EP1008826A1 - Falling film vaporizer and air distillation plant - Google Patents

Abstract

Each first main passage (G) for liquid to be vaporized, is seen in cross section transverse to the direction of liquid circulation. Each has a region of free discharge of sufficient extent to avoid impurity deposits, hence preventing blockage. Where principal passages are delimited by vertical plates (4), contours are substantially similar, parallel and spaced from each other to form flat main passages. The first main passages (L) are straighter than the second main passages (G) and contain neither wavy, heat exchange sections, nor auxiliary passages. One or more auxiliary closed passages (23) extend over the entire heat exchanger dimension parallel to the direction of liquid flow and walls of auxiliary passages contact the plates (4) defining the main passage. Preferred Features: The discharge region extends along a curve of length 10-30 cm. It extends fully transversely across the heat exchanger body. The exchanger comprises a parallel plate (4) assembly between which several first (L) and second main passages (G) are situated in alternation. The first main passage does not include wavy crosspieces between the two parallel plates where it is situated. Each first principal passage is delimited by two parallel plates defining an empty space between themselves, continued over their transverse width. The first main passage contains at least one wavy section forming thermal transfer fins.

Description

The present invention relates to a vaporizer of the type comprising a heat exchanger body which has main passages placed in heat exchange relationship, means for forming a bath of the liquid to be sprayed so that it circulates in at least one of said first passages main, and means for introducing a refrigerant into the minus a second of said main passages so that it ensures the vaporization of the liquid.

The invention applies, for example, to a vaporizer-condenser for a double column air distillation installation.

In such a vaporizer-condenser, oxygen-rich liquid, from the low pressure column tank, is vaporized in the evaporator-condenser by condensation of a nitrogen-rich gas, taken off at the head of the medium pressure column.

More generally, an air separation device such as a double distillation column includes several types of heat exchanger heat.

A main heat exchanger is used to cool the supply air of the apparatus at distillation temperature by heat exchange with a or more fluids from the distillation apparatus. In some cases, these are pressurized liquids from the device that vaporize against the air at distill in the exchanger. These exchangers are normally made entirely of aluminum or copper or alloys of these metals (W095 / 28610).

For safety reasons, these liquids sometimes vaporize in a dedicated exchanger, or vaporizer, against a single fluid such as air or nitrogen.

The apparatus also comprises at least one vaporizer-condenser which is a heat exchanger placed inside or outside of the column. These vaporizers-condensers are usually made entirely in copper, stainless steel, nickel or aluminum and are made up of at least two circuits which are connected to the rest of the installation by means of pipes welded to the equipment.

Exchangers used in air separation devices include heat exchanger bodies which are often made in parallel aluminum plates with a similar outline brazed between they.

Generally in exchangers that serve as vaporizers, a oxygen-rich liquid vaporizes against a current rich in gas nitrogen (such as air or nitrogen with a purity greater than 80%).

To improve the performance of these vaporizers, you can use so-called falling or dripping film vaporizers, that is to say of the aforementioned type and in which the oxygen-rich liquid of the bath is distributed at the top of the vaporizer in the form of a very thin film which flows vertically in the first main passages and part of which vaporizes by heat exchange with passages dedicated to nitrogen-rich gas from common way.

EP-0795349 describes the case where such a vaporizer is combined with a thermosiphon vaporizer (bath vaporizer, i.e. a vaporizer completely immersed in the liquid where the recirculation of the liquid rich in oxygen is made thanks to the hydraulic thrust due to the difference in density between the bath and the liquid vaporizing in the passages).

In the bodies of brazed plate heat exchangers used in vaporizers of the aforementioned type with trickling film such as that of EP-A-0130122, the liquid is distributed between many passages made up of waves vertical inserted between two sheets called separators and thus constituting thermal fins, and because of the pitch of these waves the bodies brazed plate heat exchangers have surfaces very large exchange.

So when the whole surface is wet, the liquid film will be very thin and to avoid dry spraying at the bottom of the first passages main or in the event of a distribution fault, liquid is poured in excess in the heat exchanger body. This excess liquid forces in general to recycle liquid by means of a pump.

