Patent Application
20150139879
The present invention relates to the sphere of deacidizing gaseous effluents comprising acid compounds such as carbon dioxide (CO2) and hydrogen sulfide (H2S) using an amine-based absorbent solution. The present invention applies in particular to CO2 capture upon hydrogen production through steam reforming of a gaseous hydrocarbon feed and to H2S removal from gaseous effluents produced upon hydrotreatment of liquid hydrocarbon feeds.
Controlling greenhouse gas emissions, notably CO2 emissions, is becoming an increasingly strong requirement for all economic sectors, in particular those concerning energy production. Industrial hydrogen production, generally based on natural gas steam reforming, is part of these sectors that emit large amounts of CO2.
One of the various possible ways of controlling CO2 emissions is CO2 capture through absorption methods using an aqueous amine solution, for example alkanolamines such as monoethanolamine (MEA), diethanolamine (DEA) or N-methyldiethanolamine (MDEA). The CO2 captured can be sequestered or re-used for various applications.
Such absorption methods can also be used for removing acid compounds contained in various types of gaseous effluents, among which the H2S-rich acid gases produced upon oil refining in petroleum cut hydrotreatment processes.
During industrial hydrogen production from natural gas, a steam reforming reaction of the natural gas (or Steam Methane Reforming SMR) leading to the formation of syngas comprising carbon monoxide (CO) and dihydrogen (H2) is carried out, followed by a reaction of conversion of the carbon monoxide (CO) to syngas so as to maximize the hydrogen production.
The steam reforming equilibrium reaction is written as follows for methane:
CH4+H20CO+3H2ΔH2980=206.0 kJ/mol (1)
The CO conversion reaction, generally referred to as Water Gas Shift (WGS) reaction, is written as follows:
CO+H20CO2+H2ΔH2980=−41.0 kJ/mol (2)
The balance of the two reactions is:
CH4+2H20CO2+4H2ΔH2980=165.0 kJ/mol (3)
The balance of these two reactions being highly endothermic, hydrogen production through steam reforming is conducted in furnaces operated at high temperature. The combustion fumes from these furnaces contain a large amount of CO2 that it is advisable to capture prior to releasing the fumes to the atmosphere. Combustion fumes thus are a first source of CO2 upon hydrogen production through natural gas steam reforming.
A second source of CO2 upon industrial hydrogen production through steam reforming is the CO conversion reaction (2). The CO2 thus formed has to be removed from the gas mixture, as well as the residual water, in order to produce almost pure hydrogen.
A hydrocarbon feed 100, typically natural gas or naphtha, is supplied, in admixture with water vapour 113, to a catalytic reforming section 1000.
Reforming section 1000 is typically an exchanger reactor consisting of a shell containing a plurality of tubes, a structure referred to as shell and tube by the person skilled in the art, where the hydrocarbon feed circulates through the tubes and a heat-carrying fluid circulates outside the tubes. This heat-carrying fluid generally consists of combustion fumes. The combustion can be external to the reactor, as illustrated by burners 1004 in
Catalysts based on nickel supported on alumina for example are typically used in the tubes heated by radiation, in a tube furnace for example. The thermodynamics of steam reforming reactions leads to operate, at the reactor outlet, at the highest possible temperature so as to maximize the conversion of methane to hydrogen, typically a temperature ranging between 850° C. and 900° C. The furnace inlet temperature ranges for example between 540° C. and 580° C. The pressure of the process generally ranges between 20 and 30 bar abs.
