TECHNICAL FIELD

[0001] The present subject matter relates generally to cracking of crude oil, and more particularly to a process and apparatus for producing petrochemical feedstock such as olefin and aromatic compounds directly from crude oil.

BACKGROUND

[0002] Crude oil is separated into different hydrocarbon products by passing the crude oil first into distillation units followed by different cracking or treating units. Existing refining processes involve multiple steps and multiple units. For example, crude oil is heated using heat exchangers followed by heating in furnaces and is then distilled in an atmospheric distillation unit to obtain naphtha, kerosene, and diesel fractions. The bottom fraction of crude oil, termed as atmospheric tower bottoms is then heated in a furnace and distilled under vacuum. The fractions thus obtained are called vacuum gas oil and vacuum tower bottoms. The vacuum gas oil is typically cracked in a fluid catalytic cracking process to produce olefins and fuels like gasoline and diesel. The vacuum tower bottoms is typically processed in a delayed coker unit to produce coke and distillate.

[0003] Thus, for obtaining a higher yield of olefinic and aromatic compounds from crude oil, various process units are used. Moreover, the refinery and petrochemical complex need to be integrated. This approach is highly energy intensive, costly, and requires a lot of space.

BRIEF DESCRIPTION OF DRAWINGS

[0004] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components where possible. [0005] Fig. 1 illustrates a schematic of an apparatus for producing petrochemical feedstock from crude oil, in accordance with an example of the present subject matter.

[0006] Fig. 2(a) illustrates an exploded view of a portion of the riser comprising multiple channels, in accordance with an example of the present subject matter.

[0007] Fig. 2(b) illustrates an example ring for directing a fraction of crude oil into a channel and Fig. 2(c) illustrates an example nozzle arrangement for directing a fraction of crude oil into a channel, in accordance with example embodiments of the present subject matter.

[0008] Fig. 2(d) illustrates cross-sectional views along line AA shown in

Fig. 2(a) of example arrangements of channels in the riser, in accordance with example embodiments of the present subject matter

[0009] Figs. 3(a)-3(c) show different flow directions in the riser channels, in accordance with example embodiments of the present subject matter.

DETAILED DESCRIPTION

[0010] The present subject matter relates to a process and apparatus for producing petrochemical feedstock, such as, olefinic and aromatic compounds, directly from crude oil.

[0011] Refining crude oil generally produces heavy fractions such as gasoline, diesel, kerosene, and the like, along with a small fraction of light olefins and aromatics. The production of olefins and aromatics is generally done by cracking the heavy fractions obtained by refining the crude oil.

[0012] Distillation of crude oil produces different fractions that have different boiling points. One such fraction produced is naphtha, besides diesel, kerosene, vacuum gas oil, and vacuum bottoms. The naphtha fraction is typically divided into two streams: light naphtha and heavy naphtha, which are treated in isomerization and catalytic reforming processes to increase the research octane number value and the products are blended to produce gasoline from the refinery. [0013] When higher olefins and aromatics are desired to be produced, the light naphtha (produced from the atmospheric distillation unit) is used as a feedstock for the petrochemical complex, wherein the light naphtha is heated thermally at high temperature (>800 °C) followed by compressing the vapors and then processing at several treatment units to produce olefins and aromatics.

[0014] Another conventional method used for the production of petrochemical feedstock from crude oil comprises a set of reactors in series, such that crude oil or products from cracking crude oil such as light naphtha and heavy naphtha in the first reactor are fractionated and sent to the next reactor, and so on such that a final product stream of olefins and aromatics is obtained.

[0015] However, conventional processes for producing olefins and aromatics from crude oil require several process units, each with its own sets of heat exchangers, reactors, distillations units, etc., making the production complex and expensive. Furthermore, such a production process also requires a large amount of space to house the different units.

[0016] The present subject matter relates to a process and apparatus for the production of petrochemical feedstock, such as olefins and aromatics, directly from crude oil without the intermediate steps used in a typical refinery and petrochemical complex. Petrochemical feedstock comprises olefins, such as, ethylene, propylene, and butylene, and aromatics such as benzene, xylene, toluene, and the like. The apparatus comprises a riser for catalytic cracking of crude oil, wherein a portion of the riser comprises two or more channels assembled therein. The channels are referred to as targeted riser-reactors and the riser with channels is referred to as a targeted rise-reactor assembly. The riser comprises a catalyst inlet to feed catalyst to the riser and the plurality of channels. One crude oil fraction is fed into one channel of the plurality of channels to crack the crude oil fraction. A channel inlet may be disposed on each of the plurality of channels to allow entry of the crude oil fraction. The catalyst and the crude oil fraction may flow in one of a co-current or counter-current flow in each channel.

