Structural studies in limestone sulfidation

Thesis/Dissertation · Sat May 01 04:00:00 EDT 1993

DOI:https://doi.org/10.2172/10178157· OSTI ID:10178157

Fenouil, Laurent A. ^[1]

---

1. Univ. of California, Berkeley, CA (United States)

This study investigates the sulfidation of limestone at high temperatures (700--900°C) as the first step in the design of a High-Temperature Coal-Gas Clean-Up system using millimeter-size limestone particles. Several workers have found that the rate of this reaction significantly decreases after an initial 10 to 15% conversion of CaCO₃ to CaS. The present work attempts to explain this feature. It is first established that millimeter-size limestone particles do not sinter at temperatures up to the CaCO₃ calcination point (899°C at 1.03 bar CO₂} partial pressure). It is then shown that CaS sinters rapidly at 750 to 900°C if CO₂ is present in the gas phase. Scanning Electron Microscope (SEM) photographs and Electron Dispersive Spectroscopy (EDS) data reveal that the CaS product layer sinters and forms a quasi-impermeable coating around the CaCO₃ grains that greatly hinders more H₂S from reaching the still unreacted parts of the stone. Moreover, most of the pores initially present within the limestone structure begin to disappear or, at least, are significantly reduced in size. From then on, subsequent conversion is limited by diffusion of H₂S through the CaS layer, possibly by S^2- ionic diffusion. The kinetics is then adequately described by a shrinking-core model, in which a sharp front of completely converted limestone is assumed to progress toward the center of the pellet. Finally, experimental evidence and computer simulations using simple sintering models suggest that the CaS sintering, responsible for the sharp decrease in the sulfidation rate, is surface-diffusion controlled.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 10178157
• Report Number(s): LBL--34308; ON: DE93019251
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
010402
CALCIUM CARBONATES
CALCIUM SULFIDES
CARBON DIOXIDE
CHEMICAL REACTION KINETICS
COAL GASIFICATION
COATINGS
COMPUTERIZED SIMULATION
CORROSION PROTECTION
DESULFURIZATION
DIFFUSION
ELECTRON SPECTROSCOPY
EXPERIMENTAL DATA
FUEL GAS
GAS TURBINES
HOT GAS CLEANUP
HYDROGEN SULFIDES
LIMESTONE
MATHEMATICAL MODELS
MICROSTRUCTURE
MORPHOLOGY
PARTICLE SIZE
POROSITY
PURIFICATION AND UPGRADING
REMOVAL
SCANNING ELECTRON MICROSCOPY
SINTERING
SULFIDATION
SURFACE AREA
TEMPERATURE RANGE 1000-4000 K
TURBINE BLADES