Patent Publication Number: US-2015072296-A1

Title: Natural Draft Combustion Mixer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     As per 35 USC §119(e), this application is related to the provisional application filed on Nov. 27, 2012. Application No. 61/730,455 (Confirmation Number: 5768) 
    
    
     STATEMENT REGARDING FEDERALLY SPONSERED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not Applicable 
     INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
     Not Applicable 
     BACKGROUND OF INVENTION 
     A natural draft combustion mixer is a device that is utilized in processes where heat is required and achieved by means of heat release from the combustion reaction of fuel and air in a combustion chamber. The mixer is used to perform the mixing of the fuel and air to achieve a mixture above the LEL (lower explosive limit) and below the UEL (upper explosive limit). The primary air shutter is used to control the amount of air that is entering the mixer to attain the required combustion properties. An orifice, of various sizes depending on capacity requirements, is used to calculate the actual volume of fuel per unit time that passes through from a point of predetermined pressure to an area of atmospheric pressure. It is also the point where the well known physics principle of high velocity creating a low pressure area is used to cause atmospheric pressure to push air into the mixer or induce air. The mixture exits through a nozzle at which point the ignition actually occurs and the combustion reaction takes place. Traditionally, the primary air shutter has been located at a point upstream from the point of fuel introduction. Thus, the flow of cold primary air must pass by the orifice and, as a result, strips heat away from the orifice. The orifice is prone to freezing due to the varying composition/water content of the fuel being used in conjunction with the pressure drop that occurs at this point. In order to change the capacity of the mixer, the orifice needs to change in size and/or the pressure adjusted. This typically involves the dismantlement of the mixer assembly to provide access to the orifice. 
     SUMMARY OF THE INVENTION 
     The object of this invention is to prevail over the drawbacks relating to prior art in this field as stated above. 
     The primary air intake has been relocated to a position downstream of the fuel gas point of introduction. Now the stream of fuel leaving the orifice is at its highest velocity, and thus, lowest pressure, at the point of air induction rather than the traditional upstream location. This design allows for a greater volume of air to be introduced than on a similarly sized traditional mixer. 
     A removable orifice holder has been designed to allow for the removal of only the holder to access the orifice for maintenance and set-up. This allows the rest of the assembly to remain stationary as it is not required to be removed from the combustion chamber. 
     A port has been positioned adjacent to the orifice location to allow the use of an orifice preheat line to be installed. This port provides a point of entrance for the high temperature, products of combustion (POC) from the mixing chamber into the mixer housing. These POC can be drawn back and directly across the orifice, using the same physics principle as previously discussed, to further prevent the freeze off issues traditionally encountered. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an exploded view of the mixer assembly with an optional venturi barrel 
         FIG. 2  is a view of all components assembled to form complete mixer 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     With reference to  FIGS. 1-2  the mixer component orientation and construction can be explained. 
       FIG. 2  shows the location of the fuel inlet  1  to the mixer. 
     As shown in  FIG. 1  the mixer is comprised of three mandatory separate components with an optional component that will assist in the mixing of the fuel if required. The main mixer body  3  contains the port for the preheating of the orifice  4  by utilizing the high temperature POC as well as the port for the orifice holder  1 . A portion of the main body  3  has a reduced diameter and four rectangular holes removed from the stock at 90 degrees in an array around the outside diameter. The reduction of diameter allows for the primary air shutter  5  to slide over top of the mixer body  3 . The reduced diameter portion of the mixer body  3  and the primary air shutter are of the same length. This is the base for the primary air shutter  5  which also has the same dimensioned four holes removed at a 45 degree offset from the mixer body  3  holes. This allows for the primary air to be adjusted within the completely open and completely closed positions of the shutter. The mixing shutter  5  has the same outside diameter as the mixer body  3  and an internal diameter slightly larger than the outer diameter of the reduced section of the mixer body  3 . This allows for the primary air shutter  5  to rotate freely about the center line axis of the mixer.  FIG. 2  shows the set screw hole  2  that allows for the primary air shutter to be secured in the desired position and also constrains the degrees of rotation between the completely open and completely closed position of the primary air shutter ( 3 ,  FIG. 1 .). The optional venturi barrel  6  is shown in  FIG. 1  and is used to aide in mixing of the air/fuel before the nozzle.  FIG. 1  shows the orifice  2  threaded into the orifice holder  1  and is threaded into the port  7  located at the back of the mixer body  3 . It is this configuration that allows the orifice holder to be removed from the assembly allowing maintenance or set-up to easily be performed on the orifice without the need to remove the entire mixer assembly from the combustion chamber. 
     With reference to  FIG. 1 , as the fuel passes through the orifice  2 , the high velocity gas creates a low pressure area at the primary air shutter  5  thus, inducing air into the mixer body  3 . The primary air shutter  3  is rotated to adjust the amount of air entering the mixer, based on the required amount of air needed to attain the desired combustion reaction. 
     A line, such as a piece of stainless steel tubing, may be connected between the orifice preheat port  4  and the flame front where the POC are produced. As the high velocity fuel enters the mixer, the low pressure created draws high temperature POC down and across the adjacent orifice, effectively heating the orifice well above the temperature at which ice will form.