Industrial Flue Gas Research Articles

Review of Power-to-Liquid (PtL) Technology for Renewable Methanol (e-MeOH): Recent Developments, Emerging Trends and Prospects for the Cement Plant Industry

The cement industry is a significant contributor (around 8%) to CO2 global emissions. About 60% of the industry’s emissions come from limestone calcination, which is essential for clinker production, while 40% are the result of fuel combustion. Reducing these emissions is challenging due to limestone’s role as the primary raw material for cement. Cement plants are required to achieve carbon neutrality by 2050, as outlined in the 13th United Nations Sustainable Goals. One strategy to achieve this goal, involves Carbon Capture and utilization (CCU). Among the options for CO2 utilization, the Power-to-Liquid (PtL) strategy offers a means to mitigate CO2 emissions. In PtL, the CO2 captured from cement industrial flue gas is combined with the hydrogen generated by renewable electrolysis (green hydrogen) and is catalytically converted into renewable methanol (e-MeOH). In this sense, this review provides a comprehensive overview of the worldwide existing pilot and demonstration units and projects funded by the EU across several industries. It specifically focuses on PtL technology worldwide within cement plants. This work covers 18 locations worldwide, detailing technology existent at plants of different capacities, location, and project partners. Finally, the review analyses techno-economic assessments related to e-MeOH production processes, highlighting the potential impact on achieving carbon neutrality in the cement industry.

Improving the removal of fine particles in cyclone using heterogeneous vapor condensation enhanced by atomization

Using a heat exchanger to cool high humidity flue gas can create a supersaturated water vapor environment, allowing fine particles to grow into large droplets by heterogeneous vapor condensation, which is conductive to the removal of fine particles by traditional equipment. However, due to the limited condensable vapor obtained by cooling, this technology can only be used in the flue gas with low particle concentration. In this study, atomization droplets were added before the heat exchanger to improve the effect of heterogeneous vapor condensation at high particle concentration, and then coupled with a cyclone separator, which was used for the deep treatment of the flue gas after the wet dedusting system. The particle removal characteristics were investigated through laboratory experiments and bypass experiments in a metallurgical company. The experimental results show that the application of atomization-heterogeneous condensation reduced the particles concentration after cyclone by 74.2 % compared with that of single heterogeneous condensation. Temperature-drop and atomized volume affected the removal of particles with size < 2 μm and > 2 μm, respectively. The industrial flue gas bypass experiment indicated that the system had strong adaptability to fluctuating conditions. When the inlet particle concentration did not exceed 2000 mg/Nm3, the outlet particle concentration can be maintained within 20 mg/Nm3.

Recent Advancements in Fe-Based Catalysts for the Efficient Reduction of NOx by CO.

The technology of CO selective catalytic reduction of NOx (CO-SCR) showcases the potential to simultaneously eliminate CO and NOx from industrial flue gas and automobile exhaust, making it a promising denitrification method. The development of cost-effective catalysts is crucial for the widespread implementation of this technology. Transition metal catalysts are more economically viable than noble metal catalysts. Among these, Fe emerges as a prominent choice due to its abundant availability and cost-effectiveness, exhibiting excellent catalytic performance at moderate reaction temperatures. However, a significant challenge lies in achieving high catalytic activity at low temperatures, particularly in the presence of O2, SO2, and H2O, which are prevalent in specific industrial flue gas streams. This review examines the use of Fe-based catalysts in the CO-SCR reaction and elucidates their catalytic mechanism. Furthermore, it also discusses various strategies devised to enhance low-temperature conversion, taking into account factors such as crystal phase, valence states, and oxygen vacancies. Subsequently, the review outlines the challenges encountered by Fe-based catalysts and offers recommendations to improve their catalytic efficiency for use in low-temperature and oxygen-rich environments.

The Catalytic Mechanisms and Design Strategies of Noble Metal Catalysts for Selective Reduction of NOx with CO

AbstractThe selective catalytic reduction of NOx by CO (CO‐SCR) is a viable method for simultaneously mitigating NOx and CO emissions in motor vehicle exhaust and industrial flue gases. Extensive research has been conducted on noble metal catalysts because of their superior catalytic activity and stability compared to non‐noble metals. Noble metal catalysts demonstrate efficient NOx conversion and high selectivity for N2. However, achieving high conversion, selectivity, and stability over a wide temperature range in the presence of excess O2, H2O, and SO2 remains a significant challenge. This review summarizes recent advancements in CO‐SCR over noble metal catalysts, providing insights for the development of CO‐SCR catalysts. This paper first examines the reaction mechanisms of CO‐SCR, followed by a discussion on the design and optimization strategies of noble metal catalysts, with a focus on composition and structural effects. This includes creating active metal sites, selecting appropriate supports, integrating catalytic additives, choosing monometallic nanoparticles, alloying, and using single‐atom catalysts. Finally, remaining challenges and potential avenues for future research have been suggested. The discovery of negatively charged noble metal single‐atom‐site catalysts presents new research opportunities.

