FR2943657A1 - PROCESS AND PLANT FOR PRODUCING COOLED AND COMPRESSED HYDROGEN - Google Patents

Abstract

In a process for producing hydrogen from a hydrocarbon feedstock comprising at least the steps of generating (3 a, 3) a hot crude synthesis gas, optional enrichment (5 a) in hydrogen of the raw synthesis gas hot, separation of hydrogen (3b, 5b) from the synthesis gas (crude or enriched) to obtain at least hydrogen (8, 8) and a waste gas (11, 11) compressing the hydrogen (8, 8) resulting from the separation to produce the hydrogen (10), in which two consecutive steps, the second being the separation step c) of the hydrogen contained in the synthesis gas (3, 5) and being carried out on a dedicated membrane, are combined in a membrane reactor (3, 5), the hydrogen compression step (8, 8) resulting from the separation step c) is carried out at least partly in a thermokinetic compressor 9a which simultaneously compresses and cools the hydrogen from the separation (8, 8) to produce compressed and cooled hydrogen (10a, 10a) using cooling water (12).

Description

Hydrogen production process and plant

The present invention relates to a method and an installation for the production of cooled and compressed hydrogen.

The process for producing hydrogen from hydrocarbons or fossil compounds comprises two major steps. The first step is the generation of syngas (a mixture of hydrogen, carbon monoxide, and other impurities) by steam reforming or auto-thermal reforming or partial oxidation.

It is followed by a second purification step, generally via an adsorption process called PSA which makes it possible to obtain hydrogen. The main steps of this process can themselves comprise other steps, depending on the nature of the process. and / or certain characteristics of the reactants and products, or depending on various constraints whether they are internal to the process or external. Thus, for a charge of light hydrocarbons, typically natural gas, it will be found in a conventional manner, and as illustrated in FIG. 1, at least the following stages: a step of hydrodesulfurization of the charge; pre-reforming step (optional), • a step of reforming methane with steam, (these three steps constituting the generation of synthesis gas (or syngas), a mixture of gases mainly containing hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2) and methane (CH4) in lesser amounts, as well as water, nitrogen, and other trace A CO conversion step (or shift) during which water is reacted with the CO of the syngas to enrich it with hydrogen; this reaction is carried out in a reactor generally called shift reactor, it is carried out at high, medium or low temperature (High Temperature Shift or HTS, Medium Temperature Shift or MTS, Low Temperature Shift or LTS); the gas produced is a syngas enriched in H2 and CO2, and highly depleted in CO. A hydrogen purification stage by pressure swing adsorption (or Pressure Swing Adsorption) which produces hydrogen, and at least one waste gas which is currently returned to the stage of generation of syngas (these latter stages constituting the main steps implemented during purification of hydrogen via the adsorption process PSA).

Recently, developments have been made which make it possible to combine in a single reactor the production of syngas and its purification in order to produce hydrogen via a membrane reactor. In this type of multifunctional reactor, the produced syngas is immediately in contact with a membrane that is passed through by hydrogen. Palladium membranes, which are used for their high temperature hydrogen permeability properties, are particularly suitable for this purpose. Two types of membrane reactors have thus been developed: The first type of membrane reactor considered combines the steam reforming reaction and the purification of the syngas. Thus, according to this diagram, illustrated in FIG. 2, for a charge of light hydrocarbons, typically natural gas, at least the following steps can be found, for example: a step of hydrodesulfurization of the feedstock; pre-reforming step (optional), • a stage of generation of the synthesis gas by vapor-reforming with methane vapor, coupled to a step of separating hydrogen on a palladium membrane in a membrane reactor, • an optional step of Adiabatic compression of the hydrogen produced (according to the customer's request). The second type of membrane reactor considered combines the conversion reaction of CO contained in syngas and the separation of hydrogen on palladium membrane. Thus, according to this scheme, and as illustrated in FIG. 3, for a light hydrocarbon feedstock, typically natural gas, there will be found, for example, at least the following stages: a step of hydrodesulfurization of the charge, • a pre-reforming stage (optional), • a vapor-reforming stage with methane vapor, • a shift stage, performed at medium or high temperature, coupled to a hydrogen separation step on palladium membrane in a membrane reactor, • an optional adiabatic compression step of the produced hydrogen (according to the customer's request). Membrane reactor technology has the advantage of considerably simplifying the steps of the hydrogen production process. At least the shift reactor and the PSA are indeed removed.

