Horizontal Reactor Research Articles

Unraveling the mechanisms of carbon nanotube growth by chemical vapor deposition

The mechanisms of carbon nanotube (CNT) growth by chemical vapor deposition of acetylene on Fe/SiO2:Al2O3 (zeolite Y) catalyst are unraveled through a combined computational and experimental study. CNTs are synthesized in a horizontal reactor under atmospheric pressure within the temperature range 650 °C–850 °C and characterized by SEM, TEM and Raman spectroscopy. A macroscopic computational fluid dynamics (CFD) model accounting for fluid flow, heat transfer and species transport is developed for the process, incorporating also kinetic expressions for acetylene surface decomposition, acetylene gas-phase reactions, carbon diffusion through the bulk of the catalyst, carbon surface accumulation on the catalyst surface and eventually, CNTs growth. The experimental behavior of the CNTs growth can be accurately described by the proposed macroscopic model. Most importantly, theoretical predictions suggest that there are two distinct temperature regimes for CNTs formation: at the low temperature regime, the process is dominated by the competition between carbon diffusion through the catalyst and carbon impurity layer formation on the catalyst surface, while at higher temperature, the gas-phase reactions of acetylene prevails, releasing byproducts that deposit on the catalyst surface in the form of carbon impurities. Finally, using the developed computational approach, the catalyst lifetime, which is directly affected by these mechanisms, is correlated with the CNTs growth process.

Numerical investigation of heat and mass transfer during hydrogen desorption in a large-scale metal hydride reactor coupled to a phase change material with nano-oxide additives

For the object of reducing heat consumption in hydrogen metal hydride (MH) storage units during the discharging cycle, the nano-PCM (i.e. phase change material containing nano-oxides) strategy is adopted herein for accelerating the release of the latent heat (LH) stocked in the PCM to the MH. The process was assessed in a large-scale horizontal cylindrical reactor equipped with 4 PCM tubes distributed homogenously in the MH-bed. Mass and heat transfer were computationally analyzed in the diverse regions of the MH-nano-PCM system using a 2D numerical model developed with Fluent 15.0 CFD-software. Temporal temperature profiles (average and contours), MH-dehydrogenation efficiency, velocity contours and PCMs solidification rate were established in the presence (5% v/v) and absence of four types of nano-oxides (Al2O3, MgO, SnO2 and SiO2). Remarkable results were obtained. The nano-PCM system participated in the MH-discharging by providing latent heat (LH) and changing its physical phase. The MH was completely discharged within 700 s. Nano-oxides additions improved the solidification rate of the PCM (i.e. accelerating the release of the LH) by more 50%, with a strong dependency on the PCM-tubes position. The PCM-tube above the H2-charging pipe solidifies more quickly than the other tubes, probably to the gravitational effect. The outcomes of this research provide insight into the use of nano-PCMs as a thermal supplier in MH storage systems during the discharging cycle.

Novel system design for high solid lignocellulosic biomass conversion

A novel system (Oregon State University High Solids Reactor; OSU-HSR) was designed and constructed for enzymatic hydrolysis at ultrahigh solids content (40%) by promoting better mixing using low energy consumption in a horizontal reactor with a new impeller design and a controllable feeding unit. System performance was evaluated using separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) methodologies. Using the dilute acid pretreated wheat straw as the substrate in the OSU-HSR system, the highest glucose (219.7 g/L) and ethanol (127.1 g/L) concentrations were achieved with the use of the SHF method while the highest ethanol concentration using SSF method was 134.5 g/L. The SSF method increased the return on investment to 12.21% with an estimated global warming potential of 54.5 g CO2 eq/MJ Ethanol. The OSU-HSR successfully provided effective mixing and different fed-batch schemes, and can be used for efficient biochemical conversion of lignocellulosic biomass into bio-chemicals and biofuels.

