Characteristic time as a descriptive parameter in steam reformation hydrogen production processes

In the study of steam reformation, space velocity has been used as a scaling parameter to quantify reactor performance. However, in a real system, reactor geometry, steam-to-carbon ratio, temperature and pressure of the reaction, flow pattern inside the reactor, etc. are all factors that affect a reformer's performance. Previous studies have proven that space velocity alone is insufficient to describe steam reformer performance. This study presents an analysis and discussion of characteristic time as a descriptive parameter. Based on the analysis, this parameter must contain the physical and chemical reaction information of a steam reformer and is generally more insightful than using space velocity alone. Accurate individual analysis of each limiting mechanism (heat transfer, mass transfer and chemical kinetics) is perhaps the preferred method for quantifying reactor performance, but the interactions between the mechanisms often make such combined analysis difficult, if not impossible. Methanol steam reformation is viewed as a first-order chemical reaction to convert methanol to hydrogen; thus, a first-order characteristic time is used to identify and characterize reactor performance across all space velocities and with various limiting mechanisms. In this study, five physical reactor conditions were tested and analyzed using each reactor's fuel conversion as the output metric. After analyzing the reactor conversion data, the characteristic time was derived and discussed as based on a fit of the data to a mean first-order conversion equation. This simplification of the reactor model to a single characteristic time embodies concentration gradients, temperature gradients, non-homogeneous flow fields, reaction chemistry, etc., yet, still provides a meaningful description of reactor performance across a range of space velocities.