CA1107495A - Controlling heating apparatus which includes a high frequency dryer - Google Patents
Controlling heating apparatus which includes a high frequency dryerInfo
- Publication number
- CA1107495A CA1107495A CA325,463A CA325463A CA1107495A CA 1107495 A CA1107495 A CA 1107495A CA 325463 A CA325463 A CA 325463A CA 1107495 A CA1107495 A CA 1107495A
- Authority
- CA
- Canada
- Prior art keywords
- high frequency
- moisture content
- frequency dryer
- mean
- dryer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B6/00—Heating by electric, magnetic or electromagnetic fields
- H05B6/46—Dielectric heating
- H05B6/48—Circuits
- H05B6/50—Circuits for monitoring or control
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F5/00—Dryer section of machines for making continuous webs of paper
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F5/00—Dryer section of machines for making continuous webs of paper
- D21F5/16—Drying webs by electrical heating
- D21F5/165—Inductive heating; Capacitive heating
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F7/00—Other details of machines for making continuous webs of paper
- D21F7/003—Indicating or regulating the moisture content of the layer
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D22/00—Control of humidity
- G05D22/02—Control of humidity characterised by the use of electric means
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Automation & Control Theory (AREA)
- Electromagnetism (AREA)
- Drying Of Solid Materials (AREA)
- Paper (AREA)
Abstract
A B S T R A C T
A method is disclosed for controlling the operation of a drying apparatus which includes a first drying section and a high frequency dryer.
The method equalizes the drying in the first drying section and the high frequency dryer to provide dried material having an improved drying profile with a reduction in the energy required to dry the material. In accordance with one aspsect of the invention, the drying load of the first drying section is varied to obtain a predetermined final moisture content in the material. The short-term drying load of the high frequency dryer is varied to minimize the deviations in the moisture content of the material from the final mean moisture content. The apparatus may be controlled according to the invention by a computer.
A method is disclosed for controlling the operation of a drying apparatus which includes a first drying section and a high frequency dryer.
The method equalizes the drying in the first drying section and the high frequency dryer to provide dried material having an improved drying profile with a reduction in the energy required to dry the material. In accordance with one aspsect of the invention, the drying load of the first drying section is varied to obtain a predetermined final moisture content in the material. The short-term drying load of the high frequency dryer is varied to minimize the deviations in the moisture content of the material from the final mean moisture content. The apparatus may be controlled according to the invention by a computer.
Description
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": ' The present invention relates to the drying of material such as paper web and to the control of heating apparatus. More particularly, the invention relates to a method for drying material such as paper web in drying apparatus which includes a high frequency dryer.
Capacitance high frequency heating apparatus are known in the art and the use of such apparatus for drying bands of dielectric material such as paper and the like has been found to be quite satisfactory. Such an apparatus is disclosed in United States Patent No. 3>681,558, for example.
It is an object of the present invention to improve the drying of material such as paper web and to do so at reduced energy consumption.
It is also an object of the present invention to improve the operation of heating apparatus which includes a high frequency dryer and to reduce the energy consumption of the apparatus.
It is another object of the present invention to improve the operation of heating apparatus which includes a high frequency dryer to provide dried material having an improved moisture profile.
It is still another object of the present invention to improve the operation of heating apparatus which includes a first drying section and a high frequency dryer.
These and other objects of the present invention are achieved according to the invention by matching the drying which takes place in a first drying section of a heating apparatus to the drying which takes place in a high frequency dryer. More particularly, the long-term mean value of the evaporation power or evaporation heating of the high frequency dryer is main-tained at a predetermined value while the evaporation power or evaporation heating of the first drying section is controlled. In other words, control of the evaporation in the first drying section permits the evaporation load in the high frequency dryer to be maintained constant. Thus, the evaporation `1- ~
~1~74~5 heating supplied to the high frequency dryer is maintained at a substantially constant and predetermined mean long-term value while the evaporation heating provided to the first drying section is varied. Selection of the evaporation power provided to the first drying section, i.e., control of the first drying section, and selection of the predetermined constant mean evaporation power supplied to the high frequency dryer are made in accordance with the final mean moisture of the material that is desired. Maintaining the high frequency dryer at a long-term constant me~an evaporation power reduces the overall energy consumption of the heating apparatus.
According to one aspect of the invention, the long-term evaporation power of the high frequency dryer is maintained at the predetermined constant mean value by variation of the electrode field strength while the mean anode current is maintained at a substantially constant and predetermined long-term value, the mean anode current being indicative of the mean evaporation power.
