Process for the explosive comminution of cellular material

A process for explosive comminution of cellular material in which the material is subjected to compressed gas in a pressure chamber and then discharged from the pressure chamber with explosive pressure release in small portions against the grinding means of a mill.

BACKGROUND OF THE INVENTION 
This invention relates to a process for the explosive comminution of 
cellular material of animal or plant origin, in which the material is 
introduced into a pressure chamber, subjected to compressed gas therein, 
and then discharged from the pressure chamber with explosive pressure 
release against an impact surface. 
Such a process and apparatus suitable for the performance thereof are 
described in U.S. Pat. No. 4,132,161. According to this document, it is 
known that the disintegration of the cellular material can be promoted by 
the material which is to be disintegrated hitting an impact surface upon 
pressure release and discharge. 
According to the findings on which the invention is based, the impact 
against the impact surface imparts to the particles a mechanical impetus. 
Often only this starts the bursting process causing the comminution. At 
the beginning of the pressure release or discharge step, the particles hit 
the free, hard wall of the impact surface and actually receive the 
mechanical impetus. In the course of the pressure release or discharge 
step, however, a layer of comminuted particles forms on the impact 
surface. This causes the subsequent particles to hit this comparatively 
softer layer on the impact surface, so that they no longer receive a 
mechanical impetus which triggers the bursting process. Moreover, the 
subsequent particles no longer have the kinetic energy of the initially 
impacting particles due to continuing discharge of the pressure chamber 
and the consequent decrease in the pressure difference. As a result 
thereof, the bursting of the material particles which impact consecutively 
does not take place uniformly, and a material is obtained which contains 
coarse fractions as well as fine fractions. 
However, the recovery of the components of a material is easier, the 
smaller the proportion of coarse fractions. Moreover, often a material 
with too great a variation of particle size is not wanted. Therefore, in 
prior art processes the coarse material was separated from the fine 
material, e.g., by sieving, and was recycled to explosive comminution. 
This causes corresponding expenses and may involve losses of valuable 
components. Even with repeated recycling of the coarse fraction, complete 
comminution of the material used cannot be achieved. This is explained by 
the fact that the recycled material is structurally damaged, and upon 
pressure release the pressure compensation takes place without a bursting 
process and hence without the desired comminution effect. If attempts are 
made to reduce the proportion of coarse material by increasing the 
pressure, however, there results such fine material that further 
processing may be made more difficult due to formation of fine dust, 
clogging of filters, etc. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide an improved process of explosive 
comminution which overcomes the drawbacks of the known processes. 
This is achieved according to the invention in that the material is 
discharged or undergoes pressure release in small portions against the 
grinding means of a mill as an impact surface. 
The advantage of such a method is first that any coarse material which may 
still occur despite explosive comminution is immediately comminuted by the 
mill, so that at last coarse material does not occur at all and in this 
respect separation or recycling can be dispensed with. Furthermore, the 
moving grinding means of the mill in conjunction with the small portions 
which are supplied ensure that the impacting material continuously meets 
with free, hard impact surfaces, namely the grinding attachments of the 
mill and, if the bursting process had not been triggered automatically, it 
is triggered by the mechanical impetus imparted upon hitting the grinding 
means.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
As used herein, the term "small portions" is understood to refer to 
portions which can be carried through or processed by the mill used within 
the period of time required by a material particle which has not been 
burst by itself to compensate for the pressure difference between the 
interior of the cell and the outer atmosphere at the moment it emerges 
from the pressure chamber. This period differs from material to material, 
but is generally of the order of magnitude of about one minute. Thus, 
"small portions" in the sense of the invention are portions which can be 
throughput by the mill used within the period of time required for a 
material particle which has not burst to undergo pressure compensation. 
Suitable mills which may be used in the process according to the invention 
are known per se. Mills which have a large throughput rate are preferred. 
Disc mills, in particular toothed disc mills, have proved particularly 
suitable. 
As a rule, it is desirable that the cellular material of animal or plant 
origin which is to be disintegrated should not come into contact with air 
or oxygen and/or moisture after comminution. In a preferred embodiment, 
the process according to the invention therefore makes provision for the 
material to be discharged or undergo pressure release into an inert gas 
atmosphere or against an inert gas atmosphere. This is achieved in the 
simplest case by making the connection between the pressure chamber and 
the mill gas-tight. This effectively excludes the ingress of air or oxygen 
and/or moisture. This is particularly the case if, according to another 
embodiment of the invention, gases such as carbon dioxide, nitrogen, 
nitrous oxide, noble gases and mixtures of these gases, preferably carbon 
dioxide, are used as compressed gases. These gases act as inert gases, 
which according to the invention are understood to be gases which do not 
undergo any chemical or enzymatic reactions with the cellular material 
and/or its components. 
