U.S. patent application number 15/954769 was filed with the patent office on 2019-08-22 for external mixing pressurized two-fluid nozzle and a spray drying method.
This patent application is currently assigned to GEA Process Engineering A/S. The applicant listed for this patent is GEA Process Engineering A/S. Invention is credited to Soren FREDSTED, Anders Bo JENSEN, Per Bo SORENSEN.
Application Number | 20190255455 15/954769 |
Document ID | / |
Family ID | 63106014 |
Filed Date | 2019-08-22 |
United States Patent
Application |
20190255455 |
Kind Code |
A9 |
SORENSEN; Per Bo ; et
al. |
August 22, 2019 |
EXTERNAL MIXING PRESSURIZED TWO-FLUID NOZZLE AND A SPRAY DRYING
METHOD
Abstract
Disclosed herein is an external mixing pressurized two-fluid
nozzle for atomising a liquid by means of liquid pressure and gas,
comprising an inner feed liquid pipe (1) extending axially between
an upstream end and a downstream end, having a feed liquid conduit
(2), a feed liquid inlet (3) positioned at the upstream end and a
feed orifice (4) positioned at the downstream end, and a co-axial
first gas pipe (5) extending radially outside the inner feed liquid
pipe (1) and forming a first gas conduit (6) between the first gas
pipe (5) and the inner feed liquid pipe (1), the first gas pipe (5)
having a gas outlet slit (7) positioned at the downstream end. Said
external mixing two-fluid nozzle provides a swirling motion of the
gas, which combined with a pressurized feed liquid enables the
production of spray dried powder at industrially applicable
capacities with low energy consumption and a small particle
size.
Inventors: |
SORENSEN; Per Bo;
(Frederiksberg, DK) ; JENSEN; Anders Bo; (Niva,
DK) ; FREDSTED; Soren; (Stenlose, DK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GEA Process Engineering A/S |
Soborg |
|
DK |
|
|
Assignee: |
GEA Process Engineering A/S
Soborg
DK
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20180229150 A1 |
August 16, 2018 |
|
|
Family ID: |
63106014 |
Appl. No.: |
15/954769 |
Filed: |
April 17, 2018 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13981800 |
Oct 1, 2013 |
9981200 |
|
|
PCT/DK2011/050060 |
Feb 28, 2011 |
|
|
|
15954769 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F26B 3/12 20130101; B22F
9/026 20130101; B05B 7/06 20130101; B22F 9/08 20130101; B01J 2/02
20130101; B05B 7/066 20130101; B05B 7/10 20130101; B22F 2009/088
20130101; B22F 9/082 20130101; B01D 1/18 20130101; B01J 2/04
20130101; B05B 7/062 20130101 |
International
Class: |
B01D 1/18 20060101
B01D001/18; F26B 3/12 20060101 F26B003/12; B05B 7/06 20060101
B05B007/06; B01J 2/04 20060101 B01J002/04; B05B 7/10 20060101
B05B007/10; B01J 2/02 20060101 B01J002/02 |
Claims
1. An external mixing pressurized two-fluid nozzle for atomizing a
liquid, in a spray drying apparatus, using a liquid pressure and an
atomization gas, the external mixing pressurized two-fluid nozzle
comprising: an inner feed liquid pipe extending axially between an
upstream end and a downstream end, the inner feed liquid pipe
comprising: a feed liquid conduit; a feed liquid inlet positioned
at the upstream end; and a feed orifice positioned at the
downstream end; the external mixing pressurized two-fluid nozzle
further comprising: an atomization gas inlet for receiving the
atomization gas, and a co-axial first gas pipe extending radially
outside the inner feed liquid pipe and forming a first gas conduit
between the first gas pipe and the inner feed liquid pipe, wherein
the first gas pipe has a gas outlet slit positioned at the
downstream end, a co-axial second gas pipe extending radially
outside the first gas pipe and forming a second gas conduit between
the second gas pipe and the first gas pipe, the second gas conduit
being adapted to receive atomization gas from the atomization gas
inlet, wherein the first gas conduit is closed at the upstream end
and the second gas conduit is closed at the downstream end, wherein
the first gas conduit and the second gas conduit are connected by
one or more slot(s) adapted for providing a swirling motion of an
atomization gas flow, and wherein the second gas conduit extends
parallel to the feed liquid conduit for the atomization gas in the
second gas conduit to flow parallel to, and in the same direction
as, a feed liquid in the feed liquid conduit.
2. The external mixing pressurized two-fluid nozzle according to
claim 1, wherein the gas outlet slit and the feed orifice are in
essentially a same horizontal position.
3. The external mixing pressurized two-fluid nozzle according to
claim 1, wherein the inner feed liquid pipe, the first gas pipe and
the second gas pipe are concentric and tubular.
4. The external mixing pressurized two-fluid nozzle according to
claim 1, wherein the gas outlet slit is annular.
