FR2932792A1 - PROCESS FOR PRODUCING SYNTHESIS GAS BY HYDROCARBON VAPOR REFORMING USING OXYGEN-ENRICHED AIR AS A FUEL - Google Patents

Abstract

The invention relates to a process for producing a synthesis gas by catalytic steam reforming of a hydrocarbon feedstock with production of the heat required for reforming by means of combustion, said step being carried out in a reformer comprising at least one combustion chamber provided with reforming tubes, as well as burners supplied with fuel and oxidizer to provide by combustion said heat necessary for reforming, and a convection chamber for evacuating the fumes emitted by the combustion; according to the invention, the reforming step uses an oxidizer consisting of air enriched with oxygen. In particular, the enrichment of the air is obtained through the recovery of the evaporation oxygen from a storage of liquid oxygen located nearby. The invention also relates to a combined installation of a source of oxygen-rich gas, preferably a storage of liquid oxygen, and a steam reforming plant for hydrocarbons.

Description

The present invention relates to a process for producing a synthesis gas from a light hydrocarbon feedstock comprising at least one step of generating a raw synthesis gas by catalytic steam reforming of said hydrocarbon feedstock with production of the heat necessary for reforming by means of combustion. The invention applies in particular to synthesis gas productions used in installations located near a potential source of oxygen in the form of a gaseous stream rich in oxygen.

It will come for example large storage of liquid oxygen, that is to say, storage containing significant amounts of liquid oxygen and which produce a rate of gaseous oxygen evaporation, also known as boil off sent conventionally in the atmosphere, but can be valued. Indeed, in any liquefied gas storage, the storage is recovered from the sky (that is to say from the space above the surface of the liquid and containing the gas in equilibrium with the storage liquid) a gaseous stream coming from the evaporation of this liquid. The potential source of oxygen may also be a gaseous stream rich in oxygen from a production of nitrogen of which it is a by-product. These gaseous currents, since they are richer in oxygen than the air conventionally used as oxidizer for steam reformer burners, and they contain no other reactive gas vis-à-vis of the combustion, can be used to enrich in oxygen the air for supplying the oxidant to the steam reformer burners. Because of the endothermic reactions used, the processes for producing synthesis gas by steam reforming a light hydrocarbon feedstock for example in the production of hydrogen and / or carbon monoxide, alone or in mixture, use heat provided by a combustion reaction. These processes therefore require very large quantities of air for the burner feed; the air containing about 21 mol% of oxygen, that means that 79% of the quantity of air injected for combustion is compressed, heated, circulates in the pipes, then, after combustion, is cooled, compressed and finally evacuated without reacting during combustion. It is therefore necessary to evacuate large amounts of smoke. The equipment necessary for the supply of combustion air and its treatment, as well as the evacuation of fumes, and in particular air compressors (blowers) and / or flue gases, as well as the pipes and heat exchangers heat must therefore be dimensioned accordingly.

The cost of reforming facilities is very high, and the person skilled in the art is constantly seeking solutions enabling him to reduce costs and / or to improve the production efficiency of his installations. Thus, oxygen is available in certain situations, for example from storage of liquid oxygen or nitrogen production units, which is generally not or poorly valued. At the same time, hydrocarbon steam reforming processes for the production of syngas use air as an oxygen supplier for combustion.

The proximity between a first facility with non-upgraded oxygen and a second facility that can advantageously benefit from an additional supply of oxygen therefore represents a valuation opportunity. The object of the present invention is to limit the sizing of a number of equipment constituting the combustion air / smoke circuit of a reforming process. Another object of the invention is to increase the production of gas. summary of an existing unit. The invention also has the advantage of recovering oxygen which is otherwise lost or poorly valued.

