Patent Publication Number: US-2015064591-A1

Title: Heater and method of operating

Description:
TECHNICAL FIELD OF INVENTION 
     The present invention relates to a heater which uses fuel cell stack assemblies as a source of heat; more particularly to such a heater which is positioned within a bore hole of an oil containing geological formation in order to liberate oil therefrom; and even more particularly to such a heater which includes electric resistive heating elements to start operation of the fuel cell stack assemblies. 
     BACKGROUND OF INVENTION 
     Subterranean heaters have been used to heat subterranean geological formations in oil production, remediation of contaminated soils, accelerating digestion of landfills, thawing of permafrost, gasification of coal, as well as other uses. Some examples of subterranean heater arrangements include placing and operating electrical resistance heaters, microwave electrodes, gas-fired heaters or catalytic heaters in a bore hole of the formation to be heated. Other examples of subterranean heater arrangements include circulating hot gases or liquids through the formation to be heated, whereby the hot gases or liquids have been heated by a burner located on the surface of the earth. While these examples may be effective for heating the subterranean geological formation, they may be energy intensive to operate. 
     U.S. Pat. Nos. 6,684,948 and 7,182,132 propose subterranean heaters which use fuel cells as a more energy efficient source of heat. The fuel cells are disposed in a heater housing which is positioned within the bore hole of the formation to be heated. The fuel cells convert chemical energy from a fuel into heat and electricity through a chemical reaction with an oxidizing agent. U.S. Pat. No. 7,182,132 teaches that in order to start operation of the heater, an electric current may be passed through the fuel cells in order to elevate the temperature of the fuel cells sufficiently high to allow the fuel cells to operate, i.e. an electric current is passed through the fuel cells before the fuel cells are electrically active. While passing an electric current through the fuel cells may elevate the temperature of the fuel cells, passing an electric current through the fuel cells before the fuel cells are electrically active may be harsh on the fuel cells and may lead to a decreased operational life thereof. 
     What is needed is a heater which minimizes or eliminates one of more of the shortcomings as set forth above. 
     SUMMARY OF THE INVENTION 
     A heater includes a heater housing extending along a heater axis. A fuel cell stack assembly is disposed within the heater housing and includes a plurality of fuel cells which convert chemical energy from a fuel into heat and electricity through a chemical reaction with an oxidizing agent. An electric resistive heating element is disposed within the heater housing. A positive conductor is disposed within the heater housing and is connected to the fuel cell stack assembly and to the electric resistive heating element and a negative conductor is connected to the fuel cell stack assembly and to the electric resistive heating element. The electric resistive heating element is arranged to elevate the fuel cell stack assembly from a first inactive temperature to a second active temperature. In this way, the positive conductor and the negative conductor may service both the fuel cell stack assembly and the electric resistive heating element, thereby eliminating the need for separate conductors for the fuel cell stack assembly and the electric resistive heating element 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       This invention will be further described with reference to the accompanying drawings in which: 
         FIG. 1  is a cross-section schematic view of a heater in accordance with the present invention; 
         FIG. 2  is schematic view of a plurality of heaters of  FIG. 1  shown in a bore hole of a geological formation; 
         FIG. 3  is an elevation schematic view of a fuel stack assembly of the heater of  FIG. 1 ; 
         FIG. 4  is an elevation schematic view of a fuel cell of the fuel cell stack assembly of  FIG. 3 ; 
         FIG. 5  is schematic view showing a first electrical connection arrangement of the heater in accordance with the present invention; 
         FIG. 6  is schematic view showing a second electrical connection arrangement of the heater in accordance with the present invention; 
         FIG. 7  is schematic view showing a third electrical connection arrangement of the heater in accordance with the present invention; 
         FIG. 8  is schematic view showing a fourth electrical connection arrangement of the heater in accordance with the present invention; and 
         FIG. 9  is schematic view showing a fifth electrical connection arrangement of the heater in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     Referring now to  FIGS. 1 and 2 , a heater  10  extending along a heater axis  12  is shown in accordance with the present invention. A plurality of heaters  10   1 ,  10   2 , . . .  10   n−1 ,  10   n , where n is the total number of heaters  10 , may be connected together end to end within a bore hole  14  of a formation  16 , for example, an oil containing geological formation, as shown in  FIG. 2 . Bore hole  14  may be only a few feet deep; however, may typically be several hundred feet deep to in excess of one thousand feet deep. Consequently, the number of heaters  10  needed may range from 1 to several hundred. It should be noted that the oil containing geological formation may begin as deep as one thousand feet below the surface and consequently, heater  10   1  may be located sufficiently deep within bore hole  14  to be positioned near the beginning of the oil containing geological formation. When this is the case, units without active heating components may be positioned from the surface to heater  10   1  in order to provide plumbing, power leads, and instrumentation leads to support and supply fuel and air to heaters  10   1  to  10   n , as will be discussed later. 