Highly Efficient and Reversible Carbon Dioxide Capture by Carbanion-Functionalized Ionic Liquids.

Due to the active unstable nature of carbon anions, it is challenging to develop carbanion-functionalized ionic liquids (ILs) for efficient and reversible carbon dioxide (CO2) capture. Here, a series of carbanion-based ILs with large conjugated structures were designed and a promising system was achieved through tuning the nucleophilicity of carbanions and screening the cation. The ideal carbanion-functionalized IL trihexyl(tetradecyl)phosphonium N,N-diethycyanoacetoamide ([P66614][DECA]) showed equimolar chemisorption of CO2 ( up to 0.98 mol CO2/mol IL) under ambient pressure and excellent absorption rate. What's more, the combined CO2 can be released easily, leading to excellent reversibility due to high stability of anion conjugated structures. More importantly, the presence of water had negligible effect on the absorption capacity, which makes it potential to be applied to the CO2 capture in industrial flue gas. The chemisorption mechanism of the carbanion and CO2 was confirmed by spectroscopic investigations and DFT calculations, where carboxylic acid product was formed through proton transfer after the carbanions reacted with CO2. Considering that high capacity, quick rate as well as excellent reversibility, these carbanion-functionalized ILs should certainly represent competitive candidates for further scale up and practical application in CO2 capture.

Promoting fine particle removal in cyclone by spray agglomeration and heterogeneous condensation

By adding a spray chamber in front of the cyclone separator, spray agglomeration and heterogeneous vapor condensation were combined to improve the removal effect of the cyclone separator on fine particles, which is used for the deep treatment of high-humidity industrial flue gas and fine particles. Fine particles can form agglomerates through the capture effect of micron droplets, and can also grow in size through heterogeneous vapor condensation in supersaturated water vapor environment, thus being effectively removed by cyclone separators. Supersaturated water vapor environment was a necessary condition for heterogeneous vapor condensation. Numerical simulation results showed that supersaturated water vapor environment can be formed in the spray chamber when the relative humidity of the original flue gas was high, and the higher the relative humidity, the higher the supersaturation and the larger the supersaturation area. The experimental results indicated that spray agglomeration and spray coupling heterogeneous condensation increased the particle removal efficiency of the cyclone separator by 11.6 % and 22.6 %, and the removal efficiency in the 2–4 μm “fish-hook” range was increased by 21.6 % and 41.7 %, respectively. This technology was successfully applied for the first time in the deep treatment of the tail gas in Fluid Catalytic Cracking (FCC) catalyst production industry, which can ensure that the particle emission concentration was within 20 mg/Nm3.

Simulation and optimization for flue gas CO2 capture by energy efficient water-lean ionic liquid solvent

Ionic liquids (IL) are treated as advanced materials for energy-saving carbon dioxide (CO2) capture from flue gas but suffer from serious challenges in energy and mass management. Herein, a water-lean IL-based deep eutectic solvent with 1,8-diazabicyclo [5.4.0] undec-7-ene imidazole ([DBU] [IM]) and ethylene glycol (EG) blends was prepared with a screened proportion of IL:EG=7:3. The CO2 loading and saturated solvent viscosity were 1.89 mol/L and 95 mPa·s, respectively. The foundational properties of the IL-EG solvent were determined by experimental measurements and thermodynamic modeling. The vacuum flashing desorption technology was innovatively adopted for energy-saving solvent regeneration. Industrial-scale process simulation of multistage flashing was used to explore the energy consumption during solvent regeneration. Meanwhile, the segmented cooling paved a route for water separation from water-lean solvent. A comprehensive analysis was performed out to optimize the operating parameters for CO2 absorption and desorption. For the recommended 3-stage flashing configuration, the specific process regeneration energy consumption amounted to only 1.54 GJ/tCO2. Consequently, the total capture cost reduced to 48.1 $/tCO2, marking a decrease of 31.28 %, 16.55 % and 10.25 %, compared with MEA solvent, water-lean solvent and biphasic solvent, respectively. This work offered insights for future endeavors in the development of IL-based CO2 capture process from industrial flue gas.

