Patent Publication Number: US-2010107880-A1

Title: Hollow fiber membrane dehumidifier

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application is a Continuation-In-Part application of an International Patent Application PCT/JP2008/001734, the Date of International Application of which is Jul. 2, 2008. This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2007-173874, filed in the Japanese Patent Office on Jul. 2, 2007, the entire content of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a hollow fiber membrane dehumidifier for removing moisture contained in radioactive gaseous wastes (to be referred to as exhaust gas hereinafter) produced from nuclear power plants. 
     Hollow fiber membrane dehumidifiers containing dehumidifying hollow fiber membranes are known as apparatus for selectively removing moisture from humid air to obtain dry air (refer to, e.g., Japanese Patent Application Laid-Open Publication No. 2003-159509, the entire content of which is incorporated herein by reference). 
     Generally, a dehumidifying hollow fiber membrane is formed by processing fibers to make them hollow fibers having an outer diameter of about 0.3 mm and showing a high steam permeation performance. A hollow fiber membrane module is formed by bundling a large number of such hollow fibers and rigidly securing them at the ends thereof by means of resin or an adhesive agent. 
     A hollow fiber membrane dehumidifier is formed by arranging a large number of such hollow fiber membrane modules in it. A dehumidifying process is conducted as gas to be processed is forced to pass through the inner surfaces of the hollow fiber membranes so as to make steam permeate to the outside of the membranes from the inner walls of the hollow fiber membranes by way of sequential processes of dissolution, diffusion and dispersion and become removed due to the pressure difference between the inside and the outside of each of the hollow fiber membranes and the difference of mol fraction between the inside and the outside of each of the hollow fiber membranes produced by flowing purging dry gas to the outside of the membranes. 
     The structure of a known hollow fiber membrane dehumidifier will be described below with reference to  FIGS. 10 and 11 . 
       FIG. 10  is a schematic longitudinal cross-sectional view of the known hollow fiber membrane dehumidifier and  FIG. 11  is an enlarged schematic partial view of the hollow fiber membrane dehumidifier of  FIG. 10 , showing the installation structure of a hollow fiber membrane module thereof. 
     As shown in  FIG. 10 , a body trunk  6  is axially divided into an exhaust gas inlet chamber  7 , an exhaust gas processing chamber  8 , a purge gas chamber  9  and an exhaust gas outlet chamber  10  by an upper tube plate  3 , a lower tube plate  4  and a partition plate  5 . A plurality of hollow fiber membrane modules  1  are arranged in the exhaust gas processing chamber  8 . 
     As shown in  FIG. 11 , a first seal member  12  and a second seal member  13  that are typically O-rings are fitted to upper head  11  of the hollow fiber membrane module  1 . A cap  15  is put on the upper head  11  so as to align a purge gas inlet  14  of the upper head  11  and the hole of the cap  15 . The first seal member  12  and the second seal member  13  are rigidly held in position by pressing the ring  16  by means of bolts  17 . A third seal member  18  and a fourth seal member  19  are fitted to the cap  15 , and the hollow fiber membrane module  1  is inserted into the through hole of the upper tube plate  3  and that of the partition plate  5 , paying attention so as not to let the third seal member  18  and the fourth seal member  19  come off. 
     Since the hollow fiber membrane module  1  is also inserted into the through hole of the lower tube plate  4 , it is necessary to make sure that the lower head  20  of each of the hollow fiber membrane modules  1  is inserted into the lower tube  4  from below. After the hollow fiber membrane module  1  is inserted, the cap  15  is provisionally fitted by means of bolts  21 . A fifth seal member  22  that is also typically an O-ring is inserted into the lower tube plate  4  from below and the through hole of the lower tube plate  4 , the hollow fiber membrane module  1  and the fifth seal member  22  are adjusted for their positions so as to make them concentrically aligned. Then, the hollow fiber membrane module  1  is rigidly secured relative to the upper tube plate  3 , the partition plate  5  and the lower tube plate  4 , as the cap  15  is rigidly held in position by means of the bolts  21  and ring  23  is rigidly secured to the lower tube plate  4  by means of bolts  24 . 
