Patent Application
20150361010
This invention relates to an apparatus and process for converting methane to acetylene with a supersonic reactor.
Light olefin materials, including ethylene and propylene, represent a large portion of the worldwide demand in the petrochemical industry. Light olefins are used in the production of numerous chemical products via polymerization, oligomerization, alkylation and other well-known chemical reactions. These light olefins are essential building blocks for the modern petrochemical and chemical industries. Producing large quantities of light olefin material in an economical manner, therefore, is a focus in the petrochemical industry. The main source for these materials in present day refining is the steam cracking of petroleum feeds.
The cracking of hydrocarbons brought about by heating a feedstock material in a furnace has long been used to produce useful products, including for example, olefin products. For example, ethylene, which is among the more important products in the chemical industry, can be produced by the pyrolysis of feedstocks ranging from light paraffins, such as ethane and propane, to heavier fractions such as naphtha. Typically, the lighter feedstocks produce higher ethylene yields (50-55% for ethane compared to 25-30% for naphtha); however, the cost of the feedstock is more likely to determine which is used. Historically, naphtha cracking has provided the largest source of ethylene, followed by ethane and propane pyrolysis, cracking, or dehydrogenation. Due to the large demand for ethylene and other light olefinic materials, however, the cost of these traditional feeds has steadily increased. In addition, the availability of low cost natural gas has driven interest in the conversion of natural gas to chemicals, such as light olefins.
Energy consumption is another cost factor impacting the pyrolytic production of chemical products from various feedstocks. Over the past several decades, there have been significant improvements in the efficiency of the pyrolysis process that have reduced the costs of production. In a typical or conventional pyrolysis plant, a feedstock passes through a plurality of heat exchanger tubes where it is heated externally to a pyrolysis temperature by the combustion products of fuel oil or natural gas and air. One of the more important steps taken to minimize production costs has been the reduction of the residence time for a feedstock in the heat exchanger tubes of a pyrolysis furnace. Reduction of the residence time increases the yield of the desired product while reducing the production of heavier by-products that tend to foul the pyrolysis tube walls. However, there is little room left to improve the residence times or overall energy consumption in traditional pyrolysis processes.
Recently, attempts have been made to use pyrolysis to convert natural gas to ethylene. U.S. Pat. No. 7,183,451 discloses heating natural gas to a temperature at which a fraction is converted to hydrogen and a hydrocarbon product such as acetylene or ethylene. The product stream is then quenched to stop further reaction and subsequently reacted in the presence of a catalyst to form liquids to be transported. The liquids ultimately produced include naphtha, gasoline, or diesel. While this method may be effective for converting a portion of natural gas to acetylene or ethylene, it is estimated that this approach will provide only about a 40% yield of acetylene from a methane feed stream. While it has been identified that higher temperatures in conjunction with short residence times can increase the yield, technical limitations prevent further improvement to this process in this regard. Furthermore, this reference fails to disclose indirect heat recovery from the pyrolysis reactor.
One proposed alternative to the previous methods of producing olefins that has not gained much commercial traction includes passing a hydrocarbon feedstock into a supersonic reactor and accelerating it to supersonic speed to provide kinetic energy that can be transformed into heat to enable an endothermic pyrolysis reaction to occur. Variations of this process are set out in U.S. Pat. Nos. 4,136,015 and 4,724,272, and Russian Patent No. SU 392723A. These processes include combusting a feedstock or carrier fluid in an oxygen-rich environment to increase the temperature of the feed and accelerate the feed to supersonic speeds. A shock wave is created within the reactor to initiate pyrolysis or cracking of the feed. However, none of these references are believed to disclose the recovery of heat from the reactor effluent.
U.S. Pat. Nos. 5,219,530 and 5,300,216 have suggested a similar process that utilizes a shockwave reactor to provide kinetic energy for initiating pyrolysis of natural gas to produce acetylene. More particularly, this process includes passing steam through a heater section to become superheated and accelerated to a nearly supersonic speed. The heated fluid is conveyed to a nozzle which acts to expand the carrier fluid to a supersonic speed and lower temperature. An ethane feedstock is passed through a compressor and heater and injected by nozzles to mix with the supersonic carrier fluid to turbulently mix together at a speed of about Mach 2.8 and a temperature of about 427° C. The temperature in the mixing section remains low enough to restrict premature pyrolysis. The shockwave reactor includes a pyrolysis section with a gradually increasing cross-sectional area where a standing shock wave is formed by back pressure in the reactor due to flow restriction at the outlet. The shockwave rapidly decreases the speed of the fluid, correspondingly rapidly increasing the temperature of the mixture by converting the kinetic energy into heat. This immediately initiates pyrolysis of the ethane feedstock to convert it to other products. A quench heat exchanger then receives the pyrolized mixture to quench the pyrolysis reaction.