A study on torrefaction of spent coffee ground to improve its fuel properties

Excessive use of fossil fuels has contributed significantly to global warming and the impending energy crisis, necessitating the promotion and development of alternative energy sources to achieve green energy or energy neutrality. Converting waste biomass into energy has a significance impact in solid waste management. Spent coffee grounds (SCG) are the primary residue from the coffee industry generated during the coffee brewing process. This study, therefore, aims to improve the fuel properties of SCG via torrefaction and investigates the characteristics of torrefied products. A horizontal tubular reactor, at temperatures ranging from 250 °C to 350 °C at 20 °C intervals, and residence times ranging from 0 to 30 min with 10-min intervals, were utilized for torrefaction. The associated physical and chemical transformations in SCG torrefaction were investigated using proximate and ultimate analysis, gas composition, thermogravimetric and derivative analyses along with Fourier Transform Infrared Spectroscopy (FTIR). The mass and energy yields decreased while the higher heating value increased with the increase in torrefaction temperature. Additionally, the decrease in the oxygen content and increase in the fixed carbon content helped to improve the fuel properties of the SCG. A torrefaction temperature of 290 °C and a residence time of 10 min was found to be the optimal conditions for SCG torrefaction.

Bacterial diversity in different outdoor pilot plant photobioreactor types during production of the microalga Nannochloropsis sp. CCAP211/78

As large-scale outdoor production cannot be done in complete containment, cultures are (more) open for bacteria, which may affect the productivity and stability of the algae production process. We investigated the bacterial diversity in two indoor reactors and four pilot-scale outdoor reactors for the production of Nannochloropsis sp. CCAP211/78 spanning four months of operation from July to October. Illumina sequencing of 16S rRNA gene amplicons demonstrated that a wide variety of bacteria were present in all reactor types, with predominance of Bacteroidetes and Alphaproteobacteria. Bacterial communities were significantly different between all reactor types (except between the horizontal tubular reactor and the vertical tubular reactor) and also between runs in each reactor. Bacteria common to the majority of samples included one member of the Saprospiraceae family and one of the NS11-12_marine group (both Bacteroidetes). Hierarchical clustering analysis revealed two phases during the cultivation period separated by a major shift in bacterial community composition in the horizontal tubular reactor, the vertical tubular reactor and the raceway pond with a strong decrease of the Saprospiraceae and NS11-12_marine group that initially dominated the bacterial communities. Furthermore, we observed a less consistent pattern of bacterial taxa appearing in different reactors and runs, most of which belonging to the classes Deltaproteobacteria and Flavobacteriia. In addition, canonical correspondence analysis showed that the bacterial community composition was significantly correlated with the nitrate concentration. This study contributes to our understanding of bacterial diversity and composition in different types of outdoor reactors exposed to a range of dynamic biotic and abiotic factors.Key points• Reactor types had significantly different bacterial communities except HT and VT• The inoculum source and physiochemical factors together affect bacterial community• The bacterial family Saprospiraceae is positively correlated to microalgal growth

Effects of organic loading rates on high-solids anaerobic digestion of food waste in horizontal flow reactor: Methane production, stability and mechanism

To maximize the methane production efficiency of high-solids anaerobic digestion (HSAD) of food waste (FW), a horizontal flow reactor was operated under mesophilic, semi-continuous condition at organic loading rates (OLRs) ranging from 1.00 to 13.80 kg-VS/(m3 d). The gas production, substrate transformation, and microbial community characteristics of the horizontal flow HSAD reactor were evaluated. The results indicated that the methane yield (0.173–0.516 L/(g d)) fluctuated with the increasing OLR, volumetric methane production rate (0.25–5.69 L/(L d)) increased with increasing OLR, and the volatile solids (VS) reduction rate ranged between 83.30% and 93.05%. The relationship of biogas or methane production with OLR and HRT in the horizontal flow HSAD reactor were characterized with an empirical equation. The concentrations of soluble COD and volatile fatty acid exhibited significant fluctuations, and free ammonia-nitrogen peaked at the OLR of 13.80 kg-VS/(m3 d). Microbial community analysis revealed that the methanogenic metabolic pathway changes along the propelling direction of the horizontal flow HSAD reactor from CH3COOH and H2/CO2 pathways to CH3COOH, H2/CO2, and H2/methyl co-dominant pathways. These results provide theoretical support for stable methane production from FW and deeper insight into horizontal flow HSAD for FW treatment.

