Patent Application
20170321127
The delayed coking process is a cyclic process that typically requires 18-24 hours for a complete cycle. To improve operational efficiency, delayed cokers typically operate in pairs with one coke drum filling and carrying out the coking conversion process while the other coke drum undergoes decoking operations. Thus, the first half of each cycle includes conversion of hydrocarbon feedstock and filling of the coker drum. Upon substantial completion of the conversion reaction, a steam-stripping step substantially removes trapped volatile compounds from within the coke-bed. Following steam stripping the first half of the cycle concludes with blow-down and water quenching of the coke. The second half of each cycle involves the de-coking process.
In the first half of the coking operation cycle, the steam-stripping step to remove volatile compounds commonly requires about an hour. The steam stripping step injects steam from a boiler through the bottom of the coke drum upward through the coke-bed thereby transferring heat to and carrying volatile compounds out through the overhead line of the coke drum.
The conversion of heavy petroleum products to coke and additional liquid products follows well known kinetics and reaction mechanisms. During the coking conversion process, thermal cracking of the heavy hydrocarbons follows first order kinetics dominated by free radical reaction mechanisms described below.
Step—1 Thermal cracking—initiation reactions—random production of free radicals
Resid or Asphaltenes Arx°+Ary°+R1°+R2°
Step—2 Propagation reactions—capping of free radicals (liquid and gas formation)
Arx°+Cx—Hy Ar—H (liquid)+free radicals
R1° or R2°+Cx—Hy R1—H or R2—H (liquid)+free radicals
R1° or R2° R3= or R4=(liquid)+H2+(C1-C4) Gaseous hydrocarbons
Step—3 Termination reactions (poly-condensation of aromatic free radicals)
Arx°+Ary° Coke formation
Disclosed herein is a system comprising a source of compressed gaseous hydrocarbons and a heater in fluid communication with the source of gaseous hydrocarbons. The heater is configured to receive a stream of flowing gaseous hydrocarbons and heat the gaseous hydrocarbons. Additionally, a coke drum is in fluid communication with the heater via a first path of fluid communication.
The system further optionally comprises a vacuum distillation unit in fluid communication with the furnace and a boiler in fluid communication with the furnace. Additionally, a compressor suitable for compressing the gaseous hydrocarbons is in fluid communication with the furnace.
Additionally, this disclosure describes an improved coking method. The improved method initially heats liquid hydrocarbons and passes the hot hydrocarbons to a coking drum. The method calls for maintaining the coking drum at a temperature sufficient to initiate the coking reaction and substantially complete the reaction while permitting the recovery of volatile hydrocarbons. The traditional steam stripping of the solid coke is replaced by the steps of heating compressed gaseous hydrocarbons and passing the hot gaseous hydrocarbons to the coking drum to effect stripping of volatile hydrocarbons from the coke drum.
With reference to
With reference to
Systems
With reference to
In the depiction of
As modified by the improvements discussed herein, system 5 may now operate without the need for steam boiler 90. Specifically, system 5 has been modified by incorporation of lines 72, 74, 76, compressor 80, compressed gas lines 78, 82, 84 and filter 50. Additionally, furnace heater 30 has been modified to accept and operate using gaseous hydrocarbon provided via gaseous hydrocarbon line 74. Further, delayed coker 40 is in fluid communication with compressed gaseous hydrocarbon line 78 and compressor 80 via compressed gaseous hydrocarbon line 82. Finally, in this system steam boiler 90 optionally provides steam to furnace heater 30 and coker feed line 34 via steam line 23. As described below, steam from boiler 90 is not utilized for stripping of volatile compounds from the coke product. Rather, boiler 90 optionally provides steam to delayed coker 40 only during the fill process.
With reference to
In the depiction of
As will be described in more detail below in the discussion of the method for increasing the production of desired hydrocarbon liquids, the use of steam produced by steam boiler 90 is now optional in view of the modifications to system 7. Specifically, system 7 has been modified by incorporation of lines 72, 74, 76, compressor 80, compressed gas lines 78, 82, 84 and filter 50. Additionally, furnace heater 30 has been modified to accept compressed gas via compressed gas line 78. Further, delayed coker 40 is in fluid communication with compressed gas line 78 and compressor 80 via compressed gas line 82. Finally, in this system steam boiler optionally provides steam to furnace heater 30 and coker feed line 34 via steam line 23. As described below, steam from boiler 90 is not utilized for stripping of volatile compounds from the coke product. Rather, boiler 90 optionally provides steam to delayed coker 40 only during the fill process.
