This study investigates the operating and design parameters of product gas compression and integrated control of nitrogen oxides (NO x ) and sulfur oxides (SO x ) in large-scale oxy-fuel and chemical ...looping combustion processes. A process model that includes a comprehensive description of nitrogen and sulfur chemistry and mass transfer is developed. The results show that the fraction of NO oxidation into NO2 will be 10–50% in a multistage compressor to 30 bars (1–4% O2 in the gas) depending on the residence times in intercoolers and pressure levels. At lower O2 concentrations (>0.1% O2 in the gas), the oxidation is limited but still active. Nitric acid formation in the compressor condensate is, thus, inevitable, although limited, as most water is condensed in the early stages, whereas the acid gases are formed in the later stages. The NO2/NO x ratio has an important effect on the total amount of NO x absorbed and extra residence time should be added after the compressor to increase this ratio. Evaluation of the process behavior in relation to simultaneous absorption of SO2 and NO x revealed that increased SO2/NO x ratio and bottom liquid recycling enhanced the total NO x absorption. In addition, maintaining the pH in the absorbing solution above 5 improves the removal efficiencies of NO x and SO2. NO x removal rates of up to around 95% can be achieved for SO2/NO x > 1 in the flue gas with appropriate design of the absorber. For SO2/NO x < 1, increasing the packing height or addition of S(IV) solutions could enhance the NO x removal rates to 95% or more. The model predictions are compared with the experimental data from a laboratory-scale absorber. The process model developed in this work enables design studies and techno-economic evaluation of absorption-based NO x and SO x removal concepts.
•A nitrogen doped carbon derived from polypyrrole shows high CO2 adsorption capacity.•Impact of water on CO2 adsorption was investigated by multicomponent breakthrough.•This N-doped carbon retains ...the majority of the CO2 adsorption capacity in moisture.•This work shows the possibility of this potential material for post combustion CCS.
Anthropogenic carbon dioxide especially emitted from coal fired power plants is a major contributor to global warming. Various carbon capture materials have been developed to mitigate CO2 emissions. However, adsorbent materials that are tolerant to the humid condition of real flue gases are rare. Here we report a N-doped porous carbon derived from polypyrrole a nitrogen-rich polymer, which can be used to capture CO2 from humid flue gases. Obtained samples were analyzed by various characterizations likewise XRD, FTIR, SEM and XPS, moreover the CO2 adsorption capacities were measured at different temperatures and relative humidities. The results indicated that the porous carbon has achieved a high CO2 adsorption amount of 7.16 mmol/g (at 273 K and 100 kPa). Three equilibrium models were used to fit CO2 adsorption isotherms, and the selectivity of CO2/N2 was calculated at flue gases condition (75% N2 and 25% CO2) based on the IAST method which shows an excellent selectivity of 35 at 273 K (100 kPa). Furthermore, binary adsorption tests of H2O/CO2 were investigated experimentally at 308, 318 and 328 K, indicating that the N-doped carbon can still retain 64%, 58% and 43% of the CO2 adsorption capacity, respectively. The binary isotherm data was fitted well by LBET (Langmuir-BET) model, enabling it for future process modeling. This work confirmed the superiority of the N-doped carbon derived from polypyrrole that will help the development of CO2 capture from humid flue gases.
•ORC working with low-temperature wet flue gases is analyzed.•Three heat recovery modes are investigated: indirect, direct and hybrid.•Indirect condensation mode leads to the maximal net power ...produced.•Direct condensation mode avoids corrosion problems but less power is produced.•Hybrid mode is the most promising. It combines the advantages of both modes.
Low-temperature flue gases (<120°C) exiting industrial processes could be recovered for electricity generation and constitute an effective mean to reduce primary energy consumption and carbon dioxide emissions. In the wet flue gases, substantial heat can be recovered if water vapor contained in the gases is condensed. Technical options include indirect contact water vapor condensation recovery, where heat is transferred between the two fluids (typically flue gases and working fluid) using an intervening wall (typically fin-and-tube heat exchanger) and direct contact water vapor condensation recovery, which involves direct mixing between flue gases and cooling fluid (typically water) through a condensing unit. In this paper, the two recovery processes are investigated using ORC (Organic Rankine Cycle). While the indirect contact condensation is the most favorable heat recovery scheme concerning the net output power, the direct contact heat exchanger has received attention because there are no heat-transfer surfaces exposed to corrosion. In a direct contact water–vapor condensation, the inlet flue-gas wet-bulb temperature determines the operating temperature levels throughout the system and limits the circulating water temperature. The maximal net turbine power for the direct contact system is reached for a final water temperature nearby the entering wet bulb temperature of the flue gases. The temperature pinch is as low as 0.5K, which is possible with a direct contact heat exchanger.
