Destruction And Removal Efficiency Research Articles

Validation of a New Method for Continuous Flare Combustion Efficiency Monitoring

A new method is described for calculating flare combustion efficiency (CE) and destruction and removal efficiency (DRE) using a numerical parametric model. The method combines key variables that affect flare performance including the flare vent gas net heating value (NHV), flare design, flow rate, exit velocity, and inert gas composition, alongside the environmental influence of crosswind speed. Each effect is characterized using a parametric model derived from experimental testing data and computational fluid dynamics (CFD). The inclusion of CFD allows the model to be extended into the high-wind conditions that cannot be adequately controlled for in empirical testing yet represent some of the most challenging conditions in which to maintain good combustion. This new parametric model method (PMM) is coupled with ultrasonic flowmeters from which the molecular weight and net heating value of the flare gas can be derived using the vent gas speed of sound measurement. In doing so, this method provides a reliable continuous flare combustion efficiency measure that can be deployed at scale with minimum hardware updates. The system was verified using an extractive sampling method with tests conducted on three full-scale industrial flares including non-assisted, single-arm pressure-assisted, and multi-arm pressure-assisted flare designs. A total of seventy valid test points were carried out with varying flow rate and flare gas heating value, covering a CE range from 46–100%. The uncertainty of the method was assessed using both traditional error propagation and Monte Carlo methodology. The results from the new method agree with the extractive method to within 0.8% in the ≥98% DRE region where flares are expected to operate to limit the impacts of flaring as a source of methane as a greenhouse gas. Uncertainty analysis revealed that the larger DRE discrepancy for DRE ≤ 98% correlates to the measurement uncertainties for both methods.

Modelling of thermal plasma-assisted carbon tetrafluoride abatement

This study focuses on the numerical modelling of the decomposition process of carbon tetrafluoride (CF4, Freon R-14), the most stable perfluorinated gas with a significant global warming potential, as experimentally carried out using a thermal argon/steam plasma in a plasma-chemical reactor. The numerical modelling approach incorporates advanced computational fluid dynamics (CFD) techniques and the kinetics of a complex chemical reaction mechanism. A two-dimensional axisymmetric model, incorporating the conservation of mass, momentum, energy and chemical balances, has been developed to simulate the species distribution under the assumption of steady flow, including turbulence effects. In order to compare the species distributions and destruction efficiencies, two chemical reaction mechanism models of different complexity were implemented: a simplified model A with 196 reactions and a model B with 258 reactions. The simulations were performed for plasma generated by steam and argon stabilized DC plasma torch under three operating conditions for arc currents of 120, 150 and 200 A. The destruction and removal efficiency (DRE) of CF4 decomposition at a high feed rate was computed by both models, with an error of less than 6% compared to the experimental data. It can be concluded that both models accurately predict the residual CF4 concentration trends depending on the feed per input torch power. While model A overestimates process efficiency, model B, with a more balanced reaction mechanism, more closely aligns with experimental results. Model B provides an accurate prediction of the DRE and captures trends as a function of input parameters. Importantly and innovatively, the model presented in this study, unlike previous models, allows for the first time the inclusion of both high concentrations and a sufficiently large reaction mechanism for CF4 abatement. This model presents a novel opportunity to perform trend simulations of operating characteristics for the CF4 abatement problem at a quantitative level, allowing experimental design to be evaluated and optimised.

Design and simulation of a utility oilfield flare in Iraq/Kurdistan region using CFD and API-521 methodology

