Distillation column comprising intermediate liquid holder for quick restart after interruption and method to use thereof

Abstract

A distillation column which comprises a device to speed up the startup phase in the event of interruptions in the operation is described.

Description

[0001] DISTILLATION COLUMN COMPRISING INTERMEDIATE LIQUID HOLDER FOR QUICK RESTART AFTER INTERRUPTION AND METHOD TO USE THEREOF

[0002] Description

[0003] Technical Field

[0004] A distillation column, in particular a fractional distillation column equipped with a device to reduce startup times in the event that the column operation is interrupted, is described below.

[0005] A method for starting up a distillation column, in particular a fractional distillation column, after an interruption in the distillation process is also described.

[0006] Background art

[0007] As is known, distillation is aimed at separating the components of liquid mixtures based on their differences in volatilities.

[0008] It is known to use devices generically known as distillation columns to carry out distillation processes.

[0009] In short, the mixtures to be processed are boiled in order to obtain a vapour flow rising up through the distillation column, in which the most volatile components of the mixture tend to concentrate.

[0010] The vapour that reaches the top of the column is then forced to exit and condensed, forming the so-called “distillate”.

[0011] Conversely, the least volatile components of the treated mixture tend to remain at the bottom of the column. It is known to carry out fractional distillation processes to enhance the distillation efficiency.

[0012] Fractional distillation is carried out using special distillation columns, known as fractional distillation columns or rectification columns.

[0013] In fractional distillation columns, a fraction of the vapour is repeatedly condensed and vaporized, so that a better separation of the least volatile components from the most volatile components can be obtained.

[0014] Basically, a fractional distillation column comprises a plurality of mass and energy exchange zones or sections, distributed vertically inside the column, in which a mass and energy exchange occurs between an upflowing vapour flow (coming from the bottom of the column or introduced into the column) and a downflowing liquid flow (introduced from the head of the column and consisting of a part of the distilled product) known as the "reflux".

[0015] Each mass and energy exchange section typically comprises trays or a (structured or random) packing which is wetted by the liquid phase downflowing by gravity.

[0016] The trays or the packing shape facilitates liquid phase and vapour mutual contact and then the mass and heat exchange.

[0017] The temperature of the upflowing vapour flow decreases as the flow rises upwards, while the temperature of the downflowing liquid flow increases as the flow drops down.

[0018] The upflowing vapour flow has a concentration of the most volatile component that increases from the bottom to top of the column, while the downflowing liquid flow has a concentration of the least volatile component that increases from the top to the of the column. The least volatile components of the mixture, therefore, tend to remain in the lower part of the column (forming the so-called “residue” or “bottom”) while the most volatile components tend to concentrate at the top of the column, from which they exit to be condensed (forming the so-called “distillate” or “head”).

[0019] A defined reflux composition profile and a defined reflux temperature profile must be created along the mass and energy exchange sections to lead a rectification column into steady state operation.

[0020] Furthermore, an interruption of the uprising vapour flow, whatever the cause, results in a rapid degradation of the reflux composition and temperature profile.

[0021] The operation of the distillation columns can be subject to operational interruptions, which can be either accidental or intentional.

[0022] An accidental cause of operational interruptions can be, for example, the interruption of the electrical supply. The distillation process can also be intentionally stopped in the event of equipment failures.

[0023] Furthermore, the distillation process can also be stopped for operational cost reasons (for example when electrical utility rates are higher) or because the production has been achieved.

[0024] The time required to start up a distillation column, that is to say to reach the steady state, in particular depends on the number of the mass and energy exchange sections and on the size of the distillation column.

[0025] In turn, the size and number of the mass and energy exchange sections depend on the characteristics of the mixture to be treated (the components and their concentrations) and on the required purity of the distillate and / or the residue.

[0026] The time required for recovering the reflux composition and temperature profile and therefore to lead a rectification column to steady state is generally significant.

[0027] For example, in case of starting up very tall columns (which are used in separation processes for separating components with small boiling temperature differences) the time to lead the distillation column back to steady state can be of the order of days or weeks.

[0028] In some particular cases, such as the separation by distillation of certain isotopes, the time to start up a distillation column can even be of the order of months.

[0029] During the non-productive period after startup, the distillation column consumes the same amount of energy used during normal production, but it does not provide the distilled product and / or the residue with the desired purity.

