Effect of High Temperature Drying Effect of High Temperature Drying - - PowerPoint PPT Presentation

Effect of High Temperature Drying Effect of High Temperature Drying

• f Recycled Paper on Heat
• f Recycled Paper on Heat

Transfer Rates and Sheet Transfer Rates and Sheet Properties Properties

Dania Dania Alsaid Alsaid, , Hussam Hussam Alkhasawneh Alkhasawneh and and John Cameron John Cameron

Objectives: Objectives:

• To study the effect of high temperature on paper

To study the effect of high temperature on paper drying rates and properties for both virgin and drying rates and properties for both virgin and recycled pulp. recycled pulp.

• The process variables studied included the

The process variables studied included the effects of temperature, moisture level, effects of temperature, moisture level, recycling, and basis weight on heat transfer recycling, and basis weight on heat transfer and paper properties. and paper properties.

• An increase in the paper drying rate will increase the

An increase in the paper drying rate will increase the production rate. production rate.

• The use of gas

The use of gas-

• fired dryers (high temperature drying)

fired dryers (high temperature drying) is one method to increase the drying rate. is one method to increase the drying rate.

• The gas

The gas-

• fired dryer can provide internal shell

fired dryer can provide internal shell temperatures in excess of 200 temperatures in excess of 200˚ ˚C, which significantly C, which significantly increases the drying rate increases the drying rate

• With gas

With gas-

• fired dryers, one or more conventional

fired dryers, one or more conventional dryers are replaced with a gas dryers are replaced with a gas-

• fired dryer.

fired dryer.

The Study of High Temperature Drying The Study of High Temperature Drying was Conducted in two Parts: was Conducted in two Parts:

• 1

1-

• A gas

A gas-

• heated cylinder (

heated cylinder (GIT) was GIT) was installed on the installed on the pilot machine at Western Michigan University. pilot machine at Western Michigan University.

• 2

2-

• An experimental system was designed to simulate

An experimental system was designed to simulate heat transfer into the paper during a typical paper heat transfer into the paper during a typical paper cylinder drying process. cylinder drying process.

Background: Background:

• Cylinder Drying

Cylinder Drying: In conventional paper : In conventional paper drying, iron drums 5 to 6 ft in diameter are drying, iron drums 5 to 6 ft in diameter are heated with steam. heated with steam.

• Due to ASTM pressure codes, the steam

Due to ASTM pressure codes, the steam pressure is limited to 160 psig or about 190 pressure is limited to 160 psig or about 190˚ ˚ C. C.

• Resistance to heat transfer from the

Resistance to heat transfer from the condensing steam in the dryer cylinder to the condensing steam in the dryer cylinder to the paper includes the condensate layer, scale, the paper includes the condensate layer, scale, the metal shell, and the contact coefficient metal shell, and the contact coefficient between the shell and the paper. between the shell and the paper.

• The contact coefficient accounts for 35 % to

The contact coefficient accounts for 35 % to 75% of the total heat transfer resistance. 75% of the total heat transfer resistance.

• Due to resistance to heat transfer, the

Due to resistance to heat transfer, the maximum surface temperature is about 150 maximum surface temperature is about 150˚ ˚C. C.

• The drying rate can be described by the rate of

The drying rate can be described by the rate of heat transfer from the dryer shell to the paper. heat transfer from the dryer shell to the paper.

• The heat entering the paper heats the water and

The heat entering the paper heats the water and solids in the paper, evaporates water or is lost solids in the paper, evaporates water or is lost by radiation and convention. by radiation and convention.

• The majority of the heat is used to evaporate

The majority of the heat is used to evaporate the water in the paper. the water in the paper.

