Note: Descriptions are shown in the official language in which they were submitted.
257
A METHOD ANL) APPARATUS IN PUI.PING
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The invention relates to a method in defibrating
wood chips in steam where the pulp produced is conveyed from
a pulper to a separator for separating pulp and steam. The
invention also relates to apparatus for carrying out the
method.
It is usual to utilize the rather high pressure of
steam in the pulper, often 0.5 - 1 MPa over atmospheric
pressure, for conveying the pulp therefrom to the separator,
the steam being allowed to expand to atmospheric pressure and
quite often allowed to flow out into the atmosphere after
completing conveying work, which means a considerable loss
of energy. Even if steam is sometimes recovered after the
separator, it is a source of energy of lower value than the
steam in the pulper, due to its reduced pressure and temperature.
The object of the in~ention is to provide a method and
apparatus for conveying the pulp between the pulper and separator,
the method and apparatus allowing recovery of all excess steam
at high pressure and temperature.
The desired results are achieved, in accordance with
the present invention, by the provision of a method in
defibrating wood chips in steam, where the pulp produced is
conveyed from a pulper to a separator for separatin~ pulp
and steam, characterized in that a flow of steam which has
been separated from the pulp is taken from the separator, is
given an increased pxessure and supplied as a driving flow
to an ejector, the ejector being used for removing a flow
2~ oE pulp and steam from the p~lper, both the flows merged in
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the ejector being supplied to the separator, which is kept
pressurized by the steam by separating it from the atmosphere,
while a limited amount of excess steam is taken off and
refluxed to a chips preheater connected to the pulper and/
or is used as a source of energy for other purposes.
In accordance with a further aspect of the present
invention, there is provided an apparatus for carrying out
the method, comprising a pipe connection between a pulper
and a separator, which is arranged for separating pulp and
steam received from the pulper, characterized by a pressure
increasing conveying means for steam, e.g. a fan, the pressure
increasing means having its suction side connected to the
steam outlet of the separator, and an ejector, the pressure
; increasing means having its pressure side connected to the
ejector inlet for a driving medium, while the ejector inlet
for a conveyed medium is connected to the pulper outlet for
pulp and steam, and the ejector out:Let is connected to the
separator inlet, the circuit formed by the pressure-increasing
means, ejector, separat~r and intermediate connecting pipes
constituting a closed system, in which the separator is
also kept pressurized by the steam by adjusted bleeding-
off of excess steam, which is refluxed to a chips preheater
connected to the pulper and/or is used as a source of energy
for other purposes.
The invention is described in detail in the following,
while referring to the accompanying schematic drawing showing
the plant.
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Uncoolsed chips, possibl~ somewhat preheated, are supplied
to the screw conveyor 1, which presses the chips in-to the preheat-
ing chamber 3 of the pulper 2. ,' supply pipe 4 for fresh steam is
connected to -the preheater 3, to heat the chips at least during
the starting phase of the defibration process. The chips heated to
defibration tempèrature are fed b~ a further screw conveyor 5 into
the pulper 2. The pulp produced in the pulper is taken o~f
together with steam both supplied to, and generated in the pulper
by means of an ejector 6, the suction side 7 of which is connected
to the outle-t ~ of the pulper.
The driving ~low of the ejector consists of steam, and
the merging flo~s departing from the ejector outlet 9 thus consist
of pulp and steum, ~hich are conveyed by the ejector to a separa-
tor lO~ to the inle-t 11 of which the ejector outlet 9 is connected
by means of a pipe. The separator consists of two serie~-coupled
cyclone collectors 12. ~;
The pulp separ~ted from steam in the collectors 12 i9
talcen off by discharging equipment for use in a conventional
manner~ this equipment being of a kind such that the disch ~-ge
ends 13 of the collectors are kept pressure-tight, so that the
latter can be pressurized~
The steam liberated from pulp is taken from the gas outlet
14 of the last collector 12 via a pipe to the suction side of a
fan 15, the pressure side of which is connected by a further pipe
to the inlet 16 of t~e ejector 6 for the driving flow.
The ejector 6~ separator 10 and fan 15 thus participate in
a ciculation circuit in a closed system in which the separa-tor is
also pressurized to the same order of magnitude as the pulper. The
driving flow of the ejector consists of steam separated from the
pulp~ talcen from the separator 10 and given the required pressure
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boost by the fan 15. The supply of fresh steam via the pipe 4
can be varied~ usually reduced, after a starting phase~ steam for
heating in the preheater 3 being taken instead from the circula-
tion circuit via the pipe 17. The grinding energy in the pulper
generates an excess of steam from the ~ioisture in the chips ~hich,
due to the whole system being put under pressure, can be taken off
a-t high pressure and -temperature via a further pipe 18~ the
apparatus in accordance with the inven-tion thus bcing able to serve
as a source of energy for many different purposes.
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