Waste Gas Streams Research Articles

Effect of Operating Parameters on the Performance of a Thiobacillus thioparus‐Immobilized Polyurethane Foam Biotrickling Filter for Hydrogen Sulfide Removal

The effect of variation in the two important process parameters of liquid recirculation rate (LRR) and empty bed residence time (EBRT), on the elimination capacity (EC), and removal efficiency (RE) of H2S from a synthetic waste gas stream in a biotrickling filter (BTF) was studied using Box‐Behnken design of experiment. The BTF employed contained Thiobacillus thioparus immobilized on polyurethane foam. The results showed that both the effect of LRR and EBRT on RE and EC depended on the concentration of H2S in the inlet gas stream (Cin). At the lower side of the range 1.85–5.55 m/h, increase in LRR always resulted in an increase in both RE and EC; however, over the higher side of this range, at high Cin, increasing LRR did not have a marked effect on RE and EC whereas at low Cin it actually lead to a slight reduction in the value of both parameters. Also, increasing EBRT exacerbated the observed negative effect of high LRR on RE. Contour plot analysis revealed that at low Cin acceptable RE can be achieved simply by reducing EBRT to sufficiently low values independent of the value of LRR. However, at higher Cin the correct setting of the level of both operating parameters is necessary in order to ensure a sufficiently high RE.

Removal of dichloromethane from waste gas streams using a hybrid bubble column/biofilter bioreactor.

The performance of a hybrid bubble column/biofilter (HBCB) bioreactor for the removal of dichloromethane (DCM) from waste gas streams was studied in continuous mode for several months. The HBCB bioreactor consisted of two compartments: bubble column bioreactor removing DCM from liquid phase and biofilter removing DCM from gas phase. Effect of inlet DCM concentration on the elimination capacity was examined in the DCM concentration range of 34–359 ppm with loading rates ranged from 2.2 to 22.8 g/m3.h and constant total empty bed retention time (EBRT) of 200 s. In the equal loading rates, the elimination capacity and removal efficiency of the biofilter were higher than the corresponding values of the bubble column bioreactor. The maximum elimination capacity of the HBCB bioreactor was determined to be 15.7 g/m3.h occurred in the highest loading rate of 22.8 g/m3.h with removal efficiency of 69%. The overall mineralization portion of the HBCB bioreactor was in the range of 72-79%. The mixed liquor acidic pH especially below 5.5 inhibited microbial activity and decreased the elimination capacity. Inhibitory effect of high ionic strength was initiated in the mixed liquor electrical conductivity of 12.2 mS/cm. This study indicated that the HBCB bioreactor could benefit from advantages of both bubble column and biofilter reactors and could remove DCM from waste gas streams in a better manner.

Synthesis and characterization of Pt/Al2O3–CeO2 nanocatalyst used for toluene abatement from waste gas streams at low temperature: Conventional vs. plasma–ultrasound hybrid synthesis methods

To assess the synergism effect of plasma and ultrasound treatment on the physicochemical properties and catalytic performance of supported-Pt nanocatalysts, a series of nanostructured Pt(1wt.%)/Al2O3–CeO2(30wt.%) catalysts were prepared by plasma and/or ultrasound-assisted impregnation methods and tested for the total oxidation of toluene. The nanocatalysts were characterized by XRD, FESEM, FTIR, EDX and N2 adsorption–desorption measurements. XRD data confirmed the formation of CeO2 as the crystalline phase with an average crystallite size of about 8.7nm for all samples. EDX dot mapping indicated homogenous dispersion of elements. The results indicated that the remarkable synergetic effect of ultrasound irradiation on the surface morphology and elemental dispersion, especially when it is coupled with plasma treatment. All treated nanocatalysts showed lower temperature activity and better catalytic performance in toluene oxidation with high stability, in particular, ultrasound–plasma assisted synthesized nanocatalyst exhibited the approximately complete oxidation of toluene at 180°C. It is observed that even at higher concentrations of toluene (3000ppm) or GHSV, plasma–ultrasound assisted synthesized nanocatalyst had still enough destruction ability to reduce the pollutant. Therefore, the plasma–ultrasound hybrid synthesis method can lead to an excellent preparation of supported nanocatalysts, esp., those for VOCs oxidation.

