Kinetic Calculations for the Calcination Reaction of Limestone Modified by Alkaline Industrial Wastes

Abstract

The enhancement of alkaline industrial wastes on the desulfurization performance and utilization of limestone has already been found. In order to explore the reason of this phenomenon from the kinetic point of view, two typical alkaline wastes, carbide slag with a high calcium content and Bayer process red mud with more metal impurities, were adopted to research. Kinetic behavior of calcination reaction was calculated using the isoconversional method of Kissinger-Akahira-Sunose method (a differential method) and Flynn-Wall-Ozawa method (an integral method) at four different heating rates: 10, 20, 40 and 80 K•min-1. Values calculated by these two methods are very close, and the calculated result shows that calcination rate constant of modified limestone is obviously greater than that of original limestone, under the same calcination temperature, which means that alkaline wastes are advantageous to the thermal decomposition of limestone.

Thermogravimetric Analysis of Desulfurization Characteristics and Kinetic Parameters of Limestone Modified by Red Mud

“…Kinetic parameters k and D s which reflect the activity of sorbents comprehensively, can exactly explain the sulfation reaction process. According to quation (8) and equation ( 9), the kinetic parameters k and D s are calculated and listed in Table 3. Obviously, red mud has little affect on the rate constant of the surface reaction k while it can greatly affect the effective diffusivity of reactant in the product layer D s .…”

“…When applied for desulfurization in coal combustion process or in flue gas, the limestone is limited in sulfation temperature range and suffers from rapid loss of reactivity and incomplete utilization which results in large limestone consumption, increased heating surface attrition and other issues. To find the calcium-based sorbents with excellent desulfurization effect in boiler injection, many studies about sorbent modified by additives have been made [1][2][3][4][5][6][7][8]. Among these studies, analytical reagent additives or pure solutions are often used to modify the calcium-based sorbents which is not economical to practical application.…”

“…All kinds of red mud contain large amounts of Fe, Na, Al and Si as well as small amounts of Mg, Ti, K and other elements. Profiting from previous studies [1][2][3][4][5][6][7][8] about using analytical reagent additives to modify the calcium-based sorbents, if red mud can be used as additives rather than directly used as desulfurization sorbent, much better results may be obtained. This paper attempts to explore the effect of red mud (two kinds of Bayer process red mud and one kind of sintering process red mud) from alumina plant on desulfurization performance, microstructure and kinetics of limestone, in order to explore the factors to affect calcium utilization rate and kinetic parameters.…”