Apparatus for preventing snow buildup in a carbon dioxide snow cyclone separator

A cyclone separator for generating snow from liquid carbon dioxide comprising a flexible frustoconical member having an open upper end and an open lower end and defining a separation chamber. Injection nozzles having orifices for injecting liquid carbon dioxide located in the upper end of the separation chamber. Each injection nozzle is radially spaced inwardly from the frustoconical member and the orifice of each nozzle is directed outwardly toward the frustoconical member so that liquid carbon dioxide injected into the separation chamber forms a mixture of snow and vapor which is discharged from the open lower end of the frustoconical member. A mechanical impactor mounted at the lower end of the frustoconical member to contact the frustoconical member and loosen snow which builds up in the separation chamber.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to cyclone type carbon dioxide snow 
generators and more particularly to a cyclone type snow generator designed 
to prevent the buildup of snow in the separation chamber. 
2. Description of the Prior Art 
In the manufacture of carbon dioxide snow by flashing liquid carbon 
dioxide, a mixture of the carbon dioxide snow and vapor is created. It is 
desirable to separate the snow from the vapor, and numerous devices have 
been developed to accomplish this result. One such device is a cyclone 
separator which operates by the combined actions of centrifugal force and 
gravity to separate the snow from the vapor. Such a separator is well 
known in the art. 
A problem which occurs with a cyclone type separator forming snow from 
liquid carbon dioxide is the buildup of snow on the inside surface of the 
separator cone as the carbon dioxide expands through the nozzle orifices. 
Snow builds up on the inside surface of the cone adjacent to the lower 
discharge end, and the buildup increases until eventually the discharge 
end of the cone is completely blocked. Additional snow builds up at the 
upper end of the cone adjacent to the injection nozzles. This snow buildup 
on the cone wall cause a progressive decrease in the efficiency of the 
cyclone type separator and eventually the separator ceases to operate. A 
fresh buildup of snow is difficult to break up because it is held together 
by a static charge and it is flexible. In order to remove built-up snow by 
vibrating the cone, the magnitude of the vibrations is so great that the 
cone is damaged. 
SUMMARY OF THE INVENTION 
The present invention prevents buildup of snow in the separation chamber of 
a cyclone type separator by the location of the liquid carbon dioxide 
injection nozzles and the direction of the orifices of the injection 
nozzles relative to the wall of the cone and by constructing the cone from 
a flexible material. Additionally, the cone wall may be mechanically 
deformed to flex the cone wall and thereby shake loose snow which has 
built up on the inside surface thereof especially at the lower discharge 
end. The mechanical deformation of the cone wall is followed by a number 
of sharp impacts. 
The location and direction of the orifices in the liquid carbon dioxide 
injection nozzles are importatnt in preventing snow buildup on the upper 
part of the inside surface of the cone. The injection nozzles are located 
toward the center of the cone and direct the carbon dioxide toward the 
outer perimeter of the cone circle rather than tangentially to the cone 
circle. This nozzle location and flow direction of the carbon dioxide 
result in a flow pattern within the separation chamber that prevents snow 
buildup and creates cone vibrations which aid in reducing snow buildup. 
The use of a flexible material for the cone assists in preventing the 
buildup of snow on the cone wall since the cone wall can flex and loosen 
built-up snow. This movement of the cone may be enhanced by a mechanical 
impactor which intermittently strikes the outside surface of the cone 
adjacent to the lower discharge end to assist in shaking loose any 
built-up snow. This deformation of the cone is analogous to a low 
frequency shock wave.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a cyclone type separator for generating snow from liquid 
carbon dioxide. The separator is located within a housing 1 having side 
walls 2, a top wall 3 and an open bottom 4. A vapor outlet 5 is formed in 
a side wall 2 and a conduit 6 is attached to the outside of wall 2 
adjacent outlet 5 for connection with an in-plant exhaust system. The 
separator includes an inverted cone 7 mounted within housing 1 with its 
longitudinal axis in the vertical position. 
The cone is actually a frustoconical member having its base 8 at the top 
and a smaller open discharge end 9 at the bottom spaced from bottom wall 4 
of housing 1. An annular member 10 is attached to the cone at base 8 and 
engages spaced parallel cross members 11 which are attached to side walls 
2 of housing 1 to support and locate the cone within the housing as shown 
in FIGS. 1 and 2. The cone defines a separation chamber 12 which extends 
from base 8 at the top to lower discharge end 9 at the bottom. 
An elongated tube 13 is located coaxially with both cone 7 and annular 
member 10 and extends from about the annular member downwardly through the 
central hole in the annular member into the upper end of separation 
chamber 12. The exterior of tube 13 is attached to the annular member to 
keep the tube in position. The location of tube 13 and the location of the 
liquid carbon dioxide injection nozzles along with the direction of the 
orifices in the injection nozzles minimize snow buildup in the separation 
chamber as explained hereinafter. 
Cone 7 and tube 13 are made from a flexible plastic material such as 
polyethylene or polypropylene. These materials have properties which make 
them suitable for making the cone and the tube. They remain flexible at 
temperatures down to about -110.degree. F. and are sufficiently durable to 
withstand the abrasive action and the impact of the carbon dioxide as it 
is ejected from the nozzle orifices. Also, the materials are inert to 
carbon dioxide and are formable while being sufficiently rigid to maintain 
a frustoconical shape once the cone has been formed. The materials also 
have low porosity and good lubricity. 