     Exhaust gas flows in the known hollow fiber membrane dehumidifier  2  along an arrow  70  in  FIGS. 10 and 11 . More specifically, the exhaust gas (wet gas) that enters the dehumidifier  2  from an exhaust gas inlet section  25  then goes into the exhaust gas inlet chamber  7  and passes through the insides of hollow fibers  26  in the hollow fiber membrane modules  1  to get to the exhaust gas outlet chamber  10 . The exhaust gas that is dehumidified as it passes through the insides of the hollow fibers  26  in the hollow fiber membrane modules  1  is then discharged from an exhaust gas outlet section  27 . 
     Purge gas is introduced into the purge gas inlet  14  from a purge gas inlet section  28  through the purge gas chamber  9  as indicated by an arrow  71 . The introduced purge gas takes out moisture from the exhaust gas that passes through the films of the hollow fibers  26  and conveys the moisture as it passes the outside of the hollow fibers  26  of the hollow fiber membrane modules  1  before it is discharged into the exhaust gas processing chamber  8  by way of purge gas outlets  29  and then to the outside of the hollow fiber membrane dehumidifier  2  from a purge gas flow out section  30 . 
     The exhaust gas containing moisture and the dry purge gas need to be separated from each other in order to prevent them from mixing and enhance the dehumidification performance. The fifth seal member  22  that is an O-ring is arranged for each hollow fiber membrane module  1  between the exhaust gas inlet chamber  7  and the exhaust gas processing chamber  8  in order to separate the exhaust gas that contains moisture and the dry purge gas. The second seal member  13  and the fourth seal member  19  are arranged between the exhaust gas processing chamber  8  and the purge gas chamber  9 . Additionally, the first seal member  12  and the third seal member  18  are arranged between the purge gas chamber  9  and the exhaust gas outlet chamber  10 . The exhaust gas (wet air) and the purge gas (dry air) are separated from each other by arranging the fifth seal member  22 , the second seal member  13 , the fourth seal member  19 , the first seal member  12  and the third seal member  18 . 
     The known hollow fiber membrane dehumidifier  2  has five seal sections formed by using seal members that are typically O-rings in each hollow fiber membrane module  1 , including the fifth seal member  22 , the second seal member  13 , the fourth seal member  19 , the first seal member  12  and the third seal member  18 . 
     Therefore, there is a problem that it is difficult to put a hollow fiber membrane module  1  into the trunk body  6  and place it in position without allowing the third seal member  18  and the fourth seal member  19  to fall down because they are not rigidly secured to the hollow fiber membrane module  1 . The seal members can fall down in the body trunk  6  when pulling out the hollow fiber membrane module  1  for replacement. 
     Additionally, the position of the hollow fiber membrane module  1  and the condition in which each of the seal members is fitted need to be adjusted delicately in order to reliably prevent exhaust gas from leaking through the five seal members that are typically O-rings. In other words, the hollow fiber membrane dehumidifier has many problems from the viewpoint of assembly and sealing. Additionally, a cap  15  is fitted to rigidly secure a hollow fiber membrane module  1  to the upper tube plate  3  and the partition plate  5 . Thus, there is a problem that each of the hollow fiber membrane modules  1  occupies a large area to make the body trunk  6  large because of the outer diameter of the cap  15 . 
     Additionally, each hollow fiber membrane module  1  has a longitudinally oblong profile that gives rise to a problem that it is difficult to concentrically arrange the third seal member  18 , the fourth seal member  19  and the fifth seal member  22  fitted to the upper head  11  and the lower head  20  by means of the conventional holding technique. 
     Furthermore, a plurality of hollow fiber membrane modules  1  are arranged in the body trunk  6 . Since the exhaust gas inlet chamber  7 , the exhaust gas processing chamber  8 , the purge gas chamber  9  and the exhaust gas outlet chamber  10  are chambers that are separately arranged, there arises a problem that the exhaust gas or the purge gas that flows through the hollow fiber membrane modules  1  can produce uneven flows depending on the flow rate of exhaust gas. 
     Finally, in the known hollow fiber membrane dehumidifier  2 , the direction of the purge gas inlet  14  and that of the purge gas outlet  29  of each hollow fiber membrane module  1  are determined arbitrarily relative to the direction of the purge gas inlet section  28  and the purge gas flow out section  30  to give rise to a problem that the exhaust gas and the purge gas that flow in the inside of each hollow fiber membrane module  1  can become uneven to degrade the dehumidification performance. 
