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Title:
OUTPUT CONTROL FOR STEAM HEATED HEAT EXCHANGER
United States Patent 3766713
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.


Application Number:
05/103603
Publication Date:
10/23/1973
Filing Date:
01/04/1971
Primary Class:
Other Classes:
95/23, 95/26, 95/123, 96/110, 96/114, 96/115, 96/130
International Classes:
B01D53/04; F28F27/00; (IPC1-7): B01D53/04
Field of Search:
55/21,33,163,179
View Patent Images:
US Patent References:
3540188METHOD AND APPARATUS FOR CONTROLLING CYCLIC SORPTIVE PROCESSESNovember 1970Barrere et al.
3282027Pressure differential control apparatus and a method for adsorptionNovember 1966Johnson et al.
3230688Fluid control method and apparatusJanuary 1966Kitchen et al.
3208230Automatic continuous feedback process controlSeptember 1965Fourroux
3080219Control systemMarch 1963Harvey
Primary Examiner:
Hart, Charles N.
Parent Case Data:


This is a division of my copending application Ser. No. 789,162, filed Jan. 6, 1969 (now U.S. Pat. No. 3,587,726).
Claims:
I claim

1. In cyclic adsorption apparatus including a gas supply line, a plurality of vessels each containing desiccant material for removing one or more components from wet gas and being cyclically connectable to said gas supply line, a dry gas output line, a regenerating gas system cyclically connectable to selectively include each one of said vessels to pass regenerating gas therethrough for regenerating such desiccant material, and means in said regenerating gas system for circulating regenerating gas through said system, the improvement comprising recirculating conduit means having one end connected in said regenerating gas system between said vessels and said circulating means and having its opposite end connected in said system on the side of said circulating means opposite said first end and defining with a portion of said regenerating gas system a recirculating circuit including said circulating means and said recirculation conduit means and excluding said vessels for recirculating flow of gas through said recirculating circuit without such recirculating flow passing through said vessels, variable flow control means for controlling the rate of flow through said recirculating conduit means, and means for adjusting said flow control means to regulate the rate of flow of such gas through said recirculating conduit means and thereby regulate the rate of flow of regenerating gas through the one of said vessels on regeneration and through the remainder of said regenerating gas system external to said recirculating circuit.

2. Cyclic adsorption apparatus as in claim 1 including a heat exchanger in said regenerating gas system, and steam generator means connected to said heat exchanger for supplying steam thereto to heat such regenerating gas, said heat exchanger being external to said recirculating circuit, whereby adjustment of said flow control means regulates the rate of flow of regenerating gas through said heat exchanger and thereby controls the demand upon said steam generator.

3. Cyclic adsorption apparatus as in claim 1 wherein said circulating means and said recirculating circuit are on the downstream side of said vessels in said regenerating system.

4. Cyclic adsorption apparatus as in claim 1 including regenerating gas dehydrating components in said recirculating circuit.

5. Cyclic adsorption apparatus as in claim 2 including conduit means connecting said heat exchanger to said dry gas output line and to one of said vessels in regenerating cycle for directing dry regenerating gas through said heat exchanger to such vessel, and said recirculating circuit being on the downstream side of such regenerating vessel in said regenerating gas system.

6. Cyclic adsorption apparatus as in claim 5 including means in said recirculating circuit for dehydrating such regenerating gas, a return line from said recirculating circuit to said gas supply line, said recirculating conduit means communicating between said return line and the input connection to said regeneration gas dehydrating means.

7. Cyclic adsorption apparatus as in claim 1 wherein said adjusting means includes a timing regulator and provides control of said flow control means which is responsive to said timing regulator and to the rate of flow of regenerating gas in said regenerating gas system external to said recirculating circuit.

8. Cyclic adsorption apparatus as in claim 1 wherein said circulating means circulates such gas therethrough at a substantially constant rate.

9. Cyclic adsorption apparatus as in claim 1 including a heat exchanger in said regenerating gas system external to said recirculating circuit.

10. Cyclic adsorption apparatus including a wet gas supply line, a dry gas output line, a plurality of vessels each containing desiccant material for removing one or more components from wet gas and being cyclically connectable to said supply and output lines, and a regenerating gas system; said regenerating gas system including: an input line connected to said dry gas output line and cyclically connectable to said vessels; a heat exchanger in said input line; a steam generator connected to said heat exchanger for supplying steam thereto in response to demand for heating the regenerating gas; a return line cyclically connectable to said vessels and connected to said supply line for flow of regenerating gas from said vessels to said supply line; means in said return line for dehydrating said regenerating gas; means in said return line for circulating regenerating gas through said system and through one of said vessels connected therewith; recirculating conduit means on the downstream side of said vessels and connected between the upstream and downstream sides of said dehydrating and circulating means and thereby completing a recirculating circuit including said dehydrating means, said circulating means and said recirculating conduit means and excluding said vessels and said heat exchanger for recirculating flow of gas through said recirculating circuit without such recirculating flow passing through said vessels or said heat exchanger; variable flow control means for controlling the rate of flow through said recirculating conduit means; and means for adjusting said flow control means to regulate the rate of flow of such gas through said recirculating conduit means and thereby regulate the rate of flow of regenerating gas through the one of said vessels on regeneration and through said heat exchanger.

