CN1878999A - Method and installation for enriching a gas stream with one of the components thereof - Google Patents

Abstract

The invention relates to a method of enriching a pressurised gas stream (1) with one of the components (A) thereof. The inventive method comprises the following steps: the stream is separated into at least first and second fractions (2, 3); at least one part of the first fraction (2) is sent to a separation unit (ASU); the separation unit supplies at least two discharges, including a first discharge (10) having a greater A content than that of the fraction (2) supplied to the separation unit; at least one part of the first discharge (10) is mixed with at least one part of the second fraction (3) such as to form a pressurised gas mixture (15); the second fraction (3) is expanded and, subsequently, at least one part of the first discharge (10) is mixed therein.

Description

Method and apparatus for enriching a component in a gas stream

technical field

The present invention relates to a method and apparatus for enriching a component of a gas stream. In particular, the invention relates to a method of enriching oxygen in air.

Background technique

Oxygen enrichment of the air has become necessary in the steel industry.

Reducing or eliminating hot coke in blast furnaces - often beneficial for pulverized coal injection (CPI) - requires this necessary shift.

It is known from EP-A-0 531 182 that a device for economically achieving this enrichment consists in cryogenic distillation of a portion of the air stream to be supplied to the blast furnace. Thereby, a nitrogen-enriched stream and an oxygen-enriched stream are obtained, which are then remixed into the air stream downstream of the air separation unit.

Since the pressure of the oxygen stream is close to that of the air stream fed to the air separation unit (ASU), a process involving a mixing column will prove particularly suitable and economical.

Figure 1 shows the separation unit described in EP-A-0 531 182 for enriching oxygen in air. It is supplied by the air system at pressure P which constitutes the charge of the blast furnace. The air distillation unit is used to produce low purity e.g. ^a purity of ^80-97 % preferably 85-95% oxygen.

The unit essentially comprises a heat exchange line 1A, a double distillation column 2A comprising a medium pressure column 3A, a low pressure column 4A and a main condenser-reboiler 5A, and a mixing column 6A. Columns 3A and 4A typically operate at pressures of about 5.45×10 ⁵ Pa and about 1.5×10 ⁵ Pa, respectively.

As specified in document US-A-4 022 030, a mixing column is of the same construction as a distillation column, but is used to combine the more volatile gases introduced at the bottom of the column with those at the top of the column in a nearly reversible manner. The introduced less volatile liquid phase mixes the column.

This mixing generates refrigeration energy, thus allowing to reduce the energy consumption associated with distillation. In the present example, this mixing is advantageously also used for the impure oxygen to be produced directly at the pressure P, as will be explained below.

With respect to FIG. 1 , the gas stream is compressed to mixing column pressure by compressor 14A, cooled in heat exchange line 1A, subcooled in subcooler 21A, and sent to the bottom of mixing column 6A.

The "rich liquid" (oxygen-enriched air) drawn from the bottom of column 3A is introduced into column 4A after being expanded through expansion valve 10A. The "lean liquor" (impure nitrogen) withdrawn from the middle position 11A of column 3A is introduced into the top of column 4A after being expanded by expansion valve 12A, thereby forming the waste gas of the plant, which may be produced at the top of column 3A The medium-pressure pure gaseous nitrogen is heated in the heat exchange line 1A, and then discharged from the equipment. These gases are indicated by NI and NG in Fig. 1, respectively.

The higher or lower purity liquid oxygen produced according to the configuration of the double tower 2A is drawn from the bottom of the tower 4A, raised to a pressure P1 slightly higher than the aforementioned pressure P by a pump 13A so as to reduce the pressure drop (P1- P less than 2×10 ⁵ Pa) is taken into account, and then this liquid oxygen is introduced into the top of column 6A.

Three fluid streams are drawn from the mixing tower 6A: from its base a liquid similar to the rich liquid is drawn and mixed with the rich liquid through a line 15A provided with an expansion valve 15A'; from an intermediate position mainly composed of oxygen and A mixed fluid composed of nitrogen, and the mixed fluid is sent to the middle position of the low-pressure column 4A through a pipeline 16A provided with an expansion valve 17A; After the temperature rises in the road, it is basically discharged from the equipment as the finished gas OI at the pressure P through the pipeline 18A.

