WO1984004048A1

WO1984004048A1 - A separation column for mounting upon a movable support

Info

Publication number: WO1984004048A1
Application number: PCT/SE1984/000130
Authority: WO
Inventors: Bo Gerdin; Haokan Svensson
Original assignee: Swedyards Dev Corp
Priority date: 1983-04-11
Filing date: 1984-04-09
Publication date: 1984-10-25
Also published as: NO844792L; SE8301980D0; BR8406591A; JPS60500997A; EP0139735A1; SE8301980L

Abstract

In order to make possible the use of a separation column (10) upon a movable support (11), for instance a barge in a floating process plant, the column is subdivided vertically by means of a number of hanging floors (12 - 15), which each carries a bed (16 - 19) of filler bodies, over which the fluid to be treated is sprayed. The beds (16 - 18) above the supply conduit (20) connection have a limited height, preferably not materially exceeding the diameter of the column, so possible tilting movements of the column will not influence the flow of fluid within the individual beds. The fluid having passed one bed is collected upon its carrying floor, and is by way of pump (26), which raises the pressure, passed on to nozzles (28) arranged above an underlying bed.

Description

A SEPARATION COLUMN FOR MOUNTING UPON A MOVABLE SUPPORT.

Many chemical processes include separation by distillation. Operating experiences from distillation columns have shown, that the support and the mounting of the column thereat is of major importance. The column should be erected so as to be exactly vertical. Even a deviation in the magnitude of one half of a degree may detrimentally affect the efficiency of the column. Vapour tends to pass along the upwardly turned portion of the envelope wall of the column, while fluid will flow downwards along an oppositely located portion of the wall.

The expansion within the offshore industry, and especially the working of "small" gas sources, has made it interresting to distill hydrocarbon products directly at the site, preferably in conjunction with a plant for further processing the products.

A distillation column forming part of a floating process plant will unavoidably be affected by the movements of sea waves. The more serious problems are related to an erronous distribution of the fluid phase within the column.

The aim of the present invention is to propose a separation column which will operate satisfactorily even if it is mounted upon a movable, or unstable support.

The column comprises a number of filler body beds, basically of standard type. The beds are, however, arranged and dimensioned in a novel manner, and the fluid is handled in a special way within the column.

The invention thus, relates to a separation column adapted for mounting upon a movable support and having a number of horizontal hanging floors, an attachment for a conduit supplying a fluid mixture, as well as equipment for condensing vapours being generated and for removing residues. Each floor carries a bed of filler bodies reaching to a predetermined level but permits an upward flow of vapour and means are provided for distributing a fluid over the top layers of filler bodies. The invention is characterized in that the bed carried by the lowermost floor and reaching about to the attachment for the supply conduit is noticeable in relation to the diameter of the column, whereas the height of a bed upon any floor above the attachment does not materially exceed the diameter of the column, that the lowermost floor is a gridlike structure and defines an underlying fluid collecting chamber connected to means for heating the collected fluid, and that a return flow conduit from the floor just above the attachment is connected to the supply conduit, wherein the arrangement permits collecting the fluid upon any of the floors above last mentioned floor and passing it through a pump for raising the pressure of the fluid before this by means of a number of nozzles is evenly distributed over the filling bodies upon an underlying floor. The column is preferably provided with a preheater for the mixture of freshly supplied fluid and return flow fluid and having a connection for transferring generated vapour directly to the column, separately from the mixed fluid attachment. The connection between the preheater and the connection preferably includes a collecting vessel provided with a level gauge.

Means are preferably provided for transferring a surplus of heating fluid from a heat exchanger at the lower column chamber to the preheater for the fluid supply.

A return flow conduit from any upper floor preferably includes a collecting vessel provided with a level gauge.

The invention will below be described with reference to the accompanying drawing, in which

Figure 1 schematically shows a distillation column mounted upon a barge forming part of a process plant producing petrochemical products based upon natural gas, and Figure 2 shows a distribution means for fluid, seen along section II - II in Figure 1. A possibility to exploit an offshore gas source, which is of a magnitude, or is so located, that it is not justified to connect it by pipeline to a shorebased consumer, is to moor a floating process plant adjacent to the gas source, where the gas can be transformed into products suitable to be carried away by ships.

The gas can for instance be transformed into methanol. The raw product will however contain about 15% of water, which is an unnecessary burden during transportation.

The processing can advantageously be developed at the seaborne plant, where cheap energy from the gas source is available. On such occasions certain residual products must be removed.

A distillation column upon a process plant barge will unavoidably tilt in relation to its vertical axis, in the first hand due to the influence of waves and wind, but also due to the trim and heel conditions of the barge changing from time to time due to the transfer of cargo and ballast.

In order to obviate the disturbing influence of such movements, the columns has been arranged to function in the manner explained in conjunction to the accompanying drawing.

The distillation column 10 is formed as a vertical tower, and is supposed to be mounted upon a barge, denoted by 11, which also will carry other components of the process plant.

The column is subdivided in the vertical direction by means of a number of hanging floors 12 - 15. The floors 12 - 14 are designed as fluid collecting troughs, while the floor

15 is a gridlike structure.

Each floor carries a bed of filler bodies of some standard type, which offers a large contact surface for the downwardly flowing fluid. In this manner a number of stacked beds 16 - 19 are obtained.