An effluent 101 mainly containing syngas H2+CO, and comprising water vapour H2O, as well as CH4 that has not been converted upon reforming, flows out of reforming section 1000. Other acid compounds such as CO2, H2S, mercaptans, COS, CS2, the SO2 initially contained in feed 100 can be present in effluent 101. Effluent 101 is sent after cooling to CO conversion section 1001 where the WGS reaction (2) described above is carried out. The water contained in hydrogen-rich mixture 102 at the outlet of section 1001 is removed by cooling and condensation in a section 1002 so as to produce water stream 103 and a hydrogen-rich and water-depleted mixture 104. Gas mixture 104 is then sent to a pressure-modulated adsorption purification unit (Pressure Swing Adsorption PSA) 1003. Two streams are then produced in unit 1003: a practically pure hydrogen stream 105 and a purge 106 containing CO2, unconverted CH4 and possibly other acid compounds initially present in feed 100. Purge 106 is generally used as fuel, in addition to another fuel 107 such as natural gas or a refinery gas/liquid, for feeding burners 1004 allowing to generate hot fumes 108 used as heat-carrying fluids in reforming section 1000.
Cooled combustion fumes 109 leaving steam reforming section 1000 can be treated in a CO2 capture unit 1005 prior to being sent to a chimney. CO2 capture can be performed using a fume scrubbing technology with an amine-based absorbent solution, by means of an absorber wherein the fumes are contacted with the absorbent solution so as to remove the CO2 from the fumes, and a regenerator for thermally regenerating the absorbent solution and releasing the absorbed CO2 it contains prior to recycling it to the absorber. Stream 110 represents the CO2-purified fumes and stream 111 represents the CO2-rich stream leaving the regenerator of capture unit 1005.
A major drawback of CO2 capture according to
A major drawback of this solution is that only part of the CO2 produced during the hydrogen production process is captured: the part resulting from the reforming and CO conversion reactions, but not the part resulting from combustion in the furnace. Indeed, the CO2 resulting from the combustion in burners 1004 is not captured. Combustion fumes 109 therefore contain the major part of the CO2 generated by the combustion of the CH4 that has not been converted in the reformer, which represents between 15% and 25% by mole of incoming CH4, plus the CO2 resulting from the combustion of backup fuel 107.
The purpose of the present invention is to overcome at least partly the problems of the prior art as described above.
The present invention thus aims to provide a deacidizing method using an amine-based absorbent solution for efficient capture of the CO2 formed upon industrial hydrogen production through steam reforming of a gaseous hydrocarbon feed, while limiting the investment cost of the CO2 capture plant and the energy needs for regeneration of the absorbent solution.
More generally, the present invention aims to provide a method for removing the acid compounds contained in at least two gaseous effluents of different origins by means of an amine-based absorbent solution, while limiting the investment cost of the acid compound removal plant and the energy needs for regeneration of the absorbent solution.
According to the invention, gaseous effluents of different origins are understood to be gaseous effluents generally produced by different reactions, which may be distinguished by their composition, and generated under distinct operating conditions, notably different pressure and temperature conditions. Thus, the pressure of each one of the two gaseous effluents that can be treated according to the invention is different, notably the partial pressure of the acid compound(s) to be removed. Two gaseous effluents of different origins according to the invention are for example a combustion fume and syngas, both generated in a hydrogen production process through natural gas reforming. The two effluents can also be two H2S-rich acid gases resulting from two distinct hydrodesulfurizations at different pressures of gasolines, kerosenes or diesel oils of different natures.
Thus, in order to reach at least one of the aforementioned purposes, among others, the present invention provides, according to a first aspect, a method of removing acid compounds contained in a gaseous effluent, comprising:
First pressure P1 in the first absorption column preferably ranges between 1 bar and 190 bar, and second pressure P2 in the second absorption column ranges between 10 bar and 200 bar.
According to an embodiment, second pressure P2 is at least 10 bar higher than first pressure P1, first pressure P1 ranges between 1 bar and 6 bar, and second pressure P2 ranges between 15 bar and 40 bar.
Preferably, the first solution enriched in acid compounds and the second solution enriched in acid compounds have an acid compound loading rate difference ranging between 5% and 30%.
The first solution enriched in acid compounds is preferably fed at an intermediate level along the regeneration column so that at least 50% of the acid compounds contained in said solution are released as gas in the regeneration column.
The partly regenerated solution is advantageously collected at a given height of the regeneration column above the height of discharge of the totally regenerated solution.
