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EP 0 744 550 B1 |
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EUROPEAN PATENT SPECIFICATION |
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Mention of the grant of the patent: |
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28.07.1999 Bulletin 1999/30 |
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Date of filing: 02.05.1996 |
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International Patent Classification (IPC)6: F04C 29/02 |
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Oil recycling in screw compressor arrangements
Ölumlauf in Schraubenverdichtern
Recirculation d'huile dans des compresseurs à vis
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Designated Contracting States: |
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BE DE FR IT |
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Priority: |
25.05.1995 GB 9510610
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Date of publication of application: |
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27.11.1996 Bulletin 1996/48 |
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Proprietor: COMPAIR BROOMWADE LTD. |
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High Wycombe,
Buckinghamshire HP13 5SF (GB) |
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Inventor: |
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- Hare, John
High Wycombe
Buckinghamshire
HP14 3SQ. (GB)
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Representative: Bucks, Teresa Anne et al |
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BOULT WADE TENNANT,
27 Furnival Street London EC4A 1PQ London EC4A 1PQ (GB) |
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References cited: :
FR-A- 2 151 406
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GB-A- 833 991
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Note: Within nine months from the publication of the mention of the grant of the European
patent, any person may give notice to the European Patent Office of opposition to
the European patent
granted. Notice of opposition shall be filed in a written reasoned statement. It shall
not be deemed to
have been filed until the opposition fee has been paid. (Art. 99(1) European Patent
Convention).
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[0001] The invention relates to oil recycling in screw compressor arrangements used to compress
a gas such as air.
[0002] Many screw compressors require the use of oil during their operation. The oil has
three major functions within the scope of compressor arrangements; it cools the compressed
gas, lubricates the bearings and seals the rotors in the air end (the actual screw
compressor itself). Unfortunately, as a result the discharged compressed gas contains
a large quantity of oil which must be extracted before it can be used. A pressure
vessel is generally used to extract the bulk of the oil from the compressed gas during
a primary separation process. This is also known as a reclaimer and usually contains
a filter or separator element to separate the remaining oil from the compressed gas.
The oil collected by the separator element is scavenged back to the air end.
[0003] In other arrangements the separator element is not fitted in the reclaimer but an
alternative special filter is provided to carry out the final separation of oil still
entrained in the gas after it has been through the reclaimer, and the oil is then
also recycled and returned or scavenged back to the screw compressor to be re-used.
In order to scavenge this oil back to the compressor a small quantity of the compressed
gas is constantly bled back with the oil to effect the scavenging process. The scavenge
line consists of a small open pipe connecting the base of the special filter to the
air end. At the end of the pipe adjacent the air end are fitted a filter, a small
orifice which limits the air flow and a non-return valve to prevent oil in the air
end passing back into the scavenge pipe.
[0004] Such an arrangement is substantially described in GB-A-833991, which forms the basis
of the preamble of claim 1.
[0005] The quantity of gas used in the scavenging process is relatively small on large compressor
packages, but in small compressor units represents a significant loss in that it circulates
in a closed loop requiring re-pressurisation after re-entry into the compressor to
achieve the compressor final discharge pressure.
[0006] It is an object of the present invention to overcome this disadvantage and to minimise
the gas losses due to the scavenging process.
[0007] According to the invention there is therefore provided a screw compressor arrangement
comprising a screw compressor, primary and secondary separating means for extracting
oil from compressed gas discharged from the screw compressor, means for returning
the oil extracted by the secondary separating means to the screw compressor and valve
means operable to regulate the flow of oil and gas from the secondary separating means
back to the screw compressor.
[0008] Preferably the valve is the solenoid or pneumatic valve which is operable to be set
normally open or normally closed.
[0009] The valve is preferably operable to vary the frequency in duration of valve operating.
There may also be provided a control system to regulate the operation of the valve
which may be electronic.
[0010] In a preferred embodiment of the invention the primary oil separating means comprise
a reservoir and the secondary or separating means comprise a filter.
[0011] The secondary separating means may be enclosed within the primary separating means
or they may be fitted downstream thereof.
