TIS 0502-01 English [PDF]

Zitiervorschau

Paper machine vacuum selection factors   

TIS 0502-01  OLD TIS NUMBER 014-9  ISSUED – 1963  REVISED – 1980  REVISED – 1992  © 1992 TAPPI  The information and data contained in this document were prepared by a technical committee of the association. The committee and the association assume no liability or responsibility in connection with the use of such information or data, including but not limited to any liability or responsibility under patent, copy right or trade secret laws. The user is responsible for determining that this document is the most recent edition published.

Paper Machine Vacuum Selection Factors Scope  This technical information sheet provides mill engineers with a reference basis for computing the approximate cubic feet per minute (ft³/min) of air capacity required by paper machine vacuum systems. With this information, mill engineers may readily compute the air capacity requirements of vacuum systems for conventional fourdriniers, fourdrinies with top wire forming units (excluding vacuum – assisted types), press section suction rolls and felt suction boxes.

Forming Section The vacuum factor determination for any new forming geometry or application is developed through the calculation that account for all of the key sizing parameters. Standard factors can only be applied to standard geometries using typical operating practices. Factors used to simplify the vacuum sizing process are not universal and must be properly applied. The specific configuration of the forming section should receive particular attention. Higher desired vacuums, more cover open area of the high – vacuum drainage elements, and thicker forming fabrics all can easily suggest an increased air flow demand, especially on lightweight grades. A through analysis also ensures that the effect of couch shell void volume and its expansion, for example, is addressed for proper pipe and pump sizing. The rate at which air is drawn through various grades of paper illustrates that sheet weight, furnish type, freeness, and sheet moisture (or consistency) affect the results. The amount of air drawn through a sheet is inversely related to its moisture content. No air is drawn through the sheet prior to the dry line, while an increasing air flow occurs as the sheet is successively dried beyond that point. Therefore, the air flow of the last suction box would be only slightly less than that of the couch’s low-vacuum box. Tables 1, 2, and 3 present paper machine vacuum selection factors. For a given paper grade and furnish, air flow rate is inversely related to sheet weight. This condition is clearly seen on linerboard and bleached paperboard owing to, the board weight ranges, but is not so readily evident on traditional lightweight grades. Stock freeness variation is significant, as evidenced by the large variation between free-draining 42 lb linerboard and low-freeness 30 lb newsprint. A 4:1 weight ratio still requires a similar air flow due to the offsetting freeness.

Page 1 of 11

Paper machine vacuum selection factors  The largest air flow requirements occur after the dry line on lightweight, free-draining paper grades. The velocity of the air as it strips water from the capillaries of the sheet produces drainage. The actual amount of water removed is very small. Thus, in a “dry” position, a narrower suction box cover using fewer slots with reduced total air flow can achieve the same dewatering as wide cover. This same drainage mechanism occurs at the couch, so two suction zones operating at successively higher vacuums and air flow levels are used on light and medium weight applications. Tables 1, 2, and 3 reflect present industrial averages for the respective applications. All references to vacuum are in ft³/min at vacuum rather than std. Ft³/min. These represent the current norm for the vacuum capability of modern paper machines in each paper grade category. Some existing machines may be operating satisfactorily at lower levels. However, the indicated values should be considered if a production upgrade is contemplated. In such instances, pay attention to pressure drop, the sizing of vacuum piping and valves, seal legs, couch roll journal open area, etc. This attention will ensure that the pressure drop between the vacuum source and the point of application does not exceed 1 in. Hg.

Table 1. Paper machine vacuum selection factors fourdrinier forming section, unit locations Nos. 1-3

Basic Weight GRADES Light Weight Special Ties MG & MG Papers Glassine Greaseproof Carbonizing Waxing Base cigarette Condenser Tissue Napkin Toweling Napkin Towel Two Ply Towel Single Ply Free Sheet Printing & Writing Book Papers

Max Speed

Low Vacuum ①

Low Vacuum ②

Low Vacuum ③

3000 ft²

gsm

fpm

mpm

no units

cfm/in unit

in H2O

no units

cfm/in unit

in H2O

no units

cfm/in unit

in H2O

         

         

