Method and system for treating a gas flow from the pyrolysis of plastic and / or the pyrolysis of biomass for the recovery of olefins

Abstract

The invention relates to a method comprising the following steps: - quenching, water washing, compressing and pressure washing the pyrolysis gas flow (12) in order to obtain a washed compressed gas flow (78); - removing acids and then drying and purifying the gas flow to form a purified gas flow (84); - adding the flow (84) to a cryogenic absorption column (42) supplied with a hydrocarbon cryogenic solvent (85) in order to obtain, at the bottom, a liquid product comprising a cut (46) of C2+ hydrocarbons and, at the top, a head flow comprising a light gaseous residue (44). The column (42) comprises, at the top, a device (D) for partially condensing the head flow and the method comprises a step of partially condensing the head flow carried out at a temperature of between –40°C and –100°C and a step of separating the condensed head flow in order to obtain the light gaseous residue flow (44).

Description

[0001] METHOD AND SYSTEM FOR TREATING A GAS STREAM FROM PLASTIC PYROLYSIS AND / OR BIOMASS PYROLYSIS FOR THE RECOVERY OF OLEFINS

[0002] The present invention relates to a method for treating at least one gas stream resulting from the pyrolysis of plastic and / or biomass.

[0003] Environmental protection requirements are leading manufacturers to plan plastic waste treatment channels and / or biomass recovery channels, particularly to produce fuels from renewable resources.

[0004] These sectors use pyrolysis to process plastics and / or biomass in order to obtain recyclable products.

[0005] Thus, the gases from pyrolysis contain a large number of high added value compounds (HVC), which are likely to be recovered.

[0006] This is particularly the case for hydrocarbon compounds such as ethylene, propylene, butadiene, benzene, toluene, paraffins and hydrogen.

[0007] However, these gases from the pyrolysis of plastic and / or biomass cannot be directly used to be sent to crackers or to autonomous olefin production units. Indeed, the plastic and / or biomass that undergoes pyrolysis contains impurities, which are found directly or degraded in the pyrolysis gases.

[0008] This includes, for example, sulfur compounds such as mercaptans, sulfur oxides such as carbon oxysulfide or hydrogen sulfide, acid gases such as hydrochloric acid or hydrocyanic acid, carbon monoxide, carbon dioxide, oxygen and oxygen derivatives, ammonia, nitrogen oxides and other nitrogen or chlorine derivatives, and metals. These contaminants can cause safety and / or operability risks in the steam cracker or stand-alone olefin recovery unit. In many cases, pyrolysis gases are therefore not used for HVC recovery, but are sent to other units such as power generation units.

[0009] US 9 01 1 578 also proposes a solution aimed at using in a downstream fermentation unit certain compounds contained in gases resulting from the pyrolysis of biomass.

[0010] Before introducing the gases into the fermentation unit, they are purified using a treatment process that removes certain compounds. This process is effective in obtaining gases compatible with fermentation, but does not allow the recovery of hydrocarbons for recycling.

[0011] One solution for recovering hydrocarbons is to fractionate the gas stream using a cryogenic absorption unit fed with a cryogenic hydrocarbon solvent.

[0012] However, losses of cryogenic hydrocarbon solvent must be minimized.

[0013] Based on this, an aim of the invention is to provide a method which makes it possible to treat pyrolysis gases very efficiently, in particular from the pyrolysis of plastic material and / or biomass, with a view to recovering compounds which these pyrolysis gases contain, in particular olefins, while limiting the loss of cryogenic hydrocarbon solvent.

[0014] To this end, the invention relates to a method for treating at least one gas stream 12 resulting from the pyrolysis of plastic and / or biomass, characterized by the following steps:

[0015] - quenching and washing with water of the gas stream resulting from the pyrolysis 12 of plastic and / or biomass in a quenching / washing unit 30 and separation of an aqueous phase 70 and a washed gas stream 72;

[0016] - compression, then cooling of the washed gas flow 72 to form a compressed gas flow 76;

[0017] - pressure washing of the compressed gas stream 76 to form a washed gas stream 78;

[0018] - passage of the washed gas flow 78 into at least one acid removal unit 36, 38 to form an acid-depleted gas flow 80;

[0019] - drying the acid-depleted gas stream 80 to form a dry gas stream 82;

[0020] - passage of the dry gas flow 82 into at least one impurity removal unit 40 to form a purified gas flow 84;

[0021] - introduction of the purified gas flow 84 into a cryogenic absorption column 42 and feeding the cryogenic absorption column 42 with a hydrocarbon cryogenic solvent 85 to obtain in the tank a liquid product comprising a fraction 46 of Cs hydrocarbons +and at the top a head flow comprising a light gaseous residue 44; characterized in that the cryogenic adsorption column comprises at the top a device D for partial condensation of the head flow and said method comprises a step of partial condensation of the head flow carried out at a temperature between - 40°C and -100°C, a step of separation of the condensed head flow to obtain said light gaseous residue flow 44. The method according to the invention may comprise one or more of the following characteristics, taken in isolation or in any technically possible combination:

[0022] - the gas stream from pyrolysis 12 contains Cs hydrocarbons + , and light compounds such as hydrogen, and methane.

[0023] - the gas stream resulting from the pyrolysis 12 contains carbon monoxide, carbon dioxide, nitrogen oxides, and / or oxygen and oxygen derivatives, in particular alcohols, aldehydes and / or ketones, nitrogen compounds such as nitrogen and ammonia and / or acid compounds, such as hydrochloric acid and hydrocyanic acid, chlorine derivatives, and / or sulfur compounds, in particular mercaptans, carbon oxysulfides, and hydrogen sulfide.

[0024] - the hydrocarbon cryogenic solvent 85 comprises C3 and / or C4+ hydrocarbons, in particular C3 hydrocarbons;

[0025] - the partial condensation of the head flow of the absorption column is carried out at least in part by heat exchange with an external flow, such as for example a C2 hydrocarbon cut coming from a cracker capable of producing an ethylene cut; by external flow is meant a flow external to the installation implementing said process;

[0026] - the process comprises a step of separating the 46 hydrocarbon cut into Cs + in a 14-fraction of C2 hydrocarbons, and in at least one 16-, 18-fraction of Cs hydrocarbons + ; at least a portion of said Cs hydrocarbon fraction + can be recycled in the cryogenic adsorption unit 42;

[0027] - at least a portion of the C2 hydrocarbon cut 14 is expanded, then vaporized by heat exchange with at least a portion of the top flow of the cryogenic absorption column in the device D to form a gas flow R, the light gas residue 44 and a condensate C.

