WO2009024672A2

WO2009024672A2 - Integration of several separation units

Info

Publication number: WO2009024672A2
Application number: PCT/FR2008/000950
Authority: WO
Inventors: Alain Briglia; Laurent Samy
Original assignee: L'air Liquide Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Priority date: 2007-07-12
Filing date: 2008-06-26
Publication date: 2009-02-26
Also published as: WO2009024672A3; FR2918741A1

Abstract

An air separation installation by cryogenic distillation comprises at least three cold chambers (5,5'), at least three air scrubbers (3,3'), at least two main air compressors (1) to compress air from ambient pressure, means (12) for delivering nitrogen from at least two cold chambers to at least two scrubbing devices passing through a collector and means (15,16) for delivering nitrogen to at least one other of the cold chambers and to at least one other scrubbing device without passing through the collector.

Description

Integration of several separation units

The present invention relates to the integration of several separation units.

The present invention is applicable to processes for separating air gases by cryogenic distillation, in particular of the internal compression type

(Oxygen gas is produced by vaporization under pressure in the exchange line) for example in the presence of air boosters, where at least three (n) cold boxes are fed by at least two (m) main air compressors and possibly (p) air boosters, with (q) air cooling towers by direct contact with water, at least three (r) overhead cleaners to purify the air, (s) towers cooling water by direct contact with nitrogen from an air separation apparatus, where p ≠ 1, q ≠ 1, s ≠ 1

When several air separation units of the same or different sizes are installed on the same site, it may be necessary in some cases to maximize the size of some type of machine or equipment and thus have less equipment to be installed or to avoid installing machine or equipment sizes out of known industrial references compatible with the size of the cold boxes or to improve the reliability of the site. o reuse existing machinery or equipment that is not necessarily compatible with the size of the cold box (s), thus limiting the investment

For this, the creation of collectors or networks, interconnecting the different equipment between them is a solution. The collectors or networks that can be used to solve the problems mentioned above can be broken down as well (note that not all the networks listed below are necessarily installed): o medium-pressure humid air network, medium-pressure dry air network, interconnecting the air compressors, before and after the overhead treatment o The humid air network makes it possible to accommodate a number of air compressors. different main air downstream equipment. For example :

• m main compressor (s) of air supplying q turns air water with q = m + x, or r purifications with r = m + x; where m ≥ 1 etx≥ 1

• m main air compressors supplying q tower (s) air water with q = m - x, or r purifications with r = m-x; where m-x> O and x ≠ O o The medium-pressure dry air network accommodates a different number of purification at the head of downstream equipment

• r purification (s) at the head supplying n cold boxes with n = r + x, or p air booster compressors with p = r + x; where r ≥ 1 and x ≥ 1 • head cleaning feeding n cold box (s) with n = r - x, or p air booster compressors with p = r-x; where rx> Oetx ≠ O o high pressure air network interconnecting the air booster compressors at the outlet o The high pressure dry air network makes it possible to accommodate a number of air compressors different from the number of equipment downstream. For example :

• compressor (s) air booster supplying n cold boxes with n = p + x; where p> 1 and x ≥ 1

• p air booster compressors supplying n cold box (s) with n = px; where px> 0 and x ≠ O o Note: In the case where there are several air overpressure compressors, it may be advantageous to slightly oversize each air compressor to improve the reliability of the site. In fact under normal conditions all air pressure compressors operate at a reduced load (preferably above 70%), and when one of these air compressors stops, the other pressure boosters remaining are pushed to their maximum so as to compensate either totally or partially the high pressure air deficit • Maximum capacity of a machine complies with the following rule:

C ^M = _C -Mr ≥ 0.70 with:

o C ^M = capacity of a machine in maximum running o C ^τ = total capacity of machines in nominal operation o C ^E = erasable capacity o N ^BAC = total number of compressors installed o C ^N = capacity of a machine in nominal operation reduced o network of impure nitrogen interconnecting the adsorber regeneration circuits o The largest portion of the waste nitrogen produced is generally used in the water cooling tower by direct contact with nitrogen from a cooling device. air separation which is close to the cold box to minimize the size of the collectors. The other part of the flow is sent into an impure nitrogen network which feeds certain adsorbers individually in order to ensure their regeneration. For example :

• n cold boxes feeding the treatment (s) at the head with r = n - x; where n - x> 0 and x ≠ O A cold box fed by two head purifications has two different fluids to regenerate each purification at the head. This avoids stalling the entire pressure circuit of the air separation unit on the worst performing head cleaning in pressure drop. For these purposes, a fluid that is not dependent on the residual nitrogen may be used, such as expanded medium-pressure nitrogen, for example.