2000 1500 2000 2000 750

610 457 610 610 229

         

         

         

1-2 2-3 2-4 1-2 2-4

1.5 1.5 1.5 1.5 1.5

26 26 26 26 26

         

         

         

12-18 14-20 28-29

20-30 23-33 47-64

4000 4000 2500

1219 1219 762

     

     

     

0-1 0-1 1-2

1.5 1.5 1.5

26 26 26

0-1 0-1 0-1

1.5 1.5 1.5

26 26 26

28-55 30-73

47-90 49-119 106169

3000 3000

914 914

3 3

1.5 1.5

26 26

2-3 2-3

1.5 1.5

26 26

1 1

3.5 3.5

38 38

1500

457

3

1.5

26

2-3

1.5

26

0-1

3.5

38

3000 914 3000 914 3000 914 3000 914 Max Speed

       

Heavy Weights

65-104

Ground Wood Painting Directory Roto Catalog SC Magazine LWC Publication Newsprint GRADES

18-45 30-73 35-45 57-73 22-45 36-73 28-33 47-54 Basic Weight

        Low Vacuum ①

       

2 1.5 26 2 1.5 26 2 1.5 26 2-3 1.5 26 Low Vacuum ②

0-1 3.5 38 1 3.5 38 1 3.5 38 1 3.5 38 Low Vacuum ③

Page 2 of 11

Paper machine vacuum selection factors 

3000 ft²

gsm

fpm

mpm

no units

cfm/in unit

in H2O

no units

cfm/in unit

in H2O

no units

cfm/in unit

in H2O

Unbleached Kraft Bag

30-70

2500

762

2-3

1.5

26

2

1.5

38

0-1

3.5

54

Saturating

65-150

1500

457

4-5

1.5

38

2-3

1.5

38

1

3.5

54

Linerboard /26 to 42"

78-126

2500

762

3-4

1.5

38

2-3

1.5

38

1

3.5

54

Linerboard /42 to 90"

126270

49-114 106244 127205 205440 108176

2000

610

4-5

1.5

38

2-3

1.5

38

1-2

3.5

54

2500

762

3

1.5

26

3

1.5

38

0-1

3.5

54

1500

457

4-5

1.5

38

2-3

1.5

38

1

3.5

54

2000 750

610 229

  4-5

  1.5

  38

1-2 2-3

1.5 1.5

25 38

0-1  

3.5  

38  

Corrugating Medium /26"

66-108

Bleached Kraft SBS Paperboard Packaging Special Ties Pulp

120300 25-100  

196489 41-163  

These tables list two different factors for the high vacuum suction box capacity requirements: (1) ft³/min/in. wire width basis, and (2) ft³/min/in² of open area basis. The first factor provides a quick total capacity requirement based upon modern machine speeds and tonnage. The second reflects the vacuum density needed to develop a desired vacuum level. The mill engineering implication is that production changes demand evaluation of both the total ft³/min needs and the suction area through which it will be applied. Drive loads and drive ability should be studied in detail when additional vacuum capacity is considered.

Low vacuum requirements (forming section) From the tables, air flow and differential pressure requirements for the units in locations No.1 and No.2 are very low as no air is being drawn through the sheet. For the units in location No.3, higher vacuum levels are generally applied as these units operate near the “dry” line and some air draw through is occurring. Only slotted cover designs are used on these units. To determine the total air flow requirements for the units in these locations: Wire (fabric) width x vacuum factor (ft³/min/in.) x no. of units = total flow required per unit Example Calculate the requirements for a 240 in. SBS paperboard machine operating at a maximum speed of 1500 ft/min with four units in location No.1, two in location No.2, and one in location No.3. (1) 240 in. x 1.5 ft³/min/in. x 4 = 1440 ft³/min at 38 in. H2O (2) 240 in. x 1.5 ft³/min/in. x 2 = 720 ft³/min at 38 in. H2O (3) 240 in. x 3.5 ft³/min/in. x 1 = 840 ft³/min at 54 in. H2O Normally, one vacuum source would service all three locations. For this example, the required pump or exhauster should be capable of providing approximately 3090 ft³/min at 54 in. of water at the point of vacuum application.

