Inlet NH3 Research Articles

CFD analysis of municipal solid waste combustion using detailed chemical kinetic modelling.

Nitrogen oxides (NO x ) emissions from the combustion of municipal solid waste (MSW) in waste-to-energy (WtE) facilities are receiving renewed attention to reduce their output further. While NO x emissions are currently 60% below allowed limits, further reductions will decrease the air pollution control (APC) system burden and reduce consumption of NH3. This work combines the incorporation of the GRI 3.0 mechanism as a detailed chemical kinetic model (DCKM) into a custom three-dimensional (3D) computational fluid dynamics (CFD) model fully to understand the NO x chemistry in the above-bed burnout zones. Specifically, thermal, prompt and fuel NO formation mechanisms were evaluated for the system and a parametric study was utilized to determine the effect of varying fuel nitrogen conversion intermediates between HCN, NH3 and NO directly. Simulation results indicate that the fuel nitrogen mechanism accounts for 92% of the total NO produced in the system with thermal and prompt mechanisms accounting for the remaining 8%. Results also show a 5% variation in final NO concentration between HCN and NH3 inlet conditions, demonstrating that the fuel nitrogen intermediate assumed is not significant. Furthermore, the conversion ratio of fuel nitrogen to NO was 0.33, revealing that the majority of fuel nitrogen forms N2.

Improvement of biodegradation in compact co-current biotrickling filter by high recycle liquid flow rate: Performance and biodegradation kinetics of ammonia removal

As a microbial-environmental-control-type deodorizing system, we have developed a compact biotrickling filter system for small-scale livestock farms. The performance of the compact co-current biotrickling filter operated at high recycle liquid flow rates was systematically examined. In particular, we studied improvements in the nitrification ability of the system due to the resultant enhancement of absorption and dissolution of NH3 and absorption of O2 with the high flow rates of recycle liquid flowing downward co-currently with gas flow. At the empty bed residence time of 50s, almost complete removal of NH3 was obtained with recycle liquid flow rates of 103 and 205Lm−3day−1 for 20 days while the inlet NH3 concentration was increased from 200 to 500ppm. With a recycle liquid flow rate of 411Lm−3day−1 the removal efficiency remained above 95% for 57 days while the inlet NH3 concentration was increased from 200 to 700ppm. The biodegradation kinetics for NH3 removal was successfully analyzed using the Haldane substrate inhibition kinetics. The present data and kinetic analyses showed that the substrate inhibition was suppressed and the biodegradation of ammonia in the compact biotrickling filter could be improved by the high recycle liquid flow rate.

Optimization of Ammonia Absorption Using Acid Spray Wet Scrubbers

<abstract> <bold><sc>Abstract.</sc></bold> Packed-bed wet scrubbers are effective for abatement of ammonia (NH₃) emissions from animal feeding operations (AFOs) but result in high air resistance. Spray scrubbers generally have relatively low air resistance and high NH₃ removal potential. This study aimed to develop a spray scrubber module (SSM) through optimization of the design and operating parameters of spray scrubbing for recovering NH₃ emissions from the exhaust air streams of animal facilities. The design parameters, including nozzle type, scrubber column size and geometry, and number of stages of the spray scrubber module, were optimized. Effects of operating parameters such as acid concentration, superficial air velocity, retention time, and inlet NH₃ concentration were quantified. Superficial air velocity adversely affected scrubber performance significantly due to its direct relationship with air residence time. The inlet NH₃ concentration was inversely proportional to the scrubber efficiency. The SSM was optimized as a hexagonal scrubber column with a diameter of 45.7 cm (18 in.) equipped with three stages of PJ40 spray nozzles, spraying 1% (w/v) H₂SO₄ scrubbing liquid counter-current to the exhaust air stream with superficial gas velocity of 3 to 4 m s^-1, equivalent to air retention times of 0.55 to 0.41 s. The SSM recovered about 91% of the NH₃ at an operating liquid pressure of 0.51 MPa, a superficial air velocity of 4 m s^-1, and an inlet NH₃ concentration of 30 ppm_v when operated with a single stage of spraying. For high inlet NH₃ concentration of 100 and 400 ppm_v, the SSM was able to reduce NH₃ by 86% and 74%, respectively, when operated at a maximum pressure of 0.62 MPa with three stages of spray nozzles and a superficial air velocity of 4 m s^-1. The pressure drop of the spray scrubber was mainly caused by the mist eliminator. The total static pressure drop of the SSM was under 15 Pa when the air velocity ranged from 2 to 4 m s^-1. The results of this study demonstrate that acid spray scrubbers could be a very effective and feasible NH₃ mitigation technology for U.S. animal farms.

