Paper making and fiber liberation – Processes and products – With measuring – inspecting and/or testing
Reexamination Certificate
2001-08-04
2003-04-15
Griffin, Steven P. (Department: 1731)
Paper making and fiber liberation
Processes and products
With measuring, inspecting and/or testing
C162S252000, C162S253000, C162S263000, C162SDIG006, C034S527000, C700S128000
Reexamination Certificate
active
06547930
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improvement in a method for performing transient operation on a dryer steam pressure at a time of papermaking exchange in a papermaking machine.
2. Description of the Prior Art
FIG. 1
shows a configuration diagram of a typical papermaking machine. In this figure, pulp material is discharged from a stock inlet
61
to a wire part
62
. The wire part
62
is moved in a direction of arrow A by rotating rolls
621
. The pulp material discharged in the wire part
62
is filtrated so that a web (paper) is formed. The web thus formed is conveyed to a press part
63
where it is further squeezed.
The web which has been squeezed in the press part
63
is conveyed to a pre-dryer
64
. Disposed in the pre-dryer
64
are many steam drums
641
, which are heated by steam introduced therein. The web is conveyed so as to pass through the steam drums sequentially while it is being wound on the steam drums. In the course of this conveyance, the web is dried until a predetermined moisture percentage or moisture content in the web is achieved.
After the dried web is subjected to such a size treatment as size (coating agent) application in a size press
65
, it is further dried in an after-dryer
66
, it is taken up or rolled as a product such as denoted by reference numeral
67
. Incidentally, the after-dryer
66
has substantially the same structure as that of the pre-dryer
64
.
Reference numerals
68
and
69
denote BM meters which detect weightings, moisture contents or the like of the webs which have just been discharged from the pre-dryer
64
and from the after-dryer
66
, respectively. The detected values are input into a control device (not shown). The control device controls a discharge amount of pulp material discharged into the wire part
62
, or an amount of steam introduced into the steam drums in the pre-dryer
64
and the after-dryer
66
, a papermaking speed and the like such that a product to be obtained meets specification values which have been determined in advance. Conventionally, a papermaking exchange control has been also employed for making different products in a continuous manner.
In the papermaking exchange control, since a product obtained during papermaking exchange where exchange is performed from a paper product making to another paper product making becomes broke out of a standard, such a papermaking exchange time should be reduced as much as possible in order to improve an operating efficiency. In order to solve the problem, there has been disclosed an invention about a method for estimating a setting value of steam pressure to be applied after a papermaking exchange according to simulation in Japanese Patent No. 3094798. The abstract of this invention will be explained below.
In the invention described in Japanese Patent No. 3094798 publication, using an iron mode where the steam drums in the pre-dryer
64
and the after-dryer
66
are arranged generally flat, contacting states among the steam drums, the web, and canvases wound on the steam drums in an endless manner are classified to five patterns to derive heat transfer differential equations of respective patterns, the differential equations are converted to difference equations, and a setting value of steam pressure is estimated by solving the difference equations.
Heat transfer differential equations of a pattern where the steam drum, the web and the canvas come into contact with one another in this order are represented in the following equations (1) to (3).
L
D
·
ρ
D
·
C
D
ⅆ
T
1
(
t
)
ⅆ
t
=
h
s
·
(
T
s
(
t
)
-
T
1
(
t
)
)
-
h
DW
·
(
T
1
(
t
)
-
T
2
(
t
)
)
(
1
)
L
W
·
ρ
W
·
C
W
ⅆ
T
2
(
t
)
ⅆ
t
=
h
DW
·
(
T
1
(
t
)
-
T
2
(
t
)
)
-
h
WC
·
(
T
2
(
t
)
-
T
3
(
t
)
)
-
Evapo
(
T
2
,
T
W
)
(
2
)
L
C
·
ρ
C
·
C
C
ⅆ
T
3
(
t
)
ⅆ
t
=
h
WC
·
(
T
2
(
t
)
-
T
3
(
t
)
)
-
h
a
·
(
T
3
(
t
)
-
T
a
(
t
)
)
(
3
)
where respective parameters in the above equations (1) to (3) are as follows:
L
D
: Drum thickness (m)
L
w
: web thickness (m)
L
c
: canvas thickness (m)
T
s
: in-drum steam temperature (° C.)
