FR3038909A1

FR3038909A1 - DEVICE AND METHOD FOR PRODUCING SYNTHETIC METHANE

Info

Publication number: FR3038909A1
Application number: FR1556748A
Authority: FR
Inventors: Yilmaz Kara; Stephane Fortin; Julia Ricard
Original assignee: GDF Suez SA
Current assignee: Engie SA
Priority date: 2015-07-16
Filing date: 2015-07-16
Publication date: 2017-01-20
Also published as: MY186992A; EP3322778B1; CN107922864A; WO2017009576A1; KR20180030678A; DK3322778T3; FR3038910B1; BR112018000922A2; EP3322778A1; FR3038910A1; BR112018000922B1

Abstract

Le dispositif (10) de production de méthane de synthèse comporte : - un réacteur (105) de méthanation comportant : - une entrée (110), pour du syngas produit par gazéification de matière hydrocarbonée, reliée à une conduite (115) d'alimentation de syngas et - une sortie (120) pour gaz naturel de synthèse, - un moyen (125) de séparation d'eau comportant : - une entrée (130) pour gaz naturel de synthèse et - une sortie (135) pour gaz naturel de synthèse déshydraté et - une dérivation (140) d'une partie du gaz naturel de synthèse déshydraté depuis la sortie du moyen de séparation d'eau vers la conduite d'alimentation de syngas pour qu'un mélange, du syngas et du gaz naturel de synthèse dérivés, soit fourni au réacteur.The device (10) for producing synthetic methane comprises: - a methanation reactor (105) comprising: - an inlet (110) for syngas produced by gasification of hydrocarbon material, connected to a feed pipe (115) of syngas and - an outlet (120) for synthetic natural gas, - a means (125) for separating water comprising: - an inlet (130) for synthetic natural gas and - an outlet (135) for natural gas from dehydrated synthesis and - a bypass (140) of a portion of the dehydrated synthetic natural gas from the outlet of the water separation means to the syngas feed pipe for a mixture, syngas and natural gas of derived synthesis, either supplied to the reactor.

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a device and a method for producing synthetic methane. It applies, in particular, to the production of synthetic natural gas.

STATE OF THE ART

The production of biomethane, belonging to the "SNG" (Synthesis Natural Gas, translated by Natural Gas Synthesis) can be achieved by thermochemical conversion of biomass. This conversion is carried out by a process consisting of three main stages that are: - the gasification of biomass to produce syngas (synthesis gas) composed essentially of H2, CO, CO2 and CH4, - the catalytic methanation which consists in converting H2 and CO at CH4 and - the specification that aims to eliminate water, residual H2, and CO2 in order to produce a synthetic natural gas closest to the injection specifications on the natural gas network .

By specification is meant, in particular: - higher heating value, abbreviated "PCS", - Wobbe index, and - maximum content of H2 and CO2.

The gasification of the biomass is carried out in a reactor in which the biomass undergoes different reaction stages.

The first step corresponds to a thermal degradation of the biomass which undergoes successively a drying then a devolatilization of the organic matter to produce: - a carbon residue, called "char", - a synthesis gas, such as H2, CO, CO2 and CH4 and - condensable compounds contained in the syngas, such as tars or tars).

The carbonaceous residue can then be oxidized by a gasifying agent, such as water vapor, air, or oxygen, to produce H2, CO. Depending on its nature, this gasification agent may also react with tars or major gases. Thus, if it is water vapor (H2O), a reaction of Dussan, called "from gas to water" and usually known by the acronym "WGS" (for Water Gas Shift, translated by reaction of the gas with water) occurs in the gasification reactor according to the following equilibrium:

The reactor pressure has little effect on this reaction. On the other hand, the equilibrium is strongly related to the temperature of the reactor and to the "initial" contents of the reagents. For existing processes, the H2 / CO ratio is never greater than 2 at the end of the gasification step. This ratio is an important factor for the production of biomethane during the next methanation stage that allows the production of CH4 and on which the SNG production process is based.

The WGS reaction can be carried out in a specific reactor placed upstream of the methanation. However, in the case of certain fluidized bed processes, the two methanation and WGS reactions can be carried out in parallel in the same reactor; the steam required for the WGS reaction is injected into the reactor together with the reaction mixture.

The production of biomethane from the syngas resulting from the gasification stage is based on the catalytic methanation reaction of CO or CO2, known as the "Sabatier reaction". Methanation involves converting carbon monoxide or carbon dioxide in the presence of hydrogen and a catalyst, usually nickel-based, to produce methane. It is governed by the following competitive equilibrium hydrogenation reactions:

AG298k = -206 kJ / g.mol

AG298k = -165 kJ / g.mol

Under the conditions generally used to produce SNG from gasification syngas, the methanation reaction of CO is very largely favored.

