Abstract:
Regenerative air dryers are disclosed for feeding pressurized air with a controlled moisture content to a header. In one embodiment, a dryer comprises first and second chambers alternating between drying and regenerating phases. One of the chambers is at the drying phase while the other is at the regenerating phase. A controller is programmed to switch the phase of the chambers between drying and regenerating when the desiccant in the chamber at the drying phase has retained water to a predetermined capacity. A bypass line bypasses both chambers. An input provides air to the chamber at the drying phase and to the bypass line. A dew point feedback system controls a volume of air passing through the bypass line. Means are included for combining air from the bypass line with air exiting the chamber at the drying phase to provide air with a controlled dew point to the header.

Description:
BACKGROUND 
       [0001]    The invention relates generally to the field of air dryers. More specifically, the invention relates to the field of regenerative air dryers employing a drying chamber and a regenerating chamber. 
       SUMMARY 
       [0002]    The present invention is defined by the claims below. According to one embodiment, a moisture control system for pressurized air comprises a first and a second chamber which alternate between drying and regenerating phases. Only one of the chambers is at the drying phase at any given point in time. An input provides compressed air to the chamber at the drying phase. The moisture control system includes a bypass line passing air that does not go through the chamber at the drying phase. The air exiting the chamber at the drying phase is combined with the air from the bypass line to obtain air with a controlled moisture content for outputting. 
         [0003]    According to another embodiment, a regenerative air dryer for feeding pressurized air with a controlled moisture content to a header comprises a first and a second chamber that alternate between regenerating and drying phases. One of the first and second chambers is at the drying phase while the other is at the regenerating phase. A controller is programmed to switch the phase of the chambers between drying and regenerating when desiccant in the chamber at the drying phase has retained water to a predetermined capacity. A bypass line bypasses both the first and the second chambers. An input provides air to the chamber at the drying phase and to the bypass line. A dew point feedback system controls a volume of air passing through the bypass line. Means are included for combining air from the bypass line with air exiting the chamber at the drying phase to provide air with a controlled dew point to the header. 
         [0004]    According to yet another embodiment, a feedback system for use with a regenerative air dryer having two chambers alternating between drying and regenerative phases includes a sensor, a bypass line, and a controller. The sensor determines moisture content of air being outputted by the regenerative air dryer. The bypass line bypasses air around both chambers. The controller selectively opens and closes a control valve to allow air to pass through the bypass line. Means are included for combining air exiting the chamber at the drying phase with air from the bypass line to control the moisture content of the air being outputted by the regenerative dryer. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0005]    Illustrative embodiments of the present invention are described in detail below with reference to the attached drawing figures. 
           [0006]      FIG. 1  is a schematic drawing outlining a regenerative air dryer with a dew point feedback system, according to an embodiment. Labels such as “open” and “closed” are used to illustrate one manner of operation. 
           [0007]      FIG. 2  is a schematic drawing outlining a regenerative air dryer with a blower and a dew point feedback system, according to another embodiment. Labels such as “open” and “closed” are used to illustrate one manner of operation. 
           [0008]      FIG. 3  is a schematic drawing outlining a regenerative air dryer with an additional cooler and a dew point feedback system, according yet another embodiment. Labels such as “open” and “closed” are used to illustrate one manner of operation. 
           [0009]      FIG. 4  is a schematic drawing showing a regenerative air dryer with a compressor and a dew point feedback system, according to still another embodiment. Labels such as “open” and “closed” are used to illustrate one manner of operation. 
           [0010]      FIG. 5  is a schematic drawing outlining a regenerative air dryer with a compressor, a dew point feedback system, and additional bypass loops, according to still yet another embodiment. Labels such as “open” and “closed” are used to illustrate one manner of operation. 
           [0011]      FIG. 6  is a graphical representation of the rate of moisture absorption of desiccants in chambers of a regenerative air dryer. 
