Liquid material drying apparatus

An apparatus for drying and powdering liquid radioactive wastes produced in radioactive material treating plants such as nuclear power stations comprising a vessel having liquid material inlet and outlet ports for liquid wastes, a support plate arranged in the vessel, a great number of spherical bodies piled in layers on the support plate, stirring means having stirring blades for rolling the spherical bodies, and heating means for heating the spherical bodies. An induction heating coil may be used as the heating means, when the spherical bodies are conductive. If electric resistance heating means is used, the spherical bodies are non-conductive. Hot air can be used for heating the spherical bodies. The electric resistance heating means consists of a plurality of resistance heaters one above the other around the vessel. The support plate is formed with slits concentric to each other and the stirring means is provided with pins rotating therewith and extending into the slits.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an apparatus for drying liquid materials as 
slurries to transform them into powders with the aid of heated spherical 
bodies, particularly suitble for powdering various kinds of liquid 
radioactive wastes produced in radioactive material treating plants such 
as nuclear power stations. 
2. Description of the Prior Art 
Radioactive waste materials as radioactive waste liquids, resins, sludges 
and the like produced in radioactive material treating plants such as 
nuclear power stations are treated or stored in accordance with their 
characteristic properties. For example, the radioactive waste liquids are 
enriched in evaporators to obtain enriched waste liquids which are stored 
as liquids or mixed with cement or asphalt to solidify in drum cans which 
are then stored in the plants. The waste resins and sludges are stored in 
slurry tanks or extracted in centrifugal hydro-extractors and then mixed 
with cement to solidify in drum cans which are also stored in the plants. 
However, these methods are low in storing efficiency requiring a great 
number of storage tanks or drum cans. To avoid this, it has been proposed 
that after the enriched waste liquids, waste resins and waste sludges are 
evaporated, dried and powdered in centrifugal membrane drying apparatuses, 
the powders are formed in pellets or mixed with asphalt or plastic 
materials to solidify, thereby reducing the volumes of the wastes. 
However, these drying apparatuses have the following disadvantages. 
Scraping blades provided in the drying apparatuses are rotated at high 
speeds, so that they are susceptible to wear of parts and vibration 
resulting in failure or trouble, requiring troublesome and expensive 
inspection and exchange of parts. Moreover, dried powders often stick to 
the blades and rotating shafts and grow, so that it requires operators to 
stop the apparatuses with constant intervals and clean the inner parts of 
the apparatuses with hot water. Accordingly, it is difficult to operate 
the apparatuses for long periods of time. Furthermore, as the apparatuses 
employ externally indirect heating system and temperatures of steam as 
heat source are lower than 200.degree. C., the efficiency of heat transfer 
is low and the treating capacity of the apparatuses is small so that the 
radioactive waste liquids prior to being enriched cannot be directly 
powdered. In case of treating enriched waste liquids mainly consisting of 
boric acid and sodium hydroxide produced from pressurized water nuclear 
power stations, particularly, it is required to adjust the mixed ratio of 
the boric acid and sodium hydroxide in constant narrow ranges before 
drying and treating the water liquids, because the mixed ratio for 
powdering is dependent upon drying or treating temperatures in a manner 
that the range of allowable mixed ratio is the widest at about 350.degree. 
C. gut as the temperature is lower, the range becomes narrower. It is 
difficult to powder the enriched waste liquids when the drying temperature 
is lower than 200.degree. C. 
SUMMARY OF THE INVENTION 
It is therefore a principal object of the invention to provide a liquid 
material drying apparatus which overcomes the above disadvantages of the 
prior art. 
In order to achieve this object, the liquid material drying method 
according to the invention comprises steps of rolling spherical bodies 
piled on a support plate in a vessel, heating said spherical bodies, and 
supplying a liquid material onto said spherical bodies so as to heat the 
liquid material to dry it. 
