Patent Application
20180304192
The present invention relates to the field of liquid-gas contacting columns, and more particularly the gas treatment, CO2 capture, dehydration or even distillation offshore columns (at sea).
The gas treatment and/or CO2 capture units based on amine washing comprise absorption and regeneration columns for fluids, liquid or gases. The latter operate under counter-current or co-current liquid-gas flow conditions. When they are offshore, the columns can be installed on vessels, floating barges or offshore platforms, for example of FPSO (Floating Production, Storage and Offloading) type or of FLNG (Floating Liquefied Natural Gas) type. On the floating barges, distillation columns or dehydration columns can also be installed.
The columns used in these gas treatment and/or CO2 capture and/or distillation and/or dehydration units (offshore or on land) generally operate on the principle of an exchange of material and/or of heat between the gas and the fluid which circulate in the columns. Conventionally, this gas treatment column comprises a number of sections, each section comprising a contactor (also called packing), and a collector tray, which is arranged above the contactor. The gas/liquid contactor contacts the gas and the liquid in order to allow the exchanges of heat and/or of material. The tray collects the liquid and allows the distribution of the liquid on the contactor.
The standard on land distribution trays used in the absorption/stripping columns or even distillation columns generally consist of a plate which is intended to be a liquid collector and distributor. The liquid collector is also intended to be a gas distributor and a liquid conveyor. The operation of these distributor trays is generally by gravity. In this respect, a liquid seal, the height of which depends on the pressure loss through the tray and the liquid flow rate, generally forms on the tray to provide the hydraulic power necessary to the good operation of the liquid distributor which consumes a pressure energy in the flow.
Several types of gas/liquid distributor trays can be used, and can generally belong to three broad families:
One of the designs proposed by those skilled in the art consists in gathering the liquid at the central axis of the column, in the middle of the collector tray. The gathered and centralized liquid is discharged in a vertical conduit which links the liquid collector tray and the distribution system by one or more relatively long vertical conduits for the distributor system to remain filled with liquid (said to be “charged”), whatever the swell conditions encountered. The vertical conduit is dimensionned so that the variation of the liquid height due to a fault of horizontal alignment is significantly lower than the height of the liquid conduit supplying the distribution system (U.S. Pat. No. 8,118,284B2, US 2004/0020238 A1). In this case, the liquid distribution system can be formed by one or more sprinklers and the gas is routed by chimneys situated at the collector tray.
For offshore applications, the movement of the swell rapidly degrades the distribution of the liquid and gas phases in the packed beds. This maldistribution is more or less significant depending on the type of packing retained, and depending on the periods and amplitudes associated with the movement of the swell. In any case, it affects the uniformity of the distribution of the liquid and of the gas in the contact beds with the creation of zones under-supplied with liquid (said to be “underloaded”), and zones over-supplied with liquid (said to be “overloaded”). These maldistributions of the liquid induce malgas distribution, with, once again, zones over-supplied and under-supplied with gas (relative to the average). The distribution of the zones depends on the conditions (movement undergone by the column, flow rates, contact technology, column size, etc.). The prior art shows that the loss of efficiency of the packed bed in the column is at its maximum when a zone over-supplied with gas encounters a zone under-supplied with absorbent liquid, which tends to degrade the efficiency of the columns concerned via the generation of marked concentration profiles.
In the gas treatment case, the hydrodynamic malgas distribution phase and of the liquid phase in a contact bed therefore leads to a more or less efficient absorption of the species to be eliminated in the gas phase via non-uniform velocity profiles, but also via non-uniform profiles of concentrations of chemical species (for example of H2S, CO2) in the two phases. In effect, the quantity of chemical species transferred between the gas and liquid phases depends partly on the composition of these phases and on the placing in contact thereof, which depends on the contactor and on the velocities of the gas and of the liquid. While the known distributor trays are supposed to redistribute the gas, they do not not remix thereof. They do not make it possible to make the chemical species concentration profile uniform over the section of the packed bed.
