DD147716A1 - PROCESS FOR CRYSTALLIZING AMORPHIC POLYESTER GRANULES IN THE FIXED BED - Google Patents

Abstract

Process for the crystallization of amorphous polyester granules, which is used in the chemical fiber industry, and has the goal to run the crystallization process and drying process with the least possible energy expenditure, the task was to conclude using known Waermeübergangseffekte the critical Teilkristallisationsvorgang in less than 10 min. According to the invention, the object was achieved by mechanically removing the granules deposited on the wall of the crystallization zone heated to 390 to 480 K from the wall within 140 to 160 times within 5 to 10 minutes, for the heat exchange to the center of this treatment zone, and from here In turn, the heated wall to be supplied, wherein withdrawn from the outlet of the downstream shaft dryer Heiszluft at 400 K in the upflow of 0.6 to 1.4 m / s loosens the amount of granules to be treated and the crystallizer with 300 to 315 K verlaeszt.

Description

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Title of the invention

Process for the crystallization of amorphous polyester granules in the plague bed

Field of application of the invention

The invention relates to a crystallization process for amorphous polyester granules, which in the heating phase for bonding and. tends to Aggloraerat formation. The application in the drying of other polymers prone to sticking, preferably in the chemical fiber industry, is possible «

Characteristic of known technical solutions

In the state of the art, a number of technical solutions for drying high-polymer granules or chips, which in the amorphous state tend to stick together when heated in the temperature range from 365 K to 400 K, are indicated everything in the transition phase from the amorphous to the partial crystallization state. lie, show the known. Solutions in large numbers a Zweistuf enverfahren that a crystallization or Teilkristallisationsstufe and. a final drying

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stage, predominantly a well-known shaft dry process contains «

Thus, in DE 26 14 231, amorphous synthetic granules are treated in a layer of 600 mm height with hot gas at 410 K to 520 K in an upflow with 50 % to 90 % of the agitation speed under mechanical stirring for less than 10 minutes and partially crystallized Good then fed to a final drying process *

The agglomeration is hereby prevented with great certainty by the loosening up of the granulate layer by means of hot gases in the upflow on the one hand and an additional movement of the loosened up layer by means of stirring elements which break up sticky particles «

However, both measures require a high specific energy expenditure, which results from the known poor heat transfer from heating surfaces to the air and the hot air to the granules «

NL 96 018 describes a drying process for polyester granules which prevents agglomeration in the phase of raising the temperature to the drying temperature by at least partial crystallisation of the granules by swelling agents until a specific weight of 1.34 kg / dm A pre-treatment for partial crystallization of the granules with, for example, saturated Y / assampfampf causes after 15 bi3 25 minutes a Kristallisajtionsgrad, in which a

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This process is too costly for continuous operation, since the drying process, a further medium liquid or vapor supplied, but after a short time again under Energieauf v / a nd must be eliminated from the granules · acetone or toluene as the swelling agent is excreted for reasons of fire hazard for use in large-scale production. "

In DE 23 17 651, it is proposed to supply amorphous granules for partial crystallization of a horizontal, wall-heated drum (Wand.temperatur .410 K to 470 K), in which a larger number of paddles on a rotating horizontal shaft on a thin layer of the granules the gesarate heat-emitting inner shell surface distributed »The near-wall and. wall-contacting granules are partially crystallized in less than 5 to 10 minutes without agglomeration to more than 30 % and. then fed to a hot-air dryer in a known shaft construction · The hot air of the shaft dryer passes into the atmosphere via a dust-separating cyclone. Here, the favorable heat transfer from the surface of the Heiamantels is used to granules to achieve overall short residence times in the partial crystallization zone, but with the adverse effects that derer the scattering range derer dwellings .er Granulatteilchen is large, a energy expenditure. to the veil-like distribution of these particles on the inner circumferential surface by acceleration impulses arises, the abrasion by wall friction and. Impulses can not be prevented and. escaping from the shaft dryer. © Insufficient amount of heat. used for pre-drying. »

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Object of the invention

The invention relates to a process which, while lowering the energy consumption for drying high-polymer granules which tend to stick and agglomerate, enables the continuous production of a crystalline and uniformly dried granulate having little abrasion Granules to find treatment parameters, the use of favorable heat transfer and maximum use of heat in less than 10 minutes Usual Durchsatζmengeη for sticking prone granules partially dry and in a second stage in a known manner *

It has been found that the object is achieved by a method., In the continuous free Pail supplied amorphous granules in a fixed bed at Aufstromgeschwind.igkeiten the hot air from 0, ß to 1.4 m / s with the heated wall of the crystallization zone, the Wall temperatures of 390 K to 480 K, initiated to initiate the first partial crystallization, mechanically deflected in multiple alternation to the inner part of the crystallization zone with a gravity component for heat exchange with the surrounding loosened Schilt and. is supplied to the heated wall again. * The number of within 5 to 10 minutes repetitive change of direction of the granules in d.er crystallization zone depends on the ratio of the heat-emitting lateral surface to the volume of the packed crystallization zone _s wherein the temperature d.er her from d. em shaft dryer with 0.8 m / s to 1 ₈ 4 ss / s supplied hot air 360 K to 380 K and

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ilire outlet temperature from the crystallization zone 300 K to 315 K amount.