[0012] The invention also provides a method of recycling oil in a screw compressor arrangement
comprising the steps of extracting oil from compressed gas discharged from the screw
compressor in a primary separation process, extracting the remaining oil from the
compressed gas in a secondary separation process, returning the oil extracted during
the secondary separation process to the screw compressor by means of a small quantity
of compressed gas via valve means operable to regulate the flow of oil and gas back
to the screw compressor.
[0013] The invention will now be described, by way of example only, with reference to the
accompanying drawing Fig. 1 which is a schematic representation of a screw compressor
arrangement according to the present invention.
[0014] The screw compressor arrangement 10 comprises a screw compressor 11 (air end) for
compressing a gas, such as air, a motor 12 which drives the air end 11 and a pressure
vessel 13. The pressure vessel 13 is a reservoir for compressed gas and oil and may
be made from aluminium, iron, steel or any other suitable material.
[0015] Gas is taken into the air end 11 via a gas intake filter 14 which is monitored by
a pressure switch 14a. The pressure switch 14a senses the differential pressure between
the atmospheric pressure existing in the vicinity of the gas intake filter 14 and
the pressure downstream between the gas intake filter 14 and the inlet to the air
end 11. As the filter 14 progressively filters out atmospheric dirt, it slowly blocks
up and the pressure switch 14a indicates when the filter 14 should be replaced. The
quantity of gas intake is also controlled via a suction regulator 15 which is connected
by a control line to the reclaimer 13.
[0016] The discharge of pressurised compressed air from the air end 11 contains a large
quantity of oil, typically 10 to 15 litres per minute for each cubic metre of free
air compressed per minute. This oil has to be separated from the compressed air before
it passes into use. The compressed gas and oil mixture is therefore discharged from
the air end 11 to the reclaimer 13 via an appropriate duct 24. A temperature thermistor
25 monitors the temperature of the gas/oil mixture.
[0017] The separation of the gas and oil is achieved in two stages; primary separation of
the oil and gas is carried out within the reclaimer 13 and final separation is completed
through the separator element in the reclaimer or alternatively through a special
filter 18 fitted downstream of the reclaimer 13.
[0018] The difference in pressure across the special filter 18 is monitored by a pressure
differential switch 18a to determine when the filter 18 must be replaced.
[0019] The fully cleaned gas is subsequently passed through an after cooler 19 before passing
to the plant discharge 20 and into use. A pressure transducer 26 responds to the pressure
in the customers gas main to energise the control system as and when required.
[0020] The reclaimed oil from the special filter is recirculated from filter 18 via a small
scavenge pipe 21 back to the air end 11. The scavenge pipe 21 conveys the oil and
a small quantity of the compressed gas which is bled back with the oil to effect the
scavenging process.
[0021] Incorporated into the pipe 21 is a solenoid valve 22 which operates to introduce
an intermittent, rather than constant, scavenge. The timing of the operation of this
valve 22 is important in that it cannot remain closed for excessively long periods
because this will lead to flooding of the bottom of the special filter 18 and reducing
its effeciency. The valve 22 must also be opened long enough to ensure that all the
oil is cleared from the filter 18 and passed back to the air end 11.
[0022] In prior art arrangements nearly 0.08m
3 per minute of free gas is used to scavenge the oil. This can represent up to 10%
of the output of a small unit, say of 5.5Kw size. To compress this gas to typically
7 bar requires approximately 0.5Kw. By using a solenoid valve 22, the power consumption
to the drive motor is reduced by nearly 0.5Kw whilst the actual gas flow remains unchanged.
As the rotors are virtually sealed, the intermitted introduction of scavenged gas
and oil after the rotor inlet closure does not increase gas losses back to the suction
and the scavenge gas and oil mixes with the charge gas to be compressed to the final
discharge pressure.
[0023] Thus during the greatest part of the running period additional power is not required
to re-compress the scavenged gas as is the case with conventional machines.
[0024] The solenoid valve 22 can also be set to be normally open or normally closed. Normally
open has the benefit of providing a fail safe function in the event of valve failure.
