Flue Gas Treatment Research Articles

Atmospheric chemical loss processes of isocyanic acid (HNCO): a combined theoretical kinetic and global modelling study

Abstract. Isocyanic acid (HNCO) is a chemical constituent suspected to be harmful to humans if ambient concentrations exceed ∼1 ppbv. HNCO is mainly emitted by combustion processes but is also inadvertently released by NOx mitigation measures in flue gas treatments. With increasing biomass burning and more widespread usage of catalytic converters in car engines, good prediction of HNCO atmospheric levels with global models is desirable. Little is known directly about the chemical loss processes of HNCO, which limits the implementation in global Earth system models. This study aims to close this knowledge gap by combining a theoretical kinetic study on the major oxidants reacting with HNCO with a global modelling study. The potential energy surfaces of the reactions of HNCO with OH and NO3 radicals, Cl atoms, and ozone were studied using high-level CCSD(T)/CBS(DTQ)//M06-2X/aug-cc-pVTZ quantum chemical methodologies, followed by transition state theory (TST) theoretical kinetic predictions of the rate coefficients at temperatures of 200–3000 K. It was found that the reactions are all slow in atmospheric conditions, with k(300K)≤7×10-16 cm3molecule-1s-1, and that product formation occurs predominantly by H abstraction; the predictions are in good agreement with earlier experimental work, where available. The reverse reactions of NCO radicals with H2O, HNO3, and HCl, of importance mostly in combustion, were also examined briefly. The findings are implemented into the atmospheric model EMAC (ECHAM/MESSy Atmospheric Chemistry) to estimate the importance of each chemical loss process on a global scale. The EMAC predictions confirm that the gas-phase chemical loss of HNCO is a negligible process, contributing less than 1 % and leaving heterogeneous losses as the major sinks. The removal of HNCO by clouds and precipitation contributes about 10 % of the total loss, while globally dry deposition is the main sink, accounting for ∼90 %. The global simulation also shows that due to its long chemical lifetime in the free troposphere, HNCO can be efficiently transported into the UTLS by deep convection events. Daily-average mixing ratios of ground-level HNCO are found to regularly exceed 1 ppbv in regions dominated by biomass burning events, but rarely exceed levels above 10 ppt in other areas of the troposphere, though locally instantaneous toxic levels are expected.

Water Vapour Promotes CO2 Transport in Poly(ionic liquid)/Ionic Liquid-Based Thin-Film Composite Membranes Containing Zinc Salt for Flue Gas Treatment

A poly(ionic-liquid) (PIL) matrix can be altered by incorporating additives that will disrupt the polymer chain packing, such as an ionic liquid (IL) and inorganic salts to boost their exploitation as materials for membrane production to be used in CO2 capture. Herein, potential of PIL/IL/salt blends is investigated on the example of poly(diallyldimethyl ammonium) bis(trifluoromethylsulfonyl)imide (P[DADMA][Tf2N]) with N-butyl-N-methyl pyrrolidinium bis(trifluoromethylsulfonyl)imide ([Pyrr14][Tf2N]) and zinc di-bis(trifluoromethylsulfonyl)imide (Zn[Tf2N]2). Composite material with IL and a higher amount of Zn2+ showed an increase in the equilibrium CO2 sorption capacity to 2.77 cm3 (STP)cm −3 bar−1. Prepared blends were successfully processed into thick, dense membranes and thin-film composite membranes. Their CO2 separation efficiency was determined using ideal and mixed-gas feed (vol% CO2 = 50 , dry and with 90% relative humidity). The dominant role of solubility in the transport mechanism is confirmed by combining direct gravimetric sorption measurements and indirect estimations from time-lag experiments. The maximum incorporated amount of Zn2+ salts increased equilibrium solubility selectivity by at least 50% in comparison to the parent PIL. All materials showed increased CO2 permeance values by at least 30% in dry conditions, and 60% in humidified conditions when compared to the parent PIL; the performance of pure PIL remained unchanged upon addition of water vapor to the feed stream. Mixed-gas selectivities for all materials rose by 10% in humidified conditions when compared to dry feed experiments. Our results confirm that the addition of IL improves the performance of PIL-based composites due to lower stiffness of the membrane matrix. The addition of Zn2+-based salt had a marginal effect on CO2 separation efficiency, suggesting that the cation participates in the facilitated transport of CO2.

