GB2155164A

GB2155164A - Heat conservation on the drier section of paper making machines

Info

Publication number: GB2155164A
Application number: GB08503307A
Authority: GB
Inventors: Friedrich Schweinzer; Reinhard Pinter; Johannes Kappel
Original assignee: Andritz AG
Current assignee: Andritz AG
Priority date: 1984-02-10
Filing date: 1985-02-08
Publication date: 1985-09-18
Also published as: IT8519445A0; ATA42784A; FR2559514A1; GB2155164B; SE8500594D0; FI850393L; IT1183227B; DE3501584A1; AT382176B; SE8500594L; SE465041B; FI850393A0; FI72548C; FR2559514B1; GB8503307D0; FI72548B

Abstract

The heat energy of exhaust fluids from the drier section of paper making machines consisting of a drying drum 2 and high temperature hood(s) 1, respectively heated by live steam 3 and blowing air 7, is conserved by passing the drum effluent to separator 19 connected to a blow-through steam line 20 and via a compressor 21 to the feed line 5; the condensate from the steam separator 19 is passed to the blow-through steam line via the heat exchanger 14; and exhaust air 10 from the high temperature hood is passed to the heat exchanger 14 and to a further heat exchanger 15 connected to the latter heat exchanger for supplying heated fresh air to the high temperature hood. <IMAGE>

Description

SPECIFICATION A device on the drier section of paper making machines The invention relates to a device on the drier section of paper making machines, consisting of a drying drum and high temperature hood(s) (dome(s)) guided over it, the drying drum being supplied with live steam generated in the boiler room and the high temperature hood(s) being supplied with blowing air.

It is the purpose of the device to improve the degree of utilisation of the energy of a drying plant by exploiting the energy content of the exhaust air.

It is known and conventional at present for high temperature hoods to discharge the exhaust air into the atmosphere following fresh air warming at a temperature of about 150 to 250"C. The condensate accumulating in the drying drum is normally relaxed to environmental pressure in two stages and fed to the boiler room. The steam for heating the drum is generated in the boiler room. A drawback in this is the fact that the relaxation of the condensate is accompanied by a large amount of flash steam which has to be precipitated in a condenser by means of cooling water. The energy content of this steam gets lost in the operation.

The relaxed condensate is compressed from environmental pressure to steam pressure or boiler pressure by means af a feed-water pump and subsequently evaporated in the boiler. This requires a large amount of energy. The energy contact of the steam is subsequently used for drying in the drying plant. The steam in the exhaust air still contains a comparativey large amount of energy the greater part of which is at present lost by discharge into the atmosphere.

It was further proposed according to AT-PS 374 214 to utilise the residual heat in paper machine steam hoods by means of a heat pump. This is achieved by means of a compressor-turbine unit in which the compressor is connected to the exhaust airline and the high pressure part is connected to the turbine via heat exchanger, with the difference in power output supplied by external drive. This apparatus does not apply to the object of the application because it relates to a steam hood with an exhaust air temperature of 80or.

Finally, DE-OS 30 03 718 describes a process and a device for drying paper and chemical pulp by direct application of superheated steam. The heat exchanger installed is a superheater for steam and the steam stream flowing through the compressor is subsequently discharged in the form of a condensate.

It is the object of the invention to exploit the energy content of the exhaust air in the drier section of paper making machines having drying drums supplied with live steam and high temperature hoods supplied with blowing air so as to reduce the consumption of primary energy for drying and at the same time provide a device which can be installed in already existing plants.This object is achieved according to the invention by providing a steam separator for separating the exhaust steam downstream from the drying drum in a manner known per se, the steam separator being connected to a blow-through (escape) steam line and via a compressor to the feed line to the drying drum, on the one hand, and the condensate line of the steam separator being connected to the blowthrough steam line via the heat exchanger, on the other hand, and by providing an exhaust air line leading from the high temperature hood to the heat exchanger and to a further heat exchanger and that a line for supplying heated fresh air to the high temperature hood is connected to the latter heat exchanger. This means that a heat exchanger in which condensate under pressure is evaporated is interposed in the exhaust air stream for energy recovery.The condensate accumulating in the drying drum is fed to the exhaust air heat exchanger at the appropriate pressure level and is there evaporated by the energy content of the exhaust air. The steam is subsequently compressed to drum steam pressure by means of a compressor. A further variant consists in that the condensate is brought to drum pressure by means of a pump prior to evaporation in the exhaust air heat exchanger. The invention is thus based on the idea of utilising the caloric content of the exhaust air for the generation of steam; the heat exchanger is a steam generator heated by means of hot exhaust air; the steam stream flowing through the compressor is brought to the required pressure level here and is recycled to the machine together with live steam, which permits a saving in large amounts of live steam.

