NO155366B - DEVICE FOR PROTECTING A LINE CIRCUIT IN TELECOMMUNICATION EQUIPMENT AGAINST OVERVOLTAGE. - Google Patents

Description

Plate column for producing intimate contact between gases and liquids.

The present invention relates to a

improvement of columns with perforated plates suitable for inducing intimate contact between gases and liquids, i.e. columns through which gases introduced at the foot flow from bottom to top

of the column, while allowing a liquid to flow from the top down the column from its top in such a way that it successively

and by the impact of gravity overflows

from one to the other of the plates that are

placed above each other in whole or in part

of the height of the column, so that the transition of the liquid from one plate to the other can

happen either by means of an overflow, in the cases where so-called slabs "with

overflow", or can happen in a controlled manner

flow through the perforations themselves, so-called plates "without overflow".

The invention relates more particularly to columns with plates which are perforated with

numerous circular holes, slits of any shape, etc., which have the function of dividing the ascending gas into many

filamentary currents to thus increase

its contact surfaces with the liquid which

covers the plates, and which helps to do

the exchange of matter or the exchange of heat

between the two phases present more effectively.

The surface tension in the constantly renewed liquid film that closes each perforation, and the pressure exerted by the gas

which rises through these perforations, obstructs the liquid which covers the plate

a certain height, and which is more or less

emulsified by the gas, in flowing through the perforations and coming down on the underlying plate. Each plate in an operating column thus permanently preserves a certain liquid height, and during the time the liquid is on a given plate and before it flows down through the overflow onto the underlying plate (plates "with overflow") or through the perforations (plates "without overflow"), a — physical or physico-chemical — equilibrium between the gas phase and the liquid phase will occur in each plate floor. which in particular gives the liquid a specific composition.

Many perforated plates and e.g. especially those equipped with overflows and which are used in modern factories for the production of nitric acid, have the disadvantage that they do not retain the liquid as soon as the gas flow supplied to the column drops below a minimum value which, very often, corresponds to approx. 15 per cent of the normal flow-through the column is designed for. The liquid from each plate then flows through the perforations, eventually flows through all the plates below and ends up at the bottom of the column where liquids from different plates, which consequently represent different compositions and/or temperatures, are mixed together into a mass of an average composition and / or temperature.

This condition of the ring, which repeats itself every time the column is stopped for one reason or another, entails several disadvantages, of which mention is made: the fact that at the bottom of the column one must ensure sufficient capacity to capture the total quantity of liquid which, at the moment the column is stopped, is

distributed on all plates; this that, in order to start the column again, it is necessary to bring up to the top, plate the entire amount of mixed liquids that are at the bottom of the column, because again, by successive overflows or by flow through the perforations, to distribute the aforementioned

quantity on the plates below; finally this, that when there is again liquid on all the plates, it still remains to restore the equilibrium which existed on each of the plates before the column was stopped.

All of these operations are expensive and entail a loss of time and material, the more the more often stoppages occur. In addition, because each restoration of equilibrium is preceded by a period of fluctuations in the column's operation, the insufficient transport of the substances flowing through the column could cause considerable disadvantages for the apparatus whose operation is linked to the column's operation during this period. Ultimately, this will lead to a reduction in the plant's efficiency and to a reduction in the factory's performance.

The purpose of the present invention is to improve the column plates regarding the establishment of contact between gases and liquids, an improvement which makes it possible to avoid the aforementioned disadvantages by means of a device which characterizes the present invention and which mainly consists of at least one receiving vessel which is specially arranged for each plate with the aim - at a stop or when the gas flow drops below a certain minimum value - to isolate, retain and store the liquid that is on the plate, and this so that the liquid's

■composition, corresponding to its physical-chemical equilibrium - before the stop - is preserved until restart or until the gas flow - but again - has obtained the sufficient value.