Equation 1 describes the heat flux from the dryer Equation 1 describes the heat flux from the dryer shell into the paper. shell into the paper. Q = Q = hc hc ( (Tshell Tshell – – Tpaper Tpaper) (1) ) (1)

• Q is the heat flux W/m

Q is the heat flux W/m2

2

• hc

hc is the paper is the paper-

• shell contact coefficient (W/m

shell contact coefficient (W/m2

2

· · ˚ ˚C) C)

• T is the temperature

T is the temperature ˚ ˚C of the paper and the C of the paper and the shell. shell.

Commercial Application: Commercial Application:

• The trial consisted of replacing one steam

The trial consisted of replacing one steam heated dryer on the pilot machine with a gas heated dryer on the pilot machine with a gas-

• fired dryer and producing 126 lb/1000 ft

fired dryer and producing 126 lb/1000 ft2

2

linear board. linear board.

• The surface temperature was increased to 260

The surface temperature was increased to 260 ˚ ˚ C, showed a significant increase in efficiency C, showed a significant increase in efficiency with low with low NOx NOx emissions. A Flynn ribbon

• emissions. A Flynn ribbon

burner model T burner model T-

• 534 was selected and the

534 was selected and the basic configuration is shown in Figure 1. basic configuration is shown in Figure 1.

Figure 1. Gas Fired Paper Dryer, US Figure 1. Gas Fired Paper Dryer, US Patent 6,877,979 (1) Patent 6,877,979 (1)

• The paper was heated only on one side through

The paper was heated only on one side through the first five steam dryer cans. the first five steam dryer cans.

• Several paper samples were collected and the

Several paper samples were collected and the curl was measured. curl was measured.

Conclusion of The Pilot Machine Trial: Conclusion of The Pilot Machine Trial:

• It was found that curl was present and the

It was found that curl was present and the sheet curled away from the heated side. sheet curled away from the heated side.

• Sheet curl was influenced by the amount of

Sheet curl was influenced by the amount of drying on each side of the sheet. The drying on each side of the sheet. The recommended location of a single gas recommended location of a single gas-

• fired

fired dryer was such that it would counteract the dryer was such that it would counteract the natural curl present in the sheet due to the first natural curl present in the sheet due to the first dryer cans. dryer cans.

Experimental System: Experimental System:

• The experimental system was designed to

The experimental system was designed to simulate the heat transfer into the paper during simulate the heat transfer into the paper during a typical paper cylinder drying paper process. a typical paper cylinder drying paper process.

• Figure 2 shows the experimental system

Figure 2 shows the experimental system designed for this study. designed for this study.

Figure 2, Experimental Paper Drying Figure 2, Experimental Paper Drying System System

Experiment: Experiment:

• Handsheets

Handsheets were made using a Noble and were made using a Noble and Woods Woods handsheet handsheet machine at 15 seconds machine at 15 seconds refining level by Mead refiner from lap SW refining level by Mead refiner from lap SW pulp and recycled pulp. pulp and recycled pulp.

• Handsheets

Handsheets were made at three basis weights, were made at three basis weights, 60g/m 60g/m2

2, 120g/m

, 120g/m2

2 and 180g/m

and 180g/m2

2.

.

• Paper samples from each grade were dried at

Paper samples from each grade were dried at 60% initial moisture content at three different 60% initial moisture content at three different temperatures. temperatures.

• The low temperature, 100

The low temperature, 100˚ ˚C, the average C, the average cylinder temperature used on conventional cylinder temperature used on conventional cylinder dryers producing newsprint. The cylinder dryers producing newsprint. The highest temperature, 200 highest temperature, 200˚ ˚C, is representative C, is representative

• f the gas
• f the gas-
• heated dryer surface temperature.

heated dryer surface temperature.

