DE1957333A1 - Drying synthetic polymer particularly poly - ester granules - Google Patents

Abstract

The granulated material is heated, at a temperature below its melting temperature, to a plastic condition. The granulate is subjected to the stages of partial crystallisation, drying and final crystallisation and subsequent homogenisation by direct contact with hot inert gases or heated air. The through of the granulate is directly controlled in all the stages by a metering unit at the dryer output or by a processing machine connected to the dryer.

Description

Method and device for drying synthetic granules linear high polymers, in particular of polyester granules Di. The invention relates a method and an apparatus for drying synthetic granules linear high polymers, especially polyester granules, which beta heat up temporarily in a plastic state and for further processing must have a suitable crystal structure and low residual moisture.

In these drying processes, the temperatures chosen are usually so high that that on the one hand the substances are not damaged and on the other hand the drying expires as quickly as possible. For economic reasons, this is where possible air is used as drying medium. Some high polymers, such as polyethylene terephthalate, undergo plastic states with the temperature increases necessary for this, in which they tend to stick together and stick to the device parts. This softening as a result of heating can have various causes: In the case of polyethylene terephthalate granules for example, this temporary plastic state is due to the fact that the amorphous granulate used for drying is introduced into the dryer there as a result of the temperature increases, it softens from around 90 ° C and Mohs certain times as a result of transformations of the internal structure passes into a state in which it no longer shows the plasticity just mentioned above 230 °. The appearance The plastic state in the meantime can lead to sticking of the entire property to lead. For this reason, the dryer types known for bulk goods can be used and methods generally fail to efficiently dry such substances insert.

There have therefore already been processes for drying such granulates suggested that the two stages - a partial crystallization and the actual drying - consist. In this case, a Pre-drying take place.

For the implementation of these individual procedural stages, some of which continuous, partly discontinuous, were almost exclusively separate Device units proposed. The partial crystallization will always be guided so that after this stage there are no agglomerates and at least the granules Is crystallized so far that on.

closing when there is little relative movement of the bulk material and Gases at a higher temperature can be dried without flowing around the granulate that there is a sticking or caking.

It has already been suggested that the partial crystallization thereby to achieve that a granulate layer is flowed through with hot gases in such a way that the layer height at least doubles as a result of the flooding and one strong relative movement with thorough mixing of the granules takes place, always at least 50% of the granules in the swirling layer are partially crystallized have to.

Furthermore, a method is known after the nit hot gases in a rustless vortex dryer brought the granulate above the critical state can be. It has also been suggested that partial crystallization by treatment of the granulate it with hot gases in rotating drums nit inclined (continuous Process stage) or horizontal (discontinuous process stage) axis and To carry out harassment.

According to another known method, the Granulate with little relative movement with swelling agents (e.g. water vapor, Toluene, etc.) and hot gases.

Belt or screw conveyors are used to carry out this process proposed in which the incoming granulate is treated iit ellmittel and then hot gases flow through the bulk material. It continues to be a device described, the u consists of a vertical cylindrical tube through which in dense bulk the granulate moves slowly, the water vapor in the upper part as Swelling agent is introduced and hot gas is supplied from below.

All of the aforementioned methods and devices for performing the Processes have the disadvantage that they require a large amount of equipment (with regard to Size and complexity) as well as a high space and energy requirement. When using a continuous vortex dryer for partial crystallization or for the drying can differ due to the residence time scatter Crystallization and drying effects result.

The only way to prevent the differences is through an extension the mean residence time can be compensated, which, however, increases the productivity the device sinks, possibly oxidative damage to the granulate occurs and the abrasion increases. In addition, there are significant difficulties in all processes mentioned, if higher for the desired degree of crystallization Temperatures than have to be set for the final drying. Those at the risk Difficulties based on oxidative and thermal damage can only be avoided by further increasing the equipment On @@ ndes, for example Installation of an intermediate cooling zone or the use of expensive inert gases (for example Nitrogen instead of air). Does not apply to processes that work with swelling agents, If the supply of swelling agent is temporarily switched off, the entire contents of the dryer become unusable.

