US3216177A - Method of controlling the flow of absorbent according to the liquid level in a presaturation zone - Google Patents

Description

Nov. 9, 1965 R. C. BRACKEN ETAL METHOD oF coNTRoLLING THE FLow oF ABsoRBENT ACCORDING TO THE LIQUID LEVEL IN A PRESATURATION ZONE Filed April 30, 1962 INVENTORS.

R. c. BRACKEN c. LsoMMERs HIGHOSBV M 14:77/ ATTORNEVS United States Patent 3,216,177 METHOD OF CONTROLLING THE FLOW OF ABSORBENT ACCORDING T0 THE LIQUID LEVEL IN A PRESATURATION ZONE Robert C. Bracken and Clair L. Sommers, Bartiesville, Okla., assignors to Phillips Petroleum Company, a corporation of Delaware Filed Apr. 30, 1962, Ser. No. 191,132 1 Claim. (Cl. 55-18) This invention relates to control of a method for extraction of gasoline from natural gas. In one aspect it relates to control of the operation of a steam turbine driven pump which transfers liquid absorbent from a presaturator zone to an absorption zone operating at a higher pressure than the pressure of the presaturator zone.

Superheated steam is frequently employed for heat eX- change purposes for heating fluids to temperatures well above the normal boiling point of water. Such heat eX- changers sometimes exhaust steam in superheated form and at pressures above atmospheric pressure. In plants in which such exhaust steam is available, its use is frequently less expensive for power purposes than electrical power. When such steam is not employed for useful purposes, it may be Vented and, therefore, wasted. Such practice is ob- Viously to be avoided whenever possible.

An object of this invention is to provide a method for the `control of a system for extraction of gasoline boiling range hydrocarbons from a natural gas. Another object of this invention is to provide means and a method for the control of the operation of a steam driven turbine pump which transfers liquid absorbent from a presaturator zone to an absorption zone operating at a higher pressure than the pressure of the presaturator zone. Another object of this invention is to provide apparatus for preventing the steam turbine driven pump from going on gas as the result of transfer of all liquid from the kettle section of the presaturator. Other objects and advantages of this invention will be realized upon reading the following description, which, taken with the attached drawing, forms a part of this specification.

This invention comprises a method for throttling the flow of steam to the steam turbine as a means for regulating the rate of pumping of liquid absorbent from the kettle section of a presaturator zone to an absorption zone operating at a higher pressure than the pressure of the presaturator zone. The operation comprises sensing the liquid level in the presaturator zone and as the level decreases throttling the flow -of steam to the steam turbine, and vice versa. Furthermore, the invention involves upon sensing a liquid level in the presaturator which is a predeterrnined low level and in response to this predetermined low level entirely closing off the flow of steam to the steam turbine so that the turbine driven pump will not go on gas, thereby tending to damage the turbine and pump from excessive speed.

The drawing illustrates, in diagrammatic form, an arrangement of apparatus parts for carrying out the method of this invention.

In the drawing, reference numeral 11 identifies a conduit for passage of feed gas containing extractable hydrocarbons into an absorber 12. Conduit 13 passes unabsorbed or residue gas from absorber 12 to a point of disposal as desired. Conduit 14 is for passage of enriched absorbent from absorber 12.

Rich absorbent flowing through conduit 14 is Vented by a first pressure reduction in the vent tank 15 with the Vented gases being passed through a conduit 16 and returned to the absorber 12. Partially Vented rich absorbent passes through a conduit 17 to a second vent tank 18, the gases from which pass through a conduit 42 with the liquid flowing through a conduit 19 to a third vent tank 20.

3,216,177 Patented Nov. 9, 1965 From this vent tank gases pass through conduit 43 while the fully Vented absorbent passes through a conduit 21, through a heater 22 and thence through a conduit 23 for introduction into a still-portion 25 of a dephlegmator-still 2.4. Gases stripped from the absorption liquid in still 25 pass upward into the dephlegmator portion 26 for condensation of any vaporized absorbent. Gases and vapors leave dephlegmator 26 through a conduit 27 and are condensed in a condenser 27a and pass to such disposal, as desired. The several venting stages are at successively reduced pressures.

