FI124076B - METHOD AND SYSTEM FOR IMPROVING THE ENERGY EFFICIENCY OF A PAPER MACHINE OR SIMILAR DRYING PART - Google Patents

Description

METHOD AND SYSTEM FOR PAPER MACHINE OR SIMILAR

DRYING COMPONENT FOR IMPROVING ENERGY EFFICIENCY

The invention relates to a method and system for improving the energy efficiency of a papermaking machine or a corresponding drying section according to the preambles of the independent claims below.

In the drying section of the papermaking machine or the like, the moving web is dried non-contact by air blowing or by contacting the web with heated cylinder surfaces. Fluid dryers are commonly used in the drying section of a papermaking machine for drying the web. In the fluid dryer, the heated air is directed towards the web to be dried on one side of the web, or alternatively simultaneously on both sides of the web, which ensures efficient heat transfer. When the hot air comes into contact with the moist web 15, the water in the web evaporates into the air and the web dries. At the same time, the air temperature drops and the humidity percentage increases. Thereafter, the air is removed from the fluidized bed dryer, and part of it is recirculated to the fluidized bed heating unit, and some of the air is removed from the fluidized bed dryer. Exhaust air from the fluidized bed dryer can be recirculated through exhaust devices which possibly recover the thermal energy contained therein.

After the first fluidized bed, there are generally 1 to 3 dryer units provided in the drying section of the coating machine, in which the web is dried by air blows normally below the temperature of the blowing air used to dry the web, e.g. 150-250 ° C.

o i) The drying air * used in the first fluidized bed dryer after the coating station typically has a temperature of about 200 to 450 ° C. The temperature of the extract air in the fluidized bed dryer is often between 100 and 30 300 ° C, even after any heat recovery. At present, the fluid from the fluid dryer is generally supplied directly to the outside air or is connected to other airflows in the paper mill and led to a general heat recovery unit. It is strongly assumed that the fluid in the fluidized bed exhaust air contains too much air without the exhaust gases generated during heating and the moisture transferred from the web 2 in order to be used in other processes, or even permissible.

Various drying solutions are disclosed in EP 0770731, US 4,137,644, WO 5 2007/085617 and WO 2009/147284

The object of the present invention is to reduce or even eliminate the above-mentioned problems in the prior art.

It is an object of the invention to improve the energy efficiency of the drying section of a papermaking machine and to reduce the amount of energy required for drying.

It is another object of the invention to provide a method and system that can enable the drying temperature to be raised in subsequent dryer units following the fluidized bed 15.

To accomplish the above purposes, the invention is characterized by what is set forth in the characterizing parts of the appended independent claims.

Some preferred embodiments of the invention are set forth in the subclaims.

The application examples and advantages mentioned in this text apply, mutatis mutandis, to the method and system according to the invention, although not always explicitly mentioned.

A typical method of the invention is set forth in claim 1.

00 in a method for improving the energy efficiency * of a papermaking machine or the like drying section, c \ j - drying the paper web or the like in the first fluidized bed by blowing heated air towards the web, oc \ j - removing air from the fluidized bed from the drying fluidized bed dryer to at least one subsequent dryer unit in which the web is dried by blowing air toward it; and - supplying the fluidized bed exhaust air to at least one of the next 5 dryer units where it is used as drying air.

A typical system according to the invention for improving the energy efficiency of a papermaking machine or equivalent drying member is set forth in claim 9, comprising 10 - a first fluidized bed dryer for drying a paper web or the like, - one or more subsequent dryer units arranged after the first fluidized dryer wherein the system comprises one in which the exhaust air of the first fluidized bed is arranged to be supplied to the air circulation of at least one subsequent dryer unit for use as drying air.

It has now surprisingly been found that the exhaust air of the first fluidized bed dryer can be used as drying air for one or more subsequent dryer units without the impurities and / or moisture of the 20 exhaust air being detrimental to the drying process of the next dryer unit. The use of fluidized-bed exhaust air at least as part of the drying air of the next dryer unit enables significant energy savings, which greatly improves the overall energy economy of the process.

