NO154823B - GAS DRYING DEVICE. - Google Patents

Description

The present invention relates to an apparatus for drying or dehumidifying gases and of the type specified in the introduction to the following independent claim 1. Such devices for dehumidifying air or gaseous media can e.g. used for dehumidifying air in compressed air systems and in rooms as well as for dehumidifying gas or air used in manufacturing processes, etc.

Devices of this type are known where the adsorbing medium or the adsorbent is divided into several layers to achieve a more uniform distribution of the gas flow over the cross-sectional area of the adsorbent used (such devices are, for example, described in US patent 3,490,201 and 3,594,990). When the adsorbing medium or the adsorbent has been used for a certain time and enriched with a certain amount of moisture, it must be regenerated. This can be done by passing heated air through the adsorbent (US Pat. 3,490,201) or by directly heating the adsorbent at the same time as passing air from the surrounding atmosphere through it (US Pat. 3,594,990). The former regeneration procedure involves a relatively large loss of heat energy, while the latter procedure is more advantageous from a heat economy point of view. In the known apparatus where the adsorbent is divided into several layers, each of which is heated during the regeneration step by means of electric heating means (US Pat. 3,594,990), the layers of adsorption medium are however limited to small amounts of a drying agent such as lithium chloride which is deposited on the heating wires by impregnation of asbestos yarn that covers these wires. It is clear that the price for the electric heating device which occurs in this known construction is relatively high compared to the adsorption capacity of the adsorbent or the desiccant placed on the heating device.

While some of the known devices work intermittently, as adsorption and regeneration processes take place alternately for the entire amount of adsorbent in the device, other known devices (e.g. described in US patents 3,487,608 and 3,490,201) can work continuously.

The applicant's previous Norwegian patent no. 147903. describes an apparatus for drying or dehumidifying gases and with a housing that forms a number of separate chambers or channels each of which contains a regenerable moisture adsorbing medium and selectively activatable electric heating means for selectively heating the adsorbing medium when this must be regenerated. In an embodiment of this, apparatus (which is described in the mentioned earlier patent, each of the chambers contains a folded or pleated sheet- or plate-like absorbent medium of a fibrous material, and electric heating elements are placed between adjacent layers of the adsorbing medium. A gas to be dehumidified can thus flow through the spaces between the adjoining layers of adsorbent, from the device's inlet to its outlet and vice versa. However, the flowing gas will thus hardly come into contact with the internal parts of the layers of adsorbent medium, but essentially only with its outer surface. Another described embodiment has a particulate adsorbent medium disposed in layers extending across the gas flow in the chamber in which the layers are disposed, and the heating means comprise stacked tray-like parts of a heat-conducting material for absorbing these layers of particulate material rials. Such a construction does not ensure a completely uniformly distributed gas flow over the entire cross-sectional area of each chamber, and as the ground-like parts must extend mainly horizontally, the gas flow must be directed mainly vertically so that the apparatus cannot be oriented as desired.

With the present invention, a very economical working apparatus has been provided which is of the type described and which can be oriented as desired.

According to the invention, this has been achieved with the help of the features that appear from the characteristics of the following independent claim 1 as well as from the subsequent non-independent claims.

The construction according to the invention ensures a uniformly distributed gas flow over the entire cross-sectional area of the chamber so that the gas flow comes into intimate contact with all parts of the adsorbent. The placement of the electric heating means between and in intimate contact with adjacent layers of adsorbing medium or adsorbent further means that each individual layer - which can have a suitably small thickness - during the regeneration process can be heated directly on both sides of the heating means. This effective direct heating of the adsorbent means that only a relatively small amount of dehumidified gas is required for the regeneration process, which is why a very advantageous heat economy can be achieved by using the device according to the invention. Furthermore, the placement of the electric heating means or heating elements between adjacent layers of the adsorbent significantly facilitates the assembly of the apparatus, just as it also facilitates a later replacement of possibly defective heating elements.

The adsorption efficiency of the adsorbent medium will normally fall as its temperature rises. It is therefore important that the adsorbent is cooled after the regeneration process before the adsorbent is used again in a new adsorption process. This can e.g. is achieved by bringing cold air or gas to flow through the adsorbent for a certain period of time after inactivating the heating means.