For this purpose, the subject of the invention relates to a process for producing a synthesis gas from a light hydrocarbon feedstock comprising at least one step of generating a raw synthesis gas by catalytic reforming at the vapor of said hydrocarbon feedstock with production of the heat required for reforming by combustion, said step being carried out in a reformer comprising at least: - a combustion chamber provided with reforming tubes filled with reforming catalyst , able to circulate a mixture containing the hydrocarbon feedstock and water vapor, so as to recover raw synthesis gas at the outlet of the tubes, and burners fed with fuel and with oxidant and able to supply by combustion said heat necessary for reforming, - a convection chamber in relation to said combustion chamber adapted to evacuate the fumes emitted by combustion, characterized in that said step e reforming uses an oxidizer consisting of air enriched with oxygen. The additional oxygen supply makes it possible, for an existing installation with the given dimensions, to increase the heat input, and thus allows an increased production of synthesis gas (debottlenecking of an existing installation).

In the case of a new installation, enriching the air with oxygen makes it possible for a given production to reduce the size of the equipment necessary for the implementation of the steps downstream of the additional oxygen injection step. . According to a preferred variant of the invention, the process comprises at least one step of producing oxygen-enriched air with: a) providing an oxygen-rich gas stream; b) injecting said gas-rich gas stream; oxygen in an air flow intended for supply by oxidizing burners to form an oxygen-enriched air flow, said injection being done either upstream of step c) or downstream of step c) c) compression of the air, which can be enriched according to b), by passage through an air blower, d) preheating, not mandatory, compressed enriched air during at least indirect heat exchange with fumes e) supply of the reformer burners in said enriched air and in fuel. At the end of the combustion, the hot fumes are recovered, cooled by indirect heat transfer, with various fluids, frequently at least one heat transfer according to step d). The cooled fumes are vented to the atmosphere via a chimney. The choice of the injection point (before or after the air blower) depends on the pressures of the different flows. In order to be injected into the air stream for the burner feed, the flow of oxygen enriching gas must be at a pressure greater than that of the air flow into which it must be injected. If its pressure is sufficient, it can be injected downstream of the blower, if its pressure is lower, it must be injected into the air circuit upstream of the air blower (it being understood that its pressure must in all the cases be greater than that of the air, that is to say in general, the atmospheric pressure). By flow of oxygen-rich gas is meant a flow of gas whose oxygen content is greater than the oxygen content of the air, ie more than 21 mol%. It must also not have vis-à-vis the combustion function other than that of oxidant, and in particular, it is desirable that it contains no combustible gas. Various sources containing oxygen may be used for this purpose. Since industrial sites often include a variety of related or independent products, it may be possible, depending on the case, to have facilities for the production of syngas, a storage of liquid oxygen, a nitrogen production unit, or other facilities for providing a gaseous stream rich in oxygen, which can be used in the context of this invention.

According to a preferred variant, when the oxygen-rich stream is injected before the compression step c), the enriched air stream feeding stage c) has an oxygen content of between 21 and 25 mol%, preferably between 21 and 23.5 mol%. Indeed, some materials used for the implementation of the method operating in a conventional manner with air are not necessarily adapted when the oxygen content is too important. Beyond a certain oxygen content in the enriched air, it will be necessary to use stainless steel designed equipment, which in the case of the air blower for example represents a substantial investment that would make the process less attractive. Moreover, even if the oxygen-rich gas is injected downstream of the blower, it will be necessary to take into account the problems which can be generated by the increase in the combustion temperature when the oxygen content is higher, among which the holding in temperature of burners and tubes, both for an existing installation and for a planned installation.

