PROCESS FOR THE VALORIZATION OF HYDROCARBON MIXTURES AND SECONDARY STREAMS OF INDUSTRIAL PROCESSES THROUGH CATALYTIC PARTIAL OXIDATION TECHNOLOGIES AND CO2 SEPARATION

Description

PROCESS FOR THE VALORIZATION OF HYDROCARBON MIXTURES AND SECONDARY CURRENTS OF INDUSTRIAL PROCESSES THROUGH TECHNOLOGIES CATALYTIC PARTIAL OXIDATION AND CO SEPARATION DESCRIPTION The present invention relates to a process for the conversion of gaseous mixtures of hydrocarbons and / or gaseous mixtures resulting from industrial processes in synthesis gas (“syngas”) and subsequently in gas mixtures rich in H and N and in gas mixtures rich in CO. 2 2 2 The invention also relates to a system for carrying out this process. More In particular, the invention relates to a process, in which the raw materials are used first gaseous mixtures containing hydrocarbons such as natural gas but also gaseous mixtures by-products of various industrial processes, and a plant for its production. Background of the invention Syngas production is used to obtain, from primary hydrocarbon sources such as Natural Gas (NG), a large number of chemicals, fuels and fertilizers; in addition, Syngas is increasingly used in iron ore reduction processes. production of methanol and its derivatives, hydrocarbon fuels, ammonia, cast iron and steel, also involves the formation of purge gases and / or by-products which They are mainly used to produce thermal energy through combustion processes. These processes also induce significant greenhouse gas (GHG) emissions. For example, estimates that in 2020 the world production of ammonia, which requires the production intermediate syngas, has caused through the use of fossil fuels approximately 450 Mt of CO emissions, equivalent to approximately 20% of the chemical sector's energy consumption. If If the ammonia industry were a country, it would be the 16th largest emitter in the world. world, between South Africa and Australia (Ammonia Technology Roadmap; IEA 2020). These considerations also apply to other processes using syngas, especially those which produce hydrocarbons, both with the Fischer Tropsch process and with the processes of refining. In these processes, the syngas is used directly or to generate hydrogen in hydrotreatment processes of petroleum products in the production of fuels. emissions and energy consumption of all these via-syngas transformations - if improved with the use of more efficient technologies that can also utilize waste products - would bring significant environmental and economic benefits. State of the art Currently, the production of urea from ammonia is based on fossil fuels. Just over 70% of ammonia production occurs through the steam reforming reaction (“Steam Methane Reforming”, hereinafter also “SMR”), which uses natural gas (“Natural Gas”, hereinafter also “NG”), while most of the remaining production uses the coal gasification. A simplified scheme of a process for the production of ammonia and urea according to the known technique is shown in Fig. 1. With reference to this figure, the fundamental phases of the process include a phase of desulfurization, a reaction step of primary steam reforming of methane (“Steam Methane Reforming”, hereinafter also “SMR”), followed by an autothermal reforming phase (“AutoThermal Reforming”, hereinafter also “ATR”) secondary, which uses Air as oxidizer. In this way a synthesis gas is obtained which contains 12 – 15% CO. The Most of this CO is converted to CO and H through reaction with vapor 2 2 of water in one or more water gas shift reactors, hereinafter also “WGS”. The CO produced in the WGS phase is removed from the synthesis gas typically with a or more pressure swing adsorption / desorption units “Pressure Swing Adsorption”, later also “PSA”, and / or with chemical absorption / desorption units using example of amino compounds. The small amounts of CO and CO remaining in the synthesis gas that They partially deactivate the catalysts used for ammonia synthesis reactions are transformed into CH in a methanation reactor, thus obtaining the purification of the H-N mixture that is used for the synthesis of ammonia. 2 2 Ammonia synthesis typically occurs at 10 – 25 MPa and 350 – 550°C. Due to the unfavorable equilibrium conditions, in the ammonia conversion reaction only 20 - 30% of the reagent mixture is converted to ammonia per step. Therefore, the ammonia produced in the reactor outlet gas is condensed and removed, while the the mixture of unconverted reagents is recirculated and fed back to the synthesis reactor of ammonia. To avoid the accumulation of inert molecules (mainly CH and Ar) in the gas recycling, it is necessary to constantly purge some of it. The purge gas is usually used as fuel in the SMR stage burners. Finally, in the urea synthesis phase, ammonia and CO2 from from the separation unit. Production processes with greenhouse gas emissions are currently emerging (“green house”). gases” hereinafter also “GHG”) close to zero, including those using electrolysis, methane pyrolysis and methods and / or processes that consider both capture and storage of CO. These methods are however significantly more expensive than conventional methods, and not CO storage is always possible, especially in contexts where ammonia is produced. With reference to the metallurgy sector, the iron and steel industry, which is one of the largest industrial emitters of CO, accounting for approximately 30% of industrial emissions global CO emissions (“Green Hydrogen-Based Direct Reduction for Low-Carbon Steelmaking”; K. Rechberger et Al.; Steel Research Int. 2020, 91, 2000110). More specifically, it has been reported that the iron ore reduction processes that occur with blast furnace technologies (“Blast Furnace”, hereinafter also “BF”), reduction direct (“Direct Reduction”, hereinafter also “DR”) and flameless reduction (“Smelting”) Reduction”, hereinafter also “SR”) have a large impact on GHG emissions and other pollutants. The main emissions in the iron ore reduction processes using Blast furnace (BF) technologies are linked to the production and consumption of coke which determines emissions of particulate matter and carcinogenic aromatic compounds in coke ovens emitting gases from coke oven gases (“Coke Oven Gases”, hereinafter also “COG”). These plants also consume a lot of heat energy. The production of pig iron using blast furnace (BF) technology is then followed by the production of steel in basic