Incondensable Gas Research Articles

Enhanced microwave assisted pyrolysis of waste rice straw through lipid extraction with supercritical carbon dioxide.

A combination of supercritical carbon dioxide (scCO2) extraction and microwave-assisted pyrolysis (MAP) have been investigated for the valorisation of waste rice straw. ScCO2 extraction of rice straw led to a 0.7% dry weight yield of lipophilic molecules, at elevated temperatures of 65 °C and pressures of 400 bar. Lipid compositions (fatty acids, fatty alcohol, fatty aldehydes, steroid ketones, phytosterols, n-alkanes and wax esters) of the waxes obtained by scCO2 were comparable to those obtained Soxhlet extraction using the potentially toxic solvent n-hexane. ScCO2 extraction positively influenced the pyrolysis heating rate, with a rate of 420 K min-1 for particles of 500-2000 μm, compared to 240 K min-1 for the same particle size of untreated straw. Particle size significantly affected cellulose decomposition and the distribution of pyrolysis products (gaseous, liquid and char), highlighting the importance of selecting an adequate physical pre-treatment. TG and DTG of the original rice straw and resulting biochar produced indicated that cellulose was completely decomposed during the MAP. While a rapid pressure change occurred at ∼120 °C (size > 2000 μm) and ∼130 °C (size 500-2000 μm) during MAP and was associated with the production of incondensable gas during cellulose decomposition, this takes place at significantly lower temperatures than those observed with conventional pyrolysis, 320 °C. Wax removal by scCO2 influences the dielectric properties of the straw, enhancing microwave absorption with rapid heating rates and elevated final pyrolysis temperatures, illustrating the benefits of combining these sustainable technologies within a holistic rice straw biorefinery.

CFD analysis of water vapor condensation in large containments: Numerical model, verification and validation

In the event of a loss of coolant accident (LOCA) in a Pressurized Water Reactor (PWR), large quantities of water vapor and hydrogen might be released into the containment building. Increasing pressure and the risk of hydrogen deflagration can threaten the containment integrity. Water vapor condensation on cold containment structures modifies the pressure load on the containment structures. On the one hand, the total pressure reduces due to the decrease of the water vapor content of the containment atmosphere. On the other hand, the concentration of hydrogen increases, which can reach locally the threshold of deflagration or detonation. A Computational Fluid Dynamics (CFD) model is developed and tested in order to predict transients of the pressure and the concentrations of gaseous species in reactor containments after a LOCA. Since the free volume of the containment of typical French PWRs is between 50,000 m3 and 80,000 m3, the CFD model requires significant simplifications.The physical model and its simplifications as well the implementation in the CEA OpenSource CFD code TrioCFD are described. Model tests are presented in two steps. In a first step, verification tests are discussed to show that the condensation model is implemented correctly in the CFD code. In a second step, the model is validated against experimental data of the International Standard Problem ISP47. In this benchmark, steady state conditions between vapor injection and condensation were reached experimentally in the MISTRA test containment of the CEA. In phase A of the benchmark, an equilibrium was achieved between water vapor injection and water vapor condensation on temperature controlled cold walls. One incondensable gas, namely air, was present in the test vessel. In phase B, a second incondensable gas was added to the containment atmosphere, namely helium. Both steady state situations were analyzed with the CFD model. The calculations represent well the experiment when the predominant condensation paths are modelled. It is shown that the pressure in the containment vessel as well as the mean mass fractions of water vapor and air, as well as of helium in phase B, are calculated in accordance to the experiment. The temperature in the containment is overestimated. Measured vertical profiles of the species concentrations are reproduced correctly.

