Self-loosening stack shipping restraint

Abstract

A fuel cell module includes a plurality of fuel cell stacks positioned in a stack array housing and a fastener assembly coupling the stack array housing to a base, the fastener assembly including a fastener that clamps a portion of the stack array housing between an end stop and the base. The fastener and every component clamped between the end stop and the base have respective coefficients of thermal expansion such that a clamping force is reduced upon an increase in temperature of the fuel cell module.

Description

Atty. Dkt. No.: 111187-2187SELF-LOOSENING STACK SHIPPING RESTRAINTCROSS-REFERENCE TO RELATED APPLICATION[00011 This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63 / 727,562, filed December 3, 2024, which is incorporated by reference herein in its entirety.BACKGROUND

[0002] A fuel cell is a device that converts chemical energy stored in hydrogen or hydrocarbon fuel into electrical energy by means of an electrochemical reaction. Generally, a fuel cell comprises an anode and a cathode that are separated by an electrolyte, which conducts electrically charged ions to produce electricity. For example, in a solid oxide fuel cell (“SOFC”), a solid, gas-impervious electrolyte is sandwiched between a porous anode and a porous cathode. Oxygen is transported through the cathode to the cathode / electrolyte interface, where it is reduced to oxygen ions, which migrate through the electrolyte to the anode. At the anode, the ionic oxygen reacts with fuels such as hydrogen or methane to release electrons, which then travel back to the cathode through an external circuit to generate electric power. Molten carbonate fuel cells (“MCFCs”) use an electrolyte composed of a molten carbonate salt mixture suspended in a porous, chemically inert ceramic matrix. At the cathode, carbon dioxide and oxygen react to form carbonate ions, which migrate through the electrolyte to react with a source of hydrogen (e.g., a hydrocarbon fuel) to produce steam, carbon dioxide, and electrons that then pass through an external circuit before flowing to the cathode. SOFCs and MCFCs typically operate at temperatures exceeding 600 degrees Celsius.

[0003] Multiple fuel cells may be arranged in stacks, and multiple stacks are arranged in a module in order to produce a desired amount of electrical power. The module may include a sealed outer module housing for containing reactants, to provide thermal insulation, and, in some -1-4906-4400-2931 .1Atty. Dkt. No.: 111187-2187 cases, to maintain the fuel cells at an elevated pressure. In typical fuel cell systems, the fuel cell stacks are positioned within a stack array housing that surrounds or partially surrounds the stacks. The stacks and stack array housing, as well as other components of the module (e.g., heat exchangers, reformers, etc.) are positioned within the outer module housing. To prevent damage to the stacks during shipping and installation, the stacks are secured to the inside of the outer housing by shipping restraints, such as screws or bolts that clamp a flange or bracket of the stack array housing to the outer module housing. However, due to the high temperature operation of the fuel cells, the fuel cell stacks and the stack array housing may thermally expand. If the stack array housing is tightly secured to the outer module housing, the stack array housing and the fuel cell stacks may be damaged due to the thermal expansion. To address this issue, the outer module housing may be opened or partially deconstructed after shipping to loosen the shipping restraints. Unsealing the fuel cell module at the installation site can be labor and time intensive and requires the module housing to undergo a lengthy resealing process to ensure that the module housing is fully sealed and insulated.[00<>4| It would be advantageous to provide a shipping restraint that can be loosened without opening or partially deconstructing the outer module housing.SUMMARY[0005| One aspect of the present disclosure relates to a fuel cell module including a plurality of fuel cell stacks positioned in a stack array housing and a fastener assembly coupling the stack array housing to a base. The fastener assembly includes a fastener that clamps a portion of the stack array housing between an end stop and the base. The fastener and every component clamped between the end stop and the base have respective coefficients of thermal expansion such that a clamping force is reduced upon an increase in temperature of the fuel cell module.[0006J In some embodiments, at 20 degrees Celsius, a first distance between the end stop and the base is equal to a combined thickness of every component clamped between the end stop and the-2-4906-4400-2931 .1Atty. Dkt. No.: 111187-2187 base, and wherein the increase in temperature causes the first distance to increase by a larger amount than an increase in the combined thickness.