oxygen furnaces (“Basic Oxygen Furnace” hereinafter also “BOF”), which They also emit basic oxygen furnace gases (“Basic Oxygen Furnace Gases”, hereinafter also “BOFG”). Another method of reducing iron ores is direct reduction (“Direct reduction” hereinafter also “DR”) which does not require the use of coke but instead uses gas synthesis (“syngas”) produced mainly by steam reforming processes and by mixtures of reagents with a high CO content (“Steam CO Reforming”, hereinafter also “SCR”). However 2 2 These iron ore reduction plants also emit direct reduction gases (“Direct Reduction Gases”, hereinafter also “DRG”). Finally, a further method of reducing ferrous minerals is that of reduction by smelting (“Smelting Reduction” hereinafter also “SR”). This technology is less widespread and even if It does not use coke, requires the use of other carbon materials and also emits gaseous mixtures (“Smelting Reduction Gases”, hereinafter also “SRG”) which are mainly used to produce thermal energy. Table 1 includes representative compositions of gases produced by processes using blast furnace technology (“Blast Furnace Gases”, hereinafter also “BFG”), the reduction direct (“Direct Reduction Gases” hereinafter also “DRG”), as well as the gases mentioned above in relation to other iron ore reduction technologies COG, BOFG and SRG. Table 1 Compound COG BFG BOFG DRG SRG %vol / vol %vol / vol %vol / vol %vol / vol %vol / vol H 56 – 66 2 – 6 1 – 5 42 15-25 N 3 – 10 45 – 65 15 - 25 2 2-10 CO 2 – 6 20 – 25 55 – 60 12 30-50 CO 1 – 5 20 – 26 17 – 23 13 25-45 CH 20 – 30 < 1 < 1 2 2-1 HO 1 – 5 5 - 10 < 1 29 saturated GB 1035724 describes an ammonia synthesis process in which the gases emitted from the reduction direct iron ores are used in the synthesis of ammonia. The reuse of ammonia synthesis purge gas and urea production. It would therefore be desirable to have a process that, in addition to allowing the use of gases emitted in the metallurgical sector, in particular in the reduction of iron ores, in the process of ammonia-urea synthesis, allows to reduce the use of fossil resources and reduce or eliminate carbon monoxide emissions. Summary of the invention One aspect of the present invention is a process for the synthesis of ammonia and urea by reaction of said ammonia and carbon dioxide in which: - the process uses as raw material a gaseous mixture comprising gases selected in group consisting of: gaseous, gases emitted as by-products of refinery processes, gases emitted as by-products of industrial processes other than refinery processes, gas emitted as by-products of iron ore reduction processes, gases derived from fermentation of biomass; wherein the gases other than gaseous hydrocarbons comprise a or more of the following elements or compounds: hydrogen, nitrogen, carbon monoxide, carbon dioxide of carbon, - this gaseous mixture is preliminarily treated to eliminate or reduce impurities choices in the group consisting of: sulfur compounds, aromatic organic compounds and the particulate matter; characterized by the fact that it includes the following phases: a) treatment of said gaseous mixture constituting said raw material with the reaction of displacement of water gas, which increases the hydrogen content of the mixture; b) removal or reduction of the carbon dioxide content of the mixture treated in said phase a), with the obtaining of a current containing carbon dioxide obtained through such removal; c) purification of hydrogen and nitrogen prior to the ammonia synthesis reaction, wherein said purification comprises the methanation reaction, d) ammonia synthesis reaction by reaction of hydrogen and nitrogen contained in said mixture, with the unreacted part constituting a recycle stream, a part which is purged to avoid the accumulation of inert substances, e) short contact time catalytic partial oxidation reaction (“SCT-CPO”) by oxygen of said purged part of said recycling stream, with the result of obtaining synthesis gas (“syngas”) having a higher hydrogen and carbon monoxide content with respect to the hydrogen and carbon monoxide content of said purge stream; f) sending said synthesis gas to said phase a) and repeated execution of the cycle of the phases to be a) to f); g) reaction of the ammonia obtained in said phase e) with the carbon dioxide obtained in called phase c), with the production of urea. According to a variant of the process, the gaseous mixture constituting the raw material of the process is subjected to the short-time catalytic partial oxidation reaction of contact (SCT-CPO) for the production of synthesis gas, before being treated with the reaction of water gas displacement (WGS) in said phase a). Oxygen used in the short-contact time catalytic partial oxidation reaction of phase e) can be pure oxygen or oxygen contained in air or contained in air enriched with oxygen. Another aspect of the invention concerns a plant for the production of urea from ammonia. and carbon dioxide using as raw material a gas mixture selected from the group consisting of gaseous hydrocarbons, gases emitted as by-products of refinery processes, gases emitted as by-products of industrial processes other than refinery processes, gases emitted as by-products of the iron ore reduction processes, gases derived from biomass fermentation, including: A. a water gas shift (WGS) reaction reactor; B. one or more units for the removal or reduction of the dioxide content from a mixture fizzy drink; C. a methanation reactor; D. an ammonia synthesis reactor, E. a reactor for the synthesis of urea from ammonia and carbon dioxide; characterized by the fact that it also includes: F. an SCT-CPO reactor connected to said ammonia synthesis reactor (D) and to said water gas shift reaction reactor (A), configured to convert the purge gases of said ammonia synthesis reactor (D) into synthesis gas and for the feeding of said synthesis gas to said reactor for the displacement reaction of the water gas (A); G. means for feeding carbon dioxide removed in said one or more units (B) to said reactor for the synthesis of urea (E). In this description the terms “carbon dioxide” are used interchangeably, “carbon dioxide” or the formula “CO ”, as they designate the same substance. In this description the terms “vapor phase” and “vapor phase” are also used interchangeably. “gas phase”. In this description the term “particulate matter” refers to unburned carbon, typically amorphous