Patent Publication Number: US-2012024498-A1

Title: Fluid Recirculating Economizer

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of US. Provisional Application Ser. No. 61/368,767 filed on Jul. 29, 2010, currently pending. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to furnace and boiler flue-gas economizers, and more particularly, this invention relates to a system of recovering flue effluent heat within a closed loop to equalize the temperature of a fuel line. 
     2. Background of the Invention 
     Furnaces or boilers combust fuel to melt ore, heat air, dry wood, or cook food. These activities generate high-temperature effluent, such as flue gas. This effluent contains wasted heat energy. 
     “Economizers” attempt to re-capture heat from effluent. 
     For example, U.S. Pat. No. 1,795,909 to Brunt et. al. describes a series of complicated flue-gas passages, dust catching channels, and other convoluted physical structures designed to pre-heat air. The &#39;909 patent relies on these structures to transfer heat from the flue gas to cold air. Consequently, Brunt uses a number of complex heat sinks. Further, Brunt admits that “dust-catching” means are required for particulate, inasmuch as build-up around the heat-sinks is a problem. 
     Another economizer is shown in U.S. Pat. No. 4,318,366 to Tompkins. This economizer includes dispersal of heat-trapping fluid in the flue-gas. However, the Tompkins system requires strict control of the temperature of flue-gas at several points, as well as single use and strict control of the temperature of the heat-trapping fluid. 
     A need exists in the art for a flue-gas economizer which is not complicated in design. The economizer should rely on inexpensive heat trapping media which is automatically recycled after it absorbs and releases energy. The heat trapping media should be the only moving element throughout the economizer. 
     SUMMARY OF INVENTION 
     An object of the present invention is to provide a device which eliminates many of the drawbacks of state of the art heat economizer systems. 
     Another object of the invention is to provide a means to extract and recycle heat from combustion effluent that would otherwise be released into the atmosphere. A feature of the invention is a heat exchange region in which reusable fluid transfers heat, via thermal conductance, from flue gas and then eventually to fuel. An advantage of the invention is that the fluid is not in fluid communication with the fuel, and as such, neither contaminates, nor is contaminated by, the fuel. 
     Still another object of the invention is to maximize the efficiency of a boiler or a furnace charged with gas or liquid fuel. A feature of the invention is the use of a completely separate device to transfer heat energy from combustion flue-gas (which is generated by the boiler or furnace) to pre-combusted fuel so as to preheat the fuel. An advantage of the invention is that the preheated fuel feature increases the efficiency of the boiler or furnace as compared to if the fuel was not preheated 
     Yet another object of the present invention is to provide a flue-gas economizer which recycles heat exchange fluid. A feature of the economizer is that the heat transfer fluid is reused and confined within a recirculation loop so as not to contaminate or clog other aspects of the combustion system, such as fuel supply lines or effluent stacks. An advantage of the invention is that the economizer works independently of boilers, furnaces, and internal combustion devices generally. 
     A further object of the invention is to transfer energy from a heat exchange fluid to a pre-combusted fuel fluid. A feature of the invention is a jacket encircling a fuel gas line, where the jacket is adapted to receive the heat exchange fluid. An advantage of the invention is that it maximizes the surface area of contact between the fuel conduit line and the heat exchange fluid (thereby allowing for high rates of flow of heat exchange fluid) while preventing direct physical contact of the fuel to the heat exchange fluid. 
     Another object of the invention is to collect heat from large volumes of effluent emanating from a combustion process. A feature of the invention is that heat transfer occurs without constraining the volume of the effluent or increasing back pressure to the combustion process gas. An advantage of the invention is that it may be used in conjunction with high-pressure boilers and furnaces which expel large quantities of flue gas. 
     Yet another object of the invention is to increase the temperature of a fuel line before a change in fuel pressure. A feature of the invention is that it can be used to heat a fuel line before or after a reduction in fuel pressure. An advantage of the invention is that it is separate from a combustion system such that it can be situated intermediate the combustion system and the fuel supply line undergoing a pressure change. Another advantage is that residual heat from a combustion system can be utilized by the invention to prevent fuel lines from freezing. 
     Another object of the invention is to facilitate cleaning of the economizer. A feature of the invention is that a cleaning cycle may be operated to rid the system of waste product. An advantage of the invention is that the cleaning cycle may be operated at any time, even when the underlying boiler or furnace is operating. 
     Another object of the invention is to provide an economizer which may be used in conjunction with a natural draught burner. A feature of one embodiment of this invention is that a fan is used to create a pressure differential within the system. An advantage of the invention is that the burners of the natural draught burner are provided with sufficient air to support combustion. 
     A further feature of the invention is to provide an economizer where the life-span of any fan used within the system is maximized. A feature of one embodiment of the invention is that the fan does not contact any fumes. An advantage of the invention is that the lifespan of the fan is maximized inasmuch as the fan is not exposed to a caustic environment. 
     Yet another object of the invention is to provide an economizer which may be used with any kind of boiler or furnace without modifying the furnace. A feature of one embodiment of the invention is an air induction fan may be located at several alternate sites depending on the type of boiler attached thereto, removing the need to induce an air draught within the boiler itself. An advantage of the invention is that it does not require the addition of an air inducer into the furnace, by creating a stand-alone air induction unit within the economizer. 
