BELT AND DRUM PRESSING APPARATUS AND HEATED DRUM FOR THE SAME

Abstract: Drum and belt press in which essentially none of the compressive forces imposed on the central drum (104, 204) are transmitted to the supporting frame (240, 410). The press provides a much greater compressive force on the material (108, 208) being pressed, in relationship to belt tension, than those heretofore available. The invention makes it possible to construct the central drum (104, 204) so as to obtain a very high heat flux to the web being pressed. Drums suitable for the press are also described. Some of the drum constructions described will give improved results when used in previously known presses of this type.

Description: BELT AND DRUM PRESSING APPARATUS AND HEATED DRUM FOR THE SAME BACKGROUND OF THE INVENTION Technical Field This invention relates to an apparatus and technique for compressing a moving web with an endless flexible belt, and particularly an apparatus and technique of this nature wherein the web is compressed by the belt while the web is guided about the heated cylindrical surface of a rotatable drum. It also relates to a heated drum which is particularly useful in this connection. Background Art Presses are used to consolidate paper and panel products. Examples of this consolidation are the formation of a pulp mat from a pulp slurry, the formation of paper from wood pulp or other fibrous material, or the formation of a panel product from wood particles or flakes. Compressive forces act on and consolidate the material as it passes through the nip formed by a pair of rolls. The greater the compressive force the greater the consolidation. The compressive forces at the nip perform another function in the formation of paper - the removal of water from the web. The compressive forces acting on a web in the nip between the two rolls is of short duration. The time that the compressive force may act on the web may be extended by the use of a belt press. In a belt press a belt is wrapped around a section of the periphery of a drum and exerts a compressive force on a web passing between the belt and drum. Tension in the belt is translated into a compressive force on the web and drum. Belt presses are used both for paper and for panel products. Gottwald et al, U.S. Patents 3,110,612 and 3,354,035 and Haigh, U.S. Patent 3,319,352 are exemplary of belt presses for paper. Gersbeck et al, U.S. Patent 3,891,376, Brinkmann et al, U.S. Patent 3,938,927 and Gerhardt et al, U.S. Patent 4,457,683 are exemplary of belt presses for panel products. Figures 1-10 illustrate compressive forces from belts and nips acting on a web. These figures " also illustrate the forces that are being passed to the frame of the apparatus. In the illustrations of the compressive forces on the web in both the background section and the detailed description section a number of parameters are held constant. These are: (a) The belt tension (T), (b) The belt materials, (c) The conditions in the nip, e.g., web thickness, roll covering, etc., (d) The constant surface temperature of the drum, and (e) The forces due the rotational drive forces and the component weight. In addition, relative roller diameters and belt angles are arbitrarily selected to simplify analysis. The diameter and belt angle options are infinite but the arbitrary selection will not greatly distort the illustration. Also, supplemental nip forces mentioned often in the art are not taken into account in the examples. The only variable " being analyzed is the total compressive force (TCF) produced by belt tension or directly by belt tensioning forces available to compress the web being processed. These forces are expressed as a multiple of belt tension T. Both T and TCF may be expressed in suitable force units such as newtons. There are three categories of compressive force acting on the web. These are: (1) The total compressive force radial to the central drum caused by that portion of the belt resting directly on the central drum and due to tension in that portion of the belt only. This quantity is equal to: T2τr (% of central drum circumference contacted/100) (2) The nip force of each of the belt tension rollers when these rollers make a nip with the central drum. (3) The nip force of each of the belt carrying idler rollers other than the tension rollers upon the central drum when these rollers make a nip with the central drum. The force is created by the belt tension only. Figures 1-10 are representative of prior art drum and belt presses. Figure 1 illustrates the configuration shown in Figure 1 of Gottwald et al, U.S. Patents 3,110,612 and 3,354,035. Figure 2 illustrates the configuration described in line 25 of column 4 of Gottwald et al, U.S. Patent 3,110,612. In both of these figures the total compressive force is created solely by the belt resting on the central drum. There is no nip force on the central drum. In Figure 1 the belt 3 circumferentially contacts 180° or 50% of the surface of central drum 4. The tension T on the belt is provided by the two tensioning rollers 5 and 6. The idler roller 7 holds the inner and outer courses of belt 3 apart. The web 8 is guided around the central drum 4 and pressed against the central drum 4 by the belt 3. The total compressive force on the central drum 4 and web 8 is equal to 3.14 T. The tensioning rollers 5 and 6 are attached to a frame and the tension of approximately 2 T is transferred to the frame from each roller. In addition, there is an axial bending force of 2 T on the central shaft of the central drum 4. There is also an axial bending force of approximately 2 T on each of the central shafts of tensioning rollers 5 and 6 and idler roller 7. The central drum 4, the tensioning rollers 5 and 8, and the idler roller 7 are all attached to the frame and the forces upon them are transmitted to the frame. Neither the tensioning rollers 5 and 6 nor the idler roller 7 form a nip with the central drum 4. In Figure 2 the belt 3a circumferentially contacts 270° or 75% of the surface of central drum 4a. The tensioning rollers are 5a and 6a and the idler rollers are 7a, 9 and 10. The web 8a is guided around the central drum 4a and pressed against the central drum 4a by the belt 3a. The total compressive force acting on the central drum 4a and the web 8a is 4.7 T. Again, there is an axial bending force applied to the central shaft of central drum 4a and an axial bending force applied to each of the tensioning rollers 5a and 6a and idler rollers 7a, 9 and 10. These forces are passed on to the frame for the apparatus and the frame must be strong enough to carry them. Haigh, U.S. Patent 3,319,352; Gersbeck et al, U.S. Patent 3,891,376; and Brinkmann et al, U.S. Patent 3,938,927 are exemplary of configurations in which one or more idler nip rolls are used. In each of the following examples the total compressive force caused by the belt on the central drum will be the same as those calculated for Figures 1 and 2 - 3.14 T at 50% circumferential contact between the central drum and the belt. Figure 3 illustrates a configuration in which there is one idler nip roll. The belt 3b and the web 8b circumferentially contacts 50% of the surface of the central drum 4b. The tensioning rollers are 5b and 6b. An idler nip roller 11 is within the belt 3b and forced toward central drum 4b by the outer course 3b' of belt 3b and forms a nip 12 with the central drum 4b. The web 8b is guided around and pressed against the central drum 4b by the inner course 3b" of belt 3b. The idler roller 11 also compresses the belt 3b and web 8b in the nip 12. The compressive force in nip 12 is 2 T. The total compressive forces - idler roller nip force and belt force - are 5.4 T. There will also be 4 T of axial bending force acting upon the central drum 4b and 2 T of axial bending force acting on each of the tensioning rollers 5b and 6b. These forces are transferred to the frame of the apparatus. Figure 4 illustrates a configuration in which there are two idler nip rollers. The belt 3c and web 8c train around 50% of the surface area of central drum 4c and the belt 3c is held in tension by tensioning rollers 5c and 6c. A pair of idler nip rollers 13 and 14 are within belt 3c and are placed at a 45° angle to the axis of central drum 4c. The idler nip rollers 13 and 14 are forced toward central drum 4c by the outer course 3c' of belt 3c and form nips 15 and 16 with the central drum 4c. The web 8c is guided around and pressed against the central drum 4c by -the inner course 3c" of belt 3e. A vector analysis of the forces acting upon each of the idler nip rollers is shown in Figure 5. Roller 13 is illustrated. The resultant compressive force is 1.4 T in each of the nips 15 and 16. The total compressive forces acting on web 8c - the belt compressive force and the nip compressive force - are 5.94 T. The axial bending forces of 2 T on each of the tensioning rollers 5c and 6c, and 4 T on central drum 4c are transferred to the frame. Figure 6 illustrates the system shown in Figure 4 and the average pressures acting on the central drum 4c and the web 8c at various locations around the drum. For purposes of illustration the following parameters were chosen - 175 newtons per meter (N/m) belt tension and a 1.3 meter drum diameter. This results in a compressive force from the belt of 275 kPa. An average nip pressure of 3.5 MPa is assumed. The belt pressure is continuous over 50% of the drum surface and the nip pressure is discontinuous as shown. Figure 7 illustrates a configuration in which there are three idler nip rollers, central idler nip roller 17 and side idler nip rollers 19 and 20. The idler nip rollers 17, 19 and 20 are forced toward central drum 4d by the outer