US20190137173A1

US20190137173A1 - Method and System for Using a Target Gas Provided by a Gas Decomposition Device

Info

Publication number: US20190137173A1
Application number: US16/094,319
Authority: US
Inventors: Benedikt Brüggemeier
Original assignee: Fritz Winter Eisengiesserei GmbH and Co KG
Current assignee: Fritz Winter Eisengiesserei GmbH and Co KG
Priority date: 2016-04-22
Filing date: 2017-03-30
Publication date: 2019-05-09
Also published as: DE102016107468B9; WO2017182250A1; DE102016107468B3; EP3446057A1

Abstract

The present invention relates to a method for utilising a target gas flow consisting of pressurised target gas, which is provided by a continuously-operated gas decomposition device, wherein the target gas flow is supplied to a target load which discontinuously decreases the target gas flow, so that occasionally an excess target gas flow that is not decreased by the target load accrues, as well as a system for supplying a target load. The excess target gases occurring in a gas decomposition device and optionally additionally resulting waste gases may be used in a resource-saving manner through the method and the system according to the invention. This is achieved by the excess target gas flow being supplied as a propellant gas to a compressor which compresses another gas and supplies it as a compressed gas in a compressed gas line, via which it is fed to another load.

Description

The invention relates to a method for using a target gas flow consisting of pressurised target gas, which is supplied by a continuously-operated gas decomposition device, wherein the target gas flow is supplied to a target load, which discontinuously decreases the target gas flow, so that an excess target gas flow that has not been decreased by the target load occasionally accrues.
Likewise, the invention relates to a system for supplying a target load with a pressurised target gas flow and another load with another compressed gas. In this case, the system comprises a gas decomposition device which provides a target gas flow for a target load which discontinuously decreases this target gas flow, so that an excess target gas flow accrues in the gas decomposition device. Furthermore, such a system comprises a compressed gas operated compressor to compress and feed the compressed gas into a compressed gas line leading to the other load.
In a gas decomposition device a gas mixture is separated into a target gas and an exhaust gas. An example of such a gas decomposition device is an Air Separation Unit (ASU) for air separation. Such air separation units separate the ambient air into its main components of nitrogen and oxygen. Depending on the field of application, however, such air separation units may also extract argon or other noble gases from the ambient air.
On an industrial scale, air separation units are used which operate on the basis of so-called cryogenic distillation or low-temperature distillation (“Linde method”). This method delivers pressurised oxygen as the target gas. In addition, a gas flow which contains the atmospheric nitrogen and the other gases which are not separated in the respective separation process and which are contained in the air, is obtained as the “waste gas” of the oxygen production process.
Devices of this type are used, for example, in the field of production of iron or steel melts, but also in many other processes in which pure oxygen is required in larger quantities. Thus, for example, for the so-called “carbon drop” oxygen is blown onto or into the respective melt to eliminate the carbon content or unwanted iron companions from the melt by oxidation.
A fundamental problem with gas decomposition devices of the type considered here is that they are generally operated continuously, because high energy and time costs are incurred at the start-up of such devices. Gas decomposition devices therefore continuously produce an optimally constant target gas flow. This is subjected to high pressure upon leaving the gas decomposition device.
Opposing the continuous provision of the target gas flow is a usually discontinuous demand, i.e. a demand that varies over time on the part of the target load. In fact, the temporarily not, or not completely, excess target gas flow may be temporarily stored in buffers in order to be kept ready for demand peaks. However, the cost of such an intermediate storage and the associated energy losses are considerable.
Various proposals are known for the valuable use of excess target gas and waste gas flows in continuously-operated gas decomposition devices in terms of resource conservation.
An example of these proposals is the integration of an air separation unit into a pig iron production process as described in US 2012/0032378 A1. In this process, the air separation unit provides oxygen for blowing into a blast furnace. The excess oxygen flow temporarily not, or only partially, decreased by the blast furnace is fed into a steam generator in order to improve the efficiency of the combustion of the process gases resulting from the production of pig iron conducted for the generation of the required heat. At the same time, the pressurised nitrogen arising as a waste gas in the air separation process is supplied, on the one hand, to a coal injection device, while, on the other hand, it is used to support the driving of a gas turbine which drives a generator for generating electrical energy.
Against the background of the above-described prior art, the object has arisen to propose a simplified method suitable for wider use and a similarly designed system, with which the excess target gases and waste gases optionally additionally generated in a gas decomposition device may be used in a resource-saving manner.
The invention achieves this object through the method specified in claim 1 and the system proposed in claim 9.
Advantageous embodiments of the invention are specified in the dependent claims and are explained in detail below as is the general inventive concept.