Structural and optical properties of CuInSe2

Thin films of polycrystalline CuInSe2 were deposited on Pyrex substrates using a simple system of close spaced vapor transport (CSVT). The used CSVT system is an open horizontal reactor, this does not require vacuum, a gas flow is enough. During the growth phase, the CSVT system is continuously crossed by argon gas. A study on the influence of the source temperature and the deposition duration on the structural properties of the deposited films is re- ported. Analyses by X-ray diffraction have shown that these films are polycrystalline and have a chalcopyrite structure. The preferential orientation of the (112) plane was obtained for the films deposited at 550 ◦C. From the X-ray spectra we calculated the lattice parameters a and c, the ratio c/a was found to be close to 2. The characterization of the de- posited films by an energy dispersion spectrometer (EDS) has shown that their chemical composition is quasistoichiometric with a ratio Cu/In varying from 0.96 to 1.10. Analysis with a scanning electron microscope (SEM) of the de- posited films surface has shown that those slightly rich in indium present a more homogeneous morphology and smaller crystallites sizes than the films slightly rich in copper. The measurement of the photoconductivity of the prepared com- pound has allowed us to determine the value of its gap at room temperature. It was found to be close to 0.99 eV.

An Investigation of Thermal Air Degradation and Pyrolysis of Per- and Polyfluoroalkyl Substances and Aqueous Film-Forming Foams in Soil

In this study, we found that thermal decomposition of per- and polyfluoroalkyl substances (PFAS) in soil was rapid at moderate temperatures of 400–500 °C, regardless of whether the soil was contaminated by a single PFAS compound or a PFAS mixture in aqueous film-forming foams. Substantial degradation (>99%) of PFAS in soil, including perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), short-chain homologues, cationic and zwitterionic precursors, and PFOA and PFOS alternatives, occurred in 30 min at 500 °C in both a sealed reactor in air and a horizontal reactor under a continuous flow of N2. The effect of the initial PFAS level in soil (0.001–10 μmol/g) and soil texture was insignificant, provided a sufficiently high temperature was applied. Furthermore, this study showed, for the first time, that kaolinite dramatically decreased the apparent yield of F from PFAS heated at >300 °C, likely due to the chemisorption of F radicals on kaolinite. This phenomenon was not observed when kaolinite and an inorganic fluoride salt (NaF) were thermally treated. Lastly, various nonpolar thermal degradation products of PFOA and PFOS were reported for the first time. The profile of fluorinated volatiles, particularly perfluoroalkenes, was similar between these two chemicals. The results support a radical-mediated degradation pathway of PFAS.

The application of a novel horizontal frame paddle reactor to remove metallic iron from reduced ilmenite in the Becher process

The leaching process of reduced ilmenite in the traditional vertical tank reactor (VR) is extremely inefficient. This study reports a new horizontal frame paddle reactor (HR) to enhance the oxidative leaching process. The oxidative leaching experiments and the hydraulic model experiments were carried out and compared in the two reactors HR and VR. Under the conditions of the leaching experiment, the oxygen transfer coefficient (kLa) of the HR reached 6 times that of VR. The results of the leaching experiment show that under the optimal conditions, the leaching time is shortened from 6 h for the VR to 3 h for the HR. Under the conditions of 1.5% (w/v) HCl, specific stirring power input per liter 67 W/L, liquid-solid ratio 2 L/kg, oxygen flow rate 0.125 m3 kg−1 h−1, the content of TiO2 and Fe in synthetic rutile obtained from the HR reached 86.1% and 4.6%, respectively.

Numerical Simulation of Gas Phase Reaction for Epitaxial Chemical Vapor Deposition of Silicon Carbide by Methyltrichlorosilane in Horizontal Hot-Wall Reactor.