In vaporizers of the aforementioned type called bath, recirculation of the liquid is also maintained to avoid dry vaporization in the top of the first main passengers.

US-A-5699671 further describes a vaporizer with an exchanger body vertically arranged tubular in which nitrogen gas condenses at contact of its tubes.

It has been found, in particular in film vaporizers-condensers dripping, that solid pollutants such as for example, hydrocarbons or nitrous oxide, can accumulate in passages dedicated to the oxygen-rich fluid, which can lead to clogging of these.

Such a blockage then deteriorates the operation of the vaporizer-condenser.

An object of the invention is to solve this problem by providing a vaporizer of the aforementioned type which limits the risk of clogging of the passage (s) dedicated to the liquid to be vaporized.

Another object of the invention is to minimize the recirculation of the liquid to be vaporized in vaporizers of the aforementioned type and ensure the safety of the optimal operation and performance.

To this end, the subject of the invention is a vaporizer of the aforementioned type, characterized in that the or each first main passage has, in current cross section to the direction of flow of the liquid to vaporize, at least one region of free flow continues sufficiently extended to allow the liquid to bypass a deposit of impurities, or, the main passages being delimited by vertical plates having a substantially similar outline, parallel and spaced apart others to form the main flat passages, at least a first main passage is either narrower than the second main passage and contains no exchange wave or auxiliary passage, either contains one or several closed auxiliary passage (s) which extend over most of the dimension of the heat exchanger body parallel to the direction of liquid to be vaporized, the walls of the passage (s) auxiliary (s) touching the plates defining the main passage.

Preferably, all the first main passages contain at least minus a closed auxiliary passage.

Thus the liquid sent into the auxiliary passage crosses the vaporizer without contacting the plates defining the first passages main. As far as possible, the liquid should be avoided between the exterior of the auxiliary passage and the passages defined by the plates.

One way to avoid this problem is to form the passages auxiliaries in a block of material (for example aluminum, nickel or copper). If the block has substantially the dimensions of a first pass main, the liquid will not be able to flow outside the passages auxiliaries which are cylindrical holes passing through the block.

Ideally, the maximum width of an auxiliary passage is greater than 50% of the distance between two adjacent plates.

In order to avoid the accumulation of impurities, the inner surface of the auxiliary passage or each auxiliary passage includes only curved surfaces and possibly convexities. The absence of cavities in the passages of the first set ("liquid" passages) never has been proposed in the prior art.

Alternatively, at least one, and preferably all, of the first main passages contain several auxiliary passages formed by a series of cylindrical tubes parallel to each other and each having a diameter at least equal to 50% of the separation between two adjacent plates.

According to another variant, at least one and preferably all of the first main passages contain several auxiliary passages consisting of tubes, each having an inner surface with at least three identical convexities and curved surfaces connecting the convexities.

The adjacent tubes may or may not be contiguous.

Preferably, there are means for directing liquid into the or each auxiliary passage and / or liquid distribution means constituted by predistribution openings, these openings leaving drop this liquid on a lining located above the means for direct liquid into one or each auxiliary passage.

Alternatively, the means for directing the liquid into the passages are inclined points whose ends are above inside the auxiliary passage (or passage).

The vaporizer can be a main exchanger which is used to cool the air purified at its distillation temperature, a sub-cooler or the vaporizer-condenser of a double column.

The invention also relates to an air distillation installation comprising at least one vaporizer as defined above.

• la figure 1 est un schéma partiel d'une installation de distillation d'air selon l'invention,
• la figure 2 est une vue schématique éclatée du vaporiseur-condenseur de l'installation de la figure 1,
• la figure 3 est une vue partielle, schématique et en coupe d'un passage du vaporiseur-condenseur de la figure 1 dédié à la circulation du liquide à vaporiser,
• la figure 4 est une vue partielle, schématique et en coupe prise suivant la ligne IV-IV de la figure 3,
• la figure 5a est une section partielle schématique illustrant la structure des passages du vaporiseur-condenseur de la figure 1 dédiés au liquide à vaporiser et au gaz à condenser,
• les figures 5b à 5d sont des vues analogues à la figure 5a illustrant des variantes de l'invention,
• la figure 6 est une vue schématique d'un vaporiseur-condenseur selon un autre mode de réalisation de l'invention, et
• la figure 7 est une vue partielle, schématique et en coupe prise suivant la ligne VII-VII de la figure 6.