The method according to the invention for utilising a target gas flow consisting of pressurised target gas, similar to the prior art explained at the outset, assumes that the target gas flow is provided by a continuously-operated gas decomposition device. However, a target load supplied with the target gas flow decreases this target gas flow only discontinuously, so that at times an excess target gas flow that has not been decreased by the target load, is obtained.
According to the invention, the excess target gas flow is now fed as a propellant gas to a compressor which compresses another gas and feeds it as compressed gas into a compressed gas line via which it is fed to another load.
Thus, according to the invention, the drive side of a compressor, which compresses “another gas” that is different from the target gas flow, and feeds it into a general compressed gas line, is supplied with the excess target gas flow. “Excess” here relates to both the case in which the target load does not decrease any target gas from the gas decomposition device, so that the excess target gas flow is equal to the target gas flow provided by the gas decomposition device, as well as the case where only a reduced amount of the target gas flow is decreased by the target load, so that only a partial flow of the target gas flow provided by the gas decomposition device is obtained as an excess target gas flow.
In a corresponding manner, a system according to the invention which supplies a target load with a pressurised target gas flow and another load with a different compressed gas, comprises a gas decomposition device which provides a target gas flow for a target load discontinuously decreasing this target gas flow, so that an excess target gas flow is produced in the gas decomposition device, and a compressed gas operated compressor for compressing and feeding the compressed gas into a compressed gas line leading to the other load. According to the invention, in such a system, the compressor is connected on the drive side through a propellant gas line to an outlet of the gas decomposition device, via which outlet the excess target gas flow flows as a propellant gas to a propellant gas connection of the compressor.
The high pressure excess target gas flow provided by the gas decomposition device is thus effectively used to generate a compressed gas that is required elsewhere, for example it may be needed in large quantities or at a lower pressure level elsewhere in the respective system network, to which the gas decomposition device and the target load also belong. The great advantage of this coupling according to the invention is that the energy stored in the excess target gas flow is used for the compressor, while simultaneously the excess target gas flow is decompressed via the compressor. In this way, the excess target gas flow, depending on the nature of the gas of which it consists, may be directly sent for re-use where it is needed at a lower pressure level.
The invention offers a particularly advantageous effect if the excess target gas is used not only to drive the compressor, but is also introduced into the pressure line fed by the compressor. For this purpose, the excess target gas flow may be mixed with the other gas to be compressed by the compressor, or with the compressed gas compressed by the compressor after or upon passing through the compressor.
Depending on the respective pressure level at which the excess target gas still is when leaving the compressor, or to which the gas to be compressed by the compressor is brought to by the compressor, this may be done by the target gas being mixed with the gas fed into the gas line in the flow direction downstream of the compressor. This avoids the problem of the excess target gas flow not being able to be fed directly into the compressed gas line usually as a result of the large pressure difference, as the proportion of the target gas or the resulting pressure increase in the compressed air line would be too great and there would be a risk of overloading the pressure line system.
Likewise, it is possible to supply the target gas to the suction side of the compressor after it has been decompressed via the compressor, so that it is mixed there with the other gas to be compressed and the resulting gas mixture is compressed by the compressor and fed into the compressed gas line.
Regardless of whether the admixing of the target gas to the other gas to be fed into the pressure line takes place upstream of the suction side or downstream of the pressure side of the compressor, for this purpose a system according to the invention may comprise a mixing device which is provided to mix the target gas or waste gas flow to be introduced into the pressure line with a further gas.
Another way to use the excess target gas flow to compress a gas and simultaneously feed it into the compressed gas line, consists in the choice of a compressor in which a drive gas flow, in this case the excess target gas flow, is fed into the respective compressor in such a way that it may be used as a propellant gas on the suction side of the compressor and accordingly entrain the gas to be compressed and compress the latter as a result of the pressure difference between the propellant gas and the gas to be compressed. The mixing of excess target gas with the other gas compressed in the compressor then takes place in the compressor itself.
The principle of such a gas jet compressor that is suitable for the purposes according to the invention is described in DE 91 01 135 U1. According to the invention, the compressor has a suction side, a drive side and an outlet side. The suction side is the side of the compressor to which the gas to be compressed is supplied. The outlet side is accordingly the side of the compressor from which the gas compressed in the compressor flows out. The drive side of the compressor according to the invention refers to the side of the compressor via which the propellant gas is supplied. The compressor therefore has two inlet volume flows: the volume flow on the drive side and on the suction side. The compressor compresses the gas supplied on the suction side as a result of the pressure difference between the compressed propellant gas and the decompressed gas fitted on the suction side.
