Method And Installation For Enriching A Gas Stream With One Of The Components Thereof

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

The invention will be described in greater detail with reference to FIGS. 3, 4 and 5. FIGS. 3 and 5 show a unit for enriching a gas stream according to the invention and FIG. 4 shows a particularly suitable separation unit for carrying out the invention.

FIG. 3 shows schematically an integrated unit for the enrichment of an airstream intended for a blast furnace according to the prior art.

A stream of air is compressed in a blower S in order to form a compressed stream 1. This stream is divided into two fractions 2 and 3. The first fraction 2 is cooled by means of a chiller R, for example a water chiller, and sent to an air separation unit (ASU) without being compressed between the chiller and the inlet of the air separation unit. The air separation unit operates for example by cryogenic distillation and includes a purification unit and an exchange line upstream of the separation columns. It produces an oxygen stream 10 containing between 80 and 95 mol % oxygen and a nitrogen stream 11, which may be a waste stream. The second air fraction 3 is expanded by means of an expansion means V, which may for example be a valve, an orifice, a reduced-diameter pipe or a turbine. At least one portion of the oxygen-enriched stream 10 is mixed, downstream of the expansion means V, with the expanded second air fraction 3. The oxygen-enriched, mixed stream 15 is heated in a cowpers W and sent to a blast furnace BF.

This solution dispenses with the air booster for raising the pressure upstream of the air separation unit. The consumption of energy of the whole system will therefore be better.

FIG. 4 adopts elements of FIG. 1 having the same reference numerals, which will not be described in detail.

The purified air 7a at the medium pressure of 5.45 bara coming from the main air compressor for the blast furnace wind or from an expansion turbine is separated into at least two separate flows before entering the medium-pressure column 2A.

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

The second flow 200 is at least partly condensed in a heat exchanger 101A. The liquefied portion is introduced into one of the distillation columns (either the medium-pressure column 2A or the low-pressure column 4A). In FIG. 4, the stream 202 is sent to the bottom of the medium-pressure column, whereas the stream 204 is sent to the low-pressure column after being subcooled in the exchanger 19A.

A liquid stream 300 enriched in nitrogen compared to air is withdrawn from the medium-pressure column 3A, compressed by means of a pump 400 or by a simple hydrostatic height, vaporized in the heat exchanger 101A against the condensation of medium-pressure air, in order to form a gaseous nitrogen stream 500 which is then fed into the bottom of the mixing column 6A. Thus, profiting from the difference in composition between the air and the nitrogen-enriched stream, the feed for the mixing column 6A takes place at a pressure above that of the air 100 feeding the medium-pressure column 3A, and does so without an additional compressor.

It is also conceivable to warm the gaseous nitrogen 500 in the main exchange line before introducing it into the mixing column.

To produce a gaseous nitrogen stream 500 at 5.9 bara, the heat exchanger 101A has a ΔT of 0.60° C.

The stream 15A coming from the bottom of the mixing column 6A, being richer in nitrogen than that of FIG. 1, is sent to just below the top of the low-pressure column 4A.

The subcooler 21A is omitted and there is no longer any withdrawal of medium-pressure gaseous nitrogen NG.

Optionally, a third flow of air is sent to a booster 8A, cooled in the exchange line 1A and expanded in the blowing turbine 9A, but other means of refrigeration are conceivable, including expansion of the air intended for the medium-pressure column.

If this booster is present, the advantage of the invention is that there is no need for an air compression step for air intended for the mixing column or for the medium-pressure column.

In the case of FIG. 4, the extraction efficiency is reduced and the separation energy of the system remains superior to the base case.

However, integrating the air separation unit of FIG. 4 into the scheme disclosed in the variant shown in FIG. 3 does allow the pressure drop in the valve to be considerably reduced.

FIG. 5 shows schematically an integrated unit for enriching a stream of air intended for a blast furnace according to the prior art.

A stream of air is compressed in a blower S in order to form a compressed stream 1. This stream is divided into two fractions 2 and 3. The first fraction 2 is cooled by means of a chiller R, for example a water chiller, compressed in a booster C and sent to an air separation unit (ASU). The air separation unit operates for example by cryogenic distillation and includes a purification unit and an exchange line upstream of the separation columns. It produces an oxygen stream 10 containing between 80 and 95 mol % oxygen and a nitrogen stream 11, which may be a waste stream. The second air fraction 3 is expanded by means of an expansion means V, which may for example be a valve, an orifice, a reduced-diameter pipe or a turbine. At least one portion of the oxygen-enriched stream 10 is mixed, downstream of the expansion means V, with the expanded second air fraction 3. The oxygen-enriched, mixed stream 15 is heated in a cowpers W and sent to a blast furnace BF. The booster C and the valve V have short-circuiting means. In a first operation of the unit, the first fraction 2 is compressed and the second fraction is not expanded. In a second operation, at least one portion of the first fraction is not compressed and the second fraction is expanded before at least one portion of the first stream is mixed therewith.