The purpose of the invention is to avoid the aforementioned disadvantages to develop a method and device for carrying out the method.

The invention is based on the object of a method and corresponding Find devices that allow continuous crystallization and drying of the granulates with a tendency to stick together without rotating internals and without insert of partial liquids while avoiding thermal and oxidative damage as much as possible short path while adhering to the final parameters that are most advantageous for further processing guarantee.

According to the invention, the method for drying synthetic granules linear high polymers, in particular polyester granulate, which when heated temporarily passes into a plastic state, characterized in that it is continuous In a simple device unit using an isolated and / or jacket-heated shaft dryer with only dormant or with dormant and vibrating inserts without the addition of swelling agents in direct contact with the Granulate with hot air or hot inert gases (hereinafter referred to as gas) in three hours under is carried out: Stage I Partial crystallization Stage lt Drying stage III Final drying and final crystallization with homogenization.

The granulate flow is only possible in all stages from the dryer exit connected dosing unit or the processing machine downstream of the dryer directly determined.

It has been found that the partial crystallization for the purpose of Achievement of a granulate, which in a further treatment sit gases of higher Temperature remains free-flowing, can be achieved that in a shaft dryer a hollow body with an inclined perforated surface on which the granulate is placed slowly slides in low dump height, is used, with that of the hollow body hot gas supplied from outside flows through the shade in such a way that it becomes strong Loosening occurs without swirling and mixing, or that in a shaft dryer a hollow body is used, which has such a low height in the shaft Reduction of the cross-section for the passage of the granules and of the Levels III and III flowing upwards hot gas causes either as a result of the strong flooding in the area of the constriction, a strong loosening occurs without swirling and mixing and the granules continuously through this Layer migrates or in the area of the constriction a very strong formation of bubbles or fountains occurs, with less than 50% of the granules involved in this strong movement participates, can be partially crystallized and the granules continuously the Area passes through, or that a hollow body is inserted into the shaft dryer, the implementation of a method that results from the combination of the two described makes possible.

It has also been found that the desired partial crystallization can also be achieved by creating a dense, pressurized layer of granules is heavily flooded with hot Ga, with the slow, continuous one Through the passage of the granulate through stage I as a result of the special shapes of the Vorriehtungsteile, which laterally delimit the layer, too little relative movement of the granulate particles comes among each other, to support the flow of granules through this stage or to dissolve any small agglomerates that may have formed Device parts can be set in oscillating motion. The required Pressure can be caused, for example, by the weight of the granulate in the shaft dryer over the 1st

Stage is stored, are applied. In this case the includes Chute dryer is also a granulate silo.

The hot gas not only serves as a heat transfer medium, but also takes loose Abrasion and dust particles with. This so-called secondary effect of the dedusting of the Granules are loosened up when carrying out the partial crystallization Condition or with strong bubbles and fountain formation greater than that Rrystallize in a dense bed.

The drying stage II of the process can be done with hot gases in the well-known, continuously operating shaft dryer for pourable bulk materials take place.

For the final drying and crystallization with homogenization a layer of granules under a thin layer of hot gases at a temperature which is equal to or greater than that of the second stage, flows through. The granulate passes through continuously this stage. The residence time is short compared to the second stage. Around To achieve gentle, effective drying, it is advantageous to use the III to use partially or completely dried gas. The use of pre-dried Gas in the second stage is also advantageous, but not absolutely necessary.

For the method or for the device for implementation Different variants of the procedure are possible.

Variants of level I: 1. There is a hollow body in the center of the shaft (for example, cone, double cone, the upper surface of which is perforated). The granules is abandoned in the middle and slides in the layer according to the decrease on the inclined surface. Circulating hot gas flows through the hollow body from the bed, which loosens it up; and is heated quickly. That for the first stage in a system that essentially consists of a suction line, the Dedusting cyclone, the blower, the heat exchanger and the feed line to the Hollow body consists, guided hot gas does not need to be pre-dried.