In accordance with another aspect of the invention, the long-term evaporation power of the high frequency dryer is maintained constant, while the evaporation power is varied over the short-term to minimize moisture deviations in the dried material from the final mean moisture value desired.
This is accomplished in accordance with the invention by maintaining the electrode field strength of the high frequency dryer constant and by short-term variation of the anode current thereof. Short-term variation of the evaporation power to the high frequency dryer while maintaining the mean long-term value of the evaporation power provided to the high frequency dryer constant, will still provide the desired final mean moisture content of the material.
In accordance with another aspect of the invention, it has been found that equalization of the deviations of the moisture content from the final mean moisture content depend upon the amount of moisture evaporated by
": ' The present invention relates to the drying of material such as paper web and to the control of heating apparatus. More particularly, the invention relates to a method for drying material such as paper web in drying apparatus which includes a high frequency dryer.
Capacitance high frequency heating apparatus are known in the art and the use of such apparatus for drying bands of dielectric material such as paper and the like has been found to be quite satisfactory. Such an apparatus is disclosed in United States Patent No. 3>681,558, for example.
It is an object of the present invention to improve the drying of material such as paper web and to do so at reduced energy consumption.
It is also an object of the present invention to improve the operation of heating apparatus which includes a high frequency dryer and to reduce the energy consumption of the apparatus.
It is another object of the present invention to improve the operation of heating apparatus which includes a high frequency dryer to provide dried material having an improved moisture profile.
It is still another object of the present invention to improve the operation of heating apparatus which includes a first drying section and a high frequency dryer.
These and other objects of the present invention are achieved according to the invention by matching the drying which takes place in a first drying section of a heating apparatus to the drying which takes place in a high frequency dryer. More particularly, the long-term mean value of the evaporation power or evaporation heating of the high frequency dryer is main-tained at a predetermined value while the evaporation power or evaporation heating of the first drying section is controlled. In other words, control of the evaporation in the first drying section permits the evaporation load in the high frequency dryer to be maintained constant. Thus, the evaporation `1- ~
~1~74~5 heating supplied to the high frequency dryer is maintained at a substantially constant and predetermined mean long-term value while the evaporation heating provided to the first drying section is varied. Selection of the evaporation power provided to the first drying section, i.e., control of the first drying section, and selection of the predetermined constant mean evaporation power supplied to the high frequency dryer are made in accordance with the final mean moisture of the material that is desired. Maintaining the high frequency dryer at a long-term constant me~an evaporation power reduces the overall energy consumption of the heating apparatus.
According to one aspect of the invention, the long-term evaporation power of the high frequency dryer is maintained at the predetermined constant mean value by variation of the electrode field strength while the mean anode current is maintained at a substantially constant and predetermined long-term value, the mean anode current being indicative of the mean evaporation power.
In accordance with another aspect of the invention, the long-term evaporation power of the high frequency dryer is maintained constant, while the evaporation power is varied over the short-term to minimize moisture deviations in the dried material from the final mean moisture value desired.
This is accomplished in accordance with the invention by maintaining the electrode field strength of the high frequency dryer constant and by short-term variation of the anode current thereof. Short-term variation of the evaporation power to the high frequency dryer while maintaining the mean long-term value of the evaporation power provided to the high frequency dryer constant, will still provide the desired final mean moisture content of the material.
In accordance with another aspect of the invention, it has been found that equalization of the deviations of the moisture content from the final mean moisture content depend upon the amount of moisture evaporated by
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the high frequency dryer as well as the desired mean final moisture content itself. In accordance with this aspect of the invention, the ratio of the deviations from the mean moisture content of the material before it enters the high frequency dryer and after it emerges from the high frequency dryer are used as a measure of the equali~ation.
A method according to the invention for drying material such as paper web to obtain a predetermined substantially constant mean moisture content in the dried material comprises the steps of: drying the material in a first drying section, thereafter further drying the material in a second capacitance high frequency dryer, maintaining the evaporation heating provided to the high frequency dryer at a predetermined, substantially constant, mean long-term value by varying the electrode field strength of the high frequency dryer, and varying the mean evaporation heating provided to the first drying section in accordance with the moisture content of the dried material after it emerges rom the high frequency dryer.
The moisture content of the material is measured ater it emerges from the first drying section and after it emerges from the high frequency dryer, and the evaporation heating provided to the first drying section is varied in accordance with the difference in the mean moisture contents of the material before it enters the high frequency dryer and after it emerges from the high frequency dryer. Preferably the evaporation heating provided to the first drying section is varied to maintain this difference in the moisture contents substantially constant.