Techno economic analysis of a micro Gas-to-Liquid unit for associated natural gas conversion

Flared and vented natural gas in remote regions of the world contribute ¿1% of the total CO2 emissions. High investment costs to build facilities to treat this gas and labor costs to operate the infrastructure are deterrents to addressing this environmental burden. Here we report a techno-economic analysis of a commercial mobile manufacturing plant that processes 2400 m3 d-1 of methane via a tandem short contact time catalytic partial oxidation (CPOX) and a single-pass Fischer–Tropsch fluidized bed to produce 7 bbl d-1. Starting from methane and air, a thermodynamic analysis identified the optimized operating conditions considering both carbon yield, CO/H2 ratio and adiabatic conditions. We studied the flammability limits of the mixture at operating pressures and temperatures. The economic analysis itemizes costs for all equipment rather than applying scale-up power law or factors. The greatest contributors to direct costs are the compressors and the CPOX reactor. Operating CPOX at 2.0 MPa reduces reactor volumes but to achieve 90% conversion and selectivity requires operating this unit above 900 °C. Avoiding syngas compression and upstream syngas conditioning reduces capital costs. The capital cost (CAPEX) reaches 570 000 USD when the whole process operates at 2.0 MPa. Considering numbering-up, the price of the 100th unit approaches 360 000 USD thus the MRU increases profitability. We demonstrate how thermodynamics constrains methane conversion and syngas selectivity. A large part of achieving low CAPEX is operating a single pass process, building multiple units, and replacing the methane to heat the treater at the oil tank battery with the incondensable gas leaving the three phases separator downstream the Fischer–Tropsch reactor.

Persistent reduction of boiling incipience of ethanol on biphilic porous textured surfaces

Boiling of highly wetting fluids is of great interest to thermal management of high-powered electronic devices, enhancement of which conventionally relies on functional modifications of surface shape and structure so as to promote bubble generation and growth. In this paper we attempt to combine the approach of porous texturing with a novel technique of surface wettability engineering to enhance saturated pool boiling of ethanol. Thin layers of microporous and nanoporous surface topographies were chemically deposited on an aluminum substrate by anodization in phosphoric acid and sulfuric acid, respectively. Boiling on the textured surfaces recorded over-twofold increases in terms of the heat transfer coefficient compared with that on a plain smooth surface, which can be attributed to a proliferation of active nucleation sites. The boiling incipience point on both porous surfaces, however, exhibited an interesting dependence on the initial wetting state of the surface. With the application of amphiphobic coatings of fluoropolymer modified with halloysite nanotubes, we managed to engender a biphilic (i.e., spatially alternating hydrophobicity and hydrophilicity) pattern on the porous-textured surfaces. The repeat control experiments on the hybrid surfaces showed an equally efficient mode of nucleate boiling, whose inception, by contrast, seemed to occur at consistently low superheats. The remarkable reduction (by more than 80%) of the minimum superheat at the boiling onset hints at an alternative nanobubble-related mechanism for heterogeneous bubble nucleation, which is notably less affected by incondensable gas, to the classic vapor-trapping-cavity model.

Effects of Oxygen and Steam Equivalence Ratios on Updraft Gasification of Biomass

Several experimental datasets available on the gasification of different lignocellulosic feedstocks were used to correlate the flow of gasifying agents with the performance of updraft gasification in an autothermic 200 kWth pilot plant. The feedstocks used included eucalyptus wood chips, torrefied eucalyptus and spruce chips, lignin rich residues from biorefined straw and reed, shells of almond and hazelnut, which were gasified in flows of air, air and steam, oxygen, oxygen and steam. Thermal profiles inside the gasifier and gas quality in terms of incondensable gas and tar content were recorded and used to calculate the energy efficiency of converting solid feedstock into gaseous and liquid carriers. Common behaviors and parametric functionalities were identified to better understand the process and the most efficient tools to achieve the desired products. In analyzing data, the ratio steam to biomass was reported in terms of the equivalence ratio, ER(H2O) i.e., the fraction of the stoichiometric quantity required to convert the feedstock into H2 and CO2. The use of steam was useful to stabilize the process and to tune the H2/CO ratio in the syngas which reached the value of 2.08 in the case of oxy-steam gasification of lignin rich residues at ER(H2O) of 0.25. Larger use of steam depressed the process by lowering the average temperature of the bed, which instead increased steadily with ER(O2). The production of tar depends on the biomass type and a substantial reduction can be achieved with the torrefaction pretreatment. The same effect was observed increasing the residence time of the syngas in the reactor, typically achieved using oxygen instead of air as main gasification flow or reducing the ER(H2O). Oxy-steam gasification of torrefied wood led to the best results in terms of cold gas efficiency and low heating value when carried out in the ranger 0.23–0.27 of both the ERs.