Because of that from stages II and III over the gap between the used The hot gas circuit is the hollow body and the gas rising up the shaft wall Level 1 constantly refreshed. A corresponding amount of gas escapes from the circuit and can partly after a refreshment with dry gas and heating in the Stage II can be reinstated. In order to keep the total energy requirement smaller, the hot gas throughput in the cycle of stage I should be 1.5 to 4 times as much the resulting hot gas feed in stages II and III.

2. The center of the shaft is in the area of the. Level I a displacer (For example: paraboloid with attached cone, ellipsoid, circular cylinder with attached cones and so on) with or without ribs arranged. It pushes the hot gas stream coming from below towards the vessel wall, so that Between him and the wall of the dryer shaft a loosened granulate fill was found without swirling and mixing or a strong movement of the granules Bubble or fountain formation occurs.

To adjust the granulate volume in the dryer to the desired one The displacement body can be in its dwell time in connection with the throughput Height can be adjusted, or displacers of different lengths can be used come into use. The displacer can become diligent.

also play as a double cone in connection with a corresponding one ring attached to the shaft wall.

result in hollow bodies. By adjusting the height of the displacer when the hollow ring body is stationary on the shaft wall, the cross-sectional area then becomes affects the granulate and gas passage.

The hot gas emerging from the dryer can be used to achieve a low energy consumption partly after dedusting, refreshing with dry Gas and heating for drying can be used again in stage tI.

3. Such a displacement body can also advantageously be used, which concentrically constricts the flow of hot gas and creates bubbles or fountains or a highly loosened granulate layer without swirling and mixing results in the cylindrical or almost cylindrical part of the constriction.

The displacement body can also be teloscpartig in his Be adjustable in length or displacers of different lengths can be used will. Regarding the reuse of the hot gas emerging from the dryer the same applies to under 2. already companions.

There is no separate hot gas circuit for variants 2 and 3 for the 1st stage, so that the expenditure on equipment is lower compared to variant 1 and the process management become easier.

4. The displacers listed under 2. can also be used on their be perforated and connected to a hot gas circuit. Will If the level is kept high, the partial crystallization begins on the perforated surface, as described under 1., and is reduced in the area of the cross-section for the passage of the granulate and that from stages II and III ascending gas, as under 2.

explained, continued.

5. In the event that the partial crystallization in a dense, should take place continuously in a granulate layer moving under pressure, an insert (hollow body) must be attached centrally in the shaft dryer. Form the shaft wall in connection with the shape of the egg-built hollow body must be be so that it is longitudinal as a result of the constantly changing flow cross-section Level I to a sufficient level, However low relative movement the granulate particles come while wandering through the 1st stage.

In Fig. 6, 7 and 8 are some embodiments for the shaft wall and the hollow body in the area of FIG.

Level shown. To achieve the appropriate pressure can the weight of the granulate stored in the shaft above level I in the silo is used worth the. To support the smooth passage of the granulate respectively to dissolve smaller agglomerates, the hollow body or an additional one in the area part used in the 1st stage (Fig.

7) are excited to vibrate. A strong flooding of the granulate bed can through that on.

rising hot gas from stages II and III in ver.

binding with the reduction of the flow cross-section tes as a result of the hollow body used in the area of level I. The hot gas can be found at the upper end of level I via corresponding perforations on the shaft wall or sucked off on the hollow body. The strong flow can also be caused by the Overlay of two partial flows, the rising hot gases from stage II and III (almost lower right partial flow) and an almost horizontally directed flow by pressing hot gas into stage I through perforations on the hollow body or on the shaft wall. The suction of the whole hot Gas then takes place depending on the introduction of the almost horizontally directed Flow on the shaft wall or on the hollow body. About the leadership of the additional some.

blown gas and the entire evacuated gas applies under 1. explained.

In any case, for example due to the design of the suction, it must be ensured that no hot air gets into the silo and the silo opposite stage 1 is so isolated that granules with temperatures above 80 ° C siob only in level 1 is located. Then there can be no bridging in the silo as a result of occurring plastic states come and a flawless granulate guidance in the stage I according to the extraction at the Tronckner exit is to be expected.

