Note: Descriptions are shown in the official language in which they were submitted.
~ ~ Q ~ ~ 7 ~
This invention relates to a process for producing a
spray-dried agglomerated product. Typical of the products which
may be produced by the process of the instant invention include
dry soluble coffee powders, bulked dextrins and the like.
Spray drying and agglomerating are well-known unit
processes that have been employed in the food processing
industry for some time. Generally, however, spray drying and
agglomerating are separate processes which are carried out in
stepwise fashion on coffee extracts, liquid milks and the like.
It is apparent that such separate stepwise processes leave much
to be desired in terms of plant economies, utilization of equip-
ment and throughput times. It would be desirous-j therefore, if
a combined spray drying and agglomerating process were able to
be devised so as to increase the production capabilities of a
food processing plant and at the same time to reduce the amount
of equipment and throughput times that might otherwise be re-
quired, The concept of a combined spray-drying/agglomerating
process has heretofore been described in several U. S. patents,
namely, U.S. Patent No. 3,514,300 to Mishkin et al. and U. S.
Patent No. 3,151,984 to Peebles et al. In the Mishkin et al.
process, recycled fines are employed in the production of an
àgglomerated soluble coffee powder, In the process described by
Peebles et al., milk concentrate with added lactose crystals is
introduced into a spray dryer and with proper control of drying
conditions is discharged as an aggregated material having a
moisture content of 10 to 20%, A second drying operation is
then employed in the Peebles et al, process to further reduce the
moisture content. In both the Mishkin et al, and Peebles et al.
processes, however, it appears that two separate drying steps are
- 2 - ~
~65t~
required: in Mishkin et al. a drying operation for the
production of coffee fines is necessary while in Peebles et al.
not only are lactose crys-tals an essential component for intro-
duction into the spray dryer but, as mentioned, to obtain the
final milk powder product a second drying operation is required
to reduce the moisture content of the aggregated material to the
final moisture content of the milk powder.
The concept of foaming coffee extracts and other ex-
tracts and suspensions of food products to control final product
color, density and particle size has also been described hereto-
fore. Thus, U.S. Patent No. 2,788,276 to Reich et al. teaches a
process for spray-drying a foamed material such as coffee. How-
ever, the objective referred to in the patent is that of produc-
ing a product with discrete spherical structures which are not
clumped, aggregated or otherwise agglomerated.
We have now discovered that a final spray-dried pro-
duct having the appearance of an agglomerated product may be
produced by employing a two-fluid nozzle for mixing an inert gas
with an extract, solution or suspension of a food product and
varying the differential pressures of the extract, solution or
suspension whereby droplets are subsequently fused together in
an oscillating pattern within a region of spray turbulence in a
conventional spray dryer. We have found that coffee extract as
well as dextrin solutions and other extracts, solutions or sus-
pensions of various food products can be spray dried and
agglomerated simultaneously in one processing step. The process
is capable of producing agglomerated products having unique
physical appearance as well as a range of colour attributes which
may be desired.
~;S~
The process has the advantage that it eliminates the
necessity of incorporating standard agglomerating equipment such
as agglomerating towers in a soluble coffee processing unit.
Moreover, the process allows for an increase in the capacity of
- a soluble coffee processing unit by permitting the conversion of
an existing agglomerating tower into a spray agglomeration
tower.
The process of the present invention comprises inject-
ing an inert gas such as nitrogen, carbon dioxide or the like
into an extract, solution or suspension of a food material
typically coffee extract or a dextrin solution utili~ing a
two-fluid nozzle and the subsequent atomization and partial
degasification of the extract, solution or suspension utilizing
a conventional spray nozzle accompanied by a spray pattern
oscillation due to unequal extract, solution or suspension and
gas pressures so as to produce a spray dried/agglomerated
product.
The invention will be better understood by reference
to the following detailed description, examples and the accom-
panying drawings.
In the drawings, Figure 1 is a flow diagram of thespray drying agglomeration process of the present invention as
specifically related to the processing of a coffee extract.
