JPS6213592B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the field of drying wet running webs carried on the surface of a rotating drum of a dryer which is heated by introducing condensable steam inside the enclosure. More particularly, the present invention relates to a heated steam rotating drum of a dryer that is equipped with a spoiler rod mounted on its inner circumference to prevent a layer of condensate from forming as the steam is condensed. More specifically, the present invention includes the following steps to improve the heat transfer coefficient of condensate:
It concerns the relationship between the number and height of spoiler rods in relation to the depth of the condensate layer. Previous documents in the above technical fields are DW
It is briefly summarized in US Pat. No. 3,724,094 to Appel and SHHong. The above prior art includes a spoiler rod attached to the inner circumferential surface when the spoiler rods are separated from each other by an inner circumferential distance in the range of 1.1√ to 3.4√ inches (where d is the internal diameter feet of the drum). It has been taught to improve the heat transfer coefficient in heated steam drums of dryers with rods. Another formula for the spacing of spoiler rods in the heated steam cylindrical drum of a dryer is a=(1±0.25)π
It is given by √ (where a: the spacing between adjacent spoiler bars in inches, R: the inside diameter of the drum in inches, and h: the average condensate depth within the drum in inches). In the prior art described above, the condensate depth of the dryer roll is measured and then minimum, average and maximum values are determined for the allowable condensate depth. For these condensate depth values, a theoretical study was introduced and the condensate splash resonance vibration between two adjacent axially extending rods mounted on the inner circumferential surface of the cylindrical drum of the dryer. Determine the number. Here, we use the radius of the inner surface of the dryer drum cylinder to develop the equation for the spacing of the spoiler rods in terms of the inner diameter of the dryer drum and the condensate depth: the number of revolutions of the dryer shell and the number of condensate splashes. and are equal. Although the spacing of the spoiler rods on the inner periphery of the heated steam cylinder of the dryer according to the prior art described above works well, it is necessary to use a significantly larger number of spoiler rods. For example, in a standard 5 foot outside diameter dryer drum commonly used in paper machines, the number of spoiler rods based on prior art teachings amounts to approximately 24 to 72 rods. Using dryer drums with spoiler bars to enhance web drying is time consuming and expensive because each spoiler bar is manufactured to exacting specifications and must be carefully and precisely installed. It is. There are only three basic ways to increase heat transfer through the heated walls of a cylinder dryer. (1) reducing the depth of condensate by placing the siphon closer to the inner wall; (2) bypassing the condensate by providing ribs along the inner surface of the dryer drum; (3) ) Creating turbulence in the condensate layer. Proximity of the siphon to the rotating wall creates and exacerbates operational problems. Also, since machining ribs on the inner surface is very expensive, it is believed that improving heat transfer by creating an agitated flow with a spoiler rod represents the most promising direction. However, prior teachings have been very specific and limited regarding the height of the spoiler rods and the spacing between the rods within the circumference of the drying cylinder. Specifically, by assuming that the preferred spoiler bar height is approximately 2 to 3 times the average condensate depth and that the optimum spoiler bar circumferential spacing is approximately 5.75 inches, the 5.75 It is stated that spoiler bar spacing that is substantially less or greater than inch spacing reduces heat transfer through the cylinder wall of the dryer drum. The present invention improves heat transfer through the heated steam rotating cylindrical drum of a dryer utilizing spoiler rods and improves the relationship between condensate depth within the dryer roll, spoiler rod height, and spoiler rod spacing. The goal is to improve teaching. For shallow layer condensate,
By increasing the height of the spoiler rods and the spacing of the spoiler rods along the inside surface of the dryer drum, greater turbulence is created in the condensate than would be expected based on prior teachings, and the heat transfer rate is increased. was found to increase. Note that the heat transfer coefficient increases due to increased turbulence because the turbulence of the condensate creates a shallow layer and increases the rate at which the inner wall of the drum is exposed to live steam. This creates turbulence in the condensate and improves heat transfer, allowing the condensate to be relatively deep and thus ensuring a precise relationship between the bottom of the siphon and the inner wall of the dryer rotating roll. The condensate can be collected by a siphon without the need for Also, the number of spoiler rods required in the dryer to achieve the desired amount of heat transfer is drastically reduced. For example, in a typical dryer roll with an inside diameter of 57.75 inches and an outside diameter of 5 feet, the optimum number of spoiler rods as taught in the prior art is about 30, whereas in the present invention the number of spoiler rods is about 8. The number ranges from 20 to 20. In this way, even if the number of spoiler rods is reduced, the heat transfer coefficient increases. For example, as shown in Table I below, even if the number of spoiler rods is reduced from 30 in the prior art to 10 in the present invention, the heat transfer coefficient is 360. from
635Btu/hr/ ^ft2 /〓). This is because turbulence is created in the condensate resulting in increased exposure of the inner drum wall to live steam, which can improve heat transfer. In the present invention, the height of the spoiler bar is determined by the formula H=
It is determined by (15)/N(1.0±0.25) (Equation (1)).
