Note: Descriptions are shown in the official language in which they were submitted.
CA 02291737 1999-11-26
WO 98/53916 FILE, P~N-th~'TH15 ~PCT/EP98/02956
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Description
Nozzle for metering very small liquid streams in a high-temperature
environment
The invention relates to an apparatus for atomizing a medium, having a
nozzle tip with an atomizing member with at least one atomizing hole and
cooling means.
Such apparatuses (nozzles) are disclosed, for example, in US 5,351,889
and US 5,253,810.
A nozzle tip having an atomizing member with at least one atomizing hole
is also disclosed in US 4,150,794. In this nozzle tip, which is designed
specially for cutting tasks, the atomizing member is followed by a seal
which prevents the emergence of the medium with bypassing of the nozzle
member.
Nozzles having the features described at the outset are also used for
metering very small amounts of catalyst in acetic acid pyrolysis to give
ketene and water. Catalytic acetic acid pyrolysis is used industrially for the
production of ketene, diketene and acetic anhydride, by the following
process: acetic acid is vaporized and is preheated to the production
temperature. The catalyst, e.g. triethyl phosphate, is then metered in liquid
form into the acetic acid vapor by means of a cooled nozzle. The mixture is
kept at the reaction temperature in a tubular reactor. After the reaction
zone, cooling is carried out so that water and unconverted acetic acid
condense. The further processing of the ketene depends on the
subsequent product desired.
The disadvantage of this process is that, owing to the metered amount of
catalyst, which is small even on a large industrial production scale, a
scaling-down of the plants to the size of experimental apparatus (100-
5000 g/h of acetic acid) under the same metering conditions for the
catalyst with the known nozzles is not possible without coking and/or
blockage impairing the operability of the known nozzles.
It was therefore the object of the invention to improve the known
apparatus.
CA 02291737 1999-11-26
2
This object is achieved, according to the invention, by an apparatus of the
type stated at the outset, wherein the or each atomizing hole has a
diameter of less than or equal to 50 Nm, the cooling means has a space
through which a coolant can flow and which surrounds the nozzle tip so
that the apparatus can be thermostated up to the outlet of the atomizing
hole, and a seal is arranged downstream of the atomizing member in the
direction of flow, which prevents the emergence of the medium with
bypassing of the atomizing member.
The invention therefore relates to an apparatus for atomizing a medium,
having a nozzle tip with an atomizing member with at least one atomizing
hole and a cooling means, wherein the or each atomizing hole has a
diameter of less than or equal to 50 Nm, the cooling means has a space
through which a coolant can flow and which surrounds the nozzle tip so
that the apparatus can be thermostated up to the outlet of the atomizing
hole, and a seal is arranged downstream of the atomizing member in the
direction of flow, which prevents the emergence of the medium with
bypassing of the atomizing member.
In a particular embodiment, the or each atomizing hole has a diameter of
less than or equal to 40, preferably less than or equal to 30, particularly
preferably less than or equal to 20 and very particularly preferably about
10 Nm. The seal used is advantageously a metal seal, preferably a silver
seal. The atomizing member is preferably produced from an alloy which
contains platinum and/or iridium.
The apparatus has at least one seal which prevents the emergence of the
medium with bypassing of the atomizing member and which, based on the
direction of flow of the medium, is arranged downstream of the atomizing
member. This prevents abraded material from the seal from blocking the
atomizing hole. In a particular embodiment, a filter, which likewise prevents
blockage of the atomizing hole, is inserted upstream of the atomizing
member.
The nozzle according to the invention affords the possibility of metering
liquid streams smaller than 20 ml/min, preferably of 0.05-1, or up to
10 ml/min continuously in liquid form into a gas space having temperatures
up to 1000°C, preferably up to 1100°C. Because the cooling is
designed
according to the invention, blockage of the atomizing hole, for example due
to frequently observed coking of the catalyst during acetic acid pyrolysis,
CA 02291737 1999-11-26
3
no longer takes place. Atomization of the catalyst as a liquid jet in a pilot
apparatus has the advantage of better scale-up of the results to large
plants. In addition, it was surprisingly found that metering as a liquid jet
is
more effective than preliminary vaporization of the catalyst and metering in
gaseous form, since in the latter case virtually immediate coking of the
nozzle occurred. In addition to use in the acetic acid pyrolysis, the nozzle
design affords the possibility of continuously atomizing very small amounts
of liquid as a fine jet into hot gases. Applications are laboratory and pilot
apparatuses in which additives must be liquid.
A possible design of the nozzle according to the invention is described by
way ofyexample below, with reference to the sectional side view shown in
the figure. A restriction of the invention in any way is not intended by this.
The figure shows a nozzle 1 by means of a liquid 13 can be transported by
means of a pump (not shown) via a stainless steel tube 2 which has a
cooling jacket 8, at a pressure up to 400 bar, through the nozzle tip 3. The
tip 3 contains two retaining screws 4,5 which fix an atomizing member, the
nozzle plate 6, in such a way that it is pressed against the first seal 9. The
nozzle plate 6 has an atomizing hole 7 with a hole diameter of 10-30 Nm.
The tube 2 and the tip 3 are surrounded by the cooling jacket 8 in such a
way that the tube 2 can be thermostated up to the nozzle tip 3, and this
can be done up to the outlet of the atomizing hole 7. This is achieved by
surrounding the tip 3 by a space 12 which a coolant 14 can flow.
The first seal 9 prevents the liquid 13 from emerging from the nozzle tip 3
with bypassing of the nozzle plate 6 between the screws 4,5. Said seal is
arranged after the nozzle plate 6. This prevents abraded material of the
seal 9 from blocking the atomizing hole 7. A second seal 10 prevents
emergence between the screw 4 and the wall of the tip 3. A filter 11, which
likewise prevents blockage of the atomizing hole 7, is inserted between the
second seal 10 and the screw 4. A conducting tube 15 creates effective
distribution of the coolant 14 in the space 12 around the nozzle tip 3.