According to one aspect, mentioned above, of the invention, the evaporation heating provided to the high frequency dryer is varied over a short term by varying the anode current thereof to minimize deviations of the moisture content in the dried material from the predetermined mesn moisture content and thereby equali~e the moisture profile of the dried material.
the high frequency dryer as well as the desired mean final moisture content itself. In accordance with this aspect of the invention, the ratio of the deviations from the mean moisture content of the material before it enters the high frequency dryer and after it emerges from the high frequency dryer are used as a measure of the equali~ation.
A method according to the invention for drying material such as paper web to obtain a predetermined substantially constant mean moisture content in the dried material comprises the steps of: drying the material in a first drying section, thereafter further drying the material in a second capacitance high frequency dryer, maintaining the evaporation heating provided to the high frequency dryer at a predetermined, substantially constant, mean long-term value by varying the electrode field strength of the high frequency dryer, and varying the mean evaporation heating provided to the first drying section in accordance with the moisture content of the dried material after it emerges rom the high frequency dryer.
The moisture content of the material is measured ater it emerges from the first drying section and after it emerges from the high frequency dryer, and the evaporation heating provided to the first drying section is varied in accordance with the difference in the mean moisture contents of the material before it enters the high frequency dryer and after it emerges from the high frequency dryer. Preferably the evaporation heating provided to the first drying section is varied to maintain this difference in the moisture contents substantially constant.
According to one aspect, mentioned above, of the invention, the evaporation heating provided to the high frequency dryer is varied over a short term by varying the anode current thereof to minimize deviations of the moisture content in the dried material from the predetermined mesn moisture content and thereby equali~e the moisture profile of the dried material.
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In accordance with another aspect of the invention, the sub-stantially constant value of the difference referred to above in the mean moisture contents of the material is selectet in accordance with a ratio of the mean deviation of the moisture content from the mean moisture content before the material enters the high frequency dryer and after it emerges from the high frequency dryer.
In a disclosed embodiment, the values of the measured moisture content of the material and the desired predetermined final mean moisture content of the dried material are supplied to a computer which includes a program memory and which is programmed to compute the mean moisture values and the mean deviations therefrom. The computer is further programmed to select an optimum ratio of the mean deviation of the moisture content from the mean moisture content of the material before the material enters the high frequency dryer and after it emerges from the high frequency dryer, and to control the first drying section and the high frequency dryer in accordanc0 with this optimum ratio and the computed and predetermined moisture content values.
In accordance with the preferred embodiment of the invention, the anode current of the high frequency dryer is used as an indication ofl and as an equivalent for, the evaporation load of the high frequency dryer. As mentioned, the evaporation load of the high frequency dryer can be held at a predetermined value by maintaining the mean value of the anode current constant. This can be done by changing the electrode field strength.
These and other aspects of the invention will be more apparent from the following description of the preferred embodiment when considered with the accompanying drawings.
The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings in which:
In accordance with another aspect of the invention, the sub-stantially constant value of the difference referred to above in the mean moisture contents of the material is selectet in accordance with a ratio of the mean deviation of the moisture content from the mean moisture content before the material enters the high frequency dryer and after it emerges from the high frequency dryer.
In a disclosed embodiment, the values of the measured moisture content of the material and the desired predetermined final mean moisture content of the dried material are supplied to a computer which includes a program memory and which is programmed to compute the mean moisture values and the mean deviations therefrom. The computer is further programmed to select an optimum ratio of the mean deviation of the moisture content from the mean moisture content of the material before the material enters the high frequency dryer and after it emerges from the high frequency dryer, and to control the first drying section and the high frequency dryer in accordanc0 with this optimum ratio and the computed and predetermined moisture content values.
In accordance with the preferred embodiment of the invention, the anode current of the high frequency dryer is used as an indication ofl and as an equivalent for, the evaporation load of the high frequency dryer. As mentioned, the evaporation load of the high frequency dryer can be held at a predetermined value by maintaining the mean value of the anode current constant. This can be done by changing the electrode field strength.
These and other aspects of the invention will be more apparent from the following description of the preferred embodiment when considered with the accompanying drawings.
The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings in which:
-4-P7~ 5 Figure 1 is a block diagram of a heating apparatus including a first drying section and a high frequency dryer and the control system therefor, and illustrates the method according to the invention, and Figure 2 is a plot of a final mean moisture content UE o~ the material in percent as the abscissa axis and the difference ~ UHF in mean moisture contents before and after the high frequency dryer as the ordinate axis for different equali~ation factors F and field strengths ~ r ~ and illustrates the relationship between the equalization of drying in the high frequency dryer and the evaporation load of the high frequency dryer.