The invention will be better understood on reading the description which follows, given solely by way of example, and made with reference to the appended drawings, in which:

• FIG. 1 is a partial diagram of an air distillation installation according to the invention,
• FIG. 2 is an exploded schematic view of the vaporizer-condenser of the installation of FIG. 1,
• FIG. 3 is a partial schematic view in section of a passage of the vaporizer-condenser of FIG. 1 dedicated to the circulation of the liquid to be vaporized,
• FIG. 4 is a partial schematic view in section taken along the line IV-IV of FIG. 3,
• FIG. 5a is a schematic partial section illustrating the structure of the passages of the vaporizer-condenser of FIG. 1 dedicated to the liquid to be vaporized and to the gas to be condensed,
• FIGS. 5b to 5d are views similar to FIG. 5a illustrating variants of the invention,
• FIG. 6 is a schematic view of a vaporizer-condenser according to another embodiment of the invention, and
• FIG. 7 is a partial diagrammatic view in section taken on line VII-VII of FIG. 6.

Figure 1 illustrates a vaporizer-condenser 2 (see description of Figure 1 in EP-A-0130122). The vaporizer-condenser 2 comprises a heat exchanger body formed by a sealed envelope 3 and a series of parallel vertical plates 4 made of aluminum, which define a multitude of main flat passages intended alternately for one of two fluid flows, for example, a gas flow containing 98% nitrogen at around 5 bar and a liquid flow containing 98% oxygen at around 1.5 bars. Obviously pressures and purities can take other values.

The passages dedicated to the liquid to be vaporized are called first main passages and are marked with the letter L in the figures, while the passages dedicated to the gas to be condensed are called second passages main and are identified by the letter G in the figures.

The space above the plates 4 contains a bath 5 of the liquid to be vaporized from a line 6.

As illustrated in Figures 1 to 4, the liquid from this bath enters each first pass L through a series of perforations in a upper distribution bar 27. It then falls on a wave 26 which is a non-perforated aluminum sheet with horizontal generators (layout so-called hardway with respect to the flow of liquid oxygen) and offset partial vertical (partial vertical offset is not illustrated so as not to overload the figures) and which ensures the fine distribution of the liquid.

The liquid falls from the wave 26 on an upper drip 25 constituted by an aluminum strip folded with a series of triangular points 29 forming an angle of 135 ° with the plane of one of the plates 4 of the passage L considered.

The end of each point 29 of the upper drip 15 is located above with a point of a lower drip 24, identical to the first but whose tips are oriented towards the other plate 4 of passage L considered.

The liquid to be vaporized then flows on the plates 4 of the first passage L considered in the form of a film streaming downwards.

The gas to be condensed enters the second passages G at by means of a pipe 9 welded in the middle of a head 8 (sometimes called "Box" or in English "headline") semi-cylindrical.

The gas then flows downwards in the second passages G to cocurrent of the liquid in the first passages L, the condensation of the gas ensuring the vaporization of the liquid in the first passages L.

As illustrated in FIG. 5a, only the second passages G each contain a spacer wave 21 consisting of a sheet corrugated perforated aluminum with vertical generators (available in "Easy-way").

Conventionally, these spacer waves 21 fill also the function of thermal fins.

The first passages L have a thickness less than that of the second passages G.

In particular, the thickness of the first passages L is included between 2.5 mm and two thirds of the thickness of the second G passages.

The first passages L are each delimited by two plates 4 neighbors and by closing bars 30 situated between them on their side edges. The plates 4, between which a first passage L is located, therefore define between them a free and continuous space practically over their entire width, this width being measured in a direction transverse to that of the flow of the streaming film.

The first passages L are narrower than the second passages G and contain neither exchange waves nor passages auxiliaries. The distance between the adjacent plates 4 of the first passages L varies between 2.5 mm and two-thirds of the separation between the plates 4 of the second passages G.