Methods
In one embodiment, the present invention provides methods for upgrading heavy crude oil from various sources to SCO. In general, the API values of the heavy crude processed according to this method will range between about zero and about 21. The discussion of this method will reference
Within atmospheric distillation unit 10, the heavy crude oil undergoes distillation to produce two products, a diluent usually a condensate and an atmospheric residual component usually known as atmospheric resid. The condensate is removed via line 14 while the atmospheric resid passes through line 16 to vacuum distillation unit 20. The atmospheric resid subsequently undergoes vacuum distillation with the resulting liquid hydrocarbon component, in this case commonly known as vacuum resid, exiting vacuum distillation unit 20 via line 24 and the vacuum gas oil component exiting vacuum distillation unit 20 via line 22.
Liquid hydrocarbon enters furnace 30 via line 24 and is heated to a temperature of about 450° C. to about 550° C., more preferably to a temperature between about 480° C. (895F) to about 510° C. (950F). Subsequently, the liquid hydrocarbon, and optionally steam, passes through line 34 into one of at least two coke drums forming delayed coker 40. Depending upon the feed material and operating conditions, surfaces within furnace 30 may be prone to fouling by carbon buildup. To preclude fouling of furnace 30, steam from boiler 90 may optionally be provided to line 24 via line 23. Thus, steam and liquid hydrocarbon enter furnace 30. Alternatively, during the coker drum 40 fill process, steam may be injected into furnace 30 via a line 23. In either case, the optional addition of steam to furnace 30 occurs only during the filling step of coker drum 40. Generally, coke drum 40 will operate at a gage pressure between 50 to 500 kPa or more preferably between 100 to 400 kPa (15 to 60 psig) and temperatures preferably between 480C (895F) and 500C (930F).
In the practice of the present method for upgrading heavy crude oil to SCO, steam injection to furnace 30, if used, ceases when the flow of liquid hydrocarbon from furnace 30 to coker drum 40 stops. Accordingly, steam injection into furnace 30 during the filling of a coker drum does not play a role stripping of volatiles from the resulting coke product. However, as described in more detail below, steam injection during coker drum filling may be replaced with gaseous hydrocarbons.
In general, when practicing the method of upgrading heavy crude oil to SCO the coking process operates coker drum 40 during the fill process at a gage pressure between about 50 to 500 kPa. More typically, the coker drum will be maintained during the fill process at a gage pressure between 100 to 400 kPa (15 to 60 psig). Within coker drum 40, the liquid hydrocarbon undergoes the thermal cracking process and reaction steps discussed above. Thus, the coking process cracks the large hydrocarbons into smaller volatile compounds and solid coke.
As the hot feedstock enters coke drum 40, larger molecules crack into smaller volatile compounds and solid coke. As the coking reaction progresses, volatile material exits coker drum 40 through line 44 while solid coke accumulates from bottom to top within coker drum 40. Under typical operating conditions, filling of coker drum 40 with coke requires between about 8 to about 12 hours. In the method of the present invention, volatile compounds trapped within the solid coke and adhering to the surface of the coke and coker drum are removed by stripping with gaseous hydrocarbons obtained from refinery operations including gaseous hydrocarbons obtained from coking fractionator 60. Following the gaseous hydrocarbon stripping step, conventional water quench and decoking steps are carried out.
In the method of upgrading heavy crude oil to SCO, the gaseous hydrocarbon stripping process replaces the conventional steam stripping currently practiced in coking operations. Additionally, the present invention optionally permits replacement of all steam used during coking operations except for the steam/high pressure water used during decoking operations.