Referring now more particularly to the drawings, a preferred embodiment of the method according to the invention may be carried out by the apparatus shown in block form in Figure 1 according to the relationships shown in Figure 2.
In Figure 1, the apparatus is used to dry paper web 1 which is advanced and is traveling in the direction of the arrow 2. The paper web is first supplied to a conventional drying section 3 and is dried to a large extent therein on drying cylinders (not shown). The paper web 1 is advanced to a capacitance high frequency dryer 4 for further drying and equalization of the moisture profile. The high frequency dryer 4 can be of the type described in United States Patent No. 3,681,558 mentioned above.
The moisture content of the paper web is measured after it emerges from the first drying section 3 and before it enters the high frequency dryer 4, and after it emerges from the high frequency dryer 4. The moisture contents are measured by a traversing measuring apparatus 7 disposed between the drying section 3 and the high frequency dryer 4 and by another traversing measuring apparatus 5 disposed at the output of the high frequency dryer 4.
In Figure 1, UE designates the final mean moisture content in percent of the web after it emerges from the high frequency dryer and ~ UE
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designates the mean deviation in percent of the moisture content of the paper web from the mean moisture content UE after the web emerges from the high frequency dryer. Ua designates the mean moisture content in percent of the paper web after it emerges from the drying section 3 and ~ Ua designates the mean deviation in percent of the moisture content of the paper web from the mean moisture content after the web emerges from the drying section 3.
Nz designates the evaporation power of drying section 3 and NH the evaporation power of the high frequency dryer 4. The mean moisture content UE and the mean deviation therefrom a UE of the paper web after it emerges from the high frequency dryer are computed from the values of the moisture content measured by traversing apparatus 5 and the mean moisture content UA and the mean deviation therefrom ~ Ua of the paper web after it emerges from the drying section 3 are computed from the values of the moisture content measured by traversing apparatus 7.
The evaporation power Nz of the drying section 3 is controlled by control 31 and the evaporation power NH of the high frequency dryer 4 is controlled by a control 41.
In accordance with the invention, to obtain a predetermined desired final mean moisture content of the paper web, the evaporation load NH of the high frequency dryer 4 is maintained substantially constant by control 41 while the evaporation load Nz of the drying section 3 is varied by control 31 in accordance with the mean value of the moisture content UE of the paper web after it emerges from the high frequency dryer.
The field strength (or the electrode voltage) of the high frequency dryer is regulated so that the mean value of the anode current of the high frequency dryer is kept constant. In this manner, the mean evaporation load NH of the high frequency dryer 4 is maintained substantially constant. The evaporation load Nz of the drying section 3 is meanwhile varied in accordance . ~ ' .
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with the difference in the mean moisture content UA of the paper web before it enters the high frequency dryer and the mea~ moisture content UE of the paper web after it emerges from the high frequency dryer. The difference UA - UE in percent is designated A UHF and is maintained substantially constant by variation of the evaporation load Nz.
In order to equalize the moisture profile of the paper web as it emerges from the hi~h frequency dryer 4, the evaporation load NH provided to the high frequency dryer 4 is varied over the short term by variation of the anode current thereof. This tends to minimize deviations of the moisture content in the dried paper web and thereby equalizes the moisture profile of the dried paper web. Short-term variation of the evaporation load NH in the high frequency dryer while maintaining the long-term evaporation load NH
substantially constant will provide the desired final mean moisture content UE in the dried paper web.
The long-term time period for forming the mean values of the moisture content can be, for example, about two minutes. In this manner, the control 41, in conjunction with five times the requlating time of the control 31, operates to provide an optimum equalization factor for drying.
As mentioned, short-term variations of the moisture content are equalized by the high frequency dryer 4 at a constant field strength.
In accordance with the invention, a relationship has been found between the final moisture content UE at the exit of the high frequency dryer 4, the mean deviation ~ UE therefrom, the mean moisture content UA at the entrance of the high ~requency dryer and the mean deviation ~ Ua therefrom.
; This relationship is shown in Figure 2 in which the final mean moisture content UE in percent isplotted against the difference ~ UHF in percent of the mean moisture content UA less the mean moisture content UE. The equali-zation factor F is defined as the ratio of UA
.
... .