     In view of the above-identified problems, it is therefore an object of the present invention to provide a hollow fiber membrane dehumidifier that can downsize the body trunk and improve the hollow fiber membrane modules from the viewpoint of assembly, handling, sealing and dehumidification performance. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a hollow fiber membrane dehumidifier comprising: a dehumidification container including a first trunk provided with exhaust gas outlet sections and a second trunk provided with exhaust gas inlet sections; a first tube plate for forming an exhaust gas outlet chamber at a side of the first trunk; a partition plate arranged in the dehumidification container to partition inside of the dehumidification container into an exhaust gas processing chamber including purge gas flow out sections and a purge gas chamber including purge gas inlet sections; a plurality of hollow fiber membrane modules respectively put into through holes formed in the first tube plate and through holes formed in the partition plate; seal members held in respective seal grooves arranged in first heads of the hollow fiber membrane modules at the side of the first trunk to seal gaps between the first heads and the first tube plate and gaps between the first heads and the partition plate; and a keep plate for pressing the hollow fiber membrane modules against the first tube plate from a side of end of the first trunk. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become apparent from the discussion hereinbelow of specific, illustrative embodiments thereof presented in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic longitudinal cross-sectional view of an embodiment of hollow fiber membrane dehumidifier according to the present invention, showing the structure thereof; 
         FIG. 2  is an enlarged schematic partial view of the hollow fiber membrane dehumidifier of  FIG. 1 , showing the installation structure of a hollow fiber membrane module thereof; 
         FIGS. 3A and 3B  schematically illustrate the hollow fiber membrane dehumidifier of  FIG. 1 ;  FIG. 3A  is a schematic perspective view of the embodiment, and  FIG. 3B  is a schematic cross-sectional view thereof taken along line B-B in  FIG. 3A  as viewed in the direction of the arrows; 
         FIG. 4  is a characteristic graph illustrating the dehumidification performance of the hollow fiber membrane dehumidifier of  FIG. 1 ; 
         FIGS. 5A through 5C  schematically illustrate the seal section of the lower head of a hollow fiber membrane module according to the present invention.  FIG. 5A  is a cross-sectional view of the first exemplar seal section,  FIG. 5B  is a cross-sectional view of the second exemplar seal section, and  FIG. 5C  is a cross-sectional view of the third exemplar seal section. 
         FIG. 6  is a schematic longitudinal cross-sectional view of another embodiment of hollow fiber membrane dehumidifier according to the present invention that is made to lie on the lateral peripheral surface thereof, showing the structure thereof; 
         FIGS. 7A and 7B  schematically illustrate still another embodiment of hollow fiber membrane dehumidifier according to the present invention, showing the partitioning structure thereof;  FIG. 7A  is a schematic perspective view of the embodiment, and  FIG. 7B  is a schematic plan view thereof; 
         FIG. 8  is a schematic longitudinal cross-sectional view of still another embodiment of hollow fiber membrane dehumidifier according to the present invention and having a structure realized by vertically arranging upper hollow fiber membrane modules on respective lower hollow fiber membrane modules, showing the structure thereof; 
         FIG. 9  is a schematic longitudinal cross-sectional view of still another embodiment of hollow fiber membrane dehumidifier according to the present invention, showing the structure thereof; 
         FIG. 10  is a schematic longitudinal cross-sectional view of a known hollow fiber membrane dehumidifier, showing the structure thereof; and 
         FIG. 11  is an enlarged schematic partial view of the hollow fiber membrane dehumidifier of  FIG. 10 , showing the installation structure of a hollow fiber membrane module thereof. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Now, the present invention will be described in greater detail with reference to the accompanying drawings that illustrate preferred embodiments of hollow fiber membrane dehumidifier according to the present invention. Throughout the following description and in the drawings, same or similar parts are denoted by the same reference symbols and will not be described repeatedly. 
       FIG. 1  is a schematic longitudinal cross-sectional view of an embodiment of hollow fiber membrane dehumidifier according to the present invention, showing the structure thereof.  FIG. 2  is an enlarged schematic partial view of the hollow fiber membrane dehumidifier of  FIG. 1 , showing the installation structure of a hollow fiber membrane module thereof.  FIGS. 3A and 3B  schematically illustrate the hollow fiber membrane dehumidifier of  FIG. 1 .  FIG. 3A  is a schematic perspective view of the embodiment and  FIG. 3B  is a schematic cross-sectional view thereof taken along line B-B in  FIG. 3A  as viewed in the direction of the arrows. 
     Firstly, the basic configuration of a hollow fiber membrane dehumidifier  31  that can be applied to dehumidification of exhaust gas in a nuclear power plant will be described below with reference to  FIG. 1 . 