However, the hydrogen produced at the outlet of the membrane reactor is at low pressure. Typically, the hydrogen outlet pressure is at most 1 bar abs.

Since the customer needs high pressure hydrogen most of the time, it is necessary to compress the hydrogen. A known solution used consists of using an adiabatic compressor.

However, this equipment represents a significant investment, and subsequently a significant cost of operation. The compression of hydrogen from one to twenty bar, via this type of compressor, in fact induces high electrical consumption. Typically, to compress 50 000 Nm3 / H of hydrogen from 1 to 4 bar, the power consumption reaches 3 MW.

In addition, the hydrogen at the outlet of the membrane reactor is hot. A known solution implemented is to recover this heat for the production of steam. However, this production of steam, which is almost systematically associated with the process, generally exceeds the needs of the process, and it is necessary to find a client user of the steam in order to exploit the heat of hydrogen and synthesis gas. . There is therefore a need for a heat recovery of the hydrogen leaving a membrane reactor other than the production of steam associated with the process. The object of the present invention is therefore to propose a process for compressing the purified product hydrogen in which the electrical consumption is greatly reduced compared with the prior art, and a process for cooling hydrogen which values the heat in exit in another way. To this end, the invention proposes compression of the (very) hot hydrogen available at the outlet of the membrane reactor - whether of the first type, that is to say combining a reforming step and a separation step. hydrogen, or the 2nd type, that is to say combining a shift step and a step of hydrogen separation-by direct injection of liquid water using a thermokinetic compressor that will allow compress the hydrogen while cooling it suddenly. This step makes it possible to partially compress the hydrogen, from 2 to 5 bar as a function of the temperature of the hydrogen stream which can be between 320 ° C. and 550 ° C., and thus to limit the costs of the adiabatic compression. Moreover, the partial cooling of the hydrogen that accompanies this compression makes it possible to limit or even eliminate the steps of subsequent cooling. The residual gas from the membrane separation, composed of CH4, CO, H2O, CO2 at high pressure and high temperature, can be directly used as a fuel in the fired heater, which supplies the heat needed to preheat the feed (gas natural and steam) for the first type of reactor where the steam reforming is combined with the purification or directly in the steam reforming furnace for the 2nd type of reactor or recycled as a reagent in the reformer. Two particularly advantageous simultaneous effects are thus combined: • an increase in the pressure of hydrogen, • a quenching of hydrogen. The thermokinetic compressor allows the self-consumption of thermal energy by the hydrogen itself, thus ensuring its immediate recovery. Indeed, a thermokinetic compressor compresses a gas by accelerating it to a high speed, preferably greater than the speed of sound (typically of the order of 330 m / s), by cooling it, for example by direct contact with water droplets, and slowing it down. Cooling can take place before, during or after acceleration. The acceleration can be produced by forcing the gas to pass through a neck, for example a Laval pass. Similarly to decelerate the gas, it is passed in a second neck, for example a Laval pass. The energy required by the thermokinetic compressor is provided by the hydrogen produced at the outlet of the membrane reactor; the preferred coolant is water, which is subsequently advantageously separated and recycled as a coolant.

An example of a thermokinetic compressor is described in the patent application FR-A-2805008. The principle is based on the cooling of a hot gas by vaporization of liquid water in fine droplets, followed by its compression, all using an arrangement of convergent and divergent nozzles. Figure 4 shows a model of thermokinetic compressor according to this concept.