The methanation reaction is an exothermic reaction with a decrease in the number of moles; according to the Le Chatelier principle, the reaction is favored by pressure and disadvantaged by temperature.

The production of methane is optimum for a composition gas close to the stoichiometric composition, that is to say whose H2 / CO ratio is close to 3. The syngas produced by gasification, in particular of biomass, is characterized by an H2 ratio. / CO weaker, of the order of 1.5 to 2. Also, to maximize the production of methane, this ratio must be adjusted by producing hydrogen by reaction between carbon monoxide and steam by the reaction from WGS. At temperatures below 230 ° C, the nickel component of the catalyst or present in the reactor wall material is capable of reacting with carbon monoxide to form nickel tetracycarbon (Ni (CO) 4) , very highly toxic compound. Therefore, it is essential that all parts of the reactor are always at a temperature above 230 ° C.

The heat generated during the CO conversion is about 2.7 kWh when producing 1 Nm3 of methane. Controlling the temperature in the reactor, and thus eliminating the heat produced by the reaction, is one of the key points in minimizing catalyst deactivation, by sintering or carbon deposition, and maximizing methane conversion rates. .

The valorization of the heat produced during the methanation, either within the unit itself or by heat sales, is one of the key points of the technical and economic equilibrium of the SNG production process. Steam production is a classic way to obtain this valuation.

The methanation reactions whose kinetics are rapid at the temperatures used, are characterized by a very strong exothermicity, for example:

AG298k = -206 kJ / g.mol

To maximize the production of UHC, and minimize the excess of CO, H2 and CO should be in a stoichiometric ratio of 3 to 1. Even with this ratio, the reaction remains incomplete due to chemical equilibrium. This ratio is obtained by performing a complementary WGS reaction. This can be carried out prior to methanation in a dedicated reactor, in the presence of specific catalysts. It can optionally be obtained directly in the same reactor as methanation with possible adaptation of the catalyst. In both cases, this reaction requires an injection of steam.

Among the methanation reactor technologies, some employ a dense fluidized bed reactor, the bed being formed by the catalyst of the methanation reaction. The removal of the heat produced by the reaction is then carried out by exchangers immersed in the fluidized bed. However, because of the very high exothermicity of the reaction, the quantities of heat to be evacuated, and therefore the required exchange surfaces, are important. Thus, the volume occupied by this exchanger leads to an overall oversizing of the reactor size and especially to a complexity of its design.

The implementation of a fluidized reactor is a simple solution to limit the reaction temperature. The fluidization of the catalyst by the reaction mixture allows an almost perfect homogenization of the temperatures in all points of the catalytic layer and the reactor can be likened to an isothermal reactor. The heat produced by the reaction is removed by means of exchangers immersed in the fluidized bed. The heat exchange coefficients between the fluidized layer and a wall immersed in the bed are very important (of the order of 400 to 600 W / K.m2, comparable to those between a liquid and a wall) and make it possible to minimize the dimensions of the exchanger and therefore the overall size of the reactor.

In the temperature range used in the fluidized bed methanation reactors (temperature of the order of 300 - 550 ° C.), the kinetics of the methanation reaction is very fast, and consequently the amount of catalyst required by the mere fact of the chemical reaction is weak. Also the size of the reactor and the amount of catalyst used result from the bulk of the exchanger implanted within the fluidized bed.

Because of the heat exchange and the fluidization regime, a major disadvantage is attributable to this technology for high pressure operation. Indeed, the decrease in the gaseous volume due to the increase in pressure leads to a smaller available section for positioning the exchanger (at equal power). Solutions of the skilled person exist, however, to overcome the adjustment of the effective surface or the fluidization regime. Non-exhaustive solutions are, for example: the reduction in the number of tubes and consequently the increase in the catalyst layer height with a high limit linked to the phenomenon of "slugging" with properties of reduced heat exchange and - modification of the physical characteristics of the catalyst (particle size, density of the support) to maintain an equivalent fluidization for a lower volume flow.

In terms of flexibility, and compared to the technologies presented above, the fluidized bed by nature allows a greater flexibility in terms of flow rate and therefore reactor power around the design conditions. At constant pressure drop (fluidization), the operating flow can easily vary within a normalized range from 1 to 6. Nevertheless, to allow such a range of operation while maintaining fluidization efficiency, particular attention must be paid to the distributor design. The design phase must already incorporate the flexibility envisaged during operation. With regard to pressure losses, the fluidized bed generates 2 to 5 times less pressure losses than a fixed bed reactor (adiabatic or isothermal) with equivalent rated power. This is also a significant advantage with an impact on operating costs. Finally, the fluidized bed allows loading and unloading of the catalyst in operation as well as regularity of composition of the SNG produced, intensified heat transfer,

From the reaction point of view, unlike fixed-bed or wall-cooled reactor technologies, methanation of fluidized-bed syngas does not require pre-WGS. A co-injection of steam with the syngas makes it possible to ensure the methanation reactions of CO and WGS in the same device.