Variants of stage II: For the drying in stage can accordingly known processes and shaft dryers are used for free-flowing bulk materials. The granulate is surrounded by hot gas, some of which are directly from stage II of is supplied externally and partially overflows from stage III.

Variants of level III: In the lower part te3 shaft dryer is A hollow body is inserted centrally, which is optionally divided into two chambers The lower chamber of this hollow body is located within stage III and part of its surface is perforated. Via reed pipe, hollow body and perforation the hot gas is supplied or discharged. The hot gas flows through M-hezu radially the granulate layer. There are perforations and one on the outer wall of the dryer Annular chamber with pipe connection to a hot gas circuit. The hot gas can both from Flow through the granulate layer from outside to inside or in the opposite direction. The amount extracted from this stage is lower, corresponding to the refreshment of the gas circulating than the one pressed in. The difference flows In stage II jiber, the upper chamber of the hollow body can be connected to the gas supply line serve the level II. The shapes of the hollow body used can be very different be parabolic, cylindrical, conical or any combination of the basic shapes.

At the gas passage points there can generally be perforations that smaller than the smallest granulate particles, larger perforations correspond.

the sieve covering or arranged at a distance like scales one above the other Truncated cones, etc. are located.

There is a metering device at the lower end of the dryer (for example rotary valve, screw conveyor) or the connection to a downstream processing machine. Through the one connected to the dryer The aggregate controls the granulate throughput 0 The process and the device should be explained on some pages.

In the accompanying drawings: FIG. 1; a cut through the device with internals and gas circuits Fig. 2; the one hung in level I. cylindrical displacement body Fig. 3; the displacement body with a central passage Fig. 4; the flaky installation and the granulate silo attached to it, FIGS. 5, 6; the Installation body in stage III in different design variants Fig. 7,8; the Installation body in stage I in different design variants according to example 4.

Example 1 (Fig. 1): In an insulated shaft 1 with a filler neck a hollow body 4 is attached to a gas supply pipe 3 in stage I. The upper Surface 5 of the hollow body 4 is perforated. A stream of hot gas passes through the gas supply pipe 3, hollow body 4 through the granulate layer into a cavity 10 of the shaft.

At the same time, hot gas flows out of stages II and III over the gap of stage I in said cavity.

From the dryer stage I, the gas is over with the help of the fan 14 the line 12 and the dedusting 13 sucked off. Part of the compressed gas then flows via the heat exchanger 15 back into stage I of the dryer. the remaining amount is over the line 29, fitting 28, to the supply line of the fan 26 out. The fan 26 pushes a gas mixture consisting of the recycled from the I. stage and an addition of dried gas over the Heat exchanger 24 in the gas distribution body 19 of stage II of the dryer. Above the armature 25 escapes an amount of gas that corresponds to that of the addition of dried gas is equivalent to.

The fan 36 sucks hot gas from stage III via the annular chamber 21 and presses it over the line 34, in which there is still an addition of dried Gas takes place in the heat exchanger 33 and in the gas distribution body 20 of the stage III of the dryer. Part of this gas flows through stages II and I into the upper one Dryer cavity. The amount of the addition of dried gas and thus the Know the humidity of the gas for stage II or III through the valve 30 and 32 are influenced.

When using air as a drying agent, some of the room air can be released Via the filter 27 and fitting 23 to whom the fan 26 is sucked in.

Example 2 (Fig. 2): In stage I of the shaft dryer 1 is a Blank body 6 (displacement body) suspended from a rod adjustable in height. Granulate and gas are displaced from the center of the shaft through this hollow body. In contrast to example 1 below, it is omitted here a separate gas circuit for level 1. The strong flow occurs only through that from level Ii and III rising gas in connection with the reduction of the flow cross-section through the displacement body 6. The other arrangements of the device parts and Mode of action are as in Bei.

game 1.