A study of the effects of NH3 maldistribution on a urea-selective catalytic reduction system

The maldistribution of urea/NH3 at the selective catalytic reduction inlet and the resulting NH3/NOx ratio variation have been reported to have negative effects on the NOx conversion efficiency and NH3 slip in heavy-duty diesel applications. Maldistribution is caused by incomplete mixing and decomposition of the injected urea water solution within the exhaust flow in the aftertreatment system. How NH3 and the NH3/NOx ratio are distributed at the selective catalytic reduction inlet in an engine aftertreatment system and how the resultant maldistribution affects the system performance and the kinetics are presented in this combined experimental and modeling study. The distribution profiles of the selective catalytic reduction inlet NH3 and NH3/NOx ratio were determined through engine experiments. The NH3 maldistribution effects on the selective catalytic reduction performance and kinetics were quantified by using a multi-channel one-dimensional model that takes into consideration the NH3 maldistribution. It was determined that the NH3 maldistribution is a major factor causing the difference in catalyst performance in the engine exhaust as compared to the laboratory reactor environment, and these results explain specific differences in the model calibrations determined from the laboratory reactor and engine data. Improving the selective catalytic reduction inlet NH3 uniformity can improve the NOx conversion efficiency by up to 7% and reduce NH3 slip by 10–20 ppm. A single-channel one-dimensional selective catalytic reduction model calibrated to the engine data that accounts for the NH3 maldistribution phenomena can be applied for the development of on-board diagnostic and control strategies.

NH3 biofiltration of piggery air

An aboveground pilot-scale biofilter filled with wood chips was tested to treat ammonia emissions from a piggery located in Brittany (France). Two long-term tests (“summer” and “autumn” experiments) were carried out to improve biofilter applications for agriculture. The influence of climatic conditions on biofilter performance was taken into account.During summer 2012, the biofilter was operated for 74 days at different empty bed residence times (EBRTs) from 6 to 15 s. Inlet NH3 concentrations were relatively constant (around 15 mg m−3). Significant NH3 reductions were achieved at EBRT = 12 s (removal efficiencies, RE, ranged between 90 and 100% for loading rates, LR, of around 4 g m−3 h−1). At a lower EBRT (6 s), RE dropped to roughly 30–50%. This was due to the dramatic increase in the loading rate (LR up to 12 g m−3 h−1) but the results showed that the change in atmospheric conditions (temperature and relative humidity) also had a significant influence on biofilter performance. It was evidenced that the use of a humidifier upstream of the biofilter must be taken into account for large-scale biofilter design, but only for specific conditions (the spraying of the biofilter having to be carried out exceptionally).During autumn 2012, the biofilter was operated for 116 days at EBRT = 12 s. RE were around 80% for LR of around 3 g m−3 h−1. In such autumnal atmospheric conditions, a demister system should be installed upstream of the biofilter in order to avoid water accumulation in the bed material.Although biofiltration was suitable for NH3 treatment of piggery air, the need to control accurately the medium moisture content implies that biofilters would not be easily managed by a pig farmer.

Simulation of a new style vertical HVPE system

In this paper, we simulate a new style vertical HVPE reactor by using computational fluid dynamics program FLUENT. In order to find the best parameter on the growth rate of Gallium nitride (GaN), we change the distance between the inlet and the substrate, GaCl and NH3 inlets, and also we add substrate rotation, separately. With the increase of the distance between the substrate and the gas inlet, GaN deposition rate decreases and the uniformity becomes better. The results show that the optimal distance in this new-style vertical hydride vapour phase epitaxy (HVPE) system is 4 cm. Besides, as the distance between the GaCl inlet and the NH3 inlet changes, the uniformity of GaN deposition varies. Our findings indicate that the optimal distance is 3 cm. Furthermore, it is found that substrate rotation also affects the growth rate of GaN.