Prior attempts to convert light paraffin or alkane feed streams, including ethane and propane feed streams, to other hydrocarbons using supersonic flow reactors have shown promise in providing higher yields of desired products from a particular feed stream than other more traditional pyrolysis systems. Specifically, the ability of these types of processes to provide very high reaction temperatures with very short associated residence times offers significant improvement over traditional pyrolysis processes. It has more recently been realized that these processes may also be able to convert methane to acetylene and other useful hydrocarbons, whereas more traditional pyrolysis processes were incapable or inefficient for such conversions.
One potential issue associated with using a supersonic flow reactor for light alkane pyrolysis, and more specifically the pyrolysis of methane feeds to form acetylene and other useful products therefrom, is the very large amount of heat must be produced in the supersonic reactor to provide the heat of reaction for the endothermic pyrolysis reactions. In order to generate a large amount of heat and flow rate of the carrier fluid, a large amount of fuel is consumed. Further, at least a portion of the heat must be removed from the process stream after pyrolysis occurs in order to halt the reaction when the desired products have been produced in so that the reactor effluent and other streams may be sent downstream of the supersonic reactor. Moreover, additional heat may be required to preheat a fuel stream or a feed stream.
U.S. Pat Pub. No. 2014/0056767 discloses a supersonic reactor that uses a combustion gas which is provided with a supersonic velocity for the pyrolysis of methane. A quench fluid is injected to stop the pyrolysis reactions. The reactor is free draining or vertically oriented; however, the reference does not disclose using a heat exchange downstream of the reactor. U.S. Pat. Pub. No. 2014/0056766 discloses a similar supersonic reactor that uses a combustion gas which is provided with a supersonic velocity for the pyrolysis of methane. A heat exchanger is used downstream of the reactor. While this reference discloses several general schemes for recovering heat into a heat exchange fluid such as hot oil or to produce high pressure steam that are applicable to the heat exchange fluid discussed herein, it would be desirable, to reduce the amount of fuel and/or energy consumed by such a supersonic reactor and to improve the overall energy efficiency thereof.
The present invention provides an apparatus for producing acetylene from a light hydrocarbon stream and a method for recovery of heat from such an apparatus.
In one aspect the present invention provides an apparatus for producing acetylene from a gaseous feed stream comprising light hydrocarbons. The apparatus includes a supersonic reactor configured to receive light hydrocarbons and heat the light hydrocarbons to a pyrolysis temperature to produce a reactor effluent, the supersonic reactor includes a combustion zone capable of combusting a fuel, a pyrolysis zone capable of pyrolyzing light hydrocarbons, a nozzle between the combustion zone and the pyrolysis zone, and, a quench zone configured to receive quench fluid injected into the supersonic reactor to stop the pyrolysis of the light hydrocarbons. The apparatus further includes a separation zone disposed downstream of the quench zone, wherein the reactor effluent is capable of freely draining into the separation zone and separating into a gas phase containing the effluent and a liquid phase containing the quench fluid, and, a heat exchanger disposed between the supersonic reactor and the separation zone.
In some embodiments of the present invention, the supersonic reactor may be vertically orientated.
In at least one embodiment of the present invention, an inlet of the heat exchanger comprises at least a portion of the quench zone of the supersonic reactor.
In various embodiments of the present invention, the heat exchanger comprises a plurality of tubes inside of a shell. It is contemplated that a heat exchange fluid flows on a tube side of the heat exchanger. It is further contemplated that the reactor effluent flows on a shell side of the heat exchanger. The tubes of the heat exchanger may be disposed parallel to a direction of flow through the shell, perpendicular to a direction of flow through the shell, at an angle relative to a direction of flow through the shell, or a combination thereof.
In some embodiments, the separation zone further comprises a pressure control device, such as a valve on an outlet for the gas phase. The separation zone may further include an outlet for removing the liquid phase, which may be configured to supply the liquid phase to the quench zone for use as quench fluid.
In at least one embodiment of the present invention, the heat exchanger further comprises at least one body with an inner cavity and at least one tube or a plurality of tubes extending within the body. Each tube from the plurality of tubes comprises an inlet wherein at least one inlet is disposed in the quench zone. It is contemplated that the tubes are configured to receive reactor effluent. It is further contemplated that cooling fluid flows within the inner cavity of the body of the heat exchanger.
In various embodiments of the present invention, the heat exchanger comprises a plurality of tubes extend within at least one body.