     As shown in  FIG. 1 , the hollow fiber membrane dehumidifier  31  has as principal component thereof a dehumidification container  67  that is supported by a leg  32 . The dehumidification container  67  includes a cylindrical body trunk  33  and a lower trunk (second trunk)  38  arranged under the body trunk  33  and having exhaust gas inlet sections  63  as annexes. On the body trunk  33 , an upper trunk (first trunk)  37  having exhaust gas outlet sections  58  as annexes, is arranged. A lower tube plate (second tube plate)  35  is arranged under the body trunk  33  and an exhaust gas inlet chamber  39  is formed under the lower tube plate  35  and defined by the lower tube plate  35  and the lower trunk  38 . An upper tube plate (first tube plate)  34  is arranged on the body trunk  33  and an exhaust gas output chamber  42  is formed on the upper tube plate  34  and defined by the upper tube plate  34  and the upper trunk  37 . 
     A partition plate  36  is arranged on the body trunk  33 . As a result of arranging the partition plate  36 , the inside of the body trunk  33  is partitioned into an exhaust gas processing chamber  40  that includes a purge gas flow out section  49  and a purge gas chamber  41  that includes a purge gas inlet section  53 . 
     As shown in  FIG. 3 , the exhaust gas inlet chamber  39  can be partitioned into four rooms, for example, by arranging a cross-shaped divisional plate  43 . Each of the rooms in the partitioned exhaust gas inlet chamber  39  is equipped with an exhaust gas inlet section  63  as shown in  FIG. 1 . Similarly, the exhaust gas outlet chamber  42  can be partitioned into four rooms, for example, by arranging a cross-shaped divisional plate  57 . Each of the rooms in the partitioned exhaust gas outlet chamber  42  is equipped with an exhaust gas outlet section  58 . 
     As shown in  FIG. 2 , an O-ring groove  66  that is a sealing groove is formed on the outer lateral surface of a lower head  50  of each hollow fiber membrane module  44 . As a first O-ring  45  is fitted as seal member to the O-ring groove  66  of each hollow fiber membrane module  44 , the exhaust gas inlet chamber  39  and an exhaust gas processing chamber  40  are isolated from each other so that exhaust gas (wet gas) and purge gas (dry gas) are separated from each other. 
     An O-ring groove  65  that is a sealing groove is formed at a lower part of the outer lateral surface of the upper head  54  of each hollow fiber membrane module  44 . A second O-ring  51  is fitted as seal member to the O-ring groove  65  of each hollow fiber membrane module  44  to seal the outer lateral surface of the upper head  54  and the inner lateral surface of the through hole  36   a  of the partition plate  36 . 
     An O-ring groove  64  that is a sealing groove is formed at an upper part of the outer lateral surface of the upper head  54  of each hollow fiber membrane module  44 . A third O-ring  56  is fitted as seal member to the O-ring groove  64  of each hollow fiber membrane module  44  to seal the outer lateral surface of the upper head  54  and the inner lateral surface of the through hole  34   a  of the upper tube plate  34 . 
     Each hollow fiber membrane module  44  can be held to stand vertically as it is put into the through holes  34   a ,  35   a ,  36   a  respectively bored through the upper tube plate  34 , the lower tube plate  35  and the partition plate  36  that are arranged concentrically. 
     Note that, after putting each hollow fiber membrane module  44  into the through holes from above, the hollow fiber membrane module  44  is pressed against the upper tube plate  34  by a keep plate  59 . The keep plate  59  is also provided with through holes  59   a  for allowing exhaust gas from flowing out from the respective hollow fiber membrane modules  44 . 
     As shown in  FIG. 3 , the exhaust gas processing chamber  40  is partitioned into four rooms, for example, by arranging a cross-shaped divisional plate  46  and a plurality of hollow fiber membrane modules  44  are arranged in each of the rooms. 
     Part of the exhaust gas that flows in the inside of hollow fibers  47  of the hollow fiber membrane modules  44  from the exhaust gas inlet chamber  39  operates as purge gas. The purge gas enters the hollow fiber membrane modules  44  from the purge gas chamber  41  by way of the purge gas inlets  55  and flows at the outside of the hollow fibers  47 . The purge gas that draws and absorbs moisture from the exhaust gas due to the steam partial pressure difference is discharged from the purge gas flow out sections  49  by way of purge gas outlets  48 . As described above, lower heads  50  of the hollow fiber membrane modules  44  are arranged in the exhaust gas processing chamber  40  and, in each of the rooms, the purge gas outlet  48  formed at the lower head  50  of each of the hollow fiber membrane modules  44  in the room is arranged in the direction same as the direction or arrangement of the purge gas flow out section  49  of the room. 