The solutions currently proposed for this technological family are not distinguished between them really on the conversion efficiency but mainly on the methodology used to cool the reactor.

Finally, the final step of specification is to separate the constituents of the gas from the methanation to obtain a biomethane meeting the injection specifications on the natural gas network. Thus, this separation generates by-products that are H2O, CO2 and H2. They are most often performed in separate equipment with sometimes very different operating conditions.

At the outlet of the methanation reactor, the water is first separated from the biomethane by cooling and condensation passing below the dew point temperature of the water under the conditions considered.

Then, the CO2 is extracted from the gas to reach the specifications of the network. The technologies allowing this separation are relatively numerous and known. The main technological families are the absorption, physical or chemical, adsorption modulated in pressure, membrane permeation or cryogenics.

Finally, in the final stage before conditioning and injection of the produced SNG, it is necessary to eliminate a significant fraction of the residual H2 of the methanation reaction in order to meet the specifications relating in particular to the PCS. The most commonly used technique for this separation is membrane permeation, which can present a level of complexity and costs, in terms of investment and operation, which are not negligible with a significant impact on the value chain.

The composition of the crude SNG at the outlet of the reactor is intimately related to the operating conditions of the reactor, in terms of pressure, temperature, the adiabatic or isothermal mode of operation of the reactor, which govern the chemical equilibrium of the above reactions. These reactions generally form water and a separation of this species is therefore required. Concerning the other species (CO, CO2 and H2), their respective contents can be modified by playing on the one hand on the mode of operation of the reactor (adiabatic or isothermal) and on the other hand on the temperature or the pressure. High pressure and low temperature will thus allow to considerably reduce the contents of these compounds. When the operation is carried out in "adiabatic" reactor, a succession of steps is also necessary to achieve a conversion quality equivalent to the isothermal reactor. In any case, the composition of the product gas is generally incompatible with respect to the injection specifications and improvement steps are necessary to remove residual CO 2 and / or H 2. Thus, the procedure constitutes a lock for the simplification of the process chain.

OBJECT OF THE INVENTION

The present invention aims to remedy all or part of these disadvantages. For this purpose, according to a first aspect, the present invention is directed to a device for producing synthetic methane, which comprises: a methanation reactor comprising: an inlet, for syngas produced by gasification of hydrocarbon material, connected to a pipe syngas feedstock and - an output for synthetic natural gas, - a water separation means comprising: - an inlet for synthetic natural gas and - an outlet for dehydrated synthetic natural gas and - a bypass of a part of the dehydrated synthetic natural gas from the outlet of the water separation means to the syngas feed line for a mixture, syngas and synthetic syngas derived thereto, to be supplied to the reactor.

The means for separating water cooling the natural synthesis gas, the supply of these products at the inlet of the reactor allows cooling of the syngas and allows the reactor not to require a heat exchanger. The design of such a reactor, particularly in terms of dimensioning, is all the more simplified. In addition, the supply of the dehydrated synthetic natural gas in the supply line improves the Wobbe index and the PCS of the products of the methanation reaction by the favorable modification of the reaction equilibria. Thus, the device object of the present invention allows a reduced dimensioning of the reactor as well as a specification for the gas network requiring little or no treatment downstream of the methanation reaction.

In embodiments, the device which is the subject of the present invention comprises means for separating carbon dioxide from the dehydrated synthetic natural gas, this separation means being positioned upstream of the bypass.

These embodiments further improve the cooling capacity and specification of the products of the methanation reaction.

In embodiments, the device that is the subject of the present invention comprises: a sensor of a temperature inside the reactor and a recirculator, products entered in the bypass, controlled as a function of the temperature sensed.

These embodiments make it possible to regulate the flow rate of recirculated reaction products as a function of the temperature sensed. If the sensed temperature is above a predetermined temperature, corresponding to optimal methanation reaction conditions, the flow of recirculated products is increased to cool the reaction medium of the reactor. Conversely, if the sensed temperature is below the predetermined temperature, the rate of recirculated products is decreased.

In embodiments, the device of the present invention comprises, upstream of the inlet of the reactor, a preheating means of the mixture at a temperature greater than 220 ° C.

These embodiments make it possible to limit the formation of coke in the methanation reactor, the coke being formed at a temperature below 230 ° C.

In embodiments, the device that is the subject of the present invention comprises a pipe for injecting water vapor into the syngas supply pipe upstream of the site where the mixture between the syngas and the methanation products issued from the derivation.

These embodiments make it possible to carry out a WGS reaction to adjust the H2 / CO ratio in the reactor, so as to avoid deactivation of the reactor by coke deposition.

