Pilot-scale Papridry drying of linerboard

Transcription

1 T88 Pilot-scale Papridry of linerboard By M. Sadeghi, N. Poirier and I. Pikulik Abstract: Conventional multicylinder dryer sections, the essential component of paper machines for printing and heavier grades, have remained relatively unchanged since the inception of industrial papermaking. The Papridry system, developed at Paprican, is perhaps the most promising among several alternative technologies proposed in the last decades. This process involves pressing the sheet onto a heated cylinder equipped with a high-temperature, high-velocity gas-impingement hood. A pilot-scale machine was constructed at Paprican and used for the of five-ply, 205 g/m 2 linerboard composed of two white and three brown plies. The objective of this work was to determine the effects of one Papridry unit on capacity and product quality when installed on an existing machine. The wet board used in these experiments was obtained by rewetting dry, calendered commercial linerboard. We examined the rates and physical properties for a board dried from three initial solids contents, 41%, 47% and 62%, using two nip loads, 50 kn/m and 100 kn/m. Very high rates, up to 400 kg/m 2 h, were achieved and the board dried by Papridry had significantly improved properties. Product smoothness was increased to the extent that little or no calendering was required. Tensile properties, compressive strength, and internal bond strength were also improved, to varying degrees. Calendering and printing tests demonstrated that linerboard dried by Papridry has lower ink penetration and greater print gloss. I. PIKULIK Paprican Pointe-Claire, QC M. SADEGHI Paprican Pointe-Claire, Q N. POIRIER Paprican Pointe-Claire, QC ULP AND PAPER, Canada s premier P industry by many measures, is extremely energy intensive, ranking fourth in energy consumption after chemicals, steel and petroleum [1]. Water evaporated in the dryer section of a paper machine accounts for the removal of less than 1% of the water originally present in the fibre-water suspension from which the sheet is formed, yet accounts for nearly 1/3 of the total energy consumption in an integrated paper mill [2] and approximately 80% of its steam requirement [3]. Although the paper industry currently generates over 56% of its energy needs, primarily by burning low-grade wood material and pulping residues [4], there is still scope to reduce the mill energy requirements of the paper machine dryer section. Because of the large scale of operation, even a small increase in the production rate or the more efficient use of energy can represent substantial economic savings. Paper has not changed significantly since the inception of paper machines. Essentially all paper and board is dried while proceeding around an assembly of some 35 to 90 revolving, steam-heated cylinders [5,6]. The conventional dryer sections are very large and expensive. In multicylinder paper, the sheet is not restrained in the open draws between the cylinders, which might result in non-uniform tension, strength and stretch of the sheet and dimensional instability. Increasing the capacity of an existing machine by installing additional cylinders is costly and not always possible due to space constraints. Several alternatives to the conventional paper process have been proposed in recent years to overcome these difficulties. A comprehensive review of these techniques is pro- vided in [7], where the advantages and limitations of each process are detailed. This paper describes the high intensity process, today known as Papridry, a technique in which the sheet is pressed onto a heated cylinder equipped with a high-velocity impingement hood. This new technology provides rates one order of magnitude greater than conventional and improves the strength and smoothness of paper. In order to confirm the potentials of the Papridry process and to assess its effect on paper properties, an off-line pilot scale unit was constructed at Paprican and used for of several paper and board grades. This paper describes the experiments carried out using multiply linerboard samples. It is important to note that complete via the Papridry process requires two or more units. However, depending on the improvements required and the paper grade, it is possible to contemplate the installation of a single unit in an existing dryer section. This paper describes pilot scale trials in which we simulated the effect of a new Papridry unit installed in the dryer section of an existing linerboard machine with the objective of increasing the capacity and improving the board print quality. Three possible locations of Papridry within a conventional dryer section were simulated by feeding the linerboard sheet into the dryer at three initial solids contents. These locations were: right after the press section without a shoe press, right after the press section with a shoe press, and in the position of an unused size press. Based on the positive results of the studies conducted on the self-standing pilot unit, two Papridry units were installed on the new pilot paper machine [8] and were used for further :5 (2007) PULP & PAPER CANADA