High vacuum requirements (suction boxes)

Page 3 of 11

Paper machine vacuum selection factors  Locations No.4 and No.5 from the tables make up the traditional “wet” and “dry” suction box or flat box region and hence air flow demand is much greater. To determine the air flow requirements for suction boxes with drilled covers: Wire (fabric) width x overall cover width (MD) x % open area of cover’s drilled pattern x vacuum factor (ft³/min/in.²) x no. of boxes = total flow required To calculate vacuum requirements for slotted suction box covers: Wire (fabric) width x no. of slots x slot width (MD) x vacuum factor (ft³/min/in.²) x no. of boxes = total flow required Table 2. Paper machine vacuum selection factors fourdrinier forming section, unit locations Nos. 5-7

GRADES

High Vacuum "Wet" ④

High Vacuum "Dry" ⑤

Low Vacuum ⑥ cfm/in surface Hg area

High Vacuum ⑦ cfm/in surface Hg area

Basic Weight

Max Speed

3000 ft²

gsm

fpm

mpm

no boxes

cfm/in open area

cfm/in fab. Width

Hg

no boxes

cfm/in open area

cfm/in fab. Width

Hg

 

2000

610

1-2

0.2

1

6

2-4

0.3

3

6

3

10

3

15

 

1500

457

2-4

0.2

1

10

2-4

0.3

3

10

3

10

3

22

   

2000 2000

610 610

2-4 1-2

0.2 0.3

2 2

6 6

2-4 2-4

0.3 0.5

3 3

6 6

3 3

10 10

4 6

20 15

Light Weight Special Ties MG & MG   Papers Glassine   Greaseproof Carbonizing   Waxing Base   cigarette Condenser   Tissue Napkin Toweling Napkin 12-18 Towel Two Ply 14-20

 

750

229

1-2

0.2

1

6

2-4

0.3

3

6

3

10

3

15

20-30 23-33

4000 4000

1219 1219

   

   

   

   

0-1 0-1

0.7 0.7

4 4

6 6

3 3

10 10

3 3

20 20

Towel Single Ply

28-29

47-64

2500

762

 

 

 

 

1-2

0.6

12

6

3

10

6.5

20

28-55

47-90

3000

914

0-2

0.4

4

10

3-4

0.7

11

10

3

10

8.5

20

3000

914

0-2

0.4

4

10

3-4

0.7

11

10

3

10

8.5

20

1500

457

1-2

0.4

4

10

3-4

0.7

11

10

3

10

7

20

30-73

3000

914

0-2

0.4

4

10

2-4

0.7

11

10

3

10

8.5

20

57-73

3000

914

0-2

0.4

4

10

2-4

0.7

11

10

3

10

8.5

20

36-73

3000

914

0-2

0.4

4

10

2-4

0.7

11

10

3

10

8.5

20

3000 914 Max Speed

0-2

0.6 6 10 High Vacuum "Wet" ④

2-4

Free Sheet Printing & Writing Book Papers

30-73

65104 Ground Wood Painting Directory Roto 18-45 Catalog SC Magazine 35-45 Heavy Weights

49119 106169

LWC Publication

22-45

Newsprint GRADES

28-33 47-54 Basic Weight

1 14 High Vacuum "Dry" ⑤

10

3 10 Low Vacuum ⑥

Page 4 of 11

8.5 20 High Vacuum ⑦

Paper machine vacuum selection factors 

3000 ft²

gsm

fpm

mpm

no boxes

cfm/in open area

cfm/in fab. Width

Hg

no boxes

cfm/in open area

cfm/in fab. Width

Hg

cfm/in surface area

Hg

cfm/in surface area

Hg

2500

762

0-2

0.8

22

10

4-5

1.5

42

10

3

10

9

20

1500

457

1-2

0.8

10

10

2-4

1.5

20

15

 

 

7

20

2500

762

1-3

0.8

22

10

4-5

1.5

42

15

 

 

7

20

2000

610

2-4

0.6

30

10

5-6

1.2

50

15

 

 

7

20

2500

762

2-4

1

16

10

3-4

1.5

24

10

 

 

7

20

1500

457

2-4

0.6

16

10

4-5

1.2

32

15

 