course 3d* of belt 3d to form nips 18, 21 and 22 with the central drum 4d. The web 8d is guided around and pressed against central drum 4d by the inner course 3d" of belt 3d. The forces acting on central idler roller 17 are the same as those shown for idler roller 13 in Figure 5. The compressive force acting on the web 8d in the nip 18 is 1.4 T. A vector diagram of forces acting on side idler rollers 19 and 20 is shown in Figure 7. The compressive force acting on the web 8d in each of the nips 21 and 22 is 0.7 T. The total compressive forces acting on the web 8d are 5.94 T. The axial bending forces of 2 T on each of the tensioning rollers 5d and 6d, 3.414 T on central drum 4d and 0.29 T on each of the side idler rollers 19 and 20 are transferred to the frame. Figure 8 illustrates a configuration in which there are four idler nip rollers, central idler nip rollers 23 and 24 and side idler nip rollers 27 and 28. The idler nip rollers 23, 24, 27 and 28 are forced toward central drum 4e by the outer course 3e' of belt 3e to form nips 25, 26, 29 and 30 with the central drum 4e. The web 8e is guided around and compressed against central drum 4e by the inner course 3e" of belt 3e. A vector diagram of forces acting on central idler nip rollers 24 and 25 is shown in Figure 9. Central idler nip roller 24 is illustrated. The compressive force acting on the web 8e in each of the nips 25 and 26 is T. The compressive force acting on the web 8e in each of the nips 29 and 30 is shown in Figure 8. It is 0.5 T. The total compressive forces acting on the web 8e during its travel around the central drum 4e are 6.14 T. Again the axial bending forces acting on the central drum 4e, the tensioning rollers 5e and 6e, and the idler nip rollers 23, 24, 27 and 28 are transferred to the frame. Figure 10 illustrates a configuration in which there is a large number of idler nip rollers. In this configuration the idler nip rollers 30 extend throughout the area of belt and web contact with the central drum 4f. The idler nip rollers 31 are forced toward central drum 4f by the outer course 3 of belt 3f to form nips 31 with the central drum 4f . Two belt and web guide rollers 32 and 33 are added. The web 8f is guided around and compressed against central drum 4f by the inner course 3f" of belt 3f. In this configuration the total compressive forces acting on the web through the nips of the idler nip rollers are approximately equal to the total compressive forces from the belt. The total compressive forces acting on the web will be 6.28 T. The axial bending forces on the tensioning rollers 5f and 6f , and the central drum 4f are transmitted to the frame. In each of the above belt loop configurations, forces from the belt and roller system are carried by the frame. In each of these configurations, the central drum must be mounted on the frame and the unbalanced compressive force on the shaft of the central drum, and on the shafts of the tensioning and some idler rollers is passed to the frame. The unbalanced compressive forces acting on the shafts and on the frame range from 1.57 T to 4 T. The central drum is heavy and the shell is thick in order to absorb these forces with allowable bending stress. If the press is used as a dryer, then the drum will usually be heated. U.S. Patent 4,324,613 discloses a pair of nip rolls for consolidating and drying paper in which one of the rolls is a heated drum. In belt presses, the belt may wrap around a heated drum. The Gottwald et al, Haigh, Gersbeck et al, Brinkmann and Gerhardt et al patents disclose a heated central drum. In conventional practice, the thickness of the shell of the central drum would severely limit the rate of transfer of heat through the shell to the web. Heat transfer drums are described in Fleissner et al, U.S. Patent 3,581,812; Kilmartin, U.S. Patent 3,838,734; and Beghin, U.S. Patent 4,090,553; Heisterkamp, U.S. Patent 3,237,685; Cappel et al, U.S. Patent 4,183,298; Appel, U.S. Patent 4,252,184; Schiel, U.S. Patent 4,254,561 and Wedel, U.S. Patent 4,440,214. A press having a free floating high pressure nip roll is described in "HI-I Press, Mark III Installed At Scott Paper, Mobile;" Pulp and Paper Magazine of Canada, November 15, 1968, pages 56- 57. : The attainable speed for drying paper is often limited by the need to maintain web integrity during the forming and drying process. At high moisture contents the web is held together by water viscosity, surface tension, and the fiber contact sites. As the web is dried, the influence of viscosity and surface tension decreases both because there is less water and because viscosity and surface tension decrease with an increase in temperature; and the influence of bonding sites increases. The web will actually lose strength as it is initially heated in the dryer. This is seen in Figure 11 which illustrates the passage of a web of paper through the forming, pressing and drying section of a paper machine and shows the change in strength characteristics of the paper web through the machine as the sheet dries. Figure 12 is a similar figure for newsprint. It shows the breaking length and web strength characteristics of a web of newsprint as it passes through the pressing and drying operation. Figure 12 is from Thomas, U.S. Patents 4,359,827 and 4,359,828 and the phenomenon is discussed in detail in these patents. There are many variables which influence the degree of drying and strengthening of the web as it passes through the first drying drum and exits from that drum. There are a number of machine variables. If a belt is used to hold the web on the drum, then the tension of the belt and the diameter of the drum are factors. If a felt is used, the permeability of the felt is a factor. If a pressure nip is used, then the pressure in the nip, the residence time in the nip and the ventilation from the nip are factors. The machine speed, the tension on the web being drawn through the machine, the temperature of the heating drum and the heat recovery rate of the drum are also factors. There are also a number of variables within the web. The freeness and permeability of the web, the compressibility of the web, the bondability of the web, the dryness or moisture content of the web as it reaches the drum, the temperature of the web, and the weight and thickness of the paper or paperboard are all factors. The tendency of the web to stick to the drum is also a factor. The limiting speed in a given situation will depend on a combination of all of the above factors. A given machine will have a maximum speed for a given web or a given web will require a certain drying capacity to achieve a given speed. The operation of the machine at a capacity below the limits influenced by these various factors is not possible. Attempting to remove moisture from the web quickly in order to accelerate the initial heating also creates a problem. If moisture vapor in the web creates interior pressure much above constraining pressures, then the internal expansion of the vapor in the web will tend to blow the web apart. The approximate maximum machine speeds for linerboard are shown in Figure 13. These are examples of commercial speeds for drying paper. Figure 13 is a plot for the drying of unbleached kraft linerboard and shows machine speed in meters per minute against grade weight in grams per square meter of web. Line 40, the dotted line, indicates the possible machine speeds versus grade weights at a constant production rate of 240 tons per day per meter of machine width. Line 41, the solid line, shows the actual approximate maximum commercial speed at various grade weights. These speeds correspond to a production rate in tons/day/meter of machine width of 130 at a grade weight of 127 g/m 2 , 190 at 205 g/m 2 , 240 at 337 g/m 2 , and 180 at 439 g/m 2 . Commercial linerboard machines use 450-600 lineal circum- ferential meters of dryer to operate at these speeds. The dryer drum temperatures will range from 100°C to 200°C and web pressures on the drum are typically up to 7-15 kPa. Water removal rates are on the order of 25-35 kg per hour per square meter of drum. For some paper grades, such as tissue, a relatively high pressure nip with the drum is made to iron the wet web onto the drum. SUMMARY OF THE INVENTION Throughout the application, the term belt may include a belt and felt assembly. The present invention relates to a belt press and a belt press dryer which allows greater forces from belt tension to be placed on the web passing through the press. The construction also causes balanced forces to be placed on the central drum allowing a lighter drum shell and dryer drum construction. In heated drums this lighter construction allows heat to be passed more quickly to the web. The construction also removes forces from the surrounding structure allowing a more economical structure. The construction also allows a new method of press drying. In the present invention, the U-shaped inner course of an endless belt is wrapped around a central drum with the outer face of the belt contacting the face of the central drum as in other belt press arrangements. A web to be treated is between the belt and the drum face and is pressed against the drum by the belt. The web may comprise various materials including plastics, fabrics, wood chips or flakes, and paper making stock. Appropriate binder and coating materials may be included. The belt tension is applied by two tensioning rollers placed within the endless belt and contacting the inner face of the belt. The tensioning rollers are located in the end loops formed at the junction of the inner and outer courses of the endless belt. The axes of the two tensioning roEers can be biased toward and away from each