[0007] In some embodiments, the fastener includes stainless steel, and at least one component clamped between the end stop and the base includes ceramic. In some embodiments, the stainless steel is 304 stainless steel, and the ceramic is AL-30 alumina ceramic.

[0008] In some embodiments, at least one component clamped between the end stop and the base includes a ceramic spacer plate positioned between the portion of the stack array housing and the base.[0009| In some embodiments, at least one component clamped between the end stop and the base includes an interface block positioned between the end stop and the portion of the stack array housing. In some embodiments, the fastener extends through a slot in the interface block, the slot elongated in a direction parallel to a longitudinal axis of the stack array housing.

[0010] In some embodiments, the end stop is a nut or a head of the fastener.

[0011] In some embodiments, the portion of the stack array housing is a flange of a mounting bracket positioned at a lower end of the stack array housing.

[0012] In some embodiments, the fastener assembly is fully enclosed within and inaccessible from outside of an outer module housing without opening or partially disassembling the outer module housing.

[0013] In some embodiments, the coefficient of thermal expansion of the fastener is at least 2.0 times the combined effective coefficient of thermal expansion of every material clamped between the end stop and the base.

[0014] In some embodiments, each fuel cell stack includes at least one solid oxide fuel cell or at least one molten carbonate fuel cell. In some embodiments, the plurality of fuel cell stacks are configured to operate at at least 600 degrees Celsius.-3-4906-4400-2931 .1Atty. Dkt. No.: 111187-2187[0015| Another aspect of the present disclosure relates to a method of installing a fuel cell module including an outer module housing and a plurality of fuel cell stacks positioned within a stack array housing. The method includes coupling, at a first location, the stack array housing to a base using a fastener assembly, the fastener assembly including a fastener that clamps a portion of the stack array housing between an end stop and the base, and operating, at a second location, the plurality of fuel cell stacks to generate electrical power, wherein the fastener and every component clamped between the end stop and the base have respective coefficients of thermal expansion such that a clamping force is reduced upon operation of the plurality of fuel cell stacks.

[0016] In some embodiments, the method further includes sealing the stack array housing and the fastener assembly within an outer module housing after coupling the stack array housing to the base, wherein the outer module housing is not opened after enclosing the stack array housing and before operating the plurality of fuel cell stacks.[0017J In some embodiments, coupling the stack array housing to the base includes clamping the portion of the stack array housing between the end stop and the base with a first non-zero clamping force, wherein when the fuel cell stacks are operated at a temperature of 600 degrees Celsius, the clamping force reduces to zero.[0018 J In some embodiments, operating the plurality of fuel cell stacks causes the fastener assembly to increase in temperature, wherein the increase in temperature causes the stack array housing to thermally expand and the portion of the stack array housing to translate relative to the fastener. In some embodiments, the portion of the stack array housing translates in a direction orthogonal to a longitudinal axis of the fastener.[0019| In some embodiments, the fastener includes stainless steel, and at least one component clamped between the end stop and the base includes ceramic.-4-4906-4400-2931 .1Atty. Dkt. No.: 111187-2187[0020| In some embodiments, the coefficient of thermal expansion of the fastener is at least 2.0 times the combined effective coefficient of thermal expansion of every material clamped between the end stop and the base.10021] The foregoing is a summary of the disclosure and thus by necessity contains simplifications, generalizations, and omissions of detail. Consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, features, and advantages of the devices and / or processes described herein, as defined by the claims, will become apparent in the detailed description set forth herein and taken in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS|0022] FIG. 1 is an illustration of a fuel cell module according to an exemplary embodiment.10023] FIG. 2 is an illustration of a fastener assembly of the fuel cell module of FIG. 1, according to an exemplary embodiment.

[0024] FIGS. 3 and 4 are respectively illustrations of the fastener assembly of FIG. 2 when the fuel cell module is at room temperature and when the fuel cell module is at operating temperature.