According to another embodiment of the process of the invention, the 
cellular material which is to be comminuted is additionally cooled. This 
cooling may prevent the loss, for instance, during the explosive 
comminution, of aroma constituents of the cellular material which have a 
low boiling point and thus are readily volatile. The manner in which the 
cooling of the material to be comminuted is carried out is known per se to 
a person skilled in the art, for instance from DE-OS 33 47 152. 
The cooling may take place indirectly, e.g., by previous storage of the 
cellular material which is to be comminuted in cooling devices, and/or by 
cooling parts of devices using known cooling apparatus. Furthermore, 
provision may be made for cooling of the grinding attachments of the mill 
etc. 
However, direct cooling of the material which is to be comminuted is 
preferred. It preferably takes place by direct contact of the cellular 
material which is to be comminuted with an inert cooling medium, 
preferably with cold carbon dioxide or nitrogen. In this case the cooling 
medium is used in a quantity of from about 0.1 to about 40 weight-%, 
relative to the cellular material. 
The inert cooling medium may be used as a gas phase or, preferably, as a 
condensed phase, e.g., as nitrogen or carbon dioxide in liquefied form. 
The use of carbon dioxide in solid form is preferred. Both dry ice and 
solid carbon dioxide in compressed form (carbon dioxide pellets) can be 
used as solid carbon dioxide. 
The cooling medium used for direct cooling may be supplied to the material 
which is to be comminuted upstream of and/or in the pressure chambers or 
pressure loading chambers by separate supply means. 
The compressed gas which is released in the process according to the 
invention upon the discharge or pressure release of the material which is 
to be comminuted against the grinding attachments of a mill may be 
discharged into the environment, optionally after separation of any 
volatile constituents taken up from the material by the gas. 
In one preferred embodiment of the process according to the invention, 
provision is made for the compressed gas to be recycled, optionally after 
separation of volatile constituents which it has taken up. 
The manner in which the separation of the volatile constituents from the 
material takes place is known to a person skilled in the art. For 
instance, the compressed gas may be separated by passage over suitable 
absorption agents and then recycled. It is also possible to condense 
volatile constituents in separators by means of changes in pressure and/or 
temperature. 
The compressed gas, which optionally has been freed from any volatile 
constituents entrained therein, may be conveyed to a gas storage vessel 
and thus stored for re-use as a compressed gas or as a cooling medium in 
the process of the invention. 
The compressed gas--optionally in the form of a diverted partial flow--may 
serve to wash the cellular material which is to be disintegrated, pipes, 
parts of the apparatus, packing machines and/or to produce the inert gas 
atmosphere against which the material undergoes pressure release. The 
contact of the cellular material with air or oxygen and/or moisture can be 
effectively decreased by this method, optionally in conjunction with the 
gas-tight construction of the connecting parts of the device used. 
In the simplest manner, the process according to the invention can for 
instance be carried out so that the material which is to be comminuted is 
introduced into a pressure chamber in portions which are sized according 
to the invention, subjected to compressed gas in the pressure chamber, and 
the entire contents of the pressure chamber thereafter are discharged or 
undergo pressure release against the grinding means of a mill. However, in 
the process according to the invention this particularly simple method is 
less preferred. 
It has been demonstrated in tests that in pressure expansion processes the 
comminution effect is particularly good when the subjection of the 
material to compressed gas lasts over a certain period of time. This 
period depends on the cellular material. Soft materials having a larger 
proportion of liquid require shorter periods; harder materials with a 
lower proportion of liquid require somewhat longer periods. As a rule, 
holding times of about one minute are sufficient for cellular materials 
having very different types of structure. However, in the simple method 
described above, this holding time necessitates a certain idle time of the 
mill, as material to be comminuted is only supplied to the mill during the 
discharge phase or pressure release phase of the pressure chamber, but not 
in the two other operational phases through which the pressure chamber has 
to pass, i.e. the build-up of pressure and the holding time. 