Alternative liquid fuel from pyrolysis of polyethylene wax

Polyethylene wax was investigated its possibility to be liquid fuel using non-catalytic pyrolysis process at pyrolysis temperature of 400, 450 and 500 °C. The results showed that at 450 °C pyrolysis temperature, the highest liquid product yield was 78.24 and the left part was the incondensable gas and a solid fuel. The results from the elemental analysis showed the products obtained from pyrolysis had similar components for all conditions. The carbon, hydrogen, nitrogen and oxygen contents were in the range of 76.49–86.38%, 12.99–14.77%, 4.67–6.38%, and 0.46–2.09%, respectively. The results of the chemical structure analysis by GC–MS showed that the increasing pyrolysis temperature resulted in the mainly increasing of the straight-chain paraffin but instead reducing the structure of the double bonds. The results from the fuel property analysis indicated that the specific gravity, viscosity, and heating value of pyrolysis oil were as 0.83, 2.17 cSt, and 10,939 cal/g respectively, that is consistent with the conventional diesel standards. However, the flashpoint still needs to be improved continuously.

The hydrothermal system of Bagni San Filippo (Italy): fluids circulation and CO2 degassing

Bagni San Filippo area is characterized by the discharge of thermal waters and deeply produced CO2-rich gases both from vents and soil diffuse degassing. The thermal waters are the results of the mixing between meteoric waters and hot fluids deriving from the condensation, at depth, of vapours uprising from a deep hydrothermal reservoir. This process gives rise to a relatively shallow thermal system at temperature close to 50°C, characterized by SO4-rich and Cl-poor waters and elevated PCO2 (~7 bar). Most of the incondensable gas of deep originated vapour is released as a free gas phase forming cold gas vents and localized spots of anomalous CO2 diffuse degassing. The location and the shape of these degassing zones are strongly controlled by the main tectonic structures of the area. Through detailed soil diffuse degassing surveys and hydrogeochemical modelling, we estimate at 226-326 t d-1 and at 965 t d-1 the deep CO2 emission and the amount of condensates discharged by the thermal springs, respectively. The thermal energy associated to the process results at ~ 29 MW, most of which (~ 25 MW) is associated with condensation occurring at depths greater than groundwater circulation.

Steam reheater with helical tube bundle for wet steam turbine

Since steam heat exchangers, used at steam cycle of Russian nuclear power stations, were designed while the knowledge about the separation and the heat exchange processes was limited, deviations between its empirical and theoretical characteristics occur. This limitation also determined application of heating pipes with simple straight shape rather than curved. This study explores a steam heat exchanger with helical heating pipes. It was shown that the model may work stably within the range of parameters, simulating work conditions of the moisture separator and steam reheater at Leningrad nuclear power plant. The experiment included processing of pure water steam as well as mixture of steam and nitrogen. It was obtained a relationship between empirical the heat transfer coefficient and the steam mass flow rate. It was noted that presence of incondensable gas does not affect significantly the heat transfer from the coils, processing high pressure steam.

Flow and mixing dynamics of phase-transforming multicomponent fluids

Despite the importance of phase-transforming, multicomponent fluids in medical diagnostics, atmospheric flows, or supercavitating vehicles, our understanding of their flow and mixing dynamics is very limited. Here, we investigate two-component flows, where one of the components is an incondensable gas and the other one is a fluid that undergoes liquid-vapor phase transformations accompanied by changes in its miscibility with the gas. We derived a continuum model from a Gibbs free energy that includes gradients of the fluid density and gas concentration, leading to a generalization of the classical equations of multiphase flow hydrodynamics. High-fidelity numerical simulations of the model show a very complex interplay between flow, mixing, and phase transformations. The model predicts quantitatively the saturation vapor pressure of water for a given mixture of air and water vapor at different temperatures. When applied to the problem of collapse of cavitation bubbles, the model allows us to study the role of gas dissolved in the liquid phase in the dynamics of the collapsing bubble. Our findings on the collapse of multicomponent bubbles have a strong bearing on the multiple applications of cavitation bubbles. The proposed model opens entirely different ways to study phase-transforming multicomponent fluids.

