JP4278053B2 - Drying apparatus and drying method using pressure vessel - Google Patents

Description

  The present invention relates to a drying apparatus and a drying method using a pressure vessel.

  As a drying apparatus using a pressure vessel, there has been one disclosed in JP-A-6-50662 (see Patent Document 1). In this apparatus, the superheated steam whose superheat is lowered in the pressure vessel is simply discarded while supplying the superheated steam to the pressure vessel for drying.

Moreover, as an apparatus which circulates superheated steam and performs drying, there existed what was disclosed by Unexamined-Japanese-Patent No. 2000-146438 (refer patent document 2). In this drying apparatus, a steam circulation operation is performed in which a part of the steam in the drying chamber is extracted and heated, and is supplied again as superheated steam into the drying chamber.
Japanese Unexamined Patent Publication No. 6-50662 JP 2000-146438 A

  However, the conventional drying apparatus described above has the following problems. First, in the apparatus described in Patent Document 1, steam having a reduced superheat degree with drying is discharged out of the pressure vessel, and the insufficient amount of superheated steam is newly generated and supplied to the pressure vessel. Therefore, there is a problem that energy loss is large and operation cost increases.

  Moreover, in the apparatus described in Patent Document 2, although superheated steam can be reused, it was simply a circulation mode. That is, it is operating under normal pressure as in a general mode, and pressure is not controlled. In addition, when the circulation is performed, the superheated steam not only consumes heat energy in the drying process in the pressure vessel but also causes heat loss in the circulation path. For this reason, superheated steam may be liquefied in the circulation path, but once it is liquefied, in order to vaporize again, very large latent heat more than sensible heat is required. Therefore, there is a problem that energy loss is large and operation cost increases.

  The present invention has been made in view of such problems, and a pressure vessel that can lower the boiling point from atmospheric pressure and reduce the operating cost by maintaining the dry atmosphere in a desired state, particularly a negative pressure state. An object of the present invention is to provide a drying apparatus using the above.

  In order to solve the above-described problems, a drying apparatus according to the present invention includes a pressure vessel that accommodates an object to be dried, a drying medium circulation path that circulates a drying medium with respect to the pressure vessel, and the drying medium. A heating means for heating and a negative pressure maintaining means for maintaining the inside of the pressure vessel at a negative pressure are provided.

  In this case, preferably, the negative pressure maintaining means includes a pressure detecting means and a pressure adjusting means that operates according to the detection result and discards the drying medium from the pressure vessel.

  Preferably, the drying apparatus further includes a circulation flow rate adjusting means for maintaining the circulation flow rate of the drying medium so that the inlet temperature of the heating means is equal to or higher than the boiling point.

  The circulation flow rate adjusting means can be configured to include a temperature detection means and a circulation device that operates according to the detection result.

  In order to solve the problem, a drying method according to the present invention includes a pressure vessel for storing an object to be dried, a drying medium circulation path for circulating a drying medium with respect to the pressure vessel, and a negative pressure in the pressure vessel. And a negative pressure maintaining means for maintaining the pressure in the pressure vessel using the negative pressure maintaining means while circulating the drying medium through the drying medium circulation path. A drying method that maintains a negative pressure.

  According to the drying apparatus and the drying method of the present invention, when the drying medium is circulated while maintaining a constant negative pressure state, the increase in boiling point can be suppressed and the drying medium can be reused. The heating energy of the medium can be reduced. Also, when the circulation flow rate of the drying medium is maintained so that the inlet temperature of the heating means is equal to or higher than the boiling point, the drying medium can be prevented from being liquefied in the circulation path. Although it is possible, it is not forced to operate with a large energy loss that requires latent heat.

  The other features of the present invention and the operational effects thereof will be described in more detail with reference to the accompanying drawings.

  Embodiments according to the present invention will be described below with reference to the accompanying drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

  The drying apparatus 1 according to the first embodiment of the present invention includes a pressure vessel 3, a circulation pipe 5 as a drying medium circulation path, a steam superheater 7 as a heating means, and pressure adjusting means (negative pressure maintaining). Means) 9 and a circulation flow rate adjusting means 11. The pressure vessel 3 is a vessel that can accommodate an object to be dried 13 therein. A dry bulb thermometer 15, a wet bulb thermometer 17, and a pressure gauge 19 are provided in the pressure vessel 3.