For a given design of gas treatment column, it seems favorable for the gas to have a concentration which is as uniform as possible over all the section to obtain the best efficiency and more easily meet the specifications in terms of residual H2S and CO2 concentrations at the column output. For on land applications, the liquid distribution systems and the heights of the beds are engineered to avoid excessively maldistributions of liquid and of gas and thus avoid notable concentration profiles. For offshore applications, the systems described do not sufficiently re-mix the gaseous phase.
The patent application WO 2014/070352A1 describes a system for mixing gas between two contact beds. The gas mixing system is formed by a plate which creates a gas passage section restriction between two contact beds so as to mix the latter before redistributing it. The gas mixing system described in this patent application does not provide any liquid distributor, and the liquid is collected at the periphery of the column before being introduced directly into the bed below, which renders the column sensitive to its inclination. Furthermore, the different gas mixing systems proposed in this document have a complex shape, the assembly of which can also be complex.
The patent U.S. Pat. No. 4,820,455 relates to a gas mixing induced by specific openings of the gas chimneys on the collector tray. The chimneys situated at the periphery send the gas to the center of the section and those situated at the center supply gas over 360°. This design can contribute to mixing the gas but this mixing remains partial in the case of maldistributions which extend over a large part of the section, notably if concentric non-uniformous gas distribution from the central axis of the column are envisaged. The invention proposed by this patent does not appear to lend itself to ensuring the re-mixing of the most peripheral zones with the gas circulating about the central axis of the column.
To overcome these drawbacks, the present invention relates to a column for exchanging heat and/or material between a gas and a liquid. The column comprises at least one collector tray, at least one packed bed, and mixing means for a gas flow. According to the invention, the mixing means for a gas flow are arranged below the collector tray and above the packing. Thus, the gas distribution is improved. Furthermore, the invention does not influence the distribution of the liquid arriving on the collector tray. Furthermore, mixing means for the gas flow are configured to distribute the gas flow over substantially all the section of the column, so as to increase the mixing of gas and to optimize the gas distribution over the upper packing.
The Device According to the Invention
The invention relates to a column for exchanging heat and/or material between a gas and a liquid, comprising at least one collector/distributor tray, and at least one packing for placing gas and liquid fluids in contact, said collector tray distributing said fluids over said packing, said column further comprising mixing means for a gas flow. Said mixing means for the flow of said gas are arranged below said collector tray and above said packing, and said mixing means for the flow of said gas are configured to distribute the gas flow over substantially all of the section of the column.
According to the invention, said mixing means are configured to drive the gas flow in a direction substantially parallel to the axis of said column.
According to an embodiment of the invention, said mixing means are configured to drive the gas flow in a substantially radial and/or ortho-radial direction relative to said column.
Advantageously, said mixing means are substantially parallel to said collector tray.
According to an embodiment, said mixing means for the flow of said gas comprise at least one plate deflecting at least a part of the current lines of said gas flow.
According to a variant embodiment, said plate is fixed relative to said collector tray.
Alternatively, said plate is rotationally mobile about an axis.
According to one aspect of the invention, said plate is substantially in the shape of a half-disk, a helix, a paddle, a blade or an inverted U.
Advantageously, said plate is mounted on a rod fixed to said collector tray.
According to an alternative, said collector tray comprises a distribution system comprising at least one supply conduit protruding below said collector tray, said plate being mounted on said supply conduit of said distribution system.
According to a variant, said mixing means for the gas flow comprise a number of plates arranged one below the other.
According to an embodiment, said mixing means for the flow of said gas generate a cyclonic movement of said gas flow.
Advantageously, said mixing means for the gas flow comprise at least one blade orientated toward the center of said column.
Alternatively, said mixing means for the gas flow comprise a deflector having a substantially helical shape of the worm screw type at the center of said column.
According to an embodiment, said collector tray comprises a distribution system comprising at least one conduit protruding below said collector tray, and in which said mixing means for the flow of said gas comprise a dry packing arranged around said conduit of said secondary distribution system.