This paper aims at reviewing and analyzing the operation and design of a utility flare in an oilfield in the Iraq/Kurdistan region. The flare supports a gas separation unit that separates 100 MMSCFD of natural gas from other liquid compounds in petroleum refining. The actual flare dimensions are 50 m high and 0.6 m diameter and works in summer where the crosswind speed is 9 m/s and a flow of 1.2 MMSCFD of treated natural gas is flaring through it. At the beginning, the flare design was performed using the API-521 recommended approach based on full operating capacity of the unit and composition of the gas to be flared. The API-521 based design resulted in a flare with a 0.76 m diameter and 48.19 m height. The effects of stack height on heat radiation in case of full capacity firing showed that as the flare height increases from 42.34 m to 133.05 m, the heat radiation decreases from 15.8 kW/m^2 to 1.6 kW/m^2 within 45.7 m dimeter. Furthermore, the relation between stack height and heat radiation was studied for the actual firing rate 1.2MMSCFD using simulation, where the results showed that as the stack height increasing from 10 m to 50 m the heat radiation decreasing from over 1000 w/m^2 to around 150 W/m^2. In fact, CFD code C3d was used to analyze flare performance at normal firing condition during summer operation of 1.2 MMSCFD with a flare diameter and height of 50 m and 0.6 m, respectively. The code was able to predict the flame shape and size during actual flare operation. The results of the simulation demonstrated by defining four locations in the domain to measure the average temperatures and emissions, and to calculate the Combustion Efficiency (CE) and Destruction and Removal Efficiency (DRE). These points were 6 m, 8 m, 10 m, 12 m far from the tip on x-axis and at height of 52 m. The results showed that the average temperature at 6 m far from the flare is 658 K and it decreasing to 490 K at 12 m away from the tip. The CO and CO2 also decreased from 7.27E-5 and 0.033 mass% to 4.53E-6 and 0.027 mass%, respectively. Generally, soot formation was low but at points 8 m and 10 m from the tip the soot formation was considerably lower, respectively at 6.16E-5 and 8.71E-5 mass%. The emissions of C1, C2, C3 and C6+ were measured at 7.46E-9, 5.39E-9, 5.13E-9 and 4.35E-9 mass% at 6 m away from the tip. The emissions increased slightly at 8 m and 10 m from the tip but at 12 m they were observed to decrease. The flare CE and DRE were estimated to be 98% and 100%, respectively. Analysis results confirmed that the flare design was safe and the flare operation was highly efficient with very little smoke produced as indicated by the predicted CE and DRE.

Pilot-Scale Thermal Destruction of Per- and Polyfluoroalkyl Substances in a Legacy Aqueous Film Forming Foam

The destruction of per- and polyfluoroalkyl substances (PFAS) is critical to ensure effective remediation of PFAS contaminated matrices. The destruction of hazardous chemicals within incinerators and other thermal treatment processes has historically been determined by calculating the destruction efficiency (DE) or the destruction and removal efficiency (DRE). While high DEs, >99.99%, are deemed acceptable for most hazardous compounds, many PFAS can be converted to other PFAS at low temperatures resulting in high DEs without full mineralization and the potential release of the remaining fluorocarbon portions to the environment. Many of these products of incomplete combustion (PICs) are greenhouse gases, most have unknown toxicity, and some can react to create new perfluorocarboxylic acids. Experiments using aqueous film forming foam (AFFF) and a pilot-scale research combustor varied the combustion environment to determine if DEs indicate PFAS mineralization. Several operating conditions above 1090 °C resulted in high DEs and few detectable fluorinated PIC emissions. However, several conditions below 1000 °C produced DEs > 99.99% for the quantifiable PFAS and mg/m3 emission concentrations of several nonpolar PFAS PICs. These results suggest that DE alone may not be the best indication of total PFAS destruction, and additional PIC characterization may be warranted.

A novel zone-based machine learning approach for the prediction of the performance of industrial flares

Industrial flares are used to burn off unwanted gas during operation. If not combusted completely, intermediate products or incomplete combustion products are formed, and they will cause significant environmental and health issues. The EPA Refinery Sector Rule emphasizes smokeless flaring with combustion efficiency (CE) ≥ 96.5% and destruction and removal efficiency (DRE) ≥ 98% for all types of flares in the refineries. In this research, a novel zone-based modeling approach was developed for predicting CE and Opacity of steam assist flares. Flare CE data were partitioned into two zones based on the partition of the carbon and hydrogen atomic ratio (CHR), then random forest (RF) and Catboost algorithms were used to develop CE predictive models, respectively. This CHR-based zone partition has a clear implication in engineering. It was also found out that no zone division for flare Opacity prediction is needed, and both RF and Catboost algorithms generated good prediction results. All the models match extremely well with all the original experimental data. These predictive models under the same zone-partition use either RF or Catboost algorithm can both give superior prediction accuracy. This demonstrates the simplicity, general applicability, and high reliability of the zone-based ML approach.