[0028] - the condensate C is recycled into the cryogenic absorption column 42 and / or the gas stream R is recycled to be compressed and cooled in the unit 32 together with the washed gas stream 72.

[0029] - the separation step comprises the production of a C3 hydrocarbon cut 16 and a C^T hydrocarbon cut 18, at least a portion of the C3 hydrocarbon cut 16 being recycled into the cryogenic absorption column 42.

[0030] - the light gaseous residue 44 contains combustible gas, in particular methane, hydrogen, as well as light compounds of the purified gas stream 84, such as carbon monoxide, nitrogen, nitric oxide, and / or oxygen. - the light gaseous residue 44 is intended to be conveyed into a cracking unit, in particular into the fuel gas network of a steam cracker and / or is intended to constitute a fuel gas.

[0031] - at least one acid removal unit comprises an amine unit 36 ​​and / or a caustic washing unit 38, the compressed gas flow 76 passing into the amine unit 36 ​​and / or the caustic washing unit 38.

[0032] - the impurity removal unit comprises at least one activated metal bed, in particular an activated alumina bed or a mixed adsorbent; the sulfur compounds, in particular hydrogen oxysulfide and mercaptans, and / or ammonia, nitrogen compounds, chlorine compounds, oxygenated compounds, in particular alcohols, and / or silicones contained in the dry gas flow being retained on the (at least one) activated metal bed;

[0033] - at least part of the Cs hydrocarbon fraction + and / or at least a portion of the C2 hydrocarbon cut 14, and / or at least a portion of the C3 hydrocarbon cuts 16, 18 + is introduced into a cracker suitable for producing an ethylene cut or into a stand-alone unit suitable for producing an ethylene cut;

[0034] - at least part of the aqueous phase produced during the quenching / washing step is pressurized and is placed in contact with the compressed gas flow during the pressure washing step;

[0035] - at least two flows from the purified gas flow, the hydrocarbon cryogenic solvent, the light gas residue, and / or at least one reflux or the top flow of the absorption column of the cryogenic absorption unit are placed in heat exchange relationship in a cold box, in particular formed from a single cryogenic plate equipment, in particular made of brazed aluminum;

[0036] - the steps of quenching and washing with water the gas stream resulting from the pyrolysis, compression, then cooling of the washed gas stream, pressure washing of the compressed gas stream, passage of the washed gas stream through at least one acid removal unit, drying of the acid-depleted gas stream, passage of the dry gas stream through at least one impurity removal unit, introduction of the purified gas stream into a cryogenic absorption unit are carried out successively in the order indicated;

[0037] - the light gaseous residue 44 is intended to be conveyed into a cracking unit, in particular into the fuel gas network of a steam cracker and / or is intended to constitute a fuel gas.

[0038] The invention also relates to an installation 10, 1 10 for treating at least one gas flow 12 resulting from a pyrolysis of plastic and / or biomass, characterized by: - ​​a quenching / washing unit 30, capable of quenching and washing with water the gas flow resulting from the pyrolysis 12 of plastic and / or biomass and of separating an aqueous phase 70 and a washed gas flow 72;

[0039] - a unit 32 for compressing / cooling the washed gas flow 72 to form a compressed gas flow 76;

[0040] - a unit 34 for pressure washing the compressed gas flow 76 to form a washed gas flow 78;

[0041] - at least one unit 36, 38 for eliminating the acids present in the washed gas flow 78 to form an acid-depleted gas flow 80;

[0042] - a unit 39 for drying the acid-depleted gas stream 80 to form a dry gas stream 82;

[0043] - at least one impurity removal unit 40 in the dry gas stream 82 to form a purified gas stream 84;

[0044] - a cryogenic absorption unit 42 capable of being supplied by the purified gas flow 84 and by a cryogenic hydrocarbon solvent 85 to obtain in the tank a liquid product comprising a fraction 46 of Cs hydrocarbons + and at the head a head flow comprising a light gaseous residue 44; characterized in that the cryogenic adsorption column comprises at the head a device D for partial condensation of the head flow configured so as to obtain the light gaseous residue 44 at a temperature between - 40°C and -100°C.

[0045] The installation according to the invention may include one or more of the following characteristics, taken in isolation or in any technically possible combination:

[0046] - the installation includes a unit 48 for fractionating the 46 hydrocarbon cut into Cs + to form a 14-fraction of C2 hydrocarbons, and at least one 16-, 18-fraction of Cs hydrocarbons + ; at least a portion of said C3+ hydrocarbon cut being able to be recycled in the cryogenic absorption unit (42).

[0047] - the installation comprises a means for expanding at least a portion E of the C2 hydrocarbon cut 14 and the device D is configured to vaporize by heat exchange said portion E of the expanded C2 hydrocarbon cut 14, said heat exchange being carried out with at least a portion of the top flow of the cryogenic absorption column so as to form a gaseous flow R, a light gaseous residue 44 and a condensate C. Note that the condensate C comprises cryogenic solvent

[0048] - the installation comprises a means for recycling the condensate C in the cryogenic absorption column 42; and a means for recycling the gas flow R in the compression / cooling unit 32. - an outlet of the quenching / washing unit 30 recovering the aqueous phase 70 is connected to an inlet of the pressure washing unit 34, a member 92 for compressing the aqueous phase 70 being interposed between the outlet of the quenching / washing unit 30 and the inlet of the high-pressure washing unit 34.

[0049] - the cryogenic absorption column comprises a cold box, in particular formed from a single cryogenic plate device, in particular made of brazed aluminum, capable of placing in heat exchange relation at least two flows among the purified gas flow, the hydrocarbon cryogenic solvent, the light gas residue, and / or at least one reflux or the head flow of the absorption column of the cryogenic absorption unit.