  The circulation pipe 5 is constituted by a pipe having one end connected to the supply port of the pressure vessel 3 and the other end connected to the discharge port of the pressure vessel 3. A steam superheater 7 is disposed in the upstream portion of the pressure vessel 3 in the circulation pipe 5. On the other hand, a circulation flow rate adjusting means 11 is disposed in the downstream portion of the pressure vessel 3 in the circulation pipe 5. The circulation flow rate adjusting means 11 includes a circulation device 21 and a circulation valve 23. In the present embodiment, a roots blower is used as the circulation device 21, but the present invention is not limited to this, and various blowers, compressors, pumps, and the like can be appropriately employed.

  A branch portion 25 is provided upstream of the steam superheater 7 in the circulation pipe 5, and a steam supply pipe 27 extends from the branch portion 25 to the outside of the drying medium circulation path. The steam supply pipe 27 is provided with a boiler 29 and a saturated steam valve 31.

  A steam superheater inlet thermometer 16 and a steam superheater inlet pressure gauge 18 are provided between the branch portion 25 and the steam superheater 7.

  A branch portion 33 is provided at the downstream portion of the pressure vessel 3 in the circulation pipe 5, and the pressure adjustment pipe 35 extends from the branch portion 33 to the outside of the drying medium circulation path. The pressure adjusting pipe 35 is provided with pressure adjusting means 9. The pressure adjusting means 9 includes a decompression pump 37 and a waste valve 39.

  Next, the operation of the drying apparatus and the drying method according to the present embodiment having such a configuration will be described. In the present embodiment, superheated steam is used as a drying medium, and the dry atmosphere in the pressure vessel 3 has a dry bulb temperature of 120 ° C., a wet bulb temperature of 90 ° C., and a pressure of −0.3 atm (negative pressure). Target set value. The inside of the pressure vessel 3 is controlled by the dry bulb temperature and the wet bulb temperature. The operation of the drying apparatus 1 can be divided into a drying circulation operation and a purge operation.

  After the wood is accommodated in the pressure vessel 3 as the material to be dried 13, the drying circulation operation of the drying device 1 is started. By opening the circulation valve 23 and operating the circulation device 21, the superheated steam in the pressure vessel 3 is sucked into the circulation pipe 5 and flows into the steam superheater 7 downstream of the branch portion 25. The superheated steam is heated to an appropriate temperature in the steam superheater 7, supplied again into the pressure vessel 3, and dried. The steam superheater 7 adjusts the amount of superheat based on the result detected by the dry bulb thermometer 15 so that the dry bulb temperature in the pressure vessel 3 becomes a target installation value. In this way, the material to be dried 13 is dried in the pressure vessel 3 while circulating the superheated steam.

  In the present embodiment, the following operation is performed to reduce the operating cost. First, as the drying of the object to be dried 13 proceeds, the moisture contained in the object to be dried 13 evaporates and is newly released into the pressure vessel 3 as a vapor. Due to the excessive steam state, the pressure (wet bulb temperature) in the pressure vessel 3 increases. When the pressure (wet bulb temperature) rises in the pressure vessel 3, the boiling point rises accordingly. However, if the temperature of the superheated steam in the pressure vessel 3 is heated to the boiling point after the increase, there is a problem that the operation cost is increased accordingly.

  Therefore, in the present embodiment, the above problem is avoided by the following operation. That is, when the wet bulb temperature rises due to excessive steam, the discharge valve 39 is opened and the decompression pump 37 is activated in order to keep the wet bulb temperature at a constant value. As a result, excess steam is sucked out and discharged out of the circulation system, and the pressure and wet bulb temperature are restored to the original target set values. When it is confirmed by the wet bulb thermometer 17 that the wet bulb temperature has returned to the target set value, the discharge valve 39 is closed and the decompression pump 37 is stopped. That is, the wet bulb thermometer 17 functions as a pressure detection unit, and the pressure detection unit and the pressure adjustment unit 9 function as a negative pressure maintaining unit. Thus, by maintaining the inside of the pressure vessel 3 at a constant negative pressure, it is possible to continuously perform a drying operation with a low boiling point.