According to its first object, the invention provides a process for producing hydrogen from a hydrocarbon feedstock comprising at least a) a step of generating a hot raw synthesis gas, b) an optional enrichment step hydrogen, hot crude synthesis gas for obtaining an enriched synthesis gas; c) a step of separating hydrogen from the raw synthesis gas (or enriched) to obtain at least one of hydrogen and a waste gas, d) a step of compressing hydrogen from the separation to produce hydrogen at the required pressure, wherein two consecutive steps, the second being the separation step c) of the hydrogen contained in the synthesis gas, and being produced on a dedicated membrane, are combined in a membrane reactor, characterized in that the compression step d) of the hydrogen resulting from the separation step c) is carried out at least partly in a compress A thermokinetic device that simultaneously compresses and cools hydrogen from c) to produce compressed and cooled hydrogen using a coolant.

According to a particular embodiment of the invention, steps a) and c) are combined in the membrane reactor to produce a flow of hydrogen at a temperature of between 450 ° C. and 600 ° C., preferably between 500 ° C. and 550 ° C and a pressure of the order of a few absolute bar or less, preferably less than or equal to 1 bar abs.

According to another embodiment of the invention, the gas entering the membrane reactor being the crude synthesis gas resulting from stage a), the first of the two stages carried out in the membrane reactor is the stage of enrichment of the membrane reactor. hydrogen synthesis gas, the second step being the step of separating the hydrogen contained in said enriched synthesis gas, the hydrogen resulting from the separation step is at a temperature of between 300 ° C. and 450 ° C. C, preferably between 320 ° C. and 440 ° C., and a pressure of the order of a few absolute bars or less, preferably less than or equal to 1 bar abs. Preferably, the compressed and cooled hydrogen exiting the thermodynamic compressor is subjected to a complementary compression step to produce pure hydrogen at the required final pressure. The coolant is preferably liquid water. Advantageously, the separation of hydrogen is carried out using a palladium membrane. Advantageously, the hydrocarbon feedstock feeding step a) is previously desulfurized, and optionally pre-reformed. According to another subject of the invention, this relates to a plant for producing hydrogen comprising at least one hydrocarbon feedstock, a membrane reactor for producing hydrogen, a thermokinetic compressor, means for supplying the membrane reactor with hydrocarbon feedstock, means for sending the gas from the membrane reactor to the thermokinetic compressor, means for supplying the thermokinetic compressor with cooling liquid. Alternatively, the hydrogen production plant according to the invention comprises at least one hydrocarbon feedstock, a reformer, a membrane reactor for producing hydrogen, a thermokinetic compressor, means for feeding the reformer with the hydrocarbon feedstock, means for feeding the reformer gas to the membrane reactor, means for supplying the gas from the membrane reactor to the thermokinetic compressor, means for supplying the thermokinetic compressor with cooling liquid. The invention will be described in more detail in connection with FIGS. 1 to 3, as well as 5 and 6, in which FIGS. 1 to 3 illustrate basic diagrams of known hydrogen production processes, FIGS. illustrating for their part basic schemes corresponding to hydrogen production processes according to the invention. FIG. 4 shows a thermokinetic compressor as described in the prior art. According to FIG. 1, a light hydrocarbon feedstock, here natural gas (NG) feeds a hydrodesulfurization reactor 1. The desulphurized feedstock, to which the steam feeds a pre-reformer 2 (optional), then the desulfurized (and optionally pre-reformed) feedstock is introduced into a steam methane reformer 3 to produce a synthesis gas 4 containing as major components essentially H2, CO, CO2. The syngas 4 thus generated is then processed to produce hydrogen; for this, it passes into the shift reactor 5 where the carbon monoxide reacts with water vapor (not referenced) in the presence of a catalyst adapted to produce hydrogen and carbon dioxide and deliver a gas 6 highly enriched in hydrogen and carbon dioxide and depleted in carbon monoxide. The hydrogen-rich syngas 6 is then introduced into a PSA unit 7 where the various constituents are separated to provide purified hydrogen 10 and at least one waste gas 11 which is recycled to the reforming stage. According to the scheme of FIG. 2, which incorporates known recent developments, the light hydrocarbon feedstock undergoes the same known stages until the desulfurized and optionally pre-reformed hydrocarbon feedstock is obtained.