Engineering Nanoporous Polyaminal Networks for Superior SO2 Capture and Selectivity.

Designing adsorbent materials with high SO2 adsorption capacities and selectivity remains a significant challenge in flue gas desulfurization. This work focuses on developing two nitrogen-rich nanoporous polyaminal networks (NPANs), which demonstrate promising capabilities for SO2 adsorption and separation. Two nitrogen-rich nanoporous polyaminal networks, NPAN-5 and NPAN-6, were synthesized via a one-pot method using thiophene-2,5-dicarbaldehyde and furan-2,5-dicarbaldehyde with 1,4-bis(2,4-diamino-1,3,5-triazine)-benzene, respectively. The Brunauer-Emmett-Teller (BET) specific surface areas of NPANs range from 838 to 956 m2·g-1. At 298 K and pressures of 0.1 and 1.0 bar, NPAN-5, featuring thiophene units, demonstrates a SO2 adsorption uptake of 5.14 and 9.63 mmol·g-1, respectively, surpassing many previously reported materials. Furthermore, at room temperature, NPAN-6, containing furan moieties, exhibits unprecedented selectivity for SO2 over CO2 and N2, with ratios reaching up to 78 and 9321, respectively. Dynamic breakthrough experiments reveal that NPANs effectively separate SO2 from a ternary gas mixture comprising SO2, CO2, and N2 at concentrations of 0.2, 10, and 89.8%, respectively. Notably, NPAN-6 achieves a prolonged SO2 retention time of 218 min·g-1 and a saturation adsorption uptake of 0.42 mmol·g-1. The remarkable SO2 adsorption capacities and selectivities demonstrated by these nitrogen-rich nanoporous polyaminal networks underscore their potential to revolutionize industrial flue gas desulfurization.

Optimization of carbon dioxide adsorption from industrial flue gas using zeolite 13X: A simulation study with Aspen Adsorption and response surface methodology

One of the best ways to prevent further warming of the planet and reduce pollutants is to remove or adsorb and recover carbon dioxide gas from the exit of cement factory exhaust. So far, several methods have been proposed for this; In this research, zeolite 13X adsorbent is used considering the operational conditions. To remove CO2 gas from the desired gas mixture, an adsorption operation unit with a column filled with zeolite 13X adsorbent was simulated in Aspen Adsorption V14 software. Changes in parameters such as temperature, and pressure and their effects on adsorption rate, adsorbent saturation time, and output heat rate were investigated to achieve higher system efficiency and optimal operating conditions. The adsorption unit was optimized by RSM to achieve maximum CO2 adsorption. Temperature and mole fraction of CO2 were identified as key influencing factors determining the adsorption performance of zeolite 13X for CO2 adsorption. It was found that the system should be operated at a temperature of 28.07 °C and a pressure of 1.202 bar to achieve maximum adsorption. Finally, 2.784 mol% CO2 gas was captured by the said process in optimal operating conditions. Further analysis revealed higher temperatures slightly decrease CO2 adsorption capacity, while increasing pressure enhances it. Conversely, elevated flow rates reduce breakthrough time, indicating a trade-off between adsorption capacity and capture efficiency.

Catalytic Co-oxidation of Dichloromethane and non-chlorinated VOC over HxPO4-RuOx/CeO2, Pt/HZSM-5 and dry-mixed Ru-Pt Catalysts

Industrial flue gases contain chlorinated VOCs (CVOCs) and hydrocarbons, along with various contaminants. Although previous studies have primarily focused on the catalytic oxidation of individual VOCs, the activity of VOCs in mixtures often differs from that of individual compounds. The catalytic oxidation of dichloromethane in the presence of a second VOC (ethyl acetate, n-hexane, and toluene) was investigated using HxPO4-RuOx/CeO2, Pt/HZSM-5, and dry-mixed Pt-Ru catalysts. The dry-mixed catalyst combines the excellent dechlorination ability of HxPO4-RuOx/CeO2 with the oxidation capability of Pt/HZSM-5. A mixture of 1000 ppm toluene and 100 ppm dichloromethane is fully oxidized over the Ru-Pt catalyst at 300 °C, 30 °C lower than the T100 observed on the other two catalysts. DFT calculation reveals that the activation of toluene and dichloromethane occurs on Pt and Ru sites, respectively, dechlorinated by proton of phosphate. Furthermore, by-product dioxin content on Pt-Ru is significantly below 0.1ng TEQ Nm-3 limit.