It is another object of the invention to provide a liquid material drying 
apparatus which is relatively simple and inexpensive to manufacture and 
easy to maintain with less failure or trouble and operates for stable 
treating of waste liquids for long periods of time. 
In order to achieve this object, the liquid material drying apparatus 
according to the invention comprises a main body in the form of a vessel 
provided at upper and lower portions with liquid material inlet and outlet 
ports for said liquid material, a support plate arranged in said vessel, a 
great number of spherical bodies piled in layers on said support plate, 
stirring means having stirring blades for rolling said spherical bodies, 
and heating means for heating said spherical bodies. 
The apparatus preferably comprises moisture removing means for removing 
moisture derived from the liquid material to prevent the moisture from 
becoming saturated condition. 
The heating means may be an induction heating coil or electric resistance 
heating means or may utilize hot air. 
When the induction heating coil is used, it is impossible to effect a 
required temperature distribution in the piled layers of the spherical 
bodies in vertical directions. At the beginning of the operation of the 
drying apparatus, there is a risk of the spherical bodies made of ceramics 
in upper layers being cracked due to difference in temperature because all 
the piled layers of the spherical bodies are preheated to relatively high 
temperatures. In normal operation, it is impossible to adjust the 
temperature of all the piled layers of the spherical bodies to the optimum 
temperature for powdering the liquid material in accordance with amounts 
of the material to be treated, contents of components, temperatures and 
the like, so that the spherical bodies are over-heated to waste the 
supplied heating energy or to dry the material insufficiently so as to 
obtain wetted powder which is likely to clog apertures of the support 
plate. 
In order to solve these problems, the electric resistance heating means 
preferably comprises a plurality of electric resistance heaters arranged 
around the vessel and one above the other so as to heat zones of the 
spherical bodies corresponding to the respective heaters in different 
temperatures in a manner that the higher the zone of the spherical bodies, 
the lower is the temperature, thereby controlling the temperature 
distribution in the piled layers of the spherical bodies. 
In order to more positively prevent clogging of the apertures of the 
support plate, the support plate is preferably formed with slits 
concentric to each other about a driving shaft of the stirring means, and 
the driving shaft is provided with pins rotating therewith and extending 
into the slits. 
In a preferred embodiment, the support plate comprises a number of annular 
bodies having different diameters and arranged concentrically and equally 
spaced apart from each other to form a plurality of concentric slits 
therebetween and a plurality of ribs connected to undersides of the 
annular bodies, and the lowermost stirring blade nearest to the support 
plate is provided with pins extending into the slits. 
The slits may have substantially the same widths in vertical direction or 
may be widened downward to facilitate removing the clogged material. The 
pins are preferably fixed to the stirring blade so as to tilt downward in 
the rotating direction. 
In order that the invention may be more clearly understood, preferred 
embodiments will be described, by way of example, with reference to the 
accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1 illustrating a first preferred embodiment of the 
apparatus according to the invention, a liquid material 1 such as 
radioactive waste liquid, enriched waste liquid or slurry of waste resin 
and waste sludge is supplied from a tank 2 into the apparatus 4 by means 
of a pump 3. The apparatus 4 comprises a main body 5 in the form of a 
vessel whose barrel 5a is made of a non-conductive material. In the main 
body 5 is provided a support plate 6 formed with a great number of 
apertures, on which a great number of spherical conductors 7 made of a 
stainless steel or the like are piled. The spherical conductors 7 are 
continuously stirred or agitated by stirring means 11 comprising stirring 
blades 10 fixed to a vertical rotating shaft 9 driven by rotatively 
driving means 8. 
Around the barrel 5a of the main body 5 is arranged an induction heating 
coil 12 which is supplied with high-frequency current from a 
high-frequency generator 13 to directly heat the spherical conductors 7 by 
the electromagnetic induction. 