The use of fluidized-bed extract air may also allow the use of a higher drying air temperature at the dryer unit following the fluidized-bed dryer.

With steam heated dryer units, the steam pressure has limited the 00 drying air temperature to a maximum of 175-180 ° C. It is now possible to * supply to the next dryer unit the exhaust gas of the first gas-heated fluidized bed, the temperature of which is well above this temperature, whereby the drying temperature can be increased accordingly if desired. Alternatively, the drying temperature of the next dryer unit can be kept at a conventional level, thereby reducing the amount of energy used by the dryer unit. The invention thus offers considerable advantages at a reasonable investment cost.

4

Thus, in the solution according to the invention, there is no need to remove moisture and / or impurities from the used extract air of the fluidized bed dryer before it is introduced into the air circulation of the next dryer unit as drying air. The exhaust air 5 can thus be directed directly into the air circulation of the next dryer without passing through the cleaning and / or drying devices.

As used herein, a fluidized bed dryer refers to a drying apparatus located in the drying section of a paper machine or the like. The fluidized bed comprises one drying box 10 or, alternatively, two opposite drying boxes or the like. The drying air is heated by burning the gas to a high temperature of 200-450 ° C and is led to the blowing nozzles of the fluidized bed drying box. Heated drying air from the blowing nozzles is blown at high speed on both sides of the web to be dried towards its surface. The drying in the fluidized-bed dryer is thus non-contact.

In this application, the following dryer unit refers to a non-contact dryer in which the paper web is dried by air blowing. The drying air temperature of the next dryer unit is lower than the drying air temperature of the fluidized bed 20. Typically, the drying air temperature of the next dryer unit is 130 to 200 ° C, more typically 150 to 180 ° C.

In one embodiment of the invention, the drying air t? consists essentially of the extract air of the fluidized bed, and optionally of circulating air of 25 dryer units, and the drying air of the dryer unit is conducted without a separate heating step towards the web to be dried. Thus, the present invention allows the dryer unit or units following the fluidized bed to have no heating device of its own, but to obtain the drying energy required for the dryer unit from the exhaust air of the fluidized bed. Next

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Thus,> 30 dryer units are substantially free of heating device. However, the recirculating air supplied to the next o cv dehumidifier unit may be blended with the recirculating air of the next dehumidifier unit or with pure replacement air if the extract air temperature from the fluid drier is too high and / or the amount of extract air is too low. In this case, the drying air of the next dryer unit consists of the raw exhaust air of the fluidized bed and the unheated replacement air or the circulation air of the next dryer unit.

In another embodiment of the invention, the next dryer unit after the fluidized bed comprises its own heating device for heating the circulating air or replacement air of the dryer unit to a desired temperature. The heater may be electrically or oil-heated, most often steam is used to heat the drying air. In the invention, the subsequent dryer unit 10 following the fluidized bed dryer is steam heated. In one embodiment, the next dryer unit after the fluidized bed is gas heated, i.e., its heater comprises a gas burner.

The fluid dehumidifier exhaust air may be led to the next drier unit 15 after the drier unit's own heater, whereby the drying air of the next drier unit consists of untreated and unheated fluid dryer dehumidifying air and the next drier unit circulating air and / or replacement air. When the temperature of the fluid air outlet air is sufficiently high, preferably at least as high, preferably higher than the drying air temperature of the next 20 dryer units, the exhaust air can be supplied to the air circulation of the next dryer unit after the heating device. The unit coming from the fluidized bed is thus connected to the air circulation network of the dryer unit after the heating device. In this case, the air heater of the next dehumidifier unit can reduce the amount of air in it,

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, 25 which saves considerable energy, r ^ o σ>

