US 3213154 A
Description (OCR text may contain errors)
ETHANE Filed May 28, 1962 Oct. 19, 1965 NGL 5 DEA NGL I3 INVENTOR. RD. BAUER BY r A TTORNEYS United States Patent ice 3,213,154 HYDROCARBON TREATING Robert D. Bauer, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed May 28, 1962, Ser. No. 198,271 6 Claims. (Cl. 260-676) This invention relates to hydrocarbon treating. In one aspect the invention relates to a process for removing an unwanted contaminant from a hydrocarbon stream by contact with a treating agent. In another aspect the invention relates to process for treating a hydrocarbon stream with a treating agent to remove a contaminant.
Frequently, it is desirable to remove a contaminant from a hydrocarbon stream. A very useful contaminant removal process comprises contacting the hydrocarbon stream with a treating agent having an affinity for the contaminant. This contacting results in a treated hydrocarbon stream and a stream of treating agent containing the contaminant, the separate streams being removed from the contacting zone. To prevent foaming and entrainment of the treating solution in the treated hydrocarbon stream, it is preferable to maintain the hydrocarbon stream in the vapor state and to prevent any condensation of the hydrocarbon during the treatment.
Although it is possible to prevent condensation by increasing the temperature of the contact zone, this is not desirable in most instances because of its adverse effect on the treating step. For example, when treating with an amine, such as diethanol amine, the elfectiveness of the treating agent in removing the contaminant is reduced since the alfinity of the treating agent for the contaminant is reduced at higher temperatures. On the other hand, it is possible to prevent condensation by reducing the pressure in the contact zone, but this in many instances is undesirable because of the relatively high pumping head required to pump the treated stream into subsequent separation means.
An object of my invention is to treat a hydrocarbon stream for the removal of a contaminant therefrom,
Another object of my invention is to prevent foaming and entrainment of a treating agent while treating a vaporous hydrocarbon with a treating agent.
Another object of my invention is to prevent condensation of the hydrocarbon while treating a vaporous hydrocarbon stream with a treating agent.
Another object of my invention is to permit treating of a relatively large quantity of a relatively high-boiling component in the vapor phase at a temperature below its boiling point.
Another object of my invention is to provide hydrocarbon treating process.
Other aspects, objects and the advantages of my invention are apparent in the written description, the drawing and the claims.
I have found that with the temperature and pressure of treating determined, if only vaporous material is fed to the treating zone and if a component is present which boils higher than the treating temperature, the amount of this component which can be treated is determined by the amount of a lower-boiling component present. The composition of a vapor in equilibrium with a liquid in a multicomponent system is determined by the temperature and pressure. Larger amounts of a relatively high-boiling component can be removed with larger amounts of a relatively low-boiling component, since the composition of the vapor is constant, the lighter component thus carrying the heavier component in the overhead vapor.
According to my invention, condensation of a vaporous hydrocarbon during treatment with a treating agent to remove a contaminant is prevented by recycling a light fraction separated from the treated hydrocarbon. A hy- Patented Oct. 19, 1965 drocarbon feed comprising a lower-boiling component and a higher-boiling component and containing a contaminant is contacted in a treating zone with a treating agent having an afiinity for the contaminant to be removed. The contacting is carried out at a temperature intermediate the boiling point of the lower-boiling component and the higher-boiling component at the pressure of the treating zone. A stream containing the treating agent and the contaminants removed from the hydrocarbon is withdrawn from the treating zone, the treating agent being discarded or regenerated for further use, and substantially contaminant-free hydrocarbon stream is withdrawn from the treating zone and separated into a first relatively light fraction and a second relatively heavy fraction. The light fraction contains the predominant amount of the lower-boiling component while the heavy fraction contains the predominant amount of the higher-boiling component. That is, of the amount in the total stream, the predominant amount of the lower-boiling component is in the light fraction and the predominant amount of the higher boiling component is in the heavy fraction.
My invention is not limited to the treatment of hydrocarbon streams having only two components. Where the stream contains appreciable amounts of three or more components, the relatively light fraction contains at least one of the lower-boiling components while the relatively heavy fraction contains at least one of the higher-boiling components.