[0030] It follows, then, that any interruption in the operation of a distillation plant, whatever the reason, leads to significant economic losses, attributable to the energy costs for starting up the plant and to the lack of production during the time necessary to start up the plant.

[0031] FR 2 437 234 Al describes a distillation column which comprises a plurality of mass and energy exchange sections passed through by a downflowing reflux liquid flow and an upflowing vapour flow.

[0032] The distillation column described by FR 2 437 234 Al provides for the possibility of partially collecting fractions of the reflux liquid from an intermediate boiling stage, allowing the remainder of the reflux liquid to run down to the fractionation stages below. For this purpose, the reflux liquid is split into a first flow, which exits the column, and a second flow, which continues downflowing through the column.

[0033] Means are also provided to control and adjust the flow rate of the second flow, so that the second flow maintains a flow rate as constant as possible over time.

[0034] Summary

[0035] A distillation column that at least partially solves of the problems of the prior art and in particular at least some of the problems indicated above is described.

[0036] In particular, a rectification column that allows to reduce the startup times after an interruption in the operation, whatever the cause, is described.

[0037] A method for managing the shutdown and startup operations of a fractional distillation column is also described.

[0038] Some possible embodiments of a fractional distillation column (for example a tray or packed fractional distillation column) and a method for managing a fractional distillation column are described below with reference to the sheets of drawings.

[0039] Brief description of the drawings

[0040] Figure 1 schematically shows a conventional fractional distillation column.

[0041] The liquid composition profile in the various mass and energy exchange sections when the column works at steady state is highlighted.

[0042] Figure 2 is the same column as in Figure 1 and shows the reflux liquid composition profile after an interruption in the column operation.

[0043] Figure 3 is the same column as in Figure 1 and shows the reflux composition profile after a first phase of the startup process.

[0044] Figure 4 is the same column as in Figure 1 and shows the reflux composition profile after a second phase of the start up process.

[0045] Figure 5 shows a fractional distillation column according to a first embodiment, highlighting the reflux composition profile when it is in steady state.

[0046] Figure 6 shows the same column as in Figure 5 and shows the reflux composition profile after an interruption in the column operation.

[0047] Figure 7 shows the same column as in Figure 5 in a first phase of the startup process, highlighting the reflux composition profile.

[0048] Figure 8 shows the same column as in Figure 5 in a second phase of the startup process, highlighting the reflux composition profile.

[0049] Figure 9 shows a variant of the column in Figure 5, highlighting the reflux composition profile.

[0050] Figure 10 is an enlarged view of a detail in Figure 5.

[0051] Figure 11 is an enlarged view of a second detail in Figure 5. Figure 12 shows a third alternative embodiment of a rectification column (version with trays).

[0052] Figure 13 is a perspective view showing a section of a portion of the column in Figure 5.

[0053] In the attached drawings, the profile of the concentration of the most volatile component, in the reflux liquid that passes through the mass and energy exchange sections, is shown by a hatching: the more concentrated hatching corresponds to a higher concentration of the most volatile component.

[0054] Detailed description

[0055] Reference number 1 indicates, as a whole, a fractional or rectification distillation column.

[0056] The column 1 can be used to carry out continuous or batch distillation processes.

[0057] The distillation column 1 comprises a container 10, extending along a vertical axis X, having a lower end or bottom 11, an upper end or head 12 and an intermediate portion 13.

[0058] The container 10 is a substantially and / or essentially cylindrical metal container.

[0059] The bottom 11 and the head 12 of the container 10 can have a rounded shape (to enhance internal pressure resistance).

[0060] A nth plurality of mass and energy exchange sections 4, for example of the packed type, is provided in which the contact between the upflowing vapour and the downflowing liquid is enhanced.

[0061] The downflowing reflux liquid wets the surfaces of the trays or the packings, while the upflowing vapour spreads and occupies in a substantially homogeneous manner the empty spaces inside the packings or the trays of the mass and energy exchange sections of the column 1.

[0062] The nth mass and energy exchange sections 4 are sequentially distributed in the intermediate portion 13 of the container 10.

[0063] Each mass and energy exchange section 4 is spaced apart from the preceding and / or next stage.

[0064] The nth mass and energy exchange sections 4 can comprise conventional trays and / or conventional (structured and / or random) packings.

[0065] The term "structured packing", as used herein, means a packing in which the individual elements have a specific orientation relative to each other and to the column axis.

[0066] The term "random packing" as used herein, comprises the packing bodies such as (but not limited to) Rashig rings or Pall rings.