The adsorbent's adsorption of moisture or steam normally involves the development of heat, whereby the temperature of the adsorbent and the gas flowing through it is increased. A higher temperature for the gas to be dehumidified causes the relative humidity of the gas to decrease. As the moisture-adsorbing ability of adsorbents is largely dependent on the relative humidity of the gas, the development of heat of adsorption can have the effect that the effectiveness of the adsorbing medium becomes rather small in a zone at the furthest end of the respective chamber in the direction of flow. In some cases, e.g. in devices that must have a large potential adsorption capacity, it can be advantageous to counteract the temperature increase as a result of the development of heat of adsorption. According to the invention, the moisture-adsorbing medium in each of the chambers or channels can be divided into axially spaced sections, and cooling means of one or another suitable type can be placed between such sections to cool the gas flowing through the respective chambers.

In the device according to the invention, the regeneration process takes place quickly and efficiently. Therefore, an apparatus containing a relatively small amount of adsorbing medium or adsorbent can have a rather large capacity. A reduction in the required amount of adsorbent entails a substantial reduction in the flow resistance in the apparatus. Consequently, even a device with a large capacity can have such a small flow resistance that it can be used not only for dehumidifying compressed air, but also for dehumidifying air at atmospheric pressure that can be passed through the device by means of a fan.

The adsorbent or adsorbent material may comprise any known adsorbent material such as molecular sieves, silica gel, activated alumina, synthetic mineral fibers and ceramic fibers. The adsorbent is preferably a particulate material, but can instead be a plate or sheet material. Such a plate or sheet material can e.g. take the form of an asbestos tape, an asbestos sheet, an asbestos web or an asbestos sheet impregnated with a hygroscopic material such as lithium chloride.

The invention will be described in more detail below with reference to the drawing, where

fig. 1 shows a preferred embodiment of the device or dehumidifier according to the invention, seen from the side

and partly on average,

fig. 2 shows on a larger scale a cross-section at one end of the device or the dehumidifier shown in fig. 1,

fig. 3 and 4 an illustration of possible arrangements of the plate or sheet-like heating elements in the chambers of the dehumidifier according to the invention,

fig. 5 a plate or sheet material seen from above, which can be used as heating elements in the device according to the invention,

fig. 6 is a diagram showing an electrical control system for controlling the function of that in fig. 1-4 shown apparatus,

fig. 7 and 8 on a larger scale and seen in perspective, a rotary interrupter device seen from opposite ends,

fig. 9 schematically and seen from the side and partly in section a fourth embodiment of the device according to the invention, and

fig. 10 seen from below and partly in cross-section that in fig. 9 display device.

The device or the dehumidifier shown in fig. 1-4, has a stationary cylindrical housing 10, which by means of a number of radially extending partitions 11 is divided into several sector-shaped passages or chambers 12 which are open at opposite ends. At one end of the housing 10 there is an inlet pipe 13 for moist gas or air, and the housing is provided at its other end with an outlet pipe 14 for dried or dehumidified gas or air.

The sector-shaped chambers or channels 12 are placed in an annular arrangement inside the housing 10 so that they surround and delimit a central space 31. Each of the chambers 12 is mainly filled with an adsorbing medium or an adsorbent 15, and between layer of the adsorbing medium, electric heating elements 4 3 are placed which will be described in more detail in the following. The ends of the chambers or passages 12 which are located near the inlet pipe 13 are connected to this pipe through connection channels 34 and via a rotary valve 20

which is fixedly mounted at one end of a central shaft 45 and which extends axially through the apparatus. House 10 has

an annular outlet manifold 24 which surrounds the rotary valve 20 and is connected to the atmosphere via an outflow pipe 25. In the inner wall of the manifold 24, an annular gap 38 is defined which along most of its peripheral length is closed by a cylindrical outer wall 36 of the valve 20. The valve 20 also has a wall 39 which extends across the inlet pipe 13, and the cylindrical wall 36 is cut away along the inner peripheral edge of the transverse wall 39 so that the valve 20 can connect a minority (e.g. one or two) of the chambers 12. with the manifold 24 via an uncovered part of the slot 38, while the other chambers 12 are connected to the inlet pipe 13.