Synthesis and physicochemical characterizations of nanostructured Pd/carbon-clinoptilolite-CeO2 catalyst for abatement of xylene from waste gas streams at low temperature

Xylene removal from waste gas streams was carried out via catalytic oxidation over Pd/carbon-clinoptilolite-CeO2. The synthesized samples were characterized by XRD, FESEM, BET, FTIR and TG techniques. The XRD patterns confirmed the formation of nano ceria with an average crystallite size of 11.6nm. FESEM results indicated a good morphology for prepared carbon with deep pores, confirmed structure modification of zeolite, and showed that nanocatalyst has nanometric particles with an average size of 60.85nm. Reaction data illustrated 98% abatement of xylene at 250°C. The stability test of catalyst demonstrated that the removal efficiency has remained constant for 1200min.

Synthesis, physicochemical characterizations and catalytic performance of Pd/carbon-zeolite and Pd/carbon-CeO2 nanocatalysts used for total oxidation of xylene at low temperatures

In this work, xylene removal from waste gas streams was investigated via catalytic oxidation over Pd/carbon-zeolite and Pd/carbon-CeO2 nanocatalysts. Activated carbon was obtained from pine cone chemically activated using ZnCl2 and modified by H3PO4. Natural zeolite of clinoptilolite was modified by acid treatment with HCl, while nano-ceria was synthesized via redox method. Mixed supports of carbon-zeolite and carbonceria were prepared and palladium was dispersed over them via impregnation method. The prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Brunauer-Emmett-Teller surface area (BET), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric (TG) techniques. Characterization of nanocatalysts revealed a good morphology with an average particle size in a nano range, and confirmed the formation of nano-ceria with an average crystallite size below 60 nm. BET analysis indicated a considerable surface area for catalysts (∼1000 m2·g−1). FTIR patterns demonstrated that the surface groups of synthesized catalysts are in good agreement with the patterns of materials applied in catalyst synthesis. The performance of catalysts was assessed in a low-pressure catalytic oxidation pilot in the temperature range of 100° C-250°C. According to the reaction data, the synthesized catalysts have been shown to be so advantageous in the removal of volatile organic compounds (VOCs), representing high catalytic performance of 98% for the abatement of xylene at 250°C. Furthermore, a reaction network is proposed for catalytic oxidation of xylene over nanocatalysts.

Potential Subsurface Impacts of CO2 Stream Impurities on Geologic Carbon Storage

A key impediment to carbon capture and storage is the cost of CO2 capture, particularly for conventional power plants whose flue gas is dominated by gases other than CO2. Waste-gas streams from power plants that use novel technologies (such as oxyfuel, the focus of this paper) can circumvent the capture step thanks to their CO2-rich composition (CO2>90%), but at the expense of stream CO2 purity (N2, O2, Ar, and other minor species may be present). Relatively high purity levels must be achieved to avoid compression and complications in pipeline transportation (two-phase flow) and, potentially, subsurface impacts. The CO2 Capture Project Phase 3 (CCP3) has started investigating the latter, which, in turn, inform techno-economic assessments of capture and transportation economics. Subsurface impacts of an impure CO2 stream could be twofold: (1) complicate flow behavior and reduce static capacity because of density and viscosity differences and (2) undermine reservoir and top seal integrity due to reaction with reactive species (O2, CO, SOx). Using a range of potential oxyfuel waste-gas compositions, we approached the first issue through a desktop study using the numerical modeling tool. So that we could work with accurate flow parameters, we performed laboratory experiments in order to determine the actual viscosity and density of the mixtures. Information on solubility of these various mixture components in the aqueous phase under various pressure, temperature, and salinity conditions was also collected. An important observation controlling all results of the study was that viscosity and density of mixtures are lower than those of pure CO2 at the same temperatures and pressures. It follows that a plume of CO2 with impurities, moving updip with no barrier, will migrate farther from the point of injection but will be trapped through residual saturation sooner than will a plume of pure CO2. A larger plume means that a larger area must be inspected for leakage pathways, such as faults and wells, but faster trapping means a shorter monitoring period. Equally important is that contrasts of viscosity and density between pure CO2 and a CO2 mixture decrease with depth, suggesting that differences in flow behavior and storage capacity are similarly reduced with depth. Whereas flow behavior may impact the whole field, geochemical impacts are more likely to be restricted to the well-bore environment and the near field. Batch experiments conducted in high-pressure, high- temperature autoclaves with rocks immersed in synthetic brine and exposed to supercritical CO2 with and without admixed O2 suggest that O2 may change the geochemistry of subsurface systems in ways that the pure CO2 case does not. Results of the study, therefore, present the CO2 project developer with tradeoffs in capacity, pressure evolution, and monitoring scenarios, with additional costs likely more than offset by reduced capture costs.

