HK1029391B - Drier-heat-exchanger - Google Patents

Description

Dryer-heat exchanger

Technical Field

The invention relates to a dryer or heat exchanger for drying or SSP (solid state polycondensation) pretreatment (gradual heating without blocking) of PET or PA or PEN pellets, but also for drying other granular bulk materials.

Background

Processes and apparatus for the crystallization and postcondensation of PET in the solid state have long been known. The postcondensation (SSP) of PET in the solid state is carried out at temperatures above 200 ℃ in suitable reactors or dryers for several hours. The problem is how to obtain high yields and high quality of the material with as little effort as possible. The process used also involves the discharge of the reaction product mass while achieving uniform heating of the PET.

It is known to use a top dryer (daechetrkner) or a column dryer for SSP treatment of PET-pellets. DE-a-4300913 discloses a preheater with a top insert in order to achieve a uniform gas flow in counterflow. These inserts should achieve a uniform flow of product (relative movement and prevent sticking) and also reduce the build-up pressure. Also known is a shaft reactor (DE-C-2753543) with a net insert, which is however expensive to produce.

In CH-PS-314655, a device for dust removal and classification of particulate material is given. The falling product material is uniformly dedusted by an upward air flow. Air enters the device laterally next to or below a displacement body.

Also, dryers are known for drying nutlets, coffee beans and the like, which are mainly composed of an upper piece with two heating zones and a lower piece with a cooling zone.

The product material passes through the dryer/roaster from top to bottom in a narrow passage. The side walls of the channel consist of a grid with a screen tension. The channel width can be varied and the mesh can be removed. The disadvantage is the small size of the component space, which limits the high throughput of product to longer dwell times. Simple "stacking" is not feasible in terms of process technology. Such dryers/roasters are air driven and not sealed. The problem of agglomeration of the product material to be treated is of no consequence. In addition, the product stocks are relatively large and their bulk density is low.

As disclosed in US-A-5033208, US-A-3875683 and US-A-2474199, dryers/heat exchangers for the thermal treatment of bulk particulate material are known, consisting of A housing with an inlet and an outlet for the product material, A connection for the inlet and outlet of process gases and A passage through which air can pass for the treatment of the pellets, wherein the passage is bounded by members having holes.

Disclosure of Invention

The purpose of the invention is: the aforementioned prior art is improved by providing a dryer for thermally pretreating pellets, in particular pellets consisting of PET, PEN or PA. It has a large structural height and enables a large flow rate in long and short standstill times of the material flow.

The object is in particular to pass such bulk material in a narrow product column at low surface pressure.

This task is accomplished by providing a channel in a conventional dryer which is circular or rectangular in cross-section, the side walls of which are perforated plate-like members. The channel preferably has a width of 25 to 40cm, a length of up to about 3.5m and a height of up to or exceeding 15 m. A displacer and/or a deflecting member may be mounted in the lower portion of the channel.

This enables a high gas throughput without loose leaks and thus a shorter heating time, at low cost and with smaller component sizes.

With separate aeration (cross-flow, counter-flow) in the direction facing the product material, it is necessary to achieve a finely distributed gas flow, i.e. a good throughflow of the product material.

The time for the product material to stop is usually 1 to 2 hours. In order to obtain good product throughflow, the perforated plate is provided with small holes of only a nominal size of a few mm and a relatively large to low pressure loss, or instead of a perforated plate, a plate which is provided with slit openings (which covers the channel surface partially or completely) is used.

The outer envelope is rectangular or circular (pressure shock resistance, maintainability). The remaining installed parts parallel to the gas flow can be installed in the channels, such as plates inclined alternately downwards, for avoiding sticking of the pellets due to non-movement.

A stationary dispenser is mounted in the product material inlet area.

Drawings

The invention is explained in more detail below with the aid of an exemplary embodiment and its illustration. Wherein:

FIG. 1: a longitudinal section of the dryer is shown,

FIG. 2: in the cross-sectional view of figure 1,

FIG. 3: the walls of the channel(s) are,

FIG. 4: the cross-section of the channel walls,

FIG. 5: an obstruction (insert) in the channel.

