JPH03502119A - Method and apparatus for recapture of waste heat contained in moist dry air exiting a paper dryer of a paper machine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Wet water flowing out from the paper dryer of a paper machine Recapture of waste heat contained in dry air Method and apparatus for The present invention is a two-component system in which thermal energy extracted from dry air is added to the low pressure side. Using a compression heat pump, from the water supply on the high pressure side by the heat pump, the paper dryer of the paper machine Process steam is generated for heating the drying cylinder and then further drying. The air used for drying is preheated in the drying air preheater, which flows from the paper dryer of the paper machine. A method for the re-capture of waste heat contained in the humid dry air that is emitted, and the use of this method. Concerning apparatus for implementation.

When paper is manufactured using a paper machine, a relatively thin fiber valve is first turned into fiber fleece. Condensed, then vacuum suction and couch roll, and finally moistened in the press section. It is dehydrated by a row of presses. The remaining water is then captured in the drying section of the paper machine. However, this drying section is located in a drying chamber and is operated under low pressure at a temperature of about 140° to 150°C. It is formed by a row of cylinders heated by steam. formerly burned with fossil fuels Process for heating drying cylinders generated in low-pressure steam boilers In a device of the type mentioned at the outset (German Patent Specification No. 3612907), the steam is It is generated from the feed water in the reabsorber of a two-component compression heat pump. On the other hand, in the dryer The moisture expelled from the paper web by It is transmitted to the dry air that is preheated by the heat pump, and then from this dry air - energy To reacquire heat - heat is drawn out again in the deaerator of the heat pump, but at that time, Some of the moisture received in the paper dryer occurs as liquid condensation, which is subjected to sitting pressure. Must be. It is then saturated with what remains of the received water vapor. The collected air is released into the surrounding atmosphere as waste air, which causes Not only does the water vapor content increase - but when it is further cooled to ambient temperature - fog or A mist will also form. This creates an undesirable environmental burden on the surrounding atmosphere. However, this environmental burden is not only due to small weather changes, but also due to changes in the winter season. Also disadvantageous is the risk of ice or frost formation. On the contrary, the high water vapor content in the atmosphere It also contributes to the ``greenhouse effect,'' which has been recognized as a relatively recent climate hazard. Change Along with the water vapor mist, (relatively small amounts) of harmful substances are also released during the paper manufacturing process. It cannot be ruled out that such environments could be reached.

The process steam for heating the drying drum is supplied in a conventional manner by a steam generator etc. or drying occurs without drying rolls using heated steam or steam-rich steam. In paper machines operated in tunnel dryers using gas-mixtures, the humidity in the drying chamber is A separate (-component) heat pump is used to utilize the waste heat contained in the waste air. This is known (West German Published Specification No. 2630853; West German Published Specification No. 3). 240611), the humid waste air is cooled in the evaporator of this heat pump and contains This cooled waste air is then allowed to condense - in part - and this cooled waste air is The air is heated again in the heat pump condenser and, in some cases, newly used as dry air for papermaking. Used in the drying room of the machine. However, it is used to utilize waste heat from dry air. The connection between the heat pump and the process steam generator is not made here.

In contrast, the problem on which the present invention is based is to As widely as possible, some of the energy required for drying is (further) reduced. and the environmental burden, e.g. from fog formation, is reduced as widely as possible. So, to improve.

Starting from a method of the type mentioned at the outset, this task can be solved according to the invention by In a paper machine, a dry air preheater, a paper dryer connected after the dry air preheater, and connected behind the paper dryer and in front of the dry air preheater, The two-component paper has a return conduit for returning the water vapor condensate Formed from a heat exchanger that is heat transfer coupled with a deaerator of a compression heat pump, it is closed The humid air flowing out of the paper dryer is guided through a A heat exchanger cools the air to a temperature significantly higher than that of the surrounding air. Resolved by rerokoto. Dry air circulation is provided for process steam generation. connection to a two-component compression heat pump system and the drying Allows air circulation to operate at a significantly higher temperature level compared to the temperature of the surrounding air. This allows the heat pump to operate at favorable performance figures. . Compared to traditional paper dryer where warmed ambient air is used as drying air , by setting a higher temperature level in the deaerator, the equivalent drying Dryness can be obtained.

Therefore, compared to the conventional paper dryer mentioned above, in order to achieve the same dryness, There is no need to circulate large amounts of dry air; Neither the essential compressor nor the conduit cross-section needs to be converted to higher performance. This is true In addition, conventional equipment, which previously operated on warmed ambient air, It also means that it can be converted at a fraction of the cost, which at the same time allows process steam The aforementioned improvement in the performance figures of heat pumps used for the generation of The total energy input required is reduced.