The liquid material, fed into the apparatus 4 drops onto the piled layers 
of the spherical conductors 7 from liquid supply means 14 having nozzles 
opening above the spherical conductors 7 and flows downward along surfaces 
of the induction heated spherical conductors 7. During such a downward 
flowing, the liquid material 1 is heated by direct heating of the high 
temperature spherical conductors 7 and by heating of high temperature 
atmosphere in spaces between the spherical conductors heated by them to 
transform into powder 15 which falls downward and is removed from a powder 
outlet 16 provided at a bottom of the main body 5. 
In order to prevent the steam in the main body from becoming saturated upon 
the powdering of the material, on the other hand, air for removing 
moisture is forced through an air supply port 17 provided at the lower 
portion into the main body 5 to carry away the evaporated moisture in the 
proximity of the spherical conductors 7 toward an exhaust port 18 provided 
at an upper portion of the main body 5. After flowing out the exhaust port 
18, the moisture condenses in a condenser 19 so as to be collected. The 
air from which the moisture has been removed is fed into a dust collector 
20 in which the dust included in the air is removed. Thereafter, the air 
is exhausted into the atmosphere by an exhaust fan 21. 
Example 
A solution including 20 weight % of Na.sub.2 SO.sub.4 as a main component 
was supplied at a rate of 8 kg/hr onto piled layers of spherical 
conductors 7 which were about 80 lit stainless steel balls having 
diameters of 20 mm in the above apparatus. High frequency current of 180 
Hz was supplied to the coil 12 by means of the high-frequency generator 13 
whose output was 30 kw so as to heat the spherical conductors 7 by the 
induction heating to maintain the maximum temperature in the main body 5 
at approximately 400.degree. C. The rotating shaft 9 was rotated at 3 
revolutions per minute so as to roll the spherical conductors 7 to dry the 
solution. The evaporated moisture was exhausted out of the main body 5 by 
means of the air of 10 Nm.sup.3 /hr. As a result, powder 15 removed from 
the powder outlet 16 was dried up to less than 1% of moisture content. 
Dried powder contained in the exhaust gas from the exhaust port 18 was 
less than 1% of the powder 15. 
This invention is not limited to the above embodiment. For example, the 
spherical conductors 7 may be conductive materials other than the 
stainless steel. The main body 5 may be made of materials other than 
nonconductive materials except of the barrel 5a in opposition to the 
induction heating coil 12. The frequency of the high-frequency current for 
the induction heating may be selected depending upon the specific 
resistance and relative permeability or permittivity of the spherical 
conductors without limiting to 180 Hz. It is preferable to select 
relatively low frequencies as 180-500 Hz. Moreover, the gas for removing 
the evaporated moisture in the barrel 5a may be gases other than the above 
mentioned air. 
Referring to FIG. 2 illustrating a second preferred embodiment of the 
invention in consideration of temperature distribution in piled layers of 
spherical bodies, a drying apparatus comprises a main body 32 in the form 
of a vessel made of a stainless steel or the like in which a support plate 
33 made of a stainless steel or the like is fixed thereto. The support 
plate 33 is formed with a number of apertures or slots enabling the powder 
to pass therethrough, or made of a grate or grid. A great number of 
spherical bodies 34 preferably made of a ceramic material are piled on the 
support plate 33 and continuously stirred or agitated by stirring means 38 
comprising stirring blades 37 fixed to a vertical rotating shaft 36 driven 
by rotatively driving means 35. 
Liquid supply means 39 having nozzles is fixed to the main body 32 above 
the layers of the spherical bodies 34. Around the barrel 32a of the main 
body 32 are provided resistance heaters 40 which are divided from the 
uppermost to the lowermost into first, second and third zones 41, 42 and 
43 connected to a power source through separate current or voltage 
regulators (not shown). The main body 32 further comprises a powder outlet 
44, an air supply port 45 below the support plate 33, and an exhaust port 
46 in the upper portion of the main body 32, to which are connected a 
condenser 47, a dust collector 48 and an exhaust fan 49. To the liquid 
supply means 39 is connected a pump 52 for supplying the liquid material 
51 in a tank 50 into the main body. 