A snow generator assembly 20 having a pair of nozzles 21 and 22 with 
orifices for injecting liquid carbon dioxide into the upper end of cone 7 
is located away from the wall of the cone and close to the outside of 
downwardly depending tube 13. This location differs from the location of 
the nozzles close to the perimeter of the cone in the prior art. The 
orifice of each nozzle is directed toward the outer perimeter of the cone 
circle rather than tangentially to the cone circle as in the prior art. 
The snow generator assembly includes a conduit 23 supplying nozzle 21 and 
a similar conduit 24 supplying nozzle 22. Each conduit extends downwardly 
through a hole in annular member 10 into cone 7. Assembly 20 is in a 
selective flow communication with a source of liquid carbon dioxide (not 
shown), and liquid carbon dioxide is supplied to conduits 23 and 24 
through a tee fitting 25. The flow to conduits 23 and 24 is controlled by 
solenoid valves 23' and 24' which are located between the conduits and tee 
fitting 25. 
The location of nozzles 21 and 22 toward the center of the cone adjacent to 
tube 13 rather than close to the outer perimeter of the cone and the 
direction of the spray toward the cone circle rather than tangentially to 
the cone circle are important in preventing snow buildup in the upper end 
of the separator cone. This nozzle location and orifice direction create a 
flow pattern within the cone which induces the cone to vibrate. The 
vibrations reduce the snow buildup on the cone. 
A mechanical impactor 30 is provided adjacent to the lower discharge end of 
cone 7 in order to flex the cone to dislodge snow built up on the cone 
adjacent to the discharge end. The mechanical impactor is mounted on a 
rotary shaft 31 which is supported at its ends in bearings 32 mounted in 
opposite walls 2 of housing 1. One end of shaft 31 is driven through a 
gear reducer by a standard electric motor (not shown) located within a 
housing 33 which is attached to the exterior of a side wall 2 of housing 
1. A flexible conduit 34 carries electrical wires to provide power to the 
electric motor. 
As seen in detail in FIG. 3 of the drawings, the impactor 30 includes a 
locking collar 35 which is locked to drive shaft 31 for rotation with the 
drive shaft and which supports impactor crank 36. An impact arm 37 is 
mounted on bearings 46 which are carried on shaft 31 on opposite sides of 
locking collar 35. The impact arm has a pair of bearing spacers 47 which 
fit over that portion of bearings 46 which surround shaft 31 so that 
impact arm 37 is not locked to shaft 31 and is not driven by shaft 31. A 
contact member 38 is pivotally attached to impact arm 37 by a machine 
screw 39 having a nut 40 in its threaded end. The machine screw 39 extends 
through spaced lugs 41 on contact member 38. A sleeve 42 surrounds the 
central portion of machine screw 39 between lugs 41, and a torsion spring 
43 is mounted around the sleeve with one end 44 in contact with contact 
member 38 and the other end 45 in contact with impact arm 37. The torsion 
spring permits contact member 38 to rotate about machine screw 39 and to 
be returned to its original position as a straight extension of impact arm 
37. 
Rotation of drive shaft 31 by the electric motor moves impactor 30 in the 
upward direction toward the lower discharge end of cone 7 so that contact 
member 38 contacts the exterior surface of the lower end of cone 7 to 
deform it inwardly and simultaneously compress spring 43. As the shaft 
continues to rotate, contact member 38 pivots about machine screw 39 
against the force of the compressed torsion spring 43 until it is out of 
contact with the exterior of cone 7 at which point the wall of the cone 
flexes outwardly and the torsion spring snaps contact member 38 into a 
straight extended relationship with impact arm 37 as shown in FIG. 3 of 
the drawings. The momentum created by the spring recoil swings impact arm 
37 and contact member 38 around shaft 31 on bearings 46 approximately ten 
times faster than the speed of rotation of the shaft, and contact member 
38 again contacts the exterior of cone 7 and imparts a shock to the cone. 
The movement of the flexible cone and spring 43 recoil contact member 38 
back into impactor crank 36 which is rotating with shaft 31 and as a 
result of this coaction between the rotating shaft and torsion spring 43, 
contact member 38 will contact the exterior of cone 7 a total of three 
times for every revolution of shaft 31 and impactor crank 36. Continuous 
rotation of shaft 31 again brings the contact member into contact with the 
lower discharge end of cone 7. The frequency of contact between contact 
member 38 and the lower discharge end of cone 7 is determined by the 
revolutions per minute of shaft 31 and the spring constant of spring 43. 
The impactor provides for deformation of the cone wall after which it 
springs back to its original position followed by several sharp impacts. 
Snow breaks loose from the cone wall, and the swirling action of the 
carbon dioxide pulls the snow away from the wall and out of the lower 
discharge end of the cone. It will be understood by those skilled in the 
art that an impactor having other than rotary motion may also be used. 
The action of the impactor combined with the flexible material from which 
the cone is formed and the location and direction of the carbon dioxide 
injection nozzles induces continuous cleaning of the inside of the cone. 
Thus, there is no buildup of snow in the cone and an efficient operation 
is achieved wherein a constant supply of snow is provided from the lower 
discharge end of the cone. Even though an impactor may not be required due 
to the location and direction of the injection nozzles and the flexibility 
of the material from which the cone is formed, it is advantageous to use 
an impactor as it assists in shaking snow loose from the inner surface of 
the cone wall. Alternatively, the cyclone type separator of the invention 
may have the injection nozzles located and directed according to the prior 
art in which case an impactor will be sufficient to shake snow loose from 
the inner surface of the cone wall. 
While preferred embodiments of the invention are described herein, it is to 
be understood that the invention may be embodied within the scope of the 
appended claims.