Paper machine dryer condensate control

July 7, 1959

E.’J. JUSTUS ETAL 2,893,136

PAPER MACHINE DRYER CONDENSATE CONTROL

Filed July 5, 1957

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Edgar cZ tfustas Robert A- JJaane

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2,893,136

Patented July 7, 1959

United States Patent Office

The prior workers in the art have proposed countless devices for minimizing the depth of condensate layer continuously forming on the inner shell surface. In contrast, the instant invention resides in the use of means for maintaining a greater condensate layer in a predetermined portion of the shell (for example, at the ends thereof) for the purpose of reducing heat transfer and heat loss at this region of the shell. In addition, the instant invention provides means for controlling the depth of condensate in such regions, so as to control the rate of heat transfer to the shell by, in effect, placing an insulator layer (of condensate) between the live steam and the cylinder shell.

It will be appreciated that the dryer drums operate at speeds sufficient to cause the condensate to be retained in substantially uniform depth around the entire inner periphery of the shell because of centrifugal force. Accordingly, the instant means employed to maintain a different condensate depth at selected axial portions of the shell are in the form of axially spaced circumferential dams, or a single circumferential dam axially spaced from one of the shell heads to maintain a predetermined level of condensate between such dam and the shell head.

It is, therefore, an important object of the instant invention to provide an improved dryer drum structure.

Another object of the instant invention is to provide an improved dryer drum having means therein to retain a layer of condensate that is controllable in radial thickness, in order to regulate heat transfer rate from the heating fluid in the dryer drum to the outer periphery of the dryer.

A further object of the instant invention is to provide a dryer drum having means to position a retained layer of condensate therein to suit the heating requirements of a web trained over the dryer drum.

Other and further objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed disclosure thereof and the drawings attached hereto and made a part hereof.

On the drawings:

Figure 1 is a partial sectional elevational view of a dryer drum embodying the instant invention;

Figure 2 is an enlarged detail view of another embodiment of the instant invention, shown in a fragmentary sectional elevational view;

Figure 3 is a fragmentary detail elevational sectional view taken substantially along the line III—ΙΠ of Figure 2;

Figure 4 is a fragmentary plan view of a connected portion of a circumferential dam used in the practice of the instant invention; and

Figure 5 is an elevational view of the connected portion shown in Figure 4.

As shown on the drawings:

The reference numeral 10 indicates generally a dryer drum of the present invention, only the lower half of which is shown in Figure 1 in sectional elevation for simplification of the description of the instant invention. The dryer drum 10 includes a cylindrical shell 11 having open ends closed by annular heads 12 and 12α, secured to the ends of the shell 11 by bolts 13 and extending radially across the ends of the shell 11. Journals 14, 14α are integrally formed with the heads 12, 12α, respectively, and extend axially outwardly therefrom to be received by suitable bearings (not shown) for rotatably mounting the drum 10. Each of the journals 14, 14α is provided with an axial bore 15, 15α. The axial bore 15α at one end is sealed off by a plate 16α in the particular structure here shown, whereas the opposite axial bore 15 mounts a plate 16 which receives a steam inlet header 17 connected to a suitable source of steam S (as shown diagrammatically). The steam flows

2,893,136

PAPER MACHINE DRYER CONDENSATE .

CONTROL ⁰

Edgar J. Justus and Robert A. Daane, Beloit, Wis., assignors to Beloit Iron Works, Beloit, Wis., a corporation of Wisconsin

Application July 5,1957, Serial No. 670,144

Claims. (CI. 34—119)

The instant invention relates to a dryer drum for a 15 paper machine, and more particularly, to an improved dryer drum structure. As conventionally employed in the art, dryer drums for paper machine drying sections generally consist of a cylindrical shell, spaced heads extending radially across the shell to close the open ends 20 thereof and carrying means for journaling the shell for rotation, and means for introducing steam into the interior of the shell and drawing condensate therefrom. The Yankee dryer drum has generally the same structural arrangement as now used in the art, except that the 25 Yankee dryer drum is ordinarily of substantially greater size than the dryer drums in the conventional dryer section of a paper machine. Nevertheless, in each case these dryer drums (whether the large Yankee dryer drum or the smaller conventional drum) has certain operating 30 limitations.