According to an embodiment, the method applies to CO2 capture in a hydrogen production process through steam reforming of a gaseous hydrocarbon feed, wherein the first gaseous effluent is a combustion fume from a combustion stage in the hydrogen production process, and the second gaseous effluent is a hydrogen-rich CO2-containing dry gas mixture, said mixture being obtained in the hydrogen production process after a stage of water gas shift reaction of the CO contained in the reforming effluents, and after a cooling and condensation stage.
According to an embodiment, the method applies to H2S capture in a hydrocarbon feed hydrotreating process, wherein the first gaseous effluent and the second gaseous effluent to be treated are recycle gases produced in a first hydrotreating unit and in a second hydrotreating unit respectively. According to this embodiment, first pressure P1 preferably ranges between 20 bar and 190 bar, and second pressure P2 preferably ranges between 45 bar and 200 bar.
The present invention also provides, according to a second aspect, a plant for removing acid compounds contained in a gaseous effluent for implementing the method according to the invention. The plant comprises:
The delivery line for the first solution enriched in acid compounds is preferably positioned at an intermediate level along the regeneration column, below the line delivering the second solution enriched in acid compounds.
Advantageously, the position of the delivery line for the first solution enriched in acid compounds is determined by taking simultaneously account of the loading rate and the temperature of said solution enriched in acid compounds entering the column, so as to minimize the heat consumption at the reboiler of the regeneration column.
Advantageously, the discharge line intended for the partly regenerated absorbent solution is positioned at a given height of the regeneration column above the discharge line intended for a totally regenerated absorbent solution.
Other features and advantages of the invention will be clear from reading the description hereafter of particular embodiments given by way of non-limitative example, with reference to the accompanying figures wherein:
In the figures, the same reference numbers designate identical or similar elements.
The present invention aims to remove the acid compounds contained in two gaseous effluents of different origins, comprising using a single amine-based absorbent solution, an absorption column for each one of the two gaseous effluents to be deacidized and a single regenerator.
The hydrogen production method and the plant for implementing it are similar to those described in connection with
Hydrocarbon feed 100 is a gaseous feed. The gaseous hydrocarbon feeds according to the invention include hydrocarbon feeds in gas form, liquid feeds after vaporization and volatile hydrocarbons from solid feeds.
Preferably, feed 100 is natural gas or naphtha. The natural gas is predominantly made up of gaseous hydrocarbons, but it can contain some of the following acid compounds: CO2, H2S, mercaptans, COS, CS2. The proportion of these acid compounds is highly variable and it can be up to 70 vol. % for CO2 and 40 vol. % for H2S. Desulfurization of the feed can be carried out upstream from reforming unit 1000. In this case, the acid gases to be removed are essentially CO2. The temperature of the natural gas can range between 20° C. and 100° C. The pressure of the natural gas can range between 10 and 120 bar.
Feed 100 preferably has a minimum steam-to-carbon (S/C) molar ratio in order to prevent coke formation on the catalyst and corrosion through metal dusting. Depending on the feeds, this ratio generally ranges between 2.5 and 3.5.
Combustion fumes 109 are produced by the combustion of a fuel 107 such as hydrocarbons, for example natural gas or a refinery gas/liquid, a biogas, etc., and preferably also by the combustion of purge 106. These fumes generally have a temperature ranging between 900° C. and 1400° C., a pressure ranging between 1 and 6 bar abs and they can contain between 50 and 80 vol. % nitrogen, between 5 and 40 vol. % CO2, between 0.5 and 17 vol. % oxygen, and some impurities such as SOx and NOx.
Effluent 104 is a dry gas mixture rich in hydrogen, in a proportion typically ranging between 70 and 90 mol. %, also comprising CO2, in a proportion ranging between 15 and 30 mol. %, mainly formed during the CO conversion reaction in unit 1001, as well as residual CH4, ranging between 2 and 7%, and residual CO, in a proportion of less than 5%, and possibly a water residue that has not condensed during the cooling and condensation stage in unit 1002, and other compounds present in the initial feed 100. The pressure of effluent 104 ranges between 15 and 40 bar, preferably between 20 and 30 bar.
