HEAVY HYDROCARBON FUEL

TECHNICAL FIELD

[0001] The present subject matter relates, generally, to fluid atomizers, and particularly but not exclusively, to fluid atomizers for atomizing a hydrocarbon 5 feed.

BACKGROUND

[0002] Generally, hydrocarbon feed is processed in refineries using reactors. For example, the process of fluidized catalytic cracking (FCC) is employed in petroleum refineries to convert hydrocarbon fractions of petroleum

10 crude oil having high boiling-point and high-molecular weight to lighter, low boiling and more valuable products, such as gasoline, olefin gases, and other products. The FCC process generally involves atomizing higher boiling fractions of crude oil and then feeding to a FCC riser reactor. During atomization, the pressurized liquid feed, such as higher boiling fractions of crude oil, interacts

15 with a gas, such as steam, due to which the higher boiling fraction liquids disintegrate into fine droplets. The atomized droplets are discharged into the FCC riser reactor for the cracking reactions.

[0003] Where the FCC unit is arranged either radially or at certain elevations, a feed nozzle or a re-slurry nozzle may be used in the FCC riser for

20 carrying out said atomization of the liquid hydrocarbon feed. For best results, a high degree of atomization is generally desired. Various feed nozzles or re-slurry nozzles with various different features for achieving high degree of atomization are known. For example, it is known that nozzle having an inlet for adding additional steam to the hydrocarbon feed may result in increased atomization of

25 the hydrocarbon feed.

[0004] Also, use of impingement plates in nozzles allowing for impinging of the feed onto the plates for higher atomization are known in the art. Such nozzles typically employ two imperforate plates - a first plate positioned at one end of the nozzle and the second plate positioned between the first plate and the outlet of the nozzle. As a result, using atomizing gas in the nozzle may lead to increased pressure drop across the feed nozzles. Further, the abrasive effects of the feed and other additives like catalysts may lead to accelerated erosion of the nozzle parts, thereby requiring frequent replacements of the same. Moreover, different types of feed may require different types of nozzles.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference the same elements.

[0006] Figure 1(a) and 1(b) illustrate a schematic representation of an atomizer assembly and a sectional view of the nozzle along the line B-B', respectively, in accordance with the present invention. [0007] Figure 2 illustrates a schematic representation of a fluid Catalytic Convertor (FCC) mounted with an atomizer, in accordance with the present invention.

DETAILED DESCRIPTION

[0008] The present subject matter relates to an atomizer assembly, for example, for atomizing liquid hydrocarbon feed for use in a Fluidized Catalytic Cracking (FCC) Process. While the following description is provided with reference to an FCC process as an example, it will be understood that the atomizer assembly of the present disclosure can be used in other reactors and processes as well. Thus, the FCC processes described herein are to be construed as examples only and not as a limitation.

[0009] FCC is a process for converting high-boiling, high-molecular weight hydrocarbon fractions of petroleum crude oil into hydrocarbons of lighter molecular weight, such as gasoline and olefinic gases. A hydrocarbon feed, which may include high-boiling, high-molecular weight hydrocarbon fractions of petroleum crude oil having initial boiling point greater than 340 °C and an average molecular weight greater than 200, is fed into the FCC unit using an atomizer or a nozzle. Subsequently, the feed may be heated to a high temperature in the presence of a catalyst. As a result, the long-chain molecules of the high- boiling hydrocarbon liquids breaks down to products of shorter-chain molecules. For best results, it is generally desired that the nozzle is capable of feeding the feed into the FCC unit at a high degree of atomization.

[0010] The conventionally known atomizers typically include a conduit having an inlet for the hydrocarbon feed, hereinafter referred to as feed, and an outlet for producing an atomized spray of the hydrocarbon. The feed may include a liquid feed of higher boiling fractions of petroleum crude oil. Further, the atomizer may include another inlet for an atomizing gas. The atomizing gas, such as steam, may be added to the feed to enhance the atomization of the feed. Such atomizers may allow for mixing of the feed with the atomizing gas in a mixing chamber within the atomizer. Such atomizers may further employ one or more impingement plates. An impingement plate is typically a circular ring shaped perforated wall having a number of apertures spread across the surface. The impingement plate may be positioned inside the conduit of the atomizer, such that the feed or a mixture of the feed and atomizing gas may strike the surface of the impingement plate. As the liquid feed or the mixture of feed and atomizing gas strikes the perforated impingement plate at high pressure, the feed further breaks down into smaller droplets as it passes across the plate through the apertures on the plate. Some atomizers may include a mixing chamber defined in the region downstream of the impingement plate. An atomized spray of the mixture of the feed and the atomizing steam is thereafter, obtained from an outlet of the atomizer.