The figures also show auxiliary heat exchangers 19A, 20A, 21A for recovering usable cold from the fluid circulating in the unit.

Figure 2 schematically shows a prior art integrated plant for enriching an air stream for a blast furnace.

The air flow is compressed in the blower S to form a compressed air flow 1 . This gas flow is split into two branches 2 and 3 . The first branch 2 is cooled by a cooler R, for example a water cooler, compressed in a booster C and sent to an air separation unit (ASU). The air separation unit works, for example, by cryogenic distillation and comprises a purification/purification device and heat exchange lines upstream of the separation column. It produces an oxygen stream 10 with an oxygen content of 80-95 mol% and a nitrogen stream 11 which may be a waste stream. At least a part of the oxygen-enriched stream 10 is mixed with the second air branch 3 . The oxygen-enriched mixed stream 15 is heated in a Coppey stove W and then sent to the blast furnace HF.

To counteract the pressure drop in the circuit comprising the air separation unit (from the blast furnace inlet to the separation unit and reinjection of the oxygen stream), a compressor C is installed. This makes it possible to increase the pressure of the total gas stream fed to the air separation unit (according to FIG. 2 ) or (as a variant of FIG. 1 ) the gas stream used to supply the mixing column (ie about 30% of the air stream treated by the separation unit).

Contents of the invention

It is an object of the present invention to integrate an air separation unit into the steelmaking process in a more economical and reliable manner without using any gas stream compressors in the air separation unit, except those used to maintain the refrigeration of the separation unit Other than the compressor connected to the shaft of the turbo expander.

A subject of the invention is a method for enriching a component A in a pressurized gas stream, the method comprising the steps of:

i) dividing the gas stream into at least a first branch and a second branch;

ii) sending at least a portion of the first branch to a separation unit;

iii) at least a first stream and a second stream are provided by the separation unit, the content of component A of the first stream being greater than the content of component A in the first branch;

iv) mixing at least a portion of the first stream with at least a portion of the second branch to form a pressurized mixed gas,

It is characterized in that the second branch is expanded before being mixed with at least a part of the first flow.

According to other optional aspects:

- the pressurized gas flow is substantially at the same pressure as the first branch, in particular only a pressure drop is responsible for the pressure difference between the two fluids;

- the pressures of the first flow and the expanded second branch are substantially the same, in particular only the pressure drop is responsible for the pressure difference between these two fluids;

- the separation unit is independent in terms of energy requirements for compressing the gas stream produced by or supplied to the unit;

- the pressurized gas stream is air, and optionally, said component A is oxygen;

- the pressurized gas stream is the air supplied to the blast furnace;

- the separation unit is a cryogenic distillation separation unit;

- the separation unit comprises a medium-pressure column, a low-pressure column thermally connected to the medium-pressure column, and a mixing column; and

- No compression of the part of the first branch feeding the distillation column or no compression of the part of the first branch feeding the mixing column or the medium pressure column after the gas flow has been divided.

According to a specific method of operation: i) in a first operation, at least a part of the first branch is compressed, and the second branch is not expanded before being mixed with at least a part of the first stream; and ii) in a second operation, (eg, when compressor C is not operating) at least a portion of the first branch is not compressed (the first branch is not compressed), and the second branch is expanded prior to mixing with at least a portion of the first stream.

Another subject of the invention is a device for enriching a component A in a pressurized gas stream, comprising:

i) means for dividing the flow of pressurized gas into at least a first branch and a second branch;

ii) separation unit;

iii) means for sending at least a portion of the first branch to the separation unit; and

iv) means for mixing at least a portion of the first stream produced by the separation unit and enriched in A compared to the first branch with the second branch to form a gas stream rich in A compared to the pressurized gas stream,

It is characterized in that the device comprises means for expanding the second branch upstream of said means for mixing the second branch with at least a part of the first flow and downstream of said means for dividing the gas flow.

According to other optional aspects:

- the separation unit is an air separation unit comprising a medium pressure column, a low pressure column thermally connected to the medium pressure column and a mixing column;

- the equipment does not include any means for compressing the air supplied to the medium-pressure column or supplied to the mixing column; and

- The apparatus comprises means for compressing the second branch, and means for conveying the second branch to mix with at least a part of the first flow without passing through the expansion device.