In embodiments, the device which is the subject of the present invention comprises a deflection line, a part of the methanation reaction products, comprising: an inlet positioned between the outlet of the reactor and the means for separating water and an outlet positioned upstream of the reactor inlet.

These embodiments make it possible to maintain the overall flow rate in the constant methanation reactor by deflecting a portion of the methanation products, hot, at the outlet of the reactor. Maintaining this rate provides the device with increased flexibility in terms of syngas input.

In embodiments, the device which is the subject of the present invention comprises: a flowmeter of the syngas upstream of the place of mixing and a recirculator of products entered in the deflection duct, controlled according to the measured flow rate.

These embodiments make it possible to maintain the overall flow rate of the flow entering the methanation reactor.

In embodiments, the water separation means configured to cool the synthetic natural gas at a temperature of between 5 ° C and 40 ° C.

These embodiments allow an increased separation of water contained in the synthetic natural gas.

In embodiments, the reactor is configured to perform a Dussan reaction called "gas to water".

These embodiments allow the use of a single reactor to perform the WGS reaction and the methanation reaction.

According to a second aspect, the present invention relates to a process for producing synthetic methane, which comprises: a methanation reaction step comprising: a step of entry into a methanation reactor, of syngas produced by gasification of hydrocarbon material by a syngas supply line and - an output step for synthesis natural gas - a water separation stage comprising: - an input stage for synthesis natural gas and - an output stage for gas natural dehydrated synthesis and - a step of derivation of a portion of the dehydrated synthetic natural gas leaving the exit step of the water separation step to the syngas feed pipe so that a mixture , synthesized syngas and synthetic natural gas, is supplied to the reactor.

Since the aims, advantages and particular characteristics of the method which are the subject of the present invention being similar to those of the device which is the subject of the present invention, they are not recalled here.

BRIEF DESCRIPTION OF THE FIGURES Other advantages, aims and particular characteristics of the invention will emerge from the following nonlimiting description of at least one particular embodiment of the device and the process for producing synthetic methane which are the subject of the present invention. with reference to the appended drawings, in which: FIG. 1 schematically represents a first particular embodiment of the device which is the subject of the present invention, FIG. 2 schematically represents a second particular embodiment of the device which is the subject of the invention. FIG. 3 represents, schematically and in the form of a logic diagram, a particular sequence of steps of the method which is the subject of the present invention; FIG. 4 represents, in the form of a curve, the index of Synthetic methane wobbe obtained by the device and method of the present invention, FIG. a curve, the PCS of synthetic methane obtained by the device and the method which are the subject of the present invention; FIG. 6 represents, in the form of a curve, the reaction equilibrium inside the methanation reactor at the time of the implementation of the device and the method which are the subject of the present invention and FIG. 7 represents, in the form of a curve, the exothermicity of the methanation reaction during the implementation of the device and the method which is the subject of the invention. present invention.

DESCRIPTION OF EXAMPLES OF EMBODIMENT OF THE INVENTION

This description is given in a nonlimiting manner, each feature of an embodiment being able to be combined with any other feature of any other embodiment in an advantageous manner. Moreover, each parameter of an exemplary embodiment can be implemented independently of other parameters of said exemplary embodiment.

It is already noted that the figures are not to scale.

FIG. 1, which is not to scale, shows a schematic view of an embodiment of the device 10 which is the subject of the present invention. This device 10 for producing synthetic methane comprises: a methanation reactor 105 comprising: an inlet 110 for syngas produced by gasification of hydrocarbon material, connected to a syngas supply pipe 115 and an outlet 120 for synthetic natural gas, a means 125 for separating water comprising: - an inlet 130 for synthetic natural gas and - an outlet 135 for dehydrated synthetic natural gas and - a bypass 140 of a part of the natural gas of dehydrated synthesis from the outlet of the water separation means 125 to the syngas feed line 115 for a syngas and synthetic syngas-derived mixture to be supplied to the reactor 105.

The reactor 105 is, preferably, a fluidized bed methanation reactor. The fluidization of the catalyst by the reaction mixture allows an almost perfect homogenization of the temperatures in all points of the catalytic layer and the reactor can be likened to an isothermal reactor. In variants, this reactor 105 may be a boiling water reactor, known to those skilled in the art under the abbreviation "BWR" (Boiling Water Reactor, translated by boiling water reactor). In other embodiments, this reactor 105 may be a fixed bed reactor or a bed cooled by the walls.

This reactor 105 is configured to perform the methanation of carbon monoxide and / or carbon dioxide.

This reactor 105 comprises the input 110 for syngas which is, for example, an orifice of the reactor 105 provided with a connector (not shown) compatible with the supply line 115 of syngas.

