Pressurized chemical-looping combustion of coal with an iron ore-based oxygen carrier
- School of Energy and Environment, Southeast University, Sipailou No. 2, Nanjing 210096 (China)
Chemical-looping combustion (CLC) is a new combustion technology with inherent separation of CO{sub 2}. Most of the previous investigations on CLC of solid fuels were conducted under atmospheric pressure. A pressurized CLC combined cycle (PCLC-CC) system is proposed as a promising coal combustion technology with potential higher system efficiency, higher fuel conversion, and lower cost for CO{sub 2} sequestration. In this study pressurized CLC of coal with Companhia Valedo Rio Doce (CVRD) iron ore was investigated in a laboratory fixed bed reactor. CVRD iron ore particles were exposed alternately to reduction by 0.4 g of Chinese Xuzhou bituminous coal gasified with 87.2% steam/N{sub 2} mixture and oxidation with 5% O{sub 2} in N{sub 2} at 970 C. The operating pressure was varied between 0.1 MPa and 0.6 MPa. First, control experiments of steam coal gasification over quartz sand were performed. H{sub 2} and CO{sub 2} are the major components of the gasification products, and the operating pressure influences the gas composition. Higher concentrations of CO{sub 2} and lower fractions of CO, CH{sub 4}, and H{sub 2} during the reduction process with CVRD iron ore was achieved under higher pressures. The effects of pressure on the coal gasification rate in the presence of the oxygen carrier were different for pyrolysis and char gasification. The pressurized condition suppresses the initial coal pyrolysis process while it also enhances coal char gasification and reduction with iron ore in steam, and thus improves the overall reaction rate of CLC. The oxidation rates and variation of oxygen carrier conversion are higher at elevated pressures reflecting higher reduction level in the previous reduction period. Scanning electron microscope and energy-dispersive X-ray spectroscopy (SEM-EDX) analyses show that particles become porous after experiments but maintain structure and size after several cycles. Agglomeration was not observed in this study. An EDX analysis demonstrates that there is very little coal ash deposited on the oxygen carrier particles but no appreciable crystalline phases change as verified by X-ray diffraction (XRD) analysis. Overall, the limited pressurized CLC experiments carried out in the present work suggest that PCLC of coal is promising and further investigations are necessary. (author)
- OSTI ID:
- 21318365
- Journal Information:
- Combustion and Flame, Vol. 157, Issue 6; Other Information: Elsevier Ltd. All rights reserved; ISSN 0010-2180
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
BITUMINOUS COAL
CARBON DIOXIDE
COAL GASIFICATION
PYROLYSIS
COMBUSTION
HYDROGEN
POROUS MATERIALS
OXYGEN
IRON ORES
REDUCTION
PRESSURE RANGE KILO PA
METHANE
TEMPERATURE RANGE 1000-4000 K
CARRIERS
CARBON MONOXIDE
STEAM
CHARS
PARTICLES
PRESSURE DEPENDENCE
QUARTZ
COMBINED CYCLES
COMBUSTION KINETICS
ASHES
CHINA
CONVERSION
MIXTURES
PACKED BEDS
CONTROL
COST
EFFICIENCY
SAND
VARIATIONS
Pressurized chemical-looping combustion