Overhead flare system for burning two types of gas

Abstract

The invention relates to an overhead flare system in a syngas production plant for thermal disposal of off-gases with at least two different carbon monoxide contents (CO contents) generated in the production of syngas and / or the treatment of syngas, in particular for simultaneous flaring or burning of hot syngas and cold cryogenic carbon monoxide. According to the invention, the overhead flare system comprises (a) a first off-gas pipe arranged perpendicular to the horizontal and made of a first material and a feed conduit for feeding off-gas with a first CO content to the first off-gas pipe, (b) a second off-gas pipe arranged perpendicular to the horizontal and made of a second material and a feed conduit for feeding off-gas with a second CO content to the second off-gas pipe, (c) wherein the first off-gas pipe and the second off-gas pipe are arranged coaxially and open at their upper ends into a common burner.

Description

TECHNICAL FIELD

[0001] The present invention relates to an elevated flare system in a synthesis gas production plant for thermal disposal of off-gases with at least two different carbon monoxide contents (CO contents) generated in the synthesis gas production and / or synthesis gas treatment, in particular for simultaneous flaring or burning of hot synthesis gas and cold cryogenic carbon monoxide.

[0002] The present invention further relates to a method for burning two types of gases obtained in a synthesis gas production plant. BACKGROUND

[0003] A gas flare (short: flare) is a device for the intentional combustion, i.e. flaring, of combustible gases which are not or cannot be utilized in terms of energy or material. Gas flares are often used when a large amount of such gases is expected to be produced discontinuously, for example this can be the case during start-up and motoring procedures and during production malfunctions. The flare converts the off-gas components by combustion into carbon dioxide which is relatively environmentally disadvantageous and climate-damaging.

[0004] Important components of a gas flare are the actual burner (i.e. one or more pilot burners for igniting the gas), a pipe for supplying the gas to be flared, optionally a support structure, and control and safety devices for the safe operation of the flare.

[0005] The most common type of flare system currently used, apart from the rarely encountered ground flare, is the elevated flare. In these systems, the flare head comprising the burner is mounted at the upper end of the flare system at a height above the ground or mounting surface, which reduces the thermal radiation to the ground or to the mounting base and improves the dispersion profile of the pollutants to be flared or their combustion products. The feed pipe is configured as a riser pipe. The overall of the riser pipe, the burner and optionally the support structure is often referred to as flare tower, or simply as flare, the distinction of the terms is not clearly defined.

[0006] The state of the art of flare systems is described in the API standards 521 and 537.

[0007] There are in principle the following types of elevated flares:

[0008] a) Self-supporting flare towers are usually used for relatively low structural heights, which have limited mounting space or ground area. They are usually limited to one flare tower or one riser pipe. The structural height can reach up to 100 m. A dedicated liquid settler for separating condensate is usually not required.

[0009] b) Guyed or guyed tower torches generally require more ground area than self- supporting or derrick supported torch towers. Their structural height can reach 250 m. The torches are usually limited to one upflow pipe and usually require a specific liquid settler.

[0010] c) Torch towers with scaffolding or tripods as support means are only suitable for relatively small, simple torches.

[0011] d) Derrick torches with drill tower-like support structures or support frames are only used in the case of relatively large torch towers, for which a self-supporting construction is not feasible or possible, and guyed tower torches are not possible due to the available erection space. Very high structural heights are possible. Some derrick designs make it possible to lower the torch tower and the torch head for inspection and maintenance. This is particularly useful if several torch towers are installed on the same derrick for space reasons (so-called multi-torch derricks). A dedicated liquid settler is usually required to separate out condensate.

[0012] The type of torch system is not only used in petrochemical plants but also in synthesis gas production plants in order to dispose of gas product streams or waste gas streams that cannot be further processed in the process chain at the time or for which no other disposal possibility is temporarily available by burning. Synthesis gas is a gas mixture containing hydrogen and carbon oxides which is used in various synthesis reactions. The technical details of synthesis gas production processes are comprehensively described, for example, in the book Ullmann's Encyclopaedia of Industrial Chemistry, Sixth Edition, 1998 Electronic Release, keyword "gas production".