other to adjust the tension on the belt. The shafts of the tensioning roEers are connected by the tensioning Enkages. The press has means for moving the tensioning roEers relatively toward one another in engagement with the end loops of the endless belt. The movement of the tensioning roEers causes the tensioning roEers to form nips with the central drum. The belt and the web are compressed between the tensioning roEers and the central drum at their nips. The inner course of the belt between the tensioning roEer nips clasps the central drum and web. The overaE forces operating against the central drum are intrinsieaEy balanced. The total compressive forces acting on the web due to belt tension, and belt tensioning forces are increased relative to the compressive forces of simEar but unbalanced arrangements without supplemental force appEcation. There may be additional idler nip roEers within the belt between the inner and outer belt courses and between the two tensioning roEers. The number of idler nip roEers is a matter of choice. The Emits of relative diameters of the central drum and the tensioning and idler roEers wiU depend upon the number of roEers. There must be more than two tensioning and idler roEers if the central drum has a diameter greater than that of the roEers. Each of the additional idler nip roEers is mounted to be movable generaEy radiaEy inwardly and outwardly toward and away from the central drum with the inward radial force being supplied by the belt tension as the belt is tensioned about the central drum. Each of the additional idler nip roEers also is fixed angularly with respect to the central drum. The adjustment of the two tensioning roEers adjusts the tension in the belt which causes aE of the roEers to apply more or less pressure on the inner course of the belt, the web and the central drum. Moving the tensioning roEers toward each other increases the tension in the belt and causes both the inner and outer courses of the belt to move inwardly toward the central drum. This inward movement wfll cause the inner belt course to apply greater compressive force against the web and the face of the central drum. This inward movement wEl also cause the outer belt course to apply greater force against the idler nip roEers, causing them to move toward the central drum and increase the compressive force at the nips of each of the idler nip roEers acting on the inner course of the belt, the web and the central drum. This inward movement wfll increase the total compressive forces acting on the web and central drum at the nips between the tensioning roEers and the central drum. Moving the tensioning roEers away from each other will decrease the belt tension and the various compressive forces. The tensioning roEer arrangement allows both greater belt forces on the drum because of the inherent ease of greater circumferential contact between the belt and the central drum and greater nip forces because of the tensioning roEer nips. The tensioning roEer arrangement also allows the overaE forces operating against the central drum - the belt force and nip forces on the drum due to belt tension and belt tensioning forces - to be intrinsieaEy balanced at aE values of belt tension. There are no forces due to belt tension transmitted to the supporting structure. There are no axial bending forces on the central drum. Neither are there axial bending forces on the idler nip roEers because each of these roEers is placed around and against the central drum and each of the idler nip roEers is placed in a position in which the entry and exit angles between the outer belt course and the radial Ene between the roEer and the central drum are equal. The balanced forces on the central drum and on the roEers simplify the support framework because the tensioning and bending forces no longer act on the support framework. The balanced forces and the absence of appreciable bending forces on the central drum make it possible for the central drum to be of lighter and simpler construction which is cheaper to construct. For example, in certain embodiments of the invention the central drum takes the form of a hoEow, open ended ring-like member which is of a material and has a waE thickness which will withstand the total compressive forces acting upon it. This construction aEows the use of combustion within the bore of the drum as a heat source. The outer sheE can also be modified, as by slitting at its outer surface, to partiaEy reUeve the thermal stresses on the surface when heat is transferred through the outer surface of the roEer. This is possible because the mechanical stresses imposed are ring crushing stresses, not axial bending stresses. The central drum can also be constructed with a thin outer sheE. In this construction the central drum has an inner cylindrical body and an outer concentric cylindrical sheE spaced apart radiaEy of the inner cylindrical body to form a shaEow annulus between the inner body and the outer sheE. There is a system of radial connections between the outer sheE and the inner body to secure one to the other. The connections are arrayed about the inner body in the annulus to provide load bearing support for the outer sheE over the entire area of the annulus as weE as the capacity to retain the sheE against internal pressure in the annulus. The annulus may be used as a conduit for the flow of heating fluid. The outer sheE would be closed and the inner body would be apertured for supply of fluid. The fluid would be removed by ducts or other means located at the ends of the annulus. It may be necessary to have additional removal sites located along the length of the annulus. These would be apertures in the inner drum body to which removal ducts are attached. In some presently preferred embodiments of the invention, for example, the drum takes the form of a hoEow, open-ended ring-Eke member having radiaEy oriented apertures in the inner body and duct means slip-jointed with the aperture for supplying fluid to the aperture, and duct means sEp- jointed to the ends of the annulus for removing the fluid from the annulus after it circulates through the annulus from the aperture. The annulus may have passages formed within it to carry the fluid or vapor. The connections would be spaced apart from one another to subdivide the annulus into a multiplicity of fluid flow passages which extend throughout the annulus generaEy axially of the drum. The connections may take the form of spaced spoke-like members. The connections could form the side waEs of the passages. The thin outer sheE aEows more heat per unit time to be transmitted through the sheE to the material being dried or compressed on the drum. A heat transfer fluid, such as steam, would be circulated through the annulus to transfer heat to the web. The radial surfaces of the passages may be extended in relation to the circumferential passage width to increase the steam condensing area and enhance the condensing rate because the extended radial surfaces have the aid of centrifugal force in removing the condensate from the condensing surface. The heat transfer surface of the passages would be greater than the outer heat transfer surface of the shell also aEowing more heat per unit time to be transmitted through the sheE. Metal stress from internal steam pressure is reduced to a smaE value because of the s aE cross section of the passages relative to the waE thicknesses of the passages. The waEs between the passages carry external mechanical loads from the outer sheE to the strong inner body of the drum. The reduction of mechanical stresses in the drum permits the use of lower strength, higher heat conductive materials such as copper in the outer sheE permitting an even higher heat flux with reduced thermal stress. The use of an outer sheE construction also aEows the inner drum body to be constructed of stronger materials since thermal conductivity in the inner drum is no longer an issue because the heat flow path does not go through the inner drum. For example, selected grades of copper and stainless steel have essentiaEy identical thermal expansion and could be used in combination for the outer sheE and inner body of the drum. The thinner outer sheE aEows greater heat transfer and conse¬ quently a smaEer peripheral surface is needed to transfer the same amount of heat transferred in a conventional drying drum. The reduced drum diameter wiE also increase the magnitude of the uniform belt pressure on the drum which will facilitate increased heat transfer and an increased restraining force on the web. The reduced drum diameter wfll also decrease ring crushing stresses in the drum due to nip loads and reduce the construction cost. The reduced diameter is possible for a given heat transfer requirement both because of the increased heat flux through the drum sheE and because of the increased nip loading on the drum by the tension roEers. The tensioning roEers may also be used to support the central drum. The roEers and the eentral drum are cylindrical and not crowned. The belt is normaEy rotated by driving one of the tensioning roEers, although any roEer can be driven. In other embodiments, the surface of the central drum can be apertured for flow of fluid to or from the web. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1-4 are diagrams showing various prior art central drum, belt and roEer combinations and the forces acting within these systems. Figure 5 is a vector analysis diagram of the forces acting on one of the idler nip roEers in Figure 4. Figure 6 is a diagram showing the compressive force pattern on the drum of Figure 4. Figures 7-8 are diagrams similar to Figures 1-4 and showing additional combinations in the prior art of a central drum and roEers. Figure 9 is a vector analysis diagram of the forces acting on one of the idler nip roEers in Figure 8. Figure 10 is a diagram simEar to Figures 1-4 showing another prior art central drum and roEer combination. Figures 11 and 12 are plots showing sheet strength as the sheet is formed and carried through the press and dryers. Figure 13 is a graph of machine speed versus grade weight in linerboard manufacture. Figures 14-20 are schematic views of embodiments of the invention. Figures 21-22 are diagrams simflar to Figures 4-7 iUustrating two embodiments of the present invention and the forces acting within these systems. Figure 23 is a vector analysis diagram of the forces acting on one of the tension roEers of the embodiment shown in Figure 22. Figure 24 is a diagram simEar to Figure 22 showing another embodiment of the present invention. Figure 25 is a vector analysis diagram showing the forces acting on one of the tension roEers of the embodiment of Figure 24. Figure 26 is a vector analysis diagram fllustrating the forces acting upon the central drum and roEers in the embodiment of Figure 24. Figure 27 is a diagram similar to Figures 21-22 showing another embodiment of the invention. Figure 28 is a diagram similar to Figure 6 illustrating the compressive force pattern on the central drum of Figure 27. Figure 29-31 are diagrams similar to Figures 21-22 fllustrating other embodiments of the invention. Figure 32 is a schematic view of another embodiment of the invention. Figure 33 is a side elevational view of a prototype unit. Figure 34 is an end elevational view partiaEy in cross section from the right hand end of Figure 33. Figure 35 is a perspective view of the belt, roEer and drum assembly in the embodiment of Figures 33 and 34. Figure 36 is a schematic view of an internaEy heated drum. Figure 37 is a portion of a stress relieved drum sheE. Figure 38 is a cross-sectional view taken along line 38-38 of Figure 37. Figure 39 is a portion of another drum sheE. Figure 40 is a cross-sectional view taken along line 40-40 of Figure 39. Figure 41 is a portion of another drum sheE. Figure 42 is a cross-sectional view taken along line 42-42 of Figure 41. Figure 43 is a portion of another drum sheE. Figure 44 is a cross-sectional view taken along line 44-44 of Figure 43. Figure 45 is a cross-sectional view of a heated drum for use in any of the foregoing assemblies. Figure 46 is an enlarged longitudinal cross-sectional view of a portion of the annulus in the heated drum of Figure 45. Figure 47 is an enlarged longitudinal cross-sectional view of one end portion of the annulus in the heated drum of Figure 45. ' Figure 48 is a transverse cross-sectional view of part of the annulus in an alternative form of fluid heated drum such as a steam heated drum. Figure 49 is a view similar to Figure 48 of another version of a fluid heated drum. Figure 50 is a view similar to Figure 48 of a preferred version of a fluid heated drum. Figure 51 is a view similar similar to Figure 48 illustrating the preferred construction of the drum of Figure 50. Figure 52 is a diagram showing the placement and size of the passageways. Figure 53 is an axial cross sectional view showing a typical construction of a fluid supply line to the distribution channel. Figure 54 is an axial cross sectional view of an optional intermediate distribution channel. Figures 55-58 are diagrams showing various fluid flow patterns in the annulus. Figure 59 is a graph which illustrates the relationship of heat flow, temperature drop and waE thickness for each of several metals commonly used in the construction of heat transfer media. Figures 60 and 61 show an alternative version of the invention having an independent belt tensioning system. Figure 62 is an alternative version of the invention having a fixed position press roE. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Figures 14-20 are examples of various embodiments of the invention. These systems may have any number of roEers. In each of these examples, the roEers 105 and 106 are the tensioning roEers. The drum 104 is the central drum and the means 100 is the movement means which moves roEers 105 and 106 reciprocaEy with respect to each other to tension or loosen the belt assembly 103. The web being pressed is 108. The felt is separately tensioned as shown in Figures 33 and 35. In each of the examples, one of the tensioning roEers 105 or 106 must have its position fixed, or controEed, on the support frame to define the location of the belt and roEer assembly. The central drum 104 is free to move radiaEy in order to form nips with the other roEers as determined by belt tension. Any two roEers can be used to support the weight of the belt, drum and roEer assembly upon the frame. It is most convenient to have the weight borne by the two tensioning roEers 105 and 106. Any, or aE, of the drum and roEers can be driven by suitable drive means. In Figure 14 the belt is wrapped about a single pair of tensioning roEers 105 and 106 which are reciprocable relative to one another, to tension the belt, using movement means schematicaEy fllustrated at 100. The roEers are sufficiently oversized with respect to the central drum 104 that the axis of the central drum paraEel to the plane of the axes of the tensioning roEers 105 and 106 will remain spaced apart from that plane, and the outer course 103' of the belt 103 wfll remain spaced apart from the U-shaped inner course 103" of the belt when the belt is tensioned by the two roEers 105 and 106. The central drum 104 is free to move radiaEy to nip with roEers 105 and 106 at 109 and 110 to press the web 108. Figure 15 fllustrates the fact that a third roEer 111, an idler nip roEer, may be added to facflitate maintaining the appropriate spaced condition between the two courses of the belt and in increased flexibility in the choice of roEer diameters. The added roEer 111 is mounted to reciprocate with respect to an axis of the central drum 104, generaEy radially thereof, but not rotate about that axis of central drum 104. Idler nip roller 111 forms nip 112 with the central drum 104. In Figure 16 a third roEer 111 is again employed, but the tensioning roEers 105 and 106 and the third roEer 111 may be substantiaEy smaller in diameter than central drum 104. This is the preferred arrangement. The assembly is supported by the tensioning roEers 105 and 106. Figure 17 illustrates a four roEer arrangement. Tensioning roEers 105 and 106 support the assembly and idler nip roEers 113 and 114 move radiaEy with respect to central drum 104 to form nips 115 and 116 with the central drum 104. Figure 18 illustrates a five roEer assembly. Again, tensioning roEers 105 and 106 support the assembly. Idler nip roEers 117, 119 and 120 are fixed spatiaEy with respect to central drum 104 except they may move radiaEy to form nips 118, 121 and 122 with central drum 104. The angles between roEers are equal when the roEer diameters are equal to avoid forces which are nonradial to central drum 104. The entry and exit angles of the outer belt course 103' with the radial axis of each, idler nip roEer are equal for each roEer. Figure 19 illustrates an assembly having a multiplicity of idler nip roEers arranged about the central drum 104. The entering and exiting angles between each of the roEers and the belt are the same. Again, the angles between roEers are the same if the roEers are of the same diameter. Each of the roEers 130 move radiaEy with respect to a radial axis of the central drum 104 to form nips 131 with the drum. In Figure 20 two central drums 104 and 104a are integrated with five roEers by employing two outer idler nip roEers 123 and 124, and an intermediate idler nip roEer 127 between the two central drums 104 and 104a. The intermediate idler nip roEer 127 is disposed within the body of the belt 103, and clasped and supported by a U-shaped bend C in the inner course 103" of the belt in the space between the central drums. AE of the roEers form nips with the central drums - idler nip roEer 123 forming nip 125 with drum 104, idler nip roEer 124 forming nip 126 with drum 104a, intermediate idler nip roEer forming nip 128 with drum 104 and 129 with drum 104a, tensioning roEer 105 forming nip 109 with drum 104a and tensioning roEer 106 forming nip 110 with drum 104. Figures 21-31 illustrate the total compressive forces on the central drum 104 and web 108 using various embodiments of the present invention. The numerals used in these figures are the same as those used in figures 14-20. Figure 21 discloses a system in which there is no tension on the belt because the tensioning roEers 105 and 106 are aligned on the center line of central drum 104 and form nips 109 and 110 with the central drum. The total compressive force due to the belt is zero and the total compressive force due to the nips is ∞T. This is a hypothetical Emiting condition. Figures 22-26 show various three-roEer assemblies and demon¬ strate the change in total compressive forces on the central drum and web caused by changing the locations of the three roEers. In Figure 22 the tensioning roEs 105 and 106 are 90° apart and the circumferential contact between the inner course 103" of belt 103 and the central drum 104 is 270° or 75% of the total surface. Thus, the compressive force due to uniform belt pressure on the drum is 4.7 T as it was in the earEer systems. The vector analysis of the forces on tensioning roEer 105 is shown in Figure 23. This shows that the force between the tensioning roEers 105 and 106 is 2.414 T in order to obtain a tension force of T in the belt. It also illustrates that the compressive force at the nip between the tensioning roEer and the central