crystallographic structure, resulting from incomplete combustion of organic matrices or from pyrolysis reactions. In this description the terms “including” and “including” are used interchangeably. “containing”, the meaning of which does not exclude the presence of other elements, in addition to those defined after these terms. This meaning also includes the term "constituted" from”. The terms “comprising” and “containing” have a broader meaning than “consisting of”, but they don't rule it out. Brief description of the figures The invention is described below with reference to the attached figures, in which: - Fig. 1 is a simplified diagram of a process for the production of ammonia and urea according to the known technique; - Figures 2-17 are simplified diagrams of different embodiments of the process for the production of ammonia and urea according to the invention; - Figures 18A and 18B are plots of the enthalpy / temperature profiles obtained with (18A) low mass velocity, high contact time, tubular catalyst bed geometry and (18B) high mass velocity, short contact time, truncated conical geometry of the catalytic bed; and - Fig. 19 shows the main zones of an SCT-CPO reactor used in the method according to the invention. Detailed description of the invention With reference to the simplified scheme of the ammonia / urea process according to the technique Note, shown in Figure 1, the natural gas (NG) used in steam reforming of the methane (SMR) is first hydrodesulfurized to remove sulfur-containing compounds, which are poisons for the catalysts. The desulfurized gas is then reacted in the SMR reactor, which uses a large heating furnace to provide the reaction heat [1], which is performed inside a series of reforming tubes filled with a nickel-based catalyst. The gas of synthesis produced by the SMR is then reacted within a subsequent stage of Air Blown autothermal reforming (ATR), called secondary reformer, to produce a mixture comprising carbon monoxide (CO), hydrogen (H), carbon dioxide (CO) and 2 2 nitrogen (N ). This mixture is sent to a water gas shift reactor (WGS) where the Carbon monoxide reacts with water to form carbon dioxide and hydrogen [2]. After removal of CO, the mixture is further treated in a reactor methanation to eliminate CO and CO residues and the resulting mixture, in which H and N 2 2 2 have a higher purity, it is compressed and sent to the ammonia synthesis reactor (see Figure 1). The synthesis of ammonia [3] typically occurs at 400–500 °C and 10–30 MPa, in the presence of an iron-based catalyst. CH + HO ⇋ CO + 3H ΔH° = 206 kJ / mol [1] 4 2 2 CO + HO ⇋ CO + H ΔH° = −42 kJ / mol [2] 2 2 2 3 H + N ⇋ 2 NH ΔH° = −46 kJ / mol [3] 2 2 3 The ammonia produced, together with unreacted H, N and CH, argon (Ar) and other impurities, 2 2 4 It is then cooled to condense it and separate it from the other gases. Hydrogen and nitrogen do not The reacted waste is then recycled and mixed with the new raw material. To avoid the accumulation of impurities, a small part of the gases is eliminated from the ammonia circuit and is often used as fuel in the SMR furnace. Table 2 includes a typical composition of synthesis reactor purge gas. of ammonia. Table 2 Purge Gas Compound %vol / vol H 40 – 60 N 20 – 40 NH 2 – 7 CH 10 – 15 Ar 1 – 6 Ammonia, together with CO , is used in the synthesis of urea at temperatures typically between 150 and 250 °C and pressures typically between 12 and 40 MPa depending on the reactions: 2 NH + CO ⇋ NH CO NH [4] 3 2 2 2 4 NH CO NH ⇋ NH CONH + HO [5] 2 2 4 2 2 2 In the first phase ammonium carbamate (NH CO NH ) is formed and in the next phase 2 2 4 This ammonium carbamate is dehydrated to obtain urea. This invention now makes available innovative plant and process solutions to use waste gases from other processes in the production of ammonia and urea industrial, such as waste gases from the reduction of iron ores, which gases containing hydrocarbons produced from biomass. Furthermore, the process of the invention allows the use also the purge gas of the same ammonia synthesis circuit. This result is achieved using the SCT-CPO reaction in a suitable reactor, which It can be fed with both industrial exhaust gases and with the purge gas from the exhaust circuit. ammonia synthesis. As mentioned above, synthesis gas, also known as “syngas”, used for the synthesis of ammonia and urea, is produced mainly by steam reforming (SMR) of natural gas (NG), often combined with a secondary Autothermal Reforming (ATR) stage, such as results from the European Commission document “Integrated prevention and reduction of pollution - Reference document on best available techniques for the production of inorganic chemicals in large volumes - Ammonia, acids and fertilizers, August 2007”. The possibility of producing synthesis gas with a partial oxidation process is also known catalytic (CPO) with short contact time, also called “Short Contact Time – Catalytic Partial Oxidation (SCT-CPO)”. This technology is described in numerous documents, such as the following patent documents: WO 2020 / 058859 A1, WO 2016 / 016257 A1, WO 2016 / 016256 A1, WO 2016 / 016253 A1, WO 2016 / 016251 A1, WO 2011 / 151082, WO 2009 / 065559, WO 2011 / 072877, US 2009 / 127512, WO 2007 / 045457, WO 2006 / 034868, US 2005 / 211604, WO 2005 / 023710, WO 97 / 37929. Catalytic partial oxidation technology is also described in the following documents scientific literature: a) “Issues in H2 and synthesis gas technologies for refinery, GTL and small and distributed industrial needs"; Basini, Luca, Catalysis Today, 106 (1-4), p.34, Oct 2005; b) “Fuel rich catalytic combustion: Principles and technological developments in short contact time (SCT) catalytic processes”;Basini, L.;Catalysis Today, 117(4), 384-393;DOI: 10.1016 / j.cattod.2006.06.043 Published: OCT 15, 2006; c) “Natural Gas Catalytic Partial Oxidation: A Way to Syngas and Bulk Chemicals Production / IntechOpen”;G. Iaquaniello, E. Antonetti, B. Cucchiella, E. Palo, A. Salladini, A. Guarinoni, A. Lainati and L. Basini; http: / / dx.doi.org / 10.5772 / 48708; and d) “Short Contact Time Catalytic Partial Oxidation (SCT-CPO) for Synthesis Gas Processes and Olefins Production”;LE Basini, A. Guarinoni, Ind. Eng. Chem. Res. 2013, 52, 17023−17037; https: / / doi.org / 10.1021 / ie402463m. The SCT-CPO process converts hydrocarbons, such as natural gas, into synthesis according to the following main reactions: CH + ½ O = CO + H