[0013] After the production of raw synthesis gas, for example by steam reforming, autothermal reforming or partial oxidation of a hydrocarbon-containing feed, there are usually a number of process steps for removing undesired gas components, for example methane, by cryogenic gas fractionation in so-called CO cold boxes. In this case, carbon monoxide as a pure product, or a synthesis gas stream with an adjusted hydrogen / carbon monoxide ratio (H2 / CO), can be obtained by sub-steps such as methane wash, partial condensation and CO wash. The pure CO product is discharged from the CO cold box as a cryogenic gas stream as a result of the cryogenic gas fractionation.

[0014] In synthesis gas production plants, it is typically necessary to burn synthesis gas (20°C to 300°C) and cryogenic CO (-180°C) in order to protect the synthesis gas production plant in the event of a failure or planned shutdown of the entire synthesis gas generation plant or parts thereof, and to facilitate disposal by burning of gas product streams or waste gas streams that cannot be further processed in the process chain at the time or for which no other disposal possibility is temporarily available.

[0015] For overhead flare systems used in practice for the combustion of synthesis gas and low-temperature CO (CO gas), various technical solutions exist to date, the construction of which depends, inter alia, on the H2 / CO ratio of the synthesis gas to be combusted.

[0016] When the main product of the plant is synthesis gas with a high H2 / CO ratio or is hydrogen alone, a flare system of the first type (type 1) can be used in the synthesis gas production plant. In this case, the small amount of CO gas that has to be processed in the flare system can be delivered by means of a small external riser pipe made of a corrosion-resistant material, for example a high-alloy steel such as stainless steel, and guided upwards outside the main flare tower to the upper end of the main flare tower made of carbon steel (C-steel). The pipe delivering the low-temperature CO gas from the low-temperature gas fractionation is particularly preferably made of a fully austenitic stainless steel, since non-alloy and low-alloy steels are extremely brittle at the typical low temperatures of the CO gas, which greatly increases the likelihood of failure, especially when there are periodic mechanical stresses (for example due to the swaying of the tower caused by the wind, pressure pulses, etc.). In comparison with non-alloy and low-alloy steels, fully austenitic stainless steels have very high low-temperature toughness. They therefore have a toughness behaviour at very low temperatures that is similar to that at room temperature. The key factor for using such a material with low-temperature toughness is not the CO content but the gas temperature; as a guideline, high-alloy materials with low-temperature toughness must generally be selected at temperatures below -50°C.

[0017] At the upper end of the main flare tower, the synthesis gas and the CO gas are combusted in dedicated burners designed specifically for the particular gas. In order to compensate for the different thermal expansions due to the use of different construction materials for the main flare tower and the CO riser pipe, as well as the high pressure drop, a sufficient number and size of expansion bends must be ensured in the construction of the riser pipe. This construction results in additional loads on the main flare tower, which limits the maximum possible overall height of the self-supporting system before the guyed flare has to be replaced.

[0018] The advantage of a flare of type 1 is that, given the gas to be flared or combusted, each burner can be optimized in terms of maximum safety and performance for the destruction of pollutants present in the exhaust gas. In order to ensure, for example, a high degree of degradation or incineration of pollutants, and at the same time to prevent the flame from detaching from the burner jet, the exit velocity of many flare systems should not exceed 25 to 30 m / s. In the case of synthesis gas, this value can be greater than 150 m / s.

[0019] The second type (type 2) of elevated flare system is similar to type 1, but comprises a combined burner configuration, in which the cold CO-rich gas from the low-temperature gas fractionation is injected into the common main burner at the same level as the synthesis gas. When the H2 / CO ratio of the synthesis gas produced in the synthesis gas production plant decreases to such an extent that the synthesis gas contains more CO than hydrogen, the dedicated CO burner becomes too large to be installed in addition to the main burner at the upper end of the flare tower. The combined burner configuration of type 2 then has the advantage.

[0020] However, this construction is limited when the CO gas stream becomes the main stream, as a result of which the CO upflow pipe becomes too large and too heavy. In addition, in the individual case of simultaneous combustion of synthesis gas, the additional injection of CO gas into the common burner results in local gas velocities which can cause the flame to break away from the burner nozzle.

[0021] In the case of a very large flow of CO gas compared to the flow of synthesis gas, a third type (type 3) of elevated flare system is used. As in the case of type 1, a dedicated burner is provided for each flare gas stream. The disadvantage of this construction is the need for a stable support structure, such as a boom design, in order to be able to withstand the increased load caused by two completely separate feed conduits and burner systems. This also requires a larger construction area.