Accordingly, in the method of upgrading heavy crude oil to SCO, a gaseous hydrocarbon stream obtained from compressor 80 passes to furnace heater 30 via line 78. The compressed gaseous hydrocarbon stream is separated into two streams 82 and 84 inside furnace heater 30. Thus, the configuration of system 5 permits the optional use of steam from steam boiler 90 during the fill process; however, the method also provides for the replacement of the steam normally used in the stripping process with compressed gaseous hydrocarbons. In this version of the improved method, compressed gaseous hydrocarbons from compressor 80 pass through line 78 to line 82 or line 84. During the stripping process the heated gaseous hydrocarbons from line 82 enter coke drum 40 through a port (not shown) in the bottom of coke drum 40. Typically, the gaseous hydrocarbons used during the hydrocarbon-stripping step are heated to a temperature between about 450° C. and about 550° C. More preferably, the gaseous hydrocarbons are heated to a temperature between about 490° (915F) and about 510° C. (950F).
Thus, in the disclosed method, the steam-stripping step for removing unreacted volatile compounds from coke drum 40 is replaced by a hydrocarbon-stripping step using the gaseous hydrocarbon product from acid gas cleanup unit or other suitable processing unit capable of producing the desired gaseous hydrocarbons. The quantity of gaseous hydrocarbon by weight injected into coke drum 40 may range from about 1% to about 5% by weight of the original feed to coke drum 40. More typically, the quantity of gaseous hydrocarbon used will be between about 1% to about 2% by weight of the original feed to coke drum 40.
In the method of upgrading heavy crude oil to SCO, liquids produced from coke drum 40 pass via line 44 to an optional filter 50. Filter 50 traps any entrained coker fine particles that may have exited through the vapor line 44. Filter 50 generally comprises a material having pores of 1 to 40 micron size or more preferable between 1 to 20 micron size suitable for trapping the majority of solid particles of greater than one micron. Filter 50 may be of ceramic or metallic composition or any other material suitable for operating under the conditions experienced. Typically, filter 50 may experience temperatures between 450° C. and 520° C. More typically, filter 50 will operate under conditions of about 480° C. (895F) to about 510° C. (950F), thereby assuring that substantially all hydrocarbons passing through line 54 remain in the vapor phase prior to entering the fractionator 60.
As depicted in
Thus the present method advantageously uses the coker gaseous stream consisting primarily of inorganic and organic gases that are usually cleaned and flared as waste stream or burned to generate heat in a refinery. To provide control over the flow of gaseous hydrocarbons from acid gas clean up unit 70 to coker 40, the initial stream from acid gas clean up unit is divided into two streams 74 and 76 before compressor 80. Splitting of the gaseous hydrocarbon stream provides control over the flow rate of the stream through line 76, such that only the amount required by coker 40 passes through line 82 or 84. A common control valve, not shown, provides the operator with the ability to manage gas flow. Typically, gaseous hydrocarbon flow through either line 82 or 84 will be maintained within 0.5 wt % to 20 wt % of the flow passing through feed line 24 into heater 30. Under most common operating conditions, gaseous hydrocarbon flow through either line 82 or 84 will be maintained within 7 wt % to about 15 wt %. In general, a target hydrocarbon flow of about 10 wt % through either line 82 or 84 will be maintained. If desired, the hydrocarbon stream in line 74 may be used as fuel to heat the furnace 30.
With continued reference to
The quantity of coke produced according to this method may vary between 20 to 30 wt % of the feedstock provided to furnace heater 30.
The resulting synthetic crude liquid has the following properties: an API ranging from about 21 to about 30; a boiling point range between about 50° C. and about 530° C. (about 120° F. to about 1,100° F.). The method and system of the present invention is capable of a SCO production rate of about 750 bbl to about 850 bbl per thousand barrels of resid feedstock.
System 5 as depicted in
Furnace 30 heats the liquid hydrocarbon to between about 450° C. to about 550° C. More typically, furnace 30 heats the liquid hydrocarbon to between about 480° C. (895F) to about 510° C. (950F). Subsequently, the liquid hydrocarbon, and optionally steam, passes through line 34 into one of at least two coke drums forming delayed coker 40. Depending upon the feed material and operating conditions, surfaces within furnace 30 may be prone to fouling by carbon buildup. To preclude fouling of furnace 30, steam from boiler 90 may optionally be provided to line 24 via line 23. Thus, steam and liquid hydrocarbon enter furnace 30. Alternatively, during the coker drum 40 fill process, steam may be injected into furnace 30 via a line 23. In either case, the optional addition of steam to furnace 30 occurs only during the filling step of coker drum 40. Further, as described in more detail below, steam injection during coker drum filling may be replaced with gaseous hydrocarbons.