Particularly advantageously, the flow of oxygen-rich gas originates for all or part of an evaporation oxygen flow emitted by a storage of liquid oxygen located near the reformer. Since the storage is sufficiently close (a few hundred meters) and sufficiently large (from a few hundred thousand to several million liters of liquid O2), the use of evaporation oxygen becomes economically viable. Oxygen is available at a pressure sufficient to be injected upstream of the air blower without having to previously raise its pressure. It should be noted that the removal of oxygen evaporation does not harm the security of said storage, in fact it has a conventional manner of a series of security elements for controlling and ensuring the maintenance of a adapted pressure in the sky of storage. among which at least one pressure controller and a heating circuit which allows, if necessary, to vaporize liquid oxygen to the gas. According to another aspect of the invention, it relates to a combined installation capable of implementing the above method, comprising at least: a source for supplying the oxygen-rich gas, a steam reformer, comprising a combustion chamber and a convection chamber, the first being provided with reforming tubes filled with reforming catalyst and burners capable of being supplied with fuel and with oxidant, and the second chamber, in connection with the first, being suitable discharging fumes emitted into the first chamber, as well as, - means ensuring circulation of the oxidant for combustion, comprising at least one combustion air inlet, a blower, means for the indirect preheating of the oxidant and / or other fluids by the fumes emitted, as well as pipes connecting these various means, means for recovering the oxygen-rich gas, means for injecting said rich gas, and n oxygen in the combustion air to produce enriched air, as well as pipes suitable for the transport of oxygen-rich gas, combustion air, oxygen-enriched air and fumes emitted during combustion. combustion. According to a preferred variant of installation, it concerns a combined installation in accordance with the installation described above, in which the source supplying the oxygen-rich gas comprises a storage of liquid oxygen in which a gaseous sky is provided. above the liquid, and means for recovering all or part of a flow of evaporation oxygen emitted by the storage. The invention will now be described with reference to the accompanying single figure and the accompanying example. It should be understood that this is a particular embodiment of the invention given by way of non-limiting example, and that the invention is not limited to this embodiment. The figure shows a diagram illustrating a preferred embodiment of the invention for the recovery of oxygen taken from the evaporation system of a liquid oxygen storage and its use for enriching the combustion air supplying the burners. of a steam reformer for the production of synthesis gas according to the invention. Liquid oxygen is contained in the storage tank 1. The oxygen is stored therein as a liquid. The liquid oxygen does not occupy the entire volume of the tank, a gaseous sky 1A is formed above the surface of the liquid. A stream 2 of gaseous oxygen is taken from the air Gaseous oxygen 2 passes first into the valve 3, then is fed via line 4 to the point 5 where it is injected into the combustion air 6 thus forming with the latter enriched combustion air 7. The enriched air 7 then passes into the blower 8 which produces a compressed enriched air 9 which is the oxidant that will supply the reformer. The enriched air 9 is then used in accordance with the usual practice of those skilled in the art; it is in particular preheated at 10 in the convector chamber of the reformer, then sent to the burners where mixed with fuel 11 (conventionally formed of natural gas 12 supplemented with process waste gases 13); it provides the oxygen necessary for combustion.

The fumes emitted during the combustion are evacuated via the convection chamber where they provide heat, in particular, but not only to the enriched air 9, they are finally discharged to the atmosphere via the chimney 14. The pressure in the gaseous sky 1A storage is controlled by a PIC-type pressure controller 20. A heating circuit 21 makes it possible, if necessary, to vaporize liquid oxygen towards the gaseous sky.

Embodiment of the invention: An industrial site comprising an oxygen storage and a reformer; the storage of liquid oxygen produces 200 Nm3 / h of evaporation oxygen (boil off) at a pressure of 50mbarg, the reformer makes it possible to produce 10,000 Nm3 / h H2, the storage is at a distance of 300 meters The reformer, in conventional operation, consumes 20,000 Nm3 / h air, or 4,200 Nm3 / h 02 (taking into account the content of 02 air, 21% mol). By applying the method of the invention, the air is enriched by supplying the gaseous oxygen evaporation produced by the storage, ie 200 Nm3 / h 02. The pressure drop experienced during the passage in the 300m of pipe is of the order 10mbar. According to a first embodiment of the invention (Case A): the synthesis gas production process operates at a constant O 2 need: - thanks to the supply of oxygen from the storage, it will be possible to reduce the air supply, - the oxygen to be supplied by the air is reduced to (4,200 to 200) or 4,000Nm3 / h, - to supply this quantity of oxygen, it will be enough (4,000 / 0.21) = 19 050 Nm3 / h, - the volume of enriched air circulating in the blower, then in the air preheating circuit is according to this first embodiment of the invention of 19 250Nm3 / h instead of 20 000Nm3 / h according to the conventional method.