In the prior art paper machine dryers, steam is admitted to the interior of the dryer and is in contact with the entire interior surface of the dryer, the inner cylinder wall being subject, therefore, to uniform temperature. 35 Condensate forms on the inner surface of the cylinder and the condensate layer depth is substantially uniform at the minimum thickness or depth obtainable with siphon equipment used. The outer wall of the dryer, however, is subject to variations in temperature. For example, the moist paper web may not extend the full length of the cylinder shell, so as to leave the ends thereof uncovered by the paper. Also, the paper web passing over the cylindrical shell may not be dried to the same extent in the central portion as it is at the edges thereof. ⁴⁵In addition, the rate of drying or rate of water evaporation from the web may vary across the width thereof, because of prior irregularities in the processing of the web, or different characteristics in the web, or different draft conditions in the dryer. In particular, however, the dryer surface in the region of the heads is not cooled by the passing damp sheet and it is subjected to cooling only from the ambient air which, of course, may vary greatly in relative humidity and/or temperature. In general, the cooling effect at the end reaches of the shell is ⁰less than that in the intermediate portion.

The instant invention provides a simple and economical means for overcoming this difficulty. It will be appreciated that the tendency for the ends of the shell to become overheated, or more greatly heated than the intermediate portion, results in a tendency to overdry the edges of the web adjacent thereto, as well as an unnecessary heat loss. In the instant invention, however, means are provided for maintaining a layer of predetermined depth of condensate against the inner periphery ^bsof the end portions of the shell to reduce heat transfer from the steam to the shell body in these regions. It will be appreciated that the instant invention may be employed to reduce heat transfer from the steam to any particular portion of the shell desired, although the main ⁷⁰problem here solved is that of reducing heat losses at the shell ends and reducing overheating of the shell ends.

2,883,136 from the source S through the steam inlet line 17 which leads into the shell 11 through the head 12, and the steam enters the interior of the shell 11 through an apertured head 18.

The steam within the shell 11 is continuously condensed and the condensate deposits as a film on the inner periphery of the shell 11. The condensate thus formed collects along the inner periphery of the shell 11 and is maintained thereagainst in a substantially uniform thickness of liquid by virtue of centrifugal force resulting from the rotation of the dryer drum 10. A siphon nozzle 19 placed against the central inner periphery of the shell 11 picks up condensate and returns the same through a radially aligned pipe 20 to a central condensate header 21 which is concentrically mounted within the steam inlet header 17 and passes out through the shell head 12 into suitable receiving means such as a drain D (shown diagrammatically).

The foregoing disclosure relating to the dryer drum 10 describes a typical prior art structure. It will be appreciated that the steam inlet line may lead through one head and the condensate line through the opposite head. Other variations in the arrangement of the elements consistent with the knowledge of the prior art are of course permitted. The instant invention provides a means for controlling the heat transfer through the shell 11 at various points. As indicated in Figure 1 a web W is trained about the outer periphery of the shell 11, but this web W leaves exposed end portions Ila and 116 of the shell 11, which are cooled only by ambient atmosphere. The web edges Wa and W6 may also be dryer than the main body of the web W, or may be inclined to dry more rapidly, if subjected to the same amount of heat.

As will be seen from Figure 1, a circumferential dam 22 is mounted on the inner periphery of the shell 11 at the shell end Ila adjacent the head 12α. The circumferential dam 22 is aligned approximately with the extreme edge of the web W, so that the end portion of the shell 11 between the head 12α and the dam 22 is the end portion 11α of the shell 11 which is not covered by the web W. The circumferential dam 22 cooperating with the head 12α maintains a level L of condensate against the inner periphery of the shell 11. This level L is substantially the same throughout the periphery in this end portion 11α of the shell because of centrifugal force. The level L of condensate, however, functions as an insulator reducing the rate of heat transfer from the live steam within the shell 11 to the outer shell periphery in the region 11α. In this way heat losses to the ambient atmosphere are reduced readily, simply and economically. At the opposite end of the shell 11 there is mounted a circumferential dam 23 which cooperates with the head 12 to maintain a level L' of condensate therebetween on the inner periphery of the shell end 116 which functions in the same manner as the level L of condensate at the opposite end of the drum 10.

If the drum 10 is to be operated at speeds below which “rimming” of the condensate occurs in the channel between the dams and end heads, paddles or baffles (not shown) can be mounted in the channels to reduce rotation of the condensate with the drum. Thus in slow speed paper machine producing heavy weight sheets or boards the centrifugal force developed in a slow rotating drum may not be sufficient to insure movement of the condensate with the drum to “rim” the liquid around the inner periphery of the drum. Transfer paddles or baffles spaced circumferentially across the channels will “drive” the liquid with the drum .