With this arrangement, the liquid material 51 consisting of radioactive 
waste liquids, enriched waste liquids, slurries of sludges, and the like 
is supplied through the liquid supply means 39 onto the spherical bodies 
34 and flows downward along surfaces of the spherical bodies 34 heated by 
the resistance heaters 40. During this downward flowing, the liquid 
material 21 is heated and dried so as to be transformed into powder 53 
which falls through the support plate 33. 
During such an operation, different electric currents or voltages are 
supplied to the first, second and third zones 41-43 of the resistance 
heaters 40 so as to maintain at different heating temperatures the 
spherical bodies 34 in the upper, middle and lower portions of the main 
body 32 corresponding to the first, second and third zones of the heaters. 
These heating temperatures are determined such that the material 23 can be 
dried to the minimum moisture content with minimum electric power. In 
experiments of inventors, good results were generally obtained by 
maintaining the spherical bodies 34 in the upper, middle and lower 
portions of the main body 32 at relatively low temperatures 
100.degree.-200.degree. C., intermediate temperatures 
200.degree.-300.degree. C. and relatively high temperatures 
300.degree.-400.degree. C., respectively. In this case, as the difference 
in temperature between the liquid material 51 and the spherical bodies 34 
in the upper portion of the main body 32 is little, cracks in the 
spherical bodies scarcely occur even if the spherical bodies are of a 
ceramic material. Moreover, as the spherical bodies 34 in the lower 
portion of the main body 32 are at the relatively high teperatures, the 
material 23 is sufficiently dried. As the temperature in the apparatus is 
at the most 400.degree. C., materials of respective parts of the 
apparatus can be easily selected because there are comparatively many 
heat-resistant materials capable of being used with radioactive materials. 
The moisture evaporated as the liquid material 51 is dried is carried 
through the exhaust port 46 along with air sucked through the air supply 
port 45 of the main body 32 for removing the moisture and then condenses 
in the condenser 47 so as to be collected. The air from which the moisture 
has been removed is fed into the dust collector 48 in which the dust 
included in the air is removed. The air is then exhausted into the 
atmosphere by the exhaust fan 49. 
In this embodiment, the heaters 40 for heating the spherical bodies 34 may 
be high-frequency induction heaters as in the first embodiment. In this 
case, the spherical bodies 34 are preferably made of a conductive material 
such as stainless steel, and the barrel 32a of the main body 32 is 
preferably made of a non-conductive material as in the first embodiment. 
Although the heaters 40 have been explained to be constructed by the three 
zones, they may have two zones one above the other or plural zones more 
than three. 
Referring to FIGS. 3-6 illustrating a third embodiment of the invention 
constructed particularly so as to prevent apertures of a support plate 
from clogging, a drying apparatus 61 comprises a main body 62 in the form 
of a vessel made of a stainless steel or the like in which a support plate 
63 made of a stainless steel or the like is fixed thereto. The support 
plate 63 comprises a number of annular bodies 64 having different 
diameters and arranged concentrically and equally spaced apart from each 
other to form a plurality of concentric slits 66 therebetween and a 
plurality of ribs 65 connected to undersides of the annular bodies 64 
(FIG. 6). In a center of the support plate 63 is provided a bearing 67 in 
which is loosely fitted a lower end of a vertical driving shaft 69 driven 
by rotatively driving means 68. To the driving shaft 69 are fixed a 
plurality of stirring blades 70 made of a stainless steel each in the form 
of a bar having a triangular cross-section including an upper surface 71 
downward oblique in its rotating direction. The lowermost stirring blade 
70 nearest to the support plate 63 is provided with pins 72 fixed thereto 
as shown in FIGS. 4 and 5. Each pin 72 has a cross-section smaller than 
the width of the slit 66 so as to be inserted between the slits 66 and has 
its lower end stopping short of an upper surface of the ribs 65. 