~7~5 As illustrated in Figure 2, it was found that theequali~ation factor F depends on the moisture difference ~ UHF, i.e. on the evaporation load NH
of the high frequency dryer 4 as well as the mean final moisture UE. The relationship, which has been confirmed by measurement results, between the equalization factor F and moisture difference ~ UHF is illustrated for different percentage final moisture contents UE. The relationship between the equalization factor F and the final moisture contents UE and the difference ~ UHF and the relative field strength ~ r is also illustrated in Figure 2. The relative field strength is equal to E J where E is E max the instantaneous field strength and EmaX is the maximum field strength in the high frequency dryer.
Referring now again to Figure 1, a computer 6 receives the measured moisture contents of the paper web from the traversing apparatus 5 and 7 as the web emerges from the drying section 3 and from the high frequency dryer 4, respectively. The computer calculates from these measurements the moisture pro~ile, i.e., the average final moisture UE in percent, the mean deviation ~ UE therefrom in percent, the mean moisture UA of the paper web in percent after the web emerges from the drying section 3 and the mean deviation ~ Ua therefrom in percent. The computer 6 is progra~med and includes a program memory 61 which enables the computer to select the evaporation loads Nz and NH of the drying section 3 and high frequency dryer 4, respectively.
The computer 6 is operative to vaTy the evaporation load Nz and select the constant long-term load NH of the high frequency dryer in accordance with the measured moisture contents to provide the final moisture content and moisture profile in conjunction with the program memory 61.
Advantageously, the relationship of the equalization Factor F, the field strength ~ r' the final moisture content UE and the moisture content difference ~ UHF is entered into the computer 6 via the program and the program :. :, 3L~ 74~i memory 61~ Thus, upon selection of the desired final moisture content, the computer 6 in accordance with the measured values of the moisture contents and the program and program memory 61, selects the optimum equalization factor F and the evaporation loads Nz, NH.
To obtain an optimum and defined equalization factor F, it was found that the moisture content difference ~ UHF should be maintained at a selected constant value rather than permitting the value of ~ UHF to vary.
Referring to Figure 2 again, if ~ UHF were not held constant, then a reduction of the equalization factor F from 2.75 (operating point A) to 2.00 (operating point B) would result in, for a desired final moisture of 7%, a reduction of the value of ~ UHF from about 7 to about 3. By maintaining the moisture con-tent difference ~ UHF substantially constant at a predetermined value, the long-term mean of the evaporation load NH may be maintained constant, as mentioned above, thd the desired final moisture content of the paper web may be obtained by varying the evaporation load Nz of the drying section 3. Thus, the field strength of the high frequency dryer 4 may be varied to move the operating point in the direction of (a). Deviations of the moisture content of the paper web as it emerges from the high frequency dryer 4 can be leveled out by maintaining the field str0ngth of the high frequency dryer constant over the short term and by varying the anode current thereof. Suitable power reserves are maintained for this purpose. Variation of the evaporation load NH of the high frequency dryer 4 moves the operating point in the direction (b)-As mentioned above, the computer is programmed and the computermemory 61 includes the information set forth in Figure 2. Thus, upon selecting the desired final moisture content, the computer controls operation of the drying section 3 and the high frequency dryer 4 to provide the optimum equalization factoT F, ~he constant long-term evaporation load NH of high _g_ .
~7~$5 frequency dryer 4, the control of the evaporation load Nz of the drying section 3, and the short-term variation of the evaporation load of the high frequency dryer 4.
In accordance with the procedure described above, equalization of the moisture profile of the paper web may be obtained with an optimum distribution of the heating power provided to the drying section 3 and the high frequency dryer 4. The drying capability of the dryer is thereby increased and energy is saved.
The advantages of the present invention as well as certain changes and modifications of the disclosed embodiments thereof will be readily apparent to those skilled in the art. It is the applicant's intention to cover by his claims all those changes and modifications which could be made to the embodiments of the invention herein chosen for the purposes of the disclosure without departing from the spirit and scope of the invention.
' . ' . ' . ... , , : `
.: . . . ~
Referring now more particularly to the drawings, a preferred embodiment of the method according to the invention may be carried out by the apparatus shown in block form in Figure 1 according to the relationships shown in Figure 2.
In Figure 1, the apparatus is used to dry paper web 1 which is advanced and is traveling in the direction of the arrow 2. The paper web is first supplied to a conventional drying section 3 and is dried to a large extent therein on drying cylinders (not shown). The paper web 1 is advanced to a capacitance high frequency dryer 4 for further drying and equalization of the moisture profile. The high frequency dryer 4 can be of the type described in United States Patent No. 3,681,558 mentioned above.