     Briefly, the invention provides a flue gas heat recovery device comprising: a packing tower adapted to receive a flue gas stream; wherein said packing tower contains at least one water inlet, a water collection reservoir and a packing tray positioned intermediate said water inlet and said reservoir; a fuel conduit in thermal communication with the reservoir, wherein the fuel conduit has a first end in close spatial relationship to a distal end of said reservoir, and a second end in close spatial relationship to a fuel output; and a fluid conduit having a first end in fluid communication with an exterior surface of the fuel gas line and a second end in fluid communication with said water inlet. 
     The invention also provides a method for recovering heat from flue effluent, the method comprising contacting the effluent with a heat transfer fluid for a time sufficient to transfer heat from the effluent to the heat transfer fluid; transferring heat from the now heated heat transfer fluid to a fuel gas so as to heat the gas and cool the heat transfer fluid; combusting the now heated fuel gas which leads to the production of additional flue effluent; and repeating the process using now cooled heat transfer fluid and additional flue effluent. 
    
    
     
       BRIEF DESCRIPTION OF DRAWING 
       The invention together with the above and other objects and advantages will be best understood from the following detailed description of the preferred embodiment of the invention shown in the accompanying drawings, wherein: 
         FIG. 1  depicts a cut-away side view of an economizer, in accordance with features of the invention; 
         FIG. 2  is a view of  FIG. 1  taken along lines  2 - 2 ; 
         FIG. 3  is a cut-away side view of an alternate embodiment of an economizer, in accordance with the features of the invention; 
         FIG. 4  is a detailed view of  FIG. 3  area  4 - 4  of one embodiment of the invention; 
         FIG. 5  is a cut-away side view of another alternate embodiment of an economizer, in accordance with the features of the invention; and 
         FIG. 6  is a detailed view of  FIG. 5  area  6 - 6  of one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. 
     Turning to  FIG. 1 , the device  10  broadly comprises a packing tower  30 , disposed in a generally vertical position, and a heat transfer jacket  64  in fluid communication with said packing tower  30 . In the embodiment shown, the heat transfer jacket  64  is positioned at approximately a 90 degree angle to the packing tower so as to be disposed in a generally horizontal direction. A recirculation pump  50  is connected to said heat transfer jacket  64 . 
     Hot exhaust generated from a combustion process occurring in a furnace or boiler is directed to a first end  34  of the packing tower  30 . While the packing tower  30  is filled with hot exhaust, a heat transferring fluid enters the second end (in this embodiment the top end)  35  of the packing tower  30  so as to be gravity-fed towards the first end  34  of the packing tower  30 . As the heat transferring fluid traverses downwardly through packing media  32  positioned intermediate the first and second ends of the tower, the temperature of the heat transfer fluid is increased as it cools the hot exhaust permeating upwardly from the first end  34 . 
     Upon draining or otherwise exiting the packing tower  30  through a means of egress or tower to jacket connection point  52 , the heat transferring fluid enters and substantially fills the volume defined by an annular space created by an outer skin  63  of a heat jacket  64 , and an exterior surface of a fuel conduit or line  66 . This facilitates transfer heat from the now heated fluid to fuel traversing the conduit  66 . Following traversal of the heat jacket  64 , the now cooled heat transferring fluid is pumped by the fluid or recirculation pump  50  back to the second end  35  of the packing tower  30  to be re-circulated through the packing tower  30  which contains tower packing media  32 . 
     Packing Tower Detail 
     In one embodiment, the packing tower  30  comprises a cylindrical structure, although other shapes are envisioned. In one embodiment, the packing tower is the vertical exhaust or smoke stack of a production environment or the portion of a vertical smoke stack. 
     The second end  35  of the packing tower  30  incorporates an exhaust aperture  36 . In the embodiment shown in  FIG. 1 , said exhaust aperture  36  is open to the atmosphere. Exhaust aperture  36  may further incorporate one or more means of attaching exhaust handling devices, such as particulate scrubbers, negative pressure means, such as exhaust fans, and the like (not shown) for downstream processing of exhaust. 
     The interior of the packing tower  30  contains a plurality of packing media  32 . Said packing media  32  is disposed between the first and second ends of the packing tower  30 . In one embodiment, the shape of said packing media is mostly cylindrical and/or other hollow geometric shapes with stamped protrusions on the inside. The stamped protrusions allow for maximum heat exchange between the packing media, the effluent permeating upwardly through the media and the heat transfer fluid permeating downwardly through the packing media. In one embodiment, the packing media elements are metallic in construction, having a diameter of about 1″ and being approximately 1.25″ tall. However, other sizes are envisioned to maximize heat transfer and control back pressure. In one embodiment, the packing media  32  is placed on a fabricated packing tray  37  made from expanded metal, which is sheet metal having diamond-shaped holes stamped there through leaving a grid of approximately ⅛ inch of material remaining. The size of the apertures formed in the expanded metal tray is selected so as to prevent packing media  32  from falling through said apertures. 
     The packing media  32  is designed to provide maximum surface area for heat exchange fluid to contact the packing media  32 . The maximum surface areas also allow the packing media  32  to transfer heat from the hot exhaust inasmuch as maximum surface area increases the time that both exhaust and heat exchange fluid contact the packing media  32 . However, the packing media  32  are not so dense as to inhibit the transit of the hot exhaust through the packing tower  30 . In one embodiment, the packing media  32  weighs 13 pounds while dry. The weight and quantity of packing media is selected to compensate for pressure loss and to optimize heat transfer. Further, the packing media is arranged such that heat exchange fluid does not pool or collect in any typographical features of the packing media  32 . 
     A heat exchange fluid nozzle  40  is disposed between the second end of the packing tower  30  and the packing media  32 . In the embodiment of the device depicted in  FIG. 1 , the nozzle  40  is disposed in the middle of a horizontal plane which runs parallel to the exhaust aperture  36 , so as to facilitate downward projection of the heat transfer fluid (such as water) onto the packing media  32 . 
