Patent Abstract:
A direct-fired, propane powered steam generator is provided with a carburetor, which receives vaporized propane from a converter arrangement which converts liquid propane to vapor, receives pressurized air and feeds a mixture of vaporized propane and air into the combustion chamber of the steam generator. The amount of air delivered to the carburetor is variable, with the amount of vaporized propane entering the carburetor being determined by the position of a metering valve which varies in accordance with the amount of air passing through the carburetor. The converter arrangement receives liquid propane and is coupled to process water heated in the water jackets of the combustion chamber and adjacent structure, the converter arrangement being designed so that heat from the water is transferred for effecting vaporization of the liquid propane. The flow of liquid propane for combustion in a pilot burner and for combustion in the main combustion chamber may be controlled using various arrangements of solenoid-operated lock off valves and/or vacuum-operated fuel lock off filters and/or air pressure balance control valves.

Full Description:
FIELD OF THE INVENTION 
   The present invention relates to direct-fired steam generators, and, more specifically, relates to systems for supplying a combustible mixture of fuel and air to the premix burners of such generators. 
   BACKGROUND OF THE INVENTION 
   Applications in which a forced airflow is used with a premix burner require a high-pressure fuel delivery system in order to overcome the high air pressures (generally from 2˜15 psi) in the burner. In the present systems, fuel is metered in a binary fashion using several solenoid valves (see U.S. Pat. Nos. 6,135,063 and 4,462,342, for example) or with electronic controls utilizing several sensors and valves (see U.S. Pat. No. 5,685,707, for example). 
   A typical known premix burner layout includes main fuel and air passages which merge at a burner inlet and are fed into the burner combustion chamber where the mixed fuel and air are ignited. Water for producing steam is introduced into an inlet at one end of the chamber and moves along an inner surface of the chamber toward an outlet at an opposite end of the chamber. Combustion occurs centrally within the chamber and the heat generated changes the water to steam. U.S. Pat. No. 4,211,071 discloses such a system. Systems of this type having fuel metered in the known ways have one or more of the following drawbacks: (1) the burner&#39;s output is changed in a step progression, with each step depending on the size and quantity of valves opened to regulate the fuel/air mixture; (2) fuel flow is often not related to the airflow through the burner; (3) to have a variety of firing rates, either a fuel flow control system including several fuel valves is needed, or a complicated variable valve system is needed, with either system adding great expense while decreasing overall reliability; and requiring a high amount of piping which makes them undesirable for mobile application. 
   It is desirable then to overcome the cost and complexity of current fuel systems for premix burners of direct-fired steam generators, while improving the firing rate control. 
   SUMMARY OF THE INVENTION 
   According to the present invention, there is provided an improved fuel control system for a direct-fired steam generator. 
   An object of the invention is to provide a fuel control system which is of a relatively low cost and which provides an infinite firing rate adjustment within the desired operating range of the steam generator. 
   The above-noted object is achieved by using off-the-shelf engine fuel control components laid out to form a fuel delivery system similar to that of a supercharged, or turbocharged, engine fuel delivery system. 
   In a standard carburetor system, the engine&#39;s pistons, while moving to bottom dead center, create a low-pressure area on the back or downstream side of the carburetor. Ambient air moves through the carburetor into the low-pressure area. As the air moves through the carburetor, a pressure drop occurs lifting a diaphragm-controlled fuel metering valve so as to allow fuel to flow. The amount of air moving through the system affects the amount of diaphragm movement, and, hence, the amount of fuel flow. 
   In a supercharged or turbocharged engine system, the air entering the carburetor is at an elevated pressure. A pressure-balance air line is connected from the downstream side of the carburetor to the diaphragm. This equalizes the pressure on the diaphragm and allows its movements to be controlled by the pressure drop through the carburetor. Instead of creating a low-pressure downstream of the carburetor, one can create a high pressure upstream of the carburetor. By using a blower or other air-pumping device to force air through the carburetor, one can induce the proper fuel flow into the air stream. 
   The present invention is achieved then by replacing the head or entry end of a known premix burner, where the combustion air and fuel meet before entering the combustion chamber, by a carburetor which controls the amount of fuel as a function of the amount of air flowing through the carburetor. A variable output air pump, such as is manufactured by the Magnuson division of Eaton Corporation, for example, is provided for controlling the amount of air delivered to the carburetor, and, hence the amount of fuel. A standard blower with a binary air bleed-off control could also be used. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a somewhat schematic perspective view of a direct-fired steam generator system including a carburetor for controlling the air/fuel mixture used in the combustion chamber of the steam generator. 