The moisture content of the paper web is measured after it emerges from the first drying section 3 and before it enters the high frequency dryer 4, and after it emerges from the high frequency dryer 4. The moisture contents are measured by a traversing measuring apparatus 7 disposed between the drying section 3 and the high frequency dryer 4 and by another traversing measuring apparatus 5 disposed at the output of the high frequency dryer 4.
In Figure 1, UE designates the final mean moisture content in percent of the web after it emerges from the high frequency dryer and ~ UE
~, -5-~ 74~S
designates the mean deviation in percent of the moisture content of the paper web from the mean moisture content UE after the web emerges from the high frequency dryer. Ua designates the mean moisture content in percent of the paper web after it emerges from the drying section 3 and ~ Ua designates the mean deviation in percent of the moisture content of the paper web from the mean moisture content after the web emerges from the drying section 3.
Nz designates the evaporation power of drying section 3 and NH the evaporation power of the high frequency dryer 4. The mean moisture content UE and the mean deviation therefrom a UE of the paper web after it emerges from the high frequency dryer are computed from the values of the moisture content measured by traversing apparatus 5 and the mean moisture content UA and the mean deviation therefrom ~ Ua of the paper web after it emerges from the drying section 3 are computed from the values of the moisture content measured by traversing apparatus 7.
The evaporation power Nz of the drying section 3 is controlled by control 31 and the evaporation power NH of the high frequency dryer 4 is controlled by a control 41.
In accordance with the invention, to obtain a predetermined desired final mean moisture content of the paper web, the evaporation load NH of the high frequency dryer 4 is maintained substantially constant by control 41 while the evaporation load Nz of the drying section 3 is varied by control 31 in accordance with the mean value of the moisture content UE of the paper web after it emerges from the high frequency dryer.
The field strength (or the electrode voltage) of the high frequency dryer is regulated so that the mean value of the anode current of the high frequency dryer is kept constant. In this manner, the mean evaporation load NH of the high frequency dryer 4 is maintained substantially constant. The evaporation load Nz of the drying section 3 is meanwhile varied in accordance . ~ ' .
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with the difference in the mean moisture content UA of the paper web before it enters the high frequency dryer and the mea~ moisture content UE of the paper web after it emerges from the high frequency dryer. The difference UA - UE in percent is designated A UHF and is maintained substantially constant by variation of the evaporation load Nz.
In order to equalize the moisture profile of the paper web as it emerges from the hi~h frequency dryer 4, the evaporation load NH provided to the high frequency dryer 4 is varied over the short term by variation of the anode current thereof. This tends to minimize deviations of the moisture content in the dried paper web and thereby equalizes the moisture profile of the dried paper web. Short-term variation of the evaporation load NH in the high frequency dryer while maintaining the long-term evaporation load NH
substantially constant will provide the desired final mean moisture content UE in the dried paper web.
The long-term time period for forming the mean values of the moisture content can be, for example, about two minutes. In this manner, the control 41, in conjunction with five times the requlating time of the control 31, operates to provide an optimum equalization factor for drying.
As mentioned, short-term variations of the moisture content are equalized by the high frequency dryer 4 at a constant field strength.
In accordance with the invention, a relationship has been found between the final moisture content UE at the exit of the high frequency dryer 4, the mean deviation ~ UE therefrom, the mean moisture content UA at the entrance of the high ~requency dryer and the mean deviation ~ Ua therefrom.
; This relationship is shown in Figure 2 in which the final mean moisture content UE in percent isplotted against the difference ~ UHF in percent of the mean moisture content UA less the mean moisture content UE. The equali-zation factor F is defined as the ratio of UA
.
... .
~7~5 As illustrated in Figure 2, it was found that theequali~ation factor F depends on the moisture difference ~ UHF, i.e. on the evaporation load NH
of the high frequency dryer 4 as well as the mean final moisture UE. The relationship, which has been confirmed by measurement results, between the equalization factor F and moisture difference ~ UHF is illustrated for different percentage final moisture contents UE. The relationship between the equalization factor F and the final moisture contents UE and the difference ~ UHF and the relative field strength ~ r is also illustrated in Figure 2. The relative field strength is equal to E J where E is E max the instantaneous field strength and EmaX is the maximum field strength in the high frequency dryer.
Referring now again to Figure 1, a computer 6 receives the measured moisture contents of the paper web from the traversing apparatus 5 and 7 as the web emerges from the drying section 3 and from the high frequency dryer 4, respectively. The computer calculates from these measurements the moisture pro~ile, i.e., the average final moisture UE in percent, the mean deviation ~ UE therefrom in percent, the mean moisture UA of the paper web in percent after the web emerges from the drying section 3 and the mean deviation ~ Ua therefrom in percent. The computer 6 is progra~med and includes a program memory 61 which enables the computer to select the evaporation loads Nz and NH of the drying section 3 and high frequency dryer 4, respectively.