[10] 4 2 2 CO + HO = CO + H [6] 2 2 2 The reactions are catalyzed by suitable metal catalysts, on whose hot surfaces the gaseous reactants collide for a few milliseconds. These conditions favor the formation of partial oxidation products, limiting the contribution of the reactions total oxidation which would form carbon dioxide instead of carbon monoxide and hydrogen. In this description the term “low contact time” or “SCT” is not used as limiting definition, as in literature this technology is also defined only with the more general term “Catalytic Partial Oxidation” or “CPO”. Table 3 below lists the main reactions involved in gas production processes. of synthesis, including the CPO reactions mentioned above. Table 3 ΔH°298 K [kJ / mole] Steam – CO2 Reforming CH + HO = CO + 3 H 206 [6] 4 2 2 CO + HO = CO + H -41 [7] 2 2 2 CH + CO = 2CO + 2 H 247 [8] 4 2 2 Autothermal Reforming (ATR) CH + 3 / 2 O = CO + 2 HO -520

[10] 4 2 2 CH + HO = CO + 3 H 206 [6] 4 2 2 CO + HO = CO + H -41 [7] 2 2 2 Catalytic Partial Oxidation (CPO) CH + ½ O = CO + H -36

[10] 4 2 2 CO + HO = CO + H -41 [6] 2 2 2 The process of the present invention achieves the synthesis of ammonia (NH ) and urea (NH -CO- 3 2 NH ) using: i. gaseous hydrocarbons, such as natural gas, ii. waste gases from other industrial processes such as those derived from reduction processes of iron ores and steel production processes, iii. mixtures containing hydrocarbons derived from refinery exhaust gases, iv. gases resulting from production in chemical and energy production plants; v. ammonia synthesis circuit purge gas; vi. mixtures containing hydrocarbons derived from biomass by fermentation, or biogas. Gases other than gaseous hydrocarbons include one or more of the following elements or compounds: hydrogen, nitrogen, carbon monoxide, carbon dioxide. It is interesting to note that waste gases from other industrial processes and gases containing hydrocarbons produced from biomass partially replace the use of other fossil fuels as raw materials and avoid greenhouse gas (GHG) emissions. Furthermore, the use of gas Ammonia synthesis circuit purge increases ammonia and urea yields. These goals are achieved using short contact time – oxidation reactors partial catalytic (SCT-CPO). Furthermore, the process implementation forms described here also include units of water gas displacement (WGS) and / or adsorption water gas displacement units increased (“Sorption Enhanced Water Gas Shift” hereinafter also “SEWGS”), as well as electrolytic systems to help produce the oxidant fluxes required by SCT reactors CPO and to balance the H / N ratios in the ammonia synthesis reactor. 2 2 In all these forms of implementation the main objectives concern the use of CO contained in industrial waste gases and the reduction of greenhouse gas (GHG) emissions. The process according to the invention therefore comprises unit operations performed in the following main equipment: i) NH / Urea synthesis reactors; ii) SCT-CPO reactors; iii) WGS reactors and, in some cases, SEWGS reactors; iv) Alkaline electrolysis (AE) electrolyzers, proton exchange membrane electrolysis (PEME) and solid oxide electrolysis cells (SOEC); v) optionally, air separation unit (ASU) or oscillating adsorption unit vacuum packed (VPSA). Furthermore, in the process of the invention the purge gas coming from the synthesis circuit of the ammonia is treated in the SCT-CPO reactor, with conversion of the purge gas into a flow that supplies additional quantities of H and N. 2 2 In more detail, the process of the invention allows to treat the exhaust gases of the processes of reduction of iron ores, namely COG, BOFG, BFG and alternatively DRG and SRG into (i) a H / N-rich synthesis gas and (ii) a CO-rich stream that can be used for 2 2 2 ammonia and urea production. In case of using a raw material consisting of waste gases such as BFG and BOFG, containing hydrocarbons, typically methane, in an amount less than 10% vol, or less than 5% vol, the process of the invention is represented with the embodiments of Figures 2- 9. These embodiments use the SCT-CPO reaction and reactor primarily for convert the purge gas produced by the ammonia synthesis circuit into syngas, to be treated together with the raw material. Oxygen used in the short-contact time catalytic partial oxidation reaction of phase e) can be pure oxygen or oxygen contained in air or contained in air enriched with oxygen. In one embodiment, pure oxygen obtained by hydrolysis of water or by separation from the air. As can be seen from the figures, gases containing a small amount of hydrocarbons such as BFG and BOFG, after an initial sulfur removal section and a cleaning section not illustrated, are treated in a WGS unit and a PSA unit (Figures 2, 3, 6 and 7), or in a SEWGS unit (Figures 4, 5, 8 and 9) before reaching a methanation reactor, where the small amounts of CO and CO remaining in the synthesis gas are transformed into CH . The gas enriched in hydrogen and 2 4 Nitrogen is then sent to the ammonia synthesis reactor. The SEWGS unit uses a catalytic-adsorbent material that promotes the conversion of CO in H and simultaneously adsorbs CO, promoting the shift of the equilibrium towards 2 2 hydrogen production. CO adsorption promotes the reaction equilibrium towards the production of hydrogen by removing a product of the WGS reaction, and at the same time it allows the removal of CO from the syngas. References describing the SEWGS technology mentioned here are as follows: (a) Cobden, Walspurger, Van Den Brink and Van Dijk, WO2010 / 059055; (b) Van Dijk, Cobden, Walspurger e Dijkstra, WO2013 / 122467; (c) Vente, Sfakianakis and Cobden, WO2020 / 025815. The H and N rich mixture produced by the PSA and / or SEWGS unit is treated in a reactor 2 2 methanation to convert the remaining CO and CO to CH4. CO + 3H ⇋ CH + HO ΔH° = -206 kJ / mol [6] 2 4 2 CO + 4H ⇋ CH + 2H O ΔH° = -165 kJ / mol