Said receiving vessels — so-called collection vessels — have "dimensions which are sufficient so that, as long as the stoppage of the column lasts, it can store the entire quantity of liquid which covers the plate below normal; drift-or, at least, a sufficient quantity of liquid to enable new, start-up and start-up in a satisfactory manner. i

Another characteristic of the invention1 consists in the fact that the collection vessel corresponding to each plate is connected to the plate by means of at least one tube immersed in the liquid which ensures fluid circulation in both directions, that is from the plate to the catch vessel during the discharge of the plate and, conversely, from the catch vessel to the plate when it comes to driving the liquid out of the catch vessel to bring it back to the plate on restart.

In accordance with another important characteristic, the collection vessel also has one or more submerged pipes with the help of which one can create atmospheric pressure on the one hand (or create a connection with an area where there is a pressure that is lower than the pressure in the column) when it comes to filling the vessels, and, on the other hand, can connect with an area in which the pressure is higher when it comes to emptying the collection vessels and driving the liquid out onto the plate.

By stopping or reducing the gas circulation in the column and simultaneously establishing the connection of the collection vessel with the atmosphere, the emptying of the plate is completed quickly, e.g. within 15 seconds under the influence of the higher pressure which still prevails over the liquid on the plate and, possibly, under the influence of gravity. The duration of the emptying is regulated taking into account the permissible pressure differences and the diameter of submerged pipes. The emptying of the collection vessel then takes place once the gas circulation has been re-established and when at the same time, as the connection between the vessel and the atmosphere is closed, the pressure inside the vessel has become sufficiently large to cause the liquid to rise, as it is pushed through the submerged pipes from which it distributes itself over the plate -as originally before stopping.

It is actually sufficient for the function of the described device that the pressure inside the collection vessel simply drops faster than in the column when a stoppage occurs, and that the pressure inside the vessel increases faster than in the column when a new initiation,' while crutches in the tub and in the column in the end

can be close to a stop and lie very close

each other when the plant is running. In any case, the regulation of the creation of atmospheric pressure in the collection vessel is arranged in such a way that the liquid is introduced completely into the vessel before

the gas flow drops to a value at which the liquid could flow through the perforations in the plate, which is the so-called

critical value which, for example, can be of an order of magnitude corresponding to 15 hundredths of the column's normal gas flow through. Furthermore, the recovery is imprinted in the collection vessels - regulated in such a way that the liquid is not pushed out: onto the plate until from

the'moment "where the :<g>aBS-:flow has reached a -value converter 'sufficient' to -to 'prevent the liquid' from flowing down through the perforation.

The gas flow and the pressure required for the aforementioned transport of the liquid can be provided directly by means of the compressor that normally feeds the column, or by means of any - other auxiliary device which can supply gas under pressure. It is often necessary that the so-called transport pressures inside the collection vessels be adjusted to the same value as the absolute pressure that prevails in the column at the relevant level, .that account is taken of the pressure loss the gases experience when passing through the underlying plates/When the qpp capture vessels are fed in series by means of a pneumatic circuit, the so-called "high-pressure circuit". In this circuit, pressure losses can be induced such that the pressure applied to a collection vessel is equal to, or slightly higher than, the pressure that prevails in the column at the same level. With regard to such a purpose, a found characteristic of the invention consists in achieving the lowering of the pump pressure between two on top of each other the following collection vessels — one. lowering..some1practically speaking.equal to the pressure loss of the gas during its,passage,-during normal operation, v through t.a .plate .which.is.located. between, disserto* acquisition vessel— vde..at~man,.on. it. pneumatic, high-pressure-cr.etch .places -a suitable .device which .is .suitable .to .-create ..this .pressure loss, for example-.a.liquid surface: with.a.height.corresponding to- .the.mentioned .pressure loss,.-e.g.-a.sic-seeding device, .a .labyrinth, .filling bodies, .a .narrowing, a spring-loaded. stamp, or.similar. JJten.en. such an arrangement would taykket-i.de, lower-vessel. could prove insufficient-to .to .transport the liquid, while. the .overhead .vessel .with .too .'high .pressure would .result .in .a -significant .gas out-flow. Apart from the appropriate features that may characterize the selection device for providing said pressure loss, for example, the dimensions of the submerged pipe, the liquid surface, writing -the vessel's j-good" func-s j on ,;at- those in submerged -tubes ;:which .'puts it-.in connection-.-with .-its <plate, •ear of insufficient [diameter, -or pea- .-sufficient.-in-number-to-enable-a^rapid -emptying, cd.e..before -.the -.pressure: in -the -column -has -decrease completely-after interruption .-of-;gas-r circulation. iThe description 3of 'the ; device *present<invention;applies, as well as to its function, is completed with view f to the attached -drawings..These rggen-;provide schematically: Own. we a vertical cdiametral .section through 'a .perforated .plate rnied < overflow: in ten absorptionBcolumn.-.The liquid levels eruie :as iman tiakttar -under . normal ;.operation .of ! the column.

