Absorber for selectively removing sour gases

Abstract

An absorber for selectively removing sour gases comprises one or several packed mass transfer sections to which an absorbent is supplied. In said sections, a housing has annular support elements arranged thereon for securing horizontal baffles which change the direction of a gas flow from counter-flow to cross-flow and which divide the mass transfer section into packed stages containing cross-flow packing assemblies. Cross-flow packing assemblies of the same height in each mass transfer section are formed from packing elements of the same height, and whereas each mass transfer section contains the same number of packing elements, a different number of packed stages is created by changing the position of the horizontal baffles in relation to the annular support elements and perforated trays. The invention solves the problem of creating a structure of an absorber for selectively removing sour gases having an invariable number of welded support fastenings for securing contact devices to the housing of the apparatus, said structure making it possible to increase the degree of purification of the feedstock, adjust the selectivity of the process and enhance the efficiency of the absorber.

Description

[0001] ABSORBER FOR SELECTIVE REMOVAL OF ACID GASES TECHNICAL FIELD

[0002] The absorber for selective removal of acid gases is designed to purify natural gas from impurities under conditions of changing their composition for

[0003] 5 production of fuel gas or liquefied natural gas and can be used in the gas processing industry.

[0004] The composition of natural gas from various fields is quite diverse, and in addition to methane, the gas contains a number of hydrocarbon components (ethane and heavier hydrocarbons, which can be

[0005] 10 feedstock for gas chemical processes), as well as nitrogen, hydrogen sulfide and other organosulfur compounds, carbon dioxide, and water vapor. These impurities are not only harmful but also undesirable, as they negatively impact both the technological characteristics of natural gas processing and the performance of the resulting end products.

[0006] PRIOR ART

[0007] Depending on the composition of natural gas, the region of production, and the purpose of subsequent use, various processing routes are developed. With a low content of hydrocarbon impurities, it is typical

[0008] 20. Fuel direction - natural gas, after preliminary purification from mechanical and gaseous impurities, can be used as fuel gas for industrial and municipal purposes or as raw material for the production of liquefied natural gas. In accordance with the fuel gas quality requirements, the content of carbon dioxide (hereinafter CO2) is limited to no more than 2.5 mol.%, oxygen - no more than 0.05 mol.%, hydrogen sulfide (hereinafter H2S) - 0.02 f / m 3 , mercaptan sulfur compounds - 0.036 g / m3 3(GOST 5542-2022). When processing natural gas into liquefied natural gas in accordance with the specifics of the cryogenic process, the carbon dioxide content in the gas should not exceed 0.005-0.030% (EAEU Technical Regulation 046 / 2018). Acid gases are removed from natural gas primarily by absorption purification when the gas comes into contact with absorbents in column-type absorption apparatus. The absorbents most often used are aqueous solutions of amines in pure form or with additives of intensifying agents.

[0009] 5. Absorption of components. Contact devices in the form of plates or packing are installed in absorbers, ensuring the formation of a large phase separation surface per unit volume of the adsorber and the structure of gas and liquid flows, which intensifies the mass transfer of carbon dioxide into the absorbent. After the absorbent is saturated with carbon dioxide

[0010] 10. The absorbent is regenerated in the desorber, during which the resulting regenerated absorbent is returned to the absorber, and the released carbon dioxide is used as a commercial product or injected into the gas field to maintain intra-formation pressure.

[0011] Because the acid gas content of natural gases from different fields varies significantly, and, furthermore, as a natural gas field is exploited and depleted, new gas fields are brought into production, and depleted gas fields are mothballed, the gas composition also changes. This dynamic situation has led to the development of numerous absorber designs.