[0011] As mentioned above, for best performance of the FCC unit, the feed may be sprayed into the FCC unit at high degree of atomization. One way of achieving high degree of atomization may be feeding the feed to the atomizer at a very high pressure. However, the method of using a high pressure feed may have certain drawbacks, such as greater erosion of the components of the atomizer. Further, using of high pressure feed entails high energy expenditure, and thereby makes the overall process lesser efficient.

[0012] Another method of achieving high degree of atomization may be adding large amount of atomizing steam to the feed. However, as it is generally observed, adding larger amount of atomizing steam leads to greater pressure drop across the atomizer.

[0013] The conventionally known atomizers are generally suited for a specific type of operation in the FCC process. As a result, for every different operation of the FCC process, a different atomizer may be required.

[0014] The present subject matter describes an atomizer assembly for atomizing liquid hydrocarbon feed that is capable of producing a high degree of atomization of the feed while causing a low pressure drop across the atomizer and that is versatile and useable with different types of feed. [0015] . The atomizer of the present subject matter includes an inner conduit and an outer conduit positioned along the length of the atomizer assembly. The inner conduit may include an inlet opening at an upstream end for receiving hydrocarbon feed. Further, the inner conduit may include an acceleration segment, such that the cross section of the inner conduit decreases along the length from an upstream end towards a downstream end of the acceleration segment. The acceleration segment is responsible for increasing the speed of fluid flowing though the acceleration segment. The inner conduit further includes a dip tube positioned inside the inner conduit. The dip tube is employed to supply an accelerating steam which is mixed with feed supplied into the inner conduit. The dip tube may include an inlet port at one end for receiving the accelerating steam, and a plurality of holes at the other for injecting accelerating steam in the acceleration segment of the inner conduit.

[0016] The nozzle assembly further includes an outer conduit, such that the outer conduit encloses the inner conduit. The outer conduit includes a first opening for receiving feed of atomizing steam which is mixed with the mixture of feed and accelerating steam. Furthermore, a shredder plate is provided within the outer conduit at which the mixture of feed and accelerating steam and atomizing steam, hereinafter referred to as feed mixture, is made to strike. The shredder plate is a perforated plate which includes a plurality of orifices on the surface. As the feed mixture strikes the shredder plate, the feed mixture is broken down to smaller droplets. The orifices on the shredder plate further help in breaking the feed mixture into even smaller droplets thereby increasing the degree of atomization of the feed mixture. [0017] Figure 1 illustrates a schematic diagram of an atomizer 100, as per an example implementation of the present subject matter. The atomizer 100 may be employed in a FCC unit 200, as illustrated in Fig. 2, for the production of various low molecular weight, low boiling hydrocarbon products, such as Propylene, Liquid Petroleum Gas (LPG), Naphtha and Cycle oil obtainable from high molecular weight and high boiling cuts of crude oil.

[0018] As illustrated in Fig. 1, the atomizer 100 includes an inner conduit 102 extending along with the length of the nozzle atomizer assembly 100. In an example, the conduit 102 has a circular cross section. The conduit 102 includes an inlet 104 at an upstream end of the nozzle assembly 100. The conduit 102 may receive the hydrocarbon feed, or feed, at the inlet 104. The feed, as discussed earlier, may include high molecular weight and high boiling hydrocarbons. In an example, the feed includes crude petroleum oil.

[0019] The conduit 102 may include an acceleration zone (108) for accelerating the motion of the feed in the nozzle. It may be understood that a greater speed of the feed may assist in greater degree of atomization of the feed. The inner conduit 102 may be formed of multiple segments along the length of the inner conduit 102. In an example, the conduit 102 includes a first segment 106 having a first cross-sectional area. The first segment 106 may include the inlet 104 for receiving the feed. Further downstream the first segment 106, the inner conduit 102 may include a second segment 108. In an example, the second segment 108 has a circular cross section and a frustoconical shape, such that the segment 108 tapers along its length toward the downstream end. Further downstream the second segment 108, the inner conduit includes a third segment 110 forming an accelerating zone having a cross sectional area lesser than the cross sectional area of the first segment 106. Further, in the said example, the cross section of the first segment 106 may have a diameter Di, while the cross section of the third segment 110 may have a diameter D ₂ , such that Di > D ₂ . It may be understood that the inner conduit 102 may have a cross section of any other shape as well. [0020] It would be appreciated by those skilled in the art, that a tapering section as provided by the accelerating zone formed by the second segment 108 may cause the speed of the fluid passing through it to increase. It may be understood that greater speed of the fluid aids in achieving better atomization of the fluid. However, it will further be appreciated that an increase in the speed may also be accompanied by drop in the pressure. As mentioned before, a large drop in the pressure across the nozzle may not be desirable.