Pore-scale study of [formula omitted] desublimation in a contact liquid

Cryogenic carbon capture (CCC) designed to operate in a contact liquid is an innovative technology for capturing CO2 from industrial flue gases, helping mitigate climate change. Understanding CO2 desublimation properties in a contact liquid is crucial to optimizing CCC, but is challenging due to the complex physics involved. In this work, a multiphysics lattice Boltzmann (LB) model is developed to investigate CO2 desublimation in a contact liquid for various operating conditions, with the multiple and fully-coupled physics being incorporated (i.e., two-phase flow, heat transfer across three phases, CO2 transport between the gas and liquid, homogeneous and heterogeneous desublimation of CO2, and solid CO2 generation). The CO2 desublimation process in a contact liquid is well reproduced. Moreover, parametric studies and quantitative analyses are set out to identify optimal conditions for CCC. The decreasing liquid temperature (Tl) and flue gas temperature (T0) are found to accelerate the CO2 desublimation rate and enhance the CO2 capture velocity (vc). However, excessively low Tl and T0 values should be avoided. These conditions increase the energy consumption of cooling while only marginally improving vc, due to the limited CO2 supply. The CCC system performs effectively when purifying flue gases with high CO2 content (Y0). This is because the large Y0 accelerates the CO2 desublimation rate and enhances the overall CO2 capture efficiency. A high gas injection velocity (or Pe) is beneficial for amplifying vc by increasing the gas–liquid interfaces and enhancing the CO2 supply. Nevertheless, too high a Pe should be avoided, as it hinders the transport of CO2 to the liquid or solid CO2 surfaces, ultimately restricting the amount of CO2 available for desublimation and inhibiting the enhancement of vc. This study develops a viable LB model to investigate CO2 desublimation in a contact liquid for varying conditions, which advances the knowledge base of CCC and facilitates its industrial applications.

Molecular Engineering of Poly(Ionic Liquid) for Direct and Continuous Production of Pure Formic Acid from Flue Gas.

Electrochemical CO2 reduction reaction (CO2RR) offers a promising approach to close the carbon cycle and reduce reliance on fossil fuels. However, traditional decoupled CO2RR processes involve energy-intensive CO2 capture, conversion, and product separation, which increases operational costs. Here, we report the development of a bismuth-poly(ionic liquid) (Bi-PIL) hybrid catalyst that exhibits exceptional electrocatalytic performance for CO2 conversion to formate. The Bi-PIL catalyst achieves over 90% Faradaic efficiency for formate over a wide potential range, even at low 15% v/v CO2 concentrations typical of industrial flue gas. The biphenyl in PIL backbone affords hydrophobicity while maintaining high ionic conductivity, effectively mitigating the flooding issues. The PIL layer plays a crucial role as a CO2 concentrator and co-catalyst that accelerates the CO2RR kinetics. Furthermore, we demonstrate the potential of Bi-PIL catalysts in a solid-state electrolyte (SSE) electrolyzer for the continuous and direct production of pure formic acid solutions from flue gas. Techno-economic analysis suggests that this integrated process can produce formic acid at a significantly reduced cost compared to the traditional decoupled approaches. This work presents a promising strategy to overcome the challenges associated with low-concentration CO2 utilization and streamline the production of valuable liquid fuels and chemicals from CO2.

Pre-treatment of waste hydrated cement used for replacement of fine aggregate using amine-based CO2 solvent

In the realm of construction and demolition (C&D) waste, a small fraction of hydrated cement waste is typically repurposed to generate supplementary cementitious material or filler for concrete. However, the conventional method of utilizing it in powder form demands significant energy consumption to achieve the necessary fineness. Therefore, this study proposes a method to use a waste-hydrated cement paste as a fine aggregate as well as the pre-treatment method to enhance its properties. The pre-treatment involves carbonating hydrated cement in a fully CO2-dissolved amine-based CO2 solvent, specifically a monoethanolamine (MEA) solution. This process eliminates vulnerable phases, such as calcium hydroxide, resulting in a higher compressive strength of mortar when incorporating the treated hydrated cement as fine aggregate. Notably, the use of fully CO2-dissolved 1% and 10% MEA solutions during carbonation demonstrates superior performance and increased CO2 uptake. Additionally, the developed pre-treatment method uses MEA CO2 solvent directly, commonly utilized for CO2 capture in industrial flue gas. It is an alternative for solvent regeneration without the need for a heating process, potentially reducing overall energy consumption.

