Method and drying plant for drying a material in batch operation

Such a drying plant has drying surfaces (4) superposed in a chamber (1) and extending over the depth of the chamber (1). The drying surfaces (4) are provided with heating plates (3). The upper run of an endless conveyor belt running on rollers (6,7) is guided over the drying surfaces. The material to be dried is applied by a dosing device via a pipe (9) having branches (10) to the moving belts (5) uniformly over the width until the entire drying surface (4) is covered. The belts (5) are then stopped and the dosing operation is completed. The drying operation is then carried out on the drying surface (4) while the belts (5) are stationary. The belts (5) are then moved in the opposite direction, so that the dried material is thrown off via the rollers (7) and discharged through a discharge opening (13) and a charging valve (14). Thus, the drying operation is carried out under optimum conditions known for drying cabinets. However, the operations of feeding and discharging the material are simplified as compared with conventional drying cabinets and can also be automated.

The present invention relates to a method for drying a material in batch 
operation in a closed drying space with the supply of heat. After putting 
the material into the drying space it is dried on at least one stationary 
drying surface. The present invention also relates to a drying plant for 
carrying out said method. 
The drying of materials, i.e. the removal of moisture from all kinds of 
materials, is a frequently applied method of process engineering by means 
of which the materials are rendered durable or put into a state suitable 
for shipments or further processing. Among the methods used the method 
with artificial heat supply is a frequently used method. In the direct 
drying process the material to be dried is directly exposed to hot gases, 
for example, combustion gases, while in the indirect drying process, which 
is used primarily for sensistive material the drying is brought about by 
means of air, water, or the like, heated by heat exchangers. 
The present invention relates to an indirect drying process which is 
carried out with a suitable drying plant. A corresponding drying plant is 
known in two embodiments. In one embodiment the drying plant is a drying 
cabinet which is a closed chamber. Heating plates which are heated by a 
heat carrier are disposed in several layers on the inside of said drying 
cabinet. The material to be dried is distributed over trays e.g. manually 
or also with a feeding device. The trays are then placed in the drying 
cabinet. The batch put into the drying cabinet in this manner is dried 
while heat is supplied. The internal pressure can be reduced to a vacuum 
and adapted to the dry process. When the drying is completed the batch 
distributed over the trays is removed from the drying cabinet, which is 
then prepared for drying the next batch. In the drying cabinet the drying 
process can be controlled in an ideal manner by adjusting the temperature 
and the pressure. Furthermore, the capital costs are relatively low. 
However, the fact that an automatic operation is practically impossible 
and that, therefore, a great deal of attendance is required is a 
disadvantage. The expenditure for keeping the drying cabinet clean also is 
high. However, any kind of material, i.e., materials ranging from the 
fluid to the lumpy state, can be dried. 
A further known drying plant is the belt-type dryer, which can also be 
designed as a vacuum belt dryer. As in the drying cabinet a 
pressure-resistant chamber is used. Heating plates are disposed in said 
heating chamber in several superposed layers and in several 
series-connected zones, usually four or more zones. The heating plates are 
located below the upper run of endless belts, which are guided over a 
friction roller and a guide roller and can be driven by a motor. The 
material to be dried is guided into the inside of the chamber by means of 
a dosing device and uniformly distributed over the belts. Corresponding to 
the motion of the belts, the material is conveyed from the first zone to 
the zones therebehind. The temperature conditions can be adjusted 
differently in each zone so that the material is heated and dried in 
stages. At the guide roller of the rearmost zone the dried product is 
exposed outwardly and can be removed by the belt, for example, by pulling 
it off. However, the pressure conditions in the chamber, for example, 
maintaining a vacuum, are identical for all the drying zones of the 
belt-type dryer. The advantage of the belt-type dryer lies in that it has 
a greater capacity than a drying cabinet operated in batches, that it 
permits continuous operation and that it can thus be operated 
automatically with justifiable expenditure. Furthermore, the operating 
costs and the expenditure for hygiene or cleaning are low. However, the 
fact that not just any material, particularly no thinly liquid or lumpy 
material, but only pumpable and fluid materials can be dried in a 
belt-type dryer is a disadvantage. 
The problem of the invention is to so develop the aforementioned drying 
method that it combines the advantages of both the drying cabinet and the 
belt-type dryer. This problem is solved in that the material introduced 
into the drying space before the drying operation is charged manually or 
mechanically onto the drying surface and distributed thereon by a 
conveying means. 
According to the invention this method is performed by a drying plant 20, 
in which the drying surface is formed by a conveyor belt which is 
stationary during the drying operation.