[0022] Overall, it can therefore be said that there is still a need for a simple construction of an elevated flare system which allows various types of gas from a synthesis gas production plant, such as CO gas and synthesis gas with a wide H2 / CO ratio, to be combusted sequentially, preferably simultaneously, in order to be safely thermally disposed of. SUMMARY

[0023] It is therefore an object of the present application to propose a novel elevated flare system which overcomes the disadvantages of the prior art described above. In particular, it is an object to provide an elevated flare system with a self-supporting flare tower which can be used over the overall range of H2 / CO ratios which occur in practice in product or waste gases from a synthesis gas production plant.

[0024] In a first aspect, this object is achieved by an elevated flare system having the features of claim 1 and by a method having the features of claim 9. Further embodiments of the application can be derived from the respective dependent claims.

[0025] The terms "synthesis gas production plant" and "synthesis gas production method" include all processes in which synthesis gas, i.e. a gas mixture containing hydrogen and carbon oxides, is first obtained as a raw product gas.

[0026] In principle, the possibility of producing synthesis gas is all known synthesis processes used in industrial production, i.e. in particular steam reforming of hydrocarbons, in particular steam reforming of natural gas (steam methane reforming, SMR) or steam reforming of, for example, naphtha or refinery residues, non-catalytic partial oxidation of hydrocarbons (POX), or autothermal reforming as a hybrid form of the two processes mentioned. The technical details of these processes are known in the art and are comprehensively described, for example, in the book Ullmann's Encyclopaedia of Industrial Chemistry, Sixth Edition, 1998 Electronic Release, keyword "gas production".

[0027] The crude synthesis gas produced in this way is generally subjected to a multi-stage treatment. In particular, these treatment steps include the execution of one or more cooling steps (with or without steam generation), heat exchange of the crude synthesis gas to be cooled with flue gas produced by a burner for preheating of process media, CO shift for maximizing the hydrogen content (CO shift), a step for removing carbon dioxide, for example by gas washing using an amine-containing washing medium, and measures for separating further gaseous components to be separated as pure products (for example methane, traces of higher hydrocarbons or carbon monoxide) by cryogenic gas fractionation in so-called cold boxes. In the latter, mainly liquid methane or liquid nitrogen is used to absorb gases with a relatively high boiling point, such as carbon monoxide, and to separate them from hydrogen thereby.

[0028] The coaxial arrangement of the two tubes is to be understood as an arrangement in which the rotational axes of the two tubes coincide in the longitudinal direction.

[0029] The term "low-alloy" refers to a steel in which the sum of the alloying elements does not exceed a content of 5% by mass. If this content is exceeded, the term "high-alloy steel" is used. Examples are carbon steel (C steel) as a low-alloy steel and high-grade steel, in particular high-grade stainless steel, as a high-alloy steel.

[0030] Qualitative information, for example a low or relatively low or high or relatively high CO content, is always to be understood as qualitative with respect to the ratio of the two or more material streams considered.

[0031] In one embodiment, the elevated flare system of the present application comprises a flare tower having a concentrically arranged stainless steel upflow pipe as an inner tube, the outer wall of the inner tube forming a radially uniformly spaced annular space with the inner wall of the outer tube. Inside the stainless steel upflow pipe, the cold CO gas originating from the cryogenic gas fractionation is conveyed to the upper end of the flare tower, where a burner is arranged.

[0032] The synthesis gas stream passes through the annular space between the inner tube and the outer tube, the outer tube can be made of non-alloyed or low-alloyed steel, for example C steel, and in this way is likewise guided to the upper end of the flare tower.

[0033] This construction makes it possible to use the flare tower according to the application for a wide range of H2 / CO ratios, in particular all H2 / CO ratios present in the product gas or off-gas from a synthesis gas production plant. The diameter of the inner tube is designed for the maximum CO gas flow. The inner diameter of the outer tube is then determined by the ratio of the outer diameter of the inner tube and the area of the annular space to the pressure difference, which is acceptable in order to allow the synthesis gas stream to be transported in the flare tower.

[0034] The outer tube is also designed statically, so that it can withstand the loads of the overall arrangement of the flare tower, i.e. the outer tube, the inner tube and the burner. No external support structure is required.

