MXPA99010096A - Process for the production of synthesis gas - Google Patents

Abstract

A process for the production of synthesis gas for obtaining compounds such as ammonia or methanol, in which hydrocarbons and steam are reacted first in a primary reforming section (11) and then - together with oxygen - in a secondary reforming section (12), thus obtaining CO, CO2, H2 and possibly N2 which are then fed to a carbon monoxide conversion section (13, 14), is distinguished by the fact of reacting hydrocarbons, steam and oxygen in an autothermal reforming section (20) provided in parallel with respect to other reforming sections (11, 12), and feeding the so produced CO, CO2, H2 and possibly N2 to the carbon monoxide conversion section (13, 14).

Description

PROCESS FOR THE PRODUCTION OF SYNTHESIS GAS DESCRIPTION Field of application The present invention relates to a process for the production of synthesis gas to obtain compounds such as ammonia and methanol. More specifically, the invention relates to a process for the production of synthesis gas comprising the steps of: feeding a first flow comprising hydrocarbons and a first gas flow comprising steam to a primary reforming section; feeding a first gas flow comprising oxygen and possibly nitrogen to a secondary reforming section; reacting the hydrocarbons and the first vapor in the primary reforming section and then - together with the oxygen - the secondary reforming section, obtaining a first gas phase comprising CO, C02, H2 and possibly N2; feed the first gas phase comprising CO, C02, H2 and possibly N2 to a carbon monoxide conversion section. Through this specification and the appended claims, the term "hydrocarbon" is used to generally indicate a source of hydrogen and carbon raw material, such as, for example, methane, natural gas, naphtha, LPG (liquefied petroleum gas) ) or refinery gas and mixtures thereof. The invention also relates to a plant for the production of synthesis gas to implement the aforementioned process, as well as to a method for converting an existing plant for the production of synthesis gas. As is well known, in the field of synthesis gas production, more and more people feel the need to carry out processes that are easy to implement and that allow achieving greater and ever greater production capacities with operation and investment costs. low and low energy consumption.

Prior art To meet such requirements, synthetic gas production processes, in which a flow comprising hydrocarbons and a gas flow comprising first vapor to a primary reforming section and subsequently - together with a gas flow, are sent. comprising oxygen and possibly nitrogen - to a secondary reforming section, have found wide application. Therefore, a gaseous phase rich in CO, C02, H2 and possibly N2 is obtained, which in turn is sent to treatment sections such as, for example, high and low temperature carbon monoxide conversion sections. The treatment sections may vary depending on the type of synthesis gas to be produced. To improve the performance of the conversion of hydrocarbons, as well as to reduce energy consumption, the processes for the production of synthesis gas are used in the field where the conversion reaction and the secondary reformation section is carried out in the presence of a catalyst. It is intended that secondary reformers to carry out such a process are those generally called autothermic, since they do not require external heat supply for their operation. Although advantageous in some aspects, the processes described above exhibit a number of disadvantages. First of all, the fact of being inflexible and not being able to adapt themselves effectively to variations in operating conditions, in particular, when a significant increase in the amount of synthesis gas to be produced is required. produced. In effect, the sections of primary and secondary reformation, responsible for the conversion of hydrocarbons, are not capable of operating properly if they deviate from the capacity of the design. Therefore, to adapt the plants that produce syngas that operate according to the processes described above to the more and more required capacity increases in this field, dramatic reconversion interventions are necessary and, finally, no less, the replacement of the reform sections themselves with sections that have greater capacity, with very high investment costs. In addition, it is important to note that the presence of a primary reforming section requires a supply that requires high amounts of heat that negatively affect the total energy consumption needed to implement such processes. Due to these disadvantages, the implementation of the processes that produce synthesis gas according to the prior art now requires high investments and energy consumption, which significantly penalize the costs of basic chemical products such as hydrogen and carbon monoxide, despite the increasing demand for these products.