     In another embodiment, not shown, the nozzle  40  is attached to the side of the wall of the packing tower  30  such that the nozzle is not adversely affected by the hot exhaust traversing the packing tower  30 . In yet another embodiment, also not shown, more than one nozzle is employed. 
     During operation of the device  10 , heat exchange fluid (such as water) exits the nozzle  40  and percolates downwardly through or otherwise traverses the packing media  32 . In the embodiment shown in  FIG. 1 , the heat exchange fluid is propelled by the application of pressure and also by action of gravity. In other embodiments, the heat exchange fluid is propelled solely by action of pressure. In yet other embodiments, only gravity is responsible for the percolation. 
     Disposed between the first end of the packing tower  30  and the packing media  32  is the hot exhaust inlet  20 . In one embodiment, the hot exhaust inlet  20  is in fluid communication with the headspace of a combustion chamber, such as those chambers found in furnaces and boilers. As such, the inlet serves as a means of ingress of combustion effluent into the device  10 . While in some embodiments of the invention, the device  10  is connected to immobile devices such as large-scale boilers, in other embodiments, the hot exhaust inlet  20  connects to a temporarily-installed device, such as a generator. 
     Positioned superior from the hot exhaust inlet  20  is a gas and fluid permeable packing tray  37 . Said packing tray  37  suspends and otherwise holds packing media  32  in place above the region of the tower receiving the hot flue gas. As such, the tray suspends the media above the head space. The hot exhaust is therefore in contact with packing media immediately upon entering the packing tower  30 . 
     In one embodiment, the internal surfaces  38  of the packing tower  30  are substantially smooth. In another embodiment, the internal surfaces  38  of the packing tower  30  define a series of corrugations or channels designed to maximize the heat transfer characteristics of the said tower walls. The channels further provide a means for anchoring the packing media  32 . 
     In one embodiment, the exterior of the packing tower  30  is insulated to prevent heat loss to the outside environment. 
     Finally, at the first end of the packing tower  30 , the tower to jacket connection point  52  forms a heat transfer fluid exit conduit which provides the drainage means or other fluid egress means to facilitate removal of heat transfer fluid from the tower to the heat transfer jacket  64  described below. 
     Transfer Jacket Assembly Detail 
     The transfer jacket assembly comprises a sleeve or jacket  64  encapsulating, a fuel line  66 . Specifically, the transfer jacket  64  resembles a tube radially displaced around a fuel conduit such that longitudinally extending portions thereof encircle or otherwise encase exterior surfaces of the fuel line  66  to form an annular space. The encasement of the fuel line  66  results in a void defined by the annular space, a fluid means of ingress (which is the heat transfer fluid exit conduit or tower to jacket connection point  52 ) situated at a first end of the void and a fluid means of egress (such as a connection conduit to pump inlet  56 ) situated at second end of the void. Further, in one embodiment of the invention, the exterior of the transfer jacket  64  is insulated so as to prevent heat loss to the external atmosphere. However, the external surface of the fuel line  66  is not insulated allowing for heat exchange between the interior of the transfer jacket  64  and the interior of the fuel line  66 . 
     In one embodiment, the fuel line  66  is downstream of a fuel distribution network. In such a network (not shown) large quantities of fuel are sent over long distances using high-pressure transmission pipes. In one embodiment, such high pressure pipes contain fuel gas at 1200 psi. Upon reaching an end point of the network, such as a township, or a private user such as an industrial facility, the fuel gas line pressure is lowered to a pressure (e.g., 80 psi) suitable for end users. If the fuel gas line is not heated before the change in pressure, the fuel line would freeze once the pressure is decreased. In this embodiment, the fuel line  66  is positioned in close spatial relationship to that portion of the distribution network that subjects the fuel to depressurization so that the flange is adapted to receive or mate with a valve (not shown) separating the high pressure line from the fuel line  66 . 
     In another embodiment, not shown, the fuel line  66  receiving heat within the transfer jacket  64  is the high-pressure transmission pipe prior to the decrease in pressure. Inasmuch as the fuel in the high-pressure line receives the heat from the heat transfer jacket, upon decreasing pressure, the lower pressure line is not liable to freeze. However, in this embodiment, the high-pressure transmission pipe must be designed to withstand not only the high-pressure fuel, but also the heated high pressure fuel which increases the pressure within the high-pressure line. 
     Finally, in further embodiments, the fuel line  66  is the upstream line side of the heater, and alternatively on the downstream line side of the heater. 
     In one embodiment, a first end or fuel output end  60  of the fuel line  66  is connected to a fuel-using device such as a furnace or a boiler. A second end or fuel input end  62  of the fuel line  66  is connected to a distribution line, or a still pressurized municipal gas supply or a fuel tank (not shown). The device  10  is capable of using any fuel, so long as the fuel may be conveyed in a fuel line, such as the fuel line  66  depicted in  FIG. 1 . The fuel must be of a type capable of being heated safely via thermal conductance and without significant expansion so as to rupture the fuel line  66 . Fuels that have been safely used with this system include liquefied petroleum gas, methane, propane, butane, and higher carbon fuels which are liquids. 
     Inasmuch as in one embodiment, fuel is consumed at the first end  60  and originates at the second end  62 , the fuel moves towards the first end  60  and away from the second end  62 , which is the direction shown by the arrow gamma (“Γ”) in  FIG. 1 . 