An interrupter-activating disc 46 with an interrupter-activating protrusion or chamber 30 located along its periphery is mounted at the end of the shaft 45 which is opposite the valve 20. The disc 46 has a ring gear 47 which meshes with the driving gear 48 of a drive motor 27 The motor 27 is mounted on an end cover 49 which includes an outlet pipe 14 and is attached to the adjacent end wall of the housing 10. The shaft 45 extends through an annular inner housing 50 which delimits the central space 31. The inner housing 50 contains a rotatable electric interrupter device 51 which has a stator part 52 which abuts the inner surface of the tubular housing 50, and a rotor 53 which is mounted on the shaft 4 5 so that it turns together with the shaft. The interrupting device 51 will be described in more detail in the following with reference to fig. 7 and 8.

Fig. 5 shows a preferred embodiment of the electric heating elements 4 3 and shows a web comprising a heat-resistant plate or sheet material and electrical circuits which are "printed" on this with a common circuit printing technique. That in fig. 5 shown web material can be divided into a number of heating elements by cutting the web crosswise, e.g. along the dashed line, which is indicated in fig. 5. Each heating element 43 has three or a multiple of three modules 54, each of which comprises a printed circuit with a number of series-connected resistance elements 55. The track's printed circuit also comprises longitudinal collecting lines 56 which parallel connect the heating elements 55 in adjacent modules and which in each module has connection points 57.

The plate or sheet-shaped material used

in the heating elements 4 3 shown in fig. 5, can e.g. be that marketed by the 3M Company under the trademark "KAPTON". This material is resistant to temperatures as high as 260-270°C. Heating elements 4 3 can be produced by etching a foil of stainless steel which is laminated with plastic foil, to produce the desired printed circuit.

It is clear that a plate or sheet material with printed circuits as shown in fig. 5, can be produced in the form of webs of any desired length, after which heating elements containing any desired number of modules 54 can be cut from this web.

A heating element 4 3 of the one in fig. 5 shown type is placed in each of the device's chambers or passages 12. The heating element is preferably folded or pleated, e.g. as shown in fig. 3 or 4, and adjacent layers of the heating elements can be placed with mutual distances by means of spacers 58 which are placed between the layers. These spacers are preferably in the form of a corrected plate or sheet material such as a woven, heat-resistant material, e.g. polyester. The spacers 58 can be impregnated with a hygroscopic material such as lithium chloride with a cellular structure. The spaces delimited by the walls 12 of the chambers, the mutually spaced layers of the heating elements 4 3 and the corrected spacers 58 are filled with a suitable fibrous or particulate moisture absorbent medium 15, e.g. molecular sieves, silica gel, activated aluminum oxide or any suitable regenerable adsorbent or hygroscopic substance. The distance between the spaced apart layers of the folded or pleated heating elements 43 must be sufficiently small to ensure rapid and efficient heating of the adsorbent layer placed in between. The distance can e.g. be of the order of 10 mm.

Fig. 6 is a diagram showing an electrical control system for controlling the function of that in fig. 1 and 2 showed apparatus. The drying or dehumidifying apparatus is designed to be supplied with power from a three-phase power supply and comprises power supply terminals R, S, T and 0. These

terminals are connected with corresponding power supply lines, resp. 1R, lg, 1T, and 1q. The power supply through these lines can be controlled by a main switch 59. The power supply through the lines 1R, 1g and 1T is used to supply power to a fan 60 and selected specimens of the heating elements 43 placed in the chambers 12. The power supply to the fan 60 and to the heating elements 43 are controlled by contactors, respectively. 61 and 62, or other suitable interrupting means. The fan 60 is used to blow air or gas to be dried into the apparatus through the inlet pipe 13. The function of the motor 27 which drives the shaft 45 as well as the interrupter activation disk 46 mounted thereon, the interrupter device 51 and the rotary valve 20, is controlled by a clock-controlled contactor or interrupter device 63 , a hygrostat 64 or another moisture-sensitive device which, in the direction of flow, is preferably placed after the dehumidifier and in the vicinity of its outlet pipe 14, and of projection or chamber 30 on the switch-activating disk 46. The hygrostat 64 controls a switch Sq, while the clock-controlled contactor 6 3 controls the interrupter S^ and S^ and the interrupter means 29 include interrupters S2 and S^.