A great number of spherical bodies 73 preferably made of a ceramic material 
are piled on the support plate 63. Liquid supply means 74 having nozzles 
is provided in an upper portion of the main body 62 so as to open the 
nozzles above the spherical bodies 73. The main body 62 comprises a powder 
outlet 75 at a lower end of the main body 62, an air supply port 76 
provided in the main body below the support plate 63 and connected to hot 
air producing means 77, and an exhaust port 78 provided in the upper 
portion of the main body 62 and connected to a dust collector 79 and an 
exhaust fan 80. A pump 83 is connected to the liquid supply means 74 for 
supplying into the main body a liquid material 82 in a tank 81. 
With this arrangement, the liquid material 82 consisting of radioactive 
waste liquids, enriched waste liquids, slurries of sludges and the like is 
supplied through the liquid supply means 74 by means of the pump 83 onto 
the piled layers of the spherical bodies 73. The liquid material flows 
downward along surfaces of the spherical bodies 73 heated by hot air at 
temperatures more than 200.degree. C. from the hot air producing means 77. 
During this downward flowing, the liquid material is dried by the surfaces 
of the spherical bodies and the hot air to be converted into powder 84 
further flowing downward. 
In the event that the liquid material 82 is slurry or the like, the powder 
84 often passes through the support plate 63 under insufficiently dried 
condition. In this case, there is a tendency of the powder 84 to stick and 
accumulate in the slits 66 of the support plate 63. However, the pins 72 
are always driven by the driving shaft 69 to rotatively move in the slits 
66 so as to scrape off the accumulated powder in the slots, thereby 
preventing the clogging of the slots. If the spherical bodies 73 are 
cracked or broken, the pins 72 prevent fragments of the broken spherical 
bodies from clogging the slits 66 in the same manner as above described so 
as to drop the small fragments through the slits 66. The large fragments 
incapable of passing through the slits still move on the support plate 63 
to serve to dry the material together with the other sound spherical 
bodies 73. On the other hand, the hot air including the evaporated 
moisture flows through the exhaust port 78 into the dust collector 79 in 
which the dust included in the hot air is removed. The air is then 
exhausted into the atmosphere by the exhaust fan 80. 
In the above embodiment, the slits 66 have the same width in a vertical 
direction. As shown in FIG. 7, however, a support plate 63' is made by 
downward tapered annular bodies 64' to form downward widened slits 66' so 
as to more facilitate the removing the sticked powder from sidewalls of 
the slits 66', thereby improving the clogging preventing effect. Moreover, 
it is preferable to fix the pins 72 to the stirring blade 70 so as to tilt 
downward in the rotating direction in order to securely scoop and remove 
the powder 84 and fragments of the spherical bodies 73 firmly fixed to the 
sidewalls of the slits 66. Furthermore, the pins 72 may directly extend 
from undersides of the stirring blade 70. Moreover, a bar for carrying the 
pin 72 may be provided on the driving shaft 69 without providing pins on 
the lowermost stirring blade. 
In the above embodiment, moreover, as the upper surface 71 of the stirring 
blades 70 are downward tilted in their rotating directions, the resistance 
of the spherical bodies 73 against the blades becomes small to reduce the 
power of the driving means 68 for driving the blades, and the spherical 
bodies 73 and also the fragments thereof are easily scooped by the tilted 
upper surfaces of the stirring blades 70, thereby preventing the fragments 
from jamming between the stirring blade 70 and the annular bodies 64. 
Other shapes of the stirring blades may of course be used. 
FIG. 9 illustrates a further embodiment of the invention, which compises 
pins 72 for preventing the clogging of a support plate 63 and which is 
similar to the third embodiment with exception that spherical bodies 90 
are made of a stainless steel and a barrel 62a of a main body 62 is made 
of a non-conductive material around which is arranged an induction heating 
coil 91 supplied with high-frequency current from a high-frequency 
generator 92 to heat the spherical bodies 90 by the induction heating as 
in the first embodiment. 