[0050] The invention will be better understood by reading the following description, given solely by way of example, and made with reference to the appended drawings, in which:

[0051] - [Fig. 1] Figure 1 is a block diagram illustrating an installation for implementing a first purification process according to the invention, intended in particular to produce a C2 hydrocarbon cut which can be recovered in a steam cracker or in an autonomous ethylene production unit;

[0052] - [Fig. 2] Figure 2 is an installation variant intended for the implementation of a second purification process according to the invention

[0053] In all that follows, the term "C hydrocarbons" n » means that the number of carbons contained in the hydrocarbon is equal to n. The term "C hydrocarbons n + » means that the number of carbon atoms contained in the hydrocarbon is greater than or equal to n.

[0054] For example, the term C2 hydrocarbons includes in particular ethane, ethylene and acetylene. The term C2 hydrocarbons + includes hydrocarbons having a carbon number greater than or equal to 2, for example ethane, propane, butane, pentane etc.

[0055] In all that follows, pressures are relative pressures and compositions expressed as percentages are mass percentages, unless otherwise indicated.

[0056] Furthermore, the same numerical reference can designate a current flowing in a pipe, or the pipe which transports them.

[0057] The term "atmospheric pressure" refers to the pressure of the ambient air mass at the installation location. This pressure is generally between 900 mbar and 1100 mbar absolute.

[0058] A first installation 10 for treating a gas flow 12 resulting from the pyrolysis of plastic material and / or the pyrolysis of biomass is illustrated in FIG. 1.

[0059] This installation 10 is intended for the implementation of a first method of treating the gas flow 12, to form at least one fraction 14 of C2 hydrocarbons intended to be introduced into a downstream installation 22. The downstream installation 22 is for example the recovery section of a steam cracker.

[0060] The gas stream 12 is treated by various stages and split into several cuts which feed the steam cracker downstream of the cracking furnaces.

[0061] The installation 10 according to the invention allows the integration of the cuts produced in steam crackers having various fractionation schemes: it may be a steam cracker having a front-end demethanizer combined with a back-end hydrogenation unit.

[0062] Alternatively, the steam cracker has a front-end deethanizer or a front-end depropanizer combined with a front-end hydrogenation unit.

[0063] Alternatively, the downstream installation 22 is an autonomous olefin recovery unit intended to produce ethylene from the C2 hydrocarbon cut 14. The autonomous unit may also be intended to produce propylene from a C3 hydrocarbon cut 17 possibly obtained in the installation 10.

[0064] The gas stream 12 is produced in a plastic and / or biomass pyrolysis installation 20, located upstream of the treatment installation 10 according to the invention.

[0065] The pyrolysis installation 20 is intended in particular to carry out the chemical decomposition of the plastic material and / or the biomass at high temperature, in the absence of oxygen, or in an oxygen-poor atmosphere to avoid oxidation and combustion.

[0066] For example, pyrolysis is carried out in at least one reactor of the installation 20, at a temperature above 500°C. The oxygen content targeted is as low as possible, the residual content being associated only with uncontrollable air inlet phenomena such as, for example, those potentially induced by the fact that the plastic and / or biomass waste is fed to the reactor by a screw conveyor system operating in ambient air. This oxygen content is, however, much lower than that of the ambient air.

[0067] Pyrolysis generally produces solid pyrolysis residues, including coke and ash and at least one pyrolysis gas forming all or part of the gas stream 12. Pyrolysis may also produce liquids, including pyrolysis liquids, particularly oils.

[0068] In the case of plastic pyrolysis, the plastics are, for example, derived from waste. They then comprise at least one polymer such as polyethylene, polypropylene, polystyrene, etc., which can be mixed with biogenic residues such as paper, food or green waste, cotton, etc.

[0069] In the case of biomass pyrolysis, the biomass is, for example, formed from organic matter of plant, animal, bacterial or fungal origin.

[0070] Biomass is for example lignocellulosic biomass, such as wood, green residues, straw, bagasse, fodder, carbohydrate biomass, such as cereals, sugar beet, sugar cane and / or oilseed biomass, such as rapeseed, palm, etc.

[0071] The gas stream 12 intended to be treated in the treatment installation 10 comprises, for example, at its entry into the installation 10, light compounds such as methane and at least one recoverable compound chosen from C2 hydrocarbons, C3 hydrocarbons, C4 hydrocarbons, benzene, toluene, hydrogen.

[0072] For example, the gas stream 12 intended to be treated in the installation 10 comprises (wet basis), between 10% by mass and 20% by mass of C2 hydrocarbons, between 2% by mass and 10% by mass of C3 hydrocarbons, between 1% by mass and 5% by mass of C4 hydrocarbons, between 2% by mass and 10% by mass of (benzene + toluene)' and between 0.3% by mass and 4% by mass of hydrogen.

[0073] The gas stream 12 generally comprises a significant quantity of water, in particular a quantity greater than 30% by mass of water.

[0074] The gas stream 12 being obtained by pyrolysis of plastic material and / or biomass, it further comprises various compounds and / or impurities which are not usable or desirable in the downstream installation 22.

[0075] The gas stream 12 comprises, for example, carbon monoxide, carbon dioxide, nitrogen oxides, and / or oxygen and oxygen derivatives (alcohols, aldehydes, ketones, etc.).

[0076] For example, it includes (wet basis) between 2% by mass and 20% by mass of carbon monoxide, between 3% by mass and 20% by mass of carbon dioxide.

[0077] The gas stream 12 optionally comprises nitrogen compounds such as nitrogen and ammonia and / or acid compounds, such as hydrochloric acid, and hydrocyanic acid and / or various other chlorine derivatives such as dioxins and furans. It comprises for example between (dry basis) 500 ppmV and 1500 ppmV of ammonia, between 5000 ppmV and 150,000 ppmv of nitrogen, between 50 ppmV and 5000 ppmV of hydrochloric acid, and between 100 ppmV mol and 200 ppmV of hydrocyanic acid.

[0078] The gas stream 12 also optionally comprises sulfur compounds, such as hydrogen sulfide, carbon oxysulfides, mercaptans and thiophenes. The content (dry basis) of hydrogen sulfide is for example between 200 ppmV and 1000 ppmV, that of carbon oxysulfides and thiophene between 5 ppmV and 100 ppmV, and that of mercaptans between 1 ppmV and 100 ppmV.

