Device for fragmenting a cryogenic liquid in a gas pipe.

Abstract

Title: Device for fragmenting a cryogenic liquid in a gas pipe. Device for fragmenting a cryogenic liquid jet in a gas flow (G), comprising a supply pipe for the cryogenic liquid (L) having one end, the liquid supply pipe has an inner diameter greater than or equal to 10 mm and a gas pipe (T) of circular section, of diameter d, the gas pipe comprising a portion having a reduction in diameter by a ratio of 20 to 50% at the liquid injection and over a distance y where: y = n × d and where the supply pipe enters the gas pipe so that its end is in the portion of the pipe line having the reduction in diameter and n is between 7 and 9. Fig.4

Description

Title of the invention: Device for fragmenting a cryogenic liquid in a gas pipe.

[0001] The present invention relates to a device for fragmenting a cryogenic liquid in a gas pipe, to a separation apparatus comprising such a device and to a method for fragmenting a cryogenic liquid in a gas pipe.

[0002] It is sometimes necessary to inject a cryogenic liquid into a pipe where a gas is circulating.

[0003] In a conventional air separation device diagram without a liquid oxygen pump, a liquid purge allows the liquid oxygen bath to be deconcentrated into hydrocarbons. The cold from this can be used in the main exchanger by being injected into the residual nitrogen after a first pass. The excess pressure which allows the liquid to be injected is mainly due to the hydrostatic height due to the weight of the liquid in the purge. We then have a small flow of cryogenic liquid which will be vaporized in a larger, superheated gas flow.

[0004] In some cases, the residual nitrogen can then pass through an expansion in a turbine. However, the wheel of a turbine is sensitive to potential droplet impacts. It is therefore necessary to ensure that the liquid is completely vaporized before the turbine.

[0005] It is also possible to inject the cryogenic liquid into a gas containing between 45 and 95 mol% of oxygen, for example between 72 and 82 mol% of oxygen.

[0006] The present invention relates to a device for injecting cryogenic liquid into a gas line. The gas is preferably at a temperature below 0°C, having been partially reheated in the main heat exchanger of the air separation apparatus, being a product of a cryogenic air distillation process.

[0007] The simplest way to proceed is to simply connect the two conduits so that they open into a single conduit. This results in wall injection. One might think that this is sufficient since there can be a temperature difference of several tens of degrees between the two fluids and the gas flow rate is significantly higher than the liquid flow rate.

[0008] However, in reality the exchange coefficients are low at the cryogenic temperatures involved. Indeed, the speed of the liquid is too low for the jet to penetrate far from the wall. In addition, the drops generated in this configuration are, according to the models available in the literature in the field of combustion, of millimetric size so that they are slow to evaporate. Indeed, the risk of blockage on the liquid line requires the use of a relatively large pipe diameter, and therefore both a low velocity on the liquid and above all a large typical size.

[0009] In addition, the drops are rapidly accelerated to the speed of the gas, then no longer having a relative speed and the transfer being mainly diffusive, less efficient than the convective transfer.

[0010] A natural way for those skilled in the art to improve the mixing is to add a static mixer in the conduit downstream of the injection. However, once the liquid is in droplets, such a device would either be ineffective, the droplets following the gas current lines, or even counterproductive, because if the drops are deposited on the mixer, then at the outlet of the mixer there would be a new fragmentation of the liquid whose drop size is difficult to predict.

[0011] Another way, classic in process engineering, is to distribute the liquid on a bed of packing which would in this case be in the pipe or to use a nozzle with a high pressure drop to spray the liquid in fine droplets. These two methods, relatively complex, are made impossible by the constraint of keeping a large passage section for the liquid in order to limit the risks of blockage.

[0012] OBJECT OF THE INVENTION

[0013] The aim of the invention is to propose a configuration that is simple to manufacture and install to promote the evaporation of the cryogenic liquid while limiting the risks of blockage in the liquid conduit.

[0014] Description and advantages of the invention

[0015] To this end, the present invention relates to a device for fragmenting a cryogenic liquid jet in a flow of superheated gas, where: - the pressure difference between the fluids is due to the hydrostatic pressure of the liquid in its pipe, - the liquid supply pipe has an internal diameter greater than or equal to 10 mm, preferably greater than or equal to 20 mm to limit the risk of blockage, - the gas superheat is between 10 and 30°C.

[0016] Characterized in that: - the liquid supply pipe penetrates to the middle of the gas pipe, - the gas pipe has a diameter reduction of a ratio of 20 to 50% at the level of liquid injection over a distance corresponding to 1 to 5 times the jet break distance y estimated according to the following correlation:

[0017] y = nxd

[0018] where d is the diameter of the liquid injection conduit, n is a number between 7 and 9, preferably between 7.5 and 8.5. - optionally a liquid injection nozzle to generate film atomization and resist clogging, - preferably of the flat jet type producing a flat or sheet-shaped jet.