According to the invention, the CO2 is captured in the gaseous effluents using a CO2 capture unit 1007 receiving combustion fumes 109 and hydrogen-rich effluent 104. Each one of these two gaseous effluents 109 and 104 is treated in a distinct absorption column (not shown in
All of the CO2 generated in the hydrogen production process can thus be potentially captured by means of the method according to the invention while minimizing the investment cost, by means of a single regenerator and a single absorbent solution used under conditions allowing optimum CO2 capture, unlike conventionally known methods.
One may refer to the CO2 capture application during hydrogen production to describe the method in reference to
The deacidizing plant comprises a first absorption column 1007-1 provided with gas-liquid contacting means, a random packing, a stacked packing or trays for example. The first gaseous effluent to be treated 109, for example combustion fumes 109 of
The deacidizing plant also comprises a second absorption column 1007-2, equipped like first absorption column 1007-1, comprising a line in the lower part of the column through which the second gaseous effluent to be treated 104, for example hydrogen-rich dry mixture 104 of
Preferably, absorbent solution 450 enriched in acid compounds flowing from second absorber 1007-2 and absorbent solution 430 enriched in acid compounds flowing from first absorber 1007-1 have an acid compound loading rate difference ranging between 5% and 30%.
Regeneration column 1007-3 is also equipped with gas-liquid contacting internals such as trays, random or packed packings for example. The bottom of column 1007-3 is equipped with a reboiler (not shown) that provides the heat required for regeneration by vaporizing a fraction of the absorbent solution. The delivery lines allowing the absorbent solutions to be supplied to the regeneration column are advantageously positioned in such a way that the temperature and the loading rate profile in the regeneration column is as monotonic as possible in relation to the natural evolution of the temperature and of the loading rate. Thus, the loading rate is higher at the regeneration column top and lower at the bottom of said column. The temperature is lower at the regeneration column top and higher at the bottom of said column. The positioning of the delivery lines of column 1007-3 takes simultaneously account of the loading rate and the temperature of the laden absorbent solution flowing into the column so as to minimize the heat consumption at the regeneration column reboiler. The final result is obtained from an iterative calculation. Among the two absorbent solutions 430 and 450 enriched in acid compounds, the one with the higher acid compound loading rate is introduced at a greater height in regeneration column 1007-3 than the one with the lower acid compound loading rate. The line carrying the first absorbent solution enriched in acid compounds 430 coming from first absorber 1007-1 opens into an intermediate part of the regeneration column, at a given height so selected that a major part of the acid compounds contained in the solution can be released through expansion with minimum energy consumption, as described above. The line allowing introduction of the absorbent solution enriched in acid compounds 450 from second absorption column 1007-2, in cases where the acid compound loading rate thereof is higher than that of solution 430, opens onto the upper part of regeneration column 1007-3, above the line delivering first solution 430 enriched in acid compounds, for deeper regeneration of this stream richer in acid compounds than solution 430. A line at the top of column 1007-3 allows discharge of the gas enriched in acid compounds released upon regeneration 111. A line arranged at the bottom of column 1007-3 allows discharge of a totally regenerated absorbent solution so as to form first absorbent solution stream 420 sent to first absorption column 1007-1. A line positioned at an intermediate level along column 1007-3, above the line allowing discharge of totally regenerated solution 420, allows extraction of a partly regenerated absorbent solution that makes up second absorbent solution stream 440 sent to second absorber 1007-2.
Heat exchangers (not shown) are preferably arranged on the absorber/regenerator circuit allowing recovery of the heat of the regenerated or partly regenerated absorbent solution from regeneration column 1007-3 in order to heat absorbent solutions 430 or 450 enriched in acid compounds and flowing out of the absorption columns. Pumps and valves, not shown, can also be arranged on the absorbent solution circuit in order to adjust the fluid pressures to the desired operating conditions and to facilitate their transportation from one column to the next.