Figures 2 to 5 are photomicrographs of soluble coffee
powder spray agglomerates produced in accordance with the pro-
cess of the present invention and conventional soluble coffee
products which have been spray dried and also agglomerated.
Figures 2 and 3 illustrate spray agglomerates produced in
accordance with the process of the present invention. Figure 4
illustrates a spray dried soluble coffee powder produced by a
conventional commercial process. Figure 5 shows an agglomerated
soluble coffee product prepared on conventional commercial
equipment utilizing the spray dried soluble coffee powder
illustrated in Figure 4.
The total magnification is 61~ for the photomicro-
graphs shown as Figures 2 to 5. The relative particle size and
shape of the product shown in Figure 2 may be contrasted with
that shown in Figure 4 and the relative particle siæe and shape
of the product shown in Figure 3 may be contrasted with that
shown in Figure 5. Further, the unique physical form of
products obtainable by the process of this invention may be
noted from Figures 2 and 3.
Figures 6, 7 and 8 are photomicrographs of several
dextrin products including a spray agglomerated product prepared
in accordance with the process of this invention. Figure 6
illustrates a commercially available bulked dextrin product.
Figure 7 illustrates a spray dried agglomerated dextrin product
prepared in accordance with the process of this invention and
Figure 8 illustrates a drum dried dextrin product. The magnifi-
cation in these photomicrographs is lOOX.
Referring to Figure l, coffee extract from a percola-
tor set and evaporated to 25-35% concentration is fed by means
of a high pressure air piston pump (supply on demand) to the
liquid intake of a two-fluid nozzle where an inert gas such as
nitrogen is intimately mixed with the coffee extract to produce
a foamed extract. The motive force from the air piston pump is
used to move the foamed extract to a conventional high pressure
core type nozzle in the spray dryer. Check valves are position-
-- 5 --
ed both between the air piston pump and the two-fluid nozzle and
between the inert gas supply and the two-fluid nozzle. The
extract and gas pressures at the two-fluid nozzle are balanced
such that when the piston pump provides the maximum extract
pressure to the two-fluid nozzle, the extract pressure is greater
than the air pressure and similarly when the pump pressure is at
its low point, the gas pressure is equal to or greater than the
liquid extract pressure to the two-fluid nozzle. This variation
in gas and liquid pressures results in an oscillation of the
nozzle pattern in the spray dryer as well as a variation in the
amount of gas mixed with the extract. This pulsating, although
at pressures above the minimum atomizing pressures, replicates
the partial agglomeration which is associated with operating
pressure spray nozzles at the minimum atomizing pressures where-
by a small drop in nozzle pressure would result in no atomiza-
tion to occur. The frequency of nozzle spray pattern pulsation
can be controlled by the relative sizing of the feed pump and
spray nozzle within the spray dryer. Spray particle collision
and subsequent fusion can be ensured by more frequent oscilla-
tion of the spray pattern. The pump pressure and consequentlythe extract pressure may vary substantially with a minimum
pressure variation of 10 to 15 psig required. Although the
most efficient agglomeration occurs when the gas and extract
pressures are almost equal, some agglomeration will occur at
lower gas to extract pressures, the degree of agglomeration
being reduced with the lower gas to extract pressures. The
agglomeration will occur at both low and high spray nozzle
pressures as the critical parameter is the extract to gas ratios
expressed in terms of liquid and gas pressures to the two-fluid
65~YO
nozæle. Thus the operating range for spray dryer nozzle
pressures is determined by desired feed rate to the spray dryer.
This agglomeration process may be applied to other food products
in addition to coffee extract such as dextrins. If desired, the
spray dried product may be after dried to obtain products with
lower moisture contents.
The following are detailed illustrative but nonlimit-
ing examples of this process:
EXAMPLE 1
Coffee extract at 35% concentration and 98F. is
passed by means of a Graco air piston pump through a Spraying
Systems two-fluid pneumatic mixing nozzle (Type 40100/1253283.