  Further, the superheated steam not only consumes heat energy in the drying process in the pressure vessel 3, but also causes heat loss in the circulation process of the circulation pipe 5. For this reason, although the superheated steam may be liquefied in the circulation pipe 5, once it is liquefied, in order to vaporize again, very large latent heat more than sensible heat is required. Therefore, there is a problem that energy loss is large and operation cost increases.

Therefore, in the present embodiment, the operation of the circulation device 21 is controlled so that the temperature detected by the steam superheater inlet thermometer 16 does not fall below a predetermined threshold. Specifically, the boiling point of superheated steam at the pressure detected by the steam superheater inlet pressure gauge 18 is set as a threshold value, and the temperature detected by the steam superheater inlet thermometer 16 is set so as not to fall below the threshold value. Maintain the mass flow (m ³ / min). Thus, the superheated steam is not liquefied even in a state immediately before heating by the steam superheater 7 whose temperature can be lowered most. Therefore, an increase in energy cost can be suppressed without causing latent heat.

  In addition, when a leak occurs in the circulation system during the dry circulation operation in the negative pressure state, the pressure in the pressure vessel 3 may gradually increase due to the inflow of air. When the pressure in the pressure vessel 3 rises, the boiling point also rises as described above, which leads to an increase in operating cost accompanying an increase in the amount of superheat in the steam superheater 7.

  Therefore, in the present embodiment, a purge operation for purging inflow air is performed. First, in order to determine the increase in the air ratio due to leakage, the difference between the theoretical wet bulb temperature converted from the detected value of the pressure gauge 19 and the actually measured wet bulb temperature detected by the wet bulb thermometer 17 is calculated. When the difference exceeds a specified value, the circulation device 21 is stopped and the circulation valve 23 is closed. Instead, the saturated steam valve 31 and the discharge valve 39 are opened and the decompression pump 37 is started.

  As a result, the atmosphere in the pressure vessel 3 is discarded through the pressure adjusting pipe 35, and the steam produced by the boiler 29 is converted into superheated steam in the steam superheater 7 and supplied into the pressure vessel 3. After performing the purge operation for several minutes until the inside of the pressure vessel 3 is replaced with newly supplied superheated steam, the operation is returned to the dry circulation operation.

  As described above, according to the present embodiment, since the drying medium is circulated while maintaining a constant negative pressure, the rise in boiling point can be suppressed and the drying medium can be reused. The heating energy of the medium can be reduced. In addition, since it is possible to prevent the drying medium from being liquefied in the circulation path, it is possible to recycle the drying medium, but to operate with a large energy loss that requires latent heat. It is never done.

  In this embodiment, the pressure adjusting means 9 is provided to be branched from the pressure vessel 3 and the circulation valve 23 in the circulation pipe 5, but instead, as shown in FIG. Alternatively, the pressure adjustment pipe 41 may be extended directly from the pressure vessel 3 and the pressure adjustment means 9 may be installed on the pressure adjustment pipe 41.

  Next, a drying apparatus and a drying method according to the second embodiment of the present invention will be described with reference to FIG. The drying apparatus 101 according to the present embodiment includes a pressure / circulation flow rate adjusting unit 110 that doubles as the function of the pressure adjustment unit 9 and the function of the circulation flow rate adjustment unit 11 in the embodiment of FIGS. 1 and 2. The pressure / circulation flow rate adjusting means 110 includes a pressure reducing pump 137, a circulation valve 123, and a waste valve 139.

  The decompression pump 137 is disposed between the pressure vessel 3 and the branch portion 33 in the circulation pipe 5. The circulation valve 123 is disposed downstream of the branch portion 33 in the circulation pipe 5. Further, the disposal valve 139 is disposed in the pressure adjustment pipe 35.

