Flue Gas Impurities Research Articles

Techno-economic feasibility of CO2 utilization for production of green urea by Indian cement industries

The cement industry contributes substantially to global carbon emissions, necessitating urgent adoption of mitigation pathways aligned with climate goals. This study investigates the technical and economic viability of capturing carbon dioxide (CO2) emissions from cement plants in India and using that captured CO2 to produce green urea. The research aims to determine the feasibility of the CCUS approach as a practical way to reduce CO2 emissions from cement production while also boosting India's self-sufficiency in producing urea, a crucial fertilizer. The research uses a multi-criteria analysis (MCA) framework to assess various factors, including the technological readiness of CCUS technologies, the capital and operating costs of setting up and running such a system, the market demand for green urea, and the potential reduction in CO2 emissions. The study focused on 32 major cement plants in India, using data from their annual reports to inform the MCA model with an assumption of a post-combustion Monoethanolamine (MEA) scrubbing capacity CO2 capture capacity of 0.5 million tonnes per year per plant and used existing data and modeling techniques to analyze the feasibility of converting the captured CO2 into urea. The key findings indicate that this approach is promising and projects a 12.4% reduction in CO2 emissions from the cement industry if these 32 plants implement the CCUS technology. Additionally, it highlights a favorable market for the green urea produced, with an estimated output of 21.82 million tonnes per year, enough to offset a significant portion of India's reliance on urea imports. Financially, the study projects a six-year payback period and a 16.7% return on investment. It concludes that implementing CCUS technology to create green urea in Indian cement plants is technically and economically feasible. The approach has the potential to significantly reduce CO2 emissions while also supporting India's goal of self-sufficiency in urea production. However, further investigation and pilot-scale projects are recommended to validate the model's findings and optimize various aspects, such as managing flue gas impurities and leveraging waste heat for energy efficiency.

Electrochemical CO2 Reduction in the Presence of Flue Gas Impurities: Effect of NOx, SOx and O2

Electrochemically converting CO2 to valuable chemical products using renewable energy sources may present solutions to alter current increasing CO2 emission trends. Currently, electrolyzer research is almost exclusively done with pure CO2 streams that - in practice - would originate from carbon capture units that prevent CO2 release to the atmosphere [1]. The capture and purification steps are cost intensive processes which is why direct usage of flue gases that contain impurities is a highly interesting approach. For this reason, the performance of CO2 electrolyzers equipped with state-of-the-art Bi2O3 or Ag catalysts is investigated in this work with an impure CO2 feed stream containing SO2, NO or O2. The short-term effect of highly concentrated SO2 (10 000 ppm) and NO (8 300 ppm) impurities during CO2 electrolysis was previously described [2,3]. Our work [4] elaborates further on this matter through 20 h experiments with flue gas-like concentrations of 200 ppm SO2 or NO. The results show a stable operation without severe FE losses (remains >90%) and structural adaptations to neither Ag nor Bi2O3 by these impurities. The presence of oxygen in flue gas streams at concentrations of several percent is common and causes a major decrease in FE to the target products (CO or HCOO-) during electrolysis. This is a result of the competition between the ORR and CO2RR with the former occurring more preferentially. To overcome this, we have discovered two possible strategies, which allow high FE’s to CO2RR products even in the presence of oxygen. (1) By operating the electrolyzer at a sufficiently high overall current density, all of the O2 entering and reaching the electrode surface gets reduced, allowing the CO2RR to become the dominant reaction. Although this approach has a higher electricity penalty, the extra cost is negligible compared to the cost otherwise associated with the CO2 purification for CO2 streams with an O2 content below 3%. (2) Given that the ORR is mostly occurring at the carbon-based gas diffusion layers another approach to improve CO2RR efficiency in the presence of oxygen is to replace this conventional support with ultra hydrophobic PTFE membrane filters. Since they are inefficient oxygen reduction catalysts, CO2RR again takes up the major fraction of the applied current density. A downside of using PTFE is that an additional conductive layer is required in case the catalyst itself (e.g. for bismuth oxide) is not conductive enough. These results thus not only offer new insights into the impact of gaseous impurities during CO2 electrolysis, but also suggest a strategy to improve electrolyzer performance with O2-containing feed streams. Bibliography [1] Lee M.Y., Environ. Sci. and Technol.; DOI: 10.1080/10643389.2019.1631991[2] Luc W.; JACS, DOI: 10.1021/jacs.9b03215[3] Ko B., Nature Comm. DOI : 10.1038/s41467-020-19731-8[4] Van Daele S ., J. Appl. Catal. B, Environ.; DOI: 10.1016/J.APCATB.2023.123345 Figure 1