Using a single regeneration column for deacidizing two gaseous effluents of different origins provides a significant investment cost gain.
The absorption performed in absorption columns 1007-1 and 1007-2 consists in contacting the gaseous effluent carried through the line at the column bottom with the absorbent solution stream carried through the line at the column top. Upon contacting, the amines of the absorbent solution react with the acid compounds contained in the effluents so as to obtain a gaseous effluent depleted in acid compounds that is discharged through the line at the absorption column top and an absorbent solution enriched in acid compounds discharged through the line at the absorption column bottom to be regenerated.
The first absorption stage carried out in first absorption column 1007-1 is performed at a pressure P1 that can range between 1 bar and 190 bar, preferably between 1 bar and 6 bar, more preferably between 1 bar and 3 bar, in the case of a combustion fume, and preferably between 40 bar and 190 bar for a recycle gas from a hydrocarbon feed hydrotreating unit. Pressure P1 preferably corresponds to the pressure of effluent 109 to be treated. The temperature in column 1007-1 can range between 20° C. and 90° C., preferably between 30° C. and 80° C. The pressures given in the present description are expressed in absolute unit (bar abs), unless otherwise specified.
The second absorption stage carried out in second absorption column 1007-2 is performed at a pressure P2 higher than pressure P1, at least 5 bar higher than pressure P1, preferably at least 10 bar higher than pressure P1 and more preferably at least 20 bar higher than pressure P1. Pressure P2 can range between 10 bar and 200 bar, preferably between 15 bar and 200 bar, more preferably between 15 bar and 40 bar in the case of H2-rich gaseous effluent 104 of
The regeneration stage in regeneration column 1007-3 notably consists in heating and optionally in expanding the absorbent solutions enriched in acid compounds coming from the two absorption columns, so as to release the acid compounds in gas form.
The first absorbent solution enriched in acid compounds 430 leaving first column 1007-1 is fed into regeneration column 1007-3 at a given height of the column, for example at the level of a given tray, so that expansion of the solution is achieved in order to release at least 50% of the acid compounds contained in the solution. According to the invention, introducing solution 430 at an intermediate position along the column is sufficient for regeneration of this solution 430, and it thus allows to optimize the energy to be supplied for global regeneration. Preferably, prior to being fed into the regeneration column, solution 430 is first heated in a heat exchanger by the stream of totally regenerated solution 420 coming from regeneration column 1007-3.
The second absorbent solution enriched in acid compounds 450 leaving second column 1007-2 is introduced through a line at the top of the regeneration column. Prior to being fed into the regeneration column, solution 450 can be heated in a heat exchanger where stream 440 flowing from regeneration column 1007-3 circulates.
In regeneration column 1007-3, under the effect of the contacting of the absorbent solutions enriched in acid compounds with the steam produced by the reboiler, the acid compounds are released in gas form and discharged through a line located at the top of column 1007-3. A totally regenerated absorbent solution, i.e. nearly totally free of acid compounds, is discharged through a line at the bottom of column 1007-3, then recycled to first absorption column 1007-1 in order to form first absorbent solution stream 420. Solution 420 is preferably cooled in a heat exchanger where solution 430 circulates. A partly regenerated absorbent solution 440 is extracted at an intermediate level along regeneration column 1007-3, above the point where totally regenerated solution 420 is discharged, collected for example at the level of a given tray, so as to be recycled and to form second absorbent solution stream 440 fed into second absorption column 1007-2. The acid compound loading rate of the partly regenerated solution is between 5% and 30% higher than that of totally regenerated solution 420. Such a partly regenerated solution is sufficient for efficient removal of the acid compounds from second gaseous effluent 104 in the second absorber operating at high pressure, while allowing the energy required for global regeneration of the absorbent solution to be saved.