 

7

20

2000

610

0-2

1

10

10

4-5

1.2

20

10

3

10

7.5

20

750

229

2-4

0.6

20

10

4-6

1.2

40

15

 

 

7

20

Unbleached Kraft Bag Saturating Linerboard /26 to 42" Linerboard /42 to 90" Corrugating Medium /26" Bleached Kraft SBS Paperboard Packaging Special Ties Pulp

65150 78126 126270 66108

49114 106244 127205 205440 108176

120300 25100  

196489 41163  

30-70

Examples Using the SBS paperboard machine with three “wet” and four “dry” suction boxes, calculate the vacuum requirements for locations No.4 and No.5. (4) Slotted covers (eleven 0.75 in. width slots): 240 in. x 11 x 0.75 in. x 0.6 ft³/min/in.² x 3 = 3654 ft³/min at 10 in. Hg* (5) Drilled covers (four 15 in. wide boxes with 42% open area): 240 in. x 15 in. x 0.42 x 1.2 ft³/min/in.² x 4 = 7258 ft³/min at 15 in. Hg (*Note: for combined air flows, expand the 3564 ft³/min at 10 in. Hg to 15 in. Hg for proper sizing of the vacuum source.)

Table 3. Paper machine vacuum selection factors fourdrinier forming section, unit locations Nos.1-2, 5-7

Page 5 of 11

Paper machine vacuum selection factors 

Basic Weight GRADES

3000 ft²

gsm

Free Sheet Printing & 2847Writing 55 90 Book 3049Papers 73 119 Heavy 65106Weights 104 169 Ground Wood Painting Directory 1830Roto 45 73 Catalog SC 3557Magazine 45 73 LWC 2236Publication 45 73 2847Newsprint 33 54 Unbleached Kraft 3049Bag 70 114 65106Saturating 150 244 Linerboard 78127/26 to 42" 126 205 Linerboard 126- 205/42 to 90" 270 440 Corrugating 66108Medium 108 176 /26" Bleached Kraft SBS 120- 196Paperboard 300 489 Packaging Special Ties

25100

41163

Max Speed

Low Vacuum ①

Low Vacuum ②

High Vacuum "Dry" ⑤

Low Vacuum ⑥ cfm/in Surface Hg area

High Vacuum ⑦ cfm/in Surface Hg area

fpm

mpm

no units

cfm/in unit

in H2O

no units

cfm/in unit

in H2O

no boxes

cfm/in open area

cfm/in fab. Width

Hg

3000

914

3

1.5

26

1

1.5

26

2-4

0.7

11

10

3

10

8.5

20

3000

914

3

1.5

26

1-2

1.5

26

2-4

0.7

11

10

3

10

8.5

20

1500

457

3

1.5

26

1

1.5

26

2-4

0.7

11

10

3

10

7

20

3000

914

 

 

 

1

1.5

26

2-4

0.7

11

10

3

10

8.5

20

3000

914

 

 

 

1

1.5

26

2-4

0.7

11

10

3

10

8.5

20

3000

914

 

 

 

1

1.5

26

2-4

0.7

11

10

3

10

8.5

20

3000

914

 

 

 

1

1.5

26

2-4

1

14

10

3

10

8.5

20

2500

762

2-3

1.5

26

1

1.5

38

4-5

1.5

42

10

3

10

9

20

1500

457

4-5

1.5

38

1

1.5

38

2-4

1.5

20

15

 

 

7

20

2500

762

3-4

1.5

38

1

1.5

38

4-5

1.5

42

15

 

 

7

20

2000

610

4-5

1.5

38

1

1.5

38

5-6

1.2

50

15

 

 

7

20

2500

762

3

1.5

26

1

1.5

38

3-4

1.5

24

10

 

 

7

20

1500

457

4-5

1.5

38

1

1.5

38

4-5

1.2

32

15

 

 

7

20

2000

610

 

 

 

1

1.5

25

4-5

1.2

20

10

3

10

8.5

20

Present-day ft³/min/in. wire width requirements are given in the tables. These data are based upon the weight and speed ranges listed. Vacuum capacity and the number of suction boxes both increase in proportion to the designed production rate.