In another embodiment of the invention the material to be comminuted is 
introduced into a suitably-sized pressure chamber in fairly large 
portions, subjected to compressed gas, and then discharged or pressure 
released against the grinding gear of a mill in small portions. The 
portioning may take place, for instance, using valves which have a very 
short opening time and only allow portions which are sized according to 
the invention to pass, which then impact on the grinding means of the 
mill. In this embodiment, the holding time only needs to be expended once 
for the large storage portion. 
A further embodiment involves use of a plurality of pressure chambers 
associated with a single mill, and the individual pressure chambers are 
cyclically filled in succession with material to be comminuted and 
compressed gas, subjected to the holding time and then discharged or 
undergo pressure release against the grinding means of the mill. Since 
about 15 seconds are required for the pressure release process and for the 
throughput of a portion in the process according to the invention, and 
since the time for introducing the pressure can be ignored, at a holding 
time of about one minute, four pressure chambers need to be provided for 
one mill so that this mill is used to capacity. 
Another preferred embodiment of the process according to the invention is 
characterized in that the material to be comminuted is introduced into a 
pressure loading chamber, subjected to compressed gas in the pressure 
loading chamber, transferred from the pressure loading chamber into a 
pressure chamber while maintaining the pressure, and then discharged or 
undergoes pressure release from the pressure chamber. Advantageously, the 
material is introduced into the pressure loading chamber in a relatively 
large quantity and is transferred therefrom into the pressure chamber in 
portions, for instance through suitable valves. In this embodiment too, 
the idle time of the mill is essentially no longer dependent on the 
holding time. 
In a particularly preferred embodiment, the cellular material which is to 
be comminuted is introduced into a pressure loading chamber, transferred 
cyclically therefrom into a succession of pressure chambers and is 
discharged or undergoes pressure release cyclically from the respective 
pressure chambers in succession. This embodiment permits a high throughput 
of material with a particularly short idle time of the mill. 
A very particularly preferred embodiment of the process according to the 
invention is characterized in that the material to be comminuted is 
subjected to compressed gas in a lock chamber, and is transferred into one 
or more pressure loading chambers while maintaining the pressure. If the 
flows of material which are supplied to the pressure loading chamber or 
removed from the pressure loading chamber into the pressure chamber or 
pressure chambers via the lock chamber correspond to each other, it is 
possible for the process to be performed continuously. Such a continuous 
performance of the process permits optimum use of the device. 
The pressure range in which the process according to the invention operates 
is mainly dependent on the cellular material and the desired degree of 
comminution. The pressure range which is most favorable in each case may 
easily be determined by simple tests. For instance, when using CO.sub.2 as 
a compressed gas and coffee as the material to be comminuted, the process 
is preferably carried out at a pressure of about 25 to 35 bar absolute. 
In the process according to the invention, "plurality" of pressure loading 
chambers or pressure chambers is understood to mean 2, 3, 4, 5, 6 or more 
chambers. A person skilled in the art can easily determine the suitable 
number of pressure chambers to be provided, if necessary using tests. The 
number of chambers needed depends, inter alia, on the desired throughput 
rate of the material, on the capacity of the pressure chambers used, on 
the type and capacity of the mill used, on the feed material used in each 
case, on the magnitude of the pressure difference upon pressure release, 
on the space available for the unit, etc. 
In the process according to the invention, optionally processed, e.g., 
sterilized, air may be used as the compressed gas, if damaging effects on 
the material which is to be disintegrated are not feared or can be 
ignored. Preferably, however, inert gases such as carbon dioxide, 
nitrogen, nitrous oxide, noble gases or mixtures of these gases are used 
as the compressed gas. Carbon dioxide is distinguished from other usable 
compressed gases, for instance, by its ability to render the material to 
be comminuted inert to undesired degradation reactions, by its 
bacteriostatic effect and by its harmlessness in accordance with 
applicable food laws. 
A person skilled in the art can easily determine, by means of simple, 
preliminary tests, the sizing of the portions in which the material to be 
comminuted in the process of the invention is to be discharged or undergo 
pressure release against the grinding means of a mill by taking into 
account the given limiting conditions, e.g., the nature of the cellular 
material to be comminuted, the pressure to which the material is 
subjected, the type and capacity of the mill used, the maximum permissible 
coarse fraction, etc. The decisive factor is that the time span between 
the emergence from the pressure chamber and the impacting and entry into 
the grinding attachment for a substantial part of the material is not 
longer than the time required for pressure compensation by unbroken cells, 
e.g. about 60 seconds for most materials. 