     The heat transfer jacket  64  comprises two ends, a first end and a second end, which correspond to the two ends  60 ,  62  of the fuel line  66 . However, in at least one embodiment, the heat transfer jacket  64  does not completely encapsulate the fuel line  66  and therefore a gap exists between the first end of the fuel line and the first end of the jacket (as well as the second end of the fuel line and the second end of the jacket) wherein the fuel line  66  remains exposed. Such a gap allows for direct manipulation of the fuel line  66  and facilitates the connection of the fuel line  66  to either a furnace or a fuel source. 
     The heat transfer jacket  64  is connected to a depending end of the heat transfer fluid exit conduit  52 , which as discussed supra resides inferior to the packing tower  30 . Proximate to the second end of the transfer jacket  64  is a pump inlet  56 . The pump inlet  56  connects the interior of the heat transfer jacket  64  to a recirculation pump  50 . The recirculation pump  50  applies negative pressure on the inlet  56 . 
     Consequently, heat transfer fluid is drawn from the second end  35  of the packing tower, through the heat transfer fluid exit conduit  52 , and to the pump inlet  56 . Therefore, as shown in the embodiment of  FIG. 1 , the heat transfer fluid will travel in the direction depicted by arrow omega (“Ω”). 
     Inasmuch as the direction of the fuel “r” is opposite of the direction of the transfer fluid flow “Ω” the amount of time that fuel will be in thermal communication with (separated only by a wall of the fuel line  66 ) the temperature transfer fluid will be maximized. 
     The packing tower  30 , transfer jacket assembly, and the recirculating pump  50  are connected through a series of conduits or piping described below. 
     Connection Detail 
     The second end  65  of the heat transfer jacket  64  is in fluid communication with the second end  35  of the packing tower  30 . The first end  34  of the packing tower  30  is in turn connected to the first end of the heat transfer jacket  64 . Consequently, the packing tower  30  and the heat transfer jacket  64  define a continuous loop to facilitate cycling of the heat transfer fluid. 
     Heat transfer fluid such as water is introduced at the recirculation pump  50 . Heat transfer fluid exits the recirculation pump  50  through the pump outlet  58  to be fed under pressure to the second end  35  of the tower. The pump outlet  58  is in turn connected to one end of external fluid conduit  46  which lies external to the tower  30 . The heat transfer fluid then traverses the external conduit  46  to reach the second end of the packing tower  30 . The external conduit  46  can take any shape such that the device  10  can be adapted to operate with any furnace and stack combination. However, in the embodiment shown in  FIG. 1 , the external conduit  46  includes one or more conduit connectors  48 , which allow the conduit to closely follow the shape of the remaining components. In other embodiments, not shown, the external conduit  46  comprises a flexible hermetically sealed passageway. Said external conduit  46  need not be made from a heat resistant material. 
     The external conduit  46  joins an internal conduit  42  at a conduit junction  44 . The internal conduit  42  is exposed to hot exhaust found within the packing tower  30 . Depending on the type of fuel being burned, the hot exhaust may be caustic. Consequently, while the external conduit  46  need not be heat and corrosion resistant, preferably, the internal conduit  42  comprises a material that is both heat safe and not subject to corrosion. The internal conduit  42  terminates in the one or more nozzles  40 , described above, or other fluid dissemination means, said means proximate the second end of the packing tower  30 . 
     The first end (in this embodiment, the depending end) of the packing tower  30  terminates in the tower to jacket connection point  52 . A tower to jacket connection valve  54  is disposed on the heat transfer fluid exit conduit  52  between the first end of the packing tower  30  and the heat transfer jacket  64 . 
     The opposite end of the heat transfer jacket  64  is connected to the pump inlet  56 . Consequently, once introduced in the system, heat transfer fluid will circulate same, except for loss through the exhaust aperture  36 , when some of the heat transfer fluid is spirited away or otherwise removed by venting exhaust fluid such as cooled flue gas. 
     While the heat transfer fluid is intended to recycle through the device  10 , the system may enter a state when excess fluid is circulating through the system causing a build-up of pressure within the tower. As shown in  FIG. 2 , a region of the tower interior near the packing tray  37  defines a secondary outlet  80 , which functions as an overflow valve. Excess heat transfer fluid that cannot be accommodated by the tower to jacket connection point  52  will exit the system through the overflow valve. While in the embodiment shown, the secondary outlet  80  is shown to be open to the external environment, in other embodiments not shown, the secondary outlet  80  is connected to a collection container for disposal. Further, the heat transfer fluid exiting the secondary outlet  80  may be measured, and the measurement may be used to control the rate of flow of the recirculation pump  50 . In instances where the heat transfer fluid is exiting the secondary outlet  80 , the recirculation pump throughput is lowered or the pump may even be turned off to maximize heat transfer between the combustion effluent and the temperature transfer fluid. The secondary outlet also serves as a means of egress for liquid products of combustion or condensed products of combustion to exit the economizer. The secondary outlet  80  also allows excess moisture to exit the system. The temperature of the exhaust of the heater may be lowered enough for the moisture within the exhaust to condense and so additional water will be introduced in the tower beyond what was used to transfer heat from the exhaust. Nonetheless, the secondary outlet  80  should not result in emptying of the tower from all liquid such that and the economizer should stay substantially full of heat transfer fluid during its operation, such that secondary outlet  80  serves as the full-point of the device 
     The device  10  further includes a means to hermetically connect the furnace or boiler to the device  10 . As shown in  FIG. 2 , the device includes a furnace inlet joining plate  82  and a fuel output join plate  88  which allow the device to be removably connected to the furnace or boiler at the first end  60  of the fuel line  66 . The outward surfaces of the join plates  82  and  88  are designed to matingly receive opposing flange surfaces of the furnace exhaust connections and fuel inlet connections. 