The extract and nitrogen gas pressures at the mixing nozzle were
100 psig and 98 psig respectively. A Spraying Systems
(Whirljet Type 1-1) nozzle was utilized in the spray dryer
whereby an average foamed extract pressure of 95 psig was
maintained on this nozzle. The spray dryer inlet and outlet
temperatures were 430F. and 268F. respectively. The product
produced had a mean particle size of 834 microns (contrasted
with the particle size for a control of 283 microns), a bulk
density of 13.8 gms/100 cc. and a final product moisture of
1.1%. No change in final product flavours is apparently detect-
able.
EXAMPLE 2
Coffee extract at 40% concentration and 70F. is passed
by means of a Graco* air piston pump through a Spraying Systems^
two-fluid pneumatic mixing nozzle (Type 100150/189251), The
extract and nitrogen gas pressures at the two-fluid mixing
nozzle were 180 to 300 psig and 200 psig respectively. An
Trademark
'
.. .
.
6S'7(~
average nozzle pressure of 250 psig was maintained on a Spraying
Systems (Whirljet Type 2-2) nozzle in the spray dryer. The
spray dryer inlet temperature was 360F. and the outlet tempera-
ture was 260F. The bulk product mean particle size was 640
microns, the density was 19.1 gms/100 cc. and the final product
moisture was 3.2%.
EXAMPLE 3
A dextrin (Morex 1918) at 60% concentration and
190F. is pumped by means o~ a Graco air piston pump through a
Spraying Systems* two-fluid mixing nozzle (Type 100150/189351).
The liquid and nitrogen gas pressures at the two-fluid nozzle
were 700 psig and 300 psig respectively. A Manton-Gaulin
positive displacement pump was then used to produce a higher
nozzle pressure of 1100 psig at a Spraying Systems nozzle
(Whirljet Type 1-1) in the spray dryer. The inlet spray dryer
temperature was 560F. and the outlet temperature was 270F. A
feed rate of 300 to 350 lbs./solids per hour was obtained. The
- bulk product density was 4.6 gms/100 cc.
While no particular theory is advanced for the results
achieved by the spray agglomeration process of this invention it
appears every pressure nozzle employed for spray drying has a
minimum threshold pressure which is required for proper atomiza-
tion to occur. By operating in this narrow band of threshold
pre~sures, large spray droplets can be formed but control in
operations is difficult and varying spray patterns are obtained.
By utilizing two-fluid nozzle pneumatic mixing as a means of
aerating the feed material to a conventional spray nozzle above
the threshold pressure:
Trademark
13.;~;5 ~C)
.
(I) No extremely wide fluctuations in spray pattern
will occur.
(II) Fine control on ratio of extract to inert gas
which controls final product density can be
obtained.
With the spray agglomeration process of this invention it is
thus possible to produce a spray dried agglomerated product,
i.e., soluble coffee, and dextrin having a new physical form,
i.e., large fused spherical buds, employing high inert gas to
extract, solution or suspension ratios.
,. 1126St70
SUPPLEMENTARY DISCLOSURE
It is known in the art of spray drying that, for a
particular spray nozzle system, optimum atomization occurs when
the liquid flow exiting from the nozzle is of sufficient magni-
tude to cause the nozzle to deliver the spray over a wide area in
the form of small droplets (fine spray). Conventionally, high
pressure positive displacement pumps are employed to force the
liquid through the spray nozzle at the desired, substantially
uniform, flow rate to form a spray pattern which conforms to the
structural dimensions of the drying tower and which has drop size
uniformity which conforms to the drying capability of the tower.
As is well known, reciprocating positive displace-
ment pumps develop a fluctuating pressure and fluctuating flow
rate of discharge liquid. The fluctuating flow rate of liquid
through the spray nozzle creates fluctuations in the spray pattern
(conical angle of discharge) and also non-uniformity of drop size
in the spray. For the most part, in conventional spray drying
practice, the magnitude of these fluctuations is minimal, and
creates a change in conical spray angle of about 3-4. Conven-
tionally, operations are conducted with systems which developsubstantially uniform flow rates. In many instances, a gear-
type positive displacement or multi-piston pump is employed to
assure the desired unfiromity of flow rate at the high pressures.