In general, when practicing the method of the present invention in the environment of a refinery the coking process maintains coker drum 40 at a gage pressure between about 50 to 500 kPa. More typically, coker drum 40 will be maintained at a gage pressure between 100 to 400 kPa (15 to 60 psig). Further, coker drum will typically operate at a temperature between about 480° C. and about 500° C. (895F to about 930F) during the fill/conversion and stripping processes. Within coker drum 40, the liquid hydrocarbon undergoes the thermal cracking process and reaction steps discussed above. Thus, the coking process cracks the large hydrocarbons into smaller volatile compounds and solid coke.
As the hot feedstock enters coke drum 40, larger molecules crack into smaller volatile compounds and solid coke. As the coking reaction progresses, volatile material exits coker drum 40 through line 44 while solid coke accumulates from bottom to top within coker drum 40. Under typical operating conditions, filling of coker drum 40 with coke requires between about 8 to about 12 hours. In the method of the present invention, volatile compounds trapped within the solid coke and adhering to the surface of the coke and coker drum are removed by stripping with gaseous hydrocarbons obtained and from refinery operations including gaseous hydrocarbons obtained from coking fractionator 60. Following the gaseous hydrocarbon stripping step, conventional water quench and decoking steps are carried out.
Thus, the gaseous hydrocarbon stripping process replaces the conventional steam stripping currently practiced in coking operations. Additionally, the present invention optionally permits replacement of all steam used during coking operations except for the steam/high pressure water used during decoking operations.
Accordingly, in the environment of a refinery using a coker 40 to increase valuable liquid products, a gaseous hydrocarbon stream obtained from compressor 80 passes to furnace heater 30 via line 78. The compressed gaseous hydrocarbon stream is separated into two streams 82 and 84 inside furnace heater 30, thereby allowing simultaneous addition of gaseous hydrocarbons through line 82 and 84. Thus, the configuration of system 7 permits the optional use of steam from steam boiler 90 when required during the fill process; however, the method also provides for the replacement of the steam normally used during the filling process with compressed gaseous hydrocarbons. Typically, the gaseous hydrocarbons used during the hydrocarbon-stripping step are heated to a temperature between about 450° C. and about 550° C. More preferably, the gaseous hydrocarbons are heated to a temperature between about 490° (915F) and about 510° C. (950F).
When practicing the improved coking method in the environment of a refinery to increase liquid yield, use of the additional gaseous hydrocarbons passing through line 82 during the fill and stripping steps improves the coker liquid yield. The quantity of gaseous stream that is injected through line 82 at the bottom of the coke drum 40 may range from 2% to 20%, more preferably between 5% to 10% by weight of the original feed passing from vacuum distillation unit 20 to coker drum 40. Thus, the present method provides for replacement of the steam-stripping step with a gaseous hydrocarbon-stripping step and optionally for replacement of all steam used during the coking process.
In the method of production of additional liquid in a refinery using delayed coker 40, the liquids produced from coke drum 40 passes via line 44 to an optional filter 50. Filter 50 traps any entrained coker fine particles that may have exited through the vapor line 44. Filter is a material having pores of 1 to 40 micron size or more preferable between 1 to 20 micron size suitable for trapping any solid particles of greater than one micron. Filter 50 may be of ceramic or metallic composition or any other material suitable for operating under the conditions experienced. Typically, filter 50 may experience temperatures between 430° C. and 520° C. More typically, filter 50 will operate under conditions of about 480° C. to about 510° C. thereby assuring that substantially all hydrocarbons passing through line 54 remain in the vapor phase prior to entering the fractionator 60.
As depicted in
To provide control over the flow of gaseous hydrocarbons from acid gas clean up unit 70 to coker 40, the initial stream from acid gas clean up unit is divided into two streams 74 and 76 before compressor 80. Splitting of the gaseous hydrocarbon stream provides control over the flow rate of the stream through line 76 such that only the amount required by coker 40 passes through line 82 or 84. Typically, gaseous hydrocarbon flow through either line 82 and/or 84 will be maintained within 0.5 wt % to 20 wt % of the feed line 24 entering the heater 30. If desired, the hydrocarbon stream in line 74 is used as fuel to heat the furnace 30.