NH3 pulsing adsorption and SCR reactions over a Cu-CHA SCR catalyst

In passive selective catalytic reduction (SCR) applications, NH3 is generated on an upstream catalyst to reduce NOx on a downstream SCR catalyst. Therefore, there is no continuous input of reductant, and in most cases the NH3 comes to the SCR catalyst as a pulse. In this paper NH3 adsorption profiles on a Cu chabazite (CHA) SCR catalyst were measured as a function of different NH3 pulse parameters, NH3 migration after adsorption was investigated and standard and fast SCR reactions on the catalyst pre-covered with different levels of NH3 were characterized. The data show that when pulsing times are short, but the upstream portion of the catalyst was still far from saturated, the amount of NH3 adsorbed decreased from inlet to outlet. As the quantity of input ammonia increased, the adsorption profiles leveled out in the front as that part of catalyst approached saturation. Also, the NH3 inlet concentration had a significant effect on the NH3 adsorption profile, when the catalyst was far from saturated. For the same amount of input NH3, a high NH3 inlet concentration with shorter pulsing time would result in steeper NH3 adsorption profiles. Catalyst aging and higher temperature reduced the catalyst's ability to adsorb NH3. Ammonia was observed migrating after NH3 was removed from the inflow. There were at least two kinds of adsorbed NH3: weakly adsorbed NH3 and strongly adsorbed NH3. Weakly adsorbed NH3 migrated out of the catalyst channel within several seconds, while strongly adsorbed NH3 did not, at least at 250°C and 300°C. Catalyst aging had little effect on strongly adsorbed NH3, but reduced the catalyst's ability in adsorbing weakly adsorbed NH3 and enhanced weakly adsorbed NH3 migration. The effect of temperature on NH3 migration was as expected; higher temperature enhanced NH3 migration but had less effect on strongly adsorbed NH3. NH3 adsorption profiles were compared with NOx consumption profiles during the fast SCR reaction. NOx consumption profiles were found to be flatter than their corresponding NH3 adsorption profiles due to the effect of NH3 migration after an NH3 pulse. The standard and fast SCR reactions on the SCR catalyst pre-covered with NH3 of similar distribution were compared at 250°C and it was found that there was no significant difference between NO and NOx consumption profiles.

Removal of high concentrations of NH3 by a combined photoreactor and biotrickling filter system

Average emission levels as high as 800 ppmv NH3 have often been found during the anaerobic fermentation process. At these levels, NH3 is regarded as an environmental toxic compound. High concentrations of NH3 gas are difficult to treat in a single treatment process, suggesting that, in terms of economic cost and treatment performance, a coupled system may be a feasible technological alternative. In the coupled TiO2 photocatalytic–biological treatment system evaluated here, the optimal gas retention time for NH3 removal – in terms of removal efficiency and capital cost – was 26 s. High gas temperatures, high NH3 concentrations, and low oxygen contents were unfavorable conditions for NH3 removal by the photoreactor. The coupled system successfully removed concentrated NH3 gas (R % > 97 %) under disrupted and shutdown conditions. The photoreactor component of the system successfully fulfilled its role as a pretreatment process and enhanced the performance of the biotrickling filter at a high inlet NH3 load (2,277 g-N m−3 day−1). Potential ammonia-oxidizing bacteria, including Bacillus cereus, Pseudomonas aeruginosa, and Stenotrophomonas sp., were isolated under the high inlet NH3 load condition. These microbial strains have a potential as biological agents in the removal of high concentrations of NH3 in waste gas or wastewater.