  Also in the drying apparatus 101 configured as described above, the circulation valve 123 is opened and the discharge valve 139 is closed, and the decompression pump 137 is operated to circulate the superheated steam in the circulation pipe 5 and in the pressure vessel 3. Drying can be performed. At that time, if the moisture contained in the material to be dried 13 is released as steam and an excessive steam state occurs, the excess steam is removed from the circulation system by opening the discharge valve 139 in the circulation operation state. It is aspirated and discarded. Therefore, by maintaining the inside of the pressure vessel 3 at a constant negative pressure, a drying operation with a low boiling point can be performed, and the amount of superheat in the steam superheater 7 can be suppressed and the operation cost can be reduced.

  Further, the operation of the decompression pump 137 is controlled so that the temperature detected by the steam superheater inlet thermometer 16 does not fall below a predetermined threshold. Thus, the superheated steam is not liquefied even in a state immediately before heating by the steam superheater 7 whose temperature can be lowered most. Therefore, an increase in energy cost can be suppressed without causing latent heat.

  Further, when a leak occurs in the circulation system during the dry circulation operation in the negative pressure state, a purge operation is performed to purge the inflowing air. That is, the circulation valve 123 is closed, the saturated steam valve 31 and the discharge valve 139 are opened, and the decompression pump 137 is started. As a result, when the steam produced by the boiler 29 is converted into superheated steam in the steam superheater 7 and supplied into the pressure vessel 3, and the inside of the pressure vessel 3 is replaced by newly supplied superheated steam, the drying circulation operation is started. Will be restored.

  Also in the present embodiment described above, since the drying medium is circulated while maintaining a constant negative pressure, the increase in boiling point can be suppressed and the drying medium can be reused. Energy can be reduced. Further, since it is possible to prevent the drying medium from being liquefied in the circulation path, it is possible to reuse the drying medium, but it is forced to operate with a large energy loss that requires latent heat. There is nothing.

  Next, a drying apparatus and a drying method according to the third embodiment of the present invention will be described with reference to FIG. The drying apparatus 201 according to the present embodiment has a steam cooler 243 as pressure adjusting means (negative pressure maintaining means) 209 between the pressure vessel 3 and the branching portion 33 in the circulation pipe 5 in the embodiment of FIG. Is provided.

  Also in the drying apparatus 201 configured as described above, the circulation valve 23 is opened and the discharge valve 39 is closed, and the circulation apparatus 21 is operated so that superheated steam is circulated in the circulation pipe 5 in the pressure vessel 3. Drying can be performed. At that time, when the moisture contained in the material to be dried 13 is released as steam and an excessive steam state occurs, the steam cooler 243 is operated in the circulation operation state, that is, the decompression pump 37 is operated. However, excess steam is drained out of the circulation system as drain 245.

  Specifically, in the dry circulation operation, when the wet bulb temperature in the pressure vessel 3 detected by the wet bulb thermometer 17 exceeds a predetermined threshold value, the water amount of the steam cooler 243 is manipulated, Steam is liquefied and drained out of the circulation system as drain 245. Therefore, by maintaining the inside of the pressure vessel 3 at a constant negative pressure, a drying operation with a low boiling point can be performed, and the amount of superheat in the steam superheater 7 can be suppressed and the operation cost can be reduced.

  Further, the operation of the decompression pump 37 is controlled so that the temperature detected by the steam superheater inlet thermometer 16 does not fall below a predetermined threshold. Thus, the superheated steam is not liquefied even in a state immediately before heating by the steam superheater 7 whose temperature can be lowered most. Therefore, an increase in energy cost can be suppressed without causing latent heat.

  Further, when a leak occurs in the circulation system during the dry circulation operation in the negative pressure state, a purge operation is performed to purge the inflowing air. That is, the circulation valve 23 is closed, the saturated steam valve 31 and the discharge valve 39 are opened, and the decompression pump 37 is started. As a result, when the steam produced by the boiler 29 is converted into superheated steam in the steam superheater 7 and supplied into the pressure vessel 3, and the inside of the pressure vessel 3 is replaced by newly supplied superheated steam, the drying circulation operation is started. Will be restored.