[11] 2 2 4 2 This step is necessary because CO and CO2 are poisons for the catalyst that produces ammonia, while CH acts as an inert in the ammonia synthesis circuit. The outflow from the methanation stage is first cooled by condensation and removing the steam produced in the methanation reaction, obtaining a low-temperature saturated gas temperature. The syngas must then be further treated in a drying unit to remove any saturated steam still present. The purified and dried syngas with a H / N ratio between 2.2 and 3 v / v is sent 2 2 to phase a) of the process, so as to implement the ammonia synthesis circuit. The process implementations depicted in Figures 6-9 are focused on consumption of the excess CO which, in case it cannot be used in the synthesis of urea, is converted into synthesis gas with the SCT-CPO reaction and reactor, possibly using a additional flow containing hydrocarbons, preferably natural gas. As regards the recycling of the purge gas in the ammonia synthesis circuit, such recycling The SCT-CPO reactor can be operated either without removing the ammonia residues (Figure 2, 4, 6 and 8), both by removing ammonia residues (Figures 3, 5, 7 and 9). It is observed that in known ammonia synthesis processes it is necessary to constantly purge a portion of the ammonia synthesis recirculation gas to avoid the accumulation of inert gases, mainly methane and argon. The purge gas contains essentially ammonia, nitrogen, hydrogen and inert gases (Table 2). The size of this purge flow controls the level of inerts in the circuit, keeping it approximately 10-15% of the recirculating gas. In conventional systems the purge gas is treated with water to remove ammonia, before being used as fuel in steam reforming burners (SMR) or sent for hydrogen recovery. In the process of the invention the purge gas is not used as fuel because it does not burners are provided, as combustion is avoided to reduce the amount of emissions generate. The process then converts the purge gas into a syngas composed primarily of H, N, CO and CO by the SCT-CPO reaction. 2 2 2 It was found that using a specific type of SCT-CPO reactor, as below described, allows the purge gas to be recycled into the process. Reactions in the SCT-CPO reactor convert methane and ammonia into hydrogen, nitrogen, and oxides of carbon that can be recirculated in the WGS or SEWGS unit, according to the different forms of illustrated implementation, to produce further fresh syngas for reintegration into the synthesis circuit of ammonia. These features are also exploited in the schemes of Figures 10-13, where the reactor SCT-CPO is fed with both the purge gas from the ammonia synthesis circuit and with gaseous hydrocarbons such as NG, gases from biomass and other industrial processes. In in these cases the operation of the SCT-CPO unit precedes the phases a) of WGS or SEWGS, and b) of PSA. The process implementation forms depicted in Figures 14-17 describe schemes of processes similar to those in Figures 10-13 respectively and are focused on consumption of the excess CO which, in case it cannot be used in the synthesis of urea, is converted into synthesis gas with the SCT-CPO reaction and reactor, possibly using a additional flow containing gaseous hydrocarbons (preferably natural gas). The SCT-CPO reactor requires moderate preheating of the reagent mixtures, and this Preheating can be achieved by recovering the heat obtained from cooling the gas of product synthesis, thus avoiding the use of burners and the associated CO emissions. Furthermore, pure oxygen, as well as air or enriched air, can be used as oxidants in the SCT-CPO reactor to balance the H / N ratio for ammonia synthesis. 2 2 The adoption of specific characteristics for SCT-CPO reactors allows to obtain gas of H-N rich synthesis suitable for ammonia synthesis. 2 2 Finally, the ammonia produced by the synthesis cycle can be used with the captured CO and separated into PSA or SEWGS units (according to the different proposed schemes), to produce urea. More specifically, Figures 2 and 3 illustrate embodiments for using BFG and BOFG in the production of ammonia and urea. The BFG and BOFG, after an unillustrated purification step that removes the compounds containing sulfur and other impurities, are converted into a gas rich in H, N and CO through 2 2 2 an initial phase of WGS (phase a). In the next step b) the produced CO is separated from the H and N stream with a PSA unit. 2 2 2 In phase c) the H and N-rich mixture from phase b) is subjected to the reaction 2 2 of methanation, to convert the remaining CO and CO2 into CH4 (reactions [6] and