drum 104 is 2.414 T also. There is also a compressive force of 2 T at the nip 112. This results in a total compressive force of 11.5 T. The diagram also fllustrates that there are no forces passed to the frame from the central shafts of any of the roEers or the central drum. In Figure 24 the two tensioning roEers 105 and 106 and idler nip roEer 111 are spaced 120° apart. The forces acting on each of the tensioning roEers are shown in Figure 25. It requires 3 T of force between tensioning roEers 105 and 106 in order to obtain a tension force of T in belt 103. The compressive force from belt 103 is 4.2 T from the 240° circumferential contact of central drum 104. The compressive force at the nip between each tensioning roEer 105 or 106 and the central drum 104 is 3.47 T and the compressive force at nip 112 is 1.73 T. The total compressive forces acting on the web are 12.9 T. No force other than assembly weight is transferred to the frame or foundation of the assembly. Figure 26 is a different vector diagram of the forces in the system shown in Figure 24. Figure 27 is a vector analysis of a four roEer system in which the roEers are spaced 90° apart. The compressive force due to the belt is the same as in Figure 22 and the vector analysis of the tensioning roEers is the same as in Figure 23. Each of the idler nip rollers 113 and 114 provides a total compressive force at the nip of 1.414 T. The total compressive forces acting on the web 108 are 12.3 T. Figure 28 is similar to Figure 6 and fllustrates the average pressures acting on the central drum 104 in Figure 27. The parameters for Figure 6 are also the parameters for Figure 28. This also shows the additional force on the web becasue of the present roEer, drum and belt configuration. Figure 29 discloses another system for placing the four roEers. The only difference between Figure 29 and Figure 27 is that the two tensioning roEers 105 and 106 are placed 15° from the centerline of central drum 104 instead of 45° as in Figure 27. This means that the compressive force due to the belt is slightly less because there is less circumferential contact between the web and the central drum 104, but the compressive force due to the tensioning roEer nips is increased substantiaEy to 7.56 T from the 2.414 T of Figure 27. A greater amount of force is required to achieve a tension force of T in the belt. It increases from 2.414 T in Figure 27 to 7.6 T in Figure 29. The total compressive forces acting on web 108 in Figure 29 are 21.62 T. The principal difference between the system shown in Figure 30 and that shown in Figure 29 is that that tensioning roEers are placed 7.5° from the centerline of central drum 104, doubling the total compressive forces at the nips of the tensioning roEers 105 and 106. The total compressive forces acting on web 108 are now 36.6 T. Figure 31 fllustrates a configuration in which there may be a large number of idler roEers 130. Again, as in the earEer illustration, the total compressive force due to the nips is equal to the total compressive force due to the belt and the total compressive force acting on the web 108 is approximately 12.56 T. This is a limiting condition and with Figure 21 defines the spectrum of alternative configurations of the present invention. Table 1 summarizes the total compressive forces for the earlier noted systems and for the present systems, and compares the total compressive forces that can be obtained with the different systems. TABLE 1 Com- Com- Com- Total Belt pressive Idler pressive Tension pressive Compressive Figure Contact Forces RoEers Forces RoEers Forces Forces % 1 50 3.1 T 0 — 2 — 3.1 T 2 75 4.5 T 0 — 2 —- 4.5 T 3 50 3.1 T 1 2.0 T ' 2 — 5.1 T 4 50 3.1 T 2 2.8 T 2 — 5.9 T 7 50 3.1 T 3 2.8 T 2 — 5.9 T 8 50 3.1 T 4 3.0 T 2 — 6.1 T 10 50 3.1 T CO 3.1 T 2 — 6.3 T 22 75 4.7 T 1 2.0 T 2 4.8 T 11.5 T 24 67 4.2 T 1 1.7 T 2 6.9 T 12.8 T * 27 75 4.7 T 2 2.8 T 2 4.8 T " 12.3 T 29 58 3.7 T 2 2.8 T 2 15.1 T 21.6 T 30 54 3.4 T 2 2.8T 2 30.4 T 36.6 T 31 100 6.3 T 6.3 T 12.6 T From this it can be seen that changing the tensioning roEers of the other systems into both tensioning and nip roEers in the present system in which these roEers are Enked together and free to nip with the drum enables far greater forces to be exerted on the web while passing none of the tensioning or compressive forces to the frame or supporting structure. Figure 32 is a modification of the basic system. In this system there are four idler nip roEers 132, 133, 134 and 135. Two of the idler nip roEers 134 and 135 as weE as the tensioning roEer 105a and optional belt loop end idler roEer 106a are mounted on a frame 140. The biasing means 100a is also mounted on the frame 140 and applies tension to tensioning roEer 105a. The frame 140 is sEdably mounted on a support structure 141. As tension is appEed to tensioning roEer 105a, the frame 140 wiE move a limited distance toward central drum 104a, as permited by band and/or web compression. Consequently, the tensioning forces are not transferred to the support structure 141. In the version shown in Figure 32 it is presumed that the drum is in fixed position and the frame and roE assu bly will move toward or away from it as belt tension is adjusted. It wiE be apparent that the opposite situation would also be suitable where the frame and roE assembly was fixed and the drum movable. Figures 60 and 61 show other variations in the construction of Figure 32. In Figure 60 idler nip roEs 412, 414 are mounted in fixed position on frame 410. These are contained within the loop ends of belt 103. Drum 104 has freedom of radial movement with regard to roEs 412, 414 and is in a nip relationship with them through belt 103. At least one idler nip roE 416 wiU be enclosed within the body of belt 103 and have freedom of radial movement with respect to the drum as belt tensioning adjustments are made. The tensioning mechanism consists of movable tensioning roE 418 within the body of the belt and fixed roEs 420, 422 mounted on frame 410 outside the body of the belt. One of roEs 420 or 422 may optionally be omitted. The belt tension is controEed by the tensioning mechanism 100 acting on the belt through roll 418. In Figure 61 two idler nip roEs 416a and 424 are shown within the body of the belt. These have freedom of radial movement with regard to drum 104 as belt tension is changed. Tension is controEed by tensioning roEs 426, 428, located outside the body of the belt, and the tensioning mechanism 100. No significant forces are transmitted to the frame. The versions of the invention shown in Figures 14-31 are diagrammatic and it is presumed that the drum is free to move toward at least one fixed idler tension roE. Again, the opposite situation is equaEy operable where the drum might be in fixed position. This is shown in Figure 62. Here drum 104 is mounted in bearing 411 on frame 410. Tension roE 430 may be free floating while tension roE 432 is restrained by strut 438, pivotaEy mounted at 435 to frame 410. Idler nip roE 434 is mounted on strut 442 pivotaEy mounted on frame 410 in bearing 440. AE three roEs have freedom of radial movement with respect to the drum 104 as belt tension adjustments are made. Figures 33-35 illustrate a prototype apparatus. The press comprises an endless flexible belt 203 and a system of spaced upper and lower cylindrical roEers 205, 206, 213 and 214 for the belt. The belt and roEers are assembled on spaced paraEel axes about a cylindrical central drum 204 and the assembly as a whole is cradled on a supporting structure 240. Each of the roEers 205, 206, 213 and 214 has a shaft 241, 242, 243 and 244. The shafts are trunnioned in and supported by sets of journal blocks 245, 246, 247 and 248 that are mounted on the structure 240 after the belt 203 is interwoven in and about the system of roEers 205, 206, 213 and 214 so that it can be used to compress a moving web 208 of paper making material passed between it and the central drum 204. Alternatively, frame members 249, 250 and 251 may be removed and the endless belt instaEed while the roEers are in position on the frame. In some instaEations, the roEers would be cantilevered and the belt may be placed over the roEers while the roEers are in position. The journal blocks 246 and 248 for the shafts 242 and 244 of the lower roEers 206 and 214 are conventional pfllow blocks which are secured fixedly to the structure 240. The journal blocks 245 for the shaft 241 of the upper roEer 205 are carriage blocks which are engaged sEdably on a frame 252 which is rotatably attached to the shaft 242 of the lower tension roEer 206. The frame 252 is attached adjustably to the shaft 242 after the belt 203 is put in place, and is equipped with a pair of hydraulic cyEnders 200 at the top thereof by which the upper tension roEer 205 can be positioned adjustably with respect to the lower tension roEer 206 to tension the belt 208. The journal blocks 247 for the shaft 243 of the upper idler roEer 213, are also conventional pfllow blocks which are mounted on the upper ends of the arms 251. The arms 251 are pivotaEy mounted on the stanchion 253 at the rear of structure 240 so that the roEer 213 can reciprocate with respect to the axis of the central drum 204 generaEy radiaEy thereof, to make a nip. When the press is put to use, the belt 203 is driven through an endless path by drive means (not shown), belt 254 (Figure 35) and the sheave 255 on the right hand end of shaft 242 of the roEer 206. When the press is used to compress water from the web 208, a loop of permeable felt 256 may be interwoven in and about the system of roEers in a common path with that of the belt 203. The felt loop 256 is extended away from the run of belt 203 at the rear of the