Article pubs.acs.org/est
Particulate Formation from a Copper Oxide-Based Oxygen Carrier in Chemical Looping Combustion for CO2 Capture Feng He,† William P. Linak,‡ Shuang Deng,∥ and Fanxing Li*,† †
Department of Chemical and Biomolecular Engineering, North Carolina State University, 911 Partners Way, Raleigh, North Carolina 27695-7905, United States ‡ National Risk Management Research Laboratory, U.S. Environmental Protection Agency, 109 T.W. Alexander Drive, Research Triangle Park, North Carolina 27709-0002, United States ∥ State Key Laboratory of Environmental Criteria and Risk Assessment, Research Academy of Environmental Sciences, Beijing 100012, China S Supporting Information *
ABSTRACT: Attrition behavior and particle loss of a copper oxide-based oxygen carrier from a methane chemical looping combustion (CLC) process was investigated in a fluidized bed reactor. The aerodynamic diameters of most elutriated particulates, after passing through a horizontal settling duct, range between 2 and 5 μm. A notable number of submicrometer particulates are also identified. Oxygen carrier attrition was observed to lead to increased CuO loss resulting from the chemical looping reactions, i.e., Cu is enriched in small particles generated primarily from fragmentation in the size range of 10−75 μm. Cyclic reduction and oxidation reactions in CLC have been determined to weaken the oxygen carrier particles, resulting in increased particulate emission rates when compared to those of oxygen carriers without redox reactions. The generation rate for particulates y
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(2)
Using this redox cycle, the oxygen carrier is exploited to transport oxygen from air to the fuel through a chemical loop. According to the U.S. Department of Energy, chemical looping represents one of, if not the most promising, approaches for efficient CO2 capture.3,9 To date, the CLC concept has been investigated for both natural gas and solid fuel conversions up to 1 MWth.5−8,10−12 A critical consideration in all CLC processes is the performance of the oxygen carrier particles. An ideal oxygen carrier should possess the ability to store and transport Received: Revised: Accepted: Published: A
September 8, 2016 January 4, 2017 January 11, 2017 January 11, 2017 DOI: 10.1021/acs.est.6b04043 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology
Figure 1. Schematic of fluidized bed experimental setup with impactors.
To date, most studies on oxygen carriers focus on improving formulations and characterizing redox characteristics.5−7 Among the several studies on attrition behavior, focus has been placed on the change in the particle size distribution (PSD) of bed materials (>75 μm) within the chemical looping reactors.22−24 Brown et al.25 investigated attrition behavior of impregnated copper oxide (CuO) using a bench-scale fluidized bed. It was reported that superficial gas velocity influences attrition mode: surface abrasion prevails at low velocity, whereas fragmentation is enhanced at higher velocities. Cabello et al.26 studied long-run attrition mode changes by comparing particle size distributions after cycling particles at different gas velocities. They also reported that fragmentation is important at higher cycle numbers under a high gas velocity. It is noted that particulates generated from the fragmentation mechanism tend to be large. Because the current study aims to investigate the fine particulate generation mechanism, our experiments are operated primarily at low superficial gas velocities under which abrasion dominates. The superficial gas velocities adopted in the current study are comparable to those in Brown et al.25 and Cabello et al.26 Garcia-Labiano et al.27 investigated particle behavior within a 10 kWth CLC operated for 100 h using a CuO-Al2O3 oxygen carrier. In addition to PSD analysis, they found that the elutriated particles were enriched in CuO. Rydén et al.28 used a customized jet cup to evaluate the attrition resistance of 25 different oxygen carriers under ambient conditions. While these studies focused primarily on the propensity of oxygen carriers to produce large (>10 μm) fragmentation particles, fewer measurements have characterized particles 1300) redox cycles using an impregnated CuO-Al2O3 oxygen carrier and characterize changes in the PSD, morphology, crystal structure, and chemical composition of the carrier over time. While we are interested in all particle sizes, special attention is given to smaller attrition particles (
