Patent Publication Number: US-6712601-B2

Title: Low power starter for catalytic heaters

Description:
FIELD OF THE INVENTION 
     This invention relates to infrared catalytic heaters and, more particularly, to a preheater or starter for an infrared catalytic heater. 
     BACKGROUND OF THE INVENTION 
     Catalytic heaters employ a catalyst bed that results in flame-less combustion of the fuel and the creation of infrared energy. Since combustion is flame-less, these heaters may operate at a temperature that is lower than the ignition temperature of the fuel to the heater, which is typically natural gas or propane. Catalytic heaters are particularly well suited for applications desiring explosion proof operation, such as various applications involving the natural gas industry. In a typical catalytic heater, a catalyst bed is heated to a temperature of about 250° F. at which time a thermostat valve is opened so that the supplied fuel and oxygen form the desired reaction with the catalyst bed. 
     One method used to start the heater is to supply fuel to the back of the catalyst pad while heating a portion of the surface of the catalyst bed with a flame, such as shown in U.S. Pat. No. 5,993,192. After the reaction is established, the flame is removed. The open flame starting method is more dangerous than the electric heater starter and is not acceptable for use in many hazardous locations. 
     Infrared catalytic heaters normally require the catalyst pad or bed to be heated above the activity temperature of about 250° F. to start the catalytic reaction. A resistive electric heating element located between the catalyst pad and the insulation pad is commonly used to preheat the catalyst above the activity temperature. When the catalyst is hot enough, i.e., at or above the activity temperature, fuel enters the back of the heater while oxygen from the air is diffused through the front. When the oxygen and fuel converge in the catalyst, an oxidation reaction takes place resulting in a flame-less combustion and creating infrared energy. After the oxidation reaction begins, power to the electric heating element can be removed and the reaction will continue until either the fuel supply or the oxygen is eliminated. 
     A 6 inch by 6 inch square heater will typically use a 150 Watt, 0.30 inch diameter, heating element forming a 4 inch diameter circle between the catalyst pad and the insulating pad. Power is applied to the electric starter element for 15 to 20 minutes to preheat the catalyst pad. To start the 6 inch by 6 inch heater requires 37.5 Watt/hours (150 Watts×0.25 hours=37.5 Wh). If a 12 volt battery is used to power the starter, over 3 Amp/hours is used every time the heater is started (37.5 Wh/12 volts=3.12 h). Larger heaters will use more power because the starting element is larger. For example, a 24 inch by 36 inch heater made by CCI Thermal Technologies Inc. of Alberta, Canada, requires a 1200 Watt starting element. After the 15 minute warmup, propane or natural gas is supplied to the back of the heater at a controlled flow rate and the catalytic reaction begins. After the reaction is fully established, power to the starting heater is removed. 
     When infrared catalytic heaters are used in hazardous locations, such as gas pipeline equipment, the power source for the electric heating element must be located away from the catalytic heater and in a safe location. Typically the electric connections for the starter heater are made in an explosion-proof housing on the back of the heater and then conductors run through rigid conduit to the safe area which can be 25 feet or more away from the heater. Lowering the maximum output of the starter power source results in a smaller power source, and smaller wire and conduit to connect the power source to the heating element, thereby significantly reducing the installation cost and increasing safety, especially for the high power heaters. 
     The disadvantages of the prior art are overcome by the present invention, and a catalytic heater with an improved electrically powered starter and method of starting and controlling the catalytic heater as hereinafter disclosed. 
     SUMMARY OF THE INVENTION 
     In a preferred embodiment, the starter for the infrared catalytic heater utilizes a low cost, low power quartz-halogen lamp to preheat a small section of a catalyst pad to the activity temperature. Several unique features of the halogen lamp make it an efficient starter for the catalyst pad. The lamp envelope is small to reduce the amount of halogen gas required and reduce the cost of the lamp. The small envelope also keeps the tungsten element close to the lamp walls, thereby allowing high heat transfer to the envelope. The heating element is hermetically sealed inside the quartz envelope, thereby eliminating corrosion issues associated with conventional resistive elements. 