Condensation of a heavier component of the hydrocarbon stream in the contacting zone is prevented by recycling a sufiicient amount of a light fraction to maintain the feed in the vapor state at the temperature and pressure existing in the treating zone.
The treating agent utilized in the practice of my invention is a material having a marked afiinity for the contaminant to be removed as compared with the affinity for the hydrocarbon stream being treated. For example, the hydrocarbon stream can be contacted with a caustic solution for the removal of an acid gas such as carbon dioxide or hydrogen sulfide. As another example, the hydrocarbon stream can be treated with an aliphatic amine for removal of the same acid gases. Of the aliphatic amines, alkanol amines have been particularly useful, especially monoethanol amine (MEA), diethanol amine (DEA) and triethanol amine (TEA). Further, combinations of agents are included in the broad designation treating agent. For example, a combination of an agent having an afiinity for an acid gas and one having an affinity for moisture, such as a solution of an amine and a liquid polybasic aliphatic alcohol such as triethanol amine and diethylene glycol, can be used. The use of an amine solution, which has added to it an alkali metal compound, such as for example sodium hydroxide, sodium sulfide or sodium carbonate, is useful in some situations.
My invention also is applicable to treating processes in which two or more treating steps are employed, such as a caustic treating step following an amine treating step. In such an instance the light fraction can be recycled to one or more of the contacting steps or can be recycled to the feed prior to the first or a subsequent step where necessary to prevent condensation. Any hydrocarbons in which the components are maintained in the vapor state during treatment are suitable for operation according to my invention. Since it is easier to maintain the relatively light hydrocarbons in the vapor state, my invention finds more applicability to these relatively light hydrocarbons. My invention finds particular utility in the treatment of a stream comprising relatively large amounts of ethane and propane from which hydrogen sulfide or carbon dioxide must be removed.
In the contacting step of my invention, vaporous hydrocarbon is intimately contacted with a liquid treating agent in which the hydrocarbon is insoluble but which agent has an affinity for the contaminant to be removed. Either the vaporous hydrocarbon or the liquid treating agent can be the continuous phase in the contacting zone. Suitable means for effecting contact between the vaporous hydrocarbon and the liquid treating agent include packed towers, columns containing bubble cap trays or valve trays, vessels with stirring means, flow conduits or vessels with turbulence-inducing means such as baffles, or other means for effecting intimate contact of the hydrocarbon and the treating agent.
Further according to my invention, there are provided hydrocarbon treating means comprising a treating vessel having means for contacting the vaporous hydrocarbon and the liquid treating agent, and having a hydrocarbon inlet for the contaminant-containing hydrocarbon, a treating agent inlet, a treated hydrocarbon outlet and a treating agent outlet. The hydrocarbon outlet communicates with a hydrocarbon separator for separating the treated stream into a relatively low-boiling fraction and a relatively highboiling fraction and means for withdrawing the two frac tions separately are provided. A recycle conduit is connected with the light fraction outlet and with the hydrocarbon inlet of the treating vessel and means are provided to control the flow through the recycle conduit to permit flow of the desired amount of light fraction to prevent condensation of a portion of the hydrocarbon during the contacting step.
In the drawing, a fractional distillation column is provided with an inlet 11, an overhead outlet 12 and a bottom outlet 13. The stream fed through inlet 11 comprises natural gas liquids and this stream is separated in such a manner that the overhead stream comprises C and C hydrocarbons, the heavier material being removed through outlet 13. A reboiler 14 is provided as shown.
The stream comprising the C and C hydrocarbon, predominantly ethane and propane, but also containing varying amounts of other hydrocarbons, and hydrogen sulfide and carbon dioxide, is partially condensed in condenser 15 and passed into accumulator 16, from which a stream of liquid is returned by pump 17 as reflux for column 10, while a vapor stream is transferred through heater 18 to treating vessel 19, and through hydrocarbon inlet 19 to treating vessel 21. Means 22 to feed a chemical treating agent to vessel 21 are provided as shown. A hydrocarbon outlet to withdraw treated hydrocarbon from vessel 21 is provided in the upper portion of the vessel and is designated by the numeral 23. Means to withdraw used treating agent are provided in the lower portion of the vessel and designated by the numeral 24. The treated hydrocarbon stream is passed through a cooler 26 and an accumulator 27 to hydrocarbon separator 28. Light fraction outlet 29 and heavy fraction outlet 31 are provided from separator 28. Separator 28 is further provided with a reboiler 31. The light fraction outlet is passed through heat exchanger 32 and cooler 33 into accumulator 34. A portion of the condensed stream is returned by pump 36 as reflux to separator 28 while the vaporous portion is removed through a light fraction conduit 37. The desired amount of the light fraction is returned through pipe 38 and heater 39 to outlet 12, and thus recycled to vessel 21. A motor valve 41, regulated by flow recordercontroller 42 controls the quantity of the light fraction recycled.