Effect of Channel Geometry and Properties of a Vapor–Gas Mixture on Volume Condensation in a Flow through a Nozzle

A method of direct numerical solution of the kinetic equation for the droplet size distribution function was used for the numerical investigation of volume condensation in a supersonic vapor–gas flow. Distributions of temperature for the gas phase and droplets, degree of supersaturation, pressure, fraction of droplets by weight, the number of droplets per unit mass, and of the nucleation rate along the channel were determined. The influence of nozzle geometry, mixture composition, and temperature dependence of the mixture properties on the investigated process was evaluated. It has been found that the nozzle divergence angle determines the vapor–gas mixture expansion rate: an increase in the divergence angle enhances the temperature decrease rate and the supersaturation degree raise rate. With an increase or decrease in the partial pressure of incondensable gas, the droplet temperature approaches the gas phase temperature or the saturation temperature at the partial gas pressure, respectively. A considerable effect of the temperature dependence of the liquid surface tension and properties on gas phase parameters and the integral characteristics of condensation aerosol was revealed. However, the difference in results obtained with or without considering the temperature dependence of evaporation heat is negligible. The predictions are compared with experimental data of other investigations for two mixtures: a mixture of heavy water vapor with nitrogen (incondensable gas) or n-nonane vapor with nitrogen. The predictions agree quite well qualitatively and quantitatively with the experiment. The comparison of the predictions with numerical results from other publications obtained using the method of moments demonstrates the usefulness of the direct numerical solution method and the method of moments in a wide range of input data.

Pyrolysis of Lantana camara and Mimosa pigra: Influences of temperature, other process parameters and incondensable gas evolution on char yield and higher heating value

Pyrolysis of invasive non-indigenous plants, Lantana camara (LC) and Mimosa pigra (MP) was conducted at milligram-scale for optimisation of temperature, heating rate and hold time on char yield and higher heating value (HHV). The impact of scaling-up to gram-scale was also studied, with chromatography used to correlate gas composition with HHV evolution. Statistically significant effects of temperature on char yield and HHV were obtained, while heating rate and hold time effects were insignificant. Milligram-scale maximised HHVs were 30.03MJkg−1 (525°C) and 31.01MJkg−1 (580°C) for LC and MP, respectively. Higher char yields and HHVs for MP were attributed to increased lignin content. Scaling-up promoted secondary char formation thereby increasing HHVs, 30.82MJkg−1 for LC and 31.61MJkg−1 for MP. Incondensable gas analysis showed that temperature increase beyond preferred values caused dehydrogenation that decreased HHV. Similarly, CO evolution profile explained differences in optimal HHV temperatures.

Early Onset of Nucleate Boiling on Gas-covered Biphilic Surfaces

For phase-change cooling schemes for electronics, quick activation of nucleate boiling helps safeguard the electronics components from thermal shocks associated with undesired surface superheating at boiling incipience, which is of great importance to the long-term system stability and reliability. Previous experimental studies show that bubble nucleation can occur surprisingly early on mixed-wettability surfaces. In this paper, we report unambiguous evidence that such unusual bubble generation at extremely low temperatures—even below the boiling point—is induced by a significant presence of incondensable gas retained by the hydrophobic surface, which exhibits exceptional stability even surviving extensive boiling deaeration. By means of high-speed imaging, it is revealed that the consequently gassy boiling leads to unique bubble behaviour that stands in sharp contrast with that of pure vapour bubbles. Such findings agree qualitatively well with numerical simulations based on a diffuse-interface method. Moreover, the simulations further demonstrate strong thermocapillary flows accompanying growing bubbles with considerable gas contents, which is associated with heat transfer enhancement on the biphilic surface in the low-superheat region.