       FIG. 2  is an enlarged perspective view of a portion of the steam generator of  FIG. 1  showing the converter coupled for supplying propane vapor to the fuel inlet of the carburetor. 
       FIG. 3  is a partial sectional view of the steam generator omitting most of the fuel supply system but showing the water and air supply systems. 
       FIGS. 4 ,  5  and  6  are schematic representations respectively of three different fuel systems for supplying fuel to the main and pilot combustion chambers of the steam generator burner. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIGS. 1–3 , there is shown a steam generator assembly  10  including a steam generator body  12  having a cylindrical inlet section  14  to which a cylindrical burner-head  16  is coupled, and having a conical outlet section  18  to which one end of an elbow  20  is coupled, the other end of the elbow  20  being coupled to a static mixer  22  ( FIG. 3 ). A pilot burner arrangement  24  includes a tube  26  mounted so as to project through and terminate at an interior surface of a lower region of the burner-head  16 . An igniter  28 , which may be a spark plug or other type of sparking device, is mounted to the tube  26  so as to selectively create a spark at an interior location of the tube  26  for igniting a fuel/air mixture resulting when vaporized fuel enters by way of a pilot fuel inlet  30  provided in a cover at an inlet end of the tube  26  and when air enters by way of an pilot burner air line  32  coupled to an upper location of the tube  26 . 
   A carburetor  34  has an outlet coupled to an inlet end of the burner-head  16  by a short tube  36 , and has a main combustion air inlet  38  ( FIGS. 2 and 3 ) coupled for receiving pressurized air from a variable output air pump arrangement  40  by an air line  42 . It is noted that the pilot burner air line  32  is coupled to the line  42  just upstream of the carburetor  34 . The carburetor  34  also has a main combustion fuel inlet  44  coupled to an outlet end of a throttle body  46 . The throttle body  46  includes a mounting portion secured to a mounting portion at an outlet of, and includes a portion projecting within, a 90° air horn  48 . 
   A fuel converter assembly  50  includes a pair of converter units  52  respectively having a pair of gaseous fuel outlets  54  coupled to a manifold  56  including a gaseous fuel outlet coupled to the fuel inlet  44  of the throttle body  46 . The amount of fuel entering the throttle body  46  is metered by the action of a metering valve which is actuated in accordance with a pressure drop across a diaphragm of a diaphragm and metering valve assembly  47  (see  FIGS. 4–6 ) located within the carburetor  34 . Air flow through the carburetor  34  is caused by the introduction of high pressure air at the air inlet  38 . The influence of the pressure of the inlet air acting on the diaphragm of the assembly  47  is nullified by a pair of pressure balance lines  58  coupled so that the high pressure at an upstream side of the diaphragm is transferred to the downstream side of the diaphragm. Specifically, the pressure balance lines  58  have respective first ends coupled to the converter units  52  so as to be in communication with the gas outlets  54 , and hence the downstream side of the diaphragm, and have respective second ends coupled to a T-connection  60  ( FIG. 1 ) having an inlet coupled to the interior of the air horn  48  at a location upstream of the throttle body  36 , and hence upstream of the diaphragm. The gas converter units  52  each include a liquid fuel inlet  62  coupled for receiving liquid propane from a pressurized propane tank  64  by a liquid fuel supply line  66  ( FIGS. 3–6 ). 
   As can best be seen in  FIG. 3 , the steam generator body  12  defines an interior combustion or flame chamber  70 . The generator body  12 , burner-head  16  and elbow  20  are all double-walled so as to define a water jacket between the walls for containing cooling water. Cooling water is supplied by a water pump  72  having an inlet coupled to a water tank  74  and an outlet coupled by a water line  76  to an inlet provided in the outer wall of the elbow  20 . The water jacket of the elbow  20  is coupled by a water transfer line  78  to the water jacket of the generator body  12 , and the water jacket of the generator body  12  is coupled to the water jacket of the burner-head  16  by a water transfer line  80 . A pair of water transfer lines  82  each have respective inlet ends coupled to the water jacket of the burner-head  16  and respective outlet ends respectively coupled to a pair of water inlets  84 , respectively of the converter units  52 . Each of the converter units  52  includes a water outlet  86  coupled, as by a T-connection  88  to an inlet of a water return line  90  having its outlet coupled to an injector assembly  92  mounted between the elbow  20  and the generator body  12  and which directs the returned water into a region at the outlet of the combustion chamber  70  where the water is contacted by the hot combustion gases and is changed to steam as it becomes mixed with these hot gases, with the static mixer  22  aiding the mixing process. 