Advantageously, the separation process uses a mixing column operating at a pressure equal to or higher than that of the medium-pressure column without the need for additional air compression equipment.

Thus, the present invention proposes to integrate the mixing tower unit into the blast furnace blower without requiring an additional air compressor, thus increasing the reliability of delivery of oxygen molecules and oxygen-enriched air to the blast furnace while minimizing the investment required for this structure.

Another subject of the invention is a method for separating air using a plant comprising at least one medium-pressure column, a low-pressure column thermally connected to the medium-low pressure column, and a Mixing tower, where:

i) sending the compressed and purified air to the medium pressure column;

ii) sending the nitrogen-enriched stream and the oxygen-enriched stream from the medium-pressure column to the low-pressure column;

iii) sending oxygen-enriched liquid from the low pressure column to the top of the mixing column; and

iv) extracting oxygen-enriched gas from the top of the mixing tower,

It is characterized in that a nitrogen-enriched liquid stream is withdrawn from a medium-pressure column, the nitrogen-enriched liquid stream is pressurized and at least partially vaporized, and at least a portion of the vaporized liquid is supplied at the bottom of the mixing column.

Preferably, the nitrogen-enriched liquid is vaporized by heat exchange with a portion of the supplied air. Thus, the liquefied air can be sent to at least one of the medium pressure column and the low pressure column.

The nitrogen-enriched liquid is pressurized by a pump and/or hydrostatically.

Another subject of the invention is an air separation plant comprising:

a) medium pressure tower;

b) the low pressure column thermally connected to the medium and low pressure column;

c) a mixing column operating at a pressure higher than that of the medium-pressure column;

d) means for sending compressed purified air to the medium-pressure column;

e) means for sending a nitrogen-enriched stream and an oxygen-enriched stream from the medium-pressure column to the low-pressure column;

f) means for sending oxygen-enriched liquid from the low pressure column to the top of the mixing column; and

g) means for extracting oxygen-enriched gas from the top of the mixing tower,

It is characterized in that the plant comprises means for withdrawing a stream of oxygen-enriched liquid from the medium-pressure column, means for pressurizing the liquid, means for at least partially vaporizing the liquid and for supplying at the bottom of the mixing column A device for at least partially vaporizing a liquid.

Description of drawings

The invention will be described in more detail below with reference to FIGS. 3 , 4 and 5 . In the attached picture:

Figure 1 shows a prior art separation unit for enriching oxygen in air;

Figure 2 schematically shows a prior art integrated plant for enriching air streams for blast furnaces;

Figure 3 shows a unit for enriching a gas stream according to the invention;

Figure 4 shows a separation unit particularly suitable for carrying out the invention;

Figure 5 shows a unit for enriching a gas stream according to the invention.

Detailed ways

Figure 3 shows an integrated unit for enrichment of the air stream fed into a prior art blast furnace.

The air flow is compressed in the blower S to form a compressed air flow 1 . This gas flow is split into two branches 2 and 3 . The first branch 2 is cooled by a cooler R, for example a water cooler, and is sent to the air separation unit (ASU) without compression between the cooler and the inlet of the air separation unit. The air separation unit works by, for example, cryogenic distillation and comprises a purification unit and heat exchange lines upstream of the separation column. The air separation unit produces a nitrogen stream 11 which may be a waste stream and an oxygen stream 10 containing 80-95 mol% oxygen. The second air branch 3 is expanded by means of an expansion device V, which may be eg a valve, an orifice, a pipe of reduced diameter or a turbine. Downstream of the expansion device V at least a portion of the oxygen-enriched stream 10 is mixed with the expanded second air branch 3 . The oxygen-enriched mixed stream 15 is heated in Cowpers W and sent to the blast furnace HF.

This solution eliminates the need for an air booster for boosting the pressure upstream of the air separation unit. Therefore the energy consumption of the whole system is reduced.

FIG. 4 employs elements with the same reference numbers as in FIG. 1 , and the elements will not be described in detail again.

Medium pressure purified air 7A at 5.45 bar a from the main air compressor for the blast furnace tuyere or from the turboexpander is split into at least two separate streams before entering the medium pressure column 2A.

