US2265527A - Separating hydrocarbon fluids - Google Patents

Description

Dec. 9, 1941` L.. R. HILL SEPARATING HYDROCARBON FLIJUIDS Filed Sept. 16, 1939 wh QQQQRU I ATTO RNEY Patented Dec. 9, i941 SEPABATING HYDBOCARBON FLUIDE Luther R. Hill, Radburn, N. L, lerici' to The M. W. Kellogg Company, Jersey City. N. J., a

corporation of Delaware Application September 16, 1939, Serial No. 295,247

(ci. esa-115.5)

6 Claims.

lcontaining hydrocarbons is compressed and cooled above the freezing point of water. The gaseous mixture is preferably passed through a drier and is then refrigerated by being passed.

for example, through a series of heat exchangers to lower the temperature thereof and to eiect liquefaction of higher molecular weight hydrocarbons. Unliqueiied gases at a relatively low temperature and vunder superatmospheric pressure are separated from the liquefied hydrocarbons and are further treated in order to obtain a sharper separation between higher and lower molecular weight hydrocarbons as will be hereinafter described.

In the heat exchangers in the specic form ci the invention the dried gases are first indirectly contacted with a suitable liquefied refrigerant auch as propane, ammonia or the like, to reduce the temperature of the gases to a relatively low temperature. In this cooling step the refrigerant is vaporized. In the next heat exchanger the partly cooled gases are indirectly contacted with cold tail gases or waste gases separated in the process to further reduce the temperature of the gases. In the third heat exchanger the cold gases have their temperature further reduced by being indirectly contacted with cold liqueed hydrocarbons which have been separated from the gases. During cooling in the heat exchangers higher molecular weight hydrocarbons and some lower molecular weight hydrocarbons are liquefied. More heat exchangers may be used, ii desired, or other means for cooling the gases may be used.

After passing through the heat exchangers as above pointed out, most of the higher molecular weight hydrocarbons together with some of the lower molecular weight hydrocarbons are liquefied and the liquened hydrocarbons are separated from unliqueiied gases. The liquefied hydrocarbons contain lower molecular weight hydrocarbons, such as methane, and it is desired to remove as large a proportion of these lower molecular weight hydrocarbons as is economically possible to obtain a liquefied portion containing a maximum yield of higher molecular weight hydrocarbons, such as butane.

According to my invention the pressure on the separated unliqueed gases is reduced to lower the temperature thereof and these gases are then mixed with the separated liqueed hydrocarbons under lower pressure to lower the temperature of the liquefied hydrocarbons. At the lower temperature and pressure a better separa tion between higher molecular weight hydro caroons and lower molecularv weight hydrocar bons is obtained. The rerrigeraticn and treatment of the dried gases is carried out under superatmospheric pressure and the separated cold and umiquened gases being at a relatively high pressure are passed through an exon engine or device to reduce the pressure on the gases. The expansion device or engine is preferably used to run a compressor for compressing the refrigerant vaporized in the first heat exchanger above descrlbed. l

'ihe separated liquefied gases or hydrocarbons are withdrawn and the pressure thereon is rcduced to about the pressure of the gases which have passed through the expansion device or engine. The expanded gases from the experision device and the liquefied hydrocarbons under lower pressure and temperature are then mixed and passed to a separating drum to separate liquefied hydrocarbons from cold, unliqueiied gases. The temperature and pressure are. so chosen as to eiect a desired separation of higher molecular weight hydrocarbons from lower molecular Weight hydrocarbons in the iiqueed hydrocarbons introduced into the last mentioned separating drum.

The cold gases separated in the last separating drum are used as the cooling medium in the second heat exchanger and the separated liqueed hydrocarbons at a low temperature are used as the cooling medium or refrigerating medium in the third heat exchanger. After passing through the third heat exchanger the liqueied hydrocarbons are still at a relatively low temperature and they are preferably used for further cooling the compressed and cooled refrigerant to further reduce the temperature of the refrigerant before it is passed to the first heat exchanger.

While three heat exchangers have been described in connection with refrigeration of the dried gas, my invention is not to be restricted thereto as the number of heat exchangers may be varied. Also, more than one drier may be used so that one drier may be revivified while the other drier is in use. The tail gases or waste gases may be heated and used as the reviviiying agent for the driers.

In the drawing I have shown a diagratic representation of apparatus adapted to be used in practicing my invention.