As depicted in
System 7 as depicted in
When compared to conventional steam heating practices, the practice of the current method in connection with a delayed coker 40 in the environment of a refinery produces additional liquid yields of better quality with increase in hydrogen to carbon ratios. Total liquid yield accounts for about 75 to 85 volume percentage of the feedstock volume. The amount of net additional liquid yield as compared the practice of conventional operation, ranges between 5% to 10% by volume of the total liquid yield. The percentage increase will depend upon the quality of the feedstock, quantity of the gaseous stream used in place of steam to provide heat during the fill cycle, pressure in the coke drum 40 and the temperature of the coker furnace 30. Further, the quantity of coke produced according to this method is reduced when compared to conventional method by about 2% to 5% by weight of the original coke produced, thus reducing the coking cycle time, and hence improve the economics of the process.
The following non-limiting examples demonstrate the capabilities of the above described methods. The data provided herein was generated using a three inch diameter continuous delayed coker pilot plant having a volume of 509 cubic inches. Examples were prepared using a vacuum resid feedstock derived from oil sands bitumen, obtained from Alberta, Canada. The vacuum resid feedstock used in examples had the following properties:
In each example, resid feedstock was stored in a feed tank maintained at 150° C. and delivered to a furnace heater at a rate of 3,600 gram/hour. The furnace outlet temperature was maintained at 930° F. (500° C.). During the coking process, the coker drum pressure operated at either 15 psig or 40 psig. On average, the fill times for the pilot plant coker required between 3 to 4 hours.
Since the examples were carried out in a delayed coker pilot plant in a laboratory, the source of gaseous hydrocarbons was simulated using pure methane or a mixture of C1 (82 mole %) , C2 (10 mole %) and C3 (mole 8 %) hydrocarbons stored in a pressurized cylinder. As in a hydrocarbon processing facility the hydrocarbon gaseous stream may contain more than 60% by volume of methane thus replacing it with the indicated gases in a laboratory situation adequately duplicates the hydrocarbon processing facility environment. When used to replace conventional steam during the coking process, methane or mixture of hydrocarbons was pre-heated to a temperature greater than 350° C. in a fluidized sand bath before injecting into the furnace. Additionally, to demonstrate the ability to increase liquid yields with the injection of additional gaseous hydrocarbons (as shown in line 82 in
The fractionator (60 in
In another example designed to demonstrate the ability to increase liquid yield using additional gaseous hydrocarbon (5 wt % to 20 wt % of the feed) during the fill cycle, the fill step was carried out using methane or mixture of hydrocarbons and the stripping step was carried out with the same hydrocarbon. To provide a comparison, immediately after the coking portion was over, select runs used water, added to the furnace at a rate of 40 ml/hr to generate steam. Steam-stripping was carried out for 60 min to recover the additional liquid from the coke bed. Regardless of whether steam or methane was used to strip the coker, following stripping the coke drum was quenched with water.
This example demonstrates that steam could be replaced by gaseous hydrocarbons, both during the step of filling the coke drum and during the stripping step at the end of the run in a commercial delayed coking process. Tables 1 and 2 provide the experimental data for two different feedstocks having API 2.5 and 7.6 respectively. Steam and hydrocarbon velocities are shown in the description of the run conditions.
In these examples, a control run was carried out using steam during the step of filling the coke drum and during the stripping step. Velocities of steam and methane were kept at the same rate of cubic feet per hour at run conditions while the coker was operated at pressures of 15 psig and 40 psig. In Column 2 methane was introduced only during the filling step but was discontinued and steam used for the stripping step. In Columns 3 and 4, methane replaces steam during both the filling and stripping steps. In Column 5, methane velocity was tripled to see if methane velocity has any effect on the process yields. Results in Table 2 were generated using the same operating conditions but replacing the API 2.5 feed with a lighter feedstock of API 7.6.
The results in Tables 1 and 2 suggest that the yields of gas, liquid and coke vary within a percentage point (within the experimental errors of the pilot plant) in all conditions when steam (in control run) is replaced by methane.