Numerical simulation of bulk condensation in gas-vapor mixtures flowing through a nozzle

The behavior of heavy water and n-nonane vapors mixed with an incondensable gas has been numerically simulated under the conditions of nonequilibrium bulk condensation. The efficiency of the employed mathematical model has been verified using available experimental data. The applicability of the conventional nucleation theory and modification thereof to the description of bulk condensation in a gas–vapor mixture flowing through a nozzle has been analyzed.

On the evolution of a multicomponent droplet during nonisothermal diffusion growth or evaporation

A set of equations has been derived for the size, composition, and temperature of a multicomponent droplet of a nonideal solution during its diffusion nonisothermal condensation growth or evaporation in a multicomponent mixture of vapors with an incondensable carrier gas. In addition to complete equations for material and heat transfer in the vapor-gas medium surrounding the droplet, the derived set, in the general case, describes the nonstationary growth or evaporation of the droplet under arbitrary initial conditions (initial size and temperature of the droplet and the concentrations of the nonideal multicomponent solution in it) and the establishment of the stationary values of the composition, temperature, and the rate of variations in the size of the droplet with allowance for heat effects and diffusion and thermodiffusion material transfer, Stefan flux, motion of the droplet surface, and the nonideality of the solution in the droplet. A simplified set of equations obtained without taking into account the contributions from the flow, cross effects, and thermal expansion in the equations of the material and heat transfer in the vapor-gas medium has been considered. Equations describing growth/evaporation in the stationary regime have been analyzed for droplets of ideal multicomponent solutions.

Bio-Oil Derived from Palm Kernel Shell in Fluidized Bed Reactor: Effect of Particle Size

Bio-oil production from pyrolysis of 0.15-0.5 mm and 1-2 mm palm kernel shell (PKS) has been investigated in a fluidized bed reactor under the nitrogen gas flow rate of 25 L(NTP)/min, with reactor temperature of 450°C. The pyrolysis unit has six successive condensers. Thus, six fractions of bio-oil samples were acquired from the six condensers. The calorific value, water content, ash content, and element content of each bio-oil samples were determined. The bio-oil yield from palm kernel shell with the size of 0.15-0.5 mm and 1-2 mm were 20 % and 26 %, respectively. The highest calorific value among the six bio-oil samples was 25.1 MJ/kg which was drawn from the forth condenser from pyrolysis of 0.15-0.5 mm of palm kernel shell. The incondensable gas was a mixture of hydrogen, methane, carbon dioxide and ethane.

The GRAUTHERMIC-Tyres process for the recycling of granulated scrap tyres

The influence of thermolysis temperature (range 500–700°C) on the products produced from granulated scrap tyres (GST) (2–6mm Ø) in a semi-batch pilot plant that uses several fixed bed reactors in parallel (GRAUTHERMIC-Tyres® process) was examined. This pilot unit consisted of six vertical fixed bed reactors in parallel, each with a capacity of 12kg GST. Thermolysis proceeded in a normal air atmosphere. The solid (char), liquid (tyre-derived oil [TDO]) and gaseous products generated at each temperature were characterised. The incondensable gas fraction was used to produce electricity via a gas turbine. The yields of the gas, TDO and char fractions were 15–22wt.%, 34–46wt.% and 39–44wt.% respectively, values that represent major recoveries from the GST feedstock. The TDOs were mainly a mixture of aliphatic and aromatic hydrocarbons and had very high GCVs (41–43MJ/kg), higher than those of conventional liquid fuels. A large increase was seen in the polycyclic aromatic hydrocarbon content above 550°C. The non-condensable gases obtained had a high GCV value (64–83MJ/Nm3), and produced 4.1–6.5kWhelectricity/g of GST in a gas turbine. The chars had a GCV of 27–28MJ/kg, high ash (17–21wt.%) and zinc contents, and an essentially macroporous texture with a low BET surface area (46–78m2/g). The thermolysis of GSTs with co-generation of gases by the GRAUTHERMIC-Tyres® method would appear to be a viable means of valorising GST.