Alternatively, the fluid from the fluid dryer may be supplied to the next dryer unit before the dryer unit own heater, whereby the exhaust air, and possibly the dryer unit recirculated air, is heated in the dryer unit heater before being led as drying air toward the dryer web. The fluid from the fluid dryer is thus connected to the air circulation network of the dryer unit before the heating device. In this case, the extract air temperature of the fluidized bed is preferably higher than the recirculating air temperature of the next dryer unit 6. In this way, the amount of energy required for the heater of the next dryer unit can be reduced, with the initial temperature of the air to be heated in the heater being higher than using only replacement air or circulating air of the next dryer unit.

5

Typically 5 to 20% by volume of drying air of the next dryer unit, more typically 10 to 20% by volume, most typically 10 to 15% by volume, is the exhaust air of the preceding fluidized bed. In one embodiment of the invention, more than 50% by volume of the drying air of the next dryer unit, possibly up to 60% by volume 10 or even 75% by volume, is the exhaust air of the preceding fluidized bed.

In one embodiment of the invention, during the start-up phase of the fluid dryer, the exhaust air is supplied to the bypass system of the next dryer unit, the exhaust air volume of the next dryer unit is reduced and the drying air of the dryer unit 15 is mainly used.

When the gas burner of a gas-fired fluidized bed dryer is started, it is most often pre-rinsed, during which the exhaust air is preferably directed directly to the outlet. The temperature of the fluidized air extractor may also be lower than in a normal stabilized driving situation. In this case, it is advantageous to direct the fluid air of the fluid drier 20 instead of the next dryer unit to an alternative bypass system which may comprise, for example, heat recovery means and / or means for purifying the gas. Thus, during the start-up phase, the exhaust air is led away from the drying process through heat recovery means and / or cleaning means. At the same time, the exhaust air volume of the next or subsequent drier units should preferably be reduced so that their air balance remains constant even during the start-up phase. Thus, preferably, the system comprises a bypass unit for the next dryer unit and adjusting means for controlling the exhaust and recirculated air volumes of the next dryer unit. As soon as possible, when the fluidized bed has reached a steady running condition with the pre-rinse completed and the fluid temperature of the fluidized bed exhaust has exceeded a predetermined limit, oc \ j starts supplying the fluidized bed exhaust air with at least in a similar way.

7

In one embodiment of the invention, the fluid from the fluid dehumidifier is passed through a heat recovery unit before being fed to at least one subsequent drier unit, i.e. the system comprises a heat recovery unit 5 arranged between the fluid drier and the next drier unit. With the extract air temperature of the fluid drier being high enough, some of the heat contained in the exhaust air can be recovered before the exhaust air is supplied to the next dryer unit. This can further improve the energy efficiency of the paper machine or similar drying unit. Even after the heat recovery unit 10, the exhaust air temperature is typically 200-250 ° C, i.e. it is well suited for conducting the drying air of the next dryer unit or part thereof.

In the invention, the system comprises a gas heated fluidized bed dryer for drying a paper web or the like and one or more subsequent steam heated dryer units. The drying air of the fluidized bed dryer is thus heated by gas combustion, and in subsequent dryer units the heat needed to heat the drying air is obtained from the convection air steam. In the fluidized bed dryer, the drying air temperature is higher than in the following dryer units, i.e. the paper web is dried by blowing it with air at a temperature of about 20200 to 450 ° C and in subsequent dryer units the paper web is dried by blowing towards it at about 130-2005 ° C. ° C.

In one embodiment, the system comprises a gas heated fluidized bed dryer for drying a paper web or the like, and one or more subsequent gas heated dryer units. Again, in the fluidized bed 00, the drying air temperature is higher than in the following dryer units, where the * drying temperature is substantially lower than the drying temperature of the fluidized bed.

The temperature difference between the drying temperatures is at least 50 ° C, preferably at least 100 ^ 30 ° C, sometimes at least 150 ° C, typically 100-200 ° C.

