The MTU Carbonate Fuel Cell HotModule®: Utilization of Biomass and Waste Originated Fuels for Polygeneration in Fuel Cells
Authors: Huppmann Gerhard 
Published: September 2008

MTU’s HotModule is a High Temperature Molten Carbonate Fuel Cell System. It transfers the chemical energy of the fuel directly to electricity, heat and a useful depleted air with an electrical efficiency in the range of 42 to 52%. It convinces by minimal emissions of contaminants. The produced heat is given by the depleted air at a temperature level of 400 °C; this ensures a multi purpose and valuable utilization of the heat. The HotModule operated with natural gas is demonstrated meanwhile together with our partner Fuel Cell Energy Inc. in approximately 25 field trial plants and reached now a pre-commercial status. It is highly suitable for the utilization of hydrocarboneous gases, such as biogas, sewage gas, coal mine gas, of synthesis gases from thermal gasification processes of different waste material. Such gases are the most important renewable energy resources. In case of a consequent utilization of such gases for Combined Heat and Power Production a contribution of 12% to 15% of stationary consumable energy consumption can be reached. Even lean gases will be converted with high efficiency to electrical power and high exergetic heat. These characteristics recommend the HotModule for applications using the big potential of regenerative and secondary fuels with all their advantages in decentralized consumable energy supply, reduction of dependence on primary energy imports and reduction of greenhouse gas and other contaminants emission. MTU started recently a HotModule fed by methanol from waste material together with BEWAG in Berlin and many experimental work concerning applications with biogas and sewage gas has been performed with promising results. Due to the high electrical efficiency the HotModule saves about 1/3 of CO2 emission in comparison to conventional “prime movers”. If fuels are used, which are originated from renewable sources like biomass via fermentation or gasification, the balance of CO2 is zero within a suitable short period (in comparison to coal, natural gas and oil, where this period is some millions of years). The advantage of the Carbonate Fuel Cell HotModule is, that these fuel gases from the renewable sources can be used with the high performance and efficiency of the HotModule, even they are low caloric gases, which decline the electric efficiency of conventional prime movers significantly. The products of the HotModule are: • Electricity: DC for telecommunication and IT - AC to grid or to stand alone networks - Applications for uninterruptible power supply. • Premium Heat: Heat from HotModule is available in form of the depleted air at a high temperature. This high exergetic heat is valuable for steam production, industrial production processes as well as for many other processes e. g. in hospitals, in the food industry, in greenhouse farming. It can also be used in cascades of steam production for additional electricity generation via steam turbines, medium temperature processes like drying, cooking, and at the low temperature end for water heating and space heating and — may be — pool heating. • Cooling Power: Another important heat utilization is the production of cooling power for air conditioning and food storage facilities by thermal driven cooling systems, e. g. absorption chillers or steam injection chillers with the overlapping of the required energy amounts over the year: Cooling in summer, heating in winter. This leads to a thermal full power operation of the HotModule all over the year decreasing the pay back period of such equipment. • Fertilizing atmosphere: The depleted air consists of nitrogen, a small amount of oxygen, lots of water vapour and a substantial amount of CO2 (in the range of 5%vol). No contaminants, no toxic ingredients, no other loads. Mixed with fresh air, this depleted air is a most valuable atmosphere for greenhouse farming: Plants need the right temperature, the CO2-contents increase the growing rate of the plants (e. g. tomatoes need an average of 2%vol of CO2 in atmosphere for optimal growing; CO2-fertilizer) and the high water vapour content saves humidification water.