That in fig. The apparatus shown in 1 and 2 works mainly like those described in the applicant's above-mentioned patent applications, which means that air or gas to be dried or dehumidified is passed through the majority of the chambers 12 and the adsorbent 15 contained therein, while a small fraction of the dried gas is returned and passed through the remaining minority of the chamber 12 in the opposite direction so that the adsorbent or adsorption medium in these chambers is heated and regenerated. At certain time intervals, the chamber or chambers in which the adsorbent is regenerated is changed, and this regeneration cycle is controlled by the one in fig. 6 showed electrical control system.

When the main switch 59 is closed, the contactor 61 will automatically connect the fan 60 to the power supply lines 1R, 1g and 1T, so that the fan will start blowing • air or gas to be dried into the inlet pipe 13. It is assumed that the switches Sq - are in its in fig. 6 shown positions, power is not supplied to the motor 27. Consequently, the valve 20 is stationary and allows air or gas to flow from the inlet pipe 13 through the majority of the chambers or passages 12 to the outlet pipe 14 as indicated by arrows in fig. 1. However, the cross-wall 39 of the valve 20 closes the passages from the inlet pipe 13 to a minority, preferably two, of the chambers 12 and at the same time the valve brings this minority of the chamber into connection with the manifold 24 through the slot 38 as mentioned above. Consequently, dry gas can flow from the outlet pipe 14 into the aforementioned minority of the chamber through one or more flow-limiting openings 65 and from the chambers out into the atmosphere through the manifold 24 and the outflow pipe 25. After a predetermined period of time, the uncontrolled contactor or timer 63 closes the interrupter Unless the hygrostat 64 determines that the moisture content of the gas leaving the outlet pipe

14 is below a predetermined value, the interrupter Sq has also been closed by the hygrostat 64, whereby current is supplied to the motor 27 through the closed contacts Sq, S^ and S.j. The motor 27 now rotates the interrupter device 51

rotor 53 and valve 20 one step forward corresponding to a fine rotation of 360°/n, where n is the number of sector-like chambers or passages 12 in the apparatus.

The valve's new angular position will be determined by the cams or protrusions 30 on the actuating disc 46 which open the breaker S^ and at the same time close the breaker. When the valve 20 has been moved to its new position, the contactor 63 closes the breaker S^, causing the contactor 62 to conduct current to the heating elements 43. As shown in fig. 6, however, only the heating elements 43 which have been short-circuited by the rotor 53 will be supplied with current. In a preferred embodiment, it contains in fig. 1 and 2 the apparatus shows six chambers or passages 12 and the valve 20 is arranged to allow gas to be dried to flow through four of these chambers while a small fraction of the dried gas is returned through the remaining two chambers, in which the adsorbent medium is regenerated . The motor 27 is controlled so that the valve 20 and the interrupter device 51 rotor 53 are turned step by step with steps corresponding to an angular rotation of 60°. Consequently, the regeneration period for the adsorbent in each chamber will be twice the time in which the uncontrollable contactor 63 activates the interrupters S, and S^. In each chamber or passage 12, the heating elements 43 are only supplied with electricity in the first of these two time periods, and in the subsequent time period cold dried gas will flow through the chamber whereby the regenerated adsorbent contained therein is cooled.