11. Cyclic adsorption apparatus as in claim 10 wherein said adjusting means includes a timing regulator and provides control of said flow control means which is responsive to said timing regulator and to the rate of flow of regenerating gas in said regenerating gas system external to said recirculation circuit.

12. Cyclic adsorption apparatus as in claim 11 wherein said adjusting means includes a control responsive to the pressure in said recirculating circuit.

13. Cyclic adsorption apparatus as in claim 12 wherein said adjusting means includes means providing a first signal proportional to the differential between the input of the timing regulator and the flow rate in said system external to said recirculating circuit, means providing a second signal proportional to the pressure in said recirculating circuit, and means for providing a flow reducing signal to said flow control means in accordance with the lower of said first and second signals.

14. In cyclic adsorption apparatus including a gas supply line, a plurality of vessels each containing desiccant material for removing one or more components from wet gas and being cyclically connectable to said gas supply line, a dry gas output line, a regenerating gas system cyclically connectable to selectively include each one of said vessels to pass regenerating gas therethrough for regenerating such desiccant material, and means in said regenerating gas system for circulating regenerating gas through said system, the improvement comprising said regenerating gas system including a heat exchanger, steam generator means connected to said heat exchanger for supplying steam thereto to heat such regenerating gas, recirculating conduit means having one end connected in said regenerating gas system between said heat exchanger and said circulating means and having its opposite end connected in said system on the side of said circulating means opposite said first end and defining with a portion of said regenerating gas system a recirculating circuit including said circulating means and said recirculation conduit means and excluding said heat exchanger for recirculating flow of gas through said recirculating circuit without such recirculating flow passing through said heat exchanger, variable flow control means for controlling the rate of flow through said recirculating conduit means, and means for adjusting said flow control means to regulate the rate of flow of such gas through said recirculating conduit means and thereby regulate the rate of flow of regenerating gas through said heat exchanger and through the remainder of said regenerating gas system external to said recirculating circuit.

15. Cyclic adsorption apparatus as in claim 14 wherein said adjusting means includes a timing regulator and provides control of said flow control means which is responsive to said timing regulator and to the rate of flow of regenerating gas in said regenerating gas system external to said recirculating circuit.

16. A cyclic adsorption gas dehydrating process utilizing a plurality of vessels each containing a desiccant material for removing one or more components from wet gas, a wet gas input to said vessels, a dry gas output from said vessels, and fluid circulating means for causing regeneration gas to flow through a related regeneration gas system which includes said vessels, comprising withdrawing gas for regeneration from said dry gas output, heating such dry regeneration gas, cyclically passing such heated regeneration gas through each of said vessels for regenerating said desiccant material therein, and subsequently returning said regeneration gas to said wet gas input, passing such regeneration gas through said circulating means at a substantially constant rate between such withdrawal thereof from said output and return thereof to said input to provide the described flow of such regeneration gas, cyclically terminating and re-initiating flow of such regeneration gas through at least one section of such regeneration system in conjunction with changing of the regeneration cycle from vessel to vessel, and controlling the flow rate and the rate of change in the flow of such regeneration gas through such section during such terminating and re-initiating of such flow therethrough by recirculating a portion of such gas through said fluid circulating means without passage of such recirculated gas through said section and varying the portion of said regeneration gas being so recirculated in accordance with a predetermined time regulated input.

17. A process as in claim 16 wherein such section of such system through which the rate of flow and rate of change of flow is so controlled includes such vessels.

18. A process as in claim 17 wherein such section of such system through which the rate of flow and rate of change of flow is so controlled includes a heat exchanger for said heating of such regeneration gas.

19. A process as in claim 16, wherein such section of such system through which the rate of flow and rate of change of flow is so controlled includes a heat exchanger for said heating of such regeneration gas.

20. A process as in claim 16 including providing a signal representative of the rate of flow of regeneration gas through said section and providing a time regulated signal, comparing said signals, and varying the portion of said regeneration gas being so recirculated in accordance with the differential between said signals.

21. A process as in claim 20 including controlling the portion of said regeneration gas being so recirculated and thereby maintaining the pressure of the recirculating gas at a predetermined value to preclude flow of regeneration gas through said section during a part of the operating cycle of said gas regeneration system.

Description:
This invention relates to apparatus for controlling the output of a steam generator. More particularly this invention pertains to apparatus for avoiding sudden substantial changes in 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 that the 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 of this invention .

In the drawing, conduit 10 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 the like.

The conduit 10 leads to a manifold 12 which includes valves 14 and 16 and inlet conduits 18 and 20 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 and 24 are provided with desiccant beds for adsorbent removal of water, hydrocarbons or the like from the gas being processed. It will be appreciated that while one of these towers is connected between conduits 10 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 "on line" 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 selevtively 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 "on line" dehydrating usage.

In the manifold 12, conduits 64 and 66 connect conduits 18 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 104. The regulator 100 provides a time-controlled variable set-point signal to the controller 104. Transducer 102 senses the pressure differential across an orifice 106 in line 38 and provides a signal to the controller 104 corresponding to the flow rate in the conduit 38. The controller 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 include an 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 has been 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. If 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 pressure 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, i.e., 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 10 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 "on line" 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 slowly changing 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 100 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 104. 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 slowly decrease 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 120 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 attandant 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 "on line" 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.