It will be noted that these circumferential dams 22 and 23 are axially spaced annular members on (and integral with) the inner periphery of the shell 11 spaced a short distance from the heads 12 and 12α. The circumferential dams 22 and 23 extend inwardly a short predetermined distance, so that condensate may flow over such dams toward the central portion of the shell 11, if excess condensate builds up between the dams 22 and 23, and the heads 12, 12α. The dams 22 and 23 thus project inwardly a short distance to retain condensate at each end of the shell 11 while permitting flow of ex5 cess condensate thereby toward the intermediate region or central portion 11c of the shell 11. It is apparent that the siphon 19 functions in the intermediate portion 11c of the shell 11, since it is important to keep the condensate film at a minimum thickness in this region in order 10 to obtain best heat transfer conditions.

It will also be noted from Figure 1 that an additional annular ridge 24 is mounted in closely spaced relation to the ridge 22, so as to align a space therebetween with the edge portion Wa of the web W. The ridge 24 func15 tions similarly to the ridge 22, except that the ridge 24 does not extend inwardly as far and the level I of condensate retained thereby opposite the web edge Wa is less than the level L of condensate maintained adjacent the head 12α. In this way more heat is transmitted from 20 the live steam within the shell through the shell 11 and to the web edge Wa than is transferred through the shell end portion 11α, but less heat is transferred to the web edge Wa than is transferred to the main body of the Web W through the central or intermediate shell portion 11c. 25 A circumferential dam 25 at the other end of the shell functions in the way the dam 24 functions to maintain a level 1' of condensate between the dams 23 and 25 that is lower than the level L' between the head 12 and the dam 23.

As will be appreciated, the means for maintaining the level of condensate against the shell wall need not be in the form of a dam (such as the dams 22, 23, 24 and 25) wherein the control means is provided in the form of the top of the dam over which the condensate flows.

Instead, as shown in Figure 2, a circumferential dam 26 may be provided with an aperture 27 therein for maintaining a condensate level L-l. In Figure 2 parts corresponding to the parts in Figure 1 are indicated with the same reference numeral in the 100 series, so it is apparent 40 that Figure 2 shows a shell 111 with an uncovered shell end 111α and a head 112α secured thereto by bolts 113. The circumferential dam 26 of Figure 2 extends around the entire inner periphery of the shell 11 and is provided with a plurality of apertures 27 through which condensate 45 may flow toward the central portion of the shell 11, but which serve to control the condensate level Iz-1.

As shown in Figure 3, a plurality of apertures at levels 27, 28 and 29 are provided in the annular ridge 26 for maintaining levels L-l, L-2, L-3, respectively. Only 50 the apertures 27 are open in Figure 3 (with the apertures 28 and 29 plugged), so that the level L-l is maintained, but when it is desired to operate at a different condensate level, the holes 28 or the holes 29 may be unplugged.

As shown in Figures 4 and 5, if the circumferential 55 dam or annular ridge is not integral such as the ridge 22 and is a separate element such as the ridge 26, then it may be mounted within the shell 111 by a number of ways. As shown in Figures 4 and 5, the annular member 26 may be split at one end 26α to receive a 60 boss portion 266 at the opposite end 26c, with a stop 26d mounted on the boss portion 266. Adjustable means in the form of a set screw 26e is carried by the split end 26α and acts against the stop 26d so as to urge the annular ridge 26 into tight contact with the inner pe65 riphery of the shell 111. Other means may, of course, be employed for mounting the ridge 26 so as to permit subsequent changes in position thereof.

It will also be appreciated that the instant invention affords a unique advantage with respect to the control 70 of heat input to the web throughout an entire dryer section, which may include as many as 50 dryer drums. . In such an arrangement the dams within the dryer drums are positioned at different locations throughout the dryer section, so that the amount of heat input to the cen75 tral portion of the web may be correlated with that to

2,893,138 the web edges (Wa and WZ&gt;). In other words, these dams may be positioned so as to produce a contoured curve of total heat input to the web. For example, in a paper machine having a dryer section of 50 dryers, the dams can be successively moved toward the center of the machine in such a manner that the edges of the web would receive a heat input of 60% of the input at the center of the machine or dryer, and by proper arrangement, the total heat input at intermediate points is precisely adjusted to the desired moisture profile, and/or to the particular characteristics of drying due to ventilation and other factors.

In such a paper machine dryer section, the circumferential dams within the dryer drums are moved progressively inward toward the center of the drums (in the direction of web travel) from the oncoming to the offrunning side of the dryer section, and with such dams mounted in the drums in this manner a substantially uniform ratio between the heat input to the central portion of the web and that to the edges may be maintained throughout the length of the dryer section.

It will be understood that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of the present invention.