Also, the spacing between spoiler bars is calculated using the formula S=π√(1.5±
0.25) (Equation (2)). Assuming that the width of the spoiler rods is negligible here, the number of spoiler rods is related to the internal radius of the dryer cylinder roll and the spoiler rod spacing according to the formula N=2πR/S (Equation (3)). where S is the spacing, R is the internal radius of the dryer cylinder roll, h is the condensate depth, and H is the spoiler bar height, all in inches. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a rotatable drum by condensable heated steam of a dryer with a spoiler bar mounted therein and extending axially at a distance from the circumference. and to provide a dryer drum in which the spacing and condensed steam are determined by the above-mentioned formulas. Another object of the present invention is to improve the heat transfer coefficient in a heated steam drum of a dryer that utilizes a spoiler rod mounted on the inner circumferential surface. Yet another object of the invention is to
It is an object of the present invention to provide a heated steam drum of a dryer designed to improve heat transfer to a condensate depth of inches and to include about 8 to 20 spoiler rods. These and other objects, features, and advantages of the present invention will become apparent to those skilled in the art when reading the description of the preferred embodiments in conjunction with the accompanying drawings. In a paper machine, a wet paper web is partially or completely dried by passing the web over the surface of one or more rotating dryer rolls having a cast iron cylindrical drum. Condensable vapor such as water vapor is introduced into the drum and condenses on its inner peripheral surface. The water vapor rejects heat through the drum wall and dries the paper held on the outer surface over a portion of the drum circumference. The higher the heat transfer coefficient of the drum wall, the more efficient the process. This is not only important from an energy standpoint, but is also a factor in determining how quickly the machine can run and dry the paper to the desired degree of dryness. It is also a factor in the A number of dryer rolls required to produce dry paper at the desired rate. However, as the vapor condenses, a layer of condensate that forms on the inner surface of the drum acts as an insulating layer that prevents heat transfer from the vapor to the inner surface of the drum. As paper machine speeds approach 1000 to 1200 ft/min, the drum rotates about a horizontally disposed longitudinal axis so that condensate dries instead of collecting in a puddle at the bottom of the drum. Begin adding a rim around the inner circumference of the machine drum. This comprises a dryer roll having a drum 10 with an inner cylindrical surface 20 and an outer cylindrical surface 22, in which the wet web is arranged to receive heat for expelling moisture and drying the web. 1, which is a cross-sectional end view of 8. From the horizontally arranged longitudinal rotation axis 14 to the inner peripheral surface 2
The radial distance to 0 is R, and the plurality of spoiler rods 12 are attached to the inner surface 20 by suitable means such as screws. These spoiler rods extend axially within the dryer roll and are spaced equidistant S apart about the circumference. The spoiler bar has a height H, and as the dryer rotates in the direction of the arrow 18, it interacts with the condensate 16 so that from the 12 o'clock position the spoiler bar tends to accumulate condensate. As it travels downward to certain 3 and 6 o'clock positions, turbulence is created in the condensate as it flows over the top of the approaching spoiler bar. For illustration purposes, the average condensation depth h is shown at a point between two successive spoiler bars at approximately the 8 o'clock position. As the condensate flows in due to the combined effects of rotational force and gravity, the shape of the condensate changes at different locations around the inner circumference of the dryer drum. At the 5 o'clock position, the condensate spills out of the bar so that it is either higher or lower than the normal depth 16. Near the 3 o'clock position, significant turbulence 16a is shown as the condensate spills off the rod.
