Fuel cell heater

This application claims priority from U.S. Provisional Patent Application Ser. No. 61/042,809, filed 7 Apr. 2008, the disclosure of which is incorporated herein by reference.

The present disclosure generally relates to heaters such as self-powered heaters, and particularly, to the replacement of thermoelectric generators currently used in a self-powered heater by the integration of an electrochemical generation fuel cell that provides a percentage of total combustion gases for heating. The combustion gases are created from liquid fuels and a common burner that has a fire rate or hot gas output sized to provide soft or hard wall shelter heat with the use of a breathable air heat exchanger.

Space heaters have wide spread success and have been in production for the military for several years. A space heater is generally one of three types, namely, non-powered, powered and self-powered. The non-powered heater is generally a “light it with a match” type vaporizing convection heater that comes in various BTU outputs. The powered heater requires external power, such as power generated from a generator or from a local power grid. The self-powered heater provides forced air heat and has all of the features of a powered heater except that no external power is required. The self-powered heater generally is thermostat controlled, producing burner turn down rates with built in diagnostic and prognostic controls. The self-powered heater typically operates by the manipulation of a single switch.

In military application, the self-powered heater is primarily used to heat soft and hard wall shelters in military field conditions, but have use in any application where space heating is desirable. The self-powered heater can be operated in ambient temperatures to −60° F., and from sea level to 10,000 feet. The self-powered heater can operate on liquid fuel, such as diesel, bio fuels and kerosene, such as JP-8 and Jet-A.

The self-powered heater generally uses an internal thermoelectric generator integrated within a main hot gas stream to extract a portion of the combustion heat to provide electricity for heater operation. Due to the required heat output, the amount of hot gas BTUs used for electrical generation is considerably less than the BTUs applied to a breathable hot air heat exchanger. Depending upon the operation cycle, excess electrical power is available for export power after an internal battery is fully charged. Current self-powered heaters use the export power for electrical heating that is added internally to the heated air stream.

The current art of the fuel cell industry is to increase electrical conversion efficiency and reduce balance of plant system cost per electrical watt produced. To increase the overall or apparent efficiency, fuel cell generators are being integrated into combined chill heat (CHP) cogeneration applications and combined chill heat and power (CCHP) tri-generation applications. Even though fuel cell generators are being integrated into CHP for home or business use, the waste heat output is not sufficient to be used for primary heat but can be used for low level heating. Additional heat and electrical power is required in order to provide the desired comfort level during peak cold weather heat load demands.

Conventional fuel cell generators cannot produce sufficient electrical wattage during high building demand periods. Fuel cells are typically designed to operate very efficiently using the least amount of fuel energy for the conversion to electrical output. The waste heat of many fuel cell applications is used to heat liquids or an air stream. This efficient operation limits the heat output of the fuel cell. Using the fuel cell electrical output to augment the rejected heat by using resistive heating can be counterproductive due to having less electrical power available for building demands.

Conventional fuel cell cogeneration designs for buildings utilize a fuel cell with an electrical output capacity (kW) that is near the time-averaged electrical power consumption rate for the building and with a heat generation capacity that is useful for meeting building heating needs. The actual onsite time-variable power demand (kW) is met by a combination of the cogeneration electrical power produced on sight and electrical power from the public electrical power grid or another external power source. When heat from the cogeneration fuel cell is insufficient to heat the building, an auxiliary heater, operated typically by burning fuel, supplements or augments the heat provided by the cogeneration of the fuel cell. The ability of using a fuel cell as a primary or single source space heater is limited due to this efficiency.

The following list of patents relate to cogeneration heat and power. However, this type of fuel cell integration, when used for primary heating, provides insufficient waste heat. Therefore, the patents further disclose provisions for external electrical and/or additional fuel burner augmentation.

WO 2005/047776 teaches a liquid cooled fuel cell system and cogeneration (CHP) of building heat. The system comprises of an auxiliary heater which is used when a primary heat exchanger is insufficient to provide desired space heating. The auxiliary heater can be connected to an external electric power source.

U.S. Pat. No. 6,054,299 teaches a fuel cell for the production of electricity, with a heating, ventilation and cooling system using waste heat generated by the fuel cell. An interface-exchanging element can be adapted to receive thermal energy from an incoming fluid having an elevated temperature. By having the ability to operate an additional burner source, the fuel cell low thermal output can be augmented during high heating demands.

GB 2404007 discloses an air heater comprising electrical air heating elements powered by a fuel cell unit.

As is evident from the above prior art, buildings that derive some or all of their electrical needs from a fuel cell require a second burner or an additional resistive heating device for adequate space heating comfort during the winter season. Using the rejected heat and power output of a fuel cell for primary space heating is not practical due to the increased cost, size and weight of a cogenerated fuel cell that is sized to produce electrical resistive and combustion heat outputs sufficient for total space heating requirements.

The following list of patents relate to start-up burners and combustors.

US Patent Application Publication No. 2005/0257427 relates to a start-up burner for rapidly heating a catalyst in a reformer as well as related methods and modules. The module can further contain an auxiliary burner adapted for warming fluids in the module.

U.S. Pat. No. 7,086,853 is directed to a start-up combustor for a fuel cell having a filter used to trap soot that is operated during start up.

U.S. Pat. No. 6,007,620 discloses a fuel cell system with a combustor-heated reformer capable of operating a combustor to heat a fuel processor over a wide range heat outputs.

U.S. Pat. No. 6,451,465 B1 teaches a method for operating a combustor in a fuel cell system to heat a fuel processor by monitoring temperature and regulation of fuel flows.

U.S. Pat. No. 6,777,123 discloses combustor temperature control of a fuel cell power plant. A combustor generates heat from the combustion of fuel. The combustion stall temperature of the combustor is controlled by regulating fuel flow.