Effect of aeration modes on the characteristics of composting emissions and the NH 3 removal efficiency by using biotrickling filter

A pilot biotrickling filter (BTF) packed with ZX02 fibrous balls as packing material was tested for the treatment of ammonia (NH 3) released from a composting plant of dairy manure. In order to investigate the effects of three compost aeration modes (mode Co-I, Co-II and In-II) on the NH 3 removal efficiency, a field experiment was continuously carried out for more than eight months. The results demonstrated that under the intermittent aeration mode (In-II), the NH 3 removal efficiency reached 99.2 ± 0.1% when the inlet NH 3 concentration was 7.5–32.3 mg m −3 (9.8–42.5 ppmv). The maximum and critical elimination capacity of the biotrickling filter was 22.6 and 4.9 g NH 3 m −3 h −1, respectively. The effluent concentration of NH 3 was lower than 1.0 mg m −3, which meets the first class discharge standards of GB14554-93. When the concentration of free ammonia in the trickling liquid was varied from 0.1 to 0.4 mg L −1, the nitrification yield was between 47.9% and 103.8%. In addition, the optimum liquid tricking velocity (LTV) of the biotrickling filter was 0.5 m 3 m −2 h −1 for low inlet concentrations and 2.2 m 3 m −2 h −1 for high inlet concentrations. Therefore, the use of the biotrickling filter for the compost under the third aeration mode (In-II) yielded an effective optimum NH 3 removal and reduced the nitrogen loss in the compost.

Diversity of the bacterial community in a bioreactor during ammonia gas removal

Polymerase chain reaction analysis in combination with denaturing gradient gel electrophoresis (DGGE) was used to determine changes in the composition of the bacterial community of a bioreactor during ammonia removal. A minimum of 13 bands were observed in the DGGE profile. Phylogenetic analysis revealed that phylum Proteobacteria was predominantly represented in the bacterial community of the bioreactor, followed by Firmicutes, Actinobacteria, and Flavobacteriaceae. However, the occurrence and predominance of specific bacterial species varied with the concentrations of NH 3 introduced into the bioreactor. The complexity of the bacterial species generally decreased with increasing inlet NH 3 concentration. Based on the characteristics of the identified species, there is a potential for nitrification, denitrification, nitrate reduction, nitrite reduction, and ammonia assimilation to occur simultaneously in the bioreactor. The strains identified in this study are potential candidate strains for the purification of waste gases containing high concentrations of NH 3.

Cordierite-like mixed oxide monolith for ammonia oxidation process

The paper deals with modeling of a two-stage catalytic system for ammonia oxidation in an UKL-7 plant, preparation and characterization of cordierite-like honeycomb monoliths (∼230 cpsi) modified with (Mn, Co, Fe, V, Bi)O x oxides as the secondary catalysts. The NO yield for as prepared monoliths was shown to depend not only on the testing temperature, nature and content of the active oxides but also on the cordierite crystallinity degree and on the inlet NH 3 concentration. The best data on NO yield (>80%) at 880–900 °C were obtained with the iron and cobalt based modified monoliths used as the secondary catalysts in the two-stage catalytic system. The data obtained by modeling indicated the possibility to use 8 (instead of 12) gauzes and one layer of as prepared cordierite-like catalysts in the UKL-7 plant to provide the NO yield typical of 12 gauzes.

Ammonium oxidation via nitrite accumulation under limited oxygen concentration in sequencing batch reactors

In this study, the effects of sludge retention time (SRT) on NH4–N oxidation and NOx–N accumulation in the nitritation reactors were studied. The gradually decrease of SRT also caused long reaction time to achieve 99% NH4–N removal. Although the target NH4–N removal was achieved in a short reaction time at 40 days of SRT, decreasing of SRT from 40 to 30, 25, 20 days, increase the reaction time from 168 to 240 and 265h, respectively. The inlet NH4–N was almost oxidized and the concentration of NO2–N accumulated to a high level of 177mg/l, while NO2–N/(NO3–N+NO2–N) ratio was about 0.9 at SRT of 40 days. However, the concentration of NO3–N increased slightly and NO2–N/(NOx–N) ratio dropped to 0.8 when the SRT was lower than 40 days. During the operation in a cycle, free ammonia concentration in the SBR was decreased from 2.8 to 0.7mg/l which is below the lowest concentration causing inhibition of nitrite oxidizing bacteria (NOB). It was assumed that combined dissolved oxygen limitation and NH3–N inhibition on NOB caused NO2–N accumulation under the experimental conditions.