[0035] The inner tube is fastened at the lower end of the flare tower, is guided upwards within the outer tube and can preferably be centred at one or more levels by spacers along its course. These spacers are more preferably configured as sliding bearings at the end opposite the fastening point. This and the coaxial arrangement allow the inner tube to have a free length variation relative to the outer tube, which is necessary when the inner tube and the outer tube are made of materials with different coefficients of thermal expansion, without additional compensation measures being required.

[0036] Due to the construction of the flare tower according to the application, the burner receives the CO gas through a central nozzle, into which the inner tube opens at its upper end. The synthesis gas enters the burner from the upper end of the annular space arranged around the CO nozzle. This symmetrical construction leads to particularly uniform combustion.

[0037] In addition, this arrangement prevents the formation of streaks and thereby prevents locally too high gas velocities at the burner, which can be too high for the gases to be burned off to be reliably combusted due to the inhomogeneity at the individual introduction points in the case of a distributed introduction of the gas stream to be burned off at a plurality of discrete points around the circumference into the burner. The calculation of the resulting mixing gas velocity of the gases in the burner is also simplified by its areal distribution in the burner.

[0038] Since the choice of the burner size is not mechanically limited, but can be chosen relatively freely by choosing a compatible size of the outer tube or a compatible ratio of the outer tube to the inner tube and appropriate dimensions of the outer tube and the distributor, for example, the inner tube can in any case be made sufficiently large to achieve any desired lower CO gas flow rate. If a safe and reliable combustion is required, the CO gas flow rate can be further reduced by choosing an appropriately larger burner diameter.

[0039] The coaxial arrangement of the inner tube inside the outer tube produces further advantageous effects of the present application. The two types of gases to be flared differ not only in their CO content but also in their temperature. The synthesis gas as end product or intermediate to be flared usually has a temperature in the range from 20°C to 300°C. On the other hand, the CO gas to be flared from the cryogenic gas fractionation is usually in a cryogenic state at a temperature of about -180°C. The arrangement of the inner tube and the outer tube according to the present application thus acts as a recuperator, so that the temperature difference between the two types of gases conveyed in the flare stack is reduced up to the outlet into the burner, which leads to a more uniform combustion and a more uniform flame profile over the cross section of the burner. DETAILED DESCRIPTION

[0040] The second aspect of the elevated flare system according to the present application is characterized in that it is built and erected in a self-supporting manner. A support framework and support structure can thus be dispensed with, which reduces the capital costs. Furthermore, the location of the flare stack can be changed more quickly, which is necessary in the event of new uses of the area within the production operation.

[0041] The third aspect of the elevated flare system according to the present application is characterized in that the first waste gas pipe and the second waste gas pipe have a circular cross section and the second waste gas pipe extends coaxially inside the first waste gas pipe as an inner tube, between the outside of the inner tube and the inside of the outer tube forming a radially uniformly spaced annular space. This leads to a more uniform distribution of the gases to be flared flowing through the annular space, and thus a more uniform combustion in the burner and a reduction in the corrosion phenomena, in particular at the inner wall of the outer tube.

[0042] The fourth aspect of the elevated flare system according to the present application is characterized in that the arrangement of the inner tube and the outer tube can be implemented by means of a plurality of spacers, in each case at least two, preferably at least three spacers being arranged radially at a specific height of the elevated flare system and being fastened to the inside of the outer tube or to the outside of the inner tube. In this way, the inner tube can be reliably centered with respect to the outer tube. It is proposed to provide such groups of spacers at least at different heights. It is particularly preferred to provide at least three spacers in each case, which are arranged in the form of a triangle or a flat tripod perpendicular to the longitudinal axis of the pipes.

[0043] The fifth aspect of the elevated flare system according to the invention is characterized in that the spacers are configured as plain bearings at the end opposite the fastening point. Since, according to the invention, the inner tube and the outer tube are composed of different materials that usually have different coefficients of thermal expansion, and the temperature difference between the annular space of the inner tube and the inner space (central space) is considerable and varies significantly over the height of the flare tower, it is advantageous to ensure that the relative change in the lengths of the two tubes with respect to each other can take place unhindered, so that no mechanical stresses can arise that could lead to deformations. This is achieved by configuring the spacers as plain bearings.