     The starter is preferably inserted into the side of the catalyst pad and spaced closer to the catalyst exterior face than to the front face of the insulation, so that the starter is surrounded by catalyst pad material. Only a small section of the pad need be preheated to the activity temperature for the catalytic reaction. After the reaction begins in the starter area, the heat generated by the exothermic catalytic reaction spreads across the catalyst pad and the startup is complete. Power to the starter is removed after partial catalyst activity takes place to maximize power savings. 
     The low power requirements of the quartz-halogen starter make it possible to include a small battery pack in an explosion-proof box near the heater for the starter power. This eliminates the long conductor wire and conduit run to the safe area for the starter power source, thereby enabling the heater to be a self-contained unit. 
     It is an object of this invention to provide a catalytic heater with an improved low power preheater or starter. 
     A further object of the invention is the provision of such a starter that heats a relatively small portion of the catalyst pad to the desired temperature in a minimum of time. Less than 2% of the flow through area of the pad preferably defines the perimeter area of the heating element, while in the prior art the perimeter area of the heating element was typically 50% or more of the catalyst pad flow through area. The cross-sectional of the heating element itself relative to the flow through area of the pad is also very small, and preferably is less than 2% of the flow through area of the catalytic pad. The wattage for the electrically powered heating element is low relative to the wattage of prior art catalytic starters, and according to the present invention is less than 15 watts regardless of the flow through area for the catalytic pad. 
    
    
     These and further objects, features, and advantages of the invention will be apparent from the following specification, wherein reference is made to the figures in the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of one embodiment of a catalytic heater with an electronically powered starter according to the present invention; 
     FIG. 2 is a schematic view of a catalytic heater system for controlling the operation of the catalytic heater and electronic starter shown in FIG. 1; 
     FIG. 3 is a schematic view of a modified catalytic heater system for controlling the operation of the catalytic heater and electronic starter shown in FIG. 1; 
     FIG. 4 is a schematic of a further modified catalytic heater system for controlling the operation of the catalytic heater and electronic starter shown in FIG. 1; and 
     FIG. 5 is a front view of the flow through area of the catalyst pad, illustrating the size of the starter relative to the pad flow through area. 
     FIG. 6 is a graph illustrating the warmup time for a catalyst pad starter according to the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring FIGS. 1 and 2, a catalytic heater  10  includes a generally rectangular enclosure or housing  11  having opposed left and right sidewalls  12 , and opposed upper and lower walls  14 . The enclosure includes a rear wall  18  to form a compartment having a generally open front face  20 . A rectangular front frame  22  fits about walls  12  and  14  and defines the perimeter of the open front face  20 , i.e., the flow through area of the catalytic pad. A screen  24  typically fits inside frame  22 . A rear channel-shaped plate  28  fits against rear wall  18  and has perforations  30  therein. A chamber  32  is thus formed between rear wall  18  and plate  28 . 
     Fitting between front screen  24  and rear screen  28  are the generally rectangular-shaped catalyst pad  34  and an insulation panel or pad  36 . The catalyst pad  34  typically engages the front screen  24  on its front side, and engages the insulation pad  36  on its rear side. The rear side of the insulation pad typically engages the rear plate  28 . Insulation or diffusion pad  36  may comprise a ceramic fiber blanket, and serves to diffuse the fuel gas across the flow through area of the catalytic pad. 
