Effect of High Temperature Drying Effect of High Temperature Drying of Recycled Paper on Heat of Recycled Paper on Heat Transfer Rates and Sheet Transfer Rates and Sheet Properties Properties Dania Alsaid Alsaid, , Hussam Hussam Alkhasawneh Alkhasawneh and and Dania 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˚ ˚C, which significantly C, which significantly temperatures in excess of 200 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- -fired dryer. fired dryer. dryers are replaced with a gas
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: : In conventional paper � Cylinder Drying Cylinder Drying : 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 � ˚ C. pressure is limited to 160 psig or about 190 ˚ C. pressure is limited to 160 psig or about 190
� 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˚ ˚C. C. maximum surface temperature is about 150
� 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 = hc hc ( (Tshell Tshell – – Tpaper Tpaper) (1) ) (1) Q = 2 Q is the heat flux W/m 2 � Q is the heat flux W/m � 2 shell contact coefficient (W/m 2 � hc hc is the paper is the paper- -shell contact coefficient (W/m � · ˚ ˚ C) C) · ˚ C of the paper and the � T is the temperature T is the temperature ˚ 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 2 fired dryer and producing 126 lb/1000 ft 2 fired dryer and producing 126 lb/1000 ft 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 NOx NOx emissions. A Flynn ribbon emissions. A Flynn ribbon with low burner model T- - 534 was selected and the 534 was selected and the burner model T 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- -fired fired recommended location of a single gas 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 handsheet handsheet machine at 15 seconds machine at 15 seconds Woods 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, � 2 and 180g/m 2 , 120g/m 2 . 60g/m 2 , 120g/m 2 and 180g/m 2 . 60g/m
� 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. ˚ C, the average � The low temperature, 100 The low temperature, 100 ˚ C, the average � cylinder temperature used on conventional cylinder temperature used on conventional cylinder dryers producing newsprint. The cylinder dryers producing newsprint. The ˚ C, is representative highest temperature, 200 ˚ C, is representative highest temperature, 200 of the gas- -heated dryer surface temperature. heated dryer surface temperature. of the gas
Results: Results: Figure 3. Heat Flux, Shell and Paper Temperatures for Figure 3. Heat Flux, Shell and Paper Temperatures for 2 Lap Pulp and 200 ˚ C Shell Temperature 120g/m 2 Lap Pulp and 200 ˚ C Shell Temperature 120g/m 250 100000 Heat Flux, W/m^2 Shell Temperature 200 80000 Temperature, 'C 150 60000 Paper Temperature 100 40000 Heat Flux 50 20000 0 0 - 10 20 30 40 50 Time, Sec.
Figure 4. Drying Curve for Recycled Paper at 40% Solid Figure 4. Drying Curve for Recycled Paper at 40% Solid 2 and 200 ˚ C Shell Temperature Content, 180g/m 2 and 200 ˚ C Shell Temperature Content, 180g/m Drying Rate versus Time 35 constant rate zone 30 Grams/(M^2 s) 25 w arm up 20 First falling zone 15 10 Second falling 5 0 - 5.00 10.00 15.00 20.00 25.00 Time, seconds
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