[0017] In operation, crude oil may be heated with reactor/fractionator bottom or product stream above the bottom using one or more heat exchangers, and different fractions may be separated using one or more flash drums. The different fractions are fed to the riser bottom via the multiple targeted riser reactors, such that each fraction passes through one channel. The length and diameter of the channels are chosen based on the composition of the feed so that each fraction is sufficiently cracked to olefins or aromatics in the presence of a catalyst in the riser. The product vapors and the spent catalyst rise up to a reactor comprising a set of cyclones to separate the product gases from the spent catalyst and a stripper zone to remove any entrained gases in the spent catalyst. The catalyst is then sent to a regenerator. The product gases can be separated by passing through a fractionator.

[0018] The process and apparatus of the present subject matter reduces the production of low value fuels, such as, kerosene, fuel oil, and the like, and gives a greater yield of olefins and aromatics compared to conventional processes. Furthermore, there is minimal production of bottom products, which reduces the amount of processing needed for the bottom products. Furthermore, since the steps for the production of olefins and aromatics from crude oil is reduced, it reduces the number of processing units, making the process simpler. This also leads to a reduced cost of production, as less and simpler equipment is used, and lesser space is used in setting up the production assembly.

[0019] Aspects of the present subject matter are further described in conjunction with the appended figures. It should be noted that the description and figures merely illustrate the principles of the present subject matter. It will thus be appreciated that various arrangements that embody the principles of the present subject matter, although not explicitly described or shown herein, can be devised from the description and are included within its scope. Moreover, all statements herein reciting principles, aspects, and implementations of the present subject matter, as well as specific examples thereof, are intended to encompass equivalents thereof.

[0020] Fig. 1 illustrates a schematic of an apparatus for producing petrochemical feedstock from crude oil, in accordance with one embodiment of the present subject matter. In an example, the apparatus 100 comprises one or more heat exchangers 114 (such as 114a, 114, and 114c) to heat crude oil, one or more flash drums 118 (such as 118a and 118b) to separate crude oil into different fractions, and a riser 150. The riser 150 comprises a catalyst inlet at the bottom of the riser to feed catalyst to the riser 150. The riser comprises a plurality of channels in a portion of the riser substantially towards the bottom of the riser 150. One crude oil fraction is fed into one channel and the crude oil fraction is cracked in the channel in the presence of the catalyst. The plurality of channels may have different lengths and diameters. A channel inlet is disposed on each of the plurality of channels to allow entry of the crude oil fraction. The apparatus 100 comprises a reactor 170 comprising a cyclone 174 and a stripper 178 to separate product and spent catalyst obtained at the outlet of the riser 150. A catalyst regenerator 158 regenerates spent catalyst and a fractionator 122 separates product fractions.

[0021] In one embodiment, crude oil 110 is heated using heat exchangers

114a, 114b... , hereinafter referred to collectively as heat exchangers 114 (heat may come from the bottom portion of a fractionator) and is passed to flash drums 118a, 118b... , hereinafter referred to collectively as flash drums 118. The flash drums 118 separate out different fractions of the crude oil 110, with the lower boiling point components being vaporized and the higher boiling point components remaining in the liquid form, and the vapor and the liquid can be separated. In one example, the liquid fraction obtained from flash drum 118a can then be passed through flash drum 118b to separate out another fraction of the components.

[0022] During operation, the process for production of petrochemical feedstock from the crude oil comprises heating the crude oil 110 using one or more heat exchangers 114. The crude oil 110 is passed through a heat exchanger 114b, where it is heated by bottom product stream from main fractionator 122. The heated crude oil may be passed into one or more flash drums 118. For example, the heated crude oil 110a is passed to first flash drum 118a. A bypass with flow control is provided around heat exchanger 114b to control temperature of heated crude oil 110a. In flash drum 118a, the low boiling components, such as the components with a boiling point of up to 70 °C, vaporize and are removed as a first stream 130a. The components that remain liquid are withdrawn from flash drum 118a as first liquid stream 134a which is passed through to the heat exchanger 114a. In heat exchanger 114a, first liquid stream 134a is heated by a bottom product stream from the fractionator 122. The heated stream 132a is passed to the second flash drum 118b. A bypass with flow control may be provided around heat exchanger 114a to control the temperature of stream 132a. In flash drum 118b, the intermediate boiling components, such as the components with a boiling point of between 70 °C to 250 °C, vaporize and are removed as second stream 130b. The remaining liquid is removed as a third stream 130c comprising components with a high boiling point, such as a boiling point greater than 250 °C. As mentioned, the crude oil 110 may be heated using the heat from the bottom stream 140 of the fractionator 122. The bottom stream 140 from the fractionator 122 is pumped using pump 144 to increase the pressure of the bottom stream 140 to overcome the pressure drops in the downstream heat exchangers 114. The stream 140a from the pump 144 is used to heat stream 134a in heat exchanger 114a. First cooled stream 140b from heat exchanger 114a is used to heat the crude oil stream 110 in heat exchanger 114b. Bypass around the heat exchangers 114a and 114b may be provided to control the required heat duty. Second cooled stream 140c from heat exchanger 114b is sent to one or more heat exchangers 114c to further cool the stream, for example, using cooling fluid such as water, before withdrawing a third cooled stream 140d as final bottom product stream. A part 140e of the second cooled stream 140c may be recycled back to the bottom of the fractionator 122 (shown as dotted line in Fig. 1) to control the temperature in the bottom of the main fractionator 122.