The invention is explained in detail by means of an embodiment under reference to the accompanying drawing.

Figure 1 shows a device for utilising the energy of the drier section; Figure 2 shows a variant of Figure 1; Figure 3 shows a device without mechanical compression.

As shown in Figure 1, the drier section of a paper making machine is formed of a high temperature hood 1 disposed around a drying drum or rotary drier 2. The paper web to be dried is guided around the drying drum 2 and heated by the steam of the drying drums 2, with the humidity contained in the material web being absorbed and discharged by the heated blowing air introduced in the high temperature hood. In order to exploit the otherwise lost exhaust heat, the device according to the invention is disposed downstream. The live steam generated in the boiler room is conveyed via the live steam line 3 to a reducing valve 4 and via feed line 5 into the drying drum 2 for heating purposes. From the drying drum 2, the condensate line 6 leads to a first steam separator 19.From there, the residual steam is conveyed via blowthrough steam line 20 to the compressor 21 driven by the motor 22 for additional drying. The condensate of the steam separator 19 is then conveyed via a branch line 30 and a reduction 31 to a further steam separator 25. The residual steam is conveyed to a condenser 29 via a flash steam line 26, cooled by means of cooling water 33 and used as a condensate. The water or condensate is further conveyed from the steam separator 25 via a boiler feed line 27 and a pump 28 to the boiler room.

From the branch line 30, the condensate is con veyed via a condensate line 24 to the heat exchan ger 14 which is heated by air discharged from the high temperature hood 1 via an exhaust air line 10.

Finally, the now evaporated condensate is con veyed from the heat exchanger 14 to the T-piece 32 and thus to the feed line 5 through a pressure line 23.

The exhaust air from the high temperature hood 1 is conveyed to a further fresh air heat exchanger 15 with an exhaust air line 10 after releasing its en ergy in the exhaust air heat exchanger 14 and is then discharged into the open air through an ex haust air blower 18. The air sucked in by means of a blower 17 and a fresh air line 16 is heated in the heat exchanger 15 and forced through air line 13 via a further blower 12 into the combustion cham ber 8 and heated to blowing air temperature. An air supply line 9 empties into the combustion chamber 8. The air thus heated is conveyed as blowing air via blowing air line 7 into the high temperature hood 1. A connecting air line 11 is in terposed between the exhaust air line 10 and the air line 13 and raises the temperature for the blow ing air.

Figure 2 shows a further variant of the device us ing the same reference numbers. The difference re sides in that the compressor 21 is arranged upstream of the T-piece 32 in the blow-through steam line 20. Although a pump 34 in the conden sate line 24 is required, the pressure of the con densate is already increased to drum pressure prior to evaporation in the exhaust air heat ex changer 14 and the energy consumption in the compressor 21 is thus reduced.

Figure 3 shows a variant without mechanical compression with emphasis of the differences in comparison to Figure 1. From the steam separator 19, the residual steam is conveyed via the steam line 20 directly into the steam jet compressor or thermocompressor 35 and into the feed line 5.

The provision of this device makes it possible to reduce the amount of accumulating flash steam which has to be precipitated. As a consequence, the amount of cooling water required is also strongly reduced. The energy requirement for achieving drum pressure is strongly reduced by the evaporation under pressure. By the generation of steam within the system, the line losses in con densate and live steam are further reduced as a re sult of the smaller volume.

The main advantage of the invention resides in the strongly reduced energy consumption for the drying operation which up to now required the generation of primary energy. It should also be considered that environmental pollution is reduced by the better utilised exhaust air.

Claims

1. A device on the drier section of paper making machines consisting of a drying drum and high temperature hood(s) guided over it, the drying drum being supplied with live steam generated in the boiler room and the high temperature hood(s) being supplied with blowing air, characterised in that a steam separator for separating the exhaust steam is provided downstream from the drying drum in a manner known per se, the steam separator being connected to a blow-through steam line and via a compressor to the feed line to the drying drum, on the one hand, and the condensate line of the steam separator being connected to the blowthrough steam line via the heat exchanger, on the other hand, and that an exhaust air line is leading from the high temperature hood to the heat exchanger and to a further heat exchanger and a line for supplying heated fresh air to the high temperature hood is connected to the latter heat exchanger.

2. The device according to claim 1, wherein the compressor is arranged upstream or downstream from the inlet site of the evaporated condensate.

3. The device according to claim 1 and 2, wherein a pump is interposed in the condensate line if the compressor is arranged upstream from a T-piece.

4. The device according to any one of the claims 1 to 3, wherein the blow-through steam line leads to a steam jet compressor.

5. The device according to any one of the claims 1 to 4, wherein a connecting air line is arranged between the exhaust air line and an air line from the heat exchanger.

6. The device substantially as hereinbefore described with reference to the accompanying drawings.