[0025] FIG. 5 is a flowchart illustrating a method of installing a fuel cell module, according to an exemplary embodiment.

[0026] It will be recognized that the figures are schematic representations for purposes of illustration. The figures are provided for the purpose of illustrating one or more implementations with the explicit understanding that the figures will not be used to limit the scope of the meaning of the claims.-5-4906-4400-2931 .1Atty. Dkt. No.: 111187-2187DETAILED DESCRIPTION[0027| In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and made part of this disclosure.[Q028| As discussed above, typical fuel cell stack shipping restraints within a fuel cell module must be loosened or removed before operating the fuel cell module because the thermal expansion of the fuel cell stacks and stack array housing that occur during operation of the module could cause damage to the stack array housing and the fuel cell stacks if the stacks and stack array housing are rigidly restrained. However, loosening or removing these restraints after shipping typically requires that the module housing be opened or partially deconstructed at the installation site. Opening and resealing the module can be a time-consuming and difficult process. For example, in some cases, a lid or housing body may be welded to a base. To open and reseal the housing, the housing would have to be cut open, re-welded, and repainted. In other cases, a lid or housing body may be bolted to a base. To open and reseal the housing, potentially hundreds of bolts would have to be removed, gaskets would have to be replaced, and the bolts would have to be retightened. In either case, it would be desirable to avoid opening and resealing the module. One less time-consuming method would be to design the module housing with smaller access holes with removable covers, which would require the removal of fewer bolts. However, this would increase the complexity of the module housing design and cause increased heat loss due to discontinuities in the insulation.-6-4906-4400-2931 .1Atty. Dkt. No.: 111187-2187[0029| In the embodiments disclosed herein, shipping restraints are provided that automatically loosen when the fuel cell module is operated. The shipping restraints include a fastener that clamps the stack array housing and other additional materials to the outer module housing. Because of differences in the coefficients of thermal expansion of the fastener and the clamped materials, the fastener thermally expands a greater amount than the clamped materials when the fuel cell module heats up to operating temperature. Because the fastener thermally expands a greater amount than the clamped materials, the clamp force provided by the fastener decreases, allowing the stack array housing to thermally expand (e.g., in a direction perpendicular or orthogonal to a longitudinal axis of the fastener) without being restrained by the shipping restraint. This allows the outer module housing to remain sealed after shipping because the shipping restraints do not need to be manually loosened or removed. This may decrease the time and expense of shipping and installing the fuel cell module and reduce the likelihood of leaks from the seals of the outer module housing.

[0030] Referring to FIG. 1, a fuel cell module 100 is shown according to an exemplary embodiment. The fuel cell module 100 includes an outer module housing 102, which defines the outer walls of the fuel cell module 100 and encloses the other components of the fuel cell module 100. The fuel cell module 100 includes a fuel cell stack array 104 that includes one or more fuel cell stacks 106. The fuel cell stack array 104 is positioned within a stack array housing 108, all of which are positioned in the outer module housing 102. The fuel cell module 100 further includes fastener assemblies 110 (i.e., shipping restraints) that couple the stack array housing 108 to a base 112 of the outer module housing 102. The fastener assemblies restrain the fuel cell stack array 104 and the stack array housing 108 during shipping of the fuel cell module 100 prior to installation. If the fuel cell stack array 104 is unrestrained or loosely restrained during shipping, the fuel cell stacks may be damaged due to movement of the fuel cell module 100, for example, due to a shipping vehicle driving over a bumpy road. Thus, during shipping, the fastener assemblies 110 may be used to tightly couple the stack array housing 108 to the base 112 of the outer module housing 102. The fastener assemblies 110 are shown in further detail in-7-4906-4400-2931 .1Atty. Dkt. No.: 111187-2187FIG. 2. It should be understood that the fuel cell module 100 may include other components not shown in FIG. 1, including reactant gas handling equipment, heat exchangers, reformers, etc.