Detailed Description

The dryer-heat exchanger consists of a rectangular housing 1 with a product inlet 2 and a product outlet 3, as well as connections 4 and 5 for the inlet and outlet of heating and cooling gas.

Internally, between the product inlet 2 and the product outlet 3 is a channel for the treatment of the product. The channel has a plate 6 through which air can pass, which spans the entire width of the housing 1 and thus forms the boundary of the channel. The plate 6 may also be mounted to be flexibly movable, if desired, to allow the width of the channel to be adjusted. Advantageously, the plate 6 should be different for the gas inlet and outlet, depending on the task it is to undertake, such as diverting the gas or preventing dust clogging. It has a corrugated or knife-shaped insert (8) in the channel in the direction of the product flow, and/or the plate (6) can be curved on its own. The plate 6 itself likewise has openings 9 (holes, slits, or webs) in the flow direction of the product stream, through which process gases and dust and the like can escape unimpeded. At the same time, the openings 9 are dimensioned such that relatively coarse particles, such as molten hair (Engelshaare), cannot pass through them, the self-cleaning of the openings 9 being achieved by the granulate. The use of a tapered configuration for the opening 9 effectively prevents contamination of the opening 9.

Product, such as PET-pellets, enters the channel bounded by the plates 6 through the product inlet 2, slowly passes through the channel, and to the product outlet 3. Heated gas 10, such as nitrogen, is passed through the nozzle 4 through the opening 9 of the plate 6 into the channel to flow through the pellets in a cross-flow or counter-flow. Through the connection 4', the heating gas 10 circulates in the entire area of the channel. The used heating gas 10 is discharged via the connection 4 "and recycled in a known manner. The cooling gas can enter through the connection pipe 5, flow through the pellets in a similar manner and exit the dryer through the connection pipe 5'.

High gas flow rates are achieved without raising the product material. Short heating times and high product throughputs are achieved. The process control of drying/postcondensation and cooling is carried out in a generally known manner with regard to the temperature control and the dwell time of the pellets in the channels.

The process can be tracked and monitored through the glass sight/service port 7.

Pellets consisting of PET, PEN, PA and the like, as output products, are homogeneous, have few impurities and do not agglomerate. After treatment with the dryer, these pellets crystallize and have a bulk density increase of about 2-5% and a uniform pellet shape. The temperature distribution is uniform and the low melting point that may occur is no longer visible.

This is achieved by flowing the heated gas 10 alternately through the product stream (cross-flow or counter-flow) in a narrow, low pressure column of product. It is supported by the insert 8. The relatively fine openings 9 in the plate 6 serve for good gas distribution on the channel walls by the pressure loss of the heated gas.

Reference number table

1 casing

2 product material inlet

3 product outlet

4 connecting pipe

4' connecting pipe

4' connection pipe

5 connecting pipe

5' connecting pipe

6 board

7 glass inspection hole/maintenance port

8 built-in parts

9 opening

10 heating the gas

Claims (7)

1. Dryer/heat exchanger for the thermal treatment, in particular drying or SSP-pretreatment, of particulate bulk material, such as PET granulate, comprising a housing (1) with a product inlet (2) and a product outlet (3), as well as connection pieces (4, 5) for the inlet and outlet of process gases, and a gas-permeable channel for the treatment of the granulate, wherein the channel is bounded by means of a component with an opening (9), wherein the size of the opening (9) is smaller than the size of the granulate particles, characterized in that: the passageway contains an internally disposed obstruction (8).

2. The dryer as claimed in claim 1, wherein: the component is a plate (6) and the opening (9) is a hole or slot.

3. The dryer according to claim 1 or 2, wherein: the openings (9) are conical slots, wherein the width of the openings (9) is smaller on the side of the plate (6) which is in contact with the product material than on the side facing away from the product material.

4. The dryer as claimed in claim 1, wherein: the channel has a slotted, square or circular cross-sectional shape.

5. The dryer as claimed in claim 1, wherein: a stationary distributor is arranged in the region of the product inlet (2).

6. The dryer as claimed in claim 1, wherein: the opening (9) is slot-shaped and is arranged in the flow direction of the product stream.

7. The dryer as claimed in claim 3, wherein: the openings (9) are arranged in the direction of flow of the product flow in a slot-like manner.