US2316251A - Process and apparatus for the drying of gases - Google Patents

Description

Patented Apr, 13, 19 43v PROCESS AND APPARATUS FOR THE DRYING F GASES Heinrich Kahle, Munich-Pullach, and Stephan Stark, Munich-Grunwald, Germany; vested in the Alien Property Custodian Application October '18, 1940, Serial No. 361,804

Germany December 27, 1938 14 Claims.

This invention relates to a process of and apparatus for drying gases and more particularly iormaintaining dry a gas normally passing from a supply source to a utilizing apparatus, portions of which gas have been temporarily stored over a liquid or in a liquid-sealed gasometer.

In plants in which a gas is delivered from a supply source, such as a gas-producing apparatus, to a receiving-means or gas-utilizing apparatus, the rates of supply and of use may not be constantly equal. In such instances, it is convenient to provide a storage device or gasometer operatively connected by a branch line with the main line between the source and the gas-receiving or utilizing apparatus. If, during short periods of time, the supply of gas exceeds the rate of use of gas, the gasometer will receive and store the surplus quantities. If utilization of gas exceeds the supply during other short periods, the gasometer will supply the balance from the temporarily stored gas-to the pipe line.

If the gasometer is sealed by water in the customary manner, the temporarily stored gas will leave the gasometer charged with water vapor. Such moistening of the gas is especially troublesome if the gas must be dry at the receiving or utilizing apparatus.

To avoid such difficulties, dry gasometers have been proposed which employ sealing liquids that do not vaporize, such as glycerine, oil, etc. Dry gasometers are not always available, and an oil or glycerine seal is expensive. Furthermore, it is not possible in most instances to permanently exclude all atmospheric humidity from the sealing liquid and thereby to exclude such moisture from the stored gas.

When gasometers having water seals are employed, the gas to be delivered to the consuming apparatus must be treated to eliminate its humidity by providing special drying devices. Heretofore, the drying of the gas assing through the additional pipe line from the gasometer has been avoided, probably because it has been assumed that because of the high water content of such gas, the drying means would be very rapidly exhausted.

It has been found that a regenerable drying agent, such as silica-gel, activated carbon, etc., interposed in the branch pipe line leading to the gasometer, oflers particular advantages. If the gasometer is operated in the normal manner and there is no leakage or loss of gas, then, even though for short periods the supply of gas may exceed the consumption and for other short periods the consumption of gas may exceed the sunply, the sum of the quantities of gas flowing to the gasometer during a long period is substantially equal to the sum of the quantities of gas flowing out of the gasometer. Thus, only a relatively small rate of exhaustion of the drying means will occur it a regenerable drying agent is used because the humidity removed from the gas and stored in the dryer during the return of gas from the gasometer during certain periods will be carried off by the reverse gas flow through the dryer during periods when dry gas flows toward the gasometer. Although in practice it will not be possible to remove the entire quantity of water deposited in the drying agent when employing the commercially available regenerable drying agents, the above-described drying process provides a great advantage as compared with the prior method of drying the entire quantity of gas passing through the main pipe line to the consuming apparatus.

It will be seen that if an ideal drying agent were employed which would release moisture as easily as it takes up moisture under conditions of equal volume temperature, and pressure of gas flow in both directions, no consumption or exhaustion of drying agent would occur. with commercial regenerable drying agents, which tend to release moisture less readily, the tendency to eventual exhaustion can be overcome according to the invention by accelerating the regeneration of the agent during the period of flow toward the gasometer by causing the total moisture carrying capacity of the dry gas flowing toward the gasometer to be greater than the total moisture carrying capacity the gas flowing from the gasometer, either by heating the gas before it passes through the dryer in the direction toward the gasometer, or by arranging the flow of gas to occur toward the gasometer during periods when the gas produced has a higher temperature than the gas which flows from the gasometer during other periods, or by arranging for the flow of a volume of dry gas through the dryer in the direction toward the gasometer greater than the volume of moist gas in th direction from the gasometer.