structure, however, to enable it to be passed about a tightening and guiding roEer 257. The belt 203 is tensioned by using the upper tension roEer 205 to bias the belt toward the lower tension roEer 206. The tension frame 252 for the upper tension roEer 205 comprises a pair of journal blocks 70 which are rotatably mounted on the shaft 242. Pairs of guide rods 259 extend through apertures 260 in journal blocks 258. The pairs of rods 259 are also equipped with header plates 261 at the tops thereof, and the cylinders 200 are mounted on the header plates 261. The carriage blocks 245 for the shaft 241 of the upper roEer 205 are sEdably guided on the respective pairs of rods 259, and are suspended from the cylinders 200 by means of individual drive connections 262. Accordingly, when the tension roEers 205 and 206 are positioned within the belt 203 and the rods 259 are secured to the bottoms of the journal blocks 258 by the nuts 263, the cylinders 200 can be used to bias roEer 205 toward roEer 206 to tension the belt 203 about the system of roEers. A doctor blade 264 is pivotaEy mounted on carriage blocks 265 which are adjustably positioned on rods 259. The doctor blade 264 ensures the release of the paper web 208 from central drum 204. The belt 203 and felt 256 configuration E has an outer U-shaped course E' and an inner U-shaped course E" which meet in loop ends L. The tensioning roEers 205 and 206 are enclosed within the bodies of belt 203 and felt 256 and disposed at the loop ends L. Idler roEers 243 and 244 are also enclosed within the bodies of belt 203 and felt 256 and disposed within the outer course E f of the belt and felt configuration. The central drum is interposed in the space defined by the roEers 205, 206, 243 and 244 and is engaged with the outer face of inner course E τ of the belt and felt configuration so that the inner course E' of the belt and felt configuration is bent about the central drum 204 in a U-shaped configuration B. The idler roEers 213 and 214 are interposed between the inner face of outer course E τ of the belt and felt configuration and the bight B f of the inner course E"; to maintain the inner faces of courses E τ and E] in spaced relationship to one another. The web 208 to be processed is passed between the roEer 206 and central drum 204, and is guided about the central drum 204 between the felt 256 and the periphery of the central drum 204. RoEer 205 is driven relatively downward on the frame 252 by the cyEnders 200 to engage the roEers 205 and 206 with the legs B] of the U-shaped configuration B. The belt and felt members are drawn taut about the central drum 204 at the bight B' of the U, and the belt 205 and felt 256 are brought into tension. As roEer 205 moves downwardly it rotates on the frame 252 about the shaft 242 of roEer 206, and the roEers 205, 206, 213 and 214 nip the belt 203, felt 256 and web 208 between their outer surfaces and that of the central drum 204, respectively, the roEers 205 and 206 nipping with central drum 204 at 209 5 and 210 and the roEers 213 and 214 nipping with central drum 204 at 215 and 216. The tension enables the roEer 206 to drive the belt 204, felt 256 and web 208 about the central drum 204. The central drum 204 is clasped by the belt between the legs B] and the bight B' of the U-shaped configuration B, and between the nips 209, 210, 215 and 216 of the roEers 205, 206, 213 and 10 214 and is supported in the assembly independently of the structure 240. Its axis of rotation is detached from the structure 240 and it is free to move to nip with roEers 205 and 213 while continuing to nip with roEers 206 and 214. RoEer 214 moves generaEy radiaEy to nip with the central drum 204. The overaE effect is to enable the web to be passed rapidly about the central 15 drum 204, whfle it is subjected to high levels of compression between the belt 203 and the central drum 204, as weE as within the nips 209, 210, 215 and 216. The combined total forces " on central drum 204 from the belt pressure of the U-shaped configuration B and the nip forces of the nips 209, 20 210, 215 and 216 are inherently balanced so there is no resultant force transmitted to the structure 240 due to belt tension and there is no axial bending moment imposed on central drum 204 due to belt tension. The principle force transferred to the structure 240 is the weight of the assembly which is carried by roEers 206 and 214 on which the central drum 2.5 204 rests. As the water is squeezed from the web, it is coEected in the felt 256 and removed from the felt by suction device 266 or passes through the felt and the belt. Axial movement of the central drum 204 is limited by a pair of 30 guide roEers 267 positioned at its ends on a pair of mountings 268 upstanding from the structure 240. A belt guide 269 is provided at the front of the stanchion 253. When it is desired to apply both heat and compression to the web, the heat may be fluxed into the web through the central drum. 35 Figures 36-59 fllustrate the flexibility to perform this function created by the present press design. Figure 36 illustrates schematicaEy a simple central heating drum. The central drum 300 is a plain, single-waE cylinder which is open ended and has no shaft. A heat source 301 is mounted within the central drum 300 on a stationary mounting beam 302. The heating source 301 may be a combustion burner or an electrical heating source. The absence of direct axial stress in the heated drum due to the absence of imposed axial bending moments creates the opportunity for a further improvement in the capability of the drum to handle higher heat flux through the drum waE. Circumferential grooves or sEts can be utilized to reduce stress levels in the drum waE created by the temperature differential associated with heat flux permitting a higher ΔT for a given waE or an increased waE thickness for a given ΔT. Figures 37-44 show various methods of accomplishing this. Each of these is shown in connection with the drum 300 of Figure 36. Figures 37 and 38 illustrate a drum or drum sheE in which there are circumferential grooves in both the inner and outer surfaces of the waE. The inner grooves 303 are offset from the outer grooves 304 and they may overlap in the center of the waE at 305. The outer grooves 304 may be fiEed with a resilient material having less strength than the drum material. The material would be a softer metal and would aEow the drum to present a smooth face to the web. Figures 39 and 40 illustrate a drum in which there are only inner circumferential grooves 303. These grooves may extend as near the outer surface as possible. The only requirement is that there be enough material between the groove and outer drum surface to hold the drum together. Figures 41 and 42 fllustrate another modification of the design shown in Figures 39 and 40. In this the waE sections 310 between the grooves 303 are tapered on their inner ends 311 to provide greater heat transfer surface. These inner ends 311 are grooved at 312 to reduce stress. Figures 43 and 44 fllustrate another modification of the structure shown in Figures 41 and 42. Li this one the entire waE of groove 303 is tapered so that there is less material in waE section 310 and greater heat transfer surface. The sections 310 are also grooved at 312 to reduce stress. Figures 45-57 fllustrate novel means of using circulating fluid such as steam as a heat source for the high rates of heat flux desired. Again, the lack of axial bending moment facilitates these constructions. The central drum 350 comprises an elongated, hoEow cylindrical drum 351 having a thin, hoEow cylindrical outer concentric sheE 352 spaced apart radiaEy of the drum 351 to form a shaEow annulus 353 therebetween. The sheE 352 is secured to the drum by a system of radial connections 354 therebetween, which are arrayed about the drum in the annulus to provide external load bearing support for the sheE over the entire area of the annulus as weE as the capacity to retain the sheE against internal pressure in the annulus. The connections 354 are spaced apart from one another to subdivide the annulus into a multipEcity of fluid flow passages 355 which extend throughout the annulus generaEy axiaEy of the drum. The connections may take the form of septa-Eke members 356 (Figures 48, 49, 50 and 51) which extend axiaEy of the drum to form dividers between the passages; or they may take the form of spaced spoke-Eke members 357 (Figures 45-47) which are arrayed in rows that extend axiaEy of the drum to form discontinuous dividers between the passages. For example, in Figures 45-47, the connections 357 take the form of headless capscrews 358 which are arrayed in spaced axiaEy extending rows and screwed into equal numbers and rows of threaded sockets 359 in the outer periphery of the drum 351, so as to upstand radiaEy therefrom. The sheE 352 has openings 360 therein corresponding to the number and sites of the capscrews, and is anchored to the tops of the screws by similar numbers and rows of machine screws 361 which are threaded into the tops of the capscrews and countersunk into the openings of the sheE. In Figure 48, the connections 356 take the form of ribs 362 which are formed between symmetricaEy spaced, axiaEy extending grooves 363 in the inner periphery of the sheE 352', the number of which is adapted so that there is a series of such grooves extending about the fuE circumference of the sheE at the inner periphery thereof. The sheE 352' is sized to engage tightly about the outer periphery of the drum 351, at the inner peripheries of the ribs 362, and the ribs are anchored to the drum by sets of machine screws 364 which are threaded through the ribs into the outer periphery of the drum and