Brief description of the invention The problem underlying the present invention is to provide a process for the production of synthesis gas that is easy to implement and allows to obtain high production capacities with low operation and investment costs as well as with a low energy consumption . The above problem is solved, according to the invention, by means of a process for the production of synthesis gas of the aforementioned type, which is characterized in that it comprises the steps of: feeding a second flow comprising hydrocarbons, a second flow gas comprising steam and a second gas flow comprising oxygen and possibly nitrogen to a photothermal reforming section provided in parallel with respect to the primary and secondary reforming sections; - reacting the hydrocarbons, steam and oxygen in the autothermal reforming section, obtaining a second gaseous phase comprising CO, C02, H2 and possibly N2; feed the second gaseous phase comprising CO, C02, H2 and possibly N2 to the carbon monoxide conversion section. Through this specification and the appended claims, the term "autothermal reforming section" is used to indicate a reforming section where hydrocarbons, steam and oxygen are reacted, preferably in the presence of catalyst, without provide heat from outside. In the production of synthesis gas for ammonia or methanol, sections of this type are generally called secondary reforming sections. Advantageously, the tanks for the passage where a second flow of hydrocarbons is reacted in the autothermal reforming section, it is possible to easily and effectively face even with variations of substantial capacity of the plant implementing the process according to the invention. In fact, according to the present invention, the hydrocarbon reforming reaction is carried out in two stages, provided in parallel, the first comprising a primary reforming section and a secondary reforming section, the latter comprising a reforming section Autothermal In this way, it is possible to provide the desired total production of synthesis gas in the two stages of reforming, whose capacity can therefore be varied from time to time and independently according to the specific demand, without negatively affecting the process remaining. In particular, the distribution of the load in the reforming sections arranged in parallel, allows - inter alia - to optimize the energy consumption, and to maximize the synthesis gas production in the autothermal reforming section and at the same time minimize the feed to the primary reformer. In other words, the synthesis gas production capacity remains the same, the process of the present allows to adequately distribute in two reforming stages arranged in parallel hydrocarbons and steam. Therefore, the total energy consumption is less than that required for the prior art. Advantageously, the gas flows comprising CO, C02, H2 and possibly N2 obtained, respectively, in the secondary reforming section and in the autothermal reforming section, are sent to the same carbon monoxide conversion section, exploding in this way only one line per equipment to carry out the subsequent steps of the synthesis gas preparation. A further advantage, resulting from the process according to the invention, is given by the fact that, having the possibility of separating the hydrocarbon feed streams to independent reforming stages from each other, it is possible to use it advantageously for the production of gaseous synthesis tools of different nature in the different stages of reform, thus adapting the process to existing natural resources and for which any requirements may arise. To obtain a synthesis gas for the production of ammonia with a high molar ratio of C02 / H2, the second gas flow comprising oxygen fed the autothermal reforming section advantageously comprises air enriched with oxygen. Through this specification and the appended claims, the term "oxygen enriched air" is used to indicate air with a molar oxygen content greater than 21%, for example comprised between 22% and 80%. This characteristic is particularly advantageous for a posterior urea synthesis, since it allows to achieve - effectively and inexpensively - a stoichiometric ratio of C02 / NH3 and therefore increase the efficiency of the conversion of carbon fed in CO2 and thus urea . For the implementation of the above process, the present invention advantageously provides a plant for producing synthesis gas comprising: a primary reforming section and a secondary reforming section arranged in series to obtain a first gas phase comprising CO, C02, H2 and possibly N2; respective means for feeding a first flow comprising hydrocarbons and a first gas flow comprising steam in the primary reforming section; - means for feeding a first gas flow comprising oxygen and possibly nitrogen to the secondary reforming section; - means for feeding the first phase comprising CO, C02, H2 and possibly N2 to a carbon monoxide conversion section; which is characterized in that it comprises: a section of autothermal reforming to obtain a second gas phase comprising CO, C02, H2 and possibly N2; - respective means for feeding the second flow comprising hydrocarbons, a second flow of gas comprising steam and a second flow of gas comprising oxygen and possibly nitrogen to the autothermal reforming section; means for feeding the second gas phase comprising CO, C02, H2 and possibly N2 to the carbon monoxide conversion section. According to a further aspect of the invention, there is provided a method for reconverting a plant for the production of synthesis gas of the type comprising a primary reforming section and a secondary reforming section arranged in series to obtain a first gaseous phase which comprises CO, C02, H2 and possibly N2, respective means for feeding a first flow comprising hydrocarbons and a first flow of gas comprising steam to the primary reforming section, means for feeding the first gas flow comprising oxygen and possibly nitrogen to the secondary reforming section, means for feeding the first gas phase comprising CO, C02, H2 and possibly N2 to a carbon monoxide conversion section, the method comprises the steps of: providing an autothermal reforming section to obtain a second gaseous phase comprising CO, C02, H2 and possibly N2; - providing respective means for feeding a second flow comprising hydrocarbons, a second gas flow comprising steam and a second gas flow comprising oxygen and possibly nitrogen to the autothermal reforming section; providing means for feeding the second gas phase comprising CO, C02, H2 and possibly N2 to the carbon monoxide conversion section. Thanks to the aforementioned reconversion method, it is possible to easily increase the production capacity in an existing plant for synthesis gas production, with operating and investment costs and with low energy consumption. The features and advantages of the invention will result in addition to the following description of a modality thereof given by way of non-limiting example with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE FIGURE Figure 1 shows a block diagram of the process for the production of synthesis gas according to the invention, in the case of ammonia and urea are the desired compounds.