Evaluation of the Variants

Prior Art

		BLOWER	Air sent to the ASU	O2 at the BF		Enriched air at the BF
FLOW RATE	Sm3/h	400 000	146 700	3 748	95% O2	284 048
					eff.
Composition	N2	0.7811	0.7811	0.03		0.700
	O2	0.2096	0.2096	0.95		0.290
	Ar	0.0093	0.0093	0.02		0.010
		1	1	1		1
PRESSURE	bara	5.85	5.55	5.50		5.50
ENERGY	kW	30 686	1201			31 887

Variant 1 With an Expansion Valve (FIG. 3)

		BLOWER	Air sent to the AsU	O2 at the BF		Enriched air at the BF
FLOW RATE	Sm3/h	400 000	146 700	30 748	95% O2	284 048
		0	0	0	eff.	0
Composition	N2	0.7811	0.7811	0.03		0.700
	O2	0.2096	0.2096	0.95		0.290
	Ar	0.0093	0.0093	0.02		0.010
		1	1	1		1
PRESSURE	bara	6.85	6.55	5.50		5.50
ENERGY	kW	33 428				33 428

Variant 2 With Expansion Valve (FIG. 3) and Air Separation Method of FIG. 4

						Enriched
		BLOWER	Air sent to the ASU	O2 at the BF		air at the BF
FLOW RATE	Sm3/h	417 259	163 959	30 748.32	85% O2	284 048
					eff.
Composition	N2	0.7811	0.7811	0.03		0.700
	O2	0.2096	0.2096	0.95		0.290
	Ar	0.0093	0.0093	0.02		0.010
		1	1	1		1
PRESSURE	bara	6.23	5.93	5.50
ENERGY	kW	33 151				33 151
				REF. CASE
	Prior art	VARIANT 1	VARIANT 2	Air blower intended for the mixing column
Overall cost	100	89	96	95
kW	100	105	104	90

Claims

1-14. (canceled)

15. A method of enriching a pressurized gas stream with one of its constituents A, which comprises the steps of: a) dividing the stream (1) into at least first and second fractions (2, 3);b) sending at least one portion of the first fraction (2) into a separation unit (ASU);c) supplying, from the separation unit, at least first and second streams, the first stream (10) of which has a content of constituent A greater than that of the first fraction; andd) mixing at least one portion of the first stream with at least one portion of the second fraction in order to form a pressurized gas mixture (15), characterized in that the second fraction is expanded before at least one portion of the first stream is mixed therewith.

16. The method of claim 15, in which the pressurized gas stream (1) and the first fraction (2) are substantially at the same pressure and, in particular, only the pressure drops are the cause of a variation in pressure between these two fluids.

17. The method of claim 15, in which the first stream and the expanded second fraction are substantially at the same pressure and, in particular, only the pressure drops are the cause of a variation in pressure between these two fluids.

18. The method of claim 15, in which the separation unit (ASU) is autonomous in terms of energy requirements for compressing the gas streams produced by the unit or intended for the unit.

19. The method of claim 15, in which the pressurized gas stream (1) is air and optionally constituent A is oxygen.

20. The method of claim 19, in which the pressurized gas stream is air intended for a blast furnace (BF).

21. The method of claim 15, in which the separation unit is a cryogenic distillation separation unit (ASU).

22. The method of claim 21, in which the separation unit (ASU) comprises a medium-pressure column (2A), a low-pressure column (4A) thermally coupled to the medium-pressure column, and a mixing column (6A).

23. The method of claim 22, in which no portion of the first fraction intended for a distillation column is compressed or no portion of the first fraction intended for the mixing column or for the medium-pressure column is compressed after the stream is divided at step i).

24. The method of claim 15, in which: a) in a first operation, at least one portion of the first fraction is compressed and the second fraction is not expanded before at least one portion of the first stream is mixed therewith; andb) in a second operation, at least one portion of the first fraction is not compressed (the first fraction is not compressed) and the second fraction is expanded before at least one portion of the first stream is mixed therewith.

25. An installation for enriching a pressurized gas stream with one of its constituents A, which comprises: a) means for dividing the pressurized gas stream (1) into at least first and second fractions (2, 3);b) a separation unit (ASU);c) means for sending at least one portion of the first fraction (2) to the separation unit; andd) means for mixing at least one portion of a first stream (10), produced by the separation unit and enriched in A compared to the first fraction, with the second fraction in order to form a stream (15) enriched in A compared to the pressurized gas stream,

26. The installation of claim 25, the separation unit of which is an air separation unit (ASU) comprising a medium-pressure column (3A), a low-pressure column (4A) thermally coupled to the medium-pressure column, and a mixing column (6A).

27. The installation of claim 26, which does not include any means for compressing air intended for the medium-pressure column or for the mixing column downstream of the means for dividing the gas stream.

28. The installation of claim 25, which includes means for compressing the second fraction and means for forwarding the second fraction to be mixed with at least one portion of the first stream without passing via the expansion means.