Referring now to the drawing, the reference character i0 designates a feed line through which a gaseous mixture containing hydrocarbons is passed. The gaseous mixture to be treated may be any mixture containing higher molecular welght hydrocarbons which are to be recovered and containing also lower molecular weight hydrocarbons. While the invention will be specifically described in connection with a gaseous mixture containing hydrocarbons separated from conversion products leaving a cracking unit, my invention is not to be restricted thereto as other gaseous mixtures, such as reiinery gases, natural gas, etc., containing higher molecular weight hydrocarbons, such as C3, C4, C5 and higher hydrocarbons may be treated according to my invention and the higher molecular weight hydrocarbons recovered from the gaseous mixture. When natural gases are treated according to my invention, natural gasoline is recovered. When stabilizer gases or other gases containing relatively large amounts of Ca and C4 hydrocarbons are used, a fraction, containing mostly Ca and C4 hydrocarbons, is obtained which may be used in a conversion zone, such as a polymerization zone.

The feed gas is preferably passed through a compressor I2 to raise the pressure on the feed gas to about 340 lbs. per square inch absolute.

If the feed gas is under sufficient pressure, the

compressor I2 may be omitted. After passing through the compressor I2, the compressed gas is passed through a suitable cooler I4 to reduce the temperature of the compressed gas and is then passed through a heat exchanger I6 to reduce the temperature of the compressed gas to a relatively low temperature but preferably above the freezing point of water. In the preliminary stages of cooling and liquefying, the gaseous feed is preferably maintained under a relatively high pressure because of the greater eflciency and smaller size of heat exchangers used and because much latent heat of condensation can be removed within a relatively narrow temperature range.

The cooled and compressed gas at a temperature of about 50 F. is introduced into a separator drum to separate any condensed moisture, dirt, etc., from the gas'. The water, dirt, etc., is withdrawn through valved line 22. Durthe compressing and cooling of certain gases, higher molecular weight hydrocarbons may be condensed and may be withdrawn from the separating drum 20.

The partly dried gas leaves the top of the sepamay be used in the drier 28. The drier is used in order to remove substantially all of the Water from the gas before further treating it in my process. If the water were not removed, solid gas hydrates and ice would form in the apparatus used in later steps in my process due to the low temperature utilized.

The dried gas leaves the drier 28 through line 30 and is passed through heat exchangers 34, 36 and 38 wherein the gas is indirectly contacted with different cooling or refrigerating mediums and the gas is refrigerated. During this cooling and refrigeration some oi' the lower molecular weight hydrocarbons and most of the higher boiling hydrocarbons are liquefied and the liquefied hydrocarbons and gases leave the rated gases still at a relatively high pressure -are passed through an expansion device to recover energy from the gases and to lower the Y pressure on the gases and to further cool -the gases. These cold gases are then mixed with the separated liquefied hydrocarbons upon which Returning now to the iirst heat exchangerl 34 wherein refrigerant is used to cool the dried and compressed gas, the reference character da designates a vessel or the like which contains liquefied refrigerant, such as propane, ammonia or the like. Cold liquefied refrigerant, such as propane, for example, is introduced into the vessel 46 by means of line 4l. The liquefied refrigerant is withdrawn from the bottom of the vessel 46 and passed through line 4a and heat exchanger 34 wherein the liquefied refrigerant indirectly contacts the dried and compressed gas and the gas has its temperature reduced to about -7 F. In the heat exchanger 34 the refrigerant becomes vaporized and the vapors are withdrawn from the heat exchanger 34 through line 50 and returned to the upper portion of th vessel 46.

The vaporized refrigerant passes from the top of the vessel 46 through line 52 and is compressed in compressor 54' to a relatively high pressure. The compressed refrigerant is then passed through cooler 56 to cool and liquefy the compressed refrigerant. The cooled and liquefied refrigerant is then passed to a collecting drum or vessel 58. The liquefied refrigerant is Withdrawn from the bottom of the drum or vessel 58 and passed through line 62 and heat exchanger 64 wherein it is indirectly contacted with re covered cold and liquefied hydrocarbons as will be hereinafter described to further reduce the temperature of the refrigerant. The cold and liquefied refrigerant is then passed through line 41 and pressure reducing valve 65 into the vessel 46. In passing through valve 65 some of the propane will be vaporized to reduce the temperature of the propane the desired amount and the vapors leave the top of the vessel 46 through line 52.

The further treatment of the cold unliquefied gases and liquefied hydrocarbons leaving separating drum 42 will now be described. The liqueed hydrocarbons withdrawn from drum l2 still contain undesired lower molecular weight hydrocarbons and by lowering the temperature thereof and pressure thereon a more selective separation is obtained between butane and methane, for example. At a relatively low pressure the equilibrium constants of butane and methane are relatively far apart and at this pressure it is necessary to lower the temperature of the hydrocarbons to have the temperature below the boiling point of butane. The optimum economical conditions for this separation are about lbs. per sq. in. absolute and 51 F. and these conditions are maintained in a drum later to be described into which are introduced under lower pressure liqueiied hydrocarbons and unliquefied gases leaving separating drum 42. The liqueed hydrocarbons and unliqueed gases from drum 42 are separately expanded and then mixed to obtain the optimum conditions above described.