The objects and novel features of the present invention will become evident from the description taken in connection with the accompanying drawing, in which:

Fig. l is a diagrammatic view showing an im proved drying arrangement according to the invention; and,

Fig. 2 is a fragmentary diagrammatic view of an alternative arrangement according to the invention.

Referring now to the drawing and particularly to Fig. l, the gas supplying means such as a dry-gas producing apparatus is indicated at l and the dry-gas receiving or utilizing apparatus is indicated at I i. The gas supplied is conducted by a main pipe line I2 from the producer I0 to the receiver i i, and a water-sealed gasometer I3 is connected by a branch pipe line II with the main pipe line I2, According to the invention there is interposed in the branch line I a regenerabie drying device I6. In the prior arrangement however, the gasometer I3 is customarily directly connected to the main pipe line I2, and before the utilizing apparatus I i, there would be interposed a duplicate set of drying devices of the customary type connected and arranged that when one became saturated with moisture it would be disconnected from the pipe line and regenerated in the customary way by an auxiliary dry gas while the other drying device is in serv- As previously mentioned, the fluctuations in the quantity and pressure of the gas in the main pip line are balanced by the flow of gas into and out of the gasometer.When, according to the prior arrangement, the pressure in the main pipe line dropped, due to the rate of consumption exceeding the rate of production of gas, water-bearing gas would flow from the gasometer into the main pipe line and be mixed with the dry gas coming from the source II). The total quantity of gas flowing through the main pipe line would then carry a relatively smaller percentage of water vapor to be deposited in one of the drying devices before the gas passes to the utilizing apparatus II. When the pressure in the pipe line increased or the rate of production of gas exceeded the rate of use, the excess gas passed into the gasometer I3 and by contact with the water in the gasometer, became saturated with water vapor. During such period of time the main pipe line will have carried only dry gas. It will be seen then that if such dry gas was passed through one of the driers in the line I2 which had already absorbed a substantial amount of water, the wet zones of the drying agent in the drier would tend to be driven in the direction of gas flow toward the side of the drier adjacent the utilizing apparatus I I. This action will have caused the efllciency of such driers to be greatly reduced, and to avoid passing any moisture to the consuming apparatus II, it was essential to renew or redry the drying agent relatively quite often. Because of the relatively low humidity of the gas, the drying agent could be charged with water vapor only to a. low degree and therefore it was necessary to renew or redry the drying agent after a relatively short period of service while the gas flow was directed through the duplicate drying device of the Pair. Since the whole quantity of gas was treated, such drying devices were of ample dimensions in order to insure a complete separation of water vapor at the relatively high rate of flow of gas. Another disadvantage of the prior arrangement is that considerabl quantities of a very dry auxiliary gas were required for redrying the drying agent in order that the necessary thorough elimination of water from the agent could be accomplished.

According to the present invention as illustrated in Fig. 1, the drier I6 interposed in the branch line I4 provides much better drying conditions and more efficient utilization of drying agent, while, at the same time, providing at least the same degree of absolute dryness of the gas entering the utilizing apparatus II. The total quantitles 01. water which are carried into the drier I8 are not larger than the quantities of water which it was necessary to remove according to the former practice. However, the relatively much higher percentage of water vapor content of the relatively smaller quantity of gas which is treated by the drier' I8 causes a more intensive charging of those layers of the drying agent which are located in the portions of the drier I6 toward the gasometer whereby the rapid establishment of an equilibrium condition occurs only in the initial layers of the drying agent, and the elimination of the water vapor is greatly facilitated by this fact and by the relatively low velocity of flow of the gas. As a result of the new arrangement, a very high utilization of the drying agent results as well as a permanently high degree of dryness of the gas which leaves the drier IS in the direction toward the main pipe line I2. A principal advantage, however, follows from the fact that the drying agent is automatically regenerated as soon as additional portions of dry gas flow back toward the gasometer. The relatively low velocity of gas flow and the relatively high degree of saturation of those layers of the drying agent which are nearest the gasometer are factors which again are very effective for adequately causing the dry gas to take up the moisture and thus regenerate the drying agent. An important additional feature is, that on the gasometer side of the drier, the gas always has a predetermined practically constant water content whereas on the opposite side of the drier, the gas is in a permanently dry condition independently of the direction in which the gas may be flowing at any one instant.