[0079] The temperature of the gas stream 12 is generally greater than 80°C at the inlet into the installation 10.

[0080] The pressure of the gas flow 12 at the inlet into the installation 10 is for example slightly higher than atmospheric pressure, for example between 1100 mbar and 3000 mbar absolute.

[0081] All of the aforementioned compounds are advantageously in gaseous form upon entering the installation 10. By liquid entrainment or volatility, the gas flow 12 may also include metals, dust and / or tars.

[0082] With reference to FIG. 1, the installation 10 comprises a low-pressure quenching / washing unit 30, a compression / cooling unit 32, and a high-pressure washing unit 34.

[0083] The installation 10 further comprises in this example units 36, 38 for removing acids, in particular an amine unit 36, and a caustic wash unit 38.

[0084] The installation 10 also comprises, downstream of the acid removal units 36, 38, a drying unit 39, an impurity removal unit 40, and, downstream of the impurity removal unit 40, a cryogenic absorption unit 42 intended for the production of a light gaseous residue 44 and a Cs hydrocarbon cut 46. + .

[0085] The installation 10 may also advantageously comprise a unit 48 for fractionating the hydrocarbon cut 46 into Cs +to form cuts 14 (C2 hydrocarbons), 16 (C3 hydrocarbons), 18 (C4+ hydrocarbons), intended at least partially to be sent to the downstream installation 22, in particular the C2 hydrocarbon cut 14. Cuts 14 and 16 will be intended to be at least partially recycled respectively in the compression / cooling unit 32 and in the cryogenic absorption unit 42.

[0086] At least a portion of the C2 hydrocarbon cut 14 undergoes expansion, for example by means of a throttle valve, then vaporization by heat exchange with at least a portion of the overhead flow of the cryogenic absorption column to form a gaseous flow R, the light gaseous residue 44 and a condensate C. The condensate C is then recycled into the cryogenic absorption unit 42. By "at least a portion of the hydrocarbon cut 14" is meant at least 10%, preferably at least 30% of the hydrocarbon cut 14. This makes it possible to reduce the losses of hydrocarbon cryogenic solvent 85 from the cryogenic absorption process. Indeed, for this it is necessary to lower the temperature of the light gaseous residue 44 in order to recover a maximum of hydrocarbon cryogenic solvent by condensation.This condensation is carried out by heat exchange with the part of the expanded C2 hydrocarbon cut, which is at a temperature between -40°C and -100°C, preferably at a temperature between -50°C and -60°C. For example, the losses of cryogenic hydrocarbon solvent are reduced by a factor of 3 by using for the condensation, a part of the expanded C2 hydrocarbon cut 14 so as to obtain a temperature of -56°C.

[0087] The gas stream R is recycled to the compression / cooling unit 32 to be compressed and cooled in the associated inter-refrigerants. This unit 32 is also used to compress the washed gas stream 72.

[0088] Advantageously, the light gaseous residue 44 is expanded, heated to ambient temperature and returned to the steam cracker fuel network.

[0089] The quenching / washing unit 30 comprises, for example, at least one quenching / washing capacity, and at least one injector of water in liquid form into the capacity. The injected water is intended to cool the gas flow 12 and to partially condense it to recover an aqueous phase 70.

[0090] The compression / cooling unit 32 comprises at least one compressor, most often multi-stage, equipped with inter-stage cooling, in particular water or air cooling.

[0091] The pressure washing unit 34 advantageously comprises at least one inlet 50 for injecting pressurized water, at least one washing chamber 52 intended to receive the pressurized water and at least one outlet 53 for discharging pressurized water from the chamber 52.

[0092] The amine unit 36 ​​typically comprises an absorber and a regenerator. In the absorber, a descending amine stream meets an ascending gas stream and receives the acid gases contained in the gas stream. The sweetened gas stream exits the absorber with a reduced acid content. The acid-enriched amine stream is discharged to the regenerator. A flash tank is typically installed between the absorber and the regenerator. To limit hydrocarbon losses, the gas stream from this step can be recycled to the compression unit 32.

[0093] In the regenerator, the acid-enriched amine stream is heated and conveyed to an evaporator to remove acid-rich vapors. The acid-poor amine stream is cooled by the enriched amine stream from the absorber and is then returned to the absorber. The caustic scrubbing unit 38 includes at least one container provided with a sodium hydroxide solution feed inlet to allow the gas stream to be scrubbed with sodium hydroxide.

[0094] The drying plant 39 usually comprises a propylene cooler, followed by a liquid / vapor separator whose overhead stream is passed through molecular sieve beds, in particular 3 Angstrom. The drying plant 39 is capable of removing water present in the gas stream while not trapping olefins present in the gas stream. The unit 39 may also comprise a mercury abatement function.

[0095] The impurity removal unit 40 is capable of providing additional protection with regard to the removal of, in particular, ammonia and other nitrogen compounds, chlorine compounds, sulfur compounds, alcohols, and water. It comprises, for example, active bed adsorbents, in particular active metal beds such as active alumina beds or other mixed adsorbents.

[0096] The cryogenic absorption column 42 has at least one solvent introduction inlet 60, and is combined with a source 62 of fresh solvent.

[0097] Source 62 is suitable for providing additional solvent.

[0098] The solvent consists, for example, of liquid hydrocarbons, in particular Ca hydrocarbons + liquids, including liquid propane.

[0099] By “cryogenic” is meant that the temperature of the solvent 85 and of the gas stream 84 feeding the cryogenic absorption column is less than - 20°C, in particular between - 30°C and - 40°C.

[0100] The absorption column intended to bring the gas stream into contact with the solvent can be equipped with trays or packing. Furthermore, in the event of manufacturing constraints, this absorption column can be divided into two columns operating in series.

[0101] The fractionation unit 48 which is optional comprises at least one distillation column, in particular at least one first distillation column capable of separating at the top the fraction 14 of C2 hydrocarbons from at least one fraction of Cs hydrocarbons + , produced in full length.

[0102] It can advantageously include a second distillation column, suitable for treating the Cs hydrocarbon cut. +, to form the 16th cut of C3 hydrocarbons, and the 18th cut of C^T hydrocarbons recovered at the bottom of the second distillation column.