In cases where the absorbent solution used is a 30 wt. % MEA aqueous solution, a partly regenerated solution 450 is for example a solution having a CO2 loading rate ranging between 0.20 and 0.50 mol CO2/mol MEA, preferably between 0.25 and 0.40 mol CO2/mol MEA, and a totally regenerated solution is for example a solution having a CO2 loading rate ranging between 0.15 and 0.45 mol CO2/mol MEA, preferably between 0.20 and 0.30 mol CO2/mol MEA.
The regeneration stage of the method according to the invention is performed by thermal regeneration, optionally complemented by one or more expansion stages.
Regeneration can be carried out at a pressure in column 1007-3 ranging between 1 bar and 5 bar, or even up to 10 bar, and at a temperature in column 1007-3 ranging between 100° C. and 180° C., preferably between 110° C. and 170° C., and more preferably between 120° C. and 140° C.
The absorbent solution according to the invention is an aqueous solution comprising at least one amine. Said amine in aqueous solution has the capacity of absorbing at least one acid compound of the gaseous effluent to be treated. Primary, secondary or tertiary amines, i.e. comprising at least one primary, secondary or tertiary amine function, can be used.
By way of non-exhaustive example, the following amines can be used for the absorbent solution utilized in the method according to the invention: monoethanolamine (MEA), 2-amino-2-methyl-propanol (AMP), 1-amino-2-propanol, 2-amino-1-butanol, 1-(2-amino-ethyl)-pyrrolidine, diethanolamine (DEA), 2 (ethylamino) ethanol, 2-methylpiperazine, N-methyldiethanolamine (MDEA), 1-(dimethylamino)-2-propanol, N,N,N′,N′-Tetramethylhexane-1,6-diamine (TMHDA), 1-amino-6-pyrodinyl-hexane, Pentamethyl-dipropylenetriamine, N,N,N′,N′-Tetraethyldiethylenetriamine, Bis[2-(N,N-dimethylamino)-ethyl]ether. These amines can be used alone or in admixture.
The formulation of the solution is preferably determined according to the acid compound(s) to be removed and the partial pressures of the acid compounds in the gases to be treated. It may be advantageous to select a hindered tertiary or secondary amine for selective H2S absorption, for example for treating recycle gases from the hydrotreatment process.
An aqueous solution is understood to be a solution containing at least 10 wt. %, inclusive, water.
The amine(s) can have variable concentrations in the absorbent solution, ranging for example between 10 and 90 wt. %, preferably between 20 and 60 wt. %, more preferably between 25 and 60 wt. %, and most preferably between 30 and 60 wt. %, inclusive of endpoints.
The absorbent solution can contain between 10 and 90 wt. % water, preferably between 25 and 80 wt. % water, more preferably between 30 and 70 wt. % water and most preferably between 40 and 70 wt. % water, inclusive of endpoints.
The absorbent solution can contain other compounds, for example one or more activator compounds allowing the absorption kinetics of the acid compounds to be accelerated, which can be a nitrogen compound comprising a primary or secondary amine function. Tertiary amines can thus be mixed with a primary or secondary amine, for example with one or more of the following amines: BenzylAmine, N-MethylBenzylAmine, N-EthylBenzylAmine, a-MethylBenzylAmine, a-EthylBenzylAmine, PhenethylAmine, TetraHydro-IsoQuinoline, IsoIndoline, ButylAmine, N-ButylPiperazine, MonoEthanolAmine, AminoEthyl-EthanolAmine, DiGlycolAmine, Piperazine, N-(2-HydroxyEthyl)Piperazine, N-(2-AminoEthyl) Piperazine, N-Methyl Piperazine, N-EthylPiperazine, N-PropylPiperazine, 1,6-HexaneDiAmine, 1,1,9,9-TetraMethylDi-PropyleneTriamine, Morpholine, Piperidine, 3-(MethylAmino)PropylAmine, N-MethylBenzylAmine.
The absorbent solution can also comprise a physical solvent such as methanol, sulfolane, polyethylene glycols that can be etherified, pyrrolidones or derivatives such as, for example, N-methylpyrrolidone, N-formyl morpholine, acetyl morpholine, propylene carbonate. For example, the absorbent solution comprises between 10 and 50 wt. % of a solvent of physical nature.