Carbon capture and storage: The way ahead

Abstract The paper gives a general introduction and overview of Carbon Capture and Storage (CCS) with an emphasis on the capture of CO 2 and other greenhouse gases from the waste gas streams of power plants and industrial processes. This stage accounts for about 80% of the overall cost of the CCS process so is the area where efficiency and cost improvements will have the greatest future impact. The major drivers for continuing to use fossil fuels for most of this century are first considered and the need to implement CCS as one of many measures to mitigate carbon emissions. Current targets will require a commercial CCS capacity to remove about 10Gte CO 2 pa by 2050. The overall features of CCS processes are described – capture, compression and transport, sub-surface storage – covering the main capture options and the three main types of storage site (deep saline aquifers, depleted oil and gas reservoirs and unmineable coal seams). The current status of large-scale CCS demonstration projects is reviewed....

Selection Separation Method for Hydrogen and Light Hydrocarbons Gases from Waste-Gas Streams of a Petroleum Refinery

The four main processes for hydrogen upgrading in refineries include pressure swing adsorption, selective permeation using polymer membranes, cryogenic separation, and dephlegmation. Each of these processes is based on a different separation principle and, consequently, the process characteristics differ significantly. Selection of an appropriate hydrogen and light gas separation process depends not only on economics but on other project considerations such as process flexibility, reliability, and ease of future expansion. A review of the separation process characteristics and equipment is provided in this article, followed by discussions of other project considerations. General and application-specific selection guidelines are then presented, along with process integrations that take advantage of the complementary characteristics of the four processes. Due to the worldwide depletion of petroleum reservoirs and the growing use of hydrotreating in petroleum refineries, much attention has been given to light hydrocarbons and hydrogen recovery from refinery waste streams.

Biofiltration of a mixture of ethylene, ammonia, n-butanol, and acetone gases

This study describes cleaning of a waste gas stream using bench scale biofilters (BFs) or biotrickling filters (BTFs). The gas stream contained a mixture of acetone, n-butanol, methane, ethylene, and ammonia, and was diverted uniformly to six biofilters and four biotrickling filters. The biofilters were packed with either perlite (BF-P), polyurethane foam (BF-F), or a mixture of compost, wood chips, and straw (BF-C), whereas the biotrickling filters contained either perlite (BTF-P) or polyurethane foam (BTF-F). Experimental results showed that both BFs and BTFs packed with various media were able to achieve complete removal of highly soluble compounds such as acetone, n-butanol, and ammonia of which the dimensionless Henry’s constants (H) are less than 0.01. Methane was not removed due to its extreme insolubility (H>30). However, the ethylene (H≈9) removal efficiencies depended on trickle water flow rates, media surface areas, and ammonia gas levels.