The lower bed 19 may have noticeable height, as it is located near the bottom of the column, where the tilting movements are not so marked, and where the heating condititions are favourable. The superposed beds 16 - 18 have, in the embodiment shown, a height about equal to the diameter of the column. The height of a bed located above the attachment of the supply conduit should not materially exceed the diameter of the columns, because otherwise there is a risk of condensed fluid flowing down along the internal envelope wall. The raw fluid mixture is supplied by way of a conduit 20 and is mixed with return flow from floor 14, transferred by way of a conduit 21. The mixed fluids are passed on to a preheater 22. Vapour generated within the preheater is transferred directly to the column by way of a conduit 23, separately from the fluid.

The preheated fluid is collected In a receptacle 24 provided with a level gauge 25, and is by means of a pump 26, by way of a conduit 27 transferred to a number of spraying nozzles 28, mounted above the lowermost bed 19.

As is evident from Figure 2 the nozzles 28 are evenly spaced over the surface of the bed, so each portion thereof will be supplied with the same quantity of fluid.

The pressurized fluid will thus be evenly distributed over the filler bodies of bed 19 and will trickle downwards along the latter. Fluid which has not been evaporated is collected at the bottom of the column. Here two preheaters are provided, of which one, 29, is heated by steam and is used during starting up of the plant. The other preheater, 30, may be heated by hot process gas. Both preheaters may be used during normal operation.

The process gas is supplied by way of a conduit 31, passes the preheater 30 and is then conveyed to the fluid supply preheater 22. The now cooled gas is from the latter transferred to a suitable recipient within the plant, by way of a conduit 32.

A conduit 33 for removing residual products is connected to the bottom of the column.

A mixture of vapour will pass upwards through floor 14 into bed 18. Above the latter there is a second series of spray nozzles 28a. These are supplied with fluid which has collected upon the superposed floor 13, and has passed a collecting vessel 24a with level gauge 25a and a pump 26a.

Fluid collected upon floor 12 is transferred to a collecting vessel 24b having a level gauge 25b, and is by means of a pump 26b sprayed through nozzles 28b above the bed 17.

The increase in pressure at each stage need not be high, only sufficient to ensure an even distribution. The level gauges will govern valves in the transfer conduits and possibly also the pumps, so the supply of fluid to any set of nozzles will be occasionally interrupted if the return flow from a superposed floor is not sufficient to maintain an amount of fluid in the vessel ensuring a satisfactory supply of fluid to the nozzles.

Methanol vapour is bled off at the top of the column, and is by way of a conduit 34 and a condenser 35 transferred to an accumulator 36. A pump 37 conveys the condensate by way of a cooler 38 to a consumer, or to a storage tank, but recirculates a portion of the condensate to spraying nozzles 28c located above bed 16.

A conduit 39 is connected to accumulator 36 for removing possible light gaseous fractions.

Further conduits 40 are connected to the lowermost bed 19 for the withdrawal of by-products, which are cooled in a a heat exchanger 41 and transferred for further processing or storage.

The embodiment shown is one example of the invention only, and the details thereof may be varied in many ways within the scope of the appended claims.

The number of hanging floors will have to be suited to local conditions and it may be appropriate, on certain occasions, to reduce the height of the beds in the direction towards the top of the column,, especially with high columns, or with columns mounted upon the support where the movements may be expected to be noticeable.

The plant is, in the first hand expected to handle a mixture of methanol and water, but it is evident that also other hydrocarbon products may be handled in the described manner.

Claims

1. A separation column (10) adapted for mounting upon a movable support and having a number of horizontal hanging floors (12 - 15), an attachment (27) for a conduit (20) supplying a fluid mixture, as well as equipment (35; 33) for condensing vapours being generated and for removing residues, where each floor (12, 15) carries a bed of filler bodies (16 - 19) reaching to a predetermined level but permits an upward flow of vapour and means (28) are provided for distributing a fluid over the top layers of filler bodies, c h a r a c t e r i z e d in that the bed carried by the lowermost floor (15) and reaching about to the attachment (27) for the supply conduit (20) is noticeable in relation to the diameter of the column (10), whereas the height of a bed (16 - 18) upon any floor (12 - 14) above the attachment (27) does not materially exceed the diameter of the column, that the lowermost floor (15) is a gridlike structure and defines an underlying fluid collecting chamber (10a) connected to means (29, 30) for heating the collected fluid, and that a return flow conduit (21) from the floor (14) just above the attachment (27) is connected to the supply conduit (20) wherein the arrangement permits collecting the fluid upon any of the floors ( 12 - 13 ) above last mentioned floor ( 14) and passing it through a pump (26) for raising the pressure of the fluid before this by means of a number of nozzles (28) is evenly distributed over the filling bodies upon an underlying floor.

2. A separation column according to claim 1, c h a r a c t e r i z e d in a preheater (22) for the mixture of freshly supplied fluid and return flow fluid and having a connection (23) for transferring generated vapour directly to the column, separately from the mixed fluid attachment (27).

3. A separation column according to claim 2, c h a r a c t e r i z e d in that the connection between the preheater (22) and the connection (27) includes a collecting vessel (24) provided with a level gauge (25).

4. A separation column according to claim 1, c h a r a c t e r i z e d in means for transferring a surplus of heating fluid from a heat exchanger (30) at the lower column chamber (10a) to the preheater (22) for the fluid supply.

5. A separation column according to either of the preceeding claims, c h a r a c t e r i z e d in that a return flow conduit from any upper floor (12 - 14) including a collecting vessel (24a, b) provided with a level gauge

(25a, b).