FI83679C - HUVA FOER EN KONTAKTTORKCYLINDER. - Google Patents

Description

1 83679

FIELD OF THE INVENTION This invention relates to a contact drying cylinder, e.g. away from the cylinder and the jacket jacket to form two concentric flow channels of circular cross-section substantially merging at one or both ends of the jacket, the outer flow passage having a dry gas inlet and preferably in the vicinity thereof, e.g.

The Yankee cylinder of the paper dryer is 4-6 to 20 m in diameter and is needed either to provide a gloss on the paper or to dry sanitary papers, which must be dried with a single cylinder.

For many reasons, the specific evaporation 25 of a Yankee cylinder is much higher than that of a conventional cylinder of a multi-cylinder machine, usually 1.5 to 1.8 m in diameter. This is due to the low contact resistance between the cylinder surface and the paper due to the paper being compressed by Yankee. -30 with a press attached to the surface of the cylinder, for the same reason the cylinders generally do not use drying felts that interfere with heat and mass transfer, due to the long contact distance the web heats - le.

In order to control the flow of drying air and also to increase the efficiency of the drying-5 event, the Yankee cylinders were originally equipped with so-called with a low-pressure Yankee cap. An essential part of it was a partition placed at a suitable distance from the web. In the gap between it and the web, the drying air preferably flowed countercurrent to the web. In this way, a heat transfer coefficient increasing the specific evaporation was obtained on the air side, and an even air distribution was able to improve the uniformity of the drying intensity in the width direction of the web. The drying air blower and the air heating fin coil coil were preferably placed in connection with the heat recovery plant.

15 At the heat recovery plant, the initial heating of the new drying air took place with exhaust air sucked from the jacket.

In recent decades, a high-power hood has generally been built on the Yankee cylinder. The reason has been that the target specific evaporations sought are so large that the capacity of the low pressure jacket has not been sufficient.

It is essential for a high power pattern that improved specific evaporation is achieved by nozzle cleaning applied to the surface of the web, which improves the heat transfer coefficient on the surface of the web. In this case, the desired higher specific evaporation occurs at a lower web temperature compared to the low-pressure jacket, and thus the heat flow inside the cylinder increases in proportion to the difference between the vapor condensation temperature and the web temperature. The heat flow from the drying air also increases, although its relative share of the total heat flow is usually quite small in the case of a robe whose drying air is heated by a steam coil.

35 The operating principle of a high-efficiency plan brings with it many structural disadvantages, which are illustrated by a concrete example. 1 3 83679

Let the length of the web contact surface be 12.5 m, the target specific evaporation 0.0278 kg / m2s is 100 kg / m2h, which can be achieved with a mass flow of blowing air relative to the surface of the web at a density of about 0.8 kg / m2s. In this case, the heat transfer coefficient on the surface of the web 5 is about 0.15 kW / m 2 OC. Let the humidity addition of the drying air be 0.2 kg H 2 O / kg dry air (ie the humidity of the exhaust air x ~ 0.21). These values can be used to calculate that per meter of web width - evaporation is 0.347 kg / s 10 - drying air demand is 1.74 kg / s - nozzle blowing air demand is 10 kg / s.

Thus, the recirculated air flow (= nozzle blowing air flow) is almost six times that of the drying air flow (= exhaust air flow). In order to prevent the recirculating air blowers and the flow cross-sections from becoming disproportionately large, it is customary to divide the robe into several blocks, two or three, which are preferably connected together so that the drying air flows from block to block upstream of the web.

20

In order to heat the recirculated air, the structure must include - when the heating takes place with steam - fin tubes with a heating surface of the order of about ten times the surface of the web, as well as filters that prevent the rib surfaces from becoming dusty.

Often the structure is such that, in order to achieve a uniform blow, the robe has to be divided in the width direction of the web into a number of pressure and suction chambers for circulating air.

30

All in all, in order to carry out the nozzle blowing, this has resulted in a structure that is complex and expensive, as well as difficult to adjust, maintain and repair. 1

The above-mentioned disadvantage of nozzle blowing, namely the increased size of fans and recirculation ducts, is often solved by placing only nozzle boxes on the cylinder, while fans and radiators (or - in the case of 4 83679 recirculated flue gas heating - burners) are placed separately next to the dryer.

It is therefore an object of the present invention to provide a contact drying cylinder cover of the type mentioned in the introduction, i.e. a so-called low pressure cover, which nevertheless achieves the specific evaporation of the above-mentioned high-power cover, i.e. to provide a contact drying cylinder cover. The advantages of 10 pressure shields and high power shields while avoiding their disadvantages.

The main features of the present invention appear from the appended claims.

15

The characteristic evaporation of the low pressure scraper according to the present invention can be raised to the same level as the high power scraper by placing the partition at a distance from the cylinder surface with a high drying gas velocity and providing the partition with heating elements to radially transfer heat to the drying gas.