According to an embodiment, said mixing means for the flow of said gas comprise means for restricting the gas passage section.
Preferably, said restricting means direct the flow of said gas to the periphery of said column.
As a variant, said restricting means comprise at least one chicane.
According to an embodiment, said mixing means for the gas are formed by a distribution system linked to said collector tray.
Advantageously, said distribution system comprises at least one conduit protruding below said collector tray, and a plurality of pipes linked to said conduit, said pipes being arranged substantially according to the generatrices of a cone, the axis of which corresponds substantially to the axis of said column so as to direct the gas.
Furthermore, said distribution system can comprise at least one conduit protruding below said tray, a gutter linked to the conduit, and a plurality of pipes linked to said gutter, said gutter comprising at least one orifice for the passage of the gas.
Furthermore, the invention relates to the use of a column according to one of the above features for a gas treatment, acid gas capture, distillation, dehydration or air separation method.
Other features and advantages of the method according to the invention will become apparent on reading the following description of nonlimiting exemplary embodiments with reference to the figures attached and described hereinbelow.
The present invention relates to a column for exchanging material and/or heat between a gas and a liquid. The column according to the invention is suitable for counter-current flows of the liquid and of the gas. However, the column according to the invention can also be suitable for co-current flows of the liquid and of the gas.
The column comprises at least one collector tray, and at least one packed bed. The collector tray makes it possible to form a liquid seal and allows the distribution of the liquid over the lower packing. Preferably, the column comprises at least two packed beds, the collector tray being situated between the two packed beds. The packing corresponds to a contactor and makes it possible to place the liquid and the gas in contact, in order to allow the exchanges of material and/or of heat between the fluids. According to the invention, the packing can be random packing or structured packing. The term packed bed is used to describe a packing section. Preferably, the exchange column comprises a plurality of collector trays and a plurality of packed beds.
According to the invention, the column further comprises mixing means for the gas flow. The mixing means for the gas flow are arranged between a liquid collector tray and a lower packed bed. The mixing means for the gas flow are situated below the liquid collector tray and above the packed bed immediately below. The notions of arrangement “below” and “above” correspond to the positioning of the different elements, when the column is in position of use, that is to say in a vertical position.
The mixing means for the gas flow are configured to distribute the gas flow over substantially all the section of the column. Thus, the gas mixing and the gas distribution over the upper packing are optimized compared to the prior art solutions, for which the gas flow is only redistributed by offering a minimum passage section which is based on the constricted fluid stream device known from the prior art. The constricted fluid stream phenomenon centralizes the fluid through a reduced orifice and then redistributes it in a passage section greater than the orifice. While this device makes it possible to ensure a good gas distribution velocities at the output of the orifice throughout the section of the column, the gas mixing however is not physically assured to the point of obtaining a uniformity of the gas distribution compositions over the section of the column, unlike the present invention which proposes devices suitable for and specific to the gas mixing.
According to an embodiment of the invention, the mixing means for the gas flow can be arranged substantially parallel to the collector tray, that is to say that the main direction of the mixing means is substantially parallel to the collector tray. Thus, in a position of use of the column, the mixing means for the gas flow are substantially horizontal. Note however that the mixing means for the gas flow can have portions protruding in another direction, reference can for example be made to the embodiment of
The mixing means for the gas flow make it possible to efficiently mix the gas at the output of a contact (packed) bed before introducing it into a second packed bed, in order to obtain a better distribution and a more uniform composition of the gas over all the section of the column, notably for the offshore applications. The mixing means for the gas flow can be combined with gas/liquid collector trays of the prior art which make it possible to distribute the gas and the liquid over all the section of the column. Physically, these mixing means for the gas flow generate the deflection of the gas stream lines, so as to create changes of trajectory which favor the mixing of a gas flow exhibiting a profile of concentration in one (or more) chemical compound(s) X. Thus, the gas concentration can be homogenized over all the section of the column. These mixing means for the gas flow can also amplify the turbulent nature of the flow which favors the mixing. The arrangement of the mixing means for the gas flow below the collector/distributor tray makes it possible to retain a good distribution of the liquid.