[0012] 20 A vortex spray absorber is known, comprising a housing with gas inlet and outlet pipes and a liquid outlet, a liquid inlet unit in the form of a perforated pipe installed along the longitudinal axis of the housing, characterized in that impellers are fixed to the perforated pipe, liquid outlet pipes are installed on the housing tangentially towards a film of liquid rotating on the wall of the housing, in the housing opposite each liquid outlet pipe a coaxially located phase separation pipe is installed, forming an annular pocket with a bottom located above the liquid outlet pipe with the wall of the housing (patent RU2380143 C2, 3 IPC BOID 53 / 18, BOID 47 / 06, declared on 17.01.2008, published on 27.01.2010). The disadvantage of the invention is the low efficiency of mass transfer in the liquid-gas system, since at a low number of impeller revolutions, the intensity of mixing of the medium in the apparatus body and turbulence of the impeller will be weak, and with an increase in the number

[0013] After 5 revolutions of the impeller, centrifugal forces will arise, throwing liquid droplets towards the wall of the apparatus, creating liquid jets with a phase separation surface smaller than that of the original droplets.

[0014] An absorber is known, comprising a cylindrical body with nozzles for the inlet and outlet of gas, nozzles for the inlet and outlet of liquid, located inside the body, a box with a liquid distributor, a mass-exchange section and a drip separator, characterized in that the mass-exchange section is made in the form of horizontal shelves with packages of regular plate packing placed on them, wherein the package of regular packing is formed from individual corrugated

[0015] 15 sheets with channels formed between the sheets (patent for utility model RU139369 Ш, IPC BOID 53 / 18, filed on August 26, 2013, published on April 20, 2014). The disadvantages of the invention are:

[0016] • with direct horizontal contact of phases in the packing placed between the shelves, due to gravity, the following will occur:

[0017] 20 phase separation, which will lead to a decrease in the interphase surface area and the efficiency of mass transfer between phases;

[0018] • the efficiency of mass transfer in direct flow during absorption is worse than in counter-flow, since at the final stage of the process the purified flow with a low concentration of the extracted component comes into contact with practically the spent (saturated) absorbent, which reduces the driving force of mass transfer, and the efficiency of the absorber decreases as the flows move between the shelves.

[0019] A known method for purifying gas from acidic components and an absorber for implementing the same, comprising a housing with nozzles for the gas inlet and outlet of the saturated absorbent in the still, mass-exchange sections with the mass-exchange section of the preliminary purification placed above the nozzle of the gas inlet, vertical partitions, characterized in that the section of the preliminary gas purification is designed as a chamber closed along the perimeter, completely separated from the housing of the absorber by partitions, and in the lower part is provided with a hydraulic seal and connected to the nozzle of the gas inlet (patent RU2278724 C2, IPC BOID 53 / 18, declared 07.10.2004, published 27.06.2006). The disadvantages of the invention are:

[0020] • low efficiency of disc contact devices;

[0021] • the invention does not solve the problem of eliminating hydrogen sulfide corrosion in the apparatus, since upon contact of the incoming gas with the already spent absorbent in the preliminary gas cleaning section, it allows only a small portion of the acidic components to be removed from the gas, and the main part of them enters the actual absorber for the targeted gas cleaning.

[0022] A gas drying absorber is known, comprising an input separation section, a mass-exchange absorption section with packages of regular structured packing, an output section located between the input separation and mass-exchange absorption sections, a semi-blind plate for collecting and removing spent absorbent, communicated with the mass-exchange absorption section and the output separation section, a partition with centrifugal separation elements located in the input separation section, characterized in that the input separation and output sections contain partitions, on each of which centrifugal separation elements are placed along the periphery, made in the form of semi-spiral chambers secured to the partitions by central nozzles for removing purified gas, having nozzles for introducing contaminated gas with rotating spring-loaded blades and connected by nozzles for removing separated impurities with cyclones located on these partitions in the center,wherein in the inlet separation section, a conical vortex stabilizer with a receiver of a part of the vortex is attached to the head of the central cyclone, the lower part of which is immersed in a water-filled impurity accumulator, and in the outlet separation section, a conical vortex stabilizer with a receiver of a part of the vortex is attached to the head of the central cyclone, the lower part of which is immersed in a collector of the captured absorbent, which is connected, in turn, by a branch pipe to a semi-blind plate for collecting and removing the spent absorbent (patent RU2757777 C2, IPC BOID 53 / 26, BOID 53 / 18, filed on 21.04.2021, published on 21.10.2021). A disadvantage of the invention is the implementation of the mass transfer zone for the implementation of the target process in the form of a single set of packages of regular structured packing, since in this case the likelihood of disruption of the flow structure in the packing and channeling increases, leading to the fact thatthat part of the liquid and gas phase flows will pass countercurrently through the packing without mutual contact, leading to a reduction in the phase separation surface, a significant deterioration in mass transfer and a decrease in the depth of gas drying.