Molten salt oxidation and process analysis of anionic exchange resin in Na2CO3-K2CO3 melt

ABSTRACT The oxidation characteristics of anionic exchange resins (AERs) during molten salt oxidation (MSO) were investigated in carbonate melt. The residue after MSO of AERs were carbon, which was confirmed by the X-ray diffraction (XRD) and Raman spectra. The remaining amount of salt-free residue after MSO was evaluated by destruction and removal efficiency (DRE), which indicates that 2 hours is a suitable oxidation time. The morphologies of the AERs after MSO were observed by scanning electron microscopy (SEM). The oxidation process of AERs in MSO was investigated by thermogravimetric analysis (TG) and Fourier Transform Infrared Spectrometer (FT-IR), which revealed that initial AERs, experienced four reaction stages in MSO: dehydration, thermal decomposition of functional groups, carbonization of styrene-divinylbenzene copolymer (ST-DVB), and gasification of carbon. The TG data proved that the presence of carbonate promotes the carbonization process of ST-DVB in AERs. The reason why salt catalyzes this stage had been proved to be that the carbonate captures the nitrogen-containing exhaust gas generated by the oxidation of the anion resin, and produces nitrate with catalytic oxidation ability, which catalyzes the oxidation of the resins effectively. This means that MSO will be an environmentally friendly and efficient method for catalytic oxidation of AERs.

Effect of dynamic low DREs from flare combustion on regional ozone pollution during a chemical plant shutdown

The destruction and removal efficiencies (DREs) for industrial flare combustion could be, in reality, less than the supposed standard values of 98%/99% because of various atmospheric and plant operating conditions. Thus, flaring during chemical plant shutdown (CPS) under low DREs would release larger quantities of VOCs and NOx than expected, which might rapidly worsen the regional ozone pollution under solar radiation. Therefore, it is vital to examine the quantity and sensitivity of ozone impacts owing to low DREs for flare combustion rather than standard values. In this paper, effect of dynamic low DREs on regional ozone impacts during CPS flaring has been systematically conducted by coupling Aspen Plus with CAMx modeling and simulation. Case studies indicated that 8-hr ozone caused by CPS flaring under low DREs could range from 6.08 to 7.28 ppb, which was much greater than that based on the standard DREs ranging from 1.8 to 2.19 ppb. This study also demonstrated that the 8-hr ozone increment could be significantly reduced from the maximum of 6.14 ppb to the minimum of 0.85 ppb by starting the CPS operations at the optimal time. Another important finding was that ozone impacts might slightly increase with the increase of flare stack height due to meteorological conditions including high wind speed and strong solar radiation. This study would provide scientific support for quantitative ozone evaluation caused by CPS flare emissions, which will enrich future solutions for cost-effective regional air-quality management and ozone pollution control.

Comparison of Abatement Models for CF4 Reacting With Nitrogen Thermal Plasma

This article proposes a numerical model to predict the abatement process of carbon tetrafluoride (CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) in a reaction chamber with the assistance of nitrogen thermal plasma generated by a nontransferred and direct-current torch. The magneto-hydrodynamic equations, that is, the continuity, momentum, energy, and current continuity equations together with turbulence transport equations, are solved by an in-house parallelized finite volume code to obtain the thermal plasma flow jetting out the plasma torch. The thermal plasma is assumed in local thermal equilibrium, optically thin and electrically neutral. In the reaction chamber, a kinetics model is adopted to describe the transport phenomena as well as the chemical interactions among various species involving in the decomposition process. Fifty-six species and 235 chemical reactions are considered in the proposed full kinetic model. Three different models, namely a full kinetic one, a reduced one, and a simplified one, are compared for the prediction accuracy of the destruction and removal efficiency (DRE) along with the abatement products formed in the decomposition process. With the full kinetic model, the predicted DRE at three CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> concentration conditions, that is, 7200, 12 600, and 16 000 ppm, has a good agreement with the experimental result indicating a nearly full decomposition except for a very small discrepancy less than 0.5% for the case of 16 000 ppm. The predicted abatement efficiency becomes saturated and approaches to a complete abatement provided the participated H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O outnumbers CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> in moles. A dry abatement process is forecast with a destruction rate decline from 97% to 92% as the CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> concentration grows from 7200 to 16 000 ppm. Although the reduced kinetic model along the simplified model using a compact set of chemical reactions underpredicts the DRE for the investigated CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> concentration in the range of 1%-2%, they practically deliver an incomplete group of abatement products that might mislead a proper design of the scrubber behind the reaction chamber. The validation with the experimental measurement justifies the employment of the proposed full kinetic model capable of delivering an accurate abatement prediction of the detoxifying process of CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> .