   Thus, it will be appreciated that as the water delivered by the pump  72  flows from the water jacket of the elbow  20  to the water jacket of the generator body  12  to the water jacket of the burner-head  16  it will be heated and that this hot water then passes into the converter units  52  which are designed such that heat from the water is transferred to the liquid propane so as to cause the latter to vaporize or change to its gaseous state before it exits the converter units  52  at the outlets  54 . In the event that the temperature of the water as it enters the converter units  52  is too high for efficient conversion of the liquid propane to gas, then the inlet ends of the water transfer lines  82  may be coupled to the water jacket of the generator body  12  at a location where the temperature of the water is more suitable for the conversion process. 
   Referring now to  FIG. 4 , there is shown a fuel system  100  for supplying propane fuel to the carburetor  34  and to the pilot burner arrangement  24 . Specifically, a pilot burner fuel supply line  102  is coupled between the propane tank  64  and the fuel inlet  30  at the top of the tube  26 . Located in series in the fuel supply line  102 , as considered proceeding from the tank  64  to the pilot burner assembly  24 , are a pressure regulator  104 , a normally closed, solenoid-operated fuel lock off valve  106  and a manually-operable needle valve  108 . The fuel line  102  has an inlet so positioned in the tank  64  that it only accesses vaporized fuel located in the tank. The pressure regulator  104  reduces the pressure of the fuel passing beyond the regulator  104  to a desired level for proper pilot light operation. Flow to the pilot burner arrangement  24  is permitted by opening the solenoid valve  106 , with this flow being tuned by adjusting the needle valve  108 . The needle valve  108  may not be required if the desired flow restriction is obtained by choosing an appropriate fuel line size. 
   The fuel system  100  additionally includes the liquid fuel line  66  for supplying the fuel for the primary combustion that takes place in the combustion chamber  44   70  once combustion has been started by the pilot burner assembly  24 . The fuel line  66  has an inlet located in the tank  40  so as to access liquid propane. The fuel line  66  contains a normally closed, solenoid-operated fuel lock off valve  112  that is located upstream of separate branches of the fuel line  66  that are respectively coupled to the liquid fuel inlets  62  of the pair of converter units  52 . A vaporized fuel line  114 , shown here in lieu of the manifold  56  of  FIG. 2 , has a branched end coupled to the vaporized fuel outlets  54  of the converter units  52  and a further end coupled to the fuel inlet  44  of the carburetor  34 . Located in the vaporized fuel line  114  is a solenoid-operated, fuel vapor control valve  116 . The air pressure balance lines  58  are coupled between the air horn  48  of the carburetor  34  and the converters  52  so that the flow of fuel into the carburetor  34  is metered in response to the pressure drop across the diaphragm of the carburetor diaphragm and metering valve assembly  47  for controlling the position of the fuel metering valve without being influenced by the pressure of the pressurized air entering the air horn at the inlet side of the diaphragm. Fuel flow between the tank  64  and the carburetor  34  is allowed by opening the normally closed, fuel lock off valve  112  and the fuel vapor control valve  116 , with it being noted that the small amount of fuel stored between the solenoid valve  116  and the converter units  52  will not flow until the vapor control valve  116  is opened. However, it is to be noted that the valve  116  may be omitted from the control system  100 , with the only change in operation being that the small amount of fuel stored between the converter units  52  and the carburetor  34  will now flow when air flow across the diaphragm-controlled metering valve causes the metering valve to open. 
   Referring now to  FIG. 5 , there is shown a fuel control system  120  which is a variant of the control system  100 , with common parts being indicated by the same reference numerals. One of the main differences between the system  120  and the system  100  is that fuel for the pilot burner arrangement  24  is supplied by liquid withdrawn from the tank  64  by the fuel supply line  66  used for supplying the fuel for the main fire within the combustion chamber  70 . Specifically, the liquid fuel supply line  66  still contains the solenoid-operated, fuel lock off valve  112  at a location upstream of a branched end of the line  66  which leads to the converter units  52 . A further branch  122  is coupled to the pilot burner assembly  24  and contains a second solenoid-operated, fuel lock off valve  124 . Located in the line  122  in series with, and downstream from, the valve  124  is an air heated regulator  126  and a manually-operable needle valve  128 . Flow of fuel to the pilot burner assembly  24  is controlled by opening both of the solenoid-operated, fuel lock off valves  112  and  124 . The liquid propane is then vaporized by the air heated regulator  126  (any source of heated air may be coupled to the regulator  126 ), with the flow of the vaporized fuel to the pilot burner assembly  24  being fine-tuned by operation of the needle valve  108 . As previously mentioned, the needle valve  108  may be omitted and the fuel line sized to provide the desired metering. 