[0023] A gas cleaning apparatus with a protective screen is known, comprising a column with pipes for the input and output of gas and liquid, a working area with trays arranged in layers and a hopper for liquid, characterized in that it is provided with three support rings fixed on the inner surface of the apparatus in parallel planes between the lower tray and the liquid level in the hopper, and vertical U-shaped plates are fixed on the rings, the bent edges of which are parallel to the central axial line of the column and are in contact with each other with the inner side so that the U-shaped plates are rotated relative to each other by 180° of the absorbent (patent RU2240173 C2, IPC BOID 47 / 14, B01J 19 / 02, declared on 12 / 17 / 2002, published on 11 / 20 / 2004).A disadvantage of the invention is the use of stacked trays for mass transfer in a liquid-gas system, which have a low efficiency factor of 0.25-0.35 with the absorption method of purification, which requires the installation of a large number of contact devices in the apparatus, leading to an increase in the height and metal content of the column and, accordingly, capital expenditures for gas purification and an increase in the cost of gas purification.

[0024] Also known is a method and column for absorption purification of gases from undesirable impurities, in which a mass-exchange column for absorption purification of gases from undesirable impurities, including a vertical body for counter-current contact of the gas being purified and the regenerated absorbent in a packed contact device, nozzles for inlet of the gas being purified and outlet of the purified gas, is characterized in that the packed contact device is divided by height into independent mass-exchange sections with counter-current or cross-current movement of the gas being purified and the regenerated absorbent, wherein each independent mass-exchange section is separated from the adjacent independent mass-exchange section by a blind plate and is equipped in the upper part with a low-pressure liquid distributor with a nozzle for inlet of the regenerated absorbent,In this case, the blind tray is equipped with an accumulator for collecting saturated absorbent with a nozzle for removing the saturated absorbent from the body of the mass-exchange column and a pipe for transferring the purified gas from the independent mass-exchange section below to the independent mass-exchange section above through the blind tray (patent RU2627847 C2, IPC B01D 53 / 18, filed on 30.12.2015, published on 14.08.2017). A disadvantage of the invention is the large proportion of the apparatus volume free from contact devices, which reduces the efficiency of the column design in terms of the ratio of the volume of mass-exchange devices to the volume of the apparatus and increases the metal consumption of the shell. Also known is a mass-exchange column with a cross-flow of liquid and gas (vapor) phases of the PETON system, which includes a body, nozzles for the feedstock input, the outlet of distillate and residue vapors, the input of reflux and vapors from the reboiler, sections of cross-flow packing, separated in height by horizontal support partitions,coupled with liquid distributors, characterized in that the liquid distributor is manufactured in the form of a set of stages, each of which is made of two coupled end and drain plates, limiting the cross-flow packing section, forming a rectangular pocket in a normal section, the drain plate of the stage is provided with perforated round holes, in each of which a positive buoyancy rod is installed with the possibility of free movement with a rod lift limiter in the lower part of the rod and a rod float in the upper part of the rod, the drain partition of the liquid distributor is located on the upper stage of the liquid distributor and continues down after the distributor, partially blocking the outlet of the gas (vapor) phase from the packing layer of the underlying section of the cross-flow packing, the section of the cross-flow packing in a vertical section parallel to the flow of the gas (vapor) phase,The upper and lower sections replicate the stepped shape of the liquid distributors and are spaced from them at a distance exceeding the free travel length of the rod (patent RU2607730 C1, IPC BOID 3 / 14, BOID 53 / 18. Claimed on 02.11.2015, published on 10.01.2017). A disadvantage of the invention is the complexity of the design and its installation, since all sections of the cross-flow nozzle are mated with each other.