A cold water network interconnects the cooling circuits resulting from the nitrogen water towers supplying the water air towers. The cold water network resulting from the direct contact turns of water cooling by heat exchange with nitrogen is revealed. Useful when the number of direct contact water nitrogen turns is different from the number of direct air water contact turns. For example :

^• turn (s) nitrogen water feeding q turns air water with q = s + x; where s> 1 and x> 1 • s turns nitrogen water feeding q tower (s) air water with q = s - x; where s - x> 0 and x ≠ O

For all the networks or collectors mentioned above, the networks or collectors also make it possible to connect together equipment of identical function but of different size, thus globalizing the flows, to be able to redistribute them on downstream equipment equal in number to those upstream but of different sizes having a total capacity identical to the upstream equipment.

According to an object of the invention, there is provided an air separation installation by cryogenic distillation comprising n cold boxes where n> 3, r air cleaning apparatus where r≥ 3,, m main air compressors where m≥ 2 to compress the air from the ambient pressure and connected to the n cold boxes to supply compressed air, a nitrogen collector from at least a first and a second of the cold boxes connected to at least a first and a second air cleaning apparatus characterized in that at least one third air cleaning apparatus is not connected to the nitrogen trap and is connected by a supply line of nitrogen to at least a third of the cold boxes.

According to other optional features: - the third air purification device not connected to the collector, the nitrogen supply line and the third cold boxes connected to the supply line are connected through an expansion means d nitrogen.

the expansion means is a turbine.

- The third cold box is connected to the first, second and third air cleaning apparatus for receiving purified air from these devices.

the third purification device is connected to the third cold box so that in operation it receives nitrogen of a purity different from that of the nitrogen circulating in the collector. the third purification device is connected to the third cold box so that in operation it receives nitrogen with a pressure different from that of the nitrogen circulating in the collector.

each of the cold boxes comprises a double air separation column constituted by a medium pressure column and a low pressure column, the medium pressure columns of each of the cold boxes preferably operating substantially at the same pressure and the low pressure columns of each of the cold boxes preferably operating substantially at the same pressure. - The nitrogen collector is connected to the low pressure columns of the first and second cold boxes while the nitrogen line is connected to the medium pressure column of the third cold box.

According to another object of the invention, a process for separating air by cryogenic distillation using at least three cold boxes, at least two air compressors and at least three air cleaning apparatus in which: sends compressed air from the at least two air compressors to the at least three air cleaning apparatuses to form purified air; ii) purified air is supplied from at least three purification apparatuses; at least three cold boxes iii) regeneration nitrogen is sent from at least two of the cold boxes to a header and then to at least two of the air-purifying apparatus and characterized in that iv) regeneration nitrogen is sent from at least one of the cold boxes to at least one of the air purification units without passing through the collector.

Optionally the regeneration nitrogen of steps iii) and iv) have different regeneration pressures and / or purities.

The nitrogen rates have different purities if their purity differs by at least 1 mol%.

Either each of the cold boxes and / or each of the purification apparatus and / or each of the cooling towers is adapted to process an identical flow rate, ie each of the cold boxes and / or each of the purification apparatus and / or each of the cooling towers is adapted to process a different flow rate.

Compressed air in at least two main air compressors is sent to an air collector connected to at least three of the cold boxes A typical water circulation circuit between the air cooling tower by direct contact with water and the water cooling tower by direct contact with nitrogen from an air separation apparatus is described in "Industrial Gas Handbook" of FG Kerry, 2007, pages 112-113. The invention will be described in more detail with reference to the figure which shows an integrated installation of three air separation apparatuses according to the invention.

In Figure 1, the installation comprises five main air compressors 1, five air cooling towers by direct contact with water 2, five air cleaning units 3, four pressure booster compressors. air 4, three cold boxes 5, three cooling towers of water by direct contact with nitrogen 6 and three pumps 7 of cooled water in the towers 6.