Methyltrichlorosilane (CH3SiCl3, MTS) has good performance in stoichiometric silicon carbide (SiC) deposition and can be facilitated at relatively lower temperature. Simulations of the chemical vapor deposition in the two-dimensional horizontal hot-wall reactor for epitaxial processes of SiC, which were prepared from MTS-H2 gaseous system, were performed in this work by using the finite element method. The chemistry kinetic model of gas-phase reactions employed in this work was proposed by other researchers. The total gas flow rate, temperature, and ratio of MTS/H2 were the main process parameters in this work, and their effects on consumption rate of MTS, molar fraction of intermediate species and C/Si ratio inside the hot reaction chamber were analyzed in detail. The phenomena of our simulations are interesting. Both low total gas flow rate and high substrate temperature have obvious effectiveness on increasing the consumption rate of MTS. For all cases, the highest three C contained intermediates are CH4, C2H4 and C2H2, respectively, while the highest three Si/Cl contained intermediates are SiCl2, SiCl4 and HCl, respectively. Furthermore, low total gas flow results in a uniform C/Si ratio at different temperatures, and reducing the ratio of MTS/H2 is an interesting way to raise the C/Si ratio in the reactor.

Single-Walled Carbon Nanotube Synthesis Yield Variation in a Horizontal Chemical Vapor Deposition Reactor.

The controlled synthesis of single-walled carbon nanotubes (SWNTs) is essential for their industrial application. This study investigates the synthesis yield of SWNTs, which depends on the positions of the samples on a horizontal chemical vapor deposition (CVD) system. Methane and Fe thin films were used as the feedstock and catalyst for SWNTs synthesis, respectively. A high-resolution scanning electron microscope was used to examine the synthesis yield variation of the SWNTs along the axial distance of the reactor. The morphology and crystallinity of the fabricated SWNTs were evaluated by atomic force microscopy and Raman spectroscopy, respectively. We observed that the highest synthesis yield of the SWNTs was obtained in the rear region of the horizontal reactor, and not the central region. These results can be applied to the synthesis of various low-dimensional nanomaterials, such as semiconducting nanowires and transition metal dichalcogenides, especially when a horizontal CVD chamber is used.

Experimental study of nitrogen conversion during char combustion under a pressurized O2/H2O atmosphere

Pressurized O2/H2O combustion is a promising oxy-fuel technology for reducing CO2 emissions while improving the overall efficiency of power plants. However, this process is complex, and the associated char-N conversion are not well understood. In the present work, a pressurized horizontal furnace reactor was used to investigate the effects of different factors on the migration and transformation of char-N. Flue gas analysis and X-ray photoelectron spectroscopy were employed to assess the effects of pressure (over the range of 0.1–1.3 MPa), steam concentration (0%–60%) and residence time (60–240 s) on NO emissions and the transformation of char-N. Pressure was found to affect NO emissions and the lowest relative migration of char-N to NO was at 0.4 MPa. With increases in pressure, the proportions of N-5 and N-X groups increased and decreased, respectively·H2O promoted the migration of char-N to NO and the formation of N-X functional groups. As the reaction time prolonged, the proportion of N-5 groups decreased in the early stage of the reaction, that of N-X groups increased in the late stage and N-6 and N-Q groups remained stable.

Study of Ga2O3 deposition by MOCVD

Growth of Ga2O3 by metalorganic chemical vapour deposition in horizontal flow reactor from trimethylgallium (TMG) and oxygen is studied in a wide temperature range. The growth rate is directly proportional to TMG flow, weakly affected by O2 flow and non-monotonically depends on temperature. Growth rate over 3 μm/h is demonstrated, indicating that TMG can be used for growth of β-Ga2O3 thick layers for device applications.