[0025] A common drawback of the absorber designs discussed is that, in all units, the installation of internal contact devices within the housing requires a hermetically sealed connection between the contact devices and the column housing to ensure proper movement of the contacting elements. This prevents bypass flows, which reduce the efficiency of the contact devices. Furthermore, during operation of absorbers for natural gas purification, particularly carbon dioxide, the impurity composition of the gas coming from the field and the volume of gas processed into fuel gas based on customer demand can vary to such an extent that the design potential of the unit in terms of gas purification quality and performance becomes unacceptable. Absorber upgrades involving replacement of existing contact devices with more efficient ones may require modification of the existing support elements, which are typically welded to the housing.Therefore, in many cases, this task becomes impossible, which necessitates the design and construction of a new device, while the old absorber, which is unique equipment costing hundreds of millions of rubles, must be disposed of after several years of operation without depreciation of capital costs.

[0026] DISCLOSURE OF THE INVENTION

[0027] When creating the invention, the task was set to develop a design for an absorber for the selective removal of acid gases - carbon dioxide and hydrogen sulfide - with invariance in the location of the welded fastenings of the contact devices to the apparatus body, while maintaining the apparatus body and the ability to change the configuration of the contact devices and replace them during the reconstruction of the absorber, while simultaneously ensuring an increase in the technical and economic performance of the absorber (increasing the depth of purification of raw materials, changing the selectivity of the process, increasing the productivity of the plant).

[0028] The solution to the stated problem is ensured by the fact that in an absorber for the selective removal of acid gases, consisting of a cylindrical body, from the bottom of which a gas containing carbon dioxide, hydrogen sulfide is supplied, and an absorbent saturated with carbon dioxide, hydrogen sulfide is removed, from the top of the body a gas purified from carbon dioxide, hydrogen sulfide is removed and regenerated absorbent is supplied, and containing one or more packed mass-exchange sections, to which the absorbent is supplied, in these sections on the body there are annular support elements for fastening horizontal partitions that change the direction of the gas flow from counter-current to cross-current and dividing the mass-exchange section into packed stages with packages of cross-current packing, and limited at the top and bottom of each packed stage by perforated webs with drain bars for organizing the flow of liquid from the overlying to the underlying packing packages, the drain bars are fixed on the vertical ribs of the packing packages,tightly adjacent to the housing along the entire edge of the packages, pressed against the housing, wherein with equal height of the sections in each section along the height annular support elements and vertical ribs are placed at an equal distance from each other, cross-flow packing packages of equal height in each mass-exchange section are formed from packing elements of equal height and with the same number of packing elements in each mass-exchange section a different number of packing stages is organized by moving horizontal partitions relative to the annular support elements and perforated webs with drain strips relative to the vertical ribs with placement of packing stages with cross-flow packing packages between them, wherein in the housing along the height of the mass-exchange section annular support elements are fixed in a quantity equal to or greater than the number of mass-exchange packing packages, and the number of horizontal partitions installed on these annular support elements and perforated webs,equal to the number of packing elements in the mass transfer section.

[0029] The presence of an excess number of annular support elements and vertical ribs in the housing allows for changing the configuration of the mass-transfer packing system within a single section and thereby changing the efficiency of mass transfer in the absorber section in accordance with the set production task, i.e., it ensures variability of the absorber's operation.

[0030] The ability to move horizontal partitions relative to the annular support elements and perforated sheets with drain strips relative to the vertical ribs with the placement of packed stages with cross-flow packing between them makes it possible to change the number of packed stages within one section of the absorber during repair work on the reconstruction of the apparatus.

[0031] The process of mass transfer in packed absorbers is characterized by the concepts of “transfer unit”, “transfer unit height” and “number of transfer units”, the most important of which is the height of the transfer unit in the gas phase hoy, m, calculated as h O y = G / (Ku S o y), (1) where G is the constant flow rate of the non-sorbed (inert) part of the gas flow along the height of the column, kg / s or kmol / s;

[0032] Ku is the average mass transfer coefficient, kg / (m 2 c)[kg / kg inert flow)] or kmol / (m 2 c)[kmol / kg inert flow)];

[0033] S - cross-sectional area of ​​the column, m 2 ; o - specific surface area of ​​dry packing, m 2 / m 3 ; y is the nozzle wettability coefficient.

