High temperature nuclear heat for isothermal reformer

High temperature nuclear heat can be used to operate a reformer with various feedstock materials. The product synthesis gas can be used not only as a source for hydrogen and as a feedstock for many essential chemical industries, such as ammonia and other products, but also for methanol and synthetic fuels. It can also be burnt directly in a combustion chamber of a gas turbine in an efficient combined cycle and generate electricity. In addition, it can be used as fuel for fuel cells. The reforming reaction is endothermic and the contribution of the nuclear energy to the calorific value of the final product (synthesis gas) is about 25%, compared to the calorific value of the feedstock reactants. If the feedstock is from fossil origin, the nuclear energy contributes to a substantial reduction in CO2 emission to the atmosphere. The catalytic steam reforming of natural gas is the most common process. However, other feedstock materials, such as biogas, landfill gas and CO2-contaminated natural gas, can be reformed as well, either directly or with the addition of steam. The industrial steam reformers are generally fixed bed reactors, and their performance is strongly affected by the heat transfer from the furnace to the catalyst tubes. In top-fired as well as side-fired industrial configurations of steam reformers, the radiation is the main mechanism of heat transfer and convection heat transfer is negligible. The flames and the furnace gas constitute the main sources of the heat. In the nuclear reformers developed primarily in Germany, in connection with the EVA-ADAM project (closed cycle), the nuclear heat is transferred from the nuclear reactor coolant gas by convection, using a heating jacket around the reformer tubes. In this presentation it is proposed that the helium in a secondary loop, used to cool the nuclear reactor, will be employed to evaporate intermediate medium, such as sodium, zinc and aluminum chloride. Then, the vapors of the medium material transfer the heat to the reformer and condense on its walls. Three configurations can be conceived. The vapors of the sodium are condensed on the outside surface of the reformer tube and the liquid is then drained into a pool-boiling-He/Na heat exchanger. Another option is internal heating of an annular catalyst bed reformer with a sodium heat pipe, for instance. The third option is reformer tubes immersed inside the boiling medium. In all cases means for the enhancement of heat transfer can be applied. The use of condensing metal vapors increases the heat transfer compared to the convective reformer, resulting in more compact reformers. The safety aspects of this approach are twofold: (a) Additional physical separation between the nuclear reactor coolant and the chemical plant. This will enable to reduce the operating pressure inside the reformer, thus reducing the working temperature and increasing the extent on the reaction and the CH4 conversion. (b) In case of a failure in the chemical plant. the liquid metal can be used as a safety buffer. In this event, the vapors of the medium material are diverted and condensed in an emergency condenser and returned to the pool boiling by natural circulation, avoiding the need to reduce immediately the power rating of the nuclear reactor or even its complete shutdown. (author)