Carbon Conversion Rate Research Articles

Simulation analysis of municipal solid waste pyrolysis and gasification based on Aspen plus

To predict and analyze the municipal solid waste (MSW) pyrolysis and gasification process in an updraft fixed bed more veritably and appropriately, numerical modeling based on Gibbs energy minimization was executed using the Aspen plus software. The RYield module was combined with the RGibbs module to describe the pyrolysis section, while the RGibbs module was used for the gasification section individually. The proposed model was used to forecast and analyze the target performance parameters including syngas composition, lower heating value (LHV) and carbon conversion rate under different conditions of the gasification temperatures, and ratios and types of gasifying agents. The results indicate that there is a good agreement between the experimental data and the simulated data obtained using this model. The predicted optimum gasification temperature is approximately 750°C, and the best ratio of water vapor as gasifying agent is around 0.4. The mixture of flue gas and water vapor has an economical and recycled prospect among four commonly used gasifying agents.

A high performance direct carbon solid oxide fuel cell fueled by Ca-loaded activated carbon

Ca-loaded activated carbon is developed as fuel for direct carbon solid oxide fuel cells (DC-SOFCs), operating without any carrier gas and liquid medium. Ca is loaded on activated carbon through impregnation technique in the form of CaO, which exhibits excellent catalytic activity and significantly promotes the output performance of DC-SOFCs. DC-SOFCs fueled by activated carbon with different Ca loading content (0, 1, 3, 5 and 7 wt. %) are tested and the performances are compared with the DC-SOFC running on the conventional Fe-loaded activated carbon. It is found that the performance of the DC-SOFC with 5 wt. % (373 mW cm−2) and 7 wt. % (378 mW cm−2) Ca-loaded activated carbon is significantly higher than that of the cells operated on 5 wt. % Fe-loaded activated carbon, 1 wt. % and 3 wt. % Ca-loaded activated carbon. The discharging time and fuel utilization of the DC-SOFC with 5 wt. % Ca-loaded activated carbon are also the optimal ones among all the cells. The microstructure, element distribution and carbon conversion rate of the Ca-loaded carbon, the impedance spectra of the corresponding DC-SOFCs are measured. The reasons for the reduced fuel utilization of 7 wt. % Ca-loaded carbon fuel are analyzed and the advantage of Ca-loaded carbon for DC-SOFCs is demonstrated in detail.

Experimental study of cyclone pyrolysis – Suspended combustion air gasification of biomass

Based on the original biomass cyclone gasifier, the cyclone pyrolysis-suspension combustion gasification technology was constituted with a bottom wind ring to build the biochar suspension combustion zone. This technology decouples the biomass pyrolysis, gasification (reduction reaction) and combustion (oxidation reaction) within the same device. With the feed amount and total air fixed, the effect of air rate arrangement on temperature distribution of the gasifier, syngas components and gasification parameters was studied. With the secondary air rate (0.20) and bottom air rate (0.50), the gasification efficiency was best, with gas heating value of 5.15MJ/Nm3, carbon conversion rate of 71.50%, gasification efficiency of 50.80% and syngas yield of 1.29Nm3/kg. The device with biochar for the tar catalytic cracking was installed at the gasifier outlet, effectively reducing the tar content in syngas, with a minimum value of 1.02g/Nm3.

Gas phase pyrolysis synthesis of carbon nanotubes at high temperature

In this study, carbon nanotubes were synthesized at high temperature (1150–1500°C) using the substrate-free gas phase pyrolysis method. The CNT sock morphology, CNT structure, impurity, process yield and growth efficiency at high temperatures were investigated. It was found that the CNTs transform from single-walled to multi-walled nanotubes at elevated temperature. The amount of amorphous impurities increases with higher temperature, possibly due to an increased non-catalytic decomposition of hydrocarbons. However the CNT quality increases, as indicated by a higher Raman spectroscopy IG/ID ratio. The process yield increase by two folds at higher temperature (1500°C) compared to a lower temperature (1200°C), but the catalyst efficiency is highest at 1400°C with 1g Fe producing 5.1g CNT. The calculated carbon conversion rate is lower than 4%. The CNT growth is not limited by the availability of carbon around the catalyst, instead of by the availability of active catalyst particles. Based on a pristine CNT sheet, the measured electrical conductivity is highest at 1400°C, due to a balance between impurities and CNT quality. The tensile strength of the CNT sheet increases with the temperature, possibly because of the “gluing” effect of the carbonaceous impurities.