[0034] Ku = ((1 / ru) + (t / Rx))' 1 , (2) where Ру and Рх are the mass transfer coefficients in the gas and liquid phases, respectively; m is the tangent of the angle of inclination of the equilibrium line to the x-axis.

[0035] The value of Py can be calculated from the value of the Nusselt criterion Nu'r through the Reynolds criterion Rer and Prandtl criterion Pr'r based on the criteria equation:

[0036] Nu'r = 0.407 Re r 0 ' 655 (Рг' г ) 0 ' 33 , (3)

[0037] Nu'r — R У dg / Dr, (4) Rer = 4 yurg / ojir, (5)

[0038] Pr'[ = / рг Dr, (6) where da is the equivalent diameter of the gas flow, m; co is the gas velocity related to the full cross-section of the column (fictitious), m / s; рг and цг are the density and viscosity of the gas, respectively;

[0039] Dr - diffusion coefficient of the absorbed component in the gas, m 2 / With.

[0040] Adapting classical mass transfer equations for gas-liquid packing to the operation of a cross-flow contact device, it can be noted that for the flow of the liquid phase (absorbent) through the packing bed of a cross-flow contact device from top to bottom, the physicochemical and hydrodynamic characteristics of the liquid flow essentially remain unchanged. This suggests that for both straight-through and cross-flow packing elements, the mass transfer efficiency in the liquid phase will be the same, all other things being equal, and the overall efficiency of the mass-transfer contact device will be determined by the mass transfer in the gas phase.

[0041] Unlike counter-current packing, which uses the "transfer unit height" for the gas phase, which essentially corresponds to the concept of "height," for cross-flow contact devices, where the vapor flow moves horizontally, the "transfer unit length" should be considered. When switching from a single horizontal gas flow through the packed contact device stack to a cross-flow arrangement, the mass transfer results will change depending on the number of gas flows through the stack.

[0042] Analysis of equations (3)-(6) showed:

[0043] 1) the value of the Prandtl criterion, calculated only based on the values ​​of the physicochemical parameters of the gas phase flow, does not depend on the design and hydrodynamic parameters of the contact device;

[0044] 2) the value of the Reynolds criterion is proportional to the gas velocity ω, therefore, when the direction of gas flow through the same cross-flow packing changes by N times, the Reynolds criterion will also increase by N times, then the Nusselt criterion will increase by N 0,655 times, and, accordingly, the mass transfer coefficient Py will increase by the same amount, which also leads to an increase in the mass transfer coefficient Ku, which is especially important, since during absorption the mass transfer process is limited by mass transfer in the gas phase. For example, during the absorption of ammonia by water for single-pass packing (N = 1) at Py = 0.243 m / s = 0.034 kg / (m 2 -s), Рх= 4.2 • 102 m / s = 0.311 kg / (m 2 c) and m = 0.546 (Ushanova V.M. Project of an absorption unit. Siberian State Technological University. Krasnoyarsk. 2014. - [Electronic resource] URL: htps: / / www.moodle.kstu.ru >pluginfile.php / 413092 / mod resource): 0.0321 kg / (m 2 With).

[0045] When moving from a single-pass to a three-pass nozzle (N = 3) we obtain: = 0.0621 kg / (m 2 c), that is, the mass transfer coefficient has increased almost twofold;

[0046] 3) in accordance with equation (1), when the direction of gas flow through the same cross-flow packing changes by N times, the cross-sectional area of ​​the packing through which the gas phase flow passes will become equal to S / N. The “length” of the transfer unit for single-pass packing will be: h O y 1 = G / (K y S o y)= Z / (Ky S )= Z / (0 / 0.321S), where Z is a generalization of constant values ​​equal to G / (o y).

