U.S. patent application number 10/533912 was filed with the patent office on 2006-07-27 for method and device for recycling gas.
Invention is credited to Heiko Fryen, Alexander Jurmann, Stephan Rief.
Application Number | 20060165533 10/533912 |
Document ID | / |
Family ID | 32115243 |
Filed Date | 2006-07-27 |
United States Patent
Application |
20060165533 |
Kind Code |
A1 |
Jurmann; Alexander ; et
al. |
July 27, 2006 |
Method and device for recycling gas
Abstract
A device and method for recycling of gas used during the
quenching process in a thermal treatment, for example, in which the
gas is removed directly from a quenching chamber and is compressed
to the pressure prevailing in the high-pressure container rather
than being decompressed into a gas buffer, an additional
compression step being connected if the pressure inside the chamber
lies below a threshold value, wherefore conduits comprising
overflow regulators lead to the individual compression steps.
Inventors: |
Jurmann; Alexander;
(Waakirchen, DE) ; Rief; Stephan;
(Remseck/Neckargroeningen, DE) ; Fryen; Heiko;
(Hamburg, DE) |
Correspondence
Address: |
CROWELL & MORING LLP;INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Family ID: |
32115243 |
Appl. No.: |
10/533912 |
Filed: |
November 3, 2003 |
PCT Filed: |
November 3, 2003 |
PCT NO: |
PCT/EP03/12259 |
371 Date: |
December 2, 2005 |
Current U.S.
Class: |
417/65 |
Current CPC
Class: |
Y02P 10/20 20151101;
C21D 1/613 20130101; C21D 2241/01 20130101; C21D 1/62 20130101;
Y02P 10/212 20151101 |
Class at
Publication: |
417/065 |
International
Class: |
E21B 43/12 20060101
E21B043/12 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 5, 2002 |
DE |
10251486.0 |
Claims
1. A method for recovery of gas released from a high-pressure
container into a closed chamber, comprising the steps of:
compressing gas drawn directly from the closed chamber with at
least one high compression stage and returning the compressed gas
to the high pressure chamber until gas pressure in the closed
chamber falls below an inlet pressure limit value; and after gas
pressure has fallen below the inlet pressure limit value,
compressing gas down directly from the closed chamber with at least
one low compression stage and feeding the output of the at least
one low compression stage into the inlet of the at least one high
compression stage for further compression and return to the high
pressure chamber.
2. The method as claimed in claim 1, wherein a multistage
compressor or multiple compressors connected in series are
used.
3. The method as claimed in claim 1, wherein the individual
compression stages are supplied with gas directly according to the
falling evacuation pressure of the chamber.
4. The method as claimed in claim 1, wherein the gas with the
highest compression capacity is compressed in the highest
compression stage.
5. The method as claimed in claim 1, wherein the pressure in the
chamber is between 6 and 60 bar at the beginning of gas recovery
and the pressure in the high-pressure container is between 8 and 62
bar.
6. The method as claimed in claim 1, wherein nitrogen, argon and
helium.
7. A device for recovery of gas released from a high-pressure
container into a closed chamber, comprising: at least one high
compression compressor stage, at least one low compression
compressor stage, gas lines directly connecting the closed
container with each compression stage without intermediate storage;
isolation devices in each gas line between each compression stage
and the closed container, said isolation devices comprising at
least one of cut-off valves and over-current regulators; and a
switching unit, said switching unit controlling selective operation
of the isolation devices to directly connect a first of the at
least one high compression stage inlet to the closed chamber to
receive and compress the gas from the closed chamber until gas
pressure in the closed chamber falls below an inlet pressure limit
value; and after gas pressure in the closed chamber has fallen
below the inlet pressure limit value, isolate the at least one high
compression stage from direct connection to the closed chamber,
connect the at least one low compression stage inlet to the closed
chamber, and feed the output of the at least one low compression
stage into the inlet of the at least one high compression stage for
further compression and return to the high pressure chamber.
8. The device as claimed in claim 7, further comprising: a pressure
sensor for detecting gas pressure in the closed chamber, wherein
the pressure sensor output is provided to the switching unit for
use in determining when to selectively operate the isolation
devices.
