Zhicheng Ye

The kinetics of the reaction of hydrogen chloride with fresh and spent Ca-based desulfurization sorbents

The absorption of hydrogen chloride by spent desulfurization sorbents containing calcium carbonate, calcium oxide and calcium hydroxide was investigated. The experiments were carried out in a fixed-bed reactor in two temperature ranges: 423-523 K for slaked lime and 673-873 K for limestone and quicklime. The spent Ca-based sorbents can still react with hydrogen chloride, and after calcining and slaking they even show the same reactivity as pure Ca(OH)(2). A model combining both fixed-bed reactor and shrinking-core model was derived. The activation energy of the surface reaction between hydrogen chloride and limestone was determined to be 84 kJ mol(-1) at 673-873 K. The pore diffusion activation energy was 11 kJ mol(-1) for limestone at 673-873 K, 29 kJ mol(-1) for CaO at 673-873 K and 12 kJ mol(-1) for slaked lime at 423-523 K. (Less)

High temperature desulfurization using fine sorbent particles under boiler injection conditions

The high temperature reaction of SO2 with CaO was investigated in three reactors: a thermogravimetric reactor (TGA), a volumetric reactor (VR) and an entrained flow reactor (EFR). Several natural limestones with super fine particles were used as sorbents. It was found that the reaction could be well characterized by a two-stage process. The initial stage was very fast and lasted about 0.1-0.4 s. The chemical kinetics of the reaction was studied and modelled. In addition to other parameters, such as particle size and Brunauer-Emmett-Teller (BET) surface area, the pore volume located in the larger pores (> 5.0 nm) was found to contribute somewhat to the high SO2 removal and CaO conversion. At Ca/S = 2 the SO2 removal was more than 90%.

Simultaneous reduction of SO2 and NOx in an entrained-flow reactor

Simultaneous SO2 and NOx reduction in flue gas by the dry furnace sorbent injection process was simulated with an entrained-flow reactor. Several ammonium salts as well as urea were tested. Urea was found to give the highest NOx removal efficiency. By using urea-limestone sorbent, >90% SO2 removal and >80% NOx removal were obtained at Ca/S and N/NOx ratios both equal to 2. The DeNO(x) process is more temperature-sensitive than the DeSO(2) process, and 900 degrees C can be chosen as the overall optimum temperature. The N2O formed was <10 ppmv at 2 s residence time. A reductive path from NO2 or NO to N-2 is proposed to explain the experimental results.

A numerical method for determination of particle size distribution of limestone based on pH-stat measurement

Abstract A numerical method for determination of particle size distribution of limestone was developed based on a pH-stat dissolution measurement. The method originated from the calculation of the layer thickness distribution of plane limestone but was expanded to the spherical particles. It was shown that the method can closely reproduce a known particle size distribution and the calculated particle size distribution is comparable with that obtained from a gravity sedimentation analysis. The evaluation of the method indicated that the data sampling and the parameters in the dissolution model are critical in applying the method.

Alkali Removal and Bed Material Agglomeration Studies Applied to Biomass Gasification

TGA and TDA methods were employed to investigate the alkali removal and its effect on the bed material agglomeration in the PFB biomass gasification process. Several silica-alumina based sorbents and bed materials as well as the bed ash from the biomass gasification process were screened for their alkali removal capacity at a temperature range of 400 – 1200 °C. Model alkali compounds were KCl, KNO3, K2SO4 and K3PO4 in these measurements. There seems to be an optimum temperature for alkali absorption and the highest alkali removal was measured at around 890 °C. Fyle sand was found capable of capturing 0.25 mol K/mol SiO2 and is the best of the tested sorbents. However the agglomeration of the sand took place at a level much lower than this ratio. The superficial gas flow only slightly affected the capturing capacity of the sorbents.

On the Intrinsic High Temperature Calcium Oxide-Sulfur Dioxide Reaction Using the Vacuum Thermogravimetric Analysis Technique

The high temperature CaO/SO2 reaction was studied using four Swedish limestones and one dolomite as sorbents. The measurements were carried out in a vacuum thermogravimetric analysis (TGA) apparatus in order to investigate the intrinsic reaction mechanism. The reaction was found to be fast at the beginning due to the surface reaction, while the subsequent stage was controlled by the product layer diffusion, showing a lower reaction rate. The reaction rate increased as temperature increased up to 1000 °C in the range tested. SO2 partial pressure weakly affected the reaction. The fine sorbent particles used in the study resulted in the high CaO conversion. Further grinding of the sorbents gave a small increase in CaO conversion. Sintering generally decreased the initial reactivity but might not affect the ultimate CaO capacity. The larger pores in nascent CaO particles were valuable for the initial reaction conversion.