In preferred embodiments, as shown in Figure 1, the reactor 105 is configured to perform a Dussan reaction called "gas to water". In these embodiments, water vapor is injected into the syngas supplied to the reactor 105.

The syngas feed line 115 is connected to a gasification unit for hydrocarbon materials (not shown), such as biomass or coal. The syngas has elements of H2, CO, CO2, H2O, CH4 and C2. This supply line 115 is sealed.

In variants, the supply line 115 receives H2 from a water electrolysis device.

The synthetic natural gas leaves the reactor 105 through the outlet 120 of the reactor. This output 120 is, for example, an orifice connected to a connector (not shown) for fixing a sealed pipe for transporting synthetic natural gas.

The water separating means 125 is, for example, a heat exchanger for cooling the synthetic natural gas to a temperature below the dew point temperature of the water. This temperature is preferably between 5 ° C and 40 ° C. Preferably, this temperature is between 5 ° C and 20 ° C. The water thus separated is collected by an outlet 227 for water and can be used by an external device or heated to be transformed into water vapor which, as indicated below, to be injected into the supply line 115 of syngas .

The water separating means 125 comprises the inlet 130 for synthetic natural gas. This inlet 130 is, for example, an orifice associated with a connector (not shown) to be connected to the sealed conduit for transporting the synthetic natural gas from the reactor 105.

The water separating means 125 comprises the inlet 135 for dehydrated synthetic natural gas. This input 135 is, for example, a port associated with a connector (not shown) to be connected to a sealed conduit (not shown) for transporting dehydrated synthetic natural gas.

The bypass 140 is, for example, a sealed pipe connected to the dehydrated synthetic natural gas transport pipe for capturing part of the flow passing through this transport pipe.

This bypass 140 injects the dehydrated synthesis natural gas into the syngas feed line 115.

In this way, syngas and dehydrated synthetic natural gas, cooled by the water separation process, form a mixture which, in reactor 105, reduces the exothermicity of the methanation reaction by improving gas specifications. natural synthesis from the reactor 105.

In particular, the mixture produced avoids the downstream separation of H2 and CO2 in the syngas.

In preferred embodiments, as represented in FIG. 1, the device 10 comprises: a sensor 150 of a temperature inside the reactor 105 and a recirculator 155, products entered in the bypass, controlled according to of the temperature sensed.

The sensor 150 is positioned inside or outside the reactor 105. This sensor 150 captures the temperature of the catalyst forming the fluidized bed, the reactor atmosphere 105 and / or the reactor wall 105.

The recirculator 155 is designed to compensate for the successive pressure losses of the flow of syngas and synthetic natural gas. Such a pressure drop is estimated between 200 and 800 mbar, for example. The recirculator 155 is, for example, a fan, a presser or an ejector. In the case of an ejector, the fluid used to produce the ejection mechanism is, for example, water vapor resulting from a WGS reaction occurring in the reactor 105.

If the sensed temperature is greater than a predetermined temperature, corresponding to optimal methanation reaction conditions, the recirculated product flow is increased to cool the reaction medium of the reactor 105. Conversely, if the sensed temperature is below the predetermined temperature, the flow rate of recirculated products is decreased.

In preferred embodiments, as shown in Figure 1, the device 10 comprises upstream of the inlet of the reactor 105, a means 160 for preheating the mixture at a temperature above 220 ° C.

The preheating means 160 is, for example, a fluid / gas heat exchanger, or electric, configured to transmit to the mixture a temperature greater than 220 ° C. Preferably, the temperature of the mixture is raised to 230 ° C.

In addition, the device 10 may comprise, in these embodiments, a temperature sensor 162 of the mixture downstream of the preheating means 160. The temperature of the preheating means 160 varies as a function of the sensed temperature and a temperature of setpoint. If the sensed temperature is higher than the set temperature, the temperature of the preheating means 160 is reduced. Conversely, the temperature of the preheating means 160 is increased when the sensed temperature is below the set temperature.

In preferred embodiments, as shown in FIG. 1, the device 10 comprises a water vapor injection conduit 165 in the syngas supply pipe 115 upstream of the site where the mixture between the syngas and the products of methanation released from the bypass 140.

The injection line 165 is, for example, a sealed line connected to a device (not shown) for forming water vapor. This steam-forming device heats, for example, water separated from the synthetic natural gas to produce water vapor injected into the syngas. The water thus injected makes it possible to carry out a WGS reaction and to limit the formation of coke in the reactor 105. In addition, the steam promotes, by the WGS reaction, the adjustment of the H2 / CO ratio close to the optimum conditions for the methanation reaction. The analysis of the prior art has shown that the WGS reaction can be carried out in a dedicated reactor located upstream of the reactor 205 or even within this reactor in parallel with the methanation reactions. In order to benefit from the economic gains and the simplification of the process, the methanation and WGS reactions are carried out in a single device.