Refinery products/waste optimization using a synthesized pinch technique

An optimal waste minimisation exchange network was designed for the control of effluent, thermal and gaseous wastes generated from process systems. The model used the concept of pinch technique, which was based on a weighted design superstructure that set design products production targets at 25, 50 and 75% against an operating benchmark status, to optimize the product/waste production from a crude distillation unit of an existing operating refinery. The linear programming model that resulted from the analysis of these waste systems and the composite plots were generated for thermal, gaseous and liquid effluent waste streams. The dynamics of waste recovery systems was investigated in relation to the movement of the pinch position as the process conditions are modified or changed based on design targets of 25, 50 and 75% of the products production scheme. The pinch point was located and the high and low waste generating systems were identified and quantified. The analysis of the composite plots and the solution of the linear programming model showed that a design target that minimized the production of gaseous and liquid wastes was obtained when the deviation of the pinch point favoured movement of product curve away from the waste curve. Thus, a new design model that allows the user to predict and minimize waste from a refinery process system was presented.

Synthesis and physicochemical characterization of nanostructured Pd/ceria‐clinoptilolite catalyst used for p‐xylene abatement from waste gas streams at low temperature

AbstractBACKGROUND: The effect of Pd loading, xylene concentration and GHSV on xylene oxidation was tested over Pd/CeO2(30%)‐clinoptilolite nanocatalysts at low temperatures. The catalysts were prepared by acid treatment of clinoptilolite, followed by the incipient wetness method of synthesized ceria and modified clinoptilolite in PdCl2 solution. The synthesized nanocatalysts were characterized by XRD, FESEM, EDAX, TEM, BET, FTIR and TG‐DTG analysis.RESULTS: The XRD patterns confirmed the formation of crystalline ceria with an average crystallite size of 11.8 nm. FESEM images showed nanostructures in cavities of natural zeolite, brought about by ceria incorporation and acid activation. TEM analysis showed high dispersion of Pd with a size distribution between 6.6 and 36.7 nm. The quantitative analysis showed that the specific surface area of Pd(1%)/CeO2(30%)‐clinoptilolite was 77 m2 g−1. The results showed that Pd(1%)/CeO2(30%)‐clinoptilolite is the most appropriate catalyst, with the conversion more than 90% at 275 °C.CONCLUSIONS: Experimental results established effective performance and durability for the catalysts. As a result, clinoptilolite modification and ceria incorporation significantly altered the samples' morphology at nanoscale, improving the structure of composites and distribution of noble metals. A reaction path was suggested based on the adsorption‐migration of species to reveal the mechanism of p‐xylene oxidation over nanocatalysts. © 2012 Society of Chemical Industry

A biofilter integrated with gas membrane separation unit for the treatment of fluctuating styrene loads

Biofiltration for volatile organic compound control in waste gas streams is best operated at steady contaminant loadings. To provide long-term stable operation of a biofilter under adverse contaminant feeding conditions, an integrated bioreactor system with a gas separation membrane module installed after a biofilter was proposed for styrene treatment. Styrene was treated effectively, with average styrene effluent concentrations maintained at less than 50mgm−3 and a total removal efficiency of over 96% achieved when the biofiltration column faced fluctuating loads. The maximum elimination capacity of the integrated bioreactor system was 93.8gm−3h−1, which was higher than that obtained with the biofiltration column alone. The combination of these two processes (microbial and chemical) led to more efficient elimination of styrene and buffering of the fluctuating loads. The factors on gas membrane separation, microbial characteristics in the integrated bioreactor and membrane fouling were also investigated in this study.

Removal of styrene from dilute gaseous waste streams using a trickle‐bed bioreactor: kinetics, mass transfer and modeling of biodegradation process

AbstractBACKGROUND: The removal of styrene from air streams in a co‐current gas‐liquid downflow trickle‐bed bioreactor (TBB) inoculated with Pseudomonas sp. E‐93486 strain was studied experimentally. The experiments were conducted to determine such parameters of the bioprocess as gas and liquid flow rates and specific styrene loading for which maximum elimination capacity was achieved.RESULT: The effect of inlet styrene concentration in gas phase on its degradation was studied in the range from 0.08 to 1.1 g m−3. The recirculation rate of the liquid medium was changed from 0.17 to 0.35 m3 h−1 whereas the gas flow rate was changed in the range from 1.2 to 6 m3 h−1. The treatment of air streams contaminated with styrene in a trickle‐bed bioreactor was described with a mathematical model. The model incorporates mass transfer in both the gas and liquid phases and a biological reaction in biofilm. The rate of the partial stages of the process was determined experimentally. Microbial growth tests in the presence of styrene as the sole carbon and energy source were performed both in batch and continuous cultures. The Haldane model was used to describe Pseudomonas sp. E‐93486 strain growth kinetics on styrene.CONCLUSION: The experiments conducted showed high activity of the examined bacterial strain in the styrene biodegradation process and relatively low sensitivity to inhibition of its growth at higher concentrations of styrene in the solution. The results of the experiments carried out in TBB were compared with the values obtained from a mathematical model. Satisfactory compatibility of the calculated and experimental data was obtained. Copyright © 2012 Society of Chemical Industry