Effect of industrial flare DREs derived by CFD and WERF on ozone pollution through CAMx simulation

Abstract Flare is the last safety measure for daily operations in oil, gas & chemical process industries (OGCPI). However, an excessive flaring releases large quantity of emissions of VOCs and NOx, which may suddenly enhance local ozone as a secondary pollution. Normally, the flare destruction and removal efficiency (DRE) of 98% or 99% is regulated as the national standard and presumed for industrial practices in the U.S. Unfortunately, real DRE values could be much lower than the standard due to impact factors including various meteorological and operating conditions such as the cross-wind speed, flare jet velocity and heating value of combustion. Thus, it is critically important to explore the sensitivity of the regional ozone impact due to low DREs of OGCPI flare combustions. In this paper, a systematic methodology has been developed to examine ozone impacts due to the low flare DREs, which have never been systematically studied before. The DRE formulas were derived from computational fluid dynamic (CFD) modeling and Water Environment Research Foundation (WERF) results and then employed to recompile the point source emission inventory. After that, comprehensive air quality model with extensions (CAMx) was employede to simulate and quantify local ozone changes impacted by flare emissions of OGCPI. Case studies indicate that the maximum hourly ozone increments due to the low DRE through CFD and WERF modeling is 0.18 ppb and 1.3 ppb, respectively. This study could enrich fundamental understandings of industrial point source emissions and provide the quantitative and valuable support for the ozone pollution caused by OGCPI flare emissions under low DRE instead of standard values.

Study on the Oxidant Effect for Nitrogen Trifluoride Abatement by Using a 2.45 GHz Microwave Plasma Torch

Among the fluorinated compounds (FCs) used in the semiconductor and display industries, NF3 gas is a popular gas for etching processes, and due to the high global warming potential (GWP), emission regulations are becoming more stringent. In the semiconductor process, a point of use (POU) scrubber is attached to the rear stage to remove fluorinated compounds. The field industry continues to increase degassing flow rates and strives to reduce energy consumption for degassing. In order to save energy, researchers have reduced the energy consumption by using a reverse vortex reactor (RVR) and have analyzed the removal efficiency according to the oxidant by using oxygen and steam as additional gases in the gas removal process. Removal rates were measured using Fourier transform infrared (FTIR) spectroscopy and detailed experiments on nitrogen trifluoride (NF3) reduction were performed in terms of the destruction and removal efficiency (DRE). In order to measure the decomposition rate, nitrogen was injected at 250 SLM and NF3 was 1.25 SLM, and the experiment was performed at a concentration of 5,000 ppm. Oxygen and steam were injected as oxidants, and an injection amount was 12 SLM with steam at 2 g/min. In the case of steam injection, there was a difference in the decomposition rate differed according to the injection port, and when injected into the view port (front part of the reactor), the decomposition rates were 90% at 6 kW and more than 98% at 7 kW. When oxygen and steam were used as oxidants, the energy consumption was reduced by 8.3% and 21.4%, respectively, depending on the location at while steam was injected.

Characteristic study of decomposing CF4 in a nitrogen microwave plasmas torch at atmospheric pressure

A microwave plasma torch operated at atmospheric pressure (APMPT) is used for abating CF4 gas diluted by nitrogen. The variation of destruction and removal efficiency (DRE) of CF4 by measuring Fourier transformation infrared spectra is investigated with respect to the microwave power, CF4 concentration, total gas flow and the length and material of discharge tube in reaction chamber respectively. The partition into annular free-discharge and central plasma regions in the cross section of discharge tube, influenced by the flow rate and microwave power, plays an important role in determining DRE value, and the measurement of vibrational temperature by means of OES along the axis in afterglow presents a minimum value on the transiting point between near and far afterglow. Meanwhile, the explanations are delivered in good agreement with the experimental observations with respect to variation of DRE for decomposing CF4 by APMPT.

WITHDRAWN: Effect of Flare destruction and removal efficiencies on regional ozone pollution from oil, gas and chemical process industries in Southeast of Texas through CAMx modeling and simulation

Flare is the last safety measure for daily operations in oil, gas & chemical process industries (OGCPI). However, an excessive flaring releases large quantity of emissions of VOCs and NOₓ, which may suddenly enhance local ozone as a secondary pollution. Normally, the flare destruction and removal efficiency (DRE) of 98% or 99% is regulated as the national standard and presumed for industrial practices in the U.S. Unfortunately, real DRE values could be much lower than the standard due to impact factors including various meteorological and operating conditions such as the cross-wind speed, flare jet velocity and heating value of combustion. Thus, it is critically important to explore the sensitivity of the regional ozone impact due to low DREs of OGCPI flare combustions. In this paper, a systematic methodology has been developed to examine ozone impacts due to the low flare DREs, which have never been systematically studied before. The DRE formulas were derived from computational fluid dynamic (CFD) modeling and Water Environment Research Foundation (WERF) results and then employed to recompile the point source emission inventory. After that, comprehensive air quality model with extensions (CAMx) was employede to simulate and quantify local ozone changes impacted by flare emissions of OGCPI. Case studies indicate that the maximum hourly ozone increments due to the low DRE through CFD and WERF modeling is 0.18 ppb and 1.3 ppb, respectively. This study could enrich fundamental understandings of industrial point source emissions and provide the quantitative and valuable support for the ozone pollution caused by OGCPI flare emissions under low DRE instead of standard values.