Valorization of waste polyethylene terephthalate plastic into N-doped microporous carbon for CO2 capture through a one-pot synthesis

Valorization of waste polyethylene terephthalate (PET) plastic into microporous carbon with N-doping treatment was successfully performed in a one-pot synthesis and the N-doped microporous carbon was used for CO2 capture, which can mitigate plastic pollution and climate change simultaneously. The PET-derived microporous carbon developed by KOH activation and urea treatment in a one-pot synthesis at 700 °C exhibited the highest CO2 adsorption uptake of 6.23 mmol g−1 at 0 °C and 4.58 mmol g−1 at 25 °C (1 atm). The Langmuir and pseudo second-order models displayed well-fitting relationships with equilibrium and kinetic experimental data obtained in this study. The N-doped microporous carbon showed high CO2 selectivity over N2, implying that it is feasible for treating flue gases (10% CO2 and 90% N2) at 50 °C. In addition, the CO2 uptake was not only affected by micropores but also related with nitrogen and oxygen functional groups. Compared to the porous carbon prepared by two-pot synthesis where KOH activation and urea treatment were conducted separately, the porous carbon prepared by one-pot synthesis had higher oxygen contents and higher CO2 adsorption uptake. All of findings implied that the N-doped microporous carbon was successfully developed from waste PET plastic for capturing CO2 and can play a promising role in both sustainable waste management and environmental protection.

Promotional role of Mo on Ce0.3FeOx catalyst towards enhanced NH3-SCR catalytic performance and SO2 resistance

The SO2 resistance of low temperature NH3-SCR in non-electric power industries has always been the bottleneck of this technology. Herein, a series of Mo-modified Ce0.3FeOx catalysts (MoaCe0.3FeOx) were synthesized by an easy to scale-up, environment-friendly two-step solid interface reaction and applied to the treatment of flue gas from the glass industry. Incorporation of Mo into Ce0.3FeOx catalyst could not only remarkably expand the operation temperature window in both low and high temperature regions, but also maintain high catalytic activity (>85% NOx conversion) under 65 h long stability test conditions even with the coexistence of H2O and SO2. The two-step interface reaction over MoaCe0.3FeOx provided an increased specific surface area and more amorphous structure, forming highly dispersed MoO3 species on the surface of the catalyst which serves as a sacrificial site to react with SO2. The process of redox reaction has been greatly improved due to the facilitated electron transfer between Fe2+ and Ce4+ as well as more oxygen vacancies and active oxygen. The enhanced presence of NH4+ could react with gaseous NO species via Eley–Rideal (E–R) mechanism due to the lack of nitrate species (greatly inhibited) while the NH4NO3 was not generated during the reaction which is responsible for excellent low temperature SCR performance as well as high N2 selectivity. Furthermore, less sulfate species and no bulk sulfate were formed, which indicated that the doping of Mo could effectively reduce the basic sites and delay the irreversible deactivation as well as reduce catalyst sulphation. The above features provide a strategy for design and development of non-vanadium-based catalysts with low temperature SO2 resistance in non-electric power industries with high NOx emission concentrations.

Use of biomass ash from different sources and processes in cement

Substitution of cement clinker with suitable excess materials from other processes is an effective way to reduce CO2 emissions of cement production. Moreover, specific properties of the resulting mortar or concrete can be designed with different clinker replacement materials and their mixing ratios. In this study, bottom and fly ashes from six biomass power plants with different power scales and various flue-gas treatment strategies were admixed to mortars, whose properties (influence of water requirement and final compressive strength) were then assessed in the laboratory by following industrial standard procedures. Results reveal that fly ash from a cyclone of a medium-scale combustor burning Miscanthus straw amended with 2 wt % Ca(OH)2 (to prevent slagging during combustion) turned out to be well suited as a clinker replacement material, even boosting final compressive strength of the mortar. Wood-chip bottom ashes and fly ash from a cyclone exhibited acceptable results, whereas fly ash from electrostatic precipitators (ESPs) and baghouse filters lowered final compressive strength of the mortar when admixed. The scale of the power plant is positively correlated with final compressive strength in the case of ESPs. Cenospheres, typical fly ash particles present in cyclone ash, seem to have a positive effect on water-to-binder ratio and final compressive strength. In contrast, potassium salts, which are most abundant in ash from ESPs and baghouse filters, appear to have a negative influence on these properties. Grinding of the biomass ashes to a typical Portland cement fineness had a positive effect on mortar quality. All fly ashes had high contents of Cd, and baghouse filter ash contained As in amounts about four times the Swiss limit value for cement of 30 ppm; only bottom ash and cyclone ash from Miscanthus exhibited concentrations below respective limit values for all critical trace elements. To assess the immobilization potential of contaminating elements during the cement hardening process, blended mortars were crushed and subjected to multistep leaching, followed by subsequent analysis of the leachates by atomic absorption spectroscopy. Immobilization of Cd by the mortar was particularly effective. Our results indicate that fly ash from wood-chip combustion is most suitable as an amendment to cement when it was trapped by a cyclone rather than by the ESPs or baghouse filters.

Innovative scrubber technology model for domestic boiler application

Many treatment technologies exist for particulate matter capture from the flue gas. Heat recovery from flue gases is a significant advantage of scrubber technology, which promotes energy efficiency increase of the combustion unit. The amount of recovered heat depends on heat and mass transfer in the scrubber. This paper presents the investigation of innovative small-scale flue gas treatment technology—fog unit. Households produce significant share of particulate matter in Europe. Therefore, there is a need to provide flue gas treatment technologies for domestic boilers in agreement with EU directive 2009/125/EC. Experimental research was done to identify the performance of proposed technology depending on inlet water flow rate, gas flow rate, water temperature, droplets diameter and water–gas flow ratio. The regression equations were developed based on performed data analysis. Equations can be used to predict the capacity of fog unit, outlet water temperature and outlet gas temperature.

Summary of Flue Gas Purification and Treatment Technology for Domestic Waste Incineration

Incineration technology is widely used in the world as a domestic waste treatment technology. The reason is that the incineration technology can reduce the weight of the treated domestic waste by 80% and the capacity by more than 90%, which is of great significance to the realization of the management goal of domestic waste treatment. However, the problem of flue gas pollution will occur when the waste incineration technology is used to treat the waste. The main harmful substances in the flue gas generated by waste incineration include: smoke, dioxin, SO2, NOx, heavy metal and other pollutants. Therefore, the flue gas can only be discharged into the atmosphere after proper technical treatment and meeting the national emission standards. This paper summarizes the domestic and foreign technologies of waste incineration flue gas purification and treatment, and puts forward suggestions for the development of domestic waste incineration flue gas purification and treatment technology.

Purification System of Domestic Waste Incineration Flue Gas

Flue gas will be emitted during the waste incineration power generation process. The flue gas contains toxic and harmful ingredients. If it is not treated, it will cause serious harm to human health and the environment. Therefore, the incineration flue gas needs to be purified. In this paper, combined with the monitoring of a large-scale waste incineration power plant incinerator flue gas purification treatment project, the combined process of “in-furnace denitrification (SNCR) + semi-dry deacidification + slaked lime and activated carbon (dry process) injection + bag filter”. The purification effect of flue gas shows that the process has a good purification effect on domestic waste incineration flue gas. This study can provide reference and basis for the treatment of incineration flue gas in the industry.

Utilization of coal fly ash in China: a mini-review on challenges and future directions.

The rapid economic development in China places a large demand for energy, and as a result, thermal power plants in China are producing an enormous amount of coal fly ash (CFA) which causes severe environmental pollution. This paper briefly describes the current production and utilization status of CFA in China and identifies the challenges confronting sustainable CFA utilization as the Chinese economy is being transformed. These issues include a regional imbalance in supply and demand, reducing demand in the real estate industry as well as stricter laws for environmental protection. Viable directions for future CFA utilization are proposed, for example, production of CFA-based ceramic tiles, recovery of elemental resources, agricultural melioration, treatment of wastewater and flue gas, and production of high-volume CFA concretes. This paper has some guiding significance for sustainable and cleaner utilization of CFA in China and even worldwide. Graphical abstract.

The environmental cost of recovering energy from municipal solid waste

Municipal solid waste (MSW) incinerators require effective flue gas treatment (FGT) to meet stringent environmental regulations. However, this in turn generates additional environmental costs through the impacts of materials and energy used in the treatment – these impacts are currently scarcely known. Therefore, this study uses life cycle assessment to estimate the impacts of different FGT systems typically found in modern MSW incinerators. A total of 12 scenarios are modelled to consider different combinations of the following eight technologies: electrostatic precipitators and fabric filters for removal of particulate matter; dry, semi-dry and wet scrubbers for acid gases; selective non-catalytic and catalytic reduction of nitrogen oxides (NOx); and activated carbon for removal of dioxins and heavy metals. The data are sourced from 90 full-scale incinerators operating in France. The results reveal that a dry system using sodium bicarbonate and selective non-catalytic reduction (SNCR) is the best option for seven out of 18 impacts, including climate change (37.1 kg CO2 eq./t MSW). By contrast, a dry system with calcium hydroxide and selective catalytic reduction (SCR) has the highest impacts in six categories, including climate change (102 kg CO2 eq./t MSW). The wet systems have higher impacts than the dry alternatives, with the semi-dry options being in between. Compared to SNCR, the use of SCR decreases the NOx-related impacts (fine particulate matter formation, terrestrial acidification and photochemical ozone formation) but increases other impacts. For example, the SCR systems have 49–284% greater climate change and 43–150% higher depletion of fossil resources than their SNCR counterparts. Overall, all FGT systems reduce significantly fine particulate matter formation (by 81–88%), photochemical ozone formation (76–90%) and terrestrial acidification (83–90%). However, they also cause 14 other impacts which would not be generated if the flue gas was left untreated, thus creating additional environmental costs. These include climate change, resource depletion and human and ecotoxicities. Therefore, these trade-offs should be considered carefully to minimise the unintended environmental consequences of flue gas treatment from incineration of MSW.

Functioning of the flue gas treatment system in Polish municipal waste incineration plants

All municipal waste incineration plants operating in Poland are discussed and their flue gas treatment systems are described in detail in the article. A comparison of performance indicators, i.e. the amount of raw materials consumed particularly in flue gas treatment systems, is presented. The article also summarizes the results of emission measurements for eight incineration plants in the years 2016–2019.

Techno-economic performance of HCl and SO2 removal in waste-to-energy plants by furnace direct sorbent injection

With the impending release of Best Available Techniques (BAT) conclusions on waste incineration, existing European waste-to-energy (WtE) plants will be required to achieve a higher efficiency in the removal of several target pollutants, such as acid gases (above all, HCl and SO2). The direct injection of a sorbent in the furnace as a primary deacidification stage may be a cost-effective option to achieve the required performances. The present study investigated the furnace injection of a specific dolomitic sorbent, with the aim of identifying the techno-economic optimum for the sorbent feed rate considering different scenarios of flue gas composition. A full-scale test run campaign was carried out on two WtE plants and a phenomenological model linking HCl and SO2 conversion to reactant feed rate was developed. The model allowed assessing the cost-effectiveness of dolomitic sorbent furnace injection for WtE plants equipped with either a single or a two-stage acid gas treatment system. The addition of dolomitic sorbent resulted particularly suitable for WtE plants equipped with a single stage treatment coping with a high SO2 concentration in the flue gas, where the injection of dolomitic sorbent can increase the redundancy of flue gas treatment with a reduction of the total operating costs.

Biomitigation of CO2 from flue gas by Scenedesmus obtusiusculus AT-UAM using a hybrid photobioreactor coupled to a biomass recovery stage by electro-coagulation-flotation.

The microalga Scenedesmus obtusiusculus AT-UAM efficiently captured CO2 from two flue gas streams in a hybrid photobioreactor located in a greenhouse. Uptake rates of CO2, NO, and SO2 from a formulated gas stream were 160.7mgL-1day-1, 0.73mgL-1day-1, and 1.56mgL-1day-1, respectively, with removal efficiencies of 100% for all gases. Exhaust gases of a motor generator were also removed with uptake rates of 111.4mgL-1day-1, 0.42mgL-1day-1, and 0.98mgL-1day-1, obtaining removal efficiencies of 77%, 71%, and 53% for CO2, NOx, and SO2, respectively. On average, 61% of the CO2 from both flue gas streams was assimilated as microalgal biomass. The maximum CO2 uptake rate of 182mgL-1day-1 was achieved for formulated flue gas flow rate above 100mLmin-1. The biomass recovery of 88% was achieved using a 20-L electro-coagulation-flotation chamber coupled to a settler with a low specific power consumption of 0.27kWhkg-1. The photobioreactor was operated for almost 7months without contamination of invasive species or a decrease in the activity. It is a very encouraging result for long-term operation in flue gas treatment.

Kinetic study of the nitric oxide oxidation between 288 and 323 K, under pressure, focus on the oxygen influence on the reaction rate constant

AbstractThe sequestration of carbon dioxide fumes from oxyfuel combustion is used to reduce significantly the carbon dioxide emissions from coal‐fired power plants. Impurities like nitric oxide, present in the fumes, can cause technical difficulties during the capture, the treatment, the transport, and the storage steps of the CO2 fumes. The purpose of this study is to better understand the oxidation of nitric oxide under pressure in the presence of carbon dioxide and in the experimental condition of flue gas treatment. This reaction is known to be a third‐order reaction, two order in nitric oxide and first order in oxygen. To examine the effect of the temperature, the pressure and the volume fraction of oxygen on the rate constant of oxidation, k1, an autoclave is used. The first experiment studies the influence of the temperature between 288 and 323 K. The results found are in the form of an Arrhenius‐type equation: k1 = 810 exp(620/T) and are in agreement with the literature. Carbon dioxide does not seem to have an influence on the rate constant, whereas our experimental measurements indicate an influence of the volume fraction of oxygen. The rate constant decreases when the oxygen volume fraction increases by up to 10%. Then the rate constant remains constant. This observation allows us to conclude that the mechanism involving the mechanism with a dimer of NO as an intermediate is more likely to be the mechanism involved in the nitric oxide oxidation in our experimental conditions: high pressure and ambient temperature. The rate constant k2, k–2, and k3 were also estimated in these conditions.

Application of electron accelerator for flue gas treatment of coal power plant to support green technology

Fossil fuels, which include coal, natural gas, petroleum, shale oil, and bitumen, are the main source of heat and electrical energy, but burning these fuels will emit pollutants to the environment. Most countries use coal burning power plant in generating electricity for living needs such as household electricity and industrial development. This power plant generates large quantities of pollutants (SOX and NOX) that create acid rain and smog leading to the water and soil degradation and they can affect living things. To meet rising worldwide energy demand, projections call for the use of coal to increase by 50 percent from 2006 - 2030, as a consequence SOX and NOX pollutions will rise. There are two conventional technologies to decrease air pollution from coal power plant, the first is FGD (flue gas desulfurization) based on SO2 absorption in lime or limestone slurry; and the second is SCR (selective catalytic reduction) based on NOx reduction over a catalyst to atmospheric nitrogen with ammonia as a reductant. But these technologies cannot treat different pollutants in one step process. To support green technology program, this paper describes a modern technology called EBFGT (electron beam flue gas treatment) which can treat SOx and NOx in one step process using electron accelerator. The technology and economy comparison between FGD, SCR, EBFGT as well as the existing EBFGT in the world are compiled.

Experimental verification of fine particle emission reduction based on acoustic agglomeration for steel sintering flue gas

The sintering flue gas in steel production has the characteristics of large discharge capacity, fine size, high temperature, corrosion and fluctuation of working conditions, and is the primary control object of PM2.5 emission source. Traditional dust removal technologies and equipment are difficult to achieve efficient collection of fine particles. In order to quantitatively study the effect and regularity of high intensity sound waves on fine particles, the online acoustic agglomeration test system was built by using high-power pneumatic source and wave tube with abrupt section. The high intensity standing wave field of 140 to 150 dB was generated in the wide frequency range between 50 Hz and 2 kHz by the acoustic resonance synthesis, and interference from compressed airflow was avoided by the acoustic-flow separation module. Variation of the sintered flue gas PSD was obtained under different sound intensities and frequencies. Data analysis shows that the high concentration condition can greatly reduce the operation time and energy consumption. Under the action of high intensity acoustic waves with a fundamental sound pressure level of 87.3-161.8dB and duration of 3s, the measured PM2.5 removal efficiency is 16%-92%, and the optimal frequency is near 800Hz. This paper verifies the feasibility of acoustic agglomeration (AA) in the treatment of sintering flue gas, and provides a theoretical reference and technical basis for the development of PM2.5 real-time emission control device for steel production.

Analysis on Flue Gas Pollution of Coal-fired Boiler and Its Countermeasures

As the main energy in industrial production, coal resources are widely used in the world. However, in the process of coal combustion will produce a certain amount of pollutants, thus causing adverse effects on the air. The analysis of flue gas treatment of coal-fired boiler aims at improving coal utilization rate, reducing flue gas emission and advocating low-carbon concept. This paper deeply analyzes the flue gas problem of coal-fired boiler, explores the effective environmental treatment technology, and makes contribution to the environmental treatment problem.

Mass balance of mercury in a pilot scale mercury recovery plant using thermal roasting technology

A pilot scale mercury recovery plant was developed to treat Hg waste by thermal treatment. The capacity of the system was 60 kg/batch and consisted of four units carrying out thermal treatment, dust separation, condensation, and flue gas treatment. The mass balances of Hg from five different wastes in three categories were calculated from Hg recovery data. From the following selected five wastes, Hg-added product, Hg-contaminated soil, byproduct of fluorescent lamp treatment process, and waste sludge from non-ferrous metal industrial process, we recovered 97.5%, 83.61%, 93.07%, 70.25%, and 29.36% of elemental mercury, respectively. Dust interfered during the condensation process, as volatilized Hg vapor was condensed with dust. Hg concentrations in leaching extract of treatment residues from the Hg-added product, Hg-contaminated soil, and the byproduct of fluorescent lamp treatment process were 0.003 mg-Hg/L, 0.0045 mg-Hg/L, and 0.002 mg-Hg/L, respectively, which are below the Korean classification standard of hazardous waste for mercury (0.005 mg-Hg/L). Hg concentration in flue gas was lower than 15 μg-Hg/m3 after passing through the activated carbon trap. Byproducts of the pilot scale system, such as activated carbon and dust can be further treated and converted to Hg free waste.

Two-dimensional MnFeCo layered double oxide as catalyst for enhanced selective catalytic reduction of NOx with NH3 at low temperature (25–150 °C)

Low temperature catalysts for selective catalytic reduction of NOx with NH3 plays an important role in flue gas treatments. Here, a two-dimensional MnFeCo layered double oxide were synthetized, characterized and employed as NH3 selective catalytic reduction catalyst, showing excellent low temperature de-NOx performance. MnFeCo layered double oxide exhibited a specific surface area of 92 m2/g with average pore size and volume of 2 nm and 1.5 cm3/g. At 100 °C, the MnFeCo layered double oxide performed an efficient NO conversion of 100 %. Even at 25 and 50 °C, NO conversions reached values of 49 and 86 %, respectively. Furthermore, the NO conversion reached an efficiency of 89 % in the presence of H2O vapor (5 %) and SO2 (100 ppm). Based on that, it can be said that this NH3 selective catalytic reduction catalyst shows great potential in NOx denitration of stationary industrial installations at a low temperature range.

Fine and ultrafine particle number and size measurements from industrial combustion processes: Primary emissions field data

This study is to our knowledge the first to present the results of on-line measurements of residual nanoparticle numbers downstream of the flue gas treatment systems of a wide variety of medium- and large-scale industrial installations. Where available, a semi-quantitative elemental composition of the sampled particles is carried out using a Scanning Electron Microscope coupled with an Energy Dispersive Spectrometer (SEM-EDS). The semi-quantitative elemental composition as a function of the particle size is presented. EU's Best Available Technology documents (BAT) show removal efficiencies of Electrostatic Precipitator (ESP) and bag filter dedusting systems exceeding 99% when expressed in terms of weight. Their efficiency decreases slightly for particles smaller than 1 μm but when expressed in terms of weight, still exceeds 99% for bag filters and 96% for ESP. This study reveals that in terms of particle numbers, residual nanoparticles (NP) leaving the dedusting systems dominate by several orders of magnitude. In terms of weight, all installations respect their emission limit values and the contribution of NP to weight concentrations is negligible, despite their dominance in terms of numbers. Current World Health Organisation regulations are expressed in terms of PM2.5 wt concentrations and therefore do not reflect the presence or absence of a high number of NP. This study suggests that research is needed on possible additional guidelines related to NP given their possible toxicity and high potential to easily enter the blood stream when inhaled by humans.