Also, in many installations a dome-type accumulator is located
between the putnp discharye and the spray nozzle to even out
the flow rate to the nozzle.
For some liquids, namely cottage cheese whey, fluct-
uations in flow rate through the spray nozzle (commonly called
"slugging) when using a high pressure reciprocating pump has been
minimized by the injection of gas into the whey in the system
between the pump and the spray nozzle (cf. Hanrahan, U.S. 3,222,193)-
. .,. 10
a
- :llZ65~0
For a particular spray drying system, the flow
rate through the spray nozzle should be of a value
for the nozzle to deliver a spray of desired
atomization without endangering the operation by
05 creating too wide a spray angle and thus wetting the
side walls of the drying tower. Too low a flow rate
will create little or no break-up of the liquid into
drops or will develop drops of such large size they
will be incompletely dried in the tower.
In contrast to the teachings and efforts of the
prior art, the method of spray drying of the instant
invention purposely utilizes flow rate fluctuations
of considerable magnitude of coffee extract liquid
through the spray tower spray nozzle to successfully
develop a physically unique soluble coffee agglomerate
product. The flow rate fluctuations of coffee
extract through the spray nozzle are controlled to
uniformly cycle (sine wave) between set maximum and
minimum flow rate values.
Concurrently, flow rates of inert gas, such as
N2, through the spray nozzle are controlled to
uniformly (sine wave) cycle between set maximum and
minimum values. The liquid coffee extract and gas
flow rate cycles are controlled to be directly out
of phase (180 sine wave curve out of phase).
The liquid coffee extract maximum flow rate
through the spray noæzle causes the nozzle to develop
- a spray pattern of a maximum area of coverage; i.e.,
maximum conical angle of spray of fine droplets just
short of wetting the side walls of the drying tower.
The liquid coffee extract minimum flow rate
causes the spray nozzle to develop a spray having a
signficantly smaller conical spray angle and to
,
--11--
a
.
~Z65~7~
develop drops of a much larger size than those
developed at the maximum flow rate. The large drops
are slower to dry than ~he small drops from the wide
spray angle.
05 The concurrent cyclic inert gas flow (directly
out of phase with the liquid flow rate through the
respective spray nozzle) is at the highest flow rate
when the largest coffee extract drops are formed and
sets up (along with the tower drying air) a turbulence
which, accompanied by the cyclic collapse and expansion
of the spray angle (spray pattern) causes the relatively
large number of fine particles from the rapidly
dried small droplets to impact the fewer, large,
partially dried, particles produced from the slower
lS drying large drops ~o form agglomerates of coffee
particles. The agglomerates are unique in that they
are essentially comprised of several relatively
large, substantially spherical, particles of dried
soluble coffee partially embedded, or otherwise
adhered to a large pa~ticle, or particles, of
partially dried soluble coffee (cf. Figures 2 and
3). These agglomerates differ in appearance from
conventional soluble coffee agglomerates which are
(usually) formed from uniformly sized wetted small
particles (cf. Figures 7 and 8).
The critical aspect of the invention and that
which leads to the production of the desired unique
agglornerates is the capability of the system to
rapidly cycle the fluctuating flow of the liquid
coffee extract and the inert gas stream (opposed
cycle) through controlled maximum and minimum flow
rates. A two-fluid venturi flow regulator (flowrator)
is successfully used for this critical phase of the
method of the invention.
C
,)
,l.Z~SqO
As the concept depends for its ultimate success
on having large drops of slowly drying liquid present
to impact with the smaller dried or partially dried
particles, a conventional afterdrier may be employed
05 to finish dry the agglomerates to a desired uniform
dryness.
The process has the advantage that it eliminates
the necessity of incorporating standard agglomerating
e4uipment such as agglolnerating towers in a soluble
coffee processing unit. Moreover, the process
reduces the detrimental heating effects on the
flavor quality of the soluble coffee as compared
with the stepwise process of spray drying followed
by agglomerating and allows for an increase in the
capacity of a soluble coffee processing unit by
permitting the conversion of an existing agglomerating
tower into a spray agglomeration tower.