In preferred embodiments, as shown in FIG. 1, the device 10 comprises a diversion duct 170, a portion of the methanation reaction products, comprising: an inlet 175 positioned between the outlet of the reactor 105 and the means 125 for separating water and an outlet 180 positioned upstream of the inlet 110 of the reactor 105.

The deflection conduit 170 is, for example, a sealed conduit. The inlet 175 is, for example, an orifice opening on the inside of the synthetic natural gas transport pipe, upstream of the water separating means 125. The outlet 180 is, for example, an injection orifice of the synthetic natural gas into the mixture, downstream of the preheating means 160.

The synthetic natural gases, hot, allow to maintain the flow in the reactor 105.

The flow rate of the gasification syngas is entirely a function of the quantities of hydrocarbon compounds available. In order to maintain the conversion stability during the methanation operation, the hydrodynamic conditions must be kept as constant as possible. Nevertheless, if the available biomass is insufficient and consequently the flow of syngas is decreased, it is necessary to maintain a constant overall flow rate into the reactor 105 or to opt for a very flexible technology. Even in the case of the fluidized bed capable of operating in a range of flow rates from 1 to 6, too low flow rates can cause degradation of the cooling and therefore of the conversion. To overcome this difficulty, in the event of a significant drop in syngas flow rate, the flow at the outlet of the preheating means 160 is supplemented by a hot recirculation coming directly from the outlet 120 of the reactor 105 via the deflection line 170. The fact of using a hot recirculation fluid does not cause thermal imbalance of the reactor 105 but makes the device 10 very flexible.

In preferred embodiments, as represented in FIG. 1, the device 10 comprises: a flowmeter 185 of the syngas upstream of the mixing location and a recirculator 190, products entered in the deflection duct 170, controlled according to the measured flow.

The flow meter 185 may be of any type known to those skilled in the art that is suitable for measuring the flow of gas, such as an anemometer, a Coriolis flowmeter, a vortex flowmeter or an electromagnetic flowmeter, for example.

The recirculator 190 is similar to the recirculator 155 in structural terms. The control of this recirculator 190 is carried out as a function of the flow rate measured by the flow meter 185 and a set flow rate value 187. If the measured flow rate is lower than a predetermined set flow 187, the recirculator 190 is actuated in such a way that fill the difference between the measured flow rate and the set flow 187 by an equivalent flow of synthetic natural gas.

In preferred embodiments, the device 10 comprises means 145 for separating carbon dioxide from the dehydrated synthetic natural gas positioned downstream of the bypass 140.

The implementation of the device 10 object of the present invention makes it possible to obtain synthetic methane close to the specifications of the gas network requiring few additional operations.

In addition, the device 10 can thus be used for a pressure range of between 1 bar and 100 bar and a temperature range between 230 ° C. and 700 ° C.

FIG. 2, which is not to scale, shows a schematic view of one embodiment of the device 20 of the present invention. This device 20 for producing synthetic methane is similar to the device 10 described with reference to FIG. 1. Thus, the references 205, 210, 215, 220, 225, 227, 230, 235, 240, 250, 255, 260, 262, 265, 270, 275, 280, 285, 287 and 290 of the device 20 correspond to references 205, 110, 115, 120, 125, 127, 130, 135, 140, 150, 155, 160, 162, 165, 170 , 175, 180, 185, 187 and 190 of the device 10.

The device 20 further comprises a carbon dioxide separation means 245 of dehydrated synthetic natural gas positioned upstream of the bypass 240. This separation means 245 may be positioned upstream or downstream of the separation means 225. 'water.

FIG. 3 shows, in the form of a logic diagram of steps, a particular embodiment of the method that is the subject of the present invention. This process for the production of synthetic methane comprises: a methanation reaction step 305 comprising: a step 310 of entry into a methanation reactor, of syngas produced by gasification of hydrocarbon material, via a feed pipe of syngas and - an exit step 315 for synthetic natural gas, - a water separation step 320 comprising: - an entry step 325 for synthetic natural gas and - an exit step 330 for dehydrated synthetic natural gas and a step 335 of bypassing a portion of the dehydrated synthesis natural gas leaving the exit step of the water separation step to the syngas feed line so that a mixture of the syngas and derived synthetic natural gas is supplied to the reactor.

This method is carried out, for example, by a device 10 or object of the present invention and described with reference to FIGS. 1 or 2.

It should be noted that FIGS. 4 to 7 are the result of simulations carried out to determine the impact of the device and method that is the subject of the present invention. These results are compared with a simulation of a recirculation case without dehydration, as is the case for example in the first stage of the boiling water reactor, for example. The purpose of the device and method that are the subject of the present invention is also to minimize the steps of setting the specifications while operating a mono-stage methanation at moderate pressure and acceptable in terms of costs. For these same reasons, the SNG is preferentially compressed at the end of the production line after the separations required for the injection on the network. The simulations carried out and presented below were carried out at 8 bar and a methanation temperature of 320 ° C.