2 peer-reviewed T89 TABLE I. Principal design parameters of the pilot Papridry. Drying cylinder diameter 1.5 m Cylinder heating Steam Maximum speed 300 m/min Trim 0.33 m Unwind stand for wet paper Electric break and automatic web tension control Impingement hood 270 wrap around the cylinder Impinging medium Air or superheated steam heated in an electrical heater Press roll 0.33 m diameter, rubber covered, hydraulically loaded FIG. 1. Off-line pilot Papridry machine. development and demonstration of the new technique. The results obtained on the pilot machine will be presented in forthcoming publications. PILOT PAPRIDRY UNIT 7AND ITS OPERATION The principal components of the self-standing pilot Papridry unit include the structural steel frame, a 1.5-meter diameter steam-heated cylinder equipped with a presser roll and surrounded by an electrically heated high-velocity impingement hood, an unwind stand, a reel, a pneumatic web tension control, and a computerized control and data collection system, Fig. 1. Impingement hoods used on Yankee dryers or MG cylinders usually recirculate hot gas obtained by combustion of natural gas or oil. The impingement gas of this pilot unit was heated by an electric heater for the following reasons: the electrical heater was less expensive and easier to operate and, for short runs and a small experimental installation, the capital cost was more important than the operating cost. The electric heater also allowed the use of superheated steam as the impingement medium. A computerized control and data acquisition system was an integral part of this fully instrumented pilot dryer. Table I lists the principal design specifications of the system, and Table II lists the measured and controlled variables. Dryer cylinder The surface of the cast iron cylinder was chromium plated and treated with polyfluorinated hydrocarbon. The surface temperature was continuously measured by 5 contact thermocouples and controlled by varying the steam pressure inside the cylinder. An oscillating doctor blade was used continuously to clean the dryer surface. Condensate and blow-through steams were evacuated from the cylinder by a stationary siphon into a separator tank. The blow-through steam was quenched in a cold-shower condenser and sent to the drain, while the condensate was returned to the boiler. The steam pressure and temperature into and out of the cylinder were continuously measured, and the pressure differential was kept constant at 3 to 4 psi. A level controller was used to keep the separator tank condensate level constant. Steam system The dryer cylinder was heated by high pressure steam. A regulator reduced the steam pressure from the boiler output of 300 psi to 160 psi. The flow of steam to the dryer, through the center of the shaft, is controlled by an electro-pneumatic valve located between the regulator and the rotary joint. The condensate was removed by blow-through steam through a stationary siphon and a rotary joint to a separator tank. Steam leaving the tank was condensed in a showered condenser. The cylinder surface temperature, measured by a bank of five thermocouples, was used to control the operation of all valves. The differential pressure between the steam inlet and outlet was maintained at 3 to 4 psi. TABLE II. Measured and controlled variables and the range of their values. Machine speed (m/min): Initial web solids content (%) Presser roll nip load(k/n/m): Cylinder temperature ( C): ambient 140 Impingement gas temperature ( C): ambient 450 Impingement speed (m/s): Web handling The pilot dryer had an undriven unwind stand, a web tensioner, and a reel with an adjustable draw. It was able to dry 12-inch wide rolls of moist paper or board, produced on Paprican s pilot paper machine or elsewhere. At top speed, nearing 300 m/min, the typical duration of a batch run is around 5 minutes for the 50-inch diameter linerboard roll or 