Stripped absorbent from the kettle section of still 25 leaves this vessel by way of a conduit 29 provided with a cooler 30 and the cooled absorbent is then passed into a lean oil surge storage tank 3. Condensed material in dephlegmator 26 is removed therefrom through a conduit 28 for such disposal as desired. When the condensate in dephlegrnator 26 is substantially only absorption oil conduit 28 can be connected with the still section 25 for return of the condensate to the main body of absorption oil. Fully stripped lens absorption oil from surge tank 31 is passed therefrom by way of a conduit 32 with a portion thereof being passed through a conduit 37, the volume of which is regulated by a flow recorder-controller 38. This absorbent passing through conduit 37 is introduced into the upper portion of a reabsorber vessel 39. Vented gases from vent tank 18 passing through conduit 42 are introduced into the lower portion of the reabsorber 39, for recovery of desired condensable components. Vent gases flowing through conduit 43 are introduced into an upper portion of still 25.

The enriched absorbent from reabsorber 39 containing recovered components is withdrawn therefrom by way of a conduit 41 and is combined with the main body of enriched absorption oil prior to introduction into vent tank 18. Unabsorbed gases from reabsorber 39 are passed by way of a conduit 40 and introduced into a presaturator vessel 44.

This presaturator vessel is intended to contact the reabsorber off gases with fully depleted lean absorption oil flowing through a conduit 45 with rate of flow of the oil being controlled by a flow recorder-controller 46. This lean absorbent is introduced into the upper portion of presaturator 44 and contacts the reabsorber off-gases therein. Certain constituents desired to be retained in the off-gases from the main absorber vessel 12 are absorbed in the presaturator. In some instances and, in fact, in most instances, a manually operable valve 35 is throttled somewhat in order to cause a pressure drop across this valve so as to divert a portion of the 'lean oil pumped by pump 68 through the reabsorber 39. Also a manually operable valve 36 is provided in conduit 32 so as to cause a pressure drop across the valve to force a portion of the lean absorption oil not required in reabsorber 39 to flow through conduit 45 into the presaturator vessel 44. In some instances manually operable valve 36 can be entirely closed or it can be merely throttled to divert a portion of the oi'l through the presaturator. Thus, if some oil flows through valve 36 it is then combined with the presaturator oil from conduit 53 and the combined stream is pumped by a pump 34a driven by a steam turbine 34. The pumped oil flows on through conduit 33 containing a check valve 67 and through a flow sensing device such as an orifice plate assembly 58 and on into absorber 12.

Residue gas from absorber 12 as mentioned hereinabove leaves this absorber by way of a conduit 13 and this gas can, if desired, flow through a valve 52, a dehydrator apparatus 49 and on through a conduit 50 for such use of a dehydrated gas, as desired. If however, it is desired, all or a portion of the unabsorbed gas flowing through conduit 13 can flow through a valve 51 in a conduit 48 and be combined with the off-gas flowing through conduit 47 from the presaturator Vessel 44.

The control portion of the apparatus illustrated in the figure includes a liquid level sensing device 54, such as a float assembly.

The apparatus as herein described is a fully pneumatic apparatus while it will be realized that electrical apparatus or combination electrical-pneumatic controls can be used. The float 54 communicates with a transducer 55 which converts the position signal of the float to a pneumatic signal, with this signal being passed on to a level transmitter 55a and to a level` controller 54a. The level controller 54a communicates with a flow recording controller 57 which also communicates with a transducer 59. This transducer 59 is a conventional apparatus which converts a pressure differential from opposite sides of the orifice plate assembly 58 to a signal responsive to the pressure differential. A conduit is provided running from the flow recorder-controller 57 through a 3-way valve 63 to the diaphragm of a normally closed diaphragm valve 61. This conduit is identified by reference numeral 62. The 3-way valve 63 is so installed in conduit 62 that in one position control air pressure can pass through conduit 62 to the diaphragm of motor valve 61 and in its other position this conduit 62 is closed off and pneumatic pressure from the diaphragm of valve 61 is vented through a vent 69.

The level transmitter 55a is operative only to a signal from transducer 55 indicating a predetermined low liquid level in the presaturator 44. This level transmitter is connected operatively with a receiver-controller 56 which communicates with a diaphragm of the 3-way valve 63. This valve 63 is a normally vent valve, that is, when there is not any pressure on its diaphragm, the valve is turned so that pneumatic pressure will vent from the diaphragm of valve 61.

A conduit 66 leads instrument air from a source, not shown, through a 3-way valve 64 to the receiver-controller 56. This 3-way valve 64 is also a normally vent valve venting pressure from the portion of conduit 66 adjacent receiver-controller 56 by way of a vent 65.

This control apparatus is actually. a safety apparatus and operates in such a manner that the steam turbine driven pump 34a will never remove all of the liquid absorbent from the kettle section of presaturator 44 and go on gas. As will be realized by those skilled in the art, a turbine driven pump should never be permitted to go on gas because with no load on the pump the turbine will race with the result that the turbine and pump may be damaged.