[0103] A first method for treating a gas stream 12 from the pyrolysis installation 20 will now be described. Initially, the gas stream 12 having the composition as described above is produced by the pyrolysis installation 20. It generally has a temperature greater than 80°C, and a pressure between 1100 mbar and 3000 mbar absolute.

[0104] As indicated above, the gas stream 12 generally contains a significant quantity of water vapor, notably more than 30% by mass of water.

[0105] The gas stream 12 is introduced into the quenching / washing unit 30. It is brought into direct contact with low-pressure washing water, to quench the gas stream 20 and at least partially condense the water contained in the gas stream 20.

[0106] The operating pressure in the quenching / water washing column 30 is less than 2 bar, in particular the pressure of the gas flow 12 from which the in-line pressure loss is deducted, i.e. a pressure very slightly higher than atmospheric pressure.

[0107] The temperature of the wash water introduced into the quench / wash unit 30 is set by the site conditions. Thus, if the cooling water temperature available on site is 35°C, a typical temperature for the wash water is 37 to 40°C.

[0108] At the bottom of the water quenching / washing column 30, an aqueous phase corresponding to the washing water and part of the water contained in the gas flow 12 is thus recovered.

[0109] The washing water is returned to the top of the column after being cooled, while the part corresponding to the condensed water is extracted. It forms an aqueous phase 70 which is therefore recovered separately from the cooled and washed gas flow 72 formed in the quenching / washing unit 30.

[0110] Advantageously, the aqueous phase 70 comprises more than 85% of the water contained in the gas stream 12 introduced into the quenching / washing unit. The cooled and washed gas stream 72 typically comprises less than 10% by mass of water.

[0111] Washing through the washing / quenching column 30 allows the removal of water-soluble compounds such as ammonia, alcohols or hydrochloric acid. Advantageously, the washing water can be acidified to enhance this function. Washing also allows the removal of potential metals, dust and / or tars present in the stream 12.

[0112] The washed gas stream 72 is recovered at a temperature set by the site conditions. Thus, if the cooling water temperature available on site is 35°C, a typical temperature for the washed gas stream 72 is 40°C to 45°C. The washed gas stream 72 is then introduced into the compression / cooling unit 32, to be compressed to a pressure greater than 10 bar, in particular between 20 bar and 30 bar.

[0113] At each compression stage, the gas stream 72 is cooled in a refrigerant, to a temperature set by the site conditions, for example 40°C. Advantageously, a final cooler with refrigerant propylene can be implemented to reduce the temperature of the stream 76, for example between 15°C and 20°C, and thus further optimize the recovery of condensates.

[0114] A hydrocarbon condensate 74 is recovered. This stream contains in particular (dry basis) benzene (for example between 60% by mass and 80% by mass), toluene (for example between 15% by mass and 25% by mass), C4 hydrocarbons (for example between 5% by mass and 15% by mass), C3 and lighter hydrocarbons (typically less than 5% by mass), C5 hydrocarbons (typically less than 2% by mass), as well as traces of dissolved gases, water, and impurities such as sulfur compounds or others.

[0115] The cut 74 is advantageously sent to the downstream installation 22, to allow the extraction of compounds having a commercial value, for example benzene, toluene and butadiene.

[0116] A compressed gas stream 76 is formed at the outlet of the compression / cooling unit 32. The compressed gas stream 76 is introduced into the high-pressure washing unit 34. It is brought into contact with pressurized washing water coming from the inlet 50, at a pressure greater than 10 bar (advantageously greater than 20 bar) and at ambient temperature.

[0117] Washing the compressed gas stream 76 reduces the amount of hydrocyanic acid present in the compressed gas stream 76. Unlike the low-pressure wash 30 which recirculates the water, this high-pressure wash is advantageously carried out with water circulating in a single pass (“one-through” in English) so as to maximize the elimination of hydrocyanic acid. Advantageously, more than 75% of the hydrocyanic acid contained in the compressed gas stream 76 is recovered in the pressurized water at the outlet 53.

[0118] The washed gas stream 78 produced at the outlet of the high-pressure washing unit 34 thus has a hydrocyanic acid content which depends on the quantity present in the gas stream 12, and therefore on the type of waste feeding the pyrolysis unit 20. For example, the content is between 50 ppmV and 500 ppmV.

[0119] High pressure washing also makes it possible to achieve more advanced specifications on the impurities already removed in low pressure washing 30. The ammonia and hydrochloric acid contents in stream 78 are, for example, less than 2 ppmV and 1 ppmV respectively.

[0120] The washed gas stream 78 is then passed successively into each acid removal unit 36, 38. In these units, it is brought into contact successively with the amine stream, and with the sodium hydroxide, in order to eliminate in particular the carbon dioxide and the hydrogen sulfide contained in the washed gas stream 78.

[0121] Operating costs of the amine unit may in particular be generated by the degradation products of the amine which are favored by the presence in the stream 78 of oxygenated compounds and residual hydrocyanic acid. To reduce these costs, the amine unit 36 ​​may include specific features such as the presence of a purifier (“reclaimer” in English) and / or ion exchange bed systems.

[0122] Advantageously, the carbon dioxide contained and the hydrogen sulfide contained in the washed gas stream 78 are eliminated in the units 36, 38 so that the acid-depleted gas stream 80 produced at the outlet of the units 36, 38 preferably comprises less than 0.5 ppmV of carbon dioxide, and preferably less than 0.1 ppmV of hydrogen sulfide.

[0123] Advantageously, the amine and soda washing of units 36 and 38 also allows the reduction of residual hydrocyanic acid and the partial reduction of certain sulfur compounds such as carbon oxysulfide and / or mercaptans.

[0124] Then, the acid-depleted gas stream 80 is introduced into the drying unit 39, where its water content is reduced. A dry gas stream 82 is thus formed.

[0125] The dry gas stream 82 advantageously has a water content of less than 1 ppm by mass. The unit 39 may also advantageously include a mercury reduction function down to typical levels below 10 ng / NM. 3 .

[0126] Then, the dry gas stream 82 is introduced into the impurity removal unit 40, to provide additional protection with regard to the removal of, in particular, ammonia and other nitrogen compounds, and / or chlorinated compounds, and / or sulfur compounds (in particular carbon oxysulfide and mercaptans), and / or oxygenated compounds (in particular alcohols) to form a purified gas stream 84. The unit 40 may also allow the reduction of other impurities (for example silicone). It comprises, for example, active bed adsorbents, in particular active metal beds such as active alumina beds or other mixed adsorbents positioned in series.