Another advantage of the new arrangement, according to the invention, is that not only is a considerably smaller amount of the drying agent suflicient to provide better drying, but also there is required no duplicate set of driers nor is there required a dry gas for redrying the drying agent.

A relatively more rapid absorption of moisture in the drier occurs only if the supply of gas should be suddenly considerably reduced and the utilization of gas is not correspondingly reduced, in which event the gasometer will be emptied to a greater degree.

According to the invention, in the event that the drier I6 should become loaded with water vapor to a degree such that the normal return flow of dry gas would not suiiiciently redry the agent, it has been found convenient to accelerate the regeneration of the drying agent by applying heat to the drying agent during the return flow of dry gas or by heating the dry gas flowing toward the gasometer I3 before it enters the drier IS. The heating should obviously be to a temperature higher than the temperature of the gas which, during the previous period, flowed out of the gasometer. The application of heat to the gas may be effected by interposing an auxiliary gas heater I! in the conduit I4 between the drier I6 and the main pipe line I2. The heater Il may be heated by electric power.

If the discharging and refilling of the gasometer occurs systematically and at freely chosen times, then, according to the present invention, the periods for filling the gasometer are chosen to coincide with the periods when the gas in the main pipe line has a relatively higher temperature and the periods for discharging the gasometer are chosen to coincide with the periods when the gas temperature in the main pipe line is relatively lower. This method of operation, of

course, will be practiced only when the gas producing apparatus produces gases at a higher temperature than the temperature of the gas in the gasometer. The filling of the gasometer during periods of higher temperature eflects a greater reversible vapor pressure on the surface of the drying agent and therefore improves the regeneration, while the step of discharging the gasometer during periods of lower temperature reduces the absolute water content as well as the volume of the gas leaving the gasometer and consequently reduces the work that the drier has to perform.

If the discharging or refilling of the gasometer is due to unexpected difficulties or interruptions in the normal operation of the'plant, it is possible in accordance with the arrangement of the present invention, to switch error to switch of! the auxiliary gas heating device H by means of an automatically operated control switch of any suitable customary type such as a switch operated by a gas fiowmeter or by a switch which is operated by the occurrence of a predetermined difference of pressure at thedrier It. In order to avoid repeated and unnecessary operations of the heater switch in response to minor fluctuations in the gas flow, the switch is arranged so that it will be operated only if a predetermined velocity of the gas flow toward the gasometer is either exceeded or if the velocity falls short of the predetermined velocity by a predetermined amount. The heater is not energized during the return of gas from the gasometer to the main pipe line although it would be preferable to provide an alarm signal so that the gas requirements of the consuming apparatus can be reduced when the gasometer empties.

A suitable arrangement is also diagrammatically illustrated in Fig. 1 in which conduits i3 and I9 are connected to the branch pipe line H on either side of the drier IE to transmit a pressure difference to a pressure switch 20 which may have a pressure responsive element such as: a bellows 2|, the closed end of which will move downward when the pressure on the main pipe line side of the drier it exceeds the pressure on the gasometer side of the drier it by a predeter: mined amount. The movable end of the bellows 2| is connected by suitable means such as a lever 22 arranged to close a switch 23. The closing of the switch 23 completes a circuit that energizes a relay 24, which in turn closes the electrical power circuit of a heater element 25 in the heater l1 which is interposed in the connection I! between the drier l6 and the main pipe line l2. It will be seen that the circuit of the heater element 25 will be closed only when flow occurs from the main pipe line l2 toward the gasometer i3 and also only when the pressure difference across the drier it exceeds an amount sufllcient to collapse the bellows 2| enough to close the switch 23. Thus, when the drier I3 becomes loaded with enough water so that its drying efficiency may be ailected, the resistance to gas flow therethrough will have increased sufficiently to operate the pressure switch.