[11] reported above). In step d) the mixture of H and N is introduced into the ammonia synthesis reactor. 2 2 In phase e) the purge gas from the ammonia synthesis reactor is sent to a unit SCT-CPO. It has been observed that the purge gas can be used directly in the reactor SCT-CPO (Figure 2) or used in the SCT-CPO reactor after separation of the residues ammonia for washing (Figure 3). In both cases the use of the SCT-CPO reactor allows to convert the methane and ammonia in the purge gas into H and N, which are used in the 2 2 f) as a make-up gas for the raw material, creating the ammonia synthesis circuit. The oxygen required by the SCT reactor can be supplied by electrolysis of water steam and / or from an air separation unit (ASU). The electrolysis of water vapor also produces a H flow that is used to balance the H / N ratio useful for the synthesis cycle 2 2 2 of ammonia. In the urea synthesis phase g) the ammonia produced by the synthesis circuit is used and the CO coming from the separation unit. Figures 4 and 5 describe embodiments of the process for converting BOFG and BFG into ammonia and urea using the SEWGS unit to separate the CO in step b). The CO is then separated from the H-N stream in a SEWGS unit, increasing the 2 2 2 conversion into H thanks to the capture and separation of CO. 2 2 In the implementation forms of the process with SEWGS units (figures 4, 5, 8, 9, 12, 13, 16, 17) it is it is possible to place the desulphurisation section downstream of the SEWGS unit, since this technology can operate with catalysts and temperature conditions where it does not occur sulfur poisoning. The positioning of the desulfurization section downstream of the SEWGS unit offers the following Advantages: (i) The SEWGS unit is able to adsorb acidic compounds (such as HS) and remove them from the H-N flow; (ii) the desulfurization section can be designed for a lower capacity 2 2 due to the removal of CO and the lower sulfur composition in the H-N stream. The stream 2 2 2 of H-N thus obtained is compressed and used in the ammonia synthesis circuit for 2 2 produce ammonia, according to step d). In phase e) the purge gas of the ammonia synthesis circuit is sent directly (Figure 4) to an SCT-CPO reactor or washed from ammonia residue (Figure 5) before recycling to the SCT-CPO reactor. Thus, the use of the SCT-CPO reactor allows to recycle and convert the methane and ammonia from the purge gas into H and N, which can be used as a buffer gas 2 2 reintegration into the ammonia synthesis circuit in phase f). Pure oxygen flows can be supplied to the SCT-CPO reactor by electrolysis of the water vapor and / or through an air separation unit (ASU). The electrolysis of water or Water vapor also produces a flow of H which is used to balance the ratio H / N useful for the synthesis of ammonia. 2 2 In the urea synthesis phase g) the ammonia produced by the synthesis circuit is used in phase d) and the CO coming from the separation unit of phase b). Figures 6 and 7 show embodiments that include, in addition to the process units of the Figures 2 and 3, the possibility of reusing any excess CO2 emissions from the phase b) in the SCT-CPO reactor, producing in phase e) additional raw material for the reactors of ammonia and urea. Figures 8 and 9 show embodiments that include, in addition to the process units of the Figures 4 and 5, the possibility of reusing any excess CO emissions in the SCT reactor- CPO producing additional raw material to be used in phase f) to increase the circuit of ammonia and urea production. Figures 10 and 11 illustrate process embodiments for the use of gaseous hydrocarbons. (preferably natural gas) with the possible addition of exhaust gases such as BFG, COG, BOFG, DRG, SRG and biogas, in which, after a cleaning section (not shown), are sent in a phase a) to an SCT-CPO reactor, also using a flow of O generated by 0 2 a steam electrolyzer and / or an ASU. The synthesis gas produced is then sent to phase a) of WGS, then to phase b) of removal of CO by PSA, then to phase c) of purification by methanation and finally fed to the ammonia synthesis reactor in phase d). In phase e) the purge gas from the ammonia synthesis circuit is sent directly (Figure 10), or after an ammonia scrubbing section (Figure 11), to the same reactor SCT-CPO. The ammonia and CO flow from the separation unit is used in the synthesis phase of Urea. Figures 12 and 13 describe process embodiments for the utilization of hydrocarbons. gaseous, preferably natural gas, with the possible addition of waste gases such as BFG, COG, BOFG, DRG, SRG and biogas which, after a cleaning section (not shown), are sent, in phase a), to an SCT-CPO reactor also using the O flow generated by a 0 2 steam electrolyzer and / or an ASU. The synthesis gas produced is then sent to the SEWGS phase a), then to the removal phase b). of CO by PSA, then to phase c) of purification by methanation and finally fed to the ammonia synthesis reactor in phase d). The purge gas from the ammonia synthesis loop is sent directly (Figure 12) or after an ammonia scrubbing section (Figure 13) to the same SCT-CPO reactor, according to phase e). The ammonia and CO streams from the separation unit are used in the phase g) of urea synthesis. Figures 14 and 15 include, in addition to the process units of Figures 10 and 11, the reuse of any excess CO2 emissions in the SCT-CPO reactor, producing raw material additional for the synthesis of ammonia and urea. Figures 16 and 17 also show embodiments that include, in addition to the process units of Figures 12 and 13, the utilization of any excess CO emissions in the SCT reactor- CPO, producing additional feedstock for ammonia and urea reactors. Another aspect of the invention relates to a reactor for carrying out the SCT-CPO reaction. It has been found that the use of SCT-CPO reactors and specific operating conditions improves the possibility of transforming a CO2-rich stream into a syngas rich in H and CO. 2 2 Figures 18 and 19 show the characteristics of an SCT-CPO reactor according to the invention. (Fig. 18B) and of a known reactor (Fig. 18A). The thermochemical properties of the reaction environment produced in a useful SCT-CPO reactor to treat the mixtures described above in relation to the ammonia synthesis process can be discussed considering the system composed of equations [1-3], [6-8] and [12-13]. CH + 2O ⇋ CO + 2H O ∆H° = -803 kJ / mol

