Analysis of Syngas Production from Biogas via the Tri-Reforming Process

Rei-Yu Chein,Wen-Hwai Hsu

doi:10.3390/en11051075

Abstract

The tri-reforming process was employed for syngas production from biogas at elevated pressures in this study. In the tri-reforming process, air and water were added simultaneously as reactants in addition to the main biogas components. The effects of various operating parameters such as pressure, temperature and reactant composition on the reaction performance were studied numerically. From the simulated results, it was found that methane and carbon dioxide conversions can be enhanced and a higher hydrogen/carbon monoxide ratio can be obtained by increasing the amount of air. However, a decreased hydrogen yield could result due to the reverse water–gas shift reaction. A higher level of methane conversion and hydrogen/carbon monoxide ratio can be obtained with increased water addition. However, negative carbon dioxide conversion could result due to the water–gas shift and reverse carbon dioxide methanation reactions. The dry reforming reaction resulting in positive carbon dioxide conversion can only be found at a high reaction temperature. For all cases studied, low or negative carbon dioxide conversion was found because of carbon dioxide production from methane oxidation, water–gas shift, and reverse carbon dioxide methanation reactions. It was found that carbon dioxide conversion can be enhanced in the tri-reforming process by a small amount of added water. It was also found that first-law efficiency increased with increased reaction temperature because of higher hydrogen and carbon monoxide yields. Second-law efficiency was found to decrease with increased temperature because of higher exergy destruction due to a more complete chemical reaction at high temperatures.

Highlights

The efficient production of syngas is gaining significant attention worldwide as it is a versatile feedstock that can be used to produce a variety of fuels and chemicals, such as methanol, Fischer–Tropsch fuels, H2, and dimethyl ether (DME) [1]
CH4 as the primary material, syngas can be produced from steam reforming (SR), partial oxidation (POX), autothermal reforming (ATR), and dry reforming (DR)
We developed this work from our previous exergy recovered to the exergy study [46] and focused on using biogas as the feedstock

Summary

Introduction

The efficient production of syngas (a mixture of hydrogen and carbon monoxide) is gaining significant attention worldwide as it is a versatile feedstock that can be used to produce a variety of fuels and chemicals, such as methanol, Fischer–Tropsch fuels, H2 , and dimethyl ether (DME) [1]. CH4 as the primary material, syngas can be produced from steam reforming (SR), partial oxidation (POX), autothermal reforming (ATR), and dry reforming (DR). The tri-reforming (TR) process for syngas production from CH4 has received growing attention because of its technical simplicity and flexible operation [2,3,4,5]. In the TR process, the syngas is produced by combining SR, DR, and POX in a single step. The TR process was proposed originally for syngas production from power plant flue gas [6,7]. As CO2 is one of the reactants, there is no need for CO2 separation from the flue gas [6,7]. The H2 /CO ratio in syngas can be altered by adjusting the relative amounts of the reactants.

Results

Discussion

Conclusion