US1332290A - Process of obtaining gasolene from natural gas - Google Patents

Description

J. B. GARNER AND H.C. COOPER.

PROCESS OF OBTAINING GASOLENE FROM NATURAL GAS.

APPLICATION FILED JUNE 8, I916.

Patented Mar. 2, 1920.

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PROCESS-0F OBTAINING GASOLENE FROM NATURAL GAS.

APPLICATION FILED. JUNE 8.1916.

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JAMES B. GARNER, OF PITTSBURGH, PENNSYLVANIA, AND HOWELL C. COOPER, OF CLARKSIBURG, WEST VIRGINIA, ASSIGNORS TO HOPE NATURAL GAS COMPANY, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF WEST VIRGINIA.

PROCESS OF OBTAINING GASOLENE FROM NATURAL GAS.

Specification of Letters Patent.

Patented Mar. 2, 1920.

Application filed June 8, 1916. Serial No. 102,489.

To all whom it may concern;

Be it known that we, JAMES B. GARNER, residing at Pittsburgh, in the county of Allegheny and State of Pennsylvania and HOWELL C. COOPER, residing at Clarksburg, in the county of Harrison and State of WVest Virginia, both citizens of the United States, have invented or discovered certain new and useful Improvements in Processes of Obtaining Gasolene from Natural Gas, of which improvements the following is a specification.

Ir United States Letters Patent No. 989,927, granted to G. M. Saybolt, there is disclosed a process for obtaining naphtha, that is to say gasolene, from combustible gas of natural origin and underground source, such method, briefly stated, consisting in subjecting the gas under pressure to a gasolene absorbing menstruum for the purpose of separating from the gas such gasolene as is liquid at atmospheric temperatures and pressures, and in subsequently removing the gasolene from the menstruum. This patent also discloses various forms of apparatus for practising the process.

The object of our invention is to modify the commercial practice of this process as it is explained in the specification of the Saybolt patent, to the end that very substantial economies may be realized both in the initial outlay for the essential apparatus and in the cost of operation, and also to the end that larger quantities of gasolene may be recovered from unit volume of gas treated.

In the practice of the process of said patent with the use of pressures which it is necessary to maintain upon the gas when subjecting it to the absorbing menstruum, in order to obtain substantial yields of gasolene, it has been found that some of the constituents of the gas which an lighter than the gasolene vapors contained therein are,

absorbed by the menstruum. When the pressure upon the gas is relieved as described in said patent some of these lighter absorbed constituent-s volatilize and in passing off into the atmosphere, necessarily carry with them some of the absorbed gaso-- lene vapors which it is desired to recover. That portion of these lighter constituents which is not thus volatilized will pass into the still, and when driven off therein together with the desired gasolene vapors,

they serve to lower the partial pressure of the gasolene vapors and correspondingly interfere with the desired liquefaction of the latter in. the, condenser. It is therefore one of the specific objects of the present invention to improve upon the Saybolt process with respect to the removal from the menstruum of the absorbed constituents of the gas which are lighter than the vapors of gasolene.

A further specific object of our invention is to improve the process to the end that all the steps thereof may be carried out under pressure maintained by the pressure of the gas treated.

Natural gas, as contemplated herein, consists of a mixture in various relative proportions of methane, ethane, propane, bu-

tane, pentane, hexane, heptane, and octane. The first four of these elements are noncondensable at atmospheric temperature and pressures, and are herein designated as the lighter combustibleconstituents of the gas.

The last four of these elements namely, penand thereafter it is again subjected to a distillation operation, but under lower pressure and at a higher temperature than the primary distillation, to effect the removal of gasolene. Finally, the gasolene vapors are condensed and the resulting liquid stored under pressure maintained by that of the gas treated.

