Yinghai Wu

Spray Water Reactivation/Pelletization of Spent CaO-based Sorbent from Calcium Looping Cycles

This paper presents a novel method for reactivation of spent CaO-based sorbents from calcium looping (CaL) cycles for CO(2) capture. A spent Cadomin limestone-derived sorbent sample from a pilot-scale fluidized bed (FBC) CaL reactor is used for reactivation. The calcined sorbent is sprayed by water in a pelletization vessel. This reactivation method produces pellets ready to be used in FBC reactors. Moreover, this procedure enables the addition of calcium aluminate cement to further enhance sorbent strength. The characterization of reactivated material by nitrogen physisorption (BET, BJH) and scanning electron microscopy (SEM) confirmed the enhanced morphology of sorbent particles for reaction with CO(2). This improved CO(2) carrying capacity was demonstrated in calcination/carbonation tests performed in a thermogravimetric analyzer (TGA). Finally, the resulting pellets displayed a high resistance to attrition during fluidization in a bubbling bed.

High CO2 Storage Capacity in Alkali‐Promoted Hydrotalcite‐Based Material: In Situ Detection of Reversible Formation of Magnesium Carbonate

Alkali-promoted hydrotalcite-based materials showed very high CO(2) storage capacity, exceeding 15 mmol g(-1) when the carbonation reaction was carried out at relatively high temperature (300-500 °C) and high partial pressure of steam and CO(2). In situ XRD experiments have allowed correlation of high CO(2) capacity to the transformation of magnesium oxide centres into magnesium carbonate in alkali-promoted hydrotalcite-based material. Moreover, it has been clearly shown that crystalline magnesium carbonate may be reversibly formed at temperatures above 300 °C in the presence of sufficient partial pressure of steam in the gas phase, conditions that are prevalent in pre-combustion CO(2) capture. The role of steam appears to be of utmost importance for the formation of the bulk carbonate phase and for its reversibility. It is proposed that a high partial pressure of steam keeps the magnesium oxide periclase phase sufficiently hydroxylated to allow magnesium carbonate formation if a relatively high partial pressure CO(2) is present in the gas phase.

Assessment of Sorbent Reactivation by Water Hydration for Fluidized Bed Combustion Application

Disposal of fluidized bed combustion (FBC) solid residues currently represents one of the major issues in FBC design and operation, and contributes significantly to its operating cost. This issue has triggered research activities on the enhancement of sorbent utilization for in situ sulfur removal. The present study addresses the effectiveness of the reactivation by liquid water hydration of FB spent sorbents. Two materials are considered in the study, namely the bottom ash from the operation of a full-scale utility FB boiler and the raw commercial limestone used in the same boiler. Hydration-reactivation tests were carried out at temperatures of 40{sup o}C and 80{sup o}C and for curing times ranging from 15 minutes to 2d, depending on the sample. The influence of hydration conditions on the enhancement of sulfur utilization has been assessed. A combination of methods has been used to characterize the properties of liquid water-hydrated materials

A SIMPLE DESCRIPTION OF HIGH-TEMPERATURE SULPHATION BEHAVIOR FOR CaO-BASED SORBENTS

A simple model is proposed for sulphation of CaO-based sorbents in fluidized bed combustion. The model focuses on the sintering effect of CaSO4 product on the sorbent particles. The resultant equation is validated with experimental data and is seen to describe the time dependence of the sulphation well. It is also shown that for short sulphation times the equation becomes equivalent to that of an existing model but gives a better description of the sulphation behavior over a long sulphation period.

Hydration of Partially Sulphated CFBC Ash With Saturated Steam

The hydration of partially sulphated fluidized bed combustion (FBC) ash with saturated steam was carried out in the laboratory. The ash samples were obtained from a commercial-scale 165 MWe circulating fluidized bed combustor (CFBC) firing a petroleum coke and coal blend. Both bottom ash and fly ash were tested, and in addition the bottom ash was also separated into five size fractions and tested. These solid streams and the “as-received” fly ashes were hydrated by steam produced in a pressure bomb for different lengths of time at different saturated temperatures. Samples of the ashes were analyzed for free lime and calcium hydroxide content before and after the hydration process. Scanning electron microscopy (SEM) with an energy dispersive X-ray system (EDX) was employed to determine physical characteristics of the samples. X-ray diffractograms (XRD) were also used to determine the phase composition. These results show that after hydration treatment with saturated steam at elevated pressures, the unreacted CaO in the partially sulphated material can be quantitatively converted to Ca(OH)2 . However, the free lime content is also observed to change throughout the hydration process, which indicates that the hydration of CaO is not the only reaction occurring in this system. It is also clear that for fines, i.e., fly ash and <75 μm size fraction bottom ash, the effectiveness of the hydration depends much more strongly on hydration time and temperature than for coarser ashes and it is also clear that the behaviour of each particle size fraction is different.Copyright