This corresponds to a gain of 5% in the design of blowers and exchangers, both air side and smoke side. The oxygen-enriched air has an O 2 content of less than 21.9% which is much lower than the preferred limit of 23.5% of O 2 and thus allows the use of conventional steel and not special steel in the blower. - * According to a second embodiment of the invention (Case B): it is desired to degoulotter the existing installation: - thanks to the increase in the amount of available oxygen, we will be able to increase the production of synthesis gas the oxygen that can be supplied by the enriched air is (4200 +200) or 4400 Nm3 / h, or a gain close to 5%, the volume of enriched air circulating in the blower, then in the air preheating circuit is according to this second embodiment of the invention of 200Nm3 / h instead of 20 000Nm3 / h according to the conventional method. This corresponds to a 1% increase in the volume flowing in the air blower and in the air preheater exchangers.

The volume of fumes remains unchanged. Oxygen enriched air has an O 2 content of less than 21.8%.

Claims (6)

REVENDICATIONS1. A process for producing synthesis gas from a light hydrocarbon feedstock comprising at least one step of generating a raw synthesis gas by catalytic steam reforming of said hydrocarbon feedstock with production of heat required for reforming by combustion, said step being carried out in a reformer comprising at least: - a combustion chamber provided with reforming tubes filled with reforming catalyst, able to circulate a mixture containing the charge of hydrocarbons and water vapor, so as to recover at the output of the tubes the raw synthesis gas, and burners fueled and oxidant and able to provide by combustion said heat required for reforming, - a convection chamber in relationship with said combustion chamber adapted to evacuate the fumes emitted by combustion, characterized in that said reforming step uses an oxidizer constituted oxygen enriched air. 2. Method according to claim 1 comprising at least one oxygen-enriched air production step with: a) provision of a flow of oxygen-rich gas, b) injection of said gaseous oxygen flow into a flow of oxygen-rich gas, air for supplying the combustion of burners to form a stream of air enriched with oxygen, said injection being done either upstream or downstream of step c), c) compression of the air, which can be enriched according to b), by passage through an air blower, d) preheating, not mandatory, of the enriched air by at least indirect heat exchange with the fumes emitted during combustion, e) supply of the reformer burners in said enriched air compressed and possibly preheated, as well as in fuel. 3. Method according to claim 2 wherein the flow of oxygen-rich gas is injected before the compression step c), characterized in that the enriched air stream feeding step c) has an oxygen content between 21 and 25 mol%, preferably between 21 and 23.5 mol%. 4. The method of claim 2 or claim 3 wherein the oxygen-rich gas stream comes for all or part of a flow of evaporation oxygen emitted by a storage of liquid oxygen located near the reformer. Combined plant suitable for carrying out the process of claim 2 comprising at least: a source for supplying the oxygen-rich gas; a steam reformer comprising a combustion chamber and a convection chamber; first being provided with reforming tubes filled with reforming catalyst and burners capable of being fed with fuel and with oxidant, and the second chamber, in connection with the first, being able to evacuate fumes emitted in the first chamber, as well as means for circulating the oxidant for combustion, comprising at least one combustion air inlet, a blower, means for indirectly preheating the oxidant and / or other fluids by the fumes emitted, as well as pipes connecting these different means, means for recovering the oxygen-rich gas, means for injecting said oxygen-rich gas into the combustion air to produce and enriched air, as well as lines suitable for the transport of oxygen-rich gas, combustion air, oxygen-enriched air and fumes emitted during combustion. 6. Combined plant according to claim 5 and suitable for carrying out the method of claim 4, characterized in that it comprises: a storage of liquid oxygen in which a gaseous sky is formed above the liquid, means for recovering all or part of an evaporation oxygen stream emitted by the storage.