[0127] The total impurity content in the purified gas stream 84 is preferably less than 1 ppm by mass.

[0128] The purified gas stream 84 is then introduced into the cryogenic absorption unit 42. It is first cooled to a cryogenic temperature, then contacted with a cold hydrocarbon solvent 85 in a cryogenic absorption column. The absorption column for contacting the gas stream with the solvent may be provided with trays or packing and may consist of two columns in series. The hydrocarbon solvent 85 is cooled to a cryogenic temperature, then is introduced through the inlet 60 into the absorption column. The hydrocarbon solvent 85 is formed of solvent from the make-up source 62 and possibly recycled solvent from the fractionation unit 48.

[0129] As indicated above, the hydrocarbon solvent 85 comprises C3 hydrocarbons and / or C4+ hydrocarbons. Preferably, it comprises more than 50 mol% of C3 hydrocarbons, and advantageously more than 90 mol% of C3 hydrocarbons, in particular propane.

[0130] The temperature of the cryogenic hydrocarbon solvent 85 is here less than -20°C, and advantageously between -30°C and -40°C. The pressure of the cryogenic absorption column is usually between 15 bar and 25 bar.

[0131] The hydrocarbon solvent 85 is advantageously introduced at the top of the absorption column, and circulates counter-current to the purified gas flow 84 introduced into the cryogenic absorption unit 42, at the bottom of the absorption column.

[0132] Thus, Cs hydrocarbons +contained in the purified gas stream 84 are collected by the hydrocarbon solvent 85 and are recovered in the form of a C2+ hydrocarbon cut 46 at the bottom of the absorption column. On the contrary, the residual gases form the light gas residue 44 recovered at the top of the cryogenic absorption unit.

[0133] The absorption column is for example reboiled with low pressure steam (for example at a pressure lower than 5 bar) so as to maintain the methane specification in the 46 C2+ hydrocarbon cut.

[0134] Optionally, the absorption column may be equipped with one or more intermediate circulating refluxes to improve the absorption efficiency of the high-value compounds added into the solvent. Usually, the intermediate circulating refluxes are cooled to a temperature advantageously between -30°C and -40°C before being reinjected into the column.

[0135] In order to limit solvent losses in the head stream of the absorption column, it is usually sent to one or more partial condensation stages. The condensate (C) formed is then returned to the solvent stream 85, while the light gaseous residue 44 (the "fuel gas" stream) is expanded, heated to ambient temperature and returned to the fuel network, for example that of a steam cracker.

[0136] Advantageously, several thermal integrations cited in this method can be combined in a single cryogenic equipment with brazed aluminum plate (called "cold box"), which optimizes the cost of the unit, as well as the energy recovery. For example, the cooling of the purified gas stream 84, the cooling of the solvent 85, the reheating of the light gas residue 44, the cooling of the circulating reflux(s) of the cryogenic absorption column, and / or the partial condensation of the cryogenic absorption column can be carried out in the same equipment.

[0137] The Cs hydrocarbon cut + 46 preferably contains more than 99.5% of the C2 hydrocarbons contained in the purified gas stream 84.

[0138] The light gaseous residue 44 advantageously contains combustible gas, in particular methane, hydrogen, as well as the other light compounds of the purified gas stream 84 such as carbon monoxide and nitrogen. It contains hydrocarbon compounds originating mainly from the solvent 85, as well as the C2 hydrocarbons present in the purified gas stream 84 not recovered in the cut 46. Finally, the light residue 44 may also contain the light impurities of the cut 46 such as for example nitrogen oxide, oxygen and / or argon as well as by volatility other impurities such as for example light sulfur compounds or ammonia.

[0139] In particular, the light gaseous residue 44 comprises the nitrogen oxide and oxygen contained in the purified gaseous stream 84. Thus, the content of these compounds in the C2+ hydrocarbon fraction 46 is below the detection limits. Furthermore, this fraction 46 has very low quantities of light compounds. For example, the methane content relative to ethylene may be less than or equal to 500 ppm molar. This guarantees the specification of methane in ethylene without additional fractionation.

[0140] In this way, the hydrocarbon cut in Cs + 46 (as well as by extension the cuts derived from it, for example cuts 14, 17, 18) are suitable for integration into a steam cracker fractionation section while avoiding the dangers linked to the presence of nitrogen oxides.

[0141] Indeed, when gases containing nitrogen oxide, oxygen, dienes and / or ammonia in combination are brought to low temperature, in particular to temperatures below -100°C, NOx gums or salts may be formed. These compounds present a risk of explosion when brought to room temperature. The purified gas stream 84 cannot therefore be brought to low temperature, in particular to the temperatures usually encountered in the cold ends of the cold boxes of a steam cracker. In particular, mixing the purified gas stream 84 with cracked gases from a steam cracker whose diagram has a front-end demethanizer would not guarantee the safety of the installation, since the combined stream would be brought to temperatures below -100°C before feeding the demethanizer.

[0142] The coldest temperature encountered in the cryogenic absorption unit 42 is much higher than -100°C since the temperature of the solvent 85 and the purified gas stream 84 at the inlet of the unit 42 is limited to the temperatures that can be reached when propylene is used as a refrigerant. This temperature is always higher than or equal to the equilibrium temperature of propylene at atmospheric pressure (-47°C). This eliminates the risk of explosion of these gums or salts when they heat up.

[0143] The method according to the invention removes nitrogen monoxide, oxygen and ammonia very efficiently, particularly in the case where it is not possible to carry out removal of nitrogen oxides and oxygen using a deoxygenation type catalyst, due to the high content of carbon monoxide and diolefinic compound in the gas stream 12.

[0144] Furthermore, the method according to the invention is very useful for the integration of stream 84 in a steam cracker whose layout is a front-end deethanizer or a front-end depropanizer combined with an upstream hydrogenation unit. The problem described above related to nitrogen oxide is minimized since in this layout only the light part that has undergone hydrogenation is brought to temperatures below -100°C. However, in this layout, the acetylene converter is very sensitive to runaways when fluctuations in carbon monoxide content occur.

