Modeling Hydrogen Synthesis with Rigorous Kinetics as Part of Plant-Wide Optimization

摘要

Hydrogen for industrial use is manufactured primarily by steam reforming hydrocarbons, or is available as a byproduct of refinery or chemical plant operations. Hydrogen demand usually is significantly greater than that available as a byproduct, and many times the plant's ability to supply hydrogen limits overall plant throughput. An operating plant can exploit existing in-place steam reformer and related equipment designs with rigor-ous models that employ kinetics. During plant design kinetics models are not necessarily used because experience and more simple models using "approach to equilibrium", space velocity , maximum heat flux, and other parameters allow designers to build hydrogen plants to supply whatever hydrogen amount, purity, and pressure that is desired. The objective of suppliers of hydrogen plants is to establish an economic feasible design, given these predetermined criteria. Additional hydrogen, or less expensive hydrogen can be manufactured from these facilities, after construction, when rigorous models are used in on-line, closed loop optimization systems. These systems manipulate independent operating conditions (degrees of freedom), maximize or minimize an objective function (usually operating profit), while honoring numerous constraints, such as tube metal temperatures, pressure drops, pressures, damper and valve positions. A good kinetic model is the cornerstone of the predictive capabilities of such on-line optimization systems. An on-line optimization system exploits equipment under operating demands and constraints that were not necessarily anticipated during design.