Near the 12 o'clock position, the condensate 16b flattens out, and near the 9 o'clock position, the condensate begins to build up again as it splashes onto the approaching spoiler rod. U.S. Pat. No. 3,724,094 to Appel et al. states that two of the four factors that affect the heat transfer coefficient of dryer drums with spoiler bars are spoiler bar height and condensate depth. It has been confirmed. In the preferred embodiment of this U.S. patent:
The above two factors are expressed in equations relative to each other. In particular, a preferred condensate depth is about 1 mm to 3 mm, and a preferred spoiler bar height is about 2 to 3 mm of the average condensate depth.
3 times or 2 to 9 mm deep. Furthermore, the spacing between adjacent spoiler bars is determined by the formula S=π√(1.0±
0.25), the preferred spacing is about 5.75 inches, depending on the condensate depth and the inside diameter of the dryer. In the present invention, the above four factors, namely bar height, bar spacing, condensate depth and inner diameter, are interrelated, but with fewer bars and higher heat than taught by the prior art. It follows the relationship given to the amount of transmission. In particular, the relationship between the above four factors is given by the above equations (1), (2), and (3). Thus, in the present invention, the height of the spoiler bars is an inverse function of the number of bars. As the number of rods decreases, the height of the rods increases. An important point in this connection is that tall bars tend to create greater turbulence in the condensate as the condensate spills over the bar and splashes onto adjacent bars. This means that large turbulence and the consequent high heat transfer are produced by a small number of rods. The spacing of the spoiler bars in the present invention is determined by the formula S=π√
(1.5±0.25), so the spoiler bar spacing is a function of the square root of the product of the radius of the inside surface of the dryer and the condensate depth. The above square root relationship is similar to that taught by the prior art. However, the proportionality constant of 1.5 is 50% greater than the proportionality constant of 1.0 taught by the prior art. Therefore, the present invention exhibits 33% fewer spoiler rods for a given condensate depth, which results in an unexpected dramatic change in the condensate heat transfer coefficient, as shown by the numbers listed here. Improvements occur. That is, according to the present invention, the spacing between the spoiler bars is determined by the above formula, and even if the number of spoiler bars is decreased, the heat transfer coefficient increases, for example, as described above with reference to Table I below. The number of spoiler rods is 30 compared to the conventional technology.
Even if the number of books is reduced to 10 according to the present invention, the heat transfer coefficient remains
It increases by 1.76 times from 360 to 635 BTu/hr/ft ² /〓. Furthermore, if the number of spoiler rods is reduced from 30 to 10, the manufacturing cost will be reduced to one-third. Therefore, such reduced manufacturing costs and increased heat transfer coefficients are of great benefit to dryer drum manufacturers and users. Note that the numerical term 0.25 in the above equation is used to provide a tolerance range for the spacing of the spoiler rods that takes into account the variability of condensate splashed onto the spoiler rods during rotation of the dryer rolls. For computational purposes, the width of the spoiler bar itself is considered negligible. The spacing S then essentially indicates the distance between adjacent spoiler bars along the inner wall of the dryer roll. In FIG. 2, spoiler bar spacing on the inner periphery of the dryer drum labeled "prior art" is determined according to the formulas in claims 1 and 7 of U.S. Pat. No. 3,724,094 to Appel et al. Graphed against condensate depth. Due to the variability of the condensate splashed within the rotating drum of the dryer, the representation of vertical width on the graph of spoiler bar spacing for a given condensate depth is limited by a tolerance factor of ±0.25 used in calculations. The shaded area above the "Prior Art" area shows the spoiler bar spacing for various condensate depths according to the present invention. These are detailed below. The curves shown in Figures 3-5 are Btu/hr/ft as a function of condensate depth for a standard 60 inch cast iron dryer drum with an inside diameter of 57.75 inches. The heat transfer coefficient of the condensate at ² /〓 is shown in the graph. Third