[0044] The sixth aspect of the elevated flare system according to the invention is characterized in that the outer tube is composed of low-alloy or non-alloy steel, preferably C steel, and the inner tube is composed of high-alloy steel, preferably stainless steel, in particular stainless steel that is ductile at low temperatures. The CO gas originating from the cryogenic gas fractionation has a lower temperature compared to other types of gas, and therefore places higher demands on the material of the inner tube in terms of embrittlement under the prevailing operating conditions. It is therefore advantageous to have the inner tube pass through the inner space, so that the CO gas is delivered to the combustor in a material that is particularly well ductile at low temperatures. This is not absolutely necessary for the outer tube, whose interior is in contact with another type of gas, so that a less expensive low-alloy or non-alloy steel can be used here.

[0045] The seventh aspect of the elevated flare system according to the invention is characterized in that the first exhaust gas has a lower CO content than the second exhaust gas and is delivered through the annular space between the interior of the outer tube and the exterior of the inner tube. This has the advantage mentioned above in connection with the explanation of the sixth aspect: the exhaust gas with the higher temperature and / or with the lower corrosion potential is delivered through the annular space.

[0046] The eighth aspect of the elevated flare system according to the invention is characterized in that the second exhaust gas has a higher CO content than the first exhaust gas and is delivered through the inner tube. This has the advantage mentioned above in connection with the explanation of the sixth aspect: the exhaust gas with the higher temperature and / or with the lower corrosion potential is delivered through the annular space.

[0047] In another aspect, the method according to the invention is characterized in that the first product stream or exhaust gas stream comprises or is formed from a synthesis gas stream to be disposed of. The CO content of the synthesis gas stream produced as an intermediate or end product in a synthesis gas production plant is lower than the CO content of the CO gas from the cryogenic gas fractionation, so that the corrosion potential of the first product stream or exhaust gas stream is less than the corrosion potential of the second product stream or exhaust gas stream. As explained in connection with the sixth aspect of the invention, it is advantageous to deliver the exhaust gas with the lower corrosion potential through the annular space.

[0048] In another aspect, the method of the present invention is characterized in that the second product stream or off-gas stream comprises or is formed from an off-gas stream from the apparatus for cryogenic gas fractionation having a high CO content. The CO content of the CO gas from cryogenic gas fractionation is higher than the CO content of a syngas stream produced as an intermediate or end product in a syngas production apparatus, such that the corrosion potential of the second product stream or off-gas stream is higher than the corrosion potential of the first product stream or off-gas stream. It is also advantageous to transport the colder off-gas with a higher corrosion potential and / or embrittlement potential through the central space, as explained in connection with the sixth aspect of the present invention.

[0049] Working example

[0050] Further developments, advantages and possible uses of the present invention can also be derived from the following description of a working example and the drawing. All features described and / or depicted form the present invention, either individually or in any combination, regardless of their combination in the claims or the reverse reference thereto.

[0051] The single drawing shows:

[0052] Figure 1 Working example of an elevated flare system according to the present invention in the form of a schematic drawing.

[0053] In Figure 1 In the schematic drawing, the elevated flare system 1 according to the present invention comprises a flare tower having an outer pipe 2 made of C steel. The outer pipe is erected in a self-supporting manner on a flat base 3 and is sealed against this flat base. It has a circular cross-section and is cylindrical, or preferably has the shape of a slightly tapered circular truncated cone in the upward direction. The wall thickness of the outer pipe should be such that the load of the entire elevated flare system, the main components of which are the outer pipe, the inner pipe and the burner, can be borne. The synthesis gas obtained temporarily as off-gas in a syngas production apparatus (not shown) is introduced into the flare tower at the lower side of the flare tower via a feed conduit 4. The temperature of the synthesis gas off-gas can be between 20°C and 300°C. This depends mainly on the location or component within the syngas production apparatus from which the off-gas is to be extracted. Thus, it is approximately 300°C at a location downstream of the production stage of the raw synthesis gas, for example the steam reformer. During the course of the subsequent processing stages, it falls further and is typically between 20°C and 50°C, for example 40°C, before being introduced into the final pressure swing adsorption stage for the production of pure hydrogen.