; Brief Description of the Drawings
A more complete understanding of the method of
the invention may be obtained by reference to the
following description and claims, taken together
with the following drawings in which:
- Fig. 9 is a schematic sketch of the
arrangement of the principal equipment components
2S employed, including the coffee extract high pressure
reciprocating pump, the inert gas supply source, the
two-fluid venturi flowrator and the drying tower
spray nozzle, and illustrates the flow path of each
of the two fluids.
Fig. 10 is a view, in partial section, of
the two~fluid venturi flowrator.
Fig. 11 is a sectional view of the spray
~, nozzle and shows the developed spray angle and
~ pattern of the exiting coffee extract at maximum
: 35 flow rate.
-13-
. . , . ..... , . . , ., . .. . .. , , ~, .
~' ¢'
,' ' ..
65~7~
Fig. 12 is a partial sectional view of the
same spray nozzle as shown in ~ig. 3 and shows the developed
spray angle and pattern of the exiting coffee extract at
minimum flow rate.
DETAILED DESCRIPTION OF T~IE D_AWINGS
Referring to Flg. 9, liquid coffee extract is fed
by means of a high pressure, single cylinder air driven
piston pump (1) (supply on demand) to the liquid intake (12)
of a two-fluid flowrator (2). An inert gas supply source (3)
under high pressure is fed to the gas intake (14) of the two-
fluid flowrator (2). The gas pressure is adjusted to remain
substantially constant at a set value by adjustment
of valve (4) and pressure gage (5). The flow rate
of coffee extract is partially controlly (see
below) by adjustment of the air pressure (6) of the
air driving the pump and, optionally, the coffee
' extract flow control valve (7). The Elow ra-te
.C~
- 112657V
variation is indicated by the change in pressure at
pressure gage (8) in the conduit to the two-fluid
flowrator. The motive force from the air piston
pump and the inert gas supply pressure is used to
05 move the mixture of extract and inert gas through a
conventional high pressure core-type spray nozzle
(9) in the drying tower (10). The combined coffee
extract and gas pressure at the intake of the spray
noz~le is mc~sured by th~ prcssure g~c (11) The
difference in pressure readings at gages (8) and
(11) represents the liquid coffee extract pressure
differential (~PL) across the two-fluid flowrator
(2) and the inert gas differential pressure (~PG~
across the two-fluid flowrator is calculated from
the difference in pressure readings at gages (11)
and (5~. -
The two-fluid flowrator (Fig. 1~ is of the
venturi-type and is (or is equivalent to) an assembled
unit manufactured by Spraying Systems Co., Wheaton,
Illinois as shown and described on pages 47 et seq
of Industrial Catalog 27 (1978). As shown in Fig. lo,
the coffee extract enters at port (12) and passes
through a constricting passageway, "extract nozzle"
(13). The inert gas (N2) enters at port (14) and
passes through a constricting passageway, "inert gas
nozzle" (15). Both "passageways" are of the type to
constrict flow such that the velocity (at constant
pressure) of both fluids increases at the points
(orifices) of outlet (16) and the venturi effect of
. each influences the flow rate of the other.
Thus, the two-fluid flowrator not only controls
the flow rate of both fluids (coffee extract and
inert gas) but also affects the flow rate of one
fluid with respect to the flow rate of the other.
Thus, even though the pressure (5) of the inert gas
-15-
,~ ,
., .. , . . . . . ,, . . ~
F~
'
~ i ~
- 1~2i570
to the flowrator intake remains constant, a change
in coffeé extract fluid pressure (8) (increase) at
the flowrator intake port not only causes a controlled
increase in extract flow but also provides a smaller
05 than expected (absent the flowrator) decrease in
inert gas flow due to the partly compensating vent`uri
effect. Similarly, a decrease in flow rate of
extract through the flowrator creates a slight
increase in inert gas flow even though the upstream
gas pressure remains substantially constant and may
be at a lower intake pressure than tha~ of the
extract.