     Operation Detail 
     In operation, at the start of the cycle, the heat transfer fluid is introduced into the recirculation pump  50 . In one embodiment, the hot exhaust is introduced only once the tower is filled with the cooling liquid. The fluid is added so that it reaches the tower secondary outlet  80 . In this embodiment, the water exiting the secondary outlet  80  signals the filling of the tower. In other embodiments, water continues to be added to the tower until a level-indication float (not shown) is triggered. Other embodiments are capable of functioning in “off duty” cycles where the cooling tower is not filled with water. 
     In one embodiment, the heat transfer fluid is water; however, other fluids may be employed and are selected to transfer heat efficiently from the exhaust passing through the packing tower  30 . Such fluids can comprise substances with boiling points lower or higher than water. 
     Upon the introduction of the heat transfer fluid, the external conduit  46  is pressurized such that the fluid traverses the internal conduit  42  to charge the nozzle  40 . In one embodiment, the external conduit is pressurized to 5 psi. While other pressures are possible and strict pressure control is not necessary, the external conduit should not exceed 30 psi of pressure. In one embodiment, the heat transfer fluid then exits the nozzle  40 . In another embodiment, the nozzle  40  incorporates a heat sensor, such that heat transfer fluid does not exit the nozzle  40  until the hot exhaust contacts the nozzle  40 . 
     Concurrently with the heat transfer fluid traversing the internal conduit  42 , hot exhaust enters the device  10  through the hot exhaust inlet  20 . The hot exhaust permeates the packing tray along with the packing media  32  held by the packing tray, and the exhaust moves upwardly towards the exhaust aperture  36  and away from the hot exhaust inlet  20 . In one embodiment, the hot exhaust entering the device  10  through the inlet  20  ranges in temperature from approximately 200 degrees Celsius to 480 degrees Celsius. As the hot exhaust contacts the packing media  32 , the hot exhaust transfers some of its heat energy to the packing media  32 . 
     Further cooling of the hot exhaust occurs when the hot exhaust contacts the heat transfer fluid exiting the nozzle  40  as the hot exhaust approaches the nozzle  40 . The heat transfer fluid further decreases the temperature of the packing media  32 . 
     Due to this heat exchange, the hot exhaust experiences a temperature decrease of as much as 90% before venting through the exhaust aperture  36 . Inasmuch as the heat transfer fluid captures the heat from the hot exhaust, in one embodiment, the heat transfer fluid&#39;s temperature increases to approximately 65 degrees Celsius as the heat transfer fluid reaches the packing tray  37 , having exited the nozzle  40  and moved through the packing media  32  and packing tray  37 , both of which are permeated with hot exhaust. 
     In an embodiment, the exhaust entered the device  10  through the hot exhaust inlet  20  at a temperature of 200 degrees Celsius. Following the heat transfer process, the heat transfer fluid reached a temperature of approximately 65 degrees Celsius after contacting the hot exhaust and packing media  32 . In another embodiment, the heat transfer fluid was at 20 degrees Celsius prior to contacting the media. 
     While it is impossible to prevent all evaporation of the heat transfer fluid, in one embodiment, heat transfer fluid is added and re-circulated so that the exiting exhaust temperature is maintained to less than 35 degrees Celsius. In this embodiment, the evaporation rate is under 10%. Further, in embodiments where the exhaust temperature is maintained under 49 degrees Celsius the liquid gained from condensation of vapor contained in combustion flue gas will approximately equal the amount of evaporation from the direct contact with the exhaust. As such, the system recuperates any water loss from evaporation of the heat transfer fluid, so as to conserve water resources. 
     After the heat transfer fluid percolates downwardly through transverse apertures formed in the packing tray  37 , it then exits the packing tower  30  through the tower to the heat transfer fluid exit conduit  52 . The heat transfer fluid which enters the heat transfer fluid exit conduit  52  contains the heat energy from the hot exhaust and is therefore hot. This heat energy from the heat transfer fluid is transferred, via thermal conductance through the walls of the fuel conduit, to heat the fuel prior to combustion of the fuel. 
     The heat transfer fluid enters the jacket through the heat transfer fluid exit conduit  52  and contacts the fuel line  66  near the first end  60  of the fuel line  66 . In an embodiment of the invented system which conserves energy costs, the fuel entering the system from the first end  60  of the fuel line  66  is not heated up or otherwise thermally pretreated. To the extent that the fuel within the fuel line  66  is from an underground source, such as buried municipal gas lines, the fuel and fuel line  66  are likely to be cold. Even in instances where the fuel originates from an above-ground source such as a truck or tank, the difference in the temperatures between the fuel and the heat transfer fluid will result in a cooling of the fluid to below 21 degrees Celsius. Given the amount of time the cooling fluid contacts the exhaust traversing the tower, in instances where the cooling fluid is below 21 degrees Celsius, the exhaust exiting the tower will be under 32 degrees Celsius. With the exhaust exiting at that temperature, it is possible for the overall heater to run at high efficiency. 
     This exact temperature is not known and is not a critical design requirement. As long as the exiting exhaust temperature is under 48 degrees Celsius, the fluid temperature leaving the tower is the only required information to properly size the length and width of the fuel heat transfer jacket  64 . 