[0023] Although not shown in Fig. 1, other product streams, such as heavy cycle oils, light cycle oils, heavy naphtha, and overhead gases may be withdrawn from the main fractionator 122. It will also be understood that any number of heat exchangers may be connected in series or in parallel for heating the crude oil or its fractions. Apart from the bottom product stream from the fractionator, other hot streams from fractionator such as Heavy Cycle Oil (HCO) product, Light Cycle Oil (LCO) product, Heavy Naphtha (HN) product, HCO pump around, LCO pump around, HN pump around, circulating oil pump around or any other suitable hot stream can also be used for heating of crude oil. [0024] Although two flash drums are shown in the above embodiment, any number of flash drums 118 may be used, depending on the number of fractions to be separated, for maximizing yield of higher olefins and aromatics. Accordingly, the range of boiling point of each fraction that is separated may also be different. For example, four flash drums 118 may be used to obtain five different fractions such that fraction 1 has components with a boiling point up to 70 °C, fraction 2 has components with a boiling point between 70 and 140 °C, fraction 3 has components with boiling points between 140 and 200 °C, fraction 4 has components with boiling points between 200 and 250 °C, and fraction 5 has components with a boiling point above 250 °C. Heat from the streams, including but not limited to the pump around streams and product streams can be used to heat the crude oil and/or liquid fractions.

[0025] The fractions 130a, 130b, and 130c (collectively referred to as fractions 130) as described above, are fed into a riser 150. A portion of the riser 150 comprises a plurality of targeted riser-reactors (not shown in this fig.), also referred to as channels, such that each of the fractions 130a, 130b, and 130c pass through one channel, as will be described later. In one embodiment, the targeted riser- reactors are located above the wye section of the riser 150, i.e., above the point of entry of catalyst in the riser 150. A feed stream 154 comprising steam or light fractions, such as, recycle naphtha or recycle C3, C4, C5 hydrocarbons are fed at the bottom of the riser 150. Regenerated catalyst from regenerator 158 is fed into the riser 150 via standpipe 162. In an example, the heaviest fraction, for example, the fraction with a boiling point above 250 °C obtained from crude oil, which is 130c in the example, may be fed via an inlet 164. Other fractions may be fed via different inlets into the different channels, as will be explained later. Catalyst may be fed in to the riser 150 via a catalyst inlet coupled to the standpipe 162 and it may then rise into the different channels. The different feed streams 130 encounter the catalyst in the different channels and are cracked to form olefinic or aromatic compounds. The cracking may continue to occur as the fractions rise along with the catalyst in the riser 150.

[0026] The cracked products and the spent catalyst rise in the reactor 170.

Cyclones 174 separate the cracked products from the spent catalyst. The spent catalyst is further stripped of any entrained gases in the stripper 178, using steam. The spent catalyst is sent to the regenerator 158 via standpipe 180 where the spent catalyst is burnt to regenerate it, generally in the presence of pressurized air 182 fed from a bottom of the regenerator 158, to remove any carbon or coke deposited on it. Catalyst flow in standpipe 180 may be controlled by slide valve 184. Air 182a, ambient or with additional oxygen, may be compressed using air blower 186. Pressurized air stream 182 may be sent to the regenerator 158. Products of combustion of coke rise up from the catalyst bed in the regenerator 158. Catalyst particles carried by these gases are separated in regenerator cyclones 188. Flue gases may be removed from the regenerator 158 as flue gas stream 190. Regenerated catalyst may be sent to riser 150 via standpipe 162. Catalyst flow in the standpipe 162 may be controlled by slide valve 194. The cracked product streams 196 from the reactor 170 are passed to the fractionator 122 for fractionation into products.

