Abstract
Chemical looping gasification (CLG) is a promising process for the thermochemical solid to liquid conversion route using lattice oxygen, provided by a solid oxygen carrier material, to produce a nitrogen free synthesis gas. Recent advances in lab-scale experiments show that CLG with biomass has the possibility to produce a carbon neutral synthesis gas. However, all experiments have been conducted in externally heated units, not enabling autothermal operation. In this study, the modification of an existing pilot plant for demonstrating autothermal operation of CLG is described. Energy and mass balances are calculated using a validated chemical looping combustion process model extended for biomass gasification. Based on six operational cases, adaptations of the pilot plant are designed and changes discussed. A reactor configuration using two circulating fluidized bed reactors with internal solid circulation in the air reactor is proposed and a suitable operating strategy devised. The resulting experimental unit enables a reasonable range of operational parameters within restrictions imposed from autothermal operation.
Highlights
The reduction of greenhouse gas emissions is one of the major challenges in the 21th century
Ilmenite as oxygen carrier (OC): For the selected thermal power, a total inventory of about 1000 kg was used during chemical looping combustion (CLC) experiments in the pilot plant [50], and the same can be expected for chemical looping gasification (CLG)
Major modifications are needed for the fuel reactor (FR) off-gases (Figure 4, blue box) when converting a CLC unit into a CLG unit, as all parts need to be designed with the consideration of explosive atmospheres
Summary
The reduction of greenhouse gas emissions is one of the major challenges in the 21th century. Gasification, the starting point of the process chain for solid to liquid conversion, is presently used for the generation of heat and electricity [4] and very little for the production of liquid biofuels [5] It is a well known process which converts solid feedstock in to a high caloric syngas and is considered to have a high potential for the decarbonization of hard to electrify aviation and maritime transport sectors. As heated solid bed material circulating between the two reactors is used to transfer the energy for the process, the transport of some amounts of carbon from the feedstock to the gasification reactor is necessary for the combustion reactor to generate the required heat, giving a substantial amount of CO2 -emission from the process. Starting from the underlying, fundamental gasification process, the existing infrastructural restrictions, and the planed operation range, mass and energy balances are calculated and required adjustments identified and implemented
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