[0019] According to an object of the invention, there is provided a device for fragmenting a jet of cryogenic liquid in a gas flow, comprising a supply pipe for the cryogenic liquid having one end, the liquid supply pipe has an internal diameter greater than or equal to 10 mm, preferably greater than or equal to 20 mm, and a gas pipe of circular section, of diameter d less than 600 mm, preferably less than 450 mm, over the majority of its length, the gas pipe comprising a portion having a reduction in diameter d by a ratio of 20 to 50% at the liquid injection and over a distance y where

[0020] y = nxd

[0021] and where the supply pipe enters the gas line so that its end is in the part of the pipe line having the reduction in diameter and n is a number between 7 and 9, preferably between 7.5 and 8.5.

[0022] According to other optional objects of the invention, it is provided:

[0023] -a liquid injection nozzle is arranged at the end of the pipe.

[0024] -the nozzle is of the flat jet type capable of producing a flat or sheet-shaped jet.

[0025] -the end of the pipe is within a radius of d / 10 around the central axis of the gas pipe.

[0026] -the supply pipe enters the gas line so that its end is at the inlet of the part of the pipe line having the reduction in diameter

[0027] - the gas pipe has a first section having a first diameter and a second section having a second diameter which is 20 to 50% smaller than the first diameter

[0028] -the gas pipe has an intermediate section between the first section and the second section

[0029] -the end of the feed pipe is in the intermediate section or the second section

[0030] According to another object of the invention, there is provided an apparatus for separating air by cryogenic distillation comprising a heat exchanger for cooling air by heat exchange with the gas, a column system comprising at least one distillation column for separating air cooled in the exchanger, the gas pipe being connected to the exchanger to be supplied with gas produced by a column of the column system and the liquid pipe being connected to the column system to be supplied with a liquid produced by a column of the column system.

[0031] According to other optional objects of the invention, it is provided:

[0032] -the column system comprises a column having a tank surrounded by a liquid enriched in oxygen relative to air, the pipe being connected to this tank.

[0033] -the column system comprises a column having a head condenser containing a liquid enriched in oxygen relative to air, the pipe being connected to the condenser.

[0034] -the apparatus comprising a turbine, the gas pipe being connected to the column system to send to the device a gas enriched in nitrogen relative to the air and the device being connected to the turbine to send there the gas enriched in nitrogen in which the liquid has been fragmented.

[0035] -the liquid pipe is arranged so that the liquid is pressurized by hydrostatic pressure.

[0036] According to another object of the invention, there is provided a method for fragmenting a jet of cryogenic liquid in a gas flow, in which a cryogenic liquid at a temperature below -100°C flows in a supply pipe having one end, the liquid supply pipe has an internal diameter greater than or equal to 10 mm, preferably greater than or equal to 20 mm, and a gas at a temperature between 10 and 30°C above its dew point temperature flows in a gas pipe of circular section, of diameter d over the majority of its length, the gas pipe comprising a portion having a reduction in diameter by a ratio of 20 to 50% at the liquid injection over a distance y where:

[0037] y = nxd

[0038] in which the liquid is sent through the supply pipe which enters the gas pipe so that its end is in the part of the pipe having the reduction in diameter and the liquid opens into this part of the pipe and n is a number between 7 and 9, preferably between 7.5 and 8.5.

[0039] Preferably the gas and liquid flow from top to bottom. Thus the hydrostatic pressure contributes to the pressurization of the mixture.

[0040] Purely hydrostatic pressure avoids the use of a complex and fragile pump.

[0041] The invention will be described in more detail with reference to the figures.

[0042] [Fig-1] shows the drop sizes calculated by different models as functions of the device charge.

[0043] [Fig.2] shows the evaporation time and the distance traveled before evaporation of a drop depending on its initial size

[0044] [Fig.3] shows models of maximum drop size as a function of the diameter of the gas line in a liquid jet configuration in a transverse gas flow

[0045] [Fig.4] shows the configuration with central injection (left) and with injection central and reduction of the diameter of the gas pipe according to the invention (right).

[0046] [Fig.l] shows the drop sizes calculated by different models as a function of the device load.

[0047] [Fig.2] shows the evaporation time and the distance traveled before evaporation of a drop as a function of its initial size.

[0048] [Fig.3] shows maximum drop size models as a function of gas pipe diameter in a liquid jet configuration in a transverse gas flow. Reducing the gas pipe diameter at the injection point and over the liquid jet fragmentation distance allows the maximum drop size to be reduced;

[0049] [Fig.4] shows the configuration with central injection (left) and with central injection and reduction of the diameter of the gas pipe according to the invention (right). The figure on the right illustrates the sending of liquid L to the center of the gas pipe T G. The figure on the left illustrates the pipe T on the left having a diameter d less than 600mm, preferably less than 450mm over most of its length and a part of the length having a reduction in diameter by a ratio of 20 to 50% at the level of the injection of liquid at a temperature less than -100°C over a distance y where:

[0050] y = nxd

[0051] where n is between 7 and 9, preferably between 7.5 and 8.5, for example 8.