The use according to the invention of an excess target gas flow occurring in a gas decomposition device proves to be particularly effective if the gas decomposition device is a conventional air separation unit which extracts oxygen as the target gas from the ambient air.
In principle, the method according to the invention may be applied to all gas decomposition devices, regardless of whether each of the gas flows obtained through the decomposition is fed to a target load or one or more of these gas flows is separated during the decomposition process as a waste gas flow for which there is no target load.
In the event that a waste gas flow results from the decomposition process, it may be expedient to collect the waste gas in a pressure accumulator and, if necessary, use this to drive the compressor. In this way, the waste gas may be used as a buffer for the time when, due to a large demand by the target load, there is not sufficient excess target gas flow available for the operation of the compressor. In this embodiment, the resulting waste gas flow that is generally high pressured as well is thus passed into a pressure accumulator, the waste gas is stored there, and then used when needed to drive the compressor. Another advantage of this embodiment is that due to the accumulator the compressor may be independent of the air separation process.
For this purpose, in a system according to the invention, an accumulator that is connected to an outlet of the gas decomposition device may be provided for a waste gas arising during the gas decomposition process.
If the waste gas should also be usable for the compression of the other gas, this may be accomplished by additionally connecting the accumulator to the drive side of the compressor via a supply line and providing a valve which releases the supply line when needed in order to drive the compressor with the waste gas stored in the accumulator.
Depending on its type and the type of the other gas to be compressed by the compressor and fed into the compressed gas line, it may also be expedient to mix the waste gas with the other gas to be compressed by the compressor, or the compressed gas compressed by the compressor.
In order to allow the mixture of waste gas with the other gas and the excess target gas optionally added, the accumulator may be connected on the outlet side to the suction side of the compressor or with the compressed gas line, in order to, if necessary, mix waste gas in the gas flow to be compressed by the compressor or in the compressed gas flow compressed by the compressor.
Regardless of where the mixing is done, the admixing of target gas or waste gas to the other gas proves to be particularly resource-saving. This applies, in particular, if the admixture of target gas and waste gas takes place simultaneously. By setting a certain mixing ratio for the admixed target and waste gas, the gas mixture formed from target gas, waste gas and the other gas and fed into the compressed gas line as compressed gas can offer optimised properties for the respective uses, or may at least be so composed that, despite the admixing of target gas or waste gas, there are at least no negative effects on the one or more other load(s) that are operated with the compressed gas mixture fed into the pressure line, and thereby the inherent energy in the target and waste gas may be used in an optimal way. In a system according to the invention, the addition of excess target gas and waste gas may be made possible by the fact that the system comprises a mixing device that is intended to mix a further gas to the target gas flow or waste gas flow that is to be introduced into the pressure line.
In the case of mixing before or in the compressor, it is of course possible to increase the proportions of the admixed target and waste gases in the gas mixture to be compressed by the compressor, so that at least temporarily, no, or almost no, other gas is needed any longer in order to produce the compressed gas flow fed into the pressure line.
Likewise, it is of course possible for the one gas, for example only the waste gas or only the excess target gas, to be admixed before or in the compressor, while the other gas may be added to the compressed gas after the compressor.
The possibility of admixing target or waste gas before, in or after the compressor is particularly advantageous, when the target gas is oxygen and the other gas to be compressed by the compressor is ambient air, and when the waste gas is made up from the other gases contained in the ambient air, in particular nitrogen. If only the excess oxygen target gas flow is to be added to the other gas (ambient air), then the admixed amount of oxygen may be so limited that a possibly critical oxygen content with respect to corrosion or oxidation of machine and line parts is not exceeded in the compressed gas fed into the pressure line. A typical limit here may be an oxygen content of 30 vol.-%. If nitrogen is also added at the same time, it is possible to produce a gas mixture which has a composition similar to that of ambient air, wherein here it is also possible to increase the proportion of excess target gas or waste gas present in each case to an innocuous limit. Another advantage of the, according to the invention, optionally provided admixture of excess oxygen target gas or waste gas comprising of nitrogen, and optionally the other gas constituents of the ambient air is that the cost of particle filtration, drying and oil separation that is customary in the field of compressed air production, is reduced, since both the waste gas as well as the target gas have already been subject to these operations in the gas decomposition device.

