US3587726A - Output control for steam heated heat exchanger - Google Patents

Abstract

A MULTIPLE TOWER GAS DEHYDRATION SYSTEM IS DISCLOSED WHEREIN THE REGENERATION GAS IS HEATED IN A STEAM HEATED HEAT EXCHANGER, WITH THE HEAT EXCHANGER IN OPEN COMMUNICATION WITH A STREAM GENERATOR. AFTER PASSAGE THROUGH THE REGENERATING TOWER, THE REGENERATION GAS PASSES THROUGH DEHYDRATING COMPONENTS, THEN THROUGH A CONTINUOUSLY OPERATED MOTORDRIVEN COMPRESSOR, AND IS RETURNED TO THE WET GAS INPUT. A BYPASS INCLUDING A VARIABLE CONTROL VALVE IS CONNECTED BETWEEN THE RETURN LINE TO THE WET GAS LINE AND THE REGENERATING GAS OUTLET FROM THE TOWERS TO PROVIDE A RECIRCULATING LOOP THROUGH THE REGENERATION GAS DEHYDRATING COMPONENTS AND THE COMPRESSOR. THE VARIABLE CONTROL VALVE IS AUTOMATICALLY SELECTIVELY CONTROLLED IN RSPONSE TO EITHER THE PRESSURE IN THE RECIRCULATING LOOP OR THE DIFFERENTIAL BETWEEN A TIMED FLOW REGULATORY SIGNAL AND THE RATE OF FLOW OF THE REGENERATING GAS THROUGH THE HEAT EXCHANGER, WHEREBY THIS CONTROL VALVE PROVIDES REGULATED CONTROL OVER THE FLOW OF REGENERTION GAS FOR REGULATED GRADUAL CHANGE IN DEMAND UPON THE STEAM GENERATOR.

Description

United States Patent [72] inventor SilvesterQlnonard Bartlesville, Okla. [2!] Appl. No. 789,162 [22] Filed Jan. 6, 1969 [4S] Patented June 28, 1971 [73] Assignee Phillips Petroleum Company [54] OUTPUT CONTROL FOR STEAM HEATED HEAT EXCHANGE]! 4 Claims, 1 Drawing Fig.

521 0.8. CI 165/39, 165/108 (5 1] Int. Cl a 86% 1/00 [50} Field oISearch 145/108, 39, 40, 62

[56] References Cited UNITED STATES PATENTS 3,203,475 8/1965 Crews et al. 165/108 Primary ExaminerCharles Sukald Attorney-Pendleton, Neuman, Seibold, Williams &

Anderson ABSTRACT: A multiple tower gas dehydration system is disclosed wherein the regeneration gas is heated in a steam heated heat exchanger, with the heat exchanger in open communication with a steam generator. After passage through the regenerating tower, the regeneration gas passes through dehydrating components, then through a continuously operated motor-driven compressor, and is returned to the wet gas input. A bypass including a variable control valve is connected between the return line to the wet gas line and the regenerating gas outlet from the towers to provide a recirculating loop through the regeneration gas dehydrating components and the compressor. The variable control valve is automatically selectively controlled in response to either the pressure in the recirculating loop or the differential between a timed flow regulator signal and the rate of flow of the regenerating gas through the heat exchanger, whereby this control valve provides regulated control over the flow of regeneration gas for regulated gradual change in demand upon the steam generator.

. OUT E7 PATENIEU JUN28 IS?! A BmQkDO This invention relates to apparatus for controlling the output of a steam generator. More particularly this invention pertains to apparatus for avoiding sudden substantial changesin demand upon the steam generator in a gas dehydrating system which utilizes steam for heating the regeneration gas flow.

Various systems are known for dehydrating gas wherein a plurality of desiccant beds in dehydrating towers are utilized sequentially with arrangements for circulating a heated gas through the beds for regeneration purposes. The operating cycle of such systems normally results in intermittent demand upon the regeneration gas system. Where steam is utilized as the heating medium for the regeneration gas, the result may be sudden high demands upon the steam generator system. This may cause water to be carried out from the generator with the steam, particularly in a system wherein the steam flows freely from the steam generator to the heat exchanger in response to demand, without control means in the steam supply line. It is desirable thatthe demand for steam from the steam generator be controlled to avoid such sudden high steam demands. It is also desirable that the demand for steam from the steam generator be gradually decreased to prevent surging in the boiler firing rate.

It is an object of this invention to overcome the problems indicated above.

It is another object of this invention to provide an improved control arrangement for a steam heated heat exchanger system.

It is a further object of this invention to provide improved control over the flow of regenerating gas in a natural gas dehydrator system.