The drying plant shown in the FIGS. 1 and 2 has a chamber 1, which is a 
pressure-and vacuum-resistant tray. At least on one front end, the chamber 
1 has a cover 2, which can be removed when required and thus provides 
access to the chamber 1. 
Four heating plates 3 are superposed inside the chamber 1, but the number 
of heating plates 3 can be greater or smaller. With their arrangement in a 
single zone this corresponds to the arrangement in a drying cabinet 
wherein stationary superposed drying surfaces 4 are provided. On said 
surfaces the material to be dried is kept in suitable receptacles which 
are prepared and introduced as charges prior to the drying process and can 
be removed as such from the drying cabinet after the drying process. 
It is important that the expensive batchwise loading and emptying of the 
drying cabinet, which cannot be avoided can be simplified and automated by 
the use of conveying devices. 
According to the embodiments shown in the FIGS. 1 and 2 these conveying 
devices are movable belts 5 which also form the stationary drying surfaces 
4. The belts 5 are endless belts and are guided via a driving pulley 6 and 
a guide roll 7. The two rolls 6 and 7 are supported in a frame fixed in 
the chamber 1 or they are supported in the chamber wall in a manner which 
is not shown. The driving pulleys 6 may be driven in various ways. Either 
all the driving pulleys are driven simultaneously or only a single driving 
pulley 6 is driven consecutively so that the belts 5 are moved 
consecutively. However, during the drying process all the belts 5 are 
stationary. For the use of the drying cabinet according to FIG. 1 for 
drying a pumpable material said material is fed by means of a conveying 
feeding device symbolized by the arrow 8 through a pipe 9 into the 
interior of the chamber 1. This feeding conveying device can be rigidly 
installed or it can be mobile and driven up to the belts through the open 
dryer. Branches 10 extend from the pipe 9 to the individual belts 5 or the 
belts are successively charged consecutively. Only one nozzle charging the 
belts consecutively is used. The belts 5 are thus put into motion so that 
the material emerging from the orifices of the branches 10 is distributed 
over both the width of the belts 5 and the length of the drying surface 4. 
When the entire drying surface 4 is covered with the material the belts 5 
are stopped. The drying operation is now the same as that in a drying 
cabinet while temperature and pressure are adjusted corresponding to the 
material to be dried. The feeding device of the belts 5 is marked by the 
arrow 11. When the drying operation is completed the belts are moved in 
the direction of the arrow 12 or 11 opposed to the direction of motion or 
in the same direction of motion as in the charging operation of the drying 
surface. The dried material is then thrown off and discharged from the 
drying chamber through a discharge opening 13. Depending on the system 
said discharge opening is disposed on the charging side or on the side 
opposed thereto and is provided with a charging valve 14. As an 
alternative a suitable retractable discharge vessel can be disposed within 
the vacuum space. The pipe 9 having the branches 10 can thus be raised and 
used for breaking the dried material into pieces so that the dried 
material can be thrown off without obstruction. 
A new batch can now be fed via the pipe 9 having the branches 10 into the 
drying chamber and the belts 5 are moved in the direction of the arrow 11 
until the entire drying surface is loaded, whereupon the drying operation 
commences with the belts at a stand still. 
In the embodiment according to FIG. 2 a fluid material, which is fed 
through a diagrammatically represented bucket wheel 15 into chamber 1, is 
processed therein. This dosing device can be installed rigidly or movable 
analogously to the feeding device for liquid products. Unlike in the 
embodiment according to FIG. 1 heating plates 3 and drying surfaces 4 
formed by belts 5 are alternately staggered in this embodiment. If the 
belts move alternately in opposite directions corresponding to arrows 16, 
17 the fluid material charged onto the uppermost belt 5 is placed on the 
beginning of the underlying belt 5, from where it in turn passes onto the 
next underlying belt 5 and so on until the material reaches the end of the 
lowermost belt 5. The belts 5 are then stopped and the drying process 
starts on the stationary drying surfaces. 
For the discharge of the dried material from the drying chamber according 
to FIG. 2, the belts are moved in the same direction of arrows 16, 17 so 
that the dried material can be discharged, for example, through discharge 
opening 13 and charging valve 14. Here again the charging valve can be 
replaced e.g. by an extendable discharge vessel installed within the 
vacuum space. Immediately on completing the discharge, the drying plant is 
ready for drying the next batch. In the drying chamber according to FIG. 
2, like that according to FIG. 1, the belts are moved only until the 
loading of the drying surface with material to be dried is completed or 
until the dried material is completely discharged after the drying 
operation. 
A further advantage of the drying chamber according to FIGS. 1 and 2 is 
that apart from automatic charging by random devices, manual charging is 
also possible for materials which are particularly difficult to treat, for 
which purpose cover 2 can be opened. Depending on the material to be 
charged, one belt 5 after another can be moved and charged in the drying 
chamber according to FIG. 1. However, all the belts 5 can be moved and 
charged simultaneously. In the drying chamber according to FIG. 2 the 
charging operation can be carried out in the same manner, but in most 
cases the charging operation is carried out with the belts 5 running in 
opposite directions from top to bottom. 
Pipe connections 18, 19 for guiding in and out the heat carrier for the 
heating plates 3 are provided on chamber 1. A further pipe connection 20 
connects a vacuum producer, for example, jet pumps or liquid seal pumps. 
Steel or plastics, for example, PTFE, can be used as the material for the 
conveyor belts 5. With the drying plants described--as in the known drying 
cabinet--particularly any material can be dried with the exception of very 
thinly liquid materials.