The method according to the invention is explained in more detail below with reference to a drawing, wherein:

FIG. 1 schematically shows a system for supplying a target load with a pressurised target gas flow and another load with another compressed gas.

FIG. 2 schematically shows a diagram illustrating the components of the method according to the invention and their interaction.

The system 1 shown in FIG. 1 for supplying a target load and at least one further load, is constructed as follows:
In the gas decomposition device 2, a highly pressurized target gas flow Z consisting of oxygen is generated from the ambient air U. In the decomposition process, a waste gas flow A consisting of the remaining gas constituents of the ambient air U, mainly nitrogen, is additionally separated in the gas decomposition device 2.
The target gas flow Z generated by the gas decomposition device 2 is supplied to a target load 4 via a supply line 3. However, the target load 4 decreases the target gas ZG only discontinuously, so that at times an excess target gas flow Zue is produced in the gas decomposition device 2.
The excess target gas flow Zue is guided via a propellant gas line 5 to the propellant gas inlet 6 of a compressor 7 that is in the form of a gas jet compressor. The commercially-available compressor 7 that is designed in a manner known per se, comprises a mixing chamber 8 with a suction connection 9 and a nozzle device 10, via which the excess target gas flow Zue is introduced into the mixing chamber 8. The nozzle device 10 is so designed that the discharged excess target gas flow Zue enters the mixing chamber 8 at high speed, entrains another gas G at the suction connection 9, and then enters a funnel-shaped compression chamber 10 a that tapers conically in the flow direction of the excess target gas flow Zue entering the mixing chamber 8, in which the gas mixture formed from the target gas flow Zue and the other gas G is compressed, so that it is fed as compressed gas DG into a compressed gas line 11. If it turns out that the power of the compressor 7 is not sufficient, it may be arranged in series with a conventional compressor which carries out the optionally still required final compression of the compressed gas DG to the respective specified pressure.
The compressed gas line 11 supplies various other loads 12,13,14 with compressed gas DG. In the event that no excess target gas flow Zue sufficient for the operation of the compressor 7 is available, pressurised gas DG is fed into the compressed gas line 11 via a conventional compressor 15.
The other gas G available at the suction connection 9 of the compressor 7, i.e. supplied separately from the excess target gas flow Zue, is mixed from waste gas AG and ambient air U. For this purpose, a mixing device 16 connected to the suction connection 9 is provided, that mixes ambient air U with a waste gas flow A′ in a specific mixing ratio. The mixing ratio is adjusted as a function of the excess target gas flow Zue guided into the compressor 7, so that, on the one hand, a sufficiently large pressure gas flow D enters the compressed gas line 11 and, on the other hand, the compressed gas DG fed into the compressed gas line 11 as a compressed gas flow D comprises an oxygen content, for example, between the oxygen content of normal air and 30 vol.-%. If a sufficiently large waste gas flow A′ is available, the amount of admixed ambient air U may be reduced to “0%”. Likewise, the oxygen content of the compressed gas DG may be set significantly higher if the corrosion resistance of the compressed gas line system 11, through which the pressurised gas DG flows, and the loads 13 which are supplied with the compressed gas DG, allow this.
The waste gas flow A′ reaches the mixing device 16 via a line 19, which is connected to an outlet of an accumulator 17. The accumulator 17 is fed by the gas decomposition device 2 with the waste gas flow A via a supply line 18. Another or several further loads 21 may be supplied with the waste gas AG via a supply line 20 connected to a further outlet of the accumulator 17. The gas decomposition device 2 is decoupled from the drive side of the compressor 7 by the accumulator 17.
FIG. 2 clarifies the sequence of the method according to the invention, implemented, for example, on a system of the type shown in FIG. 1, in a general form.
A gas mixture U (ambient air) is separated into compressed target gas ZG and waste gas AG in the gas decomposition device 2.
However, the waste gas AG is not vented unused into the environment, but is buffered in the accumulator 17.
A further load 21 may be supplied with the waste gas AG via the accumulator 17.
In addition, waste gas AG is supplied from the accumulator 17 to the mixing device 16. There, a gas mixture G is adjusted as a function of the excess target gas flow Zue introduced into the compressor 7, so that the composition of the compressed gas DG fed into the compressed gas line 11 corresponds to a target specification. If the waste gas flow A′ present in the mixing device 16 is insufficient, ambient air U may be added to the waste gas flow A′ in the mixing device 16.
In the compressor 7 the gas mixture G is compressed to the compressed gas DG, which is fed into the compressed gas line 11 as the compressed gas flow D and supplies the other loads 12-14.
If the available excess target gas flow Zue is not sufficient for the generation of a sufficiently large compressed gas flow D, compressed gas DG is additionally fed into the compressed gas line 11 via the compressor 15.