Pore-Scale Study on the Effect of SO2 on Hydrate-Based CO2 Sequestration in a High-Pressure Microfluidic Chip

Summary To mitigate the effects of greenhouse gases, the sequestration of greenhouse gases such as carbon dioxide (CO2) in seafloor sediments in the form of hydrates has become a safe and efficient method. If sulfur dioxide (SO2), one of the flue gas impurities, is also sequestered, the cost of CO2 purification and sequestration can be effectively reduced. However, there is a lack of in-situ observation of how SO2 affects the nucleation and growth process of CO2 hydrates. In this study, a visual microfluidic chip combined with in-situ Raman spectroscopy was used for the first time to investigate the impact mechanism of SO2 on the nucleation and growth kinetics of CO2 hydrates in porous media. The results indicate that SO2 could promote the nucleation and growth of CO2 hydrate in the following aspects: First, the diffusion of SO2 in solution induces spontaneous convection of the solution in the pores, which could promote the nucleation of mixed hydrates. After nucleation, dissolved SO2 acts as a “seed” for hydrate formation, and the pore solution is covered with hydrate microcrystals, providing heterogeneous nucleation sites for hydrate growth in solution. During the growth stage, SO2 could induce the preferential growth of mixed hydrates within the solution and enhance the growth rate of hydrates, acting as a promoter of hydrate formation. As CO2-SO2 mixed hydrates preferentially grow in solution and grow denser, it could quickly cement the pores, which could significantly improve the stability of the reservoir and form a strong hydrate barrier in the reservoir. These findings have important theoretical value and guiding significance for the synchronous sequestration of CO2-SO2 by hydrates.

Influence of gas impurities (SO2 and NOX) in flue gas on the carbonation and hydration of cement compacts

Flue gas with a typical CO2 concentration of 10–20 % is found to be potentially utilized for accelerating the curing process of cement compacts. However, the competitive effect of acid gas impurities (i.e. SO2 and NOX) contained in flue gas on carbonation behaviors remains unclear. In this work, multi-component gases (500 ppm SO2, 500 ppm NO2, 10 % O2, and 74.9 % N2) with a CO2 concentration of 15 % are simulated to study the carbonation reactivity of cement compacts after 2 h of curing. The influence of subsequent water curing on strength and microstructure development over time is also further investigated. The experimental results show that after exposure to CO2, the highly soluble acidic SO2 and NOX gases can considerably reduce the pH of cement compacts, and thus mitigate the carbonation efficiency. The dissolved SO2 can potentially compete with CO2 for calcium-bearing ion combination, leading to a reduction of ∼30 % in compressive strength. However, this inferior performance can be compensated by the progressive hydration reaction in subsequent water curing. The findings from this study highlight the essential consideration of gas impurities in flue gas CO2 curing, in particular their impact at an early age. Additionally, there is a need to explore the durability characteristics and interactions of gas impurities during high-temperature curing.

Adsorption behaviors for clathrate hydrates of CO2 with mixed gases

Here, the preference and adsorption capacities of guest molecules in the sI and sII hydrate of water cages when CO2 + H2S, CO2 + SO2 and CO2 + N2O gas mixture form hydrates are simulated by using grand canonical Monte Carlo and molecular dynamics hybrid simulations method. The results indicate that SO2 prefers to occupy large cages, H2S prefers small cages for CO2 + H2S and CO2 + SO2 and N2O exhibits little preference between small or large or cages of CO2 + N2O sI hydrates, respectively. The abundance ratio shows hydrate can effectively achieve the separation of flue gases. Moreover, the thermodynamics calculation results show that the impurity gases H2S, SO2 and N2O favors the formation of CO2 hydrate. The stability CO2 + H2S, CO2 + SO2 and CO2 + N2O sI hydrates is higher compared to the stability of sII hydrates. The phase equilibrium analysis provides clear evidence that enclathration of H2S and SO2 molecules into the water cages of the hydrate structure plays a crucial role in stabilizing the hydrate lattices. The findings of this study suggest that removal of certain flue gas impurities is not required during the replacement of CH4 in hydrate form with the CO2 gas. The current investigation provides theoretical background for executing replacement of CH4 in hydrate form with the CO2 gas.