In the schematic of a contact drying cylinder according to the invention, the partition wall can be heated by resistance elements connected to an external power source or the partition wall can be constructed as a heat exchanger placed so close to the cylinder surface that high air velocity-comparable heat transfer coefficients are achieved.

In a preferred embodiment of the invention, the partition can be converted into a heat exchanger by forming a plurality of channels extending substantially in the direction of rotation of the cylinder to be connected to an external steam source, for example pipes, spaced apart in the transverse direction of the partition and possibly

II

5,83679 heat-dissipating projections extending to one or both sides, preferably at least to the inner flow channel, preferably flanges extending substantially in the direction of rotation of the cylinder guiding the drying gas.

The ducts formed in the partition wall are preferably connected to a common transverse steam distribution duct to be connected to an external steam source and again to a common transverse condensate discharge duct at its lower ends. The condensate drain channels 10 can be tightly attached to the ends of the casing, with openings in the edge portions associated with the condensate drain channels of the septum through which the drying gas can flow from the outer to the inner flow channel to provide locally enhanced web drying.

The partition can also be divided into two successive partition parts, viewed in the direction of rotation of the cylinder, with separate drying gas inlets, but preferably with a common wet drying gas outlet. In this case, the dry gas flows downstream between the second partition part and the cylinder and countercurrently between the second partition part and the cylinder with respect to the direction of rotation of the cylinder.

The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 shows a cross-sectional end view of a preferred embodiment of the invention fitted to a contact drying cylinder, Figure 2 shows a section along line II in Figure 1, Figure 3 shows a cross-sectional end view of another alternative embodiment; a cross-sectional end view of a further alternative embodiment of the invention in which the partition is divided into two successive parts.

35

Figure 1 is a contact-drying cylinder usually Yankeesylinterin, the web is dried with the cylinder surface generally designated by the reference numeral 1. The web W runs the direction of arrow B, parallel 6 83 679 a and compressing the rolls P attached to the cylinder surface 1 1 and against the web of the cylinder surface W is fitted on the casing according to the invention, is generally indicated by reference numeral 2. The hood 2 consists of a heat-insulated casing 3 closed at its ends 14 and at both ends 15 so that, when placed against the cylinder surface 1 and the web W on it, it forms a substantially gas-tight space with the contact drying cylinder. As can be clearly seen in Figure 1, the space delimited by the cylinder surface 1 of the shrouds 2 and 10 is divided by a small distance from the cylinder surface 1 and a partition wall 4 parallel thereto, extending between the ends 14 of the shroud 2 but ending at a small distance from the ends 15 to a flow channel in the shape of a circular arc 15 so that drying gas can flow from one flow channel to another between the front edge of the partition wall 4 and the corresponding end 15 of the cover, respectively. In addition, between the partition wall 4 and the heat-insulated jacket 3 of the shroud 2 there is a transverse wall 10 by which the outer flow channel 20 is divided into two successive parts, the drying gas inlet 11 being arranged at the beginning of the latter part and the wet drying gas outlet 12 the opening Al 11 in the arrow direction of the partition wall 4 and the casing February 25 of the shell 3 between the outer flow channel along the direction of the arrow A2 direction, turning the inner direction of the arrow A3 direction of the intermediate wall 4, the rear edge of the casing 2 the head 15 through the gap between the between the cylinder and the intermediate wall of the flow channel, wherein the drying gas flows into the arrow A4 direction upstream of the cylinders, 30 teripinnan one on top of the web W to the transport direction, and finally drying the moist gas stream is again turned in the direction of the arrow As the partition wall 4 of the casing 2 and the front edge of the corresponding end of the gap 15 between the outer flow channel to the front portion away from the support of the arrow Ae direction of the moist powder 35 gas into the outlet opening 12. The intermediate wall 4 of the heat transfer more effective is the first part of the drying gas in the outer flow channel and the inner drying gas channel thereof disposed along the length of a plurality of substantially cylindrical l 7 83 679 rotational direction of extending and cross direction apart of spaced flanges 7 'and 7 '', which at the same time control the flow of gas.

As can be seen in Figure 1 and in more detail in Figure 2, the partition 4 acts as a heat exchanger which transfers heat convectively to the drying gas and in addition by radiating to the web W. The partition acting as heat exchanger, generally indicated by reference numeral 4 in Figure 2, consists of 10 cylinders. in the direction of rotation of the surface, parallel to each other at a small transverse distance from curved tubes 5 arranged transversely to each other by partition elements 6 and further provided with means with flanges 7 'and 7' 'extending in the direction of rotation, the height of the flanges 7' being slightly less than the distance between the tubes 5 and the heat-insulated sheath 3 of the shroud 2 and the flange the height 7 '' is slightly less than the distance between the tubes 5 and the cylinder surface 1, including the thickness of the web W. When the distance between the partition wall 4 and the cylinder surface 1 is relatively small, vortex pairs B formed by vortices rotating in opposite directions between the flanges 25 1 '', as shown in Fig. 2. These pairs of vortices significantly improve the heat transfer between the partition wall 4 and the cylinder surface 1. 1 2 3 4 5 6