[0052] The gas G is preferably at a temperature between 10 and 30°C above its dew point temperature. The end of the liquid injection pipe is located within a radius of d / 10 around the central axis of the gas pipe T; this reduction in the diameter of the gas pipe over the distance y of fragmentation of the liquid jet makes it possible to reduce the initial maximum size of the drops.

[0053] The gas pipe T of the figure on the right has a first section having a first diameter and a second section having a second diameter which is smaller by a ratio of 20 to 50% than the first diameter. The gas pipe T has an intermediate section between the first section and the second section. The end of the liquid supply pipe L is in the intermediate section or the second section, since the reduction in diameter in the narrowest part of the intermediate section is still 20 and 50% of the diameter.

[0054] Feeding the cryogenic liquid to the center of the gas pipe helps promote mixing between the gas and the liquid while limiting the risk of coalescence on the wall.

[0055] The use of a flat jet nozzle allows a first film atomization mechanism which limits the initial drop size while maintaining a sufficient passage diameter to avoid clogging. A flat jet nozzle is known from FR3113608 and FR3107659.

[0056] The device may be incorporated into an air separation apparatus by distillation. An air separation apparatus by cryogenic distillation comprises a heat exchanger for cooling air by heat exchange with the gas, a system of columns comprising at least one distillation column for separating cooled air in the exchanger.

[0057] The column system may comprise a single column or a first column operating at a first pressure and a second column operating at a second pressure, the head of the first column being thermally connected to the bottom of the second column. The gas line is connected to the exchanger to be supplied with gas produced by a column of the column system. The gas may be reheated in the heat exchanger before being sent to the device so that the gas arrives at the device at the temperature between 10 and 30°C above its dew point temperature. The liquid pipe being connected to the column system to be supplied with a liquid produced by a column of the column system at a temperature below -100°C.

[0058] According to a variant, the column system comprises a column, for example the second column, having a tank surrounded by a liquid enriched in oxygen relative to the air, the pipe being connected to this tank.

[0059] According to another variant, the column system comprises a column, for example a single column, having a head condenser containing a liquid enriched in oxygen relative to air, the pipe being connected to the condenser.

[0060] The apparatus may comprise a turbine, the gas line being connected to the column system to send to the device a gas enriched in nitrogen relative to air and the device being connected to the turbine to send thereto the nitrogen-enriched gas in which the liquid has been fragmented.

[0061] The liquid pipe is arranged so that the liquid is pressurized by hydrostatic pressure. In this case, it is sometimes possible to dispense with a pump to send the liquid to the device.

Claims

Claims

1. Apparatus for separating air by cryogenic distillation comprising a heat exchanger for cooling air by heat exchange with the gas, a column system comprising at least one distillation column for separating air cooled in the exchanger, a device for fragmenting a jet of cryogenic liquid in a gas flow (G), comprising a supply pipe for the cryogenic liquid (L) having one end, the liquid supply pipe has an internal diameter greater than or equal to 10 mm, preferably greater than or equal to 20 mm, and a gas pipe (T) of circular section, with a diameter d less than 600 mm, preferably less than 450 mm, over the majority of its length,the gas line comprising a portion having a diameter reduction by a ratio of 20 to 50% at the liquid injection and over a distance y where: y = nxd and where the feed pipe enters the gas line so that its end is in the portion of the pipe line having the diameter reduction and n is between 7 and 9, preferably between 7.5 and 8.5 the gas line (T) being connected to the exchanger to be supplied with gas produced by a column of the column system and the liquid pipe being connected to the column system to be supplied with liquid produced by a column of the column system.,

2. Apparatus according to claim 1 wherein a liquid injection nozzle is disposed at the end of the pipe.

3. Apparatus according to claim 2 wherein the nozzle is of the flat jet type capable of producing a flat or sheet-shaped jet.

4. Apparatus according to one of the preceding claims in which the end of the pipe is located within a radius of d / 10 around the central axis of the gas pipe (T).

5. Apparatus according to one of claims 1 to 4 wherein the column system comprises a column having a tank surrounded by a liquid enriched in oxygen relative to air, the pipe being connected to this tank.

6. Apparatus according to one of claims 1 to 4 wherein the column system comprises a column having an overhead condenser containing a liquid enriched in oxygen compared to air, the pipe being connected to the condenser.

7. Apparatus according to one of the preceding claims 1 to 6 comprising a turbine, the gas line being connected to the column system to send to the device a gas enriched in nitrogen relative to air and the device being connected to the turbine to send thereto the nitrogen-enriched gas in which the liquid has been fragmented.

8. Apparatus according to one of the preceding claims 1 to 7 in which the liquid pipe is arranged so that the liquid is pressurized by hydrostatic pressure.

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