Assessment of the low-temperature EnviNOx® variant for catalytic N2O abatement over steam-activated FeZSM-5

Remarkable progress towards implementation of catalytic technology for N2O mitigation in nitric acid plants has been experienced in recent years. EnviNOx®, one of the commercial processes developed by Uhde, accomplishes the tail-gas abatement of N2O and NOx over a single reactor using iron-containing zeolite catalysts. Two variants of the process are available depending on the tail-gas temperature. This manuscript evaluates the low-temperature abatement process (<700K), where NOx and N2O are selectively reduced by NH3 and CH4, respectively. To this end, activity tests in mixtures with N2O, O2, NO, NH3, and CH4 at different temperatures and partial pressures of reactants were carried out over steam-activated FeZSM-5. Ammonia and nitric oxide strongly inhibit the selective catalytic reduction (SCR) of N2O by CH4, shifting the temperature for N2O conversion over 700K. Controlled ammonia dosing is required for the efficient operation of the low-temperature EnviNOx® variant over the particular iron zeolite used in this study. The optimal inlet NH3 concentration is determined by the NO concentration in the tail-gas and its temperature. In the absence of NO and NH3, the CH4-SCR of N2O over FeZSM-5 is effective above 623K. Still, this process cannot retrofit a number of existing plants with lower tail-gas temperatures.

A Prototype Acid Spray Scrubber for Absorbing Ammonia Emissions from Exhaust Fans of Animal Buildings

Mitigation of ammonia (NH3) emissions from animal production buildings has been a challenge because of the large volume of low NH3 concentration laden air being released. Among emission mitigation technologies for concentrated animal feeding operations, acid spray scrubbers have the greatest potential for adaptation to the existing large animal facilities because of their lower fan airflow reduction, ability to simultaneously remove particulate and gaseous pollutants, and viability for zero or less waste generation by recycling effluents as liquid fertilizer. A multi-stage wet scrubber prototype that can be operated with a maximum of three stages was developed and optimized for reducing NH3 emissions using simulated conditions typically encountered at an animal building exhaust. The parameters optimized for a single-stage wet scrubber include nozzle type, nozzle operating pressure, sulfuric acid concentration, spray coverage, and air retention time. The optimized single-stage wet scrubber settings can remove emissions from 60% ±1% at 5 ppmv inlet NH3 concentration (IAC) to 27% ±2% at 100 ppmv IAC at a normal exhaust superficial air velocity (SAV) of 6.6 m s -1 . A high concentration of droplets inside the contact chamber increased the rate of inter-collision between droplets, which led to high droplet coagulation and decreased surface area for gas-liquid contact. These phenomena were prevented by operating the nozzles in the higher stages co-current to the airflow and by using fewer nozzles in higher stage. The two-stage and three-stage wet scrubbers were therefore optimized by determining the least number of nozzles in each stage that provided the most effective NH3 removal. The optimized two-stage scrubber could remove NH3 emissions from 60% ±0% at 5 ppmv IAC and 35% ±1% at 100 ppmv IAC. The optimized three-stage scrubber could remove emissions from 63% ±3% at 5 ppmv IAC and 36% ±3% at 100 ppmv IAC. Airflow retention time was found to significantly affect NH3 absorption. Reducing the superficial air velocity to 3.3 m s -1 from 6.6 m s -1 , which increased the air retention time from 0.2 s to 0.4 s, improved NH3 removal efficiencies to 98% ±3% at 5 ppmv IAC and 46% ±2% at 100 ppmv IAC for the single-stage scrubber. Similarly, the performance of the two-stage scrubber at a SAV of 3.3 m s -1 improved to 77% ±0% at 20 ppmv IAC and 57% ±1% at 100 ppm IAC. Lastly, the performance of the three-stage scrubber at a SAV of 3.3 m s -1 improved to 70% ±1% at 30 ppmv IAC and 64% ±1% at 100 ppmv IAC. It was observed that the three-stage wet scrubber did not increase the overall wet scrubber performance, as predicted theoretically. Further studies are needed so that the application of these scrubber designs becomes feasible for treating air emissions from animal buildings. The wet scrubber caused an additional backpressure of 27.5 Pa, resulting in about 8% airflow reduction for a fan operating at 12.5 Pa.

