Patent Publication Number: US-2016244682-A1

Title: Method and device for synthesis gas generation

Description:
The invention relates to a method for generation of a crude synthesis gas from a hydrocarbon-containing feed which is at a first pressure and also a steam feed which is at a second pressure that is higher than the first pressure, wherein the hydrocarbon-containing feed and the steam feed are introduced jointly into a reactor and are there reacted at a process pressure that is higher than the first pressure to form the crude synthesis gas. 
     In addition, the invention relates to a device for carrying out the method according to the invention. 
     A crude synthesis gas is a mixture of matter primarily obtained from hydrocarbons by steam reforming or auto thermal reforming, which mixture of matter largely comprises hydrogen and carbon monoxide, but in addition also substances such as water, carbon dioxide and sulfur compounds in considerable amounts. By chemical and/or physical treatment steps, hydrogen, carbon monoxide or synthesis gas —a mixture of matter which comprises hydrogen and carbon monoxide in a defined ratio—can be obtained from the crude synthesis gas as products that are used in a multiplicity of industrial processes as base chemicals. Thus, synthesis gas for instance is used for producing methanol, dimethyl ether or hydrocarbons. 
     In the case of methods of the type described at the outset, it is necessary to compress at least the feed containing hydrocarbons in order to be able to introduce it info the reactor. For this purpose, according to the prior art, machines such as screw compressors, piston compressors or turbo compressors are used which have a complicated structure and, because of the large number of moving parts, are also susceptible to wear and faults. These machines therefore give rise to high capital and operating costs which have a considerable effect on the economic efficiency of the crude synthesis gas generation. 
     It is an object of the present invention to specify a method and also a device of the type in question, by which the described disadvantages of the prior art are overcome. 
     The object in question is achieved in terms of the method according to the invention in that the pressure of at least a part of the hydrocarbon-containing feed is increased before introduction thereof into the reactor using a steam jet pump to which at least a part of the steam feed is fed as motive medium. 
     It is possible by the proposed method to dispense completely with complicated and expensive machines for compressing the hydrocarbon-containing feed, or at least to use smaller and therefore less expensive machines. Steam jet pumps have been prior art for many years and known to those skilled in the art. They have a relatively simple structure without moving parts and are robust in such a manner that they can be used at markedly lower costs than the machines used according to the prior art for compressing the hydrocarbon-containing feed. 
     In the motive nozzle of the steam jet pump, pressure energy of the part of the steam feed used as motive medium is converted into kinetic energy in such a manner that a steam jet is formed, the static pressure of which is lower than the first pressure of the hydrocarbon-containing feed. Owing to the steam jet exiting from the motive nozzle, the hydrocarbon-containing feed can therefore be taken in by suction and accelerated, in the inlet cone of the diffuser following the motive nozzle, steam and hydrocarbon-containing feed mix before they are braked again in the diffuser. Since, as a result of the braking, pressure energy is recovered, the hydrocarbon-containing feed leaves the steam jet pump together with the part of the steam feed used as motive medium at a pressure higher than the first pressure. 
     Preferably, the pressure of the at least one part of the hydrocarbon-containing feed is increased using the steam jet pump to a value which permits the at least one part of the hydrocarbon-containing feed to be introduced into the reactor without further compression. 
     Preferably, the total amount of the hydrocarbon-containing feed is compressed by means of a steam jet pump, for which purpose, expediently, the total amount of the steam feed is also used as motive medium. It is also conceivable, however, to divide the hydrocarbon-containing feed into two or more substreams and to compress them separately from one another in steam jet pumps operated in parallel, wherein, preferably, in each of the steam jet pumps a part of the steam feed is used as motive medium, and in all steam jet pumps together the total amount of the steam feed is used as motive medium. Since a steam jet pump also acts as a mixing appliance, in this manner, the two feeds after the pressure increase are completely in a mixture, in such a manner that a further mixing appliance downstream of the steam jet pump or of the steam jet pumps can be dispensed with. 
     If the pressure of the steam feed is insufficient to compress the hydrocarbon-containing feed to a pressure necessary for the introduction into the reactor, an embodiment of the method according to the invention provides for increasing at least the pressure of the part of the steam feed that is provided as motive medium, before introduction thereof into the steam jet pump, to a value which is sufficient to lift the pressure of the hydrocarbon-containing feed to a value sufficient for introduction into the reactor. Preferably, this increase is performed by elevating the operating pressure of the steam system. 