5. The external mixing pressurized two-fluid nozzle according to
claim 1, wherein the one or more slot(s) connecting the first gas
conduit and the second gas conduit extend tangentially to an outer
surface of the inner feed liquid pipe.
6. The external mixing pressurized two-fluid nozzle according to
claim 1, wherein the one or more slots are directed at either an
upwards angle or a downwards angle relative to a horizontal
plane.
7. The external mixing pressurized two-fluid nozzle according to
claim 1, wherein the inner feed liquid pipe and the first gas pipe
converge radially towards a center at the downstream end.
8. The external mixing pressurized two-fluid nozzle according to
claim 1, wherein wear parts of the inner feed liquid pipe are
comprised of a wear resistant ceramic material.
9. The external mixing pressurized two-fluid nozzle according to
claim 1, wherein at least one of: the second gas pipe outer wall is
adapted for mounting in a lance; and at least one of the inner feed
liquid pipe and the first gas pipe are at least one of exchangeable
and adapted for receiving one or more inserts.
10. A spray drying apparatus comprising: an external mixing
pressurized two-fluid nozzle for atomizing a liquid using a liquid
pressure and an atomization gas, the external mixing pressurized
two-fluid nozzle comprising: an inner feed liquid pipe extending
axially between an upstream end and a downstream end, the inner
feed liquid pipe comprising: a feed liquid conduit; a feed liquid
inlet positioned at the upstream end; and a feed orifice positioned
at the downstream end; the external mixing pressurized two-fluid
nozzle further comprising: an atomization gas inlet for receiving
the atomization gas, and a co-axial first gas pipe extending
radially outside the inner feed liquid pipe and forming a first gas
conduit between the first gas pipe and the inner feed liquid pipe,
wherein the first gas pipe has a gas outlet slit positioned at the
downstream end, a co-axial second gas pipe extending radially
outside the first gas pipe and forming a second gas conduit between
the second gas pipe and the first gas pipe, the second gas conduit
being adapted to receive atomization gas from the atomization gas
inlet, wherein the first gas conduit is closed at the upstream end
and the second gas conduit is closed at the downstream end, wherein
the first gas conduit and the second gas conduit are connected by
one or more slot(s) adapted for providing a swirling motion of an
atomization gas flow, and wherein the second gas conduit extends
parallel to the feed liquid conduit for the atomization gas in the
second gas conduit to flow parallel to, and in the same direction
as, a feed liquid in the feed liquid conduit.
11. The spray drying apparatus according to claim 10, wherein the
gas outlet slit and the feed orifice are in essentially a same
horizontal position.
12. The spray drying apparatus according to claim 10, wherein the
inner feed liquid pipe, the first gas pipe and the second gas pipe
are concentric and tubular.
13. The spray drying apparatus according to claim 10, wherein the
gas outlet slit is annular.
14. The spray drying apparatus according to claim 10, wherein the
one or more slot(s) connecting the first gas conduit and the second
gas conduit extend tangentially to an outer surface of the inner
feed liquid pipe.
15. The spray drying apparatus according to claim 10, wherein the
one or more slots are directed at either an upwards angle or a
downwards angle relative to a horizontal plane.
16. The spray drying apparatus according to claim 10, wherein the
inner feed liquid pipe and the first gas pipe converge radially
towards a center at the downstream end.
17. The spray drying apparatus according to claim 10, wherein wear
parts of the inner feed liquid pipe are comprised of a wear
resistant ceramic material.
18. The spray drying apparatus according to claim 10, wherein at
least one of: the second gas pipe outer wall is adapted for
mounting in a lance; and at least one of the inner feed liquid pipe
and the first gas pipe are at least one of exchangeable and adapted
for receiving one or more inserts.
19. A spray drying apparatus comprising: an external mixing
pressurized two-fluid nozzle for atomizing a liquid using a liquid
pressure and an atomization gas, the external mixing pressurized
two-fluid nozzle comprising: an inner feed liquid pipe extending
axially between an upstream end and a downstream end, the inner
feed liquid pipe comprising: a feed liquid conduit; a feed liquid
inlet positioned at the upstream end; and a feed orifice positioned
at the downstream end; the external mixing pressurized two-fluid
nozzle further comprising: an atomization gas inlet for receiving
the atomization gas, and a co-axial first gas pipe extending
radially outside the inner feed liquid pipe and forming a first gas
conduit between the first gas pipe and the inner feed liquid pipe,
wherein the first gas pipe has a gas outlet slit positioned at the
downstream end, a co-axial second gas pipe extending radially
outside the first gas pipe and forming a second gas conduit between
the second gas pipe and the first gas pipe, the second gas conduit
being adapted to receive atomization gas from the atomization gas
inlet, wherein the first gas conduit is closed at the upstream end
and the second gas conduit is closed at the downstream end, wherein
the first gas conduit and the second gas conduit are connected by
one or more slot(s) adapted for providing a swirling motion of an
atomization gas flow, and wherein the second gas conduit extends
parallel to the feed liquid conduit for the atomization gas in the
second gas conduit to flow parallel to, and in the same direction
as, a feed liquid in the feed liquid conduit, said spray drying
apparatus further comprising a drying chamber for receiving the
feed liquid and the atomization gas from the nozzle and having a
drying gas inlet for receiving a drying gas, and a first exit for
discharging spent gas, comprising spent drying gas and spent
atomization gas, and a second exit for discharging produced
powder.