     As the heat transfer fluid fills the inside of the heat transfer jacket  64 , the heat transfer fluid contacts the exterior surface of the fuel line  66 . Given the above difference in temperatures, the heat transfer fluid loses its heat energy to the fuel line  66  and to the fuel contained within the fuel line  66  via thermal conductance through the walls of the fuel line. The heat transfer fluid which exits the heat transfer jacket at the pump inlet  56  will approach equilibrium with the temperature of the fuel line  66  at the second end  62  of the fuel line  66 . However, since the fuel at the second end  62  of the fuel line  66  has most recently entered the device  10 , this fuel is at the lowest temperature given its recent decompression from distribution line pressures. Consequently, the heat transfer fluid will reach or approximate its equilibrium point as it exits the heat transfer jacket  64  through the pump inlet  56 . 
     The heat transfer fluid which reaches the recirculation pump  50  is pressurized to between 5 psi to 30 psi and forced out of the pump outlet  58  starting the cycle again by traversing the external conduit  46 . 
     At the end of the operation of the furnace or boiler, or when it is desirable to flush the system clean, the heat transfer fluid is collected. The fluid may be collected through several points, including at the recirculation pump  50 . At the recirculation pump  50 , the heat transfer fluid may be diverted away from the device  10  by directing the fluid to a secondary outlet (not shown) instead of the pump outlet  58 . Alternatively, the tower to jacket connection valve may be closed. Given this eventuality the heat transfer fluid will congregate and exit the device  10  through the packing tray secondary outlet  80  depicted in  FIG. 2 . 
     In the event of loss of heat transfer fluid, it may be replenished by the introduction of additional heat transfer fluid at the recirculation pump  50 . 
     The device  10  also allows for several points of control. If the hot exhaust exiting the exhaust aperture  36  is too cold, it is possible to decrease the flow out of the nozzle  40  through operation of a valve at a conduit junction  44 . The valve may be automatically controlled, via thermostat, or hand-controlled. Similarly, if the fuel exiting the fuel line  66  at the fuel line first end  60  is still too cool, the rate of flow of the heat transfer fluid may be adjusted at the tower to jacket connection valve  54  such that the fluid flow is increased around the exterior of the fuel conduit. 
     Air Induction Assembly 
     Turning to the alternate embodiment of the economizer system depicted in  FIG. 3 , the fan blower alternate embodiment  110  depicted therein does not seek to transfer heat energy to boiler fuel. Instead, the principal purpose of the alternate embodiment  110  is to ensure that the connected boiler receives a sufficient oxygen supply. Providing a sufficient oxygen supply is especially important for boilers having natural draught burners which in normal operation—i.e. operation where the boiler is not connected to an economizer—rely on air supply from the stack to maintain the flame. If an economizer is introduced to the stack, the exhaust is cooled and does not rise out of the stack. The trapping of the exhaust prevents the draught from pulling in outside air to the boiler&#39;s burners starving same of oxygen. 
     The embodiment  110  shown in  FIG. 3  is designed to use an economizer with a natural draught boiler or any other fuel burning appliance which requires air from the exhaust to maintain the flame at the burners. The economizer  110  comprises a packing tower  130  having a first end  134  and a second end  135 . A hot exhaust inlet  120  extends from the packing tower  130  at a location intermediate the two ends  134 , 135 . Preferably, as shown in  FIG. 3 , the hot exhaust inlet  120  is located one third of the length of the packing tower  130  from the packing tower first end  134  and two thirds of the length of the packing tower  130  second end  135 . 
     The hot exhaust inlet  120  comprises a heavy duty metal conduit, in one embodiment. The hot exhaust inlet  120  must withstand high temperatures and pressures of boiler exhaust traversing the inlet  120 . A hot exhaust inlet aperture  162  is defined within the inlet  120  to allow for removal of excess fluid from the inlet  120 . In one embodiment, the excess fluid is drained by gravity; in another embodiment, a pump is reversibly attached to the aperture  162  to remove fluid. The hot exhaust inlet  120  is angled with the end closest to the packing tower  130  lower than the end of the inlet  120  which is connected to the boiler. Given the angle, should excess fluid build up in the packing tower  130 , the fluid will not traverse the inlet  120 . Such fluid forms due to the cooling action of the economizer on the exhaust. If the condensation from the exhaust or other fluid were to return to the burners via the inlet  120 , the burner flames can be extinguished. 
     In yet another embodiment, the aperture  162  is also used for reversible mounting of sensors (not shown) and for other means of monitoring the presence of exhaust within the hot exhaust inlet  162 . In one embodiment, a switch (not shown) is mounted within the aperture  162 , said switch being connected to the blower fan assembly  180  described fully below. 
     As the hot exhaust exits the inlet  120  and enters the packing tower  130 , it contacts the overflow lines  160 . The overflow lines  160  are connected to the packing tower  130  at the upper overflow aperture  161  near at the first end  134  of the packing tower  130 . In one embodiment, the side of the packing tower incorporates a sight gauge tube  165  comprising clear tubing connected to the lower aperture  163  and the upper aperture  161 . The sight gauge tube  165  allows for viewing of the level of liquid build-up within the packing tower  130 . Any excess fluid that builds up within the packing tower  130  will fall down due to gravity towards the first end  134  of the packing tower  130 . Initially, such fluid will exit the packing tower by being directed through the lower  163  aperture to the external sight gauge tube  165 . However, if the amount of fluid becomes critical, and at the level of the exhaust inlet  120 , the excess fluid will also exit through the upper aperture  161 . In one embodiment, when the condensed exhaust fluid exits from the upper aperture  161 , a sensor is triggered, indicating excess fluid in the packing tower  130 . In another embodiment, when the fluid exits the upper aperture  161 , the economizer cycle is slowed down by directing less exhaust through the inlet  120 . Any fluid exiting the upper overflow aperture  161  is directed by the overflow lines  160  away from the device  110 . The overflow lines  160  are angled to prevent the fluid from exiting the economizer in multiple directions. 