Fig. 2 ground plan of the same plate, seen from above, schematically 'manufactured, according to the cut A--A'. on: fig.jl.

IFig.^fsame plate with associated collection vessel, observed in the period of time where the column was stopped.

iFig. -4 schematic representation of two plates on top of each other, with an intermediate liquid surface, which moves the coupled mind in the pneumatic high-pressure circuit between two collection vessels.

!On ?fig. "1 occupies the plate in (1'1>) — If the middle part is perforated^with 'many holes; and is^limited by two walls (2)—mostly the entire school section :(3).horizontal '.cross-sections. The plate :gets - .supplied -vliquid through a line (<4) coming from the-above-digging plate :and:mouth spout in: a Fkum x (:5); which forms a '.liquid lock to (prevent that ; gas penetrates inside the line (-4).. When the liquid on the plate (sl*) reaches the level >. (6) it flows out the overflow (7) and feeds the plate immediately below (see .fig. A). bare :"the '.thin -liquid layer; for which -ear is unnecessary, with the help of "the three:tubes-(9),-to-form

-liquid lock '.between; the vessel (:8) train plate f (ri ). "The liquid column >inside ;in /each of these .;tubes ((.9)

is kept in7place in .these-of the rdet'.the pressure which

•the liquid :in .the collection vessel (-8) is exposed to. This pressure is balanced by the pressure that prevails over the liquid covering the plate (!•), increased by the static pressure in the liquid column with a height of (10) . In 'Vifkélighetenjkan-.it heals ■normal fd-rift, :Æor -to rsure >that the collection vessels.are.clear'.to:the.year.rmiot<the-.liquid---'■that rcovers the plate: in the stop moment, -be favorable.'.to::arrange-:a.weak gas current? ('bubble rf orrboble):in<: the collection vessels, :for 3to -.avoid .the danger -a -accidental pressure reduction in the collection vessel falls a passing overpressure • in the column would -represent. When the column is stopped (fig. 3), the collection vessel :(:8) is automatically connected to the atmosphere (or to an area which has a lower pressure than that prevailing in the column) , 'which happens *via the -pneumatic .iprint circuit (11) •which.is.operated?by:three-way room coupler -'('12),

whose function is linked to the (not shown in the drawing) compressor that feeds the column. This enables the liquid on the plate (1) — under the influence of the thus created pressure difference between the plate (1) and the tub (8), and under the influence of gravity — to flow quickly through the pipes (9) and penetrate into the tub (6) .

When normal gas flow has been restored, in order to bring the column back to normal operating rhythm, the switch (12) will automatically cut off the vessel's (8) connection with the atmosphere through the "low pressure" circuit (11) and, at the same time, open for "high -pressure" circuit (13) which opens into the vessel (8). The liquid stored in the latter will then be pushed up through the pipes (9) and distributed on the plate (1), where it will remain, being supported by the pressure that prevails under the plate, and emulsified by the gas that penetrates through the perforations . The gas introduced into the collection vessels (8) is in principle the same as that which circulates in the column, although this is not an absolute condition.