20. The spray drying apparatus according to claim 19, wherein the
gas outlet slit and the feed orifice are in essentially a same
horizontal position.
21. The spray drying apparatus according to claim 19, wherein the
inner feed liquid pipe, the first gas pipe and the second gas pipe
are concentric and tubular.
22. The spray drying apparatus according to claim 19, wherein the
gas outlet slit is annular.
23. The spray drying apparatus according to claim 19, wherein the
one or more slot(s) connecting the first gas conduit and the second
gas conduit extend tangentially to an outer surface of the inner
feed liquid pipe.
24. The spray drying apparatus according to claim 19, wherein the
one or more slots are directed at either an upwards angle or a
downwards angle relative to a horizontal plane.
25. The spray drying apparatus according to claim 19, wherein the
inner feed liquid pipe and the first gas pipe converge radially
towards a center at the downstream end.
26. The spray drying apparatus according to claim 19, wherein wear
parts of the inner feed liquid pipe are comprised of a wear
resistant ceramic material.
27. The spray drying apparatus according to claim 19, wherein at
least one of: the second gas pipe outer wall is adapted for
mounting in a lance; and at least one of the inner feed liquid pipe
and the first gas pipe are at least one of exchangeable and adapted
for receiving one or more inserts.
Description
[0001] This application is a divisional of U.S. application Ser.
No. 13/981,800 filed Oct. 1, 2013, which is a National Stage of
International Application No. PCT/DK2011/050060 filed Feb. 28,
2012, the contents of all of which are incorporated herein by
reference in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to an external mixing
pressurized two-fluid nozzle for atomising a liquid by means of a
liquid pressure and a gas, comprising an inner feed liquid pipe
extending axially between an upstream end and a downstream end,
having a feed liquid conduit, a feed liquid inlet positioned at the
upstream end and a feed orifice positioned at the downstream end,
and a co-axial first gas pipe extending radially outside the inner
feed liquid pipe and forming a first gas conduit between the first
gas pipe and the inner feed liquid pipe, the first gas pipe having
a gas outlet slit positioned at the downstream end. The invention
furthermore relates to a spray processing method for producing a
spray dried powder by use of an external mixing pressurized
two-fluid nozzle for producing droplets of a liquid by means of a
liquid pressure and a gas. In addition, the invention relates to
the use of said external mixing two-fluid nozzle for producing a
spray dried powder.
BACKGROUND OF THE INVENTION
[0003] Spray drying is a drying process, which involves both
particle formation and drying. It involves atomisation of a feed,
typically a liquid concentrate, into a spray and contact between
the spray and a drying medium. The formation of the spray
(atomisation) and the contacting of the spray with the drying
medium may be achieved by use of a nozzle.
[0004] Pneumatic nozzle atomisation involves impacting a liquid
feed with a high velocity gas. The high velocity gas creates high
frictional forces and disintegrates the liquid feed into spray
droplets. The feed liquid is believed to break-up in two stages.
The first phase involves the tearing of the liquid feed into
filaments and large droplets. The second phase completes the
atomisation by breaking these liquid forms into smaller and smaller
droplets. The entire process is influenced by the magnitude of the
surface tension, density, pressure and viscosity of the liquid feed
as well as the velocity and density of the gaseous flow.
[0005] Various design techniques are available to produce the
required conditions of liquid-gas contact for atomisation. As
disclosed in the book "Spray drying" by Keith Masters, 1991
edition, page 251, the designs may be divided into 4 categories:
[0006] (1) Internal mixing in which liquid feed and atomising gas
are contacted within the nozzle head. [0007] (2) External mixing,
in which liquid feed and atomising gas are contacting outside the
nozzle head. [0008] (3) Combined internal and external mixing by
using two atomising gas flows within the nozzle head (three-fluid
nozzle). [0009] (4) Pneumatic cup atomising, in which feed liquid
and atomising gas is contacted at the rim of a rotating nozzle
head.
[0010] The different design techniques provide different properties
and result in different outcome of the final atomised product. In
the first 2 categories the feed liquid and atomising gas are passed
separately to the nozzle. Such nozzles, which are usually denoted
two-fluid nozzles (TFN), are i.a. used for atomisation of a liquid
in spray drying plants and in fluid bed agglomeration. The liquids
can be in the form of solutions, dispersion or pure substances. In
particular, two-fluid nozzles are used when atomising a fluid,
where fine droplets is the objective or where additional
atomisation energy in the form of atomising gas is required to
break up a fluid into droplets. Nozzle designs of the third and
fourth category are not the subject of the present application.