The figure shows the values taken for a dryer drum with equally spaced spoiler bars mounted on the inner surface 20 of the dryer drum. On the other hand, FIGS. 4 and 5 show
Figures taken for the same dryer drums as above with 15 and 30 spoiler rods, respectively. The spacing S between the number N of spoiler bars equidistantly spaced around the circumference C of the inner surface 20 of the dryer roll 8 is given by the geometric formula S=C/N (4). By substituting 2πR=C (R: inner diameter of the dryer drum), the following equation becomes S=2πR/N...(5) or N=2πR/S...(6). According to the invention, the optimal spacing S between spoiler bars is S=π√(1.50±0.25)...(2). From the curves in Figures 3-5 and from experience gained from conducting various tests, it has been determined that the preferred number of spoiler rods ranges from about 8 to 20. If there are fewer than 8 spoiler bars,
During rotation of the dryer rolls, condensate accumulates too deeply between the spoiler rods. This results in an excessive increase in the power required to keep the dryer rotating. With more than 20 spoiler rods, the optimum condensate depth for maximum heat transfer is too shallow to be reached with conventional siphon equipment. This is demonstrated in the following example. 1 For 20 spoiler bars in a 5-foot dryer roll, S = 2πR/N = 2π (28.875)/20 = 9.07 inches h = (S/1.5π) ² 1/R = (9 .07/1.5π) ² 1/28.875=0.12
S = 2πR/N = 2π (34.75)/8 = 27.29 inches h = (S/1.5π) ² 1/R = ( 27.29/1.5π) ² 1/34.75=0.96
The formula for the height H of the 5 inch spoiler bar was derived based on experience gained from testing. The above formula is H = (15/N) (1.0±0.25) inches...(1) Since the preferred number of spoiler bars is known, the preferred range of height for the preferred number of spoiler bars is 0.6. The height is 1.5 inches. Referring again to FIG. 2, equation (5) is used to calculate spoiler bar spacing values for various condensate depths. This range is indicated by the shaded area.
Again, a tolerance factor of ±0.25 yields a vertical width for the desired spacing range. The upper and lower limits of the spacing are determined from equation (3) using a suitable range of the number of spoiler bars. That is, S = 2πR / N S _nax = 2π (28.875) / 8 = 22.68 inches S _nio = 2π (28.975) / 20 = 9.07 inches As a result of the test study, it was found that the spoiler rods were equipped with 10 to 15 spoiler bars. It has been shown that dryers can reach higher heat transfer coefficients than dryers with 20 to 30 spoiler rods. It has been determined that this is due to the various relationships between all three major factors that affect heat transfer in dryers with spoiler bars: spoiler bar spacing, height, and condensate depth. In other words, rather than optimizing one of the main factors, e.g. making the condensate depth as shallow as possible, it is important to reduce the turbulence of the condensate in relation to the reduction of the condensate depth. The conclusion is that the task is best tackled by increasing it. Ideally, increased turbulence would increase the amount of vapor introduced by the condensate (resulting in poor insulation properties), and the high degree of turbulence would result in more dryer walls forming. Higher heat transfer coefficients can be achieved in the present invention even when the condensate depth is relatively deep (eg, about 0.25 to 0.50 inches) because of the increased incidence of steam exposure. More importantly, the above facts are achieved with a relatively small number of spoiler bars (eg, about 8 to 20). The present invention therefore relates to a combination of a relatively low number of spoiler rods with a relatively high height for use in conjunction with relatively deep but shallower layers of condensate than those taught in the prior art. The above combination reduces the potential for operational problems associated with relative motion between the siphon and the inner drum wall at high speeds, such as those that can exceed one mile per minute in modern paper machines. It has the added advantage that the siphon gap can be increased for removal. Differences between the present invention and the prior art are best explained by reference to FIGS. 3-5 in connection with an embodiment using the formula for condensate depth for a given number of spoiler bars. Dew.