From the moment equilibrium between the pressure in the vessel (8) and the pressure exerted by the liquid in the pipes (9) is restored, the system will once again be in the original functional state which is diagrammed in fig. 1.

The reversible function of the collection vessel (8) is facilitated by the presence of the washing bottle device (14) (see fig. 4) on the pneumatic "high pressure" circuit (13). The submerged pipe (15) in a washing bottle which forms a connection between two collection vessels (8) is in connection with the lower collection vessel, while the non-submerged pipe (13) is in connection with the upper collection vessel.

This description is given here only as a non-limiting example of realization of the device which is the subject of the present invention. Namely, one can change the construction and location of the elements necessary for the implementation of the invention, without therefore changing the essential characteristics that appear from the foregoing. Thus, for example, it is possible to mount the device for retaining liquid, including the washing bottle, and the pneumatic circuit, outside or inside the column itself, above or below the plane of the plate. One can also, under each plate, place several small collection vessels of a shape adapted to the available space, provided that their combined capacity at a given level is sufficient to receive the total contents of the plate or at least a quantity of liquid that is sufficiently large to do so possible rationally and quickly to restore the operating rhythm in the column. At the same time that these collection vessels are in connection with the non-perforated part of the plate in the case of submerged pipes, and in the case of a pneumatic circuit with the atmosphere, they can either be in connection with each other or be independent. The pneumatic circuit can be simple or complex. The vessels can be fed in series or in parallel, etc.

Device for retaining liquid according to the invention described above, can be used on all devices, towers and columns that have plates intended for distribution of a liquid so that one can create as intimate a contact as possible with a gas, e.g. for the purpose of washing the gas with the liquid or to cause one to absorb the other, as this absorption may or may not be accompanied by a chemical reaction between two phases, or for example with the purpose of carrying out a chemical exchange between the gas and the liquid, i.e. to generally establish an exchange of substance and/or heat between the two phases. The device is also used on rectification columns with perforated plates, on columns for liquid/liquid extraction, on columns for separation by entrainment, on stripping columns, on condensers, on evaporators and, quite generally, on all columns for exchange of matter and/or heat. The device can also be used on perforated plates intended for establishing the distribution of a liquid over a lining.

The aforementioned device for retaining liquid is used on plate columns that are used, e.g. for fractional distillation of liquid mixtures with a view to separating their constituents. The device is actually applicable in all known cases that require use

of columns with perforated plates where, due to their structure, the columns are quickly emptied the moment the gas pressure drops below a certain value.

Below is an example of an industrial-scale implementation of the device for retaining liquid according to the present invention — an example illustrating its use in an absorption column with perforated plates, with overflow, of the type used in the production of nitric acid, where the nitrogen oxides to be absorbed and oxidized circulate from below upwards in countercurrent with the absorbing liquid which flows from plate to plate. Each plate in the column has a diameter of e.g. 4.20 m and, taking into account the volume of acid emulsified on the plate, has a collection vessel with a capacity of 0.8 m<3>, which is placed inside the column below the plate, at the overflow. The tub covers an area of 0.815 m<2>, which means 5.9 per cent of the plate's total area. It has a depth of 1 m. The collection vessels on the different plates are fed in series by the pneumatic circuit, via washing bottles which are adapted to each of the plates' pressure loss.

Since the absolute pressure that prevails under the first plate is 3.410 kg/cm<2>, and since the overpressure for the collection vessel is 0.120 kg/cm<2>, corresponding to 3.5 percent of the gas pressure at the entrance, the absolute pressure becomes in the container 3.530 kg/cm<2>.