[0067] The term "trays" as used herein, comprises (but not limited to) bell-like trays, valve trays and perforated trays. Starting from the top, the first mass and energy exchange section 4 is located near the head 12 of the column 1 and the last mass and energy exchange section 4 is located near the bottom 11 of the column 1.

[0068] In the example of figure 1, the column 1 comprises an inflow duct 20 for the inflow of a mixture to be distilled, an outflow duct 15 for the outflow of the vapour from the upper end of the column 1, a condenser 22 for condensing the vapour that exits the head of the column 1 and an inflow duct 16 for the inflow of the reflux liquid (which exits the condenser 22) into the head 12 of the column 1.

[0069] A valve 9 can be provided to adjust the quantity of the distilled liquid reintroduced into the head of the column 1. The part of the distilled product that is not reintroduced into the column is progressively collected in a tank (not shown) for the collection of the distilled product.

[0070] The portion of the column 1 that is located above the inlet of the feed duct 20 forms the so-called enriching section, while the portion of column 1 that is located below the duct 20 forms the so-called stripping section. The vapour that comes into contact with the reflux flowing on the surface of the packing progressively cools and its least volatile components tend to condense and flow downwards (by gravity).

[0071] As the condensate flows down, it comes into contact with the uprising vapour, helping the condensation of the least volatile components present in the vapour, and hence the relative increase in the concentration of the most volatile components that remain in the vapour phase (mass and heat exchange between the condensed phase and the surrounding vapour).

[0072] During the operation of the distiller, the vapour condensates are gradually refluxed towards the bottom 11 of the column.

[0073] The liquid that is on the bottom 11 of the column 1 is heated and the vapours that are formed rise up through the column 1.

[0074] The heavy feed component progressively accumulates on the bottom 11 of the column.

[0075] In the illustrated example, the residue present on the bottom 11 is withdrawn, heated by means of a heat exchanger 21 and reintroduced into the bottom 11 of the column.

[0076] In the illustrated example, an outflow duct 14 is also provided at the bottom 11 of the column 1, to drain out the residue collected in the bottom 11 of the column 1.

[0077] The solution described for heating the liquid present on the bottom 11 is purely exemplary.

[0078] In an alternative embodiment, not illustrated, a reboiler can be provided, spaced apart from the column and the steam produced by the reboiler is sent towards the bottom 11 of the column through a duct.

[0079] In a further embodiment of the column 1, the reboiler can be missing (for example in the case of air distillation wherein the column is fed from the bottom in the vapour phase).

[0080] The distillation process can be carried out at atmospheric pressure, or at a pressure greater than the atmospheric pressure, or even in vacuum to space the boiling points of the various components, controlling the temperature of the mixture in the vapour phase that reaches the head of the column 1.

[0081] For this purpose, a temperature sensor (not shown) is provided to check the temperature of the mixture in the vapour phase at the head 11 of the column 1.

[0082] To further enhance the heat and mass exchange process inside the column 1, it is also possible to convert the liquid residue present at the bottom of the column to the vapour phase and recover the most volatile components which are still present (the so-called “final reflux”).

[0083] The distillation column 1 provides, above each mass and energy exchange section 4, a device 6, better described below, which comprises a first chamber, or upper chamber 91 and a second chamber or lower chamber 92. The upper chamber 91 is in communication with the overhead mass and energy exchange section (unless it is located above the first mass and energy exchange section, in which case the upper chamber 91 is in communication with a distillate liquid supply duct).

[0084] The lower chamber 92 is in communication with the lower mass and energy exchange section 4.

[0085] Each device 6 also comprises at least one chimney 60 that allows the vapours coming from the lower chamber 92 to rise upwardly the upper chamber 91.

[0086] In the illustrated examples, the two chambers 91, 92 are separated by a shield or wall 61, transversal to the axis X, for example a shield 61 having a substantially and / or essentially flat shape.

[0087] In the illustrated examples the shield 61 covers the entire cross-section of the container 10.

[0088] In the illustrated embodiment the shield 61 is made of metal.

[0089] In the illustrated examples the chimney 60 passes through the shield 61.

[0090] The shield 61 serves as the bottom of the first chamber 91 and the chimney 60 defines the maximum level of the liquid that can be accumulated in the first chamber 91.

[0091] The shield 61 also serves as a ceiling for the second room 92.