Each of the cold boxes 5, 5 'comprises a double air separation column constituted by a medium pressure column and a low pressure column, and an exchanger for cooling the air to a cryogenic temperature. The medium pressure columns of each of the three cold boxes preferably operate at substantially the same pressure and the low pressure columns of each of the three cold boxes preferably operate at substantially the same pressure. The compressed air in the five compressors 1 and sent to a wet air collector 10. From this collector 10, the moist air is distributed at five cooling towers 2 and then sent from each tower to a respective purification apparatus 3,3 'without being mixed. The purified air is sent to a manifold 13 of medium pressure dry air. The air from this collector is sent partly directly to the three cold boxes 5,5 'without being overpressed and partly to the boosters 4 connected in parallel. The outlets of the boosters 4 are connected to a high-pressure dry air manifold 14 which distributes the high-pressure air to the three cold boxes 5, 5 '.

Low pressure residual nitrogen from each cold box 5,5 'is sent to an associated water cooling tower 6,6'. The remainder of the low pressure residual nitrogen from two apparatuses 5 is sent to a nitrogen trap 12 which distributes the nitrogen to the four air cleaning apparatuses 3 to regenerate the bottles. The water cooled in each nitrogen water cooling tower 6,6 'is pumped by a respective pump 7 and then sent to a cold water collector 11 which distributes the water to the five air cooling towers by direct contact with water. 2. One of the air cleaning apparatus 3 'is supplied with nitrogen not by the collector 12 but only by medium pressure nitrogen from a line 15 connected to the third cold box 5' to through a medium pressure nitrogen expansion turbine 16.

The nitrogen trap 12 is connected only to the low pressure columns of the first and second cold boxes while the nitrogen line 15 is connected only to the medium pressure column of the third cold box.

Thus, the cold box 5 'is fed by five purification units at the top 3,3' and has two different fluids to regenerate the purification apparatus at the head which feed it, since the purification apparatus 3 are regenerated with the waste nitrogen and the purification apparatus 3 'is regenerated by expanded medium pressure nitrogen. This avoids stalling the entire pressure circuit of the air separation unit on the worst performing head cleaning loss of pressure.

Claims

1. Cryogenic distillation air separation plant comprising n cold boxes (5,5 ') where n> 3, r air cleaning apparatus (3,3') where r ≥ 3,, m main compressors (1) where m> 2 to compress the air from the ambient pressure and connected to the n cold boxes to supply compressed air, a nitrogen collector (12) from at least a first and a second of the cold boxes (5) connected to at least a first and a second air cleaning apparatus (3) characterized in that at least a third air cleaning apparatus (3 ') does not is not connected to the nitrogen collector and is connected by a nitrogen supply line (15) to at least a third of the cold boxes (5 ').

2. Installation according to claim 1 wherein the third air cleaning apparatus (3 ') not connected to the collector, the nitrogen supply line (15) and the third of the cold boxes (5') connected to the supply line are connected through a nitrogen expansion means (16).

3. Installation according to claim 2 wherein the expansion means is a turbine (16).

4. Installation according to one of the preceding claims wherein the third cold box (5 ') is connected to the first, second and third air cleaning apparatus (3,3') for receiving purified air from these devices.

5. Installation according to one of the preceding claims wherein the third purification apparatus (3 ') is connected to the third cold box (5') so that in operation it receives nitrogen of a different purity that of the nitrogen circulating in the collector (12).

6. Installation according to one of the preceding claims wherein the third purification device (3 ') is connected to the third cold box (5') of so that in operation it receives nitrogen with a pressure different from that of the nitrogen flowing in the manifold (12).

7. Installation according to one of the preceding claims wherein each of the cold boxes (5,5 ') comprises a double air separation column constituted by a medium pressure column and a low pressure column, the medium pressure columns of each of the cold boxes preferably operating substantially at the same pressure and the low pressure columns of each of the cold boxes preferably operating substantially at the same pressure.

8. Installation according to claim 7 wherein the nitrogen collector (12) is connected to the low pressure columns of the first and second cold boxes while the nitrogen line (15) is connected to the medium pressure column of the third box. cold.

9. Process for air separation by cryogenic distillation using at least three cold boxes (5,5 '), at least two air compressors (1) and at least three air cleaning devices (3,3' ) in which: i) at least two air compressors are sent compressed air to the at least three air cleaning apparatuses to form purified air; ii) purified air is supplied to minus three air cleaning units to at least three cold boxes iii) regeneration nitrogen is sent from at least two of the cold boxes to a collector (12) and then to at least two of the purification devices of air and characterized in that iv) regeneration nitrogen is sent from at least one of the cold boxes (5 ') to at least one of the air cleaning apparatus (3') without passing through the manifold.

The process of claim 9 wherein the regeneration nitrogen of steps iii) and iv) have different regeneration pressures and / or purities.