Integrations of desulfurization, carbon capture, and methanation at an isothermal intermediate temperature

Integrated CO2 capture and conversion (iCCC) technology has been recognized as the most efficient technology for Carbon Capture, Utilization, and Storage (CCUS). However, its industrialization is hindered by some unsolved engineering problems. Typically, sulfur impurities in most industrial flue gas will have significant poisoning effects on the process. Herein, we report integrations of SO2 removal, CO2 capture and conversion (iSCCC) at an isothermal intermediate temperature in a two-fixed-bed column system. By rationally developing the SO2 adsorbent pellets of ZnO-CaO, the CO2 adsorbent pellets of AMS-MgO, and the methanation catalyst pellets of Ni-La/Al2O3, each individual unit is optimized. Specifically, the in-situ dynamic structure evolution observed by the atmospheric aberration-corrected scanning transmission electron microscopy as well as the theoretical dynamics calculation provide an in-depth understanding of the CO2 adsorption and desorption performance changing with the temperature on the AMS-MgO pellets, which builds a bridge for a successful 99.3 % CO2 methanation efficiency. As a result, the matched iSCCC process demonstrates exceptional performance from simulated flue gas containing 1000 ppm SO2 and 20 vol% CO2, with full desulfurization and decarbonation and a CO2 conversion efficiency of 93.6 % after 20 cycles isothermally at 400 °C, superior to all the reported performance so far as we know, providing a promising route to practical large-scale iSCCC towards carbon neutrality.

How flue gas impurities affect the electrochemical reduction of CO2 to CO and formate

The electrochemical CO2 reduction offers a promising solution to convert waste CO2 into valuable products like CO and formate. However, CO2 capture and purification remains an energy intensive process and therefore the direct usage of industrially available waste CO2 streams containing SO2, NO and O2 impurities becomes more interesting. This work demonstrates an efficient (Faradaic efficiency > 90 %) and stable performance over 20 h with 200 ppm SO2 or NO in the feed gas stream. However, the addition of 1 % O2 to the CO2 feed causes a significant drop in Faradaic efficiency to C-products due to the competitive oxygen reduction reaction. A potential mitigation strategy is to operate at higher total current density to firstly reduce most O2 and achieve sufficient product output from CO2 reduction. These results aid in understanding the impact of flue gas impurities during CO2 electrolysis which is crucial for potentially bypassing the CO2 purification step.

Impurity-Resistant CO2 Reduction Using Reactive Carbon Solutions

Electrolyzers that electrochemically convert aqueous (bi)carbonate solutions (solutions containing captured CO2, or “reactive carbon solutions”) into commodity chemicals couple CO2 capture with CO2 conversion. Industrial exhaust streams contain nitrogen oxides (NOx) and sulfur oxides (SOx) that form redox-active anions in reactive carbon solutions that can interfere with downstream CO2 reduction. We therefore designed experiments to test how impurities produced from the dissolution of NOx (NO2– and NO3–) and SOx (SO32– and SO42–) impact the electrochemical conversion of (bi)carbonate to CO. We found that CO production was unaffected by SOx compounds in a 3.0 M KHCO3 feedstock, but 2000 ppm of NOx impurities decreased CO selectivity from ∼60% to <5%. This decrease was caused by the preferential reduction of NO2– and NO3– over CO2. Our study establishes tolerance limits for common flue gas impurities in reactive carbon solutions and provides strategies to mitigate toxification effects.