           [0012]      FIG. 7  is a graphical representation showing different rates of moisture absorption of desiccants. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Embodiments of the present invention provide systems and methods for drying air with a regenerative air dryer. A system may require compressed air with a particular moisture content for one or more applications. At a given pressure and temperature, the moisture content of air can be described by the air&#39;s dew point, where the dew point is defined as the temperature to which a given parcel of air must be cooled at constant pressure for the water vapor in the air parcel to condense into liquid water. The dew point of an air parcel increases or decreases with a respective increase or decrease in the air parcel&#39;s moisture content. The dew point, therefore, can serve to gauge the moisture content of a given parcel of air. The regenerative air dryers disclosed herein may enable a system to receive air with a particular moisture content. 
         [0014]      FIG. 1  shows one embodiment of a regenerative air dryer  100 , which may include a cooler  110 , a drying chamber  120 , a regenerating chamber  130 , a network of pipes  150 , and a dew point feedback system  160 . Compressed air with an uncontrolled moisture content is generated by a compressor (not shown in  FIG. 1 ) upstream of the cooler  110  and fed via the network of pipes  150  to the drying chamber  120  and the regenerating chamber  130 ; its moisture content is reduced below a set point; and it is ultimately fed into a system via a header  180 . 
         [0015]    A drying input control valve  122  and a regenerating input control valve  132  regulate the amount of air that enters into the drying and regenerative chambers  120 ,  130  respectively. The drying input control valve  122  may be fully open, as compared to the regenerating input control valve  132  which may only be partially open, thereby allowing a greater volume of air to flow into the drying chamber  120  as compared to the regenerating chamber  130 . Both the drying and the regenerating chambers  120 ,  130  may contain an adsorbent desiccant  152 . The adsorbent desiccant  152  can adsorb moisture from the air, and the desiccant&#39;s  152  ability to adsorb moisture decreases as it adsorbs more and more moisture, eventually coming to a point where the desiccant  152  can not adsorb more moisture. At that point, or at a time before or after the desiccant  152 &#39;s ability to retain moisture is exhausted, the desiccant  152  can be regenerated (i.e., the moisture present on the desiccant  152  can be removed so that the desiccant  152  can again function to adsorb more moisture.) 
         [0016]    Thus, in  FIG. 1 , moisture from the compressed air accumulates on the surface of the adsorbent desiccant  152  in the drying chamber  120  until the adsorbent desiccant&#39;s  152  ability to adsorb more moisture is diminished. While the drying chamber dries the compressed air, the smaller stream of compressed air entering the regenerating chamber  130  expands therein. Expansion of the smaller stream of air in the regenerating chamber  130  allows the air to absorb moisture from the regenerating chamber&#39;s  130  desiccant  152 , thereby drying and regenerating the desiccant  152  in the regenerating chamber  130 . The smaller stream of air can then be released into the atmosphere via a vent  182 . 
         [0017]    As is known in the art, the drying and the regenerating chambers  120 ,  130  are alternated; the drying chamber  120  dries air while the regenerating chamber  130  regenerates its desiccant  152 , and subsequently, the chamber  120  regenerates its desiccant  152  while the chamber  130  dries the air. When the drying chamber  120  is drying, a drying output control valve  124  is kept open and the dried air is transferred to the system via the header  180 , while a regenerating output control valve  134  is kept closed to ensure that the moisture laden stream of air does not enter the system. During this time, a regenerating vent control valve  136  is kept open so that moist air, after drying the desiccant  152  in the regenerating chamber  130 , can escape into the atmosphere via the vent  182 . A drying vent control valve  126  is kept closed to ensure that all the dried air enters the header  180  via the drier output control valve  124 , and does not escape out of the vent  182 . 
         [0018]    When the ability of the desiccant  152  in the drying chamber  120  to retain moisture from the air is diminished, the roles of the drying and the regenerating chambers  120 ,  130  are reversed. Reversing the cycle involves switching the position of the drying input control valve  122  with the regenerating input control valve  132 , the drying output control valve  124  with the regenerating output control valve  134 , and the drying vent control valve  126  with the regenerating vent control valve  136 . In other words, the drying control valves  122 ,  124 , and  126  may be opened or closed to the same extent that their corresponding regenerating valves  132 ,  134 , and  136  were open or closed, and vice versa. 