countersunk into corresponding openings in the sheE. In Figure 49, the connections 356 take the form of webs 365 which are formed between symmetricaEy angularly spaced, axiaEy extending bores 366 in the outer peripheral portion of the drum itself, the number of which is adapted so that there is a series of such bores extending about the fuE circumference of the drum adjacent the outer periphery thereof. The bores 366 are spaced apart from the outer periphery of the drum, however, to form the sheE 352 therebetween, as seen in Figure 49. In Figures 50 and 51 the connections 356 take the form of webs 367 which are formed between symmetricaEy angularly spaced axiaEy extending rectangular bores 368. The radial height of the bores 368 is greater than the peripheral width. This increases the steam condensing area, enhances the condensing rate by incorporating the extended radial surface so the centrifugal force aids condensate removal from the condensing surface. The metal stress from internal steam pressure is reduced because of the smaE cross section of the passages. The maximum condensing area is near the surface where it is needed to reduce ΔT and increase the surface temperature. The thickness of sheE 352, the distance between the outer waE of the apertures 368 and the outer periphery of the shell, must be adequate for the internal pressure of the steam and the imposed mechanical loads from the nip roEs and belt. The total thickness must also withstand this mechanical loading and keep the total stress within the aEowable stress for the material of construction. The sheE and drum may be monolithic as shown in Figure 50 or separate as shown in Figure 51. The usual length of a heating drum will normally dictate that the construction of Figure 51 wfll be used because it is easier to machine. The joint between the outer sheE 352"" and the drum 351 will be fusion joined as with silver brazing. In both constructions the thickness of the webs 367 wfll be great enough to withstand the mechanical loads placed on the central drum. In each of these constructions, the total heat transfer surface of the axiaEy oriented passages within a defined radial distance from the outer perimeter of the sheE should be greater than the outer perimeter surface of the sheE. The defined radial distance in centimeters is 0.25 vi where k is the thermal conductivity of the material of construction of the outer sheE, expessed in kilojoules per hour per square meter per unit temperature gradient, degrees Celsius per centimeter. This value is approximately 125 for steel and 1000 for copper. The axial heat transfer area of the axial passage should be significantly greater than the outer perimeter surface of the sheE, e.g., 200% or more. This is illustrated in Figure 52. The structure of Figure 50 is again shown. Three different radial distances are shown. These are 400, 401 and 402. Each is equal to 0.25 * centimeters. They are different because they represent the radial distance for three different materials of construction. When the radial distance is 400, then the peripheral surface of the axial passages 368 within that distance, the surface area between Enes 403 and 404, should be greater than the outer surface of the sheE. When the radial distance is 401, then the peripheral surface of axial passage 368 within that distance, the surface area between Enes 405 and 406, should be greater than the outer surface area of the sheE. When the axial distance is 402, then the total surface area of the axial passage should be greater than the outer surface area of the sheE. Figures 51 and 53-54 fllustrate another method of fluid distribution. The openings 371 do not egress into the hoEow 376 of the drum but instead join with central axial pipe 380 which feed a series of radial pipes 381 and radial apertures 382 in the drum. Circumferential passages 383 in the outer face of the drum provide access to the apertures 368. Figure 54 fllustrates a version in which there is a coEection chamber 384 on the interior waE of the drum. The inner end of chamber 384 is capped by member 385. An aperture 386 in member 385 provides a passage between pipe 381 and chamber 384. Aperture 382 connects chamber 384 and passage 383. Figure 45 also shows the removal of Equid or condensate from the drum. The ends of the central drum 350 are defined by a pair of end plates 369 which abut the ends of the sheE and drum when they are bolted to the drum 351 and the annular plate 370 of sheE 352 as shown. The plates have central axial openings 371 and annular grooves 372 about the inside faces of the outer peripheral portions thereof. The grooves 372 are diametricaEy sized to register with the ends of the annulus 353, and serve as coEection chambers for the steam or other heat transmission fluid used to service the roEer. The fluid is suppEed to the drum by one or two ducts 373 which are sEp jointed at 374 to the neck 375 of the face plate 369. The duct 373 is connected to the hoEow 376 of the drum through the openings 371 in the plates 369. The fluid enters the hoEow of the drum and discharges into the annulus 353 through a series of angularly spaced apertures 377 in the body of the drum. The apertures are formed about the central portion of the drum. In the embodiment of Figure 48, there is always one or more apertures 378 for each passage. In Figure 49, the bores 366 are serviced by apertures 379 in the inner peripheral portion of the drum, there again being at least one aperture for each passage. In the annulus 353, the steam or other heat transmission fluid moves lengthwise of the passages 355 toward the chambers 372. The fluid is removed from the chambers by a siphon or bleeder arrangement and ducted out of the drum through radial pipes 385, axial pipe 386, rotary joint 387 and exterior pipe 388 in a known manner. The number of entry ports 377 and exit ports 385 will depend upon the length of the drum and the amount of condensation within the drum. Figures 55-57 are diagrams taken along the axis of the drum showing multiple entry and exit points in the drum depending upon its width or the amount of condensate. Figure 55 is a diagram of the configuration shown in Figure 45, and the reference numerals for Figure 45 are used. There are central inlet ports 377 and end outlet ports 385. Figure 56 fllustrates two sets of inlet ports, and two end and one central set of exit ports. Figure 57 fllustrates three sets of inlet ports, and two end exit ports and two intermediate sets of exit ports between the inlet port sets. Although the reference numerals from Figure 45 have been used, the inlet and exit port units may be any type. Figure 58 shows the exit aperture such as one of the exit ports 385, in relationship to a number of the axial passages, such as passage 368, in the drum. The induced thermal stress in a thickness of metal is propor¬ tionate to the temperature differential (ΔT) across it which in turn is proportional to the heat flow rate. The faster drying rates made possible by the present invention require a short heat flow path through the outer sheE 352 of the drum. At the necessary high heat flux rates, a high ΔT wfll be of concern primarfly because of metal stress. However, in the case of steam heating which has economic advantages but distinct temperature Emitations, a high ΔT may also be a process parameter concern, that is, for a given steam pressure and temperature, increased ΔT reduces the available temperature of the outer drum surface thereby reducing the potential drying rate. For conventional heat transfer metals such as steel and copper, certainly a ΔT of 3°C is acceptable. A ΔT of 12°C poses some concern because of heat stress and process concerns, and a ΔT of 20°C may be unacceptable. Figure 59 is an fllustration of the relationship of sheE thickness to heat flux for steel, bronze, aluminum and copper. The heat flux from the annulus 353 to the web is also a function of the condensing rate of the steam or other heat transfer fluid in the annulus, and the rate of heat transfer to the web from the outer surface of the sheE. The latter is enhanced by the high contact pressures of the web on the outer surface of the sheE. The former is enhanced by the large amount of condensing surface provided in the annulus as weE as the novel arrangement which maximizes ΔT available to cause condensation rather than use it in heat flow through the shell. Stress due to the internal steam pressure can be reduced to a negEgible level such as 0.7 MPa or less, by reducing the diameter of the passages to a smaE figure, such as 1.5 cm or less. Nip loads upward of 175 kN/m or more can be borne by the system of radial connections 356 or 357 between the drum 351 and the sheE, where the maximum diameter of the passages 355 between connections is kept low in relation to the thickness of the sheE. The ring crushing stresses induced by the nip loads and the belt contact pressure, are absorbed in the heavy body of the drum 351, and as indicated earEer, the drum need only be sized and constructed to withstand these loads, there being no imposed axial bending moment on the drum 350. Operation of the present invention has been demonstrated on a pilot machine paper dryer equipped with a 60 cm diameter heated drum. Operating speeds of 25% to 40% of commercial speeds were attained, depending on grade of paper, indicating that commercial speeds can be attained with a reasonable sized first drum of 1.5 to 2.5 m diameter. Water removal rates up to 700 kg of water per square meter of drum per hour were attained, indicating that commercial speeds could be attained using a total Eneal circumferential length of dryer drum of 15 m versus the 450 m in present commercial practice.