The efficient capture and chemical conversion of carbon dioxide (CO2) requires a solid simultaneously with a large surface area and highly effective active sites. Herein, imidazolinium based porous ...hypercrosslinked ionic polymers (HIPs) with a high surface area, rich micro/mesoporosity and abundant ionic sites were constructed via the hypercrosslinkage of 2-phenylimidazoline and benzyl halides, in which quaternization and Friedel-Crafts alkylation happened simultaneously to afford ionic polymeric networks. The obtained HIPs were efficient in the selective capture of CO2 and cycloaddition of CO2 with epoxides. High yield, stable reusability and good substrate compatibility were achieved under mild conditions (down to ambient conditions), dramatically outperforming the homogeneous ionic liquid monomer and post-modified analogues. The synergistic adsorption and conversion enabled the efficient low-temperature conversion of diluted CO2 (0.15 bar CO2 and 0.85 bar nitrogen, the simulation of flue gas) catalyzed by HIPs in the presence of co-catalyst ZnBr2. The in situ formed ionic sites with a high leaving ability being homogeneously embedded in the hypercrosslinked polymeric skeleton responded to the high adsorption and catalysis performance. This work highlights the functional HIPs as a versatile platform to reach efficient CO2 capture and conversion under mild conditions.
Capturing carbon dioxide from the atmosphere ("air capture") in an industrial process has been proposed as an option for stabilizing global CO2 concentrations. Published analyses suggest these air ...capture systems may cost a few hundred dollars per tonne of CO2, making it cost competitive with mainstream CO2 mitigation options like renewable energy, nuclear power, and carbon dioxide capture and storage from large CO2 emitting point sources. We investigate the thermodynamic efficiencies of commercial separation systems as well as trace gas removal systems to better understand and constrain the energy requirements and costs of these air capture systems. Our empirical analyses of operating commercial processes suggest that the energetic and financial costs of capturing CO2 from the air are likely to have been underestimated. Specifically, our analysis of existing gas separation systems suggests that, unless air capture significantly outperforms these systems, it is likely to require more than 400 kJ of work per mole of CO2, requiring it to be powered by CO2-neutral power sources in order to be CO2 negative. We estimate that total system costs of an air capture system will be on the order of $1,000 per tonne of CO2, based on experience with as-built large-scale trace gas removal systems.
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•DESs containing volatile components causes secondary pollution of treated air.•Risk of significant damage to the environment when using toxic DESs.•Uncertain applicability for carbon ...capture technology due to cross-contamination.•Importance of critical evaluation of existing and future application in absorption.•Need of critical environmental assessment and sustainability of DES apps.
The industrial sector is one of the fastest-growing sources of greenhouse gases, due to its excessive energy consumption to meet the rapidly growing demand for energy-intensive products. The use of deep eutectic solvents (DESs) has been studied extensively in order to cope with these harmful gases, but their usage can be an issue in respect to ecological reasons. Do deep eutectic solvents harm the atmosphere? Yes, these solvents can be harmful if their constituents (HBA and HBD) that are volatile and toxic in nature. A number of scientific reports preset their application without care on cross-contamination of treated media. Herein, we highlight the ecotoxicity behavior of DESs as treatment materials for three major toxic gas treatment methods, including carbon dioxide (CO2) capture, biogas treatment and air purification. Special attention is given to the health consequences of HBDs due to their toxicity and emission outside of the treatment system into the environment. The physicochemical characteristics of DESs are evaluated and addressed in comparison to the benchmark solvents. Emission of DESs can be predicted based on simulation software like COSMO-RS or Molecular Dynamics (MD). Furthermore, we suggest some simple protocols to estimate this issue and thus make aware researchers to think about it when experimenting with DES for different applications.
The dynamics of heavy metal speciation and flue gas emissions during the incineration of textile dyeing sludge (TDS) were quantified as a function of four addition levels of CaO, incineration ...temperature, and ash minerals using thermogravimetric analysis and experimental tube furnace. The TDS incineration was most improved with the addition of 10% CaO. The increased fractions of CaO coupled with the ash minerals changed the retention behaviors of eight heavy metals. The CaO addition increased the Cu, Zn, As, and Pb retentions, did not significantly change Cr, Mn, and Cd, but decreased the Ni retention. The CaO addition enhanced the speciation stability of Cu and transferred the Cr, Cd, and As speciations to the mobile fractions. The increased temperature weakened the Zn and Pb retentions and the speciation stabilities of As and Pb and turned the Cr, Mn, Ni, Cu, Zn, and Cd speciations into the stable fractions. The CaO addition inhibited HCN, NO, NO2, COS, SO2, CS2, and SO3 emissions from the TDS incineration. Neural network-based multi-response optimization was implemented to determine the optimal operational temperature for the TDS incineration and the reduction of the 12 gas emissions. The range of 640–755 °C with(out) 5% CaO appeared to be most beneficial in terms of both environmental quality and economic efficiency.