In the operation of this apparatus, when the float 54 senses a normal low level for example, the signal therefrom is converted in transducer 55 toi a pneumatic signal between, for example, 3 and 15 (p.s.i.g.) pounds per square inch gauge and this signal is -transmittedfto the level controller 54a which, in turn, emits a signal to reset the set point of the flow recorder-controller 57. This controller has previously been set in order to regulate steam passing through conduit 60 containing valve 61 to the turbine 34 to pump a predetermined volume of absorbent oil to the absorber 12. While it is desired to pump a predetermined and suitable volume of liquid absorbent into absorber 12 there are times when less absorbent or more absorbent can be introduced into the absorber without markedly upsetting the operation of the absorber. Since it is desired not to have the pump 3411 go on gas, when the level sensed by float 54 reaches a level somewhat below the desired normal liquid level, a signal is emitted from transducer 55 to the level controller 54a. This level controller then resets the set point of the flow recorder-controller 57 thereby regulating the passage of instrument air through conduit 62to the diaphragm of motor valve 61 in order to throttle this motor valve 61 to reduce the flow of steam to the turbine. Thus, when the level of oil in saturator 44 decreases somewhat below the normal desired working level, steam to the turbine is throttled so that less oil is withdrawn from the presaturator. The reverse is true, that is, if the level of oil in the kettle section of presaturator 44 rises above the desired working level, the transducer emits a signal proportional to the rise of liquid level to the level controller 54a which then resets the set point of controller 57 to open somewhat valve 61 to speed up the turbine and pump.

When a dangerously low liquid level exists in the presaturator 44, the float 54 emits its signal to transducer 55 which in turn passes a signal to the level transmitter 55a. This signal is between 3 and 15 p.s.i.g. The receivercontroller 56 is a snap action on-otf controller and it can be set to operate at, for example, 14 p.s.i.g. Thus, when the dangerously low liquid level in presaturator 44 is sensed by float 54 with the continuous signal being emitted from transducer 55 to the level transmitter S511 and when the air pressure from transmitter 55a to controller 56 reaches 14 p.s.i.g., this controller snaps and cuts off flow of instrument air from conduit 66 to the diaphragms of the 3- way valves 63 and 64. Upon closing oif of this air, pressure is reduced on the diaphragm in three-way valve 63 thereby allowing the normally vent valve to vent pressure from the diaphragm of normally closed valve 61 through vent 69. This venting thus closes oif all steam to the turbine 34 and terminating all transfer of absorbent from the presaturator 44 to the absorber 12.

As a double safety feature, the 3-way valve 64 has its diaphragm in communication also with the outlet of the receiver-controller 56 so that when this controller closes off the flow of instrument air to the diaphragm of 3-way valve 63 the instrument air to the diaphragm of the 3- way valve 64 is also closed otf, thereby venting residual air pressure from the receiver-controller 56 by way of vent 65. At this time, air from the portion of conduit 66 on the air source side is closed off from entering the recorder-controller S6.

This last operation oceurs as mentioned hereinabove when the liquid level in presaturator 44 reaches a dangerously low level. With the turbine closed down then upon rise of the liquid level in presaturator 44 above the dangerously low level mark, the instrument air pressure emitted by level transmitter SSa is reduced to a value below the above-mentioned 14 p.s.i.g., thus the receivercontroller 56 snaps in the opposite direction but valve 64 is on vent and air from the source cannot pass through this valve to reach controller 56. Thus valves 63 and 64 cannot return to normal operation. In order to start the turbine 34, a bypass conduit 71 is provided around valve 64 in conduit 66. A manually operable, push button valve 72 is placed in this bypass conduit. To flow steam to the turbine, merely push the valve button of valve 72 and air then flows to the receiver-controller 56. With this instrument having snapped open, pressure passes to the diaphragms of valves 64 and 63 opening both valves to air flow and closing the vents. As soon as valve 64 opens the push button is released and operation of controller 56 is back to normal. With pressure on the diaphragm of valve 63, this valve then admits pressure to the diaphragm of valve 61 thereby opening same to permit steam flow.

The check valve 67 is provided in conduit 33 to prevent back flow of absorbent or gas through conduit 33 into presaturator 44 when the pump is not in operation. In one instance, the presaturator 44 was operated at a pressure in the vicinity of 240 p.s.i.g., while the absorber was operated at a pressure somewhat above 1000 p.s.i.g. It is, thus, realized that the point of introduction of aborbent liquid by way of conduit 33 into absorber 12 is in a normally gas or vapor contained area and upon closing down of pump 34(1, what little liquid is in conduit 33 will back flow into the presaturator, thus allowing gas at an extremely high Velocity'to back flow through this conduit, therefore racing the pump 34a in a reverse direction. Such an irregular operation obviously can seriously damage pump 34a and the turbine 34.

