DE2813744A1 - METHOD AND DEVICE FOR DRYING MATERIAL - Google Patents

Description

Patent attorneys Dipl.-Ing. H. Weickmann, DiPL ₁ -PHYS-DRrTyTFiNCKE

Dipl.-Ing. F. A-Weickmann, Dipl.-Chem. B. Huber

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S MUNICH 86, DEN3 O. MUTZ 1978

FA 8519/433 P.O. Box S6os2o

MÖHLSTRASSE 22, CALL NUMBER 98 3921/22

THE ELECTRICITY COUNCIL

30 Millbank

London SW1P ARD, England

Method and device for drying material

809841/0859

The invention relates to the drying of material in a continuous process through a drying chamber is passed through.

While the invention is particularly applicable to drying a material containing water, it is moreover generally applicable to drying materials containing liquids other than vapor that removes can be. As a result, with the invention in mind, the following is broadly referred to as a liquid and reference is made to a steam, in which context it should be pointed out that the designations "Liquid" and "vapor" refer to the same material in its different phases.

According to one aspect of the present invention, a method for drying a material by evaporating a Liquid hereof proposed, which comprises the following process steps: passing through or -lowing the material through a drying chamber; Circulating or circulating superheated steam through the chamber to evaporate liquid from the material so that, as a result, more vapor than enters the chamber, the chamber leaves; Separating and compressing the excess vapor exiting the chamber to increase its temperature; Use the heat of the compressed steam in a heat exchanger to heat that to be circulated through the drying chamber Steam, the pressure of the compressed steam being high enough that the compressed steam is in the heat exchanger condenses and thus creates a pressurized fluid (hereinafter also referred to as hydraulic fluid referred to as); rapid outflow or formation of steam by throttling the hydraulic fluid a low pressure; and feeding the rapidly evacuated steam into the steam that is circulating or is circulated.

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According to another aspect of the invention, an apparatus for drying a material for evaporating the Liquid provided therefrom comprising: a drying chamber through which the material is passed is run; circulating means for circulating superheated steam through the chamber so that liquid is vaporized by the material and consequently more vapor than enters the chamber leaves the latter; a Compressor for compressing the excess vapor which humidifies the chamber to raise its temperature; a heat exchanger device, in which the heat of the compressed steam to heat the material to be circulated through the drying chamber Steam is used; the compressor being arranged to compress the steam to a pressure such that the compressed vapor condenses in the heat exchanger and gives off latent heat of vaporization; and a throttle device to reduce the pressure of the liquid leaving the heat exchanger and thereby to generate of steam that is fed back into the circuit.

A mechanical compressor can be used to provide power to practice the present invention to the system, and it becomes possible to use the latent heat that has been applied to the liquid from the to evaporate the material to be dried, to recover it. Generally speaking, this latent heat represents you very much essential part of the energy that is required to evaporate the liquid from the material to be dried. Of the Compressor can be arranged to produce superheated output steam at a temperature above (and preferably very much above) the saturation pressure of the compressed steam. In general, no thermal energy would be required, to keep the cycle going, although when the cycle is started, heat energy or a source of steam or both are needed during the warm-up period

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fully or partially self-sustaining the cycle close.

Provided that the energy losses from the system are kept low, no additional energy is added to the Maintaining operations needed. If energy "to fill up" is required, then it can be used as thermal energy or Steam can be supplied. The condensed liquid from the heat exchanger is under pressure and it becomes additional Make-up steam obtained by throttling this compressed liquid leaving the system on the low pressure inside the chamber, which is typically atmospheric pressure, and by "rapid venting" of steam. This steam, which flows out quickly or is created, is advantageously at the entrance of the compressor is fed back into the cycle and it forms another energy supply to the system. This supply of energy helps maintain the energy balance, which depends on the leakage from the system. Such a one Leakage can occur, for example, when material to be dried is introduced into and out of the drying chamber is taken out.

The reuse of the rapidly emitted or generated steam in this way results in a significant improvement the overall performance of the facility. The improved energy efficiency (compared with a system in which steam that has been quickly released or created is not used in this way is) also makes it possible to build a cheaper and simpler system for a given drying capacity.