Gasification characteristics of sawdust char at a high-temperature steam atmosphere

Gasification characteristics of sawdust char at a high-temperature steam atmosphere were experimentally studied in a fixed bed reactor. The char was prepared at 600–1400 °C. The effects of temperature, steam flow rate, reaction time and char preparation temperature on conversion rate, the composition of product gas, the pore structure of char and ash, as well as kinetics were analyzed. Gas chromatography, scanning electron microscopy, and a specific surface area analyzer were utilized to measure the composition of the gas, the surface morphology, and the specific surface area of the char and ash. Results show that the carbon conversion rate increases with temperature, steam flow rate, and reaction time. At 800–1200 °C, H2 content in product gas increases from 53.08% to 60.01%, and CO increases from 15.35% to 21.87%, while both CH4 and CO2 decrease. At 0.94–2.61 g/min, H2 in the product gas rapidly increases, but since CO decreases, H2 and CO slightly decrease. The specific surface area of sawdust ash increases to 948.84 m2/g and 987.61 m2/g at 800 °C and 1000 °C, respectively, on account of the fact that new micropores are generated, but it reduces to 520.76 m2/g at 1200 °C as a result of the decrease of micropores and mesopores. The surface reaction controlled shrinking core model can describe high-temperature steam gasification reaction of sawdust char.

Fly-Ash-Modified Calcium-Based Sorbents Tailored to CO2 Capture

The calcium oxide looping cycle is considered to be one of the promising technologies for CO2 capture from fossil fuel power plants. How to improve CO2 capture and sintering-resistance performance of sorbents during the cycling is a challenge for researchers. An attempt was made to modify CaO sorbents by coal fly ash to improve the CO2 capture capacity and sintering resistance of sorbents, as well as utilize the solid waste. CO2 capture performance of the modified sorbents was investigated and compared with that of pure CaO. The structural properties of the resulting sorbents were characterized by X-ray diffraction (XRD) techniques and N2 physisorption, showing that the sorbents modified by fly ash presented the formation of Ca12Al14O33 and CaSiO3, as well as a wonderful microstructure. These features enable enhanced sintering resistance and great reactivity enhancement of sorbents, which gave rise to enhanced carbonation conversion and carbonation rate, especially for sorbents modified with the slag/calc...

Biowaste utilization in the process of co-gasification with bituminous coal and lignite

Biowaste utilization in co-gasification with bituminous coal and lignite gives the benefits of stable supplies of a primary energy source – coal and utilization of a zero-emission, waste material (i.e. agriculture waste, sewage sludge, etc.) with higher process efficiency and lower negative environmental impact than biomass or coal gasification, respectively. The main focus of the study presented is co-gasification of bituminous coal or lignite with biowaste to hydrogen-rich gas. The experiments were performed in the laboratory scale fixed-bed reactor installation at 700 and 900 °C. The Hierarchical Clustering Analysis complemented with a color map of studied data were applied in the selection of the optimal operating parameters for biowaste utilization in the co-gasification process based on the experimental data of gasification/co-gasification process as well as physical and chemical properties of fuels tested. The experimental results showed that the carbon conversion rate in co-gasification increased with increasing biomass content in a fuel. The total gas volume and hydrogen volume in co-gasification were higher than the values expected based on the results of the gasification process of the fuels analyzed.