24-inch diameter newsprint roll. This time was not long enough to achieve a steady state and the pilot dryer had to be heated up prior to the run so that the desired conditions were obtained once the moist sheet was going through the dryer. The unwind stand was equipped with an electric brake to provide the necessary tension while unwinding the paper. A dancer arm, loaded by an air cylinder and located on the machine slightly ahead of the unwind stand, provided a signal to the brake to maintain the sheet tension during unwinding. The web tension was controlled by adjusting the air pressure to the dancer arm cylinder. A carrier fabric was used to bring the moist paper into the dryer. The pilot dryer was equipped with a plain press which could operate with nip loads from 0 to 100 kn/m. A press fabric was used to receive water expelled in the press if the sheet moisture was low. After traveling around the hot cylinder, the dry, or partially dry, sheet was removed by suction on a pickup roll and transferred to the reel using the web transfer system developed by Paprican [9]. The reel was equipped with a variable speed drive that was controlled from the computer, or manually, for fine draw control. The total sheet mass at the wet and dry ends of the dryer were measured continuously by NDC-supplied gamma backscatter gauges located before and after the cylinder. In addition, grab samples were taken from the unwind stand and the reel for determination of basis weight, moisture content, and physical properties. Any samples which required further prior to testing were cut from the roll and dried as individual sheets sandwiched between two blotters on the Formette Dynamique sheet dryer. The hood and gas impingement system The impingement gas was circulated by a 75 hp AC motor-driven blower through a 250 kw electric heater and into the hood, which consists of two separate halves. The gas temperature was controlled by activating the appropriate proportion of electrical heating elements. Every time the hood was opened, the hood halves would retract away from the cylinder in a horizontal fash- PULP & PAPER CANADA 108:5 (2007) 27

3 T90 TABLE III. Drying conditions for selected samples. Run Ingoing Roll Nip Jet Jet Solids Temp. Load Temp. Velocity (%) ( C) (kn/m) ( C) (m/s) FIG. 2. Hood and hot-air system ion. The hot fluid was ejected onto the wet web from the plates facing the cylinder, which were equipped with an array of round nozzles. The cooled impingement gas and vapor from the paper were drawn to the return slots in the hood. A large portion of the returned impingement gas was recirculated, a smaller part was exhausted, and make-up gas was introduced to make up the difference. Rosemount oxygen sensors were used to estimate the humidity of gas entering into each half-hood and of the returning gas. The gas temperature, velocity and humidity were continuously measured and the density was calculated. The jet speed was kept at the desired set point and the controller took into account the fluid density variations caused by temperature or humidity changes. The impingement flow loop is shown in Fig. 2. The blower motor speed and process air temperature were controlled from the computer. The hoods can be opened and closed manually or from the computer. The bulk of air returning from the hood was pressurized by the main blower and heated in the electric heater, then recirculated into the hood. To control the moisture content, a small portion of air was allowed to escape and an equal amount of fresh air was introduced. EXPERIMENTAL CONDITIONS AND TESTING METHODS Two grades of 5-ply linerboard, with a basis weight of 205 g/m 2, were used in this work. They were composed of 2 top plies, which were white or brown, and 3 brown plies. The results obtained for the two grades were similar, therefore only those obtained for the white top are reported here. The brown plies were made from OCC and the white plies were made from unprinted fine paper broke and bleached virgin pulp. Dried and calendered board received from the mill was rewetted at Paprican to the target solids content. The same machine, but operating cold, was used to rewet the dry board. The dry sheet was passed at the speed of 10 to 30 m/min from the unwind stand to the reel and hot water was sprayed using fine showers on one side of the sheet before it entered the press nip. The rolls of rewetted board were wrapped in plastic foil and left to rotate slowly for at least 12 hours prior to being used in the experiment. The machine speed, water