FIGS. 4 and 5 respectively represent the Wobbe index and the SNG PCS before the H2 separation for the wet SNG recirculation reference configuration, the dehydrated SNG recirculation and the dehydrated and decarbonated SNG recirculation.

These results are presented as a function of the recirculation rate, which corresponds to the ratio of the flow rates to the normal pressure and temperature conditions of the recirculated flow and the flow of syngas. For the "reference configuration", the recirculated flow is replaced by a wet SNG flow equivalent to the flow passing through the deflection pipe.

FIG. 4 shows, on the ordinate, the Wobbe index of the synthetic natural gas produced by the device, 10 or 20, as a function of the recirculation rate, on the abscissa, and the nature of the recirculated synthetic natural gas. at the reactor inlet, 105 or 205, methanation.

It is observed, in particular, that recirculation of wet synthetic natural gas 405 has no effect on the Wobbe index of the synthetic natural gas produced by the device.

It is further observed that recirculation of dehydrated synthetic natural gas 410 improves the Wobbe index of the synthetic natural gas produced by the device.

It is observed, finally, that the recirculation of dehydrated and decarbonated synthetic natural gas 415 further improves the Wobbe index of the synthetic natural gas produced by the device, even with a recirculation rate of less than two.

FIG. 5 shows, on the ordinate, the PCS of the synthetic natural gas produced by the device, 10 or 20, as a function of the recirculation rate, on the abscissa, and on the nature of the recirculated synthetic natural gas at the inlet of the reactor, 105 or 205, methanation.

It is observed, in particular, that recirculation of wet synthetic natural gas 505 has no effect on the PCS of the synthetic natural gas produced by the device.

It is further observed that recirculation of dehydrated synthesis natural gas 510 improves the PCS of the synthetic natural gas produced by the device.

Finally, it can be observed that the recirculation of dehydrated and decarbonated synthetic natural gas 515 further improves the PCS of the synthetic natural gas produced by the device, even with a recirculation rate of less than two. According to the results obtained in terms of Wobbe index and PCS, the recirculation rate of the wet gas, ie the reference configuration, has no impact on the quality of the gas and shows that the separation H2 is essential to achieve injection specifications. Recirculation after simple dehydration or with decarbonation leads to a more or less significant increase in the Wobbe index and the PCS. These improvements could be interpreted as being the result of a simple dilution but Figure 6 highlights a real improvement in reaction equilibrium with a drastic drop in the molar flow of H2 at the device output 10 or 20.

FIG. 6 shows, on the ordinate, the molar flow of H2 at the outlet of the device, 10 or 20, as a function of the recirculation rate, on the abscissa, and on the nature of the recirculated synthesis natural gas at the inlet of the reactor, 105 or 205, of methanation.

It is observed, in particular, that recirculation of wet synthetic natural gas 605 has no effect on the molar flow of H2 at the outlet of the device.

It is observed, moreover, that the recirculation of dehydrated synthetic natural gas 610 causes a reduction in the molar flow of H2 at the outlet of the device.

It is observed, finally, that the recirculation of dehydrated and decarbonated synthetic natural gas 615 also causes a reduction in the molar flow of H2 at the outlet of the device.

Despite dilution by recirculation, the CO / H2O ratio is retained at the reactor inlet. Thus, the risk of deactivation of the coking methanation catalyst remains relatively low. Between the two devices, 10 and 20, the decarbonation upstream of recirculation of the synthetic natural gas seems more effective in terms of molar reduction of H2. Thus, to meet the criteria of injectability, a recirculation flow 4 to 8 times greater is required in simple dehydration compared to the solution with decarbonation. For the operating conditions used for the simulation, and when only the dehydration is carried out before recirculation, the minimum recirculation rate necessary to avoid the separation of H2 is estimated at 1.6. When the dehydration is completed by a decarbonation step, the required rate is of the order of 0.2. These respective rates effectively meet the constraints related to the injection but requires, however, an internal reactor cooling system to maintain the isothermicity and can not in this case not be applied to uncooled fixed bed technologies. With regard to the exchanger reactors, the boiling water or fluidized bed reactor, this novelty, under these operating conditions, makes it possible to reduce the exchanger surface by 10% and 25%, respectively.

FIG. 7 makes it possible to visualize the evolution of the normalized exothermicity of the reactor, ie the heat to be evacuated with respect to a case without recirculation, as a function of the recirculation rate for the reference configuration and the two devices, 10 and 20, described above.

FIG. 7 shows, on the ordinate, the exothermicity of the methanation reaction of the device, 10 or 20, as a function of the recirculation rate, on the abscissa, and on the nature of the recirculated synthesis natural gas at the inlet of the reactor , 105 or 205, of methanation.