The equipment used for the implementation of this method is a dry air preheater, the dry air preheater a paper dryer connected to the back of the paper dryer, and a paper dryer connected to the back of the paper dryer and the dry air preheater. For returning the water vapor condensate generated in the previously connected liquid into the paper manufacturing process. A closed dry air circulation formed by a heat exchanger with a return conduit of , characterized by a heat transfer coupling between the heat exchanger and the deaerator of the two-component compression heat pump, and the exchanger is directly connected to the deaerator. It may also be configured as part of a deaerator of a heat pump. However, especially The heat exchanger is connected to the deaerator of the two-component compression heat pump through a closed circulation of fluid, especially water. are combined. For this reason, if necessary, the heat pump can be easily removed from the dry air circulation. This also makes it possible to retrofit existing equipment with the specifications according to the invention. It becomes easier to

Drive energy required for driving the two-component compression heat pump and dry air circulation assembly If the ghee is produced by a combustion engine, the conduit flowing from the deaerator to the reabsorber A heat exchanger is installed on the high pressure side of the heat pump, parallel to the temperature converter installed in the heat pump. Preferably, engine waste heat of the combustion engine is transferred to the dilute solution in the heat exchanger. .

The condensate generated from the steam supplied to the drying cylinder of the paper dryer is transferred to the steam generator , i.e. as water supply via the condensate conduit returning to the reabsorber of the two-component compression heat pump. Preferably, it is returned.

The invention is explained in more detail in the following description in conjunction with the drawings.

FIG. 1 is a schematic connection diagram of an embodiment of a device configured according to the specifications of the present invention. Ru.

Figure 2 shows how the change of state of the drying air of the known device works with a closed drying air circulation. of humid air compared to the corresponding state changes of the device according to FIG. FIG. 2 is a diagram schematically showing a two-line sled diagram.

In the schematic connection diagram shown in Figure 1, the paper dryer (not shown in detail) Provided for the generation of steam for heating the drying cylinder - diagram 10 is marked throughout the - two-component compression pump shown in the upper right area of On the other hand, the closed dry air circulation marked 12 is shown in the lower left area of the connection diagram. .

In the drying air circulation 12, a paper dryer 14, diagrammatically shown as a heat exchanger, is connected. It is connected via pipe I6 to an air/water heat exchanger 18, in which case it is heated with steam. expelled in the form of steam from the paper web to be dried by a heated drying cylinder The blower 20 converts the air moistened by the water in the paper dryer 14 into air/water. It is sent to the heat exchanger 18. At the air/water heat exchanger 18, the water is supplied from the paper dryer. Heat is extracted from the moist, dry air, which condenses a corresponding amount of water vapor. and is discharged in liquid form via condensate conduit 22. This condensed water is used to make paper. Preferably, it is reused in the process. The cooled air is passed through a blower 26. Via the connected conduit 24, it is sent to a dry air preheater 28, where it is heated. relative humidity. From the dry air preheater 28 to the paper dryer 14 The drying air circulation is closed via the conduit 30 that is in place.

In the drawing, only the main components are shown. In the two-component compression heat pump lO, from moist dry air to air/water using an actuating agent e.g. a mixture of ammonia and water. - The thermal energy taken in the heat exchanger 18 causes a low pressure level in the deaerator 32. The bell drives the actuating agent components, e.g. ammonia, out of the concentrated actuating agent solution in gaseous form. ing. The heat transfer from the air/water heat exchanger 18 to the deaerator 32 is then In some cases, this is done via a water circulation 34 connected between The heat exchanger 18 is assembled with the deaerator 32 into one common component unit. It is clear that it is also possible that there is a be.

The dilution produced by the expulsion of gaseous components, namely ammonia, in the deaerator 32 The dilute solution is brought to increased pressure via a conduit 36 with a solution pump 38 connected therebetween. Then, it is sent to a reabsorber 40 provided on the high pressure side. On the other hand, at the same time, deaerator 3 The component of the working agent, i.e. ammonia, which was expelled in gas form in step 2, is removed from the deaerator. 32 in a conduit 42 connecting the re-aspirator 40 with a compressor 44 connected therebetween. is guided to the reabsorber 40 under increased pressure, where the reabsorbed heat is disposed of. Reabsorbed into solution once more. At this time, the solution that has become concentrated again is then passed through conduit 46. via a conduit 46 to the deaerator 32, by means of throttling means 48 connected in conduit 46. The pressure of the concentrated solution is reduced. In this way, the water is circulated again in the deaerator 32. 4 to receive the heat supplied from the air/water heat exchanger 18 to convert the ammonia into It can be expelled from concentrated solutions in gaseous form. At this time, the solution circulation conduit 36 and and 46 include a temperature converter 50 - commonly used in two-component compression heat pumps. is preferably connected.

preferable.

