Effect of mode of operation on hydrogen production from glycerol at thermal neutral conditions: Thermodynamic analysis

Abstract

Thermodynamic analysis of hydrogen production from glycerol under thermal neutral conditions is studied in this work. Heat requirement from the process can be achieved from the exothermic reaction of glycerol with oxygen in air fed to the system. Two modes of operation for air feeding are considered including (i) Single-feed mode in which air is fed in combination with water and glycerol to the reformer, and (ii) Split-feed mode in which air and part of glycerol is fed to a combustor in order to generate heat. The thermal neutral conditions are considered for two levels including Reformer and System levels. It was found that the H 2 yield from both modes is not significantly different at the Reformer level. In contrast, the difference becomes more pronounced at the System level. Single-feed and Split-feed modes offer high H 2 yield in low (600–900 K) and high (900–1200 K) temperature ranges, respectively. The maximum H 2 yields are 5.67 (water to glycerol ratio, WGR = 12, oxygen to glycerol ratio, OGR = 0.37, T = 900 K, Split-feed mode), and 3.28 ( WGR = 3, OGR = 1.40, T = 900 K, Single-feed mode), for the Reformer and System levels, respectively. The difference between H 2 yields in both levels mainly arises from the huge heat demand for preheating feeds in the System level, and therefore, a higher amount of air is needed to achieve the thermal neutral condition. Split-feed mode is a favorable choice in term of H 2 purity because the gas product is not diluted with N 2 from the air. The use of pure O 2 and afterburner products (ABP) stream were also considered at the System level. The maximum H 2 yield becomes 3.75 ( WGR = 5.21, OGR = 1.28, T = 900 K, Split-feed mode) at thermal neutral condition when utilizing heat from the ABP stream. Finally comparisons between the different modes and levels are addressed in terms of yield of by-products, and carbon formation.