Abstract:
A degasser having a flapper opening including a hinge. The hinge may permit purging of any liquids and solids without regular human intervention. There may be a fixed opening at the base of the degasser, such that there is a constant emptying from the bottom of the tank. The separation of gas from liquid may be involved in applications pertaining to pulping and oxygen delignification.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Patent Application Ser. No. 60/950,239, filed Jul. 17, 2007, which is incorporated by reference in its entirety. 
     
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
       [0002]    The present invention generally relates to the separation of gas from liquid, particularly with respect to applications pertaining to pulping and oxygen delignification. 
         [0003]    Degassing unit operations are known. For example, a conventional degasser is illustrated in  FIGS. 1A and 1B .  FIG. 1B  shows a cross-sectional view ( 1 B- 1 B) of the process shown in  FIG. 1A , and like items are identified with like numerals. The system  100  includes input stream  104 , and output streams  124  and  136 . Input stream  104  may include liquids and gasses. The liquids may comprise primarily water, and the gasses may include process waste gasses, such as carbon dioxide, carbon monoxide, oxygen, methane, etc. The system  100  separates these gases, which may exit primarily via output stream  124 . 
         [0004]    In  FIGS. 1A and 1B , input stream  104  flows through conduit  110  to pump  112 , which is connected to shaft  114  and motor  116 . As shaft  114  rotates, the liquid-gas mixture is pumped through conduit  118  to the degasser  102 . Conduits  110  and  118  may be flexible hoses. As illustrated, conduit  118  is connected to inlet pipe  120 . Inlet pipe  120  is connected to a pipe  122  at the top of degasser  102 . As the liquid-gas mixture enters the pipe  122 , the liquids tend to fall, while the gasses tend to rise and exit out of the top of the degasser  102  through output stream  124  to a gas collector (not shown). 
         [0005]    As shown by the arrows at the base of pipe  122 , the liquid flows up the approximately cylindrical tank defined by base  128  and walls  126 . The liquid exits through conduit  134  to output stream  136 , which is sent to liquid waste. 
         [0006]    At the base of the tank, there is a flushing connection  130 . As solids (e.g., pulp, etc.) accumulate at the base of the degasser, there is a potential for clogging. Those solids are generally manually removed periodically using the flushing connection  130 . As illustrated base  128  is roughly parallel with the ground, such that the walls  126  intersect base  128  perpendicularly. 
         [0007]    For applications involving low amounts of solids in the liquid-gas stream, the prior art may be suitable. That is, the periodic, manual cleaning may work well because a low-solids content will generally require a relatively long period of time before cleaning becomes necessary. 
         [0008]    But in applications having a larger (or non-insignificant) amount of solids (such as pulp, etc.) in the liquid-gas stream to be separated into gas and liquid, there may be a need for a degasser that does not clog, is easy to clean or purge (or automatically cleaning), and disposes of waste. 
         [0009]    In one aspect, certain embodiments of the present invention generally relate to a degasser having a flapper opening including a hinge and a counterweight. The hinge and counterweight may permit purging of any liquids and solids without regular human intervention. In other embodiments, there is a fixed opening at the base of the degasser, such that there is a constant emptying from the bottom of the tank. 
         [0010]    In another aspect, certain embodiments of the present invention generally relate to an inlet design that facilitates separation of any solids (e.g., pulp, etc.) by reducing the velocity of the inlet stream on entry into the degasser. For example, this may be done using a flange. Facilitating the separation of solids may prevent clogging. 
         [0011]    In one respect, certain embodiments of the present invention generally relate to a degasser for separating gas from liquid comprising: a substantially cylindrical tank comprising a top, a bottom, and a circumferential side wall; an inlet pipe for carrying a stream comprising a mixture of gas and liquid; and a vent pipe connected to the tank, wherein the vent pipe receives separated gas; wherein the bottom of the tank is connected to the circumferential side wall by a hinge such that the hinge at least partially opens when a sufficient mass of liquid weighs down on the bottom of the tank and at least partially closes when an insufficient mass of liquid weighs down on the bottom of the tank; and wherein the separated liquid exits the tank via an opening created as the hinge opens and creates a gap between the bottom of the tank and the circumferential side wall. 
         [0012]    In one respect, certain embodiments of the present invention generally relate to a method of separating gas from liquid, the method comprising the steps of feeding a mixture of gas and liquid to a substantially cylindrical tank comprising a top, a bottom, and a circumferential side wall, wherein the bottom of the tank is connected to the circumferential side wall by a hinge that opens when a sufficient mass of liquid weighs down on the bottom of the tank and closes when an insufficient mass of liquid weighs down on the bottom of the tank; removing gas from the tank using a vent pipe attached to the top of the tank; and removing liquid from the tank using an opening created as the hinge opens and creates a gap between the bottom of the tank and the circumferential side wall. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIGS. 1A and 1B  illustrate a prior art system including a degasser. 