Normally closed has the benefit of preventing small quantities of oil being driven
back when the plant is being blown down on stopping. A non-return valve may be necessary
to prevent this action for a normally open valve.
1. A screw compressor arrangement (10) comprising a screw compressor (11), primary (13)
and secondary (18) separating means for extracting oil from compressed gas discharged
from the screw compressor (11),
characterised by the provision of means (21) for returning the oil extracted by the
secondary separating means (18) to the screw compressor and valve means (22) operable
to regulate the flow of oil and gas from the secondary separating means (18) back
to the screw compressor (11).
2. A screw compressor arrangement (10) as claimed in claim 1 in which the valve means
(22) is a solenoid or pneumatic valve.
3. A screw compressor arrangement (10) as claimed in claim 1 or claim 2 in which the
valve means (22) is operable to be set normally open or normally closed.
4. A screw compressor arrangement (10) as claimed in any one of the preceding claims
in which the valve means (22) is operable to vary the frequency and duration of valve
opening.
5. A screw compressor arrangement (10) as claimed in any one of the preceding claims
in which there is provided a control system to regulate the operation of the valve
means (22).
6. A screw compressor arrangement (10) as claimed in claim 5 in which the control system
is electronic.
7. A screw compressor arrangement (10) as claimed in any one of the preceding claims
in which the primary oil separating means (13) comprise a reservoir and the secondary
oil separating means (18) comprise a filter.
8. A screw compressor arrangement (10) as claimed in any one of the preceding claims
in which the secondary separating means (18) are enclosed within the primary separating
means (13).
9. A screw compressor arrangement (10) as claimed in any one of the preceding claims
wherein the secondary separating means (18) are fitted downstream to the primary separating
means (13).
10. A method of recycling oil in a screw compressor arrangement (10) comprising the steps
of extracting oil from compressed gas discharged from the screw compressor (11) in
a primary separation process, extracting the remaining oil from the compressed gas
in a secondary separation process, characterised by the step of returning the oil
extracted during the secondary separation process to the screw compressor (11) by
means of a small quantity of compressed gas via valve means (22) operable to regulate
the flow of oil and gas back to the screw compressor (11).
1. Schraubenverdichteranordnung (10), umfassend einen Schraubenverdichter (11), primäre
(13) und sekundäre (18) Abscheidemittel zum Extrahieren von Öl aus vom Schraubenverdichter
(11) abgegebenem komprimiertem Gas,
gekennzeichnet durch das Vorsehen von Mitteln (21) zum Rückführen des durch die Sekundärabscheidemittel
(18) extrahierten Öls zum Schraubenverdichter, und durch Ventilmittel (22), welche
zum Regulieren der Strömung von Öl und Gas von den Sekundärbscheidemitteln (18) zurück
zum Schraubenverdichter (11) wirksam sind.
2. Schraubenverdichteranordnung (10) nach Anspruch 1, bei welcher die Ventilmittel (22)
ein Solenoid oder ein Pneumatikventil sind.
3. Schraubenverdichteranordnung (10) nach Anspruch 1 oder Anspruch 2, bei welcher die
Ventilmittel (22) derart betreibbar sind, daß sie im Normalzustand offen oder im Normalzustand
geschlossen sind.
4. Schraubenverdichteranordnung (10) nach einem der vorangehenden Ansprüche, bei welcher
die Ventilmittel (22) betreibbar sind, um die Frequenz und die Dauer der Ventilöffnung
zu variieren.
5. Schraubenverdichteranordnung (10) nach einem der vorangehenden Ansprüche, bei welcher
ein Steuerungssystem zum Regulieren des Betriebs der Ventilmittel (22) vorgesehen
ist.
6. Schraubenverdichteranordnung (10) nach Anspruch 5, bei welcher das Steuerungssystem
elektronisch ist.
7. Schraubenverdichteranordnung (10) nach einem der vorangehenden Ansprüche, bei welcher
die Primärölabscheidemittel (13) einen Behälter umfassen und die Sekundärölabscheidemittel
(18) einen Filter umfassen.
