US2134702A - Separation of hydrocarbons - Google Patents

Description

Nov. 1, 1938. QT C :BREWS TER 2,134,702

SEPARATION OF HYDROCARBONS Filed Sept. 29, 1956 574545 645OL/1VE INVENTOR ATTORNEYS Patented Nov. 1, 1938 2,134,702 SEPARATION or nrnnocalmons Oswald C. Brewster,

Litchfield, Conn.,. assignor to Refinery Engineers Inc., New York, N. Y., a corporation of Missouri Application September 29, 1936, Serial No. 103,124 20 Claims. (Cl. 62-17515) This invention relates to the recovery of liquefiable components from. hydrocarbon gas and more particularly to an improved method wherein the process and the-liquid condensate formed furnishes-the refrigerant used in one part of the process.

In a copending application, Serial Number 103,121 filed September 29, 1936, a novel methare that the vapor mixture is cooled prior to its expansion that the vapors evolved from the 10 that a part of such heat ab- 15 that the compressed refrigerant 25 refrigerant to make up for losses or to provide 30 continuously .or inof the cooling water available under the com- 40 ing; and that fractionation of the refrigerant, at both its high-boiling and be continuously and automatlcally maintained to the end that said pressure and temperature 5 of varying quality from a single field or from diftemperature conditions available in .through pipe ferent fields. Thus, apparatus for the practice of this invention being transportable, the appaaratus may be readily moved into any field and it will automatically select and maintain a refrigerant correctly suited to the pressure and the apparatus and field.

This invention resides in the separate or conjoint use of the several features thereof herein described and is not limited to the simultaneous use of all or of any particular number of such features.

The operation of the invention will be fully un derstood from the following description taken in connection with-the accompanying drawing, the single figure of which represents diagrammatically apparatus for the practice of a preferred embodiment of the invention. Referring to the drawing, wet hydrocarbon gas under substantial pressure enters the system and passes through heat exchanger 2 in which'it is partially cooled by indirect heat exchange with cold dry gas. From exchanger 2 the feed gas passes through pipe 3 to heat exchanger 4 in which it is further cooled by indirect contact-with a vaporizing refrigerant as will be more fully described. The feed then asses through pipe 5 to exchanger 6 in which it is still further chilled by heat exchange with cold dry gas. The cooling suffered by the feed gas results in the condensation of practically all of the desired higher boiling constituents of the gas, along with a certain quantity of lower boiling material, not desired, forming a wild" condensate. The unliquefled gas and the condensate pass through pipe 1 to separator 3 in which gas and condensate are separated.

The unliquefied dry gas passes 8 through pipe 9 to the inlet of power cylinder II of engine H. The gas expands polytropically in engine ll, its energy being converted into work, and the gas itself being cooled by the expansion according to well known thermodynamic principles. The cooled expanded gas exhausts from the engine into pipe l2 through which it passes to heat exchanger 3 in which the gas chills the wet feed gas as already described and is itself warmed. The partially warmed dry gas then passes through pipe II to exchanger 2 in which it imparts cooling to the feed gas and is in turn further warmed. The dry gas, now warmed to a point such that it is no longer available as a cooling medium for feed gas, passes through pipe l4 to any desired disposal system.

The auxiliary refrigerating system, mentioned above, operates in the following manner. Volatile hydrocarbon liquid serving as the refrigerant and maintained under a relatively high pressure is drawn from accumulator I! through pipe It to heat exchanger 4. The pressure on the liquid is released by throttle valve or orifice located in pipe l6. Due to the volatility of the liquid it vaporizes on release of pressure and is thus cooled to its boiling point under the reduced pressure and on passing through heat exchanger 4 absorbs heat from the feed gas passing therethrough thereby cooling the feed gas and vaporizing still more of the liquid in the usual manner of operation of this type of refrigerant. The vaporized refrigerant along with any unvaporized portion passes from exchanger 4 through pipe ll to separator I! where vapor and liquid are separated. The vapor passes from separator I! through pipe from separator into the system until such a 2|! to the compressor end 2| of engine II which is driven by the expanding dry gas as already described. The vapor is compressed to a relatively high pressure slightly greater than that existin in accumulator drum i5 to allow for frictional losses. The vapor, on being compressed, is heated as usual when gases are compressed and discharges from compressor 2| into pipe 22 through which it passes to reboiler coil 23 located so as to furnish the required heat for condensate stabilizer 24. The hot compressed vapor in passing through coil 23 is cooled and may be partially condensed therein and passes through pipe 25 to condenser 26 in which it is further cooled and condensed by any suitable cooling medium, such as water or air. The cooled refrigerant passes through pipe 21 to accumulator l5. Any uncondensed lighter portion is vented through valve controlled pipe 28 to any suitable disposal system. This uncondensed portion may be returned to the feed gas tail gas or otherwise Any unvaporized refrigerant collected in separator l9 may be withdrawn by pump 30 and discharged through pipe 29 to stabilizer 24 as shown or may be otherwise disposed of according to its physical characteristics. The amount of heat delivered to coil 23 is regulated by by-passing controlled amounts of the hot compressed vapor around coil 23 by means of valve controlled by-pass pipe 3|.