Growth of hafnium dioxide thin films via metal-organic chemical vapor deposition

Metal-organic chemical vapour deposition (MOCVD) is a key technique for depositing thin solid film materials for use in important technological applications. To obtain thin films of the desired standard, it is essential to design volatile, reactive and thermally stable precursors. A metal-organic precursor consisting of Hf with excellent vaporization characteristics and low decomposition temperature has been reported. Hafnium dioxide thin films on a Mo substrate were obtained via thermal MOCVD using Hafnium(IV) acetylacetonate(Hf(acac)4) in a horizontal cold-wall reactor. The Hf(acac)4 precursor was synthesized from HfCl4 and Hthd in methanol. Hf(acac)4 was characterized using elemental analysis and infrared spectroscopy. The thermal decomposition properties were studied using thermogravimetric analysis under a nitrogen atmosphere. The results showed that Hf(acac)4 was completely volatised at 245 °C. The thin films products were investigated using x-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The results from these measurements revealed that the main crystalline phase was the monoclinic phase, the surface consists of hafnium and oxygen and the morphology was densely packed and composed of visible grains.

Biomass Torrefaction Process, Product Properties, Reactor Types, and Moving Bed Reactor Design Concepts

Torrefaction, a thermal pretreatment process, is gaining attention as it improves the physical properties and chemical composition of biomass for recycling. During torrefaction, biomass is heated slowly in an inert or oxygen-deficit environment to a maximum temperature of 300°C. The torrefaction process creates a solid uniform product with lower moisture and higher energy content than the raw biomass. During torrefaction, moisture and some volatile organic compounds volatilize from the biomass. Depending on stoichiometry and other conditions, non-condensable gas species, including CO and CO2, are formed. The specific objectives of this research are to: 1) understand the impact of torrefaction on product quality in terms of the physical properties, chemical composition, and storage behavior of the biomass; 2) discuss the various reactors used for biomass torrefaction; and 3) develop a model for designing a moving bed torrefier, considering fundamental heat and mass transfer calculations. Torrefaction improves the physical properties, chemical composition, and energy and storage properties of biomass. Torrefaction of biomass at 300°C increases the energy content by about 30% as compared to the raw biomass. For example, when torrefied, the calorific value of the biomass increases from about 18–19 MJ/kg to about 20–24 MJ/kg. The torrefied material has a moisture content of about 1–3% wet basis (w.b.). The loss of the hydroxyl group during torrefaction makes the biomass hydrophobic. The brittle nature of the torrefied biomass makes it easier to grind. The devolatilization and carbonization reactions change the proximate and ultimate composition. The carbon content increases, whereas the hydrogen, oxygen, and nitrogen content of the biomass decreases. Despite its superior properties, the commercialization of torrefaction technology is slow due to challenges associated with reactor design and final product quality. The different types of reactors that are typically used for biomass torrefaction are the fixed bed, rotary drum, microwave, fluidized bed, and horizontal and vertical moving bed. The moving bed reactor has gained popularity among the different torrefaction reactor designs as it is easy to operate and scale. In addition, it helps produce a uniform torrefied product. In this paper, different moving bed torrefaction and gas recycle concepts are conceptualized to assess the features, advantages, and disadvantages of various design and operating concepts. These designs include example concepts for: 1) vertical and horizontal torrefaction reactors; 2) recycle of all or a portion of the torrefier off-gas; 3) counter and co-flowing gas and biomass in the torrefier; 4) controls for the system temperatures, pressures, flow rates, and gas compositions; and 5) the ability to sample the biomass feed, torrefied product, and gas streams for analysis as needed to investigate the thermal decomposition, physical behavior, and operational performance of the torrefaction system. The article also briefly describes the solid feed system, gas supply and recycle system, solid product management, torrefier gas monitoring, control system, and fugitive dust emissions control. The model presented in this paper includes a set of equations for basic calculations to configure the torrefaction reactor dimensions, such as diameter and height of the moving bed torrefier for different capacities based on target and calculated solids and gas velocities, residence times, and temperatures.