[0021] The inner conduit further includes an outlet 112 for exiting the feed at an accelerated speed as compared to the entry speed of the feed at the inlet 104.

[0022] As shown in Fig. 1, the nozzle assembly further includes an outer conduit 120. The outer conduit may enclose the inner conduit 102, such that an annular space 124 is formed between the inner conduit 102 and the outer conduit 120. In an example the, the outer conduit 120 includes an opening 122 near the upstream end of the nozzle assembly for receiving atomizing steam. During operation of the nozzle, the atomizing steam may enter in the said annual region between the inner conduit and the outer conduit.

[0023] The atomizing steam may be used to assist in better atomization of the feed. The atomizing steam may include additives, for example, diluting hydrocarbon streams such as naphtha and bio-oil. These additives may help reduce the viscosity of the heavy hydrocarbon feed and thereby help in better atomization. The atomizing steam entering through the opening 122 may be mixed with the feed supplied by the inner conduit 102 to prepare a final feed mixture. Further, the amount of atomizing steam used may range from 1 weight percent to 5 weight percent of the final feed. Further, the content of naphtha in the atomizing steam may range from 0 weight percent to 10 weight percent, and the bio-oil content may range from 0-10 weight percent as well.

[0024] In an example, the outer conduit 120 further includes a lateral wall 126 separating the outer conduit 120 into a first section on the upstream side of the outer conduit and a second section at the downstream side of the outer conduit 120. The wall is positioned upstream of the outlet 112 of the inner conduit so that the feed supplied by the inner conduit is received in the second section of the outer conduit. Further, the lateral wall 126 may be perforated having a number of orifices 128 on the surface of the wall 126. During, operation of the nozzle assembly, the atomizing steam received in the annular space 124 may pass through the orifices in the lateral wall 126 to thereby enter the second section of the outer conduit 120. The outer conduit 120 may preferably have a circular cross section. Accordingly, the lateral wall 126 may also be circular in shape. However, other shapes of the outer conduit as well as the lateral wall may be possible.

[0025] In an example, further downstream the lateral wall 126, the outer conduit includes a shredder plate 130 for shearing, and consequently further atomizing, the feed and atomizing steam mixture. The shredder plate 130 may be positioned downstream of the outlet 112 of the inner conduit, so as to face the outlet 112. As such, during operation of the atomizer assembly 100, the feed supplied by inner conduit 102 while flowing downstream may strike the shredder plate 130. Similarly, the flow of atomizing steam supplied by the opening 122 of the outer conduit 120 may be obstructed by the shredder plate 112.

[0026] The shredder plate may be of a circular shape depending upon the shape of cross-section of the outer conduit 120. Further, the size of the shredder plate may vary as per the requirement. For example, the diameter of the shredder plate may be in the range of 0.5 to 1.5 times of the diameter of exit opening 112 of the inner conduit 102.

[0027] Fig. 1(b) illustrates a cross- sectional view of the shredder plate 130 along a line B-B' across the atomizer assembly 100. The shredder plate 130 includes centrals section which further includes a plurality grooves 138 along the running along the radial direction. The plurality of grooves 138 may be distributed over the surface of the shredder plate 130. Around the periphery of the grooves, the shredder plate then includes multiple orifices 132. The orifices 132 may have any of the various shapes, such as circular, rectangular, triangular, and so on. Further, these orifices 132 may have sharp edges which may aid in shearing as well as accelerating the atomization of the droplets of the feed and the atomizing steam into finer droplets, as the feed and the atomizing steam strike the shredder plate 130.