Co-gasification reactivity of petcoke and coal at high temperature

Petcoke, as a byproduct of petroleum refinery process, can be used as feedstock of gasifiers due to its high carbon content and high calorific value. However, its low gasification reactivity and low ash content restrict its application to some gasifiers. In this work, experimental study on co-gasification reactivity of petcoke with coal under CO2 atmosphere was investigated in a drop-in-fixed-bed reactor in the temperature range of 1200–1400°C. Produced CO was monitored continually using an online mass spectrometry to calculate the carbon conversion and gasification rate. The experimental results reveal that the gasification reactivity of petcoke can be improved greatly by co-gasifying with coals or by loading their ashes, even at temperatures higher than the ash fusion temperature. Both the coal and its ash can improve the gasification reactivity of petcoke. The synergistic effect is closely related to the composition of minerals in coal but not coal rank. The high content of active components such as Ca- and Fe- in coal or ash is beneficial for co-gasification. Some coals, however, are lack of these active components and with high Si- and Al-components content which may retard the gasification reaction. During co-gasification, the oldhamite (CaS), anhydrite (CaSO4) and magnetite (Fe3O4) have positive catalytic effect, while mulite (3Al2O3·2SiO2) has negative effect on gasification reaction at high temperature.

Process simulation of staging pyrolysis and steam gasification for pine sawdust

A two-stage biomass pyrolysis and gasification scheme for pine sawdust are proposed. The process makes use of the gas produced by biomass pyrolysis and gasification. Part of product gas combusts in a burner outside of the gasifier and then produces the flue gas and heat required for pyrolysis and steam gasification. Aspen Plus software is used to simulate the process of staging pyrolysis and steam gasification for pine sawdust. By taking heat recovery, utilization and recycling of the product gas into consideration, the influence of temperature and the amount of steam on yield, carbon conversion rate, and lower heating value of the product gas are investigated. The results show that heat self-support is realized by combustion of 15–21% of the total product gas. As the gasification temperature increases, so do the content of H2 and CO in the product gas, and the carbon conversion rate also increases. The lower heating value of the product gas reaches a minimum at 700 °C. With the increase of the steam amount, the yield of H2 and CO increases, which lead to the increase of carbon conversion rate and the decrease of the lower heating value of product gas. The yield of CO decreases as the amount of steam increases. Meanwhile, the carbon conversion rate is almost 100% at 900–1000 °C, w(H2O)/w(B) > 0.24. The lower heating value of product gas decreases with the rise of the steam amount.

Gasification characteristics of different rank coals at H2O and CO2 atmospheres

Gasification characteristics of Shenhua bituminous (SH) and Baorixile lignite coal (BRXL) were investigated using both a thermogravimetric analyzer and tubular furnace. Coal samples were pyrolized in a tubular furnace at five different temperatures (800–1000°C in 50° increments), at two heating rates, 10°C/min and 1000°C/min. The resultant chars were gasified isothermally at (i) each of these five temperatures under a constant atmosphere (40% H2O(g) + 60% CO2) and (ii) at 1000°C while varying the atmosphere from pure H2O(g) to pure CO2 by increasing the CO2 component stepwise in 20 vol.% increments. Carbon conversion, reactivity index, and average specific gasification rate were calculated and fit to a mixed reaction model. It was found that both the gasification temperature and atmosphere composition greatly impacted gasification characteristics, and the temperature effect was more pronounced in a heterogeneous atmosphere. The char produced with a high heating rate pyrolysis process promoted gasification reactivity likely a result of the more open pore structure. The gasification reactivity was lowest under a pure CO2 gasification atmosphere and increased continuously with the H2O partial pressure. SH and BRXL char samples achieved peak gasification reactivity under atmospheres with 60% and 80% H2O(g), respectively. Also, a synergistic effect was observed for heterogeneous CO2/H2O gasification atmosphere and not all the gasification reactions obeyed a first-order reaction model. The results of this work indicate that there is an optimal gasification atmosphere and temperature combination, specific to the coal sample, for efficiently converting char to gasification products.