     Heater  10  generally includes a heater housing  18  extending along heater axis  12 , a plurality of fuel cell stack assemblies  20  located within heater housing  18  such that each fuel cell stack assembly  20  is spaced axially apart from each other fuel cell stack assembly  20 , a fuel supply conduit  22  for supplying fuel to fuel cell stack assemblies  20 , an oxidizing agent supply conduit  24 ; hereinafter referred to as air supply conduit  24 ; for supplying an oxidizing agent, for example air, to fuel cell stack assemblies  20 , and a plurality of electric resistive heating elements  26  for elevating the temperature of fuel cell stack assemblies  20  to operating temperature. While heater  10  is illustrated with three fuel cell stack assemblies  20  within heater housing  18 , it should be understood that a lesser number or a greater number of fuel cell stack assemblies  20  may be included. The number of fuel cell stack assemblies  20  within heater housing  18  may be determined, for example only, by one or more of the following considerations: the length of heater housing  18 , the heat output capacity of each fuel cell stack assembly  20 , the desired density of fuel cell stack assemblies  20  (i.e. the number of fuel cell stack assemblies  20  per unit of length), and the desired heat output of heater  10 . While heater  10  is illustrated with three electric resistive heating elements  26 , it should be understood that a lesser number or a greater number of electric resistive heating elements  26  may be included and the number of electric resistive heating elements  26  may be the same or different than the number of fuel cell stack assemblies  20 . The number of heaters  10  within bore hole  14  may be determined, for example only, by one or more of the following considerations: the depth of formation  16  which is desired to be heated, the location of oil within formation  16 , and the length of each heater  10 . 
     Heater housing  18  may be substantially cylindrical and hollow and may support fuel cell stack assemblies  20  within heater housing  18 . Heater housing  18  of heater  10   x , where x is from 1 to n where n is the number of heaters  10  within bore hole  14 , may support heaters  10   x+1  to  10   n  by heaters  10   x+1  to  10   n  hanging from heater  10   x . Consequently, heater housing  18  may be made of a material that is substantially strong to accommodate the weight of fuel cell stack assemblies  20  and heaters  10   x+1  to  10   n . The material of heater housing  18  may also have properties to withstand the elevated temperatures, for example 600° C. to 900° C., as a result of the operation of fuel cell stack assemblies  20 . For example only, heater housing  18  may be made of a 300 series stainless steel with a wall thickness of 3/16 of an inch. 
     With continued reference to  FIGS. 1 and 2  and now with additional reference to  FIGS. 3 and 4 , fuel cell stack assemblies  20  may be, for example only, solid oxide fuel cells which generally include a fuel cell manifold  28  and a plurality of fuel cell cassettes  30  (for clarity, only select fuel cell cassettes  30  have been labeled). Each fuel cell stack assembly  20  may include, for example only, 20 to 50 fuel cell cassettes  30 . 
     Each fuel cell cassette  30  includes a fuel cell  32  having an anode  34  and a cathode  36  separated by a ceramic electrolyte  38 . Each fuel cell  32  converts chemical energy from a fuel supplied to anode  34  into heat and electricity through a chemical reaction with air supplied to cathode  36 . Fuel cell cassettes  30  have no electrochemical activity below a first temperature, for example, about 500° C., and consequently will not produce heat and electricity below the first temperature. Fuel cell cassettes  30  have a very limited electrochemical activity between the first temperature and a second temperature; for example, between about 500° C. and about 700° C., and consequently produces limited heat and electricity between the first temperature and the second temperature, for example only, about 0.01 kW to about 3.0 kW of heat (due to the fuel self-igniting above about 600° C.) and about 0.01 kW to about 0.5 kW electricity for a fuel cell stack assembly having thirty fuel cell cassettes  30 . When fuel cell cassettes  30  are elevated above the second temperature, for example, about 700° C. which is considered to be the active temperature, fuel cell cassettes  30  are considered to be active and produce desired amounts of heat and electricity, for example only, about 0.5 kW to about 3.0 kW of heat and about 1.0 kW to about 1.5 kW electricity for a fuel cell stack assembly having thirty fuel cell cassettes  30 . Further features of fuel cell cassettes  30  and fuel cells  32  are disclosed in United States Patent Application Publication No. US 2012/0094201 to Haltiner, Jr. et al. which is incorporated herein by reference in its entirety. 
