Thermochemical Production of Hydrogen from Water, a Critical Review

摘要

The current status of thermochemical hydrogen technology as regards process chemistry, preliminary chemical engineering design and techno-economics for a number of cycles undergoing active research and development efforts throughout the world at this time is assessed. Three cycles are receiving the bulk of the total effort and most of the funding: the hybrid sulfuric acid cycle; the sulfuric acid-hydrogen iodide cycle; and the hybrid sulfuric acid-hydrogen bromide cycle (Mark 13) . All three cycles are at the stage where a laboratory scale continuous plant can be or is in operation. The only plant in operation is at Ispra, Italy on the Mark 13 cycle. Materials problems are endemic to all cycles. In most cases reference materials for the sulfuric acid vaporization stages and the sulfuric acid or sulfur trioxide decomposition vessels have not yet been defined. A prime difficulty is the need for the vessel walls to transmit heat to interior fluids as well as withstand their corrosive effects. Serious efforts must be undertaken in the materials area prior to demonstration of any of the sulfuric acid-based cycles on a pilot plant scale under realistic pressure (30 atm) and temperature conditions. Improvements are being made in estimating the cost and efficiency of hydrogen produced from water and a thermal energy source either by thermochemical cycle technology or by water electrolysis. These include the heat penalty analysis and the OPTIMO computer code. Costs of thermochemical hydrogen have been found to fall in the $7 to $10/10 exp 16 Btu range with efficiencies in the 35 to 45% bracket. A 10 to 15 year developmental effort with increased funding of both options (thermochemical and water electrolysis) should find a clear-cut solution and resolve the situation of the ''best'' option to use for producing synthetic hydrogen from water. (ERA citation 04:021897)