8. Schraubenverdichteranordnung (10) nach einem der vorangehenden Ansprüche, bei welcher
die Sekundärabscheidemittel (18) innerhalb der Primärabscheidemittel (13) eingeschlossen
sind.
9. Schraubenverdichteranordnung (10) nach einem der vorangehenden Ansprüche, bei welcher
die Sekundärabscheidemittel (18) stromabwärts der Primärabscheidemittel (13) eingesetzt
sind.
10. Verfahren zum Rezyklieren von Öl in einer Schraubenverdichteranordnung (10), umfassend
die Schritte Extrahieren von Öl aus vom Schraubenverdichter (11) abgegebenem komprimiertem
Gas in einem primären Abscheideprozeß, Extrahieren des verbleibenden Öls aus dem komprimierten
Gas in einem sekundären Abscheideprozeß,
gekennzeichnet durch den Schritt des Rückführens des extrahierten Öls während des
sekundären Abscheideprozesses zum Schraubenverdichter (11) mittels einer geringen
Menge von komprimiertem Gas über Ventilmittel (22), welche zum Regulieren der Strömung
von Öl und Gas zurück zum Schraubenverdichter (11) wirksam sind.
1. Agencement (10) de compresseur à vis comportant un compresseur (11) à vis, des moyens
primaire (13) et secondaire (18) de séparation destinés à extraire de l'huile d'un
gaz comprimé déchargé du compresseur (11) à vis, caractérisé par la présence d'un
moyen (21) destiné à renvoyer l'huile extraite par le moyen de séparation secondaire
(18) au compresseur à vis et d'un moyen à soupape (22) pouvant être actionné pour
réguler l'écoulement d'huile et de gaz en retour du moyen de séparation secondaire
(18) vers le compresseur à vis (11).
2. Agencement (10) de compresseur à vis selon la revendication 1, dans lequel le moyen
à soupape (22) est une soupape à commande par bobine ou pneumatique.
3. Agencement (10) de compresseur à vis selon la revendication 1 ou la revendication
2, dans lequel le moyen (22) à soupape peut être actionné pour être placé dans une
position normalement ouverte ou normalement fermée.
4. Agencement (10) de compresseur à vis selon l'une quelconque des revendications précédentes,
dans lequel le moyen (22) à soupape peut être actionné pour faire varier la fréquence
et la durée d'ouverture de la soupape.
5. Agencement (10) de compresseur à vis selon l'une quelconque des revendications précédentes,
dans lequel il est prévu un système de commande destiné à réguler l'action du moyen
(22) à soupape.
6. Agencement (10) de compresseur à vis selon la revendication 5, dans lequel le système
de commande est électronique.
7. Agencement (10) de compresseur à vis selon l'une quelconque des revendications précédentes,
dans lequel le moyen primaire (13) de séparation d'huile comporte un réservoir et
le moyen secondaire (18) de séparation d'huile comporte un filtre.
8. Agencement (10) de compresseur à vis selon l'une quelconque des revendications précédentes,
dans lequel le moyen secondaire (18) de séparation est renfermé à l'intérieur du moyen
primaire (13) de séparation.
9. Agencement (10) de compresseur à vis selon l'une quelconque des revendications précédentes,
dans lequel le moyen secondaire (18) de séparation est monté en aval du moyen primaire
(13) de séparation.
10. Procédé de recyclage d'huile dans un agencement (10) de compresseur à vis, comprenant
les étapes dans lesquelles on extrait de l'huile d'un gaz comprimé déchargé du compresseur
à vis (11) dans un processus de séparation primaire, on extrait l'huile restante du
gaz comprimé dans un processus de séparation secondaire, caractérisé par l'étape de
renvoi de l'huile extraite pendant le processus de séparation secondaire vers le compresseur
à vis (11) au moyen d'une petite quantité de gaz comprimé en passant par un moyen
à soupape (22) pouvant être actionné pour réguler l'écoulement d'huile et de gaz en
retour vers le compresseur à vis (11).
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