     A fuel gas, either natural gas or propane, is supplied through tubing line  40  to chamber  32  from a fuel storage tank  44 , which alternatively may be a pipeline. Tubing line  40  has a tubing fitting  48  and is connected by lock nuts  46  to rear wall  18 . Valve  42  controls the flow of fuel gas to chamber  32 , with the fuel gas being supplied at a regulated pressure and flow rate to chamber  32  from fuel storage tank  44  by the valve  42 . The pressure of the fuel gas typically increases in chamber  32  and flows evenly through openings  30  in perforated plate  28 . Insulation pad  36  distributes the fuel gas evenly across the catalyst pad  34 . Oxygen from ambient air passes through screen  24  from open front  20  and enters catalyst pad  34 . This catalytic reaction produces a flame-less heating, as described in U.S. Pat. Nos. 5,037,293 and 5,993,192. 
     The starter  48  for preheating catalyst pad  34  prior to the supply of fuel gas as illustrated in FIGS. 1 and 2 is a quartz-halogen lamp, although the starter may be formed of a small resistive wire element to preheat a small section of catalyst pad  34  above the activation temperature. Catalyst pad  34  conventionally has four sides  52 . A pocket  70  is formed having an entrance opening in a side  52  of pad  34 . The pocket entrance opening may be provided in the bottom side of the catalyst pad  34 , or in the right side, left side, or top side of the pad, depending on the position of related equipment to the enclosure. Pocket  70  preferably is spaced from insulation pad  36 , and is thus positioned entirely within the catalyst pad. A majority of the pocket  70 , preferably at least 90% of the pocket  70 , and most preferably all of the pocket  70  is thus within the catalyst pad. Starter  48  is then positioned within pocket  70  in catalyst pad  34  and is surrounded by catalyst pad  34  while being spaced from insulation pad  36 . 
     Starter  48  may be supported by a base or socket  50  mounted on wall  14 . For best results, starter  48  may be spaced at least about 0.05 inches and preferably about 0.1 inches from the front face of insulation catalyst pad  36 . As shown in FIG. 1, the starter extends from one wall (lower wall toward the opposing wall (top wall) a spacing of less than ⅓ the opening between the opposing walls, and preferably a spacing of less than 20% of the spacing between the mounting wall for the starter and the opposed wall. 
     Starter  48  is a quartz-halogen lamp with electrical wires  56  and  58  powering a resistive element  60 . Heating element  60  is hermetically sealed inside a quartz envelope  54  to eliminate corrosion. Power from battery  62  flows through closed switch  64  and wire  56  to starter  48  and back to battery  62  through wire  58 . Pocket  70  may be of a generally cylindrical shape and may have a width less than about 80%, and preferably about 60%, of the thickness of pad  34 . It should be understood that the pocket  70  may be formed simply by inserted the bulb  48  into a conventional catalyst pad having a uniform thickness, so that the insertion of the bulb  48  slightly increases the thickness of the pad adjacent the bulb. It is thus not necessary to preform a pocket in the catalyst pad prior to inserting the lamp to the position shown in FIG.  1 . 
     A quartz-halogen lamp is a low power, low cost element which may be used to preheat a small section of catalyst pad  34  to the activity temperature normally about 250° F. Several styles and sizes of quartz-halogen lamps and high temperature lamp sockets are readily available. An example of an acceptable quartz halogen lamp is part number Q5T3/CL from GE Lighting. A suitable socket is part number 27-07 from Leecraft Lighting Company. 
     Since starter  48  may be surrounded by catalyst pad  34 , the catalytic reaction spreads across catalyst pad  34  beginning in the area adjacent starter  48  for fully heating catalyst pad  34  and thereby complete the preheating of pad  34 . The catalyst pad  34  may be heated to the oxidation activity temperature of 250° F. in less than 60 seconds with the entire 6 inch×6 inch pad fully active in less than 3 minutes. Valve  46  is then opened (or may be opened any time after the starter  48  is activated) to start the flow of fuel gas to heater  10 . Fuel gas enters rear chamber  32  from line  40  and oxygen enters the open face of heater  10  through screen  24 . The oxidation reaction will begin when the catalyst pad temperature  34  is heated above 250° F. by starter  48 . After the oxidation reaction begins, switch  64  can be opened to remove power from starter  48 . The preheating of catalyst pad  34  spreads the oxidation reaction across the entire surface of catalyst pad  34  to fully start heater  10 . 