temperature and number of passes required to obtain the target solids contents, 41%, 47% and 62%, were found by trial and error. Samples cut near the surface and the cores of the rewetted rolls were used to determine the basis weight and the initial solids content. They also served, after, as control 1. All samples that were not completely dried by Papridry were dried under restraint, using a Formette Dynamique sheet dryer to simulate conventional. The control 2 samples were prepared from rewetted linerboard that passed through the cold Papridry machine, where they were pressed at 100 kn/m nip load and reeled, before on the Formette Dynamique sheet dryer. Thus, the control 2 samples resemble the Papridry -treated samples in having a similar history of unwinding, pressing and reeling, but differ in that they were processed cold. By comparing the physical properties of the two control samples with those of the Papridry -treated paper, it was possible to determine the effect of the process parameters on the final product quality. All Papridry -treated samples were dried in a single pass, with the white top contacting the hot roll, while machine speed was close to 250 m/min and impingement gas velocity and temperature were 95 m/s and 330 C, respectively. These are only moderate values for the hood temperature and jet velocity, as modern highvelocity impingement hoods might reach temperatures up to 700 C and impingement speed up to 200 m/s. The machine speed of 250 m/min was about 70% of the actual speed of the target board machine. The investigated variables and their range or target values are listed below: Press nip load: 50 kn/m and 100 kn/m Roll temperature: 100 C to 130 C Target ingoing solids: 40%, 55% and 70% Within the run time of one rewetted linerboard roll, it was often possible to investigate several conditions. During a run, tabs were placed in the roll to indicate the various conditions. Samples cut at the tab locations were used for a gravimetric determination of the rate and, after restrained on the Formette Dynamique dryer, uncalendered samples were used for the measurement of the product s physical properties. Parker Print Surf (S20) and bulk were determined at the Paprican laboratory for all samples. For selected samples, other physical properties were determined using standard testing methods in the member company research centre. Drying conditions for samples which underwent the full battery of physical property evaluations are shown in Table III. RESULTS AND DISCUSSION The rates of the pilot Papridry unit and physical properties of dried samples were obtained for the three initial solids contents close to our target values, namely 41%, 47% and 62%, and two nip loads, 50 kn/m and 100 kn/m. The properties of uncalendered, but fully dried linerboard were compared with those of control 1 (rewetted samples conventionally dried on the Formette Dynamique dryer) and control 2 (rewetted samples passed through the unheated Papridry machine where they were pressed at 100 kn/m nip load, then dried on the Formette Dynamique dryer). As can be seen in the remaining figures, the properties of the rewetted and conventionally dried board (control 1) varied according to the extent of rewetting. As expected, rewetting and re resulted in diminished bonding between fibres and modified linerboard properties. The magnitude of the changes depended on the extent of rewetting. Therefore, the physical properties of Papridry -treated samples cannot be compared with the physical properties of the linerboard as supplied from the mill. Similarly, the rates obtained for rewetted board might be higher than those expected at similar conditions for a neverdried board. However, the trends identified in this study are expected to represent those that would occur in a mill :5 (2007) PULP & PAPER CANADA

4 peer-reviewed T91 FIG. 3. Initial and final solids contents of Papridry -treated linerboard. FIG. 4. The rate of Papridry is one order of magnitude greater than the average conventional rate of linerboard. application of Papridry to the neverdried board. Drying rate The initial and final solids contents of Papridry -treated samples for several conditions are shown in Fig. 3. It is remarkable that on a single pass through the dryer, the solids content of samples was increased from 41% to 57%, from 47% to about 60%, and from 62% to about 73%. Clearly, very high rates were required to achieve such a substantial solids content increase on a single 1.5- m diameter cylinder. The rates obtained in these experiments