[0011] Internal mixing TFN has the advantage, compared to external
mixing TFN, that it is mixing gas and liquid before the two fluids
enter the surrounding atmosphere of the drying chamber. However,
nozzles providing internal mixing are not as well suited for
handling abrasive feeds as the internal mixing introduces
additional wearing of the equipment. Conventional two-fluid nozzles
with internal gas/liquid mixing also introduce the risk of drying
out and thereby clogging the mixing chamber.
[0012] Internal mixing nozzles give the possibility of an efficient
liquid-gas reaction, but are limited in capacity by internal
channelling and channel dimensions. Internal parts in the nozzle,
intended for improving the gas-liquid mixing, also disturb the
flow, causing the span of the droplet size distribution to rise.
Internal parts in general complicate handling, cleaning and causes
wear. Furthermore viscous liquid feeds may be difficult to
process.
[0013] Examples of nozzles of the internal mixing type are well
known in the art. U.S. Pat. No. 7,694,944 (GEA Niro) discloses a
nozzle in which the gas is supplied in the axial direction of the
nozzle. The nozzle comprises a mixing chamber, one or more liquid
inlets and at least one tangential gas inlet to the mixing chamber.
In a commercially available internal mixing nozzle the atomising
gas is supplied tangentially in a separate pipe, which contributes
to the radial dimensions of the nozzle. Furthermore, the mixing
chamber of this prior nozzle comprises edges and obstructions
resulting from structural conditions. International published
application WO 00/58014 discloses a sprayer in the form of a nozzle
having a tangential gas inlet to the mixing chamber and lateral
liquid inlets. This nozzle suffers from insufficient mixing due to
the geometry of the nozzle.
[0014] Criterions for evaluating the performance of a two-fluid
nozzle are: the mean droplet size, the span of the droplet size
distribution and not least the specific gas consumption, meaning
the amount of gas used to atomise a given amount of liquid, also
called the gas-to-feed ratio. In addition to the criterions focused
on the product quality, the production capacity of the two-fluid
nozzle is also of high importance--especially from a commercial
point of view. Furthermore, increasing focus on clean technologies
as well as increasing energy prices put forward additional
requirements with respect to energy consumption when operating and
producing by spray processes.
[0015] The contact and mixing of gas and liquid is where external
mixing TFN meet their restrictions. External mixing TFN, where the
gas mixes with the liquid after leaving the nozzle typically
through a ring-shaped aperture, meets the limitation when the gap
in the gas exit becomes so large that a larger part of the gas is
lost into the surrounding atmosphere of the drying chamber, instead
of reacting with the liquid. With external mixing TFN, the free
expansion of the gas has the disadvantage of being partly lost to
the surrounding instead of adding energy to break up the liquid. In
the prior art this problem has been attended.
[0016] Another type of nozzles utilizes pressurization of the
liquid, meaning that the feed concentrate is fed under pressure to
the nozzle. Pressure energy is converted to kinetic energy, and
feed issued from the nozzle orifice as a high speed film that
readily disintegrates into a spray as the film is unstable. Sprays
from pressure nozzles handling high feed rates are generally less
homogeneous and coarser.
[0017] EP 408 801 B1 suggests a low pressurized liquid, internal
mixing two-fluid nozzle which can function satisfactory even when
low pressure is applied during a period of start-up as small
droplets are produced. The spray nozzle unit is provided with a gas
slit between the pressure nozzle and the air nozzle to give a part
of the discharging air stream a swirling motion.
[0018] The present invention is directed to a high pressurized
liquid external mixing two-fluid nozzle that efficiently uses the
atomizing gas. It is well known within the art that the
disadvantages of pneumatic nozzles concern the high cost of
compressed air and low nozzle efficiency. Furthermore, a drawback
with several of the pre-existing, conventional two-fluid spray
nozzle units is the limited capacity when very fine droplets are
required. The object of the present invention is to provide for an
external mixing pressurized two-fluid nozzle, which is energy
efficient, provides high capacity while still producing fine
droplets.
SUMMARY OF THE INVENTION
[0019] The present invention relates to an external mixing
pressurized two-fluid nozzle for atomising a liquid by means of a
liquid pressure and a gas, comprising an inner feed liquid pipe
extending axially between an upstream end and a downstream end,
having a feed liquid conduit, a feed liquid inlet positioned at the
upstream end and a feed orifice positioned at the downstream end,
and a co-axial first gas pipe extending radially outside the inner
feed liquid pipe and forming a first gas conduit between the first
gas pipe and the inner feed liquid pipe, the first gas pipe having
a gas outlet slit positioned at the downstream end. The nozzle
further comprises a co-axial second gas pipe extending radially
outside the first gas pipe and forming a second gas conduit between
the second gas pipe and the first gas pipe, the first gas conduit
being closed at the upstream end and the second gas conduit being
closed at the downstream end, wherein the first gas conduit and the
second gas conduit are connected by one or more slot(s) being
adapted for providing a swirling motion of a gas flow.