The cold unliquefled gases leave the top of the separating drum 52 at a temperature of about -l8 F. and under a pressure of about 325 lbs. per sq. in. absolute. The cold gases are then passed through line 68 and expansion device or engine 'le to recover energy from the gas while at the same time reducing the pressure on the gases and reducing the temperature by the expension. By having the expanding gas do work, additional refrigeration is obtained. The expansion device is preferably used to run the compressor 54 for compressing the vaporized refrigerant as above described. The gases leaving the expansion device or engine 1B through line HG are at a temperature of about -63 F. and under a pressure of about 150 lbs. per sq. in. absolute. At this lower temperature some higher molecular Weight hydrocarbons in the gases may be liquefied. y

The x'st mentioned liquefied hydrocarbons are withdrawn from the bottom of the separator 42 through line l5 having a pressure reducing valve l@ to reduce the pressure on the liqueed hydrocarbons to about 150 lbs. per sq. in. absolute. At this lower pressure some of the lighter constituents are vaporized and some refrigeration is obtained. The withdrawn liquefied hydrocarbons at this lower pressure and the expanded gases passing through line 14 are mixed to lower the temperature of the liquefied hydrocarbons. The cold mixture is passed through line 80 to a separating drum t2 to separate liqueed hydrocarbons from unliqueed gases. In drum 82 the expanded liquelied gases and unliquefied gases are brought together to bring about equilibrium conditions. i3-ue to the expansion and cooling of the gas, the mixture has its temperature reduced below that in drum 62 to about 51 F. By separately reducing the pressure on the gas. I am enabled to obtain relatively low temperatures necessary for more sharply separating desired hydrocarbons, such as butane, from undesired hydrocarbons, such as methane.

The liquefied hydrocarbons which comprise the desired higher molecular weight hydrocarbons are withdrawn from the bottom of the separator 82 and passed through line 86 by means of pump 85 and are used as the refrigerating medium in the heat exchanger 38 for refrigerating the dried gas to be treated. The liquefied hydrocarbons leave the heat exchanger 38 at a temperature of about 23 F. and are passed through line S0 and heat exchanger 64 for further refrigerating the compressed and cooled refrigerant passing through line t2. One or more heat exchangers may be used. The separated desired hydrocarbons or liquefied hydrocarbons are then passed through line 92 and may be separately recovered or may be adrnixed with any condensed hydrocarbons recovered from the separating drum 20.

The unliquefled gases separated in the separator 82 are at a temperature of about 51 F. and passed through line 94 and are used as a cooling medium for the heat exchanger 38 wherein they are indirectly contacted with the dried and partly cooled gas passing through the heat exchanger 36. The gases leave the heat exchanger 36 through line SB at a temperature of about 18 F. and are then passed through heat exchanger l5 for indirectly contacting the compressed and cooled feed gas at the beginning oi the procesa to lower the temperature of the gas to about 50 F., as above described, before the leed gas is introduced into separating drum 21B. One or more heat exchangers may be used to cool the feed gas. The unliquiiled gas after passing through the heat exchanger i5 is then passed through line 98 and may be discarded or used as fuel.

As above pointed out my process may be used to separate higher molecular weight hydrocar bons from various gaseous mixtures. As a spe cinc example, hydrocarbon gases separated from products of conversion leaving a cracking unit are treated according to my process wherein the gas is maintained under the pressures above given. A gas to be treated has about the following composition and the constituents thereof in about the following amounts are used:

Mols per hour H2 115 CH4 571 C21-I4 48 02H6 161 CaHs CaHs 123 CcHs 23 04H10 36 05H12 and higher 13 The composition and amounts of the gases and liquefied hydrocarbons introduced into separating drum 42 are substantially the same as those above given for the feed gas.

The liqueed hydrocarbons withdrawn from the' bottom of separator drum l2 contain the fol-- lowing constituents in about the amounts given:

Mols per hour @H4 50.8 CzHs 1&6 02H5 63.2 CaHs 42.5 03H3 91.1

.- 04H8 20.5 C4H1o 33.4 05H12 and higher 12.8

The gaseous mixture leaving the top of separator drum l2 has about the following composi tion and amounts of constituents:

The liquefied hydrocarbons withdrawn from the bottom of separating drum @2 contain the following constituents in about the amounts given:

Mols per hour CIE-I4 31.7 02H4 12.7 C21-Ie 57.9 CaHe 44.5 CaHa 95.0 C4Ha 21.1 (34H10 34.2

05H12 and higher 12.9

The gas leaving the upper portion of the sepaabout the amounts of the constituents as given:

From the above specific example it will be seen that I am enabled to obtain a better separation of higher molecular weight hydrocarbons from lower molecular weight hydrocarbons ln gaseous mixtures by separating the gases leaving the separator drum l2, reducing the pressure on these gases to further cool them and then admixrator 82 has about the following composition and n ing these cold and expanded gases with the liquefied hydrocarbons under lower pressure withdrawn from the bottom of the separator drum 62. The optimum pressure for the initial cooling is higher than the optimum pressure for the final cooling and separation step in drum 82. It is advantageous to obtain the last stage cooling by auto-refrigeration or by expansion of the fluids under the high pressure used in the beginning of the operation.

