Effects of Oxygen and Steam Equivalence Ratios on Updraft Gasification of Biomass

Abstract

Several experimental datasets available on the gasification of different lignocellulosic feedstocks were used to correlate the flow of gasifying agents with the performance of updraft gasification in an autothermic 200 kWth pilot plant. The feedstocks used included eucalyptus wood chips, torrefied eucalyptus and spruce chips, lignin rich residues from biorefined straw and reed, shells of almond and hazelnut, which were gasified in flows of air, air and steam, oxygen, oxygen and steam. Thermal profiles inside the gasifier and gas quality in terms of incondensable gas and tar content were recorded and used to calculate the energy efficiency of converting solid feedstock into gaseous and liquid carriers. Common behaviors and parametric functionalities were identified to better understand the process and the most efficient tools to achieve the desired products. In analyzing data, the ratio steam to biomass was reported in terms of the equivalence ratio, ER(H2O) i.e., the fraction of the stoichiometric quantity required to convert the feedstock into H2 and CO2. The use of steam was useful to stabilize the process and to tune the H2/CO ratio in the syngas which reached the value of 2.08 in the case of oxy-steam gasification of lignin rich residues at ER(H2O) of 0.25. Larger use of steam depressed the process by lowering the average temperature of the bed, which instead increased steadily with ER(O2). The production of tar depends on the biomass type and a substantial reduction can be achieved with the torrefaction pretreatment. The same effect was observed increasing the residence time of the syngas in the reactor, typically achieved using oxygen instead of air as main gasification flow or reducing the ER(H2O). Oxy-steam gasification of torrefied wood led to the best results in terms of cold gas efficiency and low heating value when carried out in the ranger 0.23–0.27 of both the ERs.

Introduction to the modeling of complex chemical reaction equilibrium using gPROMS® and GAMS®

“…Without loss of generality, we will assume, for instance, that $${w}=0.1$$ and $${o}=0.3$$. For a more thorough investigation regarding the proper choice of $$o\,\text{and}\,{w}$$, one need to introduce variables called Equivalence Ratios (ER) for both oxygen and steam [22]. Then, perform a sensitivity analysis to fetch the optimal proportions (i.e., those which lead to high hydrogen yield or low tar formation, etc.)…”

A Review of Factors Affecting Gasifier Performance

“…In MBG, higher steam requirements reduce superheated spots in the bed but also decrease bed permeability, while a high S/F ratio suppresses process temperature and secondary tar cracking reactions. Cerone et al [106] found that an increase in the S/F ratio resulted in a higher proportion of tar because of a decrease in average bed temperature which favoured higher tar production. It is observed that MBG requires more steam than FBG and EFG for preventing channel burning and superheated spots in the bed.…”

“…Cerone et al. 106 found that an increase in the S/F ratio resulted in a higher proportion of tar because of a decrease in average bed temperature which favoured higher tar production. It is observed that MBG requires more steam than FBG and EFG for preventing channel burning and superheated spots in the bed.…”

Current Status of the Pyrolysis and Gasification Mechanism of Biomass

“…However, too much steam in the gas generator may negatively affect energy production, as the system loses great energy on heating the steam. Excessive steam in the gas generator may also reduce the reaction temperature, thus impairing the gas quality [87].…”