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•Interaction between CaO addition and ash minerals changed heavy metal retentions.•The optimal incineration characteristics occurred with 10% CaO.•CaO addition enhanced Cu, Zn, As and Pb retentions via physical adsorption.•CaO addition retained sulfur and nitrogen.•ANNs were used to jointly optimize emission reduction and incineration efficiency.
Currently, a novel chemical absorption-biological reduction (CABR) integrated process, employing Fe(II)EDTA as a solvent, is being under development to reduce the cost of NO.sub.x removal from flue ...gas. In this work, the NO removal profile, re-acclimation performance, and microbial characteristics in a thermophilic biofilter were investigated at the conditions typical to CABR process. The biofilter comprised of four layers of packing material with a surface area of 1200 m.sup.2 m.sup.-3. Experimental results revealed that the biofilter could remove 95 % of the fed NO at typical flue gas conditions. As the gas residence time varied from 90 to 15 s, the NO removal efficiency decreased from 100 to 56.5 % due to the NO mass transfer limitation. The longer period of the biofilter shutdown required more time for its re-acclimation. For example, after 8-day shutdown, the biofilter was re-acclimated in 32 h. Denaturing gradient gel electrophoresis analysis of PCR-amplified product showed that Pseudomonas, a group of denitrifier, was dominant in the biofilter. Because the Pseudomonas was abundant at the bottom layer of packed-bed, the bottom layer contributed to 60-70 % of the total NO removal. In addition, Pseudomonas gradually faded away along the gas flow path from the bottom to the top of biofilter, resulting in a significant decrease in NO removal at the other three packed-bed layers. These observed results will provide the process engineering and scale-up data with respect to the biofilter operations to help advance the CABR process to pilot-scale testing. Electronic supplementary material The online version of this article (doi:10.1007/s00253-015-6585-2) contains supplementary material, which is available to authorized users.
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•Emission characteristics were studied during co-combustion in a grate furnace.•Ambient air quality study was compared with gaseous emissions after combustion.•Emission observed ...during the combustion showed PM as 580–1432 mg/Nm3.•Emitted SO2 (55–147 mg/Nm3) & NOX (7.5–24 mg/Nm3) were within the prescribed limit.•Monitoring and control system can be adopted to meet the standard limits.
Distillery sludge and coal co-combustion are favorable energy recovery options which also help to overcome the individual feed sample disadvantages. The emission of PM, SO2, NOx, HCl, HC, CO and CO2 was studied during the co-combustion experiments along with monitoring of the ambient air quality at the experimental site. The combustion of coal and sludge samples was studied and the results showed that by increasing the distillery sludge mixed coal ratio from 20%, 30% and 40% (wt./wt.%), the emission values reduced. Air borne PM and gaseous pollutants did not exceed the standard limit for ambient air. The results for PM were observed within the range i.e. 580–1432 mg/Nm3. Similarly, SO2 and NOx emissions were 55–147 and 7.5–2.4 mg/Nm3 of all the substrate combinations. To regulate the flue gas composition and monitor the emitted gases, it is necessary to pass it through a proper control systems.
Microalgal-based wastewater treatment and CO2 sequestration from flue gases with subsequent biomass production represent a low-cost, eco-friendly, and effective procedure of removing nutrients and ...other pollutants from wastewater and assists in the decrease of greenhouse gas emissions. Thus, it supports a circular economy model. This is based on the ability of microalgae to utilise inorganic nutrients, mainly nitrogen and phosphorous, as well as organic and inorganic carbon, for their growth, and simultaneously reduce these substances in the water. However, the production of microalgae biomass under outdoor cultivation is dependent on several abiotic and biotic factors, which impact its profitability and sustainability. Thus, this study’s goal was to evaluate the factors affecting the production of microalgae biomass on pilot-scale open raceway ponds under Northern Sweden’s summer conditions with the help of a mathematical model. For this purpose, a microalgae consortium and a monoculture of Chlorella vulgaris were used to inoculate outdoor open raceway ponds. In line with the literature, higher biomass concentrations and nutrient removals were observed in ponds inoculated with the microalgae consortium. Our model, based on Droop’s concept of macronutrient quotas inside the cell, corresponded well to the experimental data and, thus, can successfully be applied to predict biomass production, nitrogen uptake and storage, and dissolved oxygen production in microalgae consortia.
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•Nordic microalgae strains treated wastewater and sequestered CO2 from flue gases.•Microalgae consortium outcompeted C. vulgaris monoculture in outdoor open ponds.•Microalgae consortium had higher biomass concentration and PO4 removal than monoculture.•Mathematical model on microalgae growth, N uptake/storage, and O2 generation was made.•Model simulated specific traits of microalgal behavior in complex growth conditions.
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