The influence of the type and size of the reactor and the influence of the heating interruption during curing on the solid composite propellant properties

AbstractThe solid composite propellant is a viscoelastic material that retains the treatment received during its all‐useful life. As a result, its manufacturing conditions induce differences in its final mechanical properties. The present study aims to evaluate the influence of the type and size of the reactor and the effects of the heating interruption during curing on the final mechanical properties of the propellant. Thus, four production processes with identical propellant formulations were performed in four different reactors. One of them was vertical, while the others were horizontal reactors. The heating interruption during curing was performed in 10 samples, at different moments of the curing process and with different duration. The study determines that vertical reactors tend to produce propellants less rigid than those produced in the horizontal type. In addition, the bigger the reactor size, the less rigid the propellant becomes. Finally, the heating interruptions at the beginning of the curing process tend to be insignificant. However, when they occur in an advanced stage of the curing process, they tend to hinder the curing progress, being more significant for interruptions of medium duration.

Enhanced Hydrogen Production from Waste Tires via CO <sub>2</sub>-Assisted Gasification by Using Artificial Neural Network and Thermogravimetric Analyses: Modelling and Product Analysis

This study presents the waste tire gasification in CO2 atmosphere aiming to produce higher H2 production. Therefore; the waste tire was gasified in horizontal tube reactor under different ranges of reaction temperature, heating rate, and residence time. Maximum H2 and gas yields of 46.28 mol % and 72.43 wt. % were obtained at higher temperature of 900 ℃, lower heating rate of 10 ℃/min, and lower residence time of 20 min. Tar and char products were decreased considerably from 15.34 to 4.24 wt. % and 35.23 to 23.25 wt. %, respectively. While, LHV and H2/CO molar ratio were ranged between 9.80-11.07 MJ/Nm3 and 1.41 to 2.18, respectively. Artificial neural network (ANN) model provided a strong relationship .i.e. the estimated regression coefficient (R2) values were obtained as; 0.90, 0.94, 0.93, and 0.96 for H2, CO, CO2, and CH4 respectively. The gasification was also carried out in thermogravimetric analyzer (TGA) under different heating rates hence; showed three different degradation stages. Kinetic parameters; activation energy (Ea), and R2 were estimated using Kissinger–Akahira–Sunose (KAS) model which were found to be 38.99 kJ/mol and 1.0 for stage 1, 63.01 kJ/mol and 0.94 for stage 2, and 84.73 kJ/mol and 0.91 for stage 3.

Application of O3 and O3 /H2O2 for post-treatment of horizontal-flow anaerobic immobilized biomass (HAIB) effluent, treating hospital wastewater.

Introduction: In recent years, the "emerging pollutants" in urban, industrial, and surface water bodies have called the attention worldwide. In many cases, these substances correspond to pollutants that have not been yet regulated by the environmental authorities. Hospitals are considered the main source of these contaminants as a result of different activities. However, there is no consensus about the appropriate treatments for removing this kind of pollutants in the wastewaters; independent conventional biological processes do not reach the desirable values of discharge limits. Advanced oxidation processes (AOP) are known as an appropriate technology, not only to improve the biodegradability of recalcitrant compounds, but also to contribute to the removal of certain substances that are difficult to treat during the biological process. 
 Objective: Thus, this study evaluated the application of O3z and O3 /H2O2 to the effluent of an anaerobic horizontal flow reactor and immobilized biomass (HAIB).
 Methodology: The oxidizers were applied in a lab-scale batch borosilicate glass reactor. The reaction time was 60 min and samples were taken at intervals of 15 min. Parameters such as absorbance at UV254, biodegradability ratio expressed as COD/BOD5, and color as VIS436 were measured. All samples were analyzed in duplicate.
 Results. The results showed that the application of Ozone and O3/H2O2 results in an increase in the biodegradability of 25% and 67% respectively. Concerning color, an efficiency of 85 % for Ozone and 100 % for O3 /H2O2 was observed. Besides, the AOPs applied also showed their effectiveness in removing aromatic organics, removing 40 to 50% of UV254.
 Conclusions: Finally, it is important to mention that the application of advanced oxidation processes as a post-treatment of anaerobic effluents increases biodegradability mainly due to the transformation suffered by recalcitrant compounds.