Results: Results:

Figure 3. Heat Flux, Shell and Paper Temperatures for Figure 3. Heat Flux, Shell and Paper Temperatures for 120g/m 120g/m2

2 Lap Pulp and 200

Lap Pulp and 200˚ ˚C Shell Temperature C Shell Temperature

50 100 150 200 250

• 10

20 30 40 50

Time, Sec. Temperature, 'C

20000 40000 60000 80000 100000

Heat Flux, W/m^2

Shell Temperature Paper Temperature Heat Flux

Figure 4. Drying Curve for Recycled Paper at 40% Solid Figure 4. Drying Curve for Recycled Paper at 40% Solid Content, 180g/m Content, 180g/m2

2 and 200

and 200˚ ˚C Shell Temperature C Shell Temperature

Drying Rate versus Time

5 10 15 20 25 30 35

• 5.00

10.00 15.00 20.00 25.00

Time, seconds

Grams/(M^2 s)

w arm up zone constant rate zone

First falling Second falling

Figure 5 & 6. Effect of Shell Temperature and Basis Figure 5 & 6. Effect of Shell Temperature and Basis Weight on the Average Drying Rates in the First Weight on the Average Drying Rates in the First Falling Rate Period Falling Rate Period

• 5

5-

• Virgin Pulp

Virgin Pulp 6 6-

• Recycled Paper

Recycled Paper

5 10 15 20 25 50 100 150 200 250 Shell Temperature C D ry R a te in T h e F irs t F a llin g P erio d (g /m 2 .S e c ) 180 g/m2 60 g/m2 120 g/m2 5 10 15 20 25 50 100 150 200 250 Shell Temperatue C D ryin g R ate in T h e F irst F allin g P erio d (g /m 2.S ec) 60 g/m2 120 g/m2 180 g/m2

Figures 7 & 8. Effect of Shell Temperature and Figures 7 & 8. Effect of Shell Temperature and Basis Weight on Drying Rates in the Second Falling Basis Weight on Drying Rates in the Second Falling Period Period

7 7-

• Virgin Pulp 8

Virgin Pulp 8-

• Recycled Paper

Recycled Paper

1 2 3 4 5 6 50.0 100.0 150.0 200.0 250.0 Shell Temperature C Drying Rate (g/m2.Sec) 60 g/m2 120 g/m2 180 g/m2 1 2 3 4 5 6 50.0 100.0 150.0 200.0 250.0 Shell Temperature C Drying Rate (g/m 2.Sec) 60 g/m2 120 g/m2 180 g/m2

Figure 9 & 10. Figure 9 & 10. Effect of Shell temperature and Basis

Effect of Shell temperature and Basis Weight on the Contact Coefficient in the First Falling Period Weight on the Contact Coefficient in the First Falling Period

9 9-

• Virgin pulp

Virgin pulp 10 10-

• Recycled Paper

Recycled Paper

200 400 600 800 50 100 150 200 250 Shell Temperature C Co n tact C oefficien t (w /m 2.C ) 180 g/m2 60 g/m2 120 g/m2 200 400 600 800 1000 50 100 150 200 250 Shell Temperatue C C o n tact C o efficien t (W /m 2.C ) 60 g/m2 120 g/m2 180 g/m2

Figure 11 & 12 Figure 11 & 12. Effect of Shell Temperature and Basis

. Effect of Shell Temperature and Basis Weight on the Contact Coefficient in the Second Falling Weight on the Contact Coefficient in the Second Falling Period Period

11 11-

• Virgin Pulp 12

Virgin Pulp 12-

• Recycled Paper

Recycled Paper

100 200 300 400 500 50 100 150 200 250 Shell Temperature C C o n tact C o efficien t ( W /m 2.C ) 60 g/m2 120 g/m2 180 g/m2 0.0 200.0 400.0 600.0 800.0 50 100 150 200 250 Shell Temperature C Contact Coefficient (W/m 2.C) 60 g/m2 120 g/m2 180 g/m2

Effect of High shell Temperature on Paper Effect of High shell Temperature on Paper Properties: Properties:

• 1

1-

• Curl:

Curl: The dried papers are cut into a 15 mm width and 15

The dried papers are cut into a 15 mm width and 15 cm length strips. cm length strips.

