Concentrating evaporators – Superheating and pressure release
Reexamination Certificate
2002-05-22
2004-08-24
Manoharan, Virginia (Department: 1764)
Concentrating evaporators
Superheating and pressure release
C159S027400, C159S043100, C159S047100, C159SDIG001, C159SDIG001, C528S501000
Reexamination Certificate
active
06780281
ABSTRACT:
The invention relates to a strand devolatiliser having a degassing container, a product inlet with at least a distributor tube, a product distributor, a product outlet and a vapour outlet.
Such strand devolatilisers are used in particular in polymer production, to remove the volatile constituents from the product stream (see for example R. J. Albalak, “Polymer Devolatilization”, Marcel Dekker Inc., 1996, p. 8). With them, it is attempted to subdivide the heated product stream (e.g. liquefied polymer, falling) into as many (polymer) strands as possible inside the degassing container, in order to achieve as large as possible a surface area. Thin strands allow more strands to be accommodated per unit area. Strand length and thus the height of the degassing container should remain within reasonable limits, however.
In experimental installations and installations with relatively small throughput, it is sufficient to distribute the product stream by means of a so-called plate distributor, in which a perforated plate beneath the product inlet ensures subdivision of the product stream into the individual strands. Strand devolatilisers with plate distributors are known for example from patent specifications U.S. Pat. Nos. 5,024,728 and 4,934,433. On a small scale, only a small plate diameter is required for accommodating the drill holes, only a small plate thickness therefore being necessary for strength reasons even in the event of a high initial product pressure (i.e. in the event of high throughput, high product viscosity) for uniform product distribution over the perforated plate. However, on an industrial scale the diameter of the perforated plates must be very considerable owing to the necessary initial product pressure, in order reliably to prevent sagging thereof. However, a relatively large plate diameter requires longer drill holes in the perforated plate, such that the initial product pressure increases to still higher values, which in turn have an effect on the necessary plate thickness. Owing to the restricted product throughput in the case of plate distributors, a strand devolatiliser provided with such a plate distributor cannot be enlarged however desired, in particular high polymer throughputs (>10 t/h) are not possible for most polymers with their typically high melt viscosity.
A further disadvantage of the strand devolatiliser design with plate distributor is the arrangement of the vapour outlet, which can only be to the side owing to the continuous product distribution plate, whereby strand deflection may arise.
The object of the invention is therefore to design and further develop an above-stated strand devolatiliser described previously in more detail in such a way that, in particular in large manufacturing plants, optimum loading density (product throughput per unit area) is achieved. Moreover, it is desirable for the device to exhibit high flexibility with regard to product throughput and choice of materials.
This object is achieved according to the invention by a strand devolatiliser device which comprises at least a degassing container, a product inlet, a product distributor, a product outlet and a vapour outlet, characterised in that the product distributor takes the form of a tube distributor with at least one distributor tube and a plurality of die tubes arranged in parallel, which comprise a plurality of apertures in the tube wall. The die tubes are preferably arranged in several planes one above the other and staggered relative to one another.
In the strand devolatiliser, a number of product strands corresponding to the number of apertures forms after passage of the (optionally preheated) product stream through the tube distributor and the outlet of the die tubes, which strands fall freely as a result of gravity and collect in the base area of the container.
The arrangement according to the invention of the individual tubes in the degassing container may result in optimally uniform and dense distribution of the product strands over the cross section of the container, such that the volume of the degassing container may be fully utilised. In particular, there are also advantages for vapour conduction, since the volatile constituents of the product stream may be drawn off above the product outlet without any constructional effort and thus the risk of strand deflection by lateral discharge may be eliminated. The height-staggered tubes according to the preferred embodiment allow the volatile constituents to flow upwards counter to the falling strands and in the edge area of the container.
This may also be achieved in that the die tubes are spaced laterally, irrespective of whether they are arranged in a single plane or in several superposed planes.
Alternatively, the individual tubes may exhibit a (circular) round or oval cross section with in each case downwardly directed apertures (e.g. drill holes). Depending on the geometric circumstances in the strand devolatiliser, however, a combination of these and other tube shapes mentioned below may also be appropriate.
According to further preferred teaching of the invention, the individual tubes take the form of half-tubes, which are each bounded at the bottom by an especially flat perforated plate. In this way, virtually the entire diameter of the half-tubes may be utilised for strand formation.
Due to the small width of an individual half-tube or an oval tube compared with the diameter of a conventional plate distributor, the plate thickness of the half-tubes or wall thickness of the oval tubes necessary for strength reasons may be considerably smaller than the plate thickness in conventional plate distributors.
According to a further preferred development of the invention, other tube shapes are provided instead of the half-tubes, which other tube shapes do not necessarily exhibit a round cross section, For example, a triangular or rectangular cross section may be produced from thick-walled sheets or drawn profiles.
Another particular development of the invention provides that the die tubes are arranged inclined to the horizontal, in particular sloping towards their ends, at an angle &agr; of up to 15°, in particular 10°, in order to ensure drainage of the tubes if the product supply is cut off.
According to other preferred teaching of the invention, the die tubes are fitted directly on the distributor tube of the product inlet, so that no dead spaces arise in the distributor tube. The connection may be achieved by welding or detachable fastening, e.g. by means of flange and screws.
Another particular development of the invention provides that the ends (tips) of the die tubes are made acute-angled by bevelling, in order to minimise dead space at the tube end.
In a further particularly preferred development of the invention, provision is made for the product distributor to comprise a plurality of distributor tubes, which are arranged in the degassing container, such that subdivision of the product stream into substreams proceeds inside the degassing container. The distributor tube may extend in curved manner in the inner upper area of the degassing container. Such an “internal distributor” has the advantage that only a single tube has to pass into the degassing container for product feed, such that it is ensured that the device is vacuum-tight.
However, it is also possible for the product distributor to comprise a plurality of distributor tubes located outside the degassing container, such that subdivision of the product stream into substreams proceeds outside the degassing container. This alternative development has the advantage that, where necessary, an individual blocked tube may be replaced with less effort than in the case of “internal distributors”. However, this advantage is won at the cost of the disadvantage of more complex sealing (vacuum resistance).
To achieve optimum product quality, therefore, the first alternative, i.e. the “internal distributor” is preferred for many applications.
To avoid the risk of blockage, in particular in the case of non-steady state operation, a further particular deve
Elsner Thomas
Heuser Jürgen
Kohlgrüber Klemens
Kords Christian
Bayer Aktiengesellschaft
Gil Joseph C.
Manoharan Virginia
Preis Aron
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