TECHNICAL FIELD

[0001] The present invention relates; to a. fuel cell system and more particularly relates to a high efficiency solid oxide fuel cell (SOFC) system with a passive device.

BACKGROUND

[0002] Fuel cells generate energy By the electrochemical combination of hydrogen and oxygen. In a solid oxide fuel cell an anodic layer and a cathodic. layer is separated by an electrolyte formed of a ceramic solid oxide. Further hydrogen which may be either pure or reformed from hydrocarbons, is channeled along the outer surface of the anode and diffused into the anode. Oxygen, typically from air, is channeled along the outer surface of the cathode and diffused into the cathode. Each oxygen molecule is split and dissociated into two O ^2- anions catalytically by the cathode. The oxygen anions migrate through the crystal structure of the electrolyte and combine at the anode/electrolyte interface with four hydrogen cations to- form two molecules of water and yields 4 electrons. The anode and the cathode are connected externally through a load to complete the circuit. When hydrogen is derived by "reforming" hydrocarbons such as natural gas, LPG or Biogas in the presence of limited oxygen, the. "reformate" gas includes CO which is converted to COi at the anode via an oxidation process similar to that performed on the hydrogen. In stationary fuel cell applications, reformed natural gas is commonly used as a fuel. [0003] In a partial oxidation catalytic reformer fuel and air are pre -mixed under-stoichiometrie molar ratio also called as "lambda", abbreviated as LMB, At a LMB ratio of 1, the provided fuel would be completely oxidized as in an open flame or standard combustion process. For an LMB below 1 , the fuel is just partially oxidized, providing a hydrogen-rich reformats which is used for electrochemical conversion inside the SOFC stack. If the LMB becomes too low, carbon deposition (soot formation) might occur in the reformer and stack, which is harmful for the equipment. If LMB is too high, the provided fuel may completely oxidize forming water and carbon di-oxide instead of hydrogen and Carbon monoxide as fuel for the fuel cell. In a standard configuration of the partial oxidation reformer (POX), fuel and air are pre-mixed at ambient temperatures, then provided to the POX. where the reactants are internally heated up to the reaction temperature and the reforming reactions take place, afterwards. Depending on the actual LMB-value, a certain reformer temperature will be established by the energy balance between reactant pre-heating (endothermal) andreforming. reactions (mainly exothermal).

SUMMARY

[0004] In an aspect of the present invention, a high efficiency solid oxide fuel cell (SOFC) system with- thermally - integrated hot box having a passive device is disclosed.

[0005] In one implementation thermally .integrated hotbox is disclosed.

The hot box may comprise a solid oxide fuel cell stack. Further the thermally integrated hotbox may comprise an electric air pre-heater configured to supplypre-heated air to the solid oxide fuel cell stack. Further a. partial catalytic oxidizer may be integrated within the hotbox and connected to the solid oxide fuel cell stack. The system may further comprise a non-catalytic tail gas oxidizer connected to the solid oxide fuel cell stack.

[0006] In another implementation a SOFC system may be disclosed. The system may comprise a hotbox. Further a solid oxide fuel cell stack may be integrated within the hotbox. The solid oxide fuel cell stack may be further configured to receive pre-heated air from an electric air pre-heater. Further a catalytic partial oxidation reformer may be connected to the solid oxide fuel ceil stack. The system may further comprise a non-catalytic tail gas oxidizer connected to the solid oxide fuel cell stack. Farther an oxidant pre-heater may be integrated within the hot box and connected to the catalytic partial oxidation reformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The detailed description is described with reference to the accompanying figures.

[0008] Figure 1 , illustrates a schematic of a solid oxide fuel cell (SOFC)system according to the exemplary embodiment of the present invention.

[0009] Figure 2 illustrates a SOFC in accordance with the present disclosure,

[0010] Figure 3 illustrates a wave spring compression in accordance with the present disclosure.

[0011] Figure 4 illustrates a tail gas oxidizer in accordance with the present disclosure.

DETAILED DESCRIPTION

[0012] In an exemplary embodiment of the present invention, a solid oxide fuel cell (SOFC) system is disclosed. Referring to figure 1 , illustrates a system in accordance with the present disclosure. The system 10ft as shown comprises a Hot Box 102. The hot box 102 may further comprise a solid oxide fuel cell stack (SOFC) 104 integrated within the hot box 102. The hot box 112 may further comprise a catalytic partial oxidation reformer 106 coupled to the SOFC 104. The catalytic partial oxidation reformer 106 may be integrated within the hot box 102. The catalytic partial oxidation reformer 106 may be- configured to partially oxidize intake fuel supplied to the SOFC stack 104. The hot box 102 may further comprise electric air pre-heater (EAPH) 108 integrated within the hot box 192 and configured to supply pre-heated air to the SOFC stack 104. The EAPH 108, may be configured to pre-heat intake air supplied to the SOFC siack 104. The intake air may be at ambient temperature, in order use the air in SOFC we may need to increase the temperature of the intake air. The air from the EAPH 108 may be supplied at the cathode side of the SOFC stack 104, during the start-tip and various operational modes, in another exemplary embodiment the intake air at ambient temperature may be heated before the EAPH 108, by re-capturing exhaust heat from the SOFC stack 104, via air pre-heater 114, The air pre-heater 114 may capture the exhaust air and recirculate within the system.

[0013] The system may further comprise oxidant pre-heater (OPH) 112.