Review: Green Energy Alchemy: Converting Industrial Flue Gas into Eco-Friendly Charcoal

Review: Green Energy Alchemy: Converting Industrial Flue Gas into Eco-Friendly Charcoal

Unveiling the promoting mechanism of Mo on the performance of CuCeOx catalyst for simultaneously NH3-SCR denitration and CO oxidation under oxygen-rich conditions

NOx and CO coexisted in numerous actual industrial flue gases. The simultaneous removal of NOx and CO had great potential for application but remained still a challenge. Herein, a series of Mo-modified CuCeOx catalyst was developed to simultaneously achieve NH3-SCR denitration and CO oxidation. The results indicated that the CCM3 catalyst displayed the optimal performance with 91.2 % NOx conversion and 100 % CO conversion as well as excellent long-time stability and SO2 or/and H2O tolerance at 225 ℃. It was found that the strong interaction between Cu, Ce and Mo oxides resulted in the particles highly dispersed with smaller size on catalyst surface, which could provide abundant active sites to decreasing the competitive adsorption among reactive gases. Furthermore, the Mo modification promoted the production of more oxygen vacancies, Ce3+ and Oα species, which facilitated the redox recycle and the generation of intermediates. Moreover, the H2-TPR and NH3/CO/O2-TPD analysis illustrated that the reducibility and the capacity for reaction gas adsorption and activation were enhanced, which improved low-temperature activity. The in situ DRIFTS experiment revealed that the E-R and L-H mechanism were existed in NH3-SCR process on CC and CCM3 catalysts. What’s more, the stronger acidity and strengthened E-R mechanism on CCM3 catalyst hindered the adsorption of SO2 and weakened the inhibition effect of competitive adsorption among SO2 and NO. Additionally, both surface lattice oxygen and chemisorbed oxygen could react with Cu+–CO species to produce CO2, the pathway obeyed L-H and MvK mechanism. This work may provide a novel strategy for the treatment of CO and NOx pollutants in industrial flue gas.

Efficient CO2 Desorption Catalysts: from Material Design to Kinetics Analysis and Application Evaluation

Catalytic amine-solvent regeneration has been validated as an energy-saving strategy for CO2 chemisorption by boosting reaction kinetics under mild conditions. The upscale performance evaluation and long-term durability are indispensable steps for industrial application but have been scarcely reported thus far. Here, we report a ZrO2/Al2O3 pack catalyst that possesses strong metal oxide-support interactions, a porous structure, active and stable Zr–O–Al coordination, promoted proton transfer and a 40.7% decrease in the energy activation of carbamate decomposition, which significantly accelerates CO2 desorption kinetics. The upscale experiment and cost evaluation based on industrial flue gas revealed that the use of packing catalysts can reduce energy consumption by 27.56% and optimize the overall cost by 10.49%. The active sites present excellent stability in alkaline solvents. This work is the first to investigate the ability of high-technology readiness (technology readiness level at 6 (TRL 6)) for catalytic amine-solvent regeneration, providing valuable insights for potential applications involving efficient CO2 capture with catalyst assistance.

A novel cryogenic-thermochemical approach for clean hydrogen production from industrial flue gas streams with carbon capture and storage

The present work aims to develop a novel integrated energy system for clean hydrogen production from the industrial flue gas stream. The particular system incorporates a cryogenic distillation unit for H2S and CO2 separation and a thermochemical cycle for hydrogen production. The industrial flue gaseous mixture is considered a major feedstock for the present system. H2S is retrieved from the waste gaseous stream and fed to the two-step sulfur looping thermochemical cycle to perform clean hydrogen production. In this way, clean hydrogen production, elemental sulfur production, carbon capture, and storage are achieved. The entire integrated energy system is simulated in the Aspen Plus process simulator and is investigated thermodynamically in terms of energy and exergy performances. Various parametric studies are conducted to assess the significance of operating parameters on the system performance. The H2S and CO2 removal rates from the waste feed stream are found to be 85.55 % and 84.62 %. The H2S conversion into hydrogen is determined to be 66.67 %. The energy and exergy efficiencies of the two-step thermochemical cycle are found to be 53.93 % and 23.69 %, respectively. The parametric studies show that the hydrogen production rates of 3.63 kmol/h, 2.46 kmol/h, and 1.78 kmol/h are achieved at sulfurization temperatures of 200 °C, 300 °C, and 500 °C, respectively. The study further concludes that 44.60 % of the total input exergy is lost due to the presence of irreversibilities within the system. The overall energy and exergy efficiencies of the integrated energy system are found to be 82.99 % and 55.39 %, respectively.

