Fuel cells make electricity from fuel and air. What makes fuel cell technology unique, compared to other energy technologies, is the fact that fuel cells react the fuel and air electrochemically instead of using combustion. Because fuel cells don’t burn fuel, they emit negligible amounts of NOx, SOx, and particulate matter and offer a more direct and efficient way to generate power. Carbonate fuel cells, also known as “molten” carbonate fuel cells, operate at high temperatures for optimal efficiency when generating electricity through the chemical reaction.
High-temperature operation of carbonate fuel cells
Carbonate fuel cells operate at approximately 1000°F, which is hot enough to steam-reform methane-based (CH4) fuels into hydrogen (H2) and carbon dioxide (CO2) within the fuel cell stack. The hydrogen is then used to generate power. Inside of the carbonate fuel cell stacks, the electricity producing reaction is exothermic (it releases heat), while the fuel reforming reaction is endothermic (it absorbs heat). The heat created during the fuel cell’s electricity producing reaction is used to help steam-reform fuel in a circular process.
Maximizing fuel cell system efficiency through internal reforming
The internal reforming that occurs inside the stacks is unique to FuelCell Energy’s carbonate fuel cell design. Since direct reforming of natural gas or biogas happens inside the stacks at a high temperature, the system doesn’t require costly external reforming equipment. By comparison, fuel cell systems that operate at lower temperatures must reform their fuels externally, adding cost and complexity to the system.
External reforming processes require the temperature of the natural gas to be raised to reforming temperatures to convert the gas to hydrogen (reducing system efficiency) and then cooled before it can be introduced into the lower temperature fuel cell stack (further reducing system efficiency). As a result, low temperature fuel cells are limited to efficiencies in the mid to high 30s whereas FuelCell Energy’s efficiencies range in the high 40s (based on the LHV of the fuel). In fuel cell combined heat and power systems, total efficiency can be even higher.
Generating valuable heat from a combined heat and power system (CHP)
Combined heat and power (CHP), also known as cogeneration, is an efficient and reliable approach to generating power and thermal energy from a fuel cell. Since FuelCell Energy’s carbonate fuel cells operate at approximately 1000°F, high-grade waste heat can be recovered at around 700°F as hot exhaust, hot water, or steam.
CHP transfers heat energy that would otherwise be lost from the fuel cell. This thermal energy can be used for industrial processes, domestic hot water, and space heating or cooling. FuelCell Energy is known for developing multiple large-scale fuel cell-powered district heating systems in Korea, like the one at the Hwaseong Balan Industrial Complex that is capable of powering approximately 135,000 homes and providing heat to 20,000 homes.
Heat from FuelCell Energy’s CHP systems has also been used to support anaerobic digestion at wastewater treatment plants, space heating at hospitals, and even to heat university campus buildings and swimming pools. Thermal energy from fuel cells can also drive absorption chilling for space cooling at data centers and other sites.
Complete fuel cell combined heat and power systems (CHP)
A fuel cell combined heat and power system can significantly increase overall system efficiency, reducing the total cost of operation. A 3000 Carbonate Fuel Cell System configured with condensing type heat recovery systems can theoretically achieve total LHV system efficiencies above 90%. Practically, efficiencies of 65% to 80% are more typical. CHP systems can save money and lower facility emissions by reducing, or completely avoiding, the fuel usage of on-site boilers.
FuelCell Energy offers packaged combined heat and power systems as a product option, including the heat recovery unit and associated pumps, controls, and piping to the site’s heat source as part of a turnkey project.
Contact us today to learn more about our fuel cell combined heat and power systems.