The oxidant pre-heater (OPH) 112 may be integrated within the hot box 102. Further the oxidant pre-heater (OPH) 112 may be connected to the catalytic partial oxidation reformer 106, The oxidant pre-heater 112 may be configured to receive intake air at the ambient temperature and further pre-heat the intake air using the exothermic heat from a non-catalytic tail gas oxidizer 110. Further the oxidam preheater 112 may supply/feed the pre-heated air to the catalytic partial oxidation reformer 106, to avoid the requirement of high air- fuel ratio in the catalytic partial oxidation reformer 106 and to maintain the desired temperature in the hot box 102,

[0014] For example, at LMB of 1 , i.e. under-stoichiometric molar ratio also called as air ratio or "lambda", the fuel would be completely oxidized as man open flame or standard combustion process. While with an LMB below 1 , the fuel would be partially oxidized, providing a hydrogen-rich reformats which may be used for electrochemical conversion inside the SOFC stack. Further if the LMB becomes too low, carbon deposition (soot formation) may occur in the catalytic partial oxidation reformer and solid oxide fuel cell stack. And if LMB is too high, the catalytic partial oxidation reformer may become too hot. In a standard configuration of the catalytic partial oxidation reformer, ft el and air are pre-nuxed at ambient temperatures, then provided to the catalytic partial oxidation reformer, where the reaetanis are internally heated up to the reaction temperature and the reforming reactions take place, afterwards. In the present exemplary embodiment the oxidant pre-heater, pre-heats the ambient air before mixing with the provided fuel.

[0015] Further the oxidant pre-heater (OPH) 112 may achieve a higher outlet temperature of the catalytic partial oxidation reformer 106 with a lower LMB. For e.g. with OPH the outlet temperature of catalytic partial oxidation reformer cab be maintained at 820 °C with reduced lambda 0.24 rather than having an outlet temperature of 780 °C and working with a lambda of 0.26; e.g, the outlet temperature can be maintained at 660 °C with reduced lambda 0.33 rather than having an outlet temperature of 650 °C and working with a lambda of 0.34.

[0016] Further the non-catalytic tail gas oxidizer 110 may be connected to the solid oxide fuel eell stack 184, wherein the non-catalytic tail gas oxidizer 110 is positioned at exhaust of the solid oxide fuel cell stack 104,

[0017] Now referring to Figure 2 illustrating the hot box 102, in accordance with the present disclosure. The thermally integrated hot box 102. may comprise a solid oxide fuel cell stack 104, an electric air pre-heater 108, a catalytic partial oxidation reformer 106, a non-catalytic tail gas oxidizer, and an oxidant pre-heater (OPH) 112 integrated within the hotbox 102. Further the hot box 102, may comprise an external thermal insulation 204 and an internal insulation 206 enclosing the various components within the hot box 102.

[0018] The external thermal insulation. 204 and the internal insulation 206 integrated within the hot box 102 may be arranged in such a way to facilitate the simultaneous heat transfer within the hot box 102 or reduce the heat dissipated from the hot box 102. The internal insulation 206 may have high thermal conductivity allowing simultaneous heat transfer between core components of hot box 102. The external thermal insulation 204 may have a low thermal conductivity helping to retain the heat in the hot box 102 and prevent heat loss to the externa] environment. The external thermal insulation 204 and the internal insulation 206 may provide a better thermal insulation to the solid oxide fuel cell stack 104. The external thermal insolation 204 and the internal insulation 206 may further comprise multiple insulating materials, in one of the embodiments, the external thermal insulation 204 and the internal insulation 206 may be a graded insulation comprising multiple insulating materials arranged together. In a preferred embodiment the external thermal insulation 204 and the internal insulation 206 may comprise a plurality of calcium silicate boards. Further the external thermal insulation 204 and the internal insulation 206 helps to maintain uniform heating to the solid oxide fuel cell stack 104. [0019] The hot box 102, may further comprise a ceramic housing 202 integrated within the hot box 102 and positioned below the solid oxide fuel cell stack 104, Further the non-catalytic tail gas oxidizer 110 is embedded in a form of cavity within the ceramic housing 202.

[0020] Referring to Figure 3, illustrates a wave spring compression in accordance with the present disclosure. The hot box 102 may further comprise a plurality of wave spring 306. In an exemplary embodiment at least four wave spring 306 may be mounted in the hot box 102 to provide compression force to the solid oxide fuel cell stack 104. The plurality of wave spring may be mounted on ceramic rods 304. The ceramic rods 304 may he mounted on the solid oxide fuel cell stack 104 and in a gap provided in the external thermal insulation. Further the wave springs 306, may be mounted on stiffeners 302 at the other end. The wave springs 306, may be mounted in a compressed position, in order to provide better axial load transmission and reduction in operating height. The at least four wave spring 306 may further be configured to compensate for thermal expansion of the hot box 102 during the operation.

[0021] Referring to Figure 4 illustrates a tail gas oxidizer in accordance with the present disclosure. The non-catalytic tail gas oxidizer 400 of the present embodiment may negate the need of conventional tail gas oxidizer requiring a catalyst and having metal components. Further the non-catalytic tail gas oxidizer 400, may have geometric shape like a boomerang wherein the remnants, from SOFG stack 104, i.e. the un-utilized air from cathode side and unconverted fuel from the anode side are introduced from adjacent openings 402. The adjacent openings may be at defined angle to each other, for e,g, perpendicular to each other. The geometric shape of the non-caia!yiic tail gas oxidizer 400 may further enable complete burning of the remnants. The non-catalytic: tail gas 400 may further comprise an opening 404, wherein the opening 404 may act as extended combustion enabling burning of the remnant fuel.

[0022] Although the invention has been disclosed in the context of certain aspects and embodiments, it will be understood by those skilled in the art that She present invention extends beyond the specific embodiments to alternative embodiments and/or uses of the invention and obvious implementations and equivalents thereof. Thus, it is intended that the scope of the present invention disclosed herein should not be limited by the disclosed aspects and embodiments above.