Page 6 of 11

Paper machine vacuum selection factors  Based upon the ft³/min/in. guidelines, the comparative vacuum specifications for this example would be: Location No.4: 240 in. x 16 ft³/min/in. = 3840 ft³/min at 10 in. Hg Location No.5: 240 in. x 32 ft³/min/in. = 7680 ft³/min at 15 in. Hg

Suction couch requirements Actual couch box widths are determined in relation to the roll size and wrap angle for a particular machine. The ft³/min/in.² values listed in locations No.6 and No.7 on the tables indicate present industrial averages used on couch rolls. These values refer to the active surface area of the couch. To calculate this area: Width (MD length) of box x width of forming fabric = active surface area. Continuing the SBS machine example, assume it has a 14-in.wide box operating at 20-in.Hg vacuum. Required couch vacuum is then figured as follows: 240 in. x 14 in. x 7.0 ft³/min/in. = 23,520 ft³/min at 20 in. Hg

Couch vacuum factor adjustments vs. speed Machine speed is important influence when sizing the vacuum source for the couch. The low and high vacuum factors (locations No.6 and No.7 on tables 1, 2, and 3) should be corrected whenever the machine speed exceeds the maximum speed listed for that grade. Table4. Couch vacuum factor adjustment factors

First or "Low" Box or Single Box Only Second or "High" Box

Operating Vacuum in. Hg

Adjustment Factor ft³/min/in²/1000 ft/min

10

0.25

15

0.5

20

1

20

0.5

If the SBS machine is to be run at 2000 ft/min, then this speed would exceed the maximum speed listed by 500 ft/min. Accordingly, the charted ft³/min/in.² vacuum factor would be increased by 0.50 to the new factor of 7.5 Low speed applications (under 1000 ft/min) also require special attention. These often are narrow machines having small diameter couches. More importantly, couch roll journal open areas often are insufficient to operate at the given vacuum factors without exceeding the allowable air velocity limit. Also, a greater percentage of water drained by the couch enters the shell as speeds fall below 1000 ft/min. this water must also exit through the couch journal, thereby further reducing the effective open area for vacuum air passage and increasing the frictional loss effects.

Press section/suction rolls

Page 7 of 11

Paper machine vacuum selection factors  Figures 1-10 reflect current industrial averages for press section vacuum factors. Typical suction rolls and press configurations have been illustrated to show roll nip geometries and vacuum box locations. The corresponding charts indicate box width, vacuum level, and air flow requirements. As with couch roll vacuum capacities, all press section suction roll air volumes are based on a flow rate density (vacuum factor) multiplied by the active suction area, that is: Machine direction (MD) length of box x cross direction (CD) x width of felt x listed vacuum factor = air flow (ft³/min) required at point of application. The individual vacuum factors in figures 1-10 are specific to a particular press configuration. The term “standard” under “comments” applies to all paper grades that would be produced on that configuration, with the exception of special cases as indicated. These cannot be loosely applied to alternate press configurations: The changes in the key sizing parameters such as angle of wrap around the suction roll, weight of felt, and weight of sheet must be carefully considered. For speeds above 3500 ft/min, consult machinery builders and press felt suppliers for assistance in evaluating speed adjustments for vacuum factors.