     In some circumstances, it can be logical to compress the hydrocarbon-containing feed in two or more successive stages, wherein in at least two of the stages a steam jet pump is used. In one of the steam jet pumps, in this case, a part of the steam feed at the second pressure is used as motive medium, whereas in the steam jet pump or the further steam jet pumps, in each case a part of the steam feed is used as motive medium, the pressure of which has been elevated to a value above the second pressure. 
     The steam feed can be obtained from one source or from a plurality of sources. For instance, it is possible, for example, to use import steam alone as steam feed, or else to mix the steam feed, for instance from import steam, process steam and export steam. 
     In addition, the invention relates to a device for generation of a crude synthesis gas having a reactor, feed appliances for a hydrocarbon-containing feed and a steam feed, and also a compression appliance for elevating the pressure of the hydrocarbon-containing feed, which compression appliance is connected on the exit side to the reactor. 
     The object in question is achieved in terms of the device according to the invention in that the compression appliance comprises a steam set pump that is connected to the feed appliance for the steam feed in such a manner that at least a part of the steam feed is feedable thereto as motive medium. 
     Preferably, the compression appliance consists of exactly one steam jet pump with the aid of which the total amount of the hydrocarbon-containing feed can be compressed to a pressure sufficiently high for introduction thereof into the reactor. However, the compression appliance can also comprise two or more steam jet pumps arranged in parallel and/or in series. 
     The reactor is preferably a steam reformer or an auto thermal reformer or another reactor which is suitable for generating a crude synthesis gas from hydrocarbons and steam. 
     Particularly advantageously, the invention can be used when the pressure of the hydrocarbon-containing feed gas is subject to fluctuations with time, in such a manner that there are times in which a compression of the feed is required, and those in which the feed can be fed without compression to the reactor. In particular when the fluctuations proceed rapidly and are not predictable, a machine useable for the possibly necessary compression of the hydrocarbon-containing feed would have to be running constantly, i.e. also in times of sufficiently high pressure, since otherwise there would be the risk that, in the event of falling pressure, the machine cannot be started rapidly enough in order to keep the pressure of the hydrocarbon-containing feed at the required pressure level without interruption. In contrast, a steam jet pump can ensure the required compression of the hydrocarbon-containing feed in such a case without time delay, especially, however, without intervention of the operating personnel. This is ensured in that the flow passes permanently through the steam jet pump and as a result, in every case, a pressure elevation in accordance with specifications is achieved, in the event of too high a pressure increase, the feed gas/steam mixture is expanded to the required pressure using a regulating valve. 
     Also if after a retrofitting of an existing plant, the pressure of the hydrocarbon-containing feed is no longer sufficiently high, compression of the feed by means of a steam jet pump can be an expedient alternative to installing compressor machines. 
     Hereinafter, the invention will be described in more detail with reference to an exemplary embodiment shown schematically in the drawing figure. 
    
    
     
       The drawing figure shows a preferred embodiment of the method according to the invention and of the device according to the invention for generation of a crude synthesis gas. 
     
    
    
     In the reactor R, which is, for example, a steam reformer or an auto thermal reformer, hydrocarbons are reacted with steam to form a crude synthesis gas  1 . For this purpose, via a first feed appliance, a hydrocarbon-containing feed  2 , such as natural gas, for instance, and via a second feed appliance, a steam feed  3  are introduced. The pressure of the hydrocarbon-containing feed  2  in the first feed appliance, which is typically between 15 and 30 bar(a), is lower than the process pressure at which it is reacted to form crude synthesis gas, and so it is necessary to increase the pressure of the hydrocarbon-containing feed in order to be able to feed it to the reactor R. For this purpose, the first feed appliance is connected to the compression appliance V which is constructed as a steam jet pump P, to which the steam feed  3  is fed as motive medium. On account of the mass flow rate and the pressure of the steam feed  3 , which, at a value between 40 and 120 bar(a), is markedly higher than the process pressure which is usually between 25 and 40 bar(a), the mixture of matter containing hydrocarbons and steam that is formed in the steam jet pump can be conducted to the reactor R via the line  4  without a further compression step.