As an example of the operation of such a system for the extraction of gasoline from natural gas, are the following data:

Table Stream Name Gas to Abs. L O. to Presat. R.O. from S.V.T. 11.0. from Abs. Residue Presat. Oil to Abs. bs. Vapor S.V.T.

63 54 0 2 11 3 2 2, 435 2, 370 0 1 es 2 0 0 1 0 1 0 0 0 40, 091 36, 842 0 406 3, 655 449 144 10,227 s 661 0 2, 332 3,898 1, 774 1, 292 4, 493 916 0 143 3, 720 2, 066 2, 702 450 3 0 0 447 156 327 1, 120 1 0 0 1, 119 348 846 283 0 O 0 283 61 234 261 0 0 0 261 53 218 127 0 0 0 127 16 114 24 0 0 0 24 1 23 0 0 8, 885 8, 885 8, 885 129 8, 885

Deph. L O. from L O. to Inlet Gas R.O. from Reabs. Prcsat. Stream Name 0.H.V Still Reabs to Reabs. Reabs. Residue Residue Stream No 27 29 37 42 41 40 47 Float 54, transducer and level controller 5411, when combined, are a conventional liquid level controllertransmitter apparatus, such as that manufactured by Fisher Governor Company, No. 2500-2516-24913. The receiver-controller 56 is also manufactured by said Fisher Governor Company and is advertised by that company as a receiver-controller 2506. The level transmitter SSa is also manufactured by the Fisher Governor Company and is similar to the portion 54x of the conventional liquid level controller. Both of the instruments 54a and 55a emit continuous signals proportional to the signal received from transducer 55. Instrument 57 is a pneumatic set receiver flow recorder-controller, such as one manufactured by Taylor Instrument Company and identified by that company as No. 127RF137. The transducer 59 is specifically a differential converter transmitter such as one manufactured by Mnneapolis-Honeywell Company and identified by that company as No. 292N7G4. The 3-way pneumatically operable valves 63 and 64 are such valves as No. 2VG140 and manufactured by Taylor Instrument Company. These valves are open straight through on high pressure and vent on low pressure. The flow recorder- controllers 38 and 46 are conventional flow recorder-controllers and such can be purchased from any of the hereinabove mentioned instrument manufacturing companies.

Conventional liquid level flow controllers, not shown, are employed to regulate the level of liquids in the bottom sections of the absorber 12, still 25, and reabsorber 39. The need for, installation -of and use of such liquid level controllers is well understood by those skilled in the art.

A water Circulation system 24a, with air cooler, is provided for the dephlegmator to condense vapors of the absorption oil carried from still 25 into the dephlegrnator 26.

While certain embodments of the invention have been described for illustrative purposes, the invention obviously is not limited thereto.

We claim:

In the method of operation of a gasoline plant wherein gasoline boiling range hydrocarbons are extracted from natural gas in absorption zone by an absorbent liquid' medium which flows from a separating zone to a presaturation zone and then to the absoprtion zone and the unabsorbed natural gas is separately removed from said absorption zone, the improvement which comprises passing said absorbent medium into said absorption zone from said presaturation zone by means of a steam turbine actuated pump having a flow rate of steam introduced into a valve and then into the turbine proportionately regulated by means of a level controller means and a flow recording and Controlling means having a set point varied responsive to a signal transmitted from said level controller means, said level controller means being responsive to the liquid level of said absorbent medium in said presaturation zone, and Wherein the flow rate of steam is further regulated by means of a second control means connected to the valve responsive to a second signal provided thereto from said level control means representative of a predetermined low liquid level of said absorbent medium in said presaturation zone to terminate flow of steam to said steam turbine and thereby terminating the flow of absorbent to said absorption zone from said presaturation zone.

References Cited by the Examiner UNITED STATES PATENTS 2,242,11O 5/41 Carney 55-43 i 2,299,s3o 2,339,o26 2445,043 2,5:21233 8 Legatski et al 55-43 X Mercer 202-160 Souders et al. 196-132 Latcham 55-43 Miller 55-43 Donaldson 137-95 Kirby 137-97 Hunter 137-95 Cottle 202-160 Ryden 103-35 Province 103-35 Russell 55-31 Nobles et al 103-35 X Tolin et al 202-160 15 REUBEN FRIEDMAN, Primary Examner.

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