[0054] The inner tube 5 is arranged in the inner space of the outer tube and is likewise mounted on the flat base 3 and sealed against this. It consists of high-alloy steel, for example stainless steel with a circular cross-section which is ductile at low temperatures. The CO gas obtained temporarily as waste gas in a plant for cryogenic fractionation (not shown) of the produced raw synthesis gas or previously treated synthesis gas is introduced into the flare tower on the lower side thereof via a feed conduit 6, which is then further conveyed to and introduced into the inner tube 5. Here, the feed conduit 6 is guided through the outer tube 2, the position of the passage being sealed off from the surroundings. The temperature of the CO gas is -180°C. It is preferably conveyed through a liquid settler (not shown) to separate off any condensate, and is then introduced into the inner tube.

[0055] In the present working example, the inner tube is fixed in position relative to the outer tube by spacers 7, which are provided at three different heights of the flare tower. The spacers are fastened to the inner wall of the outer tube and are configured as plain bearings on the side facing the inner tube. In each case, three spacers are provided at each height, which are spaced 120° apart from one another.

[0056] The diameter of the inner tube is designed for the maximum CO gas flow. The inner diameter of the outer tube is then determined by the ratio of the outer diameter of the inner tube and the area of the annular space to the pressure difference, which is acceptable to allow the synthesis gas stream to be conveyed within the flare tower. In selecting the diameters, it is necessary to ensure that the flow velocity at the burner mouth is sufficiently small to prevent the burner flame from lifting off, even at the maximum flow of both types of gas simultaneously. The maximum flow velocity under these conditions can have to be determined by preliminary tests.

[0057] In the flare tower, the synthesis gas waste gas is conveyed upwards from the bottom through the annular space formed between the inside of the outer tube and the outside of the inner tube and is finally introduced into the common burner 8. The CO gas waste gas flows upwards in the inner space of the inner tube, the central space, and likewise enters the common burner. There, the waste gas is ignited and burned by means of an ignition burner or pilot burner (not shown). The oxygen required for this is taken from the surrounding air. To assist combustion, steam can additionally be injected into the burner. The combustion products produced are discharged into the surroundings.

[0058] Reference signs

[0059] [1] Flare system

[0060] [2] Outer tube

[0061] [3] Base

[0062] [4] Feed conduit

[0063] [5] Inner tube

[0064] [6] Feed conduit

[0065] [7] spacer

[0066] [8] common burner

Claims

1. A method for thermally treating waste gas with at least two different carbon monoxide contents (CO contents) generated in syngas production and / or syngas treatment via an overhead flare system, said overhead flare system comprising: A first exhaust pipe arranged perpendicular to the horizontal direction and made of a first material, and a feed conduit for feeding exhaust gas having a first CO content into the first exhaust pipe. A second exhaust pipe arranged perpendicular to the horizontal direction and made of a second material, and a feed conduit for introducing exhaust gas with a second CO content into the second exhaust pipe. The first exhaust pipe and the second exhaust pipe are arranged coaxially and have openings at their upper ends leading to the common burner. The first exhaust pipe and the second exhaust pipe have circular cross-sections, and the second exhaust pipe extends coaxially inside the first exhaust pipe, which serves as the outer pipe, forming a radially uniformly spaced annular space between the outer side of the inner pipe and the inner side of the outer pipe. The first exhaust gas has a lower CO content than the second exhaust gas and is transported through the annular space between the inside of the outer pipe and the outside of the inner pipe. The second exhaust gas has a higher CO content than the first exhaust gas and is transported through the inner pipe. The method includes the following steps: (a) Producing crude syngas containing hydrogen and carbon oxides from a hydrocarbon-containing feedstock using syngas production methods. (b) The crude syngas is subjected to multi-stage processing to obtain pure syngas, including a device for cryogenic gas fractionation as one of the processing steps. (c) Discharge a first product stream or a first waste stream with a low CO content and introduce it into the annular space between the interior of the outer tube and the exterior of the inner tube of the elevated flare system. (d) Discharge the second product stream or second waste stream with a high CO content and introduce it into the inner tube of the elevated flare system. (e) Combustion of the first product stream or the first waste stream and the second product stream or the second waste stream in the common burner.

2. The method according to claim 1, characterized in that, The first product stream or the first waste stream includes the synthesis stream to be disposed of, or is formed from the synthesis stream.

3. The method according to claim 1 or 2, characterized in that, The second product stream or second waste stream includes, or is formed from, the waste stream with a high CO content from the equipment used for cryogenic gas fractionation.

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