It is also possible to throttle the liquid to a pressure between the condensation pressure and the Chamber pressure is, so that in this way some steam is generated at this intermediate pressure that in another part

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of the process can be used. The remaining liquid can then be further throttled to the chamber pressure, as already explained before, so that further steam is generated thereby.

In particular, in a continuous process in which the material to be dried is continuously fed into the drying chamber and dried material is removed therefrom, air leaks into the drying chamber and this air is circulated together with the steam. If the amount of air in relation to the steam is kept small, ie in particular less than 10% by weight , then the cycle can be continued without any great loss of efficiency. However, the compressed liquid exits the heat exchanger with a mixture of air and steam. As a result, if there is significant air leakage into the system, a separator can be provided which separates the condensed liquid from any air before that liquid is transferred from the heat exchanger to the throttle device.

When applying the invention to the drying of, for example, a flat paper or textile or cardboard material web, this web can be passed continuously at a uniform speed through a drying chamber into which superheated steam at a temperature of 150 ^° C., for example, is fed. In the drying chamber, water is evaporated from the material to generate steam, and the outlet steam from the chamber is at a lower temperature, e.g. 125 ° C. The amount of steam exiting the chamber is due to the evaporation from that to be dried Material larger than that which enters the chamber, namely in a typical case it can be, for example, 2% larger. This exhaust steam is split, with the main part going through a heat exchanger to be

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to be recirculated while the excess is fed to a compressor. It will be readily appreciated that the amount of superheated steam that is recirculated is determined by the capacity of the recirculation fan and the physical configuration of the system, and the remainder goes to the compressor; the system regulates or controls itself in this regard, and there is no problem of separating the excess steam from the amount to be recirculated. In the compressor, as a typical example, the pressure can be increased to, for example, 4.5 at, but the compressor is designed for a superheated discharge, for example at a temperature of about 300 ^° C., which is substantially above the temperature of the saturated steam is 4.5 at. This superheated, higher pressure vapor is passed through the heat exchanger where it is condensed. Typically, the outlet water to 148 ° C can be when the circulating superheated steam flowing into the chamber is at 150 ⁰ C. This outlet water is pressurized, and by throttling it to atmospheric pressure, steam is generated which is fed back into the cycle, preferably at the compressor inlet, so that further energy is used from the water before that water is released or released at atmospheric pressure will. It can be readily seen that the discharge pressure from the compressor and the amount of air present determine the condensation temperature in the heat exchanger.

The invention can be applied to a spray dryer in which wet material is atomized and the droplets or droplets dry when they are caused by the superheated steam (or other fluid) in the drying chamber go through.

The invention is illustrated below with reference to one shown schematically in the single figure of the drawing, in particular preferred embodiment explained in more detail.

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Reference is now made to this drawing, in which a drying chamber 10 is shown schematically, through which a material web 11 is continuously passed, for example paper or cardboard or textile material. Seals 12, 13 are provided for the insertion and removal of the web in the chamber walls. In addition, an automatic pull-through device is preferably provided for pulling the web 11 through the chamber 10. A fan 14 circulates superheated steam through the drying chamber at substantially atmospheric pressure. In this particular embodiment, the steam enters through an inlet 15 a at a temperature of about 150 ° C in the drying chamber, then passes through the chamber 10 to an outlet 16 where the steam tempera door is in this particular embodiment, about 125 ⁰ C; this steam is recirculated through a heat exchanger 17 and back to the fan i4. The excess steam coming from the drying chamber is led to a compressor 18 where it is compressed to 4.5 atm and so that its temperature is increased to about 300 ⁰ C (which is significantly above the temperature of saturated steam at this pressure). This compressed, overheated vapor through the aforementioned heat exchanger 17, which forms a condenser, passed, to increase to 150 ⁰ C to the temperature of the circulating steam, which is fed back into the drying chamber and pressurized water at or at about 130 ° C an outlet 19 to generate.

Although shown schematically in the drawing, the superheated steam enters the chamber 10 through an inlet passage is fed into the chamber, the way of feeding depends on the structure of the chamber and the type of to drying material. Generally, the superheated steam for the purpose of drying a web is passed through a plurality of Nozzles fed, which direct the steam to the web, so that in this way a rapid heat transfer to it drying material is ensured.