The computer 6 is operative to vaTy the evaporation load Nz and select the constant long-term load NH of the high frequency dryer in accordance with the measured moisture contents to provide the final moisture content and moisture profile in conjunction with the program memory 61.
Advantageously, the relationship of the equalization Factor F, the field strength ~ r' the final moisture content UE and the moisture content difference ~ UHF is entered into the computer 6 via the program and the program :. :, 3L~ 74~i memory 61~ Thus, upon selection of the desired final moisture content, the computer 6 in accordance with the measured values of the moisture contents and the program and program memory 61, selects the optimum equalization factor F and the evaporation loads Nz, NH.
To obtain an optimum and defined equalization factor F, it was found that the moisture content difference ~ UHF should be maintained at a selected constant value rather than permitting the value of ~ UHF to vary.
Referring to Figure 2 again, if ~ UHF were not held constant, then a reduction of the equalization factor F from 2.75 (operating point A) to 2.00 (operating point B) would result in, for a desired final moisture of 7%, a reduction of the value of ~ UHF from about 7 to about 3. By maintaining the moisture con-tent difference ~ UHF substantially constant at a predetermined value, the long-term mean of the evaporation load NH may be maintained constant, as mentioned above, thd the desired final moisture content of the paper web may be obtained by varying the evaporation load Nz of the drying section 3. Thus, the field strength of the high frequency dryer 4 may be varied to move the operating point in the direction of (a). Deviations of the moisture content of the paper web as it emerges from the high frequency dryer 4 can be leveled out by maintaining the field str0ngth of the high frequency dryer constant over the short term and by varying the anode current thereof. Suitable power reserves are maintained for this purpose. Variation of the evaporation load NH of the high frequency dryer 4 moves the operating point in the direction (b)-As mentioned above, the computer is programmed and the computermemory 61 includes the information set forth in Figure 2. Thus, upon selecting the desired final moisture content, the computer controls operation of the drying section 3 and the high frequency dryer 4 to provide the optimum equalization factoT F, ~he constant long-term evaporation load NH of high _g_ .
~7~$5 frequency dryer 4, the control of the evaporation load Nz of the drying section 3, and the short-term variation of the evaporation load of the high frequency dryer 4.
In accordance with the procedure described above, equalization of the moisture profile of the paper web may be obtained with an optimum distribution of the heating power provided to the drying section 3 and the high frequency dryer 4. The drying capability of the dryer is thereby increased and energy is saved.
The advantages of the present invention as well as certain changes and modifications of the disclosed embodiments thereof will be readily apparent to those skilled in the art. It is the applicant's intention to cover by his claims all those changes and modifications which could be made to the embodiments of the invention herein chosen for the purposes of the disclosure without departing from the spirit and scope of the invention.
' . ' . ' . ... , , : `
.: . . . ~
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for drying material such as paper web to obtain a predetermined substantially constant final mean moisture content in the dried material comprising the steps of: drying the material in a first drying section, thereafter further drying the material in a second capacitance high frequency dryer, maintaining the evaporation heating provided to the high frequency dryer at a predetermined, substantially constant, mean long-term value by varying the electrode field strength of the high frequency dryer, and varying the mean evaporation heating provided to the first drying section in accordance with the moisture content of the dried material after it emerges from the high frequency dryer.
2. The method as recited in claim 1 and including measuring the moisture content of the material after it emerges from the first drying section and after it emerges from the high frequency dryer, wherein the evaporation heating provided to the first drying section is varied in accordance with the difference in the mean moisture content of the material before it enters the high frequency dryer and after it emerges from the high frequency dryer.
3. The method as recited in claim 2, wherein the evaporation heating provided to the first drying section is varied to maintain said difference substantially constant.
4. The method as recited in claims 1 or 2 or 3, and further comprising the step of varying the evaporation heating provided to the high frequency dryer over a short term by varying the anode current thereof to minimize deviations of the moisture content in the dried material and thereby equalize the moisture profile of the dried material while providing the substantially constant mean moisture content in the dried material.
5. The method as recited in claims 1 or 2 or 3, and further comprising the step of varying the evaporation heating provided to the high frequency dryer over a short term by vary-ing the anode current thereof to minimize deviations of the moisture content in the dried material and thereby equalize the moisture profile of the dried material while providing the substantially constant means moisture content in the dried mat-erial, wherein the substantially constant value of the difference in the mean moisture content of the material before it enters the high frequency dryer and after it emerges from the high frequency dryer is selected in accordance with a ratio of the mean deviation of the moisture content from the mean moisture content before the material enters the high frequency dryer and after it emerges from the high frequency dryer.