As mentioned in the first embodiment, the apparatus according to the fourth 
embodiment operates with high thermal efficiency because of the induction 
heating capable of directly heating the spherical bodies 90, thereby 
obtaining a great treating capacity with a relatively small apparatus. 
As in the above embodiments, the moisture evaporated as the liquid material 
82 is dried is carried through an exhaust port 94 along with air sucked 
through an air supply port 93 at the lower portion of the main body 62 for 
removing the moisture and then condenses in a condenser 95 so as to be 
collected. The air from which the moisture has been removed is fed into 
the dust collector 96 in which the dust included in the air is removed. 
The air is then exhausted into the atmosphere by the exhaust fan 97. 
In the above third and fourth embodiment, resistance heaters may be used 
for heating the piled layers of the spherical bodies instead of the hot 
air producing means 77 and the high-frequency heater 91. These embodiments 
can be applied to apparatuses for drying or powdering various kinds of 
liquid materials other than the radioactive wastes. 
As can be seen from the above description, the apparatus for drying liquid 
materials is simple in construction and does not include rotating and 
sliding parts at high speeds, so that the apparatus does not fail and is 
easy to maintain. Moreover, the spherical conductors are generally made of 
a metal so as to permit a low temperature liquid material to contact the 
spherical conductors or bodies without any cracks due to difference in 
temperature. The spherical conductors or bodies slide and abut against 
each other and other parts of the apparatus to prevent the powder material 
from sticking and growing on the parts such as inner surfaces of the main 
body, the stirring blades, and spherical conductors or bodies themselves, 
thereby enabling the apparatus to continuously operate for a long period 
of time. Moreover, as the drying surface formed by a great number of the 
spherical conductors or bodies is remarkably wide and the spherical 
conductors or bodies are directly heated by the induction heating, the 
apparatus according to the invention operates with a high thermal 
efficiency and has a great treating capacity although it is of relatively 
small size. 
This invention can be applied for the purpose of treating or drying various 
kinds of liquid materials to be powdered. In an application of this 
invention to the treatment of flowable radioactive wastes produced in 
plants for handling radioactive materials such as nuclear power stations, 
it is possible to treat the wastes by the apparatus fulfilling the first 
requirement of less failure and easy maintenance as a radioactive waste 
treating apparatus, thereby decreasing the risk of exposure to radioactive 
materials. Moreover, as the heating temperature can be raised in this 
invention, the radioactive waste liquids can be directly treated to be 
powdered prior to being enriched. In treating radioactive waste liquids 
consisting mainly of boric acid and sodium hydroxide produced in nuclear 
power stations employing pressurized water reactors, the liquids can be 
treated at temperatures in the widest temperature range determined by 
percentages of the components for drying and powdering the liquids, so 
that the percentages of the components can be freely selected in a wide 
range. 
In accordance with the second embodiment of the invention, the spherical 
bodies piled on the support plate are heated in a desired distribution of 
temperature from the upper to lower portion of the main body corresponding 
to the respective zones of the heaters so as to prevent the spherical 
bodies from being cracked due to rapid cooling and to obtain the powder 
including the minimum moisture by supplying proper power input, thereby 
preventing the apertures or opening of the support plate from being 
clogged. When the apparatus is used for treating radioactive waste, 
particularly, it can continuously operate for a long period of time 
without requiring any troublesome maintenance, thereby reducing the risk 
of exposure to radioactivity. 
In accordance with the third and fourth embodiments of the invention, there 
are provided the pins revolving in the concentric slits provided in the 
support plate to prevent the slits from being clogged, thereby enabling 
the apparatus to operate continuously for long periods of time so as to 
make easy the maintenance of the apparatus. Particularly, it can be 
effectively used for a radioactive waste treating apparatus so as to 
decrease the risk of exposure to radioactive materials. 
It is further understood by those skilled in the art that the foregoing 
description is that of preferred embodiments of the disclosed apparatuses 
and that various changes and modifications may be made in the invention 
without departing from the spirit and scope thereof.