Three‐dimensional modeling of porosity development during the gasification of a char particle

This work is devoted to the three‐dimensional, direct modeling of porosity and specific surface development during the gasification of a char particle. The model was developed for heterogeneous reactions occurring inside a char particle in a kinetically controlled regime. The main goal of this work is to analyze the impact of different pore size distributions on the particle carbon conversion rate. In particular, it is shown that under certain conditions the outer particle surface can influence the specific surface area. In this context the possible adaptation of the parameter ψ from the random pore model (RPM) developed by Bhatia and Perlmutter is explained. The results of simulations are compared against the RPM and discussed. Additionally, based on the results of simulations, the physics behind several input parameters used by the RPM are explored. Finally, the possible fragmentation of a chemically reacting char particle during its gasification in dependence of instantaneous porosity was investigated numerically. It was shown that the earliest fragmentation occurs at a carbon conversion of about 0.5–0.6 due to the disaggregation of the pore walls. The results are discussed and compared implicitly with data published in the literature. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1638–1647, 2017

Effect of Ternary Eutectic Salt on the Calcium Sulfate Oxygen Carrier for Chemical Looping Combustion of Coal Char

AbstractThe effect of a ternary eutectic salt (43.5 % Li2CO3–31.5 % Na2CO3–25 % K2CO3) on the CaSO4 oxygen carrier for chemical looping combustion (CLC) of coal char is experimentally investigated in a bench‐scale fluidized‐bed reactor with steam as the gasification agent at atmospheric pressure and 925 °C. The ternary eutectic catalyst is added to the CaSO4 oxygen carrier by physical mixing and impregnation, respectively. The enhanced carbon conversion and shortened reaction time in the fluidized bed reactor, coupled with the high weight loss rate of CaSO4 reduction with CO in the thermogravimetric analyzer (TGA), suggest that the reactions of coal char gasification and CaSO4 reduction are synergistically catalyzed in the presence of the ternary eutectic salt. The modified oxygen carriers prepared by physical mixing and impregnation show no significant difference in carbon conversion and gasification rates according to the experimental results. The sample with catalyst impregnated into the mixture of anhydrite and coal char gives higher activity compared to the samples with catalyst impregnated into the coal char or anhydrite solely, due to the more uniform distribution of the catalyst.

Characteristics of pore structure of rice husk char during high-temperature steam gasification

The characteristics of the pore structure of rice husk char during high-temperature steam gasification was investigated in a fixed bed gasifier. The raw rice husk was heated to various temperatures (600–1400°C) to generate rice husk char. The yield of rice husk char decreases with char generation temperature. Carbon conversion rate of rice husk char after steam gasification decreases significantly with char generation temperature, which is 91.95% at 600°C, and 52.51% at 1400°C. The surface of the rice husk char generated at higher temperatures is rougher with more thermal etching marks. The adsorption and desorption isotherms of char and ash indicate the distribution of the pore size is relatively continuous. The desorption isotherm is greater than the adsorption isotherm at high relative pressure. The amount of adsorption and specific surface area of the rice husk char increase first and then decrease with the rise of char generation temperature. The pore structure of rice husk char is the most abundant at 1000°C, and the specific surface area is 316m2/g. After high-temperature (1000–1200°C) gasification, the pore size increases, and the surface area of the rice husk ash is significantly reduced to 1–4m2/g.