【table】

[Table] In the above example, the inner radius of the dryer is
For a geometrically identical configuration of 28.875 inches and 15 spoiler rods, the present invention has an optimum condensate depth of 0.228 inches, whereas the prior art has an optimum condensate depth of 0.228 inches. is actually deep
It shows that it is 0.513 inches. Figures 3 through 5 show condensate heat transfer coefficients for various spoiler bar heights and various condensate depths. The condensate depth of dryers according to Appel and others with spoiler bars can be calculated from equation (9) above, and similarly the condensate depth of the present invention is determined from equation (2) of the example above. Therefore, the condensate depth for a given number of pipes can be compared. This was done for 10, 15 and 30 spoiler bars in Table I below.

Table: Referring to Figure 3, for a standard dryer drum with 10 spoiler bars, the combination of a condensate depth of approximately 0.50 inches and a spoiler bar height of 1.5 inches results in a heat transfer coefficient of approximately 635 Btu/ hr/ft ² /〓, whereas the prior art exhibits condensate depths of 1 inch or more, with a preferred spoiler bar height of approximately
At 0.375 inches (approx. 9 mm), the heat transfer coefficient is approximately
70Btu/hr/ ^ft2 /〓 is shown. Similarly, in FIG. 4, the heat transfer coefficient for a drum with 15 spoiler bars according to the present invention is about 480 Btu/hr/ft ² /〓 at a condensate depth of about 0.23 inches for a spoiler bar height of 1 inch. (shown as a dotted line). At a condensate depth of 0.513 inches for a 0.375 inch height spoiler bar, the corresponding heat transfer coefficient for the same dryer roll is approximately 375 Btu/
hr/ ^ft2 /〓. In FIG. 5, for a dryer roll with 30 spoiler bars, the optimum condensate depth according to the present invention is about 0.06 inch, and the heat transfer coefficient is about
550Btu/hr/ ^ft2 /〓. At a condensate depth of about 0.129 determined by the prior art, the heat transfer coefficient is about 360 Btu/hr/ft ² /〓. Thus, a dryer apparatus with an improved spoiler bar is disclosed, which achieves an improved heat transfer coefficient through a novel combination of spoiler bar spacing, height, and condensate depth.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional end view of a cylindrical dryer drum showing a plurality of circumferentially spaced apart axially extending spoiler bars attached to an inner wall, the spoiler bars being enlarged for clarity; Although shown, its actual width is negligible compared to the spacing between spoiler bars. FIG. 2 is a graphical representation of spoiler bar spacing according to the present invention compared to the spoiler bar spacing of Appel et al., U.S. Pat. No. 3,724,094 versus condensate depth; FIG. Figure 4 shows the variation of the heat transfer coefficient through a cast iron dryer drum with ten equally spaced spoiler bars as a function of condensate depth for various heights of spoiler bars. A graphical illustration showing the variation of heat transfer coefficient in a cast iron dryer drum with 15 equally spaced spoiler rods as a function of condensate for a 3/8 inch tall spoiler rod. Figure 2 is a graphical representation of the variation in heat transfer coefficient by a cast iron dryer drum with 30 equally spaced spoiler bars as a function of depth; 8...Dryer roll, 10...Drum, 12...
... Spoiler rod, 14 ... Rotating shaft, 16 ... Condensate, 18 ... Rotation direction, 20 ... Cylinder inner surface,
22... Cylinder outer surface, W... Web, H... Spoiler bar height, h... Average condensate depth, S...
Spoiler bar spacing.

Claims (1)

[Claims] 1. A hollow cylindrical dryer that is rotatable around a longitudinal axis and equipped with a plurality of spoiler rods that are attached to the inner peripheral surface and extend substantially parallel to the longitudinal direction of the rotation axis. a drum, said drum containing condensable heating vapor, such as water vapor, therein for heating the cylindrical drum wall and equipped with a siphon in the dryer drum for collecting and removing said condensate; wherein the number of spoiler rods ranges from about 8 to 20 and is mounted within the drum; the depth of the condensate is maintained at a depth between about 0.125 and 1.00 inches; the spoiler rods are of the formula S=π√(1.50±
0.25) on the circumferential surface of the drum wall (where R: radius from the rotation axis to the drum inner surface, h: average condensate depth, S: distance between adjacent spoiler rods). A dryer drum characterized in that condensate turbulence and heat transfer in the dryer drum are improved.