9. The device as claimed in claim 7, wherein one or more
compression stages include multiple compressors conducted in
parallel.
10. The device of claim 7, wherein the closed chamber is a heat
treatment quenching process chamber.
11. The method of claim 1, wherein the recovery of gas follows
release of the gas in a heat treatment quenching process.
Description
[0001] This application claims the priority of German patent
document 102 51 486.0, filed Nov. 5, 2002 (PCT International
Application No. PCT/EP2003/012259, filed Nov. 3, 2003), the
disclosure of which is expressly incorporated by reference
herein
BACKGROUND AND SUMMARY OF THE INVENTION
[0002] This invention relates to a method for recovering gas from a
process that operates with gas under pressure. A gas sent from a
high-pressure container to a closed chamber in which the process
takes place is recovered by being compressed in multiple
compression stages and fed back into the high-pressure
container.
[0003] Furthermore, this invention relates to a device for
recovering gas from a process operating with gas under pressure,
said process removing the gas from a high-pressure container and
taking place in a closed chamber.
[0004] Gases under pressure are needed for a variety of processes.
Examples that can be given here include processes in heat
treatment, special processes in thermal spraying or laser welding.
Recovery of gases in processes in which the gas is under a high
pressure is particularly important because the quantities of gas
used are very large and consequently, economical operation of this
process is possible only if the gas is carried in circulation.
[0005] For example, the quenching process in the heat treatment of
metallic workpieces constitutes a decisive work step. It is
important here for the workpieces to be cooled very rapidly and
uniformly to prevent unwanted changes in the material such as phase
transitions or fine cracks which occur when the workpiece is cooled
slowly and irregularly. Consequently, in quenching it is of crucial
importance for a large quantity of gas to flow very rapidly into a
quenching chamber where a high pressure is built up. The quenching
process proceeds as follows in practice: when the workpiece is
ready in the quenching chamber, a valve between the high-pressure
container and the quenching chamber is opened and the gas flows
suddenly from the high pressure reservoir into the quenching
chamber. The pressure in the quenching chamber then rises to
approximately 20 bar, while the pressure in the high-pressure
reservoir drops from the starting pressure, which is approximately
30 bar, to approximately 22 bar. After quenching, a valve is opened
to release the gas from the quenching chamber. If the pressure in
the quenching chamber has dropped to ambient pressure, the
quenching chamber is opened and the workpiece is removed. A
suitable closed container or a closed chamber into which the
workpiece is introduced or the heat treatment itself may be used as
the quenching chamber. Instead of a workpiece, a batch of
workpieces may also be quenched.
[0006] It is advisable economically and technically to send the
spent gas to a circulation system because the resulting quantities
of gas are very large. Gas recovery is normally performed with the
help of a gas buffer. To do so, the quenching chamber is emptied
into a gas buffer until the pressure is equalized in the quenching
chamber and the gas buffer. The gas buffer is generally a balloon
and/or a pressure container. The balloon expands when filled. Since
the gas is ultimately under atmospheric pressure in the balloon,
the gas takes up a large volume and the filled balloon requires a
great deal of space accordingly. Before the gas is fed back into
the high-pressure container, it must be compressed from atmospheric
pressure to the pressure prevailing in the high-pressure reservoir.
Since a single-stage compressor is unable to bridge such an
enormous difference in pressure, a multistage compressor is used
for this purpose. In a multistage compressor, several compressors
are connected in series. The bottom stage compresses the gas from
the output pressure to a higher pressure. From this pressure, the
next stage in turn raises the pressure level to a higher stage.
There may be as many stages as desired before finally reaching the
end pressure prevailing in the high-pressure container by the end
stage. The great energy loss which occurs due to the fact that the
gas is depressurized in each quenching operation first from the
high pressure of the chamber to the low pressure in the gas buffer
and then is compressed again to the high pressure of the high
pressure chamber is a disadvantage of this method.
[0007] The object of this invention is to provide a method which
will avoid these disadvantages of the known method and which will
send preferably all the gas quantity available at ambient pressure
to the gas recovery system.