           [0014]      FIGS. 2A and 2B  illustrate a degasser according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The present invention generally relates to a system for separating gasses (such as carbon dioxide, carbon monoxide, oxygen, methane, etc.) from a process stream including liquids and possibly solids. The liquid may comprise primarily water. In a preferred embodiment, the present invention has particular utility in a process for oxygen delignification in pulping and paper making. For example, the present invention may be used in conjunction with a stock pump between pressurized stages, e.g., in a system utilizing low pressure steam. 
         [0016]      FIGS. 2A and 2B  illustrate a preferred embodiment of the present invention, namely degasser  250 .  FIG. 2B  shows a cross-sectional view ( 2 B- 2 B) of the process shown in  FIG. 2A , and like items are identified with like numerals. The liquid-gas stream  252  (which may contain solids, such as pulp, stock, etc.) enters via inlet pipe  254 . 
         [0017]    As compared to some prior art processes (such as the one described in  FIGS. 1A and 1B ), the inlet pipe enters at a greater radius, so as to discourage clogging of the pipe  256 . Indeed, stream  252 , inlet pipe  254 , and pipe  256  are preferably designed to decrease the velocity of the stream  252  and/or designed to discourage clogging of pipe  256  with solids (if present). Baffles, flanges, etc. may also be present in preferred embodiments. 
         [0018]    As illustrated in  FIGS. 2A and 2B , gasses exit via stream  262  through vent pipe  260 , which is connected to pipe  256  via vent connector  258 . Vent pipe  260  may be attached to a vacuum (e.g., 4 to 6 inches H 2 O) to facilitate separation and evacuation of the gasses. Liquids and solids (if present) generally are pulled via gravity downwards into tank  280 . 
         [0019]    Tank  280  may be generally defined by top  268 , circumferential side  282 , and bottom  264 . Tank  280  may be generally cylindrical; as illustrated, however, bottom  264  need not be parallel with top  268 . As illustrated, side  282  may have differing lengths along the periphery of the tank, and an angle at corner  278  (at the intersection of side  282  and bottom  264 ) may range from 0° to 90°. The stock, however, need not gather or collect in all embodiments. In a preferred embodiment, the angle at corner  278  may be approximately 45° (as illustrated in  FIG. 2A ). Such an angle facilitates the collection of solids in a manner that facilitates operation of the flapper (described below). 
         [0020]    In other embodiments, bottom  264  has a non-planar shape. For example, it may be curvilinear or parabolic when viewed from a side cross-section. These non-planar shapes may also facilitate the collection or gathering of solids. 
         [0021]    As illustrated in  FIGS. 2A and 2B , hinge  270  attaches wall  282  to bottom  264 . Bottom  264  may be reinforced with a stiffening back  266  to inhibit or prevent warpage and possibly increase durability. Rod  272  supports movable counterweight  274 , such that the bottom  264  opens when the force pushing on the bottom  264  (e.g., from the accumulating mass of liquid and solids (if present)) exceeds the balancing force on the other side of the hinge  270  (including, e.g., counterweight  274  and rod  272 ). Other conventional methods (e.g., springs, etc.) may be used to provide an upward force on bottom  264  opposing the downward force of liquids and solids. 
         [0022]    Depending on the application—including, for example, the solids content and make-up—the counterweight may be moved to permit opening of the flapper and hinge using more or less force. In some applications, the amount of force will also be affected by the strength of the vacuum being pulled through stream  262  and vent pipe  260 . For example, a stronger vacuum may decrease the force applied on the bottom  264 , e.g., by the accumulating mass of liquid and solids in tank  280 . 
         [0023]    Preferably, degasser  250  and tank  280  are located over a drain (e.g., through support by legs  276 ), such as a U-drain already existing in the facility. This would allow the hinge to open and the liquid and solids (if present) to exit to a preexisting waste stream. In other embodiments, the solids and liquids exiting tank are collected and recycled for further processing without immediate introduction into a waste stream. 
         [0024]    As illustrated, the connection (e.g., seal) between the bottom  264  and the rest of tank  280  is generally friction based. In some embodiments, it may be preferably to prevent a completely contacting seal from forming. That is, in some embodiments, the hinge  270  may be prevented from shutting. This may be accomplished, for example, with an adjustable nut and bolt mechanism that holds the flapper open by a fraction of an inch, an inch, or more. In such embodiments, the liquid is continuously draining out the bottom of tank  280  during the degassing. 
         [0025]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.