Another object of this invention is to provide a gas dehydrator system having a steam heated heat exchanger in the regeneration line with improved control over the changes in demand upon the steam generator.

Further and additional objects and advantages will appear from the description, accompanying drawings and appended claims.

In carrying out this invention in one illustrative form, a natural gas dehydration system is provided including a plurality of dehydrator towers each containing a'desiccant bed, with a control system for cycling heated regeneration gas through one tower while the main flow stream being dehydrated is passed through another of such towers. The regeneration gas passes through a steam heated heat exchanger, through the regenerating tower, which contains dehydrating components such as adsorbents, and through a motor-driven compressor. A recirculating line is provided for recirculating the regeneration gas through the compressor, and a variable valve is interposed in the recirculating. line, with control means for gradually adjusting said variable valve to avoid sudden increases or decreases in flow of the regeneration gas through the heat exchanger.

For a more complete understanding of this invention, reference should now be had to the embodiment illustrated in the accompanying drawings and described below, by way of example of the invention.

In the drawing, the single FIGURE comprises a diagrammatic representation of a two-tower gas dehydrator system embodying teachings ofthis invention.

In the drawing, conduit is the input conduit for supplying natural gas to the illustrated system for dehydration. It will be appreciated that the input gas may be subjected to pretreatment as desired, e.g., by being passed through a gas scrubber (not shown) to extract mechanically entrained water, hydrocarbons or thelike.

The conduit 10 leads to a manifold 12 which includes valves 14 and I6 and inlet conduits l8 and for selectively directing the gas to adsorbing towers 22 and 24. A manifold 26 including conduits 28 and 30, and valves 32 and 34, connects the towers 22 and 24 with the outlet conduit 36 which may be connected to further processing components as desired.

The towers or vessels 22 or 24 are'provided with desiccant beds for adsorbent removal of water, hydrocarbons or the like from the gas being processed. lt will'be appreciated that while one of these towers is connected between conduits l0 and 36 in the main flow line for dehydrating the gas being processed, the other tower is subjected to appropriate treatment for regenerating and preparing the desiccant for further online" dehydrating use.

In the illustration it is assumed that tower 22 is in use for dehydrating the main stream of gas and tower 24 is being regenerated, as indicated by the labels on the towers, the open lines, the arrows, and the depictions of the various valves.

The regeneration system utilizes gas split-off from the main outlet conduit 36 through conduit 38 and one-way valve 39. Conduit 38 leads to a heater 40, comprising a steam heated heat exchanger. A steam generator for supplying steam to heat exchanger 40 is illustrated schematically at 42 and may comprise a conventional boiler steam generating unit which is connected to the heat exchanger by an open conduit 44. The rate of heat removal from the steam, and the attendant rate of condensation in the heat exchanger, determines the steam flow rate from the generator 42 to the heater 40. The condensate from the steam used in the heat exchanger passes through conduit 46 into a condensate accumulator 48. Appropriate liquid level controls 50 operate a control valve 51 for exhausting the condensate.

A conduit 52 leads from the heater 40 to the manifold 26. Manifold 26 includes valves 56 and 58 which are connected to the line 52 and to conduits 60 and 62 which are connected to the conduits 28 and 30, for selectively directing the regenerating gas to the towers 22 and 24. The heated regenerating gas passes upward through the tower on regeneration (tower 24 in the drawing) to the manifold 12. in passing through the adsorbent in the tower the heated gas displaces the adsorbed components from the desiccant bed therein to reactivate this bed for subsequent online dehydrating usage.

In the manifold 12, conduits 64 and 66 connect conduits l8 and 20 to valves 68 and 70 which are in communication with conduit 72 of a regeneration gas treatment line indicated generally at 74. This regeneration gas treatment line includes a cooler or condenser 76, conduit 78, a separator or scrubber 80, conduit 82, a motor driven compressor 84, and conduit 86 which is connected to the input conduit 10. The condenser 76 and scrubber 80 function in a conventional manner to condense and remove by separation the stripped materials, e.g., water and hydrocarbons, carried from the generating tower by the regeneration gas. Condenser 76 may be a heat exchanger supplied with a cold water coolant from a supply 88 with exhaust to 90, as illustrated, or other suitable cooling means. The motor-driven compressor 84 is a continuously operated, constant rate compressor, and provides adequate pressure differential to impel the regeneration gas through the regeneration system in the manner described.

Control of the rate of flow of the regenerating gas is obtained by providing a bypass line 92 connecting conduit 86 to conduit 72, with a variable control valve 94 in this line for controlled recirculation of regeneration gas through a loop circuit comprising conduits and components 72, 76, 78, 80, 82, 84, 86, 92 and 94.