In the accompanying drawing we have shown, in diagrammatic form, a view in elevation of apparatus which we have provided and have found well suited, for the practice of our improved process. Figure 1 shows the apparatus for carrying out the cycle of operation to and including the primary distillation, and Fig. 2 shows the apparatus for completing the cycle of operation. It will be understood, however, that other apparatus may be employed in the practice of our invention. 7

Referring to Fig. 1, the gas from a well or series of wells 1, if not under sufficient or desired pressure, may be compressed by a compressor 2, and, if necessary, subsequently passed through a cooler 3, suitable pipe connections being indicated for thus conveying the gas. For subjecting the gas to the absorbmg menstruum any desired form of absorber may be used, that shown herein consisting of two horizontally disposed tanks 4 and 5 placed one above. the other. The gas enters the tank 4 through a pipe 6, which, within the tank, is perforated to permit the gas to escape and flow through the .body of menstruum. The gas, unabsorbed by the menstruum in this tank, is caught in a perforate pipe 7 and carried by a pipe 8 to a perforate pipe 9 in the lower part of the tank 5, and from thence flows through the menstruum in such tank. Finally, the remaining unabsorbed gas, consisting almost entirely of methane and ethane, is caught in a perforate pipe 10 and flows through a pipe 11 to a gas line to be used for any desired purpose.

The gas thus flowing through the tanks 4 and 5 in series as just explained, the menstruum is caused to flow through these tanks in series, but in a reverse direction to the,

flow of the gas. The menstruum enters the tank 5 through a pipe 12, and, as viewed in Fig. 1, flows from right to left through the tank .to a pipe 13 leading downwardly .to the left end of the tank 4, through which it flows from left to right to a pipe 14 leading to the primary still. That the quantity of menstruum in each tank may remain constant, suitable partitions or dams 15 and 16 are provided at the ends of the tanks as indicated. It will be seen that by this arrangement the gas richer in its content of gasolene and lighter combustible constituents is, in the tank 4, subjected to menstruum which has already absorbed, in the tank 5, some of these constituents from gas poorer in its content thereof.

The pressure under which the gas is treated in the absorbers 4, 5 will depend largely upon the percentages of gasolene elements in the particular gas under consideration. Gas containing larger percentages of the gasolene elements will, other things being the same, yield such elements to the menstruum under'less pressure than is required for gas poorer in such elements. However, we have discovered that substantial yields of gasolene from natural gas cannot be obtained without subjecting the gas to sufficient pressure to cause the absorption of some of its lighter constituents by the menstruum simultaneously with the absorption of gasolene. For obtaining substantial yields of gasolene the pressure should be at least 15 pounds per square inch above atmospheric.

As stated in the aforesaid patent, various liquids having an aflinity for gasolene may be used as absorbing menstruums, although the preferred liquid is petroleum hydrocarbons having an initial specific gravity of from 28 to 55 Baum at 60 F. Within this range we find that the largest yields of gasolene are obtained by the use of hydrocarbons having low Baum gravity, when maintained in the absorber at a temperature slightly above that at which the heavier paraflins of the oil will congeal.

With respect to the rate of flow of the gas'with relation to the quantity of menstruum employed, We have found that the best results are obtained when the gas flows at the rate of from about 21} to 10 cubic feet .per minute per gallon of menstruum, the gas being measured at 60 F., and under a pressure of about 8 ounces above atmospheric pressure. Experiments have shown that, when the rate is substantially increased above the maximum stated limit, there is a falling off in the yield of gasolene per unit volume of gas treated. While there will be no falling off in the yield of gasolene when operating below the minimum stated rate, nevertheless the plant efiiciency will be so low as to render it undesirable and uneconomic to so operate. We have furthermore found that, to obtain maximum yields of gasolene the menstruum,

in is travel through the absorber, should not have its gravity increased more than about 1 six degrees, Baum.