• Curl is measured by calculating the angle of curvature from

Curl is measured by calculating the angle of curvature from the edge rise and the distance between the edge and the the edge rise and the distance between the edge and the midpoint of the strip. midpoint of the strip.

• The dried papers tend to curl away from the heated surface

The dried papers tend to curl away from the heated surface toward the side last to dry. toward the side last to dry.

• The side against the dryer shell dries first and once dried

The side against the dryer shell dries first and once dried cannot shrink. This non cannot shrink. This non-

• uniform drying causes paper to curl.

uniform drying causes paper to curl.

Figure 13. Effect of Shell Temperature on Paper Curl. Figure 13. Effect of Shell Temperature on Paper Curl.

• Paper Curl for 180 g/m

Paper Curl for 180 g/m2

2 Virgin Pulp and Recycled Paper at

Virgin Pulp and Recycled Paper at 50% and 70% Humidity 50% and 70% Humidity

5 10 15 20 25 30 35 50% 70% 50% 70% Humidity at 23 deg C Angle Of Curvature (deg.) 100 deg. C 150 deg. C 200 deg. C

Recycled

2 2-

• Tensile Strength:

Tensile Strength:

Figure 14 Figure 14. . Effect of Shell Temperature on Paper Strength for Effect of Shell Temperature on Paper Strength for 180 g/m2 Virgin Pup and recycled Pulp 180 g/m2 Virgin Pup and recycled Pulp

4 8 12 16 20 24 50 100 150 200 250 Shell Temperature (deg. C) Tensile Index (N.m/g) Virgin Pulp Recycled Paper

Conclusion: Conclusion:

• 1. The paper
• 1. The paper-
• shell contact coefficient was not affected by shell

shell contact coefficient was not affected by shell temperature in the first following rate zone, but decreased temperature in the first following rate zone, but decreased with increasing temperature in the second following rate with increasing temperature in the second following rate

• zone. The decrease was present with both lap pulp and
• zone. The decrease was present with both lap pulp and

recycled pulp. recycled pulp.

• 2. Based on conclusion 1, the high temperature dryer should be
• 2. Based on conclusion 1, the high temperature dryer should be

installed near the middle of the dryer chain and both the installed near the middle of the dryer chain and both the beginning and end of the chain should be avoided. beginning and end of the chain should be avoided.

• 3. Each gas
• 3. Each gas-
• fired high temperature dryer should increase the

fired high temperature dryer should increase the drying rate by 2 to 4 %. drying rate by 2 to 4 %.

Conclusion Conclusion-

• Continued:

Continued:

• 4. High temperature drying should not affect the strength
• 4. High temperature drying should not affect the strength

properties, but can affect sheet curl. The paper will tend to properties, but can affect sheet curl. The paper will tend to curl toward the side dried last. This effect is less for curl toward the side dried last. This effect is less for recycled paper than for lap pulp. recycled paper than for lap pulp.

• 5. Based on conclusion 4, if only one high temperature dryer was
• 5. Based on conclusion 4, if only one high temperature dryer was

installed, this dryer needs to be located such that it installed, this dryer needs to be located such that it counteracts the curling tendency already present in the sheet. counteracts the curling tendency already present in the sheet.

• 6. Ideally at least two high temperature dryers
• 6. Ideally at least two high temperature dryers

should be installed. This will not only guard should be installed. This will not only guard against increases in curl, but will allow curl to against increases in curl, but will allow curl to be controlled by adjusting the relative be controlled by adjusting the relative temperatures of the high temperature dryers. temperatures of the high temperature dryers.

Acknowledgements: Acknowledgements:

• The authors would like to acknowledge the support of

The authors would like to acknowledge the support of The Minnesota Department of Commerce, Gas The Minnesota Department of Commerce, Gas Technology Institute and The US Department of Technology Institute and The US Department of Energy for their support. Energy for their support.

Thank You Thank You

Questions? Questions?