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT In Figure 1, a block diagram is shown illustrating the steps of the process according to the present invention for the production of gaseous reactants, such as H2, N2 and C02 where: H2 and N2 are used for the synthesis of ammonia, and C02 is used together with the ammonia thus produced for the synthesis of urea. The process of the present is however particularly suitable for the production of gaseous reactants not only for the synthesis of ammonia but also for the synthesis of methanol, and for various organic reactions which require H2, CO, and possibly N2 and C02. The number 10 indicates in general terms a block diagram which illustrates the steps of the process for the production of ammonia and urea, and in which the process for the production of synthesis gas according to the invention is included. In diagram 10, blocks 11-18, respectively, indicate: a primary reformation section (block 11), a secondary reforming section (block 12), a CO conversion section, a separation section of C02 (block 15), a purification section for the synthesis gas (block 16), an ammonia synthesis section ( block 17) and a urea synthesis section (block 18). According to the type of synthesis gas to be produced, the conversion section of C02 can be divided into one or more parts. In the example of Figure 1, the CO conversion section comprises a high temperature CO conversion section (block 13) and a low temperature CO conversion section (block 14). The blocks 19 and 20 advantageously indicate a (optional) preforming section (block 19) and an autothermal reforming section (block 20). Blocks 19 and 20 are provided in parallel with respect to blocks 11 and 12. The autothermal reforming section (block 20) operates with low energy consumption and may include a catalyst bed to facilitate the hydrocarbon reforming reaction. The blocks 11-18 are crossed by a flow line 1 which represents a flow having a composition which varies with the passage through the different reaction sections. In particular, at the entrance of the primary reforming section indicated by block 11, the flow line 1 comprises a first flow comprising hydrocarbons and a first gas flow comprising steam fed into flow line 1 by means of the flow line 2. The hydrocarbons entering the primary reforming section (block 11) are preferably of the gaseous type, such as, for example, natural gas. The flow line 3 indicates a first gas flow comprising oxygen fed to the secondary reforming section (block 12). Passing through the primary reforming section and the secondary reforming section (blocks 11 and 12) arranged in series, the hydrocarbons and steam contained in the feed flow 1 - together with the oxygen comprised in flow 3 react, obtaining in this way a first gaseous phase comprising CO, C02, H2. The gaseous phase leaving the secondary reforming section through line 1 will also comprise an adequate amount of nitrogen (N2) needed for the next ammonia synthesis in blog 17. Up to this point, the flow of gas comprising oxygen fed by the flow line 3 to the block 12, it also comprises nitrogen. Preferably, the flow line 3 represents the air flow. According to what kind of final synthesis is desired, the flow line 3 can be used to feed substances of different nature. For example, in the case of methanol synthesis, flow line 3 feeds only the appropriate amount of oxygen to the secondary reforming section. The carbon monoxide comprised in the gas phase leaving the block 12 is thus converted to carbon dioxide through the high and low temperature conversion sections (blocks 13 and 14), subsequently separated in the separation section of C02 (block 15) and finally fed as a reagent for the synthesis of urea through flow line 4 in block 18. From block 15, the gas phase is substantially free of CO and C02, passes through the section for purification of synthesis gas (blog 16) and is then fed - in the form of a gas flow comprising essentially hydrogen and nitrogen - to the ammonia synthesis section indicated with block 17. The ammonia produced leaving the block 17 , is then sent - always through the flow line 1 - to the urea synthesis section (block 18), where it reacts with the carbon dioxide coming from the separation section of C02 (block 15) . Therefore, the flow leaving the block 18 (flow line 1) comprises mainly urea. Advantageously, a second flow line indicated with 5 in Figure 1 crosses blocks 19 and 20 of diagram 10. At the entrance of the pre-forming section (block 19), the flow line 5 comprises a second flow comprising hydrocarbons and a second gas flow comprising steam fed to the flow line 5 by means of the flow line 6. The hydrocarbons fed to such section may be of the same type those fed to the reformation sections indicated with blogs 11 and 12, or of different types such as, for example, naphtha. In particular, thanks to the presence of the preforming section (block 19), it is possible to advantageously use any type of hydrocarbons for the reforming reaction, and to obtain at the same time the removal of energy and steam consumption fed . In this way it is always possible to adapt the process for the production of synthesis gas to any condition and type of available hydrocarbon mixtures. Block 19 must in any way be considered as optional and not necessary, particularly when gaseous hydrocarbons such as natural gas are used for the reforming reaction. In this regard, it should be clarified that it is not absolutely necessary to feed the entire second stream comprising hydrocarbons or the entire second stream comprising steam to the preform section (block 19). Indeed, in some cases, depending on the working conditions and the type of tool available, it may be more advantageous to send only a part of such flows (for example between 20% and 80%) to block 19, and the remaining directly to the autothermal reforming section (block 20).