[0145] The 46 Cs hydrocarbon cut +(as well as by extension the cuts resulting from it, for example cuts 14, 17, 18) being free of carbon monoxide, the risk of such runaway is limited, and the integration of these cuts upstream of the hydrogenation converter is made safe.

[0146] Furthermore, as discussed above, the method according to the invention guarantees compliance with the methane specifications of ethylene, while maintaining undemanding cryogenic conditions by the use of a simple cryogenic absorption unit 42, which is advantageous, in particular in the case where the downstream installation 22 is an autonomous olefin recovery unit.

[0147] The 46 Cs hydrocarbon cut + produced in the cryogenic absorption unit 42 is introduced into the fractionation unit 48, when the latter is present.

[0148] In the first distillation column of fractionation unit 48, C2 hydrocarbon cut 14 is recovered at the top.

[0149] This cut 14 contains more than 99% of the C2 hydrocarbons included in cut 46 of C2 hydrocarbons + It usually comprises more than 99.5 mol% of C2 hydrocarbons, notably ethylene.

[0150] At least a portion of the cut 14 is then introduced into the downstream installation 22, as described above.

[0151] A stream of hydrocarbons in Ca + is formed at the bottom of the first distillation column. This stream is preferably introduced into a second distillation column, to separate the 16 Cs hydrocarbon cut from the 18 C4 hydrocarbon cut + .

[0152] The C3 hydrocarbon cut 16 generally comprises the C3 hydrocarbons present in the purified gas stream 84 and those introduced into the solvent 85. A solvent recycling stream 90 is formed from at least a portion of the C3 hydrocarbon cut 16.

[0153] The recycling stream 90 is then recycled to the solvent introduction inlet 60, to constitute a part of the solvent 85 introduced into the cryogenic absorption unit 42. This limits the addition of solvent 85 from the source 62. Furthermore, the residual part 17 of the flow 16 is then introduced into the downstream installation 22 to allow in particular the recovery of propylene.

[0154] A fraction 18 of C^T hydrocarbons is recovered at the bottom of the second distillation column. It is advantageously sent to the downstream installation 22, to allow the extraction of compounds having a commercial value, for example butadiene, benzene and toluene.

[0155] The method according to the invention therefore effectively eliminates contaminants present in the gas stream 12 resulting from the pyrolysis of plastic and / or biomass which could compromise its integration into a downstream installation such as a steam cracker (or other olefin recovery unit). Indeed, they often include compounds which create risks for the safety of these installations, for the quality of the finished products and / or for the poisoning of the catalysts present in these installations.

[0156] It is thus possible to produce a purified gas stream 84 free from these contaminants. In addition, the separation of the light gas residue 44 produces a residue which can be integrated into downstream processes, for example as fuel, or for hydrogen recovery.

[0157] For example, the nitrogen monoxide present in the gas stream 12 is efficiently removed in the cryogenic absorption unit 42, limiting the risks of formation of gums or nitrogen oxide salts in subsequent stages.

[0158] The elimination of carbon monoxide in the gaseous residue 44 also avoids fluctuations in carbon monoxide content in the Cs hydrocarbon fraction 46 +(as well as by extension in the sections derived from it, for example sections 14, 17, 18), to reduce the risk of reaction runaway in the acetylene hydrogenation reactors of certain steam cracker units (or autonomous olefin recovery unit).

[0159] Thus, the 46-carbon fraction of Cs + produced in installation 10 (as well as by extension the cuts from it, for example cuts 14, 17, 18), is suitable for direct use in steam cracking units, or can be recovered in the form of a finished product, in an autonomous olefins production unit.

[0160] The description of the number and arrangement of the fractionating columns of unit 48, as well as the tapping of the recycle stream 90 discussed above corresponds to a case where the fresh solvent used comprises predominantly C3 hydrocarbons. Depending on the solvent used and the size of the unit, variations could be considered.

[0161] In the installation variant 110 illustrated by FIG. 2, the aqueous phase 70 from the quenching / washing unit 30 is recovered and sent to a compression member 92, which is here a pump.

[0162] The aqueous phase 70 is pumped up to the pressure required to carry out the high-pressure washing, a pressure advantageously greater than 20 bars, to form a compressed aqueous phase 94.

[0163] The compressed aqueous phase 94 is then introduced into the high-pressure washing chamber 52, in the pressure washing unit 34. It is brought into contact with the compressed gas flow 76, to enable high-pressure washing of the compressed gas flow 76.

[0164] Like the installation 10 of figure 1, the high-pressure washing very effectively reduces the quantity of hydrocyanic acid present in the compressed gas stream 76 to a content of, for example, between 50 ppmV and 500 ppmV. This efficiency is made possible by circulating the water in a single pass (“one-through” in English). However, the water flow rate required to maximize the efficiency of the washing is significant and the use of the aqueous phase 70, which essentially corresponds to the water of the gas stream 12 condensed in the quenching / washing unit 30, limits or even eliminates the addition of additional fresh water (process water, “boiler feed water” in English). Thus, in the installation 10 of figure 1, the wash water 50 is process water which must be brought to the unit boundary and which will therefore represent an operating cost, while in the installation 110 of figure 2, the wash water corresponds to the aqueous phase 70 produced inside the unit.

[0165] In the installation 10 of figure 1, the flow rate of water 54 to be returned to the external water treatment unit corresponds to the combined flow rate of the aqueous phase 70 and the water collected at the outlet 53, while in the installation 110 of figure 2 it is greatly reduced and corresponds only to the flow rate of the water collected at the outlet 53. This arrangement reduces the operating costs of the installation 10 and of the downstream water treatment installation.