Numerical modeling of a downdraft plasma gasification reactor

Gasification, a method of producing hydrogen, is an alternative way to obtain clean, sustainable, and domestic energy using coal and biomass resources. Gasification can be achieved with several methods or using various reactor designs, and plasma gasification is one of these methods. Plasma gasification has advantages compared to conventional gasification systems regarding syngas cleaning and gasification rates. Tar production, the greatest problem in fixed bed gasifiers, can be reduced and higher carbon conversion rates can be achieved with plasma gasification systems.In this study, a 10 kW microwave plasma-integrated down-draft coal gasifier was modeled with ANSYS FLUENT. A novel design is simulated in order to obtain the swirl effect and observe the increase in the residence time for coal particles inside the reactor. Plasma ionization is ignored due to the overlapping of the MHD (MagnetoHydroDynamics) module and combustion models. Therefore, plasma inlet conditions are determined via experimental studies instead of activating the MHD module in Fluent. SIMPLE algorithm is selected for pressure–velocity coupling. Turbulence variables are calculated with the k-ε turbulence model. The interaction between gas phase and discrete phase is followed by Eularian-Lagrangian approach and 10 injection time steps are chosen for the continuity of the reactions. The Finite Rate Chemistry/Eddy Dissipation model is selected for both combustion and gasification models. DO radiation model is used for radiation modeling. Temperature, species (CO, H2, CO2, H2O), and velocity results on different planes are obtained. According to the results, approximately 1350 K average temperature is obtained inside the reactor. Grid independency study is also performed. The results show that it is possible to obtain a syngas with 18.4% H2 and 37.2% CO mole fractions, respectively. The cold gas efficiency of the gasifier is found to be 55.3%.

Scaled-up prototype of carbon nanotube production system utilizing waste cooking palm oil precursor and its nanocomposite application as supercapacitor electrodes

A simple approach has been introduced for the first time for a scaled-up prototype of a carbon nanotube (CNT) production system by utilizing waste cooking palm oil (WCPO) as carbon feedstock. A modified thermal chemical vapor deposition (TCVD) setup is equipped with a peristaltic sprayer to continuously supply the precursor and catalyst into the system. A total amount of 1000 ml WCPO precursor was sprayed continuously during the experiment with 5.33 wt% ferrocene as catalyst at a flow rate of 30 ml/min. A total of ~433 g CNT were produced with a high carbon conversion rate of 56 %. The produced CNT were then characterized by using electron microscopy, micro-Raman spectroscopy, and thermogravimetric analysis. Growth of dense CNT with a high purity of ~87 % and good crystallinity (ID/IG ratio ~0.47) occurred. A CNT/natural rubber-latex (NRL) nanocomposite was also prepared by using latex nanotechnology for supercapacitor application. The nanocomposite exhibited a good capacitance performance with a specific capacitance of 81.82 F/g. This study determined that a high production of CNT using modified TCVD method provided benefits for its utilization as composite material, especially CNT/NRL nanocomposite, for supercapacitor application.

Towards stable kinetics of large metabolic networks: Nonequilibrium potential function approach.

While the biochemistry of metabolism in many organisms is well studied, details of the metabolic dynamics are not fully explored yet. Acquiring adequate in vivo kinetic parameters experimentally has always been an obstacle. Unless the parameters of a vast number of enzyme-catalyzed reactions happened to fall into very special ranges, a kinetic model for a large metabolic network would fail to reach a steady state. In this work we show that a stable metabolic network can be systematically established via a biologically motivated regulatory process. The regulation is constructed in terms of a potential landscape description of stochastic and nongradient systems. The constructed process draws enzymatic parameters towards stable metabolism by reducing the change in the Lyapunov function tied to the stochastic fluctuations. Biologically it can be viewed as interplay between the flux balance and the spread of workloads on the network. Our approach allows further constraints such as thermodynamics and optimal efficiency. We choose the central metabolism of Methylobacterium extorquens AM1 as a case study to demonstrate the effectiveness of the approach. Growth efficiency on carbon conversion rate versus cell viability and futile cycles is investigated in depth.

Classification of Refuse Derived Fuel (RDF) and Model Development of a Novel Thermal Utilization Concept Through Air-Gasification