     Fuel cell manifold  28  receives fuel, e.g. a hydrogen rich reformate, which may be supplied from a fuel reformer  40 , through fuel supply conduit  22  and distributes the fuel to each fuel cell cassette  30 . Fuel cell manifold  28  also receives an oxidizing agent, for example, air from an air supply  42 , through air supply conduit  24  and distributes the air to each fuel cell cassette  30 . Fuel cell manifold  28  also receives anode exhaust, i.e. spent fuel and excess fuel from fuel cells  32  which may comprise H 2 , CO, H 2 O, CO 2 , and N 2 , and cathode exhaust, i.e. spent air and excess air from fuel cells  32  which may comprise O 2  (depleted compared to the air supplied through air supply conduit  24 ) and N 2 . The anode exhaust and cathode exhaust may be communicated from fuel cell manifold  28  to the top of bore hole  14  through respective anode and cathode exhaust conduits (not shown) or the anode and cathode exhaust may be communicated to a combustor (not shown) where the anode and cathode exhaust may be mixed and combusted in order to generate additional heat within heater housing  18 . 
     Electric resistive heating elements  26  are disposed within heater housing  18  and arranged to elevate fuel cell stack assemblies  20  to the active temperature, which as mentioned previously is about 700° C. Each electric resistive heating element  26  may be positioned proximal to a respective fuel cell stack assembly  20  and may be, for example only, a resistance wire that is wrapped around a respective fuel cell stack assembly  20 . Electric resistive heating elements  26  may be designed such that the voltage required to generate the desired heat does not exceed the electrochemical potential of fuel cell stack assemblies  20  to prevent damage to fuel cell stack assemblies  20  when electric resistive heating elements  26  are being used to elevate the temperature of fuel cell stack assemblies  20 . 
     Heater  10  includes a positive conductor  44  and a negative conductor  46 , thereby defining in part an electrical circuit for communicating electricity from an electricity distribution center  48  to electric resistive heating elements  26  and for communicating electricity generated by fuel cell stack assemblies  20  to electricity distribution center  48 . Positive conductor  44  and negative conductor  46  may be located within heater housing  18  as shown. Electricity distribution center  48  may be located on the surface of formation  16  and may receive electricity from a utility grid (not shown), a power plant (not shown), or a generator (not shown) for communicating electricity to electric resistive heating elements  26 . Electricity distribution center  48  may also communicate electricity to the utility grid from fuel cell stack assemblies  20  and/or to other electricity consuming devices. 
     Reference will now be made to  FIGS. 5-9  which each illustrate three heaters  10  connected together to illustrate various arrangements for electrically connecting fuel cell stack assemblies  20 , electric resistive heating elements  26 , and heaters  10 . For clarity, heater housings  18 , fuel supply conduit  22 , and air supply conduit  24  have been omitted from  FIGS. 5-9 . 
     As shown in  FIG. 5 , fuel cell stack assemblies  20  of a respective heater  10  may be connected in series and the corresponding electric resistive heating elements  26  may be connected in series such that fuel cell stack assemblies  20  and electric resistive heating elements  26  are connected to positive conductor  44  and negative conductor  46 ; however, electric resistive heating elements  26  are connected in parallel with fuel cell stack assemblies  20 . Also as shown in  FIG. 5 , heaters  10  are connected in parallel, thereby allowing the remaining heaters  10  to continue to operate if one heater  10  fails. A switch  50  may be provided in series with electric resistive heating elements  26  of each respective heater  10  in order to selectively inactivate electric resistive heating elements  26 . Each switch  50  may be, for example only, a thermally activated switch arranged to open above a predetermined temperature, for example, a temperature indicative of the active temperature of fuel cell stack assemblies  20 . In this way, electric resistive heating elements  26  may be turned off when fuel cell stack assemblies  20  are electrochemically active and generating electricity, thereby preventing electric resistive heating elements  26  from consuming electricity generated by fuel cell stack assemblies  20 . 