[12] 4 2 2 2 CH + ½ O ⇋ CO + 2 H ΔH° = -36 kJ / mol

[13] 4 2 2 CO + HO ⇋ CO + H ∆H° = - 41 kJ / mol [7] 2 2 2 CH + CO ⇋ 2CO + 2 H H° = +247 kJ / mol [8] 4 2 2 CH + HO ⇋ 3H + CO ΔH° = +206 kJ / mol [6] 4 2 2 The exothermic total oxidation reaction

[12] has the highest probability of being localized at the beginning of the catalyst bed, while the endothermic reforming with water vapor-CO [1] and [8] and the slightly exothermic reaction (WGS) or the reverse gas shift reaction [2] of water (RGS) would have the highest probability of occurring in the next zone. Note that by increasing the reaction temperature above 830°C, reaction [2] is shifted to the left side and a slightly endothermic RWGS reaction is favored together to the reforming of water vapor-CO [1] and [8]. Furthermore, the extent and location of these reactions were found to be strongly influenced by physical and chemical factors. Total combustion

[12] was found to be the reaction more competitive on catalysts based on noble metals (Rh, Ru, Ir, Pt, Pd) at "low temperature" (T<750°C) and at high partial pressure of O. These are typically the conditions that occur produce at the beginning of the catalytic beds in tubular reactors operating with “high” contact times (longer than 1 s). In these cases, it was found that the thermal profiles of the reaction environments are determined by the strongly exothermic reaction [8] with a minor contribution from the reactions

[13] and [2], followed by the strongly endothermic water vapor reforming reactions- CO [1] and [8]. These conditions give rise to very high axial temperature gradients. Furthermore, the energy release associated with total combustion also determines the propagation of heterogeneous reactions in the gas phase, giving rise to a non-selective radical chemistry that leads to the formation of unsaturated molecules and soot. In fact, it has been found that with tubular reactors the catalytic reactions of partial oxidation cannot be carried out at high pressures as the reaction

[12] is not controllable and propagates reactions in the gaseous phase with the risk of ignition of the flame and production of radical reactions that lead to the formation of unsaturated hydrocarbons and soot. However, it was found that the temperatures of the solid catalyst can reach values above 1000°C, while the gas remains relatively cold, when using a geometry of the reaction environment which allows the contact time to be reduced to a few milliseconds at the entrance to the catalytic bed and which allows the expansion of the reaction volume when the temperature and molar flux increase due to the progress of the reaction. This effect is obtained by adopting a truncated-conical geometry of the catalytic bed, together with geometric characteristics of the catalyst that allow to reduce the pressure drop within the reaction zone. Consequently, it was found that under these short contact time conditions, the methane conversion depends largely on the O / C ratios, while it is almost unchanged from the addition of water vapor and CO. This addition instead modifies the H / CO ratios in the 2 2 synthesis gas produced, clearly indicating that the reactivity is largely determined from direct partial oxidation

[13] and from the RWGS reaction [2]. Figures 18A and 18B show qualitative images of the obtained enthalpy / temperature profiles. with (18A) low mass velocity, high contact time, tubular bed geometry catalytic and (18B) high mass velocity, short contact time, truncated conical geometry of the catalytic bed. Figure 19 shows the main zones of the SCT-CPO reactor, including a reaction zone truncated cone. These areas include: - a cylindrical inlet and mixing area; - a first preheating zone of the heat shield having a cylindrical shape; - a reaction zone that includes the catalyst, having a truncated conical shape with a radius R of the inlet section and a radius R of the outlet section and a height L; 1 2 - a second heat shield zone having a cylindrical shape; - a cylindrical reactor exit zone; - the external angle α of the inlet section of the truncated conical reaction zone is less than 90°; The external angle α shown in figure 19 is preferably less than 80°, more preferably is between 75° and 30°. The other geometric characteristics, namely: i. the entrance radius of the truncated cone R, ii. the exit radius of the truncated cone R, iii. the height of the truncated cone L, and iv. filling the catalytic bed are designed to allow pressure drop (DP) values ​​within the catalyst bed between 0.1 to 10 ATM, preferably between 0.5 and 5 ATM. For this purpose, R / R ratios are between 0.9 and 0.1, preferably between 0.8 and 0.4. 1 2 Catalytic bed packing forms that minimize the conditions are also preferred of pressure drop, using pelletized or monolithic structures and their combinations. Furthermore, the existence of a non-thermal equilibrium between the gaseous and solid phases has been explained. whereas the chemical heat generated on the surfaces, and emitted by radiation, is absorbed and dispersed much better by the solid phase than by the gas phase and is transferred along the catalytic bed from the hottest points to the coldest ones, making the temperatures uniform surfaces of the solid. The main experimental observations on the thermochemical properties of the environments of SCT-CPO reactors, performed after optimization of the characteristics of the reaction environment, are summarized as follows: - the solid phase temperature increases significantly at the beginning of the bed and the profiles of temperatures are leveled through radiative and conduction mechanisms in the directions axial and radial; - temperature differences arise between the gaseous and solid phases; - some surface temperatures are higher than adiabatic temperatures; - gas temperatures are always lower than adiabatic temperatures and increase gradually from entering to leaving the bed. It was also found that part of the heat of reaction is transferred to the reactants in entry into the first heat shield zone and in this way a preheating of the reagents inside the reactor. An SCT-CPO reactor with the above characteristics is optimal for the conduction of the process according to the invention.