[0047] When switching to a three-way nozzle, the “length” of the transfer unit will be: h Oy z = Z / (0 / (0.62 IS / 3)) = Z / (0.0207S), that is, it will increase compared to a single-pass nozzle by 62.5% due to the increase in the gas flow rate, but at the same time, with the same length of one horizontal pass L, the number of transfer units n will increase у , characterizing the intensity of change in the concentration of the adsorbed impurity in the packing. The relative increase in the intensity of change in concentration I upon transition from a single-pass packing set to a three-pass packing set will be:

[0048] I = Belly / p у 1 = (3L / hoy 3) / (L / hoy i) = 3 hoy i / hoy z = 3 • 0.0207 / 0.0321 = 1.93, that is, it will increase by 1.93 times, which allows to improve the quality of separation and reduce the concentration of the extracted component in the purified gas.

[0049] It is advisable to attach guide plates to the annular support elements of the absorber, free from the fastening of horizontal partitions, to turbulize and align the structure of the gas flow and the concentration of CO2 and H2S in the gas flow in the space between the absorber body and the packing packages in order to increase the homogeneity of the gas flow at the entrance to the packing package.

[0050] It is also advisable to place a stage with a baffle in the upper part of the absorber body or each mass-exchange section, which prevents the carry-over of droplets of fresh absorbent with the purified gas, as well as the throwing of droplets of partially saturated absorbent by the ascending gas flow of the lower mass-exchange section onto the upper one, which allows to increase the driving force to some extent.

[0051] It is useful to place a cross-flow packing section below the raw gas inlet in the absorber to degas the saturated absorbent flowing from the mass-exchange sections, which will reduce the carryover of hydrocarbon gas with the saturated absorbent and the subsequent loss of this gas when the gas enters the acid gases during absorbent regeneration.

[0052] When forming one packed stage in the mass transfer section, the mass transfer section can consist of one, two, three or four packed elements, which allows changing the mass transfer potential of the absorber when, for example, the requirements for the quality of purification, the composition of the original natural gas in terms of CO2, H2S impurities or other external factors change.

[0053] In accordance with production requirements, one, two, three or four packed stages can be formed in each mass transfer section; in this case, the mass transfer section can consist of one, two, three or four packed elements, which simplifies installation work during the reconstruction of the absorber.

[0054] It is advisable that the fastening of the packed stages to the ring support elements and vertical ribs be made detachable, which simplifies the installation and dismantling of the contact devices in the absorber body.

[0055] When detachably attaching the packed stages to the ring support elements and vertical ribs, it is essential that the fastenings be sealed using a contact seal. This will prevent the gas phase from bypassing the absorber body wall without contacting the absorbent, thereby increasing the unit's efficiency.

[0056] The most convenient way to carry out installation work is to have the detachable fastening of the packed mass transfer stage to the ring support elements and vertical ribs carried out using clamps.

[0057] To intensify the absorption process under conditions of changing natural gas productivity and composition during long-term field operation and during gas production transitions from one field to another, the cross-flow contact system between absorbent and purified gas in absorption columns typically consists of several mass-exchange sections with a gap between them to ensure fractional absorption into the column between sections. The proposed option to vary the number of packed stages allows for increasing or decreasing the number of mass-exchange sections in one, several, or all packed stages during routine maintenance, allowing for an increase or decrease in the depth of natural gas purification while simultaneously reducing the flow rate of circulating absorbent, adapting the absorption column to significantly altered feedstock parameters.

[0058] LIST OF DRAWINGS

[0059] The claimed invention of an absorber for the selective removal of acid gases is illustrated in Figures 1-5.

[0060] Figure 1 shows a diagram with options for forming one mass transfer section with a different number of contact packed stages.

[0061] Figures 2-5 show sketches of one mass transfer section of the absorber with design elements using the following designations:

[0062] 1 - absorber body;

[0063] 2 - ring support element;

[0064] 3 - packing stage;

[0065] 4 - cross-flow packing package;

[0066] 5 - nozzle element;

[0067] 6 - horizontal partition.

