Experimental investigation and optimization of the chemical looping combustion process for solid fuels

M.Sc. Kai Lyu

Introduction

Chemical Looping Combustion (CLC) is a Carbon Capture technology which allows the inherent separation of CO2 having a small energy penalty compared to other existing capture technologies. The process principle was already developed and patented in 1954 by Lewis and Gilliland. However, at that time the intended application of the process was the production of pure CO2. In recent years CLC has attracted attention again as an alternative conversion process for the carbon capture and storage (CCS) technology.

Generally the process consists of two reactors: the air reactor in which the oxygen carrier is laden with oxygen and the fuel reactor where the oxygen carrier supplies the oxygen for fuel combustion. When a gaseous fuel is used the solid oxygen carrier can directly react with the fuel gas, whereas a direct reaction of the solid oxygen carrier with a solid fuel like coal does not at a sufficient rate. Hence the solid fuel must either be gasi ed or a special oxygen carrier has to be used which has the ability of releasing gaseous oxygen within the fuel reactor (i.e. the so called chemical looping with oxygen uncoupling (CLOU). Different designs of for continuously operated CLC units have been developed in recent years. The majority of process designs currently under investigation are systems of coupled  uidized beds. However, the concepts still differ signi cantly in the  ow regimes used in the individual reactors: systems of two coupled circulating  uidized beds as air reactor and fuel reactor, respectively. At TUHH a concept with a two stage fuel reactor has been developed, with increase the combustion ef ciency and to reduce the emission of uncombusted gases.

Objective of the research

The objective of this research is to improve the efficiency, stability and operability of the CLC process. The main focus is the reactor design and operation. Furthermore different oxygen carriers with and without the release of oxygen (CLOU) will be compared. In this research ilmenite and a copper based synthetic material will be tested as oxygen carrier.

Methods

Step 1: Experimental study of the operational behavior and performance of the pilot scale CLC facility. The effect of temperature, coal particle size, coal type, volatiles content and oxygen carrier circulation on coal conversion and combustion efficiency will be assessed.

To improve the process understanding gas concentration measurements will be carried out locally and for the outflowing gas streams. Furthermore solids will be sampled locally and analyzed with respect to their grade of oxidation.

Step 2: Based on the gained detailed process understanding the design of the CLC-Loop shall be revised and optimized operating conditions shall be determined.

Experimental setups

The experimental validation is carried out at TUHH’s Chemical Looping facility with a rated power of 25 kW. Furthermore, reactivity measurements can be carried out in a small lab scale fluidized bed facility.

Selected publications

Thon A., Kramp M., Hartge E.-U., Heinrich S., Werther J. (2014). Operational experience with a system of coupled  fluidized beds for chemical looping combustion of solid fuels using ilmenite as oxygen carrier. Applied Energy 118, 309-317.

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