According to an embodiment of the invention, the mixing means for the gas flow can drive the gas flow in a substantially axial main direction (along the axis of the column, and a fortiori the axis of the collector tray and of any distribution means). The term “main direction of the flow” denotes the orientation of the gas flow within the column generated by the mixing means for the gas flow. When this main direction is substantially axial, the flow stream lines are mainly axial, and the gas flow is not angularly deflected relative to the axis of the column. Thus, the gas mixing is assured.
Alternatively, the mixing means for the gas flow can drive the gas flow in a main direction that is substantially radial and/or ortho-radial (relative to the column, and a fortiori relative to the axis of the collector tray and to optional distribution means). The term “main direction of the flow” denotes the orientation of the gas flow within the column generated by the mixing means for the gas flow. When this main direction is substantially radial or ortho-radial, the flow stream lines are mainly radial, and the gas flow is not angularly deflected relative to the horizontal plane. Thus, the gas mixing is assured. Furthermore, this design makes it possible to make the profile of the concentration(s) uniform relative to the radial direction.
The mixing means for the gas flow can take several forms: one or more fixed or mobile plate(s), dry packing, one or more blade(s), one or more restricting means, one or more chicane(s), adaptation of the shape of the distribution means etc.
The collector tray can be produced according to different prior art designs. The collector/distributor tray can be produced notably according to the designs illustrated in
According to a first embodiment of the invention, the mixing means for the gas flow comprise at least one substantially horizontal plate (parallel to the collector tray). The plate makes it possible to deflect at least a part of the flow stream lines gas flow and to limit the gas maldistribution. Indeed, the plates form obstacles to the gas flow and enable this deflection. Furthermore, the plate is configured to distribute the gas flow substantially over the entire section of the column. The plate can be mounted on a rod fixed to the collector tray, removably screwed, supported by beams, etc. For this embodiment, the main direction of the gas flow is substantially axial.
The rod can be fixed to the collector tray for example by screwing, welding, through adhesive or any similar technique.
The plate can have substantially the shape of a half-disk, a helix, a portion of a helix, a paddle, an inverted U, or any similar form. Advantageously, the plate can have a surface representing up to 80% of the section of the column, so as to optimize the distribution of the gas flow.
The plate can be fixed relative to the rod, notably by screwing, welding, through adhesive or any similar technique. Alternatively, the plate can be mounted to be rotationally mobile relative to the rod, what makes it possible to increase the efficiency of the mixing. The rotation of the plate can be implemented by a driving mechanism, for example by a motor, or can be directly driven by the gas flow.
According to a variant of this embodiment, the collector tray can comprise a plurality of rods, onto each of which at least one plate can be mounted. This design enables a greater deflection of the gas flow stream lines, notably for the columns of larger diameter. This configuration also allows for a better distribution of the gas flow substantially over of the entire section of the column.
According to a particular design, a number of plates, for example two, can be mounted on a rod. Thus, it is possible to optimize the mixing of the gas flow.
For this embodiment, the collector/distributor tray may or may not comprise a liquid distribution system.
Advantageously, the plates can be metal plates.
According to another embodiment of the invention, the collector tray comprises a liquid distribution system. The distribution system can comprise at least one vertical supply conduit protruding below the collector tray. The conduit can be linked to a set of sprinklers (horizontal pipes provided with orifices and/or nozzles for the distribution of the liquid). For this embodiment, the mixing means for the gas flow can comprise at least one plate, substantially parallel to the collector/distributor tray. The plate makes it possible to deflect at least a part of the gas flow stream linesgas flow. Indeed, the plates form obstacles to the gas flow and enable for this deflection. Furthermore, the plate is configured to distribute the gas flow over substantially the entire section of the column. The plate is mounted on the vertical supply conduit of the distribution system. The plate can be fixed relative to the conduit. Alternatively, the plate can be constructed with a device which enables it to be rotationally mobile relative to the vertical supply conduit, what makes it possible to increase the efficiency of the mixing. For this embodiment, the main direction of the gas flow is substantially axial.