In another aspect of the present invention, the present invention provides a process for producing acetylene from light hydrocarbons in a supersonic reactor. The process includes: injecting light hydrocarbons into a supersonic reactor; heating light hydrocarbons to produce an effluent from a pyrolysis zone; quenching a pyrolysis of light hydrocarbons with a quench fluid to provide a reactor effluent stream comprising effluent and quench fluid; recovering heat from the reactor effluent stream; and, separating the reactor effluent stream in a separation zone into a gas phase comprising the effluent and a liquid phase comprising the quench fluid. The separation zone is disposed so that the reactor effluent stream freely flows into the separation zone from the supersonic reactor.
In some embodiments of the present invention, the heat is recovered in a heat exchanger. The heat exchanger may be disposed between the supersonic reactor and the separation zone. Thus, it is contemplated that the heat exchanger is disposed below the supersonic reactor. The separator may be disposed below the heat exchanger.
The heat exchanger may comprise: a shell with at least one open inner cavity; and, at least one plurality of tubes extending within the at least one open inner cavity. The tubes of the heat exchanger may be disposed parallel, perpendicular, or at an angle to a direction of flow for the reactor effluent stream through the shell. In some embodiments of the present invention, the process also includes reducing a residence time of light hydrocarbon in the supersonic reactor by flowing reactor effluent stream on a tube side of the heat exchanger.
In another embodiment of the present invention, the process includes reducing a pressure drop of light hydrocarbon in the supersonic reactor by flowing reactor effluent on a shell side of the heat exchanger.
In at least one embodiment of the process, the process further includes adjusting the pressure in the supersonic reactor by controlling a flow of gas out of the separation zone.
These and other aspects and embodiments relating to the present invention should be apparent to those of ordinary skill in the art from the following detailed description of the invention.
In the drawings:
An apparatus and method have been developed in which for producing acetylene from a feed stream containing light hydrocarbons. By “light hydrocarbons,” it is meant that the feed stream comprises methane to C4 hydrocarbons (i.e., hydrocarbons with four carbon atoms), and may also comprise trace or small amounts of C5+ hydrocarbons (i.e., hydrocarbons with five or more carbon atoms). The feed stream may be provided from a remote location or at the location or locations of the systems and methods described herein. For example, while the feed stream source may be located at the same refinery or processing plant where the processes and systems are carried out, such as from production from another on-site hydrocarbon conversion process or a local natural gas field, the feed stream may be provided from a remote source via pipelines or other transportation methods. For example a feed stream may be provided from a remote hydrocarbon processing plant or refinery or a remote natural gas field, and provided as a feed to the systems and processes described herein. Initial processing of the feed stream may occur at the remote source to remove certain contaminants from the feed stream. Where such initial processing occurs, it may be considered part of the systems and processes described herein, or it may occur upstream of the systems and processes described herein. Thus, the feed stream provided for the systems and processes described herein may have varying levels of contaminants depending on whether initial processing occurs upstream thereof.
In one example, the feed stream has a methane content ranging from about 65 mol-% to about 100 mol-%. In another example, the concentration of methane in the hydrocarbon feed stream ranges from about 80 mol-% to about 100 mol-%. In yet another example, the concentration of methane ranges from about 90 mol-% to about 100 mol-% of the hydrocarbon feed.
In one example, the concentration of ethane in the feed stream ranges from about 0 mol-% to about 35 mol-% and in another example from about 0 mol-% to about 10 mol-%. In one example, the concentration of propane in the methane feed ranges from about 0 mol-% to about 5 mol-% and in another example from about 0 mol-% to about 1 mol-%.
The feed stream may also include heavier hydrocarbons, including aromatics, paraffinic, olefinic, and naphthenic hydrocarbons. These heavier hydrocarbons if present will likely be present at concentrations of between about 0 mol-% and about 100 mol-%. In another example, they may be present at concentrations of between about 0 mol-% and 10 mol-% and may be present at between about 0 mol-% and 2 mol-%.
The apparatus and method for forming acetylene from the light hydrocarbon feed stream described herein utilizes a supersonic flow reactor for pyrolyzing methane in the feed stream to form acetylene. The supersonic flow reactor may include one or more reactors capable of creating a supersonic flow of a carrier fluid and the methane feed stream and expanding the carrier fluid to initiate the pyrolysis reaction. A preferred reactor is depicted in U.S. Pat. Pub. No. 2014/0056766, which is incorporated herein by reference, in its entirety.
As illustrated in
A feed stream inlet 40 is provided for injecting the light hydrocarbon feed stream into the reactor 5 to mix with the carrier fluid. The feed stream inlet 40 may include one or more injectors 45 for injecting the feed stream into the nozzle 50, a mixing zone 55, an expansion zone 60, or a reaction zone or chamber 65. The injector 45 may include a manifold, including for example a plurality of injection ports or nozzles for injecting the feed stream into the reactor 5.