Claims

CLAIMS 1. Method for treating at least one gas stream (12) resulting from pyrolysis of plastic and / or biomass, characterized by the following steps: - quenching and washing with water of the gas stream resulting from the pyrolysis (12) of plastic and / or biomass in a quenching / washing unit (30) and separation of an aqueous phase (70) and a washed gas stream (72); - compression, then cooling of the washed gas flow (72) to form a compressed gas flow (76); - pressure washing of the compressed gas stream (76) to form a washed gas stream (78); - passing the washed gas stream (78) into at least one acid removal unit (36, 38) to form an acid-depleted gas stream (80); - drying the acid-depleted gas stream (80) to form a dry gas stream (82); - passing the dry gas stream (82) through at least one impurity removal unit (40) to form a purified gas stream (84); - introduction of the purified gas flow (84) into a cryogenic absorption column (42) and feeding the cryogenic absorption column (42) with a cryogenic hydrocarbon solvent (85) to obtain in the tank a liquid product comprising a fraction (46) of Cs hydrocarbons + and at the head a head flow comprising a light gaseous residue (44); characterized in that the cryogenic adsorption column comprises at the head a device (D) for partial condensation of the head flow and said method comprises a step of partial condensation of the head flow carried out at a temperature between - 40°C and -100°C, a step of separation of the condensed head flow to obtain said light gaseous residue flow (44) 2. Method according to claim 1, characterized in that the gas flow resulting from the pyrolysis (12) contains Cs hydrocarbons + , and light compounds such as hydrogen, and methane.

3. Method according to one of claims 1 or 2, characterized in that the gas flow resulting from the pyrolysis (12) contains carbon monoxide, carbon dioxide, nitrogen oxides, and / or oxygen and oxygen derivatives, in particular alcohols, aldehydes and / or ketones, nitrogen compounds such as nitrogen and ammonia and / or acid compounds, such as hydrochloric acid, and acid hydrocyanic acid, chlorine derivatives, and / or sulfur compounds, including mercaptans, carbon oxysulfides, and hydrogen sulfide.

4. Method according to any one of the preceding claims, characterized in that the cryogenic hydrocarbon solvent (85) comprises C3 and / or C4+ hydrocarbons, in particular C3 hydrocarbons.

5. Method according to any one of the preceding claims, characterized in that the partial condensation of the head flow of the absorption column is carried out at least in part by heat exchange with an external flow.

6. Method according to any one of the preceding claims, characterized in that it comprises a step of separating the hydrocarbon cut (46) into Cs + in a cut (14) of C2 hydrocarbons, and in at least one cut (16, 18) of Cs hydrocarbons + , at least a portion of said C3+ hydrocarbon cut (16,18) being able to be recycled in the cryogenic absorption unit (42).

7. Method according to claim 6, in which at least a portion of the C2 hydrocarbon cut (14) is expanded, then vaporized by heat exchange with at least a portion of the overhead flow of the cryogenic absorption column in the device (D) to form a gaseous flow (R), the light gaseous residue (44) and a condensate (C).

8. Method according to claim 7, characterized in that the condensate (C) is recycled in the cryogenic absorption column (42) and / or the gas flow (R) is recycled to be compressed and cooled (32) together with the washed gas flow (72).

9. Method according to one of claims 7 or 8, characterized in that the separation step comprises the production of a C3 hydrocarbon cut (16) and a C^T hydrocarbon cut (18), at least a portion of the C3 hydrocarbon cut (16) being recycled into the cryogenic absorption column (42).

10. Method according to any one of the preceding claims, characterized in that the light gaseous residue (44) contains combustible gas, in particular methane, hydrogen, as well as light compounds of the purified gas stream (84), such as carbon monoxide, nitrogen, nitric oxide, and / or oxygen.

11. Method according to any one of the preceding claims, in which the light gaseous residue (44) is intended to be conveyed into a cracking unit, in particular into the fuel gas network of a steam cracker and / or is intended to constitute a fuel gas.

12. A method according to any one of the preceding claims, wherein at least a portion of the Cs hydrocarbon cut (46) + is introduced into a cracker suitable for producing an ethylene cut or into a stand-alone unit suitable for producing an ethylene cut.

13. Installation (10; 1 10) for treating at least one gaseous flow (12) resulting from a pyrolysis of plastic and / or biomass, characterized by: - a quenching / washing unit (30), suitable for quenching and washing with water the gas flow resulting from the pyrolysis (12) of plastic and / or biomass and for separating an aqueous phase (70) and a washed gas flow (72); - a unit (32) for compressing / cooling the washed gas flow (72) to form a compressed gas flow (76); - a unit (34) for pressure washing the compressed gas flow (76) to form a washed gas flow (78); - at least one unit (36, 38) for removing acids present in the washed gas stream (78) to form an acid-depleted gas stream (80); - a unit (39) for drying the acid-depleted gas stream (80) to form a dry gas stream (82); - at least one impurity removal unit (40) in the dry gas stream (82) to form a purified gas stream (84); - a cryogenic absorption unit (42) capable of being supplied by the purified gas flow (84) and by a cryogenic hydrocarbon solvent (85) to obtain in the tank a liquid product comprising a fraction (46) of Cs hydrocarbons + and at the head a head flow comprising a light gaseous residue (44); characterized in that the cryogenic adsorption column comprises at the head a device (D) for partial condensation of the head flow configured so as to obtain the light gaseous residue (44) at a temperature between - 40°C and -100°C.

14. Installation (10, 1 10) according to claim 13, characterized in that it comprises a unit (48) for fractionating the hydrocarbon cut (46) into Cs + For form a cut (14) of C2 hydrocarbons, and at least one cut (16, 18) of Cs hydrocarbons+ ; at least a portion of said C3+ hydrocarbon cut being able to be recycled in the cryogenic absorption unit (42).

15. Installation (10, 1 10) according to one of claims 13 or 14, characterized in that it comprises a means for expanding at least a portion of the C2 hydrocarbon cut (14) and the device (D) is configured to vaporize by heat exchange said portion (E) of the expanded C2 hydrocarbon cut (14), said heat exchange being carried out with at least a portion of the overhead flow of the cryogenic absorption column so as to form a gaseous flow (R), a light gaseous residue (44) and a condensate (C).

16. Installation (10, 1 10) according to claim 15, characterized in that it comprises a means for recycling the condensate (C) in the cryogenic absorption column (42); and a means for recycling the gas flow (R) in the compression / cooling unit (32).

17. Installation (1 10) according to one of claims 13 to 16, in which an outlet of the quenching / washing unit (30) recovering the aqueous phase (70) is connected to an inlet of the pressure washing unit (34), a member (92) for compressing the aqueous phase (70) being interposed between the outlet of the quenching / washing unit (30) and the inlet of the high pressure washing unit (34).

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