Combined Partial Oxidation and Carbon Dioxide Reforming Process: A Thermodynamic Study

Jarungthammachote Jarungthammachote

doi:10.3844/ajassp.2011.9.14

Abstract

Problem statement: CO2 reforming is one of the methods to utilize a greenhouse gas to produce syngas, an important feed for methanol and Fischer-Tropsch synthesis. However, CO2 reforming is strong endothermic reaction requiring large amount of supplied energy. Partial oxidation, an exothermic reaction, is combined with CO2 reforming to serve the energy requirement. Thus, the optimum ranges of O2 and CO2 fed to the process corresponding to feedstock are needed to find. Moreover, one of the most important problems found in this process is solid carbon formation. Therefore, the operating range in which the carbon formation can be avoided is also required to study. Approach: In this study CH4 was used as feedstock. The optimum rage of O2 and CO2 fed to the process was found by using thermodynamic equilibrium method based on minimization of Gibbs free energy. The Lagrange multiplier method was conducted to form the equations and they were solved by the Newton-Raphson method. The solid carbon formation zone was also simulated. Results: The simulation showed that higher reaction temperature caused higher CH4 and CO2 conversions. Syngas production increased with increasing temperature. Operating the process with high temperature or high O2/CH4 and CO2/CH4 rations could eliminate solid carbon formation. Increase of O2/CH4 ration higher than 0.1 led decreasing syngas while increase of CO2/CH4 ration caused increasing H2 and CO. However, when CO2/CH4 ration was higher than 0.85, increasing CO2/CH4 ration showed insignificant change of syngas concentration. Conclusion: The combined partial oxidation and CO2 reforming of method should be operated with reaction temperature of 1050 K. The optimum range of CH4:CO2:O2 for this process is 1: 0.85-1.0:0.1-0.2.

Highlights

The authors indicated that a deposited carbon was one of the major products obtained from CO2CO2 is one of the most important greenhouse gases produced from combustion process (Al-Mutairi and Koushki, 2009; Bundela and Chawla, 2010; Khademi et al, 2009)
The effect of temperature on reactant conversions and gas yields: The simulation of combined partial oxidation and CO2 reforming was conducted with CH4:CO2:O2 feed ratio of 1.0:1.0:0.2
Effect of fed O2: To study the effect of added O2 on the production of combined partial oxidation and CO2 reforming, the ratio of CO2/CH4 is fixed at 1 and the reaction temperature is maintained at 1050 K, the reaction temperature was higher than 1000 K

Summary

Introduction

CO2 is one of the most important greenhouse gases produced from combustion process (Al-Mutairi and Koushki, 2009; Bundela and Chawla, 2010; Khademi et al, 2009). It can be utilized as reactant for hydrocarbon reforming to produce synthesis gas ( called syngas). CO2 reforming process is sometime called dry reforming, which is strong endothermic reaction. It requires large amount of heat supplied to the process. For coke (carbon) formation, it has been mentioned by many researchers that it is an important problem of the dry reforming reaction, because it leads to catalyst deactivation (Wurzel et al, 2000; Nagaoka et al, 200; Shamsi and Johnson, 2003)

Methods

Results

Conclusion