Example 3 (Fig. 3): This example differs from example 2 only by a different design of the displacement body in the 1st stage.

Granules and gas can only pass through the hollow body 7 a small cross-section in the middle of the shaft move it.

Example 4 (Fig. 4): A vessel 17 is placed above the shaft 1, in which amorphous granulate is stored for drying. The vessel 17 is opposite the shaft 1 isolated. This is necessary so that there is no thermal conduction comes to sticking of granules in the silo. Level I is in the middle of the shaft a displacement body attached, which consists of several widely spaced one above the other Consists of truncated cones. Likewise, truncated cones 9 are like scales on the shaft wall appropriate. There are free passages from the interior between these truncated cones of the displacement body 8 to the granulate layer or from the granulate layer to the annular chamber 10 a.

As a result of the scale-like lateral delimitation of the granulate layer and a strong narrowing of the cross-section for granules and air passage on the At the end of the first stage there is a slight relative movement of the granulate particles among each other when passing through the first stage. By the exciter 18 is the Displacement body 8 excited to longitudinal vibrations. From a hot gas circuit for The 1st stage, corresponding to Example 1, the gas is Duroh the line 76 uaa. the hollow body 8 pressed into the Granlutschicht. In addition, a flow is carried out of the granules in the 1st stage through you from the II. and III. Level ascending Gas. All of the gas from stage I is via the annular chamber 10 a and the line 12 a extracted.

The remaining arrangements of the Vorriohtungsteile and mode of operation are as in example 1.

With the proposed method and Vorriehtung accordingly of Examples 1 - 4 for drying the granules from synthetic linear high pelysers, which temporarily change into a plastic state when heated, were at the treatment of polyester granules with the dimensions 2 x 4 x 4 mm (cube granules); an input moisture of approx. 0.4%; an initial degree of crystallization of approx. 10% and air as the drying agent, the following results (Table 1) are achieved: Tabel 1 (2) (1) t2 t3 pH2O pH2O 1/2 + ° C ° C Torr Torr h%% 160 160 10 10 3 42.7 0.007 160 160 0 0 3 42.7 0.001 15o 150 10 10 2 41.0 0.012 150 @@ 0 @ 5 2 41.0 0.008 150 180 5 0 2 + 0.3 46.3 0.002 150 180 10 0 2 + 0.3 46.3 0.003 140 200 10 0 2 + 0.2 50.7 0.004 where: t2 ~ temperature of the gas injected in stage II t3 - temperature of the gas injected in stage III (2) pH2O - water vapor partial pressure of the gas injected in stage II (1) pH2O - water vapor partial pressure of the in stage III blown gas 1/2 - residence time of the granulate in the I. and II.

Stage 3 - Residence time of the granulate in the III. Level - degree of crystallization of the granulate after drying F - moisture content of the granulate after the Drying

Claims (18)