The refrigerant used in this auxiliary system is derived directly from the condensate formed and is secured in the following manner. When a plant operating in accordance with the invention is starting up for the first time, no refrigerant is available for the auxiliary system. However. enough refrigeration is available from the cold expanded dry gas in exchangers 2 and 6 that a certain amount of condensate is formed and collected in separator 8 even though exchanger 4 is idle. This condensate, or a portion of it, is drawn through pipe 32 and released into the refri erant coil of exchanger 4. The release in pressure and the fact that the feed gas passing through exchanger 4 is warmer than the condensate from separator-8 both cause vaporization of the condensate flashed into the coil of exchanger 4, resulting in some refrigerating effect. The partially vaporized material passes to separator l9 wherein the heavier, less volatile portion is eliminated from the system as a liquid through pipe 29. The vaporized portion is compressed by compressor 2| and a portion is condensed by condenser 26 and is collected in acwhich does not condense under the temperature and pressure conditions imposed is eliminated through pipe 28. The liquefied portion is flashed through pipe l6 into exchanger 4 as in normal operation. Condensate from separator 8 is fed time that sufllcient refrigerant has been accumulated. The system thus fractionates from the condensate an intermediate portion suited to the conditions. Components of too high boiling range to vaporize in exchanger 4 are eliminated at separator l9 and components of too low boiling range to condense under the conditions in accumulator I5 are rejected there as gas. Thereafter small amounts of condensate from separator 8 are introduced into the system from time to time to make up for unavoidable losses of refrigerant in operation and these added amounts are likewise fractionated by the system as they are added.

The cold "wild The lighter highly volatile portion condensate collected in sepai9 determine its characteristics; may be condensed in condenser condensate may be charged to the stabilizer without the use of pump 33 In accordance with the invention, wet feed gas containing from as little as a third of a gallon to three hundred pounds per square inch. In passing through heat exchangers 2, t, and 6 the feed gas is cooled to from 10 degrees Fahrenheit to sure under which it requires a low temperature to recover the desired components and a given recovery requires a lower temperature at low pressure than that required for higher pressures. Due to the fact that in order to recover a large The dry gas, in expanding through the engine, is cooled by an amount depending on the ratio of expansion of the gas in the engine. This cooling,

at the engine inlet, may vary from about 12% for a 2:1 expansion ratio to about 50% for a 10:1

dry gas in The cold expanded as in exchangers 2 and 6 is itself warmed to a temperature approaching that of the entering feed.

The refrigerant used in the auxiliaryrefrigeratexpansion ratio.

temperature and pressure bons such as pentane and hexane. ature to which the refrigerant vapor is heated on being compressed is a function of the compression ratio used and of the temperature at its inlet to the compressor. Depending on the compression ratio, the absolute temperature of the compressed vapor may be 50%, or over, higher than that at the compressor intake.

The temper-- This arrangement whereby part of the refrigerating load is carried by thus reducing the cost of the engine.

As an example of a specific operation in accordcondensate is collected in separator 8. The dry gas at 45 pounds gauge and '80 degrees Fahrenheit expands in the engine to about .13 pounds gauge and -125 degrees Fehrenheit, the indi cated power development of the engine being about 340 horse power. The expanded gas, in

compressed by compressor 21 to 200 pounds presthus reducing or eliminating that required from the auxiliary system, the power requirement of which would proportionately fall. Under these conditions a more would be required and there would be an excess of power developed for which some means would be required.

While the operation of this invention has been described in connection with the recovery of higher boiling components from natural gas it may equally well be used in connection with gas encountered in the refining of petroleum, such as still gas, gas produced in the cracking or polymerization of petroleum hydrocarbons, and the gas produced in the distillation of coal, shale and other bitumens, or any other gas containing such liquefiable components.

The examples herein recited are given solely by way of explanation and clarification and the scope of this invention is limited only by the appended claims.

