Danping Pan

The efficient utilization of industrial waste (containing alkaline compounds, especially Ca-based species) for flue gas desulfurization (FGD) is of great importance for both environmental protection and resource recovery. In this study, paper industry white mud was modified with Ca(OH)₂ to develop a cost-effective sorbent with enhanced SO₂ removal performance. Optimization experiments identified the best preparation conditions as a 1:1 Ca(OH)₂/white mud ratio, 60 °C modification temperature, 6 h reaction time, and a liquid-to-solid ratio of 3:1. Under these conditions, the sorbent achieved nearly 100% SO₂ removal in the first 6 h and maintained >90% efficiency after 10 h, significantly outperforming raw white mud and Ca(OH)₂ alone. Characterization revealed that the superior performance originated from structural stability and abundant active sites. BET analysis showed a high surface area (24.8 m²·g⁻¹) and pore volume (0.160 cm³·g⁻¹), which were largely preserved after desulfurization, indicating resistance to pore blockage. SEM images confirmed a transition from porous aggregates to densified product layers, consistent with a shrinking-core/product-layer mechanism. XRD identified CaSO₄·2H₂O as the dominant product, while in situ FTIR demonstrated that O₂ promotes sulfite oxidation and H₂O accelerates hydrated sulfate formation, enhancing activity but causing faster pore blocking. The presence of NO extended sorbent durability by catalyzing continuous sulfite oxidation through NO/NO₂ redox cycling. Overall, Ca(OH)₂-modified white mud combines high reactivity, durability, and structural stability, offering a promising alternative to conventional sorbents. This work provides a viable route for the resource utilization of paper industry waste and practical insights for designing efficient and sustainable materials for industrial FGD systems.

Fine particulate matter (PM) and sulfur trioxide (SO₃) from coal-fired flue gas pose significant environmental and health risks. While low-low temperature electrostatic precipitators (LLT-ESPs) enhance PM and SO₃ removal by cooling flue gas below the acid dew point, their efficiency is limited by incomplete agglomeration. This study proposes integrating turbulent agglomeration technology into LLT-ESP systems to improve collision and adhesion between droplets and particles. Experiments were conducted under three conditions: flue gas containing SO₃ alone, fly ash alone, and their mixture. Particle size distributions, mass concentrations, and removal efficiencies were analyzed using ELPI⁺ and PM samplers. Results showed that turbulent agglomeration reduced the number concentration of sulfuric acid droplets by 21.4% from 1.59 × 10⁷ cm⁻³ to 1.25 × 10⁷ cm⁻³ (SO₃-only case) and fine fly ash particles by 19.5% from 5.79 × 10⁶ cm⁻³ to 4.66 × 10⁶ cm⁻³ (fly-ash-only case). Although LLT-ESP combined with turbulent agglomeration has a certain removal effect in the case of individual pollutants, the overall effect is not unsatisfactory, especially for SO₃, whose mass-based removal efficiency was merely 16.2%. The value of the fly-ash-only case was 92.1%. Synergistic effects in the coexistence scenario (fly ash and SO₃) significantly enhanced agglomeration, increasing SO₃ and PM removal efficiencies to 82.9% and 97.6%, respectively, compared to 69.7% and 90.1% without turbulent agglomeration. The mechanism behind the efficiency improvement involved droplet–particle collisions, sulfate deposition, and improved particle charging. This work demonstrates that turbulent agglomeration optimizes multi-pollutant control in LLT-ESP systems, offering a feasible strategy for achieving ultra-low emissions in coal-fired power plants.

In this work, the influence of KCl concentration on the gasification characteristics of lignite coal char between 800–1100 °C is studied through the experiments of temperature programmed gasification and isothermal gasification using a thermogravimetric analyzer. The gasification kinetics, characteristic parameters, and the reaction mechanism of catalytic gasification is explored using the random pore model (RPM). In view of temperature programmed gasification, the gasification rate of coal char is relatively slow when the temperature is below 700 °C, and only when the temperature is higher than 700 °C, the gasification starts to accelerate. Results show that with the existence of a catalyst, the temperature required for gasification reaction is reduced and the gasification reaction rate is increased. Furthermore, the higher concentration of KCl leads to the shorter half reaction time, the higher gasification rate, and the stronger catalysis. In addition, the activation energy of AW-char (the char from acid-washed coal) is the highest, while the activation energy and the energy level required for the gasification reaction are reduced by adding KCl. Based on the analysis of the catalytic mechanism, it is found that the unified mechanism of catalytic gasification of alkali and alkaline earth metals is applicable for the KCl catalysis on coal char gasification.

Sludge-based activated carbons (SACs) prepared from sewage sludge and corn straw, were modified by ferric nitrate, and the unmodified SAC and modified SAC were used as the adsorbing agent to treat the landfill leachate, the elimination capacity for chemical oxygen demand (COD) and organic matter in leachate were studied. Based on this, the physicochemical properties of SACs and the components changes in leachate were analyzed and characterized by X-ray photoelectron spectroscopy and three-dimensional fluorescence spectroscopy. The results showed that under optimal experimental conditions, the elimination capacities of SAC372 for COD, biological oxygen demand over 5 days, and NH₄⁺–N in the leachate were 81.58%, 54.73%, and 69.08%, respectively; while the adsorption capacities of modified SAC for these three substances were 86.25%, 63.51%, and 79.15%, respectively. The ferric nitrate modification improved the ability of SAC to eliminate COD and organic matter from leachate slightly, and made the adsorption occurred easily. The adsorption process of unmodified SAC was dominated by multi-layer adsorption, while the adsorption process of modified SAC was dominated by monolayer adsorption. The mass fraction of Fe (2p) in modified SAC remarkably increased, from 0.70% to 26.01%, organic functional groups certain phase of Fe oxides with different valence states were generated in SAC, which provided a substrate for iron–carbon micro electrolysis. After adsorbed by unmodified SAC and modified SAC adsorption, the total fluorescence intensity of in the leachate increased by 17.01% and 116.84%, respectively. Both two SACs could decompose the humic acid-like substances into aromatic protein organic compounds, and modified SAC could further decompose the soluble microbial byproduct-like substances.

The entrainment of desulfurization slurry droplets out of the scrubber had a significant influence on the properties of fine particle emissions in the limestone-gypsum desulfurization system. Investigations on the relationship between entrainment of slurry droplets and generation of fine particles during the desulfurization process were carried out with an experimental system. The results showed that a large number of fine droplets and submicron particles existed in the flue gas out of the scrubber, which was attributed to the entrainment of slurry droplets during the desulfurization process. The entrained droplet sizes were closely connected with the slurry atomization characteristics, and majority of them were with sizes less than 20 μm. The mass ratio of solid contents in entrained and sprayed droplets ranged from 15% to 40%, and particles in the entrained droplets were much smaller. With the increase of superficial gas velocity, liquid–gas ratio, and desulfurization slurry concentration, the proportion of entrained micron droplets was significantly higher. Correspondingly, more fine particles were emitted with increased rates of number concentrations ranging from 20% to 50%. The optimizations of spray scrubber were beneficial for the reduction of entrained droplets and fine particles such as the adjustment of nozzle arrangement and the addition of spray layer. The decrease rate of emitted fine particle concentrations ranged from 10% to 30%.