With the heat exchanger according to the present invention, the formula 2 provided with a partition wall 4 2 makes the flow of drying gas 3 very advantageous and achieves the same drying efficiency 4 as in the high-efficiency pattern 5 with nozzle blowing, but with a lower heat transfer coefficient. 6 This is due to the lack of air circulation due to kuivatusil-ma is dry when it flows in the direction of the arrow A3 in Figure 1 of the partition wall 4 and the cylindrical surface 1 to the inner limit of the drying gas passage and thanks to this the temperature of the web W 8 is lower than 83 679 suurtehokaavussa. This increases the heat transfer not only from the drying gas to the web W but above all from the cylinder surface 1 to the web W.

The partition 4 acting as a heat exchanger is heated by condensing steam introduced into it from an external source and for this purpose the pipes 5 of the partition 4 are connected to a common steam distribution pipe 8, as shown in Figure 1, and to a common condensate outlet pipe 9 at both ends.

10

Fig. 3 shows an alternative embodiment which differs from the embodiment shown in Fig. 1 in that both ends of the partition wall with condensate drain pipes 9 are tightly attached to the ends 15 of the casing 2, whereby the drying gas flow from the outer to the inner flow channel is arranged to take place through a plurality of openings 13 arranged at the ends of the partition elements 6. This embodiment then operates locally at the openings 13 like a nozzle dryer, thus providing an enhanced drying area at the ends of the casing 20 2, in which the drying gas flows at a high speed towards the paper web W. In this way, the drying intensity is increased locally and the arrangement also has the advantage that leaks into the environment are reduced. 1 2 3 4 5 6 7 8 9 10 11 li

Leaks to or from the environment can be further reduced by the solution shown in Fig. 4, in which the drying gas 3 is fed to the middle part of the mantle from the inlets 11 'and 11' 'by the outer edges of the partition wall 4' and 5 4 '' in the direction of arrows A3 from the space between the partition wall parts 4 'and 4' ', respectively, and the cylinder surface 7 1, i.e. from the inner drying gas duct 8, through the outlet opening 12 9 between the inlet openings 11' and 11 ''. In this solution, the drying gas flows first downstream in the second inner drying gas channel 10 and then countercurrently in the subsequent inner drying gas channel with respect to the web W on the cylinder surface 1.

9 83679

Essential to the invention has long been the use of cylinders for contact drying machines, especially the so-called Construction of a partition wall known from the low-pressure patterns of Yankee cylinders as a heat exchanger which convectively transfers heat to the web, which is dried by means of the hot surfaces of the cylinders (cylinder) of the contact dryer, by means of drying gas (air). By dimensioning the structure of the mantle so that the drying air has a particularly high velocity between the drying surface and the heat exchanger, the structure can achieve a similar drying intensity as is common with high-pressure nozzle-drying formulas now in use for a few decades.

Claims (5)

10 83679 A cover (2) closed at both ends (15) and sides (14) for mounting on a part of the cylinder drying surface (1) of a contact drying cylinder to be dried, having a partition wall (4) extending substantially parallel to the cylinder surface (1) spaced apart from the cylinder surface (1) and the shroud jacket (3) to form two substantially concave circular cross-sections of at least one end of the shroud to form a converging flow channel, the outer flow channel having a drying gas inlet (11) and preferably proximity thereto; A wet drying gas outlet (12) separated by a transverse wall (10), characterized in that the partition wall (4) is provided with heating elements (5) to be connected to an external energy source 15 to transfer heat to the drying gas convectively and to the web (W). A robe according to claim 1, characterized in that the partition wall (4) has a plurality of channels (5) spaced substantially in the direction of rotation of the cylindrical surface (1) and spaced apart from the outer wall in the transverse wall and possibly from these channels (5) (4) projections for enhancing heat transfer extending to one or both sides, preferably to at least the inner flow channel, preferably flanges (7 ', 7' 'extending substantially in the direction of rotation of the cylinder surface (1) guiding the drying gas. 1 li A robe according to claim 2, characterized in that the ducts (5) are connected to a common transverse steam distribution duct (8) to be connected to an external steam source and to a common transverse condensate outlet duct (9) at its lower ends. :: 35 A robe according to claim 3, characterized in that the condensate drains (9) are attached to the ends (15) of the casing (2) and the edge portions of the partition wall (4) associated with the condensate drains (9) 11 83679 have openings (13). A3) from the outer to the inner flow channel. A robe according to any one of the preceding claims, characterized in that it has two successive partitions (4 ', 4' ') in the direction of rotation of the cylinder surface (1) with separate drying gas inlets (111, 11' ') and a common wet drying gas outlet ( 12). 10