6. The method recited in claim 5 and including the steps of measuring the moisture content of the material before it enters the high frequency dryer and after it emerges from the high fre-quency dryer using traversing measuring apparatus.
7. The method as recited in claim 5 and comprising the step of feeding the values of the measured moisture contents of the material and the predetermined mean moisture content to a computer which is programmed to provide the mean moisture values and the mean deviations therefrom, and is further programmed to select an optimum ratio of the mean deviation of the moisture content from the mean moisture content of the material before it enters the high frequency dryer and after it emerges from the high frequency dryer, the computer being operative to control the first drying section and the high frequency dryer in accord-ance with the predetermined final moisture content and with the optimum ratio, the mean moisture contents and the mean deviations therefrom which are provided by the computer.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE2816551A DE2816551C3 (en) | 1978-04-17 | 1978-04-17 | Drying control on a paper machine |
| DEP2816551.7 | 1978-04-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1107495A true CA1107495A (en) | 1981-08-25 |
Family
ID=6037153
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA325,463A Expired CA1107495A (en) | 1978-04-17 | 1979-04-12 | Controlling heating apparatus which includes a high frequency dryer |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP0004915B1 (en) |
| JP (1) | JPS54138609A (en) |
| AT (1) | AT369062B (en) |
| CA (1) | CA1107495A (en) |
| DE (1) | DE2816551C3 (en) |
| FI (1) | FI790462A (en) |
| NO (1) | NO791184L (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6425190B1 (en) | 1998-09-11 | 2002-07-30 | Voith Sulzer Papiertechnik Patent Gmbh | Method and device for moisture profiling |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4420670A (en) * | 1982-03-05 | 1983-12-13 | Cincinnati Milacron Industries, Inc. | Control for dielectric heating in blow molding machine |
| DE3735242A1 (en) * | 1987-10-17 | 1989-04-27 | Dornier Gmbh Lindauer | DRYER FOR BUILDING BOARDS |
| DE4323379A1 (en) * | 1993-07-13 | 1995-01-26 | Krieger Gmbh & Co Kg | Circuit arrangement for regulating the output of a heating element of a heating device for drying a running web |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE697509C (en) * | 1936-06-11 | 1940-10-16 | Siemens Schuckertwerke Akt Ges | Drying device for paper webs on paper machines |
| DE1149474B (en) * | 1958-07-05 | 1963-05-30 | Huels Chemische Werke Ag | Method and device for the continuous drying of plastics which are moist with diluent |
| AU445577B2 (en) * | 1968-06-14 | 1974-02-08 | Ford Russell George | Process and apparatus for moisture contents de-peaking and equalization |
| DE2027674C3 (en) * | 1970-06-05 | 1974-05-09 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Device for uniform capacitive heating of wide webs |
-
1978
- 1978-04-17 DE DE2816551A patent/DE2816551C3/en not_active Expired
-
1979
- 1979-02-12 FI FI790462A patent/FI790462A/en unknown
- 1979-04-05 EP EP79101045A patent/EP0004915B1/en not_active Expired
- 1979-04-09 NO NO791184A patent/NO791184L/en unknown
- 1979-04-12 CA CA325,463A patent/CA1107495A/en not_active Expired
- 1979-04-12 JP JP4483179A patent/JPS54138609A/en active Pending
- 1979-04-13 AT AT0280579A patent/AT369062B/en not_active IP Right Cessation
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6425190B1 (en) | 1998-09-11 | 2002-07-30 | Voith Sulzer Papiertechnik Patent Gmbh | Method and device for moisture profiling |
| US6463677B2 (en) | 1998-09-11 | 2002-10-15 | Voith Sulzer Papiertechnik Patent Gmbh | Method and device for moisture profiling |
Also Published As
| Publication number | Publication date |
|---|---|
| EP0004915A1 (en) | 1979-10-31 |
| NO791184L (en) | 1979-10-18 |
| DE2816551C3 (en) | 1981-11-26 |
| EP0004915B1 (en) | 1982-05-12 |
| AT369062B (en) | 1982-12-10 |
| DE2816551A1 (en) | 1979-10-18 |
| DE2816551B2 (en) | 1981-04-09 |
| JPS54138609A (en) | 1979-10-27 |
| ATA280579A (en) | 1982-04-15 |
| FI790462A (en) | 1979-10-18 |
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