Heater 39 is provided so that a sufficient amount of the light fraction can be introduced Without cooling the stream in pipe 12 below that desired for accumulator 16 for the reflux to column 10.
The maximum temperature which can be maintained in accumulator 16 is determined by the maximum temperature which can be permitted in treating vessel 21 and still obtain effective treatment. The composition of the vapor stream removed from accumulator 16, for a given group of components, is determined by the temperature maintained in the accumulator. Therefore, when insufficient quantities of the lighter component or components are present a relatively small quantity of the heavier components is carried to treater 21. For example, when the treated stream is substantially all ethane and propane, and the temperature which must be maintained in accumulator 16 is less than the boiling point of propane at the treating pressure, the amount of propane which can be carried to the treater is determined by the amount of ethane which is present in accumulator 16. Flow controller 42 is adjusted to maintain the desired quantity of the lighter fraction. When the composition of the natural gas liquids being fed through inlet 11 changes appreciably, the set point of controller 42 must be adjusted to compensate for the change. That is, when the proportion of light fraction decreases the flow through flow controller 42 is increased and vice versa.
Table I below shows the effect of temperature on the propane content of the vapor stream from accumulator 16 with variations in temperature. The liquid volume percent of propane in the vapor is based on a C /C ratio of 5/95. The values are determined for an accumulator pressure of 335 p.s.i.g.
TABLE I Degrees F.: L.V. percent C in vapor Example In an example according to my invention a stream of natural gas liquids containing relatively large amounts of C and C and heavier and a relatively small amount of C and lighter is fed to inlet 11. Treating vessel 21 is a tower, 8 feet in diameter, containing 20 bubble-cap trays at a spacing of 24 inches. Distillation column 10 operates at a pressure of 340 p.s.i.g. and with temperatures at the top and bottom, respectively, of 127 F. and 247 F. Separator 28 also is a distillation column and operates at a pressure of 470 p.s.i.g. with top and bottom temperatures, respectively, of 62 F. and 172 F. Accumulator 16 operates at a pressure of 335 p.s.i.g. and a temperature of 125 F. Since the vapor stream from accumulator 16 always is saturated vapor, to prevent condensation due to the slight amount of cooling occurring between the outlet of accumulator 16 and the inlet of treater 21, heater 18 is used to raise the temperature about 5 F thus feeding the stream to treater 21 at 130 F. The stream of lean diethanol amine which is fed through pipe 22 is also temperature controlled and enters at a temperature of about F. The pressure in treater 21 is 330 p.s.i.g. The composition of the various streams is given in Table II below. It is seen that suflicient C is recycled to permit continuous removal of all of the C in the overhead plus the C in the recycle and charge it to treater 21.
TABLE II Stream Num- 25 255 280 25 47 5 4, 845 5, 320 475 Trace Additional steps can be included in the over-all process. For example, in some instances it is desirable to have caustic wash, water wash and dehydration steps following the amine treating step. Means for separating the removed contaminant from the treating agent can be provided, as for example, means for heating and flashing the rich treating agent stream, thus separating the removed contaminant and providing lean treating agent to be returned through pipe 22. It will be understood by those skilled in the art that many details, which have been eliminated from the drawing to simplify the description of the invention, can be added. For example, additional meters, controls, valves, pumps, duplication of the items of equipment described, etc. can be, and in most instances will be, provided.
Reasonable variation and modification are possible within the scope of my invention which sets forth process and apparatus for treating a contaminant-containing hydrocarbon stream, including recycling a portion of the light fraction of the treated hydrocarbon to prevent condensation during treatment.