  Also in the present embodiment described above, since the drying medium is circulated while maintaining a constant negative pressure, the rise in boiling point can be suppressed and the drying medium can be reused, and the heating energy of the drying medium can be reused. Can be reduced. Further, since it is possible to prevent the drying medium from being liquefied in the circulation path, it is possible to reuse the drying medium, but it is forced to operate with a large energy loss that requires latent heat. There is nothing.

  Although the contents of the present invention have been specifically described with reference to the preferred embodiments, various modifications can be made by those skilled in the art based on the basic technical idea and teachings of the present invention. It is self-explanatory.

  First, in the embodiment described above, superheated steam is used as the drying medium, but the present invention is not limited to this, and high-temperature air such as hot air may be used as the drying medium. In that case, the boiler and its associated equipment can be omitted.

  Further, in the above embodiment, the wet bulb thermometer is used as the pressure detecting means constituting the pressure adjusting means (negative pressure maintaining means), but the present invention is not limited to this, and the pressure gauge itself. Can also be used.

  Moreover, it may replace with the aspect which arrange | positions a circulation valve and a waste valve separately, and the aspect which arrange | positions the three-way valve which combines these valves in the branch part 33 may be sufficient.

  In addition, the present invention provides a circulating flow rate at which the inlet temperature of the heating unit is equal to or higher than the boiling point in consideration of the physical properties of the material to be dried and the characteristics of the circulating drying device even in an installation without a temperature detection type circulating flow rate adjusting unit. It is also possible to calculate and to operate with the fixed value.

It is a figure which shows the structure of the drying apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the structure which provided the pressure adjustment means in the 1st Embodiment independently from the circulation pipe. It is a figure which shows the structure of the drying apparatus which concerns on the 2nd Embodiment of this invention. It is a figure which shows the structure of the drying apparatus which concerns on the 3rd Embodiment of this invention.

Explanation of symbols

1, 101, 201 Drying device 3 Pressure vessel 5 Circulation pipe (Drying medium circulation path)
7 Steam superheater (heating means)
9 Pressure adjustment means 13 Dried object 16 Steam superheater inlet thermometer (circulation flow rate adjustment means, temperature detection means)
17 Wet bulb thermometer (negative pressure maintenance means, pressure detection means)
21 Circulator (Circulating flow rate adjusting means)
37 Pressure reducing pump (negative pressure maintaining means)
137 Pressure reducing pump (negative pressure maintaining means, circulating flow rate adjusting means)

Claims (1)

A drying medium circulation path (5) for circulating superheated steam;
A pressure vessel (3) provided in the drying medium circulation path (5) and containing an object to be dried;
A heating means (7) provided in the drying medium circulation path (5) for heating the superheated steam;
Negative pressure maintaining means (17, 9) for maintaining the inside of the pressure vessel (3) at a negative pressure;
A circulation flow rate adjusting means (11);
An inlet thermometer (16) and an inlet pressure gauge (18) provided at the inlet of the heating means (7),
In the pressure vessel (3), a wet bulb thermometer (17) and a pressure gauge (19) are provided,
The circulating flow rate adjusting means (11) has an inlet temperature of the heating means (7) measured by the inlet thermometer (16) equal to or higher than a boiling point of superheated steam at a pressure detected by the inlet pressure gauge (18). Maintaining the circulating flow rate of the superheated steam so that
The negative pressure maintaining means (17,9), the wet bulb thermometer (17), and Nde including a pressure adjusting means (9) for Hai棄the superheated steam from the pressure vessel (3),
When the actually measured wet bulb temperature in the wet bulb thermometer (17) rises above the target set value, the pressure adjusting means (9) maintains the circulating operation state until the measured wet bulb temperature returns to the target set value. Drain the superheated steam in the container (3) ,
A difference is calculated by subtracting the actual wet bulb temperature detected by the wet bulb thermometer (17) from the theoretical wet bulb temperature converted from the detected value of the pressure gauge (19), and the difference is equal to or greater than a specified value. In this case, the circulation flow rate adjusting means (11) stops the circulation in the drying medium circulation path (5), and the pressure adjusting means (9) exhausts superheated steam in the pressure vessel (3). A drying apparatus in which the superheated steam is supplied to the pressure vessel (3) .

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