Abstract:
An explosion protection venting system has a plurality of vessels or reactors connected by a common vent line. A flame front diverter having a pair of opposing rupturable discs is connected to each one of a plurality of vessels for directing a deflagration away from the normal flow path and through an alternate path that prevents damage to nearby structure.

Description:
[0001]     The present application is related to U.S. application Ser. No. ______, filed ______ of Robert C. Knyrim and Timothy F. Simmons, and entitled, “Flame Front Diverter Element”, Atty. Docket No. 85220/CEB.  
       FIELD OF THE INVENTION  
       [0002]     The invention relates generally to the field of explosion protection systems. More specifically, the invention relates to a flame front diverter element when used in an explosion protection venting system having a plurality of vessels diverts a deflagration in a different direction than the normal flow path thereby virtually eliminating any impending disastrous effects to surrounding structure.  
       BACKGROUND OF THE INVENTION  
       [0003]     According to maximum achievable control technology (MACT) and European regulations, emerging emission standards will affect most manufacturing areas containing operational vents to atmosphere. A cost-effective strategy for treating hazardous flammable solvent emissions is to manifold operational vessel vents together to one emission control device. However, in the unexpected event of a flammable solvent ignition, there is a possibility of fire or deflagration propagation, which could potentially destroy any or all the devices connected in the vent system. Therefore, fire and explosion protection schemes must be in place to minimize potential consequences of a fire or explosion. Prior art includes an explosion diverter or backflash interrupter to prevent flames from propagating from one piece of equipment to another through the interconnecting piping.  
         [0004]     The basic principle of operation of a typical device as described above is that a deflagration is vented in a different flow direction than the normal flow path. Due to the inertia of the fast flow caused by the deflagration, the flow will tend to maintain its direction upward rather than making the hard degree turn as when the vessel emission flow velocity is low during normal conditions. When the high-speed deflagration flame continues upward, it pushes open either a hinged cover or bursts a rupture disc located at the top of the diverter, allowing the flame to be released to the atmosphere. The limitations placed on the existing device are that it can only be used in processes with a combustible dust with very low concentrations. The operating pressure is limited to 0.0 barg (1.5 psig) due to the pressure setting of the relief device required for approval.  
         [0005]     Another device to prevent propagation during a deflagration is the explosion isolation valve. There are high-speed sensors installed on both sides of the isolation valve to detect a high rate of pressure rise in the pipeline and then close the valve before the deflagration can pass through. This is an expensive scheme with no guarantee that the valve will close before the deflagration or flame passes through.  
         [0006]     Therefore, a need persists in the art for an explosion protection venting system having a flame front diverter element that diverts deflagration along an alternate path and away from the normal flow path that avoids a disastrous impact to nearby structures.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, an explosion protection venting system has a plurality of connected vessels, such as reactors. Each one of the plurality of vessels has a vent in fluid communications with a common connection line between the plurality of vessels. A flame front diverter is connected to each one of the plurality of vessels.  
         [0008]     The flame front diverter has an elongated channel that has opposing first and second end portions and a rupturable disc in fluid communications with the elongated channel mounted to each of the opposing first and second end portions.  
         [0009]     First and second vapor flow channels are disposed in the elongated channel. Either of the first and second vapor flow channels is connected to the common connection line to receive process vapor and to form a primary flow path for process vapor propagation between the elongated channel and the other of the first and second vapor flow channels to a downstream process. In this manner, effluent produced by excessive pressure caused by combustion of the process vapor is diverted away from the primary flow path and through one of the rupturable disc that ruptures outwardly from the elongated channel. Further, the other of the rupturable disc ruptures inwardly of the elongated channel causing an instantaneous stream of outside air to flow inwardly of the elongated channel between each of the rupturable discs thereby interrupting the combustion process.  
         [0010]     The present invention has the following advantages over prior art developments, including: it is a passive system with no moving parts; it will work up to about 5 psig operating pressure; it will operate at a vapor through put rate up to about 350 fit/min; and, it will mitigate any deflagration independent of the starting point in any pipeline connected to the venting system. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The above and other objects, features, and advantages of the present invention will become more apparent when taken in conjunction with the following description and drawings wherein identical reference numerals have been used, where possible, to designate identical features that are common to the figures, and wherein:  
         [0012]      FIG. 1  is a side view of the flame diverter element of the invention;  
         [0013]      FIG. 2  is an end view of the rupturable disc used in accordance with the invention;  
         [0014]      FIG. 3  is an perspective view of the flame front diverter partially exploded to show the rupturable discs displaced during a deflagration; and,  
         [0015]      FIG. 4  is a schematic of an explosion protection venting system of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     Turning now to the drawings, and in particular to  FIGS. 1 and 3 , the flame front diverter element  10  of the invention is illustrated. According to  FIG. 1 , flame front diverter element  10  has an elongated channel  12  having opposing first and second end portions  14 ,  16 . A rupturable disc  18 ,  20  is arranged in fluid communications with the elongated channel  12 . Either one of rupturable disc  18 ,  20  is mounted to one of the opposing first and second end portions  14 ,  16  of elongated channel  12 .  