Turning now to the primary still 17, 18,

it is provided, as already briefly explained,

for the purpose of removing from the menstruumthe lighter combustible constituents of the gas previously absorbed thereby. These constituents, consisting almost entirely of propane and butane, may, as fully explained hereinafter be condensed and utilized as liquid gas, or they may be returned to the line 11 together with the methane and ethane for the most part unabsorbed by the menstruum. While various forms of stills may be employed to carry out the operation thus explained, we provide in the apparatus shown herein, a two part still consisting of retorts 17 and 18 arranged in series. This still is at a lower horizontal level than the absorber 4, 5, and the retort 17 is above the retort 18, so.that no pump will be required to cause the men struum to flow to the still or from one retort to the other. .Means are provided to prevent the gasfrofn' flowing from the tank trap 19 in the pipe 1 1, the vertical length of each leg of which is such as to afford a column of liquid menstruum of suflicient weight to overcome all permissible or likely differences in pressure within the tank at and retort 17 The top of the retort 17 is provided with a perforate header 20, from which the men struum flows over the steam or otherwise heated surfaces within the retort. From the bottom of this retort the menstruum flows through a pipe 21 to the left end of the retort 18, through which retort it flows in a circuitous path, determined by the baflie plates 22, to a pipe 23. The retorts may be heated in series or independently by hot water or steam. When heated in series, the heating fluid, taken from a heater 2%, Fig. 2, flows through a pipe 25 to the retort 18, and thence through a pipe 26, retort 17 to an escape pipe 27. For heating the retorts independently, a pipe 28 connects the pipe 25 with the pipe 26, and, adjacent to the retort 18, the pipe 26 is provided with an cape pipe 29. By a proper regulation of the valves indicated in the several said pipes, separate and properly regulated supplies of heating fluid may be conducted to each retort independently.

The vapors propane and butane, which, in the retorts 17 and 18, are driven from the menstruum, may be separately conducted from each retort through the pipes 30 and 31, respectively. However, the vapors from the retort 18 are preferably conducted by means of pipe 32 through the retort 17, and pass out of such retort through pipe 30. As will be seen, the pipes 31 and 32 are pro vided with suitable valves to control the How of the vapors as desired, and the pipe 32 has a plurality of outlets extending through and slightly above the bottom of the retort 17.

As already stated, the vapors from the primary still may either be condensed or conducted to the line 11. In the latter event they are caused to flow through a pipe-58, valve 80 being closed and valves 81 and 82 i being open.

(See Fig. 1. When it is desirable to condense these vapors, they may be turned, into a pipe 33 leading to a condensing apparatus consisting of a compressor 34, condenser 35 and storage tank 36. To carry the vapors to the condensing apparatus, the valve 81 is closed and valves 80 and 82 are opened. These vapors consist almost entirely of propane and butane. If, mixed with the propane and butane vapors, there is some ethane uncondensable under the temperature and pressure employed in the condensing apparatus, this gas may flow through a pipe 37 into the line 11, the valve 83 being opened.

\Vhet-her the vapors of the lighter combustible constituents of the gas are condensed or are returned to the line 11, it is desirable, to the end that no gasolene be volatilized in the primary still, that the pressure within such still be not substantially less than that of the absorber; and in case these lighter constituents are returned to the line, it is desirable, to the end thatno pump be required for this purpose, that the primary still pressure be substantially the same as that of the absorber. With the apparatus which we have provided the ressures in the still may, for the purpose of returning the distillate to the line without the aid of pumps, be maintained the same as that of the unabsorbed gas after having passed through the absorbing tank 5; and furthermore, the apparatus is so constructed and arranged that the menstruum will flow by gravity from the absorber to the still. In the apparatus shown herein the pressure in the primary still maintained substantially equal to that in the absorbers 41, 5, by means of the unobstructed pipe 14, Fig. 1, through which the menstruum flows from the absorb- 111g tank 1 to the retort 17. It will be understood that the difference in these pressures may be no greater than the head of liquid in the trap 19.

The temperature in the still retorts 17 and 18 should be below the temperature at which appreciable quantities of the lightest gasolene element will volatilize under the pressure within the still. We have found that the most satisfactory results are obtained when this still is operated at a temperature of from 95 to 110 F.

The next step in the process, as already outlined, consists of subjecting the menstruum to a second distilling operation to recover its absorbed gasolene. This distilling operation is effected under less pressure and at a higher temperature than the primary distilling operation just explained. Turning now to Fig. 2 the still 38 which we provide for this purpose is so constructed that distillation may be effected by direct or indirect heating, or both. The lower part of the still is provided with suitable pipes adapted to be heated by steam flowing from a header 39 at one end of the still to a similar header 40 at the other end thereof, the header being suitably connected to a source of steam supply. For steam distillation,, that is to say, direct-heating, the bottom of the still is provided with a plurality of steam jets 41. connected to a supply pipe 42, as shown. Within the still suitable baflies 54 are provided to cause the menstruum to flow in a circuitous path from one end to the other thereof.