         [0019]    Very notably, some of the compressed air from the compressor (not shown in  FIG. 1 ) upstream of the cooler  110  may go to the dew point feedback system  160 . The dew point feedback system  160  may contain a dew point control valve  162 , a controller  164 , and a sensor  166 . The sensor  166  may be one or more dew point sensors, capable of determining dew points at compressed air pressures (pressure dew point). The sensor  166  senses the dew point of the air entering the header  180  and determines whether air with the requisite amount of moisture is entering the header  180 . It is possible, and sometimes common, that the air entering the header  180  has a lower moisture content/dew point than the moisture content required by the system. In this situation, the controller  164  may send a signal to the dew point control valve  162  to open to a controlled level, thereby allowing a desired level of compressed, moisture laden air from the cooler  110  to bypass both chambers  120 ,  130 , and via a pipe  150   a  in the network of pipes  150 , mix with the air entering the header  180 . More particularly, the air from pipe  150   a  may mix with the air entering the header  180  via the control valve  124  when chamber  120  is drying, while the air from pipe  150   a  may mix with the air entering the header  180  via control valve  134  when chamber  120  is regenerating. In this way, the dew point feedback system  160  may enable the dryer  100  to require less compressed air for the regenerating cycle, and the system to utilize less energy overall (such as discussed below regarding  FIG. 7 ) while maintaining a controlled moisture content/dew point at the header  180 . 
         [0020]    Similarly, it is possible that the air exiting the drying chamber  120  (or the chamber  130 ) and entering the header  180  has an inconsistent amount of moisture, and therefore, an inconsistent dew point. The sensor  166  may take successive readings of the dew point of air entering the header  180 . The controller  164  may then open or close the dew point valve  162  to varying degrees and allow moist air from the cooler  110  to mix with the air exiting the drying chamber  120  (or  130 ) so that the air entering the header  180  has a consistent dew point. The controller  164  may entirely close the dew point valve  162  where the air exiting the drying chamber  120  (or  130 ) has a dew point that is at a desired level for the header  180 . 
         [0021]      FIGS. 2-5  show alternate embodiments of the regenerative air dryer that are substantially similar to the embodiment  100  in  FIG. 1 , except as specifically noted and/or shown, or as would be inherent. For uniformity and brevity, corresponding reference numbers may be used to indicate corresponding parts in the various figures, though with any noted deviations. In embodiment  200  shown in  FIG. 2 , a low pressure blower  202  may be utilized to regenerate the desiccant  152  in the chamber  120  (or  130 ) instead of compressed air. Unlike  FIG. 1 , where the control valve  132  (or the control valve  122 ) of the regenerating chamber  120  (or  130 ) was partly open to allow a small volume of compressed air to regenerate the desiccant  152 , the control valve  132  (or  122 ) in  FIG. 2  remains fully closed during regeneration. The blower  202  may be connected to the drying, regenerating chambers  120 ,  130  with control valves  206  and  208  respectively. When the chamber  130  is in its regenerating cycle, the control valve  208  may be opened to allow air from the blower  202  to enter the chamber  130 , wherein the air will expand and absorb the moisture from the desiccant  152 . This moist air may then be let out of the vent  182  through the open control valve  136 . The control valve  206  is kept closed to ensure that no air from the drying chamber  120  escapes through the low pressure blower system, and the control valve  126  is kept closed to ensure that no dried air exits the vent  182 . Similarly, when the chamber  120  is regenerating, the control valve  208  is closed and the control valve  206  is opened, and the air from the blower  202  enters the chamber  120  and regenerates the desiccant  152 , exiting through the now open control valve  126  and the vent  182 . 
         [0022]    As in  FIG. 1 , the dew point feedback system  160  in  FIG. 2  may monitor the air entering the header  180  by the sensor  166 , and open or close the control valve  162  to ensure that air with a constant, desired dew point enters the header  180 . A heater  204  may be used along with the blower  202  to heat the air that will regenerate the desiccant  152  in the chambers  120 ,  130 . 