T
1
: drum surface temperature (° C.)
T
2
: web (paper) temperature (° C.)
T
3
: canvas temperature (° C.)
T
a
: in-hood air dry-bulb temperature (° C.)
C
D
: specific heat of drum (kJ/(kg·° C.)
C
w
: specific heat of web (kJ/(kg·° C.)
C
c
: specific heat of canvas (kJ/(kg·° C.)
&rgr;
D
: density of drum (kg/m
3
)
&rgr;
w
: density of web (kg/m
3
)
&rgr;
c
: density of canvas (kg/m
3
)
h
s
: heat transfer coefficient between in-drum steam and drum surface (kJ/(m
2
·sec·° C.))
h
DW
: heat transfer coefficient between drum surface and web (kJ/(m
2·sec
·° C.))
h
wc
: heat transfer coefficient between web surface and canvas (kJ/(m
2
·sec·° C.))
h
a
: heat transfer coefficient between canvas and in-hood air (kJ/(m
2
·sec ° C.))
FIG. 2
is a table showing the respective parameters in a collecting manner.
In the above equation (2), Evapo (T
2
, T
w
) is a function representing evaporation calorie taken away from a web by moisture evaporation, and it is represented as the following equation (4).
Evapo
(
T
2
,T
W
)=
V
(
MP
ABS
)·
K
·(
P
(
T
2
)−
P
(
T
W
))·
SB
(
T
2
)(
kJ
/(
m
2
·sec
)) (4)
where P(T) is a saturated steam pressure (kPa) at a temperature T(° C.); SB(T) is a heat of vaporization (kJ/H
2
Okg) at a temperature T(° C.); Tw is in-hood air wet-bulb temperature (° C.); V(MP
ABS
) is a function representing moisture evaporation intensity in an absolute moisture percentage MP
ABS
(incidentally, 0.0≦V(MP
ABS
)≦1.0 (unit free); and K is a drying speed coefficient (H
2
Okg/(m
2
·sec·kPa)).
In the invention described in Japanese Patent No. 3094798, heat transfer differential equations about contacting patterns other than the above contacting pattern are given, but explanation thereof will be omitted for avoiding complexity. The differential equations (1) to (3) are rewritten to derive difference equations by differentiating time by a ticked time period &Dgr;t determined according to a papermaking speed, the circumference of a steam drum, and the like, so that numerical values are obtained from the difference equations. Since the web is moved from an upstream position to a downstream position according to time lapse, the temperature of the web on the steam drum can be calculated from the numerical values of the difference equations.
On the basis of the above equation (4), Evapo MP(T
2
, T
w
)(H
2
Okg/(m
2
·sec)) which is evaporated moisture content per unit area and unit time from the web can be represented by the following equation (5).
EvapoMP
(
T
2
,T
W
)=
V
(
MP
ABS
)·K·(
P
(
T
2
)−
P
(
T
W
))(
H
2
Okg
/(
m
2
·sec
)) (5)
Using this equation, the absolute moisture percentage MP
ABS
(j) (j=1, . . . , N) of the web after elapse of a ticked time period &Dgr;t can be calculated according to the following equation (6).
MP
ABS
(
j
+
1
)
=
MP
ABS
(
j
)
-
10
3
·
EvapoMP
(
T
2
,
T
W
)
·
Δ
t
BD
(
6
)
where BD is an absolute dry weighting (g/m
2
); &Dgr;t is a ticked time period (sec); and MP
ABS
(j)(j=1, . . . , N) is an absolute moisture percentage at a divided mesh position j.
On the basis of this absolute moisture percentage MP
ABS
(j), a relative moisture percentage MP(j)(j=1, . . . , N)(%) can be calculated from the following equation (7).
MP
(
j
)
=
100
·
MP
ABS
(
j
)
1
+
MP
ABS
(
j
)
(
%
)
(
7
)
where MP(j)(j=1, . . . , N) is a relative moisture percentage (%) at a divided or split mesh position j.
FIG. 3
is a flowchart of an algorithm for performing simulation of a steady state using the above equations (1) to (7) to obtain a drying speed coefficient. In this figure, operation conditions, i.e., current papermaking
Maruyama Takao
Sasaki Takashi
Yahiro Kenichiro
Griffin Steven P.
Hug Eric
Kojima Moonray
Yokogawa Electric Corporation
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