The pressure in the still 38 is less than that in the retort 18, the pressure in the former being controlled by a relief valve 79 explained hereinafter. The menstruum is, by this difference in pressure caused to flow from the latter to the former by reason of this unbalanced pressure. If the difference in pressure is too great for the requirements of operation, the pipe 23 may be provided with a reducing valve 45. Before entering the still 38, the menstruum is passed through a heat exchanger 43 in which it becomes heated by the menstruum from the still 38, which flows to such exchanger through a pipe 44. From the top of the. heat exchanger 43 the menstruum flows through a pipe 46 into the upper portion of one end of the still 38, such pipe being perforate within the still. Because of the reduced pressure and increased temperature of the menstruum in the heat exchanger 43, it sometimes happens that some pentane is volatilized therein. To facilitate the secondary distillation operation it is desirable that these vapors be removed from the flowing menstruum rather than permitted to enter the still 38'. For this purpose we provide a vapor trap 47 connected to, and extending above the level of the outlet of, the pipe 46. The pentane vapors caught in this reservoir may be removed therefrom through a pipe 48 to be condensed or used otherwise as desired.

As heretofore stated, the temperature and pressure of the menstruum within the still 38 are such as to effect the distillation of the absorbed gasolene. To the end that the subsequent condensation of the gasolene vapors and the storage of the resultant liquid may be efiected at a minimum cost of operation and with little or no loss of the gasolene, both condensation and storage are effected under pressure maintained by that of the still 38. The gasolene vapors are carried from the still 38 through a pipe 49 to a condenser 50. To facilitate the with drawing of the vapors from this still, the pipe 49 may, as shown, be provided with a. suitable steam jet 51 which, acting as an ejector, has the effect of reducing the pressure withing the still 38 and of increasing the pressure upon the vapors in the condenser.

The storage reservoirs which we provide for the condensed gasolene are closed tanks 52 and 52 to the bottoms of which the gasolene is conducted through a pipe 53. By such an arrangement, the surface exposure of the gasolene, and hence its liability to vaporize, is reduced to a minimum. The water and gasolene will separate in the storage tanks and each may be drawn off separately as desired or found necessary. The pressure in the still 38, condenser 50 and tanks 52 and 52 may be kept below a desired maximum by means of a suitable relief valve 79 placed in a pipe 59 leading from the tops of such tanks.

It will of course be understood that, under practicable working conditions of temperature and pressure, some vapors will remain uncondensed by the condenser 50. In

the complete system of apparatus shown herein, we provide means for utlllzing or recovering these uncondensed vapors. For

this we provide absorbing tanks 55 and 56,

the bottoms of which are, by pipes 59, 60 and 61, connected to the tops of the storage tanks, and, by pipes 62 and 63, to a pump 64. The tops of these tanks are, by pipes 65 and 66, connected to a vapor escape pipe 67, and a pipe 68 connects the pipe 65 to the pipe 61. The tanks 55 and 56 may be partially filled with liquid hydrocarbons, which may be heavier than a marketable grade of gasolene, with which it is desired to blend the uncondensed vapors. By a suitable arrangement of the valves indicated in the several pipes described above, the vapors may be caused to flow either in series or in parallel through the liquids in the tank, and such vapors as are not absorbed by the liquidmay flow through the pipe 67 to be utilized as desired. To cause the vapors to flow in series through the liquid in the tanks 55 and 56, the valves 60, 84 and 61 are opened, and the valves 85 and 86 are closed. To cause the vapors to flow in parallel through such tanks, the valves 60, 85, 86 and 61 are opened, and the valve 84 is closed. As an alternative procedure, the tanks 55 and 56 may be provided with an absorbing menstruum by the aid of which the vapors may be absorbed. The menstruum may be taken from these tanks through pipes 62 and 63 to a pump 64, by which it is pumped through a pipe 69, pipe 46 to the still 38 to be distilled with the menstrumn flowing through pipe 46 from the primary still.