         [0017]     According to  FIG. 1 , a first vapor flow channel  22  disposed in an end portion of elongated channel  12  has an inlet end  24  and outlet end  26 . Similarly, a second vapor flow channels  28  disposed in an opposing end portion of elongated channel  12  has an inlet end  30  and an outlet end  32 . Preferably first and second vapor flow channels  22 ,  28  are welded to elongated channel although other attachment means, such as bolting, may work with similar success. It is important to the invention that the inlet end  30  has a predetermined spacing (d) from the nearest rupturable disc  20 . Each rupturable discs  18 ,  20  is sandwiched between a pair of opposing flanges  27 ,  29 , respectively, fixedly mounted to the elongated channel  12 .  
         [0018]     Referring again to  FIG. 1 , flanges  27 ,  29  each has a diameter of about 4 inches and a force rating of 150 lbs to withstand the deflagration pressure. It is our experience that the inlet end  30  of vapor flow channel  28  is preferably spaced apart ⅝ inch to 1½ inches from rupturable disc  20  at setup. Outside the lower spacing limit, i.e., ⅝ inch, the flame diverter element  10  has been observed to plug-up. Beyond the upper spacing limit, i.e., 1½ inch, the opposing rupturable disc  18  may not rupture. Similarly, it is important that the outlet end  26  of vapor flow channel  22  has a predetermined spacing (d′) from nearest rupturable disc  18  at the other end of the elongated channel  12 . According to our testing outlet end  26  is preferably spaced apart ⅝ inch to 1½ inch from rupturable disc  18  at setup. Outside the lower spacing limit, i.e., ⅝ inch, the flame diverter element  10  has been observed to plug-up. Beyond the upper spacing limit, i.e., 1½ inch, the opposing rupturable disc  20  may not rupture. Moreover, either of the first and second vapor flow channels  22 ,  28  is configured to receive process vapor from a flammable process and to form a primary flow path  34  for process vapor propagation between the elongated channel  12  and the other of the first and second vapor flow channels  22 ,  28  to a downstream process.  
         [0019]     It is preferred that elongated channel  12  has a wall thickness of at least 0.237 inches and the vapor flow channels  22 ,  28  has a wall thickness of at least 0.139 inches to withstand peak deflagration pressure.  
         [0020]     Further, rupturable discs  18 ,  20  are each bi-directional relative to the elongated channel  12  so that a deflagration can be vented in either direction relative to the interconnected vessel or reactor (see  FIG. 4 ). Also, rupturable discs  18 ,  20  are capable of rupturing at a pressure of not more than about 5 psig. The dual bi-directional rupturable discs  18 ,  20  are to account for the possibility that a deflagration can start on either side of the flame front diverter element  10 .  
         [0021]     Referring to  FIG. 3 , once the deflagration starts, one rupturable disc  18 ,  20  will burst outwards from the pressure ahead of the flame front diverter element  10  at 0.34 barg (5 psig) potentially producing fragments  21 . The high deflagration flow rate creates an aspiration effect on the opposite rupturable disc  18 ,  20  causing it to burst inwards forming potentially jagged edges  23  or fragmented pieces  21  of the disc inside elongated channel  12 . This allows a rush of ambient air into the elongated channel  12  to obstruct the continual flow of hot gases downstream of the flame front diverter  10 .  
         [0022]     Referring to  FIG. 4 , according to another embodiment of the invention, flame front diverter element  10  is specifically designed for installation in an explosion protection system  100  from a plurality of vessels  102  (for instance reactors) manifold together to a final emission control element  104 . In this embodiment, flame front diverter element  10  (described above) is connected to each of the vent lines  106  associated with each vessel  102  and final emission control element  104 . If a vessel  102  has an internal deflagration, other vessels  102  connected in the vent line  106  could become involved with the initial deflagration. Skilled artisans will appreciate that flame front diverter element  10  is designed to prevent a deflagration from propagating from one vessel  102  to another vessel  102  or to the final emission control element  104 . The operating conditions of the explosion protection system  100  can be higher than prior art design flow rates, any flammable solvent concentration, and up to operating pressure of 0.34 barg (5 psig).  
         [0023]     Referring again to  FIG. 4 , flame front diverter element  10  is designed to cause a minimal pressure drop under normal venting conditions when process vapors need to pass through the explosion protection system  100  and to other equipment connected to the manifold system. In the event of a deflagration, the flame front diverter  10  directs the high-speed pressure wave towards a bi-directional rupturable disc  18 ,  20  causing the rupturable disc  18 ,  20  to open thus creating an aspiration effect on the opposite bi-directional rupturable disc  18 ,  20 . Fresh air immediately is caused to enter the elongated channel  12  to interrupt the continuous hot gas flow, thus stopping the downstream deflagration propagation. As shown in  FIG. 4 , flame diverter element  10  can be installed in the manifold system between each vessel  102  /process equipment and upstream of an emission control element  104  in the atmospheric vent line  106  containing flammable vapors.  
         [0024]     The invention has been described with reference to a preferred embodiment. However, it will be appreciated that a person of ordinary skill in the art can effect variations and modifications without departing from the scope of the invention.  
       PARTS LIST  
       [0000]    
       
           10  flame front diverter element  
           12  elongated channel  
           14  end portion  
           16  end portion  
           18  rupturable disc  
           20  rupturable disc  
           21  fragments/fragmented pieces  
           22  first vapor flow channel  
           23  jagged edges  
           24  inlet end  
           26  outlet end  
           27  flange  
           28  second vapor flow channel  
           29  flange  
           30  inlet end  
           32  outlet end  
           34  flow path  
           100  explosion protection system  
           102  vessel  
           104  final emission control element  
           106  vent line