The first stream 100 is fed directly to the bottom of the medium-pressure column 2A in gaseous form.

The second stream 200 is at least partially condensed in the heat exchanger 101A. The liquefied fraction is introduced into one of the distillation columns (medium-pressure column 2A or low-pressure column 4A). In Figure 4, stream 202 is sent to the bottom of the medium pressure column, while stream 204 is sent to the low pressure column after being subcooled in heat exchanger 19A.

A liquid stream 300 rich in nitrogen compared to air is withdrawn from medium pressure column 3A, compressed by pump 400 or simple hydrostatic height, vaporized against condensation of medium pressure air in heat exchanger 101A to form a gaseous nitrogen stream 500. The gaseous nitrogen stream is then supplied to the bottom of mixing column 6A. Thus, thanks to the difference in composition between the air and the nitrogen-enriched stream, the feed to the mixing column 6A is achieved at a higher pressure than the air 100 fed to the medium-pressure column 3A, so that no additional compressor is required .

It is also contemplated to raise the temperature of gaseous nitrogen 500 in the main heat exchange line before introducing the gaseous nitrogen into the mixing column.

To produce a gaseous nitrogen stream 500 of 5.9 bar a, heat exchanger 101A has an AT of 0.6°C.

Stream 15A from the bottom of mixing column 6A, which is richer in nitrogen than the stream in Figure 1, is sent immediately below the top of lower pressure column 4A.

(This embodiment) The subcooler 21A is omitted, and medium-pressure gaseous nitrogen NG is no longer extracted.

Optionally, a third air stream is fed into supercharger 8A, cooled in heat exchange line 1A, and expanded in blower turbine 9A, but other refrigeration arrangements are also conceivable, including using A device for expanding the air supplied to the medium pressure column.

An advantage of the invention, if such a booster is present, is that no air compression step is required for the air supplied to the mixing column or the medium pressure column.

As far as Figure 4 is concerned, the extraction efficiency decreases, while the separation energy of this system remains better than that of the base case.

However, integration of the air separation unit of Fig. 4 into the arrangement disclosed in the variant shown in Fig. 3 does make it possible to reduce the pressure drop in the valves considerably.

Figure 5 shows an integrated unit for enrichment of the air stream fed into a prior art blast furnace.

The air flow is compressed in the blower S to form a compressed air flow 1 . This gas flow is split into two branches 2 and 3 . The first branch 2 is cooled by a cooler R, for example a water cooler, compressed in a booster C and sent to an air separation unit (ASU). The air separation unit works, for example, by cryogenic distillation and comprises a purification unit and heat exchange lines upstream of the separation column. The air separation unit produces a nitrogen stream 11 which may be a waste stream and an oxygen stream 10 containing 80-95 mol% oxygen. The second air branch 3 is expanded by means of an expansion device V, which may be eg a valve, an orifice, a pipe of reduced diameter or a turbine. Downstream of the expansion device V at least a portion of the oxygen-enriched stream 10 is mixed with the expanded second branch 3 . The oxygen-enriched mixed stream 15 is heated in a Coppey stove W and sent to the blast furnace HF. The supercharger C and valve V have a short-circuit device. In a first operation of the unit, the first branch 2 is compressed and the second branch is not expanded. In a second operation, at least a portion of the first branch is compressed and a second branch is expanded prior to mixing with at least a portion of the first stream.

Evaluation of variants:

current technology blower Air to ASU _O2 in HF Enriched Air in HF flow Nm ³ /h 400000 146700 3748 95% _O2 productivity 284048 Element N ₂ O ₂ Ar 0.7811 0.7811 0.03 0.700 0.2096 0.2096 0.95 0.290 0.0093 0.0093 0.02 0.010 1 1 1 1 pressure bar a 5.85 5.55 5.50 5.50 energy kW 30686 1201 31887

Variant 1 with expansion valve (fig. 3) blower Air to ASU _O2 in HF Enriched Air in HF flow Nm ³ /h 4000000 1467000 307480 95% _O2 productivity 2840480 Element N ₂ O ₂ Ar 0.7811 0.7811 0.03 0.700 0.2096 0.2096 0.95 0.290 0.0093 0.0093 0.02 0.010 1 1 1 1 pressure bar a 6.85 6.55 5.50 5.50 energy KW 33428 33428