[0028] The grooves 138 of the shedder plate 130 are so designed to guide the movement of the droplets of the feed and the atomizing steam towards the orifices 132. The design of the grooves 138 also allows for increasing the velocity of droplets of the feed and atomizing steam as the droplets travel towards the orifices 132. As it may be appreciated, a higher velocity of the droplets of the feed while passing through the steam orifices 132 makes the atomization process more effective and efficient.

[0029] Returning back to Fig. 1(a), further downstream the shredder plate 130, the outer conduit 120 includes a mixing chamber 134. The mixing chamber 134 is defined between the shredder plate 130 and an extreme end of the outer conduit 120. The mixing chamber allows for a proper mixing of the feed (including the acceleration feed) and the atomizing steam so as to prepare spray mixture to be dispensed into the FCC reactor. The said extreme end of the outer conduit 120 may have a plurality of spray outlets 136.

[0030] For a high degree of atomization, it may be beneficial to have the feed supplied from the inner conduit 102 at a high speed. Although, the acceleration zone may help in increasing the otherwise low speed of feed supplied at the inlet 104, but the effect of the acceleration zone may not be enough to accelerate the feed to a sufficiently high speed.

[0031] To achieve a high speed of the feed, the present subject matter introduces a dip tube for adding an accelerating steam to the feed inside the inner conduit.

[0032] Fig. 1(a) illustrates an example of an atomizer assembly 100 including a dip tube 114. The dip tube 114 is positioned inside the inner conduit. The dip tube 114 includes an inlet port 118 for receiving a supply of accelerating steam and a plurality of holes exit 116 for dispensing the accelerating steam inside the inner conduit 102. The plurality of exit holes 116 may be positioned near the acceleration zone of the 108 of the inner conduit.

[0033] The combined effect of the acceleration zone and the accelerating steam imparts a higher speed to the feed.

[0034] During operation of the nozzle assembly 100, a feed containing higher boiling fractions of petroleum crude oil may be received at the inlet 104 of the inner conduit. The feed as received at the inlet 104 may not be at sufficiently high speed for atomization. At the same, an accelerating steam may be received by the dip tube 114 at the inlet port 118 of the dip tube 114. The accelerating steam is then supplied by the exit holes 116 of the dip tube near the acceleration segment 108 of the inner conduit 102. The accelerating steam mixes with the feed thereby imparting an acceleration to the feed. Further, as the feed along with the accelerating steam passes through the acceleration segment 108, a pressure differential is created due to the tapering cross section of the acceleration segment. The said pressure differential further accelerates the feed, thereby causing the feed to move at a much higher speed. A high speed feed is thereafter ejected from the outlet 112 of the inner conduit 102.

[0035] Simultaneously, atomizing steam is received inside the annular space 124 between the inner conduit 102 and outer conduit 120 from the opening 122 in the first section of the outer conduit. As mentioned above, the atomizing steam may include additives, such as naphtha and bio-oil. As the atomizing steam moves downstream, it is confronted by the lateral wall 126 having a number of orifices 128 on the surface of the lateral wall. The atomizing steam passes through the orifices 128 to enter into the second section of the outer conduit. Here, the atomizing steam interacts with the high speed feed ejected out of the outlet 112 of the inner conduit 102 thereby forming a mixture with the feed and hence the atomizing the feed.

[0036] Thereafter, the mixture of high speed feed (including the accelerating steam) and the atomizing steam may hit upon the shredder plate 130. As the high speed feed hits the grooves 138 in central region of the shredder plate 130, the feed is guided by the grooves 138 along the radial direction towards the orifices 132 present near the periphery of the shredder plate 130. The droplets of the feed are sheared down by the sharp edges of the orifices, thereby leading to further atomization of the feed. As mentioned before, the orifices 128 may have various kinds of shapes, such as triangular and rectangular. As the feed and atomizing steam mixture moves along the grooves 138 towards the orifices 132, the process of atomization is accelerated.

[0037] The feed and atomizing steam mixture after passing through the shredder plate 130 enters the mixing zone 134. The said mixture resides for a reasonable period of time in the mixing chamber before being sprayed out from the spray outlets 136 at the nozzle tip. The spray outlets are so configured to produce a flat fan spray form flat fan spray having spray angle in the range of 60- 120°. The feed spray exiting from the spray outlets 136 thereafter enters into riser of the FCC apparatus. [0038] Fig. 2 illustrates a Fluid Catalytic Cracking apparatus 200, hereinafter referred to as apparatus 200. The apparatus 200 includes a riser 202 having a riser steam channel. The riser 202 may employ a feed atomizer 100a and a re-slurry atomizer 100b for atomizing liquid hydrocarbon feed. The feed atomizer 100a and the re- slurry atomizer 100b are arranged either radially or at different elevations in FCC riser. The riser assembly 202 is coupled to a separator assembly 208 via riser outlet 206. The reactor may include a reactor stripper 212 for stripping off catalyst of the hydrocarbons product stream. The reactor may further include a cyclone separator 210. The separator assembly 208 may then be coupled to a fractionator 224 via a separator outlet 222 to fractionate the product stream.