REFERENCE LIST

1 System
2 Gas decomposition device
3 Supply line
4 Target load
5 Propellant gas line
6 Propellant gas inlet
7 Compressor (gas jet compressor)
8 Mixing chamber
9 Suction connection
10 Nozzle device
10 a Compression chamber
11 Compressed gas line
12-14 Other loads
15 Compressor
16 Mixing device
17 Accumulator
18 Supply line
19 Line
20 Supply line
21 Further load(s)
A Waste gas flow
A′ Waste gas flow
AG Waste gas
D Compressed gas flow
DG Compressed gas
G Other gas
U Ambient air
Z Target gas flow
ZG Target gas
Zue Target gas flow

Claims

1. A method for utilising a target gas flow consisting of compressed target gas provided from a continuously operated gas decomposition device, comprising:

using the target gas flow to supply a target load;

using the target load to discontinuously decrease the target gas flow;

accruing an excess target gas flow that is not decreased by the target load;

supplying the excess target gas flow a propellant gas to a compressor;

compressing another gas; and

supplying the compressed gas in a compressed gas line which it is fed to another load.

2. The method according to claim 1, wherein the compressor is a gas jet compressor, comprising a drive side that is supplied with the excess target gas flow.

3. The method according to claim 1, wherein the target gas is oxygen, which is obtained by the gas decomposition device separating ambient air.

4. The method according to claim 1, wherein the excess target gas flow is mixed with the other gas before, during, or after its compression.

5. The method according to claim 1, wherein a waste gas flow results from the generation of the target gas the gas decomposition device.

6. The method according to claim 5, wherein the waste gas flow is fed to a pressure accumulator, the waste gas is stored there, and the waste gas is used to drive the compressor if necessary.

7. The method according to claim 5, wherein the waste gas is mixed with the other gas before or after compression.

8. The method according to claim 5, wherein both the excess target gas and the waste gas are mixed in a certain mixing ratio with the other before or after compression.

9. A system for supplying a target load with a compressed target gas flow and another load with another compressed gas, comprising:

a gas decomposition device, which provides a target gas flow to a target load that discontinuously decreases the target gas flow, so that an excess target gas flow is obtained in the gas decomposition device, and

a compressed gas operated compressor for compressing and feeding a compressed gas into a compressed gas line leading to another load,

wherein the compressor is connected to an outlet of the gas decomposition device on a drive side via a propellant gas line, through which the excess target gas flow flows as a propellant gas to a propellant gas connection of the compressor.

10. The system according to claim 9, wherein the compressor is a gas jet compressor.

11. The system according to claim 9, further comprising an accumulator which is connected to the outlet of the gas decomposition device for a waste gas arising during the gas decomposition process.

12. The system according to claim 11, wherein the accumulator is connected to the drive side of the compressor via a supply line, and a valve is provided to free the supply line if necessary, and drive the compressor by means of the waste gas stored in the accumulator.

13. The system according to claim 11, wherein the accumulator is connected on an outlet side to a suction side of the compressor or with the compressed gas line in order to mix the waste gas in a gas flow to be compressed by the compressor, or in a compressed gas flow compressed by the compressor.

14. The system according to claim 9, further comprising a mixing device which is intended to admix a further gas to the target gas or waste gas flow to be introduced into a pressure line.