It will be understood that every time a period of time determined by the clock-controlled contactor or timer 6 3 has expired, the interrupters S, and S. will be activated, whereby the contactor 62 interrupts the power supply to the heating elements, and the motor 27 is then rotated one step forward determined by the activation disc 46, which changes the positions of the switches S2 and S-, after which the contactor 62 again connects the heating elements 43 to the power supply. The rotor 53 has, however, been moved forward one turn so that the heating element in the next chamber 12, in which the adsorbent is to be regenerated, is supplied with electricity. If, however, the hygrostat 64 determines that the moisture content of the dried gas flowing from the apparatus through the outlet pipe 14 is below a preset value, the switch Sq is opened. If the breaker Sq is still open when the de-energized contactor 63 opens the breaker 64 to interrupt the power supply to the heating elements and changes the position of the breaker S^, the motor will not be supplied with power until the hygrostat 64 closes the breaker Sq, which means an extension of the air drying period in the majority of the chambers 12 and that the cooling period for adsorbent that is regenerated in two of the chambers 12.

The electric rotary switch device 51, which is shown in fig. 7 and 8, will now be described in more detail. The stator part 52 has a coil-shaped part of an insulating material. The coil-shaped part is provided at one end with three radially separated and mutually insulated metal terminal rings 66, 67 and 68 representing the electrical phases R, S and T respectively. These rings are provided with spaced apart screws 69 or connecting means for electrically connecting the heating elements 43 in the respective chambers 12, thereto. Each heating element 4 3 comprises three modules 54 as shown in fig. 5, and one terminal end of each module is connected to each of the terminal rings 66, 67 and 68. The terminal ends of the three modules 54 in each heating element 4 3 are connected to three peripherally spaced mutually insulated terminal connection parts 70 which are provided concentrically with the rings 66 to 68. Axially extending electrical conductors 71 connect each of the connecting members 70 with a contact member 72 which is placed at the other of the interrupter device 51's end faces, and the contactor 72 is as shown in fig. 7 placed in triangular groups so that the three contacts in each group are connected to the same heating element 43. The rotor 53 has an arm which at its free end has mounted a spring-actuated short circuit means or a contact plate 73. When the shaft 45 is turned in steps by the motor 27, the rotor 53 between positions in which the plate 73 lies closely against all three contacts 72 in a group so that the clamps or terminals for the three modules 54 for the associated heating element 4 3 are short-circuited, whereby current is fed to a heating element. The one in fig. 7 and 8 shown electrical interrupter device has eight groups of contacts 72 and is thus arranged to be used in connection with an apparatus with eight chambers 12. However, if the dehumidifier only has six chambers as mentioned above, the interrupter device must naturally also only have six groups of contacts 72.

Fig. 9 and 10 schematically show an embodiment of the type that has been described in connection with fig. 1-4. In fig. 9 and 10, the chambers or passages 12 are, however, divided into axial sections so that the gas or air to be dried alternately passes cooling or heating sections and adsorbing sections. If the gas to be dried e.g. contains a large amount of moisture, the first section 74 may be a condenser section in which moist gas flowing from the inlet pipe 13 is cooled by suitable means so that part of the moisture in the gas is condensed. These cooling agents can e.g. be the evaporator in a conventional cooling system or in a so-called heat pump that has a compressor 75 and a reduction valve 76. The cooling system's condenser can then be used to reheat the dried gas or air in a heating section 77 before the gas flows through a filter section 78 to the outlet pipe 14. It may be desirable to avoid cooling and heating of the regeneration gas in the condenser section and the heating section respectively. The lines in the cooling system or the heat pump can therefore be provided with solenoid valves 81 by means of which the flow of cooling medium or heat-transporting fluid in the system's lines can be controlled so that the fluid flow is stopped in the chambers or passages 12 in which the adsorbent is regenerated.

That in fig. The apparatus shown in 9 and 10 has three adsorbing sections 79 which contain adsorbing medium and heating elements and an intermediate cooling section 80 for removing the adsorption heat produced in the preceding adsorption section. The intermediate cooling sections 80 may contain cooling means of any suitable type, such as water cooling means, the evaporator in a cooling system or a heat pump, etc. The cooling means found in the intermediate cooling sections 80 must be designed to only cool in the chambers 12 through which gas to be dried flows, and not in the chambers in which regeneration takes place. Each intermediate cooling section can therefore comprise a condenser part and an evaporator part in a conventional cooling system, and there can be controllable valve means to control the fluid flow in the system so that the condenser part of the system is at all times in the chamber or in the chambers in which the regeneration of the adsorbent takes place, while the evaporator part is found in the other chambers. That in fig. The device shown in 9 is preferably placed with its longitudinal axis in an upright position and with the inlet pipe 13 facing downwards. Moisture that is condensed and separated in the condenser section 44 can thus flow out through the outflow pipe 25 together with the gas used to regenerate the adsorbent. The adsorption sections 74 may contain different types of adsorbents, and any desired combination of condensing, cooling, heating and adsorbing sections may be used.