According to a variant of this second embodiment, the plate can be substantially in the shape of a blade. Advantageously, the mixing means for the gas flow can comprise several blades mounted on the vertical supply conduit of the distribution system.
According to a variant of this embodiment, the distribution system can comprise several supply conduits protruding below the collector tray, on each of which at least one plate can be mounted. This design allows for a greater deflection of the gas flow stream current lines, notably for the columns of larger diameter.
Advantageously, the plates can be metal plates.
This embodiment is not illustrated, but can correspond to an arrangement of the plates 8 illustrated in
According to a second embodiment of the invention, the mixing means for the gas flow comprise at least one rotary plate, preferably a plurality of rotary plates. The rotation of the plate can be implemented by a driving mechanism, for example by a motor, or can be directly driven by the gas flow. The rotary plates can be substantially parallel to the collector tray. This embodiment can be combined with the embodiments previously described. The rotation of the plates allows for a gas flow distribution and the mixing thereof until a uniform composition is obtained over the entire section of the column.
According to one design, the plates can have the shape of blades mounted to be rotationally mobile about a rod fixed to the collector/distributor tray or a supply conduit of a distribution system.
Advantageously, the plates can be metal.
According to a third embodiment of the invention, the mixing means for the gas flow make it possible to form a cyclonic movement of the gas flow in the column, which allows for an efficient mixing of the gas flow. The cyclonic movement is virtually propagated over the entire section of the column, thus ensuring the distribution of the gas flow and the mixing thereof until a uniform composition is obtained.
According to a design allowing for the cyclonic movement of the gas flow, the mixing means for the gas flow can be similar to a static “turbine” which generates a cyclonic movement of the gas. Thus, the mixing means for the gas flow can be formed by “blades”, which can be profiled and inclined relative to the vertical, and weakly inclined relative to the horizontal, and capable of covering the entire gas passage section. These blades can be mounted on the shell of the column in the empty space below the collector/distributor tray and above the packing.
According to an alternative, the cyclonic movement of the gas can also be generated by a system of helical type relying on a “worm screw” mounted on a rod or on a conduit of a secondary distribution system. The “worm screw” system comprises a threading having a low angle relative to the collector tray. The gas is disturbed in its raising by the device so as to increase the mixing and the distribution uniformly over the entire section of the column.
The blades and the “worm screw” system can be metal.
This embodiment is suitable for collector trays with and without liquid distribution system.
According to a fourth embodiment, the collector tray comprises a distribution system. The distribution system comprises at least one vertical supply conduit protruding below the collector/distributor tray. The conduit can be linked to a set of sprinklers. For this embodiment, the mixing means for the gas flow comprise a packing, called dry packing, because this packing is passed through only by the gas and not by the liquid. The dry packing allows for a mixing of the gas flow, by virtue of the dispersive properties of the flows in the packing, whether it is a random packing or a structured packing. The packed bed can be substantially parallel to the collector tray. For this embodiment, the main direction of the gas flow is substantially axial. Furthermore, the dry packing occupies substantially the entire section of the column, which ensures the distribution of the gas flow over this section and the mixing thereof until a uniform composition is obtained.
This fourth embodiment is particularly suitable for offshore columns, for which the gas and the liquid are not mixed in the space between two contact beds (between two packing sections). Furthermore, the fourth embodiment has a reduced bulk, and makes it possible to occupy the smaller spaces left available between the collection zone and the existing distributors.
In the case of an onshore distributor, a packing having a significant capacity can, preferably, be installed as dry packing, in order to avoid blocking states.