The need for refuse derived fuels (RDF) standardization gets rapidly essential in the EU-member states and especially in regions where a specific market for such fuels is currently under development. The promotion of standardization practices facilitates public acceptance, supports the development of quality assurance mechanisms and enhances the marketability of selected waste streams as fuels with high biogenic content. In the present work the results of an extensive RDF sampling and characterization campaign are reported, along with the results of process calculations for the potential energy utilization of this fuel in an air blown gasifier. The studied materials recovery facility produces ~15,000 t RDF/y, derived from packaging waste, and is mainly composed of plastic and paper. Given that the produced material is not currently thermally utilized for commercial purposes, it is believed that such standardization will drastically enhance fuel marketability and public acceptance. The current work classified the aforementioned RDF as 4, 2, 1 according to the European Standard EN 15359:2011. Moreover, thermodynamic calculations on the gasification process found that the optimum operational temperature for any air gasification process that utilizes the studied RDF, in terms of carbon conversion rate and gasification efficiency, lies between 850 and 900 °C. The extended sampling average fuel composition determined the operating conditions for autothermal operation; the process simulations reveal that the ER may range from 0.27 to 0.42.

A New Subgrid Model for the Heat and Mass Transfer Between a Hot Gas and Char Particles in Dense-Bed Reactors

This work is devoted to the development and verification of a new intrinsic-based subgrid model for moving char particles gasifying in a hot flue gas or syngas environments consisting of CO2/H2O/CO species. The distinguishing feature of our model relative to the submodels published in the literature is that it takes into account the thermal and chemical nonequilibrium between the particle's surface and its center. Thus, our model is able to predict temperature and species gradients inside the particles. The main focus of the new submodel is to demonstrate the crucial role of intrinsic-based heterogeneous reactions in the adequate prediction of carbon conversion rates for char particles gasification in fixed-bed and fluidized-bed gasifiers. The new model is verified against steady-state, particle-resolved computational fluid dynamics (CFD)-based, three-dimensional simulations carried out for different volume fractions of solid phase in a control volume (CV). Acceptable agreement has been demonstrated. Finally, to demonstrate our new model's predictions, we carried out several unsteady simulations for different ambient temperatures and Reynolds numbers. The importance of simultaneous change of char porosity and particles size during gasification has been demonstrated for different regimes indicated by the Damköhler numbers.

The Concept, Design and Performance of a Novel Rotary Kiln Type Air-Staged Biomass Gasifier

Tar formation is the main bottleneck for biomass gasification technology. A novel rotary kiln type biomass gasification process was proposed. The concept design was based on air staging and process separation. This concept was demonstrated on a pilot scale rotary kiln reactor under ambient pressure and autothermic conditions. The pilot scale gasifier was divided into three different reaction regions, which were oxidative degradation, partial oxidation and char gasification. A series of tests was conducted to investigate the effect of key parameters. The results indicate that under optimum operating conditions, a fuel gas with high heat value of about 5500 kJ/Nm3 and gas production rate of 2.32 Nm3/kg could be produced. Tar concentration in the fuel gas could be reduced to 108 mg/Nm3 (at the gasifier outlet) and 38 mg/Nm3 (after gas conditioning). The cold gas efficiency and carbon conversion rate reached 75% and 78%, respectively. The performance of this gasification system shows considerable potential for implementation in distributed electricity and heat supply projects.

Experience with the Gasification of Low-Grade Coal; A Case Study of Continuously Changing Temperature inside Gasifier

Indonesian brown‐coal with high ash content is gasified by two microwave steam‐plasmas heating up a reaction chamber of 1145 liters in a swirl‐type gasifier for production of hydrogen‐rich synthetic gas. With additional heating of the gasifier by a partial oxidation of coal, the inner temperature of the gasifier can be increased from 1100C to 1700C. In this regard, the influence of the gasifier temperature on the gasification efficiency can be investigated in this experiment. The carbon conversion rate and cold gas efficiency are less than 90 percent and 65 percent, respectively, for the inner temperature of the gasifier below 1400C. On the other hand, the carbon conversion rate at the chamber temperature of 1600C is almost 100 percent, ensuring a complete gasification of carbons in a low‐grade coal. The cold gas efficiency of the hydrogen‐rich synthetic gas at the high inner temperature of the gasifier wall is 84%, very high in a relatively‐small gasifier like the experiment here. The total calorific power of the synthetic gas can be easily more than 500kW in this particular experiment.