Drying and gas or vapor contact with solids – Apparatus – Rotary drums or receptacles
Patent
1993-01-25
1994-08-09
Gromada, Denise
Drying and gas or vapor contact with solids
Apparatus
Rotary drums or receptacles
34125, 34124, 165 89, F26B 1318
Patent
active
053354273
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a device by means of which the operation of spoiler bars installed inside a cylinder can be improved. The device to which the invention is applied is a rotating device for removing condensate or water, i.e. a so-called condensate pick-up shoe. The improvement can be made in any known rotating condensate pick-up shoes by replacing the condensate-removing part pressed against the interior surface of the cylinder (or roll) with a new condensate-removing part constructed according to the method and forming a predetermined layer of condensate.
The device according to the invention is based on combining the functions of a number of prior-known devices. It has always been desired that the cylinders or rolls of a paper-making machine or other similar machine have a good performing capacity. The cylinders used for drying are heated with steam which, when cooling, condenses as water of condensation inside the cylinder. Respectively, when rolls or cylinders are cooled using water, water has been directed into the cylinder via nozzles. From inside the cylinder the water of condensation is removed in a manner known per se by means of either a rotating or a stationary condensate pick-up shoe, or also by means of a device called a siphon. The rotating pick-up shoe is supported fixedly inside the cylinder and rotates at the angular velocity of the cylinder. A stationary siphon is supported outside the cylinder against the frame structures of the machine and does not rotate together with the cylinder. A rotating siphon is widely used for removing condensate from cylinders. It is essential in the construction of a rotating siphon that the tip of the siphon is close to the interior surface of the cylinder (or roll). The condensate is removed from inside the cylinder by means of a pressure difference. Some volume of blow-through steam (or gas) is always needed for the removal of condensate. The higher the rotational velocity of the cylinder, the greater the force, caused by the centrifugal force, resisting the removal of liquid. Nowadays a high production efficiency of paper-making machines is aimed at. In practice this has meant that the rotational velocity of the cylinders has continually been increased. The constructors of the condensate pick-up shoes have construed their product so that the ratio of the rate of condensate removed to the volume of blow-through steam is at its optimum. This is important in terms of energy economy.
When the paper machine cylinder rotates, centrifugal force has a significant detrimental role in determining the drying process. The higher the rotational velocity of the cylinder, the more strongly the condensate is pressed against the interior surface of the cylinder. This force also prevents the effect of forces which produce internal turbulence of the condensate layer. The condensate layer will be laminar. Thereby the transfer of heat through the condensate layer is worsened.
The heat transfer of paper machine cylinders has been improved by known methods (e.g. U.S. Pat. No. 4,195,417). These spoiler bars installed inside the cylinder have functioned effectively and have improved the transfer of heat in the drying cylinders in paper-making machines. The higher the velocity of the dryer (=rotational velocity), the more the transfer of heat has been improved by spoiler bars.
It has also been known that spoiler bars work best if there is a correct and sufficiently thick layer of condensate in the cylinders. Without this condensate layer the spoiler bars will not work uniformly.
The manufacturers of rotating condensate pick-up shoes have in their own constructions aimed at having a maximally thin condensate layer inside the cylinder. This is important per se, since the condensate layer being thin has helped improving the transfer of heat from inside the cylinder outwards. However, the lowering effect of the rotational velocity on the transfer of heat is stronger than the effect obtainable through thinning the condensate layer. Efforts have been made to eliminate this by ins
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