According to a fifth embodiment of the invention, the mixing means for the gas flow comprise means for restricting the gas passage section. The restricting means direct the gas flow to the periphery of the column. Thus, the gas is oriented at a precise point, and is therefore efficiently mixed. The restricting means occupy substantially the entire section of the column. Thus, the restricting means allow for a distribution of the gas flow over this section. The restricting means generate a substantially radial flow (main radial direction of the flow) at the periphery of the column.
A variant consists in the collector tray being free of chimneys for the passage of gas. The gas cannot pass over the section occupied by the liquid collector, and passes over an annular section at the periphery of the column left open.
The means for restricting the gas passage section can be metal.
According to a sixth embodiment of the invention, the mixing means for the gas flow comprise means for restricting the gas passage section. The restricting means form at least one chicane, around which the gas passes. Thus, the gas, being oriented at a precise point, is efficiently mixed. Preferably, the restricting means form several chicanes. The chicanes determine a preferred passage for the gas. The chicanes can be formed by flat plates substantially parallel to the collector tray. Alternatively, the chicanes can be formed by plates of substantially chevron form. The flat plates can be mounted on a rod or on a conduit of a secondary distribution system. The restricting means occupy substantially the entire section of the column. Thus, the restricting means allow for a distribution of the gas flow over this section. The restricting means generate a main flow direction that is substantially radial.
According to a variant of this embodiment, the gas can pass on both sides of the chicanes. Alternatively, the gas can pass on only one side of the chicanes.
The passages for the gas can have different dimensions so as to create velocity gradients over the section of the column and favor the gas mixing.
Furthermore, the chicanes can also be provided with orifices/openings for the passage of the gas.
This embodiment can be produced with a collector tray with or without distribution system.
Advantageously, the means for restricting the gas passage section can be metal.
The variant of
The variant of
According to a seventh embodiment of the invention, the mixing means for the gas can be formed by a distribution system, situated under the collector tray. For this embodiment, the shape of the distribution system can make it possible to orient the gas flow, and therefore mix the gas. As a variant, the distribution system can comprise at least one orifice for the passage of the gas, so as to orient it, and therefore mix it. Alternatively, these two variants (form and orifice) can be combined so as to increase the mixing. The distributor occupies substantially the entire section of the column, thus allowing a distribution of the gas flow over this section. For this embodiment, the gas flow has a main axial direction of flow.
The distribution system can be based on the example of
According to a first variant, for which the shape of the distribution system ensures the gas mixing, the pipes are inclined and substantially oriented according to generatrices of a cone, the axis of which coincides with the axis of the column. This arrangement of the pipes notably makes it possible to favor the turbulent gas flow, thus ensuring a gas mixing between the packing and the collector tray.
According to a second variant, for which the mixing is allowed by at least one orifice, at least one orifice can be provided in a horizontal gutter. The orifice allows for the passage of the gas. Furthermore, the orientation of the orifice makes it possible to direct the gas in a desired direction, which makes it possible to optimize the mixing. Advantageously, the orifice is inclined relative to the horizontal direction. According to a first design of this variant, the orifice is inclined from the center toward the periphery of the column. Alternatively, the orifice can be inclined from the periphery toward the center of the column.
As a variant, the arrangement of pipes 6 of
The column according to the invention is advantageously an amine-based washing column but is suitable for any type of solvents.
The column according to the invention can be used in gas treatment, CO2 capture, distillation, dehydration or air separation methods. The column according to the invention can be used for applications offshore (at sea) or on land.
Furthermore, the invention relates to an offshore floating barge, notably of the FPSO or FLNG type, notably for the production and treatment of hydrocarbons. The barge comprises a column for exchanging material and/or heat between a gas and a liquid as described above. The column can form part of a gas treatment and/or CO2 capture unit for cleaning gaseous products (or fumes). On the floating barges, distillation columns and/or dehydration columns using this device can also be installed.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2015/052931 | 10/30/2015 | WO | 00 |