     Additionally, a second O-ring  51  is arranged for each hollow fiber membrane module  44  at the partition plate  36  that partitions the exhaust gas processing chamber  40  and the purge gas chamber  41  in order to isolate purge gas (dry gas) and purge gas that has absorbed moisture from exhaust gas from each other and hold the hollow fiber membrane module  44  in position. 
     Furthermore, as shown in  FIGS. 3A and 3B , the purge gas chamber  41  is partitioned into four rooms by a cross-shaped divisional plate  52  and each of the rooms is provided with a purge gas inlet section  53  for introducing part of the exhaust gas discharged from the exhaust gas outlet chamber  42  as purge gas. The upper head  54  of each hollow fiber membrane module  44  is arranged in the purge gas chamber  41 . In each of the room, the purge gas inlet  55  formed at the upper head  54  of each hollow fiber membrane module  44  in the room is arranged in the direction same as the direction or arrangement of the purge gas inlet section  53  of the room 
     A third O-ring  5 G is arranged for each hollow fiber membrane module  44  at the upper tube plate  34  that is separating the purge gas chamber  41  and the exhaust gas outlet chamber  42  in order to isolate exhaust gas and purge gas from each other and hold the hollow fiber membrane module  44 . As shown in  FIG. 3 , the exhaust gas outlet chamber  42  is partitioned into four rooms by a cross-shaped divisional plate  57  and each of the rooms is provided with an exhaust gas outlet section  58 . 
     All the hollow fiber membrane modules  44  arranged in the body trunk  33  are rigidly held in position by the keep plate  59  that presses the upper heads  54  of the hollow fiber membrane modules  44  from above and the bolts GO that rigidly hold the keep plate  59  in position relative to the upper tube plate  34 . 
     As described above, each of the plurality of hollow fiber membrane modules  44  is put into the corresponding through holes  35   a ,  36   a  and  34   a  formed respectively in the lower tube plate  35 , the partition plate  3 G and the upper tube plate  34  and held in position by the three O-rings including the first O-ring  45 , the second O-ring  51  and the third O-ring  56  arranged at respective positions. 
     In the embodiment having the above-described configuration, exhaust gas of an OG system (off gas system) can show a maximum flow rate of 80 Nm 3 /h and a minimum flow rate of 12 Nm 3 /h and the embodiment is required not to show fluctuations in the dehumidification efficiency under such a variable condition. For this reason, the hollow fiber membrane modules  44  found in all the rooms are operated at the time of a maximum flow rate (80 Nm 3 /h), whereas the hollow fiber membrane modules  44  found only in one of the rooms in the exhaust gas inlet chamber  39  are operated at the time of a minimum flow rate (12 Nm 3 /h) as measures for coping with such a variable condition. 
     Now, the operation of the embodiment will be described below in the case of a maximum flow rate (80 Nm 3 /h). 
     The exhaust gas (wet gas) that is introduced into the embodiment by way of the exhaust gas inlet section  63  is divided into four flows of 20 Nm 3 /h in the exhaust gas inlet chamber  39  that is partitioned into four rooms and the flows of exhaust gas are evenly introduced into the hollow fiber membrane modules  44 . Steam contained in exhaust gas is absorbed by the hollow fibers  47  in the hollow fiber membrane modules  44  as exhaust gas flows in the insides of the hollow fibers  47  in the hollow fiber membrane modules  44 . The absorbed steam diffuses through the film thickness of the hollow fibers  47  and gets to the surfaces thereof. Part of the exhaust gas that passes through the hollow fiber membrane modules  44  gets to the purge gas chamber  41  through the exhaust gas outlet chamber  42 , the exhaust gas outlet sections  58  and the purge gas inlet sections  53 . 
     Since the purge gas chamber  41  is partitioned into four rooms by the partition plate  52  and the purge gas inlet  55  of each hollow fiber membrane modules  44  arranged at the upper head  54  of the hollow fiber membrane module  44  is made to face the direction of the related purge gas inlet section  53 , purge gas is evenly introduced into the hollow fiber membrane modules  44 . 