[0008] This object is achieved according to this invention by
compressing the gas directly from the pressure prevailing in the
chamber, at least one additional compression stage being used when
the pressure in the chamber falls below a limit level. According to
this invention, gas is removed from the chamber until the pressure
in the chamber reaches the limit value of the intake pressure. The
limit value of the intake pressure is determined by the design of
the compression stage because for each compressor there is a
minimum intake pressure up to which the compressor is able to
compress the gas to the required pressure and below which
compression is no longer possible. Since the chamber has been
evacuated to the respective limit pressure with one compression
stage, according to this invention another compression stage is
added. With this second compression stage, it is possible to remove
the gas from the chamber at the lower pressure and compress it in
the subsequent stage. Thus with the inventive method, the pressure
level prevailing in the chamber at any given time is utilized
appropriately. Since a very high pressure prevails in the chamber
mainly at the start of removal of the gas, this pressure often
being only slightly below the pressure of the high-pressure
container and dropping with removal of the gas but still being far
above atmospheric pressure and only slowly approaching the latter,
therefore only the pressure difference prevailing between the
chamber and the high-pressure container at that moment need be
overcome with the inventive method. Compression time is shortened
considerably because consequently now only a very small amount of
the gas must overcome a great pressure difference and the energy
demand required for compression is also drastically reduced--in
comparison with compression from atmospheric pressure. Compression
starting from atmospheric pressure is necessary with the method
previously customary in which the gas is depressurized into a gas
buffer. The fact that this gas buffer is omitted in the inventive
method is a great advantage because the gas buffer takes up a large
space due to the large volume of the gas under atmospheric
pressure. This is advantageous not only in the case of tight
spatial conditions but also the space savings have an economically
advantageous effect. Furthermore, the inventive method is
characterized by a low investment cost.
[0009] The problem of emptying a closed gas chamber having a high
gas pressure and having to feed this gas into a container at a high
pressure, however, does not occur only in recovery of gases but
also occurs in plant engineering. With this invention it is now
possible to utilize the high pressure of the chamber and to convey
the gas into a container in which the prevailing pressure is above
the initial output pressure of the chamber. The inventive procedure
can be used in all cases in which such a situation occurs.
[0010] Advantageously, a multistage compressor or several
compressors connected in series are used. Two or three compression
stages are sufficient here to particular advantage to bridge the
entire pressure range from atmospheric pressure at the end of the
evacuation process up to the pressure of the high-pressure
container.
[0011] In an advantageous embodiment of this invention, the
individual compression stages are fed directly into the chamber
according to the declining emptying pressure of the chamber. In
compression of the gas, the compression stages (n stages) are run
through successively, the gas being removed from the chamber at the
lowest compression stage (first stage) and being fed into the
high-pressure container with the highest compression stage (n-th
stage). At the start of evacuation, only one compression stage
(n-th stage) is used. This withdraws the gas from the chamber,
compresses it and feeds it into the high-pressure container. In
doing so, the pressure in the chamber drops. Then according to this
invention, when the pressure drops below the limit value of the
highest stage (n-th stage), the next lower stage ((n-1)-th stage)
is added. This stage then withdraws the gas from the chamber and
compresses it to an intermediate pressure which in general
corresponds to the intake pressure of the highest stage (n-th
stage). Then from the intermediate pressure the gas is compressed
in the highest stage to the final pressure and fed into the
high-pressure container. The pressure in the chamber continues to
drop as the withdrawal is continued, reaching the cut-off pressure
to which the (n-1)-th compression stage operates. An (n-2)-th
compression stage is then added. This is the lowest compression
stage at which withdrawal and compression take place at the lowest
pressure level. The (n-1)-th compression stage compresses the gas
to the next higher pressure level and finally the end pressure is
reached with the n-th and highest stage. The pressure differences
that are overcome with the individual stages often vary and are
determined by the properties of the compressor in the particular
compression stage. For compression to the required end pressure,
any number of stages n may be run through. The individual
compression stages are then either different compressors connected
in series or the individual stages of a multistage compressor. The
various compressors and/or the different compression stages are
used according to the inventive sequence.