As will be understood by those knowledgeable in
the art of fluid flow, it is the pressure differential
(~PL) across the two-fluid flowrator coffee extract
passage as measured by gage readings (8)-(11) which
influences the coffee extract flow rate and similarly,
it is the pressure differential (~PG) across the
two-fluid flowrator inert gas passage as measured by
gage readings (5)-(11) which influences .the flow
rate of inert gas. In addition, the venturi effect
in the two-fluid flowrator developed by each fluid
further influences (partly compensates the reduction
in flow when the ~P is reduced) the flow rate of the
other fluid. The flowrator is designed such that
the venturi effect of the coffee extract flow
influences the inert gas flow to a greater degree
than the gas flow venturi effect has on the extract
flow rate.
As stated previously, the combined coffee
extract and inert gas pressure at the intake (11) to
the spray nozzle drives the mixture through the
nozzle and atomizes the mixture in the tower. By
holding the inert gas pressure constan~ (substantially)
at (5), the single cylinder pump (6) fluctuating
~16-
.. .. . ... . .. . .. .
f~
t~
~lZ6570
pressure at (8) is changed by the restrictive orifices
of the flowrator to a substantially co~stant pressure
at (11) even though the flow rate of coffee extract
fluctuate B .
05 In summary, the spray nozzle flow rate requirements
conform to the drying tower structural dimensions
and drying capability. The flowrator is sized to
provide the desired maximum and minimum coffee
exLract u~d lner~ flow raLe~ ~o conforlll wi~h the
spray nozzle atomization requirements (conical spray
angles and drop sizes). The coffee extract pump is
oversized and would deliver vastly larger amounts of
extract to the spray nozzle if the flowrator were
not in the system. The flowrator reduces the overall
flow rate of both coffee extract and inert gas. The
- flowrator, however, causes wide fluctuations in the
overall reduced flow rate of coffee extract when the
extract pressure differential across its intake and
the intake to the spray nozzle are slightly altered.
The venturi effect of the flowrator causes less
: magnitude of fluctuation of the inert gas flow (the
venturi effect partly compensates for the slight
increase in overall pressure at the entrance to the
spray nozzle when the extract is at its maximum
flow). The maximum flow of extract, accompanied by
the minimum flow of inert gas (and vice versa),
maintain a substantially constant pressure at the
intake to the spray nozzle -- it is the change in
flow rate of the liquid coffee extract which has the
,~ 30 far greater effect on the angle of spray delivery
and drop size.
Thus, for a flowrator of the types described
above, the following changes (fluctuations) in
liquid coffee extract and inert gas (N2) flow rates
to a spray nozzle located in a drying tower are
obtainable.
-17-
.. , . .................... . . . .. ., .. , .. .. .. _ _, . . _ _
'" ~C
~lZ6570
;
TABLE I
Pressure differential
(~P) across the
two-fluid flowrator
05 Extract Inert Gas
Inert ~as Extrac~ Flow Rate Z Increase Flow Rate % Decrease
- (lb/in') (lb/in~) (lb/hr) S.CF/min.
31 20 35 --- 2.8 ----
31 30 79 126 2.5 10.4
31 40 140 77 2.2 12.0
31 60 250 150 2.0 9.1
_. ..
--- 3.1 ----
66 164 2.9 6.5
100 52 2.6 10.3
220 120 2.4 ~.6
--- 2.4 ----
105 91 2.1 12.5
185 76 2.0 4.7
300 62 1.9 5.0
From Table I it can be observed that, at a constant
inert gas pressure differential (~PG) of 31 lb/in2,
a drastic increase (150%) in flow rate of coffee
extract from the flowrator is obtained if the single
piston pump on its pressure stroke increases the
pressure of the liquid intake to the flowrator to
increase the coffee extract differential pressure
(~PL) across the flowrator from 40 lb/in2 to 60
"
lb/in~ while, concurrently, the inert gas flow is
limited to a 9% reduction by the venturi effect of
the flowrator.
Without the installation of the venturi-type
flowrator in the system and for the same inert gas
pressure differential and change in coffee extract
pressure differential, the flow rate of the coffee
extract is increased only about 20% and the inert
gas flow (at 31 lb/in2) is reduced to nil.
-18-
. . . , _,, _ ., .