A steam dried municipal solid waste gasification and melting process

Considering high-moisture municipal solid waste (MSW) of China, a steam dried MSW gasification and melting process was proposed, the feasibility was tested, and the mass and energy balance was analyzed. Preliminary experiments were conducted using a fixed-bed drying apparatus, a 200 kg per day fluidized-bed gasifier, and a swirl melting furnace. Moisture percentage was reduced from 50% to 20% roughly when MSW was dried by slightly superheated steam of 150°C–350°C within 40 min. When the temperature was less than 250°C, no incondensable gas was produced during the drying process. The gasifier ran at 550°C–700°Cwith an air equivalence ratio (ER) of 0.2–0.4. The temperature of the swirl melting furnace reached about 1240°C when the gasification ER was 0.3 and the total ER was 1.1. At these conditions, the fly ash concentration in the flue gas was 1.7 g·(Nm3)−1, which meant over 95% fly ash was trapped in the furnace and discharged as slag. 85% of Ni and Cr were bound in the slag, as well as 60% of Cu. The mass and energy balance analysis indicates that the boiler heat efficiency of an industrial MSW incineration plant reaches 86.97% when MSW is dried by steam of 200°C. The boiler heat efficiency is sensitive to three important parameters, including the temperature of preheated MSW, the moisture percentage of dried MS Wand the fly ash percentage in the total ash.

Simultaneous establishing of stationary growth rate and composition of supercritical droplets at isothermal binary condensation in the diffusion-controlled regime

General integral relations expressing the droplet radius and time of the droplet nonstationary growth as nonlinear functions of solution concentration in the droplet have been derived. These relations are valid for a supercritical droplet (i.e., sufficiently large droplet, for which the Laplace pressure effect on the concentration at saturation of vapors is negligible) isothermally growing via stationary diffusion in the mixture of two condensing vapors and an incondensable carrier gas. The initial composition in the droplet may be arbitrary and partial molecular volumes of components are not fixed. Explicit analytical relations have been found for droplet composition and the droplet size as functions of time at small deviations from the stationary concentration in the growing droplet. These relations show that the assumption of the steady droplet growth rate is not valid for non-small deviations from the stationary concentration. Some illustrations of the general nonlinear theory have been done in situation when solution in the droplet can be considered ideal.

Simulation of cavitation bubbles in a convergent–divergent nozzle water jet

A model for simulating the process of growth, collapse and rebound of a cavitation bubble travelling along the flow through a convergent–divergent nozzle producing a cavitating water jet is established. The model is based on the Rayleigh–Plesset bubble dynamics equation using as inputs ambient pressure and velocity profiles calculated with the aid of computational fluid dynamics (CFD) flow modelling. A variable time-step technique is applied to solve the highly nonlinear second-order differential equation. This technique successfully solves the Rayleigh–Plesset equation for wide ranges of pressure variation and bubble original size and saves considerable computing time. Inputs for this model are the pressure and velocity data from CFD calculation. To simulate accurately the process of bubble growth, collapse and rebound, a heat transfer model, which includes the effects of conduction plus radiation, is developed to describe the thermodynamics of the incondensable gas inside the bubble. This heat transfer model matches previously published experimental data well. Assuming that single bubble behaviour also applies to bubble clouds, the calculated distance from the nozzle exit travelled by the bubble to the point where the bubble size becomes invisible is taken to be equal to the bubble cloud length observed. The predictions are compared with experiments carried out in a cavitation cell and show good agreement for different nozzles operating at different pressure conditions.

Dynamics of a bubble in a liquid under laser pulse action

Simulation was performed of the behavior of a vapor bubble in a liquid under laser irradiation in laboratory experiments. A mathematical model was developed to analyze the effect of heat conduction, diffusion, and mass transfer on the bubble dynamics under compression and expansion. It is found that at the stage of collapse, intense condensation occurs on the bubble wall, which results in a significant (more than 15‐fold) decrease in bubble mass and an increase in pressure (to 105 atm) and temperature (to 104 K(. Results of numerical calculations of the radius of the first rebound and the amplitude of the divergent shock wave in water are compared with experimental data. It is shown that small (:about 1%) additives of an incondensable gas lead to a considerable decrease in mass transfer on the bubble wall.