Claims

CLAIMS 1. Process for the synthesis of ammonia and urea by the reaction of said ammonia and carbon dioxide in which: - the process uses as a raw material a gaseous mixture comprising gases selected from the group consisting of: gaseous hydrocarbons, gases emitted as by-products of refinery processes, gases emitted as by-products of industrial processes other than refinery processes, gases emitted as by-products of iron ore reduction processes, gases derived from the fermentation of biomass; in which the gases other than gaseous hydrocarbons comprise one or more of the following elements or compounds: hydrogen, nitrogen, carbon monoxide, carbon dioxide, - said gaseous mixture is preliminarily treated to eliminate or reduce impurities selected from the group consisting of: sulphur compounds, aromatic organic compounds and particulate matter;characterized in that it comprises the following phases: a) treatment of said gaseous mixture constituting said raw material with the water gas displacement reaction, which increases the hydrogen content of the mixture; b) removal or reduction of the carbon dioxide content of the mixture treated in said phase a), obtaining a stream containing carbon dioxide obtained by such removal or reduction;(c) purification of hydrogen and nitrogen prior to the ammonia synthesis reaction, said purification comprising the methanation reaction; (d) ammonia synthesis reaction by reaction of hydrogen and nitrogen contained in said mixture, with the unreacted portion constituting a recycle stream, a portion of which is purged to avoid the accumulation of inert substances; (e) short contact time catalytic partial oxidation (“SCT-CPO”) reaction by oxygen of said purged portion of said recycle stream, resulting in synthesis gas (“syngas”) having a hydrogen and carbon monoxide content greater than the hydrogen and carbon monoxide content of said purge stream; (f) sending said synthesis gas to said stage a) and repeatedly cycling stages a) to f);g) reaction of the ammonia obtained in said step e) with the carbon dioxide obtained in said step c), to obtain urea. NXC04258 / IT; 2. Process according to claim 1, characterized in that in said step a) said gaseous mixture constituting the raw material of the process is subjected to said water gas shift reaction (WGS) and / or to an enhanced adsorption water gas shift reaction (SEWGS).

3. Process according to one or more of the preceding claims, characterized in that a part of said carbon dioxide obtained in said step b) is subjected to the SCT-CPO reaction in the reactor where said step e) of catalytic partial oxidation of said purge stream is carried out.

4. Process according to one or more of the preceding claims, characterised in that said step e) is carried out using oxygen selected from: pure oxygen, oxygen contained in air, oxygen contained in air enriched in oxygen.

5. Process according to claim 4, characterized in that said phase e) is carried out using pure oxygen produced by electrolysis of water or water vapor, with also production of hydrogen which is used to balance the H2 / N2 ratio present in the mixture fed to said ammonia synthesis phase d).

6. Process according to one or more of the preceding claims, characterised in that said gaseous mixture constituting the raw material of the process contains less than 10% vol of methane, preferably less than 5% vol of methane.

7. Process according to one or more of the preceding claims, characterized in that said gaseous mixture constituting the raw material of the process is subjected to the short contact time catalytic partial oxidation (SCT-CPO) reaction for the production of synthesis gas in a step a0), before being treated with the water gas shift reaction in said step a).

8. Process according to one or more of the preceding claims, characterized in that said removal or reduction of the carbon dioxide content of the treated mixture of said phase b) is achieved by physical and / or chemical adsorption / desorption of said carbon dioxide.

9. Plant for the production of urea from ammonia and carbon dioxide using as raw material a gaseous mixture comprising gases selected from the group consisting of gaseous hydrocarbons, gases emitted as by-products of refinery processes, gases emitted as by-products of industrial processes other than refinery processes, gases emitted as by-products of iron ore reduction processes, gases derived from the fermentation of biomass, comprising: A. a reactor for the water gas shift reaction (WGS); NXC04258 / IT B. one or more units for the removal or reduction of the dioxide content from a gaseous mixture; C. a methanation reactor; D. an ammonia synthesis reactor; E. a reactor for the synthesis of urea from ammonia and carbon dioxide; characterised in that it also comprises: F.an SCT-CPO reactor connected to said ammonia synthesis reactor (D) and said water gas shift reaction reactor (A), configured to convert purge gases from said ammonia synthesis reactor (D) into synthesis gas and to feed said synthesis gas to said water gas shift reaction reactor (A); G. means for feeding carbon dioxide removed in said one or more units (B) to said urea synthesis reactor (E).

10. Plant according to claim 9, characterized in that said SCT-CPO reactor (F) comprises: - an inlet and mixing zone having a cylindrical shape; - a first heat shield preheating zone having a cylindrical shape; - a reaction zone having a truncated cone shape with a radius Ri of the inlet section and a radius R2 of the outlet section and a height L; - a second heat shield zone having a cylindrical shape; - a reactor outlet zone having a cylindrical shape; wherein the external angle α of the inlet section of the truncated cone reaction zone is less than 90°.

11. Plant according to claim 10, characterised in that said radii Ri and R2 of said truncated-conical reaction zone have a ratio R1 / R2 between 0.9 and 0.1, preferably between 0.8 and 0.4.