H2 production with CO2 capture by sorption enhanced chemical-looping reforming using NiO as oxygen carrier and CaO as CO2 sorbent

Artikel i vetenskaplig tidskrift, 2012

A novel process for conversion of hydrocarbons to H2 has been examined. The process, sorption enhanced chemical-looping reforming, involves three interconnected reactor vessels. In the reforming reactor, hydrocarbon fuel is partially oxidized with oxygen provided via a solid oxygen carrier such as NiO. Resulting CO is shifted instantly to CO2 via sorption enhanced water-gas shift, facilitated by the capturing of CO2 with a solid CO2 sorbent such as CaO. The resulting solids, Ni and CaCO3, are regenerated downstream in separate reactor vessels. The process produces H2, CO2 and N2 of reasonable purity in separate process streams, without need for additional gas separation equipment. The basic characteristics of the proposed process have been examined by thermodynamic calculations using FactSage 6.1, and by process modelling using Aspen Plus. The results show that the process has high theoretical potential. At a pressure of 1 bar it could produce >2.8 mol H2 with a purity of >98 vol% for each mol CH4 added as fuel, while at the same time obtaining >95% of the carbon added with the fuel as CO2 in a separate process stream. Increasing the pressure reduces the theoretical performance slightly, mainly due to lower conversion of CH4. Involved reactions have also been examined in a laboratory fluidized-bed reactor at 600-750°C, with particles of NiO and CaO as bed material and CH4 mixed with steam as fuel. Although the conversion of CH4 was incomplete the results fitted well with theory and gas with a H2/(H2+CO+CO2) ratio of more than 98% was produced at 600°C.