SUPERCRITICAL WATER GASIFICATION AS A TREATMENT FOR LABORATORY ORGANIC WASTE

The thermodynamics of supercritical water gasification (SCWG) was studied in order to determine its potential for treatment of laboratory liquid organic waste. A thermodynamic model based on the minimization of Gibbs energy was developed in Aspen Plus software that simulated the SCWG of liquid lab organic wastes on an ash free basis. The feed stream contained a mixture of aliphatic (hexane), oxygenated (acetone, ethyl acetate,ethyl ether, isopropyl alcohol and methanol), aromatic (toluene and xylene) and chlorinated hydrocarbons (chloroform and dichloromethane). The showed that a pressure of 25 MPa, low organic material concentration of 5-10% in the feed and temperatures over 600oC, SCWG resulted in hydrogen rich syngas aith a trace amount of HCI in the liquid effluent. High conversion rates were obtained for oxygenated hydrocarbons having destruction and removal efficiency (DRE) greater than 99.99% with the rest of the compound having a 100% DRE. The composition of the gaseous stream was found to be such that the gas could be released safely to the atmosphere or be stored at high pressure. The study established a proof of concept that there is potential for laboratories to use this method to deal with organic lab wastes with the SCWG process effluent that is environmental friendly.

Study on regional air quality impact from a chemical plant emergency shutdown

Emergency shutdowns of chemical plants (ESCP) inevitably generate intensive and huge amounts of VOCs and NOx emissions through flaring that can cause highly localized and transient air pollution events with elevated ozone concentrations. However, quantitative studies of regional ozone impact due to ESCP, in terms of how ESCP would affect and to what extent ESCP could impact, are still lacking. This paper reports a systematic study on regional air quality impact from an olefin plant emergency shutdown due to the sudden failure of its cracked gas compressor (CGC). It demonstrates that emergency shutdown may cause significant ozone increment subject to different factors such as the starting time of emergency shutdown, flare destruction and removal efficiency (DRE) and plant location. In our studied case, the 8-hr ozone increment ranges from 0.4 to 3.3 ppb under different starting time, from 3.3 to 24.8 ppb under different DRE, and from 1.6 to 3.3 ppb under different locations. The results enable us to understand how and to what extent emergency operating activities of the chemical process will affect local air quality, which might be beneficial for decision makings on emergency air-quality response and control in the future.

Study on Degradation of SF6 in the Presence of H2O and O2 Using Dielectric Barrier Discharge

In this paper, a method using dielectric barrier discharge for SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> abatement is investigated. The destruction and removal efficiencies (DRE) of plasma abatement of 2% SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> in the presence of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O and O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> were studied. The addition of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O and O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> effectively promoted the decomposition process of the SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> . With the participation of 0.5% H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O and 2% O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , the DRE reached 98.2% at 50mL/min flow rate and the energy efficiency reached 5.73 g/kWh. By emission spectra and products composition analysis, we found that the addition of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O can generate a large amount of H and OH radicals in plasma region, making SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> tend to degrade to produce SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The addition of O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> can generate a large amount of O radicals, which promotes the production of SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The addition gas not only affects the type of products, but also determines the selectivity of each degradation product. The results in this paper provide experimental support for the treatment of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> tail gas using low temperature plasma.

Effect of MnO2 Crystalline Structure on the Catalytic Oxidation of Formaldehyde

ABSTRACTManganese oxides prove to be a promising catalyst for formaldehyde (HCHO) elimination in catalytic oxidation. In this study, MnO2 with different crystalline structure (α-MnO2, β-MnO2, γ-MnO2, and δ-MnO2) were synthesized by hydrothermal method to investigate their catalytic performances towards the abatement of formaldehyde. The prepared catalysts were characterized and analyzed by the X-ray diffraction (XRD), hydrogen-temperature programmed reduction (H2-TPR), BET specific surface area, X-ray photoelectron spectroscopy (XPS), and ammonia-temperature programmed desorption (NH3-TPD). In addition, the apparent activation energy was also calculated by using Arrhenius plots. Among the above four prepared catalysts, the γ-MnO2 has the best destruction and removal efficiency (DRE), which was approaching to 100% for HCHO at 155°C. The catalytic activity of γ-MnO2 is associated with abundant mesopores, higher reducibility of surface oxygen species, and more oxygen vacancies as compared to other types of crystalline MnO2.