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In the system described, air inevitably occurs through the seals 12, 13 into the drying chamber 10 and as a result some air and water vapor appear along with the water at the outlet 19. This water therefore becomes a separator and a separator, respectively Separator 20 out, where air and water vapor are released at 21 to the atmosphere. The water, which is still under pressure and has a temperature of approximately 130 ^° C., is then fed into a throttling device 22 in order to allow steam to develop quickly ^{at atmospheric pressure and 100 ° C.} This steam is used as make-up steam and fed back into the drying cycle. This steam is preferably fed into the compressor, as indicated at 23. Hot output water from the restrictor 22 is withdrawn at atmospheric pressure at 24 and can then be used anywhere.

Although the illustration illustrates a single-stage throttling device which generates steam at atmospheric pressure and water at or from 100 ^° C., it is also possible to use a multi-stage, for example a two-stage, throttling process in which some steam is used at a pressure above atmospheric Pressure and at a corresponding temperature above 100 ⁰ C is generated. The remaining liquid can then be throttled to atmospheric pressure in a two-stage arrangement to generate further vapor.

In a system as discussed above, the latent heat represents about 90% of the energy required for the heating and evaporation of water from the material to be dried is required. It should be noted that this latent heat is recovered through the system, and that the energy supplied to the fan and compressor, sufficient to provide all the necessary energy supply and also to compensate for heat and steam leaks from the cycle.

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Claims (9)

V claims 1. Process for drying material by evaporation a liquid thereof, characterized by the following process steps: passing the material through a Drying chamber, · Circulating superheated steam through this chamber so that liquid is evaporated from the material and consequently more steam than enters the chamber, these leaves; Separating and compressing the excess vapor exiting the chamber to raise its temperature; use the heat of the compressed steam in a heat exchanger to heat the steam passing through the drying chamber is to be circulated, the pressure of the compressed steam is high enough that the compressed steam in condenses in the heat exchanger to produce a pressurized liquid; rapid generation of steam by throttling the pressurized fluid to a lower pressure; and feeding in this quickly created Steam in the circulating steam. 2. The method according to claim 1, characterized in that the liquid to separate it from any air and any steam through a separator is passed through before the pressurized liquid quickly creates or escapes vapor leaves. 3. The method according to claim 1 or 2, characterized in that the excess steam is compressed so that one superheated output steam at a temperature above the saturation temperature, which is the pressure of the compressed Corresponds to steam. 4. Apparatus for drying material by evaporation a liquid thereof, in particular to carry out the 809841/0859 Method according to claim 1, 2 or 3, characterized by a drying chamber (10) through which the material (11) is passed will; circulating means (14) for circulating superheated steam through the chamber (10) so that liquid is evaporated by the material (11) and consequently more steam than enters the chamber (10) leaves it; a compressor (18) for compressing the excess Steam leaving the chamber (10) to raise its temperature; and a heat exchange device (17) in which uses the heat in the compressed steam to heat the steam to be circulated through the drying chamber (10) will; wherein this compressor (18) is arranged and / or designed so that it compresses the steam to a pressure such that that the compressed vapor condenses in the heat exchanger (17) so that it gives off latent heat of vaporization; and a throttling device (22) for reducing the pressure of the liquid leaving the heat exchanger (17), and thereby generating steam that is fed back into the circuit. 5. Apparatus according to claim 4, characterized in that the steam from the throttle device (22) into the entrance of the compressor (18) is fed. 6. Apparatus according to claim 4 or 5 »characterized in that a separator or a separating device (20) for Separating the condensed liquid from any air before transferring that liquid from the heat exchanger (17) to the Throttle device (22) is performed, is provided. 7. Apparatus according to claim 4, 5 or 6, characterized in that that the drying chamber (10) seals (12,13) for the passage of a flat web (11) of paper or Having textile or paperboard material through the chamber (10). 809841/0859 ■ . 3. 8. Device according to one of claims 4 to 7, characterized in that the heat exchanger (17) is arranged is that it heats the steam before the steam is fed into the drying chamber (10). 9. Device according to one of claims 4 to 8, characterized in that the compressor (18) is arranged and / or is designed that it is superheated exhaust steam at a temperature above the saturation temperature, which the Outlet pressure, delivers. _ 8U9841 / 0859