As illustrated in
In another approach, the mixing zone is integrated into the expansion zone 60 is provided, and mixing may occur in the nozzle 50, expansion zone 60, or reaction zone 65 of the reactor 5. A combination of geometric features such as for example a super-sonic diffuser and manipulation of the pressure at the outlet end of reaction zone 65 may be utilized to produce a rapid reduction in the velocity of the gases flowing therethrough, to convert the kinetic energy of the flowing fluid to thermal energy to further heat the stream to cause pyrolysis of the methane in the feed stream in reaction zone 65 of the reactor 5. A quench fluid is injected into the reactor 5 in a quench zone 72 to stop the pyrolysis reaction from further conversion of the desired acetylene product to other compounds. Any suitable structure may be utilized for the introduction of quench fluid. For example, spray bars 75 may be used to introduce a quenching fluid, for example water or steam, into the quench zone 72.
The reactor effluent exits the reactor via outlet 80 will include a larger concentration of acetylene than the feed stream and a reduced concentration of methane relative to the feed stream. The reactor effluent stream may also be referred to herein as an acetylene stream as it includes an increased concentration of acetylene. The acetylene stream may be an intermediate stream in a process to form another hydrocarbon product or it may be further processed and captured as an acetylene product stream. In one example, the reactor effluent stream has an acetylene concentration prior to the addition of quenching fluid ranging from about 2 mol-% to about 30 mol-%. In another example, the concentration of acetylene ranges from about 5 mol-% to about 25 mol-% and from about 8 mol-% to about 23 mol-% in another example.
The reactor vessel 10 includes a reactor shell 11. It should be noted that the term “reactor shell” refers to the wall or walls forming the reactor vessel, which defines the reactor chamber 15. The reactor shell 11 will typically be an annular structure defining a generally hollow central reactor chamber 15. The reactor shell 11 may include a single layer of material, a single composite structure or multiple shells with one or more shells positioned within one or more other shells. The reactor shell 11 also includes various zones, components, and or modules, as described above and further described below for the different zones, components, and or modules of the supersonic reactor 5. The reactor shell 11 may be formed as a single piece defining all of the various reactor zones and components or it may be modular, with different modules defining the different reactor zones and/or components.
Turning to
An exemplary heat exchanger 200a is shown in
As shown in
Alternatively, in
Finally, as shown in
Returning to
In an embodiment, the reactor effluent flows, for example with respect to
Alternatively, it is contemplated that the reactor effluent flow on the tube side of the heat exchanger 100. In such an embodiment, it is contemplated that the heat exchange inlet 108 will be disposed within the quench zone 106 of the reactor 102. The inlet 108 of the heat exchanger 100 may include a distribution plate 300. See,
As mentioned above, the heat recovered from the heat exchanger may used in the present process, for example to pre-heat certain process streams. Additionally and alternatively, the heat may be used elsewhere, for example, for the production of electricity. The recovery of the heat is not necessary for the understanding and the practicing of the present invention.
In at least one embodiment of the present invention, the effluent is cooled from 1000 to 1500° C. to 600-900° C. in the quench zone and subsequently cooled from 600-900° C. in the heat exchanger. In at least one embodiment of the present invention, the residence time of the effluent in the quench zone is less than 10 ms and the residence time of the effluent in the heat exchanger is greater than 30 ms or between about 30 ms and about 200 ms or about 30 ms and about 100 ms. In some embodiments the residence time for effluent with a temperature between 1000 to 1500° C. is less than 5 ms, for effluent with a temperature between 650 to 1000° C. is less than 10 ms, and for effluent with a temperature between 200 to 650° C. is less than 40 ms.
Returning to
For example, the reactor may be a relatively vertically orientated reactor (90°), with the heater exchanger disposed below the reactor, and with the separation zone disposed below the heat exchanger By arranging the separation zone so that the reactor effluent is capable of freely draining into the separation zone, any pressure drop associated with the transfer of fluids between the various components or zones can be minimized. Furthermore, excess cooling fluid that may be injected during normal operation or during transient periods such as start-up or shutdown will not accumulate in the reactor.
As shown in
As shown in
An apparatus according to one or more embodiments herein provides for efficient heat recovery from a supersonic reactor. Efficiently recovering heat from the reaction effluent, is believed to allow for the reactor to be run more efficiently. In various embodiments, the efficient recovery can be performed while utilizing a heat exchanger without excessively increasing residence time in the reactor for the effluent, or without creating too large of a pressure drop.
It should be appreciated and understood by those of ordinary skill in the art that various other components such as valves, pumps, filters, coolers, etc. were not shown in the drawings as it is believed that the specifics of same are well within the knowledge of those of ordinary skill in the art and a description of same is not necessary for practicing or understating the embodiments of the present invention.
While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.