     As shown in  FIG. 6 , fuel cell stack assemblies  20  of a respective heater  10  may be connected in parallel and each electric resistive heating element  26  may be connected in parallel with a respective fuel cell stack assembly  20  such that fuel cell stack assemblies  20  and electric resistive heating elements  26  are connected to positive conductor  44  and negative conductor  46 . In this way any individual fuel cell stack assembly  20  may fail without affecting the remaining fuel cell stack assemblies  20  within heater  10  and individual electric resistive heating elements  26  may fail without affecting the remaining electric resistive heating elements  26 . Also as shown in  FIG. 6 , heaters  10  are connected in parallel. Switch  50  may be provided in series with each electric resistive heating element  26  in order to selectively inactivate electric resistive heating elements  26 . 
     As shown in  FIG. 7 , fuel cell stack assemblies  20  of a respective heater  10  may be connected in parallel and the corresponding electric resistive heating elements  26  may be connected in series such that fuel cell stack assemblies  20  and electric resistive heating elements  26  are connected to positive conductor  44  and negative conductor  46  however; electric resistive heating elements  26  are connected in parallel with fuel cell stack assemblies  20 . Also as shown in  FIG. 7 , heaters  10  are connected in parallel. Switch  50  may be provided in series with electric resistive heating elements  26  of a respective heater  10  in order to selectively inactivate electric resistive heating elements  26 . 
     As shown in  FIG. 8 , fuel cell stack assemblies  20  of a respective heater  10  may be connected in series and the corresponding electric resistive heating elements  26  may be connected in series such that fuel cell stack assemblies  20  and electric resistive heating elements  26  are connected to positive conductor  44  and negative conductor  46 . Also as shown in  FIG. 8 , heaters  10  are connected in series. Switch  50  may be provided in series with electric resistive heating elements  26  in order to selectively inactivate electric resistive heating elements  26 . 
     As shown in  FIG. 9 , a plurality of positive conductors  44  may be provided such that each positive conductor  44  is dedicated to a respective heater  10 . While  FIG. 9  illustrates that fuel cell stack assemblies  20  of a respective heater  10  are connected in series, it should be understood that fuel cell stack assemblies  20  may be connected in parallel as shown in  FIG. 6 . Similarly, while  FIG. 9  illustrates that electric resistive heating elements  26  of each heater  10  connected in series, it should be understood that electric resistive heating elements  26  may be connected in parallel as shown in  FIG. 5 . Switch  50  may be provided in series with electric resistive heating elements  26  of a respective heater  10  in order to selectively inactivate electric resistive heating elements  26 . 
     In operation, after heaters  10  are installed within bore hole  14 , fuel cell stack assemblies  20  must be elevated to the active temperature of fuel cell stack assemblies  20  before fuel cell stack assemblies  20  may be used to generate heat and electricity. In order to elevate fuel cell stack assemblies  20  to the active temperature, electricity distribution center  48  may supply electricity to positive conductor  44 . Since fuel cell stack assemblies  20  are not electrochemically active due to being below the active temperature, fuel cell stack assemblies  20  will be an open circuit, thereby preventing the electricity supplied to positive conductor  44  from passing through fuel cell stack assemblies  20 . At the same time switch(es)  50  are closed and allow electricity to pass through electric resistive heating elements  26 , thereby causing electric resistive heating elements  26  to heat up. The heat produced by electric resistive heating elements  26  may be transferred to fuel cell stack assemblies  20  through conduction, convection and/or radiation. After fuel cell stack assemblies  20  have reached a predetermined temperature, switch(es)  50  may open, thereby ceasing operation of electric resistive heating elements  26 . After fuel cell stack assemblies  20  are electrochemically active and switch(es)  50  is/are open, electricity generated by fuel cell stack assemblies  20  may supply electricity to electricity distribution center  48  through positive conductor  44 . In this way, the positive conductor  44  and negative conductor  46  may service both fuel cell stack assemblies  20  and electric resistive heating elements  26 , thereby eliminating the need for separate conductors for fuel cell stack assemblies  20  and electric resistive heating elements  26 . 
     While this invention has been described in terms of preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.