I claim:

1. In the recovery of liquid hydrocarbons from a mixture of the vapors thereof with vapors of more volatile hydrocarbons the steps comprising compressing by the pressure energy of a portion of the mixture a volatile hydrocarbon refrigerant comprising hydrocarbons of the mixture, cooling the compressed refrigerant and then passing the refrigerant in heat exchange relation with the mixture prior to utilization of the pressure energy thereof in the compression step.

of liquid hydrocarbons from a mixture of the vapors thereof with vapors of more volatile hydrocarbons the steps comprising cooling the mixture and condensing a portion thereof, compressing by the pressure energy of a portion of the mixture a volatile refrigerant comprising hydrocarbons of said mixture, cooling the compressed refrigerant, and passing the cooled compressed refrigerant in heat exchange reation with the vapor mixture in said first mentioned cooling step.

3. In the recovery of liquid hydrocarbons from a mixture of the vapors thereof with vapors of more volatile hydrocarbons the steps comprising cooling the mixture and condensing a portion thereof, compressing by the pressure energy of a portion of the mixture a volatile refrigerant comprising hydrocarbons of said mixture, cooling the compressed refrigerant by heat exchange with said condensate and passing the cooled compressed refrigerant in heat exchange relation with the vapor mixture in said first mentioned cooling step.

4. In the recovery of liquid hydrocarbons from a mixture of the vapors thereof with vapors of more volatile hydrocarbons the steps comprising cooling the mixture and condensing a portion thereof, compressing by the pressure energy of a portion of the mixture a volatile refrigerant comprising hydrocarbons of said mixture, cooling the compressed refrigerant, passing the cooled compressed refrigerant in heat exchange relation with the vapor mixture in said first mentioned cooling step, separating from the refrigerant hydrocarbons thereof remaining in liquid form after said heat exchange step, and then passing the refrigerant hydrocarbons in vapor form to said compression step.

5. In the recovery of liquid hydrocarbons from a mixture of the vapors thereof with vapors of more volatile hydrocarbons the steps comprising cooling the mixture and condensing a portion thereof, compressing by the pressure energy of a portion of the mixture a volatile refrigerant comprising hydrocarbons of said mixture, cooling the compressed refrigerant, separating uncondensed hydrocarbons from the cooled compressed refrigerant, and passing to said first mentioned cooling step the remaining refrigerant hydrocarbons.

6. In the recovery of liquid hydrocarbons from a mixture of the vapors thereof with vapors of more volatile hydrocarbons the steps comprising subjecting a continuous stream of the vapor mixture to cooling and thereby condensing portion thereof and cyclically subjecting a re frigerant comprising hydrocarbons of said mixture to compression and then to cooling and then to heat interchange with said stream of vapor mixture in said first named cooling step and maintaining substantial uniformity of composition of said refrigerant during the cyclic operations thereon.

'I. In the recovery of liquid hydrocarbons from a mixture of the vapors thereof with vapors of more volatile hydrocarbons the steps comprising subjecting a continuous stream of the vapor mixture to cooling and thereby condensing a portion thereof, cyclically subjecting a refrigerant comprising hydrocarbons of said mixture to compression and then to cooling and then to heat interchange with said stream of vapor mixture in said first named cooling step and passing a portion of said condensate to said refrigerant and fractioning said portion of said condensate to the constituency of said refrigerant.

8. In the recovery of liquid hydrocarbons from a; mixture of the vapors thereof with vapors of more volatile hydrocarbons the steps comprising subjecting a continuous stream of the vapor mixture to cooling and thereby condensing a portion thereof, cyclically subjecting a refrigerant comprising hydrocarbons of said mixture to compression and then to cooling and then to heat interchange with said stream of vapor mixture in said first named cooling step, passing a portion of said condensate to said refrigerant, and removing from said refrigerant liquid hydrocarbons thereof passing from said heat interchange.

9. In the recovery of liquid hydrocarbons from a mixture of the vapors thereof with vapors of more volatile hydrocarbons the steps comprising subjecting a continuous stream of the vapor mixr ture to cooling and thereby condensing a portion thereof, cyclically subjecting a refrigerant comprising hydrocarbons of said mixture to compression and then to cooling and then to heat interchange with said stream of vapor mixture in said first named cooling step, passing a portion of said condensate to said refrigerant, and removing from said refrigerant hydrocarbons remaining in vapor form after the cooling of the compressed refrigerant. I

10. In the recovery of liquid hydrocarbons from a mixture of the vapors thereof with vapors of more volatile hydrocarbons the steps comprising cooling the mixture and condensing a portion thereof, compressing by the pressure energy of a portion of the mixture a volatile refrigerant comprising hydrocarbons of said mixture, passing a portion of said condensate to a stabilizing zone, passing said compressed refrigerant in heat exchange relation with said condensate in said zone and thereby cooling the compressed refrigerant, and passing the cooled compressed refrigerant in heat exchange relation with the vapor mixture in said first mentioned cooling step.