Felt conditioning Uniform removal of water and foreign contaminants from the felt is the primary performance objective for felt flow and pressure drop to remove the water from the felt as it passes over a stationary suction box. Once the air capacity has been chosen, a properly designed felt box will ensure a uniform CD profile at a low moisture content. Determine the minimum total slot width required per felt box by referring to the appropriate figure and selecting the minimum slot width based on the machine design speed. Once the open area has been established, calculate the square inched of open area in the suction box and multiply by the ft³/min/in.². This is calculated as: W x L x 15 = Q Where W = machine width L = total slot width Q = total ft³/min required per box Example For a 240 in. wide machine operating at 2000 ft/min: 240 in. x 0.80 in. x 15 ft³/min/in.² = 2880 ft³/min at 15 in.Hg Note: Develop the indicated minimum total slot width by using either multiple or single slotted covers. However, the minimum width for any individual slot is 0.5 in. to prevent fiber bridging. To prevent the felt from being drawn into the slot, the maximum individual slot width should be less than 0.8 in. multiple slot widths in a single box will be needed for design speeds above 2000 ft/min. for paper grade applications requiring more intense cleaning. Add a second box of the same design. After the total ft³/min has been calculated, pay particular attention to the air velocity within the suction box and the piping to the vacuum source. The suction box is handling felt and press water (0.5 gal/min per linear inch of felt width) and air. Therefore, friction losses become quite important when designing a system that will maintain a uniform pressure drop across the full width of the felt. Maintaining an air velocity limit of 3500 ft/min in the felt suction box and all pipes will ensure this. Suction boxes having herringbone covers have become less prevalent in the industry because they do not provide a uniform dry line. This can result in an increase in moisture level on the exit side of the box. A herringbone cover requires a vacuum factor of 12 ft³/min/in.² at 12 in.Hg.

Page 8 of 11

Paper machine vacuum selection factors 

Table 5. Felt conditioning vacuum selection factor1 Felt Speed (ft/min)

Total Slow Width/Box (in)

0-1000

0.5

1000-1500

0.6

1500-2000

0.8

2000-2500

1.0

2500-3000

1.2

3000-3500

1.4

3500-4000

1.6

4000-5000

2.0

5000-6000

2.4

ft³/min/in² Opening Area

15 @ 15 in Hg

1

Note: Additional material on felt conditioning factors and felt cleaning shower position and factors can be found in TIS 0404-27, users of TIS 0502-01 are urged to reference TIS 0404-27 as the latter contains a greater variety of felt conditioning factors. Due to the increasing use of heavier-weight felts (above 4.5 oz/ft³) on the new wide nip presses, the mill engineer should review with the press supplier and the felt supplier the recommended slot width and ft³/min/in.²of open area required for the wide nip. The industry capacities have ranged from 17-22 ft³/min/in.² of open area on wide nip presses with a resulting increase in the operating vacuum upwards of 20 in. Hg. The installed motor hp should be reviewed because of the increase in operating vacuum.

Box

"A" "B"

Box "A"

Box Width in

Vacuum in Hg

Air Flow cfm/in²

8-12

20 15 20

5-10

10

5.0 6.0 5.0 1.3 0.7

Box Width in 10-24

Vacuum in Hg 10

4-6

Air Flow cfm/in² 0.5-10

Comments "Standard" Napkin or Towel Lighweight Special Ties Bled Into Box "A" Separate outlet

Comments "Standard"

Page 9 of 11

Paper machine vacuum selection factors 

Box

Box Width in

Vacuum in Hg

"A"

4-6

20

Box Width in 4-6

Vacuum in Hg 20

Air Flow cfm/in² 4-5

Box

Box Width in

Vacuum in Hg

"B"

70-80

10

"C"

4-6

20

Air Flow cfm/in² 1-2 0.5-1.0 5-6

Box

Box Width in

Vacuum in Hg

"A"

4-6

20

"B"

70-80

10

Box "A"

Air Flow cfm/in² 5.0 6.5 3.5

Air Flow cfm/in² 4-5 0.5 0.3

Comments "Standard" Napkin or Towel Lighweight Special Ties

Comments "Standard"

Comments Belt Into Box "C" Separate Outlet "Standard"

Comments "Standard" Belt Into Box "A" Separate Outlet

Page 10 of 11

Paper machine vacuum selection factors 

Box

Box Width in

Vacuum in Hg

"A"

4-6

20

"B" "C"

70-80 4-6

10 20

Air Flow cfm/in² 4-5 0.5-0.6 0.3 5-6

Box Width in 3-10

Vacuum in Hg 10

Air Flow cfm/in² 3.0

Box Width in 4-6

Vacuum in Hg 15

Air Flow cfm/in² 5-6

Box

Box Width in

Vacuum in Hg

Air Flow cfm/in²

 

 

12

200

Box "A"

Box "A"

Vickery Conditioners

Comments "Standard" Belt Into Box "A" Separate Outlet "Standard"

Comments "Standard"

Comments "Standard"

Comments "Standard"

Page 11 of 11