are displayed in Fig. 4. It is interesting to compare the measured rates with those obtained in a typical conventional dryer section. According to the TAPPI Technical Information Sheet TIS , a good average rate in a linerboard machine is about 25 kg/m 2 h. The rates obtained in the partial of sheets with a solids content of 41% were close to 400 kg/m 2 h. As expected, the rate declined with the increasing web solids content, but even sheets dried from 62% to 72% or 74% represent rates close to 150 kg/m 2 h. The observed rates included water removal at the press nip, which was found to be minimal for an initial solids content of 50% or more, but significant for solids contents of around 40%. The effect of the press nip load on water removal is thus of greater importance at 41% ingoing solids than at 47% or 62%, as seen in Figs. 3 and 4. The very high rates obtained in these experiments with only moderate impingement conditions indicate that a single Papridry unit with a cylinder diameter of 1.8 m, operating at the wet end of the dryer section, could provide up to 20% increase in machine production. To obtain a comparable rate increase, up to 10 conventional cylinders of equal diameter would have to be added to the dryer section. Physical properties To assess the effect of the Papridry treatment on product quality, a complete set of standard property tests, as well as a few calendering and printing tests, were performed. The results of these tests are discussed in this section. Density Figure 5 shows that the density of the Papridry -treated linerboard is greater than that of control 1 by an amount ranging from 0.03 to 0.05 g/cm 3 at ingoing solids contents of 41% and 47% and by 0.06 to 0.07 g/cm 3 for an ingoing solids content of 62%. The densities of control and Papridry -dried samples are greatest at the lowest level of rewetting (62% ingoing solids content) and are quite similar for 41% and 47% ingoing solids contents. The comparison of control samples 1 and 2 reveals that cold pressing did not significantly densify the board, indicating that only the combination of pressing and heat leads to increased densification in Papridry. Changing the nip load from 50 to 100 kn/m had only a small effect on sheet density. Roughness The roughness of the white side of uncalendered board was measured by Parker Print Surf, Fig. 6, and Sheffield roughness tests, Fig. 7. The extent of rewetting had no significant effect on the surface roughness of board dried conventionally on the Formette Dynamique dryer, as demonstrated by the similar roughness values of the control 1 samples at the three initial solids contents. Cold pressing (control 2) resulted in a small reduction of the roughness, and a greater roughness reduction was observed for the less rewetted sample. The Papridry treatment caused a decrease in PPS roughness for all test conditions. A greater reduction in surface roughness occurred on sheets with a higher initial solids content. Increasing the nip load from 50 kn/m to 100 kn/m caused only a minor improvement in the surface roughness and only on sheets with higher initial solids contents, namely 47% and 62%. Figure 8 shows the roughness-bulk correlation, based on data presented in Fig. 7. The vertical line represents a bulk of 1.37 g/cm 3, which corresponds to the target caliper of 280 µm for this 205 g/m 2 grade. The maximum acceptable Sheffield roughness for this grade was 350 ml/min. It can be seen that, even without any calendering, Papridry was able to provide surface roughness which meets the product specifications. The correlation of PPS roughness with caliper is shown in Fig. 9 for all samples dried during the trial program (rather than only those which underwent a full physical property evaluation) and for the three ingoing solids ranges (40-45%, 45-50% and 55-65%). It can be seen that the roughness is greater for the sheets entering Papridry at a lower solids content (around 41%). Lower roughness was observed for the sheets entering at solids contents of 47% and 62%. The slope of the roughness-caliper line remained constant in this range of ingoing sheet solids, but the sheet entering Papridry at a higher solids content had both lower caliper and lower roughness. The fitted regression lines include both 50 and 100 kn/m data points. Figure 10, based on the data used in Fig. 9, shows the effect of cylinder surface temperature on PPS roughness. The roughness of samples decreased with the increasing ingoing solids contents, but it did not significantly change with the cylinder surface temperature in the range of 95 C to 132 C. In general, we found that the higher the solids content of the sheet leaving Papridry, the lower the roughness. The range of cylinder tem- PULP & PAPER CANADA 108:5 (2007) 29