Effects of Pressure and Electrode Length on the Abatement of N2O and CF4 in a Low-Pressure Plasma Reactor

The emission of greenhouse gases, such as N2O and fluorinated gases, has been increasingly regulated in the semiconductor industry. Pressure effects on the abatement of N2O and CF4 were investigated in a low-pressure plasma reactor by using Fourier transform infrared (FTIR) spectroscopy. The destruction and removal efficiency (DRE) of N2O and CF4 was significantly lowered below 0.2 Torr. When the pressure was increased, the DRE of CF4 with H2O as the reactant gas increased continuously, but that with O2 or without any reactant gas first increased and then decreased. A larger electrode length yielded a higher DRE of N2O and CF4, especially at lower pressures. To understand this phenomenon, the electrical waveforms for the discharge in N2O were analyzed in conjunction with its optical emission profiles, and the rotational temperatures for different electrode lengths were compared using the N2+ ion band (λ = 391.4 nm). They provided insights into the mechanism involved in terms of plasma property and gas residence time.

Abatement characteristics of N2O in low-pressure plasma reactor

The abatement characteristics of N2O were investigated in a plasma reactor positioned in front of a vacuum pump. Fourier transform infrared (FTIR) spectroscopy was used for evaluating the destruction and removal efficiency (DRE) and the identification of byproducts. The concentration of NOx (NO and NO2) was quantified by using an NOx analyzer. The DRE of N2O was enhanced by increasing the power or decreasing the N2O flow rate. A higher pressure yields a higher DRE of N2O and a lower concentration of NOx in the destroyed N2O. For understanding this phenomenon, the discharge characteristics were analyzed by using optical emission spectroscopy (OES). The spatial distribution of emission spectra from the discharge in a mixture of N2O and Ar gases was measured by varying the pressure. The mechanisms underlying the pressure effect on the N2O DRE and NOx concentration are discussed in terms of the electron density and the concentration of O radicals.

Decomposition of high concentration SF6 using an electron beam

In this study, high concentration SF6 (2–10%) was decomposed using an electron beam irradiation. Various influential factors were investigated to improve the destruction and removal efficiency (DRE) of SF6. The initial concentrations of SF6, absorbed doses, SF6/H2 ratios and retention times were the main factors of concern. As a result, the DRE increased as the adsorbed dose and retention time increased. The DRE of SF6 also increased up to 20% approximately when H2 was added to the reaction mixture. On the other hand, the DRE of SF6 decreased as initial concentrations of SF6 increased. Finally, the main by-product formed from SF6 decomposition by the electron beam was HF.

Disposal of historically contaminated soil in the cement industry and the evaluation of environmental performance

Approximately 400000t of DDTs/HCHs-contaminated soil (CS) needed to be co-processed in a cement kiln with a time limitation of 2y. A new pre-processing facility with a “drying, grinding and DDTs/HCHs vaporizing” ability was equipped to meet the technical requirements for processing cement raw meal and the environmental standards for stack emissions. And the bottom of the precalciner with high temperatures >1000°C was chosen as the CS feeding point for co-processing, which has rarely been reported. To assess the environmental performance of CS pre- and co-processing technologies, according to the local regulation, a test burn was performed by independent and accredited institutes systematically for determination of the clinker quality, kiln stack gas emissions and destruction efficiency of the pollutant. The results demonstrated that the clinker was of high quality and not adversely affected by CS co-processing. Stack emissions were all below the limits set by Chinese standards. Particularly, PCDD/PCDF emissions ranged from 0.0023 to 0.0085ngI-TEQNm−3. The less toxic OCDD was the peak congener for CS co-processing procedure, while the most toxic congeners (i.e. 2,3,7,8-TeCDD, 1,2,3,7,8-PeCDD and 2,3,4,7,8-PeCDD) remained in a minor proportion. Destruction and removal efficiency (DRE) and destruction efficiency (DE) of the kiln system were better than 99.9999% and 99.99%, respectively, at the highest CS feeding rate during normal production. To guarantee the environmental performance of the system the quarterly stack gas emission was also monitored during the whole period. And all of the results can meet the national standards requirements.