[0031] As discussed above, in typical fuel cell modules, a fuel cell stack array may be rigidly bolted to the module housing for shipping. However, due to the high operating temperatures of the fuel cells, the stack array housing may thermally expand, with the largest amount of expansion being along a longitudinal axis of the stack array housing, which may be perpendicular or orthogonal to longitudinal axes of the screws or bolts securing the stack array housing to the outer module housing. If the stack array housing remains bolted down and restrained at its ends, the thermal expansion of the stack array housing may cause damage to the stack array housing and the fuel cell stacks. Thus, upon delivery of the fuel cell module, the module housing may be unsealed, and the bolts may be loosened or removed, allowing the stack array housing to expand freely during operation of the fuel cells. Unsealing the fuel cell module at the installation site can be labor-intensive and time-intensive and requires the module housing to undergo a lengthy resealing process to ensure that the module housing is fully sealed and insulated. The fastener assemblies 110 of the fuel cell module 100 tightly couple the stack array housing 108 to the base 112 during shipping but loosen when the fuel cell module 100 heats up during operation. This allows the stack array housing 108 to expand freely (e.g., in a direction perpendicular or orthogonal to a longitudinal axis of the fasteners) when the fuel cell module 100 heats up without the need to unseal the outer module housing 102 after shipping.[0032J Referring now to FIG. 2, a fastener assembly 110 is shown in further detail, according to an exemplary embodiment. The fastener assembly 110 includes a fastener 114 coupled to a base plate 116, which is fixedly coupled to the base 112 of the outer module housing 102. The base plate 116 may be, for example, welded or bolted to the base 112 of the outer module housing 102 or to another component of the outer module housing 102. As shown in FIG. 2, a first end 118 of the fastener 114 is threadedly coupled to a threaded opening 120 in the base plate 116. In some embodiments, the fastener 114 may be coupled to the base plate 116 by other methods, such as by welding or using nuts. For example, the first end 118 of the fastener 114 may extend-8-4906-4400-2931 .1Atty. Dkt. No.: 111187-2187 through a through hole in the base plate 116 and be threaded into a nut positioned below the base plate 116.

[0033] The fastener 114 extends from its first end 118 through respective openings 121, 122, 124 in spacer plates 126, 128 and a mounting plate 130 toward the second end 132 of the fastener 114. The fastener assembly 110 includes a mounting bracket 134 fixedly coupled to the stack array housing 108. As shown in FIG. 2, the stack array housing 108 includes an inner wall 136 and an outer wall 138 coupled to the mounting bracket 134. For example, the inner wall 136 and the outer wall 138 may be coupled to the mounting bracket 134 by welding or using fasteners (screws, bolts, rivets, etc.). The mounting bracket 134 sits on the mounting plate 130, forming a slip plane therebetween. An interface block 140 is positioned on the lower flange 142 of the mounting bracket 134. The fastener 114 extends through an opening 144 or slot in the mounting bracket 134 and through an opening 145 or slot in the interface block 140.