         [0023]    An alternate embodiment  300  of the regenerative air dryer is shown in  FIG. 3 , which is different from embodiment  100  in that a dew point feedback system  160   b  may include an additional cooler  310 . Some air from cooler  110  may enter the dew point feedback system through pipe  150   b  via control valve  162 , while the cooler  310  may allow additional air to bypass both chambers  120 ,  130  and go through pipe  150   d  into the header  180 . The cooler  310  may also be connected to a liquid drain  308  via a condenser  312 . The condenser  312  may enable some or all of the water present in the air coming from the cooler  310  to pass through a pipe  150   e  and be drained through the liquid drain  308 . By drying the bypass air with the condenser  312 , the cooler  310  may further reduce the dew point of the bypass air entering the pipe  150   d , as compared to the bypass air entering pipe  150   a  in embodiment  100  ( FIG. 1 ). The additional cooler  310  in embodiment  300  may allow for a greater volume of air to bypass the chambers  120 ,  130  as compared to the embodiment  100 . 
         [0024]      FIG. 4  shows another alternate embodiment  400 , wherein the heat from a compressor  414  is used (without any cooler as is shown in embodiment  100 ) to regenerate the desiccants  152 . In the art, this arrangement is often referred to as a heat of compression dryer. The cooler  110  may be in communication with a condensate collector  312  which may separate and remove some of the water present in the air stream. The water may be drained out through the liquid drain  308 . The air may then pass through the control valve  122  (or 132) into the drying chamber  120  (or  130 ). Unlike embodiment  100  where one of valves  122 ,  132  remains partly open, in embodiment  400 , one of valves  122 ,  132  will remain fully open, while the other will remain fully closed, as no compressed air from downstream of the cooler  110  is used to regenerate the desiccant  152 . 
         [0025]    The compressor  414  may be connected to the chambers  120 ,  130  via control valves  406 ,  408 , and in addition to the valves  124 ,  134 , control valves  440 ,  442  may be used at the output of chambers  120 ,  130  respectively. Where chamber  120  is drying and valve  122  is open to allow air from the cooler  110  to enter chamber  120 , the valve  408  will be open to allow hot air from the compressor  414  to dry the desiccant  152  in chamber  130 , while valves  132 ,  406  will remain closed. Valve  442  may remain open so that the hot air from the compressor  414 , after regenerating the desiccant  152  in the chamber  130 , can circulate and be cooled by cooler  110 . Valve  440  remains closed to ensure that all the dried air reaches the header  180  through the open control valve  124 . 
         [0026]    Similarly, when chamber  120  is regenerating, valve  406  would be open to allow for the hot air from the compressor  414  to regenerate the desiccant  152 , while the valve  122  will be closed to ensure that no compressed air from the cooler  410  enters the chamber  120 ; valve  132  would be open to allow for compressed air from the cooler  110  to enter chamber  130 , while valve  408  would be closed to ensure that hot air from the compressor  414  does not enter chamber  130  while chamber  130  is drying; valve  440  would now be open so that the hot air from the compressor  414 , after regenerating the desiccant  152  in the chamber  120  can be cycled through after it is cooled by cooler  110 , while valve  442  would remain closed. 
         [0027]    Akin to other embodiments, the controller  164  in a dew point feedback system  160   c  may open or close the control valve  162  based on dew point readings of the air being fed to the header  180 , and allow for a desired amount of air to bypass either chamber  120 ,  130  at the drying phase and mix with the air entering the header  180  to control the dew point of air being ultimately fed to the header  180 . Hot air from the compressor  414 , after it interacts with and regenerates the desiccant  152 , may lose some pressure; for example, when chamber  130  is regenerating, the hot air entering the chamber  130  from the valve  408  may be at a higher pressure than the air exiting the chamber  130  out of valve  442 . 