Variant 2 of the air separation process with expansion valve (Figure 3) and Figure 4 blower Air to ASU _O2 in HF Enriched Air in HF flow Nm ³ /h 417259 163959 30748.32 85% _O2 productivity 284048 Element N ₂ O ₂ Ar 0.7811 0.7811 0.03 0.700 0.2096 0.2096 0.95 0.290 0.0093 0.0093 0.02 0.010 1 1 1 1 pressure bar a 6.23 5.93 5.50 energy kW 33151 33151 current technology Variant 1 Variant 2 reference case Total cost kW 100100 89105 96104 Air blower 9595 for mixing tower

Claims (14)

1. the method for a kind of composition A in the enrichment flow of pressurized gas may further comprise the steps:

I) this gas stream (1) is divided at least the first branch (2) and second branch (3);

Ii) at least a portion of first branch (2) is sent into separative element (ASU);

Iii) provide first-class at least by this separative element and second stream, the content of the composition A of these first-class (10) is greater than the content of the composition A in this first branch;

Iv) this first at least a portion is mixed the mist (15) that pressurizes to form with at least a portion of this second branch,

It is characterized in that, make second branch with expand before first at least a portion is mixed.

2. the method for claim 1 is characterized in that, this flow of pressurized gas (1) is in identical pressure substantially with described first branch (2), and particularly, having only pressure drop is the reason that causes the pressure gap between these two kinds of fluids.

3. method as claimed in claim 1 or 2 is characterized in that, described first-class second branch with expansion is in identical pressure substantially, and particularly, having only pressure drop is the reason that causes the pressure gap between these two kinds of fluids.

4. each described method in the claim as described above is characterized in that, described separative element (ASU) is being used to compress by this unit production or to supply with aspect the energy requirement of gas stream of this unit be independently.

5. each described method in the claim as described above is characterized in that described flow of pressurized gas is an air, and randomly, described composition A is an oxygen.

6. method as claimed in claim 5 is characterized in that, described flow of pressurized gas is to supply with the air of blast furnace (HF).

7. each described method in the claim as described above is characterized in that described separative element is low temperature distillation separative element (ASU).

8. method as claimed in claim 7 is characterized in that, described separative element (ASU) comprises medium pressure column (2A), is thermally connected to the lower pressure column (4A) and the mixing column (6A) of this medium pressure column.

9. method as claimed in claim 8 is characterized in that, in step I) in gas stream divided after, do not compress first branch the supply destilling tower part or do not compress the supply mixing column of first branch or the part of medium pressure column.

10. a described method in the claim as described above, wherein:

I) in first kind of operation, compress at least a portion of first branch, second branch with do not expand before first at least a portion is mixed; And

Ii) in second kind of operation, do not compress at least a portion of first branch-do not compress first branch, make second branch with expand before first at least a portion is mixed.

11. be used for the equipment of a kind of composition A of enrichment flow of pressurized gas, this equipment comprises:

I) be used for this flow of pressurized gas (1) is divided into the device of at least the first branch (2) and second branch (3);

Ii) separative element (ASU);

Iii) be used at least a portion of first branch (2) is delivered to the device of this separative element;

Iv) be used for and will mix by at least a portion this separative element production and compare first-class (10) of being rich in composition A with first branch and this second branch forming the device of comparing the stream (15) that is rich in composition A with this flow of pressurized gas,

It is characterized in that this equipment comprises the device (V) that is used in the described upstream that makes the device that first at least a portion mixes with second branch and in the downstream of the device of described division gas stream this second branch is expanded.

12. equipment as claimed in claim 11 is characterized in that, the separative element of this equipment is to comprise medium pressure column (3A), be thermally connected to the lower pressure column (4A) of this medium pressure column and the air gas separation unit (ASU) of mixing column (6A).

13. equipment as claimed in claim 12 is characterized in that, this equipment does not comprise any device that is used for supplying with in the downstream compression of the device of described division gas stream the air of this medium pressure column or mixing column.

14. as claim 11 or 12 described equipment, it is characterized in that this equipment comprises the device that is used to compress second branch, and be used to transport second branch so that its device that under the situation of the expansion gear of not flowing through, mixes with first at least a portion.

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