In addition, a second flow comprising oxygen and in this case also nitrogen, for example air, is sent to the autothermal reforming section (block 20) by means of the flow line 7, analogously although it has already been described with respect to the flow line 3. Passing through the pre-reformation section and the autothermal reforming section (blocks 19 and 20), the hydrocarbons and the vapor contained in the feed flow 5 react, obtaining a second gas phase comprising CO, C02, H2 and N2 which is combined with the first gas phase (flow line 1) immediately upstream of the CO conversion section and together with the one passing through the remaining blocks of diagram 10, as described above. In the example shown in Figure 1, the flow line 5 enters the flow line 1 upstream of the high temperature conversion section indicated by the block 13. In any case, the possibility is not excluded, even though it does not is represented, of the shipment of at least a portion of the second gas phase coming from the autothermal reforming section (block 20) to the upstream location of the low temperature CO conversion section, between blocks 13 and 14.

Particularly satisfactory results have been obtained by feeding oxygen enriched air to block 20 through flow line 7. By doing this, the amount of CO 2 comprised in the second gas phase and therefore can be fed to the section urea synthesis (block 18) is advantageously increased, thereby improving the conversion efficiency. By controlling the concentration and feed rate of the flow comprising air enriched with oxygen fed to the autothermal reforming section, it is possible to obtain C02 in an amount sufficient to convert all the ammonia produced into urea, and in this way, independently of the type of hydrocarbons fed to blocks 1 and 5. In addition, the use of air enriched with oxygen in the present process allows reducing the amount of inert gases sent to the ammonia synthesis section (block 17), advantageously increasing the yield of the conversion in such section. According to an alternative embodiment of the present invention, it was anticipated to divide a part of the flow comprising the hydrocarbons fed from the flow line 1 to the flow line 5 to be sent to the autothermal reforming section (block 20), of according to the indicated by the flow line 8 represented with a dotted line. In this way, it is not always necessary to implement the maximum operating capacity of the present process, it is possible to further reduce the total energy consumption, because the load to the autothermal reforming section (block 20) can be maximized and the external energy supply to the primary reforming section (block 11) can be reduced. Preferably, the portion of the first hydrocarbon stream divided to the flow line 5 is comprised between 5% and 70% of the total. Alternatively, according to a non-depicted embodiment of the present invention, the flow line 8 starts from the flow line 1 at a point downstream towards the inlet, towards line 1 of the flow line 2. In this In this case, together with a portion of the first flow comprising hydrocarbons, also the portion of the first gas flow comprising steam is fed to the flow line 5. Generally speaking, the very high flexibility of the process according to the invention allows reduce, depending on the flow rates and the amount of synthesis gas to be produced, the load to the primary reforming section with a corresponding advantage in terms of energy consumption. In this regard, particularly satisfactory results have been obtained in minimizing the amount of hydrocarbons fed to the primary reforming section and at the same time maximizing the amount of hydrocarbons to be sent to the autothermal reforming section. The operating conditions of the sections indicated by blocks 11-20, as well as the nature of the chemical reactions that occur there, are conventional and therefore will not be further described being known to those skilled in the art. According to the process for the production of synthesis gas of the present invention, a first flow comprising hydrocarbons and a first gas stream comprising steam are fed (flow lines 1 and 2) to a primary reforming section (block 11). ), although a first flow of gas comprising oxygen and possibly nitrogen (flow line 3) is fed to a secondary reforming section (block 12). The hydrocarbons and steam are reacted in the primary reforming section and then - together with the oxygen - in the secondary reforming section, obtaining a first gaseous phase comprising CO, C02, H2 and possibly N2. The gas phase thus obtained is then fed to a conversion section of carbon monoxide. Advantageously, according to the additional steps of the present process, a second flow comprising hydrocarbons, a second flow of gas comprising steam and a second flow of gas comprising oxygen and possibly nitrogen (flow lines 5-7 ) are fed to an autothermal reforming section (block 20) arranged in parallel with respect to the primary and secondary reformation sections. The hydrocarbons, steam and oxygen are reacted in the autothermal reforming section obtaining a second