Consequently, the first passages L have on all their length a rectangular cross section free of any obstacle and keep on going. This section has a width substantially equal to the width of the plates 4 and therefore the width of the heat exchanger body, that is to say a width of about 1 meter.

Due to the transverse extent of the passages L, the risks of clogging of these are therefore limited.

Indeed, if a local deposit of substances resulting from vaporization liquid occurs on the plates 4 of a first passage L, the liquid to spraying can bypass this deposit.

In addition, we see that the structure of the first passages L limits the recirculation of liquid required in the vaporizer 2.

In general, the risks of blockage can be limited using first passages L having in cross section current, that is to say over most of their length, a region unobstructed and continuous flow that extends along a guide curve C of length greater than approximately 10 cm. In the case Figures 1 to 5a, this guide curve C is a straight line parallel to plates 4, located between them, and about 1 m long. The right C is shown in dotted lines in FIG. 5a.

According to the variant of FIG. 5b, the distance separating the two plates 4 associated with a first passage L is greater than that of the variant of Figures 1 to 5a.

Two identical sheets 29 and 31, of aluminum, and of section transverse epicyloid, are arranged between the two plates 4 associated with each first pass L and extend over their entire length. Each sheet 29, 31 therefore comprises a series of semi-cylindrical sections joined at the ends to form a curved line.

Each sheet 29, 31 is carried by a plate 4. The concavities of the sheets 29, 31 are directed towards each other. The sheets 29 and 31 are offset transversely from each other so that the tips of each sheet are located opposite a hollow of the other sheet. So the two sheets 29 and 31 form a single auxiliary passage between them, in which all the fluid flowing in the first passage L considered.

The sheets 29 and 31 play the role of thermal fins and delimit thus between them the flow region of the liquid to be vaporized.

The auxiliary passage of each first passage L extends, in its cross section, continuously and freely practically over the entire width of the heat exchanger body. The mentioned guideline C above then extends between the sheets 29 and 31 following their contours. The directing curve is then sinuous and has a length greater than 1 m.

Here again, the first passages L make it possible to limit the risks closure thanks to a sufficient transverse extent so that the liquid to be sprayed bypasses any deposits.

In the variant of FIG. 5c), the auxiliary passages of the first passages L are formed by contiguous aluminum tubes 23. In the second passages G we find the generating waves 21 classic verticals.

In the variant of FIG. 5d), the auxiliary passages of the first passages L are non-contiguous tubes having a cross section shape of clover leaves.

In each case of FIGS. 5b to 5d, the auxiliary passage (s) includes only curved surfaces or convexities thus preventing the accumulation of impurities in the passages and making it possible to limit the liquid recirculation required in the vaporizer 2.

The invention is not limited to dripping film vaporizers but also applies to so-called bath vaporizers.

FIG. 6 illustrates another embodiment of the invention in which the sealed envelope 3 of the vaporizer-condenser 2 comprises a ferrule 40 of vertical axis, closed by a domed dome 41 and by a bottom domed 42. A bundle of tubes 44 is disposed inside the ferrule 40, coaxial therewith, to form with the ferrule 40 an exchanger body heat.

The tubes 44 have an outside diameter of approximately 5 mm and a thickness of about 1 mm. The tubes 44 are arranged in a bundle regular, which forms in cross section (figure 7) a mesh network about 8 mm square. Preferably, the tubes have a diameter outside less than 7 mm and are spaced at least 2 mm.

The upper ends of the tubes 44 are fixed to a plate said tubular 45 upper into which they open. Plate 45 is disposed in the dome 41. Similarly, the lower ends of the tubes 44 open into a lower tube plate 46 disposed in the bottom 42, the tubes 44 being fixed to this plate 46.

The space delimited by the tubular plate 45 and the dome 41 is connected to the pipe 9 for supplying gas rich in nitrogen to form means of introduction into the tubes 44 of the gas to be condensed.

The space delimited by the tubular plate 46 and the bottom 42 is connected to the pipe 11 for evacuating the condensed gas and to the pipe 13 for evacuating uncondensable rare gases to form means of evacuating gas condensed out of the tubes 44.

The tubes 44 therefore internally define the second passages G.