     After the hot exhaust enters the packing tower  130 , the hot exhaust moves away from the first end  134  of the packing tower  130  towards the second end  135  of the packing tower  130 . The interior of the packing tower between the inlet  120  and the second end  135  contains packing media (not shown). The packing media is inserted and removed by accessing the interior of the packing tower  130  via the packing media access portal  164 . During operation of the economizer  110 , this portal is sealed; however, if any of the media becomes deformed and is no longer able to function, it can be replaced by accessing the interior of the packing tower  130  through this access portal  164 . 
     The packing media is cooled by being showered by a heat exchange fluid exiting the nozzle  140 . The nozzle  140  is connected to the exterior of the packing tower  130  via an internal conduit  142 . The internal conduit is in turn connected to an external conduit  146 . In one embodiment, both the internal conduit  142  and the external conduit  146  comprise the same material; in other embodiments, the two conduits are made of different material, with the external conduit  146  being made from a less resistant material given that it is not exposed to the exhaust within the packing tower  130 . 
     The external conduit  146  is connected to a cold fluid inlet (not shown). In one embodiment, the cold fluid inlet is connected to a heat transfer jacket, as was shown in  FIGS. 1 and 2 . In another embodiment, the cold fluid inlet is connected to a fresh supply of cooled fluid, such as a cold water line or a cooling body of water. 
     As the fluid exits from the nozzle  140 , it traverses the packing tower  130  towards the first end  134  of the tower  130 . The flow rate of the fluid out of the nozzle  140  is set based on the stack temperature read by temperature sensor  172 . During operation, the fluid rate is set to maintain a constant temperature at  172  so that any water captured from the combustion process will be evaporated. The flow rate will vary to maintain this temperature by changing the speed of the pump  150 . 
     As can be best seen in  FIG. 6 , fluid from the packing tower  130  is collected and conveyed to the recirculation pump  150  via the pump&#39;s inlet  156 . The inlet  156  is connected to the packing tower  130  via a pump to packing tower connection pipe  270 . The pump to packing tower connection pipe  270  is in fluid communication with the first end  134  of the packing tower  130 . In the embodiment shown in  FIG. 6 , the pump to packing tower connection pipe  270  is closer to the first end  134  than the lower aperture  163 . Therefore, fluid will not reach the lower aperture  163  except unless insufficient quantity of fluid is being conducted from the packing tower  130  via the pump to packing tower connection pipe  270 . In one embodiment, if fluid is detected to have exited the lower aperture  163 , the pump  150  output is increased. 
     The recirculation pump  150  forwards the heat exchange fluid under pressure to the pump outlet  158 . The pump outlet  158  is connected to a heat exchange jacket as shown in  FIGS. 1-2  or other heat exchange means, such as an outdoor fluid cooling body. In another embodiment, the output of the recirculation pump  150  is discarded. 
     After passing over the fluid exiting the nozzle  140 , the exhaust exits the tower  130  by means of an exhaust aperture  136  located at the second end  135  of the tower  130 . The aperture  136  provides for fluid communication between the tower  130  and the economizer exhaust stack  170 . As the exhaust enters the exhaust stack  170 , it has been considerably cooled by the packing media and the heat exchange fluid from the nozzle  140 . If the exhaust has begun to condensate, fluid will fall down the packing tower  130  towards the first end  134 . A temperature sensor  172 , measures the temperature and rate of exhaust exiting the second end  135  of the packing tower  130  and adjusts the fluid flow of the nozzle  140  to prevent excess condensation given the likely make up of the exhaust. 
     An air induction unit, described below, is also connected to the exhaust stack  170 . 
     Induction Unit 
     In the embodiment shown in  FIG. 3 , the air induction unit is connected to the economizer exhaust stack  170 . In the embodiment shown in  FIG. 5 , the induction unit is connected to the inlet  120 . The placement of the induction units at either location ensures that sufficient air is introduced into the system to maintain combustion within the boiler. 
     The induction unit comprises two components, one internal to the exhaust stack  170  and another exterior to the exhaust stack  170 . The interior assembly comprises a pipe having two segments, a straight segment  174  and a curved segment  176 . The straight segment  174  has a first end which is open while the second end of the straight segment  174  is connected to the curved segment  176 . The curved segment  176  in turn is connected to the external assembly. The straight segment  174  is enclosed by the exhaust stack  170 . The straight segment  174  is parallel to the exhaust stack, such that the interior  175  of the straight segment is concentric to the exhaust stack  170 , as depicted in  FIG. 4 . 
     While as shown in the cut-away view of  FIGS. 3 and 4 , the straight segment  174  and the economizer exhaust stack  170  are substantially cylindrical in shape, other shapes may be used in other embodiments. In another embodiment, not shown, a rectangular vent is used for the exhaust stack  170 . 
     The introduction of pressurized exterior air to the interior  175  of the straight segment  174  creates a pressure differential between the interior  175  of the straight segment  174  and the interior  177  of the exhaust stack  170 . In one embodiment this pressure differential is set according to the boiler burner type and emission requirements. The pressure differential causes a partial vacuum to form in the interior  177  of the exhaust stack  170  surrounding the straight segment  174 . This vacuum pulls air in from the outside of the exhaust stack  170  down through the exhaust stack  170  to the packing tower  130  and eventually to the boiler via the inlet  120 . 