Copper selenide sensitized low-cost porous coordination polymers towards efficient capture trace gaseous elemental mercury

Mercury, as a highly toxic atmospheric pollutant, poses serious hazards to global health and ecosystems. Developing low-cost sorbents with simultaneous fast capture rate and large uptake capacity to reduce elemental mercury (Hg0) emissions from industrial flue gas remains a formidable challenge. Herein, a rationally designed surfactant-assisted method was developed to construct copper selenide (CuSe) sensitized porous coordination polymers (CAU-10-H) as an efficient Hg remediator. The CuSe/CAU-10-H (0.8NC-CAU) exhibits superior near-100 % gaseous Hg0 removal efficiency over a wide temperature range (30–120 °C), implying its adaptability under different implementations. The equilibrium Hg0 adsorption capacity and initial Hg0 uptake rate of 0.8NC-CAU are 748.09 mg·g−1 and 63.21 μg·g−1·min−1, respectively, surpassing that of conventional sorbents and comparable to the benchmark materials. Furthermore, 0.8NC-CAU can adapt to harsh conditions with different flue gas impurities containing SO2, NO, and H2O to maintain high selectivity and stability, which is advantageous for real-world applications. Density functional theory (DFT) reveals that unsaturated selenium ligands as electron acceptors are critical affinity sites for facilitating Hg0 capture, resulting in stable HgSe species. More importantly, the facile preparation, prominent uptake capacity, and rapid capture rate of the 0.8NC-CAU material make it cost-effective. This work proposes a potential trap for Hg0 capture from industrial flue gas and facilitates the development of hybrid-functionalized materials for environmental remediation.

One-step upgrading of real flue gas streams into syngas over alumina-supported catalysts

Flue gas is a major source of CO2 and the development of technologies for its utilization is of utmost interest both by environmental and industrial perspectives. Recently investigated CO2 valorization processes still face techno-economic challenges for implementation for costs associated with different steps, including CO2 purification steps. Thus, for the first time in literature, the feasibility of the direct one-step upgrading of real untreated flue gas into syngas is investigated here. For that end, classical alumina-supported catalysts (Ni, Co and Fe) were used for concept validation. The influences of temperature (500–900 °C), metal load (10–15 %), residence time (GHSV = 315–1260 h−1) and the effects of flue gas impurities (NOX and SO2) are reported here. Best CO2 and H2O conversion performances (XCO2 = 53.9 %, XH2O = 67.0 %) were obtained with the nickel catalyst with 15 wt% Ni at 900 °C and the highest residence time (GHSV = 315 h−1). The highest H2/CO ratio of the produced syngas was 0.70 and it was obtained with the same 15 wt% Ni catalyst at T = 700 °C, GHSV = 630 h−1. The NOx present in the FG was completely removed as part of the one-step upgrading strategy, while SO2 did not interact with the tested catalysts. Finally, a long-term operation strategy was proposed by supplementing the flue gas with H2 (H2/CO2 = 1.0), which yielded 24 h stable operation with around 40 % CO2 conversion and a syngas with H2/CO = 1.2–1.3. The results presented here, for the first time in the literature, demonstrate the feasibility of a novel one-step process for direct valorization of flue gas. The direct upgrading of flue gas would potentially decrease the costs associated with CO2 purification and valorization.

Exploring the influence of flue gas impurities on the electrochemical corrosion mechanism of X80 steel in a supercritical CO2-saturated aqueous environment

The influence of flue gas (100 ppmv of O2, NO2 or SO2 in CO2 steam) on the corrosion mechanism of X80 steel in a supercritical CO2-saturated aqueous (water-rich phase) environment at 8.0 MPa and 35 ℃ was explored via electrochemical methods combined with off-line analyses. While O2 mainly promoted the anodic reaction process, NO2 and SO2 primarily enhanced the cathodic reaction process. Compared with SO2, NO2 and O2 dramatically reduced the protection offered by X80 steel’s corrosion product layer in the water-rich phase. In addition, the study also found that O2 significantly promoted the localized corrosion of X80 steel in the water-rich phase.

Effects of Flue Gas Impurities on the Performance of Rare Earth Denitration Catalysts

Selective catalytic reduction (SCR) is still the most widely used process for controlling NOx gas pollution. Specifically, commercial vanadium-based catalysts have problems such as narrow operating temperature range and environmental pollution. Researchers have developed a series of cerium-based catalysts with good oxygen storage performance and excellent redox performance of CeO2. However, the anti-poisoning performance of the catalyst is the key to its application. There are many kinds of impurities in the flue gas, which has a huge impact on the catalyst. The deposition of substances, the reduction of active sites, the reduction of specific surface area, and the reduction of chemically adsorbed oxygen will affect the denitration activity of the catalyst to varying degrees, and the poisoning mechanism of different impurities on the catalyst is also different. Therefore, this review divides the impurities contained in flue gas into different types such as alkali metals, alkaline earth metals, heavy metals, and non-metals, and summarizes the effects and deactivation mechanisms of various types of impurities on the activity of rare earth catalysts. Finally, we hope that this work can provide a valuable reference for the development and application of NH3-SCR catalysts for rare earth denitration in the field of NOx control.