[0034] In the embodiment shown, the second end 132 of the fastener 114 is threadedly coupled to a nut 146, and a washer 148 is positioned between the nut 146 and the interface block 140. A locknut 150 is also threadedly coupled to the second end 132 of the fastener 114 to lock the nut 146 in place. In other embodiments, the fastener 114 may be threadedly coupled to the base plate 116, the second end 132 of the fastener 114 may have a head with a larger diameter than the body of the fastener and the openings 121, 122, 124 (e.g., a socket-head cap screw, a hexhead cap screw, etc.), and the fastener assembly 110 may not include a nut 146. In the embodiment shown, the fastener 114 captures the washer 148, the interface block 140, the lower flange 142 of the mounting bracket 134, the mounting plate 130, and the spacer plates 126, 128 between the nut 146 and the base plate 116. The nut 146, the head of the fastener 114, or any other component that captures these components between itself and the base plate 116 may be referred to as an “end stop” coupled to the fastener 114. For example, the nut 146 may be threadedly coupled to the fastener, or the head of the fastener 114 may be considered to be “coupled” to the fastener despite being integrally formed with and part of the fastener.-9-4906-4400-2931 .1Atty. Dkt. No.: 111187-2187[0035| Referring again to the embodiment shown in FIG. 2, by tightening the nut 146 with the fastener 114 coupled to the base plate 116, the mounting bracket 134 may be tightly secured to the mounting plate 130 for shipping of the fuel cell module 100. However, as discussed above, if the stack array housing 108 (e.g., the mounting bracket 134 of the stack array housing 108) is tightly secured to the base 112 of the outer module housing 102 (e.g., the mounting plate 130 of the outer module housing 102) when the fuel cell module 100 is in high-temperature operation, the thermal expansion of the stack array housing 108 may cause damage to the stack array housing 108 and the fuel cell stacks 106. Because loosening the nut 146 would require the outer module housing 102 to be unsealed to access the fastener assembly 110 and then carefully reassembled to ensure that the fuel cell module is properly insulated and sealed, the ability to loosen the fastener assembly 110 without unsealing the outer module housing 102 would be desirable.|0036] By selecting certain combinations of materials used to form the components of the fastener assembly 110, the fastener assembly 110 may self-loosen during high-temperature operation of the fuel cell module. The material of the fastener 114 may have a higher coefficient of thermal expansion than at least some of the materials captured between the nut 146 and the base plate 116. Thus, as the fastener assembly 110 heats up, the distance DI between the upper surface 152 of the base plate 116 and the lower surface 154 of the nut 146 may increase by a larger amount than the distance D2 between the lower surface 156 of the lower spacer plate 128 and the upper surface 158 of the washer 148. It should be understood that the coefficient of thermal expansion of the fastener 114 refers to the coefficient of thermal expansion of the portion of the fastener 114 between the upper surface 152 of the base plate 116 and the lower surface 154 of the nut 146, as this portion of the fastener may determine the clamping force on the stack array housing 108. For example, other portions of the fastener 114 (e.g., above the nut 146) may be made from a different material that has a different coefficient of thermal expansion, but this may not affect the expansion of the portion of the fastener 114 between the base plate 116 and the nut 146.-10-4906-4400-2931 .1Atty. Dkt. No.: 111187-2187[0037| FIGS. 3 and 4 illustrate an exemplary embodiment of a fastener assembly 110 at room temperature and after the fuel cell module heats up during operation, respectively. In this example, the fastener 114 and the interface block 140 are made of 304 stainless steel, and the spacer plates 126, 128 are made of AL-30 alumina ceramic, which may also act as an insulator for the fuel cell module 100. The washer 148, mounting bracket 134, and mounting plate 130 may also be made of 304 stainless steel or a material that has a similar coefficient of thermal expansion. However, these components may be thin enough that they do not significantly contribute to the overall thermal expansion of the components captured between the nut 146 and the base plate 116. To simplify the example, interface block 140, the washer 148, mounting bracket 134, and mounting plate 130 are shown collectively as stainless steel components 160, and the spacer plates 126, 128 are shown collectively as ceramic components 162. The coefficient of thermal expansion for 304 stainless steel is 18.8 x 10'6per degree Celsius, about 3.75 times higher than the coefficient of thermal expansion of AL-30, which is 5 x 10’6per degree Celsius.