AMMONIA ABSORPTION IN A VERTICAL SPRAYER AT LOW AMMONIA PARTIAL PRESSURES

In this article, ammonia (NH3) removal efficiency as affected by stripping factor, air mean retention time (0.8, 1.1,1.7, 2.8, and 8.1 s), and NH3 inlet concentration (5, 15, and 50 ppmv) was evaluated using a sprayer unit called thediffusion-coagulation-separation (DCS) system. The NH3 removal efficiency was calculated from the NH3 concentrationsmeasured from both air and water streams. The DCS system was found to effectively remove 84% of NH3 from the air streamat a stripping factor value of 0.5 or when the retention time of the air was 8.1 s. An empirical equation for NH3 removalefficiency as a function of stripping factor and inlet NH3 concentration was derived.

Control of H2S waste gas emissions with a biological activated carbon filter

AbstractThe removal of high concentrations of H2S from waste gases containing mixtures of H2S and NH3 was studied using the pilot‐scale biofilter. Granular activated carbon (GAC), selected as support material in this study, demonstrated its high adsorption capacity for H2S and good gas distribution. Extensive tests to determine removal characteristics, removal efficiency, and removal capacity of high H2S levels and coexisting NH3 in the system were performed. In seeking the appropriate operating conditions, the response surface methodology (RSM) was employed. H2S removal capacities were evaluated by the inoculated bacteria (biological conversion) and BDST (Bed Depth Service Time) methods (physical adsorption). An average 98% removal efficiency for 0.083–0.167 mg dm−3 of H2S and 0.004–0.021 mg dm−3 of NH3 gases was achieved during the operational period because of rapid physical adsorption by GAC and subsequently an effective biological regeneration of GAC by inoculated Pseudomonas putida CH11 and Arthrobacter oxydans CH8. The results showed that H2S removal efficiency for the system was not affected by inlet NH3 concentrations. In addition, no acidification was observed in the BAC biofilter. High buffer capacity and low moisture demand were also advantages of this system. The maximal inlet loading and critical loading for the system were 18.9 and 7.7 g‐H2S m−3 h−1, respectively. The results of this study could be used as a guide for the further design and operation of industrial‐scale systems. Copyright © 2004 Society of Chemical Industry

Hydrogen sulfide effects on ammonia removal by a biofilter seeded with earthworm casts.

Ammonia (NH3) removal efficencies were evaluated when hydrogen sulfide (H2S) and NH3 in binary mixture gases were supplied to a ceramic biofilter seeded with earthworm (Lumbricus terrestris) casts. The effect of inlet H2S concentration and space velocity (SV) on the removal of NH3 was investigated after the acclimation of the biofilter with NH3 gas. When NH3 was singly supplied to the biofilter, NH3 removal was maintained at almost 100% until inlet NH3 concentration was increased up to 600 microL L(-1) and SV up to 330 h(-1), at which the elimination capacity of NH3 was 148 g N m(-3) h(-1). When H2S was supplied simultaneously, however, the accumulation of toxic sulfide ions showed dual effects on NH3 removal efficiencies. First, no effects were observed at inlet H2S loading below 60 g S m(-3) h(-1); however, inhibition by H2S at higher loading was observed above 60 g S m(-3) h(-1). The point at which loading achieved a maximum of more than 99% NH3 removal efficiency was 139 g N m(-3) h(-1), when inlet H2S concentration was held under 100 microL L(-1), but it dropped to 76 and 30 g N m(-3) h(-1) when the inlet H2S concentration increased to 220 and 460 microL L(-1), respectively. The critical points of inlet H2S loading that guaranteed over 99% NH3 removal were determined as 100, 100, 60, and 40 g S m(-3) h(-1) at inlet NH3 concentrations of 100, 200, 400, and 600 microL L(-1), respectively. Inlet NH3 loading had synergic effects of increasing the inhibition of inlet H2S loading on the NH3 removability of the biofilter.