         [0028]      FIG. 5  shows an alternate embodiment  500 , which functions generally in the same manner as embodiment  400 , except that chambers  120 ,  130  each have an additional bypass control valve  544 ,  546  respectively to maintain the high pressure of the hot air from the compressor  414  where appropriate. In this embodiment, the dew point of the chamber  120 ,  130  performing the regeneration may be monitored, and once the chamber  120 ,  130  has reached the requisite dew point (i.e. desiccant  152  has dried to the desired level), the corresponding bypass valve  544 ,  546  may be opened. For instance, when chamber  130  is regenerating, the valve  408  is kept open to ensure that the hot air from the compressor can dry the desiccant  152  and then exit through the open control valve  442  and mix with the compressed air from the cooler  110 . Once the chamber  130  has reached the desired dew point, bypass control valve  546  may be opened; thus, the hot air from the compressor  412  would then bypass the regenerating chamber  130  and go through open control valves  546 ,  442  and mix with the compressed air from the cooler  110 . In this way, once the hot air from the compressor  414  is not needed to regenerate the desiccant  152  in chamber  130 , the bypass control valve  546  (or  544 ) ensures that the pressure of the air from the compressor  414  is not needlessly wasted. 
         [0029]      FIG. 6  is an exemplary graphical representation of the moisture content of chambers  120 ,  130  (in any of embodiments  100 ,  200 ,  300 ,  400 ,  500 ) over time. The solid line depicts the moisture content in chamber  120 , while the dotted line indicates the moisture content in chamber  130  during the same time period. The section of the graph  601   a  with the positive slope indicates the time period during which the desiccant  152  in the chamber  120  is drying; thus, the moisture content in the chamber increases as more and more moisture is retained by the desiccant  152 , until it reaches the point  601   c  and the cycle reverses. The negatively sloping section of the line  601   b  indicates that the chamber  120  is now regenerating, and therefore, the moisture in the chamber  120  decreases until it hits the point  601   d . The flat line  601   e  indicates that the desiccant  152  in chamber  120  is not dried any further. It may, for example, be during the time depicted by the flat line  601   e  that the embodiment  500  uses the bypass valve  544  ( FIG. 5 ) to ensure that pressure of the air from the compressor  414  is not wasted. 
         [0030]    The negatively sloped section of the dotted line  602   a  indicates that the chamber  130  is regenerating, until it comes to a time represented by  602   b , where more moisture from the chamber  130  is no longer removed. At point  602   c , the cycle shifts, and the positively sloping line  602   d  indicates that chamber  130  is now drying, until point  602   e.    
         [0031]      FIG. 7  shows an advantage of using the bypass feedback system  160 , with reference to  FIG. 1  (though it should be appreciated that the bypass feedback systems of other embodiments may benefit in similar ways). As part of the compressed air from the cooler  110  bypasses both chambers  120 ,  130 , the time taken by each regenerating/drying cycle increases. In other words, since some air from the cooler  110  bypasses both chambers  120 ,  130 , a smaller volume of air per unit time enters the drying chamber  120 ,  130 . To illustrate, where chamber  120  is drying and chamber  130  is regenerating, the amount of time before a cycle shift is limited by the moisture retained by the desiccant  152  in the drying chamber  120 ; once the desiccant  152  has retained water to capacity, the cycle needs to shift so as to allow the desiccant  152  in the drying chamber  120  to regenerate. As the dew point feedback system  160  bypasses some of the compressed air from entering the drying chamber  120 , less compressed air enters the chamber  120  and it resultantly takes a longer time for the desiccant  152  in the chamber  120  to retain moisture to capacity. By extending the timing of each drying/regenerating cycle, the bypass feedback system  160  may require less air regenerating cycles, and less compressed air over time may have to be wasted and relieved from the vent  182 . Hence, the energy requirements of a regenerative air drying system  100  with the dew point feedback system  160  may be lower than that of an air drying system that does not employ the dew point feedback system  160 . The regenerative air dryer  100  may also be programmed to purge only when the desiccant  152  in the drying chamber  120  (or  130 ) has reached its capacity to retain water, and not on a continual basis, which may further reduce the energy requirements of the dryer  100 . 
         [0032]    Many different arrangements of the various components depicted, as well as components not shown, are possible without departing from the spirit and scope of the present invention. Embodiments of the present invention have been described with the intent to be illustrative rather than restrictive. Alternative embodiments will become apparent to those skilled in the art that do not depart from its scope. A skilled artisan may develop alternative means of implementing the aforementioned improvements without departing from the scope of the present invention. 
         [0033]    It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations and are contemplated within the scope of the claims. Not all steps listed in the various figures need be carried out in the specific order described.