The dehumidifier according to the invention can work very economically. This is primarily due to the very small amount of regeneration gas that is required (e.g. approx. 4% of the total amount of gas being dried), and the direct effective heating of the adsorbent during its regeneration as well as the uniform distribution of the gas flow over the cross section of the chambers and the adsorbent contained therein.

It is clear that within the framework of the invention, various changes and modifications can be made to the above described embodiments. Furthermore, the features described in connection with different embodiments can be interchanged.

Claims (10)

1. Apparatus for drying or dehumidifying gases and having a housing (10) defining at least one passage or at least one chamber (12), having a gas inlet (13) and a gas outlet (14) and containing a layered, regenerable , gas-permeable, moisture-absorbing medium (15) and selectively activatable electric heating means (43) in the form of plate or sheet-shaped material, for selective heating of the absorption medium for regeneration thereof, characterized in that the layers of the absorption medium (15) are separated from each other by with the help of the mainly gas-impermeable plate or sheet-shaped material (43) which constitutes the electric heating means and which is placed in direct contact with the adjacent layers of the absorption medium and between them delimits along the length of these layers gas flow passages, each of which at its ends are in connection with the gas inlet (13) and the gas outlet (14) respectively. 2. Apparatus according to claim 1, characterized in that said plate or sheet-shaped material (43) has printed resistance circuits (55-57). 3. Apparatus according to claim 1 or 2, characterized in that spacers are placed in the gas flow passages for the plate or sheet-shaped material which delimits the relevant flow passage, which spacers preferably have the form of a corrugated plate or sheet material (58). 4. Apparatus according to any one of claims 1-3, characterized in that cooling means are arranged at the inlet end (74) of the chamber (12) for cooling the gas to be dehumidified, so that moisture is condensed in it. 5. Apparatus according to claim 4, characterized in that it further has reheating means which are arranged at the outlet end (77) of the chamber, for reheating the dehumidified gas. 6. Apparatus according to claim 5, characterized in that the cooling means and the heating means respectively comprise an evaporator and a condenser in a heat pump system (75,76). 7. Apparatus according to any one of claims 1-6, characterized in that the moisture-adsorbing medium (15) in said chamber (12) is divided into sections (79) placed at a distance from each other and that there are cooling means between the separated sections (80). 8. Apparatus according to any one of claims 1-7, and with a plurality of chambers (12), characterized in that the heating means (43) in the chambers (12) comprise star-connected heating elements (54) and that the heating means further comprise interrupting means (51) which has a contact means (73) for selectively short-circuiting the heating elements at their neutral points (72) in order to thereby supply current to the heating elements in at least one of said chambers. 9. Apparatus according to claim 8 and with a rotary valve for passing gas to be dehumidified through a first number of said chambers and for passing a stream of dehumidified gas from the outlet end of these chambers through another number of said chambers for regeneration of the adsorption medium contained therein, characterized in that the ends (72) provided with neutral points of the star-connected heating elements (54), which are contained in the aforementioned chambers (12), are grouped in a circular arrangement, and that the short-circuited contact means (73) is arranged rotatably around the axis of the circular arrangement and connected to the rotary valve (20) to ensure conformity in the rotary movements of the contact member and the valve. 10. Apparatus according to claim 9, characterized in that the interrupting means (53) are arranged to interrupt the power supply to the heating means (43) in each of said other number of chambers or passages (12) before the flow of dehumidified gas through the respective chamber or the respective passage ends, whereby the adsorbing medium contained therein is cooled by the gas flow.