     Steam in exhaust gas is driven to move into purge gas as exhaust gas is dried by the introduced dry purge gas. At this time, exhaust gas (wet gas) and purge gas (dry gas) are prevented from being mixed with each other to secure the dehumidification effect of the embodiment by the first O-rings  45 , the second O-rings  51  and the third O-rings  56  arranged respectively at the lower tube plate  35 , the partition plate  36  and the upper tube plate  34 . 
     More specifically, each hollow fiber membrane module  44  is put into the upper tube plate  34 , the partition plate  36  and the lower tube plate  35  through the corresponding through holes  34   a ,  36   a ,  35   a  respectively bored through them. The gaps between the outer lateral surfaces of the upper head  54  and the lower head  50  of each hollow fiber membrane module  44  and the inner lateral surfaces of the corresponding through holes  34   a ,  36   a ,  35   a  that are respectively bored through the upper tube plate  34 , the partition plate  36  and the lower tube plate  35  and arranged coaxially are held constant by the first O-ring  45 , the second O-ring  51  and the third O-ring  56  fitted to the upper head  54  and the lower head  50  of the hollow fiber membrane module  44  so as to secure the sealing performance of the embodiment. 
     Furthermore, a chamfered guide  62  is formed around each of the through holes  35   a  bored through the lower tube plate  35  to guide the lower head  50  of the corresponding hollow fiber membrane module  44 . Additionally, a seat  61  is formed around the through hole  35   a  to hold the lower head  50 . Thus, the lower tube plate  35  is provided with seats  61  respectively for holding the lower heads  50  of the hollow fiber membrane modules  44  and guides  62  that are chamfered by 45 degrees so as to smoothly receive the respective lower heads  50  of the hollow fiber membrane modules  44  and improve the efficiency of the operation of putting the large number of hollow fiber membrane modules  44  into the respective through holes  35   a  of the lower tube plate  35 . 
     As the guides  62  are formed, each hollow fiber membrane module  44  is concentrically put into the corresponding through holes  34   a ,  36   a  and  35   a  bored through the upper tube plate  34 , the partition plate  36  and the lower tube plate  35  respectively so that gaps between the first O-ring  45 , the second O-ring  51  and the third O-ring  56  of each hollow fiber membrane module  44  and the inner walls of the corresponding through holes  34   a ,  36   a ,  35   a  respectively bored through the upper tube plate  34 , the partition plate  36  and the lower tube plate  35  can be held constant to secure the sealing performance of the embodiment. 
     Additionally, each hollow fiber membrane module  44  is provided with grooves  66 ,  65 ,  64  respectively for holding the first O-ring  45 , the second O-ring  51  and the third O-ring  56 . In other words, the first O-ring  45 , the second O-ring  51  and the third O-ring  56  are held respectively in the grooves  66 ,  65 ,  64 . Thus, the hollow fiber membrane module  44  can be put into and pulled out from the through holes without letting any of the first O-ring  45 , the second O-ring  51  and the third O-ring  56  fall down, so that the hollow fiber membrane modules  44  can be assembled and handled with an improved efficiency. 
     Still additionally, the outer diameter of the hollow fiber membrane modules  44  can be minimized by forming O-ring grooves  66 ,  65 ,  64  for receiving the first O-ring  45 , the second O-ring  51  and the third O-ring  56  at the outer surfaces of the upper head  54  and the lower head  50  of each hollow fiber membrane module  44 . Then, as a result, the dimensions of the body trunk  33  can be reduced. Furthermore, the dehumidification performance of the embodiment of hollow fiber membrane dehumidifier according to the present invention can be optimized by making the gap separating any two adjacently located hollow fiber membrane modules  44  equal to or larger than 1.2 times of the diameter of a hollow fiber membrane module  44 . The dehumidification performance will be discussed in greater detail hereinafter. 
     Thus, if compared with comparable conventional hollow fiber membrane dehumidifiers, this embodiment can provide improved assembly and handling for a hollow fiber membrane dehumidifier and reduce about half of the time required for assembly and also the time required for disassembly by forming O-ring grooves  66 ,  65 ,  64  on the outer lateral surfaces of the upper head  54  and the lower head  50  of each hollow fiber membrane module  44  and fitting the first O-ring  45 , the second O-ring  51  and the third O-ring  56  respectively into the O-ring grooves  66 ,  65 ,  64 . 