[Q038| In the example shown in FIG. 3, the distance DI between the upper surface 152 of the base plate 116 and the lower surface 154 of the nut 146 is 5.0 inches at room temperature (20 degrees Celsius), the combined thicknesses of the spacer plates 126, 128 (the ceramic components 162) at room temperature is 4.0 inches, and the combined thickness at room temperature of the interface block 140, washer 148, mounting bracket 134, and mounting plate 130 (the stainless steel components 160) is 1.0 inch. Thus, at room temperature, the distance D2 between the lower surface 156 of the lower spacer plate 128 and the upper surface 158 of the washer 148 may also be 5.0 inches. During operation of the fuel cell module 100, the average temperature of the fastener 114 increases to 350 degrees Celsius, which causes the distance DI of 5.0 to increase to a distance DI' of 5.031. The average temperatures of the ceramic components 162 also increase to 350 degrees Celsius, which causes the ceramic components 162 to increase from 4.0 inches to 4.0065 inches. The stainless steel components 160 increase in temperature to 600 degrees Celsius, which causes their combined thickness to increase from 1.0 inches to 1.011 inches. Thus, the distance D2 increases to a distance D2' of 4.0065 + 1.011 =-11-4906-4400-2931 .1Atty. Dkt. No.: 111187-21875.0175 inches. Because the distance DI1(5.031 inches) is larger than the distance D21(5.0175 inches), the tension in the fastener 114 is released and the nut 146 loses contact with the stainless steel components 160. This reduces the friction between the stainless steel components 160 and the ceramic components 162, which allows the mounting bracket 134 and the interface block 140 to slide along the spacer plate 126 as the stack array housing 108 heats up and expands.[0039J In some embodiments, the components (layers, etc.) clamped between the end stop (e.g., the nut 146) and the base plate 116 may be considered to have a “combined effective coefficient of thermal expansion,” which represents a weighted average thermal expansion coefficient of all of the clamped materials. The combined effective coefficient of thermal expansion can be calculated based on the respective coefficients of thermal expansion of the layers and their relative thicknesses. For example, continuing the example above, the total thickness of the stainless steel components 160 and the ceramic components 162 combined is 5.0 inches, with the stainless steel components 160 accounting for 20 percent (1.0 / 5.0) of the combined thickness and the ceramic components 162 accounting for 80 percent (4.0 / 5.0) of the combined thickness. As discussed above, 304 stainless steel has a coefficient of thermal expansion of 18.8 x 10'6per degree Celsius, and AL-30 has a coefficient of thermal expansion of 5 x 10'6per degree Celsius. The combined effective coefficient of thermal expansion may be calculated by multiplying the respective coefficient of thermal expansion of each layer by its respective proportion of the total thickness and adding the results. In this example, the combined effective coefficient of thermal expansion is (0.20) x (18.8 x 10'6) + (0.80) x (5 x 10'6) = 7.76 x 10'6, approximately 0.4 times the coefficient of thermal expansion of 304 stainless steel. In some embodiments, the coefficient of thermal expansion of the fastener 114 is at least 2.0 (e.g., or 3.0) times the combined effective coefficient of thermal expansion of every component (e.g., the stainless steel components 160 and the ceramic components 162) clamped between the end stop (e.g., the nut 146) and the base plate 116. This may help to ensure that the clamping force of the fastener assembly reduces enough upon operation of the fuel cell module 100 to allow the stack array housing 108 to expand without any components of the fuel cell module buckling or breaking and the mounting-12-4906-4400-2931 .1Atty. Dkt. No.: 111187-2187 bracket 134 to translate relative to the fastener 114 in a direction perpendicular or orthogonal to a longitudinal axis of the fastener 114 without grinding or abrading.