[0092] A hydraulic connection 71, 72, 8, 9 is then provided, which connects the first chamber or upper chamber 91 with the second chamber or lower chamber 92.

[0093] The hydraulic connection 71, 72, 8, 9 comprises, in sequence,

[0094] - a first duct 71 or outflow duct for the outflow from the first chamber 91,

[0095] - a valve 8, 9, and

[0096] - a second duct 72 or inflow duct for the inflow to the second chamber 92.

[0097] The valve 8, 9 is adapted to open and close the hydraulic communication between the upper chamber 91 (above the shield 61) and the lower chamber 92 (below the shield 61).

[0098] In the illustrated example, the hydraulic connection 71, 72, 8, 9 is external to the container 10.

[0099] When the valve 8, 9 is open, all the reflux liquid coming out of the upper chamber 91 can travel to the second chamber or lower chamber 92 passing through the hydraulic connection 71, 72, 8, 9.

[0100] The reflux liquid arriving in the lower chamber 92 can then flow down to the lower mass and energy exchange section.

[0101] In the illustrated examples, the liquid flows from the upper chamber 91 to the lower chamber 92 only by gravity.

[0102] When the valve 8, 9 is closed, the upper chamber 91 acts as a container to temporarily retain the reflux liquid (up to a maximum height that depends on the height of the chimney 60).

[0103] In the illustrated examples, the chamber 91 is shaped so as to define a single container adapted to accumulate the reflux liquid.

[0104] When the valve 8, 9 is opened again, all the liquid previously accumulated in the first chamber 91 can be drained out into the lower chamber 92 through the hydraulic connection 71, 72, 8, 9.

[0105] The reflux liquid which is in the upper chamber 91 can only be drained into the lower chamber 92. The liquid normally passes from the upper chamber 91 to the lower chamber 92 through the hydraulic connection 71, 72, 8, 9 by opening the valve 8, 9.

[0106] If the valve 8, 9 is closed, the liquid flow from the upper chamber 91 to the lower chamber 92 stops.

[0107] If the liquid accumulated in the upper chamber 91 exceeds the height of the chimney 61, the excess reflux liquid passes from the upper chamber 91 to the lower chamber 92 through the chimney 61.

[0108] Under normal operating conditions in the column 1, each valve 8, 9 of each device 6 is kept open and all the reflux liquid arriving in the upper chamber 91 exits it, passes in sequence through the first duct 71, the valve 8, 9 and the second duct 72 and enters the lower chamber 92 below.

[0109] At the same time, the vapour rises up from the lower chamber 92 to the upper chamber 91 passing through the chimney 60.

[0110] It should be emphasized that the device 6 does not allow any reflux liquid to be extracted from the column 1. In fact, each device 6 is shaped in such a way that all the reflux liquid that exits the upper chamber 91 enters the lower chamber 92, to then reach the fractionation stage below (the mass and energy exchange section below).

[0111] When the operation of the column 1 is stopped, each valve 8,9 of each device 6 is closed.

[0112] When the valve 8, 9 is closed, the hydraulic communication between the upper chamber 91 and the lower chamber 92 is stopped and the reflux liquid coming from the top is accumulated in the upper chamber 91.

[0113] The quantity of the liquid that can be accumulated in each upper chamber 91 - when the valves 8, 9 are closed - depends on the height of the chimney 60, which also acts as a weir.

[0114] When the valve 8, 9 is closed, there can be no liquid flow from the upper chamber 91 to the lower chamber 92 (unless the level of the reflux liquid inside the upper chamber 91 exceeds the height of at least one chimney 6, in which case any excess reflux liquid is drained out into the lower chamber 92 through the at least one chimney 6).

[0115] The upper chamber 91 and the lower chamber 92 can be in hydraulic communication with each other only when the valve 8, 9 is open.

[0116] In the illustrated examples, the first chamber 91 has no barriers therein that can define distinct containers and retain part of the liquid, then preventing it from flowing - through the hydraulic connection 71, 72, 8, 9 - towards the lower chamber 92.

[0117] The first or upper chamber 91 therefore defines a single container for liquid.

[0118] In other words, the chamber 91 is shaped in such a way that the liquid contained therein (when the valve 8, 9 is closed) is all at the same level and when the valve 8, 9 is open the liquid accumulated in the first chamber 91 flows into the second chamber 92.

[0119] In the illustrated distillation columns, all the liquid accumulated in each upper chamber 91 can be drained out towards the lower chamber 92 until the level of the accumulated liquid exceeds the height of the chimney 60, only by opening the valve 8, 9 of the hydraulic connection 71, 72, 8, 9.