[0039] Further, the FCC apparatus may include a regenerator 216 coupled to the separator assembly 208 and the riser 202 via a first catalyst channel 214 and a second catalyst channel 220, respectively. The regenerator 216 may include a flue gas cyclone separator 226. The regenerator 216 may further include an air channel 218 and a flue gas channel 228. The regenerator may further be coupled to a heat recovery section 230 via the flue gas channel 228, while the heat recovery section 230 may further be coupled to flue gas treatment plant 232.

[0040] During operation of the FCC apparatus 200, the riser 202 receives riser steam via the riser steam channel 204. Further, at least one of the feed atomizer 100a and the re-slurry atomizer 100b receives the hydrocarbon feed which is to be atomized. As mentioned earlier, the hydrocarbon feed may include vacuum gas oil, vacuum residue, atmospheric residue, paraffin extracts, heavy fuel oil, recycled Heavy Cycle Oil (HCO) and recycled slurry. The feed atomizer 100a or the re-slurry atomizer 100b may atomize the hydrocarbon feed to produce an atomized feed as per the operation of the atomizer 100, as explained before.

[0041] As the atomized feed flows through the riser 202, and atomized feed may come in contact with upwardly flowing regenerated catalyst particles. The atomized feed may further be assisted by riser steam flowing through the riser 202. The temperature of the regenerated catalyst may generally be kept between 650-750°C, and preferably between 670-720°C. As the droplets of the atomized feed come in contact with regenerated catalyst, the feed droplets react with the regenerated catalyst and crack down to low molecular weight and low boiling cracked products, such as like propylene, LPG, naphtha and cycle oil. [0042] The cracked products along with the catalyst particles may be received from the riser 202 in the separator assembly 208 via the riser outlet 206. Thereafter, the cracked products are guided into the cyclone separators 210. The cyclone separators 210 separates the catalyst particles from the cracked products. The separated catalyst particles are retrieved back in the reactor stripper 212. In the reactor stripper, the catalyst particles are treated with a stripping steam, so as to further remove any hydrocarbons. After treatment with the stripping steam, regenerated catalyst particles largely free of hydrocarbons and spent catalyst particles containing un-strippable coke are retrieved. However, the spent catalyst particles which contain un-strippable coke particles are unfit for circulating back to the riser 202. These spent catalyst particles are lead via first catalyst channel 214 into the regenerator 216. In the regenerator, the spent catalyst particles are subjected to coke burning to remove the coke particles. The process of the coke burning may be effected in presence of air received inside the regenerator via air channel 218. Upon removing the coke particles, regenerated catalyst particles are recovered. The regenerated catalyst particles are then circulated back to the riser 202 via the second catalyst channel 220.

[0043] The cracked products produced in the separator assembly 208 may be guided by reactor conduit to be received into the fractionator 224 where the cracked products undergo distillation. In the fractionator 224, as per the generally known processes in the prior art, the cracked products are broken down into various lighter compounds, and the different lighter compounds are received based upon their corresponding boiling temperatures.

[0044] At the same time, the coke burning of the spent catalyst in the regenerator 216 results in production of mixture of catalyst fine and flue gas. To separate the catalyst fines from the flue gas, the said mixture is lead into the regenerator cyclone separators 226. The cyclone separators 226 separate the catalyst fines from the flue gas, and catalyst particles are recovered therefrom. Thereafter, the flue gas from regenerator 216 is lead via flue gas conduit 228 into a heat recovery section 230. Following this, the flue gas may enter a flue gas treatment plant 232.

[0045] The present simple and durable embodiment of the spray nozzle assembly results in effective, optimum, and relatively inexpensive atomization of the liquid feed for FCC process.

[0046] Although examples for the present disclosure have been described in language specific to structural features and/or methods, it should be understood that the appended claims are not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed and explained as examples of the present disclosure.