With average thermal conductivity of the granules of. 30.2 x 10 ~ ² kJ / mh K resulting approximately 140 to 16O exchange within 7 to 8 minutes ^ wherein an average temperature of the granules at the output of the crystallization zone is reached of 390 K to 410 K and no agglomeration occurs, that the final drying process can be initiated. The surprising, energetically advantageous result can be interpreted in the way that the heat transfer from the heated wall to the granules is cheaper than that of the hot air to the granules and the granules are kept in contact with the heated wall only until the shell of the granule particle is heat saturated. Let this heat saturation in the shell of the granules for a given specific heat flow achieved and thus initiated the partial crystallization, the targeted exchange of granules on the wall takes place against a new occupancy. Thus, the gtinstige direct heat transfer from the wall to the granules is used and the Granulatteileheη individual carries the heat absorbed by the wall directly into the center of the crystallization zone for heat exchange at a relatively high heat gradient until a sufficient, the flowability even after several changes at the exit of the crystallization zone of the granules guaranteeing degree of crystallization is reached. At usual throughputs of 150 to 400 kg / h of granules specific Ehergieaufwendungen of 550-650 kJ / kg granules can be achieved. The targeted change in position of the granulate within the crystallization zone required during the partial crystallization process is determined by the

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Loosening of the bedding in the upflow is energetically more favorable in the densely packed pest bed designed and. also causes a reduction of the abrasion, so that the energy expenditure for dedusting can be kept smaller «

Compared to the known state of the art, the process according to the invention has a number of advantages

The partial crystallization amorphous, when heating for bonding and. Agglomerating tending granules are continuously in the loosened plague bed without substantial abrasion. The flow is directly from the heated wall to the granulate, under the condition that the residence time of a granular coating on the wall is defined taking into account the heat flow in the granule body. remains superior to the heat transfer of hot air to the granules and the wall temperatures can be kept lower for the same effect in the interest of gentle treatment. The residence time of the granules in this partial crystallization zone amounts to 5 to 8 at conventional throughputs minutes. " For the above reasons, the total energy consumption can advantageously be reduced by 30 % to 40 % compared to the cited prior art values of the prior art.

The method according to the invention will be explained in more detail by way of example. "

In a drying device for polyester granules,

ρ, which had a surface area of 1.49 m per kg, 250 kg per hour were used in the crystallization zone, which was followed by a shaft dryer directly downstream.

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The ratio of the heated surface of the crystallizer to the amount of granules passing through was 5 × 10 -5 m ² h / kg.

The granulate was loosened from 380 kg / h of flowing hot air with a temperature of 393 K and the flow rate of 0.9 m / s in the crystallization zone. "The upflow air was taken from the outlet of the shaft dryer the crystallization zone of. 453 K in the loosened bed about 150 granules layer change on the wall in the rhythm of about 2 seconds, with the granules in the center of the crystallization zone and back to the wall with uniform zigzagdurch'durchlaufen the treatment zone is transported "While the partially crystallized granules flowing the Treatment zone with 398 K left to be subjected to the final drying in the shaft dryer, the hot air flowed with 313 K upwards. Only a total of 285 kJ had to be spent per kg of granulate. "

Claims (1)

invention claim 1 "process, for crystallization, amorphous. Polyester granules in a fixed bed with mechanical movement dea granules and heat supply by direct contact to a heated wall in the crystallization zone, subsequent final drying in. A known shaft dryer, characterized in that the continuously fed amorphous granules in the crystallization zone with a heated wall having a temperature from 390 K to 480 K, preferably 460 K, brought after the heat saturation of Granuiatteilchenschale mechanically moved from this heated wall to the center of the Kri3tallisationszone and back to the wall, zigzag through gravity passes through the treatment zone, the granular bed in the crystallization by hot gas with 360 K to 380 K at upstream velocities of O ₈ 8 to 1.4 m / s is loosened, and the gas leaves the crystallizer with temperatures of 300 to 315 K. " 2 _e method according to item 1, characterized in that the frequency of the detachment of the granular layers of ä.er heated wall and the supply from the center of the K-crystallization zone to them from 0.33 to 1 $ 33 s, preferably 0.5 s " ¹ · 3 * Method according to items 1 and 2 ₉ characterized in that, every kilogram of the quantity of granules to be passed through every hour is passed over a con tact surface of 4 × 10 ^-3 to 6 × 10 ^-3 m ^{2 of} heated surface.