The process according to the invention can be used to comminute cellular 
materials of animal or plant origin. Suitable cellular materials of animal 
origin may include cells or cell structures of microorganisms or parts of 
animal tissue or of animal organs. In particular, suitable materials of 
plant origin may include both parts of plants growing underground, such as 
roots or legumes, and parts of plants growing above ground, such as 
flowers, fruits and/or seeds. 
Preferably cellular material is used which contains pharmaceutically and/or 
cosmetically active components, or fats, oils, or waxes, or aromas. In 
particular, parts of known medicinal or curative plants which contain 
pharmaceutically and/or cosmetically active components may be utilized as 
cellular material to be comminuted. Examples of such materials which may 
be mentioned include fennel, hawthorn, senna, gentian, poppy or valerian. 
Examples of cellular materials which contain fat, oil or wax, include in 
particular fruits or seeds of cultivated plants. These contain mixtures of 
esters or unsaturated or saturated glycerides, which are known, for 
instance, as coconut, groundnut, linseed, soya, sunflower or jojoba oils. 
Suitable cell materials which contain aromas, i.e. components which appeal 
to the organs of taste and/or smell, include parts of plants, particularly 
leaves, fruits, flowers and/or seeds, which after appropriate preparation 
may be used as spices, flavorings or foods or beverages, or for the 
production thereof. Specific examples of such materials which may be 
mentioned include tarragon, coriander, caraway, marjoram, nutmeg and mace, 
pepper, pimento, vanilla, cinnamon, and, as a consumable beverage, coffee 
beans. Preferably, the process according to the invention is used to 
comminute roasted coffee. 
The process according to the invention has surprising advantages compared 
with the processes of the prior art. For instance, the fraction of coarse 
material, which hitherto has had to be sieved out and recycled, which 
involved additional costs and losses of components, is substantially 
decreased in the process according to the invention. The bursting forces 
upon explosive comminution are surprisingly better utilized than in 
conventional processes due to the discharge of the material to be 
comminuted in portions against the grinding means of a mill which always 
remain free. If the mill is a toothed disc mill, in addition to the large 
capacity, there is the additional advantage that it is possible to control 
the upper limit of the particle size of the comminuted material as needed 
by suitable adjustment of the mill. 
A further advantage is that when using an inert gas, preferably CO.sub.2, 
as a compressed gas, the cellular material can be processed with the 
exclusion of air/atmospheric moisture. This inert gas atmosphere can be 
produced--particularly economically by using recycled waste gas--in 
optional prior treatment stages, such as classification, sieving, drying, 
roasting etc., and can be maintained during the comminution operation 
until packing. 
The effect of the process according to the invention is particularly 
surprising. If cellular material is subjected to explosive comminution in 
the conventional manner, and coarse material is sieved out, optionally 
after multiple recyclings, and is ground sometime later, --apart from the 
loss of components--the comminuting effect of the mill is less than in the 
process according to the invention. If the material is first ground and 
then the ground material is subjected to explosive comminution, completely 
unsatisfactory results are obtained. The surprising effect of the process 
according to the invention cannot therefore be explained by simple 
combination of explosive comminution and grinding. 
The invention will now be explained with reference to the following 
non-limiting example schematically illustrated by FIG. 1. A process 
embodiment was selected in which the material to be comminuted was 
introduced into a pressure loading chamber via a lock-chamber, was 
cyclically and consecutively transferred from the pressure loading chamber 
into a plurality of pressure chambers, and was again cyclically and 
consecutively discharged or underwent pressure release therefrom into the 
inlet of a toothed disc mill, a partial stream of the waste gas, after 
condensation of the components entrained therewith, being used to rinse 
feed pipes, storage chambers, pressure loading chambers and packaging 
devices, and the remaining stream being supplied to a gas compressor for 
re-use as a compressed gas. Coffee was selected as the material to be 
comminuted, and CO.sub.2 as the compressed gas. It is, of course, easily 
possible for a person skilled in the art having knowledge of the invention 
to conceive of variations of this illustrative embodiment, e.g., by 
omitting the lock chamber, adding or omitting pressure loading chambers, 
pressure chambers, use of other cellular materials, other compressed 
gases, other mills, operating at different pressures, etc., and all such 
variations are intended to be within the scope of the invention. 