That the process which we have described may be continuous (the same menstruum being used over and over again to absorb the gasolene from the gas) ,the menstruum, flow ing from the still 38 through pipe 44 to the heat exchanger 43-, may be conducted from the exchanger through a pipe 70 to a pump 71, by which it is pumped through a cooler 72 and pipe 12 to the absorbing tank 5.

It will be observed of theprocess which we provide, first, that the lighter combustible constituents absorbed by the menstruum from the gas are removed from the menstruum before it enters the still for the removal of the absorbed gr solene; secondly, that the removal of the lighter constituents is effected in such a manner and under such conditions that little or none of the absorbed gasolene is lost; and thirdly, that not only are there removed the prejudicial effects of the presence of the lighter constituents in the menstruum, but these constituents are recovered in a practical and economic manner. t furthermore characteristic of the process which we provide that to carry the menstruum through the absorbing tanks, primary still, secondary still and heat absorber, there being but one pump required in the entire system.

We claim as our invention:

1. The process of obtaining gasolene from natural gas, which consists of subjecting such gas under pressure to a gasolene absorbing menstruum consisting of petroleum hydro-carbons having an initial gravity of from about 28 to Baum at 60 F. and by the aid thereof efiecting the separation from the gas of gasolene and lighter combustible constituents, the Baum gravity of the menstruum being raised less than about six degrees by its absorption of said gasolene and constituents, and subsequently subjecting said menstruum to successive distillation operations for the removal first of absorbed lighter combustible constituents of the gas and second of absorbed gasolene.

2. The process of obtaining gasolene from natural gas, which consists of passing such gas under pressure through a gasolene abs sorb'ng menstruum and by the aid thereof effecting the separation from the gas of gasolene and lighter combustible constituents, subsequently subjecting said menstruum to a distilling operation under a pressure substantially the same as that of the unabsorbed constituents of the gas immediately after having passed through said menstruum and at such temperatures as will effect the removal of its absorbed content of the lighter combustible constituents of the gas, and thereafter subjecting said menstruum to a second distilling operation at such temperature and under such pressure as will eflect the removal of its absorbed content, of gasolene.

3. The process of obtaining gasolene from natural gas, which consists of subjecting such gas under pressure to a gasolene absorbing menstruum and by the aid thereof effecting the separation from the gas of gasolene and lighter combustible constituents, effecting by successive distillations and under pressures maintained by the pressure of said gas, the removal from the menstruum first of its content of lighter combustible constituents and second its content of gasolene, and condensing and storing the gasolene under pressure maintained by the pressure of said gas. 1

4:. The process of obtaining gasolene from natural gas, which consists of passing such gas under pressure through a gasolene absorbing menstruum and by the aid thereof effecting the separation from the gas of gasolene and lighter combustible constituents, subsequently subjecting said menstruum to a distilling operation under a pressure sub stantially the same as that of the unabsorbed constituents of the as immediately after having passed throug said menstruum and at such temperatures as will effect the re-. moval of its absorbed content of the lighter combustible constituents of the gas, conducting the thus distilled vapors to the main body of the gas leaving the menstruum, and thereafter subjecting said menstruum to a second distilling operation at such temperature and under such pressure as will effect the removal of its absorbed content of gasolene.

5. The process of obtaining gasolene from natural gas, which consists in sub ecting such gas under pressure to a gasolene absorbing menstruum, and by the aid thereof effecting the separation from the gas of gas olene and lighter combustible constituents, and effecting by-successiv'e distillations and under pressures maintained by the pressure of said gas the removal from the menstruum, first, of its content of lighter combustlble constituents, and, second, its content of gasolene.

In testimony whereof we have hereunto set our hands.

JAlV.[ES B. GARNER.

Witnesses:

PAUL N. CRrroHLow, FRANCIS J. TOMABSON.

HOWELL C. COOPER.

Witnesses:

J. J. EVANS, Tnos. MILLER.

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