[0068] BRIEF DESCRIPTION OF DRAWINGS

[0069] Figure 1 schematically shows one mass-transfer section of an absorption column with a contact device height of H, for which four variants of an interchangeable number of packed stages are given, allowing, for example, to vary the depth of natural gas purification at a constant absorbent flow rate or with a change in the throughput of processed gas. Variants 1-4 show a mass-transfer section with one (a), two (b), three (c), and four (d) mass-transfer contact devices. For example, if the requirements for the depth of natural gas purification change due to the transition of production from gas preparation for transportation via a main pipeline to gas preparation for liquefaction to obtain LNG in the absorber, during repairs it is possible to redesign the mass-transfer section with one packed stage into four mass-transfer sections, and if the gas supply subsequently decreases due to field depletion, during absorber repairs it is possible to replace the four mass-transfer sections with two.

[0070] Figure 2 shows a fragment of absorber housing 1 with annular support elements 2, which are attached to the housing during manufacturing. During absorber design, the distance between the support elements is selected to be equal to the height of the cross-flow packing element. This will allow for subsequent adjustments to the number of packed stages in the absorber's mass-transfer section during repairs, as the height of the packed stage is a multiple of the height of the cross-flow packing element.

[0071] Figures 3-5 demonstrate how to reassemble one mass-exchange section with one mass-exchange stage (Fig. 3) in an absorber into variants with two (Fig. 4) and three (Fig. 5) mass-exchange stages with the same height of the mass-exchange section, allowing for an increase in the depth of purification of the feedstock from acid gases without replacing the absorber body.

[0072] Figure 3 shows one mass-exchange section, which is one packed stage. In the absorber body 1, on which five annular support elements 2 are fixed, the packed stage 3 is formed on the two outermost annular support elements and structurally represents a pack of cross-flow packing 4, assembled from packing elements 5. The overlapping of the free space of the absorber body 1 at the ends of the packed stage 3 with multidirectional horizontal partitions 6 forms a cross-flow in the packed stage 3: the absorbent saturated with impurities flows down along the regular packing of the pack of cross-flow packing 4, forming a thin film of the liquid phase on the surface, and the purified gas flow passes through the layer of cross-flow packing, contacting with the liquid film on the packing and renewing the surface of the packing by tearing off part of the film from the surface of the packing, forming droplets of absorbent and transferring them to new areas of the surface of the packing.Three intermediate ring support elements are not involved in the manufacture of the absorber and remain in reserve for use during reconstruction of the absorber with a change in the configuration of the mass transfer section.

[0073] Figure 4 shows a single mass-transfer section of the absorber, consisting of two packed stages. In the absorber body 1, to which five annular support elements 2 are attached, the packed stages 3 are formed on the two outer and middle annular support elements and are structurally composed of cross-flow packing 4 bundles assembled from packed elements 5. The closure of the free space of the absorber body 1 at the ends of the packed stages by three horizontal partitions 6 directed in different directions forms a cross-flow in the packed stages 3. Two intermediate annular support elements remain in reserve for use during reconstruction of the absorber with a change in the configuration of the mass-transfer section.

[0074] Figure 5 shows one mass-transfer section of the absorber, consisting of four packed stages. In the absorber body 1, on which five annular support elements 2 are fixed, the packed stages 3 are formed on all five annular support elements 2 and structurally represent packages of cross-flow packing 4, assembled from packed elements 5; in this case, each packed stage 3 is based on one packed element 5. The overlapping of the free space of the absorber body 1 at the ends of the packed stages 3 by five differently directed horizontal partitions 6 forms a cross-flow in the packed stages 3. Figure 6 shows options for forming a four-section absorber from a different number of universal packed elements of cross-flow packing with a thickness of 350 mm in sections with the number of packed stages: 9 (a), 13 (b) and 19 (c) (numbering G-19' in Fig. 6 illustrates the number of stages).A drip separator made of regular packing is installed in the upper part of the absorber above the mass-exchange sections, which further improves the quality of the purified natural gas.