It is then introduced into the membrane reactor 32, which is of the first type according to the terms of the invention, that is to say that it combines a vapor reforming reaction at 32a and a separation step of hydrogen on a palladium membrane in a 32b membrane reactor, to supply purified hydrogen 82 at a temperature T82 and a pressure P82 and a waste gas 11 which is recycled to the inlet of the membrane reactor 32. The hydrogen 82 is then subjected to a compression step in an adiabatic compressor 92 to obtain hydrogen 102 at the required pressure, according to the customer's request. According to the scheme of FIG. 3, which also includes recent known developments, the feed undergoes the same steps until the desulfurized hydrocarbon feedstock is obtained at the outlet of the optional pre-reformer 2.

The hydrocarbon feed is then introduced into a steam methane reformer 33 to produce a synthesis gas 43 containing essentially H2, CO, CO2. The synthesis gas thus generated is then introduced into a membrane reactor 53, which is of the second type according to the terms of the invention, that is to say that it combines a shift reaction at 53a and a separation step. of hydrogen on a palladium membrane in a 53b membrane reactor, to provide purified hydrogen 83 at a temperature T83 and a pressure P83 and a waste gas 113 which is recycled at steam reforming, in the charge stream incoming process, and / or in the reformer 33, as a fuel that provides heat for the reaction.

The hydrogen 83 then undergoes an adiabatic compression step in an adiabatic compressor 93 to obtain hydrogen 103 at the pressure required by the customer. According to FIG. 5, in accordance with the invention, the light hydrocarbon feed undergoes all the hydrogen production steps described in FIG. 2 making it possible to obtain purified hydrogen 82 at a temperature T82 and a pressure P82 and a waste gas 112. This purified hydrogen leaves hot from the membrane reactor, and at a pressure of the order of atmospheric pressure. In order to be in accordance with the needs of the customer, the hydrogen then passes into the thermokinetic compressor 8a where it is compressed and brutally cooled by direct injection of liquid water 12. A flow of cooled hydrogen 102a is obtained at the output of the thermokinetic compressor. at a temperature T102a, compressed at a pressure P102a and having an increased water content of the amount of cooling water injected. The water contained is recovered, it is then recycled as cooling water 12. The hydrogen 102a then undergoes, depending on the final needs, a complementary compression stage 9b, in an adiabatic compressor, intended to bring it to the pressure P102 required, for example slightly greater than the pressure of the network for which it is intended. According to FIG. 6, in accordance with the invention, the light hydrocarbon feedstock undergoes all the hydrogen production steps described in FIG. 2 making it possible to obtain purified hydrogen 83 at a temperature T83 and a pressure P83 and a waste gas 113. This purified hydrogen leaves hot from the membrane reactor, and at a pressure of the order of atmospheric pressure. In order to be in accordance with the needs of the customer, the hydrogen then passes into the thermokinetic compressor 8a where it is compressed and brutally cooled by direct injection of liquid water 12. A cooled flow of hydrogen 103a is obtained at the outlet of the thermokinetic compressor. at a temperature T103a, compressed at a pressure P103a and having an increased water content of the amount of cooling water injected. The water contained is recovered, it is then recycled as cooling water 12. The hydrogen 103a then undergoes, as needed, a complementary compression stage 9b, in an adiabatic compressor, intended to bring it to the water. pressure P103 required, for example slightly greater than the pressure of the network for which it is intended. The passage of the hydrogen leaving the membrane reactor in the thermokinetic compressor 12 making it possible to increase the hydrogen pressure offers, among other advantages: a reduction in the compression energy necessary to bring the hydrogen up to the pressure of the network, • a reduction in the costs of adiabatic compression, both in terms of investments, as well as operating costs, particularly energy consumption • cooling of the hot outgoing hydrogen from the membrane reactor, • heat utilization contained in the hydrogen leaving the membrane reactor in the process itself.