gas phase comprising CO, C02, H2 and possibly N2 which is in turn sent (flow line 5) to the conversion section of carbon monoxide. According to an alternative embodiment, the process according to the present invention further comprises the step of subjecting at least a part of the second flow comprising hydrocarbons and of the second gas flow comprising steam to a pre-reformation treatment (block 19) before of being fed to the autothermal reforming section. According to a further alternative embodiment, the process of the present further contemplates the step of feeding (flow line 8) a portion of the first flow comprising hydrocarbons to the autothermal reforming section. The plant for producing synthesis gas according to the present invention comprises the sections indicated by blocks 11-20 of Figure 1. Suitable feeding and connecting means were contemplated at the entrance and between the unique sections that constitute the plant previously. mentioned, respectively. These means are of the known type, such as for example ducts, tubes or the like, schematically represented by the flow lines 1-8 of Figure 1. Conventional heat exchangers - not shown in Figure 1 - can also be provided in the plant . A particularly important aspect of the present invention is represented by the reconversion of the preexisting plants for the production of synthesis gas. In this regard, the invention provides a method for converting a plant for synthesis gas production of the type comprising a primary reforming section, a secondary reforming section and a carbon monoxide reconversion section (blogs 11-14). connected in series, which method advantageously comprises the steps of providing an autothermal reforming section (block 20) in parallel to the existing reforming sections and suitable means for feeding to the autothermal reforming section in a second flow comprising hydrocarbons, a second gas flow comprising steam and a second gas flow comprising oxygen and possibly nitrogen, respectively, as well as connection means between the autothermal reforming section and the carbon monoxide conversion section (flow lines 5). -17). Thanks to the conversion method of the present, it is possible to significantly increase the production capacity of an existing plant, for example from 20 to 7%, without superimposing the reforming sections and especially keeping energy consumption and operating costs low if they have not yet been reduced. In addition, once reconverted, the plant gains greater flexibility, being able to operate properly with any type of hydrocarbon and working condition. In particular, it is possible to distribute the loads between the reforming stages arranged in parallel, in such a way that the conversion of primary reformation is reduced to a minimum and, consequently, the energy consumption is optimized. It is important to note that - advantageously - the reconversion method according to the invention does not require improving or replacing the existing reforming sections. In addition to this, also the downstream sections for the synthesis gas treatment produced are not subjected to particular overloads, requiring - if it is the case - only marginal and cheap interventions. It should be noted that a possible replacement or substantial modification of such sections implies, however, a much lower cost than the modification of one or even two reform sections. According to a preferred embodiment of the reconversion method of the present invention, the second gas flow comprising oxygen (flow line 7) fed to the autothermal reforming section (block 20) comprises air enriched with oxygen. By doing so, it is possible to advantageously increase the amount of CO 2 produced, for example up to the stoichiometric ratio of CO 2 / NH 3 to achieve the synthesis of urea, regardless of the type of hydrocarbon that is fed. To further reduce the energy consumption, the reconversion method according to the present invention advantageously contemplates the step of providing means for feeding a portion of the first flow comprising hydrocarbons to the autothermal reforming section (flow line 8) . Alternatively, along with the flow portion comprising hydrocarbons, also a portion of the gas flow comprising steam is sent to the flow line 5. In this case, the hydrocarbons and steam to be sent to the reforming section are preferably already taken and properly mixed and preheated from the flow line 1. By doing this, it is possible to reduce, if not eliminate, the respective apparatuses to mix and preheat the reagents to be sent to the autothermal reforming section, ensuring this savings in energy and investment costs. Finally, according to a further embodiment of the conversion method according to the present invention, there are provided the steps of providing a pre-reformation section (block 19), and of providing means of feeding at least a part of the second flow that comprises hydrocarbons and the second flow gas comprising steam to said pre-reformation section and connection means between the pre-reformation section and the autothermal reforming section (flow line 5).

