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Performance of a dual fluidized bed reactor for chemical looping combustion with oxygen uncoupling
| Content Provider | Semantic Scholar |
|---|---|
| Author | Whitty, Kevin J. Hamilton, Matthew A. Merrett, Kirsten M. Lighty, Joann S. |
| Copyright Year | 2017 |
| Abstract | Chemical looping with oxygen uncoupling (CLOU) is a variant of chemical looping combustion which uses as fluidized bed particles specific solid oxygen carriers which readily liberate gaseous oxygen (O2) in the fuel reactor. This enables much more efficient combustion of solid fuels such as coal than conventional chemical looping combustion, which relies on in situ gasification of char in to produce syngas that can react heterogeneously with the solid oxygen carrier. The CLOU process for coal is an especially interesting application of fluidized bed technology since several types of reactions take place within the reactors. For copper-based oxygen carrier particles, the copper cycles between cuprous and cupric oxide (Cu2O + 1⁄2 O2 Volatiles released from coal during pyrolysis may react with oxidized copper or with released oxygen gas. Char reacts primarily with released oxygen. Balancing oxygen supply to the fuel reactor, heat generation and temperatures and global and internal circulation rates is a challenge. The University of Utah has been researching CLOU technology for 10 years, studying fundamental reaction kinetics for copper-based CLOU oxygen carriers, performing laband bench-scale experiments in single and dual fluidized beds, and developing reactor models through Recently the university began testing a 200 kWth dual circulating fluidized bed process development unit (PDU) for processing coal. The design process for that reactor, reactor simulations, operational experience and practical challenges of the PDU system are presented. INTRODUCTION Chemical looping combustion (CLC) is an indirect combustion technology with inherent CO2 capture that involves circulation of metalso-called air reactor, which is fluidized with air, the metal is oxidized. The oxygen carrier particles are separated in e.g. a cyclone and transferred via a loop seal to a second reactor, the so-called fuel reactor, which is typically fluidized with steam or recycled CO2. Fuel fed to the fuel reactor reacts with oxygen from the oxidized metal, thus achieving indirect combustion while reducing the oxygen carrier, which is then returned to the air reactor complheting the cycle. Because nitrogen is not introduced into the fuel reactor, the effluent gas is nearly pure CO2 after water vapor has been condensed by cooling. Chemical looping with oxygen uncoupling (CLOU) is a variant of CLC technology that involves use of oxygen carriers containing oxygen as gaseous O2 in the fuel reactor. This is possible because in the air reactor, the high O2 partial pressure favors the oxidized metal but in the high temperature, low-O2 conditions of the fuel reactor, the equilibrium behavior of the carrier oxidation/reduction reaction favors gaseous O2. The advantage of CLOU over conventional chemical looping combustion of solid fuels, which relies on in situ gasification and heterogeneous combustion of the resulting syngas by a non-CLOU carrier such as ilmenite, is the much faster char conversion that is achieved by reaction with O2 versus gasification with H2O and CO2. Only a few metal complexes that exhibit CLOU behavior in the range of chemical looping combustion temperatures have been identified. Copper is one such metal and is attractive due its fast reaction rates and because it is thermodynamically favored to completely convert gaseous hydrocarbons to CO2 and H2O (Garcia-Labiano et al., 2004). When used as a CLOU carrier, copper cycles between the Cu+2 cupric (CuO) and Cu+1 cuprous (Cu2O) states: Cu2O + 1⁄2 O2 2 CuO (1) |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.cfb12.org/wp-content/uploads/2018/01/art124-PERFORMANCE-OF-A-DUAL.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