Bed mixing and leachate recycling strategies to overcome pressure drop buildup in the biofiltration of hydrogen sulfide

The effects of leachate recycling and bed mixing on the removal rate of H2S from waste gas stream were investigated. The experimental setup consisted of an epoxy-coated three-section biofilter with an ID of 8cm and effective bed height of 120cm. Bed material consisted of municipal solid waste compost and PVC bits with an overall porosity of 54% and dry bulk density of 0.456gcm−3. Leachate recycling had a positive effect of increasing elimination capacity (EC) up to 21gSm−3 bedh−1 at recycling rates of 75mld−1, but in the bed mixing period EC declined to 8g Sm−3bedh−1. Pressure drop had a range of zero to 18mm H2Om−1 in the course of leachate recycling. Accumulation of sulfur reduced removal efficiency and increased pressure drop up to 110mm H2Om−1 filter during the bed mixing stage.

Effect of surfactant on styrene removal from waste gas streams in biotrickling filters

AbstractBACKGROUND: The performance of two biotrickling filters (BTFs) was evaluated for styrene removal from gas streams at the start‐up period and at a pseudo‐steady‐state under various operating conditions.RESULTS: The BTFs exceeded 99% removal efficiency within 19 days when the average inlet styrene concentration was 250 mg m−3 and gas empty bed retention time (EBCT) was 30.0 s. The effect of a surfactant, Triton X‐100, on styrene removal was examined by comparative experiments in which one biofilter was fed with nutrient solution with the surfactant while the other without the surfactant, and the average organic loading rate of styrene was set at 65.3, 100.9 and 201.7 g styrene m−3 h−1, respectively. Results showed that the corresponding average removal efficiency was 87%, 70% and 50% for the BTF without surfactant, while the average removal efficiency for the BTF with surfactant was 96%, 92% and 82%. Excessive biomass accumulation was observed in the medium when the styrene loading rate was high. However, the biomass density within the BTF medium when the surfactant was added remained stable during the whole period of the operation.CONCLUSION: These results demonstrated that the use of Triton X‐100 can improve the degradation of styrene and control the excessive biomass accumulation. Copyright © 2012 Society of Chemical Industry

Counterions-exchangeable, multifunctional polyelectrolyte fabrics

We demonstrated multifunctional electrospun polyelectrolyte fabrics with switchable superhydrophobicity as well as oleophobicity. To produce this smart fabric, we used a strategy that combines electrospinning to fabricate nanofibrous templates with nanopores and a simple coating of the polyelectrolyte that can exchange counterions with various hydration energies. The ion exchange of polyelectrolyte embedded in nanoporous fibrous webs leads to switchable wetting behavior in water and oil. This electrospun fabric was also utilized as chemical filters for the efficient removal of sulfur dioxide (SO2) from waste gas streams.