[0040] For example, when the fuel cell module is at its operating temperature, the fastener assembly may not clamp the stack array housing 108 at all (e.g., the clamping force may be zero). It should be understood that these dimensions and materials discussed above are used for the purpose of demonstrating an example of the effect of thermal expansion on the fastener assembly 110 and are not intended to be limiting. In other embodiments, the materials and dimensions of the fastener 114 and the components clamped between the nut 146 and the base plate 116 may vary, so long as the coefficient of thermal expansion of the fastener 114 is greater than the combined effective coefficient of thermal expansion of every component clamped between the nut 146 and the base plate 116. Thus, the fastener 114 and every component clamped between the nut 146 (or end stop) and the base 112 have respective coefficients of thermal expansion such that the clamping force is reduced upon an increase in temperature of the fuel cell module.

[0041] It should be understood that, in some embodiments, the tension in the fastener 1 14 may release as the fuel cell module 100 heats up, but the distance DF between the upper surface 152 of the base plate 116 and the lower surface 154 of the nut 146 and the distance D2' between the lower surface 156 of the lower spacer plate 128 and the upper surface 158 of the washer 148 may remain equal after the fuel cell module 100 heats up, despite thermal expansion, due to pretension in the fastener. For example, upon tightening the nut 146 to secure the stack array housing 108 to the base 112, the fastener 114 may stretch as tension increases. The increase in temperature when the fuel cell module 100 is in operation may cause the length of the fastener 114 to increase, but the pre-tension in the fastener may restrict the total change in length. Instead of increasing in length based only on the thermal expansion coefficient, the fastener 114 may increase in length only by the amount that the distance D2 increases due to the increase in thickness of the stainless steel components 160 and the ceramic components 162. While in this case, no gap may form between the nut 146 and the stainless steel components 160, some of the tension in the fastener 114 will be released. Thus, the clamping force of the fastener assembly-13-4906-4400-2931 .1Atty. Dkt. No.: 111187-2187 will be reduced, which reduces the friction between the stainless steel components 160 and the ceramic components 162 and between the washer 148 and the interface block 140. This may allow the mounting bracket 134 and the interface block 140 to slide along the spacer plate 126 as the stack array housing 108 heats up and expands, even though the nut 146 is still in contact with the stainless steel components 160.[0042J FIG. 5 illustrates a method 500 of installing a fuel cell module (e.g., fuel cell module 100) according to an exemplary embodiment. At operation 502 of the method 500, a stack array housing (e.g., stack array housing 108) containing a plurality of fuel cell stacks (e.g., fuel cell stacks 106) is coupled to a base of an outer module housing (e g., base 112 of outer module housing 102) by a fastener assembly (e.g., fastener assembly 110). The fastener assembly includes a fastener (e.g., fastener 114) extending through a portion of the stack array housing (e g., the lower flange 142 of the mounting bracket 134) and coupled to the base. The fastener assembly further includes an end stop, such as a head of the fastener or a nut (e.g., nut 146) and at least one additional material layer (e.g., spacer plates 126, interface block 140, washer 148, mounting plate 130, etc.) positioned between the end stop and the base.[0043| At operation 504 of the method 500, the stack array housing and the fuel cell stacks enclosed therein are enclosed within the outer module housing. For example, an upper portion of the outer module housing may be coupled to the base of the module housing. The fastener assembly may also be fully enclosed within and inaccessible from outside of the outer module housing. The outer module housing and all of the components enclosed therein may be considered a fuel cell module.[0044| At operation 506 of the method 500, the fuel cell module is transported to an installation site. Operation 504 may include any method of transporting, moving, positioning the fuel cell module as well as fixing the fuel cell module in place, including, but not limited to shipping via truck, boat, or plane, moving via forklift, crane, or by hand, and coupling the fuel cell module to the installation site, for example, with bolts, screws, or other fasteners.-14-4906-4400-2931 .1Atty. Dkt. No.: 111187-2187[0045| At operation 508 of the method 500, the plurality of fuel cell stacks are operated to generate electrical power. The fuel cell stacks may include, for example, solid oxide fuel cells, molten carbonate fuel cells, or other fuel cells that operate at elevated temperatures (e.g., over 200 degrees Celsius, over 400 degrees Celsius, etc.). After enclosing the stack array housing in the outer module housing at operation 506 and before operating the plurality of fuel cells at operation 508, the outer module housing is not opened or deconstructed (fully or partially). The fastener assembly remains inaccessible throughout this time period. In some embodiments, the fuel cells may be operated in reverse as electrolysis cells to separate water into hydrogen and oxygen. Electrolysis may similarly be performed at elevated temperatures (e.g., over 600 degrees Celsius), which may similarly cause the loosening of the fastener assembly.[0046| As utilized herein, the terms “approximately,” “about,” “substantially”, and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numerical ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the invention as recited in the appended claims.[0047 It is important to note that the construction and arrangement of the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter described herein. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be-15-4906-4400-2931 .1Atty. Dkt. No.: 111187-2187 altered or varied. The order or sequence of any process or method steps may be varied or resequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present invention.4906-4400-2931.1

Claims

Atty. Dkt. No.: 111187-2187WHAT IS CLAIMED IS:

1. A fuel cell module comprising: a plurality of fuel cell stacks positioned in a stack array housing; and a fastener assembly coupling the stack array housing to a base, the fastener assembly comprising a fastener that clamps a portion of the stack array housing between an end stop and the base; wherein the fastener and every component clamped between the end stop and the base have respective coefficients of thermal expansion such that a clamping force is reduced upon an increase in temperature of the fuel cell module.