     Fully heating the catalyst pad before supplying fuel reduces the amount of unburned hydrocarbons during startup, but is not necessary to reliably start the reaction. Catalytic heaters must be well vented to exhaust unburned fuel and supply new oxygen to the catalyst. For every square foot of heater surface area, 60 cubic feet per hour of air supply is required to sustain the reaction. The small amount of unburned fuel is vented with the other exhaust gases during warmup as fresh air replenishes oxygen to the catalyst. 
     Using a 10 Watt quartz-halogen starter, the catalyst pad may be heated to the activity temperature (250° F.) in less than 60 seconds and the entire 6 inch×6 inch pad is fully active in less than 3 minutes. The graph as shown in FIG. 6 illustrates the warmup time in seconds required for heating the catalyst pad starter to a specified temperature. As shown in FIG. 6, the catalyst pad reaches the 250° F. activity temperature in about 50 seconds. 
     Starter power required to start the 6 inch×6 inch heater is (10 Watts×0.05 Hours=0.5) 0.5 Watt/hours. Using a 12 volt power source which provides (0.5 Wh/12V=0.04 Ah) 0.04 Amp/Hours for the 6 inch×6 inch heater, the quartz-halogen starter requires 0.5 Watt/hours, compared to 37.5 Watt/hours for the resistive element starter. Startup time is reduced from 15-20 minutes to 2-3 minutes. A quartz-halogen lamp of less than about 15 watts should be sufficient for most applications, and a lamp sized to receive less than 10 watts of power is desired for many applications. 
     A small 12 volt 1.3 Ah lithium battery pack could be used to supply enough power to start a heater with a 6 inch×6 inch catalyst pad over 30 times. The same starter will work for heaters with larger catalyst pads. Larger heaters will take longer for the catalyst activity to propagate throughout the pad during startup, and initially have more unburned hydrocarbons. Full activity startup time for larger heaters may be improved by using multiple starters spaced evenly around the catalyst pad. Multiple starters also add redundancy to the starter system thereby allowing the heater to start if one or more of the starters fail due to a burned out element. 
     While the preferred starter is the quartz-halogen lamp, a small low power, resistive element heater, e.g., 5 to 10 watt, may provide acceptable performance. The quartz-halogen starter is more readily available, can be easily mounted and serviced, and is low cost. In high volume applications, a custom resistive cartridge heater may become cost competitive. 
     As a result of having starter  48  mounted entirely within catalyst pad  34  and surrounded by catalyst pad  34 , a large catalyst active area is heated faster to decrease the startup time. It is necessary only to preheat the catalyst pad  34  as it is not necessary to preheat insulation pad  36 . Since pocket  70  is arranged entirely within catalyst pad  34 , maximum utilization of the heating energy from starter  48  is obtained. It may be desirable in some instances to have more than one starter  48  for catalyst pad  34  in the event of failure of a starter, e.g., such as a burned out element. 
     It is a particular feature of the present invention that the size of the starter  48  is substantially reduced compared to prior art starters. A conventional starter for a catalyst pad is typically in the form of a open ended loop which effectively defines a perimeter area of the heating element. A resistive heating element could have other configurations, but regardless of the configuration of the heating element, the heating element forms a generally circular, oval, or rectangular shaped perimeter which defines the outer boundary of the heating element. For most prior art applications, this perimeter size of the heating element is more than 50% of the cross-sectional flow through area of the catalyst pad, and in many applications is at least 60% of the catalyst pad flow through area. FIG. 5 shows the size of a starter  48  according to the present invention relative to the open front face  20 , which is the flow through area for the catalytic pad. FIG. 1 discloses the concept of the present invention, but the size of the starter  48  is not to scale with the size of the enclosure. FIG. 5 shows the starter at the same scale as the frame  22 . The frame  22  thus defines the boundaries of the flow through area of the catalyst pad, which typically extends outward from the edges of the frame  22  to substantially the side walls of the closure  11 . According to the present invention, the electronic starter  48  has a cross-sectional area less than 2% of the flow through area  20 , and many applications will be less than about 1% and may be 0.5% or less of the flow through area. Turning now to a discussion of the actual cross-sectional area of the heating element relative to the flow through area  20 , the prior art heating elements generally had a cross-sectional area of about 10% of the flow through area. According to the present invention as discussed above, the cross-sectional area of the heating element typically would be less than 2% of the flow through area. 