5 T92 FIG. 5. The density of Papridry -treated board is greater than that of the control samples. FIG. 6. Papridry -treated board had lower roughness. FIG. 7. Roughness was decreased by Papridry and smoother sheets were obtained at higher nip loads. FIG. 8. A greater reduction of bulk and smoothness occurred at higher ingoing solids. FIG. 9. Roughness decreased proportionally to caliper reduction. FIG. 10. Roughness was independent of cylinder surface temperature. perature was limited. To obtain an adequate rate, we aimed to reach temperatures above 100 C. However, if the temperature exceeds about 130 C, a thin film of steam is formed between the cylinder surface and the sheet, increasing the resistance to heat transfer and decreasing the rate. Slip angle To prevent the sliding of boxes in a stack, linerboard should have a high coefficient of friction. Figure 11 shows that the slip angle for the control samples depends on the incoming web solids, but Papridry tends to reduce the slip angle. The reason for the changes in the slip angle is not clear. However, the slip angle of all samples, including those with ingoing solids contents of approximately 60%, was equal or greater than the common target value of 20 degrees. Tensile properties The tensile strength in both MD and CD was improved by the Papridry treatment, Figs. 12 and 13. The best tensile strength increase was achieved during the of a low solids content (41%) web. It is well known that increasing the product density by an improved consolidation of wet webs leads to improved fibre-fibre bonding and better product strength. Figure 14 shows that the MD :5 (2007) PULP & PAPER CANADA

6 peer-reviewed T93 FIG. 11. Slip angle reduced by the Papridry treatment. FIG. 12. Effect of the Papridry treatment on MD tensile strength. FIG. 13. CD tensile strength slightly increased by the Papridry treatment. FIG. 14. The increase of MD tensile strength correlates with the density increase. FIG. 15. The larger increase of MD elastic modulus is at higher ingoing solids content. FIG. 16. CD elastic modulus was not affected by the Papridry process. tensile strength correlates with the product density, while no such correlation is observed for the CD tensile strength. In recent years, shoe presses have been installed on many older linerboard machines to increase the consolidation and the strength of linerboard. Figure 14 indicates that the Papridry treatment can lead to a small increase in the MD tensile strength. The tensile strength of paper and board often correlates with the modulus of elasticity. Figure 15 indicates that for sheets entering at higher solids contents, Papridry caused a small increase in the MD elastic modulus, but Fig. 16 provides no evidence of a similar increase in the CD modulus. Figures 17 and 18 show that the Papridry -treated board subjected to a nip load of 100 kn/m tends to have a greater elongation in MD and CD than the control samples. However, using a nip load of 50 kn/m did not lead to a significant stretch increase. The tensile energy absorption (TEA) reflects the energy required to break the board as strained either in the machine direction or cross direction. As shown in Figs. 19 and 20, Papridry process increased the TEA of the majority of samples. As expected, for both MD and CD measurements, improved elongation and tensile energy absorption were usually PULP & PAPER CANADA 108:5 (2007) 31

7 T94 FIG. 17. Greater MD elongation for Papridry -treated FIG. 18. Greater CD elongation for Papridry -treated FIG. 19. The Papridry treatment increased the TEA of linerboard in the machine direction. FIG. 20. The Papridry treatment increased the TEA of linerboard in the cross direction. FIG. 21. The Papridry treatment increased the MD STFI. FIG. 22. The Papridry treatment increased the CD STFI for an initial solids of 41%. observed for samples with improved tensile strength. Compressive strength and internal bond strength While the consolidation of wet board leads to better bonding and better tensile properties, the increased density achieved this way could have a negative effect on the stiffness and the compressive strength of the product. However, Figs. 21 to 23 demonstrate that the Papridry treatment of a web with a solids content of 41% resulted in increased STFI compressive strength and