[0027] The use of multiple channels in the riser 150 to crack different fractions allows for cracking fractions comprising components with different boiling points for different times. This is advantageous as fractions comprising lower boiling components can be cracked for a lesser time compared to fractions comprising higher boiling components, which prevents over-cracking of lower boiling fractions and production of undesired products, generally seen in conventional risers. This also reduces further processing needed to remove the undesired products. Thus, the apparatus and process of the present subject matter maximizes the yield of olefins and aromatics and there is minimal production of bottom products.

[0028] Fig. 2(a) illustrates an exploded view of a portion of the riser bottom containing a plurality of channels, in accordance with one embodiment of the present subject matter. The riser 150 comprising the plurality of channels 210 is also referred to as a targeted riser-reactor assembly, as the channels 210 allow cracking the different fractions in targeted channels, rather than cracking all fractions together in a riser comprising a single channel. In one example, each channel may be made separately and integrated or installed in the riser 150. A portion of the riser 150 comprises channels 210 (such as 210a and 210b). Catalyst enters the riser 150 via a catalyst inlet 214. Although here two channels are shown, there can be any number of channels depending on the number of fractions of the crude oil feed. Depending on the number of channels, the dimensions of the portion of the riser 150 comprising the channels 210 may be such so as to accommodate all the channels. Crude oil fractions may enter the channels 210 via separate channel inlets. In an example, the catalyst inlet 214 and the channel inlet may be disposed on a same end of the plurality of channels 210. In another example, the catalyst inlet 214 and the channel inlet may be disposed on opposite ends of the plurality of channels 210. In one example, an end of each of the plurality of channels 210 may be disposed at the same height in the riser 150, while the other end of each of the plurality of channels 210 may be at different heights depending on the length of the different channels 210.

[0029] In an example, the fraction of crude oil boiling between 70 °C to 250

°C, for example 130b, may be fed into channel 210a. The fraction of crude oil boiling below 70 °C, for example, 130a, may be fed into channel 210b. The fraction of the crude oil boiling above 250 °C, for example 130c, may be fed through nozzles 164 directly into the riser 150 rather than into a channel. In another example, the fraction boiling above 250 °C, for example 130c, may be fed into a third channel (not shown in this figure). The channel lengths may be varied from 0.5 meters to the full length of the riser 150. Each fraction may be fed through separate a channel inlet in each channel 210. In an example, the channel inlet may comprise a nozzle. In another example, fractions may be fed using a dispersion ring as the channel inlet provided at the bottom of the channel 210. Additional inlets or nozzles for steam or other crude oil fractions or recycle streams may be provided in the channels 210. In different examples, the nozzles may be located above or below the channel inlet for the fractions.

[0030] The different channels 210 may have different lengths or diameters based on the different crude oil fractions to be cracked. For example, the dimension of each channel 210 may be determined based on the composition of the crude oil fraction feed to be cracked in that channel and the weight hourly space velocity (WHSV) or residence time needed in the channel for cracking the corresponding crude oil fraction.

[0031] In operation, the different crude oil fraction feed streams encounter the catalyst in the different channels for different lengths of time and are cracked to form olefinic or aromatic compounds. The cracking may continue to occur as the fractions rise along with the catalyst in the riser 150. The components may spend about 2 seconds in the riser 150 and the time of residence in the channels 210 may vary from a few milliseconds to the total riser residence time depending on the dimensions of the channel. Thus, the total residence time of the different crude oil fractions in the riser 150 can be varied depending on the severity of the cracking reaction to be carried out by varying the WHSV and residence time in each channel.

[0032] In one example, one or more pipes of different heights or diameters may be disposed in the riser 150 to form the different channels 210. In such a case, the channel inlets may be provided in the pipe walls to introduce the crude oil fraction feeds, for example, through a nozzle arrangement or a ring, in the pipes as will be discussed with reference to Fig. 2(b) and 2(c). In another example, one or more partition walls of different heights may be provided inside the riser 150 and the partition walls may intersect at different points with each other or a wall of the riser 150 to form the different channels. For example, the channels may be formed such that each channel is bound by at least one partition wall and the wall of the riser 150. In such a case, the channel inlets may be provided in the outer wall of the riser 150 to introduce the crude oil fraction feeds, for example, through a nozzle arrangement or a ring. In one example, the channels 210 may be formed by using a combination of one or more pipes and one or more partition walls. Some example configurations of channels formed using partition walls will be discussed with reference to Fig. 2(d). It will be understood that the different channel configurations shown in Figs 2(b)-2(d) are merely examples and various other channel configurations can be devised by a person skilled in the art based on the teachings of the present subject matter.