     Additionally, if compared with comparable conventional hollow fiber membrane dehumidifiers, this embodiment can reduce the size in diameter, the cost and the necessary installation space of the hollow fiber membrane dehumidifier respectively to about ½, about ⅗ and about ¼ of the those of any conventional dehumidifier by forming the O-ring grooves  66 ,  65 ,  64  at the outer lateral surfaces of the upper head  54  and the lower head  50  of each hollow fiber membrane module  44 . 
     Now, the dehumidification performance of each hollow fiber membrane module  44  will be discussed below with reference to  FIG. 4 . 
       FIG. 4  is a characteristic graph illustrating the dehumidification performance of the hollow fiber membrane dehumidifier of  FIG. 1 . 
     As pointed out above, the gap separating any two adjacently located hollow fiber membrane modules  44  is made equal to or larger than 1.2 times of the diameter of the upper head  54  of a hollow fiber membrane module  44 . The gap separating any two adjacently located hollow fiber membrane modules  44  in the hollow fiber membrane dehumidifier is determined according to the through holes  34   a  of the upper tube plate  34  and the through holes  36   a  of the partition plate  36  for receiving hollow fiber membrane modules  44  and needs to be larger than the diameter of the upper head  54  of a hollow fiber membrane module  44 . Therefore, practically, the gap separating any two adjacently located hollow fiber membrane modules  44  is preferably about 1.2 times of the diameter of the upper head  54  or larger. 
     On the other hand, the size of the dehumidification container  67  rises when the gap separating any two adjacently located hollow fiber membrane modules  44  is increased. Additionally, the dehumidification performance of the dehumidifier falls when the gap separating any two adjacently located hollow fiber membrane modules  44  is increased because the number of hollow fiber membrane modules  44  per unit area decreases. As shown in  FIG. 4 , the time necessary for getting to the design dew point (−30° C.) is t=25 minutes when the pitch of arrangement of hollow fiber membrane modules  44  is p=1.2 and it is t=20 minutes and t=28 minutes respectively when the pitch of arrangement of hollow fiber membrane modules  44  is p=1.25 and p=1.3, while the time necessary for getting to the design dew point (−30° C.) is t=38 minutes when the pitch of arrangement of hollow fiber membrane modules  44  is p=1.35 and it is t=44 minutes when the pitch of arrangement of hollow fiber membrane modules  44  is p=1.4. From the above, the time necessary for getting to the design dew point (−30° C.) is lowest and t=20 minutes when the pitch of arrangement of hollow fiber membrane modules  44  is p=1.25. Thus, it is preferable to make the gap separating any two adjacently located hollow fiber membrane modules  44  between 1.2 times and 1.3 times of the diameter of the upper head  54  of a hollow fiber membrane module  44 . 
       FIGS. 5A through 5C  schematically illustrate the seal section of the lower head  50  of a hollow fiber membrane module according to the present invention.  FIG. 5A  is a cross-sectional view of the first exemplar seal section,  FIG. 5B  is a cross-sectional view of the second exemplar seal section and  FIG. 5C  is a cross-sectional view of the third exemplar seal section. 
     As pointed out above, an O-ring groove  66  may be formed at the outer lateral surface of the lower head  50  of each hollow fiber membrane module  44  and the first O-ring  45  may be held in the O-ring groove  66  in order to provide improved assembly, handling and sealing of the hollow fiber membrane module  44  as shown in  FIG. 5A . Alternatively, an O-ring groove  66  may be formed at the bottom surface of the lower head  50  of each hollow fiber membrane module  44  and the first O-ring  45  may be held in the O-ring groove  66  as shown in  FIG. 5B . Still alternatively, a chamfered section  66   b  may be formed at the bottom edge of the lower head  50  of each hollow fiber membrane module  44  and the first O-ring  45  may be held in the chamfered section  66   b  as shown in  FIG. 5C . 
     Thus, with this embodiment of hollow fiber membrane dehumidifier, assembly and handling of the hollow fiber membrane modules can be improved and the time required for assembly and also the time required for disassembly can be significantly reduced by forming O-ring grooves or the like  66 ,  66   a ,  66   b  at the outer lateral surface, at the bottom surface or at the edge of the lower head  50  of each hollow fiber membrane module  44  and holding the first O-ring  45  in the O-ring grooves or the like  66 ,  66   a ,  66   b , whichever appropriate. 