[0020] Spray drying procedures with the external mixing two-fluid
nozzle according to the above-mentioned design has proven to
provide a high production capacity while still retaining a mean
particle size and a span wanted for. In prior art nozzles for
external mixing the production of fine particles in spray drying
applications limit the capacity as the increased liquid flow
requires the gap in the gas exit to become larger or, alternatively
the pressure to be increased. The effect is that a larger part of
the gas is lost into the surrounding atmosphere, instead of
reacting with the liquid. However, with the external mixing
two-fluid nozzle according to the invention the gas flow pattern at
the outlet slit is designed to require a reduced gas flow, thus
ensuring increased reaction with the liquid when the feed liquid is
supplied with a substantial pressure.
[0021] According to the present invention, the liquid is
pre-atomized by an elevated liquid pressure to form a thin film,
which is subsequently atomized into fine droplets by means of the
pressurised gas. In prior art nozzles having a normal liquid
pressure this pre-atomization does not form to the same extent.
Typically, the formation of the droplets in prior art nozzles is
mostly due to the high velocity of the gas, which at high
capacities is subject to limitations as presented in the background
section i.a. incomplete atomisation leading to larger particle
sizes and broader distribution.
[0022] Surprisingly, the external mixing two-fluid nozzle of the
present invention forms powders with a small span. The span
expresses how wide the particle size distribution is. Aiming at a
specific particle size, a narrow distribution is desired. A wide
distribution of the droplet size is generally disadvantageous. The
span, evaluated as (d90-d10)/d50 is normally found in the range
from 1 to 2 for the nozzle of the invention.
[0023] Within the two gas conduits of the nozzle, the swirl motion
is generated by directing the gas flow through one or more slots
connecting the two gas conduits. The design and effectiveness of
the atomisation mechanisms provided by the pressurized two-fluid
nozzle according to the invention enables high-viscous liquid to be
atomised at industrial applicable feed rates. In addition, the
formation of a pre-atomisation of the liquid combined with the full
swirl motion of the gas enables the atomisation of the liquid feed
at low gas flow rates.
[0024] It is a further advantage of the nozzle according to the
invention that the high shear atomization takes place outside the
nozzle itself as the nozzle will be well suited for handling
abrasive feed liquids, and the risk of drying out and thereby
clogging of the nozzle is avoided due to the external contact
between gas and liquid.
[0025] In a preferred aspect of the invention, the gas outlet slit
and the feed orifice essentially are in the same horizontal
position. The effect of this feature is that an external mixing is
ensured, i.e. that the feed liquid and the atomization gas are
mixed outside the sensitive components of the nozzle. The inner
feed liquid pipe may be retracted or protruded relative to the tip
of the first gas pipe to an inessential degree, such as +/-5
mm.
[0026] Usually, the inner feed liquid pipe, the first gas pipe and
the second gas pipe are concentric and tubular. The concentric and
tubular design provides for a uniform treatment of the atomization
gas so that the flow pattern along the gas outlet slit is uniform.
Furthermore, in preferred embodiments, the gas outlet slit is
annular for a uniform gas dispersion to form, which provides for
the formation of a cloud of droplets within a restricted volume of
the drying chamber.
[0027] According to an aspect of the invention, the one or more
slot(s) connecting the first gas conduit and the second gas conduit
extend tangentially to the outer surface of the inner feed liquid
pipe. This feature adapts the one or more slots for providing a
swirling motion of the gas once it flows from the second gas
conduit through the one or more slots and into the first gas
conduit. In the event the nozzle holds more than one slot it is
important that the slots extend tangentially to the inner feed
liquid pipe in the same direction, meaning that all slots should
provide for the gas to flow in the same clockwise or
counter-clockwise direction around the inner feed liquid pipe,
thereby enhancing the swirling motion of the gas.
[0028] The two-fluid nozzle according to the invention provides for
the entire gas stream to flow through the one or more slots adapted
for providing a swirling motion. The inventors found that compared
to only providing for part of the gas to flow through means for
providing a swirling motion as suggested in EP 408 801 the design
of the present invention imparts an increased swirling motion. This
in turn results in a lowered overall gas flow of the nozzle.
However, due to the pre-atomising of the liquid by means of
pressurising the liquid feed, the required amount of atomisation
gas is at a lower level. The swirling motion of the gas, however,
provides for an improved atomisation of the liquid by imparting the
swirling/rotating motion to the liquid.
