1, characterized in that the spray drying device is free of a mechanical cleaning device, in particular a blower, for removing deposited particles. Spray drying device according to claim 1 or 2, characterized in that the rotatable atomizer unit has a speed in a range from 15,300 rpm to 19,000 rpm, in particular from 16,000 rpm to 18,000 rpm, preferably from 16,500 rpm to 17,000 RPM. Spray drying device according to one of the preceding claims, characterized in that the drying gas supply has a drying gas flow rate in a range from 1,800 kg / (m ^{2 ∗} h) to 5,000 kg / (m ^{2 ∗} h), in particular from 2,500 kg / (m ^{2 ∗} h) up to 4,500 kg / (m ^{2 ∗} h), preferably from 3,000 kg / (m ^{2 ∗} h) to 4,000 kg / (m ^{2 ∗} h). Spray drying device according to one of the preceding claims, characterized in that the spray drying device has a continuous or discontinuous product take-off (121). Method for spray drying an item to be dried, wherein a spray drying device (101) according to one of Claims 1 to 5 is used, with the following steps: - Feeding the drying gas into the drying space (103) of the spray drying device, - atomizing the material to be dried by means of the rotatable atomizing unit (109), and - drying of the atomized material to be dried to form dried particles, wherein the particles are dried in such a way that deposition of the particles on an inner wall (105) of the spray drying device is avoided. Method according to claim 6, characterized in that a speed of the rotatable atomizer unit is in a range from 15,300 rpm to 19,000 rpm, in particular from 16,000 rpm to 18,000 rpm, preferably from 16,500 rpm to 17,000 rpm min, and / or a drying gas flow rate in a range from 1,800 kg / (m ^{2 ∗} h) to 5,000 kg / (m ^{2 ∗} h), in particular from 2,500 kg / (m ^{2 ∗} h) to 4,500 kg / (m ^{2 ∗} h), preferably from 3,000 kg / (m ^{2 ∗} h) to 4,000 kg / (m ^{2 ∗} h), is or will be used. Method according to Claim 6 or 7, characterized in that the drying gas is supplied in countercurrent and / or cocurrent to the atomization. Method according to one of the preceding claims, characterized in that a sugar-containing milk product is used as the item to be dried. Dried product, in particular milk caramel powder, produced by a method according to one of Claims 6 to 9.

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