Modelling of thermal desorption of active coke loaded with sulphuric acid and ammonium sulphate

Abstract

The BF-Uhde-Mitsui Process uses active coke for SO,-and NOx-removal from flue gases in the temperature range between 100 and 190 "C. Experimental methods of thermal regeneration were applied to the evaluation of the state of the adsorbent after use in flue gas cleaning and of the parameters for desorber design. A reaction model was derived from experiments carried out in differential and back-mix reactors. The parameters were evaluated by adaptation of the model to the desorption spectra. The model was successfully applied to the regeneration of active coke in a fluidized bed reactor.

Kinetics of Thermal Regeneration of SO2-Captured V2O5/AC

“…Figure indicates that the minimum temperature is 490 K (α reaches 0.1 at a heating rate of 5 K/min) and the maximum is 575 K (α reaches 0.4 at a heating rate of 20 K/min). T iso , 509 K, is obviously in the range of 490 and 575 K, confirming that regeneration of SO 2 -captured V 2 O 5 /AC is of first-order with respect to the H 2 SO 4 concentration, which is consistent with the report of Richter …”

“…These indicate that V 2 O 5 may promote the reaction of H 2 SO 4 with carbon during the regeneration process. It should be pointed out that all E a obtained in our case are greater than any of those of the elemental reaction involved in H 2 SO 4 reduction over pure carbon reported by Richter, possibly because of the different ACs.…”

“…In the case of thermal regeneration of the SO 2 -captured carbon-based materials, it is mainly the reaction between H 2 SO 4 in the liquid phase and carbon in the solid phase to produce gaseous CO 2 , SO 2 , and H 2 O. Because the amount of carbon is wholly far more than that of H 2 SO 4 , the regeneration reaction may be first-order with regard to the concentration of H 2 SO 4 , as reported by Richter . On the other hand, H 2 SO 4 is stored in the micropores, and only the local carbon may be available for the reaction, which may lead to a second-order reaction with regard to H 2 SO 4 and carbon, a bidimensional interface controlled reaction, or a reaction controlled by diffusion of H 2 SO 4 .…”

“…The latter is reduction of H 2 SO 4 stored in the micropores with a reducing agent, such as AC, NH 3 , , and H 2 , to get a highly concentrated SO 2 , ammonia sulfate, or sulfur. Reduction regeneration using AC as the reductant is usually called thermal regeneration and has been put into practice. , Lizzio and DeBarr reported that the main products of thermal regeneration were CO 2 , SO 2 , and H 2 O. Guo et al studied thermal regeneration of SO 2 -captured V 2 O 5 /AC at 653 K and found that the catalyst kept high activities for simultaneous SO 2 removal and NO reduction after five reaction–regeneration cycles. The main reactions during the regeneration process can be described as follows: …”

BF/UHDE/MITSUI-Active Coke Process for Simultaneous SO2- and NOx-Removal

“…The latter will spontaneously reduce S03 (intermediate product of the degradation of sulphuric acid) or surface oxides as per This is why carbon losses are minimized during regeneration. The mechanisms and kinetics of thermal desorption of loaded active coke are described in detail by [3].…”