The line 6 for supplying the oxygen-rich liquid opens into the ferrule 40 under the tubular plate 45. The return pipe 7 is disposed between the tube plate 45 and the pipe 6.

A circular distribution plate 48 is disposed under the pipe 6 transversely to the axis A of the shell 40. This plate 48 is pierced with a network of circular orifices 49 6 mm in diameter each receiving coaxially a tube 44.

The bath of the liquid to be vaporized is formed above the plate 48 of distribution. The liquid is distributed under this plate 48 through the spaces annulars 50 delimited around the tubes 44 by the orifices 49.

The liquid then flows in the form of a liquid trickling on the outer surface of the tubes 44, cocurrent with gas to be condensed.

The vaporized liquid is returned via the line 14 to the low pressure column tank while excess oxygen liquid present above the tube plate 46 is returned by the line 16 and via a pump 51 to line 6.

The tubes 44 therefore delimit externally, with the ferrule 40, a only first passage L dedicated to the circulation of the liquid to be vaporized.

This first passage L has, in its current section, a region appreciably diametral, the straight line C of which passes through the axis A of the ferrule 40, has a length of the order of the inside diameter of the ferrule 40. This internal diameter may for example be equal to approximately 1 m. This embodiment of the invention therefore also makes it possible to limit the risk of blockage of the first pass L.

More generally, this effect can be obtained with other shapes and dimensions of the basic pattern of the bundle of tubes 44 than those Figures 6 and 7.

In some cases, the first passage L will include in section transverse a multitude of flow regions, free of any obstacle and continuous, which will undulate between the tubes 44. The guiding curves C of these regions will then be sinuous and preferably have a length greater than about 10 cm and, more preferably, greater than about 1 m.

Claims (33)