The height of the submerged tubes in each wash bottle, which is placed between two successive collection vessels, depends on the specific weight of the liquid it contains — in the present case, it applies to a liquid which, in terms of composition and concentration, is equal to that which is emulsified on the plate during permanent operation — and that the pressure drop between these two collection vessels, so that the pressure drop in the pneumatic circuit between two plates is equal to the pressure drop the gas suffers in the column when passing through the concerned loaded plate. Thus, the length of the submerged tube in the washing bottle which is placed between two collection vessels and which contains nitric acid with a specific weight of 1.38 kg/dm<3>, when the pressure drop between these two collection vessels, lower and upper, is 0.22 kg/cm<2> — tentatively be 0.156 m. As the pressure drop between the second collection vessel and the third, which sits still higher up, is 0.0193 kg/ cm<2>, the submerged pipe in the splash column has is inserted between these two vessels and contains the same acid (sp.v. 1.38 kg/dm<3>), a length of 0.14 m, while the height of the acid on the plate is 0.06 m at rest (the liquid still does not emulsified), and the plate's total surface is 13.85 m<2>. The internal diameter of the pipe which is installed for the inflow of the acid into the collection vessels is 0.09 m. Experience shows under certain circumstances that when the excess pressure or the effective pressure inside the column is 2.41 kg/cm<2> and the nitric acid con- the concentration is 60 per cent, the liquid that is held on the plate during permanent operation will completely penetrate into the collection vessels during approx. 15 seconds after these have been put in contact with the atmosphere.

The above, by no means limiting example, clearly illustrates that on an industrial scale it is possible, - when the gas circulation in the column stops - to completely retain the liquid emulsified by a gas which is on a plate perforated with an overflow. As the device for retaining liquid used on this occasion has no moving parts, it does not require any maintenance and is not subject to any mechanical failure because it functions exclusively under the influence of pressure variations. The excess pressure required for the device to function correctly, which is equal to the difference in pressure corresponding to the amount of liquid (which is due to the liquid lock) between the plate and the collection vessel, constitutes only a very small part of the total energy that goes into the column's operation.

Claims (3)

1. Column with perforated plates suitable for providing contact between gas and liquids, where for each plate there is at least one receiving device that can collect the total liquid load that normally covers the corresponding plate, and thus maintain the equilibrium composition that the liquid has when the circulation of the pressurized gases decreases or stops completely in the column, characterized in that the receiving device's collection vessel (8) has one or more non-immersed pipes (11) by means of which atmospheric pressure can be provided in said collection vessel (8) when this is filled with liquid from the plate (1), resp. by means of which the collection vessel (8) can be connected to an area where the pressure is lower than that which prevails in the column (3), resp. is connected to an area where the pressure is higher to transport the liquid from the collection vessel (8) over to the plate (1). 2. Column according to claim 1, characterized in that the different collection vessels (8) in the same column (3) are fed in series from a pneumatic "high-pressure" circuit (13), and that a pressure loss is provided by means of such suitable an-arrangements (14) such as wash bottle, labyrinth, packing bodies, spring-loaded piston, or narrowing of the diameter of a pipe, between two successive vessels, so that the pressure in a collection vessel becomes equal to or slightly higher than the pressure prevailing in the column at this level when taking Considering the pressure losses the gas suffers by passing through the different plates. 3. Column with perforated plates, according to claims 1 and 2, characterized by: a) The creation of a connection between the collection vessels (8) and the atmosphere through a pneumatic "low-pressure" circuit (11), or with an environment of high ere pressure through a pneumatic "high-pressure" circuit (13), is routed by means of a three-way switch (12) which is connected to the column's compressor, b) the pressure losses provided on the pneumatic "high-pressure" circuit (13) between two series-mounted collection vessels following each other, is achieved by means of a liquid bottle (14) whose submerged pipe (15) is connected to the collection vessel (8) below, while the non-submerged pipe (13) is connected to the above -gent collection vessel (8), and if liquid height is calculated in accordance with this, c) the receiving device (8) which is intended to receive the liquid load from the plate (1) consists of several collection vessels, of any shape, which are connected to each other and whose combined capacity is sufficient to receive the total liquid load that normally covers the plate, d) the receiving device, which is intended to receive the liquid load from the plate, is placed outside the column body.