With reference to Table 3, replacement of steam with a mixture of hydrocarbon gases containing methane (82 mole %), ethane (10 mole %) and propane (8 mole %) to simulate a typical refinery off-gas hydrocarbon gaseous stream, produced results are almost of the same order as that of the control runs carried over with steam and other runs using pure methane. The results clearly demonstrates that in a commercial delayed coker operation, steam use during the filling and stripping steps can be replaced with hydrocarbon mixture such as refinery off-gas or natural gas, whose quality and quantity can be varied depending on the economics of the availability of the hydrocarbon mixture.
Thus, as demonstrated by Table 3, the improved process will reduce the amount of waste water generated during coking operations. Replacement of high cost steam with readily available low cost hydrocarbon stream reduces operating costs without reducing coke yield.
Although there was no significant change in liquid yields when steam was replaced by methane, further analysis of the quality of the liquid indicates that methane actually stripped more of the heavier hydrocarbons such as distillate and gas oil (about 2 wt % more at 15 psig and 5 wt % more at 40 psig) and less of the lighter naphtha as compared to the steam.
This example demonstrates the resulting increase in liquid yields when replacing steam during the fill process with increased concentrations of methane at various conditions. Table 4 shows the results for the heavier coker feedstock of API 2.5 and Table 5 shows the results for the lighter coker feedstock of API 7.6.
As demonstrated by Table 4, operating the pilot coker with an increased amount of methane during the fill process increases the liquid yield. When operating at 40 psig, the liquid yield increased by about 5 wt % with the addition of methane at a flow rate of 13.1 cf/h (column 8), while the liquid yield increased further by 2 wt % to 70.4 wt % of the feed when methane flow rate almost doubled to 26.6 cf/h (column 9). The increase in liquid yield corresponded to a decrease in coke yield from 27.4 wt % to 24.1% to 21.1 wt % with the increase in methane concentrations.
The results in Table 4 further demonstrates that, while operating at a lower pressure of 15 psig, liquid yield increased by about 5 wt % with the addition of methane at 25.2 of/h. However, further increasing methane volume to 48.9 cf/h (column 11) did not produce any significant change in the yields of liquid, coke or gas. These results are consistent with the fact that at lower pressures addition of methyl or hydrogen radicals is ineffective as compared to higher pressures. Further, these results demonstrate that addition of excess gaseous hydrocarbon in a commercial environment operating at lower pressures will not produce an economic benefit.
Table 5 demonstrates that the method of increasing the liquid yield is not limited to one feedstock.
The example in Table 5 illustrates that when using a feedstock suitable for producing anode grade coke (of higher API or lower density), the results are quite encouraging. The feedstock used in Table 5 had an API gravity of 7.6 with an asphaltenes content of 8.0 wt % and a carbon residue of 19.3 wt %. As reflected in Table 5, when operating at a pressure of 40 psig the current method produced an increase in liquid production as the volume of methane increased during the fill process. As demonstrated, increasing the volume of methane with the increase in velocity from 1.37 cf/h to 26.6 cf/h increased the liquid yield from 68.8 wt % to 75.0 wt % of the feed. Increase in liquid yield is followed by corresponding decrease in coke yield in all cases.
For the example represented by Table 5, elemental analysis of the liquid products further continued the fact that H/C atomic ratios of the liquid product increased from 1.7 to 1.9 with the addition of methane at both pressures and flow rates.
The improved systems and methods described provide several advantages economically and environmentally. Replacing steam with gaseous hydrocarbons during the coker drum filling step or during the stripping step will enhance the liquid production, decrease the solid coke production and decrease the demand of steam. Hence the cost of steam generation and waste water production will be decreased. Though most of the experiments used in the examples rely on methane and mixtures of gaseous hydrocarbons containing from one to three carbon atoms and specific feed stocks, those skilled in the art will understand that that refinery off gases containing gaseous hydrocarbons will perform satisfactorily in the methods disclosed herein in conjunction with a wide range of API feed stocks.
Other embodiments of the improved systems and methods will be apparent to those skilled in the art. As such, the foregoing disclosure merely enables and describes the general uses, methods and descriptions of the improved systems and methods. Accordingly, the following claims define the true scope of the improvements disclosed herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US14/66649 | 11/20/2014 | WO | 00 |