The absorbent solution can also comprise amine degradation inhibitor compounds or corrosion inhibitor compounds.
The present invention is not limited to the capture of CO2 in fumes and the syngas that has undergone conversion through WGS during hydrogen production by steam reforming of natural gas.
More generally, it can apply to the treatment of gaseous effluents of different origins, notably gaseous effluents having different pressures. In order to make maximum use of the advantages afforded by the method according to the invention, the gaseous effluents to be treated exhibit a significant pressure difference, for example of the order of at least 5 bar, preferably at least 10 bar and more preferably at least 20 bar.
Thus, the method according to the invention can advantageously apply to the desulfurization of H2S-rich gases formed during hydrotreatment of hydrocarbon feeds of different natures, under different pressure conditions.
In this embodiment, the gaseous effluents to be deacidized 509 and 504 are recycle gases generated during the hydrotreatment of two different hydrocarbon feeds, for example a distillation gasoline and diesel oil requiring each separate hydrotreatment due for example to variable sulfur compounds depending on the feeds. These sulfur compounds are then referred to as more or less refractory. The more refractory a sulfur compound, the higher the hydrodesulfurization operating pressure.
Hydrotreatment of a hydrocarbon feed such as diesel oil in the sphere of petroleum refining is a process that is well known to the person skilled in the art. Such a method is for example described in U.S. Pat. No. 4,990,242. Hydrotreatment aims to desulfurize diesel oils. It consists in reacting a hydrocarbon feed mixed with a hydrogen-rich gas in a reactor at high temperature, the mixture being heated by heat exchangers and a furnace at a reaction temperature of the order of 340° C. to 370° C. prior to being fed to the reactor. The feed is sent to the reactor in vapour form if it is a light cut or in form of a liquid/vapour mixture if it is a heavy cut. The exothermicity of the reactions causes a temperature rise that can be controlled, for example through quenching with a cold liquid for cooling the mixture in the reactor. At the reactor outlet, the mixture is cooled and separated, which provides a H2S-rich gas, light products resulting from the decomposition of impurities, and a hydrorefined product of same volatility as the feed, but with improved characteristics. In the separation stage, several devices are generally used, including a high-pressure separator drum allowing a hydrogen-rich gas to be recycled by means of a recycle compressor. This recycle gas contains H2S that can be removed by washing with an absorbent amine solution. A high-pressure gas purge can also be provided to keep a sufficient hydrogen purity in the recycled gas. The deacidizing method according to the invention is implemented at this stage. In general, the separation section also comprises a low-pressure separator drum and a diesel steam stripper. The low-pressure separator drum allows to separate the liquid and vapour phases obtained by expansion of the liquid from the high-pressure drum. The gas mainly comprises hydrogen, light hydrocarbons and a large part of the hydrogen sulfide formed during the reaction. The purpose of the stripper is to remove the light hydrocarbons and the residual H2S from the cut treated. The diesel oil is withdrawn at the column bottom with control of the operation with the flash point of the diesel oil. The residual H2S is mixed with the H2S-rich gas leaving the low-pressure separator drum so as to form the H2S-rich gas leaving the hydrotreating unit.