ring crush strength in both directions. A similar treatment of webs with a higher solids content at least did not decrease the compressive strength parameters of the product. Figure 24 demonstrates that the Papridry treatment of a web with a solids content of 41% resulted in a significant increase in the Scott bond strength of board. The sheets treated at solids contents of 47% and 62% had little or no internal bond strength increase when compared with the control samples. It appears that the exposure of a low solids content web to high pressure and heat helps in the development of inter-ply bonds. At higher solids contents, this method of enhancing the internal bond strength appears to be less effective :5 (2007) PULP & PAPER CANADA

8 peer-reviewed T95 FIG. 23. CD ring crush strength improved by the Papridry treatment. FIG. 24. The Papridry treatment increased the Scott bond strength. FIG. 25. Higher print quality of Papridry -treated board. FIG. 26. Micrographs of flexo printed linerboard. Calendering and printing tests The calendering conditions were determined by assuming that the rewetted sample, which was dried on the Formette Dynamique dryer, resembles the uncalendered board. The following calendering conditions were required for this simulated uncalendered board to obtain the target Sheffield roughness: speed of 50 m/min, temperature of 50 C and nip load of 30 kn/m. The same conditions were used for Papridry -treated samples. While the of the majority of Papridry -treated samples was completed, in sheet format, in the Formette Dynamique sheet dryer, several rolls of board were dried by slowly passing the web through the Papridry unit, with the press nip and the transfer roll nip open, to simulate a conventional cylinder dryer. After being calendered using conditions simulating the mill operation, the sheet printability was tested in our laboratory by the MB flexo draw test. In this test, a drop of ink is deposited onto a sheet of paper or board and is immediately dragged by a Teflon blade. The length of the line formed under these conditions is measured. A longer draw line indicates less ink penetration and better ink holdout. The results, in Fig. 25, show that the Papridry -treated board had a longer draw line than the control sample. Rolls of calendered brown top board were delivered to the mill and sent to the mill s client for a printing test in the flexo press. The control sample was delivered directly from the mill. The print gloss of Papridry -treated board was greater than that of the mill product. While print density for solid tones was similar, the clarity and crispness of printed lines increased dramatically with the Papridry treatment, as demonstrated in Fig. 26. A closer observation of the magnified lines shows that there is considerably less feathering of the ink in Papridry -treated samples, which have a smoother and better consolidated surface than the mill provided board. SUMMARY A comprehensive experimental study was completed to evaluate the Papridry treatment of linerboard. Already dried and calendered board was rewetted to various solids contents to establish the rates and physical properties for a wide range of conditions. Three initial solids contents of 41%, 47% and 62%, as well as two press nip loads of 50 kn/m and 100 kn/m, were tested. Drying was completed for each sample on the Formette Dynamique dryer. In addition to Papridry -treated samples, two control samples were prepared to allow for a thorough understanding of the effect of Papridry conditions on the final product quality. Very high rates, up to 400 kg/m 2 h, were achieved for linerboard with a low solids content, while a rate of approximately 150 kg/m 2 h was observed even for the initial solids content of 62%. These rates are most impressive when compared to the average good value for conventional board, about 25 kg/m 2 h. These findings demonstrate that even one Papridry unit, preferably installed at the wet-end of the dryer section, could provide substantial extra capacity without the need for adding several cylinders. By comparing the physical properties of Papridry -treated samples with those of the two control samples, it was shown that the Papridry treatment significantly improved the board properties. In particular, board smoothness was increased to the point that it would require little or no calendering. The product would also have significantly improved tensile properties, slightly improved (or at least preserved) compressive strength and improved internal bond strength. This paper is based on results obtained on a pilot installation which differed from a commercial machine in several parameters. The most important differences were the use of board, which was previously dry PULP & PAPER CANADA 108:5 (2007) 33

