Yau-Pin Chyou

Various means for enhancing hydrogen content in the syngas from gasification of solid biomass in fluidized-bed reactors were investigated in this study. Steam or oxygen-rich gas can be supplied as gasification medium, to improve the syngas characteristics. Alternatively, a so-called “indirect gasification technology” realizes the thermo-chemical conversion processes in dual reactors, respectively, for combustion and gasification, where gaseous streams in between are separated while solid materials are circulated through. Hence, with air as oxidant for combustion this system features the advantage of producing nearly nitrogen-free syngas. Baseline experiments were firstly carried out to identify performance features; then, parametric studies were conducted and positive trends for enhancing hydrogen generation via biomass gasification were revealed. Moreover, hydrodynamic characteristics in dual reactors were comprehensively envisaged in the cold-flow models to facilitate subsequent investigation into thermo-chemical processes. The experimental results indicated that the circulation mass of the bed material driven by the operating air exceeded the design value, which gave a comfortable safety factor of the engineering design. In addition, the average pressure distribution measured by the cyclic operation of the system was similar to that of the published literature. Based on the experimental results of the cold model, the suggestions of the operating tests in the hot model were addressed. Further efforts will be pursued to establish databases for clean energy and carbon abatement technologies.

In this study, solid biomass is gasified in fluidized-bed reactors, to investigate the effect of various means on syngas composition, especially for enhancing hydrogen content in the production gas. Conventionally, air is supplied to the reactor as gasification medium, which inevitably results in a high nitrogen content in the syngas. Alternatively, steam or oxygen-rich gas can be supplied to improve the syngas characteristics. On the other hand, a so-called “indirect gasification technology” realizes the whole conversion processes in dual reactors, for combustion and gasification, respectively; moreover, solid materials are circulated through two reactors, while gaseous streams in between are separated from each other. Hence, this system features the advantage of producing near nitrogen-free syngas in the gasifier, with air as oxidant in the combustor. Baseline experiments with various operating parameters, including air equivalence ratio (ER) and temperature, were firstly performed in a 30 kWth bubbling fluidized-bed gasifier; then, trial tests were conducted with the aforementioned operational and constructional factors. The preliminary test data show positive trends for the enhancement of hydrogen generation via biomass gasification. Further efforts will be pursued to establish a data base, which would be beneficial to extensive researches on clean energy and carbon abatement technologies.

The objective of this study is to implement a tar condensation and re-vaporization sub-model in a previously established Computational Fluid Dynamics (CFD) model for the Entrained Slagging Transport Reactor (E-STR) gasifier, modified from the existing E-Gasifier simulation models in previous studies. The major modifications in E-STR, compared to the existing E-Gas^TM design, include higher operating pressure and lower temperature, with the aim of achieving a higher H₂/CO ratio of syngas, which is more favorable for synthetic natural gas (SNG) production. In this study, the aforementioned sub-model is described by the UDF (User-Defined Function) and incorporated in a previously developed computational model for entrained-flow gasification process, to study the syngas composition without implementing a tars-cracking catalyst in the E-STR gasifier. The results show that incorporating the tar condensation model leads to a formation of approximately 6.47% liquid volatiles and an exit temperature increase about 135 K, due to the release of latent heat. These sub-models have been successfully implemented and will be useful in the condition that the gasifier temperature is intentionally kept low, just as the E-STR gasifier. The results indicate that high pressure and less oxygen feed produce a higher H₂/CO ratio, more favorable for SNG production.

Calcium-based sorbents synthesized from CaO, CaCO₃, and Ca(OH)₂ precursors were demonstrated as high-temperature CO₂ capture materials. The effect on CO₂ capture capability of calcium-based sorbents receiving different activations was also investigated. After proper activation, the best carbon capturing material is CaO that captured 75% of available CO₂ in nine cyclic tests and captured 61% even after 40 cyclic experiments. The correlation of the structural difference in the three activated sorbents and CO₂ conversion has been discussed. The sintering effect is presumably a major cause for activity decline of calcium-based sorbents… after cyclic carbonation/decarbonation runs.