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The invention will now be described in more detail with reference to the accompanying schematic drawing in which 8

Figure 1 shows a prior art arrangement, and

Figure 2 illustrates a system 5 according to an embodiment of the present invention.

Figure 1 shows an arrangement according to the prior art. The arrangement comprises a gas-heated fluidized bed 1. The fluidized bed 1 is deaerated via the outlet conduit 2. A portion of the extracted air is fed back to the fluidized bed 1 as recirculated air 10 so that the circulating air passes through the gas heated heater 3 to the air supply 4 of the fluidized bed 1. Fresh replacement air 5 can also be fed to the fluidized dryer 1.

A portion of the fluid from the fluid dehumidifier 1 is led through a heat recovery unit 6 to an outlet 7, from which the fluid from the fluid drier 1 is directly discharged to the outside air or to the factory air circulation system. The heat recovered from the exhaust air supplied through the heat recovery unit 6 can be used to heat the fresh air entering through 8, which is supplied to the fluid heater 1 heater 3 20 for the combustion air of a gas burner.

After the fluidized bed 1, two successive steam-heated dryer units 11, 11 'are provided. The drying, typically coated paper web is led from the gas heated fluidized bed unit 1 to the first steam heated dryer unit 11, and thence to the second second steam heated dryer unit 11 '.

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Dehumidifier units 11, 11 'are deaerated through outlet ducts 12, 12'.

Part of the extracted air is recirculated to the dryer units 11, 11 '^ 30 so that the recirculated air of each dryer unit 11, 11' passes to the air supply 14, 14 'of the steam unit heating units 13, 13'.

9 fresh replacement air can also be supplied to the heating units 13, 13 'of the dryer units 11, 11' via the replacement air connections 15, 15 '. Steam is fed to the heaters through steam feed lines 18, 18 '

Figure 2 shows a system according to an embodiment 5 of the present invention. The reference numerals of Figure 2 correspond to the reference numeral of Figure 1.

In the system of Figure 2, the air removed from the gas heated fluidized bed dryer is fed to the outlet 9 after the heat recovery unit 6, by means of which the exhaust air from the gas heated fluidized bed 1 is fed into the air circulation of the next steam heated dryer units 11, 11 '. The exhaust air of the fluid drier 1 can be supplied to the air circulation network of the dryer units 11, 11 'before the heater 13, 13' of each dryer unit 11, 11 'or after the heater 13, 13' via the connections 10, 10 ', 10 ", 10". Depending on the temperature of the extract air of the fluid drier 1, the exhaust air may be supplied through the connections 10, 15 10 "directly to the air supply connection 14, 14 'of the dryer units 11, 11' or before the heating units 13, 13 'of the dryer units 11, 11'. In the latter case, the exhaust air of the fluidized bed 1 is heated to the drying temperature used by the dryer unit 11, 11 'in the heating device 13, 13'. The exhaust air of the dryer units 11, 11 'is discharged directly through the outlet connection 17 directly into the open air or into the factory air circulation system.

When starting the fluid dryer 1, the connection 9 between the fluid dryer 1 and the subsequent dryer units '11, 11' can be closed using a control member 19, whereby the exhaust air of the fluid dryer ducts through the outlet 7 directly to the outside air ^ or to the factory air circulation system. The system according to the invention may also include other control or shut-off means 16 for controlling and controlling the air circulation * of the system.

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The invention is not intended to be limited to the exemplary embodiments described above, but is to be broadly construed within the scope defined by the following claims.

