(357c) Sulphur-Iodine Plant for Large Scale Hydrogen Production by Nuclear Power

The sulphur iodine (S_I) thermo-chemical water splitting plant seems to be one of the most promising ways for massive hydrogen production. A techno-economic analysis has been carried out to investigate the potential for hydrogen production by S_I thermo-chemical cycle coupled with a 600 MW nuclear plant. In order to select suitable plant design solutions the following main aspects have been taken into consideration: ? definition of the process in terms of required unit operations and related process quantities (pressures, temperatures, compositions, heat and work requirements and so on); ? coupling between the nuclear thermal source and the S_I process; ? set up of the industrial plant lay out in order to find the most effective arrangement to perform the required operations; ? selection of appropriate technology and materials for each plant component; ? sizing of components and hydrogen production cost evaluation. A flow-sheet aimed at the achievement of the maximum efficiency developed has been assumed as a reference. The coupling between the hydrogen production SI plant and a Very High Temperature Reactor (VHTR) has been established by adopting the ?self sustaining concept?: both thermal power and electric one needed to sustain the hydrogen production overall process are supplied by the nuclear power plant. With these assumptions, only one design degree of freedom (DOF) has to be specified to completely define the VHTR-S_I cycle matching. The hydrogen production level has been assumed as DOF. A H2 production level of 633 mol/s with an overall plant efficiency of some 35% has been taken as reference. An industrial plant lay out has been defined. Plant components have been sized and costs evaluated by using standard chemical engineering methods and by means of ?ad hoc? developed databases. Suitable acid resistant materials have been selected, taking ceramic materials into particular consideration. Costs of installed equipment have been evaluated by adopting a factored method. The investment cost of the HIx section has been found approximately eight times greater than that of the H2SO4 section, and roughly 80% of HIx section overall cost is constituted by heat recovery devices. The influence of investment costs on overall production costs is of some 40%. In order to find the best compromise between investment and operating costs a parametric analysis has been carried out by varying the hydrogen production level keeping the overall available thermal power from the nuclear reactor at the reference value (600 MW). For different H2 productions detailed plant sizing and cost accounting have been performed. The reduction of H2 production level has led to a decrease of investment costs mainly due to the reduction of sizes of HIx section recovery heat exchangers. The minimum cost is achieved at 540 mol/s and does not correspond to the maximum achievable efficiency. In order to obtain further reduction of costs, technology improvements concerning the HIx section recovery heat exchangers have been introduced. To enhance heat transfer coefficients bare tubes have been replaced by corrugated ones. A reduction of costs is observed all along the production range taken into consideration and the minimum is still achieved at 540 mol/s. The work has been carried out within HYTHEC (HYdrogen THErmochemical Cycles) research project.