The method according to the invention allows to remove the H2S from recycle gases 509 and 504 coming from two distinct hydrotreating units 2000 and 3000. Each hydrotreating unit treats a different initial hydrocarbon feed 560 and 580, at different pressures, linked for example with the nature of the feed, the geographical origin of the crude oil and the distillation cut (gasoline/kerosene/diesel). A hydrorefined product 570 and a recycle gas 509 from which the H2S is to be removed are obtained in first hydrotreating unit 2000. The pressure of the recycle gas ranges for example between 40 bar and 190 bar. The same applies to second hydrotreating unit 300 from which flow a hydrorefined product 590 and a recycle gas 504 containing H2S to be removed, at a pressure ranging for example between 45 bar and 200 bar. The recycle gases are rich in hydrogen, typically between 60 and 95 mol %, and they can contain between 2% and 20% methane, between 1% and 10% ethane, less than 5% hydrocarbons with more than three carbon atoms, water traces, less than 5% water, and between 0.1% and 4% H2S, preferably between 0.5% and 1.5% H2S. Absorbers 1008-1 and 1008-2 allow the H2S to be removed from recycle gas 509 and recycle gas 504 respectively, and regenerator 1008-3 allows to regenerate the absorbent solution with production of a partly regenerated solution and a totally regenerated solution, as described above for the process illustrated in
Pressure P2 in second absorber 1008-2 is higher than pressure P1 of first absorber 1008-1, by at least 5 bar, preferably at least 10 bar, more preferably at least 20 bar, or even 30 or 40 bar.
Pressure P1 ranges for example between 1 and 190 bar, preferably between 20 bar and 190 bar, more preferably between 40 bar and 190 bar, more preferably yet between 40 bar and 150 bar, and most preferably between 40 bar and 100 bar. Pressure P1 preferably corresponds to the pressure of effluent 509 to be treated. Pressure P2 ranges for example between 10 bar and 200 bar, preferably between 45 bar and 200 bar, more preferably between 50 bar and 200 bar, more preferably yet between 50 bar and 180 bar, and most preferably between 80 bar and 150 bar. Pressure P2 preferably corresponds to the pressure of effluent 504 to be treated. For example, recycle gas 509 is treated at a pressure P1 of 80 bar in first absorber 1008-1 and recycle gas 504 is treated at a pressure P2 of 120 bar in the second absorber.
Any suitable means for subjecting the fluids circulating between the absorbers and the regenerator to pressure and expansion (e.g. valves, pumps, turbine pumps) can be provided so as to reach the operating conditions required in the various columns.
The method according to the invention is not limited to deacidizing of two gaseous effluents of different origins and it could be implemented for treating more than two gaseous effluents. For example, a third absorber could be used to receive a third gaseous effluent from which one or more acid compounds are to be removed, by contacting with a third absorbent solution stream. Depending on the operating conditions of the absorber, notably the operating pressure, the absorbent solution stream introduced can for example be a fraction of the totally regenerated solution, or a fraction of the partly regenerated solution, or two intermediate withdrawal levels can be provided at the regeneration column, thus providing three regenerated solution grades, with one dedicated to each of the three absorbers.
The example relates to the deacidizing method according to
According to
For example, effluents 104 and 109 are treated with an absorbent solution consisting of 30 wt. % monoethanolamine (MEA) aqueous solution. Each gas 104 and 109 is treated in an absorption column and brought into countercurrent contact with an amine solution having a specific CO2 loading rate, i.e. containing a certain amount of CO2. The CO2 loading rate is defined as the amount of CO2 (in mole) in relation to the amount of amine (in mole). In the present case, the MEA treating units use a 0.24 mol CO2/mol MEA absorbent solution at the absorber inlet for treating effluent 109 and a 0.28 mol CO2/mol MEA solution for treating effluent 104. The heat consumption involved in the amine regeneration is quantified in gigajoules per ton of CO2 removed (GJ/tCO2).
Table 2 hereafter gives the operating conditions of the two processes using the 30 wt. % MEA, as well as the investment in installed cost of the regenerator of each unit according to the prior art. For the unit treating effluent 104, the regenerator investment is given on a reference basis of 100. For the unit treating effluent 109, the regenerator investment is 80.
The two absorption units described above use the same solvent (30 wt. % MEA). According to the invention, the same data relative to the absorption of effluents 104 and 109 are used, and regeneration is conducted within a single regenerator, with similarly identical regenerator operating conditions as regards temperature and pressure.
In
Tables 3 and 4 below give the operating conditions of absorbers 1007-1 and 1007-2, and of regenerator 1007-3.
| Number | Date | Country | Kind |
|---|---|---|---|
| 13/61.367 | Nov 2013 | FR | national |
