(580f) Raman Gas Analysis for Chemical Looping

Abstract

Chemical looping combustion is being developed with support of the U.S. Department of Energy because it has potential for carbon capture with less efficiency penalty than conventional power cycles with post-combustion capture.  [i][ii] Chemical looping uses an intermediary, such as a metal oxide, to collect oxygen from air in the air reactor.  The oxidized particles are then transported and to the fuel reactor, where the oxygen carrier particles are reduced.  The product gas stream contains mostly carbon dioxide and water vapor, which be readily separated for carbon capture, utilization and storage.   An inert buffering gas is injected in the process between the reactors to help separate the oxidation and reduction processes.  

One of the challenges for operation of a chemical looping combustion process is the measurement of the gases produced in the oxidant and fuel reactors, which are indicative of the operating performance of those reactors.   Solids inventory and gas flows may be adjusted to better achieve the desired reactor performance.  For process development, the produced gases also provide valuable information to characterize the performance of the oxygen carriers.  While conventional gas analyzers can provide some of the data desired, the Raman Gas Analyzer is being developed to provide faster measurement of multiple gases simultaneously.   At NETL, it has been applied in the research operations of the Chemical Looping Reactor.  The chemical looping reactor operates at positive pressure at high temperature (~ 1000 °C).

The Raman Gas Analyzer (RGA) has been recently developed to be a fast, non-destructive instrument for on-line measurement of gas composition[iii].  The Raman Gas Analyzer is capable of reporting the concentrations of multiple species simultaneously, with sampling times below one second for process control applications in energy or chemical production, such as adjustments in gas turbine engines to enable optimal control based on the changes in fuel composition.  The instrument is based upon using a hollow-core capillary waveguide with a reflective lining as a flow-through sample cell.[iv]  The effect of using such a waveguide in a Raman process is to integrate Raman photons along the length of the sample-filled waveguide, greatly improving the optical collection efficiency in gas applications.  A pre-commercial field prototype has been constructed by NETL, and is being tested for potential use in energy applications such as coal gasification, turbine control, well-head monitoring for exploration or production, and non-conventional gas utilization, and chemical looping.  Reported here are results from application of the RGA to the 50 kW chemical looping reactor.