In this way, it is possible to use essentially any type of hydrocarbons as a source of coal and hydrogen sent to the autothermal reforming section, without affecting the operation of the same, but, on the contrary, allowing a reduction in the amount of steam to be sent to such a section, ensuring savings in terms of energy consumption and operating costs.

EXAMPLE In the following example, the advantages resulting from the reconversion method according to the method of the present invention are presented. In particular, energy consumption is discussed in relation to an increase in capacity equal to 50% of an existing plant for the production of synthesis gas to obtain ammonia. The results of the present example have been obtained by means of commercially available calculation algorithms. The existing plant is of the type shown and described with reference to Figure 1, blocks 11-17, and was designed to operate at an average production capacity of 1000 MTD of ammonia. The total energy consumption is normally 8300 kcal / MT of ammonia.

The use of natural gas as a source of hydrocarbons and the flow of gas comprising oxygen fed to the secondary reforming section consisted of air. The sections of primary and secondary reform of the existing plant were not designed to face an increase in capacity equal to 50%, but on the contrary were, at most, can reach peaks of production that do not exceed the average value in more 10-15%. According to the reconversion method of the present invention, the increase in the capacity of such a plant by 50%, for a total production of 1500 MTD of ammonia, is obtained by adding in parallel an adequately dimensioned autothermal reforming section fed with air, naphtha vapor and a portion of natural gas flow from the existing plant (see figure 1, reference signs 5-8, 20). The load is advantageously divided in such a way that it contains 60% of the total production in the existing reforming step (900 MTD) and the remaining 40% in the autothermal reforming section (600 MTD). Thanks to the reconversion method of the present, it has been surprisingly noted that - regardless of an increase in capacity equal to 50%, the total energy consumption has decreased to 2-3% with respect to the existing plant, and corresponds to approximately 8100 kcal / MT of ammonia. Compared with a reconversion carried out according to the prior art, which contemplates the replacement of the existing primary and secondary reform sections with new reforming sections that have a capacity increased by 50%, the reconversion method according to the present invention is extremely advantageous both for decreasing energy consumption and for - especially - decreasing investment costs. Finally, it should be understood that to implement the method herein, it does not require prolonged interruption times of the existing plant in view of the fact that the autothermal reforming section is erected in parallel to the existing sections. In this way, the existing plant can operate until the connection between the additional section and the carbon monoxide conversion section is made. On the contrary, according to the prior art, the plant must be interrupted for a prolonged period of time to allow the conversion or replacement of the reforming sections, with certain relevant production losses. From the above discussed, clearly emerge the numerous advantages achieved by the present invention; in particular, it is possible to obtain an extremely flexible process for the production of synthesis gas, easy to implement, and that allows to achieve high production capacities with low investment and investment costs and low energy consumption. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (10)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property.