[0120] In a possible embodiment, the valves 8 of the devices 6 are on / off valves, in particular motorized on / off valves. In some possible embodiments, the valve 9 of the hydraulic connection relating to the feed of the first mass and energy exchange section (that is the section closest to the head 12 of the column that first receives the reflux liquid reintroduced into the column) can be a motorized modulating valve.

[0121] Due to this feature, the valve 9 is fully opened upon startup and is then partially closed.

[0122] This modulation (partial closure) of the valve 9 allows the liquid coming from the condenser 22 partly to reform the liquid level in the head container through the duct 17, and partly to downflow as a reflux through the duct 19 towards the packing 4 below through the distributor 5.

[0123] It is therefore possible, during the filling of the head container, to work with the desired reflux flow rate. Once the volume 61 is filled, the distillate will flow through an overflow in the discharge duct 18.

[0124] The valves 8, 9 are motorized valves, for example valves with a shutter controlled by an actuator, of the electric, electropneumatic, electrohydraulic, pneumatic or hydraulic type.

[0125] The use of motorized valves 8, 9 allows the synchronized opening and closing of all the nth valves 8,9 of the distillation column.

[0126] The nth motorized valves 8, 9 of the column 1 are configured to close simultaneously.

[0127] Conversely, the motorized valves 8, 9 of the column 1 can open simultaneously or sequentially.

[0128] Preferably, a regulator can be provided, for example an electronic regulator, adapted to simultaneously close and open the motorized valves 8, 9 depending on the operating conditions of the distillation column.

[0129] In particular, the motorized valves 8, 9 are configured to close simultaneously in the event of a (intended or unintended) interruption of the operation of the distillation column in the distillation column, for example in the event of interruptions in the feed of the vapour flow inside the column 1.

[0130] Following the simultaneous closing of all the valves 8, 9, the reflux liquid coming from above (the so-called “hold up”) is retained in the upper chambers 91, above the shields 61.

[0131] When the distillation process is started up, all the valves 8, 9 can be reopened and the hydraulic communication between the mass and energy exchange sections 4 is then re-established.

[0132] Consequently, the liquid previously retained in the upper chambers 91 can fall down into the lower chambers 92 and the flow of the reflux liquid through the entire distillation column can start again.

[0133] In the example illustrated in figure 13, the upper chamber 91 is shaped in such a way as to allow all the liquid that passes, or that is temporarily accumulated, in the chamber 91 to be drained out into the lower chamber 92 through the hydraulic connection 71, 72, 8, 9 (except for any excess liquid that passes through the chimney 6). In particular, the upper chamber 91 has no barriers therein that can retain part of the liquid that flows towards the lower chamber 92.

[0134] In a possible embodiment, the valves 8, 9 are normally closed valves, for example normally closed solenoid valves.

[0135] The normally closed valves are forced open during the normal operation of the column 1 but they close immediately and simultaneously when an interruption occurs in the operation of the distillation column 1 due to an accidental or intentional interruption of the power or heat supply.

[0136] In other embodiments, the valves 8, 9 are normally open valves. In the event that the valves 8, 9 are of the normally open type, an uninterruptible power supply (UPS) should be preferably provided in order to avoid malfunctions of the column 1.

[0137] In some embodiments, the distillation column 1 can comprise at least one sensor (not shown) to observe the operating conditions of the column, in particular to check whether the vapour flow inside the column is regular. The information provided by the at least one sensor can be used to control the valve 8, 9 control regulator.

[0138] For example, a pressure sensor can be provided to control the pressure inside the distillation column, and then check whether the vapour flow is present and regular.

[0139] Alternatively, or in addition to the pressure sensor, a flow sensor can be provided to measure the flow rate of the vapour entering the distillation column and then check whether the vapour flow is regular.

[0140] Alternatively or in addition to the presence of the vapour pressure sensor and the vapour flow sensor, a sensor can also be provided to verify the presence of the power supply voltage of the distillation column.

[0141] In the event that anomalous values of the operating conditions of the column 1 are detected, for example in the event of a lack of vapour, the closing of the valves 8, 9 is commanded and the reflux liquid is retained in the upper chambers 91 of the devices 6.