     FIG. 3 discloses a control system  80  for heater  10  which is similar to the control system of FIG. 2, except for the elimination of manual switch  64  and substitution of an automatic timer  72 . A pushbutton  74  is provided for starting timer  72 . To start preheater or starter  48 , pushbutton  72  is pressed and released. The electronic timer circuit in timer  72  closes the power circuit between battery  62  and leads  56  and  58 . Gas valve  42  may be manually opened to supply fuel to catalyst pad  24 . After a delay of about 2 or 3 minutes, timer  72  is stopped automatically to open the power circuit and stop the supply of power to starter  48 . 
     A further embodiment of the starter control system  82  is shown in FIG.  4 . Fuel gas is supplied by fuel supply  44  through line  40  to heater  10 . Electronic lines  84  and  86  extend from starter controller  88  to solenoid operated valve  42 . A temperature sensor  90  for sensing the catalytic reaction is connected to the controller  88  by lines  92  and  94 . Battery  62  supplies power to controller  88  and to starter  48  through lines  56  and  58 . 
     In operation, pushbutton  74  is pressed to apply power to solenoid valve  42  for opening valve  42  for the supply of fuel gas to heater  10 . Power is simultaneously provided to starter  48  through lines  56  and  58 . When temperature sensor  90  senses that the catalytic reaction has been started, power to starter  48  is stopped. Temperature sensor  90 , which alternatively may be a thermocouple, is also effective to detect when the catalytic reaction is no longer occurring. When the catalytic reaction ceases as sensed by temperature sensor  90 , starter controller  88  is effective to close solenoid operated valve  42  and stop the flow of fuel gas to heater  10 . 
     Another embodiment of a starter control system includes a manually operated fuel valve  42  with a thermocouple connected thereto heated by the catalyst pad of the heater. The fuel valve  42  is manually held in an open position until the thermocouple is heated by the catalyst pad to a predetermined temperature sufficient to produce the power required to maintain the valve in an open position. An electric switch for the fuel valve provides power to the starter  48  through a controller when the fuel valve is manually actuated. If the catalytic reaction stops and heater  10  cools, power from the thermocouple is reduced to close valve  42  for shutting off the fuel supply to heater  10 . 
     From the above, it is apparent that a starter has been provided which is utilized for preheating only a small portion of catalyst pad  34 . Starter  48  is preferably a relatively small device such as a quartz-halogen lamp having a resistive wire element which is effective for preheating a small portion of the catalyst pad  34  above the activation temperature which may be about 250° F. Starter  48  is inserted within a side of the catalyst pad  34 , which surrounds the starter to provide a fast startup time. 
     Various control systems may be utilized for providing power to the starter and to the heater as exemplified by the starter control system embodiments shown in FIGS. 2-4. A small, low power, starter substantially surrounded by the catalytic pad has been found to be highly effective in preheating a relatively large portion of the catalytic pad. 
     It will be appreciated that various modifications can be made in the design, construction and operation of the present inventions without departing from the spirit or scope of such inventions. Thus, while the principal preferred construction and mode of operation of the inventions have been explained in what is now considered to represent their best embodiments, which have been illustrated and described herein, it will be understood that within the scope of the appended claims, the inventions may be practiced otherwise than as specifically illustrated and described.