EXAMPLE 
Comminution of freshly roasted coffee 
After the entire apparatus was rinsed with carbon dioxide to produce an 
inert gas atmosphere, fresh roast coffee was introduced into a roast 
coffee reservoir R via a conduit L1. The reservoir R is connected to a 
lock chamber S by a valve V1. The lock chamber S is connected to a 
pressure loading chamber D by a valve V2. The lock chamber S is connected 
by a valve V3 to a gas reservoir GB, and by a valve V4 and a conduit L2 to 
a fresh gas reservoir F. About 12.5 kg freshly roasted coffee beans were 
removed from the reservoir R, which was under standard pressure, and were 
transferred into the lock chamber S via the open valve V1; the valves V2, 
V3 and V4 were closed. Valve V1 was then also closed, V3 was opened, and 
the coffee beans were subjected to compressed gas from the gas reservoir 
GB until a desired pressure of about 30 bar (absolute) was achieved. After 
valve V3 had been closed, valve V2 was opened, and the contents of the 
lock chamber S were transferred into the pressure loading chamber D, in 
which there was also a pressure of about 30 bar (absolute). Subsequently 
the valve V2 was closed again and the lock chamber was re-filled, the 
overpressure in the lock chamber, compared with the reservoir, having 
previously been reduced by means (not shown), e.g., a conduit to a gas 
compressor GV. The operation of filling and emptying the lock chamber was 
repeated approximately every 3 minutes. The pressure loading chamber D has 
a capacity of about 500 liters. It is connected to four pressure chambers 
DB, which each have a capacity of about 1 liter, by four valves V5. Each 
of the pressure chambers DB is connected to the gas reservoir GB by a 
valve V6 and a conduit L4, and to the inlet of a toothed disc mill Z by a 
reversible ball valve V7. For ease of illustration, only one of each of 
valves V5, pressure chambers DB, conduits L4 and ball valves V7 is shown 
in the drawing. 
Initially, all the valves V5, V6 of the pressure chambers DB and the ball 
valves V7 were closed. The pressure chambers DB were subjected to 
compressed gas via the conduits L4 by opening the valves V6, until a 
desired value of abut 30 bar (absolute) was achieved. After closing the 
valves V6, first one of the valves V5 was opened, and an approximately 250 
g portion of roast coffee from the pressure loading chamber D was 
transferred into the associated pressure chamber DB, whereupon the valve 
V5 was closed again. In a similar manner, about 250 g of roast coffee was 
cyclically introduced into each of the pressure chambers DB in succession. 
After the introduction of the roast coffee and closing of the associated 
valve V5, the ball valve V7 of the first pressure chamber DB was switched 
to the open position, and its contents were discharged explosively into 
the inlet of the toothed disc mill Z. In the same manner, all the pressure 
chambers DB were cyclically discharged in succession into the inlet of the 
toothed disc mill Z. 
The process of subjecting the pressure chambers to compressed gas, 
introducing the roast coffee and pressure release discharging the 
pressurized coffee into the toothed disc mill was continuously repeated 
cyclically by appropriate opening and closing of the respective valves. In 
this way, the pressure chambers were each filled and discharged again four 
times within approximately one minute. 
The toothed disc mill and inlet are connected to each other and to the ball 
valve V7 so as to be gas-tight, in order to prevent the ingress of air. 
The material discharged into the inlet of the toothed disc mill was 
completely passed through the grinding gear of the mill within about 15 
seconds. The ground material M, which was free of unwanted coarse 
fractions, was supplied to a packaging device (not shown) via a conduit 
L5, in which a CO.sub.2 atmosphere was maintained. The CO.sub.2 which was 
released upon pressure release was initially conducted out of the mill via 
a conduit L6 into a separator AK for aroma condensation. The gas which was 
freed of condensate was recycled to the gas compressor GV, a diverted 
partial flow thereof being used via a conduit L7 for rinsing the coffee 
reservoir R and for rinsing the conduit L1. Inevitable, slight losses of 
compressed gas were restored by fresh gas via the conduits L2 and L8. The 
aroma condensate from separator AK was added to the ground material before 
packaging. 
The foregoing description and examples have been set forth merely to 
illustrate the invention and are not intended to be limiting. Since 
modifications of the described embodiments incorporating the spirit and 
substance of the invention may occur to persons skilled in the art, the 
scope of the invention should be limited solely with reference to the 
appended claims and equivalents thereof.