The impact of flue gas impurities and concentrations on the photoelectrochemical CO2 reduction

The photoelectrochemical reduction of CO2 provides a clean and sustainable route to produce value-added chemicals and fuels using sunlight as the energy source and greenhouse gas CO2 as the feedstock. However, the use of pure CO2 decreases the economic feasibility of the technology. Direct utilization of industrial flue gas is desirable for practical applications, but the effect of flue gas impurities and concentrations on the photoelectrochemical CO2 reduction remains unknown. Herein, we investigate the influence of NOx, SOx and O2 impurities and low CO2 concentrations on photoelectrochemical CO2 reduction performance using Au nanoparticles decorated GaN nanowire arrays on Si wafer as the model photoelectrode. It is found that the presence of NOx, SOx impurities, and low CO2 concentrations are compatible with photoelectrochemical CO2 reduction. In contrast, the inclusion of O2 impurity reduces the CO2 conversion efficiency. However, the effect of O2 impurity is reversible and the photoelectrocatalytic activity is recovered once O2 impurity is removed.

Understanding the competition between carbonation and sulfation of Li4SiO4-based sorbents for high-temperature CO2 capture

High-temperature CO2 adsorption is an important method in reducing the excessive CO2 emissions for the mitigation of global climate change. As a potential high-temperature CO2 sorbent, Li4SiO4 attracted extensive concern due to its high CO2 capacity with excellent stability. However, gas impurities in industrial flue gas, especially SO2 affect the CO2 adsorption process, and the competition between SO2 and CO2 during the adsorption process by Li4SiO4 is lack of understanding. This work studied the competitive behavior between carbonation and sulfation through experimental tests, characterizations, and DFT calculations. Results show that carbonation can slightly inhibit the proceeding of sulfation while sulfation almost prevents the occurrence of carbonation for both Li4SiO4 and K-Li4SiO4. In addition, the doping of K2CO3 in Li4SiO4 is observed to significantly promote both the carbonation and sulfation process. Furthermore, stable adsorption structures of CO2 and SO2 on Li4SiO4 were obtained via DFT calculation, which verifies the mutual inhibition between carbonation and sulfation. These results provide a well understanding of the competition between carbonation and sulfation of Li4SiO4-based sorbents, and are helpful for the design and optimization of CO2 adsorption process.

Effect of flue gas impurities in carbon dioxide from power plants in the synthesis of isopropyl N-phenylcarbamate from CO2, aniline, and 2-propanol using CeO2 and 2-cyanopyridine

Current CO2 utilization technologies generally start with purification of CO2, which requires considerable energy input. Using CO2-containing flue gases as a feedstock in chemical conversions of CO2 can help simplify pre-treatment of CO2 and reduce the carbon footprint of the process, however, study of the effects of other components in the flue gases in chemical reactions using CO2 is limited. Our previous study demonstrated that the combination catalyst system of CeO2 and 2-cyanopyridine was effective for the reaction of pure CO2, aniline, and 2-propanol to afford isopropyl N-phenylcarbamate, which is a promising precursor for polyurethane, in over 90% yield. In this study, the addition effect of other components in CO2-containing flue gases namely N2, O2, SO2 (ppm-order) and NO2 (ppm-order) on the reaction was investigated. The addition of N2 and NO2 had almost no influence on the catalytic performance, however, that of O2 and SO2 had some negative effects. The addition of O2 decreased the selectivity and yield to the target carbamate due to the formation of aniline-derived byproducts such as aniline-coupling products and aniline-oligomers. The increase of the amount of 2-cyanopyridine and 2-propanol was effective for the suppression of the aniline-derived byproducts, providing a similar yield of the isopropyl N-phenylcarbamate to the case without any additives. The catalyst system was strongly poisoned by addition of SO2, and the activity of CeO2 was not recovered even by calcination treatment.

Impact of Impure Gas on CO2 Capture from Flue Gas Using Carbon Nanotubes: A Molecular Simulation Study.