The reabsorbed heat is transferred to the feed water supplied via the conduit 52 in the reabsorber 40, and The water is here evaporated and then heated to a pressure of about 3 bar or higher than the low pressure process steam. The process steam conduit 54 is provided at a low pressure. Conduit 54 leads to paper dryer I4 , that is, it serves to heat the drying cylinder, but at this time the steam flowing into the cylinder The temperature ranges from -140° to 150°C, corresponding to the temperature of process steam in a conventional paper machine. Let's become. The steam condensed in the paper dryer is then pumped through a conduit 52 by a pump 56. The water is then returned to the reabsorber 40 as feed water.

The space through which the moist dry air of the air/water heat exchanger 18 passes is further connected via a branch conduit 58. connected to the process steam conduit, where the process steam is air/water-heat Flooding into the exchanger is caused by leakage into the branch conduit, which is normally closed. This is prevented by the deflection valve 60. The paper machine is stopped briefly due to a tear in the paper web. i.e. the supply to the paper dryer 14 has to be cut off. is a controller in which overflow valve 60 probes for an increase in pressure in process steam conduit 52. is opened and the process steam generated in the reabsorber is air/water-heat is led to exchanger 18. This further transfers thermal energy to the degassing of the heat pump IO. 32 for degassing of the working agent, thus providing an additional vapor source. The heat pump can be kept running at all times without the need for

Furthermore, the process steam is then simultaneously subjected to air/water heat exchange on the air side during normal operation. It may also be useful to remove dirt that settles on the heat exchange surfaces of the paper machine 18. At start-up, the process steam conduit 54 is simply opened to the paper dryer supply and Therefore, by closing the overflow valve 60, process steam is directly supplied again to the paper drying process. It can be used to heat the drying cylinder of the vessel 14.

Required by the dry air preheater 28 to rewarm the air cooled by the heat exchanger 18 Thermal energy that is assumed to be A conduit 46 conducting the concentrated solution from the reabsorber 40 to the deaerator 32 is connected to the reabsorber 10 and to the degasser 32. temperature converter 50 and is coupled to dry air preheater 28 via conduit 62. It will be done. The concentrated solution is directed through a cut conduit 62 to a dry air preheater for heating. The part to be cooled by the release of energy is routed through return conduit 64 into conduit 46. , and in the region between the temperature transducer 50 and the throttling means 48 . As shown in the connection diagram In this particular embodiment, the cut conduit 62 and the return conduit 64 have a A further heat cycle, e.g. The heat for operation can be extracted.

This thermal circulation 70 is a circulation between which a consumer 72 and a circulation pump 74 are connected. is shown only diagrammatically.

Necessary for the operation of the heat pump 10 assembly and the assembly provided for dry air circulation The driving energy is supplied by an electric motor 76 as shown, which may be driven by a gas engine 78. The engine waste heat of the gas engine 78 is used as a paper dryer. In parallel to the temperature transducer 50, a high pressure On the side, the dilute solution is pumped from the deaerator 32 to the reabsorber 40 via conduit 36. A heat exchanger 80 is provided through which a portion of the liquid passes.

In Figure 2, two curved lines of humid air, in which the temperature is dependent on the water component, are shown. In the figure, the conventional drying process a is carried out in the apparatus according to the invention as described above. Contrasted diagrammatically to process b, where line S is below which e.g. The water component, which is at a higher temperature than air, releases heat of condensation and reaches the saturation line where it condenses into liquid water. shall be expressed.

In a conventional paper drying process, air (at point l) is exposed to the surrounding air at an outside temperature of e. taken out of the atmosphere and warmed (up to point 2) by supplying heat, with relative air humidity It is done in such a way that the degree is lowered. When more heat is supplied (up to point 3) The air accepts the moisture from the paper dryer. By cooling the moist waste air of the paper dryer, dry air is The relative air humidity increases to 100% (up to point 4), where the temperature further decreases. As the temperature rises (up to point 5), some of the water vapor condenses and forms a liquid. Reached with 5 points In this state, it is still clearly warmer than the surrounding temperature and the relative humidity is 100. % of dry air is released into the surrounding atmosphere as waste air. Waste air generated at that time The rapid cooling of air to ambient temperature almost inevitably results in the formation of fog or fog by condensing water vapor. leading to the formation of haze. In exceptional cases, i.e. when the surrounding atmosphere is relatively dry and warm Such fog formation could only be avoided if the However, in either case An increase in the water vapor content of the surrounding atmosphere will also occur in the local microclimate. , in some cases hazardous substances contained in the humid waste air are released into the surrounding atmosphere. do.