1. A process for the production of synthesis gas to obtain compounds such as ammonia or methanol, comprising the steps of: - feeding a first flow comprising hydrocarbons, and a first gas flow comprising steam to a primary reforming section; feeding a first flow comprising oxygen and possibly nitrogen to a secondary reforming section; reacting the hydrocarbons and the first vapor in the primary reforming section, and then - together with the oxygen - in the secondary reforming section, obtaining a first gas phase comprising CO, C02, H2 and possibly N2; feeding the first gas phase comprising CO, C02, H2 and possibly N2 to a carbon monoxide conversion section; characterized in that it further comprises the steps of: - feeding a second stream comprising hydrocarbons, a second stream of gas comprising steam, and a second stream of gas comprising oxygen and possibly nitrogen to an autothermal reforming section arranged in parallel with respect to the primary and secondary reforming sections, - reacting hydrocarbons, steam and oxygen in the autothermal reforming section, obtaining a second gaseous phase comprising CO, C02, H2 and possibly N2; - feeding the second gaseous phase comprising CO, C02, H2 and possibly N2 to the carbon monoxide conversion section.

2. The process according to claim 1, characterized in that the second gas flow comprising oxygen, comprises air enriched with oxygen.

The process according to claim 1, characterized in that it further comprises the step of subjecting at least a part of the second flow of gas comprising hydrocarbons and the second flow of gas comprising steam to a pre-processing treatment before being fed to the autothermal reforming section.

4. The process according to claim 1, characterized in that it further comprises the step of feeding a portion of the first gas stream comprising hydrocarbons to the autothermal reforming section.

5. A plant to produce synthesis gas, to obtain compounds such as ammonia or methanol, comprising: a primary reforming section and a secondary reforming section arranged in series to obtain a first gas phase comprising CO, C02, H2 and possibly N2; respective means for feeding a first flow comprising hydrocarbons and a first gas flow comprising steam to the primary reforming section; - means for feeding a first gas flow comprising oxygen and possibly nitrogen to the secondary reforming section; means for feeding the first phase comprising CO, C02, H2 and possibly N2 to a carbon monoxide conversion section; characterized in that it comprises: - an autothermal reconversion section for obtaining a second gas phase comprising CO, C02, H2 and possibly N2; respective means for feeding a second flow comprising hydrocarbons, a second gas flow comprising steam, and a second gas flow comprising oxygen and possibly nitrogen to the autothermal reforming section; - means for feeding the second gas phase comprising CO, C02, H2 and possibly N2 to the carbon monoxide conversion section.

The plant according to claim 5, characterized in that it further comprises: - a pre-reformation section; means for feeding at least a part of the second gas stream comprising hydrocarbons and the second gas stream comprising steam to the pre-reformation section; - means to connect the pre-reformation section with the autothermal reforming section.

7. The plant according to claim 5, characterized in that it further comprises means for feeding a portion of the first flow comprising hydrocarbons to the autothermal reforming section.

8. A method to convert a plant for the production of synthesis gas to obtain compounds such as ammonia or methanol, of the type comprising a primary reforming section and a secondary reforming section, arranged in series to obtain a first phase gaseous comprising CO, C02, H2 and possibly N2, respective means for feeding a first flow comprising hydrocarbons and a first gas flow comprising steam to the primary reforming section, means for feeding a first gas flow comprising oxygen and possibly nitrogen to the secondary reforming section, means for feeding the first phase comprising CO, C02, H2 and possibly N2 to a carbon monoxide conversion section, the method is characterized in that it comprises the steps of: - providing a section of Autothermal reconversion to obtain a second gas phase comprising CO, C02, H2 and possibly N2; - providing respective means for feeding a second flow comprising hydrocarbons, a second gas flow comprising steam, and a second gas flow comprising oxygen and possibly nitrogen to the autothermal reforming section; - providing means for feeding the second gas phase comprising CO, C02, H2 and possibly N2 to the carbon monoxide conversion section.

9. The method according to claim 8, characterized in that it further comprises the steps of: - providing a pre-reformation section; - providing means for feeding at least a part of the second flow comprising hydrocarbons and the second gas flow comprising steam to the pre-reformation section; - provide means for connecting the pre-reformation section with the autothermal reforming section. The method according to claim 8, characterized in that it further comprises the steps of: - providing means for feeding a portion of the first flow comprising hydrocarbons and possibly a portion of the first gas flow comprising steam to the autothermal reforming section .