Claims (14)

10 A method for improving the energy efficiency of a papermaking machine or the like drying section, comprising: 5. drying a paper web or the like in a gas heated fluidized bed dryer (1) by blowing heated drying air towards the web; gas-fired fluid dryer (1) 10 to at least one subsequent dryer unit (11, 11 '), wherein the web is dried by blowing air toward it, characterized in that the exhaust air of the gas-fired fluid dryer (1) is led to at least one or more subsequent steam heated dryer units (11, 11') for use as drying air, wherein the drying air temperature of the next steam heated dryer unit (11, 11 ') is lower than the drying air temperature of the gas heated fluidized bed dryer (1). Method according to Claim 1, characterized in that the drying air of the next 20 dryer units (11, 11 ') consists essentially of the exhaust air and possibly the recirculating air of the dryer unit (11, 11') and that the drying air of the dryer unit (11, 11 ') without a separate heating step towards the web to be dried. A method according to claim 1, characterized in that the exhaust air of the fluid drier (1) is supplied to the next dryer unit (11, 11 ') after the heater unit (13, 13') of the dryer unit itself, whereupon the next dryer unit (11, 11 ') * drying air consists of the exhaust air of the fluidized bed dryer (1) and the circulating air of the dryer unit (11, 11') heated in the heating device c (j) (13,13 '). Method according to claim 2 or 3, characterized in that the temperature of the exhaust air of the fluidized bed dryer (1) is at least as high, preferably higher, than the drying air temperature of the next dryer unit (11, 11 '). 11 Method according to Claim 1, characterized in that the exhaust air of the fluid drier (1) is supplied to the next dryer unit (11, 11 ') before the heater unit's own heating device (13, 13'), whereby the exhaust air, and possibly the recirculating air of the dryer unit (11, 11 ') , is heated in the heating unit (13, 13 ') of the dryer unit (11, 11') before being guided as drying air towards the web to be dried. 6. A method according to claim 5, characterized in that the exhaust air temperature 10 is higher than the circulation air temperature of the next dryer unit (11, 11 '). Method according to one of the preceding claims, characterized in that, during the start-up phase of the fluid drier (1), exhaust air is supplied to a bypass system of the next drier unit (11, 11 '), the exhaust air volume of the next drier unit (11, 15') is reduced and the drying air (11, 11 ') is mainly used for circulating air. Method according to one of the preceding claims, characterized in that the exhaust air of the fluidized bed dryer (1) is passed through a heat recovery unit (6) before being fed to at least one subsequent dryer unit (11, 11 '). A system for improving the energy efficiency of a papermaking machine or a corresponding drying section, comprising: a gas fired fluid dryer (1) for drying a paper web or the like, 25. one or more subsequent dryer units (11, 11 ') arranged after the fluidized dryer (1); and arranged to blow-dry the web by air blowing, characterized in that the system comprises one (9) whereby the exhaust air of the gas-fired fluidized bed dryer (1) is arranged to conduct at least one or ^ 30 subsequent steam-heated dryer units (11, 11 ') air circulation for use as drying air, and that the drying air temperature of the next steam heated dryer unit (11, 11 ') is arranged to be lower than the drying air temperature of the gas heated fluidized bed dryer (1). 12 System according to Claim 9, characterized in that the following dryer unit (11, 11 ') is free of the heating device. System according to claim 9, characterized in that the following dryer unit (11, 11 ') comprises its own heating device (13, 13'), and the unit coming from the fluidized bed dryer (1) is connected to the air circulation network of the dryer unit (11, 11 '). 13 '). System according to Claim 9, characterized in that the next dryer unit (11, 11 ') comprises its own heating device (13, 13'), and the unit coming from the fluid dryer (1) is connected to the air circulation network of the dryer unit (11, 11 '). , 13 '). A system according to any one of the preceding claims, characterized in that it comprises a heat recovery unit (6) arranged between the fluidized bed dryer (1) and the next dryer unit (11, 11 '). A system according to any one of the preceding claims, characterized in that the system 20 comprises a bypass system for the next dryer unit (11, 11 ') and adjusting means for controlling the exhaust and recirculated air volumes of the next dryer unit (11, 11'). C \ J δ (M tn o sj- X Χ CL O) {M CD m δ {M 13