11. In the recovery of liquid hydrocarbons from a mixture of the vapors thereof with vapors of more volatile hydrocarbons the steps comprising,

cooling step and adding a portionof said condensate to the refrigerant passing to said heat cooled compressed refrigerant in heat exchange relation to said mixture in said first mentioned cooling step.

14. In the recovery of liquid hydrocarbons from a mixture of the vapors thereof with vapors of ing their temperature, utilizing said reduction of temperature in said cooling step, by the energy of said expansion compressing a volatile refrigerant comprising hydrocarbons of said condensate,

portion of said condensate to a stabilizing zone, passing the compressed refrigerant in heat'exchange relation to said condensate in said said first mentioned cooling step.

16. The method of recovering higher boiling liquefiable components from wet hydrocarbon gas a liquid portion and a dry gas portion, expanding the dry gas portion to perform work and to cool the dry gas, passing the cooled expanded dry gas in heat exchange relation with the'wet gas in the first mentioned cooling step, expending said work in compressing the vaporized hydrocarbon tioned cooling step. 17. The method heated compressed refrigerant vapor in indirect heat exchange with liquid undergoing stabiliza tion in the stabilizing zone to transfer heat from the compressed refrigerant vapor to the liquid undergoing stabilization, cooling and liquefying the compressed refrigerant vapor, andreturning the liquefied refrigerant at reduced pressure to said second mentioned cooling step.

18. The method of recovering higher boiling by indirect heat exchange with cold dry gas, further cooling and partially liquefying said wet gas by indirect heat exchange with vaporizing hydrocarbon liquid refrigerant, separating the cooled wet gas into a liquid portion and a dry gas portion, passing a part of duced pressure to the second mentioned cooling step as a portion of the vaporizing hydrocarbon liquid refrigerant whereby a part of said liquid is vaporized, separating the vaporized portion of the refrigerant from the unvaporized portion thereof, compressing the vaporized portion of the refrigerant, cooling the compressed refrigerant vapor to liquefy a portion thereof, and returning the liquefied portion of the refrigerant to the second mentioned cooling step' at reduced pressure as a part of the vaporizing hydrocarbon liquid refrigerant.

19. The method of recovering higher boiling components from wet hydrocarbon gas which comprises cooling and partially liquefying wet hydrocarbon gas under substantial pressure by with cold dry gas, further cooling and partially liquefying said wet gas by indirect heat exchange with vaporizing hydrocarbon refrigerant, separating the cooled wet gas into a liquid portion and a dry gas portion, ex-

step, passing a part of the liquid portion of the wet gas at reduced pressure to the second mentioned cooling step as a portion of the vaporizing hydrocarbon refrigerant, separating the vaporized the liquid portion at re- 1 portion of the refrigerant from the unvaporized portion, expending said work in compressing the vaporized portion of the refrigerant, cooling and partially liquefying the compressed refrigerant vapor and returning the liquefied portion at reduced pressure to the second mentioned cooling step as a portion of the vaporizing hydrocarbon refrigerant.

20. The method of recovering stable motor fuel from wet hydrocarbon gas which comprises cooling and partially liquefying wet hydrocarbon gas under substantial pressure indirect heat exchange with cold dry gas, further cooling and partially liquefying said wet gas by indirect heat exchange with ant, separating the cooled wet gas into a liquid portion and a dry portion, expanding the dry gas portion to perform work and to cool the gas, the cooled expanded gas being the cold dry gas in the first mentioned cooling step, passing a porvaporizing hydrocarbon refrigertion of the liquid portion of the wet gas at reduced pressure to the second mentioned cooling step as a part of the vaporizing hydrocarbon refrigerant, separating the vaporized portion of the refrigerant from the unvaporlzed portion, expending said work in compressing the vaporized refrigerant whereby it is heated, passing the remaining portion of the liquid portion of the wet gas to a stabilizing zone, passing the heated compressed refrigerant vapor in indirect heat ex- 10 change with liquid undergoing stabilization in the stabilizer to transfer heat from the compressed reirigerant vapor to the stabilizer whereby the liquid portion of the wet gas is stabilized, cooling and partially condensing the compressed 115 refrigerant vapor, and returning the condensed portion to the second mentioned cooling step at reduced pressure as a portion of the hydrocarbon refrigerant.

OSWALD C. BREWSTER. 20

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