Reevaluating the Cr Evaporation Characteristics of Ce/Co Coatings for Interconnect Applications

Solid oxide fuel cell (SOFC) is a high-temperature energy conversion device that directly converts the chemical energy of the fuel into electrical energy via electrochemical reactions with a very high efficiency. Corrosion of the interconnects, which leads to high degradation rates, is one of the key issues impeding the commercial success of SOFC. Interconnects are used to provide electrical connection between the individual cells which are stacked together to deliver high power output. Recent developments in materials and manufacturing techniques have significantly reduced the operating temperatures, allowing the use of metallic interconnects. Chromia forming ferritic stainless steels (FSS) are preferred over the other materials owing to a coefficient of thermal expansion (CTE) similar to that of ceramic components, high oxidation resistance, good thermal conductivity, and adequate electrical conductivity of Cr2O3 scale at high temperatures. Nonetheless, the use of FSS as interconnect materials poses some significant challenges.During the operation, the chromia scale grows continuously with time, which in turn increases the resistance across the cell. Moreover, chromia reacts with oxygen in the presence of water vapor to form volatile Cr(VI) species such as CrO2(OH)2. These volatile Cr(VI) species react and get deposited at the triple-phase boundaries hindering the oxygen electrochemical reaction on the cathode, leading to cell degradation, also known as chromium poisoning. Despite the various improvements to the steel composition, chromium evaporation is too high for the long-term operation of SOFC. Applying coatings in a widespread solution to suppress chromium evaporation.Spinel structure-based coatings are considered promising owing to good adhesion and are effective barriers to volatile Cr species and oxygen. (Co,Mn)3O4 spinel oxides deposited using various techniques are widely reported in the literature and are known to reduce Cr evaporation and oxide scale growth. Metallic coatings deposited using physical vapor deposition (PVD) are easier and cheaper in terms of manufacturing and eliminate the need for extra heat treatment step for coating densification used in electrophoretic deposition, dip-coating, and screen printing.PVD CeCo coated steels were reported to reduce the chromium evaporation by about 10 times compared to the uncoated on Sanergy HT, Crofer 22H, AISI 441. Nevertheless, the coated coupons investigated had the coating on the faces, but the edges were uncoated. The uncoated edges contribute to higher chromium evaporation than if the edges were coated. Thus, the reported chromium evaporation of the coated coupons is higher than the real chromium evaporation.To understand the influence of the uncoated edges on the measured chromium evaporation, uncoated coupons and two sets of coated coupons, (1) coated coupons with coated edges and (2) coated coupons with uncoated edges were used in the study. The exposures were conducted in horizontal quartz tube reactors at 800 oC for 500 hours in air humidified with 3 % H2O. The airflow is set at 6 lit/min to achieve a flowrate independent regime in the reactor. To quantify chromium evaporation, Na2CO3 coated denuders were used to capture Cr(VI) species, which were replaced at regular intervals.Although the edges made up to only 4% of the total area, the contribution to chromium evaporation from the edges is significant. The chromium evaporation of the coupons with coated edges is about 50 times lower than the chromium evaporation of the uncoated coupons.

Effect of slow pyrolysis conditions on biocarbon yield and properties: Characterization of the volatiles

Slow pyrolysis of spruce and birch was performed at various heating programs and conditions in a horizontal quartz tube reactor heated by an electric furnace. The effects of feedstock and carbonization conditions on the yield of biocarbon, liquid and gaseous products were studied. The thermal properties, volatile matter (VM) content and the evolution profiles of volatiles from the biocarbons were characterized by thermogravimetry/mass spectrometry. The composition of volatiles was analyzed in detail by pyrolysis–gas chromatography/mass spectrometry. Increased char yield was observed when staged pyrolysis program, low purging flow rate or covered sample holder were applied. Spruce produced more charcoal than birch due to the higher lignin content of softwood. The amount and the evolution profiles of the main gaseous products were similar from spruce and birch biocarbons prepared under the same conditions. The relative amount of aromatic and polyaromatic compounds in VM drastically decreased with increasing carbonization temperature.