Claims: CLAIMS 1. A drum (350) comprising: an inner cylindrical load bearing drum (351), said inner drum having a waE, an outer cylindrical sheE (352) surrounding said inner drum and spaced apart radiaEy of the inner drum to form a shallow annulus (353) between said sheE and said inner drum (351), said sheE (352) having a waE, annulus (353) being closed at each end, radial connections (354) within said annulus (353) and extending between said sheE (352) and said inner drum (351) to secure said sheE (352) to said inner drum and to transmit any load bearing against said shell (352) to said inner drum (351), said radial connection (354) being placed both axially and circumferentially of said drum (350), the radial thickness of said sheE waE (352) being significantly less than the radial thickness of said inner drum waE (351). 2. The drum (350) of claim 1 in which said radial connections (354). are rods (357, 358) extending between and fastened to said sheE (352) and said inner drum (351). 3. The drum (350) of claim 1 in which said radial connections (354) are axiaEy extending waEs (356) which define axial fluid flow passages (363, 366, 368) in said annulus (353). 4. The drum (350) of claim 3 in which the cross section of said fluid flow passages (368) is approximately rectangular. 5. The drum (350) of claim 4 in which the radial side wa of said fluid flow passages (368) is longer than said circumferencial inner and outer waEs. 6. The drum (350) of claim 3 in which at least a part of said fluid flow passages (363, 366, 368) is within a defined radial distance of the outer perimeter of the sheE (352), said defined radial distance being equal to 0.25 vM centimeters where k is the thermal conductivity of the material of construction of said outer sheE expressed in kJ/h/m per unit temperature gradient, C/cm. said fluid flow passages (363, 366, 368) within said defined radial distance having a total surface, said sheE (352) having a total outer perimeter surface, said fluid flow passages having a surf ce area greater than said sheE outer perimeter surface area. 7. The drum (350) of claim 1 in which there are circulation means connected with said annulus (353) to circulate fluid through the annulus, said circulation means comprising: first means defining apertures (377) which connect with said annulus (353) for circulating fluid into said annulus (353) and second means (385) connected with said annulus (353) at points spaced axiaEy from said apertures (377) to enable fluid to be removed from said annulus (353). 8. The drum (350) of claim 7 in which the first means (377) defines a pluraEty of circumferentiaEy spaced apertures and there is a pluraEty of first means (377a, 377b) spaced axiaEy of said drum (350) and the second means (385a, 385b) and are also located between each pair of first means. 9. The drum (350) of claim 7 in which there are first duct means (373) attached to said first means (377) to carry fluid to said annulus and second duct means (386) attached to second means (385) for removing fluid from said annulus. 10. The drum (350) of claim 7 in which said radial connections (354) are axiaEy extending waEs (356) which define axial fluid flow passages (363, 366, 368) in said annulus (353). 11. The drum (350) of claim 7 in which said second means (385) comprises a circumferential zone of the annulus in which said radial connections (356) are discontinuous for coEecting said fluid and siphoning means for removing said fluid from said zone. 12. The drum (350) of claim 10 in which said first means (377) comprises a toroidal channel (383) having access to said axial passages (363, 366, 368). 13. A press comprising: an inner cyEndrical load bearing drum (351), said inner drum (351) having a waE, an outer cylindrical sheE (352) surrounding said inner drum (351) and spaced apart radiaEy of the inner drum (351) to form a shaEow annulus (353) between said shell (352) and said inner drum (351), said sheE (352) having a waE, said annulus (353) being closed at each end, radial connections (354) within said annulus (353) and extending between said shell (352) and said inner drum (351) to secure said shell (352) to said inner drum (351) and to transmit any load bearing against said sheE (352) to said inner drum (351), said radial connections (354) being placed both axiaEy and circumferentiaEy of said drum (351), the radial thickness of said sheE (352) waE being significantly less than the radial thickness of said drum (351) waE, an endless flexible belt, and means for guiding and tensioning said belt about the outer shell (352) to compress a moving web between said belt and said drum (350). 14. A drum and belt-type press for compressing a moving web or mat which comprises: a supporting frame (240, 410) for a drum (104), belt tensioning roEs (105, 106), and belt tensioning means (100); a pair of spaced apart first and second cylindrical belt tensioning roEs (105, 106) having essentiafly paraEel axes of rotation; a central drum (104) adjacent said tensioning roEs (105, 106), said drum (104) having an axis of rotation essentiafly paraEel to the axis of rotation of the roEs (105, 106); an endless flexible belt (103) having an inner generally Ushaped course (103") and an outer generaEy U-shaped course (1030, the inner and outer courses meeting in loops which wrap around the tensioning roEs (105, 106), the tensioning roEs (105, 106) each being contained within the body of the belt (103) and the drum (104) being outside the body of the belt (103), the inner course of the belt (103") being wrapped around more than half the circumference of the inner drum (104), the tensioning roEs (105, 106) and drum (104) being sized so that the inner (103") and outer (1030 courses of the belt (103) are spaced apart, each tensioning roE (105, 106) making nip contact with the drum (104) through the interposed belt (103) so that the total compressive forees of the belt (103) and nips (109, 110, 112) on the central drum (104) are balanced and the summation of forces about the drum axis is essentiafly zero; drive means for moving the belt (103) through its endless path, so that a web or mat (108) may be compressed by interposing it between the moving belt (103) and drum (104), tensioning means (100) acting on the tensioning roEs (105, 106) to translate them relatively toward or away from each other to control belt tension while maintaining nip contact, and the drum (104) or tensioning roEs (105, 106) being mounted on the supporting frame (240, 410) and structured so that they are free for relative radial movement in response to tensioning adjustments and maintain ' nip contacts without transmitting significant belt tensioning forces to the supporting frame or significant axial bending forces to the drum. 15. The press of claim 14 in which the drum (104) is mounted in fixed position on the frame (410) and the tensioning roEs (430, 432) are free to adjust radial position relative to the drum (104) in response to belt tensioning adjustments. 16. The press of claim 14 in which the drum (204) is free floating with respect to the tensioning roEs (205, 206) and the tensioning roEs are mounted on the supporting frame (240) so as to be relatively translatable toward or away from each other, the axes of the tensioning roEs (205, 206) lying in a common plane. 17. The press of claim 16 in which one of the tensioning roEs (205, 206) is in fixed position on the frame and the other tensioning roE is mounted so as to be movably translatable by the tensioning means (200) toward or away from the fixed roE. 18. The press of claim 16 in which both of the tensioning roEs (205, 206) are mounted on the supporting frame (240) so as to be movably translatable toward or away from each other whereby the centerline of the central drum (104) normal to said common plane is stationary. 19. The press of claim 16 in which the common plane of the axes of the tensioning roEs (105, 106) Ees generaEy horizontal and the central drum (104) is entirely above said common plane and is supported by the tensioning roEs (105, 106). 20. The press of claim 14 in which the belt (103) and tensioning roEs (105, 106) generate radial compressive forees on the drum (104) at least eleven times greater than the belt tension force. 21. The press of claim 14 in which the central drum (104) has an outer sheE with a pluraEty of apertures extending circumferentiaEy around and along the axis of the outer shell to convey fluid to or from a web on the drum. 22. The press of claim 14 which further comprises at least one idler roE (111) enclosed within the flexible belt body (103) between the first and second tensioning roEs (105, 106), the idler roE (111) or roEs being radially moveable by the outer course of the belt (1030 and forming nips (112) with the central drum (104) through the interposing belt (103) when said belt (103) is in tension, the belt (103), idler (111), and tensioning roEs (105, 106) aE being in a balanced force relationship with the drum (104). 23. The press of claim 22 in which the central drum (104) has a diameter greater tϊ n that of the tensioning (105 106) and idler roEs (ill). 24. The press of claim 16 in which the central drum (104) is a hoEow, open ended metaEic cylinder (300). 25. The press of claim 24 which further comprises heating means (301) within the cyEnder (300). 26. The press of claim 24 in which the cylinder (300) has an inner waE containing a pluraEty of circumferential- stress relieving grooves (303, 304) spaced so as to define inner circumferential waE sections (310), each waE section (310) being tapered inwardly and having a plurality of axial stress reEeving grooves (312). 27. A drum and belt-type press for compressing a moving web or mat (108) which comprises: a supporting frame (140) for a pair of nip roEs (134, 135) and a belt tensioning means (100a); first and second fixed spaced apart rotatable nip rolls (134, 135) mounted on the frame (140) to form an assembly, said roEs (134, 135) having paraEel axes of rotation; a central drum (104a) adjacent the nip roEs (134, 135), the drum (104a) having an axis of rotation essentially paraEel to the nip roEs (134, 135); at least one idler nip roE (132, 133) having freedom of radial movement also located adjacent the drum (104a); an endless flexible belt (103a) having an inner generaEy Ushaped course (103a") and an outer generaEy U-shaped course (103a0, the inner and outer courses meeting in loops, one loop containing the first fixed nip roE (134) and the other loop containing the second fixed nip roE (135), the fixed nip roEs (134, 135) and moveable idler nip rolls (132, 133) being located within the body of the belt (103a), the inner course of the belt (103a") being wrapped around more than one half of the circumference of the drum (104a) so that aE the nip roEs (132, 133, 134, 135) make nip contact with the drum (104a) through the interposed belt (103a0, the drum (104a), fixed nip roEs (134, 135) and idler nip roEs (132, 133) being sized to hold the inner (103a'0 and outer (103a0 courses of the belt in spaced apart relationship; at least one moveable belt tensioning roE (105a) mounted to act against the belt (103a) to control belt tension, said tensioning roE (105a) or roEs not making nip contact with the drum (104a); tension control means (100a) to adjust the tensioning roEs (105a); and means for rotating the belt through its endless path to compress a web or mat (108) interposed between the moving belt (103a) and drum (104a), the drum (104a) being free to -move radiaEy to the fixed nip roEs (134, 135) or the nip roE and frame assembly (140) being free to move to the drum (104a) so that the nip roEs (132, 133, 134, 135) act through the belt (103a) against the drum (104a) with a force controEed by belt tension.

Inventors: MILLER RAY RAMSAY, MILLER, RAY, RAMSAY
Applicants: MILLER RAY R, MILLER, RAY, RAMSAY
Application year: 1987
Main classification: F26B13
IPC codes: B30B5, B30B9, D21F3, D21F5, F26B13, F28D11