[0029] The one or more slots may be directed at an upwards or
downwards angle relative to the horizontal plane, such as
+/-5.degree. or more. The individual slots may be placed at
different horizontal levels along the first gas pipe.
[0030] By providing a converging portion at the downstream end of
the nozzle it may improve both the mean droplet size distribution
and the span of the droplet size distribution. The converging may
be at an angle of 5.degree. to 80.degree. or more preferable of
10.degree. to 45.degree. relative to the vertical plane.
[0031] The two-fluid nozzle of the invention may be prepared in any
suitable material. For highly abrasive feed liquids, however, it
may be advantageous that at least the inner feed liquid pipe wear
parts are of a wear resistant material, such as a ceramic
material.
[0032] To adapt the nozzle of the invention to various process
conditions and feed liquids, the inner feed liquid pipe and/or the
first gas pipe may be exchangeable and/or adapted for receiving one
or more inserts, and/or the second gas pipe outer wall is adapted
for mounting in a lance. The design could be a nozzle lance with
concentric pipes and a nozzle head as described herein mounted in
the downstream end. Such nozzle head or parts hereof may be
exchangeable to adapt to a relevant feed capacity.
[0033] The invention also relates to a spray processing method for
producing a spray dried powder. The method includes the steps of:
providing a spray drying apparatus comprising an external mixing
two-fluid nozzle having inlets for feed liquid and atomization gas,
a drying chamber having a drying gas inlet and exits for spent
drying gas/atomising gas and produced powder, spraying in the
drying chamber the feed liquid through the external mixing
two-fluid nozzle by means of liquid pressure and the atomisation
gas into droplets, drying the droplets to a powder, discharging the
powder trough the exit for produced powder and the spent gas
through the exit for spent gas, wherein the atomisation gas is
supplied to the nozzle with a pressure in the range of 0.2 to 10
bar(g), the entire amount of atomisation gas in the nozzle is
provided with a swirling motion, the feed liquid is supplied to the
nozzle with a pressure at or above 8 bar(g), and the weight ratio
of atomisation gas flow to feed liquid flow is in the range of 0.1
to 10.
[0034] The inventors surprisingly found that providing a
pressurised liquid feed to a two-fluid nozzle providing the
atomizing gas with a swirling motion, results in a reduction in the
required gas pressure even for the production of powders with a
mean particle size below 50 .mu.m. In comparison to conventional
two-fluid nozzles, the external mixing two-fluid nozzle according
to the present invention has lower energy consumption. This is
presently believed to be because energy input for atomization
provided by elevated liquid pressure is utilized more efficiently
compared to energy input provided by elevated air pressure.
Conventional two-fluid nozzles apply pressurized gas for
atomization, whereas the external mixing two-fluid nozzle according
to the present invention applies a combination of pressurized
liquid and pressurized gas. Furthermore, the use of conventional
two-fluid nozzles with external mixing will have a limited capacity
when very fine droplets are required, whereas the two-fluid nozzle
according to the present invention will have an increased liquid
capacity, in some embodiments up to e.g. 500 kg/h.
[0035] The swirling motion may be provided by a number of means,
including inclining slats in the passageway of the atomising gas in
the nozzle, meandering gas channels formed in the nozzle, etc.
According to a preferred aspect of the invention the swirling
motion is provided by one or more slots, which connects a second
gas conduit and a first gas conduit, said second conduit being
connected to a gas supply and formed between a first gas pipe and a
second gas pipe extending radially outside the first gas pipe and
said first gas conduit being formed between an inner feed liquid
pipe and the first gas pipe, said second gas conduit being closed
at the downstream end, said first gas conduit being closed at the
upstream end and connected to a gas outlet slit in the downstream
end. In a certain embodiment, the external mixing two-fluid nozzle
used in the above method is a nozzle as disclosed in the attached
claims.
[0036] The slots in the nozzle are designed to give the atomization
gas the required swirl without imposing the gas flow to unnecessary
friction. In a certain embodiment, the one or more slot(s)
connecting the first gas conduit and the second gas conduit extend
tangentially to the outer surface of the inner feed liquid pipe.
Due to the fact that the entire amount of gas is guided through the
one or more slots a complete swirling motion of the gas is
obtained. The swirling motion of the gas provides for an improved
atomisation of the liquid by imparting the swirling/rotating motion
to the liquid.
[0037] The feed liquid is provided with a certain pressure before
ejection into the drying chamber. The pressure is usually not less
than 5 bar(g) if the benefits of the invention is to be obtained.
In a preferred aspect the liquid is supplied to the nozzle with a
pressure of 10-150 bar(g). In general, a highly viscous feed liquid
requires a higher feed liquid pressure than a less viscous feed
liquid.
[0038] The atomisation gas is supplied to the nozzle with a
pressure of at least 0.2 bar(g). The pressure is generally not
above 10 bar(g) due to process economics. In a preferred aspect the
atomising gas is supplied with a pressure of 0.5-5 bar(g) and more
preferred with 1-2 bar(g).