The basic schemes above are given for steam methane reformers (SMR). The schemes with the 2nd type membrane reactor where the CO conversion reaction is combined with hydrogen purification can be extended to other types of reactors. These include, but are not limited to, partial oxidation reactors (PDX) and auto thermal reforming (ATR) reactors.

Claims (9)

REVENDICATIONS1. A process for producing hydrogen from a hydrocarbon feedstock comprising at least a) a step of generating (32a, 33) a hot raw synthesis gas; b) an optional step of enriching (53a) with hydrogen hot crude synthesis gas for obtaining an enriched synthesis gas; c) a step of separating hydrogen (32b, 53b) from the raw synthesis gas (or enriched) to obtain at least one less than hydrogen (82, 83) and a waste gas (112, 113); d) a step of compressing hydrogen (82, 83) from the separation to produce hydrogen (10), wherein two consecutive steps, the second being the separation step c) of the hydrogen contained in the synthesis gas (32, 53), and being carried out on a dedicated membrane, are combined in a membrane reactor (32, 53), characterized in that the step of compressing d) hydrogen (82, 83) from the separation step c) is carried out at least in part by ns a thermokinetic compressor 9a which simultaneously compresses and cools hydrogen from c) to produce compressed and cooled hydrogen (102a, 103a) using a coolant (12). The process according to claim 1 wherein step b) is not carried out, and steps a) and c) are combined in membrane reactor 32 to produce a flow of hydrogen (82) at a pressure P82 of the order of a few absolute bars or less, preferably less than or equal to 1 bar abs, and a temperature T82 between 450 ° C and 600 ° C, preferably between 500 ° C and 550 ° C. 3. The process as claimed in claim 1, in which the gas entering the membrane reactor 53 being the crude synthesis gas from step a), the first of the two steps carried out in the membrane reactor is the enrichment step 53a. hydrogen synthesis gas by CO conversion, the second step being the separation step 53b of the hydrogen contained in said enriched synthesis gas, wherein the hydrogen from the separation step is at a temperature T83 between 300 ° C and 450 ° C, preferably between 320 ° C 440 ° C, and a pressure P83 of the order of a few absolute bar or less, preferably less than or equal to 1 bar abs. 4. Method according to one of the preceding claims wherein the compressed and cooled hydrogen (102a, 103a) is subjected to a complementary compression step to produce pure hydrogen at the final pressure P102 required. 5. Method according to one of the preceding claims wherein the coolant (12) is water. 6. Method according to one of the preceding claims wherein said separation of hydrogen is carried out using a palladium membrane. 7. Method according to one of the preceding claims wherein the hydrocarbon feedstock in step a) is previously desulfurized, and optionally pre-reformed. 15 8. Hydrogen production plant suitable for carrying out the process of claim 2 comprising at least one hydrocarbon feedstock, a membrane reactor (32) for producing hydrogen (82), a thermokinetic compressor (9a), means for supplying the membrane reactor with the hydrocarbon feedstock; means for feeding the gas from the membrane reactor to the thermokinetic compressor; means for supplying the thermokinetic compressor with cooling liquid. 9. Hydrogen production plant suitable for carrying out the process of claim 3 comprising at least one hydrocarbon feedstock, a reformer (33), a membrane reactor (53) for producing hydrogen (83), a thermokinetic compressor (9a), means for supplying the reformer with the hydrocarbon feedstock, means for feeding the reformer gas to the membrane reactor, means for feeding the gas from the membrane reactor to the thermokinetic compressor, means for supplying the thermokinetic compressor in coolant5