I claim: 1. A hydrocarbon treating process, comprising: feeding into an accumulation zone a hydrocarbon feed comprising a lower-boiling component and a higherboiling component and containing a contaminant; removing overhead from said accumulation zone in vapor state at a temperature intermediate the boiling points of said lower-boiling component and said higher-boiling component, a treater feed stream comprising an equilibrium mixture of said lower-boiling component and said higher-boiling component and said contaminant; and removing an equilibrium liquid mixture from the accumulation zone contacting said treater feed stream in an extraction zone, with a liquid treating agent having an afiinity for said contaminant, at a temperature intermediate the boiling points of said lower-boiling component and said higher-boiling component at the pressure of said extraction zone;
withdrawing a stream containing substantially all of said treating agent and said contaminant, from said extraction zone;
withdrawing a substantially contaminant-free hydrocarbon stream from said extraction zone;
separating said relatively contaminant-free hydrocarbon stream into a first fraction containing the predominant amount of said lower-boiling component and a second fraction containing the predominant amount of said higher-boiling component;
recovering said second fraction as a product of the process; and
recycling a suflicient amount of said first fraction to said hydrocarbon feed, to increase the ratio of the amount of said lower-boiling component in said feed to the amount of said higher-boiling component in said feed to maintain the desired flow of said higher-boiling component in the vapor state at said temperature and said pressure in said extraction zone.
2. The process of claim 1 wherein said treating agent is an aliphatic amine.
3. The process of claim 2 wherein said aliphatic amine is selected from the group consisting of monoethanol amine, diethanol amine and triethanol amine, and wherein said lower-boiling component is ethane and said higherboiling component is propane and said contaminant is an acid gas.
4. A hydrocarbon treating process, comprising:
separating a hydrocarbon feed in a separation zone and passing a hydrocarbon stream comprising a lowerboiling component and a higher-boiling component and containing a contaminant overhead from said separation zone;
passing said hydrocarbon stream into an accumulation zone;
in said accumulation zone separating said hydrocarbon stream into vapor and liquid;
returning liquid from said accumulation zone to said separation zone as reflux therefor;
removing vapor from said accumulation zone and passing said vapor comprising said contaminant and said lower boiling and higher boiling components into an extraction zone;
in said extraction zone contacting said vapor With a liquid treating agent having an aflinity for said contaminant, at a temperature intermediate the boiling point of said lower-boiling component and said higher-boiling component at the pressure of said extrac tion zone;
withdrawing a stream containing substantially all of said treating agent and said contaminant from said extraction zone;
withdrawing a substantially contaminant-free hydrocarbon stream from said extraction zone; separating said substantially contaminant-free hydrocarbon stream into a first fraction containing the predominant amount of said lower-boiling component and a second fraction containing the predominant amount of said higher-boiling component; and
recycling a sufficient amount of said first fraction to said accumulation zone to maintain the desired flow of said higher-boiling component to said extraction zone in the vapor state at said temperature and said pressure in said extraction zone.
5. The process of claim 4 wherein said treating agent in a aliphatic amine.
6. The process of claim 5 wherein said aliphatic amine is selected from the group consisting of monoethanol amine, diethanol amine and triethanol amine, and wherein said lower-boiling component is ethane and said higherboiling component is propane and said contaminant is an acid gas.
References Cited by the Examiner UNITED STATES PATENTS 2,311,342 2/ 43 Kerns et al. 2,374,984 5/45 Evans et al. -48 X 2,399,142 4/46 Reed.
2,596,785 5/52 Nelly et al 5573 2,608,461 8/52 Frazier 23-3 2,614,658 10/52 Maher et al 55-51 2,718,454 9/55 Wylie 23-2 2,804,488 8/57 Cobb 55-51 2,813,920 11/57 Cobb 55-51 2,815,650 12/57 McIntire et al 5551 2,860,030 11/58 Goldtrap et al. 23-3 2,877,101 3/59 Rector 23-2 2,974,750 3/ 61 Retallick 55-51 3,060,662 10/62 Parsons et al. 55-51 X 3,078,634 2/63 Milton 55-73 3,100,680 8/63 Shaw et al. 23-3 3,102,012 8/63 Dowd 55-43 3,122,496 2/ 64 Harper 208-342 FOREIGN PATENTS 837,765 6/60 Great Britain.
REUBEN FRIEDMAN, Primary Examiner.