[0039] To obtain a sufficient swirl of the atomisation gas it is
ejected from the nozzle at a rotational speed of 30 m/s or more.
Suitably, the rotational speed does not exceed 500 m/s. In a
preferred embodiment the atomising gas is ejected from the nozzle
at a rotational speed in the range of 50 m/s to 400 m/s, typically
100-200 m/s.
[0040] The advantage of the present invention is that the combined
pressuring of atomization gas and feed liquid is less energy
consuming than predominate pressurizing of the atomization gas.
According to the invention, the weight ratio of atomizing gas flow
to feed liquid flow is in the range of 0.1 to 10, suitably the
weight ratio of atomisation gas flow to feed liquid flow is from
0.5 to 5 and more suitable from 1-3.
[0041] The method of the present invention can produce droplets in
various sizes and distributions. The invention shows most of its
benefits when small droplets are produced. Therefore, in a
preferred aspect the mean size of the droplets is less than 30
.mu.m.
[0042] The present invention has the important feature of being
able to produce particles of a small size combined with a high
liquid flow capacity. In a certain embodiment of the invention, the
liquid flow capacity of the external mixing two-fluid nozzle is 100
kg/h or above.
[0043] According to an aspect of the invention, two or more
external mixing pressurized two-fluid nozzles are provided in the
spray drying apparatus. As the feed liquid flow through the nozzle
is controlled at an elevated liquid pressure it will be possible to
distribute liquid between multiple nozzles in an easy manner.
[0044] The powder produced by the method of the invention may be of
various materials. Usually, the spray dried powder is selected from
the group consisting of powders for use in lithium ion batteries or
other secondary batteries, polymer powders, starch or gelatine
powders, coffee powder, powders from abrasive feeds, inorganic
powders, hard metal powders, pharmaceutical powders and congealed
powders.
[0045] The method of the present invention is found to be suited
for viscous liquids as enabling the processing of a feed with a
higher dry matter content compared to processes using conventional
nozzles. The method, furthermore, holds the advantages of external
mixing, thus, making the spray processing method particularly
suitable for spray drying products from abrasive feeds.
[0046] The atomisation gas may be air, nitrogen, carbon dioxide, or
any other suitable gas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] FIG. 1 is a cross-sectional view along the axis of the
external mixing two-fluid nozzle in an embodiment of the present
invention, and
[0048] FIG. 2 is a radial cross-sectional view of the external
mixing two-fluid nozzle in an embodiment of the invention, in an
axial position where both gas conduits and connecting slots are
present.
[0049] FIG. 3 is a schematic view of a spray drying apparatus
according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0050] In the following an embodiment of the present invention will
be described in details with reference to FIG. 1 and FIG. 2.
[0051] The external mixing two-fluid nozzle (17) is provided with
an inner feed liquid pipe (1) extending axially between an upstream
end and a downstream end of the nozzle. The inner feed liquid pipe
(1) forms a channel, which provide for a feed liquid conduit (2).
At the upstream end of the inner feed liquid pipe is a feed liquid
inlet (3) through which the feed liquid can enter into the feed
liquid conduit (2). At the downstream end of the inner feed liquid
pipe (1) is a feed orifice (4) through which the liquid feed can
exit the liquid feed conduit (2). Surrounding the inner feed liquid
pipe (1) is a first gas pipe (5). The first gas pipe (5) extends
co-axially with the inner feed liquid pipe (1) on the outside. The
radius of the first gas pipe (5) is larger than the radius of the
inner feed liquid pipe (1), and the first gas pipe (5) provides a
pipe wall, which is spaced from the wall of the inner feed liquid
pipe (1), thus providing a first gas conduit (6) between the inner
feed liquid pipe (1) and the first gas pipe (5). The first gas pipe
is provided with a gas outlet slit (7) at the downstream end of the
nozzle. The first gas conduit does not extend all the way through
the nozzle but is closed at the upstream end of the nozzle.
Surrounding the first gas pipe (5) is a second gas pipe (8), which
extends radially outside the first gas pipe (5). Thereby, the
radius of the second gas pipe (8) is larger than the radius of the
first gas pipe (5). The walls of the first and second gas pipes are
spaced, thus providing a second gas conduit (9) between the pipe
walls of the first and second gas pipe. The second gas conduit (9)
is open at the upstream end of the nozzle but closed at the
downstream end. The nozzle features one or more slots (10) provided
in the first gas pipe (5). The one or more slots (10) go through
the wall of the first gas pipe (5) thereby connecting the first and
second gas conduits. The one or more slots (10) are adapted for
providing a swirling motion of the gas flow.