   The portion of the system  120  for supplying fuel for the main fire in the combustion chamber  70  is basically the same as that described above relative to the system  100 , with the difference being that the fuel vapor control valve  116  has been omitted and a balance air valve  128  is now mounted in the connection of the air balance lines  58  with the horn  48  of the carburetor  34 . When the balance air valve  128  is closed, supercharged air arriving at the air horn  48  of the carburetor  34  will prevent the diaphragm of the diaphragm and metering valve assembly  47  from opening the metering valve so as to permit flow of gaseous propane into the carburetor. Thus, the flow of fuel for the main fire in the combustion chamber  70  is controlled by opening the solenoid-controlled, fuel lock off valve  112  and the balance air valve  128 , with opening of the latter resulting in the nullification of the affect of the supercharged air on the diaphragm and metering valve assembly  47  so that the flow of gaseous propane into the carburetor is metered in accordance with the pressure drop across the diaphragm. With the presence of the balance air valve  128 , the small amount of fuel stored between the solenoid-operated fuel lock off valve  112  and the converter units  52  is not allowed to flow until the balance air valve  128  is opened. It is noted that the same result can be achieved by using the valve  128  to control a coupling of the vaporized fuel line  114  with the atmosphere. Further, it is possible to omit the balance air valve  128  altogether in which case the small amount of fuel stored between the fuel lock valve  112  and the converter units  52  will flow in response to air flow through the carburetor  34  since such air flow will result in the diaphragm-controlled metering valve of the assembly  47  being opened. 
   Referring now to  FIG. 6 , there is shown a further fuel control system  130  which is a variant of the control system  120 . The major difference between the fuel control system  130  and the fuel control system  120  is that the solenoid-operated, fuel lock off valve  112  is removed from the line  66 . Respectively located in the branches leading to the converter units  52  is a pair of vacuum-operated, fuel lock filters  132 . Provided for use in conjunction with the fuel lock filters  132  is the balance line valve  128 , which is removed from the line connecting the air balance lines  58  to the air horn of the carburetor  34  and, instead, positioned within an air balance line  134  extending from the vapor fuel line  114  which connects the converter units  52  to the carburetor  34 . The fuel lock out filters  132  are fuel filter devices which prevent fuel flow unless a vacuum is applied to the device. When the valve  128  is open, a positive pressure exists in the system downstream of the fuel lock out filters  132  and results in a positive pressure being applied to the fuel lock out filters  132  so as to prevent fuel flow. Accordingly, fuel flow is permitted by closing the valve  128  so that the vacuum caused by air flowing through the carburetor  34  will be applied to the fuel lock out filters  132 . 
   The operation of the steam generator assembly  10  is thought to be clear from the foregoing description and is not reiterated here for the sake of brevity. Suffice it to say that the metering valve assembly  47  of the carburetor  34  acts to vary the amount of fuel metered into the carburetor in response to changes in the amount of air flow through the carburetor and that this air flow can advantageously be changed by varying the output of the of the air pump  40 . Therefore, over a given range, the firing rate of the burner is infinitely adjustable. 
   It is also an advantage that the process water used in cooling the steam generator body  12 , elbow  20  and burner head  16  is also used as a source of heated fluid that is routed through the converter units  52  so as to impart sufficient heat to vaporize the liquid propane since the heated water is close at hand requiring only short hoses for its routing and is heated at no extra expense. 
   Finally, the fact that the carburetor  34  and all of the components used in the fuel systems  100 ,  120  and  130  are off-the-shelf components used in the automotive industry is advantageous since it results in parts which are less expensive than if they had to be specially manufactured. It is here noted that all of the fuel control components described above may be purchased off the shelf from various vendors of which Impco Technologies, Inc. and Woodward are examples. 
   Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims. 
   ASSIGNMENT 
   The entire right, title and interest in and to this application and all subject matter disclosed and/or claimed therein, including any and all divisions, continuations, reissues, etc., thereof are, effective as of the date of execution of this application, assigned, transferred, sold and set over by the applicant(s) named herein to Deere &amp; Company, a Delaware corporation having offices at Moline, Ill. 61265, U.S.A., together with all rights to file, and to claim priorities in connection with, corresponding patent applications in any and all foreign countries in the name of Deere &amp; Company or otherwise.

Technology Classification (CPC): 5