Synthesis and Physicochemical Characterization of Nanostructured Pt/CeO2 Catalyst Used for Total Oxidation of Toluene

Nanostructured Pt/CeO2 with different loadings of platinum was successfully synthesized via redox reaction along with wet impregnation method. The catalytic performance of the synthesized nanocatalysts was evaluated for abatement of toluene from waste gas stream. The synthesized nanocatalysts were characterized using XRD, FESEM, TEM, N2 adsorption, FTIR and TPR-H2 techniques. Crystallographic analysis confirmed the formation of CeO2 as crystalline phase with average crystallite size of 10.5 nm. Morphological analysis showed that majority of the synthesized CeO2 particles were less than 100 nm with average particle size of 50.62 nm. TEM analysis illustrated that platinum particles were fairly well dispersed with an average size of 5-15 nm. Specific surface analysis revealed that the synthesized nanocatalysts had large enough surface area for catalytic oxidation of toluene. Temperature programmed reduction profiles indicated that Pt/CeO2 had more reducibility compared to pure ceria. The results of catalytic experiments showed that the synthesized catalysts had the ability to remove 99% of toluene via total oxidation. According to these results, the best loading of Pt on ceria was 0.5 wt% with higher activity compared to pure ceria.

Biofiltration of Hexane Vapor: Experimental and Neural Model Analysis

AbstractBiofiltration is a commonly practiced biological technique to remove volatile compounds from waste gas streams. From an industrial view‐point, biofilter (BF) operation should be flexible to handle temperatures and inlet load (IL) variations. A compost BF was operated at different temperatures (30–45°C) and at various inlet loading rates (ILR; 8–598 g m−3 h−1) under intermittent loading conditions. Complete removal of n‐hexane was observed at 30 and 35°C at ILRs up to 330 g m−3 h−1. Besides, 20–75% of the pollutant was removed at 40°C, corresponding to the different ILs applied to the BF. Increasing the temperature to 45°C decreased the removal efficiency (RE) significantly. A feed forward neural network was used to predict the RE of BF with temperature and ILR as the input variables. The experimental data was divided into training (2/3) and test datasets (1/3). The best structure of neural network was obtained by trial and error on the basis of the least differences between predicted and experimental values, as ascertained from their coefficient of regression (R2) values. The modeling results showed that a multilayer network with the topology 2−10−1 was able to predict BF performance effectively with R2‐value of 0.995 for the test data. The results from this study showed the predicting capability of ANNs which can be considered as an alternative for conventional knowledge‐based models.

Temperature Effect on Volatile Organic Compounds –Polydimethylsiloxane Interactions

og V ) of 13 volatile organic compounds (VOCs) of environmental importance between the gas and liquid stationary phase (polydimethysiloxane) (PDMS) were studied using the gas liquid chromatographic technique (GLC). Temperature was varied from 303.15K to 423.15K to allow transport calculations for different seasons. Four PDMS polymers with average molecular weight ranging from 760 to 13 000 were used as solvents. The results of this work confirm that PDMS is well suited for VOCs scrubbing from waste gas streams. Linear plots of log g V against T 1 were obtained in all cases permitting predictions and interpolations to temperatures not studied here. Also dependable enthalpies and entropies of solute transfer from the mobile phase to the stationary phase can be calculated. The specific retention volumes reported in this work are in agreement with literature for similar systems. Efforts were taken to ensure the best possible accuracy and trace the possible sources of error. A gas liquid chromatographic system which secured a simple retention mechanism and showed reproducible solute retention over a long period of time was devised.

Early opportunities of carbon capture and storage in China

Abstract CCS technology is particularly important to China due to its large and rapidly rising emissions and high dependence on fossil fuel. There is a huge basin scale theoretical CO 2 storage capacity in China; however the CCS deployments will consider firstly those matched source-sink pairs with early opportunities at present. This paper presents the key results of evaluation of early opportunities for the deployment of CCS technologies within China. The proximity analysis suggests that there also are many early opportunities for CCS deployment, such as the promising EOR/EGR opportunities from using high concentration CO 2 sources. The combined benefits of short distance between sources and sinks, the potential hydrocarbon revenues and low CO 2 capture cost make these pairs as promising near-term CCS candidates. These near-term CCS candidates can be deployed at very low cost or even with some revenue. In this paper, several sources-sink pairs in China are analyzed in details, such as, the pairs of high purity CO 2 emission sources and aquifer, co-storage of waste gas stream and depleted gas fields, IGCC and aquifer. These early opportunities will provide China the chance to develop and spread CCS technologies steadily from early stage to commercial stage.