Valve 94 is an appropriate valve for remote positional control, and is positioned in response to controls 96. The position of this valve is determined from two inputs derived from two system conditions and one external control. One of these inputs is the differential between a regulated variable set point, supplied by a timing regulator 100, and a signal representing the flow rate of the regeneration gas through conduit 38. The other input represents the pressure in the conduit 82.

The apparatus for providing the first noted input to controls 96 comprises a flow rate transducer 102, the regulator 100 and a flow controller I04. The regulator 100 provides a timecontrolled variable set-point signal to the controller 104. Transducer 102 senses the pressure differential across an orifree 106 in line 38 and provides a signal to the controller 104 corresponding to the flow rate in the conduit 38. The con troller 104 compares the signals received from regulator 100 and transducer 102 and provides an output control signal related to the differential between these input signals. In the illustrated system, utilizing pneumatic controls, regulator 100 may includean appropriate cam driven by a timing motor for slowing opening a valve (not shown) to provide a slowly increasing pressure signal to controller 104 upon initiation of a regenerating cycle, and a decreasing signal to controller 104 after the adsorbent hasbeen stripped. Transducer 102 provides a pressure signal representative of the flow rate in conduit 38. Controller 104 serves as a subtractor relay in that it transmits a pressure signal through conduit 112, to controls 96, which is related to the differential between the pressure inputs from the regulator 100 and the transducer 102. lf the pressure input from regulator 100 exceeds the transducer 102 output, the signal transmitted by controller 104 will increase in accordance with the differential therebetween.

A flow recorder 108 may be connected with transducer 102 as desired.

The second input to controls 96 is provided by a pressure controller 114. Controller 114 receives a signal from pressure transducer 116 which is representative of the pressure in conduit 82. In the illustrated system, the pressure signal transmitted from controller 114 to controls 96, through line 118, is related to the pressure in conduit 82.

Controls 96 effectively select between the two input signals thereto from controllers 104 and 114, and control the position of valve 94 in accordance with the selected signal. In the illustrated system, a low select relay 120 selects the lower of the two input pressure signals from controls 104 and 114 and positions valve 94 in proportion to the lower signal received, by appropriate positioning of a diaphragm-type motor 122. As the effective signal received by relay 120 increases, the pres sure signal to motor 122, through line 124 is increased to adjust the valve 94 toward its closed position. Conversely,'as the effective signal to relay 120 decreases, the valve 94 is adjusted towards its open position.

A control valve 126 is provided to hand regulate pneumatic pressure for operating the motor 122 to position valve 94 when desired.

The controller 114 transmits a signal which is higher than the signal from controller 104 under normal conditions of operation. However, the signal transmitted by controller 114 will be lower than the signal from controller 104 when controller 104 is set for flow through line 38 and the flow through line 38 is decreased abnormally below the set point of controller 104, e.g., as a result of malfunction of some part of the regeneration system. Thus, under such conditions, relay 120 of controls 96 selects the lower signal from controller 114 and thereby regulates the recirculation of gas through the closed loop comprising bypass 92 and the line 74.

In operation, the illustrated system normally will provide a pressure change, Le, a pressure drop, throughout the system in the direction of flow, except across compressor 84. That is, there will be a pressure'drop across each component from the inlet conduit to the outlet of conduit 36, and from the valve 39 to the inlet to compressor 84. The compressor provides an adequate pressure increase to provide return flow therefrom into inlet conduit 10. Thereby, it will be appreciated that the pressure in conduit 86 normally is substantially above the pressure in conduit 72, and there is a corresponding pressure drop across valve 94.

When the desiccant in the online dehydrator becomes spent, appropriate controls reposition the various valves in accordance with the operating cycle to switch the flow streams between the dehydrator towers, and then start the regulator 100. As a new regeneration cycle is initiated, the regulator 100 provides a slowlychanging signal to controller 104 which in turn transmits a slowly changing signal to the controls 96 in accordance with the differential between the inputs from regulator 100 and transducer 102. Thus, at the beginning of regeneration of the adsorbent in a tower, the regulator 100 will begin to increase the setting of controller 104 which will cause the pressure transmitted to relay 120 to be increased. This in turn will cause valve 94 to begin to close to initiate the flow through line 38, and thereby will cause the pressure from transmitter 102 to controller 104 to follow the setting of controller 104. Thereafter, the controls 96 gradually adjust valve 94 toward a closed position in response to the slowly increasing signal generated by controller 104 as the set-point from regulator is slowly increased.

