Effects of the Limestone Particle Size on the Sulfation Reactivity at Low SO2 Concentrations Using a LC-TGA

Abstract

Limestone particle size has a crucial influence on SO2 capture efficiency, however there are few studies on the sulfation reactivity, which covers a broad range of particle sizes at low SO2 concentrations. In this paper, a large-capacity thermogravimetric analyzer (LC-TGA) was developed to obtain the sulfur removal reaction rate under a wide range of particle sizes (3 μm–600 μm) and SO2 concentrations (250 ppm–2000 ppm), and then compared with the results of a traditional fixed bed reactor and a commercial TGA. The experimental results showed that the LC-TGA can well eliminate the external mass transfer and obtain a better measurement performance. Both the final conversion and the reaction rate reduced with the decreasing of SO2 concentration, but ultrafine limestone particles still showed the good sulfation reactivity even at 250 ppm SO2. An empirical sulfation model was established based on the experimental results, which can well predict the sulfation process of different limestone particle sizes at low SO2 concentrations. The model parameters have a strong negative correlation against the particle size, and the fit of the reaction order of SO2 was found to be about 0.6. The model form is very simple to incorporate it into available fluidized bed combustion models to predict SO2 emission.

Limestone Attrition and Product Layer Development during Fluidized Bed Sulfation

“…This was distinguished with the sulfation test in the thermogravimetric analyzer (TGA), where the conversion degree reached the maximum value and remained unchanged within an much shorter time. 24,25 The attrition that resulted in the exposure of the fresh reaction surface via the removal of protuberances is believed to be one of the dominant reasons for the slow but continuous increase of the conversion degree in fluidized bed conditions.…”

Applications of Ultrafine Limestone Sorbents for the Desulfurization Process in CFB Boilers

“…38,39 Thus, an LC-TGA was developed to characterize the sulfation reactivity of different limestones and its reliability and accuracy had been validated in previous studies. 40 As shown in Figure 2, a heating furnace can move along the sliding rail so that the fast calcination can be achieved, which was much closer to the injection condition in fluidized beds. Prior to the experiments, 15−30 mg of limestone samples were uniformly spread on a 32 mm-ID crucible by deionized water and then dried at a temperature of lower than 150 °C in an oven.…”

“…Despite the significant effect of particle size on the sulfation process, there remain a few reports on research results regarding the sulfation reactivity exhibited by a certain type of limestone with the particle size ranging widely from several micrometers to several hundred micrometers. , Thus, an LC-TGA was developed to characterize the sulfation reactivity of different limestones and its reliability and accuracy had been validated in previous studies . As shown in Figure , a heating furnace can move along the sliding rail so that the fast calcination can be achieved, which was much closer to the injection condition in fluidized beds.…”

“…Moreover, a larger reaction gas flow rate (5 standard L/min) is conducive to improving the external mass transfer, for which the reaction rates can be closer to a differential reactor, especially in the initial sulfation stage. The detailed description about the LC-TGA and the experimental procedure can be found in previous works …”

“…The detailed description about the LC-TGA and the experimental procedure can be found in previous works. 40 Shengzhou limestone, which was also used in the pilot-scale (PS) CFB boiler, was sieved with an ultrasonic sieving machine into three groups, including the screen meshes of 0−20, 75− 106, and 400−600 μm. As shown in Figure S2 (SI), the distribution of their particle size was measured by a Malvern Mastersizer particle analyzer, with the SMDs being 3.5, 39.4, and 602.8 μm, respectively.…”