[0033] Fig. 2(b) illustrates an example ring for directing a fraction of crude oil into a channel and Fig. 2(c) illustrates an example nozzle arrangement for directing a fraction of crude oil into a channel, in accordance with different embodiments of the present subject matter. In one embodiment, a fraction of crude oil is directed into the channel 210 using the channel inlet comprising a ring 220. The ring 220 may comprise multiple outlets, such as holes, to allow the crude fraction to be distributed in the channel 210. Referring to Fig. 2(c), in another example, the channel 210 may comprise the channel inlet comprising nozzles 230 to direct a fraction of crude oil 130 into the channel 210. Thus, in some examples, channel 210a may comprise a ring 220 or a nozzle 230 and channel 210b may comprise a ring 220 or a nozzle 230. Any combination of rings 220 or nozzles 230 may also be used in the channels 210. In various examples, the channel 210 may comprise both the ring 220 and the nozzles 230.

[0034] Fig. 2(d) illustrates cross-sectional views of different channel arrangements along line A A shown in Fig. 2(a) of example arrangements of channels in the riser, in accordance with embodiments of the present subject matter. In an example, the plurality of channels 210 may be disposed adjacent to each other in the riser 150. Fig. 2(d) (I) shows a riser 150 divided into four segments forming four channels 210a, 210b, 210c, and 210d disposed at an angle of 90° to each other. Fig. 2(d)(II) shows three channels 210a, 210b, and 210c disposed at an angle of 120° to each other. Fig. 2(d)(III) shows three channels 210a, 210b, and 210c, where two channels 210a and 210b each cover one quarter of the total cross-sectional area of the riser 150 and the third channel 210c covers the remaining half. Fig. 2(d)(IV) shows the riser 150 with two channels 210a and 210b each covering half the cross- sectional area of the riser 150. Fig. 2(d)(V) shows the riser 150 with five channels. Channels 210a, 210b, 210c, and 210d are arranged around a channel 210e disposed at a center of the riser 150. In such an arrangement, channel 210e may not have any feed nozzle. Regenerated catalyst alone flows through the channel 210e and mixes with the spent catalyst within the riser 150 once the channel 210e ends. This regenerated catalyst provides additional activity for improved cracking in the remaining length of the riser 150. Fig. 2(d)(VI) illustrates an alternate arrangement of three channels 210a, 210b, and 210c, where the cross-sectional areas of each of the channels 210 are different and they are disposed beside each other. Those skilled in the art will appreciate there are numerous combinations and geometries of the channels 210 possible in the riser 150 with different angles between the channel walls covering different cross-sectional areas.

[0035] In an embodiment, fresh and/or regenerated hot catalyst enters the riser 150 via standpipe 162 and flows up through each of the channels 210 carried by the steam 154 that is introduced from the bottom of the riser 150. Feed streams, corresponding to the fractions 122, obtained from crude oil as described before, flow separately into the different channels 210 and the feed is cracked into olefins and aromatics. The cracked products and catalyst rise in the riser 150 to the reactor 170 where the cracked product and spent catalyst are separated. In another embodiment, further cracking may occur in the riser 150 in the portion of the riser 150 without the channels 210. The cracked product may be further processed as described before.

[0036] Figs. 3(a)-3(c) illustrate different directions of flow of crude oil fractions and catalyst in the channels, in accordance with example embodiments of the present subject matter. As shown in Fig. 3(a), catalyst stream 310 and crude oil fraction stream 320 may flow in the same direction in the channel 210, termed as co-current flow. Fig. 3(b) and Fig. 3(c) illustrate counter-current flow such that catalyst stream 310 flows up from the bottom and crude oil fraction stream 320 flows down (Fig. 3(b)) or catalyst stream 310 flows down into the channel and the crude oil fraction stream 320 flows up the channel (Fig. 3(c)). The counter current flow can be obtained by varying the height at which the catalyst and feed stream are introduced in the riser channels 210, or by changing the WHSV, or any other such methods. Although not described herein, those skilled in the art will appreciate that designs of stripping vessel, regenerator vessel, cyclones will vary according to the direction of the flow of catalyst and hydrocarbons.

[0037] Although embodiments for an apparatus for performing crude oil cracking for producing petrochemical feedstock are described in language specific to structural features, it is to be understood that the specific features and methods are disclosed as example embodiments for implementing the claimed subject matter.