2. The fuel cell module of claim 1, wherein at 20 degrees Celsius, a first distance between the end stop and the base is equal to a combined thickness of every component clamped between the end stop and the base, and wherein the increase in temperature causes the first distance to increase by a larger amount than an increase in the combined thickness.

3. The fuel cell module of claim 1, wherein the fastener comprises stainless steel, and at least one component clamped between the end stop and the base comprises ceramic.

4. The fuel cell module of claim 3, wherein the stainless steel is 304 stainless steel, and the ceramic is AL-30 alumina ceramic.

5. The fuel cell module of claim 1, wherein at least one component clamped between the end stop and the base comprises a ceramic spacer plate positioned between the portion of the stack array housing and the base.

6. The fuel cell module of claim 1, wherein at least one component clamped between the end stop and the base comprises an interface block positioned between the end stop and the portion of the stack array housing.-17-4906-4400-2931.1Atty. Dkt. No.: 111187-21877. The fuel cell module of claim 6, wherein the fastener extends through a slot in the interface block, the slot elongated in a direction parallel to a longitudinal axis of the stack array housing.

8. The fuel cell module of claim 1, wherein the end stop is a nut or a head of the fastener.

9. The fuel cell module of claim 1, wherein the portion of the stack array housing is a flange of a mounting bracket positioned at a lower end of the stack array housing.

10. The fuel cell module of claim 1, wherein the fastener assembly is fully enclosed within and inaccessible from outside of an outer module housing without opening or partially disassembling the outer module housing.

11. The fuel cell module of claim 1, wherein the coefficient of thermal expansion of the fastener is at least 2.0 times the combined effective coefficient of thermal expansion of every material clamped between the end stop and the base.

12. The fuel cell module of claim 1, wherein each fuel cell stack comprises at least one solid oxide fuel cell or at least one molten carbonate fuel cell.

13. The fuel cell module of claim 1, wherein the plurality of fuel cell stacks are configured to operate at at least 600 degrees Celsius.

14. A method of installing a fuel cell module comprising an outer module housing and a plurality of fuel cell stacks positioned within a stack array housing, the method comprising: coupling, at a first location, the stack array housing to a base using a fastener assembly, the fastener assembly comprising a fastener that clamps a portion of the stack array housing between an end stop and the base; and-18-4906-4400-2931.1Atty. Dkt. No.: 111187-2187 operating, at a second location, the plurality of fuel cell stacks to generate electrical power, wherein the fastener and every component clamped between the end stop and the base have respective coefficients of thermal expansion such that a clamping force is reduced upon operation of the plurality of fuel cell stacks.

15. The method of claim 14, further comprising sealing the stack array housing and the fastener assembly within an outer module housing after coupling the stack array housing to the base, wherein the outer module housing is not opened after enclosing the stack array housing and before operating the plurality of fuel cell stacks.

16. The method of claim 14, wherein coupling the stack array housing to the base comprises clamping the portion of the stack array housing between the end stop and the base with a first non-zero clamping force, wherein when the fuel cell stacks are operated at a temperature of 600 degrees Celsius, the clamping force reduces to zero.

17. The method of claim 14, wherein operating the plurality of fuel cell stacks causes the fastener assembly to increase in temperature, wherein the increase in temperature causes the stack array housing to thermally expand and the portion of the stack array housing to translate relative to the fastener.

18. The method of claim 17, wherein the portion of the stack array housing translates in a direction orthogonal to a longitudinal axis of the fastener.

19. The method of claim 14, wherein the fastener comprises stainless steel, and at least one component clamped between the end stop and the base comprises ceramic.

20. The method of claim 14, wherein the coefficient of thermal expansion of the fastener is at least 2.0 times the combined effective coefficient of thermal expansion of every material clamped between the end stop and the base.-19-4906-4400-2931.1

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