     The change in pressure in the straight segment  174  originates with the blower fan assembly  180  connected to the curved segment  176 . The blower fan assembly  180  comprises a blower motor  182 . The motor  182  operates a fan (not shown) which draws air in from the exterior of the economizer  110  through an air intake in the blower fan assembly  180 . 
     Inasmuch as the fan draws exterior air into the curved segment  176 , the fan does not contact the potentially caustic exhaust contained within the exhaust stack  170 . Therefore, the fan does need not comprise durable materials. In one embodiment the amount of air the fan introduces into the stack per minute is set to meet boiler burner air needs and any emissions requirements. In one embodiment, the fan speed is kept constant throughout the operation of the system. In another embodiment, the fan speed and resulting output is automatically calculated and set on the basis of the exhaust sensor attached to the hot exhaust monitor aperture  162 . In another embodiment, the fan is automatically turned to full speed as soon as exhaust is detected within the system. In yet another embodiment, the speed of the fan is set by the temperature of the flames within the boiler, said temperature being an indication of whether the flames have sufficient air. 
     The life span of the fan within the fan assembly  180  is maximized in this embodiment inasmuch as the fan does not contact the cooled exhaust and the condensate products within the exhaust. The condensation is instead collected and removed at the first end  134  of the packing tower  130 . A fan connected directly to the humid environment of the packing tower  130  would suffer from the effects of contact the caustic environment. 
     Exhaust Intake Cooling 
     An alternate embodiment of the economizer is depicted in  FIG. 5 . The economizer  210  comprises a hot exhaust inlet  220  connected to a boiler (not shown) and a packing tower  230 . The packing tower  230  used with this alternate embodiment  210  is analogous to the packing towers described above. 
     A testing port  262  is defined in the hot exhaust inlet  220  at a point along the length of the hot exhaust inlet between the boiler connection and the air induction segment  222 . In one embodiment, a temperature gauge is connected to the testing port  262 , while in another embodiment a combustion analyzer is connected at the testing port  262 . In one embodiment, the combustion analyzer is used during setup or commissioning of the burner. During this setup phase, air and gas ratios are set to the proper amount, to ensure a clean burn. The analyzer is removed from the system after the setup is completed. During operation, temperature is measured to maintain the air mixture setting determined during the setup phase. In one embodiment, the hot exhaust inlet  220  air induction segment  222  is a stand-alone portion of the hot exhaust inlet  220  that can be connected to the hot exhaust inlet  220  in the event that the additional air supplied by the system is needed. In another embodiment, the induction segment  222  is integrally molded into hot exhaust inlet  220 , but can be bypassed if not needed by closing the fan valve connection  223 . 
     A fan assembly  224  is connected to the induction segment  222 . The fan assembly comprises a fan  226 , the fan housing  228 , and the air introduction tube  232 . In one embodiment, the fan  226  is protected by the fan housing  228 , but at least one side of the fan  226  is exposed to the exterior atmosphere allowing the fan to draw in air from the atmosphere into the interior of the fan housing  228 . 
     The interior of the fan housing  228  is connected to the air introduction tube  232 . The fan valve  223  is found on the fluid connection between the fan housing  228  and the air introduction tube  232 . In one embodiment, the fan valve connection  232  is automatically closed when exhaust is detected in the air introduction tube  232 . Therefore, the fan  226  is protected from the hot exhaust in the inlet  220 . If the fan is blowing air into the system, the valve  223  may be open inasmuch as the pressure of the air coming from the fan will push back and protect the fan from any returning exhaust. The exhaust will instead be directed to the packing tower  230  found at the opposite end of the inlet  220 . 
     The air introduction tube  232  connects the fan valve  223  to the interior of the inlet  220 . In one embodiment, a portion  234  of the introduction tube  232  is substantially parallel with the air induction segment  222  of the inlet  220 . A connected portion  236  of the induction tube  232  turns approximately 90 degrees and becomes substantially perpendicular to the air induction segment  222 . 
     When the fan  226  is turned on, air is forced from the external atmosphere into the fan housing  228 . Inasmuch as the fan valve connection  223  is open, the air passes through the fan housing  228  to the air introduction tube  232  first the perpendicular segment  236  and then the parallel segment  234 . The parallel segment  234  is open to the interior of the inlet  220 . When the air exits the parallel segment  220 , a partial vacuum is formed at the vacuum portion  238  of the inlet  220 . The vacuum portion  238  surrounds the open end of the segment  228  between the exterior walls of the parallel segment  234  and the interior walls of the inlet  220 . 
     The air added to the inlet  220  functions to decrease the temperature of the exhaust found in the inlet  220 . A lower temperature of the exhaust allows the economizer to be used with high-temperature exhaust boilers. Further, the lower temperature of the exhaust allows for use of a cooling liquid other than water. In one embodiment, the cooling fluid comprises ethylene glycol or propylene glycol or a mix of either and water. The introduction of either ethylene glycol or propylene glycol allows the economizer to be maintained in a ready with all lines charged with cooling fluid, even when the economizer is shut down in climates where freezing occurs. These liquids would not be feasible or safe to use if the exhaust was of a high temperature. 
     The speed of the fan  226  is adjusted depending on the amount and temperature of the exhaust in the inlet  220 . A temperature and pressure sensor  240  is located on the length of the air induction segment  220  between the boiler connection and the fan assembly  224  connection. 
     As used herein, an element or step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting, but are instead are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.