~ C~
.
,
l~Z~i570
Consequently, the venturi-type flowrator provides
for large variations in coffee extract flow to the
spray nozzle with concomitant small variations in
inert gas flow even though the coffee extract liquid
05 pressure to the intake of the flowrator may be
greater than that of the inert gas pressure.
Employing similar flowrators but of different
sizes will, of course, permit larger (or smaller)
flow values for the two fluids but will have similar
affects on the flow rate fluctuations.
Thus, although the flow of coffee extract will
fluctuate throughout a wide range and cause the
spray n~zzle to alternate the spray pattern from
maximum to minimum spray angles, the inert gas flow
is always present to create the desired turbulence
within the spray patterns.
At the maximum coffee e~tract flow rate through
the spray nozzle, the spray angle of droplet discharge
is at its maximum (cf. Fig. 3) and the droplet size
is minim~M. Conversely, the minimum flow of extract
through the spray nozzle yields drops of the largest
size and the smallest spray angle pattern, ~Fig. 4).
Also, the inert gas flow rate is at its peak when
the drops are of the largest size (when the highest
degree of turbulence is desired) and at its lowest
rate when the lighter, smallest drops are being
sprayed.
The controlled alternating expansion and collapse
of the spray pattern, within the required limits
30 dictatèd by the drying tower dimensions and atomization
energy needs, plus the ever present, but varying
inert gas flow rate, create the turbulent conditions
for the production of the agglomerated coffee product.
The more rapidly drying smaller coffee particles
impact the slower drying wetter larger particles to
-19-
__ .
~ . .
iS70
create agglomerates which are comprised of small
spherical particles fixed to a larger particle (or
particles) of partially dried soluble cofee. The
agglomerate is then dried to a desired degree as it
05 falls to the base of the tower.
Figures 2 and 3 illustrate spray agglomerates
produced in accordance with the process of the
present invention. Figure 4 illustrates a spray
dried soluble coffee powder produced by a conventional
commercial process. Figure 5 shows an agglomerated
soluble coffee product prepared on conventional
commercial equipment utilizing the spray dried
soluble coffee powder illustrated in Figure 4.
The total magnification is 61X for the
photomicrographs shown as Figures 2 to 5. The
relative particle size and shape of the particles
shown in Figure 2 may be contrasted with those
shown in Figure 4 and the relative particle size and
shape of the product shown in Figure 3 may be
contrasted with that shown in Figure 5. Further,
the unique physical form of the particles and the
agglomerates obtainable by the process of this
invention may be noted from Figures 2 and 3,
EXAMPLE 4
Coffee extract at 34% concentration and at 98F
was passed by means of a air piston pump (Graco
Model No. 206842) manufactured by Gray Company,
Inc., Minneapolis, Minnesota) through a Spraying
Systems Co. two fluid venturi-type flowrator device
(set-up No. 23B. cf. page 50 of Industrial Catalog
No. 27, 1978). The valve on the flowrator was
adjusted for full flow. Nitrogen was concurrently
passed through the flowrator.
-20-
'~
~,
! I ~ i
llZ6570
The extract and nitrogen gas pressures at the
intake of the two-fluid flowrator were 160-170 psig
and 120 psig, respectively. The discharge from~the
two-fluid flowrator was then passed through a t
05 conventional spray nozzle (Whirljet Type 1-1 Spraying
Systems, Co., Wheaton, Illinois) in the spray dryer
where the nozzle pressure was maintained at 126 psig
(substantially constant). The Graco~ air piston pump
utilized to deliver the extract pressure to the
10 two-fluid venturi-type flowrator was also utilized
as the motive force to provide the required hydraulic Ir
pressure to the spray nozzle.
