Optimization of a Wet Flue Gas Desulfurization Scrubber through Mathematical Modeling of Limestone Dissolution Experiments

Abstract

Dissolution rates of two very pure limestone samples were measured experimentally by means of the pH-stat method under conditions where mechanical stirring did not affect the rates considerably. The experimental results were modeled mathematically by considering the surface areas of the particles changing dynamically through the reaction; moreover, a surface factor was introduced in order to account for the nonsphericity of the particles. The surface areas were measured by means of gas adsorption and by particle size distribution (laser diffraction). Liquid-phase concentrations were measured by inductively coupled plasma optical emission spectrometry, and surface compositions were measured by X-ray spectroscopy. Furthermore, scanning electron microscope images of the samples are presented. Subsequently, an optimization model of a scrubber was developed by using the intrinsic parameters of the samples, which were determined experimentally. The optimization results indicate that up to 34−50% of the power required for milling can be saved by milling to a coarser particle size than the commonly used size of 44 μm, depending on the sample type. The present model of the lab-scale experimental study and the optimization model can be employed to estimate the actual impact that using different types of raw material would have in the operation of a wet flue gas desulfurization scrubber.

Ultrasonic Power to Enhance Limestone Dissolution in the Wet Flue Gas Desulfurization Process. Modeling and Results from Stepwise Titration Experiments

“…This could imply that the limestone could be ground to a larger size fraction than usual and exploit the ultrasound enhancement to reduce the energy consumption of the griding process. The two samples investigated in this study have very large differences in terms of structure, age, and composition [9,40]. This reflects on the degree of crystallinity of the samples and in terms of the solid surface.…”

“…The Scanning Electron Microscopy (SEM) images of the samples are presented below and show the difference in the surface, shape, and morphology between sample types. Both samples are considered to be non-porous since the pore volume values measured by means of nitrogen adsorption were equal or less than 0.002 m 3 /g for both samples [9]. The mineral phases of the samples were assessed by X-ray diffraction (XRD) in previous works [39,40].…”

“…A WFGD unit of a 500 MWe power plant can consume between two to three percent of its produced power [7,8]. This means that an estimation of the total power consumed by wet FGD in OECD countries can be up to 64.4 TWh in one year [9] and this could be comparable with the entire energy consumption of a nation. Therefore, it is evident that an improvement in the WFGD process technology will have an enormous impact in terms of the economy and environment.…”

“…Often, the acidic conditions have been simulated by using HCl solutions [12][13][14][15][16][17]. Additionally, a common method is to carry out the experiments at conditions that simulate the steady state industrial process and, therefore, the pH is maintained approximately constant [9,18,19].…”

“…The grinding should be minimized in order to consume less power; on the other hand, the solid-liquid mass transfer rate should be maximized by having a sufficient surface of reaction. Because of this reason, optimization studies have been performed on the WFGD process [9].…”