Biotreatment of Hydrogen Sulfide- and Ammonia-Containing Waste Gases by Fluidized Bed Bioreactor

ABSTRACT Gas mixtures of H2S and NH3 are the focus of this study of research concerning gases generated from animal husbandry and treatments of anaerobic wastewater lagoons. A heterotrophic microflora (a mixture of Pseudomonas putida for H2S and Arthrobacter oxydans for NH3) was immobilized with Ca-alginate and packed into a fluidized bed reactor to simultaneously decompose H2S and NH3. This bioreactor was continuously supplied with H2S and NH3 separately or together at various ratios. The removal efficiency, removal rate, and metabolic product of the bioreactor were studied. The results showed that the efficiency remained above 95% when the inlet H2S concentration was below 30 ppm at 36 L/hr. Furthermore, the apparent maximum removal and the apparent half-saturation constant were 7.0 x 10-8 g-S/cell/day and 76.2 ppm, respectively, in this study. The element sulfur as a main product prevented acidification of the biofilter, which maintained the stability of the operation. As for NH3, the greater than 90% removal rate was achieved as long as the inlet concentration was controlled below 100 ppm at a flow rate of 27 L/hr. In the NH3 inlet, the apparent maximum removal and the apparent half-saturation constant were 1.88 x 10-6 g-N/cell/day and 30.5 ppm, respectively. Kinetic analysis showed that 60 ppm of NH3 significantly suppressed the H2S removal by Pseudomonas putida, but H2S in the range of 5-60 ppm did not affect NH3 removal by Arthrobacter oxydans. Results from bioaerosol analysis in the bioreactor suggest that the co-immobilized cell technique applied for gas removal creates less environmental impact.

Biological Removal of Gaseous Ammonia in Biofilters: Space Travel and Earth-Based Applications

ABSTRACT Gaseous NH3 removal was studied in laboratory-scale biofilters (14-L reactor volume) containing perlite inoculated with a nitrifying enrichment culture. These biofilters received 6 L/min of airflow with inlet NH3 concentrations of 20 or 50 ppm, and removed more than 99.99% of the NH3 for the period of operation (101, 102 days). Comparison between an active reactor and an autoclaved control indicated that NH3 removal resulted from nitrification directly, as well as from enhanced absorption resulting from acidity produced by nitrification. Spatial distribution studies (20 ppm only) after 8 days of operation showed that nearly 95% of the NH3 could be accounted for in the lower 25% of the biofilter matrix, proximate to the port of entry. Periodic analysis of the biofilter material (20 and 50 ppm) showed accumulation of the nitrification product NO3 - early in the operation, but later both NO2 - and NO3 - accumulated. Additionally, the N-mass balance accountability dropped from near 100% early in the experiments to ~95 and 75% for the 20- and 50-ppm biofilters, respectively. A partial contributing factor to this drop in mass balance accountability was the production of NO and N2O, which were detected in the biofilter exhaust.

SCR Performance on a Hydrogen Reformer Furnace

ABSTRACT In late 1993, Air Products and Chemicals, Inc. began operating a new steam-methane reformer at the Tosco Refining Co.’s Avon refinery in Martinez, CA, to provide hydrogen and steam to the refinery under a long-term supply agreement. The hydrogen plant—owned, operated, and maintained by Air Products—includes a selective catalytic reduction (SCR) unit on the reformer-furnace flue gas for environmental control. SCR is a commercially proven process capable of abating emissions of nitrogen oxides (NOx) to extremely low levels; however, documented experience in a refinery setting has been limited. This paper discusses performance of the SCR, primarily during its first two years of operation; it incorporates theory and prior research findings sufficient to understand the relationship between key system variables and SCR performance. Test results demonstrate that NOx, ammonia (NH3) slip, and carbon monoxide (CO) emissions are in compliance with permit limits. NOx removal efficiency is nearly linear with the inlet NH3:NOx molar ratio up to almost 90% NOx conversion, where ammonia slip begins to rise steeply. The stoichiometric reaction ratio of NH3 to NOx is close to the theoretical 1.0. Catalyst life is estimated at four years, in line with published figures for SCR catalysts in clean-gas service.