[0075] Based on the above description, calculations were performed to implement an absorber for the selective removal of acid gases. At one of the gas processing plants, when purifying natural gas containing 4.5% by weight of CO2 and 0.03% by weight of H2S, an absorber with four mass-exchange sections and nine packed stages of cross-flow contact devices consisting of 350 mm thick packed elements was used (Fig. 6a). When the plant switched to a new feedstock containing 4.5% by weight of CO2 and 4.5% by weight of H2S, the absorber ceased to provide high-quality purification: while maintaining the productivity of the purified gas, the depth of CO2 absorption decreased to 40%. The reconstruction of the absorber according to the claimed invention with the installation of 19 packed stages (Fig. 6c) in the same four-section apparatus body based on the same packed elements made it possible to increase the depth of CO2 absorption to 100% while maintaining the design capacity of the absorber.

[0076] Also, when switching the installation to a new raw material containing 4.5% by weight of CO2 and 4.5% by weight of H2S, and there was no need for complete purification from CO2 (up to 2.5% by weight) with complete absorption of H2S, the absorber was reconstructed according to the claimed invention with the installation in the same four-section apparatus body of 13 packed stages (Fig. 6b) based on the same packed elements.

[0077] Thus, the claimed invention addresses the problem of developing an absorber design for the selective removal of acid gases—carbon dioxide and hydrogen sulfide—by maintaining the welded support fastenings of the contact devices to the apparatus casing, preserving the apparatus casing, and allowing for the configuration of the contact devices to be changed and replaced during the absorber reconstruction, simultaneously improving the absorber's technical and economic performance (increasing the depth of feedstock purification, changing the process selectivity, and increasing the plant's productivity). The proposed technical solution enabled the absorber to be reconstructed while preserving the casing and the existing set of packed contact elements, increasing the depth of natural gas purification from carbon dioxide, and increasing the CO2 absorption depth to 100%.

Claims

CLAUSES OF THE INVENTION 1. An absorber for the selective removal of acid gases, consisting of a cylindrical body, from the bottom of which a gas containing carbon dioxide, hydrogen sulfide is supplied, and an absorbent saturated with carbon dioxide, hydrogen sulfide is removed, from the top of the body a gas purified from carbon dioxide, hydrogen sulfide is removed and regenerated absorbent is supplied, and containing one or more packed mass-exchange sections, to which the absorbent is supplied, in these sections on the body there are annular support elements for fastening horizontal partitions that change the direction of the gas flow from counter-current to cross-current and divide the mass-exchange section into packed stages with packages of cross-current packing, and limited at the top and bottom of each packed stage by perforated webs with drain bars for organizing the flow of liquid from the overlying to the underlying packing packages, the drain bars are fixed on the vertical ribs of the packing packages, tightly adjoining the body along the entire edge of the packages,pressed against the housing, characterized in that, with equal height of the sections, in each section, annular support elements and vertical ribs are placed at equal distances from each other along the height, cross-flow packing packages of equal height in each mass-exchange section are formed from packing elements of equal height and, with the same number of packing elements in each mass-exchange section, a different number of packing stages is organized by moving horizontal partitions relative to the annular support elements and perforated webs with drain strips, relative to the vertical ribs with the placement of packing stages with cross-flow packing packages between them, while in the housing, along the height of the mass-exchange section, annular support elements are fixed in a quantity equal to or greater than the number of mass-exchange packing packages, and the number of horizontal partitions, installed on these ring support elements and perforated sheets, equal to the number of packing elements in the mass transfer section.

2. An absorber according to paragraph 1, characterized in that guide plates are attached to the annular support elements that are free from the fastening of horizontal partitions.

3. An absorber according to paragraph 1, characterized in that a stage with a baffle is placed in the upper part of the housing or each mass transfer section.

4. An absorber according to claim 1, characterized in that a cross-flow packing section is placed below the input of the unpurified gas for degassing the saturated absorbent flowing from the mass-exchange sections.

5. An absorber according to paragraph 1, characterized in that when forming one mass transfer section, one, two, three or four packed stages are used.

6. An absorber according to paragraph 1, characterized in that the fastening of the packing stages to the annular support elements and vertical ribs is made detachable.

7. An absorber according to paragraph 6, characterized in that during the detachable fastening of the packing stages to the annular support elements and vertical ribs, the fastenings are sealed using a contact seal.

8. An absorber according to paragraph 6, characterized in that the detachable fastening of the packed mass transfer stage to the annular support elements and vertical ribs is performed using clamps.

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