An alternative arrangement, according to the invention, is diagrammatically illustrated in Fig. 2 which arrangement is particularly useful in plants where the gas may be conducted to more than one place of utilization and particularly wherein it is possible to supply some moist gas to one or more of the utilizing devices. In such cases it is possible to eliminate any renewal or special revivification of the drying agent by withdrawing some of the moist gas from the gasthrough the drying agent in the direction toward the gasometer than the volume of moist gas that will flow through the drier in the direction from the gasometer. Even though the total quantity of moist gas withdrawn and supplied to the moist gas consuming device may be relatively small, it will guarantee an excess of dry gas available for regeneration of the drying agent as compared with the quantity of gas to be dried and therefore a special or external redrying or renewal of the drying agent at the end of a period of operation will be completely avoided.

In Fig. 2 the gas-producing device is indicated at II and may comprise a gas separator which treats a raw gas that enters through the conduit 30. The gas separator ll produces a residue gas which is discharged through a conduit 3i and also a pure and dry gaseous product which is discharged through a conduit 32 connecting with the main pipe line l2 and the branch pipe line H. The main flow of the dry gaseous product passes from the conduit 32 through the main line l2 to the dry-gas consuming apparatus I I. A valve 32' in conduit 32 normally remains open. The gas which passes through the branch pipe line H toward the gasometer l3 passes through the drier l6 which is interposed in the branch line H as described in connection with Fig. 1. A moist gasconsuming apparatus is indicated at 34 and a conduit'33 conducts relatively smaller portions of gas from the branch line H to the moist gasconsuming apparatus 34. The conduit 33 could obviously be connected directly to the gasometer ii, if desired. For emptying the gasometer l3 and for starting the gas separating or producing plant 10', a gas compressor 35 may be provided and connected to receive ,dry gas from the main line i2 through a conduit 33 and to discharge such gas to the producing apparatus l3 through a conduit 31.

It will be seen that due to the withdrawal of portions of moist gas through the auxiliary pipe line 33 to the moist-gas-utilizing apparatus 34, a preponderance of dry gas will be passed through the drier l6 and therefore the drying agent will not become overloaded with moisture. Under the most unfavorable working conditions, e. g., a deficiency of supply of dry gas and a continuance of the rate of utilization of gas, the process according to the invention insures against the passage of moisture from the gasometer II to the main pipe line i2. If desired, for example, when starting up the gas separating apparatus Ill, the gasometer II can be entirely emptied of gas by closing the valve 32, and operating the compressor 35 whereby gas will flow from the gasometer is through the branch line H, the drier IS, the main line I2, connection 36, compressor 33 and connection 31 to the gas separation apparatus i3. No moisture will be carried into the gas separating apparatus Ill and no special steps will be required for subsequently redrying and the drying agent in the drier i6. because when the producing apparatus l0 begins to deliver the dry gas product, such product will flow through the conduit 32 after the valve 32' is opened and the flow of such dry gas through branch line I4 and the drier ii in the direction toward the gasometer l3 will automatically regenerate or redry the drying agent.

We claim:

1. In a process for maintaining dry a gas which is conducted from a source of dry gas to a drygas utilizing means through a main pipe line having a liquid sealed gasometer connected thereto by a branch pipe line, the steps comprising providing a regenerable drying agent in a drier interposed in. said branch pipe line, passing portions of moist gas through said drier in one direction from said gasometer to said main pipe line during periods when the rate of utilization exceeds the rate of supply of gas from said source, and passing other portions or dry gas from said main pipe line to said gasometer through said drier in the reverse direction during periods when the rate of supply exceeds the rate 01 utilization of gas, whereby a substantially uniform state of dryness is maintained in the gas on the main pipe line side of said drier.