In contrast, in the drying process carried out with the device according to the invention, the drying air is It is not removed from the atmosphere and no humid waste air is released into the outside atmosphere. Rather point 1 ’, well above the ambient temperature exiting the air/water heat exchanger 18. A certain amount of dry air is heated in a dry air preheater 28 to a temperature corresponding to point 2''; Relative humidity decreases correspondingly. In the paper dryer 14, this warmed dry air is The water vapor expelled from the paper web by the steam-heated drying cylinder (point 3) Up to N) Accept.

This dry air, which is not yet fully saturated, then the air/water Heat is removed by the heat exchanger 18 and transported to the deaerator 32. In other words, the temperature is first at point 3" to point 4N, ie the dry air becomes saturated. Next, the initial temperature at point l is Upon further cooling to the corresponding temperature, water vapor condensation occurs and the condensate produced is It is returned to the paper making process via condensate conduit 22. Here, the total heat of condensation is air/water - received in the heat exchanger 18, i.e. the operation of the two-component compression heat pump in the deaerator 32; It can be used to expel the gaseous form of the actuating agent component, namely ammonia, from the agent. Ru.

It becomes clear from the above comparison of Gi drying processes a and b that and potentially other harmful substances into the surrounding atmosphere. , conducting dry air in a closed circulation is important for reasons of reducing environmental impact. However, beyond this, there is also a decisive saving in some of the energy that must be input. This is because the paper wafer dried in the paper dryer 14 All of the heat of condensation of the water vapor expelled from the heat pump IO is transferred to the low pressure This is because it can be used for side degassing. Origin of paper drying equipment A significant advantage of the configuration according to the present invention is that it does not operate according to the conventional, i.e. drying process a. later reequipment of the equipment to the operating specifications illustrated in process b. However, in this case, the initial temperature of the drying air should be selected to be higher. By choosing the The relative humidity at the end, i.e. point 3 or 3', can also be left unchanged. (*l = Vl・ and ψ3 = ψko), so the flow path used for conveying dry air The cross section of the fan and the performance of the blower remain the same, that is, these components are reused without changing. be able to.

international search report international search report PCT/EP　89101305

Claims (1)

[Claims] 1. Two-component compression heat in which thermal energy extracted from dry air is added to the low pressure side Drying the paper dryer of the paper machine using a pump, from the water supply on the high pressure side by the heat pump Process steam for heating the cylinder is generated and then further dry air The air used for drying is preheated in the preheater and flows out of the paper dryer of the paper machine. In a method for re-capturing the waste heat contained in moist dry air, the dry air In a paper machine, a drying air preheater, a paper dryer connected after the drying air preheater, and connected behind the paper dryer and before the dry air preheater to Binary pressure with a return conduit for returning water vapor condensate to the paper making process Almost closed, formed from a heat exchanger that is heat transfer coupled with a deaerator of a heat condensing pump The humid air flowing out of the paper dryer is connected to the A heat exchanger cools the air to a temperature significantly higher than that of the surrounding air. A method characterized by: 2. a dry air preheater (28), a paper dryer (28) connected behind the dry air preheater (28); 14), and after the paper dryer (14) and before the paper dryer preheater (28) A return is connected to the water vapor condensate formed in the liquid and returned to the paper manufacturing process. an almost closed dry air circulation formed by a heat exchanger (18) with (12), the heat exchanger (18) and the deaerator (32) of the two-component compression heat pump (10). ). Place. 3. A heat exchanger (18) that cools the moist dry air flowing out from the paper dryer (14) of the two-component compression heat pump (10) through a closed circulation (34) of fluid, in particular water. Device according to claim 2, characterized in that it is combined with a deaerator (32). . 4. For driving the assembly of the two-component compression heat pump (10) and the dry air circulation (12) The driving energy required for this purpose is generated by the combustion engine (78). In the device according to scope 2 or 3, On the one hand, the engine waste heat of the combustion engine (78) is added, and on the other hand, the second from the deaerator (32) is added. The component is sent to the reabsorber (40) of the compression heat pump (10) and is brought to the pressure of the reabsorber. An apparatus characterized by a heat exchanger (80) through which at least a portion of the dilute solution passes. 5. The condensate generated from the steam supplied to the drying cylinder of the paper dryer (14) is A condensate conduit ( 52) The device according to any one of claims 2 to 4, characterized in that: