SO2 In Flue Gas Research Articles

Flue Gas Desulfurization and Denitrification by Activated Coke: A Mini- Review

SO2 and NOx in flue gas are major air pollutants responsible for acid rain and photochemical smog. The removal of SO2 and NOx by activated coke is a technology with some advantages, such as simultaneous removing SO2, NOx and particulate, high efficiency of purification and no secondary pollution. The used activated cokes can be regenerated by heating or water washing treatment to recover their activity, and the concentrated sulfur desorbed can be recycled as elemental sulfur, sulfuric acid or liquid SO2. This paper describes the principle and process of flue gas desulfurization and denitrification by activated coke. The paper also systematically summarizes the raw materials and production processes of activated coke, regeneration of used activated coke published in patents. Finally, future research directions are suggested. Keywords: Activated coke, Desulfurization, Denitrification, SO2, NOx, Flue gas.

The integrated photocatalytic removal of SO2 and NO using Cu doped titanium dioxide supported by multi-walled carbon nanotubes

In this paper, the titanium dioxide supported by multi-walled carbon nanotubes (MWCNTs/TiO2), and Cu doped TiO2 supported by MWCNTs (MWCNTs/Cu-TiO2) were synthesized in a sol–gel method. Characterizations of the prepared photocatalysts were done by means of transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and UV–Vis diffuse reflectance spectra (DRS). The introduction of MWCNTs inhibited the grain growth of TiO2. The excellent optical properties in the UV and visible region were observed on 10% MWCNTs/Cu–TiO2 and 15% MWCNTs/Cu–TiO2. The oxidation and removal efficiencies of SO2 and NO in simulated flue gas were investigated experimentally in a fix-bed reactor. The optimal conditions (73mg/m3 NO, 155mg/m3 SO2, 8% O2, 5% H2O) were determined, and 62% and 43% of total SO2 and NO removal were achieved on 15% MWCNTs/Cu–TiO2. The enhancement of 15% MWCNTs/Cu–TiO2 on photocatalytic oxidation was related to modified electronic structure and surface Oxygen vacancies, and also to good conductivity of MWCNTs. The integrated desulfurization and denitration efficiencies were lower than that in baseline experiments due to SO2 and NO competing for adsorption sites. O2 and H2O played important roles in the formation of O2-, O− and OH. In addition, the possible reaction mechanism involved in the integrated desulfurization and denitration was also proposed here.

Mercury Oxidation by Halogens under Air- and Oxygen-Fired Conditions

Gas-phase mercury oxidation by halogens under air- and oxygen-fired (27% O2 in CO2) conditions was studied in a bench-scale, laminar, methane-fired, 300 W, quartz-lined reactor. The experiments provided data on the extents of elemental mercury oxidation in the presence of various flue gas components, including chlorine, bromine, SO2, and NO. A wet conditioning system and a Tekran 2537A mercury analyzer were used to determine mercury speciation and concentrations. Under the same experimental conditions and for both halogens, oxy-firing produced modest increases in mercury oxidation. Extents of oxidation at chlorine concentrations of 100–500 ppmv (as HCl) ranged from 6 to 21% for oxy-firing and from 4 to 15% for air-firing. Oxidation by bromine at concentrations of 10–50 ppmv (as HBr) ranged from 43 to 69% for oxygen-firing and from 15 to 46% for air-firing. Under both firing conditions, the addition of NO (below 300 ppmv) had little or no effect on mercury oxidation by chlorine or bromine and the addition ...

A Novel Process Concept for the Capture of CO2 and SO2 Using a Single Solvent and Column

The presence of SO2 in flue gas has a negative impact on typical CO2 capture processes utilising aqueous amines. For countries like Australia, that do not have flue gas desulfurisation, retrofitting such equipment to existing coal fired power stations is of the order of 100's of millions of dollars. In this work a new process configuration is described in which SO2 is absorbed into a fraction of the absorbent used for CO2 capture. SO2 absorption is carried out in the bottom of the absorber column into a bleed stream from the bulk solvent, and a recycle flow allows the absorbent to be near saturation in SO2. This high concentration allows a number of low cost options for sulfur removal from the absorbent such as chemical treatment and precipitation. The principles underlying the concept, have been studied in the laboratory, and a rate based model of an absorber column has been used to model the SO2 removal column section. The laboratory and modelling results support both the feasibility and utility of the process concept.

Investigation on mercury reemission from limestone-gypsum wet flue gas desulfurization slurry.

Secondary atmospheric pollutions may result from wet flue gas desulfurization (WFGD) systems caused by the reduction of Hg2+ to Hg0 and lead to a damping of the cobenefit mercury removal efficiency by WFGD systems. The experiment on Hg0 reemission from limestone-gypsum WFGD slurry was carried out by changing the operating conditions such as the pH, temperature, Cl− concentrations, and oxygen concentrations. The partitioning behavior of mercury in the solid and liquid byproducts was also discussed. The experimental results indicated that the Hg0 reemission rate from WFGD slurry increased as the operational temperatures and pH values increased. The Hg0 reemission rates decreased as the O2 concentration of flue gas and Cl− concentration of WFGD slurry increased. The concentrations of O2 in flue gas have an evident effect on the mercury retention in the solid byproducts. The temperature and Cl− concentration have a slight effect on the mercury partitioning in the byproducts. No evident relation was found between mercury retention in the solid byproducts and the pH. The present findings could be valuable for industrial application of characterizing and optimizing mercury control in wet FGD systems.

Mercury and SO3 Emissions in Oxy-fuel Combustion

This paper presents results on experiments carried out at a 20 kW combustion rig simulating different extents of oxy-fuel recycle gas cleaning by impurities injection to the oxidant gas of the once-through combustion reactor. A comprehensive set of total (Hgtot), elemental (Hg0) and oxidized (Hg2+) mercury as well as SO3 concentrations was obtained before and after the combustion rig's baghouse filter for in total 14 air and oxy-fuel experiments with 3 Australian coals. Based on this data, an assessment in respect to Hg oxidation, SO2/SO3 conversion and Hg and SO3 capture on the test rig's filter was performed. The air and the oxy-fuel experiments with different extents of recycle gas cleaning, revealed differences in the Hg and SO3 formation and capture behavior: The Hg2+/Hgtot ratios in the flue gas are higher during oxy-fuel combustion compared to air-firing. This effect is even more pronounced at the filter outlet, after flue gas has passed through the filter ash. In some experiments, even a net oxidation of Hg0 entering the filter to Hg2+ was observed. The Hg capture by ash in the baghouse filter has been found to reduce the Hg emissions considerably. However, the Hg capture was altered by the different oxy-fuel recycle configurations, leading to decreased Hg capture efficiencies on the filter for one of the coals. A coal-specific trend of increased SO2/SO3 conversion ratios with increased flue gas SO2 levels was observed that could be related to the ash composition of the three different coals. This and the higher SO2 concentrations in the flue gas lead to considerably higher SO3 levels in oxy-fuel combustion with SO2 recycling. During the experiments, also a considerable capture of SO3 in the baghouse filter was observed (up to 80% under air- and up to 66% under oxy-fired conditions). A reduction of the SO3 capture on the filter under oxy-fuel conditions may be related to the higher SO3 levels in this process.

Online monitoring of flue gas emissions in power plants having multiple fuels

This paper introduces an online monitoring application for flue gas emission measurements. The monitoring is conducted by analytical redundancy by estimating the monitored measurement variables. The estimated variables are CO2, H2O, flue gas flow and combustion air flow. Additionally, SO2 content in the flue gas can be estimated with certain limitations. The monitoring method is based on physical combustion modeling and is therefore boiler structure and fuel independent. The model is valid for multiple fuels as long as the fuel flow measurements, fuel properties and flue gas O2 measurement are available. The estimates can further be improved by flue gas CO measurement. The monitoring method was successfully tested in an industrial wood, peat, bark and slurry fired power plant. The results verify that the method is able to automatically separate sensor faults and process disturbances.

Evaluation of Copper–Aluminum Oxides as Sorbents for High-Temperature Air Separation

Oxygen production in an economic way is critical to oxy-firing combustion, a carbon capture technology. Oxygen-deficient oxides have been used for absorption of oxygen from air and desorption of oxygen in recycled flue gas for oxy-firing combustion. Cuprous/cupric oxide equilibrium with alumina can be used as an alternative for oxygen production and absorption. In this work, the effect of the spinel phase (CuAl2O4) content on oxygen sorptive/desorptive properties of CuO–CuAl2O4 sorbents has been investigated using thermogravimetric analysis. The desorption rate and oxygen sorption capacity were shown to be dependent upon the amount of alumina addition. The effect of SO2 and H2O in flue gas was investigated using FACTSage over a range of conditions. It was found that, at temperatures above 750 °C, CuO is inert to these species, making it a proper choice for oxygen carrier. Cyclic stability was also investigated using the same instrument. The molar CuAl2O4 content of 20% was observed to have the most positive cyclic stability effect. A stable morphology was observed in the scanning electron microscopy microstructure of the sorbent with this CuAl2O4 content. Sintering at a lower CuAl2O4 content and attrition because of second-phase agglomeration can destabilize the sorbents.

Structural Characterization of 1,1,3,3-Tetramethylguanidinium Chloride Ionic Liquid by Reversible SO2Gas Absorption

A unique new ionic liquid-gas adduct solid state compound formed between 1,1,3,3-tetramethylguanidinium chloride ([tmgH]Cl) and sulfur dioxide has been characterized by X-ray diffraction and Raman spectroscopy. The structure contains SO2 molecules of near normal structure kept at their positions by Cl-S interactions. The crystals belong in the orthorhombic system, space group Pbcn, with unit cell dimensions of a = 15.6908(10) Å, b = 9.3865(6) Å, and c = 14.1494(9) Å, angles α = β = γ = 90°, and Z = 8 at 120 K. The [tmgH]Cl has a very high absorption capacity of nearly 3 mol of SO2 per mol of [tmgH]Cl at 1 bar of SO2 and at room temperature. However, part of the absorbed SO2 was liberated during the crystallization, probably because the crystal only accommodates one molecule of SO2 per [tmgH]Cl. The nature of the high absorption capacity of [tmgH]Cl as well as of the homologous compounds with bromide and iodide are discussed. Some of these salts may prove useful as reversible absorbents of SO2 in industrial flue gases.

Spray Absorption and Electrochemical Reduction of Nitrogen Oxides from Flue Gas

This work developed an electrochemical reduction system which can effectively scrub NO× from flue gas by using aqueous solution of Fe(II)(EDTA) (ethylenediaminetetraacetate) as absorbent and electrolyte. This new system features (a) complete decomposition of NOX to harmless N2; and (b) fast regeneration of Fe(II)(EDTA) through electrochemical reaction. The Fe(II)(EDTA) solution was recycled and reused continuously during entire process, and no harmful waste was generated. The reaction mechanism was thoroughly investigated by using voltammetric, chromatographic and spectroscopic approaches. The operating conditions of the system were optimized based on NOX removal efficiency. Approximately 98% NO removal was obtained at the optimal condition. The interference of SO2 in flue gas and the system operating stability was also evaluated.

Effect of SO2 in flue gas on coal ash hot corrosion of Inconel 740 alloy – A high temperature electrochemical sensor study

• New high temperature corrosion sensor applied to study the coal ash hot corrosion of Alloy 740. • EN, EIS, and PDP data from the sensor were compared with the results from weight loss test. • A reasonable good correlation between the electrochemical data and the actual degradation processes. • Current noise analysis for the quantitative determination of hot corrosion rate discussed. Our newly developed high temperature electrochemical sensor was applied to study the effect of SO 2 in flue gas on thin film coal ash corrosion of Inconel 740 superalloy at 750 °C. The response of electrochemical noise (EN), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) test data from the sensor is compared with the results from a weight loss test. There is a good correlation between the electrochemical data and the actual degradation processes. The current noise analysis in time and frequency domains for the quantitative determination of hot corrosion rate in service is discussed.

Reversible Capture of SO2 through Functionalized Ionic Liquids

Emission of SO2 in flue gas from the combustion of fossil fuels leads to severe environmental problems. Exploration of green and efficient methods to capture SO2 is an interesting topic, especially at lower SO2 partial pressures. In this work, ionic liquids (ILs) 1-(2-diethylaminoethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Et2 NEMim][Tf2 N]) and 1-(2-diethylaminoethyl)-3-methylimidazolium tetrazolate ([Et2 NEMim][Tetz]) were synthesized. The performances of the two ILs to capture SO2 were studied under different conditions. It was demonstrated that the ILs were very efficient for SO2 absorption. The [Et2 NEMim][Tetz] IL designed in this work could absorb 0.47 g(SO2)g(IL)(-1) at 0.0101 MPa SO2 partial pressure, which is the highest capacity reported to date under the same conditions. The main reason for the large capacity was that both the cation and the anion could capture SO2 chemically. In addition, the IL could easily be regenerated, and the very high absorption capacity and rapid absorption/desorption rates were not changed over five repeated cycles.

Interactive Effect for Simultaneous Removal of SO2, NO, and CO2 in Flue Gas on Ion Exchanged Zeolites

A purification system for simultaneous removal of SO2, NO, and CO2 in flue gas was considered in this study. For improving the purification performance of candidate adsorbent NaX zeolite, ion exchange experiments were conducted with cation K+, Ca2+, Mn2+, and Co2+, respectively. The texture properties of series zeolites were examined by N2 porosimetry, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses. Among the sorbents investigated, K–NaX zeolite exhibited the best result to remove SO2, NO, and CO2 all together. XPS results revealed that SO2 has been oxidized to form SO42– on the solid surface; however, species N and C have not been observed. In order to understand the coadsorption effects, pure component, binary, ternary components, and mimic flue gas breakthrough experiments were designed and carried out. It suggested that SO2 and NO was bonded on the adsorbent surface with degradation of NO. A little competitive effect of CO2 on SO2 and NO adsorption system were found. Finally, monitoring of coadsorption venting gas, thermodynamic equilibrium species simulation, TPD experiment, and quantum chemical calculation technology were used to examine the interactive effect.

Identification and stabilization of combusting animal waste with active participation of bone material — Emission of SO2 and HCl

The paper presents the results of the experimental research conducted on an industrial scale and directed at stabilizing the process of the thermal destruction of biomass in the form of animal post-slaughter waste and dead animals. During the realization of the combustion process with the participation of oxygen from 6 to 17% the interaction between such gas products of the process of thermal destruction as SO2 and HCl was analyzed. The results of the experiment clearly indicate that the concentration of SO2 in flue gas is dependent on the participation of O2 in the process of combustion. Hydroxyapatites in the high temperature atmosphere were decomposed, among others, to CaO and P2O5. Particles of CaO, in largely oxidizing atmosphere, carried in the stream of exhaust gases bonded SO2. When the participation of O2 oscillates around 16 to 17%, the concentration of SO2 is close to zero. However, at the same time there are no clear premises concerning the influence that the participation of O2 has on the concentration of HCl. The results in the form of the dependence HCl → f(O2) only suggest that the concentration of HCl in outlet gases decreases for large participation of oxygen of more than 13%.

Influence of SO2 in incineration flue gas on the sequestration of CO2 by municipal solid waste incinerator fly ash

The influence of CO2 content and presence of SO2 on the sequestration of CO2 by municipal solid waste incinerator (MSWI) fly ash was studied by investigating the carbonation reaction of MSWI fly ash with different combinations of simulated flue gas. The reaction between fly ash and 100% CO2 was relatively fast; the uptake of CO2 reached 87 g CO2/kg ash, and the sequestered CO2 could be entirely released at high temperatures. When CO2 content was reduced to 12%, the reaction rate decreased; the uptake fell to 41 g CO2/kg ash, and 70.7% of the sequestered CO2 could be released. With 12% CO2 in the presence of SO2, the reaction rate significantly decreased; the uptake was just 17 g CO2/kg ash, and only 52.9% of the sequestered CO2 could be released. SO2 in the simulated gas restricted the ability of fly ash to sequester CO2 because it blocked the pores of the ash.

(Keynote) Separation of Flue Gas Components by SILP (Supported Ionic Liquid-Phase) Absorbers

Reversible absorption of the flue gas components CO2, NO, NO2 and SO2 has been tested for different ionic liquids (ILs) at different temperatures and flue gas compositions where porous, high surface area carriers have been applied as supports for the ionic liquids to obtain Supported Ionic Liquid-Phase (SILP) absorber materials. The use of solid SILP absorbers with selected ILs were found to significantly improve the absorption capacity and sorption dynamics at low flue gas concentration, thus making the applicability of ILs viable in technical, continuous flow processes for flue gas cleaning. The results show that CO2, NO and SO2 can be reversible and selective absorbed using different ILs and that Supported Ionic Liquid-Phase (SILP) absorbers are promising materials for industrial flue gas cleaning. Absorption/desorption dynamics can be tuned by temperature, pressure and gas concentration.

Carbonate melt regeneration for efficient capture of SO2 from coal combustion

Sulfur emission in the form of SO2 in flue gas is the most serious pollutant associated with coal combustion. Calcium carbonate sulfur scrubbing, the process most commonly in use today, is costly, produces a large amount of waste and leaves a considerable amount of SO2 in the gas. The carbonate eutectic method for removing SO2 from flue gas at 450–650 °C was initially proposed in the 1970's but despite its great efficiency could not be used due to the complexity of the carbonate melt regeneration stage. We propose a simple way to remove sulfur from the carbonate eutectic melt by purging it with CO. In contrast to expectation, this reaction leads to the reduction of sulfate to carbonyl sulfide gas that leaves the melt, rather than to sulfide ions that remain in the melt. The experiments conducted show that nearly complete sulfur removal from the melt is possible at 550 °C and that the reaction rate is sufficiently high for a large scale process. The proposed modifications provide solutions to two critical issues: (i) at 550 °C there is no problem of corrosion because a reaction cell of stainless steel with high chromium content is stable with respect to the carbonate eutectic melt at that temperature and (ii) removal of sulfur in the form of COS, rather than H2S, provides considerable freedom in choosing the final product: either sulfuric acid or elemental sulfur. In addition, we verified that fly ash does not dissolve in the carbonate eutectic melt and therefore will not interfere with SO2 removal. One can foresee that the carbonate melt-based SO2 removal technique may become a practical and viable method for limiting sulfur emission to the atmosphere.

Ammonia emission kinetics of monoethanolamine (MEA) based CO2 absorption process

Kinetics of NH3 emission in the absorption process of carbon dioxide (CO2) from fossil fuel power plant flue gases was studied using a typical range of CO2 absorption conditions (i.e., 3–7mol/L MEA, 6–21% O2, 0–0.45 CO2 loading, 0–800ppm SO2 and NO2 derived products in MEA solution; H2SO3 and HNO3, and 328–393K temperature). This study presents kinetic rate information of NH3 emission as a function of CO2 capture parameters in which an increase of MEA and flue gas O2 concentrations and temperature all increased the emission rate of NH3. On the other hand, increase of CO2 loading and concentration of H2SO3 and HNO3 inversely affected the emission rate. A useful kinetic rate equation for estimation of NH3 emissions is also proposed: rNH3 emission={1.75×10−6e−(0.62/RT)[MEA]0.38[O]3.41}/{1+0.86[CO2]0.57+0.46[H2SO3]0.16+1.45[HNO3]0.08}. The goal is to help plant operators to quickly identify NH3 release from the CO2 capture system. The rate equation developed in this study represents one of only a few capable of providing truly quantitative information on NH3 emissions.

An experimental investigation of a direct burning of crude Jatropha oil (CJO) and pitch in a commercial boiler system

We conducted a test of a direct burning of crude Jatropha oil (CJO) and pitch in a commercial boiler system. The fuel, crude Jatropha oil is not biodiesel which comes from transesterification process of bio oil, but it is pure plant oil like cooking oil. The higher heating value (HHV) of the CJO is 39.3 MJ/kg (9380 kcal/kg) and is lower than that of commercial heating oil, 44.0 MJ/kg. The kinematic viscosity of CJO is 36.2 mm2/s at 40 °C and 8.0 mm2/s at 100 °C. The burner used in the test is a commercial burner for a commercial heating oil and its capacity is 140 kW (120,000 kcal/h).We did a preliminary test whether the combustion is stable or not. The preliminary test was a kind of open air combustion test using the commercial burner with crude Jatropha oil. We found that the combustion can be stable if the crude Jatropha oil temperature is higher than 90 °C. We measured the flue gas concentration by using a gas analyzer. The NOx concentration of crude Jatropha oil is 80 ∼ 100 ppm and CO concentration is nearly 0 ppm at flue gas O2 concentration of 2.5 and 4.5%. We also tested a pitch combustion and the result shows that the NOx concentration of pitch is about 90 ∼ 110 ppm and CO concentration is below 30 ppm at flue gas O2 concentration of 2.5 and 4.5%. As a reference data, combustion of heating oil was conducted. The NOx concentration of heating oil is about 80 ppm which is the lowest value of tested fuels.

Post-combustion CO2 capture using super-hydrophobic, polyether ether ketone, hollow fiber membrane contactors

The feasibility of utilizing a super-hydrophobic polyether ether ketone (PEEK) hollow fiber membrane contactor in combination with chemical solvents to separate and capture CO2 from simulated flue gases was investigated. Greater than 90% CO2 capture with greater than 95% CO2 purity has been achieved in one stage with both activated methyldiethanolamine (aMDEA) and activated K2CO3 solvents. The measured volumetric mass transfer coefficient was as high as 1.7s−1, which is more than 20 times greater than the mass transfer coefficient of a packed column. Preliminary tests indicated that the CO2 capture performance was not affected by flue gas contaminants, including O2, NO2, and SO2, with aMDEA solvent. The PEEK membrane module showed good mechanical properties and stable permeation properties at process design conditions for duration of the test (120h). The process economics were evaluated assuming direct substitution of the conventional absorber by the membrane contactor, while using a conventional packed column in the regeneration step. Relative to the cost estimation with no CO2 capture, the evaluation indicates a 56% increase in the levelized cost of electricity (LCOE) for the PEEK membrane contactor technology, which is 29% lower than DOE’s benchmark amine absorption technology (85% increase in LCOE).