2. A process as defined in claim 1 in which the total volume of moist gas passed through said drier to the main pipe line is less than the total volume of said other portions of dry gas passed through the drier in the reverse direction.

3. A process as defined in claim 1 which includes the step of heating said other portions of dry gas before passage through said drier in said reverse direction, said dry gas being heated to an average temperature exceeding the average temperature of said moist portions of gas.

4. A process as defined in claim 1 which includes the step of heating said drying agent only during the passage of dry gas through said drier in said reverse direction.

5. Process as defined in claim 1 in which the flow of gas in said reverse direction toward said gasometer is effected during periods when the dry gas flowing in said main pipe line has a relatively higher temperature and in which the flow of gas from said gasometer is effected during periods when the dry gas flowing in said main pipe line has a relatively lower temperature.

6. Process according to claim 1 which includes the steps of applying heat to said other portions of dry gas upon passage through said drier in the reverse direction toward the gasometer only when a predetermined pressure diflerence across said drier during said flow in the reverse direction is exceeded.

7. Process according to claim 1 which includes the steps of supplying heat to said other portions of dry gas upon passage through said drier in the reverse direction when a predetermined velocity of flow of gas toward the gasometer is exceeded and discontinuing said heating when said velocity of flow is less than a predetermined lower velocity.

8. A process as defined in claim 1 which includes the step of initiating an alarm signal when the velocity of flow of gas out of said gasometer toward the main pipe line exceeds a predetermined value.

9. A process as defined in claim 1 which includes the step of passing portions of moistureladen gas from the gasometer to another gas-receiving means in such amounts that the average volume of gas flowing through said drier in the direction toward said gasometer exceeds the average volume of gas flowing through said drier in the direction toward said main pipe line by an amount at least suii'icient to insure complete regeneration of said drying agent.

10. In gas apparatus including a source oi dry gas, a dry-gas utilizing means, said source of dry gas and said dry gas utilizing means being so constructed and arranged that the rate oi utilization exceeds the rate of supply of gas during certain periods 0! operation and during other periods of operation the rate of supply exceeds the rate of utilization of gas, a main pipe line connected therebetween, a liquid sealed gasometer, and a branch pipe line connecting said gasometer to said main pipe line; a drier interposed in said branch pipe line; and a regenerable drying agent in said drier, whereby moisture-laden, gas passes through said drier always in one direction from said gasometer toward said main pipe line and dry gas passes through said drier always in the reverse direction.

11. A gas apparatus according to claim 10 including a gas heating device interposed in said branch pipe line between said main pipe line and said drier for supplying heat to the portions of dry gas passing through said drier in said reverse direction irom said main pipe line to said gasometer.

12. 15 gas apparatus according to claim 10 which includes means for supplying heat to the portions of dry gas passing through said drier in said reverse direction; means for controlling said supply of heat; and means responsive to a diflerence of gas pressure across said drying agent for operating said controlling means to supply heat when said pressure dlfierence exceeds a predetermined value.

13. A gas apparatus according to claim 10 including means for supplying heat to the portions 01 dry gas passing through said drier in said reverse direction; means for controlling said supply of heat; and means responsive to the velocity of flow of gas through said drier in said reverse direction for operating said controlling means to supply heat when said velocity exceeds a predetermined value and to discontinue said supply of heat when said velocity is below a predetermined lower value.

14. A gas apparatus according to claim 10 which include another gas utilizing means; and an auxiliary pipe line connected to conduct portions of moist gas from said gasometer to said other utilizing means whereby the average volume of gas flowing through the regenerable drying agent in said reverse direction exceeds the average volume of gas flowing through said drying agent in the direction from said gasometer.

HEINRICH KAI-111E. S'I'EPHAN STARK.

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