[0142] In the illustrated examples, the valves 8, 9 are adjusted regardless of the level of the liquid accumulated in the upper chamber 91 or of the flow rate of the liquid that drops - through the hydraulic connection 71, 72, 8, 9 - from the upper chamber 91 to the lower chamber 92.

[0143] In the illustrated example, the hydraulic connection 71, 72, 8, 9 comprises a hydraulic guard, for example a siphon.

[0144] For this purpose, the duct 71, 72 can comprise a generally “U” or “J”-shaped section.

[0145] The hydraulic guard prevents a part of the vapour flow from passing through the hydraulic connection 71, 72, 8, 9, by hindering the downflow of the reflux liquid from the upper chamber 91 to the lower chamber 92.

[0146] In other words, the hydraulic guard avoids “hiccups” or “regurgitations” in the liquid flow and therefore maintains the flow rate more uniform over time.

[0147] If the mass and energy exchange sections 4 are of the packing type, a conventional liquid and vapour distributor 5 is provided, positioned below the device 6 but above the mass and energy exchange section 4 to distribute the reflux liquid coming from above.

[0148] The function of the distributors 5 is to make the distribution of the phases (liquid and vapour) that pass, in countercurrent, through the column 1 more uniform.

[0149] The distributors 5 may comprise a shield 51, one or more chimneys 50, and a plurality of small tubes 52 with lateral holes.

[0150] The distributors 5 may be conventional liquid and vapour distributors, such as those described in the US document US 4 427 605.

[0151] In a possible embodiment of the distillation column 1, a temperature sensor (not shown) is provided to measure the temperature of the liquid retained in each upper chamber 91 , above each shield 61 and a device (not shown) for controlling the temperature of the liquid retained in the upper chambers 91 when the column operation is stopped. Because of this feature, it is possible to maintain the liquid retained by each device 6 at the operating temperature during the downtime of the column.

[0152] It is, therefore, possible to maintain not only the composition profde of the rectification liquid, but also the temperature profile thereof.

[0153] The temperature control device can be, for example, a conventional coil (not shown) in which a heating or cooling fluid flows.

[0154] In the embodiment of figure 5, a collection basin 6 is also present under the lowest mass and energy exchange section (the one which is the closest to the bottom 11 of column 1).

[0155] During normal operation of the distillation column, the reflux will flow back towards the column, while during the stop, before starting up, the hold up of the packing above the bottom, but contaminated with light substances, can be drained outside, by opening the valve 81

[0156] This feature may be preferred for further reducing the risk of contamination (with the lighter fraction) of the residue contained in the bottom 11 when the operation of the column 1 is shut down.

[0157] In detail, in the event of a stop in the vapour flow in the column 10 (and therefore in the event of an interruption the distillation process) the reflux liquid coming from above is retained in the upper chambers 91 and starts to downflow again towards the lower chambers 92 only when the valves 8, 9 are reopened, that is to say when the column 1 is started up.

[0158] In other words, when the operation of the column 1 is interrupted, the reflux liquid that passes through the heat and energy exchange sections is retained and collected separately above each heat and energy exchange section 4.

[0159] This feature avoids contamination of the residue present in the bottom of the column 11 with the fractions having lower boiling temperatures.

[0160] Moreover, this feature allows to reduce the time for starting up the reflux composition profile inside the column.

[0161] When the column 1 is started up, the valves 8, 9 are simultaneously reopened, and since all the rectified liquids have been saved, it takes very little time for the reflux, which ends up in the bottom 11 and the distillate to have the desired concentrations.

[0162] The valve 9 at the device 6 located near the top of the column is subsequently modulated to obtain the desired reflux and to start up the operation of the column 1.

[0163] The rectification column 1 (having a nth plurality of vertically distributed and hydraulically connected in series mass and energy exchange sections 4 for exchanging mass and energy between an upflowing vapour flow and a downflowing reflux liquid flow) can be managed by a method that comprises the steps of: a) checking the operating conditions of said distillation column 1, in particular checking whether the vapour rises up through the column; b) in the event of an interruption in the vapour flow, closing the hydraulic connection between each mass and energy exchange section 4 and the mass and energy exchange section below and retaining the reflux liquid destined for the mass and energy exchange section below; c) in the presence of the vapour flow, keeping the hydraulic connection between each mass and energy exchange section 4 and the mass and energy exchange section 4 below open to allow the reflux liquid flow to be recovered.

[0164] In a preferred embodiment, the column management method can also provide, during the operation shutdown phase, to measure the temperature of the liquid retained above each heat and energy exchange section and to supply calories or frigories for maintaining a desired temperature profde.