Since the compressor operates at a substantially uniform rate, the closing adjustment of valve 94 causes a drop in the pressure in conduit 82, and hence in conduit 72, which causes the regenerating gas to flow through the conduit 38, the heater 40 and the tower being regenerated. The drop in pressure in conduit 82 decreases the input signal from controller 114 to relay 120, but not lower than the pressure signal from controller I04. Thereby, controller 104 continues to provide a lower signal than controller 114, and controller 104 remains in control of valve 94.

Accordingly, continued gradual increase of the set-point to controller 104 by regulator 100 further increases the differential over the actual flow signal from transducer 102 and causes further adjustment of valve 94 toward a closed position. This further decreases the recirculating flow through bypass 92, and causes attendant continued gradual increase in the rate of regenerating flow through heater 40. As the rate of flow of regenerating gas through heater 40 thus is slowly increased, the rate of condensation of steam in heat exchanger 40 will be similarly increased for'concomitant gradual increase of demand upon the steam generator 42, thereby gradually increasing the steam flow rate until the generator boiler is generating at the maximum required rate.

Since the movement of valve 94 in response to controller 104 is dependent upon the differential between the signals from regulator 100 and transducer 102, the flow rate through conduit 38 will continue to lag the increasing set-point of regulator 100. Accordingly, the maximum set-point of regulator 100 is such that an equilibrium condition is established wherein the differential between the two signals to controller 104 is adequate to provide an input to controls 96 appropriate to maintain valve 94 in the partially closed position appropriate to sustain the maximum desired regenerating flow.

When the adsorbent in a tower has been regenerated, the regulator 100 will slowly reduce the set-point of controller 104 to zero. Upon such decrease of the set-point from regulator 100, the differential between this set-point and the flow signal from transducer 102 will slowlydecrease to slowly open valve 94, and the regeneration flow rate will decrease accordingly. With the set-point of controller 104 at zero, controller 104 will transmit a signal of zero pressure to relay 120. Relay will transmit a signal of zero pressure to motor 122 which causes valve 94 to be fully open.

Thus, the described apparatus and method conveniently and economically provide accurate control over the flow of the regenerating gas, with attendant control of the flow through the heat exchanger and thus of the changes in demand upon the steam generator equipment. The varying load upon the heat exchanger is accommodated and the attendant changes in the rate of flow of steam from the steam generator to the heat exchanger are obtained under the desired control without the use of valves in the steam line.

A line 130, and control valves 132 and 134, may be provided for bypassing heater 40 to direct dry gas through a tower to cool the desiccant bed therein subsequent to regeneration and prior to return to online" use. The described regeneration control system may be programmed to control such cooling flow as desired.

The various valves for controlling the cycling of the illustrated system may be positioned by any suitable means, one example being the use of piston motor valves, as indicated in the drawing, with the piston motors being operated by a pneumatic control system. Further processing equipment may be included in line 36, or downstream therefrom, as desired.

It will be appreciated that an improved system and method have been provided which meet the aforestated objects.

While a particular embodiment of this invention has been shown, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. Therefore, it is contemplated by the appended claims to cover any such modifications as incorporate those features which may be said to constitute the essential features of these improvements, within the true spirit and scope of the invention.

lclaim:

1. Steam heating apparatus including a heat exchanger, steam generator means'connected to said heat exchanger for supplying steam thereto, a primary flow line connected to said heat exchanger, means for circulating fluid at a predetermined rate, said circulating means being connected in said primary flow line for impelling fluid through said primary flow line, a recirculating line having one end connected to said primary flow line between said heat exchanger and said circulating means and having its opposite end connected to said primary flow line on the side of said circulating means opposite said first end to provide a recirculating circuit including said circulating means and said recirculating line, variable flow control means in said recirculating line, and means for adjusting said flow control means to control the rate of flow of such fluid through said heat exchanger independently of said predetermined rate and thereby to control the demand upon said steam generator.

2. Steam heating apparatus as in claim 1 wherein said fluid circulating means is a compressor operated at a uniform rate.

3. Steam heating apparatus as in claim 1 wherein said adjusting means includes a timing regulator and provides a control output for said variable flow control means which is responsive to said timing regulator and to the rate of flow through said heat exchanger.

4. Steam heating apparatus as in claim 3 wherein said timing regulator provides a predetermined timed input signal, other means provides an input signal representative of the actual rate of flow through said heat exchanger, and said adjusting means adjusts said flow control means in proportion to the differential between such input signals.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,5 7,726 Dated June 2'8 197].

Inventor(s) Silvester C. Leonard It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Title page, Primary Examiner "Sukald" should read Sukalo Column 2, line 1, "or" (second occurrence) should read and and Column 6, line 1 4 (Claim 3), after "flow" insert of such fluid Signed and sealed this 1 8th day of January 1 972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Acting Commissioner of Patents

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