[0012] In an embodiment of this invention, the individual
compression stages have different compression capacities. It is
particularly advantageous here that the gas in the highest
compression stage (n-th stage) with which this gas is compressed
with the highest compression capacity of the individual compression
stages before any other additional stage, i.e., (n-1)-th stage is
added. This may be accomplished through appropriate dimensioning of
this compressor or through a parallel circuit of multiple
compressors. A high compression output in the highest compression
stage greatly reduces the time required for compression because in
particular at the beginning of withdrawal large quantities of gas
are generated.
[0013] In an embodiment of this invention, the pressure in the
chamber at the beginning is between 6 and 60 bar and the pressure
in the high-pressure chamber is between 8 and 62 bar. Thus the
quenching pressures conventional in the heat treatment in the
quenching chamber are also between 6 and 60 bar.
[0014] It is also particularly advantageous that the inventive
method is used for recovery nitrogen, argon or helium and mixtures
thereof. In the heat treatment, quenching is often performed with
nitrogen. Therefore, the inventive method has been designed for
recovery of nitrogen with particular advantages. However, recovery
of other quenching gases, e.g., argon or helium as well as mixtures
of nitrogen, argon and helium is also possible to advantage. Since
the inventive method is characterized by a low investment cost, it
also permits economical recovery of relatively inexpensive gases
such as nitrogen. When expensive gases or gas mixtures which have
previously also been sent for recovery are used for quenching, the
inventive method makes the recovery much less expensive.
[0015] This object is achieved for this device according to this
invention by the fact that the chamber communicates with at least
two compressors that are connected in series and form at least two
compression stages or with each compression stage of a multistage
compressor communicates via connecting lines directly without an
intermediate reservoir, whereby the connecting lines include
opening and closing overcurrent regulators or cut-off elements
which are connected to a switch unit that controls the cut-off
elements and whereby the highest compression stage (n-th stage) of
the compressors connected in series or of the multistage compressor
communicates with the high-pressure container. With the inventive
device it is thus possible in a multistage compressor to separately
supply the individual compression stage responsible for different
pressure ranges or the different compressors which form a
multistage compressor through a series connection. It is thus
possible to use the respective compression stage according to its
design with respect to the pressure range. The lines lead between
the stages according to this invention and carry the gas to the
next higher compression stages. The gas does not reach them until
after compression in this stage. If there is no higher stage, the
gas enters the high-pressure container. Overcurrent regulator or
cut-off elements cut off the lines leading to the lower compression
stages and cause the gas to be sent to higher compression stages.
Overcurrent regulators are mechanical regulators which determine
the pressure prevailing upstream from the valve and open or close
according to this pressure. However, the switching unit assumes
control of the cut-off elements. The switching unit preferably
includes a pressure sensor for determining the pressure in the
chamber. If the pressure in the chamber drops below the specific
limit value for the particular compression stage, the overcurrent
regulators then open and close in such a way and/or the switching
unit sets the cut-off elements in such a way that another lower
compression stage assumes the role of compression in the pressure
range below that of the previous compression stage, and the
previous stage recompresses the gas coming from the lower stage. On
evacuation of the chamber, consequently the highest compression
stage (n-th stage) performs the compression first, then the switch
unit switches the next lower compression stage ((n-1)-th stage) and
so far until all the compression stages are in operation.
Consequently with the inventive device it is not necessary to
depressurize the gas of the chamber into a gas buffer and to use
all the stages according to their sequence for the total quantity
of gas. Saving by eliminating the gas buffer means enormous savings
in terms of space.
[0016] In an advantageous embodiment, the switching device is
connected to a pressure sensor situated on the chamber.
[0017] Advantageously one or more compression stages include
multiple compressors connected in parallel because the compression
performance of one stage is increased by the parallel switching.
However, the compression performance of a compression stage is also
increased through appropriate dimensioning.
[0018] The inventive method and device are used to particular
advantage in the quenching process in heat treatment.
[0019] Other objects, advantages and novel features of the present
invention will become apparent from the following detailed
description of the invention when considered in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 shows a schematic view of a device for gas recovery
in accordance with an embodiment of the present invention.