The degree and frequency to which the extract '
pressure varied was a function of the relative size
15 of the feed pump to both the two-fluid flowrator and i;
the spray nozzle and, also, the feed rate required
at the spray nozzle. In this particular example
with an average feed rate of 142 lbs/hr of extract
the spray nozzle pattern oscillated once every 10
20 seconds. At the low end of the piston stroke (suction~
the extract pressure was about 10 lb/in2 lower than
at the high end of the piston stroke resulting in a
significantly reduced (30%) liquid feed rate at this
point. The following.data were obtained:
TABLE II
Extract
Extract Flow N2 Flow Particle
Pressure Rate Rate (Drop)
At Flow- ThruN Pressure Thru Spray Nozzle Size
- 30 'rator SprayA~ Flowrator Spray Discharge Distri- `
Intak~ _Nozzle_ Intak~ Nozzle Spray Angle bution
~lbs/in ) (lbs/hr.) (lbs/in ) SCF/min (0) (~)
160 110 120 2.4 40-45 300 -1000
Avg.- 700
35 170 170 120 2.1 60-70 150 - 500 ,
Avg.-400
-21-
_ _ .. .. ,, .,, , , . ,,, , , . _ . .. . . ... _ . _ ., _ . _ _ . _ _
11 ~ 6~ 7 ~
Atomization ranged from considered normal at the
highest extract flow rate to marginal at the lowest
extract flow rate.
The spray dryer inlet air temperature was
05 maintained at 415~F; the agglomerated product had a
bulk density of 12.3 grns/lO0 cc. The color of the
soluble coffee agglomerates was 33.0 photo units (as
measured by a Lumetron Photovoltmeter; (cf. U.S.
Patent No.3,~2/~3v) and a u~ean particle size of
735 ~ with a standard deviation of 300 ~. ~or this
particular example, the product moisture content out
of the spray dryer was 5-5.5%. A conventional
after-dryer could ~e employed to reduce the moisture
to any desired lower value. The example product
contained a relatively small amount (10-25% by wgt.)
of satellite particles (fines) but these particles
were larger than those satellites produced in
conventional spray drying. A microscopic inspection
of the agglomerates revealed small hollow spherical
particles adhered to one or more larger particles,
also, in most cases to have hollow centers. Fig. 7
and 8 are photomicrographs of the product of this
example. As with typical spray drying of soluble
coffee, higher extract concentrations would produce
denser particles (and agglomerates) with the particular
system described in this example.
EXAMPLE 5
Soluble coffee agglomerates were produced
accordin~ to the method of the invention with processing
conditions similar to those in Example 4 but employing
a different pump, two fluid venturi-type flow regulator,
spray nozzle, and a larger spray drying tower.
-22-
1~
;
llZ6570
Coffee extract at 34h concentration and at 97F
was delivered by a Graco~ Model No. 206421 air
piston pump through a Spraying System Co. two fluid
venturi-type flow regulator (flowrator) set-up
05 No. 42 (cf. page 48 of Industrial Catalog No. 27,
1978) to a Whirljet Type 5-6 spray nozzle. Nitrogen
gas was concurrently forced through the flowrator
and spray nozzle.
The pressure at the intake to the spray nozzle
was maintained at 135 lb/in2 (substantially constant).
For this run, with an average feed rate of 663
lbs/hr, the air driven single cylinder pump created
a spray nozzle pattern oscillation once every 3
seconds. At the low end of the piston stroke (suction)
the extract pressure was approximately 78 lbs/in~
lower than at the high (top) of the piston stroke.
The following data were obtained:
TABLE III
Extract
20 Extract Flow N Flow Particle
Pressure Xate R2te ~Drop)
At Flow- Thru N Pressure Thru Spray Nozzle Size
rator Spray A~ Flowrator Spray Discharge Distri-
Intak~ N~zzle Intak~ Nozzle Sprav Angle bution
25 (lbs/in') (lbs/hr.) (lbs/in') SCF/min (0) t~)
156 241 160 3.0 40-45 300-1000
Avg. 700
2341085 160 2.4 60-70 120-200
Avg. 400
. Again, atomization ranged from considered
normal at the highest extract flow rate to marginal
at the lowest extract flow rate.
Spray dryer conditions in the larger tower were
maintained to dry the agglomerated product to about
5% moisture. The physical properties of the soluble
coffee agglomerated product were similar to those of
the product obtained in Example 4.
-23-
, _ .. . . .... ... .
!