It is observed, in particular, that recirculation of wet synthetic natural gas 705 reduces the exothermicity of the methanation reaction.

It is further observed that recirculation of dehydrated synthetic natural gas 710 also reduces the exothermicity of the methanation reaction.

It is observed, finally, that the recirculation of dehydrated and decarbonated synthetic natural gas 715 also reduces the exothermicity of the methanation reaction.

It appears that the increase in the recirculation rate leads to a linear decrease in the exothermicity of the reactor. Here, the recirculated SNG plays the role of thermal flywheel which is more marked in the presence of H2O because of a higher caloric capacity. The condition of thermal ideality of the devices 10 and 20 is reached for a recirculation rate of the order of 6.4 for an operation at 8 bar and a methanation temperature of 320 ° C. This level of recirculation makes it possible to dispense with the internal exchanger of the reactor and the separation of H2 from specification. Beyond this, the reactor is allothermal and therefore requires extra heat to maintain the reactions.

The molar fractions of the H2, CO2, CO and CH4 species as a function of the recirculation rate for the different simulated configurations evolve in the direction of improving the quality of the SNG. However, the molar fraction of CO increases drastically with the dehydrated SNG recirculation device. For the operating conditions under consideration, the threshold value is exceeded but an optimization of the system by adjusting the WGS vapor, the pressure and the reaction temperature make it possible to reach more acceptable levels. In this case, simple dehydration leads to over-focusing the CO2 content at the reactor inlet and shifts the equilibrium of the WGS reaction to CO production and H2 consumption. For the device 20, the CO2 extraction integrated in the recirculation loop makes it possible to favor the reaction of WGS towards the production of H2 which is then converted into Chk.

Claims

1. Device (10, 20) for producing synthetic methane, characterized in that it comprises: - a methanation reactor (105, 205) comprising: - an inlet (110, 210), for syngas produced by gasification of hydrocarbon material, connected to a syngas supply line (115, 215) and an outlet (120, 220) for synthetic natural gas, means (125, 225) for separating water comprising: inlet (130, 230) for synthetic natural gas and - an outlet (135, 235) for dehydrated synthetic natural gas and - a bypass (140, 240) of a part of the dehydrated synthetic natural gas from the outlet of the means separating water to the syngas feed so that a mixture, synthesized syngas and synthetic natural gas, is supplied to the reactor.

2. Device (20) according to claim 1, which comprises means (245) for separating carbon dioxide from dehydrated synthetic natural gas, said separating means being positioned upstream of the branch (240).

3. Device (10, 20) according to one of claims 1 or 2, which comprises: - a sensor (150, 250) a temperature inside the reactor and - a recirculator (155, 255), products entered in the bypass, controlled according to the temperature sensed.

4. Device (10, 20) according to one of claims 1 to 3, which comprises, upstream of the inlet of the reactor (105, 205), means (160, 260) for preheating, mixing at a temperature greater than 220 ° C.

5. Device (10, 20) according to one of claims 1 to 4, which comprises a pipe (165, 265) for injecting water vapor into the line (115, 215) supply syngas upstream where the syngas is mixed with the methanation products from the bypass (140, 240).

6. Device (10, 20) according to one of claims 1 to 5, which comprises a conduit (170, 270) deflection, a portion of the methanation reaction products, comprising: - an inlet (175, 275 ) positioned between the reactor outlet (105, 205) and the water separation means (125, 225) and - an outlet (180, 280) positioned upstream of the reactor inlet (110, 210) (105). , 205).

7. Device (10, 20) according to claim 6, which comprises: - a flowmeter (185, 285) of the syngas upstream of the place of mixing and - a recirculator (190, 290), products entered in the pipe (170 , 270), controlled according to the measured flow rate.

8. Device (10, 20) according to one of claims 1 to 7, wherein the means (125, 225) of water separation configured to cool the synthetic natural gas at a temperature between 5 ° C and 40 ° C.

9. Device (10, 20) according to one of claims 1 to 8, wherein the reactor (105, 205) is configured to perform a Dussan reaction called "gas to water".

10. Process (30) for producing synthetic methane, characterized in that it comprises: a step (305) of methanation reaction comprising: a step (310) of entry into a methanation reactor, of syngas produced by gasification of hydrocarbonaceous material, via a syngas feed line and - a step (315) of output for synthetic natural gas, - a step (320) of water separation comprising: - a step (325) of entry for synthetic natural gas and - an exit step (330) for dehydrated synthetic natural gas and - a step (335) for bypassing a portion of the dehydrated synthetic natural gas leaving the exit step of the step of separating water to the syngas feed so that a syngas and synthetic syngas-derived mixture is supplied to the reactor.