[0165] This feature allows to further reduce the time to bring the column back to steady state after an interruption in the operation since the rectified liquids that have been stored have not only the composition required at steady state but also the temperature required at steady state.

[0166] This allows the concentration and temperature profile of the reflux liquid inside the column 1 to be started up in even shorter times.

[0167] Finally, the distillation column described above allows to start up the production of distillate according to the specification in a very short time.

[0168] As there is no need for the residue (liquid present on the bottom 11) to be rectified at startup, this allows to save further time for the startup of the column and energy.

[0169] It should be emphasized that the technical solution described above does not require the use of pumps, since the liquid collected by each device 6 is then drained out by gravity.

[0170] This allows to contain the production costs and improve the operational reliability.

[0171] Schedule of Reference Numerals

Claims

Claims1. A distillation column ( 1 ) comprising : a container (10) extending along a vertical axis (X), said container having a lower end (11), an upper end (12) and an intermediate portion (13); an inflow duct (20) for the inflow of a mixture to be distilled; an outflow duct (15) for the vapour outflow from said upper end (12) of said column (1); an inflow duct (16) for the inflow of the reflux liquid into said upper end (12) of said column (1); a nth plurality of mass and energy exchange sections (4), which are sequentially distributed in said intermediate portion (13) of said container (10), a device (6) being provided above each mass and energy exchange section (4) which comprises a first chamber or upper chamber (91), a second chamber or lower chamber (92) a shield (61) that separates said first chamber (91) from said second chamber (92), at least one chimney (60), that passes through said shield (61), that allows the vapours that are in the lower chamber (92), below said shield (61), to rise upwards the upper chamber (91) above said shield (61), which delimits the maximum level of liquid that can be accumulated in said first chamber (91), ahydraulic connection (71, 72, 8, 9) which connects said first chamber (91) with said second chamber (92), said hydraulic connection (71, 72, 8, 9) comprising a valve (8, 9) which is adapted to open and close the hydraulic communication between said first chamber (91) and said second chamber (92), the liquid present in said upper chamber (91) being able to be drained out only in said lower chamber (92).

2. The distillation column according to claim 1, wherein the valve (9) of the device (6) placed on the highest part of the column (1) is a modulating valve, while the remaining nth -1 valves (8) are on-off valves.

3. The distillation column according to claim 1 or 2, wherein the nth valves (8, 9) are motorized valves, comprising a regulator adapted to simultaneously close or open said nth valves (8, 9) depending on the operating conditions of said distillation column.

4. The distillation column according to claim 3, comprising a sensor to check the operating conditions of said column, in particular to measure the pressure or the flow rate of the vapour flow in said column (1) or to verify the presence of the power supply voltage of the distillation column.

5. The distillation column according to one of the preceding claims, wherein each said hydraulic connection (71, 72) between said first chamber (91) and said second chamber (92) comprises ahydraulic seal, namely a siphon.

6. The distillation column according to one of the preceding claims, wherein said mass and energy exchange sections (4) are filling sections, and wherein a liquid and vapour distributor (5) is provided above eachfilling section (4) and below each shield (61) to distribute the vapour coming from the filling stage below (4) and distribute the reflux liquid coming from above.

7. The column according to one of the preceding claims, comprising a temperature sensor to measure the temperature of the liquid retained in said first chamber (91) of each device (6) when said valves are closed and a device to adjust the temperature of the retained liquid.

8. A method for managing a rectification column having a nth plurality of mass and energy exchanging sections which are vertically distributed and hydraulically connected in series, to exchange mass and energy between a downflowing vapour flow and an upflowing reflux liquid flow (4), comprising the steps of: a) checking the operating conditions of said distillation column (1), in particular verifying whether the vapour rises up; b) in the event of an interruption in the vapour flow, closing the hydraulic connection between each mass and energy exchange section (4) and the mass and energy exchange section below and retaining the reflux liquid destined for the mass and energy exchange section below; c) in the presence of the vapour flow, keeping the hydraulic connection between each mass and energy exchange section (4) and the mass and energy exchange section (4) below open to allow the reflux liquid flow to be recovered.

9. The method according to claim 8, wherein, during the step of interrupting the column operation, the step is also provided of measuring, for each mass and energy exchange section (4), the temperature of the retained liquid, and providing calories or frigories to maintain a desired temperature profile.

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