Development of an active sorbent from fly ash for dry desulphurization of simulated flue gas in a fluidized-bed reactor
Introduction
Dry flue gas desulphurization by direct injection of calcium-based absorbents into the flue gas duct offers an attractive alternative to semidry or wet methods for controlling SO2 emission at low temperature with a simple technology as a retrofit option for existing coal-fired power plants. Since the residence time of the solids in the duct injection of absorbents is short, a highly active absorbent must be used to achieve acceptable levels of SO2 removal [1]. One method of obtaining that absorbent under medium temperatures is by using a mixture prepared from coal fly ash, calcium oxide and gypsum [2], [3], [4], [5]. It was considered that the high activity of the mixture resulted according to the literature on one hand from the presence of calcium silicate hydrate material formed by the hydration reaction between calcium and alumina silicate in the fly ash, and the difference in reactivity was caused by the structure of calcium silicate hydrate material formed [6]. In this case, the surface area from the formation of hydrated calcium silicates is effective in the desulphurization process. On the other hand, the significant increase of calcium utilization rate was mainly attributed to the Ca(OH)2 covering the surface of fly ash particles, and the hydration reactions did not play an important role under the absorbent preparation condition at ambient temperature [7]. On the contrary of these findings in literature, the desulphurization activity of the absorbent depends on which step calcium sulphate is added in the preparation of absorbents. Recently Ishizuka et al. [8] found that the addition of calcium sulphate in the step of slaking calcium oxide with fly ash brings about a negative effect while the addition of that in the step of hydrothermal treatment following slaking brings about a positive effect.
With this state of knowledge given above, the purpose of this work is to develop highly active desulphurization sorbent by exploring the reaction of this sorbent composed of a mixture of lignite fired power plant waste (a disposed mix of FGD-gypsum and fly ash of Çayırhan/Ankara power plant) and calcined Turkish limestone (Mengen/Bolu) at the simulated conditions of real flue gases of that power plants for regenerative calcium utilization.
Section snippets
Apparatus
The experimental setup consisted of mainly a fluidized-bed reactor (FBR) surrounded by an electrically heated tubular ceramic furnace, and auxiliary equipment for fluidizing gas preparation, gas analysis and on-line data logging system. The FBR is a stainless steel tube of 46 mm inside diameter and 500 mm length. It is fitted with a stainless steel sieve (325 mesh) gas distributor. The reactor is heated by Kanthal-A1 heating wire and the bed temperature is measured by a NiCr/Ni thermocouple, and
Comparison of experimental sulphation conversion values of CS and AS
Experimental sulphation conversion values (Xs,exp) obtained in 15 min reaction time are given in Fig. 2, Fig. 3 as a function of SO2-feedstock concentration at 500 °C according to the sulphite, sulphate and total sulphate conversion of the CS and AS at 500 °C, respectively. As can be discerned from Fig. 2, Fig. 3, the sulphation conversion of the AS was greater than that of the CS at the operating conditions of this study given in Table 3. Therefore, it was concluded that the AS prepared as given
Conclusions
The highly active sorbent for dry desulphurization of simulated flue gas was developed from the LFA, CS and FGDG. For the preparation of this highly active sorbent (AS), FGDG was added in the hydrothermal treatment step after the slaking step of CS and fly ash giving a positive effect reported also in literature. The sulphation conversion of the AS obtained was found to be greater than that of the CS of this study and the previous studies. The lower activation energy values of the sulphation
Acknowledgments
The authors gratefully acknowledge the financial support from Ankara University Scientific Research Projects Directorate (BAP Project No. 98-05-04-012), Gesellschaft für Technische Zusammenarbeit (GTZ Project No. 9120/Germany) as well as the Scientific and Technical Research Council of Turkey (TÜBİTAK) and Cement Producers Association of Turkey (TÇMB) under Grant No. MİSAG/KTÇAG-116.
References (20)
Investigation of the SO2 adsorption properties of Ca(OH)2-fly ash systems
Fuel
(1996)- et al.
Potentiometric titration of sulphate, sulphite and ditionate mixtures with use of lead ion-selective electrode
Talanta
(1983) - et al.
Study of the effect of fly ash on desulfurization by lime
Fuel
(2001) - et al.
A guide to flue gas desulphurisation for the industrial plant manager
Trans. IChemE Part B
(1993) - et al.
Highly active absorbent for SO2 removal prepared from coal fly ash
Ind. Eng. Chem. Res.
(1995) - et al.
Removal of sulfur dioxide from flue gas by the absorbent prepared from coal ash: effects of nitrogen oxide and water vapor the composition of the absorbent on the activity
Ind. Eng. Chem. Res.
(1996) - et al.
Preparation of active absorbent for dry-type flue gas desulfurization from calcium oxide, coal fly ash and gypsum
Ind. Eng. Chem. Res.
(2000) - et al.
Preparation, characterization, and calcium utilization of fly ash/Ca(OH)2 sorbents for dry desulfurization at low temperature
Ind. Eng. Chem. Res.
(2002) - et al.
High calcium utilization and gypsum formation for dry desulfurization process
Energy Fuels
(1999) - et al.
Effect of calcium sulfate addition on the activity of the absorbent for dry flue gas desulfurization
Energy Fuels
(2001)
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