While I have shown one form of apparatus and have given a specific example ofa particular gas to be treated it is to be understood that my invention is not to be restricted thereto as various changes and modifications may be made and different operating conditions may be used where the same composition gases or different gases are to be treated without departing from the spirit of my invention.

I claim:

l. A method for separating higher molecular weight hydrocarbons from gaseous mixtures containing hydrocarbons which comprises passing a gaseous mixture while under superatmospheric pressure through a series of heat exchangers wherein the gaseous mixture is indirectly contacted with cooling mediums andthe gaseous mixture is refrigerated to llquefy higher molecular weight hydrocarbons, initially separating liquefied hydrocarbons from unliqueiied gases, reducing the pressure on the liquefied hydrocarbons, separately reducing the pressure on the unliqueed gases to recover energy therefrom and to lower the temperature of the gases at the same time, mixing the expanded and cold gases and first mentioned liquefied hydrocarbons at the lower temperature and pressure and passing the mixture to a separating zone to separate liquefied hydrocarbons from gases and obtaining a sharper separation between higher molecular weight hydrocarbons and lower molecular weight hydrocarbons, using the last mentioned liqueed hydrocarbons as a cooling medium in one of said heat exchangers and using the last mentioned separated unliqueiied gas as a cooling medium in another of said heat exchangers.

2. A method as defined in claim 1 wherein liquefied refrigerant is used as the cooling means for the first heat exchanger, the refrigerant being in a closed cycle and the refrigerant, after being heated and vaporized by indirect contact with the gaseous mixture. being passed through a compressor and cooled before being returned to the first heat exchanger.

3. A method as defined in claim 1 wherein liqueed refrigerant is used as the cooling means for the first heat exchanger, the refrigerant being in aclosed cycle 'and the refrigerant, after being heated and vaporized by indirect contact with the gaseous mixture, being passed through a compressor and cooled and liqueed before being returned to the rst heat exch s; the energy from the expanded gas being used to opcrate the compressor for compressing the va porized refrigerant.

4. A method for separating valuable hydrocarbons from gaseous mixtures containing hydrocarbons which comprises compressing and cooling a gaseous mixture. drying the gaseous mixture and then passing the dried and compressed gaseous mixture through a series of heat exchangers wherein the gaseous mixture is indirectly contacted with cooling mediums and the gaseous mixture is refrigerated to liquefy hydro-z carbons, separating liquefied hydrocarbons from unliqueiied gases, reducing the pressure on the liquefied hydrocarbons, separately reducing the pressure on the unliqueiied gases to recover energy therefrom and to lower the temperature of the gases at the same time, mixing the expanded and cold gases and liquefied hydrocarbons and passing the mixture to a separating zone to separate liquefied hydrocarbons from gases.

5. In a method of recovering valuable hydrocarbon'constituents from gaseous mixtures containing hydrocarbons wherein a gaseous mixture under superatmospheric pressure is refrigerated and some of the hydrocarbons are liqueed, the steps which comprise separating liquefied hydrocarbons under superatmospheric pressure from unliqueiied gases, reducing the pressure on the separated unliqueiled gases to recover energy therefrom and to lower the temperature of the gases to a relatively low temperature, reducing the pressure on the liquefied hydrocarbons,

mixing the expanded and .cold gases with liqueed hydrocarbons under lower pressure to reduce the temperature of the mixture and then sep arating liquefied hydrocarbons from said mixture as the desired product having a larger proportion of higher molecular weight hydrocarbons and a smaller proportion of lower molecular weight hydrocarbons than the rst mentioned liquefied hydrocarbons at higher pressure.

6. In a method of recovering valuable hydrocarbon constituents from gaseous mixtures con= taining hydrocarbons wherein a gaseous mixture is compressed and cooled and dried and then refrigerated to subzero temperatures to liquefy some of the hydrocarbons therein, the steps which comprise separating liquefied hydrocarbons under superatmospheric pressure from unliquefied gases, reducing the pressure on the separated liquefied hydrocarbons, reducing the pressure on the separated unliquefied gases to recover energy therefrom and to lower the temperature of the gases to a relatively low temperature, mixing the expanded and cold gas with the liquefied hydrocarbons under lower pressure to reduce the temperature of the mixture, passing the mixture to a separating zone and separating liquefied hydrocarbons from unliquefled gases -in said separating zone.

LUTHER R. HILL.

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