[0021] FIG. 2 shows a schematic view of a device for gas recovery
in accordance with another embodiment of the present invention.
DETAILED DESCRIPTION
[0022] FIG. 1 shows a high-pressure container 1, a quenching
chamber 2 provided for a heat treatment, compressors 3, 4, cut-off
elements 5, 6, 7, a switching unit 8 having a pressure sensor 9,
lines 10, 11 and a gas supply 12. The workpieces are in the
quenching chamber 2 for a quenching process. In the high-pressure
container 1 which is filled with nitrogen, for example, a pressure
p1 of 30 bar prevails. When the valve 5 is opened, gas suddenly
flows out of the high-pressure container 1 into the quenching
chamber 2. Then the pressure in the high-pressure container drops
from 30 bar to 22 bar and the pressure in the quenching chamber
rises to 20 bar. Then the cut-off element 5, which is designed as a
valve like the other cut-off elements is closed. Now the cooling of
the workpieces may be accomplished by means of the quenching gas
which is carried in circulation. After cooling, the gas is
recovered from the quenching chamber. To do so, first the valve 6
is opened while the valve 7 remains closed. The gas flows through
the line 10 into the compressor 4 which forms the compression stage
and is compressed there to 30 bar and sent into the high-pressure
container 1. When the gas is removed from the quenching chamber 2,
the pressure p2 in the quenching chamber consequently drops. Then
when the pressure in the quenching chamber 2 drops below the limit
value, which is 6 bar, for example, for the compressor 4, the valve
6 is closed and the cut-off element 7 is opened. The gas then goes
through the line 11 into the compressor 3 which forms the (n-1)-th
compression stage and from there goes further into the compressor 4
which forms the n-th compression stage. The direct path to the
compressor 4 via the line 10, however, is blocked by the cut-off
element 6. The control of the cut-off elements is assumed by the
switching unit 8. Therefore the pressure sensor 9 which measures
the pressure p2 in the quenching chamber is assigned to the
switching unit 8. Then if the cut-off pressure is determined by
this pressure sensor in the quenching chamber 2, the switching unit
8 performs the switching operation. Consequently the gas is first
compressed to 6 bar, for example, in the compressor 3 before being
compressed to 30 bar in the compressor 4 and fed into the
high-pressure container 1. The gas supply 8 is needed to increase
circulation during operation and to compensate for gas losses.
[0023] FIG. 2 shows another advantageous embodiment of the
inventive method. The reference notation which is the same as that
in FIG. 1 denotes the same element. In addition there are
overcurrent regulators 13, 15 and a valve 14. To recover gas after
the quenching process in the quenching chamber 2, first the valve
14 is opened. The overcurrent regulator 13 which is mounted in the
connecting line 11 is closed at the beginning of the recovery while
the overcurrent regulator 15 of the connecting line 10 is open. The
gas goes from the quenching chamber 2 through the connecting line
10 into the compressor 4 and is compressed by the compressor 4 to
the pressure p1 of the high-pressure container 1 and is fed into
the latter. In doing so, the pressure p2 in the quenching chamber 2
drops. The compressor 4 thus forms the n-th compression stage. When
the pressure p2 in the quenching chamber 2 drops below the minimum
intake pressure of the n-th compression stage, the overcurrent
regulator 15 closes and the overcurrent regulator 13 opens. The gas
then goes from the quenching chamber into the compressor 3 where it
is compressed to the intake pressure of the compressor 4. Then it
is compressed by the compressor 4 to the pressure p1 of the
high-pressure container and fed into the high-pressure container 1.
Consequently the gas is compressed first from the (n-1)-th
compression stage without intermediate storage from the quenching
chamber and from the pressure p2 prevailing in the quenching
chamber and then is compressed from the n-th compression stage to
the pressure p1 of the high-pressure container.
[0024] The inventive method may be used for example in hardening
tools made of steel.
[0025] The foregoing disclosure has been set forth merely to
illustrate the invention and is not intended to be limiting. Since
modifications of the disclosed embodiments incorporating the spirit
and substance of the invention may occur to persons skilled in the
art, the invention should be construed to include everything within
the scope of the appended claims and equivalents thereof.
* * * * *