[0052] During operation of the external mixing two-fluid nozzle a
liquid feed stream typically enters the nozzle at the feed liquid
inlet (3) and flows axially through the nozzle via the feed liquid
conduit (2). Thus, the feed liquid flows downstream through the
nozzle. The feed liquid stream exits the nozzle at the feed orifice
(4). An atomisation gas initially flows parallel to the feed liquid
stream and in the same downstream direction. The atomisation gas
enters the nozzle at the upstream end into the second gas conduit
(9) of the second gas pipe (8), which is open at the upstream end.
From the second gas conduit (9) the atomisation gas flows into the
first gas conduit (6) of the first gas pipe (5) through the the
four slots (10). As the atomisation gas flows through the one or
more slots (10) it obtains a swirling motion. Maintaining the
swirling motion the atomisation gas flows through the first gas
conduit (6) and exits through the gas outlet slit (7).
[0053] In the present description subsequent claims the term bar(g)
refers to the pressure in bars above ambient or atmospheric
pressure. When the present description and claims refers to spray
processing or spray drying, a variety of different spray methods
and processing methods is comprised in the term, including spray
drying, spray congealing and spray granulation. It will be
understood by a person skilled in the art that when spray
congealing is performed, the drying gas is substituted with a
cooling gas.
[0054] The powders for use in lithium-ion batteries produced by the
present invention may be any of the various lithium ion salt used
for rechargeable batteries. By way of examples only, the powders
produced by the method of the present invention may be of the
following materials: lithium cobalt oxide, lithium iron phosphate
or another polyanion, LiNiO.sub.2 or lithium manganese oxide or
another spinel. Also other secondary battery powders than powders
for use in lithium-ion batteries may be produced by this method.
The powder material may also be a mixture of salts, such as
LiCo.sub.1/3Ni.sub.1/3Mn.sub.1/3O.sub.2. The powders may optionally
be doped with aluminium, niobium or zirconium.
[0055] A spray drying apparatus for implementing the present
invention includes the above external mixing pressurized two-fluid
nozzle (17) having an inlet (11) for receiving a feed liquid and an
inlet (12) for receiving atomization gas, a drying chamber (13) for
receiving the feed liquid and the atomization gas from the nozzle
(17) and having a drying gas inlet (14) for receiving a drying gas,
and an exits (15), (16) for discharging spent gas, comprising spent
drying gas and spent atomizing gas and produced powder,
respectively.
EXAMPLES
Example 1
[0056] Spray Drying of Lithium Ion Battery Powder
[0057] A lithium ion battery powder was spray dried in a GEA Niro
SD 6.3 pilot spray dryer using a conventional two-fluid nozzle with
external mixing and the GEA Niro COMBI-NOZZLE.TM. according to the
present invention with the following results:
TABLE-US-00001 TABLE 1 Conventional two-fluid GEA Niro nozzle
COMBI-NOZZLE .TM. Liquid feed rate kg/h 15 13 Air consumption kg/h
30 22 Air pressure bar(g) 3 2 Feed pressure bar(g) 0.5 11 Air to
liquid ratio kg/kg 1.8 1.7 Average particle size .mu.m 14 7 Span of
particle size n 2.1 1.8
Example 2
[0058] Spray Drying of e-PVC Latex
[0059] e-PVC latex is often spray dried to make fine powder
particles and usually a large number of conventional two-fluid
nozzles are required for this purpose as the maximum capacity of
these nozzles are around 50-65 kg/h in order to make the required
average particle size of around 20 micron. By application of the
nozzle according to the invention it is possible to achieve a
smaller average particle size with a significantly lower
consumption of compressed air. Furthermore the liquid feed capacity
of one COMBI-NOZZLE.TM. can be 200 kg/h, 500 kg/h, or higher.
TABLE-US-00002 TABLE 2 Nozzle type Conventional two-fluid GEA Niro
nozzle COMBI-NOZZLE .TM. Air to feed kg/kg 1 1.25 1.5 1 1.25 1.5
ratio Average .mu.m 38 33 28 33 23 17 particle size
Example 3
[0060] Atomization of High Viscosity Melts
[0061] A highly viscous melt of a polymer has been spray congealed
using the COMBI-NOZZLE.TM. at the below conditions. By conventional
atomization technique the melt could not be satisfactorily
congealed due to formation of filaments caused by poor droplet
formation.
TABLE-US-00003 TABLE 3 Melt feed rate kg/h 95 Liquid pressure
bar(g) 100 Air to liquid ratio kg/kg 1.4 Average particle size
.mu.m 21
Example 4
[0062] Control of Span of Droplet Size
[0063] The span of the droplet size distribution from the
COMBI-NOZZLE.TM. has been examined by spraying of water and the
span has been influenced by varying the theoretical spray angle of
the liquid injection nozzle. The following results have been
achieved using Malvern droplet size measurement apparatus:
TABLE-US-00004 TABLE 4 Theoretical spray angle degree 50 65 80 Mean
droplet size .mu.m 18 15 13 Span of droplet size n 0.95 1.1 1.2
* * * * *