Vaporizer (2), of the type comprising a heat exchanger body heat which presents main passages (G, L) placed in relation heat exchange means for forming a bath (5) of the liquid to spray so that it circulates in at least a first (L) of said passages main, and means (8, 9; 9) for introducing a refrigerant in at least a second (G) of said main passages so that it ensures the vaporization of the liquid, characterized in that the or each first main passage has, in current cross section to the direction of circulation of the liquid to be vaporized, at least one region continuous free flow large enough to allow liquid to bypass a deposit of impurities, or, the main passages being delimited by vertical plates (4) having a substantially contour similar, parallel and spaced from each other to form the flat main passages, at least one first main passage (L) is is narrower than the second main passage and contains no wave exchange or auxiliary passage, or contains one or more passage (s) auxiliary (s) closed (23, 50) which extend over most of the dimension of the heat exchanger body parallel to the direction of flow of the liquid to be vaporized, the walls of the auxiliary passage (s) touching the plates (4) defining the main passage. Vaporizer according to claim 1, characterized in that said flow region extends along a length guide curve (C) greater than about 10 cm. Vaporizer according to claim 2, characterized in that said guide curve (C) has a length greater than or equal to about 30 cm. A vaporizer according to any one of claims 1 to 3, characterized in that said flow region extends substantially over a whole dimension of the heat exchanger body transverse to the direction of circulation of the liquid to be vaporized. Vaporizer according to any one of claims 1 to 4, characterized in that the heat exchanger body is formed from an assembly of parallel plates (4) between which several first (L) and second main passages (G) are alternately located. Vaporizer according to claim 5, characterized in that each first main passage (L) does not include a spacer wave between the two parallel plates (4) between which it is located. Vaporizer according to claim 6, characterized in that each first main passage (L) is delimited by the two parallel plates (4) between which it is located, these two plates defining between them a substantially free and continuous space over most of their width transverse to the direction of circulation of the liquid to be vaporized. Vaporizer according to claim 5 or 6, characterized in that each first main passage (L) contains at least one wave (29, 31) forming thermal fin. Vaporizer according to claim 8, characterized in that each first passage (L) contains two waves (29, 31) forming fins thermals arranged opposite one another, and defining between them a substantially free and continuous auxiliary passage over most of their width transverse to the direction of circulation of the liquid to be vaporized. Vaporizer according to claim 8 or 9, characterized in that the or each wave (29, 31) forming a thermal fin of a first passage (L) has a cross section to the direction of circulation of the liquid to be vaporized substantially in epicycloid. Vaporizer according to claims 9 and 10 taken together, characterized in that the epicycloid waves of the same first pass (L) are offset from each other transversely to the direction of circulation of the liquid to be vaporized. Vaporizer according to any one of claims 1 to 4, characterized in that the heat exchanger body is formed from a ferrule (40) and a bundle of tubes (44) arranged inside the ferrule parallel to its axis (A), and in that the tubes delimit internally each a second passage (G), and delimit, externally, with the ferrule (40), the first passage (L). Vaporizer according to claim 12, characterized in that the tubes have an outside diameter less than 7 mm and are spaced at least 2 mm. Vaporizer according to any one of Claims 1 to 13, characterized in that the means for forming a bath of the liquid to be vaporized and the means for introducing the refrigerant are arranged so that the refrigerant and the liquid to be vaporized co-flow in the heat exchanger body. Vaporizer according to any one of Claims 1 to 14, characterized in that the vaporizer is a vaporizer-condenser, the means for introducing refrigerant being means (8, 9; 9) for introducing a gas to be condensed and the vaporizer further comprising means (10, 11; 11) for evacuating the condensed gas. Vaporizer according to claim 1, characterized in that the or each auxiliary passage (23, 50) prevents the liquid to be vaporized from entering in contact with the plates (4) of the first main passage (L) corresponding. The vaporizer according to claim 1 or 16, wherein each first main passage (L) contains at least one closed auxiliary passage (23, 50). A vaporizer according to claim 1, 16 or 17, wherein the maximum width of an auxiliary passage is greater than 50% of the distance between two adjacent plates (4). A vaporizer according to any of claims 1 and 16 to 18, wherein the interior surface of the or each auxiliary passage (23, 50) includes only curved surfaces and possibly convexities. Heat vaporizer according to any one of the claims 1 and 16 to 19, in which at least one, and preferably each first main passage (L) contains several auxiliary passages constituted by a series of cylindrical tubes (23) parallel to each other and having each a diameter at least equal to 50% of the separation between two adjacent plates (4). A vaporizer according to any of claims 1 and 16 to 20, in which at least one, and preferably each first pass main contains several auxiliary passages constituted by tubes (50) each having an interior surface with at least three convexities identical and curved surfaces connecting the convexities. A vaporizer according to claim 20 or 21, wherein the tubes adjacent (23, 50) are contiguous. A vaporizer according to claim 20 or 21, wherein the tubes adjacent (23, 50) are not contiguous. A vaporizer according to any of claims 1 and 16 to 23, comprising means (24, 25) for directing the liquid from the bath to the or each auxiliary pass. A vaporizer according to claim 24, comprising means for distribution of the bath liquid comprising predistribution openings, these openings dropping this liquid on a lining (26) located above means (24, 25) for directing liquid into one or each auxiliary passage. A vaporizer according to claim 24 or 25 wherein the means (24, 25) for directing the liquid into the auxiliary passages are inclined points whose ends are above the interior of the auxiliary passage (or passage). A vaporizer according to claim 1 or 16 in which the auxiliary passages are formed in a block of material placed in the first main pass (L) and having substantially the same dimensions than this one. A vaporizer according to any one of claims 1 to 27, characterized in that the means for forming a bath of the liquid to be vaporized are means for forming a bath (5) above the passages main (G, L), the vaporizer further comprising means for introducing the bath liquid (5) into the or each first pass main so that it flows there in the form of a streaming film. Air distillation installation comprising at least one vaporizer (2) according to any one of claims 1 to 28. Installation according to claim 29 in which the vaporizer (2) is a main exchanger which is used to cool purified air at its distillation temperature. Installation according to claim 29 or 30 wherein the vaporizer (2) is a sub-cooler. Installation according to any one of claims 29 to 31 comprising a first column supplied with air and connected thermally to a second column by means of the vaporizer (2). Air distillation plant according to claim 32, in which the first column is a medium pressure column (1), the second column is a low pressure column and the vaporizer (2) is a vaporizer-condenser for connecting heat exchange low-pressure column tank oxygen and overhead nitrogen from the medium pressure column.

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