We used a grand canonical Monte Carlo simulation to study the influence of impurities including water vapor, SO2, and O2 in the flue gas on the adsorption of CO2/N2 mixture in carbon nanotubes (CNTs) and carboxyl doped CNT arrays. In the presence of single impure gas, SO2 yielded the most inhibitions on CO2 adsorption, while the influence of water only occurred at low pressure limit (0.1 bar), where a one-dimensional chain of hydrogen-bonded molecules was formed. Further, O2 was found to hardly affect the adsorption and separation of CO2. With three impurities in flue gas, SO2 still played a major role to suppress the adsorption of CO2 by reducing the adsorption amount significantly. This was mainly because SO2 had a stronger interaction with carbon walls in comparison with CO2. The presence of three impurities in flue gas enhanced the adsorption complexity due to the interactions between different species. Modified by hydrophilic carboxyl groups, a large amount of H2O occupied the adsorption space outside the tube in the carbon nanotube arrays, and SO2 produced competitive adsorption for CO2 in the tube. Both of the two effects inhibited the adsorption of CO2, but improved the selectivity of CO2/N2, and the competition between the two determined the adsorption distribution of CO2 inside and outside the tube. In addition, it was found that (7, 7) CNT always maintained the best CO2/N2 adsorption and separation performance in the presence of impurity gas, for both the cases of single CNT and CNT array.

The Impact of Flue Gas Impurities and Concentrations on the Photoelectrochemical Co2 Reduction

The Impact of Flue Gas Impurities and Concentrations on the Photoelectrochemical Co2 Reduction

Characterization of 13Cr steel corrosion in simulated EOR-CCUS environment with flue gas impurities

For a better understanding of the pitting corrosion mechanism of 13Cr steel in a supercritical (SC) CO2–H2O environment with flue gas impurities, experiments were conducted with different exposure time with and without rotation and Cl–. The results show that the corrosion products formed in CO2 phase and water phase varied in morphologies and compositions. The corrosion scale in CO2 phase mainly consisted of amorphous FeCO3 while the corrosion scale in water phase was mainly made up of crystalline FeCO3. Pitting corrosion was the predominant corrosion type in supercritical CO2 with flue gas impurities and it was more severe in CO2 phase than that in water phase. No pitting corrosion occurred in both CO2 and water phase with the presence of flow. Cl– enhanced uniform corrosion in both phases and had ability to break down corrosion products. Secondary localized corrosion could be observed at the boundary of pit holes.

Assessing the corrosion product scale formation characteristics of X80 steel in supercritical CO2-H2O binary systems with flue gas and NaCl impurities relevant to CCUS technology

The corrosion product scale formation mechanism of X80 steel in the supercritical (SC) CO2-H2O binary phase containing flue gases and NaCl impurities at 8 MPa and 60 °C was investigated. The formation process of corrosion product scale was significantly different in the SC CO2-saturated aqueous and water-saturated SC CO2 phases. In the SC CO2-saturated aqueous phase, an amorphous product scale was formed initially, then a crystalline product scale was precipitated. The formation process of the corrosion product scale in the saturated-water SC CO2 phase proceeded in just the opposite way. In the water-saturated SC CO2 phase, the inner scale had better protectiveness to the substrate than the outer scale, but it was just the opposite in the SC CO2-saturated aqueous phase. The severity of pitting in the SC CO2-saturated aqueous phase was much greater than the pitting corrosion in the water-saturated SC CO2 phase.

Exploring the Acid Gas Sorption Properties of Oxidatively Degraded Supported Amine Sorbents

Amine-supported mesoporous oxide materials have proven to be effective acid gas sorbents. While the primary application of these supported amine species has been CO2 capture, they have also shown to be proficient at adsorbing other damaging flue gas impurities such as SOx and NOx. The precise nature of the amine (primary, secondary, or tertiary) is known to dictate the gas–amine interactions, with tertiary amines of particular interest due to their inability to adsorb dry CO2, favoring SOx and NOx species. The different amine sites also provoke differences in oxidative stability, when exposed to temperatures similar to those used for thermal desorption procedures. Herein we focus on the structural and chemical changes that occur in a range of class 1 (amine-impregnated) and class 2 (amine-grafted) sorbents upon oxidation and correlate these with their variation in acid gas (CO2, NO2, and SO2) uptakes, as a function of the oxidation temperature. These studies suggest that oxidatively degraded or “spent” su...