Claims: 4. Process tin drying of synthetic granules linear high polymers, & nspecially polyester granulated, which when heated temporarily change to a plastic state below the melting temperature, in a continuously operating shaft dryer without the use of a swelling agent, characterized in that the granules are only at rest or with a low amplitude vibrating displacement bodies in constant direct contact with hot inert gases or hot air in a cylindrical vessel in a partial crystallization, drying, Final drying and final crystallization stage including homogenization the granules pass through in all stages only from the one connected to the dryer outlet Dosing device or the processing machine downstream of the dryer directly is controlled. 2. The method according to claim 1, characterized in that in the partial crystallization stage thin, sliding layers due to the increased flow velocity of the hot gas of the granules are generally traversed transversely to the direction of movement so that it There is strong loosening in the layers without turbulence and mixing. 3. The method according to claim 1, characterized in that at constriction points the granules sliding against the gas flow due to the strong flow with hot Gases a strong loosening obno eddies, or at higher gas velocities experiences a bubble or fountain formation, with less than 50% of the granulate, that participates in this continuous movement, crystallizes before the beginning of the flow could be. 4. The method naoh claim 2 and 3, characterized in that the Partial crystallization by flooding with hot gases both across and against the granulate movement takes place one after the other. 5. The method according to claim 1, characterized in that a dense, Granulate layer under the pressure of the amorphous granulate stocks lying above it strong with hot gases along and / or across the direction of movement of the granulate is traversed, whereby it is through special shapes of the side delimiting parts In the downward sliding granulate column, there is little relative movement of the granulate parts comes among each other. 6. The method still claim 2 and 5, characterized in that within Level 1 individual parts of the device perform oscillating movements. 7. The method according to claim 1, characterized in that the granules in the final stage with a short dwell time, preferably by means of dried hot water Gases whose temperature is equal to or higher than that of the gas in the preceding one The drying stage is heated, with the same temperature only a homogenization the moisture content and the degree of crystallization causes, while the higher temperature reduces the moisture content, at the same time increases the degree of crystallization and both Parameters of the granulate particles homogenized among each other, depending on the requirement for the subsequent processing stage. 8. Apparatus for performing the method according to claim 1 to 7 in a vertical shaft dryer without rotating internals, thereby characterized in that in the free cross section of the shaft dryer (1) centrically on a longitudinally displaceable hot air supply pipe (3) under the filling opening (2) a double-conical hollow body (4) with a perforated upper jacket (5) of this type is suspended that between the hollow body (4) and the one on the wall of the shaft dryer (1) attached hollow body (11) there is a gap, whereby the interior of the hollow bodies (4) and (19) and the upper part (10) of the shaft dryer (1) Are components of a hot air system. 9. Apparatus according to claim 8, characterized in that in the Stage III (Fig. 1) centrally a perfonter hollow body (20) is attached, which with hot gas, the temperature of which is equal to or higher than that of the gas in the stage II, is applied from a hot air system, the perforated surfaces of the Hollow body (20) close to a suction system, which is designed as an annular chamber (21), lie and the hollow body (20) and the annular chamber (21) are part of a hot gas circuit are. 10. Apparatus according to claim 8, characterized in that the shaft cross-section at the level of step I a circular ring-shaped one lying on the inner wall of the shaft (1) Hollow body (7) is inserted and a suction line (12) is connected to the cavity (10) is. 11. The device according to claim 8, characterized in that centrally a displacement body (6) under the filling opening (2) of the shaft dryer (1), (Fig. 2), on an adjusting device (37) angled is brought and the space (10) above the displacement body (6) is connected to a suction system. 12. The device according to claim 8, 9 and 10, characterized in that Let the hollow body (4, 6, 7, 20) be cone, pyramid, ellipsoid or paraboloid, Zy. linder, hemisphere or any combination of these basic shapes represent (Figs. 5 and 6). 13. Apparatus for performing the method according to claim 5, characterized characterized in that centrally in the upper part of the shaft dryer (1) a hollow body (8) is arranged with truncated cone shells placed on top of each other, from which the hot gas blown in through the hot air supply pipe (3) emerges; and on the inner wall of the shaft dryer plate-like rings (9) in the amount of perforated shaft wall and the annular chamber (10 a) are arranged, the hollow body (8) and the annular chamber (10 a) are connected to a hot air system. 14. Apparatus according to claim 5 and 13, characterized in that the shaft dryer (1), which is extended upwards, is designed as a silo (17) for granules is. 15. Apparatus according to claim 5 and 13, characterized in that the one at the hot air supply. tube (3) attached hollow body (8) with a vibration exciter (18) connected is. 16. The apparatus according to claim 10, characterized in that the Suction line (12), which carries hot gas laden with dust, in front of the fan (16) opens in a per se known dedusting device. 17. The device according to claim 9, characterized in that the annular chamber (21) in stage III via line (34 a) with hot gas b. Is added and the Suction line (35 a) is connected to the hollow body (20) and the fan (36). 18. The device according to claim 13, characterized in that the Annular chamber (10 a) is acted upon with hot gas via line (12 a) and the suspended hollow bodies (8) are connected to the suction system via the line (3) is. L e r s e i t e