THERMAL-VACUUM FELT CONDITIONING SYSTEM

SYSTEME DE CONDITIONNEMENT VACUOTHERMIQUE DE FEUTRE

English Abstract

The invention comprises a method and an apparatus for felt conditioning in the
process of
paper manufacture. The design of the device is featured by a vacuum head
equipped with two
lenghtways suction slots installed under the felt, and from the side opposite
to felt equipped with
blow head fed by air-steam mixture. In the vacuum head vacuum is maintained by
steam jet ejector.
Slot of blow box is situated axially towards the first slot of vacuum head on
the opposite side of the
felt.
The concept of the invention utilises both kinetic energy and enthalpy of
steam for felt
dewatering and conditioning being in a constant motion. Kinetic energy of
steam allows to generate
vacuum necessary for sucking away water contained in the felt. Enthalpy of
decompressed steam is
utilised for preheating the felt and its effective conditioning.
The characteristic feature of the solution is vacuum dewatering device
connected with a separator,
steam jet ejector powered by steam through control valve and lengthways blow
nozzle mounted over
the felt, fed by hot air- steam mixture from steam jet ejector.

Claims

-3-
CLAIMS
1. The device designed for conditioning felt (Fig.1) which is in a constant
motion, characterized
by vacuum head (3) equipped with two lengthways suction slots (4 and 5) fitted
under the felt (1)
and from the opposite side equipped with blow box (6) featured by a slot (10)
fed by pre-heated gas
(advantageously by mixture of steam and air) with temperature above 100
° C (advantageously
110-130 ° C) and absolute pressure 100 to 120 kPa [ advantageously 105
kPa]. In the vacuum head
(3) vacuum is maintained at the level 25-75 kPa [advantageously 40 kPa]
generated by vacuum
device [advantageously by steam jet ejector]. Slot (10) of head (6) is
situated axially towards the
first slot (4) of vacuum head (3) within 5- 15 mm of felt (1).
2. The method of dewatering and conditioning felt (Fig.2) being in a constant
motion characterised
by vacuum dewatering device (11) mounted under the felt (10) connected with
separator (14) and
vacuum steam jet ejector (13) fed by steam with an absolute pressure 200 to
3000 kPa through
control valve (15) and lengthways blowing nozzle (12) fitted over the felt,
powered by hot mixture
of steam and air from the steam jet ejector (13). Water from the separator
(14) is returned to the
process cycle(16).

Description

CA 02510896 2005-05-30
-1_
DESCRIPTION
The invention comprises apparatus and method for conditioning felt in the
process of paper
manufacture. In the paper manufacture process there is the need of dewatering
and final drying end
product_ The grade to which paper is dewatered is of great importance for
achieving beneficial
energy consumption indexes in the further production line, particularly in the
drying process.
The invention concerns an apparatus for improving felt conditioning [Fig. lJ.
The essence of the invention is the device, equipped with two-slot vacuum head
(3) that sucks
away water & sir and a blow box that is fed by hot air- steam mixture. The
vacuum head (3) is
connected with steam jet ejector which in the head (3) generates absolute
underpressure 25-75
kPa. Axially towards the first slot (4), on the opposite side of the felt is
installed blow box (6) fed
by decompressed air- steam mixture ('~ of the absolute pressure 100- 120 kPa
generated by the
steam jet ejector. A directed stream of hot air- steam discharged from the
slot (10) of the blow box
(6) is sucked in by felt (1) into slot (4) of de-watering head (3). Air from
the surrounding is sucked
in through second slot (5) of dewatering head (3). The Double Slot System
featuring the
dewatering head and deep underpressure contained inside contributes to highly
effective felt de-
watering. Simultaneous pre-heating felt and its water content together with
reducing hydraulic
pressure in the structure of felt causes effective partial suction of moisture
to slot one (4). Sudden
felt cooling (1) facilitates water evaporation to slot two (5). Felt
conditioned in this way is more air
permeable and improves paper dewatering.
The invention also concerns the method of felt conditioning [Fig. 2).
The essence of felt conditioning with the described system is the double
utilization of steam energy
due to employment of steam jet ejector generating vacuum (13), blow nozzle
(12) for blowing hot
air steam mixture after steam jet ejector, suction box (11) for sucking away
water from preheated
felt and a separator (14). Steam jet ejector (13) is fed by steam with an
absolute pressure 200-3000
kPa that is regulated by valve (15), suction pipe of the steam jet ejector is
connected with suction
box ( 11 ) through separator ( 14) and the outlet pipe with a blow nozzle (
12) is mounted axially over
the suction box. Water from the separator ( 14) is returned to the process
cycle( 16).
Steam, after decompressing in the steam jet ejector diffuser (13) imparts its
kinetic energy to the
sucked air with coincident generating deep underpressure in the suction box
(11).
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CA 02510896 2005-05-30
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Sucked air with diffused steam is a heating medium for feeding blowing nozzle
(12). Hot
air- steam mixture from blowing nozzles is sucked in to suction boxes ( 11 )
through the felt
that is conditioned at the same time in the process. It leads to preheating
material and
water that it contains. A portion of moisture evaporates in the form of vapor
and is sucked
away. The rest of water in the liquid form is substantially easier sucked away
in higher
temperature due to decrease in its viscosity and density. As a consequence,
simultaneous
sucking and preheating felt by means of air-steam flow influences the
intensification of
conditionig and increases paper dewatering.
As a result, paper web subjected to thermal drying is characterized by higher
dryness.
Steam jet ejector is designed to automatically adjust to the factual condition
of felt. In case
of poor felt permeability, steam jet ejector sucks little air: vacuum under
the felt deepens
and the temperature of air-steam mixture blown onto the felt increases. It
causes opening
the felt and changes operating parameters of the steam jet ejector. The amount
of sucked air
increases, pressure in suction box rises and the blow temperature drops.
The overall impact of the increase in felt permeability is improved vacuum and
mechanical
dewatering and advantageous energy balance of a paper machine.
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Representative Drawing