       FIG. 6  is a schematic longitudinal cross-sectional view of another embodiment of hollow fiber membrane dehumidifier according to the present invention that is made to lie on the lateral peripheral surface thereof, showing the structure thereof. 
     As shown in  FIG. 6 , a seat  61  for supporting the hollow fiber membrane modules  44  may be formed at the lower tube plate  35  to rigidly secure the hollow fiber membrane modules  44  in position and the hollow fiber membrane modules  44  may be arranged horizontally. 
     With this arrangement, the hollow fiber membrane dehumidifier of this embodiment can reduce the height of the building for containing the hollow fiber membrane dehumidifier because the hollow fiber membrane modules  44  are arranged horizontally. 
       FIGS. 7A and 7B  schematically illustrate still another embodiment of hollow fiber membrane dehumidifier, showing the partitioning structure thereof.  FIG. 7A  is a schematic perspective view of the embodiment and  FIG. 7B  is a schematic plan view thereof. 
     As pointed out above, the number of operating hollow fiber membrane modules  44  is varied depending on the flow rate in order to improve the dehumidification performance. In the instance of  FIG. 3 , cross-shaped divisional plates  43 ,  46 ,  52 ,  57  are provided to respectively partition the exhaust gas inlet chamber  39 , the exhaust gas outlet chamber  42 , the exhaust gas processing chamber  40  and the purge gas chamber  41 . 
     In the instance of  FIGS. 7A and 7B , the divisional plates  43 ,  46 ,  52 ,  57  are replaced by a cylindrical divisional plate  68  to partition the exhaust gas processing chamber  40  into a plurality of rooms and each of the rooms is provided with an inlet section and an outlet section (nozzle) according to the objective of operation. 
     Since the hollow fiber membrane dehumidifier of this embodiment is provided with a cylindrical divisional plate  68 , exhaust gas and purge gas flow efficiently to improve the dehumidification effect. 
       FIG. 8  is a schematic longitudinal cross-sectional view of still another embodiment of hollow fiber membrane dehumidifier according to the present invention and having a structure formed by vertically arranging upper hollow fiber membrane modules on respective lower hollow fiber membrane modules to produce two stories, showing the structure thereof. 
     Any attempt to increase the diameter of the dehumidification container  67  faces a limit as shown in  FIG. 1  because the number of hollow fiber membrane modules  44  that can be contained in the container is increased due to the raise of the flow rate of exhaust gas and that of purge gas. Therefore, the embodiment of  FIG. 8  has a structure where hollow fiber membrane modules  44  are vertically arranged in a plurality of stories, or two stories in the illustrated instance. 
     Thus, the hollow fiber membrane dehumidifier of this embodiment can reduce the outer diameter of the dehumidification container  67  containing the hollow fiber membrane dehumidifier and downsize the hollow fiber membrane dehumidifier by vertically arranging hollow fiber membrane modules  44  in a plurality of stories. 
       FIG. 9  is a schematic longitudinal cross-sectional view of still another embodiment of hollow fiber membrane dehumidifier according to the present invention, showing the structure thereof. No lower tube plate  35  that each of the embodiments illustrated in  FIGS. 1 through 3  has is found in this embodiment while the body trunk  33  and the lower trunk  38  are integrally formed in this embodiment. The integrated component will be referred to as lower trunk  38  here. The purge gas outlet  48  of each hollow fiber membrane module  44  (see  FIG. 2 ) is directly connected to the corresponding purge gas flow out section  49  that communicates with the outside of the lower trunk  38  in this embodiment. 
     In this embodiment, exhaust gas flows into the lower trunk  38  from the exhaust gas inlet section  63  and rises up through the inside of the hollow fibers  47  in each of the hollow fiber membrane modules  44  before it flows out of the hollow fiber membrane dehumidifier  31  by way of the exhaust gas outlet chamber  42  and the exhaust gas outlet sections  58 . 
     On the other hand, purge gas flows into the purge gas chamber  41  in the lower trunk  38  from the purge gas inlet sections  53  and flows down by way of the outside of the hollow fibers  47  in each of the hollow fiber membrane modules  44  before it flows out of the hollow fiber membrane dehumidifier  31  by way of the purge gas flow out sections  49  located near the lower ends of the hollow fiber membrane modules  44 . 
     The present invention is described above by way of embodiments. However, the present invention is by no means limited to the above-described embodiments, which may be combined and modified in various different ways in terms of configuration without departing from the scope of the present invention.