Tandem Catalysis for Simultaneous Removal of NOx and C3H8 with Inhibition of N2O.

Tandem catalysis is widely adopted for multipollutant control in mobile sources but has rarely been reported in stationary source emission elimination. This work proposed a tandem arrangement way with up-streamed V2O5/TiO2 + down-streamed Cr2O3/TiO2 catalysts, which could achieve the efficient synergistic control of NOx and C3H8 in industrial flue gas. Moreover, this arrangement successfully alleviated the unwanted N2O formation during the NH3 -SCR process. Compared to the conventional impregnation method of the Cr2O3-V2O5/TiO2 catalyst, the tandem catalysts of V2O5/TiO2 + Cr2O3/TiO2 could enhance the NOx and C3H8 conversion by 4.2% and 39.5%, respectively, at 350 °C. It might be attributed to the fact that Cr species was the active site for C3H8 oxidation, and the tandem arrangement of catalysts was beneficial to even dispersion of active components on supports. Furthermore, due to the preferential NOx removal over the up-streamed V2O5/TiO2 catalyst, the tandem catalysts obviously alleviated the N2O formation caused by Cr species during the NH3-SCR process. Herein, it significantly decreased N2O formation by 240.5% at 350 °C compared to the Cr2O3-V2O5/TiO2 catalyst, achieving multipollutant emission control from industrial flue gas with the performance of "one stone three birds".

Upcycling rice husk ash and coal-fired fly ash as si/al sources into hierarchical ZSM-5 for efficient mercury capture from industrial flue gas

Limiting gaseous Hg0 emission is pressing due to the high toxicity in the ecosystem. Zeolites can be regarded as a promising alternative to carbon-based Hg0 adsorbents. However, the mass transfer limitations of conventional singe-sized zeolites constrain the industrial application of zeolites. This study explores the synthesis of hierarchical ZSM-5 zeolites using rice husk ash (RHA) and coal-fired fly ash (FA) as sustainable sources of silicon and aluminum, aimed at enhancing Hg0 removal from industrial flue gases. By adopting a one-step hydrothermal method, we introduced hierarchical porosity into the ZSM-5 framework, enhancing mass transfer and adsorption efficiencies. Iron (III) chloride (FeCl3) was utilized as an active species for modifying the hierarchical ZSM-5, significantly boosting its Hg0 adsorption capabilities. Fe/6RF-hZ demonstrating more than 92% mercury removal efficiency in 60 min under mixed flue gas condition. The structural and chemical attributes of the synthesized ZSM-5 were detailedly characterized, revealing notable differences in surface chemistry and porosity that correlate with varying calcination temperatures of RHA. TEA analysis reveals that hierarchical ZSM-5 zeolites outperform traditional sorbents in demercuration (DeHg) applications, with exceptional DeHg efficiency, energy efficiency (12 kWh), synthesis cost (860 $/ton), and carbon content (non-carbon). This study not only sheds light on the upcycling of solid wastes in synthesizing novel adsorbents but also contributes to the broader application of zeolitic materials in environmental remediation.

Preparation of Gypsum–Urea with Enhanced Sustainability from Flue Gas Desulfurization Gypsum in Saturated Urea Solution

Gypsum–urea is a kind of urea product with substantially reduced aqueous solubility and lower hygroscopicity that increases the soil retention time of urea and thus enhance its environmental sustainability. Here, gypsum–urea was prepared using bulk industrial solid waste flue gas desulfurization (FGD) gypsum as a raw material in a saturated urea solution via immobilizing urea molecules into the crystal lattice. The preparation process was achieved through a dissolution–recrystallization mechanism during which FGD gypsum dissolved into Ca2+ and SO42−, which then recrystallized with CO(NH2)2 to form gypsum–urea. The preparation process was almost completed within 10 min, and the formed gypsum–urea presented a uniform size distribution of 30–90 μm and a much lower hygroscopicity and nitrogen release efficiency than that of urea. With a high efficiency of synthesis, and sustainable features, and the recyclability of the saturated mother urea solution, the dissolution–recrystallization-based urea immobilization approach is highly promising regarding the preparation of gypsum–urea with the desired environmental sustainability and contributes to the realization of the sustainable reutilization of FGD gypsum.