9 T96 and rewetted, and the relatively low machine speed. We would expect to observe similar trends for commercial Papridry installations, but the specific results might be different. Papridry technology does not require any new or unproven equipment. The results of this study show that the very high rate achievable through the installation of Papridry units does not come at the cost of board property degradation, as most surface and strength properties are in fact improved to varying degrees. The combination of a high rate and improved properties makes Papridry technology an ideal alternative for mills interested in acquiring extra capacity. LITERATURE 1. SALAMA, S.Y., MINSKER, B.S., OLSEN, K.G. Competitive Positions of Natural Gas: Industrial Solids Drying, Energy and Environmental Analysis Inc., Arlington, VA (1987). 2. CHIOGIOJI, M.H. Industrial Energy Conservation, Marcel Dekker, New York (1979). 3. REARDON, S.A. A Mathematical Model for the Simulation of Paper Drying Energy Consumption. Ph.D. Thesis, University of Tasmania, Tasmania, Australia (1994). 4. STORAT, R.E. The U.S. Pulp and Paper and Paperboard Industry: A Profile. Tappi J. 76(3): (1993). 5. HEIKKILA, P., TIMOFEEV, O., KIISKINEN, H. Multicylinder Drying. Chapter 3, Papermaking Science and Technology, Papermaking Part 2, Drying. Ed. M. Karlsson, Fapet Oy, Helsinki, Finland (2000). 6. PIKULIK, I.I., LEGER, F. Secherie d une machine a papier - Etude et depannage. Ed. Technical Section CPPA, Montreal, Canada (1997). 7. PIKULIK, I.I., POIRIER, N.A. New Developments in Paper and Board Drying. Proceedings, Chemical Technology of Wood, Pulp and Paper, Slovak Technical University, Bratislava, September 2003, p. 56 (2003). 8. CROTOGINO, R.H., PIKULIK, I.I., LEGER, F., DAUNAIS, R., GOULET, B., HAMEL, J. Paprican s New Pilot Paper Machine. Pulp Paper Can. 101(10): 48 (2000). 9. MCDONALD, J.D., DAUNAIS, R., PIKULIK, I.I., PYE, I.T. A New Web Transfer System for Closing the Draw Between the Last Press and the Dryer Section. Pulp Paper Can. 92(3):T62 (1991). Résumé: La sécherie multicylindrique classique, élément essentiel d une machine à papier impression ou à papier de plus fort grammage, est demeurée relativement inchangée depuis qu on a commencé à fabriquer du papier en usine. La technologie Papridry, développée par Paprican, est peut-être la plus prometteuse des technologies proposées depuis quelques années. Le séchage comprend le pressage de la feuille contre un cylindre chauffé doté d une hotte à jet de gaz haute température et haute vitesse. Une machine à l échelle pilote a été construite à Paprican et utilisée pour le séchage d un carton couverture de 205 g/m 2 formé de deux couches blanches et de trois couches brunes. La recherche visait à analyser les effets d une unité Papridry sur la capacité de séchage et la qualité du produit lorsque l unité était installée sur une machine existante. Pour obtenir le carton humide pour ces essais, nous avons remouillé du carton couverture commercial sec et calandré. Nous avons examiné le taux de séchage et les propriétés physiques d un carton entièrement séché à des teneurs initiales en matières solides de 41 %, 47 %, et 62 %, à l aide de deux chargements à la pince à 50 kn/m et 100 kn/m. Des vitesses de séchage très élevés, jusqu à 400 kg/m 2 /h ont été réalisés, et les propriétés du carton séché à l aide de Papridry ont été substantiellement améliorées. Le lissé du papier s est accru au point où il a fallu par la suite peu ou pas de calandrage. Les propriétés d allongement, la résistance à la compression, et la cohésion interne ont aussi été améliorées à divers degrés. Les essais de calandrage et d impression ont démontré que le carton couverture séché à l aide de Papridry absorbe moins l encre et donne un brillant d impression accru. Reference: SADEGHI, M., POIRIER, N., PIKULIK, I. Pilot-Scale Papridry Drying of Linerboard. Pulp & Paper Canada 108(5):T88-96 (May 2007). Paper presented at the 91st Annual Meeting in Montreal, QC, Canada, February 7-10, Not to be reproduced without permission of PAPTAC. Manuscript received on November 18, Revised manuscript approved for publication by